ORGANOSOLV PULPING A review and distillation study related to peroxyacidpulping

ESAMUURINEN

Department of Process Engineering

OULU 2000

ORGANOSOLV PULPING A review and distillation study related to peroxyacid pulping

ESA MUURINEN

Academic Dissertation to be presented with the assent of the Faculty of Technology, University of Oulu, for public discussion in Savonsali (Auditorium L 4), Linnanmaa, on June 30th, 2000, at 12 noon.

OULUN YLIOPISTO, OULU 2000

Copyright © 2000Oulu University Library, 2000

Manuscript received 16 May 2000Accepted 18 May 2000

Communicated by Professor Juhani Aittamaa Doctor Jorma Sundquist

ALSO AVAILABLE IN PRINTED FORMAT

ISBN 951-42-5661-1

ISBN 951-42-5660-3ISSN 0355-3213 (URL: http://herkules.oulu.fi/issn03553213/)

OULU UNIVERSITY LIBRARYOULU 2000

TTTToooo PPPPaaaauuuullllaaaa aaaannnndddd DDDDiiiijjjjoooonnnn

Muurinen, Esa, Organosolv pulping, a review and distillation studyrelated to peroxyacid pulpingDepartment of Process Engineering, University of Oulu, FIN-90014 University of Oulu,Finland2000Oulu, Finland(Manuscript received 16 May 2000)

A b s t r a c t

More than 900 papers related to organosolv pulping have been reviewed in this thesis.From the information included in those papers it can be concluded that organosolvpulping processes are still in a developing stage and are not yet ready to seriously threatthe position of the kraft process as the main pulp manufacturing process in the world.

Distillation seems to be the main alternative as the process for recovering the solventin organosolv pulping. A good reason for this is that using simple distillation nopotentially harmful components are introduced to the process.

The effect of the feed composition on the operation of a separation sequence in anorganosolv process using aqueous formic and acetic acids and corresponding peroxyacidswas studied. When simple distillation was used as the separation method the effect wasfound to be significant. The unideal nature of the formic acid-acetic acid-water mixture, theseparation of which was studied, makes the ternary composition space divide into fourdistillation regions. Which region the feed is located in, obviously determines theeconomy of the distillation sequence.

Shortcut calculation methods cannot be recommended for use in designing a distillationsequence for the ternary mixture studied, but they give useful information for thecomparison of such sequences. They were used to choose a limited number of alternativesfor studies with rigorous calculation methods.

Minimum work of separation can also be used to make a satisfying estimate for therelative easeness of separation of the formic acid-acetic acid-water mixture.

Thermal integration using pinch technology was also tested and found to be very usefulfor decreasing the thermal energy consumptions of distillation processes.

Thermodynamic efficiencies for separating the formic acid-acetic acid-water mixture bysimple distillation were estimated. They were found to be lower than the average value fordistillation presented in literature.

Keywords: solvent recovery, pinch analysis, formic acid, acetic acid

Acknowledgements

This research work was carried out in the Mass and Heat Transfer Process Laboratory ofthe Department of Process Engineering, University of Oulu, Finland, in 1994-1999.

I would like to thank my supervisor, Professor Jorma Sohlo, for his encouragementand valuable comments during this research.

I want to acknowledge Professor Juhani Aittamaa and Dr. Jorma Sundquist for theirreview of the thesis and for their useful recommendations.

The financial support from Oulun yliopiston tukisäätiö, Jenny ja Antti Wihurinrahasto and Tekniikan edistämissäätiö is gratefully acknowledged.

Oulu, May 2000 Esa Muurinen

Contents

AbstractAcknowledgementsContents1. Introduction............................................................................................... 132. Pulping with organic chemicals.....................................................................16

2.1. Alcohols............................................................................................162.1.1. Methanol.................................................................................. 16

2.1.1.1. Catalyzed methanol pulping........................................... 17 2.1.1.2. Methanol in sulphite pulping......................................... 20 2.1.1.3. The ASAM process...................................................... 21 2.1.1.4. Methanol in soda pulping.............................................. 29 2.1.1.5. The Organocell process..................................................31 2.1.1.6. Other alkaline methanol processes................................... 36 2.1.1.7. Methanol lignins..........................................................37 2.1.1.8. Summary....................................................................39

2.1.2. Ethanol.................................................................................... 392.1.2.1. Catalyzed and autocatalyzed ethanol pulping..................... 40

2.1.2.2. The Alcell process........................................................49 2.1.2.3. Alkaline ethanol pulping............................................... 57 2.1.2.4. Ethanol in sulphite pulping............................................62 2.1.2.5. Simulation of ethanol pulping........................................63 2.1.2.6. The kinetics and mechanism of delignification................... 64 2.1.2.7. Ethanol lignins............................................................65 2.1.2.8. Summary....................................................................66

2.1.3. Other alcohols........................................................................... 67 2.1.3.1. Propanol and isopropanol...............................................67

2.1.3.2. Butanol...................................................................... 68 2.1.3.3. Glycols...................................................................... 70

2.1.3.4. Summary....................................................................732.2. Organic acids...................................................................................... 73

2.2.1. Formic acid............................................................................... 73

2.2.1.1. Pulping and bleaching with formic acid............................ 74 2.2.1.2. The Milox process........................................................75 2.2.1.3. Milox bleaching...........................................................79 2.2.1.4. Solvent recovery in Milox pulping..................................80 2.2.1.5. The chemistry of Milox pulping..................................... 84

2.2.1.6. Summary....................................................................852.2.2. Acetic acid................................................................................ 85

2.2.2.1. Acetic acid pulping and bleaching.................................. ..85 2.2.2.2. Peroxyacetic acid..........................................................92 2.2.2.3. Acetosolv pulping...................................................... ..96 2.2.2.4. Acetocell pulping....................................................... ..99 2.2.2.5. Formacell pulping...................................................... ..99

2.2.2.6. Summary................................................................. 1002.2.3. Other organic acids................................................................... 100

2.2.4. Salts of organic acids................................................................ 1012.2.5. Summary................................................................................102

2.3. Phenol and cresols............................................................................. 1022.3.1. Phenol....................................................................................102

2.3.2. Cresols...................................................................................1062.3.3. Summary................................................................................108

2.4. Ethyl acetate.....................................................................................109 2.5. Amines and amine oxides....................................................................110 2.5.1. Ethylenediamine.......................................................................110 2.5.2. Hexamethylene diamine............................................................. 111 2.5.3. Methylamine........................................................................... 112

2.5.4. Ethanolamine.......................................................................... 112 2.5.5. Amine oxides...........................................................................113

2.6.6. Summary................................................................................113 2.6. Ketones........................................................................................... 114 2.7. Dioxane...........................................................................................117 2.8. Other organic compounds....................................................................120

2.9. Summary.........................................................................................1223. Solvent recovery in peroxyacid pulping.........................................................124

3.1. The search for feasible separation methods..............................................125 3.1.1. Wells and Rose........................................................................ 125 3.1.2. Lee........................................................................................ 126

3.1.3. Barnicki and Fair...................................................................... 1273.1.4. Null.......................................................................................128

3.2. Feasible separation methods................................................................ 128 3.2.1. Simple distillation....................................................................129 3.2.2. Azeotropic distillation............................................................... 131 3.2.3. Extractive distillation................................................................ 131 3.2.4. Liquid-liquid extraction.............................................................. 133 3.2.5. Membrane processes................................................................. 134 3.2.6. Adsorption.............................................................................. 134

3.2.7. Summary................................................................................135

3.3. The effect of the feed composition on the separation of the formic acid-aceticacid-water mixture..............................................................................135

3.3.1. Minimum work of separation......................................................135 3.3.2. Vapour-liquid equilibrium data for the formic acid-acetic acid-water mixture...................................................................................138 3.3.3. Shortcut simulation of the first separation stage............................. 142 3.3.3.1. Simple distillation at 20 kPa as the first separation stage...143

3.3.3.2. Simple distillation at 101.3 kPa as the first separation stage........................................................................145

3.3.3.3. Simple distillation at 300 kPa as the first separation stage........................................................................151

3.3.3.4. Extractive distillation as the first separation stage.............156 3.3.3.5. The first separation stage for the peroxyformic acid pulping

process.....................................................................160 3.3.3.6. Summary of the simulation results for the first separation

stage........................................................................1613.3.4. Shortcut simulation of the second separation stage..........................164

3.3.4.1. Simple distillation at 20 kPa as the second separationstage........................................................................165

3.3.4.2. Simple distillation at 101.3 kPa as the second separation stage........................................................................169

3.3.4.3. Simple distillation at 300 kPa as the second separation stage...................................................................... 174

3.3.4.4. Extractive distillation at 101.3 kPa as the second separation stage........................................................................178

3.3.4.5. The second separation stages for the peroxyformic acid pulping process......................................................... 178

3.3.4.6. Summary of the simulation results for the second separation stage........................................................................180

3.3.5. Shortcut simulation of the third separation stage.............................182 3.3.5.1. Simple distillation at 20 kPa as the third separation stage.. 182 3.3.5.2. Simple distillation at 101.3 kPa as the third separation

stage........................................................................184 3.3.5.3. Simple distillation at 300 kPa as the third separation

stage........................................................................187 3.3.5.4. Extractive distillation with n-methyl-2-pyrrolidone at 101.3

kPa as the third separation stage....................................191 3.3.5.5. The third separation stages for the peroxyformic acid

pulping process..........................................................192 3.3.5.6. Summary of the simulation results for the third separation

stage........................................................................1943.3.6. Shortcut simulation of the fourth separation stage.......................... 196

3.3.6.1. Simple distillation at 20 kPa as the fourth separation stage........................................................................197

3.3.6.2. Simple distillation at 101.3 kPa as the fourth separation stage........................................................................197

3.3.6.3. Simple distillation at 300 kPa as the fourth separation stage........................................................................198

3.3.6.4. The fourth separation stages for the peroxyformic acid pulping process......................................................... 1993.3.6.5. Summary of the simulation results for the fourth separation

stage....................................................................... 200 3.3.7. The recycle stream.................................................................... 200 3.3.8. Rigorous simulations................................................................205

3.3.8.1. Feed containing 10% formic acid, 20% acetic acid and 70% water........................................................................2063.3.8.2. Feed containing 10% formic acid, 10% acetic acid and 80% water........................................................................2083.3.8.3. Feed containing 30% formic acid, 30% acetic acid and 40% water........................................................................2103.3.8.4. Feed containing 30% formic acid, 60% acetic acid and 10% water........................................................................2123.3.8.5. Feed containing 40% formic acid, 50% acetic acid and 10% water........................................................................2153.3.8.6. Feed containing 12.1% formic acid, 0.2% acetic acid and 87.7% water..............................................................2173.3.8.7. Summary of the rigorous calculations............................ 220

3.3.9. Thermal integration of the separation processes.............................. 2214. Discussion...............................................................................................251 4.1. Organosolv pulping........................................................................... 251 4.2. Solvent recovery in peroxyacid pulping..................................................253

4.2.1. Feasible separation methods........................................................2534.2.2. Minimum work of separation......................................................2544.2.3. Phase equilibria........................................................................2544.2.4. Shortcut simulations of the separation sequences............................ 2574.2.5. Rigorous simulations................................................................2594.2.6. Thermal integration using pinch technology.................................. 260

5. Conclusions.............................................................................................262References...................................................................................................263

1. Introduction

Alkaline kraft pulping is the dominant chemical pulping process today, but it has someserious shortcomings. These are air and water pollution and the high investment costs.

The air pollution is mainly caused by the release of organic sulphur compounds anddust particles. The main source of water pollution in the kraft process are the effluentwater streams from pulp bleaching containing organic chlorine compounds. (Schweers1972a, Schweers 1972b).

The problems related to kraft pulping have been partly solved by using extendeddelignification, oxygen delignification, chlorine dioxide substitution and nonchlorinebleaching in order to minimize the use of chlorine in pulp bleaching. (Bowen & Hsu1990)

The odour problems of a kraft mill cannot be totally eliminated, but a partialelimination of the malodorous emissions is possible by using burning of the sulphurcompounds or by absorbing them into alkaline or polythionate solutions. (Teder et al.1990)

The replacement of the kraft process could be possible if a new process having thefollowing characteristics (Worster 1974, Palenius 1987, Franzreb 1989, Leopold 1993,Schroeter 1993) were introduced:- To avoid malodorous emissions the process should be totally sulphur free.- It should have pulping conditions that do not degrade cellulose and dissolvedhemicelluloses.- It should be capable of solubilizing most of the lignin with very little loss ofcellulose and only a modest loss of hemicelluloses.- It should not require higher temperatures, pressures or pulping times than used inkraft and sulphite pulping.- It should have an efficient and simple chemical recovery system.- It should not cause any environmental problems.- The optimal size of the process should be smaller than the optimal size of the kraftprocess.- Both hardwoods and softwoods should be possible raw materials.- Valuable by-products should be recovered.- The pulp quality should be at least equal to the quality of the kraft pulp.

- The pulp should be bleached without chlorine chemicals.- The pulp yield should be high.- The specific energy consumption of the process should be low.- It should be possible to close the chemical cycle of the process.

Organic chemicals were originally used to separate wood into its components in orderto study lignin and carbohydrates (Klason 1893, Klason 1908, Klason & Fagerlind1908, Hägglund & Urban 1928, Kleinert and Tayenthal 1931, Engel & Wedekind 1933,Aronovsky and Gortner 1936, Brickman et al. 1939). In recent years the search forpulping processes that could fulfil the requirements listed above has led to thedevelopment of several organosolv methods capable of producing pulp with propertiesnear those of kraft pulp (Dahlmann and Schroeter 1990, Sundquist and Poppius-Levlin1992, Lora and Pye 1992, Funaoka and Abe 1989, Gottlieb et al. 1992, Young 1989).

In 1992 two organosolv processes were operating at full scale and two more weretested at pilot scale. The full scale processes were Organocell (methanol) and ASAM(methanol). The Acetosolv (acetic acid) and Milox (peroxyformic acid) processes werestill at pilot scale (Teder & Olm 1992).

In 1993 Schroeter (Schroeter 1993) reported that the operation of the Organocell plantwas threatened by problems in chemical recovery. The problems associated withchemical recovery seemed at that time to be largely unanswered in all organosolvprocesses.

According to Aziz and Goyal (Aziz & Goyal 1993) cleavage of alpha-ether linkages isthe most important reaction in the lignin molecule breakdown during organosolvpulping. Cleavage of beta-ether linkages is believed to occur in the pulping liquor whenthe lignin has been removed from wood.

According to McDonough (McDonough 1993) the alpha-ether linkage cleavage is themost important lignin breakdown in acidic organosolv pulping. Especially in alkalineprocesses the cleavage of beta-ether linkages also play a role. The easier delignificationof hardwoods compared to softwood is primarily a result of differences in beta-etherreactivity, alpha-ether concentration, lignin content, and propensity to undergocondensation reactions.

In general, the strength properties of organosolv pulps are inferior to those ofcorresponding kraft pulps. However, their strength properties can be improved bytreatment with aqueous solutions of inorganic salts or organic solvents. (Young 1994)

Studies of organosolv processes have shown that the washing operation has animportant role for the whole process (Laxen 1987). A problem is the recovery ofexpensive solvent at the high temperatures required in some processes. Another problemis the solubility conditions of lignin. On the other hand soap and extractives cause muchless problems than in conventional pulping.

One of the most promising organosolv processes is pulping of birch with formic oracetic acid and corresponding peroxy acids (Laamanen et al . 1986, Poppius et al . 1986,Sundquist 1986, Laamanen et al. 1987, Poppius et al . 1987, Laamanen et al. 1988,Poppius et al . 1989, Poppius-Levlin et al . 1991, Koljonen et al . 1992, Sundquist andPoppius-Levlin 1992, Poppius-Levlin et al. 1993, Sundquist 1996). The method iscalled Milox pulping and uses no sulphur and chlorine chemicals.

Recovering the solvent in Milox pulping economically has been shown to bedifficult. The main reason for this is the nature of the solvent system. The spent pulpingliquor contains water, formic acid, and acetic acid as the main volatile components.These three components form a ternary azeotrope. In addition, water and formic acid forma binary azeotrope. In order to find more economical process alternatives for the Miloxmethod, a study was carried out on the effect of the feed liquor composition on theeconomy of a distillation plant separating the three-component mixture.

2. Pulping with organic chemicals

2.1. Alcohols

Alcohols have been used to split lignocelluloses into their components in order to studylignin (Pauly et al. 1934).

Koll and co-workers (Koll et al . 1979) have treated birch with several organicsolvents in the supercritical state. In the temperature range 523-553 K, at pressuresaround 10 MPa, alcohols showed the highest delignifying capability. Carbohydrates arealso attacked. The highest ratio of lignin to carbohydrate degradation is achieved withethanol. The optimum water content of the aqueous ethanol solvent is 25-50 %. Withhigher water content the wood is almost totally liquefied.

More conventional alcohol pulping methods have also been developed.

2.1.1. Methanol

Methanol is most widely used as an additional chemical in pulping. It has been used inkraft, sulphite and soda pulping. Demonstration plants using the alkaline sulphite-anthraquinone-methanol process (ASAM) and the soda pulping method with methanol(Organocell) have been built. A full scale plant using the Organocell method has alsobeen built.

Catalyzed methanol pulping and various pretreatments with methanol have also beenproposed. Methanol can also be used as a solvent when extracting the chemicalcomponents from a lignocellulosic material that has been dissociated by a steamexplosion process (DeLong et al. 1990a, DeLong et al. 1990b).

Muurinen and co-workers (Muurinen et al. 1988a) have made a preliminarycomparison between 27 organosolv methods presented in the literature. When thecomparison criteria were cooking conditions, pulp quality, solvent properties etc., alkali-methanol-anthraquinone pulping of spruce (Gasche 1985a, Gasche 1985b) was found outto be a very promising new pulping method.

The relatively good strength properties of methanol pulps (ASAM and Organocell)have been explained by the distribution of hemicelluloses and DP (degree ofpolymerization) in their fibre walls. The largest portion of hemicelluloses has beenfound to be located in the outer layers of the primary wall while high DP values weredetermined in the outer secondary wall. (Bachner et al. 1993)

If methanol pulps are bleached using xylanase enzyme, a thorough washing is requiredin order to prevent the negative effect of methanol on enzyme activity. (Pekarovicova etal. 1995)

Jimenez and co-workers (Jimenez et al. 1997a) have used aqueous methanol todelignify wheat straw. Their results showed that pulps suitable for papermaking can beproduced even without any catalysts.

Bonn and co-workers (Bonn et al . 1988) have compared organosolv degradation ofwheat straw with methanol and hydrothermal degradation. No qualitative or quantitativedifferences were found in the organic acid composition in the products of the twomethods. It was therefore concluded that methanol does not influence the reactionmechanism of acid formation. Acetic acid, formic acid, glycolic acid and lactic acid werefound in the degradation products of both methods.

Methanol has also been used as an additive in kraft pulping liquors in order to increasethe delignification rate. (Olm & Teder 1990, Norman et al. 1992)

Compared to the sulphite process, methanol pulping will probably increase the costsof certain parts of the plant and also lead to an increase in primary energy consumption(Gasche 1990). The capital costs of a methanol pulping process will probably be in thesame order of magnitude as for sulphite and kraft processes.

2.1.1.1. Catalyzed methanol pulping

The use of absolute methanol as a pulping liquor in the presence of sulphur dioxide hasbeen proposed (Ettel & Hnetkovky 1965). Alkali or earth alkali formates were also addedto the mixture. At 408 K, the pulp was only half delignified having a yield of 80-85 %.

Paszner and Chang (Paszner & Chang 1982) have patented a method where high yieldpulp is produced by cooking fragmented lignocellulose material at a temperature of 453-513 K with aqueous methanol containing 80-98 v-% alcohol. 0.001-0.5 M of analkaline earth metal salt catalyst is added to the mixture. Mineral acids, organic acids andacid reacting metal salts can also be used as the catalyst.

The lignocellulosic material can be cooked using a liquor-to-wood ratio of 4:1(kg:kg). The cooking liquor is a water-methanol mixture containing 50-80 w-%methanol. Magnesium, calcium or barium chloride or nitrate is used as a catalyst (0.005-1 M). The cooking temperature is 453-483 K and the cooking time is less than twohours. Spruce pulp produced by this method has a high hemicellulose content but a lowresidual lignin content. The kappa number of the pulp is 63 and the brightness is about50 %. The pulp can easily be bleached to a brightness of 80 %. (Chang & Paszner 1982)

A mineral acid can also act as a catalyst (Paszner & Chang 1983a). Hydrochloric,sulphuric and phosphoric acids are useful catalysts in concentrations 0.0005-0.008 N.

When spruce chips are delignified with aqueous methanol using calcium chloride asthe catalyst, the pulp yield is 49 % and the kappa number is 15. The rate ofdelignification is highest when the temperature is above 573 K and the methanol contentof the cooking liquor is more than 80 %. (Paszner & Chang 1983b)

When the calcium chloride content of the cooking liquor is 0.05 %, dissolving pulpcan be produced (Paszner & Chang 1983c). 98 % of the original a-cellulose can bepreserved, even after bleaching.

When magnesium sulphate is used as the catalyst, spruce chips can be delignifiedwith a liquor containing 75-85 % methanol (Paszner & Behera 1984, Paszner & Behera1985). After cooking for 45 minutes, the kappa number is 35 and the pulp yield afterbleaching is about 60 %. The energy consumption of the process is low. Methanol isrecovered using distillation and by-products can also be recovered. The process can beoperated economically with a production between 50 to 80 tons of pulp per day.

Neutral alkali earth metal catalyzed methanol pulping has been shown to be aneconomically feasible method for producing pulp from aspen wood. (Paszner & Cho1987)

Alkali earth metal salt, e.g. calcium chloride or magnesium sulphate, catalysedaqueous methanol (78 v-%) pulping of spruce wood indicates two distinct stages ofdelignification, both having first-order kinetics (Paszner & Behera 1989). Initial fast,bulk delignification removes 70 % of the lignin. Loss of residual lignin occurs at aslower rate in the residual delignification stage. Complete fibre liberation is observed ata pulp yield of 57 % and kappa number 72.

When calcium or magnesium chlorides, sulphates or nitrates are used as catalysts(0.05 M), both hardwoods and softwoods can be delignified to a low kappa number usinga methanol-to-water ratio of 80:20 (Paszner & Cho 1989). The viscosity of the pulpremains high. The pulp can be efficiently washed with pulping liquor and it can bebleached without chlorine.

When lignin is precipitated from the black liquor (Abad & Paszner 1989), extractiveswill co-precipitate affecting the properties of the lignin. They also affect thefermentability of the sugars. Recovery of the extractives (resin and fatty acids etc.) willprovide economic advantages for methanol and other organosolv pulping methods. If thepulping liquor is aqueous methanol (80 %), all the resin and fatty acids present in pinewood survive the high pulping temperature (478 K). 78 % of the resin acids and 72 % ofthe fatty acids are found in the black liquor. If lignin is completely precipitated from theblack liquor, 98 % of the resin acids and 60 % of the fatty acids will also precipitate.

Black cottonwood can be delignified with aqueous methanol (70 w-%). The liquor-to-wood ratio is 10:1, and the cooking temperature is 403-483 K (Tirtowidjojo et al. 1988).Sulphuric acid (£ 0.05 M) is used as a catalyst. In a flow-through reactor, pulp with akappa number of 8 and a yield of 47 % can be produced in 180 minutes. The use of aflow-through reactor increases the rate of delignification because precipitation ofdissolved lignin on pulp fibres upon cooling is eliminated. The pulp fibres are also lessdegraded. The recovered lignin has a high molecular weight and is likely to have goodchemical feedstock characteristics.

The lignin recovered from the black liquor after pulping in a flow-through reactor (Pla& Yan 1991) has been found to be very similar to the lignin from alkaline pulping

liquors, when the pulping liquor is aqueous methanol (70 v-%) containing 0.01 Msulphuric acid as the catalyst.

Aspen chips can be delignified with aqueous methanol (30-70 v-%) using sulphuricacid (0.01-0.05 M) or phosphoric acid (0.05 M) as the catalyst (Chum et al . 1988).When the pulping time is 150 minutes at 438 K, and the liquor-to-wood ratio is 4:1, thepulp produced can be digested by enzymes. The yield of fermentable sugars is 36-41 %on wood.

Phosphoric acid has been found to be a better catalyst than sulphuric acid in themethanol pulping of poplar (Chum et al . 1990). It improves the recovery rate of sugarsand lignin removal.

In the organosolv treatment of aspen chips, more than 95 % of hexosan, 80 % ofxylan and more than 90 % of lignin is dissolved in the pulping liquor, when sulphurdioxide is used as the catalyst (Chum et al . 1989). The treatment is carried out for 40-200 minutes at 397-418 K with a liquor-to-wood ratio of 10:1. The cooking liquorcontains 45- 70 v-% methanol and 0.2-1.7 w-% sulphur dioxide. Under these conditions,very little sugar degradation has been observed. The pulp produced has a low xylancontent and is digestible with enzymes into glucose that can be fermented into ethanol.

Cellulose containing raw materials can be pulped in aqueous methanol (60-80 %) inthe presence of oxygen in amounts of 13.7-22.2 % of the o.d. wood at 408-433 K. Theuse of oxygen increases the selectivity of delignification and decreases the energy costs.Ethanol and n-propanol can be used to substitute methanol. (Deineko et al. 1988a)

Pulp from wheat straw has been produced using a pulping liquor containing 0.9 w-%sodium hydroxide, 35.6 w-% methanol and 63.5 w-% water. The delignification can becarried out without any catalyst, but the addition of ammonium oxalate to the pulpingliquor increases the pulp yield. Strength and optical properties of pulps produced by thismethod have been found to be better than the properties of conventional soda pulps.(Ray et al. 1993)

The pulp produced at 438-443 K with aqueous methanol (50 v-%) and a small amountof phosphoric acid can be hydrolysed with enzymes to sugars (Chum et al . 1987). Thepulp has low residual lignin and hemicellulose contents.

The behaviour of extractives in pine wood during pulping with catalyzed 80 %aqueous methanol has been studied, and resin and fatty acids have been characterizedbefore and after pulping trials (Quinde-Abad 1990). Large amounts of resin acids werefound in cooking liquor after 5 minutes of cooking, and after 60 minutes, the blackliquor contained 78.1 and 71.6 % of the resin and fatty acids respectively, while the pulpretained 11.7 and 8.2 % respectively.

The beating resistance was doubled and the tear strength of the paper produced wasincreased, when water soluble hemicelluloses obtained by alkylation of aspen wood flourwere added to fully bleached spruce organosolv pulps produced by using the methodpresented by Paszner and Chang (Paszner & Chang 1983a). (Antal et al. 1991)

Huth and Cole (Huth & Cole 1994) have synthesized a water soluble lignincopolymer by modifying organosolv lignin at the phenolic hydroxyl position withpoly(ethylene glycol)methyl ether (MPEG). The lignin was isolated from blackcottonwood by pulping with aqueous methanol (70 %) using NaHSO4 as the catalyst.

Ferraz and co-workers (Ferraz et al. 1996) have studied a pretreatment with lignolyticfungi followed by organosolv pulping of eucalyptus wood with aqueous methanol (78%)containing magnesium sulphate and calcium chloride. The delignification rate in pulpingwas improved by a one month pretreatment with Trametes versicolor.

In a paper published in 1998, Paszner (Paszner 1998) calls the neutral alkali earthmetal catalysed methanol pulping process the NAEM-ALPULP process. The pulpingliquor consist of 80 % alcohol, 20 % water, and 0.012 % NAEM salt catalyst. Pulpingis carried out in a continuous digester at high pressure (12.7-30.4 MPa). The pulp yieldis up to 60 % and the strength properties are acceptable. The spent pulping liquor isevaporated. When the alcohol content of the liquor drops below 25 %, lignin precipitatesand is recovered. The carbohydrates can be used to produce ethanol and xylitol. The totalloss of methanol in the process is lower than the amount of methanol formed duringpulping.

2.1.1.2. Methanol in sulphite pulping

It has been proved that inorganic additives influence and regulate the sulphite pulpingprocess in presence of methanol (Schorning 1961). Varying the additives of Na2SO4 and

NaHSO4 in methanol-water solutions of SO2 allows rapid pulping.

A modified sulphite pulping process has been developed to produce high yield (53-70%) fully defibered pulps from western hemlock (Bublitz & Hull 1981). Three bases(sodium, ammonium and magnesium) were compared, and only minor differences inpulping characteristics were found. The addition of methanol (30 w-%) to the sulphitepulping liquor offers the promise of rapid pulping of softwoods.

Chip size has been shown to be an important factor influencing pulping rates inmethanol-sulphite pulping (Bublitz & Hull 1982). The recommended size is a thicknessof 4-6 mm. Mixed hardwood can be pulped retaining their advantages over softwoods ofrapid delignification and higher yields at equivalent the kappa number. pH of the freshpulping liquor is shown to be a major factor in determining delignification rates, acidliquors produce pulps most rapidly. No loss of methanol has been detected during thepulping. The addition of methanol to a conventional aqueous sulphite pulping processproduces such benefits as rapid delignification and high yield of good quality pulp. Theseresult in savings in wood costs, energy costs and investment costs. A minimum of 95% recovery of methanol is needed to balance solvent make-up costs against savings inwood costs. About 98 % of methanol is potentially recoverable.

Relative to aqueous sulphite pulps, methanol-sulphite pulps produce denser paperswith higher tensile, burst and fold strengths, yet equivalent tearing strengths at equalpulp yields (Bublitz et al. 1983). Small quantities of DMSO (5 % on wood) can increasesignificantly the delignification rate of methanol-sulphite systems.

Adding methanol to an acid sulphite pulping process reduces the pulping time from 5-6 hours to one hour (Bublitz & Wilson 1983). Because the carbohydrates in wood areexposed to the pulping chemicals for a shorter time, they are less degraded, resulting in ahigh pulp yield of 60-65 %. Methanol improves the penetration of the pulping liquor to

the chips. Small amounts of methanol are chemically combined with lignin, possiblypreventing lignin condensation. Only negligible amounts of methanol are combinedwith wood carbohydrates. Therefore the loss of methanol due to chemical bonding doesnot prevent its recovery.

Adding 30 % methanol to the sulphite pulping liquor increases the delignifying rateof western hemlock (Bublitz 1987, Bublitz 1998a, Bublitz 1998b). When the chemicalcharge is 20 % sulphur dioxide based on o.d. wood, and the cooking time is 60 minutesat 438-443 K, completely defibered pulp is produced. The pulp yield is 60-65 % and thebrightness is normal. Pulp strength is better than that of conventional sulphite pulps inthe same range of total yield. Only 8 kg of methanol is consumed per ton of pulp.

Softwoods and hardwood can be delignified with a sulphite liquor containing methanoland 0.5-3 w-% sulphur dioxide (Chiang et al . 1987). Birch pulp with a kappa number of20-25 and a yield of 44-46 % can be produced when the cooking temperature is 413-418K, the cooking time is 100-200 minutes, the liquor contains 55 % methanol and 1.25-1.5 % sulphur dioxide and the liquor-to-wood ratio is 6:1. With the same liquor-to-woodratio, spruce pulp with a kappa number of 30-40 and a yield of 42-44 % can be producedwhen the cooking temperature is 433-438 K, the cooking time is 120-150 minutes andthe liquor contains 60-65 % methanol and 3-3.5 % sulphur dioxide.

When the pulp produced by the alkaline sulphite-anthraquinone method (ASAQ) isextracted with methanol (Oh et al. 1988), the strength properties become better than theproperties of kraft and ASAM (alkaline sulphite-anthraquinone-methanol) pulps.

The yield of pulp can be increased by adding 35-40 % methanol to the magnesiumsulphite pulping liquor (Kordsachia et al. 1988). The strength of the pulp is alsoimproved when the number of bonds between fibres increases. The delignification canproceed to a lower residual lignin content without impairing the quality of pulp. Thisdecreases the chemical charge in bleaching.

The addition of methanol to acidic sulphite (pH = 1.6) and bisulphite (pH = 3.5)pulping has been tested (Krull et al . 1989). In sulphite pulping, the methanolconcentration 35 % gave the best yield and pulp properties. In bisulphite pulping, theoptimal methanol concentration was 20-25 %. The modification of the magnesiumsulphite process by adding methanol increases the yield and improves the pulpproperties. The delignification can proceed to a lower lignin content and the cookingtime is shorter.

Pulp with good strength properties can be produced from pine by adding methanol tothe magnesium sulphite process (Krull et al . 1991). The cooking temperature is 438 Kand the digester pressure is 1.4 MPa. The pulping liquor contains 30 v-% methanol, 0.8w-% magnesium oxide and 4 w-% sulphur dioxide. A short delignification (45-60minutes) results in pulp having the kappa number 20. The pulp is easy to bleach.

2.1.1.3. The ASAM process

By adding methanol and anthraquinone to the alkaline sulphite liquor pulp with highyield, low residual lignin content, high brightness and good strength properties can be

produced (Patt & Kordsachia 1986). The method is called the ASAM process. The pulpproduced is easy to bleach and the yield after bleaching is 5 % higher than the yield ofkraft pulp. In laboratory experiment chips are steamed for 20 minutes. After steaming,the pulping liquor is added and the temperature is raised to 388 K in 35 minutes. Thepulping liquor is allowed to impregnate for 60 minutes. After impregnation, thetemperature of the mixture is raised to 448 K, where the delignification continues 180minutes. The liquor-to-wood ratio is 4:1. The liquor contains 35 % methanol and 25 %on wood inorganic chemicals. The inorganic chemicals used are sodium hydroxide,sodium carbonate and sodium sulphite. Most of the methanol (70-80 %) is recovered inthe digester flashing after pulping. The same wood species can be used as raw-materialsas in the kraft process. Compared to the kraft process, the ASAM process uses 10 %less inorganic chemicals, the cooking temperature is 5-10 K higher and the digesterpressure (1.3-1.4 MPa) is higher.

70-80 % of the inorganic chemical charge is sodium sulphite (Patt et al. 1987a). Thepulp yield is 14-18 % higher than in kraft pulping. The residual lignin content is lowbecause no lignin condensation occurs. The pulp can be bleached without chlorine and ithas strength properties superior to those of kraft pulp. The methanol content of thepulping liquor can be dropped from 35 % to 20 % without impairing the pulp quality. Inthe pressure relief of the digester, even 95 % of the methanol is recovered. By steamstripping the pulp, the recovery rate can be increased to over 97 %. The recovery of theinorganic chemicals is similar to the recovery in sulphite pulping.

When 25 % on wood sodium sulphite and sodium hydroxide (80:20), 0.2 % on woodanthraquinone and 35 % methanol of liquor are used in ASAM pulping, all wood speciescan be delignified with the liquor-to-wood ratio 4:1 (Patt et al. 1987b). The cookingtemperature is 448 K, and the digester pressure is 1.3-1.4 MPa. The kappa numbers ofthe softwood pulps are about 13, and the kappa numbers of the hardwood pulps are about6. The optical and physical properties of the pulps are good.

The ASAM method can be used to produce beech pulps with very low residualcontents (Kordsachia & Patt 1987). The pulp can be bleached without chlorine chemicalsand its strength properties are better than those of kraft and sulphite pulps. When sodiumsulphite and sodium hydroxide are used as the inorganic pulping chemicals, the methodis called ASAM I. If the chemicals are sodium sulphite and sodium carbonate, themethod is called ASAM II. When sodium carbonate is used instead of sodium hydroxide,no recovery boiler is needed.

Methanol improves the impregnation of the chemicals, acts as a buffer, preventslignin from condensing and stabilizes carbohydrates (Patt & Kordsachia 1988). Thebeech pulp produced by the ASAM method has a kappa number between 10 and 20 and ayield between 49 % and 55 %. The inorganic chemical charge is 20-25 % on dry woodwith the alkali ratio 80:20-70:30 (Na2SO3:NaOH/Na2CO3). The anthraquinone charge is

0.1 % on wood. The liquor-to-wood ratio is 3:1-4:1 and the liquor contains 15-20 %methanol. The pulp can be bleached to the brightness 98.2 ISO without chlorine.

There is no difference in the qualities of pulps bleached without chlorine or with aconventional sequence. (Kordsachia & Patt 1988a)

The environmental compatibility of the ASAM process is based on the followingfactors (Kordsachia & Patt 1988b):

- Very small amounts volatile sulphur compounds are produced.- It is possible to avoid the emission of sulphur containing gases by closing the gascycle.- Chlorine-free bleaching can be used.

It has been discovered that the addition of methanol to sulphite pulping (the ASAMprocess) increases the rate of delignification and improves the selectivity (Paik et al .1988). At kappa numbers 18-20, the yield of ASAM pulp is 0.5-1 % higher than theyield of kraft pulp. The brightness of unbleached pulp is 42-43 %. The best strengthproperties are achieved, when the pulping liquor contains 20 % methanol. Tensile andburst strengths are better, but the tear strength is lower than for kraft pulp.

The ASAM process has been found to be well suited for pulping of pine, poplar,mossy oak and robinia (Winkler & Patt 1988). Pulp properties were found to be good,except for robinia. Commercial pulp production seemed to be most advantageous usingpoplar as the raw material.

The ASAM poplar pulps have 10 % higher strength properties than the correspondingkraft pulps (Patt et al . 1989a). The ASAM pulp has also a higher yield and it is easierto bleach than the kraft pulp.

In principle, it is possible to close the water circulation of the ASAM processbecause the pulp can be bleached without chlorine (Patt et al . 1989b). Methanol isalmost completely recovered during the pressure relief of the digester and during theevaporation of the black liquor. Spruce pulp with the kappa number 27.6 can bebleached to the brightness 84.5 % ISO. After bleaching, the pulp yield is 49.1 %. Birchpulp with the kappa number 14.7 can be bleached to the brightness 90.3 % ISO and theyield after bleaching is 54.7 %.

The suitability of FTIR spectroscopy has been investigated for feedback processcontrol in ASAM pulping (Faix et al . 1989). The correlation between kappa numbersand IR responses for inorganic chemicals is good.

Selectively to a low residual lignin content delignified poplar pulps can be producedby the ASAM process (Kordsachia et al. 1989). The pulp is easy to bleach and has goodstrength properties. Even pulps produced from unbarked wood can be bleached withoutchlorine.

In October 1989, an ASAM pilot plant was started (Anon. 1990a, Anon. 1990b). Thepilot plant can produce 1000 metric tons of pulp per year in a 10 m3 digester. Theinvestment costs of the equipment were 16 million DM. The unit operations included inthe pilot plant are cooking, washing, screening, bleaching, evaporation and distillation.The black liquor is evaporated to the solid content 50-60 %. Methanol is concentrated to98 % in the distillation plant. The methanol loss in recovery is 0.7 %.

The effluent waters from the ASAM process can easily meet the Germanenvironmental regulations (Anon. 1990c):- Chemical oxygen demand (COD) 70 kg/t

ASAM 10 kg/t- Biological oxygen demand (BOD) 5 kg/t

ASAM 3 kg/t- Adsorbable organic halides (AOX) 1 kg/t

ASAM 0

Spruce pulps with kappa numbers of 9-35 have been produced in the pilot plant (Pattet al . 1990a). The cooking temperature was 453 K and the cooking time was 120-180minutes. The inorganic chemical charge was 24-30 % and the anthraquinone charge was0.1-0.15 % on wood. Methanol concentration in the pulping liquor was 9-14 %. Thestrength properties of the pulp can almost be preserved in chlorine free bleaching andthey are slightly improved in conventional bleaching.

The advantages and disadvantages of the ASAM process compared to the kraft processcan be summarized as follows (Patt et al. 1990b):

Advantages:- Higher yield in softwood pulping- Better pulp strength properties- Chlorine-free bleaching in a sequence with low chemical demand- No odour problems- Good heat economy- No or only a small caustizising system- No or minimized effluent treatment- Alkali can be recovered from the bleaching stages- Low fresh water consumptionDisadvantages:- Higher temperature and pressure- Longer cooking time- Increased chemical demand for cooking- Higher shive content of the pulp- Methanol recovery is needed- Conversion plant for chemicals is needed.High yield birch pulps can be produced by the ASAM method (Kordsachia et al .

1990a). The pulp has excellent strength properties at kappa numbers of around 10.Because of the low residual lignin content and the high original brightness, the birchpulp is easy to bleach. A chlorine free sequence can be used to bleach the pulp to thebrightness 90 % ISO. The pulp quality is not impaired. In birch pulping, the liquor-to-wood ratio 4:1 is used and the pulping temperature is 448 K. The pulping liquorcontains 35 v-% methanol and 0.2 % on dry wood anthraquinone. The alkali charge is 25% on wood calculated as sodium hydroxide. Sodium sulphite, sodium hydroxide andsodium carbonate can be used as alkali. Better results are achieved using hydroxide, butcausticizing can be avoided by the use of carbonate.

When pulping Spanish eucalyptus (Kordsachia et al. 1990b) the pulp produced has alower kappa number and similar strength properties as the corresponding kraft pulp. Thecharge of bleaching chemicals is lower than in kraft pulping.

The slow thermal degradation of ASAM waste liquor (Faix et al. 1990) has beenstudied between 303 and 1233 K using thermogravimetry-mass spectrometry (TG-MS).Dried liquors were heated on the thermobalance in argon atmosphere or in anargon/oxygen (70/30) mixture with a 20 K/min heating rate. The weight loss of theASAM liquors is similar in both atmospheres up to 713 K. Although ten times moresulphur dioxide is liberated in the argon/oxygen atmosphere than in inert gas, the

sulphur cannot be completely recovered as sulphur dioxide. Smelt bed pyrolysis withtemperatures over 1223 K will be needed for an ASAM recovery cycle.

When softwoods are delignified in the ASAM pilot plant, the liquor-to-wood ratio 5:1is used and the digester pressure is 1.2-1.4 MPa (Schubert 1990). The typicalcomposition of the pulping liquor calculated as sodium hydroxide on dry wood is:- Na2SO3 15-20 %

- Na2CO3 0-7 %

- NaOH 0-10 %- Anthraquinone 0.05-0.15 %- CH3OH 10-20 v-% in liquor.

In spruce pulping (Schubert 1990), the lowest kappa number (17) and the highestbrightness (32 % ISO) are achieved at the alkali ratio 17:3:4 (Na2SO3:NaOH:Na2CO3).

The alkali ratio does not affect the strength properties of the pulp. Also the effect of themethanol amount used is small. In pine pulping, the anthraquinone charge can bedecreased to 0.075 % without impairing the pulp quality.

Softwoods can economically be pulped with the ASAM method to kappa numbersaround 20, and hardwoods to kappa numbers around 10 (Schubert et al. 1990). Withthese grades of delignification, the pulp quality is equal to the quality of correspondingkraft pulps.

The most significant differences between the ASAM and the kraft processes are(Kopfmann 1991a):- If sodium hydroxide is not used, no causticizing and no lime kiln are needed in theASAM process.- Methanol recovery is needed in the ASAM process.- The use of methanol increases the digester pressure to 1.2-1.4 MPa.

If an existing kraft mill is converted to an ASAM mill, the following modificationsare needed (Kopfmann 1991a):- A new digester is needed because of the higher pressure.- The methanol recovery system has to be built.- Chemical conversion has to be used to recover alkali (Na2SO3 and Na2CO3).

The investment costs of the ASAM process are similar to the costs of the kraftprocess (Kopfmann 1991a).

The use of methanol in the ASAM process requires additional considerationsconcerning explosion-prevention and general safety at work (Kopfmann 1991b). Attemperatures over 284 K, methanol forms above the liquid phase an inflammable vapourphase. To prevent explosions, the formation of an explosive vapour phase (5.5-31 v-%methanol) has to be prevented and all ignition sources have to be eliminated. Methanolis poisonous and respirators have to be used when handling it.

Most of the methanol is recovered by condensing the vapours formed during digesterflashing (Black 1991). The recovery rate can be increased by stripping the black liquor.Methanol is concentrated by distillation. Anthraquinone is consumed during pulping andcannot be recovered. After stripping, the black liquor is concentrated in an evaporationplant. The concentrate from evaporation is burned in a boiler under reducing conditions.Inorganic chemicals are recovered in the smelt of the boiler as sodium sulphide andsodium carbonate. The smelt is dissolved in water and the solution is causticized. The

inorganic chemicals used in the ASAM process can be converted in a process that issimilar to the chemical cycle in alkaline and neutral sulphite processes.

When North American Douglas-fir is delignified with the ASAM method, lowerkappa numbers (22 vs. 33) and higher yields (48 vs. 46) are achieved than in kraftpulping (Zimmermann et al . 1991). In conventional bleaching, the ASAM pulp needshalf the amount of chlorine chemicals needed for kraft pulp. The yield loss of the ASAMpulp is also lower. Tear strength for the bleached pulps are about the same, but tensilestrength for the ASAM pulp is about 20 % higher. ASAM pulp can also be bleached bythe chlorine-free OZPN sequence (oxygen, ozone, peroxide with nitrilamine).

When the maximum temperature of the ASAM pulping has been reached, about 60 %of the sodium sulphite has been consumed (Patt et al . 1991a, Patt et al. 1991b). 10-12% has been converted to sulphate and 1-2 % to thiosulphate. At the end of thedelignification, 75 % of the sodium sulphite has been consumed. The recovery rate ofmethanol is 99 %. About 1 % of methanol reacts irreversibly with lignin. About 0.02-0.04 % of the total methanol is adsorbed or chemically bound in the pulp. When themaximum cooking temperature is reached, 50 % of the lignin has dissolved. About 30% of the methoxyl groups in lignin are eliminated during ASAM cooking and 1% ondry wood of methanol is formed. Also xylanes form methanol. The molecular weight ofthe dissolved lignin is low (ca. 1800). The presence of methanol protects thecarbohydrates. Methanol also improves anthraquinone solution and reduces thedissociation of cooking chemicals. The black liquor contains 15 % carbohydrates andtheir degradation products.

ASAM pulps have been compared with methanol-sulphite (MS) pulps (Patt et al.1991c). Both methods produce pine pulps that can be bleached without chlorine(alkali/oxygen, ozone, hydrogen peroxide). Unbleached MS pulp has a high originalbrightness and chlorine-free bleaching is easy. Good strength properties do requirethough a comparatively high residual lignin content. Also ASAM pulps are easy tobleach and their strength properties are superior to those of MS pulps.

Softwood ASAM and kraft pulps can be bleached chlorine-free using oxygen, ozone,peracetic acid, Caroic acid and peroxide (Hammann et al. 1991). Strength losses occurmainly during peracetic acid bleaching and peroxide treatment. Due to its good strengthproperties and high initial brightness, ASAM pulp is better suited for chlorine-freebleaching.

The use of methanol in pulping affects the design of the equipment (Hudeczek &Lindow 1992). In pulping, methanol increases the pressure and improves the solution ofsulphur dioxide. Vapour formed in washing of the pulp contain methanol and theexplosion risk is apparent. Methanol is a poisonous and inflammable liquid and has tobe stored properly.

Eucalyptus pulps produced by the ASAM method are easy to bleach when comparedwith kraft pulps (Kordsachia et al. 1992). Chlorine-free bleaching can also be used.

The ASAM black liquor can be used to produce lignin-phenol gluing agents forparticleboard production. (Pecina & Kuhne 1992b)

Ozone bleaching of oxygen delignified pine ASAM paper grade pulp and beechASAM dissolving pulps at high and medium consistency have been studied (Oltmann etal. 1992). Medium consistency bleaching resulted in similar delignification and pulp

viscosity as ozone treatment at high consistency. Due to fibre deformations resultingfrom fluidization in the medium consistency bleaching, the pulps showed superior tearstrength and lower tensile strength in comparison with those pulps bleached at highconsistency.

Experiences gained through three years’ operation of the ASAM pilot plant have beenreported (Schubert et al. 1993). Spruce chips were delignified up to kappa numbers of 16and pulps were bleached to brightnesses of over 88 % ISO using a OZP sequence. Thestrength properties of the ASAM pulps corresponded to those of the kraft pulps. Therecovery rate of methanol was 99.3 %.

The Borgards group (Borgards et al. 1993) has compared ASAM and kraft pulping ofsouthern pine. When both processes were applied in order to obtain pulps at kappa levels15, 20 and 25, ASAM pulping resulted in slightly higher yields. The ASAM pulps hadmuch higher viscosities, better strength properties and higher brightnesses.

When pulping Japanese red pine using the ASAM method, optimum results wereobtained using 20 % methanol, sodium sulphite and sodium hydroxide at a ratio of 8:2,and a cooking time and temperature of 448 K and 150 minutes. Tall oil from the ASAMprocess was found to contain higher amounts of abietic acid and linoleic acid and lowerlevels of dehydroabietic acid, palmitic acid and oleic acid, when compared to the kraftprocess. (Paik et al. 1994a)

Optimum pulping conditions for producing ASAM pulps from oak and birch havebeen determined by Paik (Paik et al. 1994b). Oak pulp with a kappa number of 19.7 anda screened yield of 43.1 % was obtained by using an active alkali (as Na2O) charge of 17

%, 20 % methanol addition, a cooking temperature of 438 K and cooking time of 150minutes. When similar conditions, except for a 30 % methanol addition, were used forbirch, pulp with a kappa number of 17.8 and a screened yield of 56.8 was obtained. Theoptical and strength properties of birch pulps were superior to those of oak pulps. Whencompared with corresponding kraft pulps, the ASAM pulps had higher yields and betterstrength properties.

If an existing kraft batch digester is used to pulp beechwood by the ASAM method,the cooking temperature has to be reduced to 433 K in order to keep the operatingpressure at 1.0-1.1 MPa. This results in the need to prolong the cooking time if lowkappa number pulps are desirable. The beech ASAM pulps are easily bleached.Conventional bleaching sequences need only about half the amount of active chlorinecompared with corresponding kraft pulps. (Obrocea et al. 1994)

Oltmann et al. (Oltmann et al. 1994) and Kordsachia et al. (Kordsachia et al. 1994)have studied the transition points between pulping and bleaching. They producedsoftwood ASAM pulps with kappa numbers 33, 28, 22 and 19. These pulps wereoxygen delignified to kappa numbers around 9 and then bleached in a ZEP sequence tobrightnesses between 86 and 88 % ISO. Their results showed that it was favourable tostop pulping at a kappa number above 25, because the bleachability of ASAM pulpswas good. The yield advantage obtained by stopping pulping at a relatively high lignincontent was mainly kept during chlorine-free bleaching. Higher final brightness andbetter pulp viscosity were also achieved in this way. When pulping was stopped at akappa number above 25, the pulps had higher tensile and burst strength after OZEPbleaching than the more intensively cooked pulps.

When compared to the kraft process, the ASAM process requires two additionalchemical recovery steps: methanol recovery and conversion of Na2S to Na2SO3.

Methanol is flashed in the first stage of the evaporation plant. The condensate of theevaporator is stripped and then rectified. The methanol recovery rate is more than 99.5%.(Glasner et al. 1994)

Kordsachia’s group (Kordsachia et al. 1995) has studied OZ(E)P bleaching of ASAMsoftwood pulp with a kappa number of 28. In order to avoid severe damage of thecarbohydrates, the ozone charge should be below 1 %. When the first bleaching stagewas an oxygen delignification to kappa number 9, only 0.9 % ozone and 1 % hydrogenperoxide were needed to achieve a brightness above 87 % ISO.

Glasenapp et al. (Glasenapp et al. 1996) have studied totally chlorine-free bleachingof spruce ASAM pulps with and without an ozone stage in the bleaching sequence. Thesequences were O(OP)AZP and OA(OP)P. Higher brightness levels were achieved withthe sequence containing an ozone stage. Other pulp properties were similar. Thechemical costs of the bleaching sequence with ozone were estimated to be about 50 %lower.

According to Schild and co-workers (Schild et al. 1996) ASAM delignification ofEucalyptus globulus wood meal can be expressed by means of a kinetic model with threeparallel pseudo-first order rate reactions. They calculated the activation energy of the fastinitial delignification as 88 kJ/mol. For bulk delignification they obtained a value of101 kJ/mol when paper grade pulp was produced.

The Obrocea group (Obrocea et al. 1996) has studied bleaching of alkaline ethanol,alkaline methanol and ASAM beech pulps using the sequence CEHD, DED or D(EP)D.The ASAM pulp was found to have the highest bleachability. It could be bleached tofull brightness with 40 % less chlorine than a corresponding kraft pulp. The strength ofthe ASAM pulp was only slightly lower than that of the kraft pulp.

According to Patt (Patt et al. 1996), ASAM pulps can be peroxide bleached using ascatalysts binuclear manganese complexes incorporating manganese in a high oxidationstate. Considerable lignin degradation occurs at 423 K and the selectivity of thedelignification is very good. Short totally chlorine-free sequences can be used to achievehigh brightnesses without the use of ozone.

Puthson’s group (Puthson et al. 1997) has compared three modifications of theASAM process and the kraft process in order to delignify eucalyptus chips. Thesemodifications were ASAM I with sodium hydroxide, ASAM II with sodium carbonate,and PH ASAM with a mild prehydrolysis. The strengths of unbleached and bleachedASAM pulps were found to be up to 20 % higher than those of the kraft pulps. The bestresults were obtained with the ASAM I process.

According to Schubert et al. (Schubert et al. 1998), the ASAM process stabilisescelluloses at acid sulphite pulp levels and hemicelluloses at kraft pulp levels. Thisexplains the increased pulp yield. ASAM pulps can be produced at existing kraft mills.Due to the higher sulphidity level, only 33 % of the total production may be ASAMpulp if the recovery boiler is not changed.

The development of the ASAM process has been reviewed by Patt and co-workers(Patt et al. 1998). According to them, commercial scale operation of the process ispossible without a major risk.

2.1.1.4. Methanol in soda pulping

Methanol solutions of sodium hydroxide have been found to be more efficientdelignifying agents than aqueous solutions with the same concentration. (Larocque &Maass 1941)

Delignification by alkali-methanol cooking is more rapid and the pulp yield is 7-8 %higher than in kraft pulping (Nakano et al . 1976). One of the optimum conditions is apulping liquor containing sodium hydroxide 40 g/dm3 and methanol 400 g/dm3,maximum temperature 433 K, cooking time 30-60 minutes. The alkali-methanolmethod results in more rapid dissolution of lignin and a higher retention of carbohydratesthan kraft pulping.

In alkali-methanol pulping of birch and beech (Nakano et al . 1977), the pulp yieldsare 4-5 % higher than in kraft pulping. With the same residual lignin content of pulp,only the tear strength is lower than for kraft pulp. The methanol loss in cooking is 13-21 kg per ton of wood. Methanol can be formed from lignin and hemicelluloses 6-13 kgper ton of wood. Methanol is easily removed from the pulp by washing and can berecovered at the black liquor evaporation.

In alkali-methanol pulping (Kobayashi et al. 1978) of hardwoods, where the liquor-to-wood ratio is 4:1, the pulping liquor contains 40 % (w/v) methanol and the active alkalicontent is 16 % calculated as sodium oxide, the yield of pulp is about 2 % higher atkappa numbers 20-25 than in kraft pulping. The delignification is slower than in kraftpulping but faster than in soda pulping. The strength properties of the pulp are nearthose of kraft pulps but the tear strength is lower. The price of the pulp is estimated tobe slightly higher than the price of kraft pulp, which is mainly caused by the methanolrecovery. The use of methanol requires closed equipment, increasing the investmentcosts. Based on the comparison the authors claimed that the alkali-methanol process willnot be economically feasible in the near future.

The rapid delignification in alkali-methanol pulping is due to the prevention ofcondensation through the methylation of active benzylalcohol groups in lignin molecule(Daima et al. 1978).

When studying the behaviour of lignin and carbohydrates in alkali-methanol pulping,it has been found that the peeling-off reaction is suppressed (Daima et al . 1979). Thismay suggest that the isomerization rate of the glucose end group to a fructose end groupis slower in alkali-methanol pulping than in soda pulping.

When liquor-to-wood ratio of 15:1, a temperature of 433 K, a pulping time of 30-60minutes, a methanol concentration of 40 % and sodium hydroxide concentration 40g/dm3 are used in alkali-methanol pulping (Nakano et al. 1981), delignification is fasterand the pulp yield is 4-5 % higher than in kraft pulping. The fast delignification iscaused by the prevention of lignin condensation. The tear strength is lower but the otherstrength properties are equal to those of kraft pulp. The methanol loss is about 14 kg perton of chips. 99 % of the methanol can be recovered by washing or vacuum evaporatingthe pulp.

Pulps with good strength properties can be produced from hardwoods and softwoodusing a pulping liquor containing sodium hydroxide and 40 % methanol (Gasche 1985a,Gasche 1985b). The high residual lignin content of the pulp can be decreased by adding

anthraquinone 0.5-2 kg per dry wood to the pulping liquor. When the liquor-to-woodratio is 4:1, the active alkali charge is 22 % per dry wood, the pulping temperature is433 K and the pulping time is 300 minutes, beech pulp with a quality near that of kraftpulp can be produced. Methanol is formed at 10 kg per ton of pulp from the methylethergroups of lignin. The yields of hardwood pulps are 15 % higher than in sulphitepulping.

Alen (Alen 1988a) has studied the formation of carboxylic acids during the sodapulping of birch wood in aqueous methanol, ethanol and isopropanol. In addition toformic and acetic acids, 20 monocarboxylic acids and 12 hydroxy dicarboxylic acids wereidentified. The total amount of formic and acetic acids were 55-60 % of total acids. Thedicarboxylic acids represented only a minor fraction (4-6 %) of the total acids. Thedominant hydroxy monocarboxylic acids were glycolic, lactic, 2-hydroxybutanoic,xyloisosaccharinic and glucoisosaccharinic acids.

The formation of carboxylic acids during the soda pulping of pine wood in aqueousmethanol, ethanol and isopropanol has also been studied (Alén 1988b). In addition toformic and acetic acids, 20 monocarboxylic acids and 12 hydroxy dicarboxylic acids wereidentified. The total amount of formic and acetic acids were 35-45 % of total acids. Thedicarboxylic acids represented only a minor fraction (9-15 %) of the total acids. Thedominant hydroxy monocarboxylic acids were glycolic, lactic, 3,4-dideoxypentonic andglucoisosaccharinic acids.

The soda-anthraquinone-methanol method (Melo & Muller 1989) can be used toproduce pulps suitable for papermaking. The adding of methanol produced higher yields,higher kappa numbers, lower viscosities, higher breaking lengths and lower tear factors.Methanol also improves the selectivity of delignification. The main process variable ishowever the amount of soda.

Pine chips have been pulped in aqueous methanol, then treated in an additionalpulping stage to which sodium hydroxide was added (Martinez & Sanjuan 1990). Thisprocess produced pulps with mechanical properties similar to those of industrial pinekraft pulps. It was found that the temperature in the first pulping stage affected pulpbrightness and the extent of delignification.

Methanol can be added to the soda pulping of sugar cane bagasse (Mogollon 1991).The best pulp is produced when the methanol concentration in the pulping liquor is 30% and the sodium hydroxide content is 12 %. The pulping temperature is 433 K and thepulping time is 15 minutes.

When the active alkali charge in alkali-methanol pulping (Abe 1993) is 15 % forhardwoods and 19 % for softwoods, the methanol charge is 50 v-% in the pulping liquor,the anthraquinone charge is 0.2 % on wood and the liquor-to-wood ratio is 5:1,delignification is faster and selectivity is better than in kraft pulping. The yield at thesame kappa number is 5-10 % higher than the yield of a kraft pulp.

Sugar cane bagasse can be pretreated with a soda-methanol liquor for the production ofchemimechanical pulps (Ramos et al. 1993).

The El-Sakhawy group (El-Sakhawy et al. 1995a) has studied pulping of sugar canebagasse with methanol and ethanol. Their studies indicated that sodium hydroxide shouldbe added to the pulping liquor in order to obtain easily bleachable pulps at a suitablepulping temperature.

2.1.1.5. The Organocell process

The Organocell process was originally called the MD process. Pulp produced by the MDprocess has strength properties near (90-95 %) those of kraft pulp (Edel 1984). Thepulping has two stages. The first stage is cooking with aqueous methanol at 468 K. Themain part of the sugars and 20 % of lignin is dissolved in this stage. The secondcooking stage is carried out with a methanol-water-sodium hydroxide solution at 443 K.Methanol is recovered by evaporation and distillation. Lignin is precipitated inevaporation and it can be separated using a centrifuge. The lignin from the second stagecan only be precipitated by decreasing the pH of the liquor. The energy content of driedlignin is 25 MJ/kg.

The spent liquors from the two pulping stages can be fractionated by precipitation.The liquor from stage one is weakly acidic and contains as solvents only methanol andwater. Liquor number two contains additionally sodium hydroxide, which makes thefractionation more complicated. The salt can be separated by ion exchange orelectrolysis. Only 10-20 % of the carbohydrates can be precipitated. (Feehl 1984)

Lignins from the MD process have been incubated with different types of fungi.White-rot fungi converted the lignin by splitting the aryl-ether linkages. A water solubleacid-precipitable polymerizate was formed. (Haars et al. 1985)

The MD process starts with the impregnation of the liquor to the chips (Baumeister& Edel 1983a, Baumeister & Edel 1983b, Baumeister & Edel 1985). Both of thepulping stages are carried out in the same digester. The solvent of the first stage containsmethanol 90 w-% in water. The pulping time is 40-120 minutes, the temperature is 453-483 K, the pH is 3.8-4.9, the liquor-to-wood ratio is 7:1-10:1 and the pressure is 1.2-4MPa. In the second stage, the water content of the solvent is increased and 5-30 %sodium hydroxide and 0.01-0.15 anthraquinone on dry wood is added. The pulping timeis 10-80 minutes and the temperature is 423-463 K. The pulp is washed in two stagesand methanol can be recovered from the spent washing liquor by stripping. Methanol isrecovered from the spent liquor from the first pulping stage by flashing. Lignin isprecipitated by neutralizing the liquor and it is separated by filtration. The remainingliquor is evaporated and the alkali is re-used.

In 1987, the MD alias the Organocell process had reached the pilot plant stage (Anon.1987a). The production capacity of the plant was five metric tons of bleached pulp perday. The pulping stages are continuously carried out in the same digester and the stagesare separated by the density difference of the liquors. The alkali is recovered and thelignin is separated electrolytically. The precipitated lignin is separated by filtration anddried in a spray dryer.

Lignin and alkali can be recovered electrolytically (Edel et al. 1986). The alkalinelignin solution is introduced into the anode chamber of a divided electrolytic cell andelectrochemically acidified therein. Simultaneously the liquor is electrochemicallyconcentrated in the cathode chamber. The cell is divided by an ion exchange membrane.The precipitation of the lignin starts at pH 9.5 and is complete at pH 4. The oxygendeveloped at the anode produces with the liquor and the precipitated lignin a foam whichcan be separated by a flotation installation.

The power consumption of the electrolysis equipment is about 25 Ah per litre ofliquor (Wabner et al. 1986). The investment costs are about 5000 DM per square meterof anode surface. The operating costs are about two times the price of sodium hydroxide.

Feckl and Edel (Feckl & Edel 1987) reported that the production of the Organocellpilot plant was raised to six tons per day. The properties of the pulp were near those ofkraft pulp. The temperature of the first pulping stage was 468 K and 15 % of the woodwas dissolved. Half of the dissolved material was lignin. In the second pulping stage, themethanol content of the liquor was decreased to 30 % and the sodium hydroxide contentwas 5-10 %. The cooking temperature was 443 K and anthraquinone was used as thecatalyst. Methanol was recovered by distilling the spent liquors. In the distillation of thespent liquor from the first pulping stage, lignin precipitated and it was separated by acentrifuge. After distilling the spent liquor from the second stage the remaining alkalineliquor was treated electrolytically to precipitate the lignin and to recover sodiumhydroxide. The pilot plant was compatible with the environment and was operatedaround the clock in a highly populated residential area (Dahlmann & Schroeter 1989).

Lindner and Wegener (Lindner & Wegener 1987) have analyzed lignins obtained fromthe Organocell process. At the end of the second pulping stage, the lignins had thehighest oxygen contents which is an indication of oxidation. The first stage ligninscontained 1.3-2.2 % nitrogen which is an indication of the presence of proteins. Afterthe second stage, no nitrogen was found.

Lignins separated from the spent liquors of the Organocell process are sulphur-free andof low molecular nature (Lindner & Wegener 1988a). They are chemically much lesschanged than kraft and sulphite lignins.

All wood species can be delignified by the Organocell method (Lindner & Wegener1988b). Pulp with kappa number 30 can be produced by pulping spruce using 50 %methanol in the first stage. The lignin dissolved in the first pulping stage contains aconsiderable amount of organic impurities. Second stage lignin showed characteristicchanges in elemental composition and functional groups, except for the methoxylgroups, as reaction time progressed. The residual lignins are less changed than thedissolved lignins (Lindner & Wegener 1989). Lignin methylation by methanolic liquoris almost negligible.

In the Organocell demonstration plant, pulp was bleached with the three-stagechlorine-free sequence EEP/D/EP (Edel 1989, Williams 1989). In addition to thebleaching, the demonstration plant contained wood storage, an impregnation unit, adigester, an evaporation train, chemical recovery (distillation and electrolysis), washers, ascreen, a dryer and a boiler. The precipitated lignin was recovered using a filter press anda spray dryer. The low price and boiling point, as well as the easy separation ofmethanol from pulp, were good reasons for its use. A shortcoming of methanol is thehigh operating pressure of the equipment. Pulping was carried out in two stages becausesodium hydroxide and anthraquinone in the second stage shortened the pulping time andmade it possible to delignify softwoods. Spruce pulp with a kappa number of 30 can beproduced. Aqueous methanol (50 %) was used in the prehydrolysis and impregnation (30min) at 423 K. In the first pulping stage, the liquor contained 50 % methanol, thetemperature was 463 K, the pulping time was 20 minutes, pH was 4-5, the liquor-to-wood ratio was 3.5:1 and the pressure was 2.8-3.2 MPa. In the second stage, the liquor

contained 30 % methanol, the sodium hydroxide charge was 18-22 % on wood, thetemperature was 443 K, the pulping time was 40 minutes and the liquor-to-wood ratiowas 4:1. The pulp was washed at 388 K for three hours using 2.5 tons of washing liquorper ton of pulp. The evaporate from black liquor evaporation contained 70 % methanoland the concentrate was distilled to 90 %. The methanol loss was 0.8 %.

During the first pulping stage (methanol-water), the lignin content of the secondarycell walls decrease slowly, but in the compound middle lamella only the reactivity oflignin increases. During the second stage (methanol-sodium hydroxide) thedelignification proceeds fast in both layers but the residual lignin content in thecompound middle lamella remains higher than in the secondary walls. (Fengel et al .1989)

In 1990 (Dahlmann & Schroeter 1990a, Dahlmann & Schroeter 1990b), thedemonstration plant produced three metric tons per day of bleached (87 % ISO) pulp. Thebleaching was carried out in three stages: oxygen with peroxide addition, chlorine dioxideand alkaline peroxide.

The molecular weights of lignins isolated during delignification at the demonstrationplant have been found to reveal substantial differences depending on the origin (firststage, second stage etc.). Lignins from the second cooking stage can be classified as lowmolecular lignins having molecular weight ranges similar to kraft lignins. (Lindner &Wegener 1990a)

Dissolved and residual spruce lignin have been subjected to permanganate oxidationand thioacidolysis in order to study changes in lignin’s structure during Organocellpulping (Lindner & Wegener 1990b). Lignin degradation reactions known from sodapulping are dominant in the second pulping stage, including enol ether formation. Thechemical effect of methanol is restricted to a minor methylation of the alpha-C-atom.Methanol also improves the liquor diffusion into the chips and prevents lignincondensation.

The Organocell demonstration plant used the bleaching sequence OEP-D-P to producepulp with a brightness of 88 % ISO (Pappens 1990). The amount of AOX compoundsin the effluent waters from bleaching was less than 0.5 kg/ton of pulp. The two stagecontinuous digester had been designed with the help of Kamyr. The pulp was washed atthe bottom of the digester. After bleaching, the pulp was mechanically dewatered to asolids content of 42 %. Spent liquors were evaporated resulting in a methanol recoveryrate of 50 %. An electrolysis unit recovered the caustic soda from the second pulpingstage, but in full scale a recovery boiler was planned to be installed.

The modification of a sulphite mill to an Organocell mill, producing 430 metric tonsof bleached pulp per day, was planned. The mill was estimated to start operation in1992. (Zitzelsberger 1990)

The electrolytic recovery of lignin has been found to modify the structure of ligninfrom the Organocell demonstration plant. These changes included polymerizationreactions and reactions of the side-chain. (Lobbecke et al. 1990)

When pulping spruce, most of the hemicelluloses and a part of the lignin is dissolvedin the first pulping stage (Puls 1991). The dissolved hemicelluloses are well preservedand 25 % of them can be precipitated. Over 40 % of the precipitated hemicelluloses ismannane.

In the first pulping stage, the alcohol-water mixture hydrolyses the a-aryl ether bondsof lignin, forming phenolic and benzyl alcohol groups (Schroeter 1991). Anthraquinoneis added to the second stage, causing benzyl alcohol to oxidize to alpha-carbonyls, whichare less susceptible to the secondary condensation reactions that occur in the presence ofalkali. The effective delignification in the two-stage process is caused by ligninfragmentation during the first pulping stage and prevention of condensation reactionsduring the alkaline second pulping stage.

It has been found that the first pulping stage of the Organocell process can beeliminated (Schroeter & Dahlmann 1991, Brodersen et al. 1992). This simplificationresults in a stronger pulp. The reduction of the methanol charge to 30 v-% results in asignificant reduction of the operating pressure, decreasing the overall costs of the plant.

The organic solvent only prevents the dissolved lignin from condensing. Thedelignification is caused by an acidic hydrolysis. In the one-stage Organocell process, thechips are impregnated with aqueous methanol (50 %). The cooking in the presence ofalkali is carried out at 438 K. During the cooking, the alkali displaces the methanol inthe chips. The cooking time is two hours and the alkali is recovered in a boiler. Usingozone bleaching a pulp brightness of 88 % ISO can be reached. (Leopold 1991)

Lignin-powder can be obtained from the spent liquors by acidic precipitation. Thelignins are chemically less altered than comparable technical lignins, and they haverelatively low molecular weights, as well as low sugar contents. The lignins can be usedto split emulsions, to produce vanillin and vanillic acid, and to protect agricultural seedfrom being eaten by birds. (Kopra-Schafer 1991)

The electrolytic recovery of lignin in the Organocell process has been found to causesevere changes on the structure of the lignins. The molecular weights of the ligninsincrease due to polymerization reactions. Changes in aromatic and phenolic structuresand side chains were also observed. The degree of modification were mostly dependent onthe current densities applied. (Lobbecke et al. 1991).

In 1991, a full scale Organocell digester was built (Anon. 1991a). It was the first fullscale organosolv digester in the world. The investment costs of the plant producing150000 metric tons of pulp per year were estimated to be 350 million DM.

Wegener (Wegener et al . 1991) has subjected lignin obtained from the Organocelldemonstration plant to hydroxypropylation in order to improve the reactivity of thelignin in isocyanate particle-board resins. The hydroxypropylation was effectively carriedout with an almost total exchange of phenolic hydroxyl groups. Chemical conversionwithout the removal of, for example, autopolymeric products did not improve thereactivity of the lignin with isocyanate resins. A major drawback of the method was alsothe poor solubility of the lignin in isocyanate.

Lignins obtained from the Organocell process can be converted and liquefied byhydropyrolysis in order to be used as raw materials in the chemical industry. The yieldsof oils produced depend strongly on the hydrogen pressure. The oils contain mainlyphenol, m/p-cresol, o-cresol, 4-ethyl- and 4-propyl-phenol. (Meier & Faix 1991)

Full scale production with the Organocell method was started in October 1992(Young 1992a, Jende 1992, Anon. 1993). The annual production of the plant was150000 metric tons of pulp. 65 % of the production was fluff pulp and 35 % paper gradepulp. Before cooking, the chips were steamed to remove air and impregnated with

aqueous methanol. The one-stage cooking was carried out at 433-438 K. The liquor-to-wood ratio was 4.2:1. No methanol was added to the digester and its concentration in thepulping liquor was 25-30 %. The pulping liquor also contained sodium hydroxide 125g/dm3 and anthraquinone 0.1 % on dry wood. The digester pressure was 2 MPa. Thepulp was bleached with the sequence OE/PPP to the a brightness of 90-92 % ISO. Theblack liquor was flashed and the vapour formed was used to heat the evaporator trainwhere the rest of the liquor was concentrated to a solid content of 55 %. Methanol wasconcentrated by distillation. No methanol loss occurred in cooking but the loss in theother parts of the process was 5-10 kg per ton of pulp. Alkali was recovered in a similarway as in kraft pulping. The process consumed 8 tons of steam and 780 kWh of powerper ton of pulp. The power excess was 3-5 %.

A linear scale-up of the process was not possible (Leopold 1992), because differentpieces of equipment affect the pulp quality in different ways. Continuous pulping resultsin better pulp than batch pulping. The bleachability of the pulp depends on the pulpwashing, which should be carried out at a high pH and at a high stock consistency.

The lignins dissolved under alkaline conditions during Organocell pulping can be usedto make lignin-phenol gluing agents. Up to 65 % of the pure phenol can be substitutedwith natural polyphenols obtained from the spent pulping liquors. The properties of theparticle-boards using this gluing agent meet the demands of building materials. (Pecina& Kuhne 1992a)

Meier’s group (Meier et al . 1992) has subjected Organocell lignins to catalytichydropyrolysis. Using a palladium catalyst, they have produced up to 80 w-% oils asliquid products. The solid residue was only 1 % of the original material.

Merkle et al. (Merkle et al . 1992) have acetylated Organocell lignins and studied thehigh-molecular-weight fractions by means of combined static and dynamic lightscattering. Weight average molecular weights between two and ten millions were found.Low molecular weight lignin fractions were found to have a tendency to cluster togetherforming large aggregates. These aggregates are not stable, which leads to a highflexibility of the overall particle structure.

The following goals for the air and water emissions of the Organocell full scale millproducing 430 metric tons of pulp per day have been set (Weidenmuller 1992):- SO2 0 t/a

- NOx 490 t/a

- CO 360 t/a- Dust 70 t/a- Chlorine 0.15 t/a- AOX 0.05 t/d

In 1993 it was reported that there had been some problems with the operation of thefull-scale digester. The higher delignification rate and the higher content of fines in woodin comparison with laboratory-scale pulping caused instability in the digester operation.Methanol can be recovered with a loss of only 10 kg per metric ton of pulp. BayerischeZellstoff GmbH decided to start the full-scale production with Organocell fluff pulps.The price of fluff pulp is higher than the price of paper pulps and the strength of fibresin fluff pulp is of secondary importance. (Leopold 1993)

The incorporation of Organocell lignin into polypropylene in amounts of 2-10 wt-%has been found to be a cheap and simple process to utilize it. Polypropylene films withsufficient tensile strengths can be obtained in the absence of commercial stabilizers. Theaddition of Organocell lignin makes the films partially biodegradable. (Kosikova et al .1993a, Kosikova et al. 1993b, Kosikova et al. 1994)

Organocell lignin can be used as a filler for polypropylene (PP) and poly(ethene-co-vinylacetate) (EVA) containing 13 wt-% vinylacetate. Both lignin-filled thermoplasticsshow matrix reinforcement with increasing lignin content. A 30 wt-% lignin addition toEVA doubles Young’s modulus maintaining high elongation at break. (Rosch &Mulhaupt 1994)

Fagerlind and Agren (Fagerlind & Agren 1995) have invented a process for theevaporation of spent pulping liquors and recovery of volatile substances from the spentliquors of alkaline alcohol pulping processes. Evaporation and solvent recovery arecarried out simultaneously in a multiple effect evaporation train where pure water,vapour condensate or steam may be injected to the warmer side of an evaporator effect inorder to increase the condensing temperature of the vapour. Heat transfer in theevaporator effects is further improved by divided heat surfaces which makes an earlyseparation of the alcohol, such as methanol, possible. A high organic solvent content inthe spent liquor lowers the condensing temperature and impairs heat transfer.

The Gliese group (Gliese et al. 1996) has studied enzymatic prebleaching of softwoodOrganocell pulps with xylanase. Their results showed that this pretreatment improvedthe bleachability of the pulps. Low enzyme dosages (2-6 IU/g) and short reaction times(30-60 min) are preferable in order to maintain pulp yield and to avoid losses inviscosity and strength properties. The treatment should also be carried out at lowconsistency in order to prevent a possible attack of the enzyme on the fibre surface,leading to deteriorating mechanical properties in pulp.

The bleachability of softwood Organocell pulps can be increased by removing residuallignin from the pulp by hemicellulase enzyme treatment. The bleaching chemicalconsumption is also reduced. (Zimmermann & Tajana 1996)

The quality of the pulp produced by the one-stage Organocell process at theBayerische Zellstoff mill in Kelheim did not meet the market requirements. This lead tothe bankruptcy of the company. According to Neumann (Neumann et al. 1997), the one-stage cooking of pine shows a serious lack of selectivity in delignification. In order toimprove the process, they suggest that the caustic soda should be added at a later time incooking. This would divide the cooking process into two stages. First a prehydrolysis inaqueous methanol at 433 K, then alkaline cooking at the same temperature would beconducted. After bleaching to 85 % ISO, the strength of the pine pulp is on the level ofTCF softwood kraft pulps.

2.1.1.6. Other alkaline methanol processes

Sarkanen (Sarkanen 1982) has patented a method for selective defiberizing anddelignifying of lignocellulose in the presence of alkali. The pulping liquor contains

water, a water-miscible organic reagent and a sulphide or bisulphide compound selectedfrom the group consisting of alkali metal sulphides and bisulphides, ammoniumsulphide and ammonium bisulphide. The yield (70 %) is higher than in kraft pulping.Best results are achieved when the organic reagent is methanol and/or ethanol. The bestsulphide or bisulphide compounds are sodium sulphide and/or ammonium sulphide. Bothhardwoods and softwood can be delignified. When the water-organic reagent ratio is50:50-80:20, the sulphide charge 0.2-1 M, the liquor-to-wood ratio 4:1-10:1, theoriginal pH of the liquor 8.5-11, the cooking temperature 433-443 K and the cookingtime 1-5 hours, a pulp is produced with higher burst and tensile strengths but lower tearstrength than the kraft pulp.

Ahmed and Kokta (Ahmed & Kokta 1992) have presented a pulping method wherewood chips are impregnated with methanol, steam cooked at 453-468 K for 1-4 minutes,then subjected to explosive decompression and refined to produce pulp. Theimpregnation liquor contains 20-80 % methanol and 0-8 % inorganic alkali.

Ku’s group (Ku et al. 1993) has compared alkaline methanol pulping and ethanolpulping of taiwania and eucalyptus. Their results showed that the alkaline process had abetter delignification selectivity. The alkaline methanol eucalyptus pulps had higheryields and equal strength properties when compared to the corresponding kraft pulps.

2.1.1.7. Methanol lignins

Methanol lignin has been prepared by extracting spruce wood meal with absolutemethanol and using hydrochloric acid as the catalyst (Brauns & Hibbert 1935). Themethoxyl content of the lignin obtained was 21.6 %. The formula of the native ligninwas estimated to be C47H52O16. When lignin was prepared on a larger scale, the

presence of a second fraction, soluble in ether-dioxane, was detected (Compton et al.1936). The original lignin and this second fraction can be obtained in a pure state byfractionation with dioxane and benzene. The benzene-dioxane-soluble fraction has amethoxyl to hydroxyl group ratio of 5:3.

The composition of spruce methanol lignin prepared by the action of anhydrousmethanol-hydrogen chloride on spruce meal has been found to vary with the temperatureand time of extraction (Compton & Hibbert 1937). The reaction mixture contained twoproducts, having a methoxyl content of 21.6 % and 24 %, respectively. Highertemperatures and longer time of heating favour the formation of the latter.

Characteristics of lignins obtained from acidic methanol delignification of blackcottonwood have been studied. At the beginning of the delignification, over 60 % of thedissolved lignin is water-soluble. As delignification progresses, the amount of water-insoluble lignin increases in the dissolved material. (Pla et al. 1986)

Lignin can be liquefied by hydrogenolysis in the presence of a lower aliphatic alcoholand a catalytic composition of metal sulphides. When methanol is used in the presenceof a catalytic mixture of the sulphides of divalent iron, copper and tin, the total yield ofmonophenols can be as high as 65 % and the total yield of cresols is about 45 %.(Urban & Engel 1988)

Bennacer et al. (Bennacer et al. 1989) have studied lignin reactions with methanol,ethanol and DMSO discovering that the beta -ether bonds in lignin are the strongest andthe glucoside bonds are the weakest.

When methanol lignins solubilized in aqueous dioxane were treated with laccaseenzyme, 13C-NMR analysis showed that the main difference between treated anduntreated lignins is the increase of the aliphatic alcohol and ether carbon concentrationduring enzyme treatment. Laccase in its immobilized form seems to be suitable forcarrying out conversion processes with lignin derivatives in organic media. (Milstein etal. 1990)

Cook and Hess (Cook & Hess 1991) have used lignin obtained from catalyticmethanol pulping to produce resins. The cooking liquor contained 70 w-% methanol and10 w-% sulphuric acid. The resins were produced by treating the lignin with aqueoussodium hydroxide, aqueous formaldehyde and phenol. Up to 40 % of phenol ororganosolv lignins in wood adhesives can be replaced with this resin without affectingthe performance of the adhesive.

Balogh and co-workers (Balogh et al. 1992) have isolated lignin from pine sawdustand studied it by using chemical analysis and infrared spectroscopy. The sawdust was pre-treated with a methanol-benzene mixture (1:1) and then pulped with methanol in thepresence of hydrochloric acid (2 N). The isolated lignin presented incorporation ofsolvent molecules in the lignin. Similar results were obtained by pulping the pre-treatedsawdust with ethanol and 1-propanol.

The Robert group (Robert et al . 1993) has characterized organosolv lignins with the13C NMR method. The lignins studied were produced among other things by phosphoricacid catalyzed methanol cooking of spruce and by a acetic acid catalyzed TMP method.Both methods produced lignin with high yield. When the mineral acid acts as catalystlignin is degraded and condensed. The changes in lignin are negligible when using theorganic acid as catalyst.

Lignin has been isolated from pine using nine organic solvents with aqueoushydrochloric acid (2.0 N). The molecular weights of lignins obtained were determined.The results show that lignins isolated with alcohols (methanol, ethanol, 1-propanol, 1-butanol and 2-butanol) have similar molecular weights that are considerably higher thanthe molecular weights of the lignins obtained using other solvents (chloroform, acetone,dioxane and tetrahydrofuran). (Balogh 1993)

When aspen chips are cooked in aqueous methanol (70 %) with or without a catalyst(0.01 M H2SO4), the most important reaction in delignification is the cleavage of

arylethers and condensation of lignin (Lai & Mun 1993). Methanol prevents lignincondensation.

Purina (Purina et al . 1994) has separated and analyzed the outer fibre cell wall layersP and S1 of Organocell and ASAM birch and pine pulp fibres. The residual lignin

contents in layers P and S1 of Organocell and ASAM birch pulp fibres were determined

to be 7.0 % and 3.3 %, which were 4.7 times the concentration in layers S2 and T. The

residual lignin content of layers P and S1 in Organocell and ASAM pine pulp fibres

were 6.3 % and 7.3 %, being two times the content in layers S2 and T. The

hemicellulose contents were also analyzed and the distributions were found to be moreeven in pine pulps than in birch pulps.

2.1.1.8. Summary

Methanol improves penetration of the pulping liquor into the lignocellulosic materialand therefore increases the delignification rate. It also prevents lignin from condensingduring the process, which results in low pulp kappa numbers. Pulp quality is typicallynear the quality of a corresponding kraft pulp. Methanol is one of the componentsformed during pulping. This is a probable reason for the very low methanol lossesreported.

Methanol is a poisonous chemical and forms inflammable vapours at relatively lowtemperatures. Therefore a pulping process using it has to be carefully designed andoperated.

Methanol is a low boiling alcohol and therefore it can be relatively easily recoveredby distillation.

The most promising methanol pulping method is the ASAM process. The pulpquality seems to be acceptable and existing kraft mill equipment may be used. Thepresence of methanol however requires additional equipment and makes the recoverycycle more complicated and expensive than in a kraft process.

2.1.2. Ethanol

Ethanol has been used to separate the wood components in order to study them (Klason1893a, Klason 1893b, Klason 1908, Klason & Fagerlind 1908, Holmberg & Runius1925, Hagglund & Urban 1928, Kleinert & Tayenthal 1931, Rassow & Lude 1931,Ritter & Barbour 1935, Wacek & Morghen 1937, Wacek & David 1937, Brickman etal. 1939, Hunter et al . 1939, Sarkanen & Schuerch 1957, Sarkanen et al . 1981,Fullerton 1983, Vuorinen 1983, Sousa et al. 1986). Today it is one of the mostpromising organic pulping chemicals.

In many ethanol pulping studies small, amounts of organic acids have been used ascatalysts (Sarkanen 1980). When high pulping temperatures are applied, no catalystaddition is needed. These methods are probably catalysed by the organic acids releasedfrom wood.

Lyublin et al. (Lyublin et al . 1988) state as a result of their studies that ethanolpulping could replace all the heavily polluting sulphite mills in the USSR.

Lignin can be eliminated from exploded wood by washing with ethanol or otheralcohols. (Delong & Delong 1991)

Kleinert (Kleinert 1933) has shown that ethanol and water form azeotropic mixturescontaining about 95 w-% at temperatures between 393 and 453 K. This behaviour will

not cause problems in ethanol recovery because nearly pure ethanol is not needed in anymethod presented so far.

In addition to chemical pulping, ethanol can also be used as an additive in mechanicalpulping in order to reduce energy consumption. (Aravamuthan et al. 1993)

Ethanol extraction can also be used as a bleaching stage in a sequence includingchlorine dioxide treatment. (Brogdon et al. 1997)

Ethanol pretreatment has been shown to improve the efficiency of enzymatichydrolysis of wood. (Holtzapple & Humphrey 1984, Skachkov et al. 1991)

2.1.2.1. Catalyzed and autocatalyzed ethanol pulping

Campbell (Campbell 1929) examined the simultaneous effect of ethanol andhydrochloric acid on spruce wood. He found out that two main reactions were involved,namely, hydrolysis of carbohydrates, caused by the presence of alcohol, and the action ofalcohol on lignin in the presence of hydrochloric acid.

A method for pulping wood and other fibrous plant material using aqueous ethanolwas patented 1932 (Kleinert & Tayenthal 1932). The water content of the pulping liquorcould be varied between 20 and 75 %. Delignification was carried out under elevatedpressure at temperatures above 423 K and the pulping liquor was changed several timesduring delignification. The pH of the liquor was adjusted by adding basic or acidicchemicals in concentrations less than 0.1 %.

As a result of experiments where cotton was treated with water-ethanol mixtures ofvarious concentrations, Kleinert (Kleinert 1940) has stated that ethanol protects celluloseduring the delignification.

The reaction conditions in aqueous ethanol-hydrochloric acid pulping of maplewoodmeal have no effect on the yield of distillable oils. The mechanism of ethanoldelignification (ethanolysis) have been shown to involve both depolymerization andpolymerization reactions. Distillable oils are formed by cleavage of high molecularlignin aggregates, while simultaneous polymerization reactions yield a complex ethanol-insoluble polymer. (Hewson et al. 1941a)

Delignification of maple wood by ethanolysis involves cleavage of lignin-lignin orlignin-carbohydrate linkages, or both, and is catalyzed by the presence of hydrogen orhydroxyl ions in the pulping liquor. The temperature increase accelerates the cleavageand dissolution of the lignin is facilitated by the presence of an appropriate solvent.(Hewson et al. 1941b)

In 1971 Kleinert patented (Kleinert 1971) a process for pulping fibrous plant materialusing a mixture of water and ethanol as the pulping agent. Pulping was carried out in acounter-current manner. The fibrous material was immersed in the pulping liquor atelevated temperature and pressure. The spent cooking liquor was conducted into a multi-stage flash evaporator from which ethanol was recovered and recycled for make-up of thepulping liquor. The pulping liquor contained 20-75 w-% ethanol. The maximumpulping temperature was 453 K. After washing and screening, the pulp yield was 54 %and the lignin content of the pulp was 1.9 %.

Aqueous ethanol in a medium concentration range can be used to delignify bothhardwoods and softwoods (Kleinert 1974a). Delignification rates of hardwoods areconsiderably higher than those of softwoods. The major cause for the increased yields (50-56 %) of ethanol pulps is carbohydrate retention. Strength properties of the ethanolpulps are in the same range as those of bisulphite pulps produced from the same wood.After distilling off ethanol from the black liquor, a major fraction of the solubilizedlignin separates as a quasi-molten phase. Continuous ethanol pulping with recovery ofboth the solvent and the solubilized wood substances is technically and economicallyfeasible.

Ethanol delignification can be carried out at a pH near the neutral value (Kleinert1974b). This reduces the thermal degradation of cellulose and hemicelluloses resulting in4-4.5 % higher total yields than in kraft pulping. Ethanol is not consumed duringpulping and the total loss of less than 1 % on wood occurs during recovery.

Aqueous ethanol penetrates easily into the structure of freshlycut softwoods andhardwoods (Kleinert 1975a). This results in practically uniform delignification. The fibreseparation on ethanol-water pulping is related to the removal of both lignin andhemicellulose fractions.

In laboratory and pilot plant ethanol pulping of beech, the pulp yields before and afterbleaching are 3.3 % and 4.1 % respectively higher than in kraft pulping (Kleinert 1976).The moisture content of the wood used was 30 % and the delignification was carried outat 458 K. The pulping time was 30 minutes and the liquor-to-wood ratio was 10:1.

The desired pH value (4-7) of the aqueous ethanol solvent can be adjusted usingammonia or ammonium hydroxide (Kleinert 1978).

Paszner and Chang (Paszner & Chang 1979) have presented a method for treatingminced lignocellulose. The process consists of boiling the material in an acidifiedmixture of aqueous solvents. The mixture contains 30 to 70 % water and 70 to 30 % anorganic solvent. Preferable solvents are ethanol and acetone. The pH of the pulpingliquor is adjusted to 1.7-3.5 by adding a catalytic compound, for example, oxalic acid.The cooking time is preferably between 453 and 473 K. The minimum cooking time isthree minutes.

Baumeister and Edel (Baumeister & Edel 1980) found out that the results regardingpulp quality, published by others, could not be reproduced. By adding a catalyst toethanol-water pulping they were able to improve the delignification and to reducecarbohydrate degradation. The strength properties of the pulps produced were comparablewith sulphite pulps. A liquor-to-wood ratio of 6:1 was used. The minimum cookingtime was 23 minutes at 478 K. The maximum digester pressure was 4.1 MPa. Thepulping liquor contained 50 % ethanol and its pH was adjusted with acetic acid. Low pHvalues gave the lowest kappa numbers.

A method has been proposed (Myerly et al. 1981), where chips are contacted in apressure vessel with the solvent mixture. After delignification, the cellulosic cut isfiltered and washed with fresh solvent. The filtrate and the spent washing liquor arecombined and evaporated. The evaporation is carried out under reduced pressure, and thelignin separates as a solid and can be recovered. The pulping liquor contains 50 w-%ethanol and the pulping temperature is 473 K. The hardwood fibres produced have atensile strength which is almost as good as kraft pulps.

During aqueous ethanol pulping the pH of the pulping liquor decreases from theoriginal 7 to 3.8. This can be explained by the cleavage of acetyl groups from thehemicelluloses. The dissolved ethanol water lignins showed no distinct differences fromkraft lignins with the exception of the sulphur and ethoxyl contents. (Meier et al. 1981)

Baumeister and Edel (Baumeister & Edel 1982) have patented a method for continuouspulping of plant fibre material, wherein the material was countercurrently treated with anorganic solvent. The solvent was ethanol or isopropanol and the pulping liquorcontained 40-60 % of it. The chips were impregnated before cooking, with the solvent atatmospheric pressure and at a temperature between 313 K and 353 K. Pulping wascarried out at 453- 473 K. Ethanol was recovered from the spent pulping liquor usingflash evaporation.

When using the ethanol-water system, the pulping results are highly dependent on themaximum pulping temperature and the liquor-to-wood ratio (Young & Achmadi 1983).To achieve a low kappa number with reasonable carbohydrate retention, a liquor-to-woodratio close to 20:1 is preferable. The secondary lignin condensation reaction can beavoided using a dilute pulping medium, a two stage cook or a continuous recycling ofthe pulping liquor. Aspen chips should be preconditioned in the ethanol-water liquor toimprove the extent of delignification. The best approach is a gradual rise to themaximum pulping temperature from 373 K for one hour. The pulping continues for anhour at the maximum temperature 438 K. Pulps with kappa numbers around 30 andtotal yields near 50 % can be produced with this method.

Single stage uncatalysed pulping of Eucalyptus globulus with aqueous ethanol (50 v-%) at the temperature of 438-453 K produces pulps with yields above 60 % and residuallignin contents of about 10 %. The pulps have low energy requirements for beating, buttheir strength properties are comparable only to bisulphite pulps. (Pereira et al. 1986)

The ethanol pulping procedure has been studied with regard to its suitability for theproduction of dissolving pulp from beech wood (Peter & Hoeglinger 1986). Pulp ofrather good quality was produced in a pilot plant. The viscose fibres processed from thepulps were comparable with those made of sulphite pulps. The dissolved solids areseparated from the black liquor in a spray dryer and ethanol is concentrated in adistillation column. Ethanol is formed during the pulping and its recovery rate is 101-102 %.

A method for chemical recovery in ethanol pulping has been patented (Peter et al.1984). The black liquor is flashed and evaporated before ethanol recovery by distillation.In an alternative method, the dissolved solids are removed from the black liquor by spraydrying and ethanol is recovered by distillation.

For the acidic ethanol process (Lonnberg et al. 1987a, Lonnberg et al. 1987b) thewashing is proposed to start with HiHeat-type displacement of spent liquor with freshcooking liquor (Laxen 1987). The pulp is then washed countercurrently with water.

Birch wood has been treated in a flow apparatus with ethanol-, 1-butanol- andethylenglycol-water (50/50 v/v) mixtures (Koell & Lenhardt 1987). Higher temperatures(498-523 K) can be used than in batch delignification. Hemicelluloses and lignin can beseparated from the cellulose without severe decomposition of pentosans. The pulps weredelignified by more than 90 % and can be bleached easily. Due to the high pulpingtemperature, the cellulose had low DPw values and may be used as dissolving pulps.

Pulps with satisfactory strength properties were obtained by pulping rice straw withaqueous ethanol (1:1) and ethylenediamine (6 v-% on solvent) at 393 K.. The pulp yieldwas 51 % and the kappa number was about 23. (Guha et al. 1987)

The effects of various inorganic additives on aqueous ethanol pulping have beenstudied. Well delignified pulps with good physical properties in fairly high yields wereobtained. The functions of the additives were found to include reaction anddepolymerization of the lignin and protection of polysaccharides by restricting theirdegradation by end-group peeling. The solvent was found to improve the selectivity ofdelignification by increasing the solubility of lignin and by reducing the hydrolysingpower of the liquor. It also improves the transfer and adsorption of reagents in the wood.Among the additives tested, ammonium sulphide fulfilled its functions well. Goodresults were also obtained with sodium sulphite in ammonia and ammonium chloride.(Ivanow & Robert 1987)

Laxen (Laxen et al. 1988) has studied the solvent recovery of acid ethanol pulping(Lonnberg et al . 1987a, Lonnberg et al. 1987b). They found that some formic andacetic acids are formed during pulping. When fresh solvent was initially used in brownstock washing as displacement liquor in order to avoid lignin precipitation, the acidswere partly conveyed to the digester. The load of dissolved organic matter also increasedin the cooking liquor. The solvent loss was calculated to be less than 15 kg per metricton of pulp. The energy consumption was estimated to be at the same level as in kraftpulping.

Park and Phillips (Park & Phillips 1988) have studied ammonium hydroxide catalyzedsolvent pulping of poplar. Delignification parameters included in the study were theconcentration of ammonium hydroxide, time and temperature of the reaction, and type ofsolvent. The addition of 0.82 M ammonium hydroxide to the pulping liquor increaseddelignification and decreased carbohydrate degradation. Further increase of theconcentration had no additional effect. At low pulping temperatures the extent ofdelignification increased with reaction time. At high temperatures it was found that woodwas relignified. No major differences between the three solvents studied (ethanol,butanol, phenol) were observed.

A process where cellulosic material is delignified by rapidly heating it in a liquorcontaining water, ethanol and a buffer, has been patented (Roberts et al. 1988). Sodiumbicarbonate is used as the buffer to maintain a neutral solvent extraction.Methylanthraquinone is also added to the liquor. The material is cooked in the liquor asit is heated from 423 K to the maximum temperature of 473-553 K. The mixture is thenrapidly cooled to a temperature below 423 K.

Optimum parameter values for larchwood pulping in aqueous ethanol solutions ofsulphur dioxide are: pulping temperature 398-418 K, sulphur dioxide concentration 15-24 % and pulping time 25-60 minutes. Under these conditions, a pulp with a yield of57.6 % and a kappa number of 28.6 was produced. Ethanol can be recovered in twostages. The spent liquor is first treated in a cyclone. It is then fed into a settling tank toprecipitate lignin followed by distillation. (Primakov & Barbash 1988, Primakov &Barbash 1989)

Organosolv pulping does not require acidic or basic conditions to delignify wood(Faass et al . 1989). Relatively neutral pulping liquors at high temperatures for short

residence times can be used without significantly damaging the carbohydrate pulp.Sodium bicarbonate can be used to buffer an ethanol-water-methylanthraquinone liquor.The maximum cooking temperatures (473-513 K) with low residence times (less than 20minutes at maximum temperature) can be used to produce high quality pulps.

Sinner et al. (Sinner et al. 1989) have patented a method where lignocellulosicmaterials are pulped with an aqueous mixture, containing ethanol or acetone 30-70 v-%,at 373-463 K and at elevated pressure. The pulping time is from two minutes to fourhours. If mineral acids (0.001-1.0 N) are added to the mixture, the pulping is carried outat 443-493 K and the pulping time is 2-180 minutes. The black liquor is vacuumdistilled to separate lignin.

According to Sabatier et al. (Sabatier et al. 1989) the reaction pH is the mostimportant parameter affecting the selectivity of bagasse ethanol pulping. Acid catalystsprovoke carbohydrate hydrolysis. This leads to low pulp yields. Dissolving pulps can beproduced by this method through adequate control of the pulping parameters. If moredrastic conditions are applied to achieve a complete hydrolysis of the lignocellulosicmaterial, it is possible to obtain a fermentable sugar solution. Aluminium chlorideseems to be the most suitable catalyst. If paper grade pulps are produced, soda-ethanolpulping seems to be a better choice.

Aravamuthan and co-workers (Aravamuthan et al. 1989) have compared acid catalyzed(H2SO4) ethanol delignification with uncatalyzed ethanol delignification and ethylene-

diamine-ethanol-anthraquinone delignification. The sulphuric acid catalyzed ethanol-water(7:3) system was found to be more effective than the two others.

Prehydrolysis of bagasse with 0.1 % sulphuric acid at 398 K for four hours has beenfound to remove 41 % of hemicellulose without remarkable degradation of lignin orcellulose. Aqueous ethanol (50 %) pulping of this prehydrolysed bagasse at 473 K fortwo hours results in the removal of more than 90 % of the lignin and most of theremaining hemicellulose. Degradation of cellulose during pulping is negligible. (Patel &Varshney 1989)

Bamboo can easily be delignified with aqueous ethanol (50 %). The strengthproperties of the pulp can be improved by adding 1 % sodium xylene sulphonate. Thetensile index of the pulp was comparable to that of a corresponding kraft pulp but tearand burst indexes were lower. (Singh et al. 1989)

The Puech group (Puech et al. 1990) has studied the delignification of oak wood withaqueous ethanol (55 v-%) in a flow-through reactor. This method reduces to a minimumthe secondary reactions generally affecting lignin in a closed reactor.

Products ready for commercial use can be recovered from pine wood by extracting itwith, for example, ethanol (Caperos Sierra et al . 1990). The products are mainly rosinand fatty acids. The extracted wood can be used for papermaking. Extracting the chipsprior to pulping reduces the consumption of pulping chemicals.

Nunez and Reinoso (Nunez & Reinoso 1990) have studied the conversion of thekappa number to residual lignin content for bagasse pulps produced by cooking inaqueous ethanol. At pulp yields below 60 %, they found the following linearcorrelations: insoluble klason lignin 0.123, kappa number 2.20; soluble klason lignin0.016, kappa number 0.14; total klason lignin 0.139, kappa number 2.34.

Pulp yields are increased and the use of organic solvent decreased when 20-65 w-% onwood of aluminium oxide is added to an aqueous ethanol pulping liquor (Komissarenkov et al. 1990). If the cooks are carried out in the presence of aluminium palmitate, or a 15-25 % aqueous solution of aluminium propylate, the pulp yield is increased and theamount of residual lignin in pulp is decreased (Komissarenkov et al. 1991a). If thegamma-oxide of aluminium that has been modified by the ion of a metal (sodium, zinc,magnesium, cobalt, nickel, chromium or iron) is added to an aqueous ethanol pulpingliquor, the amount of residual lignin in the pulp is reduced (Komissarenkov et al. 1991b).

The effect of ethanol concentration and liquor-to-wood ratio has been investigated forautocatalyzed solvent pulping of a mixture of hardwoods (Goyal et al. 1991,Goyal et al.1992). Delignification increased with decreasing ethanol concentration over the rangestudied (50-70 v-%). Optimum selectivity in terms of delignification and pulp viscositywas found at 60 % ethanol concentration. When pulping was carried out at 468 K in 60v-% ethanol, the kappa number increased slightly when the liquor-to-wood ratio wasincreased to 4.5:1. Under these conditions, cellulose was almost completely resistant todissolution.

When softwood chips are delignified with oxygen in aqueous ethanol solutions, pulpis produced with a yield of 51 %, when the degree of delignification is 90 % (Deineko &Makarova 1991). The amount of oxygen needed is 14 % on dry wood. Up to 80 % of thesolubilized lignin are polymers containing more than 5 % carbonyl and carboxyl groups.

Pulp with optical and strength properties suitable for newsprint paper can be producedfrom sugar cane bagasse using a multistage method. In the first stage the bagasse iscooked in aqueous ethanol at 448-458 K. The resulting pulp is then subjected to a fourstage alkali-oxygen extraction. The yield of the resulting pulp is high. (Sanjuan &Gomez 1991).

According to Buryachenkov (Buryachenkov et al. 1991) acid-catalyzed aqueous ethanolpulping of aspen followed by washing, thickening and alkaline extraction produces pulpswith yields of 50-55 % and kappa numbers of 10-20. Delignification in the presence ofcatalytic amounts of hydrochloric acid, aluminium chloride, phosphoric acid,hydroxylamine hydrochloride or oxalic acid at 428-448 K was found to follow first-stagekinetics. The most effective catalysts were phosphoric acid and hydroxylaminehydrochloride. These two catalysts gave pulps with 2-3 points higher yields at similarkappa numbers.

Synthetic polymers can be grafted to wood polymers concurrent with the pulping.This method is called graft pulping (Young & Achmadi 1992). Free radicals are formedduring pulping and they can be used to initiate copolymerization of synthetic monomerswith lignocellulosic fibres. Vinyl monomers can be grafted to aspen wood pulp inethanol based solvent pulping. Only low levels of polymer loading were obtained whensingle monomers were added to the pulping system. Better results were obtained byusing a binary monomer system of acrylonitrile and styrene. Lignin was the main site ofgrafting.

A high-yield (70 %) birch pulp has been obtained by using as the pulping liquor anaqueous ethanol solution containing sulphur dioxide and ammonium hydroxide. They

have found that the fibre walls of this pulp have high hemicellulose contents, especiallyin the two outer layers. (Purina et al. 1992)

The delignification rate of aqueous ethanol pulping can be increased by the addition ofa sorbent to the pulping liquor. Komissarenkov et al. (Komissarenkov et al. 1992a)have proposed several additives to aspen pulping in an aqueous 20 % ethanol solution.The best results were obtained by using �-aluminium oxide. The sorbents permitted areduction in the ethanol concentration and reduced lignin condensation.

Elnitskaya and co-workers (Elnitskaya et al. 1992) have proposed a pulping methodwhere chips are delignified in aqueous ethanol in the presence of acetic acid. The residuallignin content of the pulp can be reduced and the cooking time shortened if the chips areball-milled in the cooking liquor prior to cooking.

The Komissarenkov group (Komissarenkov et al. 1992b) has invented a pulpingmethod comprising cooking of wood chips in aqueous ethanol in the presence of analuminium containing additive (10-40 w-% on wood). Delignification is improved whenthe additive consists of the product from the precipitation of kraft lignin with aluminiumsulphate that has been pyrolysed.

Hemp (Cannabis sativa) stem wood chips can be delignified in an ethanol:water(60/40 v/v) mixture (Tjeerdsma & Zomers 1993, Zomers et al. 1995). In autocatalyzedbatch pulping, the best selectivity was obtained by cooking the chips 2.5 hours at 468K. The pulp yield is 48.6 % and the kappa number is 24.8.

When whole stem hemp is pulped with aqueous ethanol (60 v-%), bast fibers areoverpulped, resulting in lower tear strength. Optimum pulp properties are only reachedwhen core and bast fibers are separated. (Zomers et al. 1993, Zomers et al. 1995)

Tjeerdsma (Tjeerdsma et al. 1994) has found second order polynomial regressionmodels to be appropriate to describe the autocatalysed ethanol pulping process of hempstem wood fibres as a function of time, temperature, ethanol concentration and liquor towood ratio. The estimated models can be used to predict the kappa number, the yieldsand the DP of the pulp.

Sansigolo and Curvelo (Sansigolo & Curvelo 1994, Sansigolo & Curvelo 1995)have studied aqueous ethanol pulping of eucalyptus in order to identify optimum pulpingconditions. Their results showed that pulp yield increased with increasing temperature,and time at maximum temperature. The optimum cooking temperature was found to be468 K. The pulp kappa number decreased when pulping at high temperatures and forlonger periods. The relationship between yield and pulping time and between residuallignin and pulping time were found to be linear with regard to residual delignification,indicating approximately first-order kinetics.

Liang et al. (Liang et al. 1994) have studied the bleaching of ethanol pulps producedusing bagasse and wheat straw as raw materials. Both OH and HAP sequences werefound to be suitable for the this task.

Abramovitch and Iyanar (Abramovitch & Iyanar 1994) have studied the use ofmicrowaves as the energy source in organosolv pulping of poplar and pine. Underoptimum conditions, poplar pulps with yields of 45-60 % and residual lignin contents of2-4 % were obtained using an aqueous pulping liquor containing 70 % ethanol orbutanol. The delignification of pine was found to be more difficult and to result in pulpswith higher residual lignin contents.

Black liquors from oxygen-organosolv pulping of eucalyptus wood in aqueous ethanol(50 v-%) and aqueous acetic acid (80 v-%) have been characterized by Neto and co-workers (Neto et al . 1994). Lignin was precipitated and separated by filtration. Thedegradation products in solution were separated by simple extraction techniques. Fivemain groups were isolated: lignin (11-12 % on dry wood), sugars (10-17 % on drywood), aliphatic acids (12.5 % on dry wood), aromatic acids (2 % on dry wood) and lowmolecular weight phenols (1 % on dry wood).

Pulping of juvenile (9-year old) poplar with aqueous ethanol has been studied.According to these studies, the best pulping conditions are an ethanol concentration of60 v-%, a pulping time of 210 minutes and a temperature of 468 K. Under theseconditions pulps with low kappa numbers (20) and good yields (54 %) can be produced.(Sierra-Alvarez & Tjeerdsma 1995a, Sierra-Alvarez & Tjeerdsma 1995b)

The Curvelo group (Curvelo et al. 1995) has studied the kinetics of pulpingeucalyptus with aqueous ethanol (1:1 by volume). As in the kraft process, the kineticbehaviour shows three phases: initial, bulk and residual. The initial and residual phasesare not selective for lignin removal. A major part of the delignification occurs in thebulk phase with high selectivity.

Deineko (Deineko 1995) has studied the conversion of lignin during pulping of woodby oxygen in the presence of aqueous ethanol. The lignin transformations during theprocess have been found to be connected by the interaction of its reactivity centres bothwith the solvent components and oxygen.

It has been shown that a biological pretreatment of aspen chips with fungi results in akappa number reduction of 6-9 units after aqueous ethanol pulping. Kappa numbers from10 to 13 can be reached when the chips are pretreated with Trametes villosus,Phanerochaete chrysosporium or Phanerochaete sanguinea followed by delignificationwith aqueous ethanol (45 v-%) containing 0.2 % hydrochloric acid on wood at 438 K.(Aleksandrova et al. 1995)

Oxidation of the main components of wood can be carried out using molecularoxygen in aqueous ethanol. Methanol, 1-propanol and 2-propanol can also be usedinstead of ethanol. Oxygen pressure of 2 MPa, an oxidation temperature of 423 K and anethanol concentration of 40 v-% were used to delignify spruce and aspen chips in arocking digester. The rate of lignin destruction during the process was found to far exceedthe rate of dissolution of carbohydrates. This suggests that no acidic or basic reagent areneeded in this process in order to delignify wood. Both hardwood and softwood pulps canbe produced in high yields. (Deinko et al. 1995)

Gosselink (Gosselink et al. 1995) has analyzed the acid contents of spent liquorresulting from aqueous ethanol (60 v-%) pulping of fibre hemp. Acetic acid and formicacid were found to be the main acids responsible for lowering the pH of the spent liquorand autocatalyzing the the delignification process. Hemp core and hemp bast fiberscontain respectively 4.3 w-% and 1.3 w-% acetyl groups and 0.2 w-% formyl groups.Trace amounts of glycolic acid, lactic acid, fumaric acid, levulinic acid, 5-hydroxy-methylfurfural and furfural were also found. The main source of these compounds isprobably the polysaccharides of the raw material.

Hakansson and co-workers (Hakansson et al. 1996) have used reed canary grasscontaining about 25 % leaves as the raw material in autocatalyzed ethanol pulping at453 K. Kappa numbers below 35 were obtained by using ethanol concentrations of 50 to60 % in the pulping liquor, and high liquor to raw material ratios (10 dm3/kg). Thestrength properties of grass pulps were lower than those of birch kraft pulps.

About 85 % of the ethanol used in a batch cook of white birch (Betula papyrifera) at408 K can be recovered by flushing from the digester. After condensing, this ethanolmixture may be used to prepare cooking liquor. The pulp yield and the mechanicalproperties are not affected by the use of recycled ethanol, but the kappa number isincreased. (Li & Chen 1996)

The Aleksandrova group (Aleksandrova et al. 1996) has studied the effect of fungalpretreatment on hydrochloric acid catalysed aqueous ethanol pulping. When aspen chipswere treated with Trametes villosus for six days either a two point increase in pulpyield, an up to nine point reduction in kappa number, or a significant reduction incooking time was achieved.

When delignifying wheat straw at 348 K with a 60:40 (v/v) mixture of ethanol andwater using sulphuric acid as a catalyst, optimum pulping occurs according to Sun (Sun et al. 1997) in 1.0 N sulphuric acid and with a two-hour cooking time.

Billa’s group (Billa et al. 1997) has studied enzyme treatment of sulphuric acid (2 N)catalyzed aqueous ethanol (80 v-%) pulps. The treatment of wheat straw and sweetsorghum stem pulps with manganese peroxidase in oxalate or malonate buffers degraded15-30 % of the beta-O-4 linked guaiacyl and syringyl lignin monomers.

The catalysis in ethanol pulping can be performed by the acetic acid liberated from thehydrolysis of acetyl groups in wood. According to Araujo and Curvelo (Araujo &Curvelo 1997a) the change of the pH value of the digester content reduces the efficiencyof the delignification reactions. When chloroacetate is used as a buffering agent inaqueous ethanol pulping of Eucalyptus urograndis wood, the efficiency of thedelignification is improved.

Aqueous ethanol (1:1/v:v) pulping of Mimosa hostilis Benth has been found toremove only 65 % of the original lignin at 463 K when the pulping time is 150minutes. (Araujo & Curvelo 1997b)

Girard and Heiningen (Girard & Heiningen 1997) have constructed mass balances forethanol based birch cooks, obtaining an overall average closure of 98.0 ± 2.6 %. Ligninprecipitation is a problem when determining the pulp yield. This problem can beeliminated by subjecting the pulp to a hot ethanol wash. The potential by-products ofthe process are lignin, methyl and ethyl acetates, methanol, acetic acid, and furfural.

The effects of different cooking parameters on the pulping of eucalyptus in aqueousethanol has been studied by Gilarranz et al. (Gilarranz et al. 1997, Botello et al. 1998).They have found that the amount of water used in the process has no significant effecton pulp properties. In addition, they found that no additive used (sulphuric acid,magnesium salts, and calcium salts) enhanced pulp properties enough to justify theiruse.

Aqueous ethanol in the presence of hydrochloric acid can be used to delignify oil palmfibers of trunks, empty fruit bunches, and fronds. Pulps with kappa numbers around 20

are obtained when 20 % hydrochloric acid is added to a 60 % aqueous ethanol solution.(Suleman & Yusoff 1997)

2.1.2.2. The Alcell process

Diebold and co-workers (Diebold et al. 1978, Diebold et al. 1983, Diebold et al. 1988)have presented a method were wood chips are delignified using an aqueous solution of alower aliphatic alcohol in a plurality of batch extraction vessels. The charge in eachvessel is rapidly heated to the delignification temperature by recirculating a primaryextraction liquor having a relatively high dissolved solids content. Thereafter, the chargeis subjected to a series of once-through extractions or washes with successively cleanerliquors. The final extraction or wash is carried out with fresh solvent. The extractionliquor from one stage is used in another extraction stage in another vessel. When theextraction is completed, the liquor is drained from the vessel, the vessel is depressurizedand the remaining solvent is steam stripped from the charge. The alcohol recoverysystem contains flash vaporization, condensation of the solvent vapours and vacuumstripping of the residual liquor with steam. Lignin and carbohydrates are then recoveredfrom the alcohol-free extract. Aqueous ethanol (40-60 w-%) is the preferred solvent. Thepulping temperature is 453-483 K and the pressure is 2-3.5 MPa. The extraction time isabout 5 minutes in each stage.

A typical commercial plant of this process, originally called the APR process, hasbeen sized at 136 metric tons per day (Katzen et al . 1980a). The plant would use ninebatch extractors, each operating at a three-hour cycle. The fresh pulping liquorcontaining ethanol 50 v-% is pumped at its atmospheric boiling point into the extractorto pre-soak the chips and purge the air. The liquor is then drained back to the fresh liquoraccumulator, leaving saturated ethanol-water vapour behind. In primary extraction, theliquor (solid content 5-7 w-%) from the primary extraction accumulator (473 K and 2.86MPa) is rapidly circulated through the extractor for less than five minutes. During thisisothermal stage 70-80 % of lignin is removed. The flow from the extractor is divertedto the recovery feed accumulator, from which a continuous flow of liquor, containingabout 10 % solids, is taken to the recovery cycle. In secondary extraction, the solvent istaken from the extractor undergoing tertiary extraction. This liquor flows once throughthe extractor to the primary extraction accumulator. In tertiary extraction, the feed to theextractor is switched so that liquor is discharged from the fresh liquor accumulator toanother extractor as secondary extraction liquor. At the end of the tertiary extraction, theliquor is drained back to the fresh liquor accumulator, leaving saturated ethanol-watervapour behind. Controlled depressurization vents the extractor vapour to the blowdowncondenser for recovery and recycling. The residual pulp in the extractor is steam strippedat atmospheric pressure to remove the remaining ethanol. Steam and stripped ethanol arefed to the blowdown condenser. Finally, the extractor is filled with water and the pulpflushed to a hold tank.

The black liquor from the recovery feed accumulator is first fed to a flash drum(Katzen et al. 1980a). Vapours are condensed and fed to the fresh liquor accumulator. The

black liquor slurry from the flash drum contains about 15 w-% dissolved and precipitatedsolids. This slurry is continuously stripped in the solvent recovery tower operating undervacuum. Steam and ethanol vapours from the top of the tower are condensed and fed tothe fresh liquor accumulator. Tower bottoms is a slurry containing precipitated ligninsuspended in an aqueous sugar solution. The lignin is separated using a clarifier and acentrifugal. The remaining aqueous sugar solution is concentrated to a solid content ofabout 60 w-% in a double-effect evaporator, to which heat is supplied by flash vapourfrom the black liquor.

The costs of an APR plant, producing 150 tons of pulp per day, have been estimated(Katzen et al. 1980b). With no byproduct credits, the payback time of the investmentwas estimated to be 4.4 years and the return on fixed investment was estimated to be 13%. If byproduct credits are taken into account, the corresponding values are 3.2 years and22 %.

A pilot plant for the APR process was started up in August 1983 (Lora & Aziz1985). The main variables affecting the extent of delignification and cellulosedegradation of unbleached APR pulps are: extraction time, extraction temperature,solvent composition and hydrogen ion concentration. Red oak pulp has been producedwith a kappa number of 14 and a pulp yield of 43 %. Aspen and birch seemed to beeasier to delignify. The brightness and the strength properties of the APR pulps are nearthose of corresponding kraft pulps. The commercial potential of fibres produced by theAPR method has been tested in pilot paper machine trials. APR pulps can successfullyreplace the hardwood kraft component in printing and tissue grades. The potential of theprocess in producing dissolving pulp has been shown in pilot viscose production runs.

At equal kappa numbers, the APR process produced in the pilot plant aspen pulpswith screened yields 1.2-1.7 % higher than kraft pulps produced in the same plant (Loraet al. 1985). The ethanol pulps were easier to bleach than the kraft pulps. The strengthproperties of unbleached ethanol pulps were 62-82 % of kraft. After bleaching to 88brightness, the difference between ethanol and kraft pulps was practically eliminated.

In 1987, the APR process was renamed and called the Alcell process (Pye et al .1987). The process was claimed to offer several advantages over the conventionalmethods:1. It can economically operate at a smaller scale than the kraft process. This is mainlycaused by the less complicated chemical recovery and by the need for less pollutioncontrol equipment.2. The quality of pulp is competitive with conventional pulps.3. The production costs are lower at any scale than the costs of kraft or sulphite pulps.4. The process isolates lignin in a relatively pure form.5. The hemicellulose saccharides are also recovered.6. If the by-products can be marketed, the Alcell process would be more profitable thanconventional pulping processes.7. The process is environmentally friendly compared with the kraft and sulphiteprocesses.

Alcell pulps can be bleached to 90 % ISO. The only effluent from the process comesfrom the bleaching plant and can easily be treated (Evans 1987, Williamson 1987,Williamson 1988). Bleached Alcell pulps are stronger than both sulphite and TMP pulps

and compare well with kraft pulps. Production costs in an Alcell mill are estimated to be85 % of those in a kraft mill.

The Alcell process gives pulp mills the ability for the capacity expansion at about 60% of the cost of the kraft mill (Pye 1987). The process is most suitable for hardwoodsand has been tested with red maple, aspen, birch, red oak, white oak and sweet gums.Pulping conditions can be changed to optimize papermaking conditions of a variety ofpulps. Each oven dry ton of wood can yield about 53.5 % pulp, 18.4 % lignin and 21 %fuel.

The Alcell process can, according to its developers, be used to (Anon. 1987b):1. Expand an existing kraft mill.2. Build a small mill capable of exploiting limited forest resources.3. Build a less expensive greenfield pulp mill.4. Produce pulp from non-wood feedstocks.

In 1988, it was reported that Repap Enterprises was investing C$ 45,000,000 in anAlcell trial plant. Once the trial plant is operating satisfactorily it will be expanded toproduce 230 tons of pulp per day and to include an oxygen-based bleaching sequence.(Fales 1988, Karl 1988)

Lignin can be precipitated from the black liquor by diluting the liquor with water andan acid to form a solution with a pH value of 3 or less, an alcohol content of 30 v-% orless and a temperature of 348 K or less (Lora et al. 1988, Lora et al. 1990). Theprecipitated lignin is, after drying, in the form of a powder.

The start-up of the Alcell demonstration facility producing 33 tons of pulp per dayoccurred in March 1989 (Mullinder 1989). The hardwood pulp produced at the start-uphad a quality equivalent to kraft pulp. The unbleached pulp was clean, free of shives andhad a kappa number of 22.

In the Alcell demonstration plant in New Brunswick, Canada, hardwood chips werecooked in batch extractors with an aqueous ethanol liquor (Lora et al . 1989). The blackliquor was flashed and then the lignin was recovered by precipitation (Lora et al. 1988)followed by settling, centrifugation (or filtration) and drying.

The demonstration plant had only one extractor and four liquor accumulators (Pye1989a). The pulp could be bleached without chlorine but chlorine dioxide had to be used.The pulps had a higher bending stiffness than kraft pulps, but they were more brittlethan kraft pulps. The wood is cooked to quite high kappa numbers in order to preservethe strength.

The Alcell process was found to be particularly suitable as a pulp source fornonintegrated pulp mills. Those mills often cannot site full-scale kraft pulping facilitiesdue to environmental restrictions. (Pye 1989b)

Lignin recovered from the Alcell process can be used as adhesives for waferboard.When the adhesive contains 20-30 % lignin, the product quality is identical towaferboards produced using 100 % phenolic resin as the adhesive. (Wu et al. 1989)

Without a need for a recovery furnace, lime kiln, causticizers and brownstock washers,the Alcell process has a clear capital cost advantage over a comparably scaled kraft mill(Petty 1989, Pye 1990, Pye & Lora 1991). An Alcell mill becomes economicallyattractive with a pulp capacity of 300 metric tons per day or even less. When norecovery furnace and other high-maintenance equipment are used, an Alcell mill should

have lower maintenance and operating labour costs than a kraft mill. Wood costs are alsolower due to the higher pulp yield of the Alcell process. The recovery and sale of ligninand other by-products lead to a lower energy production in the process. This increases thedemand for externally generated energy, increasing the utility costs of the mill. Thecooking chemical (ethanol) costs for the Alcell mill are also higher than for a kraft mill.These two disadvantages should however be compensated for by the value of therecovered by-products.

The spent pulping liquor, from which lignin has been precipitated, can be distilled torecover ethanol (Dillen 1990). Sodium hydroxide is fed to the top of the distillationcolumn in order to prevent ester formation. Aqueous ethanol is taken as vapour from thetop of the column and as liquid from a lower stage of the column. These streams aremixed and used as pulping liquor. A side stream is taken from the mid part of thecolumn. It contains furfural and some of the more volatile compounds in wood. Thebottom product contains carbohydrates and sodium salts of organic acids (acetic acidetc.). It is concentrated by evaporation to a solid content of 50 %. This syrup can beused as animal fodder or hydrolysed to be used in ethanol fermentation.

Alcell pulps can be bleached from relatively high kappa numbers to high brightnessand high cleanliness pulps with strength properties comparable to kraft hardwood pulps(Cronlund & Powers 1990). Organic chlorine compound levels in bleaching effluentstreams and bleached pulp are low. Alcell pulps also show high potential for non-chlorine bleaching.

The Alcell process produces hardwood pulp equal to commercial kraft pulp (table 1).The pulp properties have been determined for a furnish of 50 % maple, 35 % birch and15 % poplar. 10 % kraft softwood pulp was also added to the Alcell pulp. (Harrison1991, McCready 1991, Anon. 1991b).

Table 1. Physical properties of Alcell and commercial kraft pulp at a CanadianStandard Freeness of 400 (Harrison 1991, McCready 1991, Anon 1991b).

----------------------------------------------------------------------------------------------------------------------Alcell Commercial kraft

----------------------------------------------------------------------------------------------------------------------Tensile (km) 7.47 7.40Tear (mN·m2/g) 7.20 6.75Burst (kPa·m2/g) 5.08 5.18Brightness (ISO) 88.7 89.6----------------------------------------------------------------------------------------------------------------------

Compared with a kraft mill, the Alcell process is dependent on the sale of its by-products for competitive operation (Jamieson 1991, Karl 1991a, Karl 1991b). Of the by-products, furfural is the easiest to market. About 1.8 million kg per year would bedistilled from the black liquor in a 300 tons per day plant. It can be used, for example, asa solvent in the production of lubricating oil. The Alcell lignin is a brown, hydrophobicpowder. A 300 tons per day mill would precipitate about 100 tons per day of lignin at 3% moisture content. It can be also used, for example, to produce glue for the waferboard

industry. Other by-products that could have market value are acetic acid, and suchessences and flavours as vanillin and ethyl acetate.

The costs of Alcell pulping have been compared with the costs of conventionalchemical pulping. The cooking liquor (ethanol) in Alcell is about 4-5 times more costlythan caustic liquor, but Alcell produces pulp with an up to 2% higher yield. In bleachingcosts, there no difference between the methods. The equipment used in Alcell pulping issimpler leading to reduced capital costs and lower labour costs. If lignin is marketed as aby-product, the energy costs of Alcell pulping will be higher than for conventionalchemical pulping. (Henry 1991)

The lignin obtained by the Alcell process has a low molecular weight, high purity,low glass transition temperature and relatively high decomposition temperature (Lora etal. 1991a). Mill scale trials have shown that this lignin can be used to partially replacephenol formaldehyde resins used in plywood and other applications. The process alsoproduces a water soluble, very low molecular weight lignin fraction that can be used inthe adhesives industry.

Agricultural residues can be pulped using the Alcell method. Kenaf pulps havestrength properties between those of commercial hardwood and softwood pulps. Sugarcane bagasse and sugar cane rind chips result in bleached pulps with similar physicalproperties, that are comparable to conventional mixed hardwood pulps. During cookingof rind chips 2.3 % per weight of dry chips of furfural is generated. The fact that noinorganic solids are recycled in the process, means that there is no accumulation ofsilica. (Winner et al. 1991a, Winner et al. 1991b, Lora & Pye 1992)

One of the major advantages of the Alcell method is its recovery of by-products andthe selling of these byproducts to reduce operating costs. Sulphur-free lignin, furfuraland wood sugars can be recovered. The Alcell process needs only one-third of the 1000ton per day production needed for a kraft mill to operate economically. The Alcellprocess has lower operating costs than a kraft mill because of the higher pulp yield.(Koncel 1991)

Lignin obtained as a dry powder in the Alcell process has been tested as an alternativefor petroleum-based resins in plywood. Mill trials have shown that 15 to 20 % of theresins needed can be substituted with this lignin without any changes in the strengthproperties of the panels. (Lora et al. 1991b)

In designing a distributed control system (DCS) for the Alcell process there has beena need to take into account some unique components, such as:- an unproven process design,- unknown control requirements and- a potentially volatile environment.These have led to more emphasis on field and rack room wiring, use of a digital fieldcommunication bus, better definition of the information system requirement andpartition of the plant utilities into their own controller modules. (Henry & Seely 1991,Henry & Seely 1992)

In 1992, it was reported that an Alcell mill with a capacity of 300 tons of pulp perday was under design (Lora et al . 1992). The scale-up will be done after successfuloperation of the demonstration plant (table 2).

Table 2. Characteristics of industrially produced Alcell pulps after 4000 revolutionsin a PFI mill (Lora et al. 1992).

----------------------------------------------------------------------------------------------------------------------Birch 50% maple

35% birch15% poplar

----------------------------------------------------------------------------------------------------------------------Unbleached kappa no. 27 30Bleaching sequence EoDED EoDEDBrightness, ISO 88 + 88 +Bulk density, cm3/g 1.32 1.36Tear index, mN·m2/g 6.8 6.7Burst index, kPa·m2/g 4.7 3.2Breaking length, km 7.5 5.1CSF, mL 420 416----------------------------------------------------------------------------------------------------------------------

The Alcell process operates at high pressure (2.8 MPa) and temperature (468 K) using60 % ethanol as the extraction medium (Detweiler 1992). These conditions are above theflash point of ethanol and result in potential hazards of fire, explosion and accidentalrelease of toxic process materials. The fact that the process is operated indoors due to theclimatic conditions in Northeastern Canada, greatly increases the hazard potential topersonnel and equipment. These risks can be minimized by proper management of risks.The Process Safety Management technique can be useful to develop strategies to eitherprevent the event from occurring by excellence in process and equipment design, oroperating and maintenance procedures, or to minimize the potential impact through theuse of a competent consultant and experienced personnel.

Alcell hardwood pulps with optimal strength properties have higher kappa numbersthan kraft pulps, but they can be further delignified to low kappa numbers in an oxygenbleaching stage with excellent preservation of pulp strength properties (Cronlund &Powers 1991, Cronlund & Powers 1992). Ozone and other nonchlorine bleaching stagescan also be used. The best strength preservation, economics and lowest levels of AOX inthe effluent waters are however achieved with chlorine dioxide bleaching.

In 1992 a simple chemical recovery was introduced for the Alcell method. Initially theblack liquor was flashed, and then diluted to precipitate lignin. The lignin was recoveredusing a solid/liquid separation step and then dried. The remaining stream, containingwater, ethanol, dissolved wood sugars, furfural and acetic acid as the main components,was fed to a distillation column. Ethanol was recovered as the top product from thecolumn. Furfural was taken as a side stream and the bottom product was partly recycledto dilute the black liquor. (Lora & Pye 1992)

Leszczynski (Leszczynski 1992) has reported that the Alcell process needs only one-third of the amount of water used in a kraft mill of similar size. The effluents of theprocess are easily purified.

The residual lignins that remain with the fibres in Alcell pulps have higher molecularweight, less aromatic hydroxyl groups, more aliphatic hydroxyl groups and resemble

native lignin to a greater extent than the lignins that are dissolved during pulping. (Loraet al. 1993a)

In 1993, over 2000 cooks had been completed in the Alcell demonstration plant sincestart-up. Lora and others (Lora et al . 1993b) reported that the process seemed to beideally suited for a closed cycle mill, because the cooking chemical (ethanol) was easilyseparated due to its volatility.

Lignin obtained during Alcell pulping of North American hardwoods is a polyphenolcharacterized by its high purity, low molecular weight, low polydispersity, low glasstransition temperature and relatively high decomposition temperature. The material canbe used industrially as a partial replacement for phenolic resins in, for example,waferboards. Another potential field of use for this material is as a rubber tackifier andantioxidant. (Lora et al. 1993c)

The physical properties of the lignin obtained as a co-product in Alcell pulping havebeen measured (Sellers et al . 1994, Sellers 1994). The lignin was used to partiallysubstitute phenol in resole phenol-formaldehyde (PF) resins. The physical properties ofthe formulated resins were also measured and the resins were used as binders instrandboard production. The results indicate that Alcell lignin can be used to replace upto 35 % of the phenol in PF resins used in strandboard production.

Maldas and Kokta (Maldas & Kokta 1994) have studied the use of Alcell lignin as abonding agent for wood fibre-filled polystyrene composites. The mechanical propertiesof the composites were improved by the addition of lignin. The optimum concentrationof bonding agents was found to be 2-3 %.

Ni and Heiningen (Ni & Heiningen 1994, Ni & Heiningen 1996) have studiedwashing of Alcell pulps with aqueous ethanol. Displacement washing was found to offermuch better results than a stirred batch operation. A pulp with an initial kappa numberof 54 was delignified to a kappa number about 25 by extended displacement washing.Practical operation conditions for washing were found to be: dilution factor 3.0 cm3/g,ethanol concentration 50 %, temperature 336 K and residence time 6.17 minutes. Highertemperatures and ethanol concentrations improve the lignin removal.

One of the disadvantages of the Alcell process is that it needs more purchased energythan a kraft mill. The Ronan group (Ronan et al . 1994) has performed a pinch analysisand found that the potential thermal energy savings in Alcell pulping are about 15 %.These savings can be reached primarily by modifying the heat exchanger network of theprocess. Because the analysis was made at an early stage of design these modificationscould be made without an excessive amount of additional pipework.

In 1994, it was reported that the defibration of chips occurs in the Alcell process in ahigh-pressure extractor at a temperature of 468 K and a pressure of 2.9 MPa. Lignin isrecovered from the cooled extraction liquor by diluting it with water. Also acetic acid andfurfural are obtained as by-products. The kappa number of the pulp is below 30 afterwashing. (Anon. 1994)

The swelling of Alcell fibres in aqueous ethanol as a function of the ethanolconcentration has been studied. The results showed that the swelling of the fibresdecreased continuously as the ethanol concentration increased. (Ni & Heiningen 1995, Ni& Heiningen 1997)

The solubility of the Alcell lignin has been found to strongly increase when theethanol concentration of the solvent increases from 9.5 % to 47.5 %. When the ethanolconcentration is increased from 47.5 %, the solubility increases much more slowlyreaching a maximum at an ethanol concentration of about 70 %. This behaviour isexplained by the theory that lignin exhibits the maximum solubility when the solubilityparameter value of the solvent is close to that of the Alcell lignin and the hydrogenbonding capacity of the solutions with different ethanol contents is similar. (Ni & Hu1995)

In January 1995, it was reported that Repap Enterprises Inc. had bought an existingpulp mill in order to convert it to produce 142,000 metric tons of hardwood Alcell pulpper year. The mill was scheduled to begin production in 1997. (Anon. 1995)

The commercial scale Alcell mill will be producing fully bleached market pulp and asbyproducts also lignin, furfural and acetic acid. Acetic acid may be used to produceperoxyacetic acid for pulp bleaching and recovered at the mill. This may be a steptowards a totally effluent-free mill. (Lora & Pye 1995)

Alcell pulps show advantages in bleaching by totally chlorine free methods, such asozone bleaching. They can be bleached with lower chemical charges than kraft pulps.(Singh et al. 1995, Zhang et al. 1996)

Formaldehyde emissions can be significantly reduced when organosolv ligninfractions are used as a partial replacement for PF in the manufacture of waferboard andparticleboard. A reduction of 38 % was obtained when 20 % PF resin solids werereplaced with a lignin dispersion. (Senyo et al. 1996)

Blends of PVC and Alcell lignin have been studied (Feldman et al. 1996). The tensilestrength of the blend increased with increasing lignin content. The presence of lignin didnot have a negative effect on the processing of the blends but led to breaking ofintermolecular bonds in the PVC structure.

Two lignin fractions can be recovered during the Alcell process when hardwoods aredelignified. The first fraction is obtained by dilution and precipitation of the spentpulping liquor. The second fraction is obtained by concentrating the aqueous stream fromdistillation. This fraction has a lower molecular weight, a lower glass transitiontemperature and a higher carboxyl content than the first fraction. Potential uses of thesecond lignin fraction are in novolac resins, concrete superplasticizers and particleboardproduction. (Creamer et al. 1997)

Wheat straw and reed can be used as raw materials for producing bleachable gradeAlcell pulps that have properties competitive with commercially available hardwoodkraft pulps. The total yield of saleable products, including pulp and by-products, isaround 70 %. In conventional annual fibre pulping, the accumulation of silica is aproblem. In Alcell pulping only about 15 % of the silica enters the pulping liquor.(Winner et al. 1997)

An elemental chlorine-free (ECF) bleaching sequence for the Alcell process has beenintroduced (Ni & Heiningen 1998). The method consists of a wash by aqueous ethanol,followed by ozone bleaching of the pulp impregnated with an acidified ethanol solution,and then extraction with aqueous ethanol. Finally, the pulp is bleached in two chlorinedioxide stages. The physical properties of the pulp are at least similar to thecorresponding ODED bleached pulp. When no caustic is used, the ECF sequence has an

economic advantage over the ODED sequence. The load of the waste water treatmentoriginating mostly from the oxygen stage can also be reduced.

Ooi and Ni (Ooi & Ni 1998) have proposed a totally chlorine-free (TCF) bleachingsequence for the Alcell process. The brownstock is first displacement washed withaqueous ethanol (70%). Then it is impregnated with a 30 % ethanol solution acidified topH 2 and delignified with 2 % ozone. In the next step, the pulp in again displacementwashed with 70 % ethanol. The resulting pulp has a kappa number of 10 and can befurther bleached using hydrogen peroxide and peracetic acid stages.

In July 1998, it was reported that Repap Enterprises had terminated its December1997 agreement to sell Alcell Technologies to Malaspina Capital Ltd. Repap could notafford to continue to support Alcell in anticipation of finding another buyer. (Anon1998a)

2.1.2.3. Alkaline ethanol pulping

Marton and Granzow (Marton & Granzow 1982a) have patented a method for producingwood pulp using a mixture of ethanol and sodium hydroxide. The aqueous pulping liquorcontains 10-25 w-% of sodium hydroxide and 10-60 v-% of ethanol. The pulping time is0.5-4.0 hours and the pulping temperature is 373-473 K. Essentially, any wood can bepulped.

Adding ethanol to a caustic soda cook greatly improves its selectivity with respect tolignin (Marton & Granzow 1982b). Likewise the presence of sodium hydroxideimproves the delignifying ability of ethanol. The chips pulped with an aqueous mixtureof ethanol and sodium hydroxide are easier to defiberize than those pulped with soda orby the kraft process. The organic solvent reduces the surface tension of the pulpingliquor at high temperature promoting the penetration of the alkali into the chips and thediffusion of the breakdown products of lignin from the chips to the liquor.Simultaneously, the alcohol also degrades lignin and prevents it from condensing.Spruce pulps have been produced using the liquor-to-wood ratio 5:1 and the ethanol-water volume ratio 1:1. The cooking temperature can be varied from 423 K to 443 K.The use of ethanol allows considerably shorter pulping times to be applied. At the sameyield, the residual lignin content of the ethanol-NaOH pulp is slightly higher than forkraft pulp. The strength of the pulp is also slightly lower but the brightness of theunbleached pulp is higher than for kraft pulp.

Sarkanen (Sarkanen 1982) has presented an alkaline method for selective defiberizingand delignifying of lignocellulose. The pulping liquor contains water, a water-miscibleorganic reagent, and a sulphide or bisulphide compound. The organic reagent can be analiphatic alcohol, for example, ethanol, or a ketone. Extremely high pulp yieldscompared to kraft pulping can be reached.

Chiang and Sarkanen (Chiang & Sarkanen 1983) have found that 0.3 M ammoniumsulphide in 30-50 % ethanol-water is a satisfactory pulping medium for delignifyingindustrial hemlock chips at the liquor-to-wood ratio 10:1. The optimal pulpingtemperature is 453 K. The extent of delignification increases with increased ammoniumsulphide charge. A hemlock pulp with the kappa number 45.8 was found to be easily

bleached by a conventional CEDED sequence to a brightness of 86 % G.E. in 55 %yield. The bleached pulp had a high viscosity value (1970 cP TAPPI) and both tensileand burst strengths were adequate, while the tear strength was low. Cottonwood chipswere easier to delignify than hemlock chips. Lower ammonium sulphide charges wererequired and low kappa numbers around 15 were reached. The yield of cottonwood pulpswere 12-13 % higher than those of corresponding kraft pulps. Unbleached cottonwoodpulps beat fast to high tensile strength values. The tear strengths were comparable tokraft pulp, but the burst strengths were lower than those of cottonwood kraft pulps.

Semichemical type pulps can be produced by cooking sugarcane bagasse in aqueousethanol (40-60 w-%). These pulps have high yields, high kappa numbers and lowstrength properties. Adding sodium hydroxide to the pulping liquor increases theselectivity of delignification and results in pulps with good yields, low kappa numbersand acceptable strength properties. Adding anthraquinone as catalyst to the ethanol-water-sodium hydroxide system increases the pulp yields, decreases the kappa numbers andimproves the strength properties. (Valladares et al. 1984)

The addition of ethanol has a complex influence on the performance of variousderivates of anthraquinone in alkaline pulping (Chacon & Lai 1985). Ethanol increasesthe solubility of the additive in the solvent system. With most additives it alsostabilizes carbohydrates. A positive effect on the delignification efficiency can beobserved with a small addition of ethanol, but high ethanol concentrations (>50%)hinder delignification.

Simultaneous addition of ethanol and anthraquinone to sodium hydroxide cookingliquors has been found to offer advantages that are not possible with the use of eachadditive alone. The alkali consumption during pulping decreased by 10-25 % whenethanol was present in soda-anthraquinone pulping. The pulp yield increased by 1-4 %on wood. The optimum ethanol concentration in the pulping liquor is 25-30 %. Thepulps produced by this method are somewhat weaker than kraft pulps. The feasibilitystudy performed showed, however, that this method is not economically attractive.(Janson & Vuorisalo 1986)

When comparing pulping of spruce with three methods: aqueous ethanol mixed withsodium hydroxide or a catalytic amount of calcium chloride or ethanol without anyadditional agents, it has been found that the kappa number is not a good indication of thepulp quality. Instead, the total lignin content should be used. The fiberising point of thedelignification was at 9 % lignin content after anthraquinone catalysed ethanol-alkalicooking and at 16 % after calcium chloride catalysed ethanol cooking. Cooking withethanol only at 468 K did not lead to fiberising at all. Simulation of the solventrecovery with flashing and distillation indicated that ethanol losses can be keptnegligible if the energy consumption is allowed to be high. (Aittamaa et al . 1986,Lonnberg et al. 1987a)

The alkaline ethanol pulps needed five bleaching stages (DEPDEPD), where the

alkaline extraction steps were strengthened with peroxide, for bleaching to a brightnessof around 85 % ISO (Lonnberg et al. 1987b). The acidic pulps needed only threebleaching stages (DEPD) to reach the same brightness. The alcohol pulps required short

beating times and low beating load. The strength properties of the alkaline pulps were

comparable with those of kraft pulps, but the acidic pulps were weaker. The acidicethanol pulp had a particularly poor tear index.

Tissot and Launay (Tissot & Launay 1987) have presented a two-stage soda pulpingprocess where ethanol is added. The first stage (373 K) allows penetration of the cookingliquor to the chips, followed by the actual cooking stage (443 K). The pulping liquorcontains 13 % ethanol and 10 % sodium hydroxide. The pulps produced are inferior tokraft pulps.

The aqueous ethanol delignification of wheat straw in the presence of sodiumhydroxide and anthraquinone can be divided into bulk delignification during the heating-up period and supplementary delignification. Yields of alkaline ethanol pulps are about12 % higher than those of corresponding soda and soda-anthraquinone pulps. Thephysical properties of ethanol pulps are similar to those of conventional pulps. (Lianget al. 1988)

When pulping bagasse in aqueous ethanol systems, acids have been found to beharmful in ethanol pulping, but alkali has shown good catalytic selectivity. Theproperties of the bagasse ethanol pulps were similar to those of corresponding sodapulps. (Weisheng et al. 1988)

Eucalyptus has been subjected to two-stage organosolv pulping with ethanol (Sanjuanet al . 1989, Sanjuan & Chavez 1989). The first pulping stage used aqueous ethanol towhich soda was added in the second stage. The pulps had kappa numbers between 15 and44 and breaking lengths similar to those of kraft pulps. It was possible to extract tanninfrom the spent liquor of the first pulping stage with a yield of 6.2 % on dry wood.

The use of a solution of ethanol, water and sodium hydroxide (15 %) as the pulpingliquor for hornbeam wood results in rapid delignification (90 % in 2 hours at 443 K).The addition of anthraquinone improves both delignification and pulp yield. The ethanol-water solution transforms soda to a superbase and doubles polysaccharide adsorption ofhydroxyl ions. The high ion concentration leads to rapid cleavage of the intermolecularlignin bonds and speeds up delignification. (Ivanow & Robert 1989)

When pulping bagasse meal with organic solvents, the best results have beenobtained with aqueous ethanol. Adding sodium hydroxide to the system improved theselectivity with respect to lignin. If the process was acid catalysed, the degradation ofcarbohydrates increased. The highest yields, lowest kappa numbers and best bleachabilitywere achieved when anthraquinone was used as the catalyst. Pulp properties were betterthan those of corresponding soda pulps. (Bharati et al. 1989)

Tubino and Filho (Tubino & Filho 1989, Tubino & Filho 1990) have presented amethod where eucalyptus wood is pulped with an aqueous solution containing 20 %ethanol and 19-20 % sodium hydroxide. The pulping is carried out at 433 K for 65minutes.

Chen et al. (Chen et al . 1990) have introduced a two-stage ethanol pulping method.The first pre-treatment stage is vacuum impregnation of wood chips in aqueous ethanolwith the presence of sodium hydroxide. In the second stage, the pre-treated chips aredelignified with a sulphur dioxide-ethanol-water mixture. This process produces softwoodpulps with a 6-10 % higher yield than kraft pulps. The fibre strengths approach a levelwhich is about 90 % of kraft strength. The black liquor is flashed and evaporated.

Ethanol is recovered by distillation. The concentrate from the evaporator plant is fed to arecovery boiler.

A pulping method consisting of cooking wood chips in an aqueous mixture ofsodium hydroxide, hydrazine and alcohol has been patented. Pulp yields are improved ifthe alcohol used is ethanol and its concentration in the mixture is 30-50 v-%.(Pazukhina & Shan 1990)

A pulping method including cooking of chips in aqueous ethanol (25-50 v-%) in thepresence of 10-20 g/dm3 sodium hydroxide at 438-443 K for 90-180 minutes has alsobeen patented. Process selectivity and the mechanical strength of pulp are improved if,after the removal of the spent liquor, the pulp is treated with aqueous ethanol (40-60 %)at 323-353 K for 30-60 minutes. (Beigelman et al. 1991)

The physical properties of wheat straw alkali-ethanol and soda pulps have beencompared. Alkali-ethanol pulps have a rapid response to beating and satisfactory physicalproperties when the beating degree is above 40˚SR. (Liang & Xiao 1992)

Ultra-high-yield (91.5 %) pulps with good mechanical and optical properties can beproduced from aspen by impregnating the chips with aqueous ethanol and sodiumhydroxide prior to steam explosion pulping (Ahmed et al. 1992).

Girard and Chen (Girard & Chen 1992) have delignified white birch using a blend ofcaustic soda and denatured ethanol as the solvent. They used a liquor-to-wood ratio of5:1, a total heating time of 165-170 minutes, a cooking temperature of 443-453 K, analkaline charge of 15-20 w-% and an ethanol concentration of 20-50 v-%. The pulpquality is well comparable with hardwood kraft pulp, when the same active alkali chargeis used. The organosolv pulp has a better brightness, and at a given breaking length, itstear index is higher than that of the kraft pulp.

Sobral (Sobral et al. 1992) has studied a process called ASAE (alkaline sulphiteanthraquinone ethanol) pulping. Compared with kraft pulping, the ASAE process ismore selective and produces pulps with high yields (52 %) and low kappa numbers (13).In addition, ASAE pulps are easier to bleach than kraft pulps and have mechanicalproperties similar to those of kraft pulps.

When studying alkaline ethanol pulping of Acacia confusa and Alnusa formosanaWang and Tseng (Wang & Tseng 1993) have found that the optimum pulpingconditions are: alkali charge 16 %, temperature 433 K and time at maximum temperature60 minutes. The yields of Acacia confusa pulps are 3-7 % higher than the yields ofkraft and soda-anthraquinone pulps. The yields of Alnusa formosana pulps are somewhatlower. The beating time of ethanol-alkali pulps are 9-17 minutes shorter than those ofkraft and soda-anthraquinone pulps at about 400 CSF, and it requires less beating energy.The strength properties of the ethanol-alkali pulps are better than those of soda-anthraquinone pulps but not so good as those of kraft pulps.

When eucalyptus (Eucalyptus cilriodora) chips are cooked in an aqueous solutioncontaining 8 % sodium hydroxide and 50 % ethanol at 453 K for four hours, they can bedefiberated with a screened pulp yield of 65 % (Xiao et al. 1993). The pulping time canbe reduced to three hours and the pulp quality can be improved by adding 0.05 %anthraquinone to the pulping liquor. The pulp yield is however reduced to 63.5 %. Thedelignification activation energy of eucalyptus is 42.0 kJ/mol.

Adding inorganic reagents (e.g. NaOH) to one-stage aqueous ethanol pulping of sugarcane bagasse reduces the digester pressure and produces pulps with better mechanicalproperties (Sanjuan et al. 1993). The soda-ethanol pulps give a better response tobleaching than soda pulps. The most suitable bleaching sequences are OZP, OPD andO/PHP. When a brightness 80-85 % ISO is required, an unbleached bagasse pulp with akappa number of 12-15 is needed. The pulping can also be carried out in two or morestages using aqueous ethanol in the first stage and aqueous soda-ethanol-anthraquinonemixture in the other stages. This would enable by-product recovery from the first stage.

Martinez and Sanjuan (Martinez & Sanjuan 1993) have compared ethanol-water-sodapulping of Chihuahua pine with kraft pulping. They found that the organosolv pulpshad strength properties similar to those of kraft pulps.

A pulping method where chips are delignified using an aqueous solution of ethanol(30-40 v-%), ammonia (10-20 % on wood) and sulphur dioxide (5-30 % on wood) at 433-438 K for 1-3 hours has been presented. Pulp yields are 67-70 % for hardwoods and 57-60 % for softwoods. The delignification is carried out in a process called drip percolationpulping. Wood chips are drip wetted in the digester with the liquid being a pulping andwashing liquor simultaneously. This liquid partly evaporates, condenses, drips onto thematerial being pulped, percolates through the layer and extracts dissolved componentscarrying them away. Aspen pulps with a yield of 70.6 %, a kappa number of 22.6 and abrightness of 62.5 % have been produced in a laboratory scale unit. The advantages ofthe method are claimed to be: pulping at low liquor ratios, simultaneous pulping andwashing, formation of high concentrated spent liquors, closed cycle operation, areduction of the energy consumption, prevention of pollution and compact equipment.(Krotov 1993)

Alkaline ethanol pulping of wheat straw can be significantly improved by an acidcatalyzed prehydrolysis. The breaking length was improved by 8 % and the tear index by25 %. (Papatheophanus et al. 1995)

Kulkarni’s group (Kulkarni et al. 1994) has delignified Agave sisalana underatmospheric conditions using aqueous ethanol (50 %) and alkali (2 %) at 353 K for fourhours. The yield of unbleached pulp was 88.6 % and the kappa number was 37. Thestrength properties of the pulp were found to be comparable with corresponding kraftpulps.

El-Sakhawy et al. (El-Sakhawy et al. 1995b) have studied pulping of cotton stalkswith aqueous ethanol and alkaline ethanol processes. The alkaline ethanol methodproduced pulps with acceptable quality under mild conditions while the aqueous ethanolprocess required the use of a catalyst.

When pulping wheat straw with aqueous ethanol, the addition of sodium hydroxideand anthraquinone improves the screened yield of pulp. (El-Sakhawy et al. 1996a)

Kinetic studies of wheat straw pulping using the alkaline ethanol method haveindicated that the delignification reaction rate increases directly with temperature. It alsodoubles if the alkali concentration is doubled. (El-Sakhawy et al. 1996b)

Alkaline ethanol pulping of wheat straw, bagasse and cotton stalks produces pulpsthat are easier to bleach than corresponding soda and ethanol pulps. (El-Sakhawy et al.1996c)

Hultholm and co-workers (Hultholm et al. 1998) have presented a new pulpingmethod they call the IDE-process. The method is a three stage process - Impregnation,Depolymerization (Delignification) and Extraction. The raw materials are impregnatedwith alkali in water and then cooked in an aqueous ethanol solution. The depolymerizedlignin is extracted and washed out from the pulp. Pulp yields are 2-5 % higher comparedto kraft pulps of the same raw materials. The addition of a 0.3 mole fraction of ethanol to the kraft pulping liquor whendelignifying aspen or spruce has been found to improve the productivity of the process.This is due to the combined effect of faster delignification, increased pulp yield, anddecreased activation energy of delignification. (Yoon et al. 1997, Yoon & Labosky1998)

2.1.2.4. Ethanol in sulphite pulping

Ethanol can be used to extract xylose from birch sulphite waste liquor. When theextraction is carried out in three stages, the isolated xylose after one recrystallization ispure enough to be used in pharmaceutical and food products. (Saarnio & Kuusisto 1971)

The yields of eugenol and isoeugenol can be improved during Mg-base alcohol-bisulphite pulping of softwoods by adding air to the digester and adjusting the alcoholconcentration and the sulphite dosage. The pulps produced under favourable conditionsfor the production of these phenols have higher yields than kraft pulps at the same kappanumber levels. Unbleached pulps have inferior strength properties to those ofcorresponding kraft pulps. The physical properties can be improved by alkali treatment.(Mun et al. 1988)

Adding of alcohols to bisulphite cooking of aspen has been found to enhancedelignification. Optimal sulphur dioxide dosage and alcohol (ethanol or isopropanol)concentration were 4-5 and 50 v-% respectively. When the yield of low molecular weightphenols was optimized, the sulphur dioxide dosage was 5-6 % and the alcohol (ethanol,propanol or isopropanol) concentration was 40-50 %. (Mun & Wi 1991a, Mun & Wi1991b)

Hemicellulose and cellulose can be converted to sugars in a three-stage process.Sulphur dioxide is used in the first stage to remove hemicellulose from hardwoods. Inthe next stage, a sulphur dioxide-ethanol-water mixture is used to remove lignin and theremaining hemicellulose. The third stage is an acid hydrolysis of cellulose to glucose.The use of the organosolv stage to remove lignin allows more efficient acid hydrolysisat less severe conditions. (Westmoreland & Jefcoat 1991)

The Timermane group (Timermane et al. 1992) has studied the kinetics of birchdelignification in aqueous ethanol with the addition of sulphur dioxide and ammonia.The results indicated that the process deviates from a first order reaction, but somecorrelation with the diffusion kinetics theory was found. The delignification rate wasfound to be limited by the diffusion rate of the delignification products.

Agricultural residues have been cooked with 15 w-% ammonia and 10 w-% sulphurdioxide (on dry material) in aqueous ethanol (65 %). Their results indicated that this

method produces pulps with higher yields than those obtained in kraft, soda or soda-anthraquinone pulping of agricultural residues. (Krotov & Frank 1993)

The methanol using ASAM process has been modified by replacing methanol withethanol. The new method is called ASAE (alkali-sulphite-anthraquinone-ethanol). PineASAE pulps were found to have better physical and optical properties than control kraftpulps with the exception of breaking length. (Kirci et al. 1994)

Sanjuan (Sanjuan et al . 1995) has compared ethanol-magnesium sulphite pulping ofwhole kenaf with kraft and soda pulping. Using aqueous ethanol (50 %) and a totalsulphur dioxide content of 4 %, they were able to produce pulps with higher yields thanthose produced with the conventional methods. The mechanical and optical properties ofthe kenaf pulps were found to be better than those of bagasse pulps.

2.1.2.5. Simulation of ethanol pulping

Muurinen et al. (Muurinen et al . 1988b) have proposed a solvent recovery process foralkaline ethanol pulping (Marton & Granzow 1982). Spent pulp washing liquor isevaporated and the residue is burned. Alkali is recovered by causticizing. Ethanol isconcentrated by distillation. This process was simulated and the costs of the equipmentand production were estimated. The costs of alkaline ethanol pulping was compared withthe costs of an alkali-methanol-anthraquinone pulping (Gasche 1985a, Gasche 1985b)process having a similar recovery section. The difference between equipment costs isnegligible but the production costs of ethanol pulping are lower.

When peroxyformic acid pulping of birch (Poppius et al. 1987) and acetic acidpulping of aspen (Young & Davis 1986) were added to the comparison, alkaline ethanolpulping (Marton & Granzow 1982) still seemed to be the most economical of theprocesses studied. (Muurinen & Sohlo 1988b)

Vanhanen and co-workers (Vanhanen et al. 1989) have preliminarily dimensioned arecovery process for ethanol-alkali-anthraquinone pulping using computer simulations.In the recovery process, pulp is washed after digester flashing, spent pulping andwashing liquors are concentrated in a vacuum evaporator plant, and ethanol isconcentrated by distillation. Methanol is recovered as a by-product by distilling thevapour formed during digester flashing. The energy consumption of the process wasestimated to be near that of kraft pulping. The pulp manufacturing costs seem to behigher than the costs of a kraft process because of the higher chemical costs.

New chemical industry simulators (e.g. HYSIMTM and ASPEN PLUSTM) appear tobe capable of predicting vapour-liquid equilibria for ethanol-water and methanol-watersystems (Barna et al . 1991). Evaporator train simulations performed with ASPENPLUSTM are also able to handle model compounds representing lignin and sugars.

2.1.2.6. The kinetics and mechanism of delignification

The kinetics of beech wood delignification by ethanol-water mixtures have been studied(Kleinert 1967). Two different mechanisms both of first the order were found: relativelyfast bulk delignification and slow residual delignification. The latter resulted inconsiderable cellulose losses. The pulping liquor contained 40 w-% ethanol at the startof the pulping.

The bulk delignification in ethanol-water pulping is a composite phenomenoninvolving breakdown of high molecular lignin and solubilization of its breakdownproducts (Kleinert 1975b). The removal of wood moisture reduces the rate constant ofdelignification. Ethanol acts as a scavenger for the free radicals formed during pulpingand reduces the extent of lignin condensation.

It has been shown that organic solvent bulk delignification occurs in two steps whichcan be described by first-order kinetics. After testing several solvent systems, includingthe ethanol-water system, they have concluded that the mechanisms of bulkdelignification do not change in various systems. (Hansen & April 1982)

Heating aspen wood with 50-75 % ethanol-water mixtures for 30-90 minutes at 468K and yields unbleached pulps with kappa numbers, viscosities and yields in commercialranges. Solubilization primarily occurs through cleavage of beta ether linkages, yieldingan isolated lignin with a phenolic hydroxyl content more than twice as high as thelignin as it exists in the wood. Some side chain rearrangement and ethoxylation ofbenzyl alcohol groups occurs. These reaction prevents the lignin molecule fromrecondensing during the pulping process. (Gallagher et al. 1989)

The variation of the chemical component of bagasse during sodium hydroxidecatalyzed ethanol pulping has been studied (Liang et al. 1989). The delignificationprocess is divided in two phases: the bulk delignification phase and the supplementarydelignification phase. The delignification rates are 70 % and 16 % respectively. Thedissolved lignin to dissolved carbohydrate ratio is 1.52. The molecular weight of ethanollignin is higher than that of bagasse kraft lignin.

Delignification of birchwood with a 35:35:30 mixture of ethanol, water and aceticacid has been studied with respect to reaction time (15-380 min) and temperature (423-463 K). The dissolved lignin was found to pass through stages of degradation andcrosslinking. At higher temperatures, condensation became dominant over degradation.When the pulping time was increased, a part of the lignin was absorbed in the pulpfibres. (Aliev et al. 1990)

Autocatalyzed delignification of birch in 60:40 ethanol:water in the temperature range448-478 K has been studied. The delignification followed a bulk phase which wasfollowed by a slower residual phase. When the reaction was assumed to be first orderwith respect to lignin concentration, an activation energy of 82.8 kJ/mol was calculatedfor the bulk delignification phase. The acidity of the system increased with increasingtemperature and time. If this acidity effect is taken into account and the rate constant isassumed to be directly proportional to average hydrogen ion concentration, an activationenergy of 67.8 kJ/mol was calculated. The low activation energy values point out thatdiffusion is a very important factor in the delignification process. (Goyal & Lora 1991)

Deineko (Deineko 1992) has proposed a possible mechanism of wood delignificationby oxygen in aqueous organic (e.g. ethanol) media. The initial rate determining stage ofthe process is an acid catalyzed eliminative reaction proceeding through the carboniumcation formation.

The main products accumulated in the spent liquor from oxygen-ethanol pulping ofspruce have been found to be partially oxidized lignin (17-20 %) and ether-soluble (1.8-2.0 %) and ether-insoluble (21-24 %) substances. Lignin dissolution is suggested to beassociated with lignin degradation by opening of the aromatic rings and rupture of the1,2 carbon-carbon bonds of the propane side chains. Vanillin and vanillic acid were foundin the spent liquor. Also glycolic, oxalic, pyropyruvic, glyceric, succinic, glutaric,muconic, formic and acetic acids were found. (Deineko et al. 1993)

The mechanism of ethanol and alkaline methanol delignification of eucalyptus hasbeen studied using scanning electron microscope observations of the resulting pulp. Thefindings suggested that delignification during ethanol pulping proceeds from the lumenwall toward the middle lamella, then reaching the cell corners. There was not enoughevidence to suggest the same mechanism for the alkaline methanol pulping. (Wang etal. 1993)

Balakshin and Deineko (Balakshin & Deineko 1995) have studied the delignificationreactions during oxygen-ethanol pulping (pH=3, 413 K, 60 % ethanol) of sprucesawdust. According to their results, reactions of benzyl alcohol and benzyl aryl structuresare the major reactions in delignification.

While the aqueous ethanol delignification kinetics of wood occurs in three phases(initial, principal and residual), the delignification of sugar cane bagasse presents onlythe principal and residual phases. The Arrhenius activation energy for the principal stagehas been calculated to be 101.9 kJ·mol-1. (Curvelo & Pereira 1995)

2.1.2.7. Ethanol lignins

Cooking of spruce wood meal in ethanol-hydrochloric acid yields, in addition to water-insoluble lignin, a mixture of distillable oils in amounts equal to about 8.2 % of thelignin present in wood. The mixture contains aldehydic, acidic, phenolic and neutralproducts. (Cramer et al. 1939)

Schweers and Meier (Schweers & Meier 1979) have analytically characterized, throughethanol-water pulping isolated beech and spruce lignin. In comparison to alkali ligninthe ethanol-water lignin has a significantly higher yield of monomeric phenols. Theyield and composition of the phenol mixture does not make pyrolysis a technicallypromising process for destruction of the lignin.

After studying the decomposition of beech and spruce by pyrolysis in a fluidized-sandbed equipment, Kaminsky (Kaminsky et al. 1980) found the method to be promising.

Lignins isolated by ethanol-water pulping from beech, oak, birch, spruce and pine andalkali lignins from beech and spruce have been decomposed by alkaline oxidation underpressure, using oxygen as the oxidizing agent. Yields of the carbonylic products obtainedfrom ethanol-water lignins were higher than those obtained from alkali lignins. Vanillin

can be produced in amounts comparable with those obtained from sulphite waste liquors.(Meier & Schweers 1979)

Lignins from beech, oak, birch, spruce and pine isolated by ethanol-water pulpinghave been degraded by catalytic hydrogenolysis. Because of the small yields of themonomeric phenolic products, no economic utilization of lignin using this methodcould be deduced. (Meier & Schweers 1981)

Lignin has been isolated by pulping beech and pine wood with aqueous ethanol using0.0-0.75 % on wood ammonium chloride as the catalyst (Lange et al. 1981). Increasingthe catalyst charge was found to increase the methoxyl content of the lignins and todecrease the hydroxyl content. The catalyst also increased the lignin yield.

Lignins isolated from beech wood and pine wood by the ethanol-water pulpingmethod can be used as a wood glue either alone or together with phenolic resins (Ayla1982). The use of a mixture of 90 % ethanol-lignin and 10 % of a phenolic resin leadsto boiling proof bonds.

Lange’s group (Lange et al. 1983) has separated ethanol-water lignins from birch andspruce into five fractions of increasing molecular weights. The deciduous wood characterof the birch lignin fractions are more pronounced at higher molecular weights.

The lignin recovered from Alcell pulping has a low molecular weight (about 1000), ishighly hydrophobic and insoluble in neutral or acidic aqueous media, but soluble inmoderate to strong alkaline solutions and certain organic solvents (Lora et al . 1989). Ithas many potential applications. It shows promise as a partial replacement of oil basedresins in wood composites.

Solubilized lignin recovered from the black liquor of with sodium bicarbonate bufferedaqueous ethanol (50 %) pulping is relatively uncondensed with few carbohydratesassociated with it (DeLange et al. 1991). Solubilized syringyl lignin removed first ismore etherified than syringyl lignin removed later.

Oxidation of lignin by hydrogen peroxide in ethanol has been found to result in 3- to10-fold higher chemiluminescence than with oxidation of lignin in water. (Selentev1991)

Oliveira et al. (Oliveira et al. 1994) have extracted lignins from pinus caribaeahondurensis sawdust using ethanol, methanol, acetone, chloroform, tetrahydrofuran, 1,4-dioxane, 1-butanol, 2-butanol and 1-propanol) and made Langmuir monolayers of them.The behaviour of organosolv lignins was found to differ considerably from the behaviourof lignins from traditional pulping processes. The different behaviour of lignins extractedwith different solvents was explained by the different values of the surface potentials andareas per molecule.

2.1.2.8. Summary

As with most of the organosolv pulping processes, ethanol pulping is more suitable forhardwoods than for softwoods. Aqueous ethanol penetrates easily into the structure ofwood resulting in uniform delignification. Ethanol also reduces the surface tension of the

pulping liquor which improves the diffusion of other pulping chemicals, for example,alkali.

High pressures and temperatures used in ethanol pulping cause potential hazards offire, explosion, and release of toxic chemicals. This has to be taken into account whendesigning the process.

The most advanced ethanol pulping method is the Alcell process. It produceshardwood pulps of satisfactory quality. The solvent recovery is claimed to be easy. Onthe other hand, some researchers have found that black liquor from aqueous ethanolpulping contains, in addition to the components of the pulping liquor, lignin and sugarsalso aliphatic acids, aromatic acids and phenols. This highlights that the purification ofthe solvent may not be as easy as claimed.

The addition of ethanol to conventional pulping liquors also seems to have positiveeffects on pulping productivity. The use of ethanol probably causes an increase in theproduction costs. If small amounts are added, ethanol is probably not recovered but lostduring chemical recovery. Large amounts of added ethanol makes it necessary to investin its recovery.

2.1.3. Other alcohols

Methanol and ethanol are the most popular alcohols used in pulping. However, severalother alcohols have also been proposed to be used as pulping chemicals. Propanol,butanol and glycols appear in several papers which are therefore referred to here. Otheralcohols proposed are benzyl alcohol (Heden & Holmberg 1936, Friedman & McCully1938), tetrahydrofurfuryl alcohol (Johansson et al. 1987, Aaltonen et al. 1987,Aaltonen et al . 1989), glycerol (Hibbert & Phillips 1930, Demirbas 1998) andchloroethanol (Schutz 1941a, Nimz et al. 1986b, Pellinen & Nimz 1986).

2.1.3.1. Propanol and isopropanol

Semichemical and chemical pulps of Japanese cedar have been produced with sulphitesolutions containing 40-50 % isopropanol. Adding the alcohol to sodium andmagnesium sulphite solutions resulted in significant savings of energy for fiberizingsemichemical pulps. Pulps produced by this method had better strength properties thancorresponding conventional semichemical pulps. Chemical pulps could be produced withacidic magnesium sulphite and isopropanol. Pulp yield was 42-45 %. The strengthproperties of these pulps were lower than those of corresponding kraft pulps. (Sakai etal. 1983)

Alcohol-magnesium bisulphite pulping of pine provides isoeugenol and eugenol asby-products (Sakai et al. 1987). The yield of softwood alcohol-bisulphite pulps is higherthan that of kraft pulps at the same kappa number level. Of the alcohols tested, the bestresults were achieved with isopropanol and sec-butanol.

Addition of 40 % isopropanol to the neutral sulphite pulping of pine accelerates thedelignification, but has a negligible effect on neutral sulphite-anthraquinone pulping(Sakai & Uprichard 1987). Both the rate and selectivity of delignification are improvedby isopropanol addition in magnesium bisulphite and magnesium acid-bisulphitepulping. Isopropanol-bisulphite pulps have better yields, lower kappa numbers andbetter papermaking properties than conventional bisulphite pulps. Isopropanol acidbisulphite pulps have similar strength properties to conventionally prepared pulps, butthe rate and selectivity of delignification is improved.

Deineko and Nikitina (Deineko & Nikitina 1989) have studied the use of oxygen as adelignifying agent during pulping of spruce sawdust in propanol and aqueous propanol.When oxygen was present in pulping with anhydrous alcohol, the amount of lignin andcarbohydrates dissolved was more than twice the amount dissolved in an inertatmosphere. Pulps produced by cooking in 60 % propanol at 433 K for two hours arehighly delignified, containing about 7 % lignin and have yields around 50 %.

The advantages of oxygen-alcohol pulping over straight alcohol pulping include alower cooking temperature and the possibility of using both hardwoods and softwoods(Deineko & Kikitina 1989).

Mun (Mun 1989) has delignified a softwood (sugi) using aqueous isopropanol (50 v-%) and magnesium bisulphite. The lignin recovered from the black liquor exhibited arather high molecular mass and only small modifications had occurred in its chemicalstructure.

When sugi (Cryptomeria japonica) and buna (Fagus crenata) were pulped with 50 %aqueous isopropanol, high amounts of low-molecular-weight phenols were obtained.Higher or lower concentrations resulted in lower yields. (Kim et al. 1996)

2.1.3.2. Butanol

As with many other alcohols, butanol was originally used as a solvent to decomposewood in order to study lignin (Hagglund & Urban 1927).

Aronovsky and Gortner (Aronovsky & Gortner 1936) have cooked aspen sawdust withaqueous solution of aliphatic monohydroxy and polyhydroxy alcohols. Normal butylalcohol pulping resulted in a pulp comparable with commercial aspen soda pulp instrength characteristics. Softwoods were not pulped as easily as the aspen. The spentpulping liquor consisted of two layers. The top alcoholic layer contained the organicsubstances dissolved from wood, and the lower aqueous layer contained only smallamounts of water soluble substances. The solubility of n-butyl alcohol in water is 8 - 9parts per 100.

Hardwoods and softwoods have been delignified with aqueous butanol. The hardwoodswere pulped satisfactorily, but the softwoods were only partly pulped. Birch andbasswood were most efficiently delignified. (McMillen et al. 1938)

Bailey has patented (Bailey 1939) a process producing pure cellulose from wood bytreating it with an aqueous mono-hydroxy alcohol having at least four carbon atoms. Atleast three of the carbon atoms have to be in a straight chain. The alcohol has to be

substantially insoluble in water at temperatures below 373 K, but soluble therein attemperatures above 373 K. An inorganic alkali is also added to the pulping liquor inamounts from 2 % to 10 %. Pulping is carried out at 373-473 K.

Aspen and pine have been digested in aqueous butanol that was buffered to preventhydrolysis. It was found that all the lignin from aspen and 80 % of the lignin from pinewas removed. The remaining pine lignin was easily dissolved in the same solvent in thepresence of 2 % sodium hydroxide. Lignin studies indicated that lignin may exist partlyin chemical combination with cellulose and partly free. (Bailey 1940a)

The addition of 2 % alkali (NaOH) to a pulping liquor containing equal amounts ofbutanol and water considerably accelerates the delignification. Almost white pulpscontaining 0.33 % lignin were produced in yields of 43-50 %, by cooking aspen for 15minutes and pine for 1 hour. Butanol was easily recovered. Only 10 % of the total liquorvolume had to be distilled, because 95 % of the butanol was immiscible in the liquorand could be separated. Extraction with di-isopropyl ether can also be used to recoverbutanol from spent pulping liquor. (Bailey 1940b, Bailey 1942)

If the butanol pulping liquor is made alkaline by adding sodium hydroxide, the spentliquor is separated into two layers upon cooling. The lignin is concentrated in the loweraqueous layer. The upper alcoholic layer can be directly used in the preparation ofpulping liquor. (Bailey 1940c)

Aqueous n-butanol (50 v-%) can be used to effectively delignify southern yellow pinemeal. At 478 K and 2.2 MPa the original lignin content of wood (30.2 w-%) can bereduced to 16.1 % when the residence time is 12 hours. (Bowers & April 1977)

McGee and April (McGee & April 1982) have compared aqueous ethanol and aqueous1-butanol pulping of pine. They found that butanol pulping produced significantlyhigher delignification levels than ethanol pulping.

Rice straw has been delignified with aqueous butanol in the presence of catalysts.Acid-catalyzed treatment with aqueous butanol (50 %) at 443 K for one hour resulted inalmost complete (> 90 %) lignin removal. The lignocellulose components can be easilyseparated when pulping with butanol. The solvent phase contains lignin, the aqueousphase contains sugars and the cellulose remains in the solid phase. (Selvam et al. 1983)

Ghose and co-workers (Ghose et al . 1983) have compared butanol and ethanol inpulping of rice straw. Both alcohols are effective delignifying agents for agriculturalresidues. Due to the higher swelling of the material and increased accessibility ofsolvents, pre-soaking improves the delignification process. Butanol has a largermolecular size and may be a better lignin solvent due to its polarity, but it is not aseffective as ethanol in the decrystallization of cellulose.

The influence of the solvent on the yields of dissolved lignins from PinusHondurensis Caribaea has been studied. The highest yield (81.5 %) based on Klasonlignin was obtained with n-butanol. The other solvents were methanol, ethanol, n-propanol, 2-butanol, tetrahydrofuran, 1,4-dioxane, acetone and chloroform. (Curvelo etal. 1990b)

The Terenteva group (Terenteva et al. 1990) has analyzed the structure of the fibrousmaterial of aspenwood after delignification with aqueous butanol (50 %) in the presenceof 0.5-1.0 v-% hydrochloric acid as the catalyst. To accelerate delignification, and toprevent lignin condensation, the chips were first extracted with aqueous butanol. The

main factors affecting fibre structure were the amount of the catalyst used and thepreliminary extraction process.

A process for combined pulping and bleaching has been presented. Pulping is carriedout in an alcohol solvent containing, for example, tert-butyl alcohol. Tert-butyl peroxideis used as the bleaching agent. Alcohol formed from the hydroperoxide during bleachingis recycled to the pulping. (Shaban & Suciu 1993)

2.1.3.3. Glycols

Glycols have been used to isolate lignin from wood (Fuchs 1929, Hibbert & Rowley1930, Hibbert & Marion 1930, Rassow & Gabriel 1931a, Rassow & Gabriel 1931b,Rassow & Gabriel 1931c, Rassow & Gabriel 1931d, Gray et al. 1935, Freudenberg &Acker 1941) and to produce pulp (Anon. 1920, Rassow & Gabriel 1931d).

Pulping of spruce with glycol using hydrochloric acid as the catalyst yields a lignin-free pulp containing 2 % pentosan. After removing the pentosan, the pulp yield is 41.8%. (Rassow & Wagner 1931a, Rassow & Wagner 1931b)

Annual plants can be delignified at high temperatures (403-433 K) and elevatedpressure using glycol or glycerol as solvents. The delignification can be carried outwithout a catalyst but the addition of 0.2 % formic acid or acetic acid accelerates theprocess. (Erbring & Geinitz 1938)

Erbring (Erbring 1939) has delignified annual plants and milled birch and pine woodswith glycol using mineral or organic acids as catalysts. The pulps produced can easily bebleached with alkaline hydrogen peroxide and they can be used in paper production.

Wheat straw, pine chips and milled spruce have been delignified at 423-433 K withglycol or glycerol in the presence of small amounts of hydrochloric acid or formic acid.Even aqueous glycol with water contents up to 50 % can be used. (Erbing & Peter 1941)

Anhydrous ethylene glycol has been used to delignify spruce at 423 K. If aqueousglycol is used, the temperature has to be increased. The moisture content of the chipshas to be 10-13 %. The delignification rate can be increased by adding organic acids,phenol or methanol, but these catalysts have a negative effect on pulp quality. Pulpsproduced by this method are soft. (Nakamura & Takauti 1941)

Grondal and Zenczak (Grondal & Zenczak 1956) have patented a pulping processwhere triethylene glycol is used as the solvent. The pulping liquor contains anhydroustriethylene glycol and 0.03-0.5 % by weight of the wood chips of aluminium chloride.The pulping is carried out at 393-408 K and at atmospheric pressure for a period of 1-4hours. If superatmospheric pressures are used, no catalyst is needed. Lignin isprecipitated from the black liquor by adding water. The remaining liquor is concentratedby evaporating water therefrom and re-used as pulping liquor.

A pulping process where ligno-cellulosic material is treated at atmospheric pressureand a temperature of 313-363 K with a liquor containing a glycol with two to threecarbon atoms and an alkaline reagent has been patented by Meyer (Meyer et al. 1961).The alkaline reagent can be selected from the group consisting of alkali metal hydroxides

and carbonates. The alkali charge is 5-50 % on wood calculated as sodium hydroxide.Alkali metal sulphides can also be used, the charge being 3-10 % on wood.

Schwenzon (Schwenzon 1965) has made pulp using a liquor containing glycol andsalicylic acid. The cooking temperature was 433-443 K and the method can easily pulpbirch and poplar. He (Schwenzon 1966) has also used acetylsalicylic acid (3 %) inglycol. The poplar pulps he obtained were so bright that no bleaching was needed. Thedissolved lignin precipitated by diluting the spent pulping liquor was very reactive.

Eucalyptus (E. regnans) pulps have been prepared with a three per cent solution ofsalicylic acid in glycol at 443 K. The pulps have low kappa numbers and yields of about50 %. The method is acid catalyzed and the papermaking properties of the pulps aresimilar to those of bisulphite pulps. (Nelson 1977)

Ethylene-, propylene-, and butyleneglycols or other higher alcohols can be used todissolve lignocellulosic materials. Prior to the alcohol treatment, the material has to beimpregnated with acids (eg. sulphuric acid) and dried at a temperature below 373 K. Thealcohol treatment is carried out at a temperature above 473 K for 2 to 60 minutes. Thematerial is partly or totally dissolved during the treatment. The dissolved material can beused in production of plastics. Also cellulose can be produced with this method. (Unger et al. 1979)

The Gast group (Gast et al . 1983) has studied the pulping efficiencies ofmonohydroxy and polyhydroxy alcohols. The most promising candidates were n-butanoland ethyleneglycol. The delignification efficiency of the ethylene glycol system wasimproved by catalyst [Al2(SO4)3 or AlCl 3] addition.

The kinetics of birch pulping in ethylene glycol-water solutions (50:50) attemperatures 453-473 K has been studied. The delignification has two phases which canbe described by first order reactions. The activation energies for the first and seconddelignification phases were determined to be 81.2 and 152 kJ/mol respectively. (Gast &Puls 1984)

In a later paper, Gast and Puls (Gast & Puls 1985) reported that the activation energyof the second delignification phase is 135.5 kJ/mol. Sufficiently delignified pulps areobtained in pulping of hardwoods. Lignins recovered from the black liquor can be used asextenders in phenolic resin adhesives.

A process for producing cellulose paste from wood or vegetable shavings has beenpatented (Bruniere & Galichon 1988). The lignocellulosic material is cooked in anaqueous solution containing 2-20 w-% of alkaline metal hydroxides, alkali metal salts,or alkaline earth metal salts at 423-473 K for 15-60 minutes. If the process is operated atatmospheric pressure, the aqueous solution may also contain 2-20 w-% of a solvent, forexample, a glycol.

A liquefaction process, the UDES-A process, for concentrated pastes of finely dividedlignocellulosics has been presented (Vanasse et al. 1988). When ethylene glycol wasused as the solvent in the process, only partial liquefaction was achieved. The probablecause of this behaviour is complex formation between ethylene glycol and cellulose.

Thring and co-workers (Thring et al . 1989a) have isolated a prototype solvolysislignin from poplar using ethylene glycol as a solvent. The characteristics of the ligninsuggested that it is a native-type lignin.

Ethylene glycol and kraft lignins have been fractionated by extraction with ethylacetate and methanol. Glycol lignin fractions showed a lower carbon content than thekraft lignin fractions. Ethyl acetate was found to be a good solvent for selectiveextraction of low molecular weight material from glycol lignin. (Thring et al. 1989b)

Burkart has patented (Burkart 1989) a method for removal of lignin and other non-carbohydrates as well as non-cellulosic carbohydrates from lignocellulosic materials. Thematerial is first impregnated with a solution that is a reaction product oftriethyleneglycol and an organic acid. After impregnation, the material is rapidly heatedto a temperature between 392 and 403 K, where it is maintained for 2-5 minutes.Conventional techniques can be applied to separate the pulp and the spent liquor.

The recovery of lignin from the black liquor after ethylene glycol pulping has beenfound to be more practically carried out by dilute acidification of the spent glycol liquorthan by evaporation. At low temperatures, the lignin recovered is a gel-like materialimpossible to filtrate, but at higher temperatures (> 343 K) the lignin precipitates intofine particles and forces a very slow filtration. The optimum temperature for ligninprecipitation is 323-333 K. One part of an acidic aqueous solution is added to three partsof black liquor. The concentration of hydrochloric acid in the precipitation liquor is 0.05w-%. Gel permeation chromatography indicated that the average molecular weight of theglycol lignin is 4762 g/mol. Electron microscopy showed that the lignin containsessentially spherical particles of size range 0.5-2.5 �m. (Thring et al. 1990a)

After alkaline hydrolysis of glycol lignin, the lignin residue has higher carbon andlower oxygen contents than the original lignin. The calorific values of these residuallignins is increased during the depolymerization by alkaline hydrolysis. (Thring et al.1990b)

Thring (Thring et al. 1991) has fractionated glycol lignin by solvent extraction.Lignin and its fractions were characterized by determination of methoxyl and totalhydroxyl groups. 13C NMR spectroscopy was also used. 26 % of the lignin was foundto consist of a low molecular weight fraction soluble in ethyl acetate. This fraction isricher in guaiacyl units and hydroxyl groups than the other fractions.

They (Thring et al . 1993a) have also characterized glycol lignins using 1H and 13CNMR spectroscopy. The lignins were fractionated by sequential solvent extraction.Fractions with the highest molecular weights were found to have structures linked bybeta-O-4 type bonds. The lowest molecular weight fractions contained a high number ofaliphatic side-chain structures.

Up to 60 % of hardwood glycol lignin can be converted to liquid and gaseous productsby thermal treatment in the presence of tetralin. At low treatment temperatures,syringols, guaiacols, aromatic aldehydes and ketones are formed. At higher temperatures,phenol, catechol and their methyl and ethyl derivates are the main monomers at highseverities. (Thring et al. 1993b)

Finely divided poplar wood or sawdust can be can be fractionated into cellulose,hemicellulose and lignin by a two-stage process. The first stage is autohydrolysis byaqueous-steam treatment. This pretreatment step removes over 90 % of thehemicelluloses and about 20 % of the lignin. The second stage is an organosolvtreatment with aqueous ethylene glycol (6-10 w-%). This step yields 100 % of thecellulose fraction. (Thring et al. 1993c)

When pulping aspen, birch and beech with ethylene glycol at a liquor ratio of 5:1,Rutkowski and co-workers (Rutkowski et al. 1993) obtained pulps at yields of 48-65 %,with kappa numbers of 10-63 and brightness up to 50 %. The best results were obtainedusing an 80 % aqueous solution of ethylene glycol at a maximum cooking temperatureof 448-453 K and cooking time of 180 minutes. The results were further improved byadding 2 % sodium bisulphite to the cooking liquor and by evacuating all air from thedigester.

The Rutkowski (Rutkowski et al. 1994a, Rutkowski et al. 1994b) has proposed theadding of acetic acid as a modification for glycol pulping of aspen. The optimumpulping liquor composition was found to be 20 % water, 20-40 % glycol and 40-60 %acetic acid. When acetic acid is added to the pulping liquor lower pulping temperaturescan be used. Glycol-acetic aspen and pine pulps are easily beatable but their strengthproperties are inferior to those of corresponding kraft pulps.

Ethylene glycol has been proposed to be used as a pulping agent for bagasse. Theequipment can be adapted from the beet sugar industry. Lignin is precipitated from thespent pulping liquor by adding water. Lignin is filtrated and the filtrate is distilled. Thetop product of the distillation contains organic acids and the bottom product contains theethylene glycol. (Chaudhuri 1996)

The losses of ethylene glycol during the pulping process are caused by a reaction ofthe solvent with wood chemicals, chemical changes in the substance itself and finallyevaporation. (Surma-Slusarska 1998)

2.1.3.4. Summary

Compared to methanol and ethanol, very little attention has been paid to the use of otheralcohols as pulping solvents. The probable reason for this is the fact that they all,except for ethylene glycol, are more expensive than methanol and ethanol. The relativelyhigh boiling point (471 K) of ethylene glycol probably decreases its attractiveness.

2.2. Organic acids

2.2.1. Formic acid

Formic acid is a good solvent for the lignin and extractives present in wood. It alsocauses hydrolytic breakdown of wood polymers into smaller and more solublemolecules. (Sundquist 1996)

Peroxyformic acid makes lignin more soluble by oxidizing lignin and making it morehydrophillic. As a highly selective chemical, peroxyformic acid does not react withcellulose and other wood polysaccharides. (Sundquist 1996)

As with most of the organic solvents, formic acid has been used in addition topulping also as solvent in order to study wood components (Pauly 1918a, Pauly 1918b,Pauly 1921, Freudenberg e t al. 1936, Staudinger & Dreher 1936, Wright & Hibbert1937, Pew 1957, Wang et al. 1990).

2.2.1.1. Pulping and bleaching with formic acid

Reznikov and Zilbergleit (Reznikov & Zilbergleit 1980) have reported that a pulpintermediate product is obtained by cooking wood chips with formic acid in the presenceof hydrogen peroxide as the oxidant and sulphuric acid as the catalyst.

Pulp can be produced from hardwoods and their barks by refluxing in aqueous formicacid (65-90 %) at atmospheric pressure. The resulting pulp has a high hemicellulosecontent and a very high holocellulose yield. The spent pulping liquor has a very lowcarbohydrate content and the molecular weight of the dissolved lignin is less than 1000.The wood pulps can be used in paper production or as animal feed. Bark pulp is useful,for example, as animal feed and as a replacement for tobacco. (Jordan 1982)

Pulp can be produced with aqueous formic acid (80 %) containing a small amount ofa catalyst. Pulping is carried out at atmospheric pressure and after 45 minutes cookinghardwoods result in pulps with kappa numbers of 60-65 and yields near 60 %. Thedelignification is a result of hydrolysis, where water catalyzed by formic acid and by theother catalyst reacts with lignin-hemicellulose bonds. Hemicellulose is furtherhydrolysed forming acetic acid and sugars. Formic acid is not consumed chemically andthe only loss (10-20 kg per metric ton of pulp) is a result of acid left in pulp afterwashing. About 70 kg of formic acid per metric ton of pulp is formed during pulping ofhardwoods. Lignin, whose molecular mass is less than 1000 g/mol, can be used toproduce, for example, methanol, phenol and benzene. (Bucholtz & Jordan 1983)

In pulping hardwood chips with formic acid, delignification can be intensified by theaddition of an organic solvent. The solvent may be acetone, ethanol or methanol. Thepulping temperature is 343-383 K and liquor-to-wood ratios from 2:1 to 5:1 can be used.The ratio of the organic solvent to formic acid is 0.15-0.5 and the pulping liquorcontains less than 25 w-% water. The cellulose produced by this method is easilybleached. (Avela et al. 1988)

Arnoldy and Petrus have patented (Arnoldy & Petrus 1989, Arnoldy 1989, Arnoldy &Petrus 1990, Arnoldy & Petrus 1992) a process for pulping lignocellulose-containingmaterials with a pulping medium containing at least 75 w-% of a solvent system. Thesolvent system contains 20-95 w-% formic acid, 5-80 w-% at least one C1-3 primary

alcohol or ester of formic acid with primary alcohol, and optionally up to 70 w-% atleast one component selected from acetic acid and C1-3 esters of acetic acid with primary

alcohols. The pulping temperature is 413-473 K. When the solvent system contains 39w-% formic acid, 50 w-% acetic acid and 11 w-% ethanol pine can be delignified at 453K to a kappa number of 12.

When Eucalyptus globulus is cooked for 90 minutes at 363 K with 80 v-% formicacid using the liquor-to-wood ratio 30:1 and catalyst concentration 0.44 %, pulp with a

yield of 56 % and a kappa number of 22 is obtained. Eucalyptus grandis needs 99 %formic acid, a temperature of 368 K, 0.22 % catalyst and a liquor-to-wood ratio of 10:1to produce pulp with a kappa number of 31 and a yield of 43 %. Hydrochloric acid hasbeen used as the catalyst. (Baeza et al. 1991)

Nimz and Schone (Nimz & Schone 1993) have applied for a patent for a pulpingmethod where the delignification is carried out with acetic acid and formic acid. Thepulping liquor contains 50-95 w-% acetic acid, less than 40 w-% formic acid and lessthan 50 w-% water.

Fir and spruce pulping experiments have been carried out on a laboratory scale at aliquor-to-wood ratio of 10:1 and a temperature of 353 K for 60 minutes. The cookingliquor contained 50 v-% of formic acid or acetic acid and 50 v-% of a 25 v-% aqueoushydrogen peroxide solution. Sulphuric acid was used as a catalyst. Strength properties ofthe pulps produced were comparable to those of kraft and sulphite pulps at similardegrees of delignification. (Pen et al. 1993)

Sun (Sun et al . 1994a, Sun et al. 1994b) has found that a peroxyformic acidpretreatment accelerates the rate of UV-peroxide bleaching of eucalypt kraft pulp. Thebest results were achieved when the bleaching was started with a nitric acid catalysedperoxyformic acid pretreatment followed by sodium hydroxide extraction and UV-peroxide bleaching.

Fungal treatment of pine with Punctularia artropurpurascens or Ceriporiopsissubvermispora prior to pulping with a mixture of formic acid and acetone (7:3) has beenfound to slightly increase tensile and burst indexes of the resulting pulp, whilst tearindexes are reduced by up to 30 %. Pretreated samples require shorter cooking times andthe resulting pulps have 29 % lower kappa numbers. (Ferraz et al. 1998a)

Obrocea and Cimpoescu (Obrocea & Cimpoescu 1998) have studied delignification ofspruce by peroxyformic acid. They obtained uniform delignification by cooking thechips for 2...4 hours at the maximum temperature. The best pulp yield was obtainedwhen using the cooking temperature 363 K.

A mixture of formic acid and peroxyformic acid has been successfully used todelignify eucalyptus wood and sugar cane bagasse. Resulting pulps have low kappanumbers. (Silva Perez et al. 1998)

2.2.1.2. The Milox process

The idea of using peroxyformic acid as a pulping solvent was introduced by Russianresearchers (Reznikov & Zilbergleit 1980, Zilbergleit et al. 1981). The Milox processis a Finnish development of this idea.

Sundquist (Sundquist 1985) presented in 1985 a two-stage atmospheric pulpingmethod using formic acid and peroxyformic acid as solvents. In the first stage, formicacid and hydrogen peroxide form peroxyformic acid, which is a good delignifying agent.When the formic acid concentration in solvent was 60-80 %, and hydrogen peroxide wasused, 20-60 % of the dried chips, pulps with kappa numbers of 2-20 and yields of 50-60% were produced. The second stage of the method was alkaline peroxide bleaching.

The amount of hydrogen peroxide needed could be reduced by pretreating the chips atreflux temperature. The brightness of bleached peroxyformic acid pulps was about 90 %ISO and birch pulps were reported to be nearly as good as corresponding kraft pulps.(Poppius et al. 1986)

Pulps obtained from one-stage cooking with a high peroxide charge had high tensilestrength but low tearing strength. Two-stage cooking, where the solvent in the firststage is aqueous formic acid and 5 % on wood of hydrogen peroxide is added to thesecond stage, resulted in better pulps. The strength properties of birch pulp could beeven better than those of corresponding kraft pulp. When the pulp was bleached with thealkaline peroxide method to full brightness, the strength fell slightly. (Laamanen et al .1986)

The amount of hydrogen peroxide needed to produce fully bleached hardwood pulpwith the two-stage formic and peroxyformic acid pulping and following alkaline peroxidebleaching can be as low as 2 % on wood. When softwood pulp is produced the hydrogenperoxide charge needed is 10 % on wood, which is too high for economic operation.(Sundquist 1986)

The two-stage formic acid/peroxyformic acid process can be used to produce highviscosity (> 900 dm3/kg SCAN) fully bleached (90 % ISO) pulp with a reasonable yield(40-48 %) from both hardwoods and softwoods. The pulping stages were carried out atatmospheric pressure and temperatures below 373 K. The resulting pulps had kappanumbers between 5 and 35. (Sunquist et al. 1986)

The hydrogen peroxide charge needed can be reduced by using a three-stage cookingmethod. The first and third cooking stages are carried out at 353 K with peroxyformicacid, and the second stage at the boiling point of the aqueous formic acid mixture.Another way to reduce hydrogen peroxide consumption is to carry out the only formicacid using stage at slightly elevated pressure (383 K). The hydrogen peroxide charge isalso reduced when the liquor-to-wood ratio in the first and third stages of the three-stageprocess is reduced from 4:1 to 2:1. Hardwood and softwood pulps produced by thismethod can easily be bleached to full brightness with an alkaline hydrogen peroxidetreatment. The minimum total hydrogen peroxide consumptions (cooking + bleaching)is 2.6 % on wood for birch and 7.9 % on wood for pine. (Poppius et al. 1987)

The method has been patented in Finland (Laamanen et al. 1987), the USA(Laamanen et al. 1988) and Canada (Laamanen et al. 1991).

Sundquist’s group (Sundquist et al. 1988) has examined problems related toorganosolv processes using the peroxyformic acid process as an example. The mostimportant problems are: raw-material limitations, pulping technology, washing andbleaching, pulp quality, solvent recovery, by-products and economic considerations. Theenvironmental compatibility of many organosolv methods is very apparent, because thepulp has to be bleached using chlorine chemicals in many cases. The authors state thatthe peroxyformic acid process is completely free from the use of sulphur and chlorinechemicals and therefore friendly to the environment.

Three-stage peroxyformic acid cooking can be used to produce birch pulps with yieldsof around 43 %, low kappa numbers (around 3) and high viscosities (1000-1400dm3/kg). The method is now called the Milox process. The yield of non-chlorinebleaching to the brightness of 90 % ISO is 90-92 %. If the bleaching sequence contains

only peroxide stages, the total hydrogen peroxide consumption in pulping and bleachingis 60-200 kg per metric ton of pulp. The hydrogen peroxide charge can be furtherdecreased by replacing some of the peroxide bleaching stages with oxygen or ozonestages. (Poppius et al. 1989a)

The spent pulping liquors from Milox pulping of both birch and pine can be used forgrass preservation using the AIV system. This makes it possible to decrease the formicacid loss occurring during chemical recovery. (Sundquist et al. 1989)

The operation of a Milox pilot plant was started in 1991. The equipment can be usedto study the three-stage Milox pulping and the Milox bleaching of kraft pulps. Thebatch digester can be used to treat 250 kg of wood or 120 kg of kraft pulp. (Anon.1992a)

Besides the digester, there are two bleaching reactors treating 150 kg of pulp and awashing press in the pilot equipment. The digester has been surfaced with zirconium andthe other parts of the equipment have been manufactured from stainless Duplex steel.The pulps produced at the pilot plant have slightly higher kappa numbers than thoseproduced on a laboratory scale. The pilot pulps are more easily bleached to a higherbrightness than the laboratory pulps. The pulp viscosity is decreased too much duringbleaching. This is probably due to the high copper content of the water used. Thestrength properties are somewhat lower than those of the laboratory pulps because of theheavier mechanical treatment in the pilot plant. (Sundquist & Poppius-Levlin 1992)

Birch pulp was produced in the first pilot plant experiments. The pulp was bleachedwith alkaline hydrogen peroxide to the brightness of 85 % and it was used to producepaper containing 60 % Milox pulp and 40 % softwood kraft pulp. With the exception ofstrength, the paper had properties similar to those of paper produced from kraft pulp.(Koljonen et al. 1992)

In the pilot plant, dried birch chips are mixed with preheated formic acid and hydrogenperoxide. The mixture is heated to 333-353 K. When the oxidising potential of thesolvent is nearly used, the temperature is raised to the boiling point (383 K) of themixture. The total pulping time is 4-5 hours. The softened chips are removed from thedigester, pressed and treated again with formic acid and hydrogen peroxide at a maximumtemperature of 353 K. When the pulp has been pressed, washed with formic acid andscreened in water, it is bleached with alkaline peroxide. The hydrogen peroxide charge inpulping is 2 % on wood and the kappa number of the pulp after digesting is 25-30.Pulps produced at laboratory scale have a lower kappa number. This is mainly caused bythe use of recycled impure formic acid in the pilot plant. The washing is probably alsonot effective enough. (Poppius-Levlin et al. 1993)

The hydrogen peroxide consumption in three-stage Milox pulping of softwoods canbe decreased from 10 % to 4 % by properly adjusting the process conditions in thesecond pulping stage. The result is achieved by increasing the pulping temperature to413 K and by cooking the chips for only one hour. The resulting pulps can be bleachedusing alkaline peroxide. (Seisto 1993)

Seisto and Poppius-Levlin (Seisto 1994, Seisto & Poppius-Levlin 1995, Seisto etal. 1995, Seisto et al . 1996) have found that the two-stage Milox method is moresuitable for pulping of agricultural plants than the three-stage method, which is used forpulping wood species. They have pulped tall fescue, reed canary grass, goat’s rue and

common reed using a method comprising cooking with formic acid alone (373-393 K,60-120 min), followed by reaction in an aqueous mixture of formic acid and hydrogenperoxide (353 K, 180 min). Pulps with low kappa numbers and high viscosities wereproduced using only 1.5 % hydrogen peroxide on grass. The yield of unbleached pulpswas 40-50 % and the pulps were easily bleached with hydrogen peroxide only. Theperoxyformic acid grass pulps can be used to replace 30-50 % of the short-fibre materialin fine papers without any decrease in the strength properties of the paper. When theoptical properties are more important than the strength properties, nearly 70 % grasspulp may be used.

When the Milox method is used to delignify agricultural plants, the resulting pulpcontains all the silicon present in the plant. This enables the use of a similar chemicalrecycling system as in a corresponding wood pulping process. The silica is dissolvedduring the alkaline peroxide bleaching. (Seisto & Sundquist 1994)

Tuominen (Tuominen 1995) has calculated the chemical balance for a full scale Miloxprocess. His results show that the acid concentration in the pulping liquor should be atleast 83 w-% in order to keep the acid concentration in the first pulping stage highenough.

Argyropoulos et al. (Argyropoulos et al. 1995) have used the three stage Miloxmethod to delignify birch chips. Dissolved lignins were isolated after each stage andsubjected to quantitative 31P NMR and oxidative degradation analyses. During the firstperoxyformic acid pulping stage, approximately 45 % of the beta-O-4 aryl ether linkageswere found to be cleaved. The magnitude of these reactions was intensified during thesecond formic acid pulping stage. The formic acid delignification was found topreferentially cleave the syringyl rich lignin structures in the secondary cell wall.Condensation reactions were found to be predominant in the second pulping stage.

A preliminary design for a commercial size Milox plant with the capacity of 200000metric tons of pulp per year has been made. When the process was compared with a kraftmill of similar size, the results pointed out that while the investment costs were thesame, production costs were higher for the Milox process. (Pohjanvesi et al . 1995,Poppius-Levlin et al. 1995)

Puuronen and co-workers (Puuronen et al . 1995, Puuronen et al. 1997) havemodified the two stage Milox process by replacing the formic acid partly by acetic acid.Acetic acid was found to stabilize the peroxy acids in the pulping liquor, resulting in alonger preservation of the oxidation potential of the liquor. With this method pulps ofgood quality were produced from common reed and reed canary grass.

According to Sundquist (Sundquist 1995), the main difference between the Miloxmethod and conventional pulping methods is that no sulphur is used in the Miloxprocess. At the present state of development, the costs of Milox pulping and the pulpquality do not differ enough from those of the kraft process in order to make the Miloxmethod an attractive alternative for the pulping industry.

Hemicelluloses obtained as by-products in the Milox process have been used toproduce lactic acid. Batch fermentations with Lactobacillus pentosus produced 27 g/dm3

lactic acid and 11 g/dm3 acetic acid when the sugar content of the initial liquor was 41g/dm3. (Perttunen et al. 1996)

The investment costs of a Milox plant have been estimated to be the same as for akraft mill of similar size. The Milox process would be about 20 % more expensive torun because of the higher chemical and energy costs. (Sundquist 1996)

According to Seisto and Poppius-Levlin (Seisto & Poppius-Levlin 1997a), the effectof formic acid on birch carbohydrates and lignin depends on the time and temperatureused in the treatments. At 353 K, the selectivity towards lignin decreases as a functionof time. At 380 K, the delignification selectivity improves when longer treatment timesare used. The selectivity of peroxyformic acid in a mixture of formic acid and hydrogenperoxide is high and is further improved at higher concentrations.

The degree of deformation has been found to be greater in birch Milox fibres than inkraft fibres. This explains why the strength properties of Milox pulps are not as good asthose of corresponding kraft pulps. The deformations in Milox fibres are estimated to becaused mechanically. Therefore the authors (Seisto & Poppius-Levlin 1997b)recommend that more attention should be given to mechanical treatments during Miloxpulping in order to improve the strength properties of the pulps.

According to Seisto (Seisto 1998), the addition of grass Milox pulp to paper furnishimproves bulk and optical properties but reduces strength.

2.2.1.3. Milox bleaching

Chlorine chemicals have to be used to reach full brightness when bleaching kraft pulps.The reactivity of residual lignin in pulp towards alkaline peroxide bleaching can beimproved by peroxyformic acid pretreatment. A kraft pulp with kappa number 33 reacheda delignification degree of 20-80 % in peroxyformic acid treatment, depending onhydrogen peroxide charge, formic acid concentration and temperature. In the alkalineperoxide bleaching, following the peroxyformic acid treatment, a brightness 80-85 %was reached. When an OZPP bleaching sequence followed the peroxyformic acidpretreatment, pulp with a brightness 89 % ISO was produced. (Poppius et al. 1989b)

The reactivity of residual lignins of both birch and pine kraft pulps in oxygenbleaching is significantly improved by pretreating the pulps with peroxyformic acidbefore bleaching. Peroxyformic acid creates oxidized structures and additional phenolicgroups making alkaline peroxide or oxygen bleaching easier. The pretreated pulp can bebleached with alkaline peroxide to a brightness of 83-86 %. When the final bleaching iscarried out sequentially with oxygen, ozone and alkaline peroxide, both pine and birchkraft pulps reach a brightness 90 % completely without chlorine chemicals. (Poppius-Levlin & Tuominen 1991, Poppius-Levlin et al. 1991a)

The method is called Milox bleaching. When the peroxyformic acid treatment isfollowed by an alkaline peroxide stage, or an oxygen stage and an alkaline peroxidestage, the bleaching of birch kraft pulp consumes hydrogen peroxide at 40-45 kg permetric ton of pulp. The corresponding consumption in bleaching of pine kraft pulp is 75kg. When an ozone stage is added to the bleaching sequence, the hydrogen peroxideconsumption is decreased to 24 kg for birch pulp and to 39 kg for pine pulp. Both birch

and pine pulps have similar strength and optical properties to the corresponding kraftpulps bleached using conventional methods. (Poppius-Levlin et al. 1991b)

When bleaching is carried out in a concentrated formic acid solution, peroxyformicacid has a higher delignification rate than peroxyacetic acid, peroxypropionic acid, Caro’sacid or polyoxomolybdate. In aqueous solutions, peroxyformic acid reacts with waterforming formic acid and hydrogen peroxide. In the case of peroxyacetic acid, thecorresponding reaction is slower and the delignification rate is therefore as high as inconcentrated acetic acid. The viscosity of bleached pulp was found to fall linearly withdecreasing delignification pH due to degradation of the carbohydrates. (Jaaskelainen 1996)

2.2.1.4. Solvent recovery in Milox pulping

Muurinen (Muurinen 1986) has proposed a solvent recovery cycle for two-stage formicacid/peroxyformic acid pulping. After cooking, the pulp is washed in a five-stagewashing plant. The spent washing liquor, together with the black liquor, is evaporated.Formic acid remaining in the evaporation residue is recovered by spray drying before thedissolved solids are burned. The recovered formic acid is concentrated by distillation.

Muurinen and Sohlo (Muurinen & Sohlo 1988a) have proposed a solvent recoverycycle for three-stage formic acid/peroxyformic acid pulping of birch. After cooking, thepulp is first washed with fresh solvent in order to prevent lignin condensation, and thenwashed with water. The black liquor and the spent washing liquor are concentrated inseparate vacuum evaporation plants. The evaporation residues are dried and burned.Formic acid recovered in the evaporation and drying is concentrated by pressure shiftdistillation. The investment and production costs of this process are quite high.

Muurinen and Sohlo (Muurinen & Sohlo 1988b, Muurinen & Sohlo 1989) haveproposed recovery cycles based on evaporation and distillation for alkali-methanol-anthraquinone (Gasche 1985a, Gasche 1985b), alkaline ethanol (Marton & Granzow1982), acetic acid (Young & Davis 1986) and peroxyformic acid pulping processes.These processes were compared with kraft pulping. The results of the comparisonpointed out that in 1988 organosolv processes were not yet serious competitors for kraftpulping.

When ethanol-alkali-anthraquinone pulping (Laxén et al . 1988) and peroxyacetic acidpulping (Laamanen et al. 1987) were added to the comparison, alkaline ethanol pulpingstill seemed to be the most economic organosolv method. The investment costs oforganosolv processes seemed to be near those of a kraft process, but the operating costsof organosolv pulping are higher due to high recovery costs. (Muurinen et al. 1989)

Koivusaari (Koivusaari 1990) has in his master’s thesis studied the use of adsorptionin the recovery section of the peroxyformic acid pulping process. The mordenitemolecular sieve (AW300) tested can be used to pass the azeotropic point of the water-formic acid mixture.

Lahtinen (Lahtinen 1991) has in his thesis studied the selectivity of entrainerssuitable for extractive distillation of the formic acid-acetic acid-water mixture. For closerstudies, he has chosen butyric acid, which can be used to separate the mixture in a three-

stage distillation sequence. Nearly pure water is obtained as distillate from the firstcolumn to which butyric acid and the acid-water mixture are fed. The bottom product isfed to the second column, from which formic acid is obtained as distillate. The bottomproduct of the second column is fed to the third column, from which acetic acid isobtained as distillate. The bottom product of the third column is nearly pure butyric acidand is recycled to the first column.

Muurinen and Sohlo (Muurinen & Sohlo 1991a, Muurinen & Sohlo 1991b,Muurinen & Sohlo 1992) have studied the effects of chip moisture content, liquor-to-wood ratio and formic acid concentration in pulping on the economy of a suggestedMilox pulping and recovery process (figure 1). The optimum liquor-to-wood ratio isaround 4:1, when the chip moisture content is 20 % and the formic acid concentration inpulping is 83.5 %. The operating costs of the process and the investment costs of therecovery cycle are nearly constant with formic acid concentrations 75-88 %. Higherconcentrations increase the investment costs.

Washing with solvent

Spent liquor

Washing with water

H2O

Pulp

Evaporation orDistillation

Drying Boiler

HCOOHDrying of chips

Digester 1 353 K101,3 kPa

Chips

HCOOH

Digester 2 398 K 172 kPa

H2O2

HCOOH

HCOOH

H2O2

Digester 3 353 K101,3 kPa

HCOOH

Flashing to101,3 kPa

Evaporation

Distillation orAdsorption

Extraction

HCOOH

Fig. 1. The flowsheet used in simulations.

The operating costs and investment costs of four alternative recovery cycles have beencompared. Four separation methods were tested: pressure shift distillation, distillation of

spent washing liquor instead of evaporation, extraction of spent washing liquor withisobutyl acetate after evaporation and adsorption. Distillation seemed to be the basicseparation method although adsorption also seemed to be a promising alternative. Theeffect of various flow configurations in Milox pulping was also tested by calculating theamounts of spent pulping liquor. A counter-current flow configuration produces lessspent pulping liquor than the co-current and crosscurrent configurations, and wastherefore estimated to be the most economic configuration. (Muurinen & Sohlo 1991a)

The Mattila group (Mattila et al. 1992) has patented a method for recovering formicacid from pulp. The pulp is first vacuum evaporated at 343-373 K and then washed withhot water. The washing can be replaced with steam stripping at 373-413 K.

Lignin can be precipitated from the black liquor by adding water. The precipitatedlignin is recovered by filtration. Most of the formic acid has to be evaporated from theblack liquor before precipitation. (Vuori et al. 1990)

After lignin removal formic acid and sugars can be recovered by multi-stageevaporation. The concentrated liquor from an evaporation stage is diluted by thecondensate from the next stage. The condensate from the first stage is concentratedaqueous formic acid. The concentrate from the last stage is a nearly pure sugar-watersolution. (Saari et al. 1992)

The economy of the Milox process can be improved by selling a fraction of the blackliquor to be used to produce animal feed. Changing the flow configuration of the three-stage Milox pulping to a system operating both co-currently and counter-currently mayalso improve the economy. The relatively high operating costs of the Milox process aremainly due to the high energy consumption especially in the recovery section. Usingpinch technology (Linnhoff et al. 1982) to integrate the heat flows of the unit operationscan cut the operating costs down by about 14 %. (Muurinen et al. 1992)

The heat integration of the Milox process (fig. 1) using pinch technology reduces theneed for external heating and cooling by about 40 % and 50 % respectively. (Muurinen& Sohlo 1993a, Muurinen 1994)

When separation process selection methods found in literature were applied to theMilox process, it was found that distillation, azeotropic distillation, extractivedistillation, extraction, membrane processes and adsorption are potential separationmethods. A mordenite molecular sieve was tested on a laboratory scale and the resultsshowed that the capacity and selectivity of the adsorbent were too low. (Muurinen et al.1993a, Muurinen 1994)

Pressure shift distillation, extractive distillation with butyric acid and three-stagedistillation without a mass separating agent have been compared as possible methods forrecovering formic acid and acetic from the spent liquors of the Milox process. Apreliminary evaluation showed that pressure shift distillation is the most attractiveseparation method. The situation was unchanged even after a thermal integration carriedout using pinch technology. (Muurinen & Sohlo 1993b)

Acetic acid is formed during Milox pulping and has to be separated to avoidaccumulation. The feed liquor to the recovery cycle contains less than 1 w-% of aceticacid. This makes the recovery and especially distillation complicated. If pulping could becarried out with a mixture of formic acid and acetic acid, significant savings could be

made in separation costs. Preliminary laboratory experiments show that pulping withthe mixture is possible. (Muurinen et al. 1993b, Muurinen & Sohlo 1997a)

Muurinen and Sohlo (Muurinen & Sohlo 1994) have studied the thermal integrationof a proposed Milox process configuration (fig. 2). Pressure shift distillation andextractive distillation with butyric acid were used as alternative separation methods. If aheat exchanger network is designed according to a pinch analysis, the primary energyconsumption of a Milox process using pressure shift distillation as the separationmethod is reduced by 30 %. If extractive distillation is used, the corresponding reductionis 25 %.

Lahtinen (Lahtinen et al . 1994) has studied the the vapour-liquid equilibrium of theternary system water-formic acid-acetic acid. They also measured the equilibrium of n-methyl-2-pyrrolidone (NMP) with water and the acids. These results showed that NMPis a potential entrainer in extractive distillation of the ternary system.

CHIPS

DRYING

HCOOH

PULPING +SOLVENTWASHING

SPENT LIQUOR

ACID

EVAPORAT-ION

PRECIPITAT-ION

LIGNIN

EVAPORATI-ON

CARBOHYDRATES

WASHING

SPENT LIQUOR

PULP

HCOOH

SEPARATIONWATER

ACETIC ACID

Fig. 2. Milox pulping and recovery.

The use of pervaporation in separating the formic acid-acetic acid-water mixture hasbeen studied using a polyvinyl alcohol membrane, which was recommended for organicacids with two or more carbons. The best results were achieved with solutionscontaining less than 15 % formic acid. The best separation factor values for the acidswere 3-4. (Matinheikki & Sohlo 1994)

Muurinen and Sohlo (Muurinen & Sohlo 1997b) have used shortcut simulationmethods in order to study the effect of feed liquor composition on the economy of adistillation sequence separation a mixture of formic acid, acetic acid, and water. Veryhigh or low water contents in the feed liquor seem to result in the lowest thermal energyconsumptions.

2.2.1.5. The chemistry of Milox pulping

The molecular weight of residual lignin in peroxyformic acid pulp increases whendelignification proceeds. At the same time, the amount of unsubstituted guaiacyl units,arylether bonds and free phenolic groups decreases. Peroxyformic acid residual ligninseems to be more oxidised than residual lignin in kraft pulp. (Hortling et al. 1987)

Ede’s group (Ede et al . 1988) has found that lignin model compounds werecompletely consumed after treating with 85 % formic acid for one hour at refluxtemperature. During the early stages of the reaction, primary, secondary and phenolichydroxyl groups were partially converted to corresponding formates. 1H NMR spectrapointed out that during long reaction times, components with high molecular masses areformed.

Phenolic diaryl methanols are formed during pulping as a result of acidic hydrolysis.Significant amounts of benzofurans are also formed. (Ede & Brunow 1989a)

The primary reactions of lignin model compounds in 99 % formic acid arecondensation reactions between the a carbon and available aromatic groups. Thesecondensation reactions increase the polymerisation degree of lignin. Lignindepolymerisation is therefore probably not necessary in formic acid pulping. (Ede &Brunow 1989b)

Residual lignins in Milox pulps have higher molecular weights than the dissolvedlignins. A part of the residual lignins have lower molecular masses. This fraction isdissolved during enzymatic hydrolysis with cellulase and it is probably more accessibleto the pulping chemicals than the other fraction, that is insoluble during enzymatichydrolysis. (Hortling et al. 1989)

When five moles of hydrogen peroxide per mole of lignin model compounds wereused, about 20 % of the model compounds degraded to compounds with lower molecularmasses. (Ede & Brunow 1989c)

Lignin can be precipitated from the black liquors of the three-stage Milox pulping byadding water. beta-aryl ether bonds are hydrolysed during the second pulping stage andtherefore most of the lignin is precipitated from the black liquor of this stage. Ligninwith the lowest molecular mass is obtained from the first stage, and lignin with thehighest molecular mass from the third stage. It is apparent that the lignin fraction withthe highest molecular mass is dissolved later than the lighter fractions. The lignindissolved from birch in the first pulping stage has a high xylose content. The highestglucose content for softwood lignins is observed in the second stage. (Hortling et al.1990, Hortling et al. 1991)

Zule et al. (Zule et al . 1995) have determined the C9 formula of Milox lignin to be

C9H7.36O2.82(OCH3)1.20(OH)0.58. The average molecular weight of the lignin was found

to be from 1000 to 3000.

2.2.1.6. Summary

Formic acid seems to be a good solvent for the lignin and extractives present in wood. Ithas been found that it also causes hydrolytic breakdown of wood polymers into smallerand more soluble compounds. It is claimed not to be consumed chemically duringpulping, but its thermal instability makes it necessary to operate using short residencetimes in the unit operations.

Peroxyformic acid has been found to make lignin more soluble by oxidizing it andmaking it more hydrophillic. It is a selective solvent and does not react with celluloseand other polysaccharides.

The solvent recovery in formic acid pulping is relatively complicated due to theformation of a binary azeotrope of formic acid with water and a ternary azeotrope withwater and acetic acid which is formed in small amounts during pulping.

Sundquist and Poppius-Levlin (Sundquist & Poppius-Levlin 1998) have published apaper where they present a summary of the research related to the Milox process. Theyalso present the following list of the most important areas for future development work:- improving the quality uniformity of the pulp- minimising the loss of formic acid- minimising the amount of water used in the process- assessing the value of by-products.This list shows that the industrial use of a formic acid-based pulping process seems tobe unlikely in the near future, because several problems still have to be solved.

2.2.2. Acetic acid

Acetic acid, like most of the organic chemicals used to produce pulp, was originally usedto isolate lignin from wood (Pauly 1918a, Pauly 1918b, Pauly 1921, Pauly 1943).

Apostol and Kozlov (Apostol & Kozlov 1979) have studied the effect of impregnatingbirch chips with aqueous acetic acid. The swelling was found to be significantly lower inchips impregnated with various concentrations of acetic acid (9-90 %) than in chipsimpregnated with pure water. When the concentration of acetic acid was increased, theamount of liquid absorbed by the chips also increased. The acetic acid impregnated chipsdid not show any significant changes in density and compression strength.

In addition to pulping and bleaching, acetic acid can be used to inhibit colourreversion in pulp. (DeLong 1990)

2.2.2.1. Acetic acid pulping and bleaching

According to Schutz and Knackstedt (Schutz & Knackstedt 1942) wood cannot bedelignified with aqueous acetic acid at 379-380 K, but the addition of 1-2 % hydrochloric

acid makes it possible. Also magnesium chloride can be used as a catalyst when pulpingwith aqueous acetic acid (90 %).

Wood has been delignified with aqueous acetic acid containing sulphuric acid as acatalyst. Pulping temperature of 391 K, one hour pulping time, atmospheric pressure,wood moisture content of 15 % and a liquor-to-wood ratio of 8:1 were used. Theoptimum catalyst concentration was determined to be 3 %. The pulp properties weresatisfactory and were slightly improved by adding 0.5-2.5 % acetic anhydride to thepulping liquor. (Wiltshire 1943)

Koval and Slavik (Koval & Slavik 1963) have used a mixture of acetic acid,hydrochloric acid and acetone as a pulping liquor. The use of this solvent results in good-quality pulps. The main advantages of this process are: a low temperature ofdelignification, pulping is carried out in atmospheric pressure, a simple chemicalrecovery by distillation, a simple method of obtaining lignin by filtration, a relativelyhigh pulp yield and no water pollution. The main drawback of the process is thedifficulties in the complete recovery of acetic acid.

It has been found that optimum yields of pulps with the best acetylation propertieswere obtained by pulping wood in acetic acid containing 10 % water and 0.2 % sulphuricacid for four hours at 423 K. Both hardwoods and softwoods can be used. The acetic acidcelluloses have low pentosan and mannan contents. They give acetates with propertiesnear those of acetates produced from cotton linters. (Herdle et al. 1964)

Haas and Lang have patented (Haas & Lang 1971) a pulping method wherelignocellulosic material is treated with an aqueous solution containing at leat 50 w-%acetic acid. Liquor-to-wood ratios from 1:1 to 12:1 can be used and the system is heatedto a temperature between 423 K and 478 K. The pulping time is 30 minutes at thehigher temperature and 16 hours at the lower temperature. The pulp is reported to haveexcellent quality.

Acetic acid or formic acid (pH 2) pretreatment of kraft pulp before ozone bleachinghas been found to result in bleached pulp with higher viscosity and lower kappa numberthan the corresponding water-pretreated pulp. The amount of ozone consumed inbleaching is also decreased. (Mbachu & Manley 1981)

Laboratory scale pulping of aspen and spruce chips has shown that gooddelignification can be achieved by cooking with aqueous acetic acid (50-95 %) for 30-60minutes at 448-493 K. The stronger conditions are needed for softwoods. Acetic acid canbe recovered using liquid-liquid extraction with ethyl acetate. (Young et al. 1985, Young1985)

Nimz and Robert (Nimz & Robert 1985) have studied the lignins obtained fromspruce chips by continuous extraction with 95 % acetic acid and 0.1 % hydrochloric acidusing the 13C NMR method. The spectra indicated the presence of acetylated g-hydroxylgroups. The splitting of the beta-O-4 linkages is also confirmed.

Good delignification (kappa numbers 10-40) has been achieved by cooking aspenchips in aqueous acetic acid (50-87.5 %). The pulp yields were 50-60 %. It may benecessary to wash the pulp with acetone to remove precipitated lignin after the cooking.The pulps had satisfactory to good water absorbencies. (Young & Davis 1986)

Young and co-workers (Young et al. 1986) have studied delignification of spruce withacetic acid. Pulping at a high temperature (488-493 K) for a short time (1 h) provided the

highest degree of delignification. When an acetic acid concentration of 87.5 % and aliquor-to-wood ratio of 8:1 was used, pulp with a kappa number of 16 and a yield of46.2 % was produced. The tensile strength of the pulp was comparable to that of aspruce kraft pulp with the same lignin content. Acetic acid is assumed to both promotesolvation of lignin fragments and to reduce swelling of the predominantly carbohydratefibres.

The use of acetic acid-water and acetic acid-water-phenol systems as pulping solventshas been studied. Beech chips were easily delignified by cooking with aqueous acetic acidat 433 K. The pulping rate was greatly increased by adding small amounts of phenols tothe pulping liquor. The optimum strength properties for the pulp were achieved withhigh acetic acid concentrations (> 90 %). (Sano et al. 1986)

Nimz and others (Nimz et al. 1986c) have patented a method where wood is pulpedwith aqueous acetic acid containing up to 10 % chloroethanol. The pulping time (1-8 h),the pulp yield (40-60 %), and the pulping temperature (373-388 K) depend on thechloroethanol and water (1-55 %) content of the pulping liquor. The solvent is recoveredby vacuum distillation. Both softwoods and hardwoods can be pulped.

Arylglycerol-beta-guaiacyl ethers have been used as model compounds to study thedelignification reactions occurring during acetic acid pulping. Ether cleavage followedtwo reaction paths. The first one leads to the formation of Hibbert’s ketones, while thesecond one yields an enol acetate. (Davis et al. 1987)

Davis (Davis 1987) has in his PhD thesis reported that acetic acid pulping trials gavethe lowest kappa numbers (10-16), highest pulp yield, and the best strength properties,when cooking at a high temperature for less than 60 minutes, using a high acetic acidconcentration (87.5 %). Softwoods needed more drastic pulping conditions thanhardwoods. The best pulps had excellent tensile strength, marginal burst strength andlow tear strength relative to reference kraft pulps.

According to Zilbergleit and others (Zilbergleit et al . 1987a) lignins dissolved inacetic acid pulping of birch, aspen and pine have similar properties compared to those ofkraft lignins. The acetic acid lignins were more active adsorbents than kraft lignins. Bothsoftwood and hardwood acetic acid lignins have hydrophillic properties.

The data obtained during hardwood and softwood aqueous acetic acid (75 %) pulpinghas indicated that the reactivity of lignin changes during delignification. (Zilbergleit etal. 1987b)

Yasuda and Ito (Yasuda & Ito 1987) have studied the behaviour of softwood lignin inacetic acid pulping by using model compounds. The treatment of veratryl alcohol,creosol and 1-guaiacyl-3-propanol in 90 % acetic acid gave a condensation product withCa-C6 linkage and a phenolic acetate in high yields.

Papermaking properties of birch and poplar pulps produced by cooking the chips in75 % aqueous acetic acid at 428 K for four hours have been studied. At pulp yields of50.0 and 48.3 %, the strength properties of the two pulps were better than those ofcorresponding sulphite pulp. When the spent pulping liquor was reused for pulping withthe addition of 33 % fresh acetic acid, no significant changes in pulp properties wereobserved over ten pulping cycles. (Simkhovich et al. 1987)

About 50 % of phenolic phenylcoumaran was consumed during a three hour treatmentof lignin model compounds with 90 % acetic acid at 453 K yielding phenylcoumarone, a

stilbene derivate and a condensation product, but the non-phenolic model was verystable. Phenolic and non-phenolic 1,2-diaryl-1,3-propanediols were unstable. Theydegraded within an hour giving stilbene derivates as the main products. (Yasuda 1988)

Muurinen and Sohlo (Muurinen & Sohlo 1988a) have estimated the investment andoperating costs of acetic acid pulping and recovery, and compared them with the costs ofperoxyformic acid pulping. The investment costs of the acetic acid process seemed to belower than for the peroxyformic acid process, which in turn had lower operating costs.When methanol and ethanol pulping were added to the comparison (Muurinen & Sohlo1988b), the acetic acid process seemed to have investment costs near those of alcoholprocesses. The operating costs were estimated to be much higher for the acetic acidprocess than for the other processes included in the comparison.

Acetic acid (70 %) pulping of beechwood has been studied. The cooking temperaturewas 30-150 minutes and the temperature was 428-443 K. Liquor-to-wood ratios werevaried between three and five. Pulps had yields of 42-60 % and kappa numbers of 20-60.The best results were obtained using a liquor-to-wood ratio of 4.5:1 and a pulpingtemperature of 438 K. (Obrocea & Gavrilescu 1988)

Reznikov (Reznikov 1988) has pulped aspen and birch with aqueous acetic acid for180 minutes at 418 K. The greatest degree of delignification was achieved at an aceticacid concentration of 60-90 %. Hardwoods can also be delignified at the gas phase usinga temperature of 433 K and an acetic acid concentration of 75 %.

It has been reported that up to 35 % of resin phenol in lignin-PF resins can besubstituted with acetic acid lignin, making it possible to improve the strength propertiesof plastics and particle boards by up to 20 % and to reduce the amount of free phenol by50 %. (Zilbergleit et al. 1989a)

Cellulose, especially rayon, can be acetylated easily by acetic acid using pyridinecontaining sulfonyl chlorides. The maximum degree of substitution of the products wasobtained with equimolar concentrations of p-toluenesulfonyl chloride and acetic acid.(Shimizu & Hayashi 1989)

The Burov group (Burov et al. 1989a) has reported that the optimum concentration ofacetic acid in pulping liquor is 25-35 %. The rest of the liquor should consist of equalparts of water and ethanol. Aspenwood treatment with this solvent mixture producedpulp with acceptable strength properties.

The effects of acidity and the dielectric constant of the solvent system on thedelignification of aspen, birch and pine with an acetic acid-ethanol-water mixture havebeen studied. Determination of the acidity and dielectric constant was found to be a goodmethod for estimating the delignification capacity of a solvent. (Burov et al. 1989b)

Deineko and Kostyukevich (Deineko & Kostyukevich 1989) have presented a methodwhere softwood and hardwood chips are delignified in aqueous acetic acid at elevatedtemperatures in the presence of an oxidizing agent. Pulp properties are improved and lesschemicals are needed if the oxidizer is oxygen (15.6-19.5 % on wood) and the process isconducted at 403-433 K using a liquor-to-wood ratio of 7:1-10:1.

Birch and aspen have been delignified with 75 % acetic acid in the vapour phase. Afterdelignification the pulps were treated at room temperature with a 2 % sodium hydroxidesolution. Pulps with normal yields and low residual lignin contents could be producedusing a liquor-to-wood ratio of 1:1-2:1. (Zilbergleit et al. 1989b)

Treated with aqueous acetic acid (90 %) containing more than 5 % p-phenolsulfonicacid, hardwood chips have produced pulps with satisfactory delignification. The rate andselectivity was improved significantly when small amounts of phenol was added to thesystem. Pulps produced from birch chips had sheet properties comparable to those ofkraft pulps. (Sano et al. 1989a)

Hardwood pulps can be produced by treating the chips with 95 % acetic acid for 4-5hours at atmospheric pressure. 1 % hydrochloric acid was added to act as a catalyst. Thepulp can be bleached with sequences PEDED or C/DEDED. The physical properties ofthe bleached pulps are not as good as those of the corresponding kraft pulps. (Paik et al.1989)

Burov and co-workers have patented (Burov et al. 1989c) a pulping methodconsisting of cooking wood chips at elevated temperature in an aqueous organic solventbased on acetic acid. Pulp yields are increased and selective delignification is improved ifthe aqueous solution containing 30-95 v-% acetic acid also contains ethanol. The aceticacid-ethanol ratio should be 0.17:1-8:1.

It has been reported that microwave irradiation of wood chips in solutions of organicsolvents is a possible method for the production of pulps with low lignin contents. Thebest results obtained were produced with a solution of acetic acid (43 w-%), ethyleneglycol (43 w-%) and water (14 w-%). When the irradiation was carried out for twominutes, pine chips produced pulp with a kappa number of 31 and a yield of 48 %. Thecorresponding values for aspen pulp were 15 and 54 %. (Davis & Young 1989, Davis &Young 1991b)

Kin (Kin 1990) has reported that beech wood can be pulped at normal pressure with80 % acetic acid containing inorganic acids as catalyst. The process yielded 45-49 %pulp, 19.7-20 % acetic lignin and 2.5-5.5 % furfural. The lignins contain 5.9-6.75 %phenolic groups. The pulp contains about 93 % alpha-cellulose and 4.8-5.2 %pentosans.

A two-stage method for pulping of birch has been presented. In the first stage chipsare treated with aqueous acetic acid (90.4-92.8 %) at atmospheric pressure for 30-90minutes. The second stage is a 2-3 hour treatment with 90 % acetic acid containing 1.6-2 % sulphuric acid as a catalyst. The pulp yields are 51-54 % and the strength propertiesare comparable with the corresponding commercial kraft pulps. (Sano et al. 1990)

Burov (Burov et al. 1990) has studied the degradative capacity of acetic acid (0.5-20 v-%) in aqueous ethanol with respect to cellulose and lignin in aspenwood. The hydrogenion activity in solutions containing 5-20 % acetic acid influenced changes in thecellulose DP during the delignification. The lignin molecular weight characteristicsvaried with acetic acid concentration and water-ethnol ratios (4:6-6:4).

Casuarina wood can be pulped with 50 % aqueous acetic acid, but higher acetic acidconcentrations (up to 90 %) accelerate the delignification, improve the delignificationselectivity, increase the pulp yield, enhance carbohydrate protection, and facilitatebleaching. The best results were obtained by using a pulping temperature of 423 K and apulping time of 2 hours. (El-Meadawy et al. 1990)

Uraki’s group (Uraki et al . 1991) has tested the pretreatment stage of the two-stageacetic acid pulping method presented by Sano et al. (Sano et al. 1990) using sixhardwood species. Birch was effectively delignified by refluxing in 90 % aqueous acetic

acid for 60 minutes. The pulp yield and delignification of beech were improved byremoving the pretreatment liquor containing water soluble extracts, which significantlyinhibited the delignification. Permeation of the pretreatment liquor to chips under reducedpressure accelerated the pulping of alder and eucalyptus, but did not affect pulping ofacacia. Poplar was delignified under the same conditions as beech.

Acetic acid-based pulping processes using high concentrations of acetic acid (70 or 85%) produce lignins with higher average molecular weights (Mw) than the processes

using low acetic acid concentrations (33 or 43 %). The high acetic acid concentration isassumed to promote better solvation of large lignin fragments. (Young & Davis 1991,Davis & Young 1991a)

Spruce chips have been delignified by oxygen in aqueous acetic acid (80 v-%) at 423K for 150-240 minutes using a liquor-to-wood ratio of 10:1. The initial oxygen pressurewas 1.5 MPa. Pulps with good mechanical properties were obtained after pulping for180-210 minutes. Longer pulping times result in decreased pulp quality. (Deineko &Kostjukevich 1991)

Gamma-radiation is able to penetrate into wood and to initiate destructive reactions.This kind of treatment may decrease the costs of hardwood pulping in acetic acid orethanol. (Zilbergleit et al. 1991a)

The addition of 5.3 w-% potassium or sodium halides per wood lignin has been foundto accelerate delignification in acetic acid pulping. A basic study with model compoundssuggested that the halides have a good effect on the retardation of condensation and onthe facilitation of hydrolytic solvolysis. (Yasuda et al. 1991)

Kaneko and co-workers (Kaneko et al . 1991) have studied aqueous acetic acid andacetic acid-water-phenol solutions in pulping of softwoods. Todomatsu (Abiessachalinensis) was easily delignified in 70-90 % aqueous acetic acid with or withoutphenols at 443-453 K. Karamatsu (Larix leptolepis) was difficult to delignify withoutphenols, which improved the delignification. The strength properties were comparablewith those of corresponding kraft pulps.

The conversion of pine and aspen lignin during pulping with acetic acid has beenstudied. The results indicated that lignin is subjected to intermolecular condensation inthe liquid phase during pulping. The chemical composition of the acetic acid ligninsindicated that delignification was accompanied by the degradation of alkylaryl etherlinkages, alpha-beta and beta-alpha elimination reactions, condensation, methoxylation,partial acylation, and the accumulation of carbonyl and carboxyl groups. (Zilbergleit etal. 1991b)

Furfural and hydroxymethyl furfural (HMF) are formed during acetic acid pulping. Theformation of polymers from these highly reactive monomers is undesirable, because itcan retard delignification. Zilbergleit and Glushko (Zilbergleit & Glushko 1991) havestudied polymerization in 75 % acetic acid at 438 K. They found that furfural and HMFcondensation in acetic acid was accompanied by polymerization and the oxidation ofcarbonyl and hydroxyl groups to carboxyl groups, followed by decarboxylation.

The Akishima group (Akishima et al. 1991) has studied structural changes ofamorphous cellulose during acid pulping. During acetic acid (93 %) pulping, partialacetylation of the amorphous cellulose occurred.

Optimum conditions for acetic acid pulping of aspen and birch have been determinedusing breaking length, bursting strength, folding endurance and tearing strength asoptimization parameters. For aspen, the optimum properties were achieved whenpulping at 418 K for 2.25-2.28 hours in an aqueous solution containing 70 % aceticacid. If the cooking temperature is raised to 438 K, and the same acetic acidconcentration is used, the optimum cooking time is 0.48 hours. The optimum cookparameters for birch pulping were found to be 423-424 K, 2.28-2.55 hours and 70 %acetic acid. Using these conditions, aspen pulps with yields of 52-61 % and birch pulpswith yields of 48-53 % were obtained. (Zilbergleit et al. 1991c)

Wood chips can be digested in a solution containing acetic acid, ethanol and water inthree stages using an acetic acid concentration of 5-10 v-%. The first and second stagesare carried out at 423-438 K for 45-90 minutes, and the third stage is carried out at 393-413 K for 10-20 minutes. (Burov et al. 1991)

Results achieved by Kostyukevich and Deineko (Kostyukevich & Deineko 1992)indicate that wood delignification by oxygen in 80 v-% aqueous acetic acid producespulps with relatively high yields and good properties. The high carbohydrate content ofthe spent pulping liquor makes it, after lignin removal, an attractive raw material formicrobiological processing.

Vazquez (Vazquez et al. 1992) has fractionated Eucalyptus globulus wood at 383 Kusing aqueous acetic acid containing catalytic amounts of hydrochloric acid. The effectsof time (5-6 h), acetic acid concentration (70-95 %) and catalyst concentration (0-0.2 %)on yield and composition of delignified material were examined. The yield and the lignincontent of pulp were mainly influenced by catalyst concentration. The polysaccharidecontent depended on both the acetic acid and hydrochloric acid concentrations. Thetreatment time was predicted to be an insignificant variable in the range tested.

Wood and other lignocellulosic material can be delignified with a mixture containingat least 90 w-% acetic acid, 2-8 w-% alkyl acetate (e.g. butyl acetate), 0-8 w-% water,and a catalyst. The catalyst may be potassium acetate, aluminium acetate, ammoniumacetate, calcium acetate, magnesium acetate, sodium acetate, lithium acetate, acetone, a 1-4 carbon alcohol, or a mixture of these. (Heckrodt & Thompson 1992)

Dievskii and Burov (Dievskii & Burov 1993) have derived mathematical diffusionmodels taking into account the change in the gradient of lignin concentration. They usedthe models to analyze pulping of pine and aspen with a mixture of acetic acid andethanol. Their results showed that it could be possible to increase the delignification rateby applying mechanical or chemimechanical pretreatments in order to improve internalmass transfer in the lignocellulosic materials.

Oxygen-acetic acid cooks of spruce chips and sawdust have been carried out byNikandrov (Nikandrov 1993) in a 1 dm3 autoclave at a maximum temperature of 403-423 K, liquor-to-wood ratio of 50:1, and acetic acid concentration of 80 %. When themaximum cooking temperature was reached, 5.25 dm3 of oxygen was added. Theselectivity of delignification was found to be independent of the particle size of thewood. Because there seem to be no problems with diffusion of the reagents into thechips or sawdust, oxygen-acetic acid pulping can probably be carried out in conventionaldigesters.

Leonova and co-workers (Leonova et al. 1994) have delignified aspen chips in acooking liquor containing equal volumes of glacial acetic acid and an 18 % aqueousformic acid solution. Sulphuric acid was used as a catalyst. Cooking was carried out at aliquor-to-wood ratio of 4:1 and a temperature of 353 K for 60 minutes. The pulpobtained had a yield of 73 %, a lignin content of 10 %, a breaking length of 5.1 km anda bursting strength of 137 kPa. Reducing the liquor-to-wood ratio to 2:1 did not reducethe delignification selectivity but the cooking time had to be increased to 90 minutes.

Lindholm’s group (Lindholm et al. 1995) has extracted a pulping liquor from thelight fraction of the pyrolysis of agricultural waste materials. The liquor contains about90 % organic acids. 80 % of the acid content is acetic acid. The spent pulping liquor isreturned to the pyrolysis and no further recovery stages are needed. Pulps with goodquality can be produced from especially decorticated flax straw. When cooking for 1-3hours at 373-383 K, kappa numbers between 10 and 20 are reached.

Lignins from aqueous acetic acid pulping can, without any chemical modifications, beconverted into fibers that are precursors of carbon fibres. After a thermal treatment, theycan be meltspinned. The mechanical properties of these fibres are similar to those offibres made from phenolated steam-exploded lignin. (Uraki et al. 1995)

2.2.2.2. Peroxyacetic acid

Poljak (Poljak 1948) has shown that pinewood can be quickly delignified at 333-353 Kin one stage using an aqueous solution of peroxyacetic acid (10 %) as solvent. Lignin isalmost completely dissolved and the carbohydrates are only slightly attacked.

He (Poljak 1951) has also presented a method of predicting the cellulose content ofwoody material using peroxyacetic acid. After a 30 minute treatment of woodmeal with10 % peroxyacetic acid at 348 K, the cellulose contains no lignin.

Haas and others (Haas et al . 1955) have used the method presented by Poljak (Poljak1948) to obtain ashfree holocellulose from beech, spruce and pine.

A method for pulping of wood at 333-373 K with peroxyacetic acid having aconcentration between 10 and 40 w-% has been presented. A liquor-to-wood ratiobetween 8:1 and 20:1 is used. The pulp yield is 44-56 % when hardwoods are delignified.(Wayman & Harris 1960)

Leopold (Leopold 1961) has compared the chlorine-ethanolamine, chlorite andperoxyacetic acid methods for producing holocellulose from pine. His results showedthat the peroxyacetic acid method, modified by a subsequent sodium borohydride step,gave a superior holocellulose.

Holocelluloses produced by a modified chlorite oxidation process and by theperoxyacetic acid method have been compared. No differences were observed in thestrength properties. (Thompson & Kaustinen 1964)

Bailey and Dence (Bailey & Dence 1966) have found that maximum brightening ofkraft and sulphite pulps occur in the pH range 7-9, when peroxyacetic acid is used as thebleaching agent. Consistency (3-6 %) and temperature (323-358 K) had little effect onpulp properties in this pH range. Increasing the peroxyacetic acid application in the 1-8

% range produced lower kappa numbers and viscosity values, and higher brightnesspulps.

Large increases in the strength properties of mechanical pulps as a result of a post-treatment with peroxyacetic acid have been observed. Strength properties were improvedwhen peroxyacetic acid was used at low pH (3.5-4.0). When the pH was changed to 7.0-8.0 peroxyacetic acid functioned as a bleaching agent. A pretreatment of wood chipsbefore mechanical fiberizing resulted in a reduction in the power needed for fiberizing andhigher pulp strength properties. (Stevens & Marton 1966)

Yiannos and Secrist (Yiannos & Secrist 1968) have invented a two-stage process forobtaining a lignin derivative from lignocellulosic materials. In the first stage, thelignocellulosic material is impregnated with a strongly oxidizing compound at atemperature below 323 K and a pH between 4 and 5. In the second stage, lignin isdissolved in an alkaline solution. Lignin is recovered by precipitation. The oxidizingcompound can be an organic peroxide, preferably peroxyacetic acid. Also peroxyformicacid can be used. The alkaline solution can be aqueous sodium hydroxide.

A method for removing lignin from lignin containing materials has been presented.The material is first pretreated with alkali to swell the material and to limit carbohydratelosses. Lignin is then dissolved under oxidizing conditions. These conditions include theuse of chlorine dioxide, peroxyformic acid, peroxyacetic acid or peroxypropionic acid,and the use of temperatures between 323 and 373 K. (Thompson & Kaustinen 1969)

Farrand and Johnson (Farrand & Johnson 1972) have studied peroxyacetic acidoxidation of several phenolic compounds in aqueous acetic acid. The oxidation processwas found to have competitive pathways involving hydroxylation at activated ringpositions, demethoxylation, ortho and para quinone formation and aromatic ringcleavage.

Loblolly pine has been delignified with 3 % peroxyacetic acid at 333 K and thedissolved lignin analysed. The results they have obtained show that the aromatic ringsand unsaturated sidechains of lignin were degraded in the fraction having molecularweights 10000-16000. (Albrecht & Nicholls 1974)

Oki et al. (Oki et al . 1974) have studied the mechanism of peroxyacetic aciddegradation of guaiacylglycerol-beta-aryl ether units in softwood lignin. They treatedguaiacylglycerol-beta-guaiacyl ether, guaiacylglycol-beta-guaiacyl ether andveratrylglycol-beta-guaiacyl ether with an aqueous acetic acid (50 %) solution containing2.6 % peroxyacetic acid at 303 K for 48 hours. The main degradation products wereguaiacol, vanillic acid, catechol, 2-methoxyphenoxyacetic acid, muconic acid. Acetic acidwas also found to be a better solvent for peroxyacetic acid than ethanol or dioxane.

Peroxyacetic acid is a highly selective delignifying agent. This is due to its ability tooxidize the electron-rich aromatic ring systems in lignin generating intermediate productswhich are often more easily oxidized than the initial ring system. Peroxyacetic acid inmildly alkaline media is a bleaching agent causing little material dissolution. (Johnson1975)

Nimz and Schwind (Nimz & Schwind 1981) have studied the oxidation of lignin andlignin model compounds with peroxyacetic acid. Both synthetic lignin and spruce ligninreacted smoothly at their alpha-carbonyl and olefinic groups. Dilignol structures showed

a decreasing reactivity in the order phenylcoumaran, pinoresinol, beta-aryl ether structure.A method where cellulose material is treated with peroxyacetic acid and an alkaline

reagent has been patented. In order to decrease the chemical consumption, the materialwas treated with alkaline reagent before the peroxyacetic acid treatment. (Kosaya et al.1981)

Birch and pine can be delignified using acetic acid and peroxyacetic acid in a two-stageprocess. In the first stage, chips were treated with acetic acid at atmospheric pressure inthe presence of a catalyst, or at elevated pressure without any catalyst. Hydrochloric acidand sulphuric acid were used as catalysts. In the second stage, chips from the first stagewere treated with a mixture of acetic acid and hydrogen peroxide. Citric acid was added tostabilize the peroxyformic acid formed through a reaction between acetic acid andhydrogen peroxide. The catalyzed method produced birch pulp with a kappa number of2.4 and consumed hydrogen peroxide 2.4 % on wood. The corresponding pine pulp had akappa number of 11.3 and 4.8 % on wood of hydrogen peroxide was consumed. Whenelevated pressure was used instead of a catalyst, only 1.2 % on wood of hydrogenperoxide was needed to produce birch pulp with a kappa number of 5.2. When producingpine pulp the hydrogen peroxide consumption was 3.5-4.8 and the kappa numbers were13.1-7.7. The strength properties of the birch pulp produced at elevated pressure was nearthose of kraft pulps. (Kurvinen 1988)

When formic acid and peroxyformic acid were replaced with acetic acid andperoxyacetic acid in the Milox process, a two-stage pulping produced better pulp than athree-stage process. The first stage could be carried out at atmospheric pressure usinghydrochloric acid as a catalyst, or at high temperature and pressure without any catalyst.In the second stage, hydrogen peroxide is added to form peroxyacetic acid. Birch and pinepulps with low kappa numbers (2-11) and acceptable yields (43-46 %) were produced.The pulps were easily bleached to 90 % brightness with alkaline peroxide only. Theunbleached birch pulps had high tensile indexes, which were significantly reduced duringalkaline bleaching. (Poppius-Levlin et al. 1991c)

Brolin and co-workers (Brolin et al. 1991) have studied the delignification of softwoodkraft pulps with hydrogen peroxide, oxygen and ozone in acetic acid media. Oxygendelignification in acetic acid comprised both phenolic and non-phenolic structures but theselectivity of the method was limited. The addition of small amounts of hydrogenperoxide to the oxygen delignification in acetic acid improved the selectivity. Thetreatment of pulp with ozone in acetic acid was found to be more selective than atreatment with ozone in water. The selectivity was further improved by conventionalalkaline oxygen treatment before ozonation.

The peroxyacetic acid products used in early studies was an equilibrium product ofhydrogen peroxide, acetic acid, peroxyacetic acid and water. The concentrations of aceticacid and hydrogen peroxide may be equal to or even higher than the concentration ofperoxyacetic acid. The unreacted reagents increase the cost of using peroxyacetic acid andmay damage the fibres. According to Hill and coworkers (Hill et al . 1992) theseproblems can be eliminated when distilled peroxyacetic acid is used.

Peroxyacetic acid can also be used as a slime control agent instead of organic biocidesin paper machines. (Rantakokko et al. 1994)

The Chang group (Chang et al. 1994) has found that chlorine-containing bleachingagents can be replaced by a mixture of peroxymonosulphuric and peroxyacetic acidsproduced by mixing 50 % hydrogen peroxide, 93 % sulphuric acid and glacial acetic acid.A mixed peroxy acid bleaching stage can replace conventional stages in a bleachingsequence and improve the properties of the bleached pulp.

The reactions of lignin model compounds with peroxyacetic acid andperoxymonosulphuric acid have been studied by Kawamoto (Kawamoto et al. 1994).

According to Liebergott (Liebergott 1994) peroxyacids can replace ozone in bleachingsequences. The capital and operating costs of using peroxyacids are lower than those ofusing ozone.

If the effluents from a conventional bleaching sequence are partially or totallyrecirculated, they have to be treated with significant amounts of sodium hydroxide andsulphuric acid. When a stage using distilled peroxyacetic acid is used as the firstbleaching stage followed by a hydrogen peroxide stage, no sulphuric acid andsignificantly less sodium hydroxide is needed. (Basta et al. 1994)

The Kawamoto group (Kawamoto et al. 1995) has studied the reactions of lignin andlignin model compounds with peroxyacetic acid and peroxymonosulphuric acid.Reactions of the model compounds with the more nucleophilic peroxyacetic acidproduced more ring-opening products. The reaction with peroxymonosulphuric acidresulted in accumulation of hydroxylated products and p-quinone.

A four-stage sequence for bleaching of aspen wood delignified with aqueous butanolhas been presented. The first and third stages in the sequence are peroxyacetic acid stages,while the other stages use hydrogen peroxide. Pulp brightness from 82 to 86 % can bereached with low losses of pulp (5.5-6.3 %). The resulting bleached aspen pulp hasgood strength properties but is inferior to a corresponding kraft pulp. (Pazukhina et al .1995)

Lachenal and Delagoutte (Lachenal & Delagoutte 1996) have comparedperoxymonosulphuric acid and peroxyacetic acid as bleaching chemicals. Examination ofresidual lignin in kraft pulp after treatment with the acids showed that onlyperoxymonosulphuric acid led to an increase in the number of free phenolic groups. Bothacids generated new carbonyl groups. Peroxymonosulphuric acid was a more efficientdelignification agent, but peroxyacetic acid had a more positive effect on brightness. Thedifferent chemical structure of the acids explain, according to the authors, these results.

When oxygen-treated softwood kraft pulps are delignified with equilibriumperoxyacetic acid, the carbonyl group contents of the pulps increases to figures that areclose to those of ozonated pulps. However, the viscosities of the pulps decreased only by13-15 %. Similar results were obtained also when using peroxyformic acid as thedelignifying agent. (Poppius-Levlin et al. 1996)

When oxygen-treated pine kraft pulp is delignified with peroxyacetic acid, the mainfactors affecting the rate of the delignification reaction are peroxyacid charge,temperature, pH and the metal content of the pulp. (Jaaskelainen & Poppius-Levlin1997)

Ni and Entremont (Ni & Entremont 1997) have investigated the oxidation of ligninmodel compounds with peroxyacetic acid. They have concluded that the overall oxidationof the model compounds can be generally characterized by four reactions: formation of

hydroquinone via oxidation of alpha-carbonyl compounds, oxidation of para-benzoquinone, demethylation and formation of other OCH3 containing compounds.

The BOD7, COD and TOC loads and the toxity in effluents from a peroxyacetic acid

bleaching stage are higher than those of effluents from an ozone stage when bleachingsoftwood kraft pulps. This is explained by the 2 % residual peroxyacetic acid content ofthe effluents. (Liukko & Poppius-Levlin 1997)

Yuan and co-workers (Yuan et al. 1998a) have presented an improved peroxyaceticacid bleaching process. This improved stage has a final pH of around neutral when aconventional peroxyacetic acid stage has a final pH of around 5. This modificationresults in higher pulp brightnesses.

A single peroxyacetic acid stage cannot produce a fully bleached pulp. The pulpbrightness can be increased by applying sequentially a peroxyacetic acid and a hydrogenperoxide reinforced extraction stage. (Yuan et al. 1998)

20.6 % of wood components have been found to be transformed into volatile productsduring peroxyacetic acid delignification of fir. (Pazukhina & Ostrik 1998)

When delignifying an acid-washed, oxygen-delignified, softwood kraft pulp withperoxyacetic acid, the Zhang group (Zhang et al. 1998) has found that Mn2+, Fe3+,Cu2+, V5+ and Co2+ catalyse wasteful decomposition of peroxyacetic acid when presentat a concentration of 5 ppm on pulp.

Water prehydrolysis of birch pulp has been found to improve delignification by aceticacid. The addition of 1...4 % hydrogen peroxide in the acetic acid liquor increasesdelignification but decreases the degree of polymerisation of the pulp. (Rutkowski et al.1998)

When studying bleaching with peroxyacetic acid Pazukhina and Teploukhova(Pazukhina & Teploukhova 1998) have found that the best results in terms of pulpwhiteness are achieved by using hydrogen peroxide and chlorine dioxide treatments as thefollowing bleaching stages after the peroxyacetic acid stage.

2.2.2.3. Acetosolv pulping

Nimz (Nimz & Casten 1985, Nimz et al. 1986a) has presented a pulping method wherewood is continuously extracted for 2-5 hours at 383 K with 95 % acetic acid containing0.1 % hydrochloric acid. At the end of the extraction, 3-5 % on wood of hydrogenperoxide is added and the mixture is stored for eight hours at 353 K. The hydrogenperoxide reacts with the acetic acid forming peroxyacetic acid. When beech is delignified,pulp with a kappa number of seven is obtained. Spruce pulps have kappa numbersbelow 30. The process is operated at atmospheric pressure and it is called Acetosolvpulping.

Hemicelluloses and lignin are obtained from the Acetosolv process in a low condensedand relatively reactive form that can be converted into chemical raw materials. (Nimz &Casten 1986a)

The Acetosolv method has been patented. According to the patent claims, wood andannual plants are cooked at 373-385 K with aqueous acetic acid containing 0.05-0.2 %

hydrochloric acid in the beginning of the cook and 0.5-2 % hydrogen peroxide at the end.Pulp yields 40-60 % and kappa numbers 2-30 are obtained with pulping times from twoto five hours. (Nimz & Casten 1986b)

Acetosolv pulps can be bleached in two stages. Before the first stage the pulp (kappanumber 59) is washed with hot 93 % acetic acid, which decreases the kappa number to24. The first bleaching stage is a treatment with hydrogen peroxide followed by washingwith hot acetic acid. After the first bleaching stage, the pulp has a kappa number of 3.8and a brightness of 39.5 % ISO. The second stage is an ozone treatment, which decreasesthe kappa number to 0.27 and increases the brightness to 71.5 % ISO. (Nimz & Berg1989, Nimz & Berg 1991)

Acetic acid can be partly replaced in bleaching by an acetate. The same acetate (e.g.butyl acetate) can be used as an entrainer in azeotropic distillation which is used torecover acetic acid from the spent pulping and bleaching liquors. (Nimz et al. 1989a)

Hardwood Acetosolv pulps have strength properties between sulphite and kraft pulps.Pulp bleaching can be carried out entirely with ozone (1.5-3 %) in acetic acid. The ozonecan partly be replaced by nitrogen dioxide. (Nimz et al. 1989b)

The Acetosolv process uses 93 % aqueous acetic acid containing 0.1-0.2 %hydrochloric acid as solvent. The pulping is carried out for 4-6 hours at 383 K. Arotating extractor is used as digester. The pulp is prebleached with ozone. The finalbleaching is done with peroxyacetic acid. A pilot plant was started in early 1989. (Nimzet al. 1988, Nimz et al. 1989b)

Ozone in acetic acid is a more selective bleaching agent than ozone in aqueoussystems. This due to a higher solubility of ozone, reduced formation of OH radicals andhigher solubility of lignin degradation products. (Nimz et al. 1989c)

Curvelo et al. (Curvelo et al. 1990a, Curvelo et al. 1990c) have invented a method toanalyze chloride ions in aqueous acetic acid. The method is based on the use of anelectrode sensitive to chloride ions. The method is useful in analyzing Acetosolvpulping liquors, because too little hydrochloric acid (catalyst) leads to an incompleterupture of the covalent bonds in lignin, and too much hydrochloric acid leads to increasedrecombination of the lignin fragments.

Lignin degradation during Acetosolv pulping in the presence of various catalysts (HCletc.) has been studied using dimeric lignin model compounds. Because lignin reacts as adonor of electrons during pulping, catalysts with a catalytic activity exceeding that ofhydrochloric acid are recommended. (Savov 1990)

Lignins recovered from Acetosolv pulping of sugar cane bagasse have been analyzedby high pressure size exclusion chromatography. The chromatograms were divided intothree regions corresponding to high (0-20 %), middle (90-75 %) and low (4 %) molecularweight fractions. (Groote et al. 1991a)

Groote and co-workers (Groote et al. 1991b) have analyzed lignins obtained bypulping sugar cane bagasse using the Acetosolv method. Results indicate a lowrecombination behaviour of the lignin during pulping and the high reactivity potential ofthe lignin. Using a sulfomethylation process the lignin yields a lignosulfonatepresenting good quality as a dispersing agent.

Basic variables affecting Acetosolv pulping have been studied. A soaking pretreatmentof the chips in pulping liquor for 60 minutes increased the screened yield of pulp by 3

%, but did not affect the kappa number. The optimum pulping time for oakwood was60 minutes cooking and 120 minutes extraction. The pulp produced had a yield of 41.4% and a kappa number of 11. Bleachable grade pine pulp could not be produced. (Kim etal. 1991)

Jakab and others (Jakab et al . 1991) have studied the thermal decomposition of kraftand acetosolv lignins using thermogravimetry/mass spectrometry (TG/MS) in thetemperature range 303-1223 K in an inert atmosphere using 20 a K/min heating rate.During the slow thermal decomposition, cleavage of functional groups plays animportant role and leads to the evolution of low molecular mass products and to theformation of char.

Lignin obtained from sugarcane bagasse by Acetosolv pulping has beensulfomethylated. The lignin was reacted with sodium hydroxymethanesulfonate at pH 9and 403 K to yield a product that had good potential as a dispersant. (Groote et al .1992a)

Groote and co-workers (Groote et al. 1992b) have pulped depithed sugar cane bagasseusing the Acetosolv method. Based on their analysis, they suggested the followingempirical formula for the lignin: C9H8.04O2.81(OCH3)0.92(OH)0.73phenolic.

Bleaching of mongolian oak Acetosolv pulps with formic acid and conventionalbleaching stages has been studied. When magnesium sulphate was added as a bleachingstabilizer, the pulp yield was increased. Sodium silicate improved the brightness. Whenperoxide bleaching was used, the pulp yield and strength properties were improved incomparison with conventional chlorine bleaching sequences. (Kim & Paik 1993)

The Parajo group (Parajo et al. 1993) has optimized the operational conditions of theAcetosolv process when hydrochloric acid is used as a catalyst. The optimum conditionsthey determined were an acetic acid concentration of 88 %, a liquor to wood ratio of 8and a catalyst concentration of 0.24 %. Under these conditions, solid residues containing8 % lignin, 88.5 % polysaccharide and 84.7 % glucan compared to the original amountswere obtained at 45.4 % pulp yield.

The economy of Acetosolv pulping of Eucalyptus globulus has been studied whenhydrochloric acid is used as the catalyst. The profitability of the process depends on theprices of the byproducts. A positive profitability is obtained when the price of lignin is0.48 DM/kg. (Parajo & Santos 1995)

The Acetosolv process can be carried out in three stages. The cellulose containing rawmaterial is initially with an aqueous acetic acid solution at an elevated temperature andunder an elevated pressure. The resulting pulp is treated in a second stage with anaqueous acetic acid solution, with the addition of nitric acid and is then washed orextracted with water or with the pulping liquor. In a third stage, the pulp is treated withan ozone-containing gas. (Berg et al. 1995)

Savov and co-workers (Savov et al. 1996) have compared the use of aluminiumtrichloride and hydrochloric acid as catalysts in Acetosolv pulping. Lignindecomposition was found to be greater when AlCl3 was used.

The oxidation of sugar-cane bagasse Acetosolv lignin catalyzed by Co+2, Mn+2 andHBr produces an oxidized lignin up to 21 % more carbonyl groups. Kinetic studies have

shown that lignin is oxidized by a two-step reaction. First, C-O linkages are cleaved andafter two hours the formation of C=O linkages takes place. (Goncalves et al. 1997)

2.2.2.4. Acetocell pulping

During the operation of the Acetosolv pilot plant, severe material and corrosionproblems occurred in the equipment. This was the reason why the original process wasmodified and called the Acetocell process. The main modification were (Gottlieb et al .1992):- The acetic acid concentration in pulping liquor was decreased from 93 w-% to 80-90 w-%.- No catalyst was used.- The pulping temperature was raised from 383 K to 443-463 K.- The digester pressure was raised from atmospheric to 0.8-1.5 MPa.- The pulping time was reduced from 180-300 minutes to 120-180 minutes.- The carousel extractor was replaced by a conventional digester.

Spruce chips were delignified by the Acetocell process to kappa numbers 15-20 athigh yield. Treating the resulting pulp with ozone (1-2 % on pulp) and mild extraction,the kappa numbers could be reduced to 2-4. The completely chlorine-free bleaching wasconcluded with a hydrogen peroxide and/or peroxyacetic acid treatment. Final yields ofbleached pulps were from 43 to 46 %. (Gottlieb et al . 1992, Nimz et al. 1992a, Nimz et al. 1992b)

In 1993 Neumann and Balser (Neumann & Balser 1993) reported that the Acetocellprocess was being extended to technical scale. It has been demonstrated that annualplants may also be delignified using the process. The Acetocell pulps are also suitablefor chemical production.

2.2.2.5. Formacell pulping

Nimz and Schone (Nimz & Schoene 1993, Nimz & Schoene 1994) have invented aprocess where lignocellulosic material is delignified under pressure with a mixture ofacetic acid (50-95 w-%), formic acid (< 40 w-%) and water (< 50 w-%). The pulpingtemperature is between 403 K and 463 K. Liquor-to-wood ratios from 1:1 to 12:1 can beused. Continuous extraction is achieved by connecting 2-20 digesters in line. Theextraction is carried out counter currently and the pulp is prewashed with fresh pulpingliquor. Pulps with very low residual lignin contents are produced and they can bebleached to full brightness using ozone and peroxyacetic acid. Azeotropic distillationwith butyl acetate is used to separate water from the acids. The method is calledFormacell pulping.

In addition to the reduction of kappa numbers, the pulp strength properties areimproved, when 5-10 % of formic acid is added to aqueous acetic acid. Formacell pulps

have lower tear strengths than kraft pulps, but this is in most cases compensated for bythe higher values of burst and tensile strengths. Formacell pulps produced from annualplants have better strength properties than corresponding soda pulps. Spruce pulp is dueto its low kappa number (3.6) easily bleached in two stages with ozone in acetic acid andwith peroxyacetic acid in butyl acetate. In the case of Formacell pulps produced fromhardwoods or annual plants, only two peroxyacetic acid stages are needed to bleach thepulps. (Nimz & Schoene 1993)

Low kappa numbers of around 10 for beech and pine and around 2 for aspen can beobtained using the Formacell process. The losses of formic acid under the pulpingconditions were determined to be less than 1.5 % at 433 K, and less than 2.8 % at 453K. (Saake et al. 1995a)

Low pulping temperatures and high acetic acid concentrations should be used in theFormacell process in order to preserve hemicelluloses for paper grade pulps. The use ofhigher temperatures and water concentrations in the pulping liquor results in dissolvingpulps with hemicellulose contents below 3 %. (Saake et al. 1995b)

Aspen Formacell pulp can be bleached to a brightness of 86 % in a purely organicsolvent system. The bleaching steps used are ozone, peroxyacetic acid, and butyl acetate.(Saake et al. 1998)

2.2.2.6. Summary

Young (Young 1998) has reviewed acetic acid-based pulping processes. When comparingthe economy of various processes he states the following:- The separation of acetic acid and water is the most expensive unit operation in theprocess.- For dilute acid systems, chemicals should be recovered by extraction with ethylacetate.- For more concentrated acid systems distillation is the preferred recovery method.

Acetic acid is assumed to both promote solvation of lignin fragments and to reduceswelling of pulp fibres. The addition of oxygen has been found to improve diffusion ofthe reagents into wood chips.

Technical problems related to acetic acid pulping are corrosion of the equipment and arelatively expensive solvent recovery. The vapour-liquid equilibrium of acetic acid andwater is unfavourable and leads to high numbers of equilibrium stages in distillation.

2.2.3. Other organic acids

Chloroacetic acid can be used to produce pulp at atmospheric pressure. Pinewood wasquickly delignified and the pulp had a good viscosity. (Schutz 1940)

The lignin recovered from the spent pulping liquor after delignification with aqueouschloroacetic acid is pure and has a high methoxyl content. The yield of sugars is twice ashigh as in sulphite pulping. (Schutz 1941b)

Likon and Perdih (Likon & Perdih 1995) have tested the use of chloroacetic acid,iodoacetic acid, difluoroacetic acid, dichloroacetic acid, dibromoacetic acid, trifluoroaceticacid, trichloroacetic acid and tribromoacetic acid in the delignification of spruce woodmeal. Those haloacetic acids stronger than acetic acid, especially dichloroacetic acid andtrichloroacetic acid, are efficient delignifying agents at temperatures below 373 K evenwithout the presence of water.

Zule (Zule et al. 1995) has studied lignin isolated from the spent liquors of sprucepulping with trichloroacetic acid. The C9 formula of the lignin was calculated to be

C9H6.05O2.56(OCH3)0.88(OHf)0.68(TCA)0.29. The average molecular weight of the lignin

was determined to be vary in the range 2000-3000.Thioacetic acid has been used to totally dissolve lignin from spruce wood and to study

lignin reactions using model compounds (Nimz 1969a, Nimz 1969b).Thioglycolic acid has been used to isolate lignin from lignocellulosic materials. The

methoxyl content of softwood and hardwood lignins obtained by this mean is 14-17 %and 20-23 %, respectively. Also cellulose can be isolated, although it cannot bequantified. (Anon. 1935)

Holmberg (Holmberg 1936) has isolated lignin from spruce using thioglycolic acid,thiolactic acid and several other thioacids. Based on the lignin analyses he has suggestedthe formula C9H8.90O2.85(OCH3)0.92 for thioacid lignins.

Holmberg (Holmberg 1947) has isolated lignin from aspen with thioglycolic acid andthioacrylic acid. Using the results of the lignin analyses, he has drawn the conclusionthat aspenwood contains several lignin fractions. The fractions with high methoxylcontents are easily dissolved with thioacids.

2.2.4. Salts of organic acids

Robert (Robert 1955) has presented a pulping method using sodium benzoate as thedelignification agent. The pulping liquor was an aqueous mixture of sodium benzoate(40 %). When the pulping was carried out at a liquor to wood ratio 7 and 393 K for 10.5hours, the yield of the resulting unbleached pulp was 43 %. Conventional bleachingstages were used and the strength properties of the bleached pulps were reported to begood.

Woody material can be converted into chemicals by treating it under heat and pressurewith a substantially neutral aqueous catalytic solution of an alkali metal salt ofcymenesulfonic acid, toluenesulfonic acid, benzoic acid or salicylic acid. The products ofthis treatment are furfural, acetic acid, carbon dioxide, lignin and cellulose. (McKee1961)

2.2.5. Summary

Formic acid, acetic acid and corresponding peroxy acids are the only organic acids thathave been intensively studied as pulping solvents. Atmospheric pulping is possiblewhen using organic acids as solvents. This makes the operation of a plant safer.Operating costs of pulping are reduced by the fact that catalysts are not necessarilyneeded. On the other hand, the relatively complicated solvent recovery increases thecosts. Investment costs are probably relatively high due to the need for corrosionresistant materials.

2.3. Phenol and cresols

2.3.1. Phenol

Buhler (Buhler 1897) has in the late 19th century patented a method wherelignocellulosic materials were treated with phenol at temperatures above 423 K. Thecellulose was not attacked and it had a quality suitable for paper production.

A pulping method where wood or other lignocellulosic material is delignified withphenol has also been patented. The solvent can be concentrated or diluted with water,alcohols, benzene, benzene derivates or carbohydrates. The mixture is heated in thepresence of catalytic amounts (0.01 %) of hydrochloric acid. (Hartmuth 1920)

Pulping can be carried out at 375 K with phenol diluted to 35-40 % with alcohol orwater. The water addition decreases though the pulp quality. Good results have beenachieved by cooking wood chips in concentrated phenol at 353-373 K in the presence of0.1-1.0 sulphuric acid for 4-5 hours. The yield of pulp was about 45 %. Significantamounts of phenol were bound to the dissolved material from wood. (Legeler 1923)

Kalb and Schoeller (Kalb & Schoeller 1923) have studied the possibility ofdetermining the amount of cellulose in wood by phenol delignification. They found thatdelignification with phenol, in the presence of small amounts of mineral acids, is rapidand can be carried out at temperatures below 373 K. During the delignification, thepolysaccharides are partly hydrolysed. This makes it impossible to use phenoldelignification as the basis for a method determining the total carbohydrate content.

Phenol lignins have been reported to be amorphous and dark coloured. They dissolveeasily, for example, in glacial acetic acid, methanol, ethanol, amyl alcohol and acetone.They do not dissolve, for example, in water, chloroform, aqueous ammonia and dilutemineral acids. The phenol lignin contains 71.6 % carbon, 5.3 % hydrogen, 23.1 %oxygen and 12.1 % methoxyl. (Hillmer 1925)

Wedekind and co-workers (Wedekind et al. 1931) have proposed the formula[(C8H7O2)(OCH3)(OH)(C6H4OH)]x for phenol lignin.

Pulping of spruce meal with phenol, using hydrochloric acid as a catalyst, has giventwo chemically different lignin fractions. The ratio of ether-insoluble and ether-dioxane-soluble lignins was about 3 to 1. When compared with the formula of native lignin(Brauns & Hibbert 1933), the ether-insoluble phenol lignin contained three new free

phenolic hydroxyl groups, while one phenol group had reacted with one hydroxyl groupin the lignin, forming a phenyl-oxygen ether linkage. The analysis of the ether-dioxane-soluble phenol lignin indicated that a significantly larger quantity of phenol hadcondensed with the native lignin unit than in the case of ether-insoluble lignin.(Buckland et al. 1935)

Fuchs (Fuchs 1936) has found that phenol lignin and methoxy glycol lignin areclosely related substances that can be separated into several fractions. Phenol can becleaved from phenol lignin using a method consisting of a treatment with hydriodic acidand acetic acid in the presence of phosphor.

It has been shown that in condensations of phenol with lignin, the phenol reacts inthe ortho position. Also the para position undergoes the same reaction, which has beenproved by the isolation of p-hydroxybenzoic acid. (Kratzl et al. 1962)

The Ploetz group (Ploetz et al. 1963) has patented a method where lignin ishydrolysed with hydrogen in the presence of aromatic compounds in two stages. Thefirst stage is carried out at 703 K, and the partial pressure of hydrogen is 42.5 MPa. Thesecond stage is carried out in the presence of lignin degradation products from the firststage containing about 38 % phenols. The temperature of the second stage is 753 K, andthe partial pressure of hydrogen is 42.5 MPa. The product contains 21 w-% phenols, 36w-% oils, 26 w-% gases and 18 w-% water.

When spruce wood is treated with phenol, mainly lignin is reacting with phenol.Condensation reactions between phenol and the polymeric wood carbohydrates are notassumed to occur. Phenol has been found to condense with lignin. (Kratzl et al. 1964)

Schweers and Pereira (Schweers & Pereira 1972) have studied the penetration ofdifferent wood species by phenol. Beech and spruce chips were well penetrated atatmospheric pressure, but pine chips needed elevated pressure for the penetration.

Lignins dissolved during phenol pulping can be used to produce a phenolic blend bypyrolysis. This blend can be used as the pulping liquor. The phenol-lignin can also bereduced to polyoles, which can be transformed into polyurethanes. (Schweers & Rechy1972)

Phenol remaining in the pulp after delignification can be recovered by washing withmethanol. When the methanol is recovered by distillation, only negligible phenol lossesoccur. The main source for phenol losses is the phenol recovery by distillation.(Schweers et al. 1972)

Pine and beech woods can be delignified with phenol or phenol mixtures in thepresence of catalytic amounts of hydrochloric acid. An atmospheric pulping producedpulps with yields of about 50 % and satisfactory mechanical properties. The pulp werebleachable with conventional bleaching sequences. (Schweers & Rechy 1973)

Pine wood has been delignified with aqueous phenol (90 %) containing 0.05 %hydrochloric acid as catalyst. The cooking was carried out in three stages (383 K, 413 K,443 K) using a liquor-to-wood ratio of 4:1. After cooking, the pulp was washed withmethanol or isopropanol. The pulping liquor could be reused at least twice before itbecame necessary to separate the phenol lignin by distilling. (Schweers 1974)

According to Vorher and Schweers (Vorher & Schweers 1975) phenol lignin can beconverted to mixtures of phenol and lower methyl and methoxyl substituted phenolsusing pyrolysis. The yield of simple composition phenols is approximately 30 %

which, together with the composition of the product, makes it possible to use it as apulping chemical.

Aqueous phenol (1:1) can reduce the lignin content of pine wood meal from 30 w-%to 3 w-%, when the material is treated with the solvent for two hours at 478 K in astirred batch reactor. Aqueous n-butanol delignification was found to be less effective.The phenol recovery rate was shown to be 70-78 %. (April et al. 1979)

According to Lipinsky (Lipinsky 1983), the temperature needed in phenol pulping iswell below that which causes furfural formation.

Johansson (Johansson et al . 1983) has presented a phenol pulping method where thelignocellulosic material is extracted leaving the cellulosic fraction untouched. Themethod is called the Battelle-Geneva process. Pulping is carried out at 373 K andatmospheric pressure. The pulp yield is around 40 %.

According to Millner (Millner 1983) the Battelle-Geneva process has the followingadvantages:- several raw materials can be used- the pulp yield is high- the pulp quality can be adjusted- low temperatures and pressures can be used- hydrolysis of hemicelluloses and extraction of lignin is carried out in one processstage- the process produces phenol- the process is environmentally friendly- the investment costs are relatively low- the process can be economically used, even at low production rates.

Vanharanta and Kauppila (Vanharanta & Kauppila 1984) have studied the feasibilityof the Battelle-Geneva process. The pulping is carried out at 373 K and atmosphericpressure using aqueous phenol (40 %) as the solvent. When the spent pulping liquor isallowed to cool, it separates into two phases. The organic lignin containing phaseseparates from the aqueous hemicellulose containing phase. In bench-scale batchdigestion, hydrochloric acid (1.85 % in water) was used as catalyst. After cooking forfour hours, birch pulps with a yield of around 44 % and kappa numbers around 11 wereobtained. The pulp was washed first with hot water to achieve high lignin andhemicellulose yields. To remove the residual phenol in pulp, it was washed in thesecond stage with dilute sodium hydroxide. The phenol present in the aqueous phase ofthe spent pulping liquor can be recovered by extraction with toluene. Phenol can berecovered from the organic phase by vacuum distillation. An analysis showed that goodprofitability could be achieved with this phenol pulping method.

Both softwoods and hardwoods have been delignified with aqueous n-propyl alcohol(50 %) containing 45 % phenol and 67 % acetic acid. This method, calledphenorganosolv pulping, easily separates woods into their main components. (Sano &Sasaya 1985)

Tournier’s group (Tournier et al. 1986) has patented a pulping method wherelignocellulosic material is treated in an acidic aqueous solution in the presence of phenolcompounds. The solution is acidified by adding 0.5-4.0 w-% of hydrochloric acid,sulphuric acid, phosphoric acid or a strong organic acid. The phenol content of the

pulping liquor is at least 40 w-%. The cooking is carried out at nearly atmosphericpressure and at the boiling point of the solution using a liquor-to-wood ratio 2:1-4:1.After pulping, the spent liquor is separated into two liquid phases. The phenolcontaining organic phase is distilled to recover phenol. The distillation residue is treatedby pyrolysis to give phenol compounds in amounts so large that no external solventmake-up is needed.

Acetone-soluble phenol pulping lignin from spruce has been examined by N.M.R.spectroscopy. The result have provided evidence that the beta-0-4-aryl ether linkage haserythro stereochemistry. (Hawkes et al. 1986)

According to Laxén (Laxén 1987) lignin will precipitate both inside the fibres and onthe surfaces of the fibres, if the pulp is washed directly with water after phenol pulping.This lignin will, however, dissolve in caustic or acetone. An alkaline washing stage canlower the kappa number of the pulp significantly, but the application of such a stage isexpensive and makes it difficult to recover lignin as a by-product. The results of alaboratory pulping and washing simulation showed that after direct counter-currentwashing with water, 88 % of the lignin remained in pulp. If the spent pulping liquorwas before washing displaced with fresh solvent, the remaining amount of lignin was 20%.

Ekman (Ekman 1988a, Ekman 1991a) has invented a method of separating lignin andphenol from the spent phenol pulping liquor. When the organic lignin and phenolcontaining phase of the spent liquor is extracted with hot water, two liquid phases areformed: a phenol containing aqueous phase and a lignin containing organic phase. Whenthe aqueous phase is cooled, two liquid phases are formed: a phenol phase with a lowwater content and an aqueous phase with a low lignin content. The aqueous phase isrecycled to the hot water extraction and the phenol phase is used in preparing the pulpingliquor. Lignin is precipitated with water from the lignin containing organic phase.

Ekman (Ekman 1988b, Ekman 1991b) has also proposed the method for recycling thesolvent in phenol pulping. The phenol containing solution is first used as washingliquor for the pulp coming from digestion. Then the solution is used as pulping liquorand finally it is used in the lignocellulosic material soaking stage before pulping.

In a Japanese patent (Shiraishi et al. 1988), a method is described wherelignocellulosic material is immersed in aqueous chlorine (0.01-0.5 w-%). After washingwith water, the material is cooked in aqueous phenol or cresol (1-50 w-%) at 373-423 Kfor 30-90 minutes. Pulps without cellulose degradation are produced in yields of 50-80%.

Araki et al. (Araki et al. 1989) have compared phenol pulping with other organosolvmethods. Alkaline systems were found to be superior to acidic systems in delignificationselectivity. The pulp qualities were similar in most cases, but pulps produced with acidicsolvents had lower tear indexes.

Spent pulping liquor from phenol pulping can be used as a lignin-containing rawmaterial for producing phenols. The phenols obtained can be used as solvent in pulping.The lignin-containing material is mixed with a double ring aromatic hydrocarbon, andthe mixture is decomposed at a temperature of 533-673 K, under pressure of 0.5-9.8MPa, for 5-180 minutes. (Kakemoto et al. 1990)

Vega and Bao (Vega & Bao 1993) have used phenol and dilute hydrochloric acid todelignify an annual plant (Ulex europeaus ) at atmospheric pressure and 373 K. Theyexamined the kinetics of the pre-hydrolysis and delignification processes. The hydrolysisof cellulose can be satisfactorily modelled with a simple kinetic model proposed bySaeman (Saeman 1945). The delignification process can be explained using a simplemodel of two parallel pseudo first-order reactions.

The influence of reaction time, phenol concentration, and hydrochloric acid charge onpulp yield, total polysaccharide content, residual lignin in pulps, dissolved reducingsugars, and pulp yield versus residual lignin has been studied in the Battelle-Genevaprocess when pulping elephant grass. The experimental results were fitted to second-order linear models. The model specified maximum selectivity for a reaction time of 108minutes, a phenol concentration of 53.2 %, and a hydrochloric acid charge of 0.0394 g/gelephant grass. (Vega et al. 1997a)

The hydrochloric acid charge was found to be the most influential variable, followedby reaction time and phenol concentration. (Vega et al. 1997b)

Jimenez and co-workers (Jimenez et al. 1997b) have developed a second-orderpolynomial model for phenol pulping of wheat straw using three independent processvariables. According to the model, high yield and waste water pH can be ensured bysetting the variables to low values. If high holocellulose and alpha-cellulose contentsand low lignin contents are desired, then a long cooking time (120 min) at hightemperature (473 K) and intermediate phenol concentration (65 %) has to be used.

2.3.2. Cresols

Birch and spruce have been delignified with aqueous cresols at 443-463 K for 2-3 hours.Birch pulp with strength properties near those of kraft pulp was obtained with a cresols-water ratio of 4:1. A solvent mixture composed from lignin degradation products gavesimilar results. Birch was more difficult to delignify and the pulps showed lowerstrength properties. However the addition of acetic acid improved the pulp quality. Ingeneral, the pulp yield was slightly higher than that of corresponding kraft pulps, butthe residual lignin content was also higher. The most advantageous feature of thismethod is that the solvent can be produced by pyrolysis or hydrocracking of the lignindissolved during pulping. After pulping, the solvent mixture was separated into twophases. The organic phase contained lignin and the aqueous phase contained sugars.(Sakakibara et al. 1983, Sakakibara et al. 1984)

The addition of 10-50 w-% acetic acid to the aqueous cresol pulping liquor has beenfound to improve the selectivity of delignification and the pulp strength properties inspruce pulping. When birch was pulped, the addition of acetic acid had no effect.(Sakakibara & Edashige 1984)

Takeyama and Sasaya (Takeyama & Sasaya 1988) have hydrocracked beech ligninseparated in cresol pulping. Up to 20 % of the hydrocracked lignin could be separated bysteam distillation. The volatile fraction contained phenol, o-, m- and p-cresols, o- and p-ethylphenols, 2,4-xylenol and p-propylphenol.

According to the Sano group (Sano et al. 1988), beech and birch are easily delignifiedby treating with a cresol-water-acetic acid mixture for 2-3 hours at 443 K. The cresol towater ratio of the solvent mixture was 7:3 and the acetic acid concentration was 10 %.

Kachi and Tsuchiya (Kachi & Tsuchiya 1988, Kachi & Tsuchiya 1989) havesubjected wood chips to pulping with an aqueous solution of phenols from lignindegradation products. Both unbleached hardwood and softwood pulps were easily defiberedeven at high kappa numbers (30-60) and the yields were from 50 to 60 %. The pulpswere washed with solvent and hot water. After oxygen delignification and a conventionalthree-stage bleaching, the pulps were bright and strong enough to be used for theproduction of printing papers.

Wood can be separated into carbohydrates and lignin within 10-20 minutes with aconcentrated sulphuric acid-cresol system. The separation includes the swelling ofcarbohydrates and the solvation of lignin. During the treatment, lignin is protected fromthe attack of sulphuric acid through solvating with cresol. The technique gives perfectseparation of any lignocellulosic material because the tissue structures are destroyed bythe swelling of carbohydrates. (Funaoka & Abe 1989)

Miyazaki (Miyazaki et al . 1989) has presented a pulping method using a mixture ofcresol and water (4:1) as solvent. Because the selectivity of the method was not goodenough for hardwoods, and the pulping time needed for softwood was twice the timeapplied in conventional pulping, the effect of some additives was examined. Tertiaryamines were found to effectively remove the acetic acid from hardwoods. Lewis acidscombined with tertiary amines were found to be efficient catalysts in softwood pulping.

A method where softwoods are delignified with aqueous cresols (70 %) containingacetic acid has been presented. The pulping was carried out at 453 K for 120 minutes.When the acetic acid addition was 40 % on wood, good delignification was achieved. Thecresols were reused several times before recovery by distillation. (Sano 1989)

Polyurethane has been prepared from lignin obtained by delignifying wood withaqueous cresols. Lignin in polyurethane retarded the thermal degradation of the polymerin the air. Polyurethane containing polyol and phosphorus were also produced and theywere found to be nonflammable in air. (Hirose et al. 1989)

Cresol delignification is affected by the solvent-water ratio and the pulpingtemperature. A high solvent ratio or a low temperature increase the pulp yield andimproves its properties. The pulping time can be decreased by the addition of someacetic acid or by circulating the liquor. The yields of hardwood pulps are equal to thoseof kraft pulps, and the yields of softwood pulps are even higher than the yields ofcorresponding kraft pulps. The strength properties of cresol pulps are inferior to those ofkraft pulps. (Takagi et al. 1989)

Takagi and Kachi (Takagi & Kachi 1989) have studied the bleaching of cresol pulpswashed with methanol. When conventional chlorine bleaching was used, cresol pulpswere easier to bleach than kraft pulps. Beech cresol pulps and kraft pulps had equalyields, but pine cresol pulps had 15-20 % higher yields. Strength properties of bleachedcresol pulps were somewhat inferior to those of kraft pulps. The cresol remaining inbleached pulps was less than 1 ppm.

The sugar content of wood meals cooked with cresol and water layers of the spentpulping liquors has been studied. The sugar found in the meals was mainly glucose.

When formic acid was added as a catalyst, the glucose content increased. The water layercontained mostly oligosaccharides, but the amount of monosaccharides increased withincreasing cooking temperature and time. (Chang & Lee 1989)

Nishiyama’s group (Nishiyama et al . 1989) has studied the recovery of cresols fromthe aqueous phase of an cresol pulping process. They have found that methyl isobutylketone, butyl acetate, i-amyl acetate and benzene can be used as a solvent in liquid-liquidextraction of cresols from water.

Fir, spruce and larch chips have been delignified in aqueous cresols (70 %) containingvarious amounts of acetic acid for two hours at 453 K. Good results were obtained byadding 40 % on wood of acetic acid. Spruce and larch yielded pulps with lower kappanumbers than fir. Spruce and fir yielded pulps with satisfactory strength properties.(Sano et al. 1989b)

Kachi et al. (Kachi et al . 1990) have presented a solvolysis pulping method using asolvent containing cresols and phenols produced by pyrolysis or hydrogenolysis oflignin and about 20 % water. Hardwood and softwood pulps produced by this methodcontain about 5 % lignin. The pulps can be almost completely defiberized even atrelatively high lignin contents, which indicates the solvents’ effectiveness in swellingwood.

The kinetics of delignification and carbohydrate dissolution in a cresol-water systemhave been studied. The results have indicated that, during delignification, the diffusion ofthe cooking liquor and the surface chemical reaction were the rate-determining steps inthe early cooking period. The opposite was observed for carbohydrate dissolution, wherethe diffusion of the reaction products was the rate-determining step in the early cookingperiod. (Jeong & Park 1990)

Nakamura and co-workers (Nakamura et al. 1991) have prepared polyurethanes fromlignins obtained as a by-product in aqueous cresol pulping of Japanese beech.Polyurethanes prepared from only cresol lignin were hard and brittle. The adding ofpolyethylene glycol into the polyurethane system allows the preparation of differenttypes of polyurethanes.

Softwood pulps produced by organosolv pulping with aqueous cresols have beentreated with sodium chlorite. The crystallinity, degree of polymerization and alpha-cellulose content were measured. An increase in the crystallinity was observed withincreasing delignification. A further delignification though caused a slight destruction ofthe crystalline regions. The degree of polymerization and the alpha-cellulose content ofthe pulps decreased during delignification with sodium chlorite. (Uraki et al. 1993)

2.3.3. Summary

Phenol and cresols are chemicals which can be produced using wood as raw material.This makes on site production of the pulping chemicals possible and reduces the costs ofpulp manufacturing. The costs of solvent recovery are probably relatively high becausevacuum distillation has to be used.

2.4. Ethyl acetate

According to the Young group (Young et al . 1985), water can be partly replaced byethyl acetate in acetic acid pulping. The addition of ethyl acetate has the followingpositive implications:1. The amount of water required in the system is reduced.2. The cooking time is reduced.3. The pulping temperature for a given pressure is reduced.4. Pulp strength is improved.5. Pulp yield is increased.6. The solubility of lignin in the solvent is enhanced.7. The solvent recovery is simplified.

Ethyl acetate is totally miscible with acetic acid and water. By proper adjustment ofthe solvent ratios, the system is, however, divided into two liquid phases. The ethylacetate-acetic acid phase and the aqueous phase can be separated by decantation, whichreduces the energy consumption of the solvent recovery. (Young et al . 1985, Anon.1985, Smith 1987, Haggin 1995)

Since ethyl acetate has good lignin solvent properties, it can be used to replace aceticacid as well as water. A wide variety of pulps can be produced. The pulp grade isdetermined by the ethyl acetate-acetic acid-water ratio in the solvent, the pulpingtemperature (433-473 K) and the pulping time (15-120 min). When aspen pulp producedby the ethyl acetate method is compared with a typical sulphite pulp, it can be noted thatat equivalent kappa numbers the yield of the ester pulp is about 20 % higher. Thestrength properties are roughly equivalent, but the ester pulp has a 20 % higher breakinglength. (Young & Baierl 1985, Young et al. 1987a)

The spent pulping liquor is flashed to atmospheric pressure. When the liquor is cooledduring flashing, it is divided into two liquid phases, if the acetic acid concentration isless than 22 w-%. The organic phase contains most of the dissolved lignin. The aqueousphase contains suspended lignin particles. The organic phase is reused as pulping liquor.The aqueous phase is further treated to separate lignin and traces of the organic solvents.The pulping liquor contains 5-95 w-% ethyl acetate, 5-80 w-% acetic acid and 10-60 %water. The liquor-to-wood ratio can be varied from 1:1 to 20:1. (Baierl et al. 1986)

Generally, the strength properties of ester pulps are between kraft and sulphite pulps.The use of phase separation in recovery should result in lower investment costs than inconventional pulping. (Young et al. 1987c)

According to Aziz and McDonough (Aziz & McDonough 1987), other hardwoodspecies do not respond to ester pulping as well as aspen, and the process is unlikely tobe capable of producing market-grade pulps from softwoods.

The recovery section of the ester pulping process includes liquid-liquid phaseseparators, a filter to recover the lignin, distillation columns to recover volatile organiccompounds, an extraction column for acetic acid separation, and a burning system tohandle sugars etc. (Young et al. 1987b)

Coppen (Coppen et al. 1988) has tested the ester pulping process using eucalyptus asraw material. He concludes that the claims for ester pulping cannot be extended tomaterials other than aspen.

The use of the acetic acid-ethyl acetate-water solvent system for pulping wheat strawhas been studied. Cooking conditions were: maximum pressure 745 kPa, temperature429 K, pulping time 340 minutes, and pulp yield 50 %. The pulp produced by thismethod may be suitable as furnish for writing and printing papers. (Jiwei et al. 1988)

According to Young (Young 1989), stronger reaction conditions are required inpulping softwoods. Pulping temperatures of 463-473 K and times of 60-120 minutes arerequired. The ethyl acetate-acetic acid-water ratio of 33:33:33 has been used. By properselection of the pulping conditions, pine pulps of good quality have been obtained.

Young (Young 1992b) has reported that the optimum ethyl acetate-acetic acid-waterratio is 15:70:15.

2.5. Amines and amine oxides

2.5.1. Ethylenediamine

Ethylene diamine can be used together with cadmium oxide to predict the behaviour ofcellulose in the viscose process. The solvent has shown promise for rapidcharacterization of viscose filterability potential and end product colour. (Smith et al.1963)

Softwoods and hardwood can be delignified at rates faster than in the kraft process in asoda liquor containing 40 % ethylenediamine. Compared to kraft pulps, the softwoodsoda-ethylenediamine pulps showed lower bleached yields, higher tear strengths, lowerbleach chemical consumptions and lower shrinkage during bleaching. For hardwoodpulps, no tear strength improvements were observed. (Kubes et al. 1978)

Aqueous ethylene diamine, alone or together with sodium hydroxide, can be used todelignify wood. Kappa numbers 17.8 and 24.5 can be reached for aspen and pine,respectively. The corresponding pulp yields are 56.0 and 47.2 %. The pulp strengthproperties are equivalent to those of corresponding kraft pulps. (Julien & Sun 1979)

MacLeod’s group (MacLeod et al. 1981) has found that the addition of small amountsof ethylenediamine (EDA) to soda-anthraquinone (AQ) pulping liquor results inbleachable grade black spruce pulps with better tear strengths than soda-anthraquinonepulps. The soda-AQ-EDA pulps could be bleached to full brightness with less chlorinethan the soda-AQ pulps. The higher the EDA charge (0.1-10 % on wood) was, the betterthe tear strength of the pulps.

The addition of methanol and ethylenediamine or monoethanolamine to soda pulpingliquor increases the rate and selectivity of delignification, with increasing concentrationof the organic components. Pulps obtained at low amine charges have tear valuessuperior to kraft pulps. At high amine levels, the alkali requirement is reduced, but thecellulose viscosity and pulp properties deteriorate. (Green & Sanyer 1982)

The delignification of lignocellulosic material can be carried out using an aqueoussolution of ethylenediamine and ethanol in combination with catalytic amounts ofanthraquinone. The method is highly selective and can be used to delignify both

hardwoods and softwoods. Softwoods can be delignified to kappa numbers as low as 20.(April et al. 1983)

Amines and alcohols alone cannot delignify softwoods to very low lignin contents.Addition of ammonium sulphide to ethanol or ethylenediamine gives the desired extentof delignification for softwoods. Very high selectivity is observed in delignification. Thestrength properties of ethylenediamine-sulphide pulps are superior compared to ethanol-sulphide pulps. The best cooking temperature has been found to be 453 K. Nosignificant effect on selectivity has been observed when the liquor-to-wood ratio ischanged from 10:1 to 1.62:1. The optimum ammonium sulphide concentration inpulping liquor is 0.3 M. (April et al. 1983)

Ethylenediamine can be removed from spent pulping liquor solids by sodiumhydroxide distillation with only 0.77 % ethylenediamine remaining in the solids (Aprilet al. 1983)

Abbot and Bolker (Abbot & Bolker 1984) have studied the kinetics of soda-ethylenediamine pulping. Studies were also conducted with primary and tertiary amines.Their results suggest that primary and secondary amines play a similar role to that ofhydrosulphide ion in kraft pulping.

Zargarian et al. (Zargarian et al. 1988) have studied aqueous ethylenediamine-ethanol-anthraquinone (EDA-EtOH-AQ) pulping of pine. Yields at the same kappa numbers werehigher than those of conventional pulping processes. In order to achieve good pulpquality and a low kappa number the EDA concentration in the pulping liquor had to befrom 40 to 50 %. The liquor contained also 10 % ethanol and 1.5 % anthraquinone.With a 99 % recovery of the organic chemicals, the chemical costs of the process wereestimated to be significantly higher than the costs of kraft pulping.

2.5.2. Hexamethylene diamine

High pulp yields, up to 68 %, have been achieved when pulping aspen withhexamethylene diamine. The addition of sodium hydroxide to the amine-water systemenhances the rate of delignification but decreases the yields. Breaking lengths of theamine-sodium hydroxide pulps are generally as high as those of softwood kraft pulp, butthe tear factors are lower. (Julien & Sun 1979)

Hexamethylene diamine alias 1,6-hexanediamine alias 1,6-diaminohexane (HMDA)has been used to delignify aspen and pine at 473 K for 15 minutes. HMDA has beenfound to selectively remove lignin from the wood chips. The HMDA aspen pulps areeven stronger than kraft aspen pulps, whereas the pine pulps are weaker. Both pulps aredifficult to bleach to high brightness levels with conventional bleaching stages. (Julien1979)

Julien and Barna (Julien & Barna 1980) have studied the economy of an HMDApulping plant, and compared it to a kraft mill. In the amine aspen process, the solvent isrecovered by distillation. Spent pulping liquor is fed directly to a distillation column.The pulp is washed with water and the spent washing liquor is concentrated in anevaporator plant before feeding to the distillation column. Lignin is recovered from the

distillation bottom product by spray drying. Potential advantages of the amine processinclude decreased investment costs and improved yield. The operating costs are howeverhigher than in kraft pulping.

Hou and An (Hou & An 1989) have pulped wheat straw for 2 hours at 423 K withHMDA (200 % on straw) using a liquor ratio of 1:8. Delignification was found to be athird-order reaction with an efficiency of 90.7 % at the defibration point with anactivation energy of 66.51 kJ/mol.

2.5.3. Methylamine

Beer and Peter (Beer & Peter 1985) have digested spruce wood at supercritical conditions(423-453 K) with aqueous methylamine. A very soluble product was extracted. Thedigestion reaction was found to be of the first order.

In a later study, Beer and Peter (Beer & Peter 1986) have used aqueous methylamineto separate lignin from pine chips by supercritical extraction. The extraction was carriedout at 453 K and 11.0 MPa using a solvent containing 40 w-% methylamine and 60 w-% water. Lignin was recovered from the extract by isobaric cooling. The condensate wasan aqueous solution containing 70-80 w-% lignin.

Li and Kiran (Li & Kiran 1988) have compared several solvents for supercriticalextraction of wood. The extractions in carbon dioxide, ethylene, nitrous oxide and n-butane were not substantial, and the interactions with wood components appeared to benonreactive. The dissolutions in ammonia and methylamine were found to be results ofreactive interactions. The results of extraction with binary solutions were stronglydependent on the compositions of the solvents. Methylamine was found to be morereactive with lignin, while ammonia and carbon dioxide-water mixtures were morereactive with carbohydrates.

Spruce has been delignified by supercritical methylamine and by a mixture ofmethylamine and nitrous oxide at temperatures of 323-470 K and pressures of 0.4-27.5MPa. The extent of lignin removal was found to increase with extraction time,temperature, pressure and the methylamine content of the extraction fluid. The extractedlignins precipitated as solvent-free solids. (Li & Kiran 1989a, Li & Kiran 1989b)

2.5.4. Ethanolamine

Wallis (Wallis 1976) has treated lignin model compounds with ethanolamine either at473 K or in benzene solutions at 353 K. He found three types of condensation reactionsof ethanolamine with lignin:- replacement of one hydroxyl group in cathecols at 473 K to give n-substituted arylgroups,- condensation with compounds containing carbonyl groups in benzene at 353 K togive oxazolidines or imines, and

- condensation with compounds containing p-hydroxybenzyl alcohol moieties inbenzene at 353 K.

Wallis (Wallis 1978) has delignified eucalyptus and pine with monoethanolamine(MEA), diethanolamine (DEA) and triethanolamine (TEA). MEA showed the highestpulping rate and TEA the lowest. Eucalyptus was pulped rapidly with MEA at 443 K,with DEA at 473 K, and with TEA at 503 K. Pine was pulped rapidly only with DEA at503 K. The pulp yields were 60-70 %. The yields of MEA pulps were 11-16 % higherthan the yields of corresponding kraft pulps. The strength properties of the DEA pulpswere comparable with those of kraft pulps.

Pinus elliottii wood chips have been delignified with monoethanolamine at 473 K,producing pulps with similar strengths and significantly higher yields when compared tocorresponding kraft pulps. When pulping to a kappa number of 34, 36 % (on wood) ofthe amine was consumed. Black liquor analyses showed that the liquor containsmethanol, acetaldehyde-ammonia and several derivates of monoethanolamine. The resultsindicated that monoethanolamine enters into extensive chemical combination with woodcomponents. (Wallis 1980)

Obst and Sanyer (Obst & Sanyer 1980) have found that monoethanol amine, whenadded to an alkaline pulping liquor, increases the rate of beta-O-4 ether cleavage ofblocked phenolic units in lignin. The extent of free phenolic beta-ether splitting isdecreased in the presence of monoethanol amine. The reaction of the amine with thequinone methide intermediates may prevent condensation and thereby promotedelignification.

2.5.5. Amine oxides

Cellulose and lignocellulose materials, for example, water extracted exploded wood fromaspen, can be dissolved in n-methylmorpholine n-oxide or dimethylethanolamine n-oxide. The resulting solution can be used to spin fibers and to produce films. (Chanzy etal. 1986, Chanzy et al. 1987, Peguy 1989)

2.6.6. Summary

No studies related to the use of amines as pulping chemicals have been published sincethe 1980’s. This is probably due to the fact that amines have a tendency to enter intoextensive chemical combinations with wood component. Therefore their recovery isdifficult and expensive.

2.6. Ketones

DeHaas and Lang (DeHaas & Lang 1974) have studied pulping using various ketonesand ammonia. They used acetone, methyl ethyl ketone, cyclohexanone and theirmixtures. Compared with kraft pulping ketone-ammonia pulping of softwoods seemedto be more selective when the pulping liquor contained 30 % ketones and 18 %ammonia at a liquor-to-wood ratio of seven. The strength properties of the pulpsobtained were generally similar to those of kraft pulps, with the exception of tearstrength. The heat of evaporation of ketones is less than 25 % of the value for water andit has been suggested that the spent pulping liquor can be evaporated to a dry powdersuitable for hydrogenation to phenols and by-product ketones.

Significant yields of soluble material can be obtained by supercritical extraction ofwood using, for example, acetone as solvent. The extracts contained phenols, cresols,guaiacols, eugenol, isoeugenol and coniferyl alcohol. (Calimli & Olcay 1978)

Koll and Metzger (Koll & Metzger 1978) have used supercritical acetone (Tc = 508.5

K, pc = 4.7 MPa) to dissolve cellulose. About 98 % of the cellulose was dissolved in a

ten hour extraction at 523-613 K. The extract contained mostly low molecular weightcomponents.

The use of underflow tar from acetone-ethanol-ammonia pulping as a low percentageadditive to petroleum refinery feed has been proposed. (Griffith et al. 1980)

Paszner and Chang (Paszner & Chang 1981) have patented a method using all typesof lignocellulosic materials found in the nature as raw materials for producing naturallignin, paper grade pulps, pure xylose, pure mannose or dehydration products of thesugars. The pulping liquor contains 30-70 % of an organic solvent, which can beethanol or acetone. The cooking temperature is about 473 K. The pH value of thesolution is adjusted to 3.5 or less by a mild acid, e.g. formic acid, or an acid-saltmixture, for example HCl-KCl. The liquor-to-wood ratio of 4:1 is preferred.

Cellulose-containing materials, for example wood or delignified pulps, can be rapidlysaccharified to convert pentosans and hexosans to sugars. The process is conducted bycooking the material under pressure at 453-493 K with an acetone-water solvent mixturecontaining 0.05-0.25 w-% phosphoric, sulphuric or hydrochloric acids. The solventmixture contains 60-70 v-% of acetone. A predominantly cellulosic material producesrelatively pure glucose and whole wood yields mixed pentoses and hexoses. (Paszner &Chang 1983d)

Cellulosic materials can be partially or totally hydrolysed using an aqueous acetonemixture containing a small amount of an acidic compound. The mixture contains from70 to 100 v-% acetone and the process is performed at temperatures between 418 and 503K. Acetone at high concentrations forms stable complexes with the sugars preventingtheir degradation. Lignin and sugars produced by this method are claimed to becommercially useful compounds. (Paszner & Chang 1984)

Paszner and co-workers (Paszner et al. 1985) have presented a process called ACOS(acid catalysed organosolv saccharification). It uses aqueous acetone and a minor amountof a mineral acid to hydrolyse wood. All wood species can be used as raw materials andthe process separates a natural lignin and fermentable sugars.

When the ACOS process is conducted using aqueous acetone (60 %) and hydrochloricacid (0.025-0.1 N) at 473 K, Douglas-fir wood is completely dissolved. High quality,mostly low molecular weight lignin is obtained. (Cho & Paszner 1987)

The Deineko group (Deineko et al. 1988b) has patented a pulping method consistingof cooking wood in an aqueous aprotic organic solvent at 403-433 K. The reagent useand environmental pollution can be reduced, while accelerating delignification andincreasing pulp yield, if oxygen is present in the process in amounts of 12.6-23.2 w-%on wood. Liquor-to-wood ratios of 5:1-10:1 and solvent-to-water ratios of 1:1-5.7:1 canbe used. The aprotic solvent can be acetone.

When spruce sawdust is oxidated at 433 K for two hours in aqueous acetone (66 v-%)in the presence of molecular oxygen, nearly 90 % of the initial lignin in the sawdust isdissolved. (Deineko & Evtyugin 1988)

Xylitol can be produced from vegetable material including hemicelluloses containinga xylane component. The raw material is pretreated with aqueous acetone or ethanol at373-463 K for a period of from two minutes to four hours. About 20 % of the xylanecontaining hemicelluloses are dissolved during this first step. The residue is treated witha solution containing 50 % water and acetone or ethanol at 393-493 K for a period offrom two minutes to six hours. The rest of the hemicelluloses are dissolved during thisstep. Xylose is recovered from the hemicelluloses containing solutions and reduced toxylitol. (Sinner et al. 1988)

Oxidative delignification of spruce and aspen with oxygen in 60 % aqueous acetonehas produced pulps in yields of 42-46 % and 56-62 % respectively. The residual lignincontents of the pulps were 5.8-6.7 % and 2.2-7.0 % respectively. (Deineko & Evtyugin1989)

Both hardwoods and softwoods can be delignified by oxygen in aqueous acetonewithout the use of any catalyst. The optimum process conditions are: liquor-to-woodratio 50 dm3/kg, oxygen pressure 1.5 MPa, maximum temperature 423 K, temperatureraising time 60 minutes and time at temperature 120 minutes. Spruce pulps containing8.2 % lignin have been obtained at yields around 49 %. Acetone can be recovered bydistillation. The remaining aqueous solution can be concentrated and dried. (Deineko etal. 1989, Zarubin et al. 1989)

The temperature required for the anodic conversion of acetone soluble spruce lignin, inaqueous alkaline solutions, can be lowered by the addition of nitrobenzene or 1,3-dinitrobenzene. (Smith et al. 1989)

Chang (Chang 1990) has presented a method for continuous countercurrent productionof lignins and sugars from lignocellulosic materials. The raw material is continuouslyfed with a natural moisture content into a reactor. The cooking liquor containing 70-90 v-% acetone, water, and a small amount of sulphuric acid is fed into the reactorcountercurrently with the raw material. The method is conducted at 423-483 K and aliquor-to-wood ratio of 5:1-15:1 is used. When aspen chips are treated with the method,99.5 % of the original wood is dissolved.

The pulp produced with oxygen in aqueous acetone is partially dehydrated. This causesstrong hydrogen bondings between polysaccharide chains in the cell wall, leading torigidity of the fibers. As a result of these pulp properties, the paper made from oxygenorganosolv pulps have low strength properties. Washing the pulp after delignification

with fresh solvent, followed by a treatment with 0.1 N sodium hydroxide favours therehydration of the fibers resulting in paper strength properties near those of a kraft pulp.(Evtuguin et al. 1993a)

Oxygen delignification in aqueous acetone has been proposed as a suitable method fortransformation of hydrolysis lignin into microcrystalline cellulose and soluble activeoxidized lignin. The main low molecular products are vanillin and vanillic acid.(Evtuguin et al. 1993b)

Kostyukevich (Kostyukevich et al. 1993) has separated and analyzed lignins fromoxygen pulping in a medium of water and acetone, ethanol or acetic acid. The molecularweights and polydispersities of the lignins were found to be similar to those of dioxanelignins and lower than those of alkali lignins. The type of solvent did not affect themolecular weight.

Low-molecular weight products in spent liquors from oxygen-acetone pulping ofNorway spruce and trembling aspen have been studied. Based on the composition of theidentified reaction products they have proposed probable mechanisms for the oxidativeand hydrolytic degradation of lignin. (Evtyugin & Deineko 1994)

Evtyugin’s group (Evtyugin et al. 1994a) has compared oxygen-organosolv pulpingof trembling aspen with corresponding kraft pulping. The organosolv cooks were carriedout with 60 v-% acetone or ethanol, or 80 v-% acetic acid. Their results indicated thatthe higher yield of the oxygen-organosolv pulps is more due to reduced dissolution ofcellulose in the pulping liquor than to preservation of the hemicelluloses. They(Evtyugin et al. 1994b) have also carried out comparative studies on the degree ofdegradation of the polysaccharide complex in the pulps. Results from these studiesindicated that one of the main reasons for the low strength properties of oxygen-organosolv pulps is the depolymerization of the polysaccharide complex.

It has been suggested that oxygen attacks double bonds of lignin during oxygen-organosolv delignification resulting in breaking and dissolution of the lignin. Thepulping method is also called oxysolvolysis. (Vedernikov & Deineko 1994)

Evtuguin et al. (Evtuguin et al . 1995) have used acetone, ethanol and acetic acid assolvents in oxygen delignification of aspen chips. The comparison of the results suggestthat the acidity of the pulping liquor has a more important influence on thedepolymerization of wood polysaccharides than the oxidation potential.

Delignification of wood with oxygen in aqueous acetone partially removes boundwater from pulp. This dehydration causes rigidity of the fibres and low strengthproperties of a paper produced using these pulps. When the pulp is washed with freshpulping liquor after cooking and then treated with alkali, pulp fibres are rehydrated andthe strength properties approach those of a kraft pulp. (Evtuguin et al. 1996)

The delignification kinetics of Eucalyptus urograndis in acetone-water pulping hasbeen found to be very similar to other hardwood pulping processes. Bulk and residualdelignification phases have been identified. Most of the lignin removal occurs in thebulk phase. (Perez & Curvelo 1997)

2.7. Dioxane

Engel and Wedekind (Engel & Wedekind 1933) have patented a pulping method wheredioxane is used as solvent in the presence of a catalyst. When pinewood meal is cookedin dioxane using a liquor-to-wood ratio of 8:1, for 5-10 hours at 353-363 K, in thepresence on 1 % or less on dioxane of hydrochloric acid, pulp containing less than 3 %lignin is obtained in yields around 60 %. While soluble in water, dioxane can be easilywashed from the pulp. Dioxane can be recovered by distilling the spent pulping liquor.Lignin can also be precipitated from the spent liquor by adding an ether. The ether isthen separated from dioxane by distillation.

Beech pulp produced by cooking in dioxane contained 87.8 % a-cellulose and 0.3 %lignin. The pulp yield was 41.3 % after pulping and 40.3 % after bleaching. (Wedekind1936)

The Pepper group (Pepper et al . 1959) has studied the isolation of a lignin fractionfrom spruce and aspen wood meals by low temperature (363-368 K) acidolysis, using aaqueous dioxane (90 %) containing hydrochloric acid (0.2 N). For both species, increasedextraction times led to greater yields of lignin with lower methoxyl contents.

When hydrolysing lignin with dioxane coniferyl alcohol and its 2,4-dinitrophenylether, coniferyl aldehyde and vanillin as corresponding 2,4-dinitrophenyl hydrazones havebeen identified. Also vanillinic acid was found in the hydrolysis product of spruce wood.From beech wood hydrolysis products, also syringic acid and from poplar hydrolysisproducts also p-hydroxy benzoic acid were found. (Sakakibara & Nakayama 1962a)

In further studies, Sakakibara and Nakayama (Sakakibara & Nakayama 1962b)delignified sixteen species of wood with aqueous dioxane (50 %) at 453 K for 40minutes. In the hydrolysis products from softwoods, they found coniferyl alcohol, p-coumar alcohol, coniferyl aldehyde and vanillic acid. The hydrolysis products ofhardwoods were found to include sinapyl alcohol, coniferyl alcohol, coniferyl aldehyde,syringic acid and vanillic acid. Only poplar wood produced p-hydroxy benzoic acid duringhydrolysis with aqueous dioxane.

Acidolysis of spruce wood has been found to correspond to a pseudo-first orderreaction mechanism. When the acidolysis with hydrochloric acid is carried out inanhydrous media, methanol shows higher yields for isolated lignin than dioxane. Addingup to 10 % water to dioxane increases the lignin yield making dioxane a better acidolysismedium than methanol. (Kosikova and Polcin 1973)

Kayama and Takagi (Kayama & Takagi 1978) have studied alkaline dioxane pulpingof oak wood. The aqueous pulping liquor contained 40 g/dm3 sodium hydroxide and 33-50 v-% dioxane and the liquor-to-wood ratio was 4 dm3/kg. When the pulping wascarried out at 453 K for 90 minutes, screened pulp yields varied from 45 to 48 %. Therate of delignification increased with increasing dioxane concentration in the pulpingliquor but the pulp strength properties decreased.

It has been reported that autohydrolysis of aspen and eucalyptus at temperatures 448-493 K induced lignin solubility in aqueous dioxane (90 %). From aspen about 90 % ofthe lignin could be extracted after autohydrolysis with aqueous dioxane for 4-25 min at468-488 K. Longer extraction times reduced lignin solubility. (Lora & Wayman 1978)

Argyropoulos and Bolker (Argyropoulos & Bolker 1987) have isolated lignin fromspruce sawdust with dioxane:water:hydrochloric acid (90:8:1.8 by volume). Duringbatchwise extraction, irreversible recondensation of the lignin fragments took place.

Pine wood and pine bark dioxane lignins have been compared. The Klason lignincontent of bark was found to be 33 % lower than that in wood. The results also pointedto certain differences in the structure of bark and wood lignins. The nature ofhemicelluloses bonded with lignin in pine and wood cell walls was predicted to bedifferent. (Solar et al. 1988)

The results obtained by analyzing two dimensional NMR spectra of dioxane lignintreated with lignin peroxidase have shown that the lignin may possess a threedimensional structure. (Gilardi et al. 1990)

Montanari (Montanari et al. 1991) has determined the Klason lignin values and kappanumbers for wood residues from the dioxane-water pulping of Caribbean pine usinghydrochloric acid as a catalyst. Yields of pulp and wood residues obtained with variouspulping times, various concentrations of hydrochloric acid and related process variationswere included in the factors studied. A proportional factor of 0.2 was determined.

Degradation of lignin model compounds on acid treatment in aqueous dioxane hasbeen studied in order to find the acid-catalyzed reactions of lignin during organosolvpulping. Hydrochloric and hydrobromic acids catalyse elimination of the hydrogen at thebeta position of the lignin units and the release of formaldehyde from terminal methylolgroups. (Karlsson & Lundquist 1991)

Dovgan and Leonovich (Dovgan & Leonovich 1992) have studied the softeningpoints of dioxane lignin from softwood, hardwood, and algae. The softening point curvesof these lignin were found to be different. This is mainly caused by the differences inreactivity, molecular weights, and methoxyl group contents.

A dehydropolymer has been produced by synthesizing from ferulic acid and dioxanelignin. The hydrodynamic behaviour was found to be similar for the lignin and thepolymer. (Karmanov et al. 1992)

Curvelo’s group (Curvelo et al. 1992a) has studied the delignification of Eucalyptusgrandis by both batch and continuous pulping in aqueous dioxane. After a five hourextraction, the lignin removal was negligible in both processes. The lignin yield fromthe continuous process was lower. The pulp yield in continuous pulping was also lowerdue to a higher level of carbohydrate dissolution.

Dioxane lignins from Pinus caribaea have been isolated using various catalyticconcentrations of hydrochloric acid. They found an increase on the appearing of highmolecular weight fractions, when the catalyst concentration was increased. (Curvelo etal. 1992b)

Montanari et al. (Montanari et al. 1993) have extracted lignins from Pinus caribaeawith aqueous dioxane (90 %) containing hydrochloric acid (1.0 N) using variousextraction times (30-300 minutes). The lignin yields indicated that the delignificationrate decreases with the extraction time. The analytical results pointed out that thedelignification occurs mostly in the middle lamella.

Eucalyptus chips have been extracted with aqueous dioxane (90 %) containinghydrochloric acid (2 N) at 362-363 K for 1-6 hours and the lignins obtained analyzed.

The results indicated that all lignins have similar functional group distributions and thatcondensation reactions were not significant. (Curvelo et al. 1993)

Solar and Kacik (Solar & Kacik 1993) have used dioxane to isolate lignins fromCaribbean pine wood and bark in order to study the differences in these lignins. Theirdata indicated differences in condensed bis-guaiacyl structure contents of the lignins.They also found differences in the thermostability and the molecular weights of thecompared lignins. The bark lignin is more crosslinked and contains more aromaticcarbon linkages than wood lignin. The bark lignin has a lower thermostability.

Lignins isolated from algae and sea-grasses by aqueous dioxane delignification havebeen studied. The isolated lignins were high molecular compounds with averagemolecular weights from 9000 to 10000 and a polydispersity degree from 1.9 to 2.3.(Dovgan’ & Medvedeva 1993a)

The relatively low yield of products of nitrobenzene oxidation of algae and sea-grasslignins has indicated that this lignin has a higher degree of condensation than woodlignins. (Dovgan’ & Medvedeva 1993b)

Dioxane lignins from algae and seagrasses are split by 27-41 % under the effect ofnucleophilic agents (hydrazine in n-butanol or hydroxylamine in alkaline media).Phenols, oxyaromatic acids and higher fatty acids have been identified in the degradationproducts. (Dovgan’ & Medvedeva 1993c)

Kanitskaya and co-workers (Kanitskaya et al. 1993) have bleached spruce dioxanelignin with hydrogen peroxide or sodium borohydride. Spectrophotometric, UV andNMR analyses showed that oxidative bleaching resulted in an increase in the content ofnon etherified fragments with an alpha-CO group. During sodium borohydride bleaching,the number of structures containing a carbonyl group decreased by 240 %. The contentof non etherified aromatic fragments also decreased. The degree of lignin condensationwas reduced and the degradation of the coniferyl aldehyde structure occurred during bothtypes of bleaching.

It has been found that base-catalysed dioxane pulping results in an increase in yield, a-cellulose, DP and a decrease in the hot alkali solubility. The favourable effects areinduced by the formation of hydrogen bonds between the cellulose hydroxyls and the 1,4-oxygen atoms of dioxane. When borax is present during soda-dioxane pulping, theresulting cotton pulp is almost completely composed of pure alpha-cellulose. (Mostafa1994)

Povarova and Chupka (Povarova & Chupka 1994) have used chemiluminescence andmicromanometry in order to study the effect of oxygen pressure and temperature on theoxidation of wood and dioxane lignin in alkaline (NaOH) and alkaline-ethanol media. Anincrease in temperature and pressure resulted in an increase in the oxidation rate. Theoxygen consumption was found to be three-fold higher in the alkaline-ethanol mediathan in the alkaline media.

Ultracentrifuging, viscometry and calorimetry have been used to study solvation ofdioxane lignin in dimethyl sulfoxide, pyridine and dioxane. The results showed that thesolvation effect became stronger when the solvent polarity increased. Solvation effectswere negligible with pyridine and dioxane as solvents. (Bogolitsyn et al. 1994)

Curvelo and Balogh (Curvelo & Balogh 1995) have compared continuous and batchpulping of eucalyptus with aqueous dioxane (90 %) containing hydrochloric acid (0.2 M)

as the catalyst. The batch procedure was found to be the more selective one. Thedelignification rate constants were also higher in batch pulping.

Dioxane lignins have been isolated from maple sawdust extracted with a solventcontaining dioxane, water, and hydrochloric acid. The isolation was carried out usingseveral methods. The results pointed to an increased lignin degradation occurring at hightemperatures. (Solar & Kacik 1995)

2.8. Other organic compounds

Kuster and Daur (Kuster & Daur 1930) have used beta-naphthol in the presence of somehydrochloric acid to dissolve residual lignin from pulp.

2-naphthol has been used to prevent lignin self-condensation during theautohydrolysis of aspen wood. A highly delignified product could be obtained with 2 %2-naphthol at autohydrolysis temperatures around 448 K for two hours. (Wayman &Lora 1978)

Hossain (Hossain 1958, Hossain 1959) has found that dimethyl sulphoxide (DMSO),in the presence of small amounts of mineral acids, is a powerful delignifying agent forboth high-lignin sulphite pulps and wood chips. The delignifying process is conducted ata temperature between 399 and 448 K in an aqueous solution containing 75 w-% DMSOin the presence of catalytic amounts of sulphuric acid or hydrochloric acid.

A solution of 5 % sulphur dioxide (SO2), 2 % nitrogen dioxide (NO2) and 5 %

chlorine (Cl2) dissolved in DMSO has shown good pulping properties. Cooking times

were short and the temperature did not exceed 413 K. The pulp yield varied from 42 to80 % depending on the pulping conditions. Both sawdust and chips of spruce could bepulped and the pulps were easy to bleach. (Clermont and Bender 1961)

The efficiency of alkaline catalysis at wood and lignin oxidation increasesconsiderably when the process is conducted by adding DMSO. Proper adjustment of thepH-values can considerably improve the selectivity of the process. (Chupka et al. 1993)

Aqueous solution containing 35 % sodium m-xylenesulfonate acidified with smallamounts of sulphuric acid (0.1-0.4 N) have been used to delignify aspenwood attemperature from 373 to 423 K. At 423 K, using a solution containing 0.4 N sulphuricacid, the wood substance went into solution in 300 seconds. At higher temperatures,substances precipitated from the solution onto the solid residue. (Springer et al. 1963)

Acidified aqueous solutions of sulfolane (tetramethylene sulphone) have been provedto be highly effective delignifying agents for finely divided aspen wood. Sulfolaneconcentrations 300-900 g/dm3, sulphuric acid concentrations 0.05-0.40 N and isothermalreaction temperatures of 403-433 K were used. High sulfolane concentrations and thereaction temperature were most effective in lignin removal. High acid concentrationsimproved the delignification rate but, at 0.4 N, caused lignin to precipitate on the solidresidues. (Springer & Zoch 1966)

Starr and Casebier (Starr & Casebier 1970) have patented a pulping process where thesodium sulphide pulping liquor contains an organic solvent (30-70 %). The solvent isselected from the group consisting of alkyl polyols, cyclic sulfones, acyclic sulfones and

mixtures thereof. Pulping is carried out at 433-463 K for 2.5-4 hours. A liquor-to-woodratio of 5:1 is used.

A pulping method where cellulosic material is extracted at 443-483 K under elevatedpressure with an aqueous solution of dimethyl formamide in two stages has beenpatented. The extraction is conducted using liquor-to-wood ratios between 7:1 and 20:1.The pulp is washed after each extraction stage with fresh solvent. (Lenz et al. 1984)

Sameshima and Takamura (Sameshima & Takamura 1987) have found that aqueousammonium oxalate solutions (5 g/dm3) are good pulping agents for bast fiberscontaining pectin as the main bonding substance. Pulping was carried out at 358 Kusing a liquor-to-wood ratio of 25:1. The strength properties of pulps produced by thismethod were better than those of conventional soda pulps.

It has been reported that high yield bamboo pulps can be produced using aqueoussodium xylenesulphonate as the pulping liquor. The solution containing 30-50 %sodium xylenesulphonate can be used several times before a simple recovery. Lignin isprecipitated from the spent liquor by diluting it with water and the remaining liquidphase is returned to its original concentration by evaporation. The pulping temperatureis 453-463 K and the resulting pulp can be used to produce, for example, dissolvingpulp. (Lau 1941)

Hardwoods and sugarcane bagasse have been delignified with approximately neutral 30-40 % solutions of sodium xylenesulphonate. The same solutions were used for six orseven cooks before recovery. Poplar wood was delignified at 423 K for 11-12 hours,giving pulps with yields of about 52 %. Bagasse was cooked for three hours at 433 K.The yield of unbleached bagasse pulps was about 48 %. The installation costs of a millusing this method was estimated to be only one third of the costs for a kraft mill ofsimilar size. This is mainly due to the simple chemical recovery with only precipitationof lignin and evaporation. (McKee 1946)

McKee (McKee 1954) has compared his hydrotropic pulping process with the kraftprocess. The McKee hydrotropic process uses sodium xylenesulphonate as the pulpingchemical and gives an about 5 % higher pulp yield than the kraft process. The alphacellulose content of the McKee pulp is higher, and so the quality of the pulp can bejudged to be better than the quality of kraft pulps. The chemical costs of the hydrotropicprocess are 75 % lower than for kraft pulping when compared in 1954. The cookingliquor of the hydrotropic process can be used five to six times before it has to berecovered. There are several advantages with the use of sodium xylenesulphonate:- Penetration of the chemicals into the chips is twice as rapid as in the kraft process.- It is neutral, odourless and non-volatile.- Air oxidation of the cellulose does not lower the pulp yield.- The chemical concentration does not decrease during the pulping cycle.

Sodium xylenesulphonate is a selective delignifying agent and no sugars are presentin the spent pulping liquor, which can be reused until it is saturated with lignin. Thehydrotropic process can be operated without any effluents and malodorous gaseousemissions. (McKee 1954)

The Hinrichs group (Hinrichs et al. 1957) has found that hydrotropic pulping, using a30 % solution of sodium xylenesulphonate, is an effective method for dissolving lignin,but gives pulps with lower strength properties and brightness than alkaline pulping

methods. Lignin is precipitated when the solution is diluted with water, leading todifficulties in pulp washing.

McKee (McKee 1960) has listed the advantages and disadvantages of hydrotropicpulping using sodium xylenesulphonate. The advantages were:1. The hydrotropic process requires only two-thirds of the equipment costs of a kraftmill.2. It requires only two-thirds of the mill labour.3. It has lower chemicals costs than conventional processes.4. Its water consumption is low.5. The pulp can be bleached with less chemicals than kraft pulps.6. The pulp yield is higher than in conventional processes.7. Valuable by-products can be recovered.8. Both hardwoods, softwoods and mixtures of them can be used as raw-material.9. The process is free from odours and aqueous effluents.

A major disadvantage is the need for counter-currently operating screw presses forpulp washing. This type of equipment is more expensive than the filter pressescommonly used in the pulp industry. (McKee 1960)

Troitskii (Troitskii et al. 1989) has presented a pulping method consisting of treatingsoftwood or hardwood chips in an aqueous alkaline solution at an elevated temperatureand pressure. If the alkaline reagent is tetraethylammonium or tetrabutylammoniumhydroxide, pulp yields are improved and residual lignin contents decreased. A reagentconcentration of 0.75-1.25 M is needed for softwoods, and 0.5-1.0 M for hardwoods.

Kuznetsov’s group (Kuznetsov et al. 1995) has proposed methods for processingsilver-fir and larch barks. The bark is first activated by steam cracking. Silver-fir bark isthereafter subjected to benzene extraction in order to isolate silver-fir oil. The solidresidue is subjected to catalytic pyrolysis in order to produce carbon sorbents. Theactivated larch bark is also extracted with benzene in order to isolate larch oil. The solidresidue is activated by non-isobaric steam treatment, and the activated residue is subjectedto water extraction in order to isolate tanning matter. The remaining solid residue issubjected to catalytic pyrolysis producing carbon sorbents.

2.9. Summary

Several organic chemicals have been proposed to be used as pulping chemicals, but onlythose processes using lower aliphatic alcohols or lower organic peroxyacids havesurvived. The most severe problems related to organosolv methods are the pulp quality,which typically is lower than the quality of corresponding kraft pulps, and solventrecovery. Organic solvents are more expensive than the inorganic chemicals used in kraftpulping. They have to be recirculated at high recovery rates.

No single organosolv pulping method fulfils all the requirements for a processcapable of replacing the kraft process. The ASAM process, which produces the bestquality pulp, is a modified sulphate process, and therefore not sulphur free. Severalorganosolv solvent are selective pulping chemicals and do not degrade cellulose.

Alcohols are solvents with high vapour pressures. This leads to high pressures indigesters which have to be redesigned. The simplicity of the recovery cycles depends onthe number of by-products that are recovered. The recovery of by-products is necessary tobalance the economy of most organosolv processes, but every product typically adds atleast one unit operation to the recovery cycle. All the methods are capable of producingby-products. Some by-products, like alcohols and organic acids, are not especiallyvaluable and some by-products, for example lignins, are produced in such large amountsthat it is difficult to find markets for them. Environmental problems can be eliminated ifthe chemical cycle can be closed. This requires a TCF bleaching sequence which can beapplied to most organosolv methods. The ASAM method is the only organosolv processproducing both hardwood and softwood pulps with a quality comparable withcorresponding kraft pulps. The optimal size of an organosolv pulping plant seem to besignificantly smaller than the optimal size of a kraft pulping plant. This is mainly dueto the fact that no recovery boiler is needed in organosolv processes. It is therefore to bepresumed that an organosolv pulping plant will be built in an area with limited forestresources. Many organosolv methods are also capable of pulping annual plant whichalso point in that direction. The most probable recovery method is distillation, which isa unit operation with a high thermal energy consumption. It was therefore decided tostudy the possibilities for reducing distillation costs in one of the processes. The processchosen was the peroxyacid pulping method because it has been developed in Finland andtherefore it is of particular interest.

3. Solvent recovery in peroxyacid pulping

As the strongest organic acid, formic acid is a good delignification solvent. The cookingprocess can be operated at atmospheric pressure. When the boiling temperature of formicacid is 374 K, the cooking temperature can be kept significantly lower than in otherorganosolv processes or in conventional pulping processes. The process is also suitablefor pulping of nonwood materials. Silica does not cause problems in a process operatedat acidic conditions (Rousu 1996).

In order to replace an existing process, the new process should produce a better orcheaper product. When producing paper grade pulps, the peroxyformic acid (Milox)process at the present stage of development does not differ enough from the kraft processin terms of production costs or pulp quality. The major difference is that theperoxyformic acid process is totally sulphur-free. (Sundquist 1996)

A major drawback in the peroxyformic acid process seems to be the relatively highenergy consumption of the chemical recovery sequence and especially distillation.Therefore optional separation methods were evaluated and the reduction of distillationcosts was studied.

No exact data for the composition of the spent peroxyformic acid pulping liquor hasbeen published. It is obvious that the liquor contains small amounts of severaldegradation products resulting from lignin and carbohydrates. The amount of acetic acidformed during birch pulping is around 4 % on wood (Muurinen et al. 1992). Theamounts of other compounds are probably significantly lower. Therefore the liquorentering the separation section of the process was assumed to contain only water, formicacid and acetic acid.

The effect of distillation feed composition on the economy of the process was studied.The composition of this liquor depends on the composition of the pulping liquor and onthe operation conditions in the unit operations preceding distillation. This made itdifficult to determine the desired separations for individual feed compositions. Thereforeit was decided that the mole fraction of all products should be 98 %.

3.1. The search for feasible separation methods

When the dissolved solids have been removed from the spent pulping and washingliquors resulting from peroxyformic acid pulping of birch, the remaining liquor containswater, formic acid and acetic acid as the main components (Muurinen & Sohlo 1994).Available methods for the selection of feasible separation processes were applied to thisternary liquid mixture.

3.1.1. Wells and Rose

Wells and Rose (Wells & Rose 1986) have given rules (table 3) for the selection of aseparation method. The rules are based on the following heuristics:- Avoid solid-handling in the process fluid if possible, because this is generally moreexpensive than the handling of liquids and gases.- Avoid adding a mass separating agent (MSA) if possible, because this has to beremoved from the products. If a MSA has to be used, it should be removed in the nextseparation stage. The MSA should be a component already present, if possible.- Use processes which offer economy of scale.

Table 3. Rules for the selection of a separation process.

----------------------------------------------------------------------------------------------------------------------1 . Tabulate all components in their boiling point sequence. Indicate the mole

fractions and the desired separations.2 . If the required separation can be achieved by simple splitting, take the

appropriate action.3 . Consider the phase or phases of the feed mixture over a range of appropriate

conditions.4 . Are there two or more phases present and can this be used as the basis for

separation?5 . If solid and gas phases are present separate them by gas cleaning methods.6 . If the phases are solid and liquid separate them on the basis of solid particle size and

content.7 . If the phases are liquid and gas separate them as follows:

Choice number 1: gravity settlersChoice number 2: flash vaporization, partial condensationChoice number 3: simple distillationChoice number 4: other distillation methods, evaporationChoice number 5: change phase, chemical reaction etc.

8 . Is only one phase present?----------------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------------Table 3. Cont.

----------------------------------------------------------------------------------------------------------------------9 . If the only phase is liquid separate it as follows:

Choice number 1: settling if two or more liquid phasesChoice number 2: fine particle separation, liquid-liquid extractionChoice number 3: sorptive mass transfer, change the phase to liquid/gasChoice number 4: liquid permeation, split and blend, chemical reaction,

phase change.10. If the only phase is gas separate it as follows:

Choice number 1: gas permeationChoice number 2: adsorption, absorptionChoice number 3: change of phaseChoice number 4: other methods.

11. If the only phase is solid separate it as follows:Choice number 1: screening, sortingChoice number 2: chemical reaction, change of phase.

12. Review product specifications, recycle and feed streams. Consider the separation of small impurities with finishing methods.13. Review the sequence of separations as follows:

Choice number 1: remove early any component which may cause furtherundesired reaction or which is hazardous

Choice number 2: remove early any component which requires the useof expensive materials of construction or highpressures or vacuum.

Choice number 3: perform the most difficult separation as the last oneChoice number 4: separate the main components earlyChoice number 5: perform the easiest separations first.

14. Review the selected separation sequence. Give particular attention to sequencesinvolving technical extrapolation of equipment and equipment with high costs.

----------------------------------------------------------------------------------------------------------------------

When this method is applied to the feed of the separation section of the peroxyformicacid pulping process, the use of ultrafiltration, pervaporation, flash evaporation,distillation, evaporation and crystallisation is suggested.

This method favours separation processes where no mass separating agents arepresent.

3.1.2. Lee

In the selection method of Lee (Lee 1986), the pairs of components that have to beseparated are identified using the following rule:- Separation is required when the maximum (or minimum) mass or mole ratio of twocomponents in the available process streams is less (or greater) than that in the desiredproduct.

When the pairs to be separated are identified, feasible methods for each binaryseparation are listed. The appropriate separation methods can be found when themolecular and chemical characteristics of the components are known. The separationsequences obtained must be compared in order to select the best one. If the number ofseparation sequences is large it may be reduced using the following rules:- Separate components present in large amounts first.- Separate corrosive and hazardous components first.- Minimize the difference between the enthalpies of the product streams in order toreduce the work of energy recovery.- Perform the easiest separation first.

Applying this method to the present separation problem suggests the followingfeasible separation methods: membrane processes, distillation, crystallisation, stripping,evaporation and flashing.

Membrane processes and separation methods involving the use of an energyseparating agent seem to be favoured by this selection method. Again no separationmethod using mass separating agents are suggested. This is due to the higher costs ofthose methods.

3.1.3. Barnicki and Fair

The separation process selection method presented by Barnicki and Fair (Barnicki & Fair1990) is based on the application of the following rules:- Identify product streams and product specifications in order to ensure that nounnecessary separations are done.- Rank components in order of decreasing adjacent relative volatilities which give astrong indication of the ease of separation and the favorability of simple distillation.- Identify all azeotropic mixtures that may interfere with product specification, becauseazeotropes require special processing considerations.- Perform splits in the order specified by sequential heuristics.

The following list of heuristics that may be used is based on the work of Nadgir andLiu (Nadgir & Liu 1983):- Separate corrosive and hazardous components first.- Separate reactive components first.- Separate azeotropic mixtures last.- Perform other difficult separations last, but before azeotropic separations.- Separate components in order of decreasing contents in the feed.- Favour 50/50 splits.- If the order of separations cannot be chosen using preceding heuristics, perform theseparation with the smallest coefficient of difficulty of separation (CDS) first (Nath &Motard 1981):

CDS

X

X

X

X

a

D

D B

D B

D B

LK

LK

HK

HK

LK HK

=−

⋅−

⋅+

⋅ + −

+

ln

ln ,

1 11

(1)

where CDS is the coefficient of difficulty of separation,XLK is the mole fraction of the light key component,

XHK is the mole fraction of the heavy key component,

aLK,HK is the relative volatility of the light key component

with respect to the heavy key component,D is the overhead product flow rate andB is the bottom product flow rate.

When the split sequencing has been done, possible separation methods for each splitare identified using component properties. Simple distillation should be used if possible.

This method suggests the use of simple distillation, extractive distillation, azeotropicdistillation, membrane processes, liquid-liquid extraction and adsorption as the methodsto separate the formic acid-acetic acid-water mixture.

The method seems to favour simple distillation, and separation methods involving theuse of mass separating agents are not rejected. The reason for this is that the methodtakes into account also more complex feed solutions, for example, azeotropic mixtures.

3.1.4. Null

According to Null (Null 1987), there is no rote procedure by which separation processesare chosen, but certain guidelines can be followed in order to design the separationprocess sequence. The most important criterion in the design is economics. The firststep in the selection of a separation process is to define the problem. The next step is todetermine which separation processes are capable of accomplishing the separation.During this step component property differences, unit operation classification, scale ofoperation, design reliability, necessity for pilot plant tests, number of steps required,capital costs and energy requirements have to be taken into account. This methodsuggest the use of distillation, liquid-liquid extraction, crystallisation and adsorption asmethods of solving the separation problem being considered.

3.2. Feasible separation methods

In order to determine the potential of the separation processes suggested by the selectionmethods, the properties of the components in the mixture and phase equilibria of themixture have to be studied. Some useful properties of the components are listed in table4.

Table 4. Properties of formic acid, acetic acid and water (Wagner 1978, Wagner 1980,Matter-Muller & Stumm 1984, Weast 1978).

----------------------------------------------------------------------------------------------------------------------Property HCOOH CH3COOH H2O

----------------------------------------------------------------------------------------------------------------------melting point (K) 281.6 289.84 273.2boiling point (K) 373.9 391.1 373.2density (kg/m3)

at 293 K 1220 1049at 298 K 1213 998liquid at 273 K 1000solid at 273 K 907

viscosity (mPa·s)at 293 K 1.784 11.83at 298 K 10.97 0.8949at 313 K 8.18steam at 293 K 96·10- 6

heat of vaporization (J/g)at boiling point 900.2 694.8 2258.9

heat capacity (J/g·K)at 290 K 2.15steam at 397 K 5.029solid at 100 K 0.837steam at 373 K 2.078liquid at 298 K 4.179steam at 273 K 2.06

dipole moment (D) 1.52 1.74 1.83molecule diameter (Å) 5.5 5.3 3.0----------------------------------------------------------------------------------------------------------------------

Evaporation and stripping are useful processes when dissolved solids are separatedfrom spent pulping liquor, but liquid components cannot be selectively separated.Crystallization is mainly used, if a solid product is desired. The other separation methodsare evaluated.

3.2.1. Simple distillation

Formic acid and water form maximum boiling azeotropes containing 77.5 % acid at101.3 kPa and 83.2 % acid at 2.4 MPa (Wagner 1980). At the 101.3 kPa, the azeotropicmixture boils at 380.3 K, and at 2.4 MPa it boils at 407.8 K. This dependence uponpressure makes it possible to produce concentrated formic acid using pressure shiftdistillation (fig. 3). Formic acid, acetic acid and water form a saddle type ternaryazeotrope boiling at 380.3 K and containing 39.3 % water, 48.2 % formic acid and 12.5% acetic acid at 101.3 kPa (Hunsmann & Simmrock 1966).

WATER

300kPa

FEED

FORMIC ACID

20 kPa

Fig. 3. Pressure shift distillation of binary mixture containing formicacid and water (Muurinen & Sohlo 1994).

The pressure shift distillation method can produce nearly pure water but cannotseparate the acids. The feed liquor is pumped to a column operated at 300 kPa producingnearly pure water as distillate. The bottom product is fed to a vacuum (20 kPa) columnproducing nearly pure formic acid as distillate. The bottom product from the vacuumcolumn is circulated to the pressurized column. When the acetic acid formed duringdelignification has to be separated, the distillate from the pressurized column can beextracted.

No method capable of separating a feed mixture containing mainly water and lessacetic acid than formic acid without any mass separating agent has been reported so far.If the feed to the separation process were to contain, for example, 60 wt-% acetic acid,20 wt-% formic acid and 20 wt-% water, the mixture could be separated into three nearlypure products in a three stage distillation plant (fig. 4) using no mass separating agents(Jahn et al. 1979).

The first and second columns are operated at atmospheric pressure. The distillate ofthe first column is nearly pure water and the bottom product is fed to the second column.The second bottom product is nearly pure acetic acid and the distillate is fed to the thirdcolumn operated at 26 kPa. The third distillate is nearly pure formic acid and the bottomproduct is circulated to the first column.

H2OCH3COOHHCOOH H2O HCOOH

CH3COOH

100kPa

100kPa

26kPa

Fig. 4. A distillation sequence for the separation of an aqueous mixturecontaining formic acid and acetic acid (Muurinen & Sohlo 1994).

3.2.2. Azeotropic distillation

In azeotropic distillation an entrainer is added to a mixture to make distillation separationfeasible. The entrainer forms an azeotrope with one of the components giving arespectable relative volatility between the azeotrope and the rest of the components.

Hunsmann and Simmrock (Hunsmann & Simmrock 1966) have proposed the use ofethyl-n-butyl ether as the entrainer in order to separate water from formic acid and aceticacid. When water has been separated, the acids may be separated using 1-chloro butane(Hunsmann & Simmrock 1966) or chloroform (Othmer & Conti 1962) as an entrainer.

Water may be separated from the acid mixture also by using n-propyl formate (Clarke& Othmer 1928), butyl formate, amyl formate, isoamyl formate (Ricard & Guinot1928), ethylene dichloride (Nakamura et al. 1966), n-propyl acetate, n-butyl acetate,ethyl acetate (Econompoulos 1978), n-hexane (Horlenko 1973) and pentane (Anon.1955) as entrainers.

Acetic acid may be separated from the ternary mixture by an esterification-azeotropicdistillation method using butanol as the esterification agent. Formic acid and water areremoved from the system as a butyl formate-water azeotropic mixture. (Xu et al. 1990).

When benzene is used as the entrainer, nearly pure acetic acid is produced byseparating formic acid and water from the mixture (Null et al. 1967).

3.2.3. Extractive distillation

An extraneous material is added to the system also in extractive distillation. Thefunction of this material, called solvent, is to enhance the relative volatility of the key

components. The solvent is normally a high-boiling material, which in some cases mayform loose chemical bonds with one of the key components.

Solvents used to separate the formic acid-acetic acid-water mixture should not havevery high boiling points. Formic acid decomposes slowly, even at low temperatures.When the temperature of formic acid (99.9 %) is raised from 313 K to 373 K, the rateconstant of the decomposition reaction increases from 700 s-1 to 4.7·105 s -1 (Barham &Clark 1951). The presence of water in the system has been found to act as a negativecatalyst on the decomposition reaction.

Solvents proposed for separating the formic acid - acetic acid - water mixture are n-methyl-2-pyrrolidone (Cohen 1986), triethanol amine (Mahapatra et al. 1988), n,n-dimethylacetamide, isophorone, sulfolane, hexanoic acid and octanoic acid (Berg et al .1990).

Lahtinen (Lahtinen 1991) has proposed the use of butyric acid (fig. 5) as the solventin the separation of this ternary mixture. The feed liquor and the solvent are introduced toa column operated at 150 kPa and producing nearly pure water as distillate. The bottomproduct is fed to the second column operated at 20 kPa and producing nearly pure formicacid as distillate. The second bottom product is fed to the third column operated at 71kPa and producing nearly pure acetic acid as distillate. The third bottom productcontaining mainly butyric acid is circulated to the first column.

H2OCH3COOHHCOOH

Makeup

H2O HCOOH CH3COOH

C3H7COOH

152kPa

20.3kPa

70.9kPa

Fig. 5. Extractive distillation of the formic acid-acetic acid-watermixture with butyric acid (Muurinen & Sohlo 1994).

N-formyl morpholine has been proposed for use as the solvent when separating waterfrom formic acid (Bulow et al. 1977). Mixtures of di-n-butyl formamide or di-n-pentylformamide with formamide, methyl formamide, dimethyl formamide or acetamide canalso be used as solvents (Bott et al. 1984). Berg (Berg 1988) has proposed the use ofethylene carbonate or propylene carbonate either alone or mixed with heptanoic acid,benzoic acid, isophorone or 2-hydroxyacetophenone. Sulfones like thiophan sulphone,

dimethyl sulphone, adiponitrile, phenyl sulphone and acetophenone are also feasiblesolvents (Berg & Yeh 1987).

Acetyl salicylic acid (Berg 1990) can be used as the solvent in order to separate formicacid from acetic acid. Butyl benzoate or ethylene carbonate can be used as diluents.Carboxylic acids in the range of hexanoic acid to neodecanoic acid can be used assolvents with or without diluents such as methyl benzoate, cetophenone andnitrobenzene (Berg 1987).

3.2.4. Liquid-liquid extraction

Liquid-liquid extraction (LLE) is a separation method in which a liquid solution (thefeed) is contacted with a second liquid (the solvent). The solvent is immiscible or nearlyimmiscible with the feed and extracts a desired component (the solute).

Several solvents capable of extracting formic acid and acetic acid from dilute aqueoussolutions have been presented: ethyl acetate (Garner et al . 1955), tri-n-octylamine(Jagirdar & Sharma 1980, Mishra & Tiwari 1988, Chen et al. 1989, Ziegenfuss &Maurer 1994, Kirsch et al. 1997, Kirsch & Maurer 1998), trioctyl-phosphine oxide(Golob et al . 1981, Ricker et al . 1979, Helsel 1977, Wardell & King 1978, Grinstead1974, Rickelton & Boyle 1988), methylisobutyl-ketone (Pilhofer and Dichtl 1986,Kirsch & Maurer 1998), 1,1,1-trichloroethane (Marr et al. 1987), tri-n-decylamine(Wojtech et al. 1986), s-butyl-di-n-octylphosphine oxide (Weferling et al. 1988) and tri-n-butyl phosphate (Shah and Tiwari 1981). Tertiary and quaternary amines have also beensuggested as solvents for acetic acid extraction (Ricker et al. 1980, Tamada et al. 1990,Tamada & King 1990a, Tamada & King 1990b, Yang et al . 1991, King 1992).Hohenschutz and co-workers (Hohenschutz et al. 1985) have proposed the use of di-n-butylformamide to extract formic acid from water and n-n-butyl-n-ethylhexylacetamidefor the extraction of acetic acid.

The Andrae group (Lorenz & Dichtl 1993) has presented a new extraction method forthe recovery of acetic acid from aqueous streams containing 5-50 wt-% acetic acid. Themain difference between this method and conventional methods is that a sidestream istaken from the distillation column recovering the solvent and recycled to the extractioncolumn. According to the inventors, this makes it possible to handle higher acetic acidconcentrations than in conventional processes. Ethyl acetate and methyltertiarybutylether can be used as solvents in this method.

According to Van Brunt (Brunt 1992) di-2,4,4-trimethylpenthyl-n-octyl phosphineoxide, tri-2,4,4-dimethylpenthyl phosphine oxide and mixtures thereof diluted with atleast one high molecular weight ketone can be used to extract acetic acid from aqueoussolutions. Mixtures with acetic acid concentrations of up to 65 wt-% can be extracted.

Gentry and Solazzo (Gentry & Solazzo 1995) have reported that an improvedextraction based recovery method for formic acid and acetic acid from aqueous streamsuses only one third of the energy of a conventional extraction system. This method usesa blend of phosphine oxides as the solvent. This blend is a high-boiling solvent whilemost commercial extraction systems use low-boiling solvents. The aqueous acid stream

is extracted counter-currently with the solvent. The co-extracted water and any lightimpurities are removed from the solvent-acid mixture by stripping. In the next stage theacids are stripped overhead from the solvent which is recycled to the extractor. This typeof design is claimed to be economic for aqueous streams containing 1-30 % acids.

3.2.5. Membrane processes

The molecule diameters of formic acid, acetic acid and water are between 3·10-10 and5.5·10-10 m (table 4). According to Rautenbach and Albrecht (Rautenbach & Albrecht1989) reverse osmosis could be used to separate molecules of these sizes. The pressureneeded for reverse osmosis separation of aqueous organic solutions is commonly highand they suggest the use of pervaporation to separate such mixtures.

Pervaporation is a membrane separation method where a membrane is employed to actas a selective barrier between the liquid mixture to be separated and the gas phase towhich the separated components are transmitted. The separation can be brought aboutusing low vacuum pressure in the gas phase, a sweeping flow of gas to remove thevapour permeate or a temperature difference.

Acetic acid-water mixtures can be separated by pervaporation using a poly-(tetrafluoroethylene) membrane (Aptel et al . 1976) but no successful experiments toseparate formic acid-water mixtures have been reported.

Zheleznov and co-workers (Zheleznov et al. 1998) have studied the use of diffusiondialysis and neutralization dialysis in order to remove organic acids from dilute aqueoussolutions. Diffusion dialysis uses water as a stripping agent and the driving force is thegradient of acid concentration. It actually transports the acid. Neutralization dialysis usesan aqueous base as dialysate. The organic acid anions of the feed are exchanged againstOH-anions. The transport rate of acetic acid anions through the membrane inneutralization dialysis is significantly higher than the transport rate of acetic acidmolecules in diffusion dialysis. The authors suggest neutralization dialysis to becombined with fermentation processes in order to improve fermenter performance.

3.2.6. Adsorption

The adsorption process is a selective concentration method for one or more components(adsorbates), that may be gases or liquids, at the surface of a microporous solid(adsorbent). Adsorption may be competitive with distillation when the relative volatilityof the key components is below 1.25 (Ruthven 1984).

Activated carbon and polymeric sorbents can be used as adsorbents in order to separateaqueous acetic acid mixtures (Baierl 1979, Kuo et al. 1987, Munson et al. 1987,Frierman et al. 1987).

3.2.7. Summary

Distillation seems to be the basic method for separating the ternary mixture formic acid-acetic acid-water. Membrane processes and adsorption can be excluded at this stagebecause no membranes or adsorbents suitable for this separation task have beenpresented.

The use of mass separating agents involves a significant risk. Small amounts of theagent will always be present in the pulping liquor. Therefore the effect of a massseparating agent on the delignification process should be carefully evaluated before aselection is made.

The availability of vapour-liquid equilibrium data guided the decision to focus theresearch on simple distillation and extractive distillation.

3.3. The effect of the feed composition on the separation ofthe formic acid-acetic acid-water mixture

In previous studies (Muurinen et al . 1993b) it has been pointed out that the smallamount of acetic acid formed during peroxyformic acid pulping (Milox) has to beremoved from the process in order to prevent the accumulation of acetic acid in thepulping liquor. The separation of this small amount of acetic acid makes the chemicalrecovery process more complicated and increases both operating and investment costs.

This study was conducted in order to find out if it is possible to lower the energyrequirements of the peroxyacid pulping process by increasing the amount of acetic acidin the pulping liquor. Solvent separation, including distillation, has been found to be thelargest energy consumer in the total process. Therefore it was decided to study the effectof the feed liquor composition on the energy consumption of the separation process. Theconcentrations of formic acid, acetic acid and water were varied from 10 % to 80 % with10 % intervals.

Simple distillation and extractive distillation were considered to be the feasibleseparation methods. Initial screening of the solvent compositions was carried out bysimulating these separation methods using shortcut methods. The minimum work ofseparation was calculated for all feed compositions in order to see if it can be used topredict which composition results in the lowest energy consumption.

3.3.1. Minimum work of separation

The minimum mechanical work required for separation of a homogeneous liquid mixtureinto pure products at constant temperature and constant pressure is (King 1986, p. 661)

W RT x xT jF jF jFj

min, ln= - ( )Â g (2)

where Wmin,T is minimum work per mole of feed,

R is gas constant,xjF is mole fraction of component j in feed and

gj F is liquid activity coefficient of component j in feed mixture.

The activity coefficients of formic acid, acetic acid and water were calculated using theUNIFAC method (Fredenslund et al. 1977, Danner & Daubert 1983) and they arepresented in table 5. The composition 26.0 % formic acid, 0.6 % acetic acid and 73.4 %water is assumed to be the composition of the feed stream to the separation section ofthe Milox recovery process (Muurinen & Sohlo 1993b)

Table 5. The activity coefficients (g i) of components (i) at various mixturecompositions.

----------------------------------------------------------------------------------------------------------------------x1 x2 x3 g1 g2 g3

----------------------------------------------------------------------------------------------------------------------0.8 0.1 0.1 1.0078 1.5818 1.07010.7 0.2 0.1 1.0302 1.3846 1.10580.7 0.1 0.2 1.0056 1.5998 1.07420.6 0.3 0.1 1.0630 1.2541 1.15290.6 0.2 0.2 1.0259 1.3966 1.11310.6 0.1 0.3 1.0029 1.6259 0.07480.5 0.4 0.1 1.1041 1.1650 1.20950.5 0.3 0.2 1.0567 1.2621 1.16370.5 0.2 0.3 1.0200 1.4135 1.11660.5 0.1 0.4 1.0004 1.6628 1.07220.4 0.5 0.1 1.1523 1.1032 1.27460.4 0.4 0.2 1.0956 1.1700 1.22400.4 0.3 0.3 1.0476 1.2728 1.17000.4 0.2 0.4 1.0130 1.4372 1.11600.4 0.1 0.5 0.9990 1.7148 1.06660.3 0.6 0.1 1.2066 1.0603 1.34790.3 0.5 0.2 1.1414 1.1057 1.29310.3 0.4 0.3 1.0832 1.1760 1.23340.3 0.3 0.4 1.0360 1.2874 1.17160.3 0.2 0.5 1.0053 1.4700 1.11150.3 0.1 0.6 0.9998 1.7872 1.05810.2 0.7 0.1 1.2669 1.0311 1.42910.2 0.6 0.2 1.1931 1.0608 1.37060.2 0.5 0.3 1.1254 1.1081 1.30580.2 0.4 0.4 1.0670 1.1839 1.23730.2 0.3 0.5 1.0223 1.3074 1.16830.2 0.2 0.6 0.9977 1.5155 1.10310.2 0.1 0.7 1.0044 1.8885 1.0474----------------------------------------------------------------------------------------------------------------------

Table 5. Cont.

----------------------------------------------------------------------------------------------------------------------x1 x2 x3 g1 g2 g3

----------------------------------------------------------------------------------------------------------------------0.1 0.8 0.1 1.3328 1.0124 1.51850.1 0.7 0.2 1.2504 1.0298 1.45640.1 0.6 0.3 1.1733 1.0600 1.38680.1 0.5 0.4 1.1043 1.1107 1.31200.1 0.4 0.5 1.0471 1.1946 1.23520.1 0.3 0.6 1.0068 1.3349 1.16000.1 0.2 0.7 0.9912 1.5784 1.09110.1 0.1 0.8 1.0149 2.0311 1.03520.121 0.002 0.877 1.0950 2.8656 1.0046----------------------------------------------------------------------------------------------------------------------

Using the activity coefficients presented in table 5, the minimum work of separation canbe calculated at 298 K using equation 2. The gas constant value 8.314 J·K-1·mol-1 wasused. The results are presented in table 6.

Table 6. Minimum work of separation (Wmin,T) at the temperature ( T ) 298 K forvarious mixtures containing formic acid (1), acetic acid (2) and water (3).

----------------------------------------------------------------------------------------------------------------------x1 x2 x3 Wmin,298K

kJ·mol-1

----------------------------------------------------------------------------------------------------------------------0.8 0.1 0.1 1.4370.7 0.2 0.1 1.7490.7 0.1 0.2 1.8250.6 0.3 0.1 1.9300.6 0.2 0.2 2.0980.6 0.1 0.3 2.0460.5 0.4 0.1 2.0160.5 0.3 0.2 2.2350.5 0.2 0.3 2.2730.5 0.1 0.4 2.1420.4 0.5 0.1 2.0150.4 0.4 0.2 2.2670.4 0.3 0.3 2.3560.4 0.2 0.4 2.3120.4 0.1 0.5 2.1250.3 0.6 0.1 1.9240.3 0.5 0.2 2.2010.3 0.4 0.3 2.322

_______________________________________________________________________

Table 6. Cont.

----------------------------------------------------------------------------------------------------------------------x1 x2 x3 Wmin,298K

kJ·mol-1

----------------------------------------------------------------------------------------------------------------------0.3 0.3 0.4 2.3270.3 0.2 0.5 2.2250.3 0.1 0.6 1.9970.2 0.7 0.1 1.7230.2 0.6 0.2 2.0230.2 0.5 0.3 2.1670.2 0.4 0.4 2.2030.2 0.3 0.5 2.1480.2 0.2 0.6 2.0040.2 0.1 0.7 1.7470.1 0.8 0.1 1.3840.1 0.7 0.2 1.6940.1 0.6 0.3 1.8550.1 0.5 0.4 1.9130.1 0.4 0.5 1.8880.1 0.3 0.6 1.7880.1 0.2 0.7 1.6110.1 0.1 0.8 1.3350.121 0.002 0.877 0.907

_______________________________________________________________________

When the value of the reference mixture is not taken into account, the averageminimum work of separation is 1.981 kJ/mol. For a highly nonideal solution, like theformic acid-acetic acid-water mixture, the UNIFAC-based method of calculating theactivity coefficients gives only a rough estimate of the real situation.

3.3.2. Vapour-liquid equilibrium data for the formic acid-acetic acid-water mixture

Lahtinen and co-workers (Lahtinen et al. 1994) have published vapour-liquid equilibriumdata at the pressures 20 kPa, 101.3 kPa and 300 kPa for the binary pairs formic acid-water, formic acid-acetic acid and acetic acid-water. The total errors of the variables wereestimated to be: temperature 0.1 K, pressure 0.1 %, liquid phase composition 0.5 % andvapour phase composition 1 %.

The vapour-liquid equilibrium data was regressed using the PRO/II Regress program(Anon 1991c). The Wilson liquid activity coefficient model was used at atmospheric andhigher pressures. It was combined with the Hayden-O’Connell model in order to take

into account the vapour phase association. The binary interaction parameters for formicacid, acetic acid and water are presented in table 7.

Table 7. The energy terms of the Wilson model for binary pairs of water, formic acidand acetic acid at the pressures 101.3 kPa and 300 kPa.

----------------------------------------------------------------------------------------------------------------------Pressure (kPa) Components ( l 1 2 - l1 1 ) ( l 2 1 - l2 2 )

----------------------------------------------------------------------------------------------------------------------300 (1) water

(2) formic acid -37.3714 432.742

300 (1) formic acid(2) acetic acid 29.9568 42.5987

300 (1) water(2) acetic acid 379.128 -17.3002

101.3 (1) water(2) formic acid -94.1944 538.953

101.3 (1) formic acid(2) acetic acid 289.184 -205.372

101.3 (1) water(2) acetic acid 1257.05 -524.041

----------------------------------------------------------------------------------------------------------------------

Table 8. Parameters of the eight parameter NRTL model for binary pairs of water,formic acid and acetic acid at the pressure 20 kPa.

----------------------------------------------------------------------------------------------------------------------Components a1 2 a2 1 b1 2 b2 1 c12 c21 a 1 2 b12

----------------------------------------------------------------------------------------------------------------------(1) formic acid(2) acetic acid -0.739 1.177 443.4 -488.8 0.10 0.10 -1.0 -0.01

(1) water(2) acetic acid 0.887 0.103 -131.3 92.6 -0.06 -0.65 1.0 -0.01

(1) water(2) formic acid -0.641 0.348 54.7 -47.3 10.88 0.10 -1.0 0.01----------------------------------------------------------------------------------------------------------------------

At the pressure 20 kPa, the best regression results were achieved using the eightparameter form of the Non-random Two Liquid (NRTL) model together with the Hayden-O’Connell model. These regression results are presented in table 8.

In order to study extractive distillation as the separation method for the formic acid-acetic acid-water system phase equilibrium data for binary pairs of the components withn-methyl-2-pyrrolidone (NMP) at 101.3 kPa were regressed using the Wilson/Hayden-O’Connell model (table 9). The data was produced by the Lahtinen group (Lahtinen etal. 1994).

Table 9. The energy terms of the Wilson model for binary pairs of NMP with water,formic acid and acetic acid at the pressure 101.3 kPa.

----------------------------------------------------------------------------------------------------------------------Components ( l 1 2 - l 11) ( l 2 1 - l2 2 )

----------------------------------------------------------------------------------------------------------------------(1) acetic acid(2) NMP -441.344 -384.949

(1) formic acid(2) NMP -907.599 854.613

(1) water(2) NMP 184.431 -102.789----------------------------------------------------------------------------------------------------------------------

The azeotropic compositions were predicted by performing equilibrium flashcalculations in order to find similar compositions for the liquid and vapour phasespresent at equilibrium. The PRO/II 3.32 Flowsheet Simulation Program (Anon. 1991d)was used for the calculations and the results are shown in table 10.

Table 10. Azeotropic compositions of the binary mixture HCOOH-H2O and the ternarymixture HCOOH-CH3COOH-H2O.

----------------------------------------------------------------------------------------------------------------------Pressure Azeotropic compositionskPa - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

HCOOH-H2O HCOOH-CH3COOH-H2O% %

----------------------------------------------------------------------------------------------------------------------20 47.0 - 53.0 30.8 - 19.2 - 50.0101.3 59.2 - 40.8 55.1 - 20.5 - 24.4300 75.2 - 24.8 75.8 - 3.5 - 20.7----------------------------------------------------------------------------------------------------------------------

JB

J Binary azeotrope

B Ternary azeotrope

1 0.8 0.6 0.4 0.2 0

0

0.2

0.4

0.6

0.8

1

1

0.8

0.6

0.4

0.2

HCOOH

CH3COOH

H2O

Fig. 6. Distillation boundaries for the HCOOH-CH3COOH-H2O mixture at

20 kPa.

J

B

J Binary azeotrope

B Ternary azeotrope

0

0.2

0.4

0.6

0.8

1

1

0.8

0.6

0.4

0.2

01 0.8 0.6 0.4 0.2 0

HCOOH

CH3COOH

H2O

Fig. 7. Distillation boundaries for the HCOOH-CH3COOH-H2O mixture at

101.3 kPa.

The azeotropic compositions were placed on ternary diagrams (fig. 6, 7 & 8). Thedistillation boundaries, which cannot be crossed by simple distillation, were drawn asstraight lines combining the two azeotropes and the ternary azeotrope with each edge ofthe diagram. According to Fien and Liu (Fien & Liu 1994), the error in approximating

true boundaries with straight lines is inconsequential, especially at the flowsheet-synthesis stage.

JB

J Binary azeotrope

B Ternary azeotrope

0

0.2

0.4

0.6

0.8

1

1

0.8

0.6

0.4

0.2

01 0.8 0.6 0.4 0.2 0

HCOOH

CH3COOH

H2O

Fig. 8. Distillation boundaries for the HCOOH-CH3COOH-H2O mixture at

300 kPa.

3.3.3. Shortcut simulation of the first separation stage

Due to the availability of phase equilibrium data, simple distillation at the pressures 20kPa, 101.3 kPa and 300 kPa and extractive distillation with n-methyl-2-pyrrolidone(NMP) at the pressure 101.3 kPa were studied as the main separation stages. They weresimulated with various feed liquor compositions using shortcut calculation methods inthe PRO/II Flowsheet Simulation Program version 3.32 (Anon. 1991d) where ageneralised Fenske method is used to predict product distributions. The minimum refluxratio is determined by the Underwood method. The number of theoretical trays, the actualreflux rates, and condenser and reboiler duties are determined using a Gilliland-typecorrelation.

Typical heuristic rules for column sequencing are (Rose 1985):- Sequences removing components one by one in the column overheads should bepreferred.- Sequences giving a more equimolar division between the products should be preferred.- If the feed mixture contains one component in excess, this component should beremoved as early as possible.

The feasible first separation stages for each feed composition were chosen usingfollowing rules:

(1) The number of equilibrium stages was limited to 100 in order to keep theinvestment costs reasonable.(2) The most plentiful component should be the product of the first separation stage inorder to keep the operating costs reasonable.(3) The molar flow of a product should be at least 10 % of the feed flow in order toconfirm the operability of the column.

If a separation method according to the simulation results did not fulfil theserequirements, it was rejected. Specifications used in simulations were:(1) The molar fraction of one component in a product is 0.98.(2) The recovery rate of one component into a product is 98 %.

3.3.3.1. Simple distillation at 20 kPa as the first separation stage

The simulation results used to either accept or reject simple distillation at 20 kPa as thefirst stage for the separation of formic acid-acetic acid-water mixtures are presented intables 11 and 12.

When the feed liquor contains 10 % formic acid, simple distillation at 20 kPa isaccepted as the first separation stage only for mixtures containing 70 % or 80 % water.The feed composition 10 % formic acid, 70 % acetic acid and 20 % water was rejectedbecause the most plentiful component (acetic acid) could not be obtained as a product ofthe column. Other feed compositions were rejected because the number of equilibriumstages was higher than 100.

Table 11. Simulation results of simple distillation at 20 kPa as the first separation stagewhen the feed contains 10 % formic acid. Formic acid is FA, acetic acid is AA andwater is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA80 % AA 1292 FA 9.97 -10 % W

10 % FA70 % AA 57 W 19.99 -20 % W

10 % FA60 % AA 1221 FA 9.98 -30 % W______________________________________________________________________

Table 11. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA50 % AA 1122 FA 10.00 -40 % W

10 % FA40 % AA 987 FA 9.99 -50 % W

10 % FA30 % AA 151 W 40.00 -60 % W

10 % FA20 % AA 64 W 30.00 +70 % W

10 % FA10 % AA 41 W 20.00 +80 % W----------------------------------------------------------------------------------------------------------------------

Table 12. Simulation results of simple distillation at 20 kPa as the first separation stagewhen the feed contains 20 % formic acid. Formic acid is FA, acetic acid is AA andwater is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA70 % AA 1250 FA 20.00 -10 % W

20 % FA60 % AA 1228 FA 20.00 -20 % W_______________________________________________________________________

Table 12. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA50 % AA 1162 FA 20.00 -30 % W

20 % FA40 % AA 1058 FA 20.00 -40 % W

20 % FA30 % AA 1755 FA 20.00 -50 % W

20 % FA20 % AA 151 W 40.00 -60 % W

20 % FA10 % AA 66 W 30.00 +70 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 20 % formic acid, simple distillation can be accepted asthe first separation stage only when the water content is 70 %. All the other feedcompositions required a number of equilibrium stages above 100.

When the feed liquor contains 30 %, 40 %, 50 %, 60 %, 70 % or 80 % formic acidsimple distillation at 20 kPa cannot be accepted as the first separation stage. All the feedcompositions required a number of equilibrium stages that was above 100.

3.3.3.2. Simple distillation at 101.3 kPa as the first separation stage

The simulation results used to either accept or reject simple distillation at 101.3 kPa asthe first stage for the separation of formic acid-acetic acid-water mixtures are presented intables 13 to 18.

Table 13. Simulation results of simple distillation at 101.3 kPa as the first separationstage when the feed contains 10 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA80 % AA 129 AA 20.00 -10 % W

10 % FA70 % AA 39 W 20.00 -20 % W

10 % FA60 % AA 48 W 30.01 -30 % W

10 % FA50 % AA 59 W 40.00 -40 % W

10 % FA40 % AA 60 W 50.00 +50 % W

10 % FA30 % AA 50 W 40.02 +60 % W

10 % FA20 % AA 40 W 30.01 +70 % W

10 % FA10 % AA 27 W 20.01 +80 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 10 % formic acid, simple distillation at 101.3 kPa isaccepted as the first separation stage for mixtures containing at least 50 % water. Thefeed composition 10 % formic acid, 80 % acetic acid and 10 % water was rejectedbecause the number of equilibrium stages was above 100. The others were rejectedbecause the most plentiful component could not be obtained as the product of thecolumn.

Table 14. Simulation results of simple distillation at 101.3 kPa as the first separationstage when the feed contains 20 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA70 % AA 74 AA 30.00 +10 % W

20 % FA60 % AA 66 W 19.99 -20 % W

20 % FA50 % AA 66 W 30.00 -30 % W

20 % FA40 % AA 64 W 40.00 +40 % W

20 % FA30 % AA 50 W 50.00 +50 % W

20 % FA20 % AA 43 W 40.01 +60 % W

20 % FA10 % AA 35 W 30.00 +70 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 20 % formic acid, simple distillation at 101.3 kPa canbe accepted as the first separation stage when the water content is 10 % or at least 40 %.The others were rejected because the most plentiful component could not be obtained asthe product of the column.

Table 15. Simulation results of simple distillation at 101.3 kPa as the first separationstage when the feed contains 30 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA 74 AA 40.00 +10 % W

30 % FA50 % AA 178 W 20.00 -20 % W

30 % FA40 % AA 123 W 30.00 -30 % W

30 % FA30 % AA 86 W 40.00 +40 % W

30 % FA20 % AA 69 W 50.00 +50 % W

30 % FA10 % AA 49 W 40.02 +60 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 30 % formic acid simple distillation at 101.3 kPa canbe accepted as the first separation stage when the water content is 10 % or higher than40 %. The other feed compositions were rejected because the number of equilibriumstages was above 100.

Table 16. Simulation results of simple distillation at 101.3 kPa as the first separationstage when the feed contains 40 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------40 % FA50 % AA 94 AA 50.00 +10 % W

40 % FA40 % AA 130 AA 40.00 -20 % W

40 % FA30 % AA 160 AA 30.00 -30 % W

40 % FA20 % AA 190 AA 20.00 -40 % W

40 % FA10 % AA 199 AA 9.99 -50 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 40 % formic acid, simple distillation at 101.3 kPa canbe accepted as the first separation stage only when the water content is 10 %. The otherfeed compositions were rejected because the number of equilibrium stages was above100.

When the feed liquor contains 50 % formic acid, simple distillation at 101.3 kPacannot be accepted as the first separation stage because the number of equilibrium stagesis above 100.

Table 17. Simulation results of simple distillation at 101.3 kPa as the first separationstage when the feed contains 60 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------60 % FA30 % AA 45 FA 41.86 +10 % W

60 % FA20 % AA 58 FA 45.15 +20 % W

60 % FA10 % AA 90 FA 37.49 +30 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 60 % formic acid, simple distillation at 101.3 kPa canbe accepted as the first separation stage for all liquor compositions.

Table 18. Simulation results of simple distillation at 101.3 kPa as the first separationstage when the feed contains 70 % or 80 % formic acid. Formic acid is FA, acetic acidis AA and water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------70 % FA20 % AA 38 FA 38.83 +10 % W

70 % FA10 % AA 50 FA 40.88 +20 % W

80 % FA10 % AA 36 FA 49.25 +10 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 70 % or 80 % formic acid, simple distillation at 101.3kPa can be accepted as the first separation stage for all liquor compositions.

3.3.3.3. Simple distillation at 300 kPa as the first separation stage

The simulation results used to either accept or reject simple distillation at 300 kPa asthe first stage for the separation of formic acid-acetic acid-water mixtures are presented intables 19 to 24.

Table 19. Simulation results of simple distillation at 300 kPa as the first separationstage when the feed contains 10 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA80 % AA 29 W 20.01 -10 % W

10 % FA70 % AA 44 W 20.00 -20 % W

10 % FA60 % AA 40 W 30.00 -30 % W

10 % FA50 % AA 37 W 40.00 -40 % W

10 % FA40 % AA 35 W 50.00 +50 % W

10 % FA30 % AA 32 W 40.00 +60 % W----------------------------------------------------------------------------------------------------------------------

Table 19. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA20 % AA 31 W 30.00 +70 % W

10 % FA10 % AA 29 W 20.01 +80 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 10 % formic acid, simple distillation at 300 kPa isaccepted as the first separation stage for mixtures containing at least 50 % water. Theother feed compositions were rejected because the most plentiful component (acetic acid)could not be obtained as a product of the column.

Table 20. Simulation results of simple distillation at 300 kPa as the first separationstage when the feed contains 20 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA70 % AA 58 AA 30.00 +10 % W

20 % FA60 % AA 63 W 20.00 -20 % W

20 % FA50 % AA 48 W 30.01 -30 % W

20 % FA40 % AA 44 W 40.00 +40 % W----------------------------------------------------------------------------------------------------------------------

Table 20. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA30 % AA 41 W 50.00 +50 % W

20 % FA20 % AA 38 W 40.00 +60 % W

20 % FA10 % AA 34 W 30.00 +70 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 20 % formic acid, simple distillation at 300 kPa can beaccepted as the first separation stage when the water content is 10 % or higher than 40%. The other feed compositions were rejected because the most plentiful component(acetic acid) could not be obtained as a product of the column.

Table 21. Simulation results of simple distillation at 300 kPa as the first separationstage when the feed contains 30 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA 65 AA 40.00 +10 % W

30 % FA50 % AA 79 W 20.00 -20 % W

30 % FA40 % AA 68 W 30.00 -30 % W----------------------------------------------------------------------------------------------------------------------

Table 21. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA30 % AA 58 W 40.00 +40 % W

30 % FA20 % AA 48 W 50.00 +50 % W

30 % FA10 % AA 44 W 40.01 +60 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 30 % formic acid, simple distillation at 300 kPa can beaccepted as the first separation stage when the water content is 10 % or higher than 40%. The other feed compositions were rejected because the most plentiful component(acetic acid) could not be obtained as a product of the column.

Table 22. Simulation results of simple distillation at 300 kPa as the first separationstage when the feed contains 40 % formic acid. Formic acid is FA, acetic acid is AAand water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------40 % FA50 % AA 71 AA 50.00 +10 % W

40 % FA40 % AA 114 W 20.00 -20 % W

40 % FA30 % AA 86 W 30.00 -30 % W----------------------------------------------------------------------------------------------------------------------

Table 22. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------40 % FA20 % AA 75 W 40.00 +40 % W

40 % FA10 % AA 64 W 50.00 +50 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 40 % formic acid, simple distillation at 101.3 kPa canbe accepted as the first separation stage when the water content is 10 % or higher than40 %. The other feed compositions were rejected because the most plentiful component(acetic acid) could not be obtained as a product of the column.

When the feed liquor contains 50 % or 60 % formic acid, simple distillation at 300kPa cannot be accepted as the first separation stage because the most plentifulcomponent (formic acid) cannot be obtained as a product of the column.

Table 23. Simulation results of simple distillation at 300 kPa as the first separationstage when the feed contains 70 % or 80 % formic acid. Formic acid is FA, acetic acidis AA and water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------70 % FA20 % AA 105 AA 20.00 -10 % W

70 % FA10 % AA 128 AA 9.99 -20 % W

80 % FA10 % AA 57 FA 10.00 +10 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 70 % formic acid, simple distillation at 300 kPa cannotbe accepted as the first separation stage because the most plentiful component (formicacid) cannot be obtained as a product of the column. When the liquor contains 80 %formic acid, simple distillation at 300 kPa is an acceptable first separation stage.

3.3.3.4. Extractive distillation as the first separation stage

The simulation results used to either accept or reject extractive distillation with n-methyl-2-pyrrolidone (NMP) at 101.3 kPa as the first stage for the separation of formic acid-acetic acid-water mixtures are presented in tables 24 to 27. The amount of NMP fed tothe extractive distillation column is twice the molar flow of the feed. The ratiosolvent/nonsolvent should be as low as possible to avoid excess costs (Fair 1987).

Table 24. Simulation results of extractive distillation with NMP at 101.3 kPa as thefirst separation stage when the feed contains 10 % formic acid. Formic acid is FA,acetic acid is AA and water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA80 % AA 14 W 3.33 -10 % W

10 % FA70 % AA 13 W 6.67 -20 % W

10 % FA60 % AA 13 W 10.00 -30 % W

10 % FA50 % AA 12 W 13.33 -40 % W

10 % FA40 % AA 13 W 16.67 +50 % W_______________________________________________________________________

Table 24. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA30 % AA 13 W 19.98 +60 % W

10 % FA20 % AA 13 W 23.31 +70 % W

10 % FA10 % AA 13 W 26.64 +80 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 10 % formic acid, extractive distillation with NMP at101.3 kPa is accepted as the first separation stage for mixtures containing at least 50 %water. When the water content of the feed liquor is below 50 % the most plentifulcomponent (acetic acid) cannot be obtained as a product of the column.

Table 25. Simulation results of extractive distillation with NMP at 101.3 kPa as thefirst separation stage when the feed contains 20 % formic acid. Formic acid is FA,acetic acid is AA and water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA70 % AA 14 W 3.33 -10 % W

20 % FA60 % AA 13 W 6.67 -20 % W

20 % FA50 % AA 13 W 10.00 -30 % W----------------------------------------------------------------------------------------------------------------------

Table 25. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA40 % AA 12 W 13.33 +40 % W

20 % FA30 % AA 13 W 16.67 +50 % W

20 % FA20 % AA 13 W 19.98 +60 % W

20 % FA10 % AA 13 W 23.31 +70 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 20 % formic acid, simple distillation at 300 kPa can beaccepted as the first separation stage when the water content is at least 40 %. When thewater content of the feed liquor is below 40 %, the most plentiful component (aceticacid) cannot be obtained as a product of the column.

Table 26. Simulation results of extractive distillation with NMP at 101.3 kPa as thefirst separation stage when the feed contains 30 % formic acid. Formic acid is FA,acetic acid is AA and water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA 14 W 3.33 -10 % W

30 % FA50 % AA 13 W 6.67 -20 % W_______________________________________________________________________

Table 26. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA40 % AA 13 W 10.00 -30 % W

30 % FA30 % AA 13 W 13.33 +40 % W

30 % FA20 % AA 13 W 16.67 +50 % W

30 % FA10 % AA 13 W 19.98 +60 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 30 % formic acid, extractive distillation with NMP at101.3 kPa can be accepted as the first separation stage when the water content is at least40 %. When the water content of the feed liquor is below 40 %, the most plentifulcomponent (acetic acid) cannot be obtained as a product of the column.

Table 27. Simulation results of extractive distillation with NMP at 101.3 kPa as thefirst separation stage when the feed contains 40 % formic acid. Formic acid is FA,acetic acid is AA and water is W.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------40 % FA50 % AA 14 W 3.33 -10 % W

40 % FA40 % AA 13 W 6.67 -20 % W_______________________________________________________________________

Table 27. Cont.

----------------------------------------------------------------------------------------------------------------------Feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------40 % FA30 % AA 13 W 10.00 -30 % W

40 % FA20 % AA 13 W 13.33 +40 % W

40 % FA10 % AA 13 W 16.67 +50 % W----------------------------------------------------------------------------------------------------------------------

When the feed liquor contains 40 %, 50 %, 60 %, 70 % or 80 % formic acid, simpledistillation at 101.3 kPa can be accepted as the first separation stage when the watercontent is at least 40 %. When the water content of the feed liquor is below 40 %, themost plentiful component (formic acid or acetic acid) cannot be obtained as a product ofthe column.

3.3.3.5. The first separation stage for the peroxyformic acid pulpingprocess

The composition of the liquor fed to the separation sequence in the peroxyformic acidpulping process has been estimated to be 12.1 % formic acid, 0.2 % acetic acid and 87.7% water. Simple distillation at the pressures 20, 101.3 and 300 kPa and extractivedistillation with n-methyl-2-pyrrolidone (NMP) at 101.3 kPa were simulated as the firstseparation stage for this feed composition. Shortcut calculation methods were used. Theresults are shown in table 28.

All four separation methods seem to be feasible first separation stages in theperoxyformic acid pulping process.

Table 28. Simulation results for the first separation stage in the peroxyformic acidpulping process. SD is simple distillation and ED is extractive distillation with NMP.

----------------------------------------------------------------------------------------------------------------------Separation number of trays Product Lowest product Accepted(+)/method and at 1.2·Rmin flow/feed flow rejected(-)

pressure (kPa) %----------------------------------------------------------------------------------------------------------------------SD 20 27 W 12.30 +SD 101.3 21 W 12.30 +SD 300 25 W 12.30 +ED 101.3 13 W 29.21 +----------------------------------------------------------------------------------------------------------------------

3.3.3.6. Summary of the simulations of the first separation stage

Feasible separation methods for the feed compositions studied are listed in tables 29 to35.

Simple distillation at 20 kPa seems to be a feasible first separation stage only whenthe water content of the feed is 70 % or higher. Water contents below 10 % and above40 % seem to favour the use of simple distillation at atmospheric pressure, or at 300kPa. Extractive distillation may be used at high water contents. When the feed contains50 % formic acid no feasible separation methods were found.

Table 29. Feasible first separation stages when the feed contains 10 % formic acid. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------10 80 10 -10 70 20 -10 60 30 -10 50 40 -10 40 50 SD101.3,SD300,ED101.310 30 60 SD101.3,SD300,ED101.310 20 70 SD20,SD101.3,SD300,ED101.310 10 80 SD20,SD101.3,SD300,ED101.3

----------------------------------------------------------------------------------------------------------------------

Table 30. Feasible first separation stages when the feed contains 20 % formic acid. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------20 70 10 SD101.3,SD 30020 60 20 -20 50 30 -20 40 40 SD101.3,SD300,ED 101.320 30 50 SD101.3,SD300,ED101.320 20 60 SD101.3,SD300,ED101.320 10 70 SD20,SD101.3,SD300,ED101.3

----------------------------------------------------------------------------------------------------------------------

Table 31. Feasible first separation stages when the feed contains 30 % formic acid. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------30 60 10 SD 101.3, SD 30030 50 20 -30 40 30 -30 30 40 SD 101.3, SD 300, ED 101.330 20 50 SD 101.3, SD 300, ED 101.330 10 60 SD 101.3, SD 300, ED 101.3

----------------------------------------------------------------------------------------------------------------------

Table 32. Feasible first separation stages when the feed contains 40 % formic acid. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------40 50 10 SD 101.3, SD 30040 40 20 -40 30 30 -40 20 40 SD 300, ED 101.340 10 50 SD 300, ED 101.3

----------------------------------------------------------------------------------------------------------------------

Table 33. Feasible first separation stages when the feed contains 50 % formic acid. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------50 40 10 -50 30 20 -50 20 30 -50 10 40 -

----------------------------------------------------------------------------------------------------------------------

Table 34. Feasible first separation stages when the feed contains 60 % formic acid. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------60 30 10 SD 101.3

60 20 20 SD 101.3

60 10 30 SD 101.3----------------------------------------------------------------------------------------------------------------------

Table 35. Feasible first separation stages when the feed contains 70 % or 80 % formicacid. FA is formic acid, AA is acetic acid, W is water, SD is simple distillation and EDis extractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methodsFA AA W and pressures (kPa)% % %

----------------------------------------------------------------------------------------------------------------------70 20 10 SD 101.3

70 10 20 SD 101.3

80 10 10 SD 101.3, SD 300----------------------------------------------------------------------------------------------------------------------

The fact that no feasible separation methods were found for some feed compositionsdoes not mean that these compositions are impossible to separate. The rejection criteriawere chosen particularly in order to reject those separation methods and feedcompositions that are likely to result in high separation energy consumptions andinvestment costs, when compared with other methods and feed compositions.

All four separation methods seem to be feasible first stages for the estimated feedcomposition of the separation sequence of the peroxyformic acid pulping process.

3.3.4. Shortcut simulation of the second separation stage

Simple distillation at the pressures 20 kPa, 101.3 kPa and 300 kPa and extractivedistillation with n-methyl-2-pyrrolidone (NMP) at the pressure 101.3 kPa were studiedas potential second separation stages. They were simulated using shortcut calculationmethods in the PRO/II Flowsheet Simulation Program version 3.32 (Anon. 1991d)where a generalised Fenske method is used to predict product distributions. Theminimum reflux ratio is determined using the Underwood method. The number oftheoretical trays, the actual reflux rates, and condenser and reboiler duties are determinedusing a Gilliland-type correlation.

The feasible second separation stages for each feed composition were chosen using thefollowing rules:(1) The number of equilibrium stages was limited to 100 in order to keep theinvestment costs reasonable.(2) The most plentiful component should be the product of the first separation stage inorder to keep the operating costs reasonable.(3) The molar flow of a product should be at least 10 % of the feed flow in order toconfirm the operability of the column.

If a separation method according to the simulation results did not fulfil theserequirements, it was rejected. Extractive distillation with NMP always removes water asthe distillate. Therefore it was only considered as the separation method for those feedstreams with water as the most plentiful component. Only simple distillation wasconsidered as the second separation stage following the extractive distillation (Cohen1986). Specifications used in the simulations were:(1) The molar fraction of one component in a product is 0.98.(2) The recovery rate of one component into a product is 98 %.

3.3.4.1. Simple distillation at 20 kPa as the second separation stage

The simulation results used to either accept or reject simple distillation at 20 kPa as thesecond separation stage following the accepted first stages for the separation of formicacid-acetic acid-water mixtures are presented in tables 36 and 37.

Table 36. Simulation results of simple distillation at 20 kPa as the second separationstage when simple distillation at 101.3 kPa is an accepted first separation stage.Formic acid is FA, acetic acid is AA and water is W. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA 1162 AA (+) 20.00 -50 % W

10 % FA30 % AA 1210 AA (+) 24.99 -60 % W

10 % FA20 % AA 1188 FA (-) 33.29 -70 % W

10 % FA10 % AA 1156 FA (+) 49.08 -80 % W

20 % FA70 % AA 369 FA (+) 35.23 -10 % W_______________________________________________________________________

Table 36. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA40 % AA 959 AA (+) 33.30 -40 % W

20 % FA30 % AA 935 FA (-) 39.86 -50 % W

20 % FA20 % AA 911 FA (+) 49.64 -60 % W

20 % FA10 % AA 875 FA (+) 35.03 -70 % W

30 % FA60 % AA 51 FA (+) 26.40 +10 % W

30 % FA30 % AA 918 FA (+) 49.20 -40 % W

30 % FA20 % AA 906 FA (+) 40.70 -50 % W

30 % FA10 % AA 811 FA (+) 26.71 -60 % W

40 % FA50 % AA NO SOLUTION WAS FOUND10 % W

60 % FA30 % AA 939 FA (-) 31.87 -10 % W_______________________________________________________________________

Table 36. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------60 % FA20 % AA 877 FA (-) 27.86 -20 % W

60 % FA10 % AA 702 FA (-) 36.59 -30 % W

70 % FA20 % AA 929 FA (+) 48.28 -10 % W

70 % FA10 % AA 727 FA (-) 28.20 -20 % W

80 % FA10 % AA 810 FA (+) 39.43 -10 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 20 kPa can be accepted as the second separation stage aftersimple distillation at 101.3 kPa only when the original feed contains 30 % formic acid,60 % acetic acid and 10 % water.

Table 37. Simulation results of simple distillation at 20 kPa as the second separationstage when simple distillation at 300 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA 1089 FA (-) 19.46 -50 % W_______________________________________________________________________

Table 37. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA30 % AA 1071 FA (-) 24.38 -60 % W

10 % FA20 % AA 1038 FA (-) 32.53 -70 % W

10 % FA10 % AA 1021 FA (+) 48.03 -80 % W

20 % FA70 % AA 375 FA (+) 35.33 -10 % W

20 % FA40 % AA 963 FA (-) 32.73 -40 % W

20 % FA30 % AA 934 FA (-) 39.32 -50 % W

20 % FA20 % AA 911 FA (+) 49.15 -60 % W

20 % FA10 % AA 873 FA (+) 34.80 -70 % W

30 % FA60 % AA 51 FA (+) 26.48 +10 % W

30 % FA30 % AA 918 FA (+) 49.28 -40 % W_______________________________________________________________________

Table 37. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA20 % AA 908 FA (+) 41.02 -50 % W

30 % FA10 % AA 358 FA (+) 01.50 -60 % W

40 % FA50 % AA 36 FA (+) 20.78 +10 % W

40 % FA20 % AA 852 FA (+) 33.88 -40 % W

40 % FA10 % AA 821 FA (-) 20.74 -50 % W

80 % FA10 % AA 770 FA (+) 22.08 -10 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 20 kPa can be accepted as the second separation stage aftersimple distillation at 300 kPa only when the original feed contains 30 % formic acid, 60% acetic acid and 10 % water or 40 % formic acid, 50 % acetic acid and 10 % water.

3.3.4.2. Simple distillation at 101.3 kPa as the second separation stage

The simulation results used to either accept or reject simple distillation at 101.3 kPa asthe second separation stage following the accepted first stages for the separation offormic acid-acetic acid-water mixtures are presented in tables 38, 39 and 40.

Table 38. Simulation results of simple distillation at 101.3 kPa as the secondseparation stage when simple distillation at 20 kPa is an accepted first separationstage. Formic acid is FA, acetic acid is AA and water is W. + is accepted and - isrejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA20 % AA 39 AA (+) 34.20 +70 % W

10 % FA10 % AA 124 AA (+) 48.95 -80 % W

20 % FA10 % AA 80 FA (+) 03.47 -70 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 101.3 kPa can be accepted as the second separation stage aftersimple distillation at 20 kPa only when the original feed contains 10 % formic acid, 20% acetic acid and 70 % water.

Table 39. Simulation results of simple distillation at 101.3 kPa as the secondseparation stage when simple distillation at 300 kPa is an accepted first separationstage. Formic acid is FA, acetic acid is AA and water is W. + is accepted and - isrejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA 32 AA (+) 21.22 +50 % W

10 % FA30 % AA 36 AA (+) 26.68 +60 % W_______________________________________________________________________

Table 39. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA20 % AA 42 AA (+) 35.47 +70 % W

10 % FA10 % AA 169 AA (-) 47.28 -80 % W

20 % FA70 % AA 144 FA (+) 35.30 -10 % W

20 % FA40 % AA 36 AA (+) 33.38 +40 % W

20 % FA30 % AA 41 AA (+) 40.18 +50 % W

20 % FA20 % AA 81 FA (+) 49.65 +60 % W

20 % FA10 % AA 49 FA (+) 34.80 +70 % W

30 % FA60 % AA 65 FA (+) 26.18 +10 % W

30 % FA30 % AA 53 FA (+) 49.95 +40 % W

30 % FA20 % AA 71 FA (+) 39.94 +50 % W______________________________________________________________________

Table 39. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA10 % AA 51 FA (+) 26.32 +60 % W

40 % FA50 % AA 22 FA (+) 22.56 +10 % W

40 % FA20 % AA 30 FA (+) 37.30 +40 % W

40 % FA10 % AA 26 FA (+) 20.62 +50 % W

80 % FA10 % AA 36 FA (+) 49.58 +10 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 101.3 kPa as the second separation stage after simpledistillation at 300 kPa was rejected only when the original feed contains 10 % formicacid, 10 % acetic acid and 80 % water or 20 % formic acid, 70 % acetic acid and 10 %water.

Simple distillation at 101.3 kPa can be accepted as the second separation stage afterextractive distillation at 101.3 kPa only when the original feed contains 30 % formicacid and 20 or 30 % acetic acid, or when the feed contains 40 % formic acid, 20 % aceticacid and 40 % water.

Table 40. Simulation results of simple distillation at 101.3 kPa as the secondseparation stage when extractive distillation with NMP at 101.3 kPa is an acceptedfirst separation stage. Formic acid is FA, acetic acid is AA and water is W. + isaccepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA 108 NMP (+) 21.14 -50 % W

10 % FA30 % AA 121 NMP (+) 18.17 -60 % W

10 % FA20 % AA 238 NMP (+) 14.86 -70 % W

10 % FA10 % AA 188 NMP (+) 06.67 -80 % W

20 % FA40 % AA 205 NMP (+) 24.01 -40 % W

20 % FA30 % AA 218 NMP (+) 21.34 -50 % W

20 % FA20 % AA 246 NMP (+) 18.32 -60 % W

20 % FA10 % AA 1221 NMP (+) 14.95 -70 % W

30 % FA30 % AA 56 NMP (+) 24.31 +40 % W_______________________________________________________________________

Table 40. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------30 % FA20 % AA 87 NMP (+) 21.51 +50 % W

30 % FA10 % AA 791 NMP (+) 18.41 -60 % W

40 % FA20 % AA 70 NMP (+) 24.52 +40 % W

40 % FA10 % AA 140 NMP (+) 21.62 -50 % W----------------------------------------------------------------------------------------------------------------------

3.3.4.3. Simple distillation at 300 kPa as the second separation stage

The simulation results used to either accept or reject simple distillation at 300 kPa asthe second separation stage following the accepted first stages for the separation offormic acid-acetic acid-water mixtures are presented in tables 41 and 42.

Table 41. Simulation results of simple distillation at 300 kPa as the second separationstage when simple distillation at 20 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA20 % AA 46 AA (+) 34.20 +70 % W_______________________________________________________________________

Table 41. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA10 % AA 51 AA (+) 48.95 +80 % W

20 % FA10 % AA 64 AA (-) 32.97 -70 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 300 kPa can be accepted as the second separation stage aftersimple distillation at 20 kPa when the original feed contains 10 % formic acid and 10 or20 % acetic acid.

Table 42. Simulation results of simple distillation at 300 kPa as the second separationstage when simple distillation at 101.3 kPa is an accepted first separation stage.Formic acid is FA, acetic acid is AA and water is W. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA 20 AA (+) 19.52 +50 % W

10 % FA30 % AA 25 AA (+) 25.29 +60 % W

10 % FA20 % AA 32 AA (+) 40.72 +70 % W

10 % FA10 % AA 67 AA (-) 46.63 -80 % W_______________________________________________________________________

Table 42. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------20 % FA70 % AA 163 AA (-) 01.87 -10 % W

20 % FA40 % AA 44 AA (+) 33.78 +40 % W

20 % FA30 % AA 50 AA (+) 41.14 +50 % W

20 % FA20 % AA 54 AA (-) 48.86 -60 % W

20 % FA10 % AA 65 AA (-) 32.57 -70 % W

30 % FA60 % AA 165 AA (-) 01.18 -10 % W

30 % FA30 % AA 52 AA (+) 49.83 +40 % W

30 % FA20 % AA 56 AA (-) 39.92 -50 % W

30 % FA10 % AA 73 AA (-) 24.89 -60 % W

40 % FA50 % AA 144 FA (+) 37.92 -10 % W_______________________________________________________________________

Table 42. Cont.

----------------------------------------------------------------------------------------------------------------------Original feed number of trays Product Lowest product Accepted(+)/composition at 1.2·Rmin flow/feed flow rejected(-)

%----------------------------------------------------------------------------------------------------------------------60 % FA30 % AA 76 W (-) 17.13 -10 % W

60 % FA20 % AA 47 W (+) 36.06 +20 % W

60 % FA10 % AA 48 W (+) 47.42 +30 % W

70 % FA20 % AA 185 W (-) 16.32 -10 % W

70 % FA10 % AA 41 W (+) 48.43 +20 % W

80 % FA10 % AA 305 W (-) 20.26 -10 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 300 kPa can be accepted as the second separation stage aftersimple distillation at 101.3 kPa when the original feed contains 10 % formic acid and20...40 % acetic acid, or when it contains 20 % formic acid and 30 or 40 % acetic acid,or when it contains 30 % formic acid, 30 % acetic acid and 40 % water, or when itcontains 60 % formic acid and 10 or 20 % acetic acid, or when it contains 70 % formicacid, 10 % acetic acid and 20 % water.

3.3.4.4. Extractive distillation at 101.3 kPa as the second separationstage

The first separation stages did not result in a water rich product needing further treatmentwith any feed composition or separation method that was studied. Therefore extractivedistillation with NMP at 101.3 kPa was not considered as a potential second separationstage.

3.3.4.5. The second separation stages for the peroxyformic acidpulping process

The composition of the liquor fed to separation sequence in the peroxyformic acidpulping process has been estimated to be 12.1 % formic acid, 0.2 % acetic acid and 87.7% water. Simple distillation at the pressures 20, 101.3 and 300 kPa and extractivedistillation with n-methyl-2-pyrrolidone (NMP) at 101.3 kPa were simulated as thesecond separation stage for this first stage feed composition. Shortcut calculationmethods were used. Results are shown in tables 43 to 46.

Table 43. Simulation results for the second separation stage in the peroxyformic acidpulping process when simple distillation at 20 kPa is the first stage. SD is simpledistillation and ED is extractive distillation with NMP. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Method and 1.2 · minimum Product Lowest product Accepted(+)/pressure number of trays flow/feed flows rejected(-)(kPa) %----------------------------------------------------------------------------------------------------------------------SD 101.3 24 FA (+) 07.24 -SD 300 22 W (-) 05.93 -----------------------------------------------------------------------------------------------------------------------

The separation methods considered in this study are not feasible second stagesfollowing simple distillation at 20 kPa in the separation sequence of the peroxyformicacid process. Extractive distillation was not considered because water was not the mostplentiful component in the feed.

Table 44. Simulation results for the second separation stage in the peroxyformic acidpulping process when simple distillation at 101.3 kPa is the first stage. SD is simpledistillation and ED is extractive distillation with NMP. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Method and 1.2 · minimum Product Lowest product Accepted(+)/pressure number of trays flow/feed flows rejected(-)(kPa) %----------------------------------------------------------------------------------------------------------------------SD 20 27 FA (+) 09.19 -SD 300 20 W (-) 07.64 -----------------------------------------------------------------------------------------------------------------------

No separation method considered was a feasible second stage following simpledistillation at 101.3 kPa when the selection criteria presented in chapter 3.3.3 wereapplied. Extractive distillation was not considered because water was not the mostplentiful component in the feed.

Table 45. Simulation results for the second separation stage in the peroxyformic acidpulping process when simple distillation at 300 kPa is the first stage. SD is simpledistillation and ED is extractive distillation with NMP. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Method and 1.2 · minimum Product Lowest product Accepted(+)/pressure number of trays flow/feed flows rejected(-)(kPa) %----------------------------------------------------------------------------------------------------------------------SD 20 26 FA (+) 08.05 -SD 101.3 44 W (-) 06.59 -----------------------------------------------------------------------------------------------------------------------

The separation methods considered in this study are not feasible second stages followingsimple distillation at 300 kPa in the separation sequence of the peroxyformic acidprocess. Extractive distillation was not considered because water was not the mostplentiful component in the feed.

Table 46. Simulation results for the second separation stage in the peroxyformic acidpulping process when extractive distillation with NMP at 101.3 kPa is the first stage.SD is simple distillation and ED is extractive distillation with NMP. + is accepted and -is rejected.

----------------------------------------------------------------------------------------------------------------------Method and 1.2 · minimum Product Lowest product Accepted(+)/pressure number of trays flow/feed flows rejected(-)(kPa) %----------------------------------------------------------------------------------------------------------------------SD 101.3 319 FA (+) 07.92 -----------------------------------------------------------------------------------------------------------------------

Even simple distillation at 101.3 kPa following extractive distillation seems to be anunfeasible second separation stage.

No separation sequence for the peroxyformic acid process was, despite the results,rejected because in the actual process the specifications for the distillation columns arenot necessarily as strict as in this study. With less strict specifications, the sequencesmight be accepted. Another reason for not rejecting any sequence was the fact that thereference process could not be totally rejected at this stage of the study.

3.3.4.6. Summary of the simulation results for the second separationstage

Feasible combinations of two separation stages for the feed compositions studied arelisted in table 47.

Table 47. Feasible first two separation stages for various feed compositions. FA isformic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methods and pressures (kPa)

-------------------------------------------- ----------------------------------------------------------------------FA AA W 1. stage 2. stage% % %----------------------------------------------------------------------------------------------------------------------10 20 70 SD 20 SD 101.310 20 70 SD 20 SD 30010 20 70 SD 101.3 SD 30010 20 70 SD 300 SD 101.310 40 50 SD 101.3 SD 300_______________________________________________________________________

Table 47. Cont.

---------------------------------------------------------------------------------------------------------------------- Feed composition Feasible separation methods and pressures (kPa)

-------------------------------------------- ----------------------------------------------------------------------FA AA W 1. stage 2. stage% % %----------------------------------------------------------------------------------------------------------------------10 40 50 SD 300 SD 101.310 30 60 SD 101.3 SD 30010 30 60 SD 300 SD 101.310 10 80 SD 20 SD 30020 40 40 SD 101.3 SD 30020 40 40 SD 300 SD 101.320 30 50 SD 101.3 SD 30020 30 50 SD 300 SD 101.320 20 60 SD 300 SD 101.320 10 70 SD 300 SD 101.330 60 10 SD 101.3 SD 2030 60 10 SD 300 SD 2030 60 10 SD 300 SD 101.330 30 40 SD 101.3 SD 30030 30 40 SD 300 SD 101.330 30 40 ED 101.3 SD 101.330 20 50 SD 300 SD 101.330 20 50 ED 101.3 SD 101.330 10 60 SD 300 SD 101.340 50 10 SD 300 SD 2040 50 10 SD 300 SD 101.340 20 40 SD 300 SD 101.340 20 40 ED 101.3 SD 101.340 10 50 SD 300 SD 101.360 20 20 SD 101.3 SD 30060 10 30 SD 101.3 SD 30070 10 20 SD 101.3 SD 30080 10 10 SD 300 SD 101.3----------------------------------------------------------------------------------------------------------------------

Simple distillation at 20 kPa seems to be a feasible second separation stage when thefeed to the first stage contains 30 to 40 % formic acid and 10 % water. Distillation atatmospheric pressure or at 300 kPa are the most common separation methods feasiblefor use as the first two stages.

All possible pairs of the four separation methods were accepted as potential separationsequences for the peroxyformic acid pulping process.

3.3.5. Shortcut simulation of the third separation stage

Simple distillation at the pressures 20 kPa, 101.3 kPa and 300 kPa and extractivedistillation with n-methyl-2-pyrrolidone (NMP) at the pressure 101.3 kPa were studiedas potential third separation stages. They were simulated using shortcut calculationmethods in the PRO/II Flowsheet Simulation Program version 3.32 (Anon. 1991d)where a generalised Fenske method is used to predict product distributions. Theminimum reflux ratio is determined using the Underwood method. The number oftheoretical trays, the actual reflux rates, and condenser and reboiler duties are determinedusing a Gilliland-type correlation.

The feasible third separation stages for each feed composition were chosen using thefollowing rules:(1) The number of equilibrium stages was limited to 100 in order to keep the investmentcosts reasonable.(2) The most plentiful component should be the product of the separation stage.

For the third separation stage it was no longer required that the flow of a productshould be at least 10 % of the feed flow. The strict specifications used in the simulationof the first and second stages result in low flow rates of some components to the thirdstage. In the real separation process, the recovery rates may be lower, resulting in higherflow rates in the following stages.

If a separation method according to the simulation results did not fulfil therequirements, it was rejected. Extractive distillation with NMP always removes water asthe distillate. Therefore it was only considered as the separation method for those feedstreams with water as the most plentiful component. The specifications used insimulations were:(1) The molar fraction of one component in a product is 0.98.(2) The recovery rate of one component into a product is 98 %.

3.3.5.1 Simple distillation at 20 kPa as the third separation stage

The simulation results used to either accept or reject simple distillation at 20 kPa as thethird separation stage following the accepted first and second stages for the separation offormic acid-acetic acid-water mixtures are presented in table 48.

Simple distillation at 20 kPa is not an acceptable third separation stage when simpledistillation at 101.3 kPa is the first stage, because very high numbers of equilibriumstages are required for the separation.

Simple distillation at 20 kPa can be accepted as the third separation stage after simpledistillation at 300 kPa as the first stage and simple distillation at 101.3 kPa as thesecond stage only when the original feed contains 20 % formic acid, 20 % acetic acid and60 % water or 40 % formic acid, 50 % acetic acid and 10 % water.

Table 48. Simulation results of simple distillation at 20 kPa as the third separationstage when simple distillation at 300 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA SD 101.3 711 FA (+) NO -50 % W

10 % FA30 % AA SD 101.3 652 FA (+) NO -60 % W

10 % FA20 % AA SD 101.3 529 FA (+) NO -70 % W

20 % FA40 % AA SD 101.3 561 FA (+) NO -40 % W

20 % FA30 % AA SD 101.3 478 FA (+) NO -50 % W

20 % FA20 % AA SD 101.3 A THIRD SEPARATION STAGE IS NOT NEEDED60 % W

20 % FA10 % AA SD 101.3 793 FA (-) YES -70 % W

30 % FA60 % AA SD 101.3 NO SOLUTION WAS FOUND10 % W

30 % FA30 % AA SD 101.3 A THIRD SEPARATION STAGE IS NOT NEEDED40 % W_______________________________________________________________________

Table 48. Cont.----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------30 % FA20 % AA SD 101.3 A THIRD SEPARATION STAGE IS NOT NEEDED50 % W

30 % FA10 % AA SD 101.3 NO SOLUTION WAS FOUND60 % W

40 % FA50 % AA SD 101.3 44 FA (+) YES +10 % W

40 % FA20 % AA SD 101.3 945 FA (-) YES -40 % W

40 % FA10 % AA SD 101.3 836 FA (+) YES -50 % W

80 % FA10 % AA SD 101.3 813 FA (+) YES -10 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 20 kPa is not an acceptable third separation stage when it hasbeen used also as the first stage, or when extractive distillation with n-methyl-2-pyrrolidone is used as the first stage, because the number of equilibrium stages neededfor the separation is above 100.

3.3.5.2. Simple distillation at 101.3 kPa as the third separation stage

The simulation results used to either accept or reject simple distillation at 101.3 kPa asthe third separation stage following the accepted first and second stages for the separationof formic acid-acetic acid-water mixtures are presented in tables 49...51.

Table 49. Simulation results of simple distillation at 101.3 kPa as the third separationstage when simple distillation at 20 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------10 % FA20 % AA SD 300 13 FA (+) NO +70 % W

10 % FA10 % AA SD 300 11 FA (+) NO +80 % W----------------------------------------------------------------------------------------------------------------------

Simple distillation at 101.3 kPa can be accepted as the third separation stage whensimple distillation at 20 kPa is the first stage, simple distillation at 300 kPa is thesecond stage and the original feed contains 10 % formic acid and 10 or 20 % acetic acid.

Simple distillation at 101.3 kPa can be accepted as the third separation stage aftersimple distillation at 300 kPa and 20 kPa as the first and second stages when theoriginal feed contains 30 % formic acid, 60 % acetic acid and 10 % water or 40 % formicacid, 50 % acetic acid and 10 % water.

Simple distillation at 101.3 kPa is an acceptable third separation stage for all thoseoriginal feed compositions for which simple distillation at 101.3 kPa can be accepted asthe first stage and a feasible second stage is found.

When extractive distillation with n-methyl-2-pyrrolidone is used as the first separationstage the second stage is always simple distillation at 101.3 kPa. Therefore simpledistillation at 101.3 kPa was not considered as the third separation stage.

Table 50. Simulation results of simple distillation at 101.3 kPa as the third separationstage when simple distillation at 300 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA SD 20 14 W (+) NO +10 % W

40 % FA50 % AA SD 20 15 W (+) NO +10 % W----------------------------------------------------------------------------------------------------------------------

Table 51. Simulation results of simple distillation at 101.3 kPa as the third separationstage when simple distillation at 101.3 kPa is an accepted first separation stage.Formic acid is FA, acetic acid is AA and water is W, SD is simple distillation and EDis extractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA SD 300 33 AA (+) YES +50 % W

10 % FA30 % AA SD 300 38 AA (+) YES +60 % W

10 % FA20 % AA SD 300 52 FA (+) NO +70 % W

20 % FA40 % AA SD 300 23 FA (+) NO +40 % W_______________________________________________________________________

Table 51. Cont.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------20 % FA30 % AA SD 300 9 FA (+) NO +50 % W

30 % FA60 % AA SD 20 14 W (+) NO +10 % W

30 % FA30 % AA SD 300 14 FA (+) NO +40 % W

60 % FA20 % AA SD 300 48 AA (+) NO +20 % W

60 % FA10 % AA SD 300 31 FA (+) YES +30 % W

70 % FA10 % AA SD 300 48 FA (+) YES +20 % W----------------------------------------------------------------------------------------------------------------------

3.3.5.3. Simple distillation at 300 kPa as the third separation stage

The simulation results used to either accept or reject simple distillation at 300 kPa asthe third separation stage following the accepted first and second stages for the separationof formic acid-acetic acid-water mixtures are presented in tables 52...54.

Simple distillation at 300 kPa can be accepted as the third separation stage whensimple distillation at 20 kPa or 101.3 kPa is the first stage.

When the first stage is extractive distillation with NMP, no solution was found.

Table 52. Simulation results of simple distillation at 300 kPa as the third separationstage when simple distillation at 20 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------10 % FA20 % AA SD 101.3 21 FA (+) NO +70 % W----------------------------------------------------------------------------------------------------------------------

Table 53. Simulation results of simple distillation at 300 kPa as the third separationstage when simple distillation at 101.3 kPa is an accepted first separation stage.Formic acid is FA, acetic acid is AA and water is W, SD is simple distillation and EDis extractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA SD 20 18 W (+) NO +10 % W----------------------------------------------------------------------------------------------------------------------

Table 54. Simulation results of simple distillation at 300 kPa as the third separationstage when simple distillation at 300 kPa is an accepted first separation stage. Formicacid is FA, acetic acid is AA and water is W, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------10 % FA40 % AA SD 101.3 18 W (-) YES -50 % W_______________________________________________________________________

Table 54. Cont.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------10 % FA30 % AA SD 101.3 22 W (-) YES -60 % W

10 % FA20 % AA SD 101.3 22 W (-) YES -70 % W

20 % FA40 % AA SD 101.3 8 W (-) YES -40 % W

20 % FA30 % AA SD 101.3 3 W (-) YES -50 % W

20 % FA20 % AA SD 101.3 A THIRD STAGE IS NOT REQUIRED60 % W

20 % FA10 % AA SD 101.3 46 W (-) YES -70 % W

30 % FA60 % AA SD 20 18 W (+) NO +10 % W

30 % FA60 % AA SD 101.3 20 W (+) NO +10 % W

30 % FA30 % AA SD 101.3 A THIRD STAGE IS NOT REQUIRED40 % W

30 % FA20 % AA SD 101.3 A THIRD STAGE IS NOT REQUIRED50 % W_______________________________________________________________________

Table 54. Cont.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------30 % FA10 % AA SD 101.3 50 W (-) YES -60 % W

40 % FA50 % AA SD 20 18 W (+) NO +10 % W

40 % FA50 % AA SD 101.3 169 AA (-) YES -10 % W

40 % FA20 % AA SD 101.3 50 AA (+) NO +40 % W

40 % FA10 % AA SD 101.3 74 AA (-) NO -50 % W

80 % FA10 % AA SD 101.3 207 W (-) YES -10 % W----------------------------------------------------------------------------------------------------------------------

When the original feed contains 30 % formic acid, 60 % acetic acid and 10 % water,simple distillation at 300 kPa can be accepted as the third separation stage when the firststage is simple distillation at 300 kPa and the second stage is simple distillation at 20 or101.3 kPa. When the second stage is simple distillation at 20 kPa, simple distillation at300 kPa can be accepted as the third stage for the original feed composition of 40 %formic acid, 50 % acetic acid and 10 % water. When the second stage is simpledistillation at 101.3 kPa, simple distillation at 300 kPa can be accepted as the third stagefor the original feed composition of 40 % formic acid, 20 % acetic acid and 40 % water.

3.3.5.4. Extractive distillation with n-methyl-2-pyrrolidone at 101.3kPa as the third separation stage

The simulation results used to either accept or reject extractive distillation with n-methyl-2-pyrrolidone (NMP) at 101.3 kPa as the third separation stage following the acceptedfirst and second stages for the separation of formic acid-acetic acid-water mixtures arepresented in tables 55 and 56. Extractive distillation was considered as the thirdseparation stage only when water was the most plentiful component in the feed streamof the stage.

Table 55. Simulation results of extractive distillation with NMP at 101.3 kPa as thethird separation stage when simple distillation at 101.3 kPa is an accepted firstseparation stage. Formic acid is FA, acetic acid is AA and water is W, SD is simpledistillation and ED is extractive distillation with n-methyl-2-pyrrolidone. + isaccepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA SD 20 13 W (+) NO +10 % W----------------------------------------------------------------------------------------------------------------------

Extractive distillation with NMP at 101.3 kPa can be accepted as the third separationstage following simple distillation at 101.3 kPa and 20 kPa as the first and secondstages only when the original feed contains 30 % formic acid, 60 % acetic acid and 10 %water.

Extractive distillation with NMP at 101.3 kPa can be accepted as the third separationstage when the original feed contains 30 % formic acid, 60 % acetic acid and 10 % waterand simple distillation at 300 kPa is the first separation stage, followed by simpledistillation at 20 kPa or 101.3 kPa as the second stage. It may also be accepted whensimple distillation at 300 kPa and 20 kPa are the first and second stages, and the originalfeed contains 40 % formic acid, 50 % acetic acid and 10 % water.

When the first separation stage was simple distillation at 20 kPa, or extractivedistillation with NMP at 101.3 kPa, the extractive distillation method was not found tobe a feasible third stage for any original feed compositions. Using extractive distillationas the third stage would have required the use of at least one additional separation stage.

Table 56. Simulation results of extractive distillation with NMP at 101.3 kPa as thethird separation stage when simple distillation at 300 kPa is an accepted firstseparation stage. Formic acid is FA, acetic acid is AA and water is W, SD is simpledistillation and ED is extractive distillation with n-methyl-2-pyrrolidone. + isaccepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Original 2nd stage Number of Product Are further Accepted(+)/feed and pressure trays at stages rejected(-)composition [kPa] 1.2·Rmin required?

----------------------------------------------------------------------------------------------------------------------30 % FA60 % AA SD 20 13 W (+) NO +10 % W

30 % FA60 % AA SD 101.3 13 W (+) NO +10 % W

40 % FA50 % AA SD 20 14 W (+) NO +10 % W----------------------------------------------------------------------------------------------------------------------

3.3.5.5. The third separation stages for the peroxyformic acid pulpingprocess

The composition of the liquor fed to the separation sequence in the peroxyformic acidpulping process has been estimated to be 12.1 % formic acid, 0.2 % acetic acid and 87.7% water. Simple distillation at the pressures 20, 101.3 and 300 kPa and extractivedistillation with n-methyl-2-pyrrolidone (NMP) at 101.3 kPa were simulated as the thirdseparation stage for this first stage feed composition. Extractive distillation wasconsidered as the third stage only when water was the most plentiful component in thefeed to the stage. Shortcut calculation methods were used. Results are shown in tables57 to 60.

Only simple distillation at 20 kPa following simple distillation at 101.3 kPa wasrejected because no solution was found.

All those third stages that were considered can be accepted when simple distillation at101.3 is the first separation stage.

A third separation stage is not needed when the second stage is simple distillation at101.3 kPa. When the second stage is simple distillation at 20 kPa, all the stagesconsidered can be accepted.

Simple distillation at 20 kPa or at 300 kPa seems to be a feasible third separationstage following extractive distillation with NMP at 101.3 kPa and simple distillation at101.3 kPa as the first two stages.

Table 57. Simulation results for the third separation stage in the peroxyformic acidpulping process when simple distillation at 20 kPa is the first stage. SD is simpledistillation and ED is extractive distillation with NMP. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Second stage Third stage Number of Product Are further Accepted(+)/and pressure and pressure stages at stages rejected(-)(kPa) (kPa) 1.2·Rmin needed?

----------------------------------------------------------------------------------------------------------------------SD 101.3 SD 20 NO SOLUTION WAS FOUNDSD 101.3 SD 300 32 W (+) YES +SD 101.3 ED 101.3 11 W (+) YES +SD 300 SD 20 26 FA (+) YES +SD 300 SD 101.3 25 FA (+) YES +----------------------------------------------------------------------------------------------------------------------

Table 58. Simulation results for the third separation stage in the peroxyformic acidpulping process when simple distillation at 101.3 kPa is the first stage. SD is simpledistillation and ED is extractive distillation with NMP. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Second stage Third stage Number of Product Are further Accepted(+)/and pressure and pressure stages at stages rejected(-)(kPa) (kPa) 1.2·Rmin needed?

----------------------------------------------------------------------------------------------------------------------SD 20 SD 101.3 24 W (+) YES +SD 20 SD 300 26 W (+) YES +SD 20 ED 101.3 13 W (+) YES +SD 300 SD 20 29 FA (+) YES +SD 300 SD 101.3 28 FA (+) YES +----------------------------------------------------------------------------------------------------------------------

Table 59. Simulation results for the third separation stage in the peroxyformic acidpulping process when simple distillation at 300 kPa is the first stage. SD is simpledistillation and ED is extractive distillation with NMP. + is accepted and - is rejected.

----------------------------------------------------------------------------------------------------------------------Second stage Third stage Number of Product Are further Accepted(+)/and pressure and pressure stages at stages rejected(-)(kPa) (kPa) 1.2·Rmin needed?

----------------------------------------------------------------------------------------------------------------------SD 20 SD 101.3 26 W (+) YES +SD 20 SD 300 26 W (+) YES +SD 20 ED 101.3 12 W (+) YES +SD 101.3 A THIRD STAGE IS NOT NEEDED----------------------------------------------------------------------------------------------------------------------

Table 60. Simulation results for the third separation stage in the peroxyformic acidpulping process when extractive distillation with NMP at 101.3 kPa is the first stage.SD is simple distillation and ED is extractive distillation with NMP. + is accepted and -is rejected.

----------------------------------------------------------------------------------------------------------------------Second stage Third stage Number of Product Are further Accepted(+)/and pressure and pressure stages at stages rejected(-)(kPa) (kPa) 1.2·Rmin needed?

----------------------------------------------------------------------------------------------------------------------SD 101.3 SD 20 6 FA (+) YES +SD 101.3 SD 300 8 W (+) YES +----------------------------------------------------------------------------------------------------------------------

3.3.5.6. Summary of the simulation results for the third separationstage

Feasible combinations of three separation stages for the feed compositions studied arelisted in table 61. Feasible three-stage separation processes for the original feedcomposition of the peroxyformic acid process are presented in table 62.

Table 61. Feasible three-stage separation processes for various feed compositions. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

----------------------------------------------------------------------------------------------------------------------Feed composition Feasible separation methods and pressures Are further

(kPa) stages ------------------------- -------------------------------------------------------- needed?FA AA W 1. stage 2. stage 3. stage% % %----------------------------------------------------------------------------------------------------------------------10 40 50 SD 101.3 SD 300 SD 101.3 YES10 30 60 SD 101.3 SD 300 SD 101.3 YES10 20 70 SD 20 SD 300 SD 101.3 NO10 20 70 SD 20 SD 101.3 SD 300 NO10 20 70 SD 101.3 SD 300 SD 101.3 NO10 10 80 SD 20 SD 300 SD 101.3 NO20 20 60 SD 300 SD 101.3 - NO20 40 40 SD 101.3 SD 300 SD 101.3 NO20 30 50 SD 101.3 SD 300 SD 101.3 NO30 60 10 SD 101.3 SD 20 SD 101.3 NO30 60 10 SD 101.3 SD 20 SD 300 NO30 60 10 SD 101.3 SD 20 ED 101.3 NO_______________________________________________________________________

Table 61. Cont.

----------------------------------------------------------------------------------------------------------------------Feed composition Feasible separation methods and pressures Are further

(kPa) stages ------------------------- -------------------------------------------------------- needed?FA AA W 1. stage 2. stage 3. stage% % %----------------------------------------------------------------------------------------------------------------------30 60 10 SD 300 SD 20 SD 101.3 NO30 60 10 SD 300 SD 20 SD 300 NO30 60 10 SD 300 SD 20 ED 101.3 NO30 60 10 SD 300 SD 101.3 SD 300 NO30 60 10 SD 300 SD 101.3 ED 101.3 NO30 30 40 SD 101.3 SD 300 SD 101.3 NO30 30 40 SD 300 SD 101.3 - NO30 20 50 SD 300 SD 101.3 - NO40 50 10 SD 300 SD 20 SD 101.3 NO40 50 10 SD 300 SD 20 SD 300 NO40 50 10 SD 300 SD 20 ED 101.3 NO40 50 10 SD 300 SD 101.3 SD 20 YES40 20 40 SD 300 SD 101.3 SD 300 NO60 20 20 SD 101.3 SD 300 SD 101.3 NO60 10 30 SD 101.3 SD 300 SD 101.3 YES70 10 20 SD 101.3 SD 300 SD 101.3 YES----------------------------------------------------------------------------------------------------------------------

Several feasible three-stage separation processes can be found when the feed stream tothe process contains 10...40 % formic acid. At higher formic acid contents, only fewpossible separation processes are found. When the feed stream contains 30 % formic acidand 20 or 30 % acetic acid, or 20 % both formic and acetic acids and is distilled at 300kPa followed by a distillation at atmospheric pressure, a third stage is not needed. Whenthe original feed contains 10 % formic acid and 30 or 40 % acetic acid, a fourthseparation stage has to be added to the SD101.3+SD300+SD101.3 sequence in order toget a formic acid product. When the original feed contains 40 % formic acid and 50 %acetic acid, a fourth separation stage has to be added to the SD300+SD101.3+SD20sequence in order to get a water rich product. When the original feed contains 60 %formic acid and 10 % acetic acid, or 70 % formic acid and 10 % acetic acid, a fourthseparation stage has to be added to the SD101.3+SD300+SD101.3 sequence in order toget an acetic acid rich product.

Further separation stages for the peroxyformic acid process are needed because noacetic acid product is produced by the three stages. The acetic acid product may beextracted from a product stream containing mostly water. Even when the first twoseparation stages are simple distillations at 300 kPa and 101.3 kPa, an extraction stageis needed. When extractive distillation is the third separation stage, a fourth distillationstage is needed in order to recycle the mass transfer agent.

Table 62. Feasible three-stage separation processes for the peroxyformic acid pulpingprocess. FA is formic acid, AA is acetic acid, W is water, SD is simple distillation andED is extractive distillation with n-methyl-2-pyrrolidone.

----------------------------------------------------------------------------------------------------------------------Separation stages and pressures [kPa] Are further

--------------------------------------------------------------------------------------- stages needed?1. stage 2. stage 3. stage----------------------------------------------------------------------------------------------------------------------SD 20 SD 101.3 SD 300 YESSD 20 SD 101.3 ED 101.3 YESSD 20 SD 300 SD 20 YESSD 20 SD 300 SD 101.3 YESSD 101.3 SD 20 SD 101.3 YESSD 101.3 SD 20 SD 300 YESSD 101.3 SD 20 ED 101.3 YESSD 101.3 SD 300 SD 20 YESSD 101.3 SD 300 SD 101.3 YESSD 300 SD 20 SD 101.3 YESSD 300 SD 20 SD 300 YESSD 300 SD 20 ED 101.3 YESSD 300 SD 101.3 - NOED 101.3 SD 101.3 SD 20 YESED 101.3 SD 101.3 SD 300 YES----------------------------------------------------------------------------------------------------------------------

3.3.6. Shortcut simulation of the fourth separation stage

Simple distillation at the pressures 20 kPa, 101.3 kPa and 300 kPa was studied as apotential fourth separation stage. They were simulated using shortcut calculationmethods in the PRO/II Flowsheet Simulation Program version 3.32 (Anon. 1991d)where a generalised Fenske method is used to predict product distributions. Theminimum reflux ratio is determined using the Underwood method. The number oftheoretical trays, the actual reflux rates, and condenser and reboiler duties are determinedusing a Gilliland-type correlation.

The feasible fourth separation stages for each feed composition were chosen using thefollowing rules:(1)The number of equilibrium stages was limited to 100 in order to keep the investmentcosts reasonable.(2)The most plentiful component should be the product of the separation stage.(3)No further separation stages should be needed.

If a separation method according to the simulation results did not fulfil therequirements, it was rejected. Extractive distillation with NMP was not considered as thefourth separation stage because in order to recycle the mass transfer agent, a fifth stagewould be needed. Specifications used in the simulations were:

(1)The molar fraction of one component in a product is 0.98.(2)The recovery rate of one component into a product is 98 %.

3.3.6.1. Simple distillation at 20 kPa as the fourth separation stage

Using simple distillation as the fourth separation stage results in columns with severalhundreds of equilibrium stages. Therefore it was rejected as the fourth stage.

3.3.6.2. Simple distillation at 101.3 kPa as the fourth separation stage

The simulation results used to either accept or reject simple distillation at 101.3 kPa asthe fourth stage in a process separating formic acid-acetic acid-water mixtures arepresented in table 63.

Simple distillation at 101.3 kPa can be accepted as the fourth separation stage whenthe original feed contains 30 % formic acid and 60 % acetic acid and the three previousstages are simple distillation at 300 kPa, simple distillation at 20 kPa and extractivedistillation with NMP at 101.3 kPa. It may also be accepted when the original feedcontains 40 % formic acid and 50 % acetic acid, and the first three stages are simpledistillations at 300 kPa, 101.3 kPa and 20 kPa.

Table 63. Simulation results of simple distillation at 101.3 kPa as the fourth separationstage. Formic acid is FA, acetic acid is AA and water is W, SD is simple distillationand ED is extractive distillation with n-methyl-2-pyrrolidone. + is accepted and - isrejected.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd and Number of Product Are further Accepted(+)/feed 3rd stages trays at stages rejected(-)composition and pressures 1.2·Rmin required?

[kPa]----------------------------------------------------------------------------------------------------------------------30 % FA SD101.360 % AA SD 20 1747 FA (+) NO -10 % W ED 101.3

30 % FA SD 30060 % AA SD 20 11 FA (+) NO +10 % W ED 101.3----------------------------------------------------------------------------------------------------------------------

Table 63. Cont.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd and Number of Product Are further Accepted(+)/feed 3rd stages trays at stages rejected(-)composition and pressures 1.2·Rmin required?

[kPa]----------------------------------------------------------------------------------------------------------------------30 % FA SD 30060 % AA SD 101.3 576 FA (+) NO -10 % W ED 101.3

40 % FA SD 30050 % AA SD 101.3 14 W (+) NO +10 % W SD 20

40 % FA SD 30050 % AA SD 20 1254 FA (+) YES -10 % W ED 101.3----------------------------------------------------------------------------------------------------------------------

3.3.6.3. Simple distillation at 300 kPa as the fourth separation stage

The simulation results used to either accept or reject simple distillation at 300 kPa asthe fourth stage in a process separating formic acid-acetic acid-water mixtures arepresented in table 64.

Table 64. Simulation results of simple distillation at 300 kPa as the fourth separationstage. Formic acid is FA, acetic acid is AA and water is W, SD is simple distillationand ED is extractive distillation with n-methyl-2-pyrrolidone. + is accepted and - isrejected.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd and Number of Product Are further Accepted(+)/feed 3rd stages trays at stages rejected(-)composition and pressures 1.2·Rmin required?

[kPa]----------------------------------------------------------------------------------------------------------------------10 % FA SD 101.340 % AA SD 300 57 FA (+) NO +50 % W SD 101.3----------------------------------------------------------------------------------------------------------------------

Table 64. Cont.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd and Number of Product Are further Accepted(+)/feed 3rd stages trays at stages rejected(-)composition and pressures 1.2·Rmin required?

[kPa]----------------------------------------------------------------------------------------------------------------------10 % FA SD 101.330 % AA SD 300 60 FA (+) NO +60 % W SD 101.3

40 % FA SD 30050 % AA SD 101.3 18 W (+) NO +10 % W SD 20

60 % FA SD 101.310 % AA SD 300 56 AA (-) NO -30 % W SD 101.3

70 % FA SD 101.310 % AA SD 300 19 AA (+) NO +20 % W SD 101.3----------------------------------------------------------------------------------------------------------------------

Simple distillation at 300 kPa was rejected when the original feed contained 60 %formic acid and 10 % acetic acid and the three previous stages were simple distillations at101.3 kPa, 300 kPa and 101.3 kPa. The reason for the rejection was that the fourthstage gave an acetic acid product, and acetic acid was not the most plentiful componentin the feed of the stage.

3.3.6.4. The fourth separation stages for the peroxyformic acid pulpingprocess

The composition of the liquor fed to the separation sequence in the peroxyformic acidpulping process has been estimated to be 12.1 % formic acid, 0.2 % acetic acid and 87.7% water. Simple distillation at the pressures 20, 101.3 and 300 kPa were simulated asthe fourth separation stage for this first stage feed composition. Extractive distillationwas not considered as the fourth because its use would lead to the need for a fifthseparation stage in order to recycle the mass transfer agent.

Those separation cycles needing a fourth stage were rejected mainly because there wastoo high a number of equilibrium stages, and because an acetic acid product was notobtained.

3.3.6.5. Summary of the simulation results for the fourth separationstage

Feasible combinations of four separation stages for the original feed compositionsstudied are listed in table 65. No feasible four-stage separation processes for theperoxyformic acid process were found.

Table 65. Feasible four-stage separation processes for various feed compositions. FAis formic acid, AA is acetic acid, W is water, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

----------------------------------------------------------------------------------------------------------------------Feed composition Feasible separation methods and pressures

(kPa)-------------------------------- ----------------------------------------------------------------------------FA AA W 1. stage 2. stage 3. stage 4. stage% % %----------------------------------------------------------------------------------------------------------------------10 40 50 SD 101.3 SD 300 SD 101.3 SD 30010 30 60 SD 101.3 SD 300 SD 101.3 SD 30030 60 10 SD 300 SD 20 ED 101.3 SD 101.340 50 10 SD 300 SD 101.3 SD 20 SD 101.340 50 10 SD 300 SD 101.3 SD 20 SD 30070 10 20 SD 101.3 SD 300 SD 101.3 SD 300----------------------------------------------------------------------------------------------------------------------

3.3.7. The recycle stream

In most separation sequences studied one of the products from the last separation stage isnot pure enough and has to be recycled to the first separation stage. This recycle streamwas added to the simulation models of the sequences accepted during the previoussimulation stages.

Feasible separation sequences were chosen using the following rules:(1) The number of equilibrium stages for one separation stage was limited to 100 inorder to keep the investment costs reasonable.(2) The energy consumption of the sequence should be below the average consumptionof the sequences.

Specifications used in the simulations were:(1) The molar fraction of one component in a product is 0.98.(2) The recovery rate of one component into a product is 98 %.

The simulation results are presented in table 66.

Table 66. Simulation results for separation sequences with recycling. Formic acid isFA, acetic acid is AA and water is W, SD is simple distillation and ED is extractivedistillation with n-methyl-2-pyrrolidone.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd 3rd Number of The energy consumptionfeed and 4th stages trays at of the separation composition and pressures 1.2·Rmin sequence

[kPa] [MJ/kmol of feed]----------------------------------------------------------------------------------------------------------------------10 % FA SD 101.3 6040 % AA SD 300 21 10.33·106

50 % W SD 101.3 33SD 300 56

10 % FA SD 101.3 4930 % AA SD 300 25 10.49·106

60 % W SD 101.3 40SD 300 60

10 % FA SD 20 5520 % AA SD 300 48 54.7470 % W SD 101.3 34

10 % FA SD 20 6720 % AA SD 101.3 41 67.4170 % W SD 300 40

10 % FA SD 101.3 5320 % AA SD 300 21 10.80·106

70 % W SD 101.3 60

10 % FA SD 20 4110 % AA SD 300 54 44.1980 % W SD 101.3 26

20 % FA SD 101.3 5140 % AA SD 300 46 242.3740 % W SD 101.3 42

20 % FA SD 101.3 4630 % AA SD 300 51 236.8450 % W SD 101.3 22

30 % FA SD 101.3 7460 % AA SD 20 54 117.7210 % W SD 101.3 14_______________________________________________________________________

Table 66. Cont.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd 3rd Number of The energy consumptionfeed and 4th stages trays at of the separation composition and pressures 1.2·Rmin sequence

[kPa] [MJ/kmol of feed]----------------------------------------------------------------------------------------------------------------------30 % FA SD 101.3 7160 % AA SD 20 54 158.1310 % W SD 300 17

30 % FA SD 300 6960 % AA SD 20 53 118.6210 % W SD 101.3 14

30 % FA SD 300 6660 % AA SD 20 54 155.9710 % W SD 300 17

30 % FA SD 300 6560 % AA SD 101.3 65 15.26·106

10 % W SD 300 18

30 % FA SD 300 6960 % AA SD 20 54 158.1110 % W ED 101.3 9

SD 101.3 11

30 % FA SD 101.3 28030 % AA SD 300 49 286.2840 % W SD 101.3 25

40 % FA SD 300 7550 % AA SD 20 37 136.3110 % W SD 101.3 15

40 % FA SD 300 7150 % AA SD 20 37 174.6010 % W SD 300 18

40 % FA SD 300 7550 % AA SD 101.3 21 133.0510 % W SD 20 46

SD 101.3 14_______________________________________________________________________

Table 66. Cont.

----------------------------------------------------------------------------------------------------------------------Original 1st, 2nd 3rd Number of The energy consumptionfeed and 4th stages trays at of the separation composition and pressures 1.2·Rmin sequence

[kPa] [MJ/kmol of feed]----------------------------------------------------------------------------------------------------------------------40 % FA SD 300 7150 % AA SD 101.3 21 177.1710 % W SD 20 46

SD 300 18

70 % FA SD 101.3 4910 % AA SD 300 42 272.5520 % W SD 101.3 50

SD 300 21

12.1 % FA SD 20 2700.2 % AA SD 101.3 24 188.6687.7 % W

12.1 % FA SD 101.3 2100.2 % AA SD 20 27 0.92·106

87.7 % W

12.1 % FA SD 300 2700.2 % AA SD 20 22 114.1587.7 % W

12.1 % FA SD 20 2100.2 % AA SD 101.3 15 5.41·106

87.7 % W ED 101.3 11SD 101.3 57

12.1 % FA SD 101.3 1700.2 % AA SD 20 33 1.95·106

87.7 % W ED 101.3 10SD 101.3 143

----------------------------------------------------------------------------------------------------------------------

Three separation sequences with only two stages have been found during previoussimulations. The energy consumptions of those sequences are presented in table 67.

Table 67. The energy consumptions of separation sequences with two stages. Formicacid is FA, acetic acid is AA and water is W, SD is simple distillation and ED isextractive distillation with n-methyl-2-pyrrolidone.

----------------------------------------------------------------------------------------------------------------------Original 1st and 2nd The energy consumptionfeed stages and of the separation composition pressures sequence

[kPa] [MJ/kmol of feed]----------------------------------------------------------------------------------------------------------------------20 % FA SD 30020 % AA SD 101.3 177.8760 % W

30 % FA SD 30030 % AA SD 101.3 161.3040 % W

30 % FA SD 30020 % AA SD 101.3 246.7050 % W----------------------------------------------------------------------------------------------------------------------

When energy consumptions higher than 1.0 TJ per kmol of feed are not taken intoaccount, the average consumption calculated from the data presented in tables 66 and 67is 162.99 MJ per kmol of feed. Those sequences having an energy consumption lowerthan the average consumption were chosen for simulations with rigorous calculationmethods. If several sequences resulted in feasible energy consumptions for the same feedcomposition, only the sequence with the lowest consumption was chosen. Table 68 liststhe sequences selected for further examination.

Table 68. Separation sequences selected for simulations with rigorous calculationmethods. Formic acid is FA, acetic acid is AA and water is W. SD is simple distillationand ED is extractive distillation with n-methyl-2-pyrrolidone.

----------------------------------------------------------------------------------------------------------------------Original Separation stages and pressures [kPa]feed - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - compositions First Second Third Fourth______________________________________________________________________10 % FA20 % AA SD 20 SD 300 SD 101.3 -70 % W_______________________________________________________________________

Table 68. Cont.

----------------------------------------------------------------------------------------------------------------------Original Separation stages and pressures [kPa]feed - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - compositions First Second Third Fourth______________________________________________________________________10 % FA10 % AA SD 20 SD 300 SD 101.3 -80 % W

30 % FA30 % AA SD 300 SD 101.3 - -40 % W

30 % FA60 % AA SD 101.3 SD 20 SD 101.3 -10 % W

40 % FA50 % AA SD 300 SD 101.3 SD 20 SD 101.310 % W

12.1 % FA00.2 % AA SD 300 SD 20 - -87.7 % W----------------------------------------------------------------------------------------------------------------------

3.3.8. Rigorous simulations

Separation sequences for the feed streams shown in table 68 were designed and simulatedusing rigorous calculation methods. The PRO/II 3.32 Flowsheet Simulation Program(Anon. 1991d) was used. The sequences used in shortcut simulations could not be solvedusing rigorous methods. Therefore the sequences were redesigned using the followingspecifications:(1) The first distillation stage operates at the same pressure as in the sequencedesigned using shortcut methods.(2) The product purity is 98 %.(3) The highest possible recovery rate is used.(4) The feed flow rate is 100 kmol/h.

The columns were chosen to be packed in order to minimize the risk of formic aciddecomposition. Ceramic Super Intalox saddles with a nominal packing diameter of 50.8mm and an HETP of 88.9 cm were used as the packing material.

Heat exchangers were added to the separation sequences in order to raise the feedstream temperature of each column to its bubble point at the column pressure. Also

pumps raising the feed stream pressures to the corresponding column pressure were added.

3.3.8.1. Feed containing 10 % formic acid, 20 % acetic acid and 70 %water

When the first distillation stage operates at 20 kPa, the feed stream containing 10 %formic acid, 20 % acetic acid and 70 % water can be separated using the sequence shownin figure 9.

20kPa

300kPa

101kPa

300kPa

FH1

CB1

FH2

CB2 CB3 CB4

D1

F

B1 B2

D2 D3

B3

D4

B4

C1 C2 C3 C4

FH4

H2O H2O HCOOH

CH3COOH

Fig. 9. Separation sequence for a feed stream containing 10 % formicacid, 20 % acetic acid and 70 % water.

Column data, thermal energy consumptions and stream compositions are presented intables 69, 70 and 71.

Table 69. Column data for the separation sequence shown in figure 9.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3 Column 4

----------------------------------------------------------------------------------------------------------------------Pressures (kPa)

Top 20 300 101 300Bottom 23 305 106 303

Temperatures (K)Top 329.2 407.0 374.0 419.8Bottom 336.3 422.2 384.8 430.6

Equilibrium stages 28 41 30 15Feed trays (from top) 12 12, 26 22 4Reflux ratio 2.7 4.6 30.0 10.8_______________________________________________________________________

Table 69. Cont.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3 Column 4

----------------------------------------------------------------------------------------------------------------------Flow rates (kmol/h)

Total feed 100.00 97.64 60.50 51.45Distillate 34.29 37.13 9.06 31.95Bottom 65.71 60.50 51.45 19.50

Specifications1 : Stream D1 D2 D3 B4

Component H2O H2O HCOOH CH3COOH

Type fraction fraction fraction fractionValue 0.98 0.98 0.98 0.98

2: Stream D1 D2 D3 B4Component H2O H2O HCOOH CH3COOH

Type recovery recovery recovery recoveryValue 0.48 0.90 0.39 0.57

Packed height (m) 23.11 34.67 24.89 11.56Column inner diameter (m) 1.4 1.2 1.4 1.4----------------------------------------------------------------------------------------------------------------------

Table 70. Thermal energy consumption of the separation sequence shown in figure 9.

----------------------------------------------------------------------------------------------------------------------Unit Thermal energy consumption

- - - - - - - - - - - - - - - - - - - - - - - - - - -GJ/h MW

-----------------------------------------------------------------------------------------------------------------------FH1 0.346 0.096FH2 0.520 0.144FH4 0.283 0.079CB1 5.377 1.494CB2 8.065 2.240CB3 5.657 1.571CB4 9.150 2.542

29.40 8.166----------------------------------------------------------------------------------------------------------------------

Table 71. Stream compositions in the separation sequence shown in figure 9.

----------------------------------------------------------------------------------------------------------------------Stream Flow rate HCOOH CH3COOH H2O

kmol/h % % %----------------------------------------------------------------------------------------------------------------------F 100.0000 10.0000 20.0000 70.0000B1 65.7091 14.7745 29.8373 55.3882D1 34.2909 0.8510 1.1496 97.9995B2 60.5046 37.6178 55.6995 6.6827D2 37.1333 1.1308 0.8693 97.9998B3 51.4468 26.9869 65.1541 7.8590D3 9.0578 98.0000 1.9984 0.0016B4 19.4960 1.9765 98.0000 0.0235D4 31.9508 42.2479 45.1119 12.6401----------------------------------------------------------------------------------------------------------------------

3.3.8.2. Feed containing 10 % formic acid, 10 % acetic acid and 80 %water

When the first distillation stage operates at 20 kPa, the feed stream containing 10 %formic acid, 10 % acetic acid and 80 % water can be separated using the sequence shownin figure 10.

20kPa

300kPa

101kPa

300kPa

FH1

CB1

FH2

CB2 CB3 CB4

D1

F

B1 B2

D2 D3

B3

D4

B4

C1 C2 C3 C4

FH4

H2 O H2O HCOOH

CH3COOH

Fig. 10. Separation sequence for a feed stream containing 10 % formicacid, 10 % acetic acid and 80 % water.

Column data, thermal energy consumptions and stream compositions are presented intables 72, 73 and 74.

Table 72. Column data for the separation sequence shown in figure 10.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3 Column 4

----------------------------------------------------------------------------------------------------------------------Pressures (kPa)

Top 20 300 101 300Bottom 25 305 105 302

Temperatures (K)Top 329.2 407.0 374.0 417.6Bottom 337.7 419.4 382.9 430.6

Equilibrium stages 28 42 30 17Feed trays (from top) 16 12, 29 22 5Reflux ratio 1.1 2.3 20.0 18.7Flow rates (kmol/h)

Total feed 100.00 88.54 46.09 36.98Distillate 39.18 42.44 9.12 27.73Bottom 60.82 46.09 36.98 9.25

Specifications1 : Stream D1 D2 D3 B4

Component H2O H2O HCOOH CH3COOH

Type fraction fraction fraction fractionValue 0.98 0.98 0.98 0.98

2: Stream D1 D2 D3 B4Component H2O H2O HCOOH CH3COOH

Type recovery recovery recovery recoveryValue 0.48 0.87 0.39 0.54

Packed height (m) 23.11 35.56 24.89 13.34Column inner diameter (m) 0.9 0.95 1.2 1.8----------------------------------------------------------------------------------------------------------------------

Table 73. Thermal energy consumption of the separation sequence shown in figure10.

----------------------------------------------------------------------------------------------------------------------Unit Thermal energy consumption

- - - - - - - - - - - - - - - - - - - - - - - - - - -GJ/h MW

-----------------------------------------------------------------------------------------------------------------------FH1 0.319 0.089FH2 0.420 0.117FH4 0.180 0.050CB1 3.536 0.982CB2 5.393 1.498CB3 3.852 1.070CB4 14.012 3.892

27.712 7.698----------------------------------------------------------------------------------------------------------------------

Table 74. Stream compositions in the separation sequence shown in figure 10.

----------------------------------------------------------------------------------------------------------------------Stream Flow rate HCOOH CH3COOH H2O

kmol/h % % %----------------------------------------------------------------------------------------------------------------------F 100.0000 10.0000 10.0000 80.0000B1 60.8164 15.6794 15.9179 68.4027D1 39.1837 1.1851 0.8149 98.0000B2 46.0943 49.6904 36.8259 13.4836D2 42.4436 0.9846 1.0155 97.9999B3 36.9793 37.7826 45.4110 16.8064D3 9.1151 97.9999 1.9967 0.0034B4 9.2526 1.9721 97.9994 0.0285D4 27.7268 49.7327 27.8621 22.4053----------------------------------------------------------------------------------------------------------------------

3.3.8.3. Feed containing 30 % formic acid, 30 % acetic acid and 40 %water

When the first distillation stage operates at 300 kPa, the feed stream containing 30 %formic acid, 30 % acetic acid and 40 % water can be separated using the sequence shownin figure 11.

300kPa

20kPa

300kPa

FH1

CB1 CB2 CB3

D1

F

B1 B2

D2 D3

B3

C1 C2 C3

FH3

FH2

H2O HCOOH

CH3COOH

HCOOH

Fig. 11. Separation sequence for a feed stream containing 30 % formicacid, 30 % acetic acid and 40 % water.

Column data, thermal energy consumptions and stream compositions are presented intables 75, 76 and 77.

Table 75. Column data for the separation sequence shown in figure 11.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3

----------------------------------------------------------------------------------------------------------------------Pressures (kPa)

Top 300 20 300Bottom 301 22 306

Temperatures (K)Top 407.0 327.6 414.2Bottom 418.9 335.1 431.6

Equilibrium stages 15 19 45Feed trays (from top) 10, 11 8 23Reflux ratio 11.8 5.9 48.7Flow rates (kmol/h)

Total feed 162.51 122.92 60.42Distillate 39.59 60.42 31.28Bottom 122.92 62.51 29.13

Specifications1 : Stream D1 D2 B3

Component H2O HCOOH CH3COOH

CH3COOH

Type fraction fraction fractionValue 0.98 0.98 0.98

2: Stream D1 D2 D3Component H2O HCOOH HCOOH

CH3COOH

Type recovery recovery recoveryValue 0.60 0.61 0.999

Packed height (m) 11.56 15.11 38.23Column inner diameter (m) 1.8 2.4 2.8----------------------------------------------------------------------------------------------------------------------

Table 76. Thermal energy consumption of the separation sequence shown in figure 11.

----------------------------------------------------------------------------------------------------------------------Unit Thermal energy consumption

- - - - - - - - - - - - - - - - - - - - - - - - GJ/h MW

-----------------------------------------------------------------------------------------------------------------------FH1 1.294 0.359FH2 0.557 0.155FH3 0.725 0.201CB1 19.523 5.423CB2 7.929 2.203CB3 34.258 9 .516

64.286 17.857----------------------------------------------------------------------------------------------------------------------

Table 77. Stream compositions in the separation sequence shown in figure 11.

----------------------------------------------------------------------------------------------------------------------Stream Flow rate HCOOH CH3COOH H2O

kmol/h % % %----------------------------------------------------------------------------------------------------------------------F 100.0000 30.0000 30.0000 40.0000B1 122.9230 38.1681 40.7926 21.0393D1 39.5852 1.2493 0.7510 97.9997B2 62.5071 27.8506 32.7078 39.4416D2 60.4158 48.8426 49.1574 2.0000B3 29.1349 0.1022 99.8978 0.0000D3 31.2812 94.2401 1.8970 3.8629----------------------------------------------------------------------------------------------------------------------

3.3.8.4. Feed containing 30 % formic acid, 60 % acetic acid and 10 %water

When the first distillation stage operates at 101 kPa, the feed stream containing 30 %formic acid, 60 % acetic acid and 10 % water can be separated using the sequence shownin figure 12.

101kPa

20kPa

101kPa

101kPa

FH1

CB1 CB2 CB3 CB4

D1F

B1 B2

D2 D3

B3

D4

B4

C1 C2 C3 C4

FH4FH3

CH 3COOH

HCOOH

H2O

Fig. 12. Separation sequence for a feed stream containing 30 % formicacid, 60 % acetic acid and 10 % water.

Column data, thermal energy consumptions and stream compositions are presented intables 78, 79 and 80.

Table 78. Column data for the separation sequence shown in figure 12.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3 Column 4

----------------------------------------------------------------------------------------------------------------------Pressures (kPa)

Top 101 20 101 101Bottom 104 23 106 102

Temperatures (K)Top 381.7 327.7 374.0 373.5Bottom 391.6 336.2 382.7 380.7

Equilibrium stages 16 20 22 14Feed trays (from top) 5, 6, 10 8 21 13Reflux ratio 3.7 7.5 36.0 5.5_______________________________________________________________________

Table 78. Cont.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3 Column 4

----------------------------------------------------------------------------------------------------------------------Flow rates (kmol/h)

Total feed 551.54 491.10 307.07 184.03Distillate 491.10 307.07 29.86 10.29Bottom 60.44 184.03 277.21 173.74

Specifications1 : Stream B1 D3 D4

Component CH3COOH HCOOH H2O

Type fraction reflux ratio fraction fractionValue 0.98 7.5 0.98 0.98

2: Stream B1 D2 D3 D4Component CH3COOH HCOOH HCOOH H2O

CH3COOH

Type recovery recovery recovery recoveryValue 0.22 0.75 0.20 0.12

Packed height (m) 12.45 16.00 17.78 10.67Column inner diameter (m) 4.4 5.6 2.6 0.75----------------------------------------------------------------------------------------------------------------------

Table 79. Thermal energy consumption of the separation sequence shown in figure 12.

----------------------------------------------------------------------------------------------------------------------Unit Thermal energy consumption

- - - - - - - - - - - - - - - - - - - - - - - - - - - GJ/h MW

-----------------------------------------------------------------------------------------------------------------------FH1 1.090 0.303FH3 2.069 0.575FH4 0.873 0.243CB1 59.268 16.463CB2 54.750 15.208CB3 23.456 6.516CB4 2.660 0 .739

144.166 40.047----------------------------------------------------------------------------------------------------------------------

Table 80. Stream compositions in the separation sequence shown in figure 12.

----------------------------------------------------------------------------------------------------------------------Stream Flow rate HCOOH CH3COOH H2O

kmol/h % % %----------------------------------------------------------------------------------------------------------------------F 100.0000 30.0000 60.0000 10.0000B1 60.4424 1.9917 97.9994 0.0089D1 491.0987 38.6851 42.7652 18.5498B2 184.0312 23.7313 30.6080 45.6607D2 307.0680 47.6471 50.0513 2.3017B3 277.2068 42.2228 55.2276 2.5496D3 29.8612 98.0011 1.9985 0.0004B4 173.7418 25.1230 32.3160 42.5610D4 10.2894 0.2324 1.7678 97.9999----------------------------------------------------------------------------------------------------------------------

3.3.8.5. Feed containing 40 % formic acid, 50 % acetic acid and 10 %water

When the first distillation stage operates at 300 kPa, the feed stream containing 40 %formic acid, 50 % acetic acid and 10 % water can be separated using the sequence shownin figure 13.

300kPa

101kPa

20kPa

101kPa

FH1

CB1 CB2 CB3 CB4

D1

F

B1 B2

D2D3

B3

D4

B4

C1 C2 C3 C4

FH4

FH2

FH3

CH3COOH

HCOOH H2O

Fig. 13. Separation sequence for a feed stream containing 40 % formicacid, 50 % acetic acid and 10 % water.

Column data, thermal energy consumptions and stream compositions are presented intables 81, 82 and 83.

Table 81. Column data for the separation sequence shown in figure 13.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2 Column 3 Column 4

----------------------------------------------------------------------------------------------------------------------Pressures (kPa)

Top 300 101 20 101Bottom 303 108 25 105

Temperatures (K)Top 416.2 374.0 327.2 373.4Bottom 430.7 381.9 337.9 381.2

Equilibrium stages 26 40 31 30Feed trays (from top) 2, 4, 13 32 5 16Reflux ratio 3.8 7.6 10.3 15.3Flow rates (kmol/h)

Total feed 284.40 234.19 194.59 114.36Distillate 234.19 39.60 80.23 10.19Bottom 50.21 194.59 114.36 104.17

Specifications1 : Stream B1 D2 D3 D4

Component CH3COOH HCOOH HCOOH H2O

CH3COOH

Type fraction fraction fraction fractionValue 0.98 0.98 0.98 0.98

2: Stream B1 D2 D3 D4Component CH3COOH HCOOH HCOOH H2O

CH3COOH

Type recovery recovery recovery recoveryValue 0.65 0.2485 0.67 0.20

Packed height (m) 21.34 33.78 25.78 24.89Column inner diameter (m) 2.6 1.4 3.2 1.2----------------------------------------------------------------------------------------------------------------------

Table 82. Thermal energy consumption of the separation sequence shown in figure 13.

----------------------------------------------------------------------------------------------------------------------Unit Thermal energy consumption

- - - - - - - - - - - - - - - - - - - - - - - - - - - GJ/h MW

-----------------------------------------------------------------------------------------------------------------------FH1 1.553 0.431FH2 0.845 0.235FH3 0.380 0.106FH4 0.502 0.139CB1 28.538 7.927CB2 6.310 1.753CB3 18.467 5.130CB4 6.687 1 .858

63.282 17.579----------------------------------------------------------------------------------------------------------------------

Table 83. Stream compositions in the separation sequence shown in figure 13.

----------------------------------------------------------------------------------------------------------------------Stream Flow rate HCOOH CH3COOH H2O

kmol/h % % %----------------------------------------------------------------------------------------------------------------------F 100.0000 40.0000 50.0000 10.0000B1 50.2100 1.9844 97.9998 0.0159D1 234.1865 66.6788 11.3140 22.0072B2 194.5911 60.3055 13.2114 26.4831D2 39.5955 98.0001 1.9895 0.0104B3 114.3630 45.4128 10.9286 43.6585D3 80.2283 81.5347 16.4653 2.0000B4 104.1730 49.6655 11.9915 38.3430D4 10.1899 1.9365 0.0632 98.0003----------------------------------------------------------------------------------------------------------------------

3.3.8.6. Feed containing 12.1 % formic acid, 0.2 % acetic acid and 87.7% water

When the first distillation stage operates at 300 kPa, the estimated feed stream of theperoxyformic acid pulping process containing 12.1 % formic acid, 0.2 % acetic acid and87.7 % water can be separated using the sequence shown in figure 14.

300kPa

20kPa

FH1

CB1 CB2

D1

F

B1 B2

D2

C1 C2FH2

H2O

HCOOH

Fig. 14. Separation sequence for a feed stream containing 12.1 % formicacid, 0.2 % acetic acid and 87.7 % water.

Acetic acid cannot be separated from the mixture by the sequence shown in figure 14.It is concentrated in the distillate of the second column and cannot be separated from thisstream using simple distillation. Alternative separation methods should be considered forthe separation of acetic acid.

Column data, thermal energy consumptions and stream compositions are presented intables 84, 85 and 86.

Table 84. Column data for the separation sequence shown in figure 14.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2

----------------------------------------------------------------------------------------------------------------------Pressures (kPa)

Top 300 20Bottom 304 24

Temperatures (K)Top 406.9 326.6Bottom 415.9 336.3

Equilibrium stages 28 22_______________________________________________________________________

Table 84. Cont.

----------------------------------------------------------------------------------------------------------------------Column 1 Column 2

----------------------------------------------------------------------------------------------------------------------Feed trays (from top) 13, 13 11Reflux ratio 71.3 24.0Flow rates (kmol/h)

Total feed 141.13 52.53Distillate 88.59 11.41Bottom 52.53 41.12

Specifications1 : Stream D1

Component H2O

Type fraction reflux ratioValue 0.98 24.0

2: Stream D1 D2Component H2O HCOOH

Type recovery recoveryValue 0.87 0.29

Packed height (m) 23.11 17.78Column inner diameter (m) 5.8 1.8----------------------------------------------------------------------------------------------------------------------

Table 85. Thermal energy consumption of the separation sequence shown in figure14.

----------------------------------------------------------------------------------------------------------------------Unit Thermal energy consumption

- - - - - - - - - - - - - - - - - - - - - - - - - - - GJ/h MW

-----------------------------------------------------------------------------------------------------------------------FH1 0.931 0.259FH2 0.338 0.094CB1 248.483 69.023CB2 5.449 1 .514

255.201 70.890----------------------------------------------------------------------------------------------------------------------

Table 86. Stream compositions in the separation sequence shown in figure 14.

----------------------------------------------------------------------------------------------------------------------Stream Flow rate HCOOH CH3COOH H2O

kmol/h % % %----------------------------------------------------------------------------------------------------------------------F 100.0000 12.1000 0.2000 87.7000B1 52.5336 73.5806 1.4851 24.9343D1 88.5915 0.9986 0.0013 99.0001B2 41.1223 66.7397 1.4138 31.8465D2 11.4113 98.2325 1.7422 0.0252----------------------------------------------------------------------------------------------------------------------

3.3.8.7. Summary of the rigorous calculations

The thermal energy consumptions of the separation sequences simulated using rigorouscalculation methods are summarized in table 87.

Table 87. Thermal energy consumptions of the separation sequences presented infigures 9 to 14.

----------------------------------------------------------------------------------------------------------------------Feed compositions (%) Sequence shown Thermal energy

HCOOH CH3COOH H2O in figure consumption (MW)

----------------------------------------------------------------------------------------------------------------------10 20 70 9 8.16610 10 80 10 7.69830 30 40 11 17.85730 60 10 12 40.04740 50 10 13 17.57912.1 0.2 87.7 14 70.890

----------------------------------------------------------------------------------------------------------------------

The energy consumption of the separation sequence for a feed stream containing 30 %formic acid, 60 % acetic acid and 10 % water is considerably higher than for the otherfeed stream compositions. Therefore this sequence was rejected and not studied further.The energy consumption for separating the reference feed composition is even higher.

3.3.9. Thermal integration of the separation processes

The separation of the remaining feed compositions was further studied by performing apinch analysis (Linnhoff et al. 1982) in order to estimate the total costs of theseparation sequences. The analysis was carried out using the SYNSET program (Anon.1992b).

Streams included in the pinch analysis are shown in figures 15 to 19 and thecorresponding stream data is presented in tables 88 to 92.

All product streams (B1...B4, C1...C4) are cooled to 293 K which is also the supplytemperature of the feed stream F.

20kPa

300kPa

101kPa

300kPa

D1

F

B1

D2 D3

B3 B4

C1 C2 C3 C4

U1 U2 U3 U4

L1 L2 L3 L4

Fig. 15. Streams included in thermal integration when the feed streamcontains 10 % formic acid, 20 % acetic acid and 70 % water.

Table 88. Stream data for the separation sequence in figure 15.

----------------------------------------------------------------------------------------------------------------------Stream Type Heat capacity Supply Target

flow rate temperature temperatureMW/K K K

----------------------------------------------------------------------------------------------------------------------U1 HOT 2.4829 329.8 329.2U2 HOT 11.1778 407.2 407.0U3 HOT 16.6083 374.1 374.0U4 HOT 2.3101 420.9 419.8D1 HOT 0.0007 329.2 293.0D2 HOT 0.0008 407.0 293.0D3 HOT 0.0003 374.0 293.0B4 HOT 0.0009 430.6 293.0F COLD 0.0024 293.0 332.5L1 COLD 14.9360 336.2 336.3

_______________________________________________________________________

Table 88. Cont.

----------------------------------------------------------------------------------------------------------------------Stream Type Heat capacity Supply Target

flow rate temperature temperatureMW/K K K

----------------------------------------------------------------------------------------------------------------------L2 COLD 2.2400 421.2 422.2L3 COLD 2.6190 384.2 384.8L4 COLD 12.7080 430.4 430.6B1 COLD 0.0019 336.4 414.3B3 COLD 0.0020 384.9 424.1

----------------------------------------------------------------------------------------------------------------------

Streams to be cooled in the process are called hot streams, and streams to be heatedare called cold streams. The heat capacity flow rates are obtained by multiplying the heatcapacity of a stream with its mass flow rate. For streams U and L, the heat of phasechange is also taken into account.

20kPa

300kPa

101kPa

300kPa

D1

F

B1

D2 D3

B3 B4

C1 C2 C3 C4

U1 U2 U3 U4

L1 L2 L3 L4

Fig. 16. Streams included in thermal integration when the feed streamcontains 10 % formic acid, 10 % acetic acid and 80 % water.

Table 89. Stream data for the separation sequence in figure 16.

----------------------------------------------------------------------------------------------------------------------Stream Type Heat capacity Supply Target

flow rate temperature temperatureMW/K K K

----------------------------------------------------------------------------------------------------------------------U1 HOT 1.3929 329.9 329.2U2 HOT 7.4861 407.2 407.0U3 HOT 11.3167 374.1 374.0U4 HOT 6.4861 418.2 417.6D1 HOT 0.0008 329.2 293.0D2 HOT 0.0009 407.0 293.0D3 HOT 0.0003 374.0 293.0B4 HOT 0.0004 430.6 293.0F COLD 0.0023 293.0 331.6L1 COLD 1.9640 337.2 337.7L2 COLD 2.4970 418.8 419.4L3 COLD 3.5670 382.6 382.9L4 COLD 19.4610 430.4 430.6B1 COLD 0.0015 337.7 412.3B3 COLD 0.0013 382.9 420.9

----------------------------------------------------------------------------------------------------------------------

300kPa

20kPa

300kPa

D1

F

B2

D2 D3

B3

C1 C2 C3

U1 U2 U3

L1 L2 L3

Fig. 17. Streams included in thermal integration when the feed streamcontains 30 % formic acid, 30 % acetic acid and 40 % water.

Table 90. Stream data for the separation sequence in figure 17.

----------------------------------------------------------------------------------------------------------------------Stream Type Heat capacity Supply Target

flow rate temperature temperatureMW/K K K

----------------------------------------------------------------------------------------------------------------------U1 HOT 27.1194 407.2 407.0U2 HOT 5.1111 328.1 327.6U3 HOT 95.1194 414.3 414.2D1 HOT 0.0008 407.0 293.0D3 HOT 0.0011 414.2 293.0B3 HOT 0.0014 431.6 293.0D2 COLD 0.0019 327.6 421.9F COLD 0.0032 293.0 417.1L1 COLD 6.0260 418.0 418.9L2 COLD 22.0250 335.0 335.1L3 COLD 95.1610 431.5 431.6B2 COLD 0.0018 335.1 417.2

----------------------------------------------------------------------------------------------------------------------

300kPa

101kPa

20kPa

101kPa

F

B1

D2D3

B3

D4

B4

C1 C2 C3 C4

U1 U2 U3 U4

L1 L2 L3 L4

Fig. 18. Streams included in thermal integration when the feed streamcontains 40 % formic acid, 50 % acetic acid and 10 % water.

Table 91. Stream data for the separation sequence in figure 18.

----------------------------------------------------------------------------------------------------------------------Stream Type Heat capacity Supply Target

flow rate temperature temperatureMW/K K K

----------------------------------------------------------------------------------------------------------------------U1 HOT 79.1583 416.3 416.2U2 HOT 10.0833 374.2 374.0U3 HOT 9.0083 327.8 327.2U4 HOT 6.2111 373.7 373.4D2 HOT 0.0013 374.0 293.0D4 HOT 0.0002 373.4 293.0B1 HOT 0.0024 430.7 293.0D3 COLD 0.0024 327.2 417.0F COLD 0.0030 293.0 421.9L1 COLD 39.6360 430.5 430.7L2 COLD 8.7640 381.7 381.9L3 COLD 51.2970 337.8 337.9L4 COLD 18.5750 381.1 381.2B3 COLD 0.0059 337.9 382.5B4 COLD 0.0030 381.2 415.4

----------------------------------------------------------------------------------------------------------------------

300kPa

20kPa

D1

F

B2

D2

C1 C2

U1 U2

L1 L2

Fig. 19. Streams included in thermal integration when the feed streamcontains 12.1 % formic acid, 0.2 % acetic acid and 87.7 % water.

Table 92. Stream data for the separation sequence in figure 19.

----------------------------------------------------------------------------------------------------------------------Stream Type Heat capacity Supply Target

flow rate temperature temperatureMW/K K K

----------------------------------------------------------------------------------------------------------------------U1 HOT 690.5167 407.0 406.9U2 HOT 8.1972 326.8 326.6D1 HOT 0.0019 406.9 293.0D2 HOT 0.0003 326.6 293.0F COLD 0.0022 293.0 409.5L1 COLD 690.2310 415.8 415.9L2 COLD 3.0270 335.8 336.3B2 COLD 0.0011 336.3 416.5

----------------------------------------------------------------------------------------------------------------------

The streams that are included in the analysis are placed in temperature intervals. Theinterval boundary temperatures are set at 0.5·∆Tmin below hot stream temperatures and

0.5·∆Tmin above cold stream temperatures. ∆Tmin is the minimum temperature

difference. When it is 10 K, the streams can be placed in intervals as shown in figure 20for the sequence separating a mixture containing 10 % formic acid, 20 % acetic acid and70 % water (fig. 15 and table 88).

When the stream population in every temperature interval is known, the intervals areanalyzed by calculating their enthalpy balances using equation 3.

∆H T T CP CPi i i C H i= −( ) −( )+ ∑ ∑1 (3)

where ∆Hi is the enthalpy change at interval i,

Ti is the upper boundary temperature of interval i,

Ti+1 is the lower boundary temperature of interval i,

CPC is the CP value of a cold stream and

CPH is the CP value of a hot stream.

An example of the temperature interval analysis is shown in table 93.

435.6K

435.4K

429.1K

427.2K

426.2K

425.6K

419.3K

415.9K

418.8K

402.2K

402.0K

389.9K

389.8K

389.2K

369.1K

369.0K

341.4K

341.3K

341.2K

337.5K

324.8K

324.2K

298.0K

288.0K

I

II

III

IV

V

VI

VII

VIII

IX

X

XI

XII

XIII

XIV

XV

XVI

XVII

XVIII

XIX

XX

XXI

XXII

XXIII

U1

U2

U3

U4

D1

D2

D3

B4

F

L1

L2

L3

L4

B1

B3

Fig. 20. The placement on temperature intervals of the streams shownin table 88, when the minimum temperature difference is 10K.

Table 93. Temperature interval analysis for the sequence separating the feedcontaining 10 % formic acid, 20 % acetic acid and 70 % water (fig. 15 and table 88).

----------------------------------------------------------------------------------------------------------------------

Interval Ti + Ti+1 SCPC - SCPH DHi Surplus

number K MW/K MW ori deficit

---------------------------------------------------------------------------------------------------------------------- 1 0.2 12.7100 2.5420 deficit 2 6.3 0.0000 0.0000 3 1.9 0.0020 0.0038 deficit 4 1.0 2.2423 2.2423 deficit 5 0.6 0.0020 0.0012 deficit 6 6.3 0.0011 0.0069 deficit 7 3.4 0.0030 0.0101 deficit 8 1.1 - 2.3071 - 2.5379 surplus 9 12.6 0.0030 0.0373 deficit10 0.2 - 11.1748 - 2.2350 surplus11 12.1 0.0022 0.0261 deficit12 0.1 0.0001 1·10- 5 deficit13 0.6 2.6191 1.5715 deficit14 20.1 0.0001 0.0029 deficit15 0.1 - 16.6082 - 1.6608 surplus16 27.6 - 0.0001 - 0.0039 surplus17 0.1 - 0.0020 - 0.0002 surplus18 0.1 14.9341 1.4934 deficit19 3.7 - 0.0020 - 0.0074 surplus20 12.7 0.0004 0.0054 deficit21 0.6 - 2.4824 - 1.4895 surplus22 26.2 - 0.0003 - 0.0079 surplus23 10.0 - 0.0027 - 0.0273 surplus

----------------------------------------------------------------------------------------------------------------------

Assuming that no heat is supplied to the hottest interval (1) from a hot utility, thenthe deficit 2.542 MW from interval 1 is cascaded into interval 2. There it joins the zeroenthalpy change from interval 2, making 2.542 MW cascade into interval 3. Interval 3has a 0.004 MW deficit. After accepting the 2.542 MW, it passes on a 2.545 deficit tointerval 4. The heat cascade composed using this principle is shown in figure 21(a). Thenegative heat flows in figure 21(a) are thermodynamically infeasible. By adding 4.806MW of heat a from hot utility as shown in figure 21(b) and cascading it through thesystem, all the heat flows between intervals are given a value of at least zero. As a resultof this, the minimum utility requirements have been predicted. They are 4.806 MW forthe hot utility and 4.833 MW for the cold utility. The position of the pinch has alsobeen located. It is the interval boundary temperature 415.9 K where the heat flowbetween intervals is zero. This means that the pinch point temperature for hot streams is420.9 K and for cold streams it is 410.9 K.

FROM HOT UTILITY

0 kW

DH=2.542 MW

-2.542MW

DH=0.000MW

1

2

-2.542MW

3 DH=0.004MW

-2.545MW

4 DH=2.242MW

-4.788MW

5 DH=0.001MW

-4.789MW

435.6K

435.4K

429.1K

427.2K

426.2K

425.6K

4.806MW

1 DH=2.542MW

2.264MW

2 DH=0.000MW

3 DH=0.004MW

2.264MW

2.260MW

4 DH=2.242MW

0.018MW

5 DH=0.001MW

0.017MW

FROM HOT UTILITY

DH=0.001MW

DH=0.007MW

DH=0.010MW

DH=-2.538MW

DH=0.037MW

DH=-2.235MW

6

7

8

9

10

419.3K

415.9K

414.8K

402.2K

402.0K

-4.796MW

-4.806MW

-2.268MW

-2.305MW

-0.070MW

DH=0.026MW

DH=1·10-5MW

DH=1.571MW

DH=0.003MW

DH=-1.661MW

389.9K

389.8K

389.2K

369.1K

369.0K

-0.096MW

-0.096MW

-1.668MW

-1.671MW

-0.010MW

11

12

13

14

15

DH=-0.004MW

DH=-2·10-4MW

DH=1.493MW

DH=-0.007MW

DH=0.005MW

341.4K

341.3K

341.2K

337.5K

324.8K

-0.006MW

-0.006MW

-1.499MW

-1.492MW

-1.497MW

16

17

18

19

20

DH=-1.489MW

DH=-0.008MW

DH=-0.027MW

324.2K

298.0K

288.0K

-0.008MW

0.000MW

0.027MW

21

22

23

DH=0.007MW

DH=0.010MW

DH=-2.538MW

DH=0.037MW

DH=-2.235MW

DH=0.026MW

DH=1·10-5MW

DH=1.571MW

DH=0.003MW

DH=-1.661MW

DH=-0.004MW

DH=-2·10-4MW

DH=1.493MW

DH=-0.007MW

DH=0.005MW

DH=-1.489MW

DH=-0.008MW

DH=-0.027MW

0.010MW

0.000MW

2.538MW

2.501MW

4.736MW

4.709MW

4.709MW

3.138MW

3.135MW

4.796MW

4.800MW

4.800MW

3.307MW

3.314MW

3.309MW

4.798MW

4.806MW

4.833MW

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

TO COLD UTILITY TO COLD UTILITY

INFEASIBLE � � PINCH , QHmin , QCmin

(a) � � � � (b)

Fig. 21. The heat cascade for the temperature intervals presented intable 93.

All the separation sequences were analyzed using the minimum approach temperatureof 10 K. Data presented in table 94 were used when performing the analyses andconstructing the heat exchanger networks with the SYNSET program. The results arepresented in tables 95 and 96.

Table 94. Data used in pinch analysis.

----------------------------------------------------------------------------------------------------------------------Property Value Reference----------------------------------------------------------------------------------------------------------------------Steam temperature 450 KSteam latent heat 1785 kJ/kg Perry & Chilton 1973Steam specific cost 0.06 FIM/kgWater inlet temperature 278 KWater outlet temperature 333 KWater specific heat capacity 4187 kJ/m3K Perry & Chilton 1973Water specific cost 5.6 FIM/m3 Isoaho 1998Overall heat transfer coefficients:

exchangers and coolers 264 W/m2K Anon. 1992bheaters 347 W/m2K Anon. 1992b

Annual working hours 8500 h/aAnnual rate of return 0.1 a- 1 Anon. 1992b-----------------------------------------------------------------------------------------------------------------------

Steam was supposed to be produced in a heavy fuel oil fired boiler with an overallefficiency of 90 %. When the heat content of heavy fuel oil is 40.6 MJ/kg (Kinnula1986) and the price is 1.1 FIM/kg (Finnish Oil Association 1998), the price of energy is0.03 FIM/MJ. When this is multiplied with 2.042 MJ/kg, which is the enthalpy changeneeded to produce the steam from water at 278 K, the steam specific cost of 0.06FIM/kg was obtained.

The products are cooled to 293 K. Therefore higher minimum approach temperaturescan not be used if water is the cold utility to be used. The pinch analysis was carried outwith the minimum approach temperature of 5 K in order to find out if lower minimumapproach temperatures would have a positive effect on the energy consumptions of theseparation sequences. The results are presented in tables 97 and 98.

Table 95. Pinch analysis results when DTmin is 10 K (F is formic acid, A is aceticacid, and W is water).

----------------------------------------------------------------------------------------------------------------------Original feed Separation steps Minimum utility Pinch temperaturescomposition requirements- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F A W 1st 2nd 3rd 4th Hot Cold Hot Cold% % % kPa kPa kPa kPa MW MW K K----------------------------------------------------------------------------------------------------------------------10 20 70 20 300 101 300 4.806 4.833 420.9 410.910 10 80 20 300 101 300 5.407 5.429 418.2 408.230 30 40 300 20 300 - 15.014 15.049 414.3 404.340 50 10 300 101 20 101 7.993 8.007 416.3 406.312.1 0.2 87.7 300 20 - - 69.054 69.097 407.0 397.0----------------------------------------------------------------------------------------------------------------------

Table 96. Pinch analysis results when DTmin is 10 K (F is formic acid, A is aceticacid, and W is water).

----------------------------------------------------------------------------------------------------------------------Original feed Separation steps Number of heat Annual costscomposition exchangers- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F A W 1st 2nd 3rd 4th Minimum Actual Steam Water% % % kPa kPa kPa kPa FIM/a FIM/a----------------------------------------------------------------------------------------------------------------------10 20 70 20 300 101 300 16 18 5.2·106 6.5·106

10 10 80 20 300 101 300 16 18 5.8·106 6.0·106

30 30 40 300 20 300 - 13 16 18·106 14·106

40 50 10 300 101 20 101 16 19 13·106 15·106

12.1 0.2 87.7 300 20 - - 9 10 73·106 53·106

----------------------------------------------------------------------------------------------------------------------

Table 97. Pinch analysis results when DTmin is 5 K (F is formic acid, A is acetic acid,and W is water).

----------------------------------------------------------------------------------------------------------------------Original feed Separation steps Minimum utility Pinch temperaturescomposition requirements- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F A W 1st 2nd 3rd 4th Hot Cold Hot Cold% % % kPa kPa kPa kPa MW MW K K----------------------------------------------------------------------------------------------------------------------10 20 70 20 300 101 300 4.789 4.818 420.9 415.910 10 80 20 300 101 300 5.394 5.417 418.2 413.230 30 40 300 20 300 - 14.979 15.015 414.3 409.340 50 10 300 101 20 101 7.951 7.965 416.3 411.312.1 0.2 87.7 300 20 - - 69.039 69.080 407.0 402.0----------------------------------------------------------------------------------------------------------------------

Table 98. Pinch analysis results when DTmin is 5 K (F is formic acid, A is acetic acid,and W is water).

----------------------------------------------------------------------------------------------------------------------Original feed Separation steps Number of heat Annual costscomposition exchangers- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F A W 1st 2nd 3rd 4th Minimum Actual Steam Water% % % kPa kPa kPa kPa FIM/a FIM/a----------------------------------------------------------------------------------------------------------------------10 20 70 20 300 101 300 16 17 5.2·106 6.3·106

10 10 80 20 300 101 300 16 17 5.8·106 5.9·106

30 30 40 300 20 300 - 13 16 18·106 14·106

40 50 10 300 101 20 101 16 19 13·106 14·106

12.1 0.2 87.7 300 20 - - 9 10 73·106 53·106

----------------------------------------------------------------------------------------------------------------------

In order to compare the processes, the total annual costs have to be calculated. Theheat exchanger networks were designed for the separation processes using the SYNSETprogram. Results are shown in tables 99...108.

Item costs of the heat exchangers were estimated using equation 4 (Rose 1985).

HEIC f f f AT p M19680 651000 1 0 73 0 30= + + +( ) +( ). . .

(4)

where HEIC1968 is the item cost of a heat exchanger in 1968 (US$),

fT is the exchanger type factor,

fp is the pressure factor,

fM is the material factor and

A is the heat transfer area (m2).

All the exchangers were supposed to be floating head exchangers which have the value0.0 for the factor fT (Rose 1985). Factor fp also has the value 0.0 because the pressures

of all streams are below 1.0 MPa (Rose 1985). Factor fM has the value 2.0 when

stainless steel was chosen to be the construction material of the exchangers.According to Schillmoller (Schillmoller 1997) type 304L is the preferred material for

storage tanks when formic acid is handled. This alloy is resistant to formic acid in anyconcentration at ambient temperatures. Type 316L can be used in all concentrations atambient temperatures and up to the formic acid content of 10 % at boiling temperature.For intermediate strengths (30-70 %) of formic acid at elevated temperatures, alloys 20,28, 904, or 825 can be considered. They can withstand mixtures of formic and aceticacids. Several high-nickel alloys, such as G-3, 625, and C-276, can be used for allconcentrations at temperatures up to the boiling point. The nominal analyses of theabove mentioned alloys are presented in table 99.

Table 99. Nominal analyses of some stainless steel and high-nickel alloys.(Schillmoller 1997)_______________________________________________________________________Component Nominal analysis, %

------------------------------------------------------------------------------------------------304L 316L 20 28 904 825 G-3 625 C-276

_______________________________________________________________________C (max.) 0.03 0.03 0.03 0.02 0.02 0.025 0.015 0.10 0.015Cr 18.0 17.5 20.0 27.0 20.5 21.0 22.0 21.5 16.0Ni 10.0 13.5 37.5 31.0 25.0 42.0 41.0 61.0 57.0Mo - 2.5 2.5 3.5 4.7 3.0 7.0 9.0 16.0Cu - - 3.5 1.0 1.5 2.5 2.0 - -N - - - - - - - - -Cb/Ta - - 0.30 - - - 0.30 3.65 -Others - - Cb - - Al,Ti Co,W Ti,Co Ti_______________________________________________________________________

Equation 4 gives the item costs in the year 1968. These were converted to year 1998and FIM using equation 5.

IC CERPCI

PCIIC1998

1998

19681968= ◊ ◊

(5)

where IC1968 is the item cost in 1968 (US$),

IC1998 is the item cost in 1998 (FIM),

CER is the currency exchange rate (FIM/US$) andPCIi is the Chemical Engineering plant cost index in year i.

The currency exchange rate was 5.38 FIM/US$ in June 1998 (Bank of Finland 1998).The Chemical Engineering plant cost index had the value 113.6 in 1968 (Desai 1981)and the value 435.5 in January 1998 (Anon 1998b).

The heat transfer areas of the exchangers were calculated by the SYNSET program.The heat exchanger data for the separation processes are presented in tables 100...104when the minimum approach temperature is 5 K and in tables 105...109 when DTmin is

10 K.

Table 100. Heat exchanger data for the process separating a feed containing 10%formic acid, 20% acetic acid, and 70% water (figure 15) , when DTmin is 5 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 324.2D1 329.2 293.0 10.9 132861

water 278.0 333.0D2 407.0 293.0 9.4 124815

water 278.0 333.0D3 374.0 293.0 3.4 86293

water 278.0 333.0B4 420.9 293.0 10.8 132337

steam 450.0 450.0F 293.0 332.5 2.0 74296

steam 450.0 450.0B1 336.4 414.3 6.2 105939

steam 450.0 450.0B3 384.9 415.9 3.7 88616

U4 420.9 420.9L3 384.2 384.8 163.6 555196

U4 420.9 420.9L1 336.2 336.3 66.8 330099

water 278.0 324.8U1 329.8 329.2 284.3 775617_______________________________________________________________________

Table 100. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 333.0U2 407.2 407.0 85.5 379681

water 278.0 333.0U3 374.1 374.0 97.3 409006

water 278.0 333.0U4 420.9 419.8 85.4 379427

steam 450.0 450.0B3 415.9 424.1 1.6 70363

water 278.0 333.0B4 430.6 420.9 0.3 53656

steam 450.0 450.0L2 421.2 422.2 228.0 678006

steam 450.0 450.0L4 430.4 430.6 375.4 920265

1434.7 5296474----------------------------------------------------------------------------------------------------------------------

Table 101. Heat exchanger data for the process separating a feed containing 10%formic acid, 10% acetic acid, and 80% water (figure 16) , when DTmin is 5 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 324.2D1 329.2 293.0 12.5 141026

water 278.0 333.0D2 407.0 293.0 10.8 132337

water 278.0 333.0D3 374.0 293.0 3.4 86293

water 278.0 333.0B4 418.2 293.0 5.1 98693_______________________________________________________________________

Table 101. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------steam 450.0 450.0F 293.0 331.6 1.9 73341

steam 450.0 450.0B1 337.7 412.3 4.7 95926

steam 450.0 450.0B3 382.9 413.2 2.2 76158

U4 418.2 418.2L3 382.6 382.9 114.4 449383

U4 418.2 418.2L1 337.2 337.7 46.1 269061

water 278.0 324.9U1 329.9 329.2 186.0 599562

water 278.0 333.0U2 407.2 407.0 57.3 303059

water 278.0 333.0U3 374.1 374.0 66.3 328711

water 278.0 333.0U4 418.2 417.6 133.9 492925

steam 450.0 450.0B3 413.2 420.9 0.9 62502

water 278.0 333.0B4 430.6 418.2 0.2 51689

steam 450.0 450.0L2 418.8 419.4 139.6 505224

steam 450.0 450.0L4 430.4 430.6 574.8 1199473

1359.9 4965364----------------------------------------------------------------------------------------------------------------------

Table 102. Heat exchanger data for the process separating a feed containing 30%formic acid, 30% acetic acid, and 40% water (figure 17) , when DTmin is 5 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 323.1U2 328.1 327.6 498.2 1097002

water 278.0 333.0D1 407.0 293.0 9.9 127544

water 278.0 333.0D3 414.2 293.0 12.4 140527

water 278.0 333.0B3 414.3 293.0 16.2 158622

steam 450.0 450.0D2 327.6 409.3 6.1 105300

steam 450.0 450.0F 293.0 409.3 12.6 141524

steam 450.0 450.0L2 335.0 335.1 55.2 296875

steam 450.0 450.0B2 335.1 409.3 5.2 99373

water 278.0 333.0U1 407.2 407.0 207.4 640228

water 278.0 333.0U3 414.3 414.2 338.7 863661

steam 450.0 450.0D2 409.3 421.9 2.0 74296

steam 450.0 450.0F 409.3 417.1 2.0 74296

steam 450.0 450.0B2 409.3 417.2 1.1 64917

water 278.0 333.0B3 431.6 414.3 0.8 61225_______________________________________________________________________

Table 102. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------steam 450.0 450.0L1 418.0 418.9 495.1 1092743

steam 450.0 450.0L3 431.5 431.6 1485.5 2184863

3148.5 7222997----------------------------------------------------------------------------------------------------------------------

Table 103. Heat exchanger data for the process separating a feed containing 40%formic acid, 50% acetic acid, and 10% water (figure 18) , when DTmin is 5 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 333.0U2 374.2 374.0 118.0 457606

water 278.0 333.0U4 373.7 373.4 110.0 439208

water 278.0 333.0D2 374.0 293.0 14.9 152618

water 278.0 333.0D4 373.4 293.0 2.4 77961

water 278.0 333.0B1 416.3 293.0 27.8 206331

steam 450.0 450.0D3 327.2 411.3 7.9 116305

steam 450.0 450.0F 293.0 411.3 11.9 138010

steam 450.0 450.0L2 381.7 381.9 74.0 349702

steam 450.0 450.0L4 381.1 381.2 77.7 359515_______________________________________________________________________

Table 103. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------steam 450.0 450.0B3 337.9 382.5 8.6 120341

steam 450.0 450.0B4 381.2 411.3 5.0 98009

U1 416.3 416.3L3 337.8 337.9 247.8 713205

water 278.0 333.0U1 416.3 416.2 276.5 762527

water 278.0 322.8U3 327.8 327.2 1059.6 1762985

steam 450.0 450.0D3 411.3 417.0 1.1 64917

steam 450.0 450.0F 411.3 421.9 2.7 80570

steam 450.0 450.0B4 411.3 415.4 1.0 63731

water 278.0 333.0B1 430.7 416.3 1.1 64917

steam 450.0 450.0L1 430.4 430.7 1176.9 1884311

3225.0 7912770----------------------------------------------------------------------------------------------------------------------

Table 104. Heat exchanger data for the process separating a feed containing 12.1%formic acid, 0.2% acetic acid, and 87.7% water (figure 19) , when DTmin is 5 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 321.8U2 326.8 326.6 324.1 840551

water 278.0 333.0D1 406.9 293.0 22.3 184816

water 278.0 321.6D2 326.6 293.0 4.6 95221

steam 450.0 450.0F 293.0 402.0 7.4 113345

steam 450.0 450.0L2 335.8 336.3 38.3 243647

steam 450.0 450.0B2 336.3 402.0 2.7 80570

water 278.0 333.0U1 407.0 406.9 2644.5 3158017

steam 450.0 450.0F 402.0 409.5 1.1 64917

steam 450.0 450.0B2 402.0 416.5 1.1 64917

steam 450.0 450.0L1 415.8 415.9 5819.6 5242916

8865.6 10088918----------------------------------------------------------------------------------------------------------------------

Table 105. Heat exchanger data for the process separating a feed containing 10%formic acid, 20% acetic acid, and 70% water (figure 15) , when DTmin is 10 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 319.2D1 329.2 293.0 8.1 117470

water 278.0 333.0D2 407.0 293.0 9.4 124815

water 278.0 333.0D3 374.0 293.0 3.4 86293

water 278.0 333.0B4 420.9 293.0 10.8 132337

steam 450.0 450.0F 293.0 332.5 2.0 74296

steam 450.0 450.0B1 336.4 410.9 5.7 102706

steam 450.0 450.0B3 384.9 410.9 2.9 82253

U4 420.9 420.9L3 384.2 384.8 163.6 555196

U4 420.9 420.9L1 336.2 336.3 66.8 330099

water 278.0 319.8U1 329.8 329.2 223.8 670404

water 278.0 333.0U2 407.2 407.0 85.5 379681

water 278.0 333.0U3 374.1 374.0 97.3 409006

water 278.0 333.0U4 420.9 419.8 85.4 379427

steam 450.0 450.0B1 410.9 414.3 0.5 56998_______________________________________________________________________

Table 105. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------steam 450.0 450.0B3 410.9 424.1 2.4 77961

water 278.0 333.0B4 430.6 420.9 0.3 53656

steam 450.0 450.0L2 421.2 422.2 228.0 678006

steam 450.0 450.0L4 430.4 430.6 375.4 920265

1371.3 5230871----------------------------------------------------------------------------------------------------------------------

Table 106. Heat exchanger data for the process separating a feed containing 10%formic acid, 10% acetic acid, and 80% water (figure 16) , when DTmin is 10 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 319.2D1 329.2 293.0 9.2 123710

water 278.0 333.0D2 407.0 293.0 10.8 132337

water 278.0 333.0D3 374.0 293.0 3.4 86293

water 278.0 333.0B4 418.2 293.0 5.1 98693

steam 450.0 450.0F 293.0 331.6 1.9 73341

steam 450.0 450.0B1 337.7 408.2 4.3 93074

steam 450.0 450.0B3 382.9 408.2 1.7 71376_______________________________________________________________________

Table 106. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------U4 418.2 418.2L3 382.6 382.9 114.4 449383

U4 418.2 418.2L1 337.2 337.7 46.1 269061

water 278.0 319.9U1 329.9 329.2 146.5 519879

water 278.0 333.0U2 407.2 407.0 57.3 303059

water 278.0 333.0U3 374.1 374.0 66.3 328711

water 278.0 333.0U4 418.2 417.6 133.9 492925

steam 450.0 450.0B1 408.2 412.3 0.4 55401

steam 450.0 450.0B3 408.2 420.9 1.3 67182

water 278.0 333.0B4 430.6 418.2 0.2 51689

steam 450.0 450.0L2 418.8 419.4 139.6 505224

steam 450.0 450.0L4 430.4 430.6 574.8 1199473

1317.1 4920813----------------------------------------------------------------------------------------------------------------------

Table 107. Heat exchanger data for the process separating a feed containing 30%formic acid, 30% acetic acid, and 40% water (figure 17) , when DTmin is 10 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 318.1U2 328.1 327.6 391.6 944630

water 278.0 333.0D1 407.0 293.0 9.9 127544

water 278.0 333.0D3 414.2 293.0 12.4 140527

water 278.0 333.0B3 414.3 293.0 16.2 158622

steam 450.0 450.0D2 327.6 404.3 5.4 100719

steam 450.0 450.0F 293.0 404.3 11.5 135969

steam 450.0 450.0L2 335.0 335.1 55.2 296875

steam 450.0 450.0B2 335.1 404.3 4.7 95926

water 278.0 333.0U1 407.2 407.0 207.4 640228

water 278.0 333.0U3 414.3 414.2 338.7 863661

steam 450.0 450.0D2 404.3 421.9 2.7 80570

steam 450.0 450.0F 404.3 417.1 3.1 83896

steam 450.0 450.0B2 404.3 417.2 1.7 71376

water 278.0 333.0B3 431.6 414.3 0.8 61225_______________________________________________________________________

Table 107. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------steam 450.0 450.0L1 418.0 418.9 495.1 1092743

steam 450.0 450.0L3 431.5 431.6 1485.5 2184863

3041.9 7079375----------------------------------------------------------------------------------------------------------------------

Table 108. Heat exchanger data for the process separating a feed containing 40%formic acid, 50% acetic acid, and 10% water (figure 18) , when DTmin is 10 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 333.0U2 374.2 374.0 118.0 457606

water 278.0 333.0U4 373.7 373.4 110.0 439208

water 278.0 333.0D2 374.0 293.0 14.9 152618

water 278.0 333.0D4 373.4 293.0 2.4 77961

water 278.0 333.0B1 416.3 293.0 27.8 206331

steam 450.0 450.0D3 327.2 406.3 7.1 111536

steam 450.0 450.0F 293.0 406.3 10.9 132861

steam 450.0 450.0L2 381.7 381.9 74.0 349702

steam 450.0 450.0L4 381.1 381.2 77.7 359515_______________________________________________________________________

Table 108. Cont.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------steam 450.0 450.0B3 337.9 382.5 8.6 120341

steam 450.0 450.0B4 381.2 406.3 3.9 90129

U1 416.3 416.3L3 337.8 337.9 247.8 713205

water 278.0 333.0U1 416.3 416.2 276.5 762527

water 278.0 317.8U3 327.8 327.2 832.6 1513818

steam 450.0 450.0D3 406.3 417.0 1.9 73341

steam 450.0 450.0F 406.3 421.9 3.8 89376

steam 450.0 450.0B4 406.3 415.4 2.0 74296

water 278.0 333.0B1 430.7 416.3 1.1 64917

steam 450.0 450.0L1 430.4 430.7 1176.9 1884311

2998.0 7673600----------------------------------------------------------------------------------------------------------------------

Table 109. Heat exchanger data for the process separating a feed containing 12.1%formic acid, 0.2% acetic acid, and 87.7% water (figure 19) , when DTmin is 10 K.

----------------------------------------------------------------------------------------------------------------------Streams Tin Tout A IC1998

connected K K m2 FIM----------------------------------------------------------------------------------------------------------------------water 278.0 316.8U2 326.8 326.6 254.5 724891

water 278.0 333.0D1 406.9 293.0 22.3 184816

water 278.0 316.6D2 326.6 293.0 3.4 86293

steam 450.0 450.0F 293.0 397.0 6.8 109699

steam 450.0 450.0L2 335.8 336.3 38.3 243647

steam 450.0 450.0B2 336.3 397.0 2.4 77961

water 278.0 333.0U1 407.0 406.9 2644.5 3158017

steam 450.0 450.0F 397.0 409.5 1.7 71376

steam 450.0 450.0B2 397.0 416.5 1.5 69328

steam 450.0 450.0L1 415.8 415.9 5819.5 5242858

8794.8 9968962----------------------------------------------------------------------------------------------------------------------

Column costs are composed of the shell cost and the cost of the internals. Shell costscan be estimated using equation 6 (Rose 1985).

SIC f f Cp M B shell1968 = , (6)

where SIC1968 is the shell item costs in 1968 (US$) and

CB,shell is the base cost (US$).

The base cost of a column shell can be estimated using equation 7 (Rose 1985).

C FB shell, exp . .= ◊ -( )1000 1 33 0 541 (7)

where

F L D L= -( ) ( ) + -0 778 0 000082 3 281 0 9199 1 433. . ln . . . (8)

where L is the column height (m) andD is the column diameter (m).

If the columns are made of stainless steel the material factor fM has a value of 3.67.

At operating pressures below 1.0 MPa, the value of the pressure factor fp is one. (Rose

1985)The cost of packing can be estimated using equation 9 (Rose 1985).

PC D LCB packing= p4

2,

(9)

where PC is the costs of packing in 1968 (US$) andCB is the packing price in 1968 (US$/m3).

The price for stoneware saddles with a nominal size of 50 mm was in 1968 180US$/m3 (Rose 1985).

The total installed cost of the distillation plants were estimated using equation 10(Rose 1985).

TIC item ts fI= ( ) ◊ ◊ cos ,4 0 (10)

where TIC is the total installed cost in 1998 (FIM) andfI is a correction factor for inflation and currency.

The correction factor fI can be calculated using equation 11.

f CERPCI

PCII = ◊ 1998

1968 (11)

where CER is the currency exchange rate (FIM/US$) andPCIi is the Chemical Engineering plant cost index in year i.

The same values for the currency exchange rate and the plant cost indexes were used aswhen calculating the heat exchanger costs. These resulted in a value of 20.6 for thecorrection factor.

The total annual costs of the distillation plants were estimated using equation 12(Anon. 1992b).

TAC I TIC OC= ◊ + (12)

where TAC is the total annual costs,TIC is the total installed cost of equipment,OC is the annual operating cost andI is the rate of return.

The annual operating cost was presumed to consist of the annual costs of steam andwater. When the value 0.1 a-1 was used as the rate of return, the results shown in tables110 and 111 were obtained.

Table 110. Total annual costs of the distillation sequences when DTmin is 5 K (F isformic acid, A is acetic acid, and W is water).

----------------------------------------------------------------------------------------------------------------------Original feed Separation steps Total annual costscomposition 106 FIM/a- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F A W 1st 2nd 3rd 4th% % % kPa kPa kPa kPa----------------------------------------------------------------------------------------------------------------------10 20 70 20 300 101 300 41.310 10 80 20 300 101 300 43.130 30 40 300 20 300 - 69.940 50 10 300 101 20 101 74.812.1 0.2 87.7 300 20 - - 153.5----------------------------------------------------------------------------------------------------------------------

The lowest annual costs are achieved when the feed to the distillation sequencecontains 10% formic acid, 20% acetic acid and 70% water. When the feed liquor contains10 % formic acid, 10% acetic acid and 80% water, the annual costs are only slightlyhigher. The effect of the minimum approach temperature is negligible.

Table 111. Total annual costs of the distillation sequences when DTmin is 10 K (F isformic acid, A is acetic acid, and W is water).

----------------------------------------------------------------------------------------------------------------------Original feed Separation steps Total annual costscomposition 106 FIM/a- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F A W 1st 2nd 3rd 4th% % % kPa kPa kPa kPa----------------------------------------------------------------------------------------------------------------------10 20 70 20 300 101 300 41.410 10 80 20 300 101 300 43.130 30 40 300 20 300 - 90.540 50 10 300 101 20 101 75.312.1 0.2 87.7 300 20 - - 153.7----------------------------------------------------------------------------------------------------------------------

4. Discussion

4.1. Organosolv pulping

Ethanol seems to be the first organic chemical whose potential as a pulping solvent wasdiscovered. During the 100 years plus of organosolv pulping research it has been themost popular solvent, if the number of references is used as a measure. The distributionof papers referred in this work and dealing with the use of organic solvents in pulpingand pulping chemistry is shown in tables 112 and 113.

55 % of the papers are related to the use of alcohols, and 80 % of the papers havebeen published during the 1980’s and 1990’s. The popularity of alcohols is probablybased on their relatively low prices when compared to other organic chemicals. The largenumber of publications during the 1980’s and 1990’s is a result of the growingawareness of pollution problems related to conventional pulp production. During thesame time, the kraft process has also been developed keeping it still highly competitive.

Table 112. The number of papers dealing with the use of organic solvents in pulpingand pulping chemistry.

---------------------------------------------------------------------------------------------------------------------Solvent Number of papers

----------------------------------------------------------------------------------------------------------------------Methanol 186Ethanol 259Other alcohols 72Formic acid 105Acetic acid and ethyl acetate 156Other organic acids 11Phenol and cresols 58Other organic chemicals 98

945----------------------------------------------------------------------------------------------------------------------

Table 113. The number of organosolv papers at various decades.

---------------------------------------------------------------------------------------------------------------------- Years Number of papers

----------------------------------------------------------------------------------------------------------------------≤ 1900 31901 - 1910 21911 - 1920 61921 - 1930 141931 - 1940 431941 - 1950 181951 - 1960 151961 - 1970 271971 - 1980 591981 - 1990 3751991 - 1998 383

945----------------------------------------------------------------------------------------------------------------------

The quality of organosolv pulps is not competitive with the quality of correspondingkraft pulps. Particularly in alcohol pulping, the pulp quality can be improved by addingalkali to the system. By doing this, the capital cost advantage of the organosolvprocesses is lost, because the alkali has to be recovered using an expensive recoveryboiler.

Many authors state that the organosolv process they are presenting is environmentallyfriendlier than the kraft process. This is not necessarily true, because:- the kraft process has been improved and the environmental problems have beenpartially solved.- unlike the kraft process, the organosolv processes are not energy self-sufficient, whichprobably leads to an increased energy production by fossil fuels.- the use of organosolv methods in pulp bleaching may result in higher BOD7, COD

and TOC loads and higher poisonous qualities in effluents when compared to, forexample, ozone bleaching. (Liukko & Poppius-Levlin 1997)

These problems can probably be solved by further research and better process design.In order to make organosolv pulping processes competitive with conventional methodsthe problems have to be solved.

Solvent recovery has been discussed in very few papers. Solutions presented areconventional, including unit operations like evaporation and distillation. In many cases,recovery cycle designs seem to be based on incomplete data. Feed streams are presumedto be simple binary mixtures, which leads to simple designs. In reality, the streamsentering the recovery cycles are multicomponent mixtures. Most components are presentin very low concentrations. If closed liquid circulation is used they have to be removedin order to prevent their accumulation in the system. This will result in the use ofcomplex multi-stage separation processes, which have high investment and operatingcosts.

Distillation is the most popular unit operation proposed for use as the solventpurification stage. It is a major energy consumer in the process and has therefore to bedesigned carefully. In addition, it has to be thermally integrated to other parts of theprocess.

When organosolv processes are evaluated using the list of requirements for a newpulping process presented in chapter 1, it seems to be unlikely that any process will beapplied on an industrial scale in the near future.

In order to be able to replace conventional pulping methods in existing plants, or innew investments, the organosolv methods should offer significant benefits. In order toreach that status, the processes have to be further developed. This may be done byoptimising the existing process configurations, by designing new ones, or by addingnew stages, e.g. fungal pretreatment (Ferraz et al. 1998b), to existing configurations.

4.2. Solvent recovery in peroxyacid pulping

4.2.1. Feasible separation methods

When the separation process selection methods found in the literature are applied to theternary mixture formic acid-acetic acid-water, they suggest the use of the following unitoperations as possible methods:- adsorption- azeotropic distillation- crystallisation- evaporation- extractive distillation- flash evaporation- liquid-liquid extraction- pervaporation- simple distillation- stripping- ultrafiltration

Simple distillation, azeotropic distillation, extractive distillation and liquid-liquidextraction are separation processes that have been used in published studies for separatingthe ternary mixture. Research in this field has been almost completely focused on thepurification of the product in acetic acid production or waste water treatment. The aceticacid product contains only small amounts of formic acid and water as impurities. Wastewaters contain small amounts of both acids. The feed of the separation section in apulping process using the Milox method contains water as the main component andsignificantly more formic acid than acetic acid. Therefore the separation methodspresented in the literature cannot be directly applied.

Simple distillation was chosen for further studies in order to keep the separationprocess simple. Extractive distillation was also chosen as a representative for processes

using mass separating agents. The selection of a mass separating agent to be used in anorganosolv process is critical. Small amounts of the agent follow the recovered solventto the digester and the possible effect of that has to be studied before a mass separatingagent can be selected.

4.2.2. Minimum work of separation

When minimum work of separation calculated for the feed compositions studied areranked in increasing order, the results shown in table 114 are obtained for thosecompositions that reached the final stage of this research.

Table 114. Minimum work of separation rankings compared with the total annualcosts (x1 is the molar fraction of formic acid in feed, 2 and 3 refer to acetic acid andwater).

----------------------------------------------------------------------------------------------------------------------x1 x2 x3 Wmin,298K Ranking out of 37 Total annual costs

kJ·mol-1 106 FIM/a----------------------------------------------------------------------------------------------------------------------

0.1 0.2 0.7 1.611 5 . 41.40.1 0.1 0.8 1.335 2 . 43.10.3 0.3 0.4 2.327 36. 90.50.4 0.5 0.1 2.015 19. 75.30.121 0.002 0.877 0.907 1 . 153.7

______________________________________________________________________

Minimum work of separation seems to give a reasonable first estimate for the ease ofseparating the ternary mixture of formic acid, acetic acid and water, when significantamounts of each three components are present

4.2.3. Phase equilibria

According to Walas (Walas 1985) the Wilson model is generally a superiorrepresentation for activity coefficient behaviour of both polar and nonpolar mixtures. Itis capable of representing multicomponent behaviour with only binary parameters. Thisis probably the reason for the fact that the Wilson model gave best fits for the vapour-liquid equilibrium data at the pressures 101.3 and 300 kPa.

The large number of parameters (8) in the NRTL model resulted in the best data fit atthe system pressure of 20 kPa. According to Walas (Walas 1985), the NRTL gives morefrequently the best fit than the Wilson model for aqueous organics.

When the distillation feed mixtures that reached the final stage of this research areplaced on ternary diagrams, the presentations shown on figures 22, 23 and 24 areobtained. Mixtures containing 10 % formic acid, 20 % acetic acid and 70 % water (10-20-30) and 10 % formic acid, 10 % acetic acid and 80 % water (10-10-80) reached thelowest total costs when the distillation sequence started with a column operating at 20kPa. Both mixtures are located in figure 22 in the distillation region which is limited bythe boundaries drawn between the ternary azeotrope and the upper and left edges of thediagram. This suggests that it is favourable to start the distillation sequence with avacuum column when the formic acid concentration in feed is below 30.8 % and the feedcomposition is located in the left triangle.

BJ

H

F

B Binary azeotrope

J Ternary azeotrope

H 10-20-70

F 10-10-80

30-30-40

40-50-10

Milox

0

0.2

0.4

0.6

0.8

1

1

0.8

0.6

0.4

0.2

01 0.8 0.6 0.4 0.2 0

HCOOH

CH3COOH

H2O

Fig. 22. Feed compositions placed on the ternary diagram at 20 kPa.

B

J

H

F

B Binary azeotrope

J Ternary azeotrope

H 10-20-70

F 10-10-80

30-30-40

40-50-10

Milox

0

0.2

0.4

0.6

0.8

1

1

0.8

0.6

0.4

0.2

0

HCOOHH2O

1 0.8 0.6 0.4 0.2 0

CH3COOH

Fig. 23. Feed compositions placed on the ternary diagram at 101.3 kPa.

BJ

H

F

B Binary azeotrope

J Ternary azeotrope

H 10-20-70

F 10-10-80

30-30-40

40-50-10

Milox

0

0.2

0.4

0.6

0.8

1

1

0.8

0.6

0.4

0.2

01 0.8 0.6 0.4 0.2 0

HCOOH

CH3COOH

H2O

Fig. 24. Feed compositions placed on the ternary diagram at 300 kPa.

No sequences that were selected for this study started with an atmospheric column,but three of the five feed mixtures are located in the distillation region limited byboundary lines between the ternary azeotrope and the upper and the left edge of thediagram (fig. 23).

Mixtures containing 30 % formic acid, 30 % acetic acid and 40 % water (30-30-40),40 % formic acid, 50 % acetic acid and 10 % water (40-50-10) and 12.1 % formic acid,0.2 % acetic acid and 87.7 % water (Milox) started with a pressurized column. Themixture 30-30-40 is located on figure 24 in the distillation region limited by boundariesdrawn between the ternary azeotrope and the upper and the left edge of the diagram. Thissuggest that it is favourable to start a distillation sequence when the formic acidconcentration in the feed is below 75.8 %. The mixture 40-50-10 is located on one ofthe boundary lines. It is therefore obvious that the real boundary lines are not straightlines. The Milox feed mixture is located in the distillation region formed when lines aredrawn between the azeotropes and between the ternary azeotrope and the upper edge of thediagram. The total costs of separating this mixture are significantly higher than the costsof separating the four other mixtures. Obviously the acetic acid concentration in theliquor fed to a distillation sequence should therefore be higher. This would place theMilox mixture on the same distillation region with the other mixtures.

As a conclusion, it can be noted that vacuum distillation is a favourable first unitoperation in a sequence separating the formic acid-acetic acid-water mixture when theformic acid concentration is below 30.8 %. Pressurized distillation is likely to be thebest choice when the formic acid concentration is between 30.8 and 75.8 %. When theconcentration is above 75.8 % other separation methods should be considered.

4.2.4. Shortcut simulations of the separation sequences

The total number of feed streams with different compositions was 37. When the firstseparation stage was simulated with these feed streams:- simple distillation at 20 kPa was accepted in four cases,- simple distillation in an atmospheric column was accepted in 21 cases,- simple distillation at 300 kPa was accepted in 18 cases and- extractive distillation using NMP was accepted in 14 cases.

Vacuum distillation at 20 kPa seems to be an acceptable first separation stage onlyfor feed streams with high water contents. When the formic acid content of the feed is 50%, no feasible separation method is found. At 20 kPa, the number of equilibrium stagesrequired is very high. At the higher pressures, the most plentiful component (formicacid) cannot be obtained as a product. This is an indication for the distillation boundarieson the ternary diagrams being curves instead of straight lines.

When studying the second separation stage, 99 cases were simulated. The number ofcases accepted for further studies was 40. When vacuum distillation was tried as thesecond separation stage after atmospheric distillation, no solution was found for theoriginal feed composition 40 % formic acid, 50 % acetic acid and 10 % water. In thiscase, the distillate of the first column contains 80 % formic acid, 1 % acetic acid and 19% water. If this composition is placed on the ternary diagram at 101.3 kPa published byHunsmann and Simmrock (Hunsmann & Simmrock 1966), it is located on one of thedistillation borders, which makes the separation impossible.

Of the 86 different three stage separation sequences simulated, 46 could be accepted.Several possible combinations were found for feed streams containing 40 % formic acidor less. At higher formic acid concentrations only few possible three stage separationsequences were found. Again some cases could not be solved. This is probably caused bythe location of the feed composition on an actual distillation border line.

In some cases, a three stage separation sequence, which did not produce three pure (98%) components, was accepted according to the constraints used in this research. A fourthstage was simulated for those cases. Only six four stage processes out of the 17simulated could be accepted. Most of the rejections were based on far too high a numberof equilibrium stages. Some of the sequences were also rejected because all threecomponents were not obtained as products. A fifth stage was not considered.

In the last stage of the shortcut simulations, recycle streams were added to theseparation sequences. Those sequences having an energy consumption lower than theaverage were chosen for simulations with rigorous calculation methods. When thethermodynamic efficiency for the separation is determined as

ηthermodynamicactual

= W

Wmin

(13)

where hthermodynamic is the thermodynamic efficiency,

Wmin is the minimum work of separation and

Wactual is the actual energy consumption of the separation

sequence

the efficiencies based on shortcut simulation results are presented in table 115.

Table 115. Thermodynamic efficiencies based on shortcut simulation results forseparation of HCOOH-CH3COOH-H2O mixtures.

_______________________________________________________________________ Feed composition Minimum work Actual energy Thermo-- - - - - - - - - - - - - - - - - - - - - work of consumption dynamicHCOOH CH3COOH H2O separation kJ/mol of feed efficiency

% % % kJ/mol of feed______________________________________________________________________

10 20 70 1.611 54.74 0.02910 10 80 1.335 44.19 0.03030 30 40 2.327 161.30 0.01430 60 10 1.924 117.72 0.01640 50 10 2.015 133.05 0.01512.1 0.2 87.7 0.907 114.15 0.008

_______________________________________________________________________

The average thermodynamic efficiency is 1.9 % for the separation sequences chosenfor rigorous simulations. If the energy consumption of separating the reference mixture

is not taken into account, the average efficiency is 2.1 %, which is a fairly typical valuefor distillation because, according to Null (Null 1980), the average thermodynamicefficiency of distillation is around 2.5 %.

4.2.5. Rigorous simulations

The sequences used in shortcut simulations could not be solved as such using rigorouscalculation methods. This is probably caused by the highly unideal nature of the formicacid-acetic acid-water mixture. Therefore the sequences had to be redesigned. Thespecifications used were:1. The pressure determined in shortcut calculations was used for each distillation stage.2. The product purity was 98 %.3. The highest possible recovery rate was used.

According to the rigorous calculation results, four distillation stages were required inmost cases to separate the mixtures. This is caused by the specifications used. Acceptinglower product purities or recovery rates would decrease the number of distillation stagesrequired. It also could make the compositions of the feed streams to the following stagesmore favourable for separation.

The recovery rates in columns simulated by rigorous methods were significantlylower than the corresponding recovery rates in columns simulated by shortcut methods.This led to significantly higher recycle stream flow rates and higher energyconsumptions.

The energy consumption of separating the reference mixture is significantly higherthan the energy consumption of the other distillation sequences. The composition of theestimated distillation feed in the peroxyformic acid process would be located in theternary diagrams in a more favourable distillation region if the acetic acid content wereincreased.

Table 116. Thermodynamic efficiencies based on rigorous simulation results forseparation of HCOOH-CH3COOH-H2O mixtures.

_______________________________________________________________________ Feed composition Minimum work Actual energy Thermo-- - - - - - - - - - - - - - - - - - - - - work of consumption dynamicHCOOH CH3COOH H2O separation kJ/mol of feed efficiency

% % % kJ/mol of feed______________________________________________________________________

10 20 70 1.611 293.98 0.00510 10 80 1.335 277.13 0.00530 30 40 2.327 642.85 0.00430 60 10 1.924 1441.69 0.00140 50 10 2.015 632.84 0.00312.1 0.2 87.7 0.907 2552.04 0.0004

_______________________________________________________________________

When the energy consumptions obtained by rigorous calculations are used to estimatethe thermodynamic efficiencies of the distillation sequences according to equation 13, theresults presented in table 116 are obtained. The effect of thermal integration is not takeninto account in these results. The efficiencies are significantly lower than those based onshortcut simulations. This is caused by the unideal nature of the ternary mixture studied.The average thermodynamic efficiency is 0.3 %. If the energy consumption value forseparating the reference mixture is not taken into account, the average efficiency is 0.4%, which is a fairly low value.

4.2.6. Thermal integration using pinch technology

When the pinch analysis was performed, the separation sequence designed for the feedcomposition 10 % formic acid, 20 % acetic acid and 70 % water showed the lowest totalannual costs. This liquor composition may be near the composition of spent washingliquor if an aqueous mixture of the acids is used as pulping liquor. The effect of theminimum temperature approach value was tested by using the values 5 K and 10 K. Theeffect was found to be negligible.

The cost estimates are rough and cannot be used as the basis for any investmentdecisions. They are calculated in a similar way for all process alternatives, and cantherefore be used to compare the alternatives.

A probable reason for the lowest costs occuring with the feed composition 10 %formic acid, 20 % acetic acid and 70 % water is that water seems to be the componentmost easily separated from the mixture in the first separation stage. When a largeamount of one component is separated, the volume fed to the following separation stagedecreases significantly causing both operating and investment costs to also decrease.

The composition 10 % formic acid, 20 % acetic acid and 70 % water is located in themost favourable distillation region in the ternary diagrams for the pressures 20 kPa,101.3 kPa and 300 kPa (figures 22...24). The composition with the second best results(10 % formic acid, 10 % acetic acid and 80 % water) is also located in the same region.Therefore it is probable that it is favourable to have around 10 % formic acid, 10-20 %acetic acid and 70-80 % water in the feed of a distillation sequence separating the ternarymixture. These distillation feed liquor compositions can be obtained by using a mixtureof formic acid and acetic acid as the pulping liquor and by reducing the amount of waterfed to the process. The water amount can be reduced by pulping dried chips and by usingless water consuming methods for pulp washing.

A feed composition where the acetic acid content is higher than the formic acidcontent is also favourable because more acetic acid is formed during pulping and formicacid is less stable.

It also seems to be favourable to start the distillation sequence with a vacuum columnseparating most of the water, followed by pressurised distillation, atmosphericdistillation and pressurised distillation.

Thermal integration decreases the energy consumptions of the distillation sequencesby up to 40 % when compared to a situation with no integration. In some cases, thedecrease is significantly lower because the temperature levels of the streams in those

cases are not suitable for integration. Changing the overall design of the distillationsequences would probably make it possible to make greater savings using thermalintegration.

When the energy consumptions obtained after thermal integration are used to estimatethe thermodynamic efficiencies of the distillation sequences according to equation 13, theresults presented in table 117 are obtained.

Table 117. Thermodynamic efficiencies based on thermal integration results forseparation of HCOOH-CH3COOH-H2O mixtures.

_______________________________________________________________________ Feed composition Minimum work Actual energy Thermo-- - - - - - - - - - - - - - - - - - - - - work of consumption dynamicHCOOH CH3COOH H2O separation kJ/mol of feed efficiencies

% % % kJ/mol of feed______________________________________________________________________

10 20 70 1.611 172.40 0.00910 10 80 1.335 194.18 0.00730 30 40 2.327 539.24 0.00440 50 10 2.015 286.24 0.00712.1 0.2 87.7 0.907 2485.40 0.0004

_______________________________________________________________________

Thermal integration has a significant effect on the thermodynamic efficiencies of mostof the distillation sequences. The average efficiency is 0.5 %. If the energy consumptionof separating the reference mixture is not taken into account, the average efficiency is0.7 %, which still is significantly lower than the estimate 2.5 % given by Null (Null1980).

Optimising both the sequence and column designs would probably improve theefficiencies. However, the thermodynamic efficiency for the separation of this highlyunideal ternary mixture is considerably below the average values for distillation.

5. Conclusions

The research related to organosolv pulping has been so far mainly focused on optimisingthe delignifying process. Very few papers dealing with the solvent recovery have beenpublished. This, together with the fact that the organosolv pulping processes have veryfew advantages compared with the kraft process, indicates that they are not ready tocompete with the kraft process at this stage of development. The future of organosolvprocesses is highly dependent on environmental legislation, which in the future maycause problems for the economic operation of present pulping processes.

Simple distillation seems to be the preferable solution for recovering the solvents inthe peroxyacid pulping process. If only formic acid and peroxyformic acid are used assolvents, the small amount of acetic acid formed during pulping causes the distillationfeed composition to be located in a region not favourable for distillation. In order tomake the separation more economic, the water content of the distillation feed should bedecreased to around 70 %, which means that less water should be used in the precedingunit operations. The feed should also contain more acetic acid than formic acid. This canbe achieved by using a mixture of formic acid and acetic acid as the delignifying solvent.

The minimum work of separation can be used to estimate the ease of separatingvarious ternary mixtures containing formic acid, acetic acid and water. Shortcutsimulations can be used to to compare various distillation sequences. Because of thehighly unideal nature of the mixture the results of shortcut simulations should not beused for designing a separation sequence for a particular feed composition.

Pinch technology is a useful tool in process synthesis. Energy savings of up to 40 %can be achieved in a distillation plant where the formic acid-acetic acid-water mixture isseparated. When the total pulp manufacturing process is integrated, the savings may beeven higher.

Thermodynamic efficiencies of simple distillation sequences separating the formic acid-acetic acid-water mixture seem to be less than 1 %, which is lower than the averagevalue 2.5 % given for distillation in the literature.

The significant effect of the distillation feed composition on the total costs of theseparation sequence stresses the importance of simultaneous optimisation of all unitoperations in an organosolv pulping process.

References

Aaltonen O, Ylinen P, Johansson A & Oksanen H (1987) Valtion teknillinentutkimuskeskus, assignee. Menetelma lignoselluloosapitoisen raaka-aineendelignifioimiseksi. FI patent 73013.

Aaltonen O, Johansson A & Ylinen P (1989) Organosolv pulping: softwooddelignification kinetics and selectivity in THFA HCl-pulping. In: Kennedy JF, PhillipsGO & Williams PA (eds) Wood Processing and Utilization. Ellis Horwood, Chichester,p 62-68.

Abad AQ & Paszner L (1989) Fate and recovery of resin- and fatty acids fromcooking liquors on organosolv pulping of Pinus elliottii. 1989 Solvent PulpingConference, Seattle, WA, p 1-6.

Abbot J & Bolker HI (1984) Alkaline delignification with amines and alcohols. SvenskPapperstidning (12): R105-R109.

Abe Z (1993) Alkali-alcohol-anthraquinone pulping. Seventh International Symposium onWood and Pulping Chemistry Proc., Beijing, PR China, 3: 189-194.

Abramovitch RA & Iyanar K (1994) Organosolv pulping using a microwave oven.Holzforschung 48(4): 349-354.

Ahmed A & Kokta BV (1992) Nonsulfur process for preparing pulps for papermaking. CApatent 1.336.546. (ABIPST 66:18255(P)).

Ahmed A, Kokta BB & Carrasco F (1992) Steam explosion pulping of aspen pretreatedwith alcohol mixed with a non-sulfur chemical. 1992 Solvent Pulping SymposiumNotes, Boston, MA, p 67-72.

Aittamaa J, Laxen T, Lonnberg B & Sjoholm R (1986) Studies on the alcohol pulpingprocesses. XXII Eucepa Conf., Florence, Italy, 1: 7:1-7:20.

Akishima Y, Isogai A, Onabe F & Usuda M (1991) Structural changes of amorphouscellulose by acid pulping treatments. Nordic Pulp and Paper Res J 6(4): 166-169.

Albrecht JS & Nicholls GA (1974) Fractionation and examination of soluble products fromperoxyacetic acid delignification of loblolly pine. Paperi ja Puu (11): 927-943.

Aleksandrova G, Medvedeva S, Kanitskaya L, Babkin V & Zakazov A (1995) Anecologically sound pulping process involving microbiological delignification. The 8thInternational Symposium on Wood and Pulping Chemistry Proc., Helsinki, Finland, 2:273-278.

Aleksandrova G, Buryachenkov M, Medvedeva S, Zakazov A & Babkin V (1996)Organosolv delignification of wood with microbiological pretreatment. Iz VUZ Lesn Zh(1/2): 30-34. (ABPST 69:349(AS)).

Alen R (1988a) Formation of aliphatic carboxylic acids from hardwood polysaccharidesduring alkaline delignification in aqueous alcohols. Cellul Chem Tech 22(4): 443-448.

Alen R (1988b) Formation of aliphatic carboxylic acids from softwood polysaccharidesduring alkaline delignification in aqueous alcohols. Cellul Chem Tech 22(5): 507-512.

Aliev RG, Burov AV & Rusakov AE (1990) Molecular weight characteristics of ligninisolated during organic solvent treatment of birchwood [betula]. Khim Drev (Riga) (3):45-49. (ABIPST 62:5436).

Anon (1920) Koln-Rottweil Akt.-Ges., assignee. Verfahren zur herstellung von zellstoff.German patent 329566.

Anon (1935) Thioglycollic acid as a new lignin reagent. The Paper Industry 16, 787-788.Anon (1955) Celanese Corporation, assignee. Purifying acetic acid by azeotropic

distillation. GB patent 727 078.Anon (1985) Organic acid pulping of wood reduces chemical costs and energy

requirements. Paper Trade J, (11): 50-51.Anon (1987a) Die demonstrationsanlage für das Organocell-verfahren vor dem anlauf.

Dtsch Papierwirtsch, (1): T62-T63.Anon (1987b) Radical new technology in chemical pulping. Paper 108(6): 19-20.Anon (1990a) Asam-pilot-zellstoffanlage in Baienfurt. Wochenbl Papierfabr 118(11/12):

524-529.Anon (1990b) Pilot ASAM plant - harbinger of a german pulp industry. Paper Tech 31(8):

36-37.Anon (1990c) ASAM-pilotanlage erfolgreich in betrieb. Allg Papier-Rundsch, (24/25):

712-716.Anon (1991a) Bayerisches richtfest fur den ersten Organocell-kocher der welt. Dtsch

Papierwirtsch, (3): 50-56.Anon (1991b) Alcell can offer a green solution. Pulp Paper Int 33(4): 53-57.Anon (1991c) PRO/II regress user guide. Simulation Sciences Inc.Anon (1991d) PRO/II pc user guide. Simulation Sciences Inc.Anon (1992a) Ymparistoa saastava sellun valmistusprosessi koetehdasvaiheessa. Kemia-

Kemi 19(2): p. 150.Anon (1992b) SYNSET user manual. ChemEng Software and Services Ltd.Anon (1993) Weltpremiere in Kehlheim. Wochenbl Papierfabr 121(1): 27-29.Anon (1994) Alcell process - technology of the future - today. Dtsch Papierwirtsch (4): 34-

35, 38-39. (ABIPST 66:8836(AS)).Anon (1995) Repap buys Atholville for Alcell mill. Pulp Pap Week 17(1): 7.

(ABIPST 65:16836).Anon (1998a) Alcell sale terminated. PIMAs North American Papermaker (6): 18.

(Paperbase 00512640).Anon (1998b) Economic indicators. Chem Eng 105(4): 180.Antal M, Ebringerova A & Micko MM (1991) Kationisierte hemicellulosen aus

espenholzmehl und ihr einsatz in der papierherstellung. Das Papier 45(5): 232-235.Apostol AV & Kozlov VP (1979) Effect of impregnating birchwood chips with various

concentrations of acetic acid on some physical and mechanical properties. Izv VUZLesnoi Zh, (1): 64-66. (ABIPC 50:9447).

April GC (1983) Cemicals from wood by organic solvent delignification. TheNational Science Foundation, BER Report No. 311-124.

April GC, Kamal MM, Reddy JA, Bowers GH & Hansen SM (1979) Delignification withaqueous-organic solvents: southern yellow pine. Tappi 62(5): 83-85.

Aptel P, Challard N, Cuny J & Neel J (1976) Application of the pervaporation process toseparate azeotropic mixtures. J Membr Sci 1: 271-287.

Araki H, Iwata H, Aoyagi T & Kachi S (1989) Solvolysis pulping process: a comparativestudy on reactions and products. In: Kennedy JF, Phillips GO & Williams PA (eds)Wood Processing and Utilization. Ellis Horwood, Chichester, p 69-74.

Araujo ES & Curvelo AAS (1997a) Buffered organosolv delignification, 1., effect of bufferconcentration. 9th International Symposium on Wood and Pulping Chemistry OralPresentations, Montreal, Canada, p J4 1-4.

Araujo GT & Curvelo AAS (1997b) Organosolv pulping of (mimosa hostilis benth.), 1.,kinetics of ethanol-water delignification. 9th International Symposium on Wood andPulping Chemistry Poster Presentations, Montreal, Canada, p 4:1-4.

Aravamuthan R, Chen W, Zargarian K & April G (1989) Chemicals from wood:prehydrolysis/organosolv methods. Biomass 20(3/4): 263-276.

Aravamuthan RG, Valade JL, Law KN & Lanouette R (1993) Organosolv TMP, CTMP andCMP from aspen. 1993 Pulping Conference Proc., Atlanta, GA, 1: 193 - 204.

Argyropoulos DS & Bolker HI (1987) Condensation of lignin in dioxane-water-HCl. JWood Chem Tech 7(1): 1-23.

Argyropoulos DS, Hortling B, Poppius-Levlin K, Sun Y & Mazur M (1995) Miloxpulping: lignin charaterization by 31P NMR spectroscopy and oxidative degradation.The 8th International Symposium on Wood and Pulping Chemistry Proc., Helsinki,Finland, 1: 495-502.

Arnoldy P (1989) Shell Internationale Research Maatschappij B.V., assignee. Process forpulping lignocellulose-containing material. GB patent 2.209.772A.

Arnoldy P & Petrus L (1989) Shell Internationale Research Maatschappij B.V., assignee.Verfahren zum aufschließen lignozellulosehaltigen materials. DE patent 38.30.993.A1.

Arnoldy P & Petrus L (1990) Shell Oil Company, assignee. Process for pulpinglignocellulose-containing material. US patent 4.904.342.

Arnoldy P & Petrus L (1992) Shell Canada Ltd., assignee. Process for pulpinglignocellulose-containing material. CA patent 1.300.324. (ABIPST 66:11422(P)).

Aronovsky SI & Gortner RA (1936) The cooking process, IX, pulping wood withalcohols and other organic reagents. Ind Eng Chem, p 1270-1276.

Avela ES, Sandell E & Avela A (1988) Suomen Sokeri Oy, assignee. Menetelmasellumassan ja sokereiden tuottamiseksi lehtipuuhakkeesta. FI patent 76845.

Ayla C (1982) Uber eigenschaften und abbarbaukeit von mit alkohol-wasser-gemischenisolierten ligninen, 7. mitteilung: verwendung von ethanol-wasser-ligninen zurherstellung von holzleimen. Holzforschung 36(2): 93-98.

Aziz S & Goyal GC (1993) Kinetics of delignification from mechanistic and processcontrol point of view in solvent pulping processes. 1993 Pulping Conference Proc.,Atlanta, GA, 3: 917-920.

Aziz S & McDonough TJ (1987) Ester pulping - a brief evaluation. Tappi Journal 70(3):137-138.

Bachner K, Fischer K & Baucker E (1993) Zusammenhang zwischen aufbau der zellwandund festigkeitseigenschaften bei faserstoffen von konventionellen und neuenaufschlußverfahren. Das Papier 47(10A): V30-V40.

Baeza J, Urizar S, Erismann N, Freer J, Schmidt E & Duran N (1991) Organosolv pulping,V: formic acid delignification of Eucalyptus globulus and Eucalyptus grandis. BioresTech 37(1): 1-6.

Baierl KW (1979) Adsorber-regenerator. US patent 4.155.849.Baierl KW, Young RA & Young TR (1986) Biodyne Chemicals Inc., assignee. Menetelma

lignoselluloosan liuottamiseksi. FI patent application 863069.

Bailey AJ (1939) Reagents of the University of Minnesota, assignee. Alcoholictreatment of ligneous cellulosic material. US patent 2.166.540.

Bailey AJ (1940a) The chemistry of lignin, I: the existence of a chemical bond betweenlignin and cellulose. Paper Trade J 110(1): 29-34.

Bailey AJ (1940b) The chemistry of lignin, II: the butanolysis of wood. Paper Trade J110(2): 29-32.

Bailey AJ (1940c) The alcoholysis of wood. Pacific Pulp Paper Ind 14: 24-27.Bailey AJ (1942) Recovery of butanol in butanol pulping. Ind Eng Chem 34(4): 483-485.Bailey CW & Dence CW (1966) Peroxyacetic acid bleaching of chemical pulps. Tappi

49(1): 9-15.Balakshin M & Deineko I (1995) The role of individual lignin fragments during wood

delignification with oxygen in water-ethanol mixture. The 8th International Symposiumon Wood and Pulping Chemistry Proc., Helsinki, Finland, 1: 323-330.

Balogh DT, Curvelo AAS & Groote RAMC (1992) Solvent effects on organosolv ligninfrom Pinus caribaea hondurensis. Holzforschung 46(4): 343-348.

Balogh DT (1993) Molecular weights of organosolv lignins. In: Kennedy JF (ed)Cellulosics: Chemical, Biochemical and Material Aspects. Ellis Horwood, Chichester, p279-284.

Bank of Finland (1998) Http://www.bof.fi/env/fin/new/fixlist.stm.Barham HN & Clark LW (1951) The decomposition of formic acid at low temperatures. J

Am Chem Soc 73: 4638-4640.Barna BA, Pylkkanen VA, Kivimaki JK & Yang Y (1991) Applications of process design

software in organosolv pulping. 1991 Tappi Pulping Conf. Proc., Orlando, FL, 2: 637-644.

Barnicki SD & Fair JR (1990) Separation system synthesis: a knowledge based approach,1: liquid mixture separations. Ind Eng Chem Res 29(3): 421-432.

Basta J, Holtinger L, Hallstrom AS & Lundgren P (1994) Peroxo compounds in tcfbleaching. 1994 Pulping Conference Proc., San Diego, CA, p 953-956.

Baumeister M & Edel E (1980) Athanol-wasser-aufschluss. Das Papier 34(10A): V9-V18.Baumeister M & Edel E (1982) MD-Papierfabriken Heinrich Nicolaus GMBH, assignee.

Verfahren und vorrichtung zum kontinuierlichen aufschliessen von pflanzenfaser-material. EP patent 0.012.960.B1.

Baumeister M & Edel E (1983a) MD-Organocell Gesellschaft für Zellstoff- undUmwelttechnik mbH, assignee. Menetelma ja laite kasvikuitumateriaalin liuottamiseksiyhtajaksoisesti. FI patent 71360.

Baumeister M & Edel E (1983b) MD Verwaltungsgesellschaft Nicolaus GmbH & Co. KG,assignee. Verfahren und reactor zum kontinuierlichen aufschliessen vonpflanzenfasermaterial. DE patent 32.12.767.A1.

Baumeister M & Edel E (1985) MD-Verwaltungsgesellschaft Nicolaus G.m.b.H & Co. KG,assignee. Method and reactor for continuous extraction of vegetable-fibermaterial. CA patent 1.196.155.

Beer R & Peter S (1985) High pressure extraction of lignin from wood. In: PenningerJML, Radosz M, McHugh MA & Krukonis VJ (eds) Supercritical Fluid Technology.Elsevier, Amsterdam, p 385-396.

Beer R & Peter S (1986) Lignin-extraktion aus holz mit alkylaminen unter druck. Chem-Ing-Tech 58(1): 72-73.

Beigelman AV, Burov AV, Maltsev SM & Soldatenkova TS (1991) LTITsBP, assignee.Method of producing pulp. USSR patent 1.677.121. (ABIPST 63:6467(U)).

Bennacer EM, Kiruyshina MF & Zarubin MY (1989) Effect of organic solvents oncleavage of beta-alkyl-0-arylic and glucosidic bonds kinetics. 1989 InternationalSymposium on Wood and Pulping Chemistry Poster Sessions, Raleigh, NC, p 139-146.

Berg L (1987) Celanese Chemical Co., assignee. Separation of formic acid from acetic acidby extractive distillation. US patent 4.692.219.

Berg L (1988) Dehydration of formic acid by extractive distillation. US patent4.786.370.

Berg L (1990) Hoechst Celanese Chemical Co., assignee. Separation of formic acid fromacetic acid by extractive distillation with acetyl salicylic acid. US patent 4.909.907.

Berg L & Yeh AI (1987) Dehydration of formic acid by extractive distillation. US patent4.642.166.

Berg L, Szabados RJ, Wendt KM & Yeh AI (1990) The dehydration of the lower fatty acidsby extractive distillation. Chem Eng Comm 89: 113-131.

Berg A, Janssen W, Balle S, Kunz RG & Klein W (1995) Acetocell GmbH & Co. KG,assignee. Delignification of cellulosic raw materials using acetic acid, nitric acid andozone. US patent 5.385.641.

Bharati R, Bharati S, Singh SP, Karunanidhi MSP, Baskaran S & Paramsivam M (1989)Prospects of organosolv pulping of bagasse. Silver Jubilee International Seminar &Workshop: Appropriate Technologies for Pulp & Paper Manufacture in DevelopingCountries, 2: paper 34. (ABIPST 67:13930(AC)).

Billa E, Kurek B, Koutsoula E, Monties B & Koukios E (1997) Effect of manganeseperoxidase on the cell wall components of wheat straw and sorghum organosolv pulps.9th International Symposium on Wood and Pulping Chemistry Oral Presentations,Montreal, Canada, p I2-1-4.

Black NP (1991) ASAM alkaline sulfite pulping process shows potential for large-scaleapplication. Tappi J 74(4): 87-93.

Bogolitsyn KG, Ryabeva NV, Volkova NN & Wadso I (1994) Conformationaltransformations of dioxane lignin in organic solvents. Izv VUZ Lesn Zh (5/6): 109-117. (ABIPST 67:475(AS)).

Bonn G, Oefner PJ & Bobleter O (1988) Analytical determination of organic acids formedduring hydrothermal and organosolv degradation of lignocellulosic biomass.Fresenius Zeitsch Anal Chemie 331(1): 46-50.

Borgards A, Patt R, Kordsachia O, Odermatt J & Hunter WD (1993) A comparison ofASAM and kraft pulping and ECF/TCF bleaching of southern pine. TAPPI 1993 PulpingConference, Atlanta, GA, p 629-636.

Botello JI, Gilarranz MA, Rodriguez F & Oliet M (1998) Wood fractionation by cookingin alcohol-water media. Fifth European Workshop on Lignocellulosics Chemistry forEcologically Friendly Pulping and Bleaching Technologies, Aveiro, Portugal, p 217-220. (Paperbase 00522858).

Bott K, Kaibel G, Hartmann H, Irnich R & Bulow H (1984) BASF AG, assignee.Verfahren zur destillativen gewinnung von ameisensaure. DE patent 33.19.651.A1.

Bowen IJ & Hsu JCL (1990) Overview of emerging technologies in pulping andbleaching. Tappi J 73(9): 205-217.

Bowers GH & April GC (1977) Aqueous n-butanol delignification of southern yellow pine.Tappi 60(8): 102-104.

Brauns F & Hibbert H (1933) Studies on lignin, X: the identity and structure of sprucelignins prepared by different methods. J Am Chem Soc 55: 4720-4727.

Brauns F & Hibbert H (1935) Studies on lignin and related compounds, XII:methanol lignin. Can J Res 13B: 28-34.

Brickman L, Pyle JJ, McCarthy JL & Hibbert H (1939) Studies on lignin and relatedcompunds, XXXIX: the ethanolysis of spruce and maple woods. J Am Chem So 61:868-869.

Brodersen KH, Dahlmann G & Leopold H (1992) Organocell Gesellschaft fur Zellstoff- undUmwelttechnik mbH, assignee. Verfahren zum delignifizieren von pflanzenfasermaterial.DE patent 41.03.572.A1.

Brogdon BN, Dimmel DR & McDonough TJ (1997) Bleaching of softwood kraft pulpsusing an ethanol-based partial sequence. 9th International Symposium on Wood andPulping Chemistry Oral Presentations, Montreal, Canada, p A2-1-4.

Brolin A, Gierer J & Zhang Y (1991) Delignification of softwood kraft pulps by oxygen-containing species in acetic acid media. 6th International Symposium on Wood andPulping Chemistry Proc., Melbourne, Australia, 2: 205-209.

Bruniere PMF & Galichon JPM (1988) Societe Tag Pulp Industries S.A., assignee. Processfor the pulping of lignocellulose materials with alkali or alkaline earth metal hydroxideor salt and a solvent. US patent 4.790.905.

Brunt V (1992) The University of South Carolina, assignee. Process for recovering aceticacid from aqueous acetic acid solutions. US patent 5.175.357.

Bublitz WJ (1987) Full chemical pulping with mixtures of methanol and sulfite liquors.Solvent Pulping - Promises & Problems, Appleton, WI, p 42-54.

Bublitz WJ (1998a) Full chemical pulping with mixtures of methanol and acid sulfiteliquors. 1998 Tappi Pulping Conf., Montreal, Canada, 2: 691-702. (Paperbase00523482).

Bublitz WJ (1998b) Full chemical pulping with mixtures of methanol and acid sulfiteliquors. 1998 Breaking the Pulp Yiels Barrier Symp., Atlanta, GA, p 229-239.(Paperbase 00505158).

Bublitz WJ & Hull JL (1981) A rapid process for production of high yield, fullchemical sulfite pulp. 1981 Tappi Pulping Conf., Denver, CO, p 305-315.

Bublitz WJ & Hull JL (1982) Recent developments in solvent-sulfite pulping. 1982International Sulfite Pulping Conf., Toronto, Canada, p 263-268.

Bublitz WJ & Wilson KP (1983) The role of methanol in a methanol acid sulfite pulpingprocess. 1983 Tappi Pulping Conference Proc., p 423-427.

Bublitz WJ, Gidlof P, Hull JL & Wilson K (1983) Recent developments in solvent sulfitepulping. International Symposium on Wood and Pulping Chemistry, Tokyo, Japan, 3:38-43.

Bucholtz M & Jordan RK (1983) Formic acid woodpulping could yield valuablechemical products. Pulp & Paper 57(9): 102-104.

Buckland IK, Brauns F & Hibbert H (1935) Studies on lignin and related compunds, XVI:phenol lignin from spruce wood, from freudenberg spruce lignin and willstatter sprucelignin. Can J Res 13B(2): 61-77.

Buhler F (1897) Verfahren zur darstellung von zellstoff mittels theereölen, bzw. denphenolen der theereolen. German patent 94467.

Bulow H, Hohenschutz H, Schmidt JE & Sachsze W (1977) BASF AG, assignee.Verfahren zur reindarstellung von ameisensaure. DT patent 25.45.730.A1.

Burkart LF (1989) Le Tourneau College, assignee. Rapid dissolution of lignin and othernon-carbohydrates from ligno-cellulosic materials impregnated with a reaction productof triethyleneglycol and an organic acid. US patent 4.826.566.

Burov AV, Beigelman AV, Lukanina TL, Maltsev SM & Vinogradova LI (1989a)Organosolv delignification of wood. Bum Prom (2): 15-16. (ABIPST 60:6317).

Burov AV, Lukanina TL & Beigelman AV (1989b) Effect of acidity and the dielectricconstant of the acetic acid-ethanol-water system on wood delignification. Khim Drev(Riga) (6): 27-30. (ABIPST 62:4297).

Burov AV, Beigelman AV & Lukanina TL (1989c) Method of producing pulp. USSR patent1.509.467. (ABIPST 62:3757(U)).

Burov AV, Lukanina TL & Aliev RG (1990) Degradation of cellulose and changes in themolecular weight characteristics of lignin during delignification of wood in aqueous-ethanol solutions of acetic acid. Khim Drev (Riga) (6): 53-57. (ABIPST 62:13775).

Burov AV, Lukanina TL, Aliev RG & Beigelman AV (1991) Method of delignification ofwood chips. Russian patent 1.622.469. (ABIPST 64:8355(T)).

Buryachenkov MM, Zakazov AN & Babkin VA (1991) Kinetics of water-ethanoldelignification of trembling aspen [populus tremula] in the presence of acid catalysts.Irkutsk, Russia, Institut khimii drevesiny, Issledovaniya v oblasti khimii drevesiny 9.(ABIPST 65:6569(AC)).

Calimli A & Olcay A (1978) Supercritical-gas extraction of spruce wood. Holzforschung32(1): 7-10.

Campbell WG (1929) CXXXVI, the degradation of wood by simultaneous action of ethylalcohol and hydrochloric acid. Biochem J 23: 1225-1232.

Caperos Sierra A, Romero Salvador A & Garcia-Ochoa Soria F (1990) Extraction of woodwith solvents. Tappi J 73(11): 221-224.

Chacon GM & Lai YZ (1985) Effect of ethanol on soda-anthraquinone pulping. 1985International Symposium on Wood and Pulping Chemistry Technical Papers,Vancouver, Canada, p 291-294.

Chang RP (1990) Pierre A. Tonachel, assignee. Method for continuous countercurrentorganosolv saccharification of comminuted lignocellulosic materials. US patent4.941.944.

Chang JP & Lee JY (1989) Separation of wood main components by solvolysis, 2:characteristics of cooked wood meal and soluble sugar in water layer. J Tappik 21(2):18-24. (ABIPST 60:6320).

Chang PC & Paszner L (1982) Bau- und Forschungsgesellschaft Thermoform A.C.,assignee. Pulping of lignocellulose with aqueous methanol/calyst mixture. CA patent1131415.

Chang HM, Jameel H, Wang S & Geng ZP (1994) Mixed peroxy acids as bleachingagents. Proc. of the International Symposium on Fiber Science and Technology,Yokohama, Japan, p 228-229.

Chanzy H, Paillet M & Peguy A (1986) Spinning of exploded wood from amine oxidesolutions. Polym Comm 27: 171-172.

Chanzy H, Paillet M, Peguy A & Vuong R (1987) Dissolution and spinning of explodedwood in amine oxide systems. In: Kennedy JF (ed) Wood and cellulosics: industrialutilization, biotechnology, structure and properties. Ellis Horwood, Chichester, p 573-579.

Chaudhuri P (1996) Solvent pulping of bagasse - a process and system concenpt. TappiPulping Conference Proc., p 583-594.

Chen F, Tanaka H, Naka Y & O’shima E (1989) Extraction of lower carboxylic acids fromaqueous solutions by tri-n-octylamine. J Chem Eng Japan 22(1): 6-11.

Chen ZT, Chen YI, Diebel JF, Chiang VL, Barna BA & Moffitt GE (1990) Pulpcharacteristics and mill economics for a conceptual SO2-ethanol-water mill. 1990 Tappi

Pulping Conf., Toronto, Canada, 2: 663-672.

Chiang VL, Moffitt GE, Puumala RJ & Sako T (1987) Linear regression modelling andresponse surface analysis of sulfur dioxide organosolv pulping. Solvent Pulping -Promises & Problems, Appleton, WI, p 68-92.

Chiang VL & Sarkanen KV (1983) Ammonium sulfide organosolv pulping. Wood Sci Tech17: 217-226.

Cho H & Paszner L (1987) Processing of lignins to converging chemical by-products, partI, macrostructure and shape of ACOS organosolv hydrolysis lignin. In: Granger C (ed)6th Canadian Bioenergy Research and Desing Seminar, p 364-367.

Chum HL, Johnson DK, Ratcliff M, Black S, Schroeder HA & Wallace K (1985)Comparison between lignins produced by steam explosion and organosolvpretreatments. 1985 International Symposium on Wood and Pulping ChemistryTechnical Papers, Vancouver, Canada, p 223-226.

Chum HL, Black S, Johnson DK & Sarkanen KV (1987) Organosolv pretreatment forbiomass-to-ethanol and lignins. Solvent Pulping - Promises & Problems, Appleton,WI, p 35-41.

Chum HL, Johnson DK, Black S, Baker J, Grohmann K, Sarkanen KV, Wallace K &Schroeder HA (1988) Organosolv pretreatment for enzymatic hydrolysis of poplars, I:enzyme hydrolysis of cellulosic residues. Biotech Bioeng 31(7): 643-649.

Chum HL, Johnson DK & Black SK (1989) Organosolv pretreatment. 1989 InternationalSymposium on Wood and Pulping Chemistry Proc., Raleigh, NC, p 691-696.

Chum HL, Johnson DK & Black SK (1990) Organosolv pretreatment of poplars, 2:catalyst effect and the combined severity parameter. Ind Eng Chem Res 29(2): 156-162.

Chupka EI, Selentiev DG, Semenov SG & Khodyreva NV (1993) Oxidation of wood and itscomponents in water-organic media. Seventh International Symposium on Wood andPulping Chemistry Proc., Beijing, PR China, 3: 373-382.

Clarke HT & Othmer DF (1928) Method of the dehydration of formic acid. US patent1.826.302.

Clermont LP & Bender F (1961) Effect of solutions of nitrogen dioxide, sulfur dioxide, andchlorine in dimethylformamide and dimethylsulfoxide on wood. Pulp Paper Mag Can62(1): T28-T34.

Cohen LR (1986) Badger B.V., assignee. Method for separating carboxylic acids frommixtures with non-acids. US patent 4.576.683.

Compton J, Greig M & Hibbert H (1936) Studies on lignin and related compounds, XXII:fractionation of methanol lignin. Can J Res 14B(4): 115-119.

Compton J & Hibbert H (1937) Studies on lignin and related compounds, XXVII:methylation and structure of methanol lignin (spruce). Can J Res 15B: 38-45.

Cook PM & Hess SL (1991) Eastman Kodak Company, assignee. Organosolv lignin-modified phenolic resins and method for their preparation. US patent 5.010.156.

Coppen JJW, Gibbs JA & Palmer ER (1988) A small-scale pulping process for developingcountries? Paper Tech Ind 29(6): 298-299.

Coulson JM, Richardson JF & Sinnott RK (1983) Chemical engineering vol 6. PergamonPress, Oxford.

Cramer AB, Hunter MJ & Hibbert H (1939) Studies on lignin and related compounds,XXXV: the ethanolysis of spruce wood. J Am Chem Soc 61: 509-516.

Creamer AW, Blackner BA & Lora JH (1997) Properties and potential applications of alow-molecular-weight lignin fraction from organosolv pulping. 9th InternationalSymposium on Wood and Pulping Chemistry Poster Presentations, Montreal, Canada, p21:1-4.

Cronlund M & Powers J (1990) Bleaching responses of alcell organosolv pulps. AIChE1990 Annual Meeting, Chicago, IL.

Cronlund M & Powers J (1991) Bleaching responses of alcell organosolv pulps usingconventional and nonchlorine bleaching sequences. 1991 Tappi Pulping ConferenceProc., Orlando, FL, 2: 547-552.

Cronlund M & Powers J (1992) Bleaching of alcell organosolv pulps using conventionaland nonchlorine bleaching sequences. Tappi J 75(6): 189-194.

Curvelo AAS & Balogh DT (1995) Organosolv lignin extraction of Eucalyptus grandis,part III: successive and batch processes. The 8th International Symposium on Woodand Pulping Chemistry Proc., Helsinki, Finland, 2: 219-223.

Curvelo AAS & Pereira R (1995) Kinetics of ethanol-water delignification of sugar canebagasse. The 8th International Symposium on Wood and Pulping Chemistry Proc.,Helsinki, Finland, 2: 473-478.

Curvelo AAS, Alaburda J, Botaro VR, Lechat JR & Groote RAMC (1990a) Acetosolvpulping of sugar cane bagasse, analysis of the chloride content in the Acetosolvprocess of wood and related materials. Tappi J 73(11): 217-220.

Curvelo AAS, Groote RAMC & Balogh DT (1990b) Solvent effect on organosolv ligninfrom Pinus caribaea hondurensis (part II). 1st European Workshop onLignocellulosics and Pulp, Bergedorf, FR Germany, p 59-65.

Curvelo AAS, Alaburda J, Botaro VR, Lechat JR & Groote RAMC (1990c) Analysis of thechloride content in the acetosolv process. Cell Chem Tech 24(3): 371-379.

Curvelo AAS, Balogh DT & Groote RAMC (1992a) Organosolv pulping of Eucalyptusgrandis. 25th Congresso Anual Celulose Papel ABTCP, Sao Paulo, Brazil, p 213-221.(ABIPST 65:5047(M)).

Curvelo AAS, Groote RAMC & Montanari E (1992b) Dioxan lignins from Pinus caribaeavar. hondurensis, part 1: effect of catalyst concentration. Paperi ja Puu 74(4): 324-327.

Curvelo AAS, Balogh DT & Groote RAMC (1993) Organosolv lignin extraction fromEucalyptus grandis, part II: characterization of lignins obtained by batch process.Seventh International Symposium on Wood and Pulping Chemistry Proc., Beijing, PRChina, 3: 177-182.

Curvelo AAS, Araujo ES & Sansigolo CA (1995) Kinetics of organosolv pulping ofEucalyptus globulus. The 8th International Symposium on Wood and PulpingChemistry Proc., Helsinki, Finland, 2: 213-218.

Dahlmann G & Schroeter MC (1989) The Organocell process - pulping with theenvironment in mind. 1989 Solvent Pulping Conference, Seattle, WA, p 7-15.

Dahlmann G & Schroeter MC (1990a) Pulping of spruce and pine with alcohol and alkaliby the Organocell process. 1990 Tappi Pulping Conference, Toronto, Canada, 2: 657-661.

Dahlmann G & Schroeter MC (1990b) The Organocell process - pulping with theenvironment in mind. Tappi J 73(4): 237-240.

Daima H, Hosoya S & Nakano J (1978) Studies on alkali-methanol cooking (part III)behavior of lignin during cooking. Japan Tappi 32(4): 49-52.

Daima H, Hosoya S, Nakano J & Ishizu A (1979) Studies on alkali-methanol cooking (IV) -model experiments for the behaviors of lignin and carbohydrate during cooking. JapanTappi J 33(6): 54-58.

Danner RP & Daubert TE (1983) Manual for predicting chemical process design data.AIChE, New York.

Davis JL (1987) Acetic acid pulping of wood. Ph.D. Thesis, Univ. of Wisconsin. (ABIPC59:2752(DU)).

Davis JL & Young RA (1989) Microwave-assisted solvent pulping. 1989 InternationalSymposium on Wood and Pulping Chemistry Proc., Raleigh, NC, p 651-653.

Davis JL & Young RA (1991a) Production and characterization of lignins from acetic acidbased pulping processes, part 1: lignin preparation and molecular weight distribution.Holzforschung 45(Suppl.): 61-70.

Davis JL & Young RA (1991b) Microwave-assisted solvent pulping. Holzforschung45(Suppl.): 71-77.

Davis JL, Young RA & Deodhar SS (1986) Organic acid pulping of wood III, acetic acidpulping of spruce. Mokuzai Gakkaishi 32(11): 905-914.

Davis JL, Nakatsubo F, Murakami K & Umezawa T (1987) Organic acid pulping of wood

IV: reactions of arylglycerol-b-guaiacyl ethers. Mokuzai Gakkaishi 33(6): 478- 486.Deineko IP (1992) Chemistry of oxygen-organosolv pulping. In: Kennedy JF, Phillips

GO & Williams PA (eds) Lignocellulosics - Science, Technology, Development andUse. Ellis Horwood Limited, Chichester, p 239-246.

Deineko I (1995) The chemical conversion of lignin during oxygen-organosolvdelignification. The 8th International Symposium on Wood and Pulping ChemistryProc., Helsinki, Finland, 2: 225-229.

Deineko IP & Evtyugin DV (1988) Wood oxidation by molecular oxygen in organicsolvents. Khim. Drev. (Riga) (6): 51-55. (ABIPC 59:11199).

Deineko IP & Evtyugin DV (1989) Oxygen pulping of chips in aqueous acetone solutions.Khim Drev (Riga) (3): 106-107. (ABIPST 61:1278).

Deineko IP & Kikitina OV (1989) Oxygen pulping of chips in water-alcohol solutions.Lesn Zh (1): 128-130. (ABIPST 61:7190).

Deineko IP & Kostjukevich NG (1991) Products of pulping by oxygen in aqueous aceticacid solution. 6th International Symposium on Wood and Pulping Chemistry Proc.,Melbourne, Australia, 2: 129-130.

Deineko IP & Kostyukevich NG (1989) Method of producing pulp. USSR patent1.490.199. (ABIPST 62:3758(U)).

Deineko IP & Makarova OV (1991) Products of wood destruction by oxygen-alcoholicpulping. 6th International Symposium on Wood and Pulping Chemistry Proc.,Melbourne, Australia, 2: 125-127.

Deineko IP & Nikitina OV (1989) Oxidation of wood by oxygen in low molecular weightalcohols. Khim Drev (Riga) (4): 60-63. (ABIPST 61:8252).

Deineko IP, Nikitina OV & Zarubin MY (1988a) RSFSR, assignee. Method of producingpulp. USSR patent 1.440.995. (ABIPST 60:3891(U)).

Deineko IP, Evtyugin DV & Zarubin MY (1988b) Method of producing pulp. USSR patent1.397.581. (ABIPC 59:5829(U)).

Deineko IP, Evtuguin DV & Zarubin MY (1989) Oxygen-aceton wood pulping, productscharacterization and mechanism. 1989 International Symposium on Wood and PulpingChemistry Proc., Raleigh, NC, p 719-726.

Deineko IP, Makarova OV & Pranovich AV (1993) Characteristics of products of oxygen-alcohol pulping. Khim Drev (1-3): 45-50. (ABIPST 65:6572(AS)).

Deinko IP, Makarova OV & Zarubin MY (1992) Delignification of wood by oxygen in low-molecular-weight alcoholic media. Tappi J 75(9): 136-140.

DeLange M, Trummer JA, Roberts RS, Muzzy JD & Gelbaum LT (1991) 13CNMRcharacterization of tulip poplar lignin solubilized by buffered solvent pulping.Holzforschung 45(5): 361-365.

DeLong EA (1990) Process to dissociate and extract the lignin and the xylan from theprimary wall and the middle lamella or lignocellulosic material which retains thestructural integrity of the fibre core. US patent 4.908.099.

Delong EA & Delong EP (1991) Manufacture of bleached cellulose. Japan Kokai patent249.290/91. (ABIPST 63:7424).

DeLong EA, DeLong EP, Ritchie GS & Rendall WA (1990a) Tigney Technology Inc.,assignee. Method for extracting the chemical components from dissociatedlignocellulosic material. US patent 4.908.098.

DeLong EA, DeLong EP, Ritchie GS & Rendall WA (1990b) Tigney Technology Inc.,assignee. Method for extracting the chemical components from dissociatedlignocellulosic material. CA patent 1.275.286.

Demirbas A (1998) Aqueous glycerol delignification of wood chips and groundwood.Biores Tech 63(2): 179-185. (ABPST 69: 353(AS)).

Desai MB (1981) Preliminary cost estimating of process plants. Chem Eng 88(15): 65-70.Detweiler RR (1992) Safety issues in design and operation of solvent pulping mills. 1992

Solvent Pulping Symposium Notes, Boston, MA, p 87-96.Diebold VB, Cowan WF & Walsh JK (1978) C P Associates Limited, assignee. Solvent

pulping process. US patent 4.100.016.Diebold VB, Walsh JK & Cowan WF (1983) C P Associates Limited, assignee.

Liuotinuutto-sellutusmenetelmä. FI patent 65290.Diebold VB, Cowan WF & Walsh JK (1988) Repap Technologies Inc., assignee.

Losungsmittelextraktionsverfahren zur herstellung von cellulosepulpe. DE patent26.37.449.C2.

Dievskii VA & Burov AV (1993) Diffusion model of organosolv pulping kinetics. IzvVUZ Lesn Zh (5/6): 136-140. (ABIPST 66:726(AS)).

Dillen S (1990) Nya massaprocesser: “kottkvarn” och sprit loser miljoproblem. SvenskPapperstidn 93(6): 38-44.

Dovgan IV & Leonovich AA (1992) Softening features of soluble lignin preparations.Lesn Zh (6): 90-95. (ABIPST 65:465).

Dovgan IV & Medvedeva EI (1993a) Studies of algae and sea-grasses lignins, 2: dioxanelignins from algae and sea-grasses. Khim Drev (1-3): 86-91.

Dovgan IV & Medvedeva EI (1993b) Studies of algae and sea-grasses lignins, 3:nitrobenzene oxidation of dioxane lignins of the algae and sea-grasses. Khim Drev (1-3): 92-95.

Dovgan IV & Medvedeva EI (1993c) Studies of algae and sea-grasses lignins, 4:degradation of algae lignins by nucleophilic agents. Khim Drev (1-3): 96-100.

Econompoulos AP (1978) Acetic acid dehydration: process and control. Chem Engineer(3): 199-202.

Ede R, Brunow G, Poppius K, Sundquist J & Hortling B (1988) Formic acid/peroxyformic

acid pulping, part 1: reactions of b-aryl ether model compunds with formic acid. NordicPulp Paper Res J 3(3): 119-123.

Ede R & Brunow G (1989a) Formic acid/peroxyformic acid pulping, II: synthesis of 3-aryl-2,3-dihydro-7-methoxy-2-benzofuranmethanols-model compunds for lignin acidolysisproducts. Holzforschung 43(2): 127-129.

Ede R & Brunow G (1989b) Formic acid/peroxyformic acid pulping, III: condensation

reactions of b-aryl ether model compunds in formic acid. Holzforschung 43(5): 317-322.

Ede R & Brunow G (1989c) Reactions of b-aryl ether model compunds under formic acidand peroxyformic acid pulping conditions. 1989 International Symposium on Wood andPulping Chemistry Proc., Raleigh, NC, p 139-143.

Edel E (1984) Das MD-organosolv-zellstoffverfahren. Dtsch Papierwirtsch (1): 39-45.

Edel E (1989) Das organocell-verfahren - bericht über den betrieb einer demonstrations-anlage. Papier 43(10A): V116-V123.

Edel E, Feckl J, Grambow C, Huber A & Wabner D (1986) MD-Organocell Gesellschaft furZellstoff- und Umwelttechnik mbH, assignee. Process for obtaining lignin fromalkaline solutions thereof. US patent 4.584.076.

Ekman K (1988a) Neste Oy, assignee. Menetelma ligniinin ja fenolin erottamiseksifenoliliuoksista. FI patent 77061.

Ekman K (1988b) Neste Oy, assignee. Menetelma fenolin kierrattamiseksi lignoselluloosa-materiaalien fenolikeittoprosessissa. FI patent 77062.

Ekman K (1991a) Neste Oy, assignee. Procedure for separating lignin and phenol fromphenol solutions. CA patent 1.284.491.

Ekman K (1991b) Neste Oy, assignee. Procedure for recirculating phenol in alignocellulosic materials digestion process. CA patent 1.282.714.

El-Meadawy SA, Shukry N & Nassar MA (1990) Pulping with organic acids, I: acetic acidpulping of Casuarina sp. Papir Celuloza 45(10): V63-V67.

Elnitskaya ZP, Burov AV, Aliev RG, Luferova LB & Turushev SL (1992) LTITsBP,assignee. Method of producing pulp. Russian patent 1.721.152. (ABIPST63:14253(U)).

El-Sakhawy M, Fahmy Y, Ibrahim AA & Lonnberg B (1995a) Organosolv pulping, (1)alcool pulping of bagasse. Cellul Chem Technol 29: 615-629.

El-Sakhawy M, Lonnberg B, Ibrahim AA & Fahmy Y (1995b) Organosolv pulping, (2),ethanol pulping of cotton stalks. Cellul Chem Technol 29: 315-329.

El-Sakhawy M, Lonnberg B, Fahmy Y & Ibrahim AA (1996a) Organosolv pulping, (3),ethanol pulping of wheat straw. Cellul Chem Technol 30: 161-174.

El-Sakhawy M, Lonnberg B, Ibrahim AA & Fahmy Y (1996b) Organosolv pulping, (4),kinetics of alkaline ethanol pulping of wheat straw. Cellul Chem Technol 30: 281-296.

El-Sakhawy M, Lonnberg B, Fahmy Y & Ibrahim AA (1996c) Organosolv pulping, (5),bleachability and paper properties. Cellul Chem Technol 30: 483-495.

Engel O & Wedekind E (1933) Verfahren zum aufschluss von pflanzenfaserstoffen. Germanpatent 581.806.

Erbing H & Peter H (1941) Till kannedom om lignin. Kolloid-Zeitschrift 96: 47-71.(Svensk Papperstidning 44(22): 509)

Erbring H (1939) Ueber den aufschluß von faserrohstoffen durch mehrwertige alkohole.Papier-Fabrikant 37(20): 168-170.

Erbring H & Geinitz H (1938) Uber die aufschließung pflanzlicher faserstoffe mitmehrwertigen alkoholen. Kolloid-Zeitschrift 84(2): 215-222.

Ettel W & Hnetkovky V (1965) Ceskoslovenska academie ved, assignee. Verfahren zurgewinnung von nativem lignin und halbzellstoff aus nadel- oder laubholz. DE patent1.176.464.

Evans JCW (1987) Repap plans alcohol pulping system at its newcastle kraft and lwcmill. Pulp Paper 61(11): 75-77.

Evtuguin DV, Silvy J, Robert A & Zarubin MY (1993a) The pecularities of papermakingproperties of the oxygen-organosolv pulp. Seventh International Symposium on Woodand Pulping Chemistry Proc., Beijing, P.R. China, 3: 167-172.

Evtuguin DV, Deineko IP & Sheng LG (1993b) Oxygen-organosolv delignification:application for the hydrolysis lignin utilization. Seventh International Symposium onWood and Pulping Chemistry Proc., Beijing, P.R. China, 3: 577-582.

Evtuguin DV, Shatalov AA & Kostukevich NG (1995) Degradation of polysaccharidesunder conditions of oxygen delignification in organic solvent media. The 8thInternational Symposium on Wood and Pulping Chemistry Proc., Helsinki,Finland, 2: 325-330.

Evtuguin DV, Robert A, Zarubin MY & Deineko IP (1996) The effect of oxygen-organosolv pulping conditions on pulp properties. Cell Chem Tech 30(1/2): 105-115.

Evtyugin DV & Deineko IP (1994) Low-molecular reaction products from oxygen-acetonewood delignification. Wood Chem (3):46-52. (ABIPST 66:7048(AS)).

Evtyugin DV, Shatalov AA & Zarubin MY (1994a) Degradation of polysaccharides in thepresence of oxygen in different types of aqueous organic media, (1) change in thechemical composition of the carbohydrate complex during oxygen-organosolvdelignification. Izv VUZ Lesn Zh (3):64-70. (ABIPST 66:3609(AS)).

Evtyugin DV, Shatalov AA & Zarubin MY (1994b) Degradation of polysaccharides in thepresence of oxygen in different types of aqueous organic media, (1) depolymerization ofthe polysaccharide complex during oxygen-organosolv delignification. Izv VUZ LesnZh (3):70-76. (ABIPST 66:3608(AS)).

Faass GS, Roberts RS & Muzzy JD (1989) Buffered solvent pulping. Holzforschung 43(4):245-250.

Fagerlind O & Agren E (1995) A. Ahlstrom Corporation, assignee. Process for theconcentration of spent liquors. US patent 5.382.321.

Fair JR (1987) Distillation. In: Rousseau RW (ed) Handbook of separation processtechnology. Wiley-Interscience, New York, p 229-339.

Faix O, Schubert HL & Patt R (1989) Continuous process control of pulping by ftirspectroscopy. 1989 International Symposium on Wood and Pulping Chemistry Proc.,Raleigh, NC, p 1-8.

Faix O, Jakab E, Fuchs K, Patt R, Till F & Szekely T (1990) Thermal behaviour of ASAMwaste liquors. Paperi Puu 72(3): 239-247.

Fales G (1988) Repap readies alcell trial plant for further expansion. Paper Age 104(10):40. (ABIPC 59:7193).

Farrand JC & Johnson DC (1971) Peroxyacetic acid oxidation of 4-methylphenols andtheir methyl ethers. J Org Chem 36(23): 3606-3612.

Feckl J & Edel E (1987) Organosolv pulping with addition of alkali - procedure andproducts. Fourth International Symposium on Wood and Pulping Chemistry Proc.,Paris, France, 1: 369-372.

Feehl J (1984) Studies of soluble by-products resulting from organosolv-pulping. In:Ferrero GL (ed) Anaerobic digestion and carbohydrate hydrolysis of waste. ElsevierApplied Science Publishers Ltd, Essex, p 440-443.

Feldman D, Banu D, El-Raghi S & Lora J (1996) Rigid poly(vinyl chloride)-organosolvlignin blends for applications in building. J Appl Polym Sci 61(12): 2119-2128.(ABIPST 67:5651(AS)).

Fengel D, Wegener G & Greune A (1989) Studies on the delignification of spruce wood byorganosolv pulping using sem-exda and tem. Wood Sci Tech 23(2): 123-130.

Ferraz A, Mendonca R, Cotrim AR & Silva FT (1996) The use of white-rot decay as apretreatment for organosolv delignification of eucalyptus grandis wood. In: Srebotnik E& Messner K (eds) Biotechnology in pulp and paper industry. Facultas-Universitatsverlag, Vienna, p 221-224.

Ferraz A, Rodriguez J, Freer J & Baeza J (1998a) Fungal-organosolv pulping of pinusradiata softwood. Proc. 7th International Conference on Biotechnology in the Pulp andPaper Industry, Vancouver, Canada, B: 29-32. (Paperbase 00527145).

Ferraz A, Christov L & Akhtar M (1998b) Fungal pretreatment for organosolv pulping anddissolving pulp production. In: Young RA & Akhtar M (eds) Environmentally FriendlyTechnologies for the Pulpo and Paper Industry. John Wiley & Sons, New Youk, NY, p421-447.

Fien GJAF & Liu YA (1994) Heuristic synthesis and shortcut design of separationprocesses using residue curve maps: a review. In Eng Chem Res 33: 2505-2522.

Finnish Oil Association (1998) Http://www.oil.fi/keskusliitto1.html.Franzreb JP (1989) Was erwartet die klassische zellstoffindustrie von den neuen

herstellungsverfahren? Papier 43(10A): V94-V97.Fredenslund A, Gmehling J & Rasmussen P (1977) Vapor-liquid equilibria using UNIFAC, a

group contribution method. Elsevier, Amsterdam.Freudenberg K, Janson A, Knopf E & Haag A (1936) Zur kenntnis des lignins (15.

mitteil.). Ber Dtsch Chem Gesellsch 69: 1415-1425.Freudenberg K & Acker L (1941) Uber die einwirkung von glycolchlorhydrin auf

fichtenlignin. Ber Dtsch Chem Gesellsch 74(8): 1400-1406.Friedman L & McCully CR (1938) Isolation of lignin with benzyl alcohol. Paper Trade J

107(26): 28-29.Frierman M, Kuo Y, Joshi D, Garcia AA & King CJ (1987) Use of adsorbents for recovery

of acetic acid from aqueous solutions, part III - solvent regeneration. Separ Purif Meth16(1): 91-102.

Fuchs W (1929) Uber den aufschluss des lignins mit methylglykolischer salzsaure. BerDtsch Chem Gesellsch 62B: 2125-2133.

Fuchs W (1936) Investigations concerning phenol lignin and methoxy glycol lignin fromspruce wood. J Am Chem Soc 58: 673-680.

Fullerton TJ (1983) The hydrolysis of hard beech sawdust with aqueous ethanol. FRIBulletin 38.

Funaoka M & Abe I (1989) Rapid separation of wood into carbohydrate and lignin withconcentrated acid-phenol system. Tappi J 72(8): 145-149.

Gallagher DK, Hergert HL, Cronlund M & Landucci LL (1989) Mechanism ofdelignification in an autocatalyzed solvolysis of aspen. 1989 International Symposiumon Wood and Pulping Chemistry Proc., Raleigh, NC, p 709-718.

Garner FH, Ellis SRM & Pearce CJ (1955) Extraction of acetic acid from water, 4: ternary-vapour-liquid equilibrium data. Chem Eng Sci 4: 273-278.

Gasche UP (1985a) Schwefelfreie katalysierte verfahren zur erzeugung von zellstoff. Papier39(10A): V1-V8.

Gasche UP (1985b) Schwefelfreies verfahren zur erzeugung von zellstoff aus holz. SwissBiotech 3(1a): 47-52.

Gasche U (1990) Hat das sulfitverfahren heute noch eine existenzberechtigung?, vergleichdes sulfitprozesses mit den neuen aufschlussverfahren. Papier 44(3): 85-91.

Gast D, Ayla C & Puls J (1983) Component separation of lignocelluloses by organosolv-treatment. In: Strub A (ed) Energy from biomass, 2nd E.C. Conf. Applied SciencePublishers Ltd, Barking, p 879-882.

Gast D & Puls J (1984) Ethylene glycol-water pulping, kinetics of delignification. In:Ferrero GL (ed) Anaerobic digestion and carbohydrate hydrolysis of waste. ElsevierApplied Science Publishers Ltd, Essex, p 450-453.

Gast D & Puls J (1985) Improvement of the ethylene glycol water system for thecomponent separation of lignocelluloses. In: Palz W (ed) Energy from biomass, 3rdE.C. Conf. Elsevier Applied Science Publishers Ltd, Essex, p 949-951.

Gentry JC & Solazzo, AJ (1995) Recovery of carboxylic acids from aqueous streams.Environmental Prog 14(1): 61-64.

Ghose TK, Pannir Selvam PV & Ghosh P (1983) Catalytic solvent delignification ofagricultural residues: organic catalysts. Biotech Bioeng 25(11): 2577-2590.

Gilardi G, Harvey PJ, Cass AEG & Palmer JM (1990) NMR studies of lignin degradation.In: Kirk TK & Chang HM (eds) Biotechnology in pulp and paper manufacture,applications and fundamental investigations. Butterworth-Heinemann, Boston, MA, p367-373.

Gilarranz M, Oliet M, Rodriguez F, Poveda P, Villar J & Barbadillo P (1997) Preliminarystudy on the manufacture and bleaching of organosolv pulps from Eucalyptus globulus.Invest Tech Pap 34: 600-619. (ABIPST 68:11153(AS)).

Girard RD & Chen R (1992) Optimization of an organosolv process for white birch. 1992Solvent Pulping Symposium Notes, Boston, MA, p 73-78.

Girard RD & Heiningen ARP (1997) Yield determination and mass balance closure of batchethanol-based solvent cookings. Pulp & Paper Canada 98(8): 65-68.

Glasenapp A, Kordsachia O, Odermatt J & Patt R (1996) TCF-bleiche von ASAM-fichten-zellstoffen mit und ohne ozon. Papier 50(6): 300-309.

Glasner A, Reinharter E & Schubert, HL (1994) Chemical energy and water balance ofASAM pulping. TAPPI Pulping Conference, San Diego, CA, p 155-165.

Gliese T, Kleemann S & Fischer K (1996) Enzymatic bleaching of organosolv-pulp. In:Srebotnik E & Messner K (eds) Biotechnology in pulp and paper industry. Facultas-Universitatsverlag, Vienna, p 63-67.

Golob J, Grilc V & Zadnik B (1981) Extraction of acetic acid from dilute aqueoussolutions with trioctylphosphine oxide. Ind Eng Chem Proc Des Dev 20: 433-435.

Goncalves AR, Urbano MP, Cotrim AR & Silva FT (1997) Oxidation of lignin-containingliquor from acetosolv pulping of sugar-cane bagasse. 9th International Symposium onWood and Pulping Chemistry Oral Presentations, Montreal, Canada, p I4 1-3.

Gosselink RJA, Dam, JEG & Zomers FHA (1995) Combined hplc analysis of organic acidsand furans during organosolv pulping of fiber hemp. J Wood Chem Tech 15(1): 1-25.

Gottlieb K, Preuss AW, Meckel J & Berg A (1992) Acetocell pulping of spruce andchlorine-free bleaching. 1992 Solvent Pulping Symposium Notes, Boston, MA, p 35-39.

Goyal GC, Lora JH & Pye EK (1991) Autocatalyzed organosolv pulping of north americanhardwoods: effect of pulping conditions on the pulp properties and characteristics ofthe soluble and residual lignin. 1991 Tappi Pulping Conf. Proc., Orlando, FL, 2: 627-635.

Goyal GC, Lora JH & Pye EK (1992) Autocatalyzed organosolv pulping of north americanhardwoods: effect of pulping conditions on the pulp properties and characteristics ofthe soluble and residual lignin. Tappi J 75(2): 110-116.

Goyal GC & Lora JH (1991) Kinetics of delignification and lignin characteristics inautocatalyzed organosolv pulping of hardwoods. 6th International Symposium on Woodand Pulping Chemistry Proc., Melbourne, Australia, 1: 205-212.

Gray KR, King EG, Brauns F & Hibbert H (1935) Studies on lignin and related compounds,XIII, the structure and properties of glycol lignin. Can J Res 13B: 35-47.

Green J & Sanyer N (1982) Alkaline pulping in aqueous alcohols and amines. Tappi 65(5):133-137.

Griffith WL, Compere AL, Rao TK & Griest WH (1980) Potential use of organosolvunderflow tar lignin as a petrochemical refinery feed. Tappi Papermakers Conference,Atlanta, GA, p 181-185.

Grinstead RR (1974) The Dow Chemical Company, assignee. Extraction of carboxylicacids from dilute aqueous solutions. US patent 3.816.524.

Grondal BL & Zenczac P (1956) Research Corporation, assignee. Process of pulpingcellulosic materials with triethylene glycol. US patent 2.772.968.

Groote RAMC, Curvelo AAS, Frangiosa PC, Pinto MFT & Zambon MD (1991a) Molecularweight distribution of sugar cane bagasse lignin in the acetosolv process. 6thInternational Symposium on Wood and Pulping Chemistry Proc., Melbourne, Australia,2: 385-391.

Groote RAMC, Curvelo AAS, Alaburda J & Botaro VR (1991b) The reactivity of sugar-cane-bagasse lignin from the acetosolv pulping process. In: Faix O & Meier D (eds)Mitteilungen der Bundesforschungsanstalt fur Forst- und Holzwirtschaft, 168: 228-233.

Groote RAMC, Curvelo AAS, Alaburda J & Botaro VR (1992a) Acetosolv pulping ofsugarcane bagasse: use of the pulp and the lignin. Papel 53(1): 43-46. (ABIPST63:2811).

Groote RAMC, Curvelo AAS, Frangiosa PC & Zambon MD (1992b) Some properties ofacetosolv sugar cane bagasse lignin. Cellul Chem Tech 26(1): 53-61.

Guha SRD, Sirmokadam NN, Goudar TR & Dhopeshwar R (1987) Pulping of rice straw bypollution free organosolv process. IPPTA 24(1): 24-26.

Haars A, Majcherczyk A, Trojanowski J & Huttermann A (1985) Bioconversion oforganosolv lignins by different types of fungi. In: Palz W (ed) Energy from biomass,3rd e.c. conference. Elsevier Applied Science Publishers Ltd, Essex, p. 973-977.

Haas GG & Lang CJ (1971) Weyerhaeuser Company, assignee. Non-catalytic process forthe production of cellulose from lignocellulosic materials using acetic acid. US patent3.553.076.

Haas GG & Lang CJ (1974) Delignification with ketones and ammonia. Tappi 57(5): 127-130.

Haas H, Schoch W & Strole U (1955) Herstellung von skelettsubstanzen mit peressigsaure.Papier 9(19/20): 469-475.

Haggin J (1986) Ester pulping process avoids use of sulfur compounds. Chem Eng News64(4): 25-26.

Hagglund E & Urban H (1927) Zur kenntnis der ligninacetale I. Cellulosechemie 8(7): 69-71.

Hagglund E & Urban H (1928) Zur kenntnis der ligninacetale II. Cellulosechemie 9(6): 49-53.

Hakansson H, Sjoberg LA & Ahlgren P (1996) Autocatalyzed ethanol pulping of reedcanary grass. Nord Pulp Pap Res J 11(2): 100-104. (ABIPST 67:3109(AS)).

Hammann M, Kordsachia O & Patt R (1991) Bleaching of kraft pulp and asam pulpwithout chlorine containing chemicals. International Pulp Bleaching Conference Proc.,Stockholm, Sweden, 3: 185-200.

Hansen SM & April GC (1982) Prediction of solvent effects in aqueous-organic solventdelignification. Ind Eng Chem Prod Res Dev 21(4): 621-626.

Harrison A (1991) Repap produces high-quality pulp at newcastle with alcell process. Pulp& Paper 65(2): 116-119.

Hartmuth R (1920) Verfahren zur behandlung von holz oder zellulosehaltigen stoffenzwecks gewinnung von zellulose und kunstlichem harz, lack, asphalt u. dgl. Germanpatent 326705.

Hawkes GE, Smith CZ, Utley JHP & Chum HL (1986) Key structural features of acetone-soluble phenol-pulping lignins by 1H and 13C N.M.R. spectroscopy. Holzforschung40(Suppl.): 115-123.

Heckrodt W & Thompson N (1992) Biodyne Chemical Inc., assignee. Pulping. CA patent2.055.040. (ABIPST 66:14811(P)).

Heden S & Holmberg B (1936) Bisulfitkok med aromatiska alkoholer. Svensk KemiskTidskrift 48: 207-211.

Helsel RW (1977) Waste recovery: removing carboxylic acids from aqueous wastes. ChemEng Prog 73(5): 55-59.

Henry WR (1991) The future of organosolv pulping. 1991 Tappi Pulping ConferenceProc., Orlando, FL, 2: 653 - 656.

Henry W & Seely B (1991) DCS challenges at the alcell pre-commercial facility. 77thCPPA Annual Meeting Prep., Montreal, Canada, p A395-A398.

Henry W & Seely B (1992) DCS challenges at the alcell pre-commercial facility. Pulp &Paper Canada 93(12): 143-145.

Herdle LL, Pancoast LH & MacClaren RH (1964) Acetylation celluloses from pulping ofwood in acetic acid. Tappi 47(10): 617-620.

Hewson WB, McCarthy JL & Hibbert H (1941a) Studies on lignin and related compounds,LVII, mechanism of the ethanolysis reaction. J Am Chem Soc 63: 3041-3045.

Hewson WB, McCarthy JL & Hibbert H (1941b) Studies on lignin and related compounds,LVIII, the mechanism of the ethanolysis of maple wood at high temperatures. J AmChem Soc 63: 3045-3048.

Hibbert H & Marion L (1930) Studies on lignin and related compounds, II., glycol-ligninand glycol-ether-lignin. Can J Res 2(6): 364-375.

Hibbert H & Phillips JB (1930) Studies on lignin and related compounds, III, glycerol-chlorohydrin-lignin. Can J Res 3: 65-69.

Hibbert H & Rowley HJ (1930) Studies on lignin and related compounds, I., a new methodfor the isolation of spruce wood lignin. Can J Res 2(6): 357-363.

Hill RT, Walsh PB & Hollie JA (1992) Part 1: Peracetic acid - an effective alternative forchlorine compound free delignification of kraft pulp. 1992 Pulping Conference Proc.,Boston, MA, p 1219-1230.

Hillmer A (1925) Die loslichkeit von lignin in phenolen. Cellulosechemie 6(11): 169-187.

Hinrichs DD, Knapp SB, Milliken JH & Wethern JD (1957) Sugarcane bagasse as a fibrouspapermaking material, VI, modified alkaline and hydrotropic pulping of bagasse. Tappi40(8): 626-633.

Hirose S, Yano S, Hatakeyama H & Hatakeyama T (1989) Heat-resistant polyurethanesfrom solvolysis lignin. In: Glasser W & Sarkanen K (eds) Lignin properties &materials. ACS, Washington, DC, p 82-99. (ABIPST 60:8967(B)).

Hohenschutz H, Schmidt J & Kiefer H (1985) BASF AG, assignee. Verfahren zurgewinnung von carbonsauren aus ihren waßrigen losungen. DE patent 25.45.658.C2.

Holmberg B (1936) Lignin-untersuchungen, XI mitteil., fichtenholz und mercapto-sauren.Berichte der Deutschen Chemischen Gesellschaft 69: 115-119.

Holmberg B (1947) Espenholzer und mercaptosauren. Arkiv for Kemi, Mineralogi ochGeologi 24A(29): 1-11.

Holmberg B & Runius S (1925) Alkoholys af tra. Svensk Kemisk Tidskrift 37(8): 189-197.

Holtzapple MT & Humphrey AE (1984) The effect of organosolv pretreatment on theenzymatic hydrolysis of poplar. Biotech Bioeng 26(7): 670-676.

Horlenko T (1973) Celanese Corporation, assignee. Distillation process for recoveringsubstantially anhydrous formic acid from aqueous solutions. US patent 3.718.545.

Hortling B, Ranua M & Sundquist J (1987) Influence of the pulping process on theresidual lignin in kraft and peroxyacid pulps. Fourth International Symposium on Woodand Pulping Chemistry Proc., Paris, France, 2: 203-210.

Hortling B, Poppius K & Sundquist J (1989) Comparison of the lignins in kraft andperoxyacid fibers with lignin in corresponding spent liquors. 1989 InternationalSymposium on Wood and Pulping Chemistry Proc., Raleigh, NC, p 279-289.

Hortling B, Poppius-Levlin K, Kataja K, Backman I & Sundquist J (1990) Spent liquorlignins from peroxyformic acid pulping compared with products from milled wood andkraft lignin obtained under similar conditions (abstract). 1st European Workshop onLignocellulosics and Pulp, Hamburg, Germany, p 5.

Hortling B, Poppius K & Sundquist J (1991) Formic acid/peroxyformic acid pulping, IV,lignins isolated from spent liquors of three-stage peroxyformic acid pulping.Holzforschung 45(2): 109-120.

Hossain S (1958) Action of dimethyl sulphoxide on wood and sulphite pulps. Pulp andPaper Magazine of Canada 59(8): 127-130.

Hossain S (1959) Abitibi Power & Paper Company, assignee. Process for pulpinglignocellulosic material. CA patent 573.329.

Hou SZ & An YQ (1989) Study of the defibration point and kinetics of pulping wheatstraw with HMDA (hexamethylene diamine). J Northwest Inst Light Ind 7(1): 69-79.(ABIPST 62:8467(U)).

Hudeczek W & Lindow J (1992) Verwendung von methanol in der zellstoff-erzeugung -einflussfaktoren auf die planung. Papier 46(7): 335-340.

Hultholm T, Robertsen L, Lonnberg B, Henricson K & Laxen T (1998) The IDE-process, anew concept suitable for softwood, hardwood and nonwood. Fifth European Workshopon Lignocellulosics Chemistry for Ecologically Friendly Pulping and BleachingTechnologies, Aveiro, Portugal, p 577-580. (Paperbase 00522911).

Hunsmann W & Simmrock KH (1966) Trennung von wasser, ameisensaure und essigsauredurch azeotrop destillation. Chemie-Ingenieur-Technik 38(10): 1053-1059.

Hunter MJ, Cramer AB & Hibbert H (1939) Studies on lignin and related compounds,XXXVI, ethanolysis of maple wood. J Am Chem Soc 61: 516-520.

Huth SP & Cole BJW (1994) Synthesis and nmr characterization of a lignin-poly(ethyleneglycol)methyl ether copolymer. Holzforschung 48(1): 23-28.

Isoaho M (1998) Verbal communication. City of Oulu, Oulu.Ivanow T & Robert A (1987) Delignification via solvolysis: role of solvent and of

different additives. 4th International Symposium on Wood and Pulping ChemistryProc., Paris, France, 2: 189-192. (ABIPC 59:8216(M)).

Ivanow T & Robert A (1989) Delignification of hornbeam [carpinus] wood by alkalinesolvolysis; ethanol-water solutions. Papeterie (132): 22-27. (ABIPST 60:7418).

Jaaskelainen AS (1996) Peroksiyhdisteiden kaytto havupuusulfaattimassan valkaisussa.PSC Comm 88.

Jaaskelainen AS & Poppius-Levlin K (1997) Factors affecting the kinetics of pine kraftpulp delignification with peroxyacetic acid. 9th International Symposium on Wood andPulping Chemistry Oral Presentations, Montreal, Canada, D5 1-5.

Jagirdar GC & Sharma MM (1980) Recovery and separation of mixtures of organic acidsfrom dilute aqueous solutions. J Sep Proc Tech 1(2): 40-43.

Jahn H, Hackethal U & Fleck U (1979) VEB Chemische Werke Buna, assignee. Verfahrenzur schleppmittelfreien destillativen auftrennung waßriger essigsaure-ameisensaure-gemische. DD patent 133.559.

Jakab E, Faix O, Till F & Székely T (1991) Thermogravimetry/mass spectrometry ofvarious lignosulfonates as well as of kraft and acetosolv lignin. Holzforschung 45(5):355-360.

Jamieson S (1991) Alcell pulping: world class research rigth here in canada. Pulp & PaperCanada 92(3): 16-18.

Janson J & Vuorisalo R (1986) Alcohol-hydroxide-anthraquinone pulping. Paperi ja Puu68(9): 610-615.

Jende UL (1992) The industrial-scale implementations of the Organocell process inKelheim. 1992 Solvent Pulping Symposium Notes, Boston, MA, p 79-85.

Jeong HC & Park CY (1990) Kinetic studies on solvolysis cooking reaction. J TAPPIK22(2): 31-44. (ABIPST 62:4318).

Jimenez L, Maestre F, Torre MJ & Perez I (1997a) Organosolv pulping of wheat straw byuse of methanol-water mixtures. Tappi J 80(12): 148-154.

Jimenez L, Torre M, Maestre F & Perez I (1997b) Organosolv pulping of wheat straw byuse of phenol. Bioresour Technol 60(3): 199-205. (ABIPST 68:3905(AS)).

Jiwei C, Dazhen Z, Yulin W, Junsuo W, Ruisheng Z & Znongren S (1988) A preliminarystudy of organosolv pulping wheat straw with acid-acetate process. 1988 InternationalNon-Wood Fiber Pulping and Papermaking Conference Proc., Beijing, PR China, 1:180-186.

Johansson A, Sachetto JP & Roman A (1983) A new process for the fractionation ofbiomass. In: Strub A (ed) Energy from biomass, 2nd e.c. conference. Applied SciencePublishers Ltd, Barking, p 868-872.

Johansson A, Ebeling K, Aaltonen O, Aaltonen P & Ylinen P (1987) Wood pulping withaqueous tetrahydrofurfurylalcohol. Paperi ja Puu 69(6): 500-504.

Johnson DC (1975) Lignin reactions in delignification with peroxyacetic acid. 1stInternational Symposium on Delignification with Oxygen, Ozone and Peroxides,Raleigh, NC, p 217-228.

Jordan RK (1982) Formic acid pulping. PCT patent 82/01902.Julien LM (1979) Characteristics of pulps obtained from HMDA pulping. 1979 Tappi

Pulping Conference Proc., p 23-29.Julien LM & Barna BA (1980) Amine pulping with 1,6-diaminohexane. In: New process

alternatives in the forest products industries. AIChE Symposium Series 76: 209-216.Julien LM & Sun BCH (1979) Pulping with amine and soda-amine systems. Tappi 62(8):

63-65.Kachi S & Tsuchiya H (1988) Characteristics of solvolysis pulping. CPPA Spring

Conference Preprints Session 5 Paper 3, Jasper, Alta. (ABIPST 62:4320(M).Kachi S & Tsuchiya H (1989) Research and development of solvolysis pulping, (1),

characteristics of the process and the pulp. Japan Tappi J 43(9): 905-910. (ABIPST60:6328).

Kachi S, Iwata H, Araki H & Aoyagi T (1990) Research and development of solvolysispulpung, (6), delignification of wood chips with phenolic cooking solvent. MokuzaiGakkaishi 36(2): 108-115. (ABIPST 61:9772)

Kakemoto G, Sagara H, Suzuki N & Kachi S (1990) JGC Corporation and Japan Pulp &Paper Research Institute, assignees. Method of manufacturing phenols from lignin. USpatent 4.900.873.

Kalb L & Schoeller V (1923) Zur frage der cellulose-bestimmung mit phenol.Cellulosechemie 4(4): 37-40.

Kaminsky K, Schweers W & Schwesinger H (1980) Properties and decomposition oflignins isolated by means of an alcoholic-water-mixture, part 3: decomposition bypyrolysis in a fluid-bed. Holzforschung 34(3): 73-76.

Kaneko N, Sano Y, Sasaya T & Otani J (1991) Phenorganosolv pulping, (3), pulping ofsoftwoods with acetic acid-water-phenols system. Japan Tappi J 45(12): 1392-1399.(ABIPST 63:1865).

Kanitskaya LV, Zakazov AN, Rossinskii OA, Rpkhin AV & Babkin VA (1993) Structuralchanges in spruce [picea] dioxane lignin under the action of hydrogen peroxide andsodium borohydride. Izv Vyssh Uchebn Zaved Lesn Zh (2/3): 147-154. (ABIPST65:6393(AS)).

Karl W (1988) Repap’s Alcell process: is it all it’s cracked up to be? Pulp & Paper J41(7): 17, 21.

Karl W (1991a) By George, they’ve done it. Pulp & Paper J 44(1): 106-109.Karl W (1991b) Repap’s Alcell process. Paper 215(1): 46-47.Karlsson O & Lundquist K (1991) Chemical modification of lignins during organosolv

pulping in acid media. In: Faix O & Meier D (eds) Mitteilungen derBundesforschungsanstalt fur Forst- und Holzwirtschaft, 168: 66-68.

Karmanov AP, Belyaev VY & Monakov YB (1992) Hydrodynamic properties of adehydropolymer-macromolecular model of lignin. Khim Drev (Riga) (2-3): 25-31.(ABIPST 64:238).

Katzen R, Frederickson R & Brush BF (1980a) The alcohol pulping & recovery process.Chem Eng Prog (2): 62-67.

Katzen R, Frederickson RE & Brush BF (1980b) Alcohol pulping appears feasible forsmall incremental capacity. Pulp & Paper (8): 144-149.

Kawamoto H, Chang H & Jameel H (1994) Reaction of lignin model compounds withperacetic acid or peroxymonosulfuric acid. The International Symposium on FiberScience and Technology Proc., Yokohama, Japan, p 230.

Kawamoto H, Chang HM & Jameel H (1995) Reactions of peroxyacids with lignin andlignin model compounds. The 8th International Symposium on Wood and PulpingChemistry Proc., Helsinki, Finland, 1: 383-390.

Kayama T & Takagi H (1978) Alkali-dioxane pulping (part I), cooking conditions andpulp properties. Japan Tappi J 32(1): 31-38.

Kim DH & Paik KH (1993) Peroxide bleaching of [mongolian] oak [quercus mongolica]acetosolv pulp. J TAPPIK 25(1): 53-59. (ABIPST 64:7596).

Kim DH, Paik KH & Kang CH (1991) Acetosolv pulp at atmospheric pressure for thereduction of pollution and energy. J TAPPIK 23(2): 21-32.

Kim YH, Shimokawa A, Sakai K & Takahashi I (1996) Effect of organic solvents on theyield of low-molecular-weight phenols during organosolv pulping. Proc. 1996 (63rd)Pulp and Paper Research Conference, p 164-169. (ABIPST 67:6460(AC)).

Kin Z (1990) The acetolysis of beech wood. Tappi J 73(11): 237-238.King CJ (1986) Separation processes. Tata McGraw-Hill Publishing Company Limited,

New Delhi.King CJ (1992) Amine-based systems for carboxylic acid recovery. Chemtech 22(5): 285 -

291.Kinnula T (1986) Sulfaattisellutehtaan mitoitus ja kannattavuus. Univ Oulu, Dept Process

Eng, Report 103.Kirçi H, Bostançi S & Yalinkiliç MK (1994) A new modified pulping process alternative

to sulphate method “alkali-sulfite-anthraquinone-ethanol (ASAE)”. Wood Sci Tech28(2): 89-99.

Kirsch T & Maurer G (1997) Distribution of binary mixtures of citric, acetic and oxalicacid between water and organic solutions of tri-n-octylamine, part I, organic solventtoluene. Fluid Phase Equilibria 131: 213-231.

Kirsch T & Maurer G (1998) Distribution of binary mixtures of citric, acetic and oxalicacid between water and organic solutions of tri-n-octylamine, part II, organic solventmethylisobutylketone. Fluid Phase Equilibria 142: 215-230.

Kirsch T, Ziegenfuss H & Maurer G (1997) Distribution of citric, acetic and oxalic acidsbetween water and organic solutions of tri-n-octylamine. Fluid Phase Equilibria 129:235-266.

Klason P (1893a) Bidrag till kannedomen om sammansattningen af granens ved samt dekemiska processerna vid framstallning af cellulosa darur. Teknisk Tidskrift, Afdelningenfor Kemi och Metallurgi 23(2): 17-22.

Klason P (1893b) Framstallning af rent lignin ur granved och denna sednares kemiskasammansattning. Teknisk Tidskrift, Afdelningen for Kemi och Metallurgi 23: 55-56.

Klason P (1908) Bidrag till kannedom om granvedens kemiska sammansattning, I. Arkivfor Kemi, Mineralogi och Geologi 3(5): 1-20.

Klason P & Fagerlind O (1908) Bidrag till kannedom om granvedens kemiskasammansattning, II. Arkiv for Kemi, Mineralogi och Geologi 3(6): 1-10.

Kleinert T (1933) Zur kenntnis der dampf-flussigkeitsgleichgewichte von aethylalkohol-wassergemischen bei temperaturen von 120 bis 180 C. Beihefte zu den zeitschriften desvereins deutscher chemiker nr 2. Verlag Chemie G.M.B.H., Berlin.

Kleinert T (1940) Uber das verhalten von cellulose bei der druckerhitzung in alkohol-wassermischungen. Cellulosechemie 18(5): 114.

Kleinert TN (1967) Thermischer holzaufschluss in alkohol-wassermischungen.Holzforschung und Holzverwertung 19(4): 60-65.

Kleinert TN (1971) Organosolv pulping and recovery process. US patent 3.585.104.Kleinert TN (1974a) Organosolv pulping with aqueous alcohol. Tappi 57(8): 99-102.Kleinert TN (1974b) Der alkohol-organosolv-aufschluss des holzes. Das Oesterreichische

Papier 11(11): 14-19.Kleinert TN (1975a) Ethanol-water delignification of sizable pieces of wood,

disintegration into stringlike fiber bundles. Holzforschung 29(3): 107-109.Kleinert TN (1975b) Ethanol-water delignification of wood - rate constants and activation

energy. Tappi 58(8): 170-171.Kleinert TN (1976) Der alkohol-wasser-aufschluss des holzes, technologie und

wirtschaftliche bedeutung. Papier 30(10A): V18-V23.Kleinert TN (1978) Kontinuierliches aufschluss- und ruckgewinnungsverfahren fur

pflanzliche faserrohstoffe zur herstellung von zellstoff im organischen losungsmittel.DE patent 26.44.155.C2.

Kleinert T & Tayenthal K (1931) Uber neuere versuche zur trennung von cellulose undinkrusten verschiedener holzer. Angewandte Chemie 44(39): 788-791.

Kleinert T & Tayenthal K (1932) Satt for uppslutning av fibrosa vaxtmaterial med alkohol-vatten-losningar. Sweden patent 75178.

Kobayashi M, Sasaki N, Gobara K & Nagasawa T (1978) Economic evaluation of alkali-methanol cooking. Japan Tappi 32(9): 525-532.

Koivusaari P (1990) Adsorption kaytto peroksimuurahaishappokeiton jateliemenregeneroinnissa. MSc. thesis, Univ Oulu, Dept Process Eng.

Koljonen J, Pohjanvesi S, Sundquist J & Poppius-Levlin K (1992) Pilot scale developmentof the Milox pulping and bleaching process. The European Pulp and Paper Week.Bologna, Italy, 1: 108-122.

Koll P, Bronstrup B & Metzger J (1979) Thermischer abbau von birkenholz mitsuperkritischen gasen (organischen losungsmittel) in einer hochdruck-, hochtemperatur-stromungsapparatur: die verflussigung von holz und weitere hinweise auf einealternative zellstoffgewinnungstechnologie. Holzforschung 33(4): 112-116.

Koll P & Lenhardt H (1987) Organosolv-aufschluss von birkenholz in einemdurchstromten reaktor. Holzforschung 41(2): 89-96.

Koll P & Metzger J (1978) Thermischer abbau von cellulose und chitin in uberkritischemaceton. Angew Chemie 90(10): 802-803.

Komissarenkov AA, Aliev RG, Burov AV, Sharkov VV & Badilovskaya TF (1990)LTITsBP, assignee. Method of producing pulp. USSR patent 1.608.275. (ABIPST62:13064(U)).

Komissarenkov AA, Aliev RG, Burov AV & Sharkov VV (1991a) LTITsBP, assignee.Method for producing pulp. USSR patent 1.689.481. (ABIPST 63:9047(U)).

Komissarenkov AA, Aliev RG, Burov AV & Filatova GA (1991b) LTITsBP, assignee.Method for producing pulp. USSR patent 1.689.480. (ABIPST 63:9048(U)).

Komissarenkov AA, Aliev RG, Burov AV, Sharkov VV & Luferova LB (1992a) Effect ofinorganic sorbents on the delignification of wood by the organosolv process. Les Zh(2): 104-108. (ABIPST 64:4770).

Komissarenkov AA, Aliev RG, Burov AV, Sharkov VV & Luferova LB (1992b) LTITsBP,assignee. Method of producing a fibrous cellulosic intermediate product. Russia patent1.721.153. (ABIPST 63:14255(U)).

Koncel J (1991) Alcell pulping process moves to first commercial installation. AmPapermaker 54(1): 22-26.

Kopfmann K (1991a) Conversion of an existing kraft pulp mill to an ASAM mill. 1991Tappi Pulping Conference Proc., Orlando, FL, 2: 925-931.

Kopfmann K (1991b) Explosions- und arbeitsschutz beim einsatz von methanol fur dasASAM-verfahren. Papier 45/7): 396-402.

Kopra-Schafer M (1991) Utilization possibilities of Organocell lignins. In: Faix O &Meier D (eds) Mitteilungen der bundesforschungsanstalt fur forst- und holzwirtschaft,168: 22 - 28.

Kordsachia O & Patt R (1987) Untersuchungen zum aufschluss von buche nach dem ASAMverfahren und zur bleiche der zellstoffe in untershiedlichen sequenzen. Papier 41(7): 340-351.

Kordsachia O & Patt R (1988a) Full bleaching of ASAM pulps without chlorinecompounds. Holzforschung 42(3): 203-209.

Kordsachia O & Patt R (1988b) Holzaufschluss nach dem ASAM-verfahren. Holz-Zentralblatt 114(81): 1220-1222.

Kordsachia O, Patt R & Rachor G (1988) Untersuchungen zum methanol-sulfitaufschluss.Papier 42(6): 261-269.

Kordsachia O, Patt R & Mix N (1989) Aufschluss von pappelholz nach dem ASAM-verfahren. Papier 43(7): 293-301.

Kordsachia O, Reipschlager B & Patt R.(1990a) ASAM pulping of birch wood and chlorinefree pulp bleaching. Paperi ja Puu 72(1): 44-50.

Kordsachia O, Wandinger B & Patt R (1990b) Study on asam pulping and chlorine-freebleaching of spanish eucalyptus. Invest Tec Papel (104): 257-277. (ABIPST 61:12159).

Kordsachia O, Wandinger B & Patt R (1992) Some investigations on asam pulping andchlorine free bleaching of eucalyptus from Spain. Holz Roh Werkstoff 50(3): 85-91.

Kordsachia O, Oltmann E, Odermatt J & Patt R (1994) TCF bleaching of ASAM softwoodpulp. TAPPI Pulping Conference Proc., San Diego, CA, p 277-287.

Kordsachia O, Oltmann E & Patt R (1995) Abgrenzung der prozessschritte zur herstellungchlorfrei gebleichter ASAM-zellstoffe, teil 2, untersuchungen zur grenzpunkt-bestimmung innerhalb der bleichsequenz OZ(E)P. Papier 49(6): 308-315.

Kosaya GS, Mironova TY, Prokopeva MA & Kosheleva VD (1981) All-Union Scientific-Industrial Enterprises of the Cellulose-Paper Industry, assignee. Pulp. USSR patent829.747. (CA 95:82684z).

Kosikova B & Polcin J (1973) Isolation of lignin from spruce by acidolysis in dioxane.Wood Sci Tech 7: 308-316.

Kosikova B, Demianova V & Kacurakova M (1993a) Sulfur-free lignins as composites ofpolypropylene films. J Appl Polym Sci 47: 1065-1073.

Kosikova B, Kacurakova M & Demianova V (1993b) Photooxidation of the compositelignin/polypropylene films. Chem Papers 47(2): 132-136.

Kosikova B, Demianova V & Mikulasova M (1994) Effect of lignin on degradation ofpolyolefins with Phanerochaete chrysosporium. Drev Vysk 39(3): 15-23.

Kostyukevich NG (1991) Acetylation of wood components during oxygen-acetic acidpulping. St. Petersburg, Russia, Institut khimii drevesiny, Issledovaniya v oblastikhimii drevesiny 43. (ABIPST 65:6582(AC)).

Kostyukevich NG & Deineko IP (1992) Delignification by oxygen in acetic acid as newmethod of pulping. In: Kennedy JF, Phillips GO & Williams PA (eds) Lignocellulosics:Science, Technology, Development and Use. Ellis Horwood Limited, Chichester, p.331-337.

Kostyukevich NG, Evtyugin DV & Nikandrov AB (1993) Molecular-weight characteristicsof oxygen-organosolv lignins. Izv Vyssh Uchebn Zaved Lesn Zh (2/3): 131-137.(ABIPST 65:6396(AC)).

Koval J & Slavik I (1963) Acetic acid in wood delignification. Papir Celulosa 18: 215-216. (CA 60:12221).

Kratzl K, Buchtela K, Gratzl J, Zauner J & Ettingshausen O (1962) Lignin and plastics, thereaction of lignin with phenol and isocyanates. Tappi 45(2): 113-119.

Kratzl K, Zauner J & Claus P (1964) Reaktionen mit markierten ligninen und modellen, I.mitteilung: kondensation mit phenol. Holzforschung 18(1/2): 47-52.

Krotov VS (1993) Drip percolation pulping with aqueous and aqueous organic ammoniaand sulphur dioxide solutions: environment-orientated technology. Khim Drev (1-3): 39-44.

Krotov VS & Frank AY (1993) Ammonium-sulfite-alcohol pulping: basis of prospectivetechnology for the processing of nonwoody raw material. Tsellyul Bum Karton (5): 10-11. (ABIPST 65:797).

Krull M, Rachor G, Patt R & Kordsachia O (1989) Einfluss von methanol auf den saurensulfit- und bisulfitaufschluss von buchenholz. Papier 43(2): 41-49.

Krull M, Kordsachia O & Patt R (1991) Der methanol-sulfitaufschluss von kiefer. Papier45(11): 673-680.

Ku YC, Wang IC & Kuo ML (1993) Alcohol pulping of plantation taiwania andeucalyptus, (1), pulping and pulp properties. Bull Taiwan For Res Inst 8(3): 169-176.(ABIPST 66:2178(AS)).

Kubes GJ, Fleming BI, MacLeod JM & Bolker HI (1978) Sulphide-free alkalinedelignification, IV, extension of soda-ethylenediamine pulping to various species.1978 Tappi Pulping Conference, New Orleans, LA, p 27-31.

Kulkarni HG, Sirmokadam NN, Shenvi AK, Hegde GM, Padwalkar SN & Guha SRD (1994)Organosolv pulping of Agave sisalana. IPPTA 6(1): 15-18.

Kuo Y, Munson CL, Rixey WG, Garcia AA, Frierman M & King CJ (1987) Use ofadsorbents for recovery of acetic acid from aqueous solutions, part I - factors governingcapacity. Sep Purif Methods 16(1): 31-64.

Kurvinen T (1988) Puun delignifiointi etikka- ja peroksoetikkahapolla. MSc. thesis, UnivHelsinki, Dept Polymer Chemistry.

Kuster W & Daur R (1930) Ueber die einwirkung von aromatischen diazokorpern auf ligninund cellulose. Cellulosechemie 11(1): 4-6.

Kuznetsov BN, Levdanskii VA, Polezhaeva NI & Shilkina TA (1995) The wastelessprocessing of wood bark by non-isobaric steam cracking and fractional extractionmethods. The 8th International Symposium on Wood and Pulping Chemistry Proc.,Helsinki, Finland, 1: 669-675.

Laamanen L, Poppius K, Sundquist J, Wartiovaara I & Kauliomaki S (1986) Bleached pulpby peroxyacid/alkaline peroxide delignification, part II, papermaking properties ofperoxy pulps. Paperi ja Puu 68(9): 622-628.

Laamanen LA, Sundquist JJ, Wartiovaara IYP, Kauliomaki SVM & Poppius KJ (1987) OyKeskuslaboratorio - Centrallaboratorium Ab, assignee. Menetelma valkaistun selluloosa-materiaalin valmistamiseksi ligniinipitoisesta raaka-aineesta. FI patent 74750.

Laamanen LA, Sundquist JJ, Wartiovaara IYP Kauliomaki SV & Poppius KJ (1988) OyKeskuslaboratorio - Centrallaboratorium Ab, assignee. Process for bleaching organicperoxyacid cooked material with an alkaline solution of hydrogen peroxide. US patent4.793.898.

Laamanen LA, Sundquist JJ, Wartiovaara IYP, Poppius KJ & Kauliomaki SV (1991) OyKeskuslaboratorio - Cetrallaboratorium Ab, assignee. Process for preparing pulp out oflignocellulosic raw material. CA patent 1.284.557.

Lachenal D & Delagoutte T (1996) Effect of peracids on lignin - application to bleaching.Fourth European Workshop on Lignocellulosics and Pulp, 203-210.

Lahtinen I (1991) Laimean muurahaishappoliuoksen vakevointi ja puhdistus. MSc. thesis,Univ Oulu, Dept Process Eng.

Lahtinen I, Jurva E, Matinheikki S & Sohlo J (1994) Fischer labodest model 602-laitteistolla maaritettyja hoyry-nestetasapainotietoja. Univ Oulu, Dept Process Eng,Report 142.

Lai YZ & Mun SP (1993) The role of organic solvents in acidic delignification of aspen.Seventh International Symposium on Wood and Pulping Chemistry Proc., Beijing, PRChina, 1: 266-271.

Lange W, Schweers W & Beinhoff O (1981) Uber die eigenschaften und abbarbaukeit vonmit alkohol-wasser-gemischen isolierten ligninen, 5. mitteilung: orientierende unter-suchungen uber ausbeuten und eigenschaften von unter verschiedenen aufschluss-bedingungen mit und ohne katalysatorzusatz isolierten ligninen. Holzforschung 35(3):119-124.

Lange W, Faix O & Beinhoff O (1983) Uber die eigenschaften und abbarbaukeit von mitalkohol-wasser-gemischen isolierten ligninen, VIII, the inhomogeneity of the ligninsfrom birch and spruce wood. Holzforschung 37(2): 63-67.

Larocque GL & Maass O (1941) The mechanism of the alkaline delignification of wood.Can J Res 19B(1): 1-16.

Lau H (1941) Bamboo pulp by the use of a hydrotropic solvent. Paper Ind Paper World 23:247-255.

Laxen T (1987) The impact of organosolv processes on washing. Pulp WashingSymposium Prep., Mariehamn, Finland, 2: 503-512.

Laxen T, Aittamaa J & Lonnberg B (1988) Chemical pulping of softwood chips byalcohols, part 3, solvent recovery and energy consumption. Paperi ja Puu 70(10): 891-894.

Lee HL (1986) Selection of separation processes. In: Calo JM & Henley EJ (eds) AIChEmodular instructions series B: stagewise and mass transfer operations volume 6:separation processes. AIChE, New York, p 17-23.

Legeler E (1923) Der holzaufschluss mittels phenol. Cellulosechemie 4(6): 61-62.

Lenz J, Peter W & Krassig, H. (1984) Chemiefaser Lenzig Aktiengesellschaft, assignee.Verfahren zur herstellung von zellstoffen mit niedrigem ligningehalt. AT patent373.303.

Leonova MO, Levina LF, Suvorova SI, Shapiro IL & Pen RZ (1994) Low-temperatureoxidative delignification of wood, (2), pulping of trembling aspen chips with forcedimpregnation and low liquor ratio. Izv VUZ Lesn Zh (3): 76-80. (ABIPST 66:3616(AS)).

Leopold B (1961) Chemical composition and physical properties of wood fibers, I,preparation of holocellulose fibers from loblolly pinewood. Tappi 44(3): 230-232.

Leopold H (1991) Derzeitiger entwicklungsstand des Organocell-verfahrens. DeutschePapierwirtschaft (3): T48-T49.

Leopold H (1992) Fiber properties of Organocell pulps. 1992 Solvent Pulping SymposiumNotes, Boston, MA, p 41-43.

Leopold H (1993a) Organocell - ein neues konzept zur faserherstellung. XXV EUCEPAConference Proc., Vienna, Austria, 1: 87-94.

Leopold H (1993b) Technologische eigenschaften des Organocell-zellstoffs neuesteerkentnisse nach der inbetriebnahme der anlage in Kelheim. Papier 47(10A): V1-V5.

Leszczynski C (1992) Alcell - an ecologically friendly pulping technology. PrzegladPapierniczy 48(5): 166-167. (ABIPST 64:3366).

Li Q & Chen R (1996) Alkaline-ethanol pulping of white birch [betula papyrifera] withrecovery and reuse of ethanol. 82e Congres annuel Section technique Associationcanadienne des pates et papiers: Faconner aujour dhui lenvironnement de demain,Montreal, Canada, B: 159-163. (ABIPST 67:844(AC)).

Li L & Kiran E (1988) Interaction of supercritical fluids with lignocellulosic materials. Ind Eng Chem Res 27(7): 1301-1312.

Li L & Kiran E (1989a) Supercritical fluid extraction of lignin from wood. In: Glasser W &Sarkanen K (eds) Lignin properties & materials. ACS, Washington, p 42-57. (ABIPST60:8976(B)).

Li L & Kiran E (1989b) Delignification of red spruce by supercritical methylamine andmethylamine-nitrous oxide mixtures. Tappi J 72(4): 183-190.

Liang W & Xiao X (1992) Studies on the properties of wheat straw alkali ethanol pulp. In:Kennedy JF, Phillips GO & Williams, PA (eds) Lignocellulosics - Science, Technology,Development and Use. Ellis Horwood Limited, Chichester, p. 447-456.

Liang WZ, Zhou FC, Xiao XR & Wang ZH (1988) Organosolv pulping characteristics ofwheat straw. 1988 International Non-Wood Fiber Pulping and Papermaking ConferenceProc., Beijing, PR China, p 271-280.

Liang WZ, Qia HX & Wang ZH (1989) Studies on ethanol pulping of bagasse. In:Kennedy JF, Phillips GO & Williams PA (eds) Wood processing and utilization. EllisHorwood Limited, Chichester, p 93-98.

Liang W, Xiao X, Chen M & Han Y (1994) The bleaching of ethanol pulp. SecondInternational Nonwood Fibre Pulping and Papermaking Conference Proc., Shanghai, PRChina, p 700-707.

Liebergott N (1994) Peracid delignification and bleaching. 1994 Pulping ConferenceProc., San Diego, CA, p 357-370.

Likon M & Perdih A (1995) Haloacetic pulping. The 8th International Symposium onWood and Pulping Chemistry Proc., Helsinki, Finland, 2: 243-248.

Lindholm J, Yilmaz Y, Johansson A, Gullichsen J & Sipila K (1995) A new process forcombined energy and pulp production from agricultural plants. The 8th InternationalSymposium on Wood and Pulping Chemistry Proc., Helsinki, Finland, 2: 455-460.

Lindner A & Wegener G (1987) Isolierung un charakterisierung von organosolv-ligninen.Holz Roh Werkstoff 45(9): 390.

Lindner A & Wegener G (1988a) Isolierung und chemische eigenschaften von ligninen ausaufschlussen nach dem Organocell-verfahren und ihre bedeutung fur eine potentiellenichtenergetische verwertung. Papier 42(10A): V1-V8.

Lindner A & Wegener G (1988b) Characterization of lignins from organosolv pulpingaccording to the Organocell process, part 1, elemental analysis, nonlignin portions andfunctional groups. J Wood Chem Tech 8(3): 323-340.

Lindner A & Wegener G (1989) Characterization of lignins from organosolv pulpingaccording to the Organocell process, part 2, residual lignins. J Wood Chem Tech 9(4):443-465.

Lindner A & Wegener G (1990a) Characterization of lignins from organosolv pulpingaccording to the Organocell process, part 3, molecular weight determination andinvestigation of fractions isolated by GPC. J Wood Chem Tech 10(3): 331-350.

Lindner A & Wegener G (1990b) Characterization of lignins from organosolv pulpingaccording to the Organocell process, part 4, permanganate oxidation andthioacidolysis. J Wood Chem Tech 10(3): 351-363.

Linnhoff B, Townsend DW, Boland D, Hewitt GF, Thomas BEA, Guy AR & Marsland RH(1982) A user guide on process integration for the efficient use of energy. TheInstitution of Chemical Engineers, Rugby.

Lipinsky ES (1983) The cellulose challenge: where do we go from here? Tappi J 66(10):47-49.

Liukko S & Poppius-Levlin K (1997) Characteristics of different peroxyacid effluents. 9thInternational Symposium on Wood and Pulping Chemistry Poster Presentations,Montreal, Canada, p 65:1-4.

Lobbecke JG, Lindner A, Wegener G & Wabner DW (1990) Anodic modification of ligninsduring electrolysis in the Organocell process. Holzforschung 44(6): 401-406.

Lobbecke JG, Lindner A, Wegener G & Wabner DW (1991) Effects of electrolysis on thechemistry of Organocell lignins. In: Faix O & Meier D (eds) Mitteilungen derbundesforschungsanstalt fur forst- und holzwirtschaft (168): 50-52.

Lora JH & Aziz S (1985) Organosolv pulping: a versatile approach to wood refining.Tappi J 68(8): 94-97.

Lora JH & Pye EK (1992) The Alcell process. 1992 Solvent Pulping Symposium Notes.Boston, MA, p 27-34.

Lora JH & Pye EK (1995) Solvent pulping opens door to viable chlorine-free, effluent-freeoptions. Pulp & Paper 69(2): 109-110.

Lora JH & Wayman M (1978) Delignification of hardwoods by autohydrolysis andextraction. Tappi 61(6): 47-50.

Lora JH, Cronlund M, Powers J, Orlowski G & Wu L (1985) A comparative study oforganosolv and kraft pulps. International Symposium on Wood and Pulping Chemistry,Vancouver, Canada, p 181-182.

Lora JH, Katzen R, Cronlund M & Wu CF (1988) Repap Technologies Inc., assignee.Recovery of lignin. US patent 4.764.596.

Lora JH, Wu CF, Pye EK & Balatinecz JJ (1989) Characteristics and potential applicationsof lignin produced by an organosolv process. In: Lignin: properties and materials.American Chemical Society Symposium Series, 397: 312-323.

Lora JH, Katzen R, Cronlund M & Wu CF (1990) Repap Technologies Inc., assignee.Process for lignin recovery. CA patent 1.267.648.

Lora JH, Creamer AW, Wu LCF & Goyal GC (1991a) Chemicals generated during alcoholpulping: characteristics and applications. 6th International Symposium on Wood andPulping Chemistry Proc., Melbourne, Australia, 2: 431-438.

Lora JH, Wu LCF & Klein WR (1991b) Mill trials on the use of ALCELLTM lignin as anadhesive for structural panels (abstract). 25th International Particleboard/CompositeMaterials Symposium, Pullman, WA, p 352.

Lora JH, Winner SR & Pye EK (1992) Industrial scale alcohol pulping. In: Lisius JD (ed)1989 and 1990 Forest Products Symposium Proc., Tappi Press, Atlanta, p 35-39.

Lora JH, Goyal GC & Raskin M (1993a) Characterization of residual lignins after Alcellpulping. Seventh International Symposium on Wood and Pulping Chemistry Proc.,Beijing, PR China, 1: 327 - 336.

Lora JH, Powers JL, Pye EK & Branch BA (1993b). Recent developments in Alcelltechnology - towards a closed cycle mill. 1993 Pulping Conference Proc., Atlanta, GA,3: 921-924.

Lora JH, Creamer AW, Wu LCF & Goyal GC (1993c) Industrial scale production oforganosolv lignins: characteristics and applications. In: Kennedy JF (ed) Cellulosics:chemical, biochemical and material aspects. Ellis Horwood Limited, Chichester, p 251-256.

Lonnberg B, Laxen T & Sjoholm R (1987a) Chemical pulping of softwood chips byalcohols, 1., cooking. Paperi ja Puu 69(9): 757-762.

Lonnberg B, Laxen T & Backlund A (1987b) Chemical pulping of softwood chips byalcohols, 2., bleaching and beating. Paperi ja Puu 69(10): 826-830.

Lorenz M & Dichtl G (1993) QVF Glastechnik GmbH, assignee. Verfahren zurruckgewinnung von hochsiedenden komponenten aus abwasser. DE patent42.22.783.C1.

Lyublin VS, Baranova LE & Germer EI (1988) Effectiveness of ethanol pulping. Bum Prom(3): 16-17. (ABIPC 59:1341).

MacLeod JM, Kubes GJ, Fleming BI & Bolker HI (1981) Soda-anthraquinone-ethylenediamine pulping. Tappi 64(6): 77-80.

Mahapatra A, Gaikar VG & Sharma MM (1988) New strategies in extractive distillation:use of aqueous solutions of hydrotropes and organic bases as solvent for organic acids.Sep Sci Tech 23(4&5): 429-436.

Maldas D & Kokta BV (1994) Use of lignin as a bonding agent for wood fiber-filledpolystyrene composites. Drevarsky Vyskum 39(3): 25-41.

Marr R, Siebenhofer M, Resch M & Bunzenberger G (1987) ExtraktionstechnikGesellschaft fur Anlagebau m.b.H., assignee. Verfahren zur gewinnung von furfural undmonocarbonsauren aus wassrigen losungen. EP patent 0.111.699.B1.

Martinez R & Sanjuan R (1993) Study of an organosolv process (ethanol-water-soda).Investigacion y Tecnica del Papel (117): 520-531. (ABIPST 65:799).

Martinez R & Sanjuan R (1990) Advantages of the organosolv process. Amatl 4(4): 9-18.(ABIPST 63:9629).

Marton R & Granzow SG (1982a) Use of ethanol in alkaline pulping. PCT patent WO82/01568.

Marton R & Granzow S (1982b) Ethanol-alkali pulping. Tappi 65(6): 103-106.Matinheikki S & Sohlo J (1994) HCOOH-CH3COOH-H2O-seoksen pervaporaatioerotus

PVA-kalvon avulla. Univ Oulu, Dept Process Eng, Report 143.Matter-Muller C & Stumm W (1984) Water properties. In: Grayson M (ed) Kirk-Othmer

encyclopedia of chemical technology, John Wiley & Sons, New York, 1: 276-294.Mattila T, Saari K & Vuori A (1992) Kemira Oy, assignee. Menetelma alemman

alifaattisen hapon ottamiseksi talteen. FI patent 85510.Mbachu RAD & Manley R (1981) The effect of acetic and formic acid pretreatment on pulp

bleaching with ozone. Tappi 64(1): 67-70.

McCready M (1991) Alcell pulping: it works! PaperAge 107(3): 14-15,19,33.McDonough TJ (1993) The chemistry of organosolv delignification. Tappi Journal 76(8):

186-193.McGee JK & April GC (1982) Chemicals from renewable resources: hemicellulose behavior

during organosolv delignification of southern yellow pine. Chem Eng Comm 19: 49-56.

McKee RH (1946) Use of hydrotropic solutions in industry. Ind Eng Chem 38(4): 382-384.

McKee RH (1954) Comparison of wood pulping processes; outline of principle andprocedure of the hydrotropic pulping process. Pulp Paper Mag Canada 55(2): 64-66.

McKee RH (1960) A new american paper pulp process, part I - pulping by the fullhydrotropic process. Paper Ind 42(4): 255-257,266.

McKee RH (1961) McKee Development Corp., assignee. Process for producing chemicalsfrom wood. CA patent 631.051.

McMillen JM, Gortner RA, Schmitz H & Bailey AJ (1938) Butanol cooking of hardwoodsand softwoods. Ind Eng Chem 30(12): 1407-1409.

Meier D, Faix O & Lange W (1981) Uber eigenschaften und abbaubarkeit von mit alkohol-wasser-gemischen isolierten ligninen, 6. mitteilung: chemische und spektroskopischecharakterisierung. Holzforschung 35(5): 247-252.

Meier D, Ante R & Faix O (1992) Catalytic hydropyrolysis of lignin: influence ofreaction conditions on the formation and composition of liquid products. Biores Tech40: 171-177.

Meier D & Faix O (1991) Hydroliquefaction of lignins. In: Faix O & Meier D (eds)Mitteilungen der Bundesforschungsanstalt fur Forst- und Holzwirtschaft, 168: 198-203.

Meier D & Schweers W (1979) Uber eigenschaften und abbaubarkeit von mit alkohol-wasser-gemischen isolierten ligninen, 2. mitteilung: alkalische druckoxidation mitluftsauerstoff zur gewinnung von vanillin und syringaaldehyd. Holzforschung 33(6):177-180.

Meier D & Schweers W (1981) Uber eigenschaften und abbaubarkeit von mit alkohol-wasser-gemischen isolierten ligninen, 4. mitteilung: katalytische hydrogenolyse zurerzeugung monomerer phenole. Holzforschung 35(2): 81-85.

Melo SR & Muller GP (1989) Effects of adding MeOH to soda-AQ pulping of eucalyptus.Celulosa Papel 5(1): 10-4. (ABIPST 60:10113).

Merkle G, Auerbach S, Burchard W, Lindner A & Wegener G (1992) Light scattering ofacetylated lignin. J Appl Polym Sci 45(3): 407-415.

Meyer FJ, Humiston CG & Moyle CL (1961) The Dow Chemical Company, assignee.Wood pulping process. CA patent 618.297.

Millner D (1983) Ny fraktioneringsmetod: cellulosafibrer, lignin och kemikalier urbiomassa. Cellulosa (8): 20-21.

Milstein O, Huttermann A, Ludemann HD, Majcherczyk A & Nicklas B (1990) Enzymaticmodification of lignin in organic solvents. In: Kirk TK & Chang HM (eds)Biotechnology in pulp and paper manufacture, applications and fundamentalinvestigations. Butterworth-Heinemann, Boston, p 375-387.

Mishra RK & Tiwari KK (1988) Liquid-liquid equilibrium in carboxylic acids (formic acidand acetic acid)-water-trioctylamine (with halogenated hydrocarbons) systems. Indian JTech 26: 447-452.

Miyazaki K, Iwanaga Y & Tsuchiya H (1989) Effect of amine on cresol pulping. In:Kennedy JF, Phillips GO & Williams PA (eds) Wood processing and utilization. EllisHorwood Limited, Chichester, p 75-80.

Mogollon G (1991) Effect of organic solvent on the alkaline delignification of sugar canebagasse. 6th International Symposium on Wood and Pulping Chemistry Proc.,Melbourne, Australia, 2: 251.

Montanari S, Curvelo AA & Groote RAMC (1991) Organosolv delignification of pinuscaribaea hondurensis: relationship between kappa number and klason lignin. Proc. 24Congresso Anual de Celulose e Papel (ABTCP), p 137-151. (ABIPST 66:3619(AC)).

Montanari S, Curvelo AAS & Groote RAMC (1993) Dioxan lignins from pinus caribaeavar. hondurensis, part 2, effect of the extraction time. Paperi ja Puu 75(7): 512-514.

Mostafa NYS (1994) Base-catalyzed dioxane and dioxane-borax pulping and the finestructure, chemical reactivity and viscose filterability of cotton cellulose. Cell ChemTech 28: 171-175.

Mullinder J (1989) Repap happy with Alcell results, in engineering phase forexpansion. Pulp Paper J 42(7): 31.

Mun SP (1989) Alcohol-bisulfite pulping: mechanism of delignification. In: Kennedy JF,Phillips GO & Williams PA (eds) Wood processing and utilization. Ellis HorwoodLimited, Chichester, p 99-104.

Mun SP & Wi H (1991a) Alcohol-bisulfite cooking of hyun-aspen [populus alba xglandulosa L.] wood, (1), determination of delignification conditions. J TAPPIK 23(1):55-61. (ABIPST 62:8473).

Mun SP & Wi H (1991b) Alcohol-bisulfite cooking of hyun-aspen [populus alba xglandulosa L.] wood, (2), conditions for the production of low-molecular-weightphenols. J TAPPIK 23(2): 15-20. (ABIPST 62:8472).

Mun SP, Sakai K & Imamura H (1988) Delignification with organic solvents andsulphites, (5), conditions for producing low-molecular-weight phenols and preparationof chemical pulp, (6), pulp quality and improvement of pulp strength. MokuzaiGakkaishi 34(3): 234-245. (ABIPC 59:6356).

Munson CL, Garcia AA, Kuo Y, Frierman M & King CJ (1987) Use of adsorbents forrecovery of acetic acid from aqueous solutions, part II - factors governing selectivity.Separ Purif Methods 16(1): 65-89.

Muurinen E (1986) Peroksihappomenetelmalla toimivan sellunvalmistusprosessinkeittoliuoksen talteenotto ja regenerointi. MSc. thesis, Univ Oulu, Dept Process Eng.

Muurinen E (1994) Peroksimuurahaishappoprosessin regenerointi ja prosessisynteesi. Lic.Sc. thesis, Univ Oulu, Dept Process Eng.

Muurinen E & Sohlo J (1988a) Liuottimen regenerointi organosolv prosesseista, 3.happokeitot. Univ Oulu, Dept Process Eng, Report 113.

Muurinen E & Sohlo J (1988b) Liuottimen regenerointi organosolv prosesseista, 4.alkoholi- ja happokeittojen vertailu. Univ Oulu, Dept Process Eng, Report 114.

Muurinen E & Sohlo J (1989) Recovery of chemicals from organosolv woodpulpingprocesses. In: Kennedy JF, Phillips GO & Williams PA (eds) Wood processing andutilization. Ellis Horwood Limited, Chichester, p 81-86.

Muurinen E & Sohlo J (1991a) Recovery of chemicals from peroxyformic acid pulping.6th International Symposium on Wood and Pulping Chemistry Proc., Melbourne,Australia, 2: 169-173.

Muurinen E & Sohlo J (1991b) Recovery of chemicals from peroxyformic acid pulping.4th World Congress of Chemical Engineering Prep., Karlsruhe, Germany, 1: 3.1-10.

Muurinen E & Sohlo J (1992) Recovery of chemicals from peroxyformic acidpulping. In: Kennedy JF, Phillips GO & Williams, PA (eds) Lignocellulosics - Science,Technology, Development and Use. Ellis Horwood Limited, Chichester, p 385-392.

Muurinen E & Sohlo J (1993a) Heat integration of a new formic acid pulping and recoveryprocess. In: Pilavachi PA (ed) Energy efficiency in process technology. ElsevierScience Publishers Ltd, Barking, p 996-1004.

Muurinen E & Sohlo J (1993b) Peroksihappokeiton erotusmenetelmat 2. Univ Oulu, DeptProcess Eng, Report 137.

Muurinen E & Sohlo J (1994) Simulation of recovery methods for pulping withperoxyformic and peroxyacetic acids. Comp Chem Eng 18(Suppl.): 609-613.

Muurinen E & Sohlo J (1997a) Separation methods for the peroxyacid pulping process.9th International Symposium on Wood and Pulping Chemistry Poster Presentations,Montreal, Canada, p 75:1-4.

Muurinen E & Sohlo J (1997b) Solvent recovery in peroxyacid pulping. In: Darton R (ed)Distillation and absorption 97 vol 2. IChemE, Rugby, p 543-552.

Muurinen E, Kivela E & Sohlo J (1988a) Liuottimen regenerointi organosolv prosesseista,1, kirjallisuuskatsaus ja tutkimuskohteiden valinta. Univ Oulu, Dept Process Eng,Report 111.

Muurinen E, Tuomisto S & Sohlo J (1988b) Liuottimen regenerointi organosolvprosesseista, 2, alkoholikeitot. Univ Oulu, Dept Process Eng, Report 112.

Muurinen E, Sohlo J, Vanhanen T & Kivela E (1989) Recovery of chemicals fromorganosolv woodpulping processes. 1989 International Symposium on Wood andPulping Chemistry Poster Sessions, Raleigh, NC, p 223-225.

Muurinen E, Jurva E & Sohlo J (1992) Peroksihappoprosessin regenerointi japrosessisynteesi. Univ Oulu, Dept Process Eng, Report 122.

Muurinen E, Silvennoinen J & Sohlo J (1993a) Peroksihappokeiton erotusmenetelmat.Univ Oulu, Dept Process Eng, Report 131.

Muurinen E, Jurva E, Lahtinen I & Sohlo J (1993b) Peroxyacid pulping and recovery.Seventh International Symposium on Wood and Pulping Chemistry Proc., Beijing, PRChina, 3: 195-200.

Myerly RC, Nicholson MD, Katzen R & Taylor JM (1981) The forest refinery. Chemtech11(3): 186-192.

Nadgir VM & Liu YA (1983) Studies in chemical process design and synthesis: part V, asimple heuristic method for systematic synthesis of initial sequences formulticomponent separations. AIChE J 29(6): 926-934.

Nakamura H & Takauti E (1941) Zellstoffherstellung mittels aethylenglykol. Cell Ind17(3): 19-26.

Nakamura T, Yamaguchi T & Murayama H (1966) Tekkosha Co., assignee. Process for therecovery of lower carboxylic acids from the product of the liquid phase oxidation ofparaffinic hydrocarbons. GB patent 1.049.901.

Nakamura K, Morck R, Reimann A, Kringstad KP & Hatakeyama H (1991) Mechanicalproperties of solvolysis lignin-derived polyurethanes. Polym Adv Tech 2(1): 41-47.

Nakano J, Takatsuka C & Daima H (1976) Studies on alkali-methanol cooking, (part 1),behavior of dissolution of lignin and carbohydrate. Japan Tappi 30(12): 33-38.

Nakano J, Takatsuka C, Daima H, Kobayashi M & Sasaki N (1977) Studies on alkali-methanol cooking, (2), strenght of pulp sheet and recovery of methanol. Japan Tappi31(11): 762-766. (ABIPC 48:9255)

Nakano J, Daima H, Hosoya S & Ishizu A (1981) Studies on alkali-methanol cooking.International Symposium on Wood and Pulping Chemistry, Stockholm, Sweden, 2: 72-77.

Nath R & Motard RL (1981) Evolutionary synthesis of separation processes. AIChE J27(4): 578-587.

Nelson PJ (1977) Pulping of wood with glycol solutions of salicylic acid derivates.Appita 31(1): 29-32.

Neto CP, Evtuguin D & Robert A (1994) Chemicals generated during oxygen-organosolvpulping of wood. J Wood Chem Tech 14(3): 383-402.

Neumann N & Balser K (1993) Acetocell - ein innovatives verfahren zur absolut schwefel-und chlorfreien zellstoffproduktion. Papier 47(10A): V16-V24.

Neumann U, Kordsachia O & Patt R (1997) Aufschluss von kiefernholz imnatronlauge/AQ/methanol-system. Papier 51 (11): 573-579.

Ni Y & Entremont M (1997) Peroxyacetic acid oxidation of lignin model compounds. 9thInternational Symposium on Wood and Pulping Chemistry Oral Presentations,Montreal, Canada, p D-6 1-5.

Ni Y & Heiningen ARP (1994) Lirnin removal of alcell pulp by washing with ethanol-water solution. 1994 Tappi Pulping Conference Proc., p 5-12.

Ni Y & Heiningen ARP (1995) The swelling of pulp fibers derived from the Alcellprocess. The 8th International Symposium on Wood and Pulping Chemistry Proc.,Helsinki, Finland, 2: 255-260.

Ni Y & Heiningen ARP (1996) Lignin removal from Alcell pulp by washing with ethanoland water. Tappi J 79(3): 239-243.

Ni Y & Heiningen ARP (1997) The swelling of pulp fibers derived from the ethanol-basedorganosolv process. Tappi J 80(1): 211-213.

Ni Y & Heiningen ARP (1998) An ECF sequence for the Alcell process including anethanol-assisted ozone stage. Tappi J 81(4): 141-144.

Ni Y & Hu Q (1995) Alcell lignin solubility in ethanol-water mixtures. J Appl Polym Sci57: 1441-1446.

Nikandrov AB (1993) Effect of wood dimensions on the dissolution of lignin duringoxygen-acetic acid pulping. Izv Vyssh Uchebn Zaved Lesn Zh (2/3): 87-90. (ABIPST65:6586(AS)).

Nimz H (1969a) Uber ein neues abbauverfahren des lignins. Chem Ber 102: 799-810.Nimz H (1969b) Spaltung vom aetherbindungen durch benachbarte mercaptogruppen,

modellversuche mit thioessigsaure. Chem Ber 102: 3803-3817.Nimz HH & Berg A (1989) Kunz Holding GmbH & Co. KG, assignee. Verfahren zur

delignifizierung von zellstoffen. EP patent 0.325.890.A1.Nimz HH & Berg A (1991) Acetocell GmbH & Co. KG, assignee. Lignin removal method

using ozone and acetic acid. US patent 5.074.960.Nimz HH & Casten R (1985) Organosolv pulping with acetic acid. International

Symposium on Wood and Pulping Chemistry Technical Papers, Vancouver, Canada, p265-266.

Nimz HH & Casten R (1986a) Chemical processing of lignocellulosics. Holz RohWerkstoff 44: 207-212.

Nimz HH & Casten R (1986b) Holzaufschluss mit essigsaure. DE patent 34.45.132.A1. Nimz HH & Robert D (1985) 13C NMR spectra of acetic acid lignins. International

Symposium on Wood and Pulping Chemistry Technical Papers, Vancouver, Canada, p267.

Nimz HH & Schoene M (1993) Non-waste pulping and bleaching with acetic acid. SeventhInternational Symposium on Wood and Pulping Chemistry Proc., Beijing, PR China, 1:258-265.

Nimz HH & Schwind H (1981) Oxidation of lignin and lignin model compounds withperacetic acid. International Symposium on Wood and Pulping Chemistry, Stockholm,Sweden, 2: 105-111.

Nimz HHH & Schone M (1993) Gebruder Kummerer Projekt Agentur GmbH, assignee.Puun kuidutus etikkahapolla siten, etta lisataan muurahaishappoja. FI patent appl933729.

Nimz HH & Schone M (1994) Gebruder Kummerer Projekt Agentur GmbH, assignee.Holzaufschluss mit essigsaure unter zusatz von ameisensaure. DE patent 42.28.171.A1.

Nimz HH, Granzow C & Berg A (1986a) Acetosolv pulping. Holz Roh Werkstoff 44: 362.Nimz HH, Roth M, Tschirner U & Casten R (1986b) Organosolv pulping with

chloroethanol. Holzforschung 40(Suppl.): 125-132.Nimz HH, Casten R & Roth M (1986c) Holzaufschluss mit essigsaure und chlorethanol. DE

patent 34.23.024.A1.Nimz HH, Berg A, Granzow C & Casten R (1988) Schadstofffreie gewinnung von

gebleichtem zellstoff, lignin und hemicellulosen nach dem Acetosolv-verfahren.Mitteilungen der Bundesforschungsanstalt fur Forst- und Holzwirtschaft (160): 343-355.

Nimz HH, Berg A, Granzow C & Casten R (1989a) Acetosolv pulping and bleaching. Non-waste Technology, VTT Symposium 102, Espoo, Finland, 1: 399-408.

Nimz HH, Berg A, Granzow C, Casten R & Muladi S (1989b) Zellstoffgewinnung undbleiche nach dem Acetosolv verfahren. Papier 43(10A): V102-V108.

Nimz HH, Berg A & Casten R (1989c) Kunz Holding GmbH & Co. KG, assignee.Verfahren zur gewinnung von gebleichtem zellstoff. EP patent 0.325.891.A1.

Nimz H, Berg A, Janssen W, Balle S, Kunz RG & Klein W (1992a) Acetocell GmbH & Co.KG, assignee. Verfahren zur delignifizierung von cellulosehaltigen rohstoffen. DEpatent 41.07.357.C1.

Nimz H, Berg A, Janssen W, Balle S, Kunz RG & Klein W (1992b) Acetocell GmbH & Co.KG, assignee. Verfahren zur delignifizierung von cellulosehaltigen rohstoffen. EPpatent 0.503.304.A1.

Nishiyama M, Hosokawa J & Yoshihara K (1989) Basic study on removal of cresols fromwaste water. Shikoku Kogyo Gijutsu Shikensho Hokoku 21(1): 1-8. (ABIPST61:4976(U)).

Norman E, Olm L & Teder A (1992) Methanol-reinforced kraft pulping. 1992 SolventPulping Symposium, Boston, MA, p 51-60.

Null HR (1980) Energy economy in separation processes. Chem Eng Prog 76(8): 42-49.Null HR (1987) Selection of a separation process. In: Rousseau RW (ed) Handbook of

separation process technology. John Wiley & Sons, New York, p 982-995.Null HR, Bowe LE & Binning RC (1967) Monsanto Company, assignee. Production of

acetic acid and recovery by plural stage distillation. US patent 3.335.179.Nunez C & Reinoso M (1990) Aqueous alcohol pulping of bagasse - conversion from

kappa number to residual lignin. 26th ATIPCA Congr Tec Celulosa Papel, BuenosAires, Argentina, p 401-412. (ABIPST 64:6163(M)).

Obrocea P & Cimpoescu G (1998) Contribution to sprucewood delignification withperoxyformic acid. Cellul Chem Technol 32(5-6): 517-525. (Paperbase 00530945).

Obrocea P & Gavrilescu D (1988) Delignification of beechwood acetic acid solutions.Celuloza Hirtie 37(4): 157-159. (ABIPST 60:8200)

Obrocea P, Gavrilescu D & Stancana R (1994) Organosolv pulping of wood in alkalinemedium, I., ASAM pulping of beechwood at low temperature. Cell Chem Tech 28: 339-349.

Obrocea P, Gavrilescu D & Stancana R (1996) Bleachability of some beech [Fagus]organosolv pulps. Celul Hirtie 45(1): 41-45. (ABIPST 67:12655(AS)).

Obst JR & Sanyer N (1980) Effect of quinones and amines on the cleavage rate of beta �-O-4ethers in lignin during alkaline pulping. Tappi 63(7): 111-114.

Oh SW, Paik KH & Kang CH (1988) Comparison of asaq (alkaline sulfite/aq) pulpextracted with organic solvents and ASAM (alkaline sulfite/aq/meoh). J Tappik 20(3):42-48. (ABIPST 60:5298)

Oki T, Okubo K & Ishikawa H (1974) The oxidative degradation of guaiacylglycerol- �-guaiacyl ether by peracetic acid. Mokuzai Gakkaishi 20(11): 549-557.

Oliveira ON, Constantino CJL, Balogh DT & Curvelo AAS (1994) Langmuir monolayersof lignins from pinus caribaea hondurensis sawdust. Cell Chem Tech 28: 541-549.

Olm L & Teder A (1990) Nya kokprocesser for blekt massa: mindre klor med metanol. SvPapperstidn 93(10): 22-24.

Oltmann E, Gause E, Kordsachia O & Patt R (1992) Ozone bleaching technology: acomparison between high and medium consistency, part I. Papier 46(7): 341-350.

Oltmann E, Kordsachia O & Patt R (1994) Abgrenzung der prozessschritte zur herstellungchlorfrei gebleichter ASAM-zellstoffe, teil 1, untersuchungen zur grenzpunkt-bestimmung zwischen dem aufschluss und der chlorfreien bleichsequenz OZEP. Papier48(2): 55-68.

Ooi T & Ni Y (1998) Development of an ozone-based TCF sequence for bleaching ahardwood ALCELL pulp. Tappi J 81(5): 255-259.

Othmer DF & Conti JJ (1962) Process of azeotropic distillation of formic acid from aceticacid. US patent 3.024.170.

Paik KH, Oh SH & Koo JO (1988) Alkaline sulfite pulping with the additions ofanthraquinone and methanol. J Tappik 20(2): 24-32. (ABIPST 60:502)

Paik KH, Nahm WS, An BJ & Moon CK (1989) Separation of wood components by aceticacid under atmospheric conditions and their utilization. J Tappik 21(3): 35-47.

Paik KH, Kim DH & Moon CK (1994a) Alkaline sulfite pulping with the additions ofathraquinone and methanol, (1), pine ASAM pulping and the composition of tall oilrecovered from ASAM black liquor. J TAPPIK 26(1): 37-44. (ABIPST 65:18822).

Paik KH, Kim DH & Nho MB (1994b) Alkaline sulfite pulping with the additions ofathraquinone and methanol, (2), oak and birch ASAM pulping. J TAPPIK 26(4): 51-57.(ABIPST 65:18821).

Palenius I (1987) Was sollte von neuen aufschlussverfahren gefordert werden? Papier41(10A): V1-V6.

Selvam PV, Ghose TK & Ghosh P (1983) Catalytic solvent delignification of agriculturalresidues: inorganic catalysts. Process Biochem 18: 13-15.

Papatheophanus MG, Koullas DP & Koukios EG (1995) Alkaline pulping of prehydrolysedwheat straw in aqueous organic solvent systems at low temperatures. Cell Chem Tech29(1): 29-40. (ABIPST 66:15422(AS)).

Pappens R (1990) Organocell: high quality, low pollution. Pulp Paper Int 32(3): 74-77.Parajo JC & Santos V (1995) Preliminary evaluation of acetic acid-based processes for

wood utilization. Holz Roh Werkst 53: 347-353.Parajo JC, Alonso JL, Vazquez D & Santos V (1993) Optimization of catalysed Acetosolv

fractionation of pine wood. Holzforschung 47(3): 188-196.Park JK & Phillips JA (1988) Ammonia catalyzed organosolv delignification of poplar.

Chem Eng Comm 65: 187-205.Paszner L (1998) Catalyzed alcohol organosolv pulping. In: Young RA & Akhtar M (eds)

Environmentally Friendly Technologies for the Pulp and Paper Industry. John Wiley &Sons, New York, NY, p 69-100.

Paszner L & Behera NC (1984) Beating behaviour and sheet strenght development ofconiferous organosolv fibers. XXI Eucepa International Conference, Torremolinos,Spain, 1: 83-98.

Paszner L & Behera NC (1985) Beating behaviour and sheet strength development ofconiferous organosolv fibers. Holzforschung 39(1): 51-61.

Paszner L & Behera NC (1989) Topochemistry of softwood delignification by alkali earthmetal catalysed organosolv pulping. Holzforschung 43(3): 159-168.

Paszner L & Chang PC (1979) Bau- und Forschunggesellschaft Thermoform AG, assignee.Verfahren zum entlignifizieren und verzuckern von pflanzlichen lignocellulose-materialien unter mitverwendung organischer losungsmittel. PCT patent WO 79/00119.

Paszner L & Chang PC (1981) Organosolv delignification and saccharification process forlignocellulosic plant materials. CA patent 1.100.266.

Paszner L & Chang PC (1982) Bau- und Forschunggesellschaft Thermoform AG, assignee.Pulping of lignocellulose with aqueous alcohol and alkaline earth metal salt catalyst.PCT patent WO 82/00483.

Paszner L & Chang PC (1983a) Bau- und Forschungsgesellschaft Thermoform AG,assignee. Lignocelluloseaufschlussverfahren mit einem gemisch von wasser und niedrigmolekularem aliphatischem alkohol und metallsalz. DE patent 29.20.731.C2.

Paszner L & Chang PC (1983b) Catalysed organosolv pulping of softwoods. InternationalSymposium on Wood and Pulping Chemistry, Tsukuba Science City, Japan, Suppl.: 21-28.

Paszner L & Chang PC (1983c) Productions of high-yield dissolving pulp by the catalysedorganosolv process. 1983 International Dissolving and Speciality Pulps Conference,Boston, MA, p 81-88.

Paszner L & Chang PC (1983d) Thermoform Bau- und Forschungsgesellschaft, assignee.Organosolv delignification and saccharification process for lignocellulosic plantmaterials. US patent 4.409.032.

Paszner L & Chang PC (1984) High efficiency organosolv saccharification process. USpatent 4.470.851.

Paszner L & Cho PHJ (1987) Innovations for hardwood utilization: catalyzed organosolvpulp and saccharification. Proc. of the Workshop on Aspen [Populus], Pulp, Paper andChemicals, 1: 63-78. (ABIPST 67:2122(AC)).

Paszner L & Cho HJ (1989) Organosolv pulping: acidic catalysis options and their effecton fiber quality and delignification. Tappi J 72(2): 135-142.

Paszner L, Quinde AA & Meshgini M (1985) ACOS - accelerated hydrolysis of wood byacid catalysed organosolv means. International Symposium on Wood and PulpingChemistry, Vancouver, Canada, p 235-240.

Patel DP & Varshney AK (1989) The effect of presoaking and prehydrolysis in theorganosolv delignification of bagasse. Indian J Tech 27(6): 285-288.

Patt R & Kordsachia O (1986) Herstellung von zellstoffen unter verwendung vonalkalischen sulfitlosungen mit zusatz von anthrachinon und methanol. Papier 40(10A):V1-V8.

Patt R & Kordsachia O (1988) Anforderungen an neue zellstoffherstellungsverfahren.Wochenbl Papierfabr 116(17): 709-713.

Patt R, Kordsachia O & Reuter G (1987a) Wirtschaftliche und technische aspekte desASAM verfahrens. Deutsche Papierwirtschaft (3): T96-T102.

Patt R, Kordsachia O & Knoblauch J (1987b) The ASAM process - alkaline sulfite,anthraquinone, methanol pulping. Fourth International Symposium on Wood andPulping Chemistry, Paris, France, 1: 355-360.

Patt R, Kordsachia O & Mix N (1989a) Uber die eignung von pappelholz zurzellstoffherstellung nach dem ASAM-verfahren. Holz-Zentralblatt 115(4): 1,22,26.

Patt R, Kordsachia O & Kopfmann K (1989b) Wirtschaftliche, technologische undoekologische aspekte der zellstoffherstellung nach dem ASAM-verfahren. Papier43(10A): V108-V115.

Patt R, Kordsachia O, Schubert HL & Hammann M (1990a) Actual status of the ASAM-process. 24th Eucepa Conference: Control, Maintenance, Environment, Stockholm,Sweden, p 442-446.

Patt R, Schubert HL, Kordsachia O, Oltmann E & Ridder W (1990b) The ASAM process -competitor to kraft pulping? Sunds Defibrator Symposium, Pori, Finland, p 1-17.

Patt R, Knoblauch J, Faix O, Kordsachia O & Puls J (1991a) Lignin and carbohydratereactions in alkaline sulfite, anthraquinone, methanol (ASAM) pulping. Papier 45(7):389-396.

Patt R, Knoblauch A, Faix O, Kordsachia O, Puls J & Robert D (1991b) Lignin andcarbohydrate reactions in alkaline sulfite, anthraquinone, methanol (ASAM) pulping.6th International Symposium on Wood and Pulping Chemistry Proc., Melbourne,Australia, 1: 609-617.

Patt R, Schubert HL, Kordsachia O, Oltmann E & Krull M (1991c) Chlorfreie bleiche vonsulfit- und ASAM-zellstoffen im labor- und pilot-masstab. Papier 45(10A): V8-V16.

Patt R, Jaschinski T & Mielisch HJ (1996) Stabilizierte und katalysierte peroxidbleiche.Wochenbl Papierfabr 124(17):750, 752-755. (ABIPST 67:12657(AS)).

Patt R, Kordsachia O & Schubert HL (1998) The ASAM process. In: Young RA & AkhtarM (eds) Environmentally Friendly Technologies for the Pulp and Paper Industry. JohnWiley & Sons, New York, NY, p 101-131.

Pauly H (1918a) Aktiengesellschaft fur Zellstoff- und Papierfabrikation in Aschaffenburg,assignee. Verfahren zur gewinnung der das sogenannte lignin bildenten stoffe ausholzarten. German patent 309551.

Pauly H (1918b) Aktiengesellschaft fur Zellstoff- und Papierfabrikation, assignee. Satt attutvinna lignin ur cellulosahaltigt material. Swedish patent 45010.

Pauly H (1921) Aktiengesellschaft fur Zellstoff- und Papierfabrikation in Aschaffenburg,assignee. Verfahren zur gewinnung der das sogenannte lignin bildenten stoffe auszellulosehaltigen materialien. AT patent 83396.

Pauly H (1943) Gewinnung huminfreier essigsaure-lignole. Berichte der DeutschenChemischen Gesellschaft 76(9): 864-871.

Pauly H, Foulon A, Hansen O, Haberstroh O, Bailom H & Sextl J (1934) Scheidung vonlignin-komponenten. Berichte der Deutschen Chemischen Gesellschaft 67: 1177-1199.

Pazukhina G & Ostrik S (1998) LIgnin destruction by peracetic acid during the fir cookingin moderately mixed liquids. Proc. Fifth European Workshop on LignocellulosicsChemistry for Ecologically Friendly Pulping and Bleaching Technologies, Aveiro,Portugal, p 429-432. (Paperbase 00522248).

Pazukhina GA & Shan DS (1990) LTA, assignee. Method of producing pulp. USSR patent1.542.983. (ABIPST 62:5054(U)).

Pazukhina GA & Teploukhova MV (1998) Bleaching of organosolvent pulp by oxygen-containing reagents. Lesn Zh (6): 75-78. (Paperbase 00542458).

Pazukhina GA, Teploukhova MV & Khakimova FK (1995) Chlorine-free bleaching oforganosolv pulp. The 8th International Symposium on Wood and Pulping ChemistryProc., Helsinki, Finland, 2: 265-268.

Pecina H & Kuhne G (1992a) Die eignung von Organocell-zellstoffablaugen alsphenolsubstituent in phenolischen spanplattenleimen. Holzforsch Holzverwert 44(3):39-43.

Pecina H & Kuhne G (1992b) Lignin-phenol-bindemittel auf der basis von ASAM-dicklauge. Holz-Zentralblatt 118(28): 464-466.

Peguy A (1989) New materials from cellulose or lignocellose solutions in amine oxidesystems. In: Inagaki H & Phillips GO (eds) Cellulosics utilization. Elsevier SciencePublishers Ltd, Barking, p 19-24.

Pekarovicova A, Jonekova A & Pekarovic J (1995) Use of xylanase and ligninase inbleaching of beech [fagus] organosolv pulp. Przegl Papier 51(9): 451-454, 457.(ABIPST 67: 4413(AS)).

Pellinen J & Nimz HH (1986) Extraction of lignin from birch wood using chloroethanoland acetic acid. Paperi ja Puu 68(8): 548-552.

Pen RZ, Suvorova SI & Leonova MO (1993) Low-temperature oxidative delignification ofwood and properties of the pulps. Izv Vyssh Uchebn Zaved Lesn Zh (2/3): 57-60.(ABIPST 65:6588(AS)).

Pepper JM, Baylis PET & Adler E (1959) The isolation and properties of lignins obtainedby the acidolysis of spruce and aspen woods in dioxane-water medium. Can J Chem 37:1241-1248.

Pereira H, Oliveira MF & Miranda I (1986) Kinetics of ethanol-water pulping and pulpproperties of eucalyptus globulus lab. Appita 39(6): 455-458.

Perez DS & Curvelo AAS (1997) Kinetics of acetone-water organosolv delignification ofeucalyptus urograndis . 9th International Symposium on Wood and Pulping ChemistryPoster Presentations, Montreal, Canada, p 88:1-4.

Perry RH & Chilton CH (1973) Chemical engineers handbook. McGraw-Hill BookCompany, New York.

Perttunen J, Sohlo J & Maentausta O (1996) The fermentation of birch hemicelluloseliquor to lactic acid. In: Srebotnik E & Messner K (eds) Biotechnology in pulp andpaper industry. Facultas-Universitatsverlag, Vienna, p 295-298.

Peter W & Hoglinger O (1986) Herstellung von kunstfaserzellstoff nach dem organosolv-aufschlussverfahren. Lenzinger Ber 61: 12-16.

Peter W, Krassig H & Lenz J (1984) Chemiefaser Lenzig Aktiengesellschaft, assignee.Verfahren zur aufarbeitung von gebrauchter aufschlussflussigkeit sowie anlagen zurdurchfuhrung dieses verfahren. AT patent 373.932.

Petty G (1989) Canadians pioneer a small-scale pulp mill. Paper Tech 30(2): 10-13.Pew JC (1957) Properties of powdered wood and isolation of lignin by cellulytic enzymes.

Tappi 40(7): 553-558.Pilhofer T & Dichtl G (1986) Liquid-liquid extraction as an alternative to distillation for

the recovery of organic material. ISEC86 Prep., Frankfurt am Main, FR Germany, 3:723-729.

Pla F & Yan JF (1991) Viscosity and functionality of alkali and organosolv lignins.Holzforschung 45(2): 121-125.

Pla F, Dolk M, Yan JF & McCarthy JL (1986) Lignin, 23., macromolecular characteristicsof alkali lignin and organosolv lignin from black cottonwood. Macromolecules 19(5):1471-1477.

Ploetz T, Richtzenhain H, Deiters W & Giesen J (1963) Feldmuhle Aktiengesellschaft,assignee. Verfahren zur herstellung von niedrigsiedenden spaltprodukten aus lignindurch kontinuierliche druckhydrierung in gegenwart organischer flussigkeiten. DBPpatent 1.142.853.

Pohjanvesi S, Saari K, Poppius-Levlin K & Sundquist J (1995) Technical and economicalfeasibility study of the milox process. The 8th International Symposium on Wood andPulping Chemistry Proc., Helsinki, Finland, 2: 231-236.

Poljak A (1948) Holzaufschluss mit peressigsaure. Angewandte Chemie 60A(2): 45-46.Poljak A (1951) Holzaufschluss mit peressigsaure II. Holzforschung 5(2): 31-33.

Poppius K, Laamanen L, Sundquist J, Wartiovaara I & Kauliomaki S (1986) Bleached pulpby peroxyacid/alkaline peroxide delignification. Paperi ja Puu 68(2): 87-92.

Poppius K, Laamanen L, Sundquist J, Wartiovaara I, Toikkanen L & Keranen E (1987)Multi-stage peroxyformic acid pulping. Fourth International Symposium on Wood andPulping Chemistry, Paris, France, 2: 211-214.

Poppius K, Sundquist J & Wartiovaara I (1989a) Chemical pulping of birch and pine chipsby the three stage peroxyformic acid method. In: Kennedy JF, Phillips GO & WilliamsPA (eds) Wood processing and utilization. Ellis Horwood Limited, Chichester, p 87-92.

Poppius K, Hortling B & Sundquist J (1989b) Chlorine-free bleaching of chemical pulps -the potential of organic peroxyacids. 1989 International Symposium on Wood andPulping Chemistry, Raleigh, NC, p 145-150.

Poppius-Levlin K & Tuominen I (1991) Koivusulfaattimassan valkaisu milox-menetelmalla. PSC Comm 24.

Poppius-Levlin K, Toikkanen L, Tuominen I & Sunquist J (1991a) Increased reactivity ofkraft pulps towards non-chlorine bleaching chemicals. 6th International Symposium onWood and Pulping Chemistry Proc., Melbourne, Australia, 1: 99-106.

Poppius-Levlin K, Toikkanen L, Tuominen I & Sundquist J (1991b) Chlorine-freebleaching of kraft pulps. International Pulp Bleaching Conference, Production ofBleached Chemical Pulp in the Future, Stockholm, Sweden, 3: 103-120.

Poppius-Levlin K, Mustonen R, Huovila T & Sundquist J (1991c) Milox pulping withacetic acid/peroxyacetic acid. Paperi ja Puu 73(2): 154-158.

Poppius-Levlin K, Hortling B & Sundquist J (1993) Milox pulping and bleaching -possibilities to avoid chlorine chemicals. Seventh International Symposium on Woodand Pulping Chemistry Proc., Beijing, PR China, 1: 214-222.

Poppius-Levlin K, Tuominen I, Kauliomaki S, Pohjanvesi S, Saari K, Sundquist J & HarmaT (1995) Milox-prosessin koelaitos vuosina 1990-1994; Laitteisto, massan valmistusja ominaisuudet. PSC Comm 81.

Poppius-Levlin K, Jaaskelainen AS & Sundquist J (1996) Delignification of oxygen-treatedsoftwood kraft pulp by different peroxy compounds. Fourth European Workshop onLignocellulosics and Pulp, p 216-222.

Povarova AY & Chupka EI (1994) Effectiveness of acid-alkaline and oxidation-reductioncatalysis during oxidation of wood in aqueous organic media, (3), effect of oxygenpressure and temperature on the rate of wood and lignin oxidation in alkaline media. IzvVUZ Lesn Zh (3): 81-85. (ABIPST 66: 3396(AS)).

Primakov SF & Barbash VA (1988) Optimization of parameters for pulping with aqueousalcohol solutions of sulfur dioxide. Khim Drev (Riga) (2): 44-47. (ABIPC 59:4013).

Primakov SF & Barbash VA (1989) Delignification of wood with aqueous alcoholsolutions of sulfur dioxide. Bum Prom (1): 6-7. (ABIPST 60:6073).

Puech JL, Sarni F, Labidi A, Mouttet B & Robert A (1990) Delignification of oak woodwith an ethanol-water solution in a flow-through reactor. Holzforschung 44(5): 367-371.

Puls J (1991) Characterization of hemicelluloses from organosolv pulping. 6thInternational Symposium on Wood and Pulping Chemistry Proc., Melbourne, Australia,1: 21-25.

Purina LT, Treimanis AP & Timermane GB (1992) Structural and chemical compositioncharacteristics of pulp fibers isolated from hardwood by organic-solvent delignification.Khim Drev (Riga) (1): 3-12. (ABIPST 63:12217).

Purina L, Treimanis A & Timermane G (1994) Distribution of residual lignin andhemicelluloses in the outer and cetral layers of organosolv pulp fiber walls. Nordic PulpPaper Res J (2): 101-119.

Puthson P, Kordsachia O, Odermatt J, Zimmermann M & Patt R (1997) ASAM pulping ofeucalyptus camaldulensis and TCF bleaching of the resulting pulp. Holzforschung51(3): 257-262.

Puuronen M, Muurinen E & Sohlo J (1995) Organosolv pulping of reeds. The 8thInternational Symposium on Wood and Pulping Chemistry Proc., Helsinki, Finland, 2:467-472.

Puuronen M, Muurinen E & Sohlo J (1997) Peltobiomassat erikoissellujen raaka-aineina.Univ Oulu, Dept Process Eng, Report 168.

Pye K (1987) Alcell offers savings with quality pulps, by-products. PIMA 69(11): 21-23.Pye EK (1989a) The Alcell process. 1989 Solvent Pulping Conference Proc., Seattle, WA,

16-32.Pye EK (1989b) Alcohol pulping - environmentally sound opportunity for nonintegrated

paper mills. 6th International Pulp Symposium Prep., 2: paper 6. (ABIPST67:13950(AC)).

Pye EK (1990) The Alcell process - a proven alternative to kraft pulping. 1990 PulpingConference, Toronto, Canada, 991-996.

Pye EK & Lora JH (1991) The Alcell process - a proven alternative to kraft pulping. TappiJ 74(3): 113-118.

Pye EK, Klein WR, Lora JH & Cronlund M (1987) The AlcellTM process. Solvent Pulping -Promises & Problems Conference, Appleton, WI, 55-67.

Quinde-Abad A (1990) Behavior of the major resin and fatty acids of slash pine (pinuselliottii) during organosolv pulping. PhD. thesis, Univ British Columbia. (ABIPST64:743(DU)).

Ramos J, Davalos F & Gonzales P (1993) Sugar cane bagasse pretreatment with soda-methanol for the chemimechanical pulp production. Seventh International Symposiumon Wood and Pulping Chemistry Proc., Beijing, PR China, 3:274-279.

Rantakokko J, Maunuksela J & Malone J (1994) Einsatz von peroxyessigsaure anstellevon bioziden - erfolgreicher versuch zur schleimbekampfung in einer papierfabrik.Papier 48(11): 681-686.

Rassow B & Gabriel H (1931a) Ueber das fichtenholz-lignin. Cellulosechemie 12(8): 227-235.

Rassow B & Gabriel H (1931b) Ueber das fichtenholz-lignin. Cellulosechemie 12(9/10):249-254.

Rassow B & Gabriel H (1931c) Ueber das fichtenholz-lignin. Cellulosechemie 12(11): 290-295.

Rassow B & Gabriel H (1931d) Ueber das fichtenholz-lignin. Cellulosechemie 12(12): 318-320.

Rassow B & Lude R (1931) Ueber bambuslignin. Zeitschrift Angew Chemie 44(40): 827-833.

Rassow B & Wagner K (1931a) Ueber die einwirkung von glykol-salzsaure auf kiefernholz.Wochenbl Papierfabr 62(23A): 35-42.

Rassow B & Wagner K (1931b) Ueber die einwirkung von glykol-salzsaure aufkiefernholz. Wochenbl Papierfabr 62(31): 741-743.

Rautenbach R & Albrecht R (1989) Membrane processes. Ellis Horwood, Chichester.Ray AK, Rao NJ, Mohanty B & Garceau JJ (1993) Methanol based organosolv pulping of

wheat straw of indian origin. 1993 Pulping Conference Proc., Atlanta, GA, 1: 281-286.Reznikov VM (1988) Acetic acid delignification of hardwoods. Bum Prom (9): 12-13.

(ABIPC 59:9137).

Reznikov VM & Zilbergleit MA (1980) Belorussian Technological Institute, assignee.Paper pulp intermediate product. USSR patent 761.647. (CA 93:222146m).

Ricard E & Guinot HM (1928) Manufacture of anhydrous formic acid. US patent1.896.100.

Rickelton WA & Boyle RJ (1988) Solvent extraction with organophosphines -commercial & potential applications. Separ Sci Tech 23(12&13): 1227-1250.

Ricker NL, Michaels JN & King CJ (1979) Solvent properties of organic bases forextraction of acetic acid from water. J Separ Process Tech 1(1): 36-41.

Ricker NL, Pittman EF & King CJ (1980) Solvent extraction with amines for recovery ofacetic acid from dilute aqueous industrial streams. J Separ Process Tech 1(2): 23-30.

Ritter GJ & Barbour JH (1935) Effect of pretreatments of wood on the lignindetermination, distribution of methoxyls in wood. Ind Eng Chem Anal Ed 7(4): 238-240.

Robert TA (1955) Hydrotropic pulping of a tropical wood. Tappi 38(9): 149A-150A.Robert D, Neirinck V, Pan X, Evtuguine D, Neto CP & Chum HL (1993) Production and

characterization of organosolv lignins: 13C NMR as a process control. SeventhInternational Symposium on Wood and Pulping Chemistry Proc., Beijing, PR China, 2:889-893.

Roberts RS, Muzzy JD & Faass GS (1988) Georgia Tech Research Corp., assignee. Processfor extracting lignin from lignocellulosic material using an aqueous organic solvent andan acid neutralizing agent. US patent 4.746.401.

Ronan P, Rossiter A, Agar R & Cheung L (1994) Timely pinch analysis improves energyefficiency of new pulping process. 1994 Tappi Engineering Conference Proc., p 937-951.

Rosch J & Mulhaupt R (1994) Mechanical properties of organosolv-lignin-filledthermoplastics. Polym Bull 32: 361-365.

Rose LM (1985) Distillation design in practice. Elsevier Science Publishers, Amsterdam.Rousu E (1996) Muurahaishappo keittokemikaalina, erikoisselluloosaa non-wood-raaka-

aineista. Paperi ja Puu 78(10): 594- 596.Ruthven DM (1984) Principles of adsorption and adsorption processes. John Wiley &

Sons, New York.Rutkowski J, Mroz W, Surma-Slusarska B & Perlinska-Sipa K (1993) Glycolic

delignification of hardwood. Progress 93 Conference Proc., 1: 190-205. (ABIPST67:13953(AC)).

Rutkowski J, Mroz W & Perlinska-Sipa K (1994a) Glycol-acetic wood delignification. CellChem Tech 28: 621-628.

Rutkowski J, Mroz W & Perlinska-Sipa K (1994b) Glycol-acetic acid delignification ofwood. Przegl Papier. 50(9): 437-439. (ABIPST 66:3624(AS)).

Rutkowski J, Wendelt P & Perlinska-Sipa K (1998) Contribution to the technology ofbirch wood pulping with acetic acid solutions. Cellul Chem Technol 32(1-2): 89-96.(Paperbase 00530350).

Saake B, Lehnen R, Lummitsch S & Nimz HH (1995a) Production of dissolving and papergrade pulps by the formacell process. The 8th International Symposium on Wood andPulping Chemistry Proc., Helsinki, Finland, 2: 237-242.

Saake B, Lummitsch S, Mormanee R, Lehnen R & Nimz HH (1995b) Erzeugung vonzellstoffen nach dem Formacell-verfahren. Papier 49(10A): V1-V7.

Saake B, Lehnen R, Schmekal E, Neubauer A & Nimz HH (1998) Bleaching of formacellpulp from aspen wood with ozone and peracetic acid in organic solvents. Holzforschung52(6): 643-650. (Paperbase 00526322).

Saari K, Vuori A & Mattila T (1992) Kemira Oy, assignee. Menetelma alifaattistenhappojen ja sokerien talteenottamiseksi. FI patent 85511.

Saarnio J & Kuusisto R (1971) D-xylose from sulphite waste liquor. Paperi ja Puu 53(6):367-370.

Sabatier J, Irulegui A & Tomas J (1989) Ethanolic pulping of sugar cane bagasse. 1989International Symposium on Wood and Pulping Chemistry Proc., Raleigh, NC, p 781-783.

Saeman JF (1945) Kinetics of wood saccharification. Ind Eng Chem 37: 43-54.Sakai K, Kuroda K & Kishimoto S (1972) Delignification in peracid bleaching, VI,

reaction of the beta-aryl ether type model compounds with peracetic acid. Tappi 55(12):1702-1706.

Sakai K, Mun SP, Fukuda J & Imamura H (1983) Delignification with sulfites and anorganic solvent - semichemical and chemical pulping of sugi (japanese cedar). 2ndInternational Symposium on Wood and Pulping Chemistry, Tsukuba Science City,Japan, 4: 194-197.

Sakai K, Mun SP & Imamura H (1987) Organosolv pulping which produces valuable by-products. Fourth International Symposium on Wood and Pulping Chemistry, Paris,France, 2: 193-195.

Sakai K & Uprichard JM (1987) Isopropanol-sulphite pulping studies on radiata pine.Appita 40(3): 193-200.

Sakakibara A & Edashige Y (1984) Solvolysis pulping (part 2), solvolysis pulping ofspruce wood (picea glehnii) with cresol-water system, and the pulp strength. JapanTappi 38(3): 73-80.

Sakakibara A & Nakayama N (1962a) Hydrolysis of lignin with dioxane and water, II,identification of hydrolysis products. J Japan Wood Res Soc 8: 153-166.

Sakakibara A & Nakayama N (1962b) Hydrolysis of lignin with dioxane and water, III,Hydrolysis products of various woods and lignin preparations. J Japan Wood Res Soc8: 157-162.

Sakakibara A, Edashige Y, Sano Y & Takeyama H (1983) Solvolysis pulping with lignindegradation products. 1983 International Symposium on Wood and Pulping Chemistry,Tsukuba Science City, Japan, 3: 33-49.

Sakakibara A, Edashige Y, Sano Y & Hatakeyama H (1984) Solvolysis pulping withcresols-water system. Holzforschung 38(3): 159-165.

Salentev DG (1991) Chemiluminescence during oxidation of wood and its componets inwater-organic systems. Institut khimii drevesiny, Issledovaniya v oblasti khimiidrevesiny 14. (ABIPST 65:6594(AC)).

Sameshima K & Takamura N (1987) The ammonium oxalate pulping of bast fiber. FourthInternational Symposium on Wood and Pulping Chemistry, Paris, France, p 199-201.

Sanjuan R & Chavez A (1989) Organosolv pulping with eucalyptus globulus. Amatl3(3/4): 3-9. (ABIPST 61:12171).

Sanjuan R & Gomez F (1991) Multistage pulping of sugarcane bagasse. Amatl 5(1/2): 3-11. (ABIPST 63:13607).

Sanjuan R, Chavez H & Vargas J (1989) Organosolv pulping of eucalyptus globulus.ABTCP Congr. Anual Celulose Papel 22nd, Sao Paulo, Brazil, p 165-176. (ABIPST62:11080(M)).

Sanjuan R, Prado J, Romero N & Irulegui A (1993) Low pollution alternative processes toobtain bleached pulp from sugar cane bagasse. Seventh International Symposium onWood and Pulping Chemistry Proc., Beijing, PR China, 3: 280-283.

Sanjuan R, Vargas J, Anzaldo J, Munguia L & Delgado E (1995) Comparative study ofthree processes to obtain pulp from kenaf (hibiscus cannabinus). The 8th InternationalSymposium on Wood and Pulping Chemistry Proc., Helsinki, Finland, 2: 449-454.

Sano Y (1989) Solvolysis pulping of softwood. In: Kennedy JF, Phillips GO & WilliamsPA (eds) Wood processing and utilization. Ellis Horwood, Chichester, p 111-116.

Sano Y & Sasaya T (1985) Studies on phenorganosolv pulping I, delignification of woodsby modified organosolv pulping. Mokuzai Gakkaishi 31(10): 836-842.

Sano Y, Umemoto M, Takahashi A & Sasaya T (1986) Phenorganosolv pulping II,pulping of beechwood with acetic acid-water-phenols system. Mokuzai Gakkaishi32(12): 1003-1010.

Sano Y, Sasaya T & Sakakibara A (1988) Solvolysis pulping of hardwoods. Japan Tappi J42(5): 487-496. (ABIPC 59:9138).

Sano Y, Maeda H & Sakashita Y (1989a) Pulping of wood at atmospheric pressure I.,pulping of hardwoods with aqueous acetic acid containing a small amount of organicsulfonic acid. Mokuzai Gakkaishi 35(11): 991-995.

Sano Y, Endo M & Sakashita Y (1989b) Solvolysis pulping of softwoods with aqueouscresols containing a small amount of acetic acid. Mokuzai Gakkaishi 35(9): 807-812.

Sano Y, Nakamura M & Shimamoto S (1990) Pulping of wood at atmospheric pressure II,pulping of birch wood with aqueous acetic acid containing a small amount of sulfuricacid. Mokuzai Gakkaishi 36(3): 207-211.

Sansigolo CA & Curvelo AAS (1994) Delignification in aqueous ethanol of eucalyptusglobulus: characteristics of lignin and pulp. Papel 55(8): 22-29. (ABIPST 65:18825).

Sansigolo CA & Curvelo AAS (1995) Kinetics of pulping in ethanol and water andproperties of eucalyptus globulus pulp. Papel 56(8): 38-42, 44-45. (ABIPST66:17375(AS)).

Sarkanen KV (1980) Acid-catalyzed delignification of lignocellulosics in organic solvents.In: Sarkanen KV & Tillman DA (eds) Progress in biomass conversion, New York, 2:127-144.

Sarkanen KV (1982) University of Washington, assignee. Method and system for selectivealkaline defiberization and delignification. US patent 4.329.200.

Sarkanen K & Schuerch C (1957) Lignin structure, XI, quantitative study of thealcoholysis of lignin. J Am Chem Soc 79: 4203-4209.

Sarkanen S, Teller DC, Hall J & McCarthy JL (1981) Lignin, 18, associative effectsamong organosolv lignin components. Macromolecules 14: 426-434.

Savov K (1990) Donor-acceptor reactions during degradation of lignin in an acid medium.Tselul Khartiya 20(4): 12. (ABIPST 63:8357).

Savov KA, Tzanova SE & Draganova RJ (1996) Comparison of the catalytic activities ofaluminium trichloride and hydrochloric acid in the acetic acid-lignin system.Holzforschung 50(2): 188-192. (ABIPST 67:2125(AS)).

Schild G, Muller W & Sixta H (1996) Prehydrolysis kraft and ASAM paper grade pulpingof eucalypt wood, a kinetic study. Papier 50(1): 10-22.

Schillmoller CM (1997) Control organic-acid corrosion with these metals and alloys.Chem Eng Prog 93(2): 66-71.

Schorning P (1961) Untersuchungen zur steuerung des sulfitaufschlusses von holzern inmethanol-wasser bei gegenwart von Na2S O 4 bzw NaHSO 4 bzw Na 2SO3.

Faserforsch Textiltech 12(3): 105-108.Schroeter MC (1991) Possible lignin reactions in the Organocell pulping process. Tappi J

74(10): 197-200.

Schroeter MC (1993) Solvent pulping can be an alternative to the kraft process. ChinaPaper 1993 Proc., p 63-68.

Schroeter MC & Dahlmann G (1991) Organocell simplifies the solvent pulping process.1991 Pulping Conference Proc., Orlando, FL, 2: 646-651.

Schubert HL (1990) Asam report 1. Kraftanlagen Aktiengesellschaft, Heidelberg.Schubert HL, Kordsachia O & Patt R (1990) Pilotanlagenversuche zum ASAM-verfahren.

Wochenbl Papierfabr 118(22): 977-981.Schubert HL, Fuchs K, Patt R, Kordsachia O & Bobik M (1993) Der ASAM-prozess - eine

industriereife zellstofftechnologie. Papier 47(10A): V6-V15.Schubert H, Kordsachia O, Shackford L & Shin N (1998) High yield and easy bleachability -

the ASAM process. 1998 Breaking the Pulp Yield Barrier Symp., Atlanta, GA, p 241-246. (ABPST 69:373(AC)).

Schutz F (1940) Ueber den aufschluss von faserrohstoffen mit wasserhaltigermonochloressigsaure. Cellulosechemie 18(4): 76-83.

Schutz F (1941a) Ueber den aufschluss von faserrohstoffen mit chlorhydrinen.Cellulosechemie 19(2): 33-38.

Schutz F (1941b) Untersuchung der beim holzaufschluss mit wasserhaltiger chloressigsaureentstehenden lignine. Cellulosechemie 19(4): 87-89.

Schutz F & Knackstedt W (1942) Holzaufschluss mit salzsaure oder chloriden alskatalysator in essigsaurer losung. Cellulosechemie 20(1): 15-22.

Schweers W (1972a) Belastung von luft und gewassern durch holzchemische prozesse.Forstarchiv 43: 43-49.

Schweers W (1972b) Umweltbelastung durch holzchemische prozesse. Ber Landwirtsch 50:312-324.

Schweers WHM (1974) Phenol pulping - a potential sulfur-free papermaking process.Chemtech 4(8): 490-493.

Schweers W & Meier D (1979) Ueber eigenschaften und abbaubarkeit von mit alkohol-wasser-gemischen isolierten ligninen, 1. mitteilung: halbmikropyrolyse im stationarensystem. Holzforschung 33(1): 15-18.

Schweers W & Pereira H (1972) Ueber den holzaufschluss mit phenolen, 1. mitt., trankungverschiedener holzer mit phenol. Holzforschung 26(2): 51-54.

Schweers W & Rechy M (1972) Moglichkeiten eines schwefelfreien holzaufschlusses.Papier 26(10A): 585-590.

Schweers W & Rechy M (1973) Ueber den holzaufschluss mit phenolen, 3. mitt., ueberden aufschluss von kiefern- und buchenholz. Papier 27(12): 636-639.

Schweers W, Behler H & Beinhoff O (1972) Ueber den holzaufschluss mit phenolen, 2.mitt., vorlaufige untersuchungen uber die phenolbilanz. Holzforschung 26(3): 103-105.

Schwenzon K (1965) Hydrotroper aufschluss von pflanzen. Zellstoff Papier 14(7): 199-201.

Schwenzon K (1966) Hydrotroper aufschluss von pflanzen. Zellstoff Papier 15(7): 202-204.

Seisto A (1993) Havupuumassan valmistus milox-menetelmalla. PSC Comm 55.Seisto A (1994) Peltokasvien keitto ja valkaisu milox-menetelmalla. PSC Comm 60.Seisto A (1998) Effect of peroxyacid delignification on pulp and papermaking properties.

PSC Comm 107.Seisto A & Poppius-Levlin K (1995) Milox pulping of agricultural plants. The 8th

International Symposium on Wood and Pulping Chemistry Proc., Helsinki, Finland, 1:407-414.

Seisto A & Poppius-Levlin K (1997a) Formic acid/peroxyformic acid pulping of birch -delignification selectivity and zero-span strength. Nord Pulp Pap Res J 12(3): 155-161.

Seisto A & Poppius-Levlin K (1997b) Fibre characteristics and paper properties of formicacid/peroxyformic acid birch pulps. Nord Pulp Pap Res J 12(4): 237-243.

Seisto A & Sundquist J (1994) Silikaatit milox-ruohomassan keitossa ja valkaisussa. PSCComm 68.

Seisto A, Poppius-Levlin K & Jousimaa T (1995) Grass pulp for papermaking by theperoxyformic acid pulping method. 1995 TAPPI Pulping Conference Proc., p 487-494.(ABIPST 66:7039(AC)).

Seisto A, Poppius-Levlin K & Jousimaa T (1996) Grass pulp for papermaking by themilox method. PSC Comm 87.

Sellers T (1994) Modification of phenolic resin with organosolv lignins and evaluation ofstrandboards made by the resin as binder. PhD. thesis, Univ Tokyo. (ABIPST65:8714(BDU)).

Sellers T, Lora JH & Okuma M (1994) Organosolv-lignin-modified phenolics asstrandboard binder, I., organosolv lignin and modified phenolic resin. MokuzaiGakkaishi 40(10): 1073-1078.

Senyo WC, Creamer AW, Wu CF & Lora JH (1996) Use of organosolv lignin to reducepress-vent formaldehyde emissions in the manufacture of wood composites. For Prod J46(6): 73-77. (ABIPST 67:4298(AS)).

Shaban A & Suciu GD (1993) ABB Lummus Crest Inc., assignee. Process of pulping andbleaching fibrous plant material with tert-butyl alcohol and tert-butyl peroxide. USpatent 5.252.183. (ABIPST 66:9747(P)).

Shah DJ & Tiwari KK (1981) Recovery of acetic acid from dilute aqueous streams usingliquid-liquid extraction with tri-n-butyl phosphate as solvent. J Separ Process Tech2(4): 1-6.

Shimizu Y & Hayashi J (1989) Esterification of cellulose with organic acids. In: KennedyJF, Phillips GO & Williams PA (eds) Cellulose: structural and functional aspects. EllisHorwood, Chichester, p 187-193.

Shiraishi N, Fu S, Yokota T & Tsujimoto N (1988) Oji Paper Company Ltd., assignee.Solvolytic pulping of lignocellulose. Japan Kokai patent 21.993/88. (ABIPC59:1199).

Sierra-Alvarez R & Tjeerdsma B (1995a) Organosolv pulping of juvenile poplar wood. The8th International Symposium on Wood and Pulping Chemistry Proc., Helsinki, Finland,2: 207-211.

Sierra-Alvarez R & Tjeerdsma B (1995b) Organosolv pulping of poplar [populus] woodfrom short-rotation intensive-culture plantations. Wood Fiber Sci 27(4): 395-401.(ABIPST 66: 17379(AS)).

Silva Perez D, Terrones MGH, Grelier S, Nourmamode A, Castellan A, Ruggiero R &Machado AEH (1998) Peroxyformic acid pulping of eucalyptus grandis wood chips andsugar cane bagasse in one stage and characterization of the isolated lignins. J WoodChem Technol 18(3): 333-365. (Paperbase 00522189).

Simkhovich BS, Zilbergleit MA & Reznikov VM (1987) Papermaking properties of aceticacid pulp from hardwoods. Bum Prom (7): 25-26. (ABIPST 60:478(T)).

Singh SV, Bhandari SS & Singh SP (1989) Organosolv pulping of Dendrocalamus strictusand Eucalyptus tereticornis with aqueous ethanol. Silver Jubilee International Seminar& Workshop: Appropriate Technologies for Pulp & Paper Manufacture in DevelopingCountries (IPPTA), paper no. 35. (ABIPST 67:13956(AC)).

Singh UP, Berry JC, Lora JH & Pye EK (1995) TCF bleaching of pulps from the Alcellprocess. International Non-Chlorine Bleaching Conference Proc., 12, paper no. 2.(ABIPST 66:19398(AC)).

Sinner M, Dietrichs HH, Puls J, Schweers W & Brachthauset KH (1988) Bau- undForschungsgesellschaft Thermoform AG, assignee. Process for production of xylitolfrom lignocellulosic raw materials. US patent 4.742.814.

Sinner M, Dietrichs HH, Puls J, Schweers W & Brachthauset KH (1989) Bau- undForschungsgesellschaft Thermoform AG, assignee. Verfahren zum aufschluss vonlignocellulosischen pflanzlichen rohstoffen zur gewinnung von zuckern, lignin undcellulose sowie dessen anwendung. DE patent 27.37.118.C2.

Skachkov VM, Tanicheva RV, Mikhailov GS, Kozhevnikov PS & Sokov AN (1991)Enzymolysis of oxygen-solvolysis pulp. Gid Les Prom (7): 4-5. (ABIPST 63:8527).

Smith DE (1987) Ester pulping of aspen [populus]. Workshop on Aspen [Populus], Pulp,Paper and Chemicals, 2: 172-176. (ABIPST 67:2127(AC)).

Smith DK, Bampton RF & Alexander WJ (1963) Use of new solvents for evaluatingchemical cellulose for the viscose process. Ind Eng Chem Fund Pro Des Prod Res 2(1):57-62.

Smith C, Utley JHP, Petrescu M & Viertler H (1989) Biomass electrochemistry: anodicoxidation of an organosolv lignin in the presence of nitroaromatics. J ApplElectrochem 19: 535-539.

Sobral MF, Gomide JL & Colodette JL (1992) ASAE (alkaline sulfite anthraquinoneethanol) process for producing eucalyptus pulp. 25th Congresso Anual Celulose PapelABTCP, Sao Paulo, Brazil, p 179-193. (ABIPST 65:5064(M)).

Solar R & Kacik F (1993) Comparative study of caribean pine (pinus caribaea l.) wood andbark dioxane lignin. Holz Roh Werkst 51(5): 347-352.

Solar R & Kacik F (1995) Alteration of maple [acer] wood lignin under conditions oftreatment in dioxane-water-HCl agent. Drev Vysk 40(1): 3-16. (ABIPST 66:13615(AS)).

Solar R, Melcer I & Kacik F (1988) Comparative study of pine wood and pine bark (pinussilvestris l.) dioxan lignins. Cell Chem Tech 22: 39-52.

Sousa M, Schuchardt U & Rodrigues JAR (1986) Separation and identification of sugarcane bagasse constituents by the organosolv process. Ciencia Cultura 38(1): 181-188.(ABIPC 59:2016).

Springer EL & Zoch LL (1966) Delignification of aspen wood with acidified aqueoussolutions of sulfolane. Svensk Pappersatidn 69(16): 513-516.

Springer EL, Harris JF & Neill WK (1963) Rate studies of hydrotropic delignification ofaspenwood. Tappi 46(9): 551-555.

Starr LD & Casebier RL (1970) Rayonier Incorporated, assignee. Process for pulping woodchips with sodium sulfide and organic solvent. US patent 3.513.068.

Staudinger H & Dreher E (1936) Ueber hochpolymere verbindungen, 142. mitteil., ueberdas lignin. Ber Deutschen Chem Ges 69: 1729-1737.

Stevens WP & Marton R (1966) Effect of peracetic acid on the properties of high yieldpulps. Tappi 49(10): 452-456.

Suleman Y & Yusoff M (1997) thanol-water pulping of oil palm (Elaeis guineensis) fibersusing hydrochloric acid as a catalyst and test-paper characterization. J Jpn Wood ResSoc 43(12): 1016-1021. (ABIPST 68:11919(AS)).

Sun YP, Abbot J & Yates B (1994a) UV-peroxide bleaching of peroxyformic acidpretreated eucalypt kraft pulp - tcf bleaching. 48th Appita Annual General ConferenceProc., p 155-162.

Sun YP, Abbot J & Chen CL (1994b) UV-peroxide bleaching of peroxyformic acidpretreated eucalypt kraft pulp: tcf bleaching. Appita 47(6): 459-462.

Sun R, Lawther J & Banks W (1997) Physico-chemical characterization of organosolvlignins from wheat straw. Cellul chem Technol 31(3/4): 199-212. (ABIPST68:6582(AS)).

Sundquist J (1985) The multiform nature of residual lignin in chemical pulps. 1985International Symposium on Wood and Pulping Chemistry Technical Papers,Vancouver, BC, p 23-25.

Sundquist J (1986) Bleached pulp without sulphur and chlorine chemicals by aperoxyacid/alkaline peroxide method - an overview. Paperi ja Puu 68(9): 616-620.

Sundquist J (1995) Muurahaishappoa sellunvalmistukseen. Tekniikan Nakoalat (5): 48-49.Sundquist J (1996) Chemical pulping based on formic acid, summary of Milox research.

Paperi ja Puu 78(3): 92-95.Sundquist J & Poppius-Levlin K (1992) Milox pulping and bleaching - the first pilot scale

trials. 1992 Solvent Pulping Symposium Notes, Boston, MA, p 45-49.Sundquist J & Poppius-Levlin K (1998) Milox pulping and bleaching. In: Young RA 6

Akhtar M (eds) Environmentally Friendly Technologies for the Pulp nad Paper Industry.John Wiley & Sons, New York, NY, p 157-190.

Sundquist J, Laamanen L, Wartiovaara I, Poppius K & Kauliomaki S (1986) Manufacture ofbleached pulp without sulphur and chlorine - utopia or not? EUCEPA Symposium Proc.,Helsinki, Finland, p 29-33.

Sundquist J, Laamanen L & Poppius K (1988) Problems of non-conventional pulping inthe light of peroxyformic acid cooking experiments. Paperi ja Puu 70(2): 143-148.

Sundquist J, Poppius K, Hortling B, Setala J, Heikonen M & Moisio T (1989) Spent liquorfrom peroxyformic acid pulping as preserving agent for animal fodder. 1989International Symposium on Wood and Pulping Chemistry Poster Sessions, Raleigh,NC, p 233-234.

Surma-Slusarska B (1998) Balance of ethylene glycol in organosolv pulping of hardwood.Przegl Pap 54(12): 712-714. (Paperbase 00537502).

Takagi H & Kachi S (1989) Research and development of solvolysis pulping, (4),bleaching of solvolysis pulp. Japan Tappi J 43(12): 1290-1297. (ABIPST 61:339).

Takagi H, Wakai M & Araki H (1989) Research and development of solvolysis pulping,(3), cooking conditions and pulp properties. Japan Tappi J 43(11): 1171-1178.(ABIPST 60:9147).

Takeyama H & Sasaya T (1988) Hydrocracking of solvolysis lignin (3). Enshurin Ken Hok(Hokkaido) 45(2): 637-651. (ABIPC 59:8077).

Tamada JA & King CJ (1990a) Extraction of carboxylic acids with amine extractants, 2.chemical interactions and interpretation of data. Ind Eng Chem Res 29(7): 1327-1333.

Tamada JA & King CJ (1990b) Extraction of carboxylic acids with amine extractants, 3.effect of temperature, water coextraction, and process considerations. Ind Eng Chem Res29(7): 1333-1338.

Tamada JA, Kertes AS & King CJ (1990) Extraction of carboxylic acids with amineextractants, 1. equilibria and law of mass action modelling. Ind Eng Chem Res 29(7):1319-1326.

Teder A & Olm L (1992) Alternativa kokprocesser: favoriten modifierat sulfatkok -utmanaren alkalisk sulfitprocess. Svensk Papperstidn 95(7): 26-32.

Teder A, Tormund D & Ulmgren P (1990) Luktfri sulfatmassafabrik en mojlighet?; jaktenpa H2S och CH3SH ger resultat. Svensk Papperstidn 93(7): 155-160.

Terenteva EP, Zorina RI, Varvarskaya SV & Dievskii VA (1990) Changes in the structureof aspenwood [populus] during pulping by the organic solvent method. Khim Drev(Riga) (3): 41-44. (ABIPST 62:5721).

Thompson NS & Kaustinen OA (1964) Some chemical and physical properties of pulpsprepared by mild oxidative action. Tappi 47(3): 157-162.

Thompson NS & Kaustinen OA (1969) The Institute of Paper Chemistry, assignee. Fibrousmaterial and its treatment. CA patent 806.573.

Thring RW, Chornet E, Overend RP & Heitz M (1989a) Production and hydrolyticdepolymerization of ethylene glycol lignin. In: Glasser W & Sarkanen K (eds) Ligninproperties & materials. ACS, Washington, p 228-244. (ABIPST 60:8994(B)).

Thring RW, Chornet E, Vidal PF, Bouchard J & Overend RP (1989b) Solvent fractionationof ethylene glycol lignin. 1989 International Symposium on Wood and PulpingChemistry Poster Sessions, Raleigh, NC, p 343-345.

Thring RW, Chornet E & Overend RP (1990a) Recovery of a solvolytic lignin: effects ofspent liquor/acid volume ratio, acid concentration and temperature. Biomass 23(4): 289-305.

Thring RW, Chornet E, Bouchard J, Vidal PF & Overend RP (1990b) Characterization oflignin residues derived from the alkaline hydrolysis of glycol lignin. Can J Chem68(1): 82-89.

Thring RW, Chornet E, Bouchard J, Vidal PF & Overend RP (1991) Evidence for theheterogeneity of glycol lignin. Ind Eng Chem Res 30(1): 232-240.

Thring RW, Chornet E & Overend RP (1993a) Fractionation of woodmeal by prehydrolysisand thermal organosolv; alkaline depolymerization, chemical functionality, andmolecular weight distribution of recovered lignins and their fractions. Can J Chem71(6): 779-789.

Thring RW, Chornet E & Overend RP (1993b) Thermolysis of glycol lignin in thepresence of tetralin. Can J Chem Eng 71(2): 107-115.

Thring RW, Chornet E & Overend RP (1993c) Fractionation of woodmeal by prehydrolysisand thermal organosolv; process strategy, recovery of constituents, and solventfractionation of lignins so produced. Can J Chem Eng 71(2): 116-123.

Timermane GB, Purina LT, Ioelovich MY & Treimanis AP (1992) Kinetics of hardwooddelignification in an organic solvent. Khim Drev (Riga) (4-5): 36-40. (ABIPST64:4790).

Tirtowidjojo S, Sarkanen KV, Pla F & McCarthy JL (1988) Kinetics of organosolvdelignification in batch- and flow-through reactors. Holzforschung 42(3): 177-183.

Tissot M & Launay A (1987) Study of a two-phase soda cooking process of eucalyptus inpresence of alcohol. 4th International Symposium on Wood and Pulping Chemistry,Paris, France, 1: 373-383. (ABIPC 59:8240(M)).

Tjeerdsma BF & Zomers FHA (1993) Organosolv pulping of hemp. Seventh InternationalSymposium on Wood and Pulping Chemistry Proc., Beijing, PR China, 1: 514-522.

Tjeerdsma BF, Zomers FHA, Wilkinson EC & Sierra-Alvarez R (1994) Modellingorganosolv pulping of hemp. Holzforschung 48(5): 415-422.

Tournier H, Sachetto JP, Michel JP, Roman A, Johansson AA & Armanet JM (1986) NesteOy, assignee. Menetelma puiden ja muiden lignoselluloosatuotteiden delignifioimiseksi.FI patent 70938.

Troitskii VV, Kiryushina MF, Ermakova MI & Zarubin MY (1989) Method of producingpulp. USSR patent 1.461.800. (ABIPST 61:3412(U)).

Tubino M & Filho O (1989) Hybrid process for pulping wood: pulping of eucalyptus woodwith an aqueous solution of ethanol and sodium hydroxide having a low alcoholcontent. ABTCP Congr Anual Celulose Papel 22nd, Sao Paulo, Brazil, p 177-201.(ABIPST 62:11091(M)).

Tubino M & Filho O (1990) Hybrid pulping process - pulping of eucalyptus with anaqueous solution of ethanol and sodium hydroxide with a low alcohol content. Papel51(7): 33-47. (ABIPST 61:7209).

Tuominen I (1995) Milox-prosessin kemikaalitaseen tarkastelu tuotantomittakaavassa.PSC Comm 80.

Unger A, Kletzin J, Reichelt L & Poller S (1979) Institut fur ForstwissenschaftenEberswald, assignee. Verfahren zur auflosung von lignozellulosehaltigen materialien.DD patent 136.845.

Uraki Y, Sano Y & Sasaya T (1991) Cooking of hardwoods with organosolv pulping inaqueous acetic acid containing sulfuric acid at atmospheric pressure. Japan Tappi J45(9): 1018-1024.

Uraki Y, Ogawa S, Sano Y, Sasaya T & Takai M (1993) Influence of delignification onphysicochemical properties of solvolysis pulp. Sen-I-Gakkaishi 49(7): 367-372.

Uraki Y, Kubo S, Nigo N, Sano Y & Sasaya T (1995) Preparation of carbon fibers fromorganosolv lignin obtained by aqueous acetic acid pulping. Holzforschung 49(4): 343-350. (ABIPST 66:8564(AS)).

Urban P & Engel DJ (1988) UOP Inc., assignee. Process for liquefaction of lignin. USpatent 4.731.491.

Valladares J, Rolz C, Bermudez ME, Batres FR & Custodio MA (1984) Pulping of sugarcane bagasse with a mixture of ethanol-water solution in the presence of sodiumhydroxide and anthraquinone. In: Seaquist AJ & Cobb EC (eds) Nonwood plant fiberpulping, progress report. Tappi Press, Atlanta, 15: 23-28.

Vanasse C, Chornet E & Overend RP (1988) Liquefaction of lignocellulosics in modelsolvents: creosote oil and ethylene glycol. Can J Chem Eng 66(1): 112-120.

Vanhanen T, Muurinen E & Sohlo J (1989) Liuottimen regenerointi organosolvprosesseista, etanoli-alkali-AQ-prosessi ja sivutuotteiden talteenotto. Univ Oulu, DeptProcess Eng, Report 115.

Vanharanta H & Kauppila J (1984) Engineering aspects and feasibility of a wood pulpingprocess using Batelle-Geneva aqueous phenol process by Rintekno Oy. Proc. of SPCIWorld Pulp & Paper Week, p 92-96.

Vazquez D, Lage MA, Parajo JC & Vazquez G (1992) Fractionation of eucalyptus wood inacetic acid media. Biores Tech 40: 131-136.

Vedernikov D & Deineko I (1994) Lignin model compounds conversions under oxygen-organosolv delignification conditions. Third European Workshop on Lignocellulosicsand Pulp, p 226-227. (ABIPST 66:10000(AC)).

Vega A & Bao M (1993) Organosolv fractionation of ulex europaeus with dilutehydrochloric acid and phenol, two simple kinetic models for pre-hydrolysis anddelignification. Wood Sci Tech 27: 61-68.

Vega A, Bao M & Lamas J (1997a) Application of factorial design to the modeling oforganosolv delignification of miscanthus sinensis (elephant grass) with phenol anddilute acid solutions. Bioresour Technol 61(1): 1-7. (ABIPST 68:8498(AS)).

Vega A, Bao M & Rodriguez J (1997b) Fractionating lignocellulose of miscanthussinensis with aqueous phenol in acidic medium. Holz Roh Werkst 55(3): 189-194.(ABIPST 68:1125(AS)).

Vorher W & Schweers WHM (1975) Utilization of phenol lignin. Proc. of the EighthCellulose Conf., Syracuse, NY, 1: 277-284.

Vuori A, Mattila T & Saari K (1990) Kemira Oy, assignee. Menetelma ligniininottamiseksi talteen. FI patent appl. 902676.

Vuorinen T (1983) Alkali-catalyzed oxidation of d-glucose with sodium 2-anthraquinonesulfonate in ethanol-water solutions. Carbohydr Res 116(1): 61-69.

Wabner TW, Grambow C & Ober J (1986) Ein umweltfreundliches verfahren zurelektrochemischen lignin-ausfallung. Chem-Ing-Tech 58(4): 328-330.

Wacek A & David E (1937) Ueber die einwirkung von lauge und natriumaethylat aufsubstituirte chalkone und dehydro-di-isoeugenol-methylaether, modellversuche zurligninspaltung, II mitteil. Ber Deutschen Chem Gesells 70B(2): 190-195.

Wacek A & Morghen I (1937) Spaltung von propenyl-brenzcatechin-aethern mitnatriumalkoholat, modellvesuche zur ligninspaltung, I mitteil. Ber Deutschen ChemGesells 70B(2): 183-189.

Wagner FS (1978) Acetic acid. In: Grayson M (ed) Kirk-Othmer encyclopedia of chemicaltechnology, John Wiley & Sons, New York, 11: 124-147.

Wagner FS (1980) Formic acid and derivates. In: Grayson M (ed) Kirk-Othmerencyclopedia of chemical technology, John Wiley & Sons, New York, 24: 251-258.

Walas SM (1985) Phase equilibria in chemical engineering. Butterworth, Boston.Wallis AFA (1976) Reaction of lignin model compounds with ethanolamine. Cell Chem

Tech 10: 345-355.Wallis AFA (1978) Wood pulping with mono-, di- and triethanolamine. Appita 31(6): 443-

448.Wallis AFA (1980) Wood pulping with monoethanolamine in pressure vessels. Appita

33(5): 351-355.Wang H & Tseng HY (1993) Studies on the ethanol-alkali pulping of some Taiwan

hardwoods. Seventh International Symposium on Wood and Pulping Chemistry Proc.,Beijing, PR China, 1: 272-278.

Wang WX, Chen ZH, Liu SC, Qiu ST & Wu YY (1990) Wheat-straw pulping anddefibration point. Jiangsu Zaozhi (2/3): 10-14. (ABIPST 62:11093(U)).

Wang IC, Kuo ML & Ku YC (1993) Alcohol pulping of plantation taiwania andeucalyptus, (2), scanning electron microscope observations. Bull Taiwan For Res Inst8(3): 177-185. (ABIPST 66:2183(AS)).

Wardell JM & King CJ (1978) Solvent equilibria for extraction of carboxylic acids fromwater. J Chem Eng Data 23(2): 144-148.

Wayman M & Harris GR (1960) Columbia Cellulose Company Ltd., assignee. Pulping oflignocellulosic material. US patent 2.939.813.

Wayman M & Lora JH (1978) Aspen autohydrolysis, the effects of 2-naphtol and otheraromatic compounds. Tappi 61(6): 55-57.

Weast RC (1978) CRC handbook of chemistry and physics. CRC Press Inc, West PalmBeach.

Wedekind E (1936) Eigenschaften und verwendungsarten des buchenzellstoffes.Cellulosechemie 17(5/6): 45-49.

Wedekind E, Engel O, Storch K & Tauber L (1931) Zur erkenntnis des lignins, 11.mitteilung, phenol-lignine und ihre acetylderivate. Cellulosechemie 12(6): 163-173.

Weferling N, Pfuller P, Kanzler W, Schedler J & Thalhammer H (1988) Hoechst AG,assignee. Kontinuierliches verfahren zur extraktion von carbonsauren, aldehyden,ketonen, alkoholen und phenolen aus verdunnten wassrigen losungen. DE patent36.26.968.A1.

Wegener G, Rothe A & Lindner A (1991) Chemical modification of Organocell lignin bymeans of hydroxypropylation. In: Faix O & Meier D (eds) Mitteilungen derBundesforschungsanstalt fur Forst- un Holzwirtscahft 168: 145-150.

Weidenmuller R (1992) Schwefelfreier zellstoff - umweltgerecht und wirtschaftlich, dasOrganocell-verfahren. Papier 46(10): 611-614.

Weisheng L, Hanqiang Z, Fengmei C & Jie G (1988) Organosolve pulping of bagasse withethanol-water system. 1988 International Non-Wood Fiber Pulping and PapermakingConference Proc., Beijing, PR China, p 281-290.

Wells GL & Rose LM (1986) The art of chemical process design. Elsevier SciencePublishers, Amsterdam.

Westmoreland RA & Jefcoat IA (1991) Sulfur dioxide-ethanol-water pulping of hardwoods.Chem Eng Comm 104: 101-115.

Williams W (1989) Organocell: cooking the books. Paper 211(10): 34, 37.Williamson PN (1987) Repaps Alcell process: how it works and what it offers. Pulp Paper

Canada 88(12): 47-49.Williamson PN (1988) Repaps Alcell-process: ny demonstrationsanlaggning visar vagen

till billigare massabruk. Svensk Papperstidning 91(7): 21-23.Wiltshire WA (1943) Acetic acid digestion of wood. Technical Section of the Paper

Makers Association of Great Britain & Ireland 24: 347-353.Winkler A & Patt R (1988) Herstellung von zellstoffen aus vier verschiedenen holzarten

nach dem ASAM-verfahren. Holz Roh Werkst 46: 341-345.Winner SR, Goyal GC, Pye EK & Lora JH (1991a) Pulping of agriculture residues by the

Alcell process. In: Nonwood plant fiber pulping, progress report 20, Tappi Press,Atlanta, p 171-175.

Winner SR, Goyal GC, Pye EK & Lora JH (1991b) Pulping of agriculture residues by theAlcell process. 1991 Pulping Conference Proc., Orlando, FL, 1: 435-439.

Winner SR, Minogue LA & Lora JH (1997) Alcell pulping of annual fibers. 9thInternational Symposium on Wood and Pulping Chemistry Poster Presentations,Montreal, Canada, p 120:1-4.

Wojtech B, Steppich W, Freudenberger D & Riedel K (1986) Hoechst AG, assignee.Verfahren zur extraktion von carbonsauren aus verdunnten wassrigen losungen. DEpatent 34.36.348.A1.

Worster HE (1974) The present and future of alkaline pulping. Pulp Paper Canada 75(10):45-50.

Wright GF & Hibbert H (1937) Studies on lignin and related compunds, XXVI, theproperties of spruce lignin extracted with formic acid. J Am Chem Soc 59(1): 125-130.

Wu LCF, Lora JH & Edwardson CF (1989) Alcell lignin: a new adhesive for waferboard.23rd International Particleboard/Composite Materials Symposium, Pullman, WA, p 281.

Xiao X, Fan P & Liang WZ (1993) The alkali-ethanol pulping of eucalyptus cilriodora .Seventh International Symposium on Wood and Pulping Chemistry Proc., Beijing, PRChina, 3: 173-176.

Xu Q, Lu F, Li X, Luo R & Jiang F (1990) A study on separation of acetic acid, water andformic acid system - refinement of acetic acid by esterification-azeotropic distillation.Chem J Chinese Univ 11(11): 1236-1239.

Yang ST, White SA & Hsu ST (1991) Extraction of carboxylic acids with tertiary andquaternary amines: effect of pH. Ind Eng Chem Res 30(6): 1335-1342.

Yasuda S (1988) Behavior of lignin in organic acid pulping, II, reaction ofphenylcoumarans and 1,2-diaryl-1,3-propanediols with acetic acid. J Wood Chem Tech8(2): 155-164.

Yasuda S & Ito N (1987) Bahavior of lignin in organic acid pulping I, reaction of

arylglycerol- �aryl ethers with acetic acid. Mokuzai Gakkaishi 33(9): 708-715.Yasuda S, Abe Y & Hirokaga Y (1991) Behavior of lignin in organic acid pulping, part

III, additive effects of potassium and sodium halides on delignification. Holzforschung45(Suppl.): 79-82.

Yiannos PN & Secrist RB (1968) Scott Paper Company, assignee. Process for removinglignin from lignin-polysaccharides. CA patent 801.727.

Yoon SH & Labosky P (1998) Ethanol-kraft pulping and papermaking properties of aspenand spruce, part II, delignification kinetics, activation thermodynamics, and pulpingproductivity. Tappi J 81(4): 145-151.

Yoon SH, Labosky P & Blankenhorn PR (1997) Ethanol-kraft pulping and papermakingproperties of aspen and spruce. Tappi J 80(1): 203-210.

Young RA (1985) Organic acid pulping of wood reduces chemical costs and energyrequirements. Paper Trade J 169(11): 50-51.

Young RA (1989) Ester pulping: a status report. Tappi J 72(4): 195-200.Young J (1992a) Commercial Organocell process comes online at Kelheim mill. Pulp

Paper 66(9): 99-102.Young RA (1992b) Acetic acid based pulping. 1992 Solvent Pulping Symposium Notes,

Boston, MA, p 61-66.Young RA (1994) Comparison of the properties of chemical cellulose pulps. Cellulose

1(2): 107-130.Young RA (1998) Acetic acid-based pulping. In: Young RA & Akhtar M (eds)

Environmentally Friendly Technologies for the Pulp and Paper Industry. John Wiley &Sons, New York, NY, p 133-156.

Young RA & Achmadi S (1983) Efficient utilization of woody biomass: a cellulose-particleboard-synfuels model. In: Cote WA (ed.) Biomass utilization. New York, NY, p567-584.

Young RA & Achmadi S (1992) Graft pulping in organosolv systems. J Wood Chem Tech12(4): 485-510.

Young RA & Baierl KW (1985) Ester pulping of wood: a revolutionary process. SouthernPulp Paper 48(12): 15-17.

Young RA, & Davis JL (1986) Organic acid pulping of wood, part II, acetic acid pulpingof aspen. Holzforschung 40(2): 99-108.

Young RA & Davis JL (1991) Molecular weight characterization of lignins from aceticacid-based pulping processes. 6th International Symposium on Wood and PulpingChemistry Proc., Melbourne, Australia, 1: 463-466.

Young RA, Davis JL, Wiesmann EB & Baierl KW (1985) Organic acid pulping of wood,part I, an overview of applications. International Symposium on Wood and PulpingChemistry, Vancouver, BC, p 169-172.

Young RA, Davis JL, Wiesmann EB & Young TR (1987a) Ester pulping of wood. In:Kennedy JF (ed) Wood and cellulosics: industrial utilization, biotechnology, structureand properties. Chichester, England, John Wiley & Sons, p 367-373.

Young RA, Fredman T, Keith T & Nelson J (1987b) Pulping of wood with organic acidsand esters. Fourth International Symposium on Wood and Pulping Chemistry, Paris,France, 2: 185-187.

Young RA, Keith T, Nelson J & Fredman T (1987c) Ester pulping. Solvent Pulping -Promises & Problems, Appleton, WI, p 28-34.

Yuan Z, Ni Y & Heiningen A (1998a) An improved peracetic acid bleaching process.Appita 51(5): 377-380. (Paperbase 00522261).

Yuan Z, Ni Y & Heiningen A (1998b) Peracetic acid and hydrogen peroxide brightening ofa softwood kraft pulp delignified by methanol-assisted ozonation. Paperi ja Puu 80(4):310-314.

Zargarian K, Aravamuthan R & April GC (1988) Organosolv delignification of southernpine - an alternative pulping process. Chem Eng Tech 11(3): 195-199.

Zarubin MY, Dejneko IP, Evtuguine DV & Robert A (1989) Delignification by oxygen inacetone-water media. Tappi J 72(11): 163-168.

Zhang X, Ni Y & Heiningen ARP (1996) Basic engineering design data for ozone/solventbleaching of Alcell-derived pulp. 1996 International Pulp Bleaching Conference Proc.,p 601-612. (ABIPST 66:19418(AC)).

Zhang XZ, Francis RC, Dutton DB & Hill RT (1998) The role of transition metal speciesin delignification with distilled peracetic acid. J Wood Chem Technol 18(3): 253-266.(Paperbase 00522184).

Zheleznov A, Windmoller D, Korner S & Boddeker KW (1998) Dialytic transport ofcarboxylic acids through an anion exchange membrane. J Membrane Sci 139: 137-143.

Ziegenfuss H & Maurer G (1994) Distribution of acetic acid between water and organicsolutions of tri-n-octylamine. Fluid Phase Equilibria 102: 211-255.

Zilbergleit MA & Glushko TV (1991) Products from the polymerization of furfural andhydroxymethyl furfural in acetic acid. Khim Drev (Riga) (1): 66-68. (ABIPST62:13800).

Zilbergleit MA, Reznikov VM & Yukhnovich ZK (1981) Belorussian TechnologicalInstitute, assignee. Pulp semifinished product. USSR patent 821.621. (CA 95:45056a).

Zilbergleit MA, Korneichik TV & Reznikov VM (1987a) Wood delignification by aqueousacetic acid solutions, (6), physical properties of acetic acid lignins. Khim Drev (Riga)(6): 21-27. (ABIPC 59:228).

Zilbergleit MA, Simkhovich BS & Reznikov VM (1987b) Wood delignification byaqueous acetic acid solutions, (7), kinetics of the process. Khim Drev (Riga) (6): 28-34.(ABIPC 59:489).

Zilbergleit MA, Korneichik TV, Revyako MM, Lisova VS & Dolinskaya RM (1989a)Wood delignification by aqueous acetic acid solutions, 11., use properties of acetic acidlignins. Khim Drev (Riga) (6): 43-48. (ABIPST 62:4081).

Zilbergleit MA, Simkhovich BS, Reznikov VM & Kirov SM (1989b) Delignification ofhardwoods with aqueous solutions of acetic acid in the vapor phase. Bum Prom (12): 17-18. (ABIPST 61:8279).

Zilbergleit MA, Simkhovich BS, Korneichik TV, Beigelman AV, Burov AV, Galov LI &Mikhailov AI (1991a) Organosolv delignification of irradiated wood. 6th InternationalSymposium on Wood and Pulping Chemistry Proc., Melbourne, Australia, 2: 219-223.

Zilbergleit MA, Korneichik TV & Reznikov VM (1991b) Wood delignification by aqueousacetic acid solutions, (12), conversion of lignin macromolecules under acetic acidpulping conditions. Khim Drev (Riga) (2): 17-22. (ABIPST 63:314).

Zilbergleit MA, Simkhovich BS, Korneichik TV, Kushner MA, Karalchuk TV & GlushkoTV (1991c) Optimizing hardwood pulping with aqueous solutions of acetic acid. BumProm (12): 4. (ABIPST 64:6171).

Zimmermann W & Tajana E (1996) Hydrolysis of kraft and organosolv pulps by bacterialand fungal hemicellulases. In: Srebotnik E & Messner K (eds) Biotechnology in pulpand paper industry. Facultas-Universitatsverlag, Vienna, p 135-138.

Zimmermann M, Patt R, Kordsachia O & Hunter WD (1991) ASAM pulping of Douglas-firfollowed by a chlorine-free bleaching sequence. Tappi J 74(11): 129-134.

Zitzelsberger W (1990) Production of lignin from the Organocell pulping process. 1stEuropean Workshop on Lignocellulosics and Pulp, Bergedorf, FR Germany, p 15-21.

Zomers FHA, Tjeerdsma BF & Gosselink RJA (1993) Organosolv pulping and test papercharacterization of fiber hemp. 1993 Pulping Conference Proc., Atlanta, GA, 2: 475-484.

Zomers FHA, Gosselink RJA, Dam JEG & Tjeerdsma BF (1995) Organosolv pulping andtest paper characterization of fiber hemp. Tappi J 78(5): 149-155.

Zule J, Likon M, Oblak-Rainer M, Moze A & Perdih A (1995) The characteristics of ligninfrom haloacetic acid pulping. The 8th International Symposium on Wood and PulpingChemistry Proc., Helsinki, Finland, 2: 249-254.