valorization of crude glycerol from biodiesel …

Chemical Industry & Chemical Engineering Quarterly

Available on line at Association of the Chemical Engineers of Serbia AChE www.ache.org.rs/CICEQ

Chem. Ind. Chem. Eng. Q. 22 (4) 461−489 (2016) CI&CEQ

461

SANDRA S.

KONSTANTINOVIĆ BOJANA R. DANILOVIĆ

JOVAN T. ĆIRIĆ SLAVICA B. ILIĆ

DRAGIŠA S. SAVIĆ VLADA B. VELJKOVIĆ

Faculty of Technology, University of Niš, Niš, Serbia

REVIEW PAPER

UDC 662.756.3:547.426.1:66

DOI 10.2298/CICEQ160303019K

VALORIZATION OF CRUDE GLYCEROL FROM BIODIESEL PRODUCTION

Article Highlights • Effective utilization of crude glycerol is crucial to further development of biodiesel pro-

duction • Biological and chemical conversions of crude glycerol can produce value-added

chemicals • The addition of crude glycerol as a co-substrate can increase the production of biogas• Significant biohydrogen yield can be achieved on crude glycerol by various micro-

organisms • The promising use of crude glycerol as a feedstuff for non-ruminant animals Abstract

The increased production of biodiesel as an alternative fuel involves the simul-taneous growth in production of crude glycerol as its main by-product. Therefore, the feasibility and sustainability of biodiesel production requires the effective utilization of crude glycerol. This review describes various uses of crude glycerol as a potential green solvent for chemical reactions, a starting raw material for chemical and biochemical conversions into value-added chemicals, a substrate or co-substrate in microbial fermentations for synthesis of valuable chemicals and production of biogas and biohydrogen, as well as livestock feedstuff. Special attention is paid to various uses of crude glycerol in biodiesel production.

Keywords: biodiesel, bioconversion, biogas, biohydrogen, crude gly-cerol, solvent.

Glycerol is extensively used in the food industry as a sweetener and preservative, in the pharma-ceutical and medical industry, and the cosmetic ind-ustry as an ingredient in personal care products (toothpaste, glycerol soap, etc.). According to Werpy and Petersen [1], glycerol is detected as one of 12 most important bio-based chemicals in the world. It is readily available at a large scale and is relatively cheap. Glycerol is generated as a by-product in large amounts during the production of biodiesel from dif-ferent kind of feedstocks such as vegetable oil, waste cooking oils, animal fats or microalgae oil. Crude gly-cerol represents approximately 10% by weight of the starting materials during the production of biodiesel [2]. In the recent years the biodiesel production exp-onentially increased. According to the European Bio-diesel Board, the production of biodiesel in 2014 in

Correspondence: V.B. Veljković, Faculty of Technology, Univer-sity of Niš, 16000 Leskovac, Bulevar oslobodjenja 124, Serbia. E-mail: [email protected] Paper received: 3 March, 2016 Paper accepted: 31 March, 2016

Europe was 23,093,000 t [3], which resulted in appro-ximately 2.6 million t of glycerol. Presently, depending on the purity degree, its price is 0.27-0.41 US$/kg for pharmaceutical grade (99.9%) and 0.09–0.20 US$/kg for the technical grade (80%) [4]. A prediction is that the global production by 2020 will be 41.9 billion L of glycerol [5]. Obviously, too much surplus of crude glycerol from biodiesel production will not only dra-matically decreases its price influence the market of refined glycerol but also generated environmental concerns associated with contaminated glycerol dis-posal [6,7]. The biodiesel production cost increases by 0.021 $/L for every 0.22 $/kg reduction in glycerol selling price [8]. Therefore, economic utilizations of glycerol for value-added products are critically impor-tant for the sustainability of commercial biodiesel pro-duction. In this way, crude glycerol will be regarded as a desirable byproduct and not as a waste product with a disposal cost associated to it.

Crude glycerol can be easily handled and stored over a long period of time [9], but if its exploitation is non-profitable, its disposal may create problems to

S.S. KONSTANTINOVIĆ et al.: VALORIZATION OF CRUDE GLYCEROL… Chem. Ind. Chem. Eng. Q. 22 (4) 461−489 (2016)

462

the viability of biodiesel industry [10]. However, crude glycerol generated from biodiesel production is imp-ure as it usually contains, beside glycerol, numerous impurities such as water, methanol, soaps, catalysts, salts and non-glycerol organic matter (free fatty acids, FFAs). Therefore, purification of crude glycerol is needed to remove impurities order to meet the requirements of existing and emerging uses. The con-ventional techniques for purification of crude glycerol for reuse are cumbersome and too costly. Hence, valorization of crude glycerol as intact through various uses has become very important for the biodiesel ind-ustry. The main applications of crude glycerol are in a number of chemical processes as a reactant or a sol-vent or in various biological processes for the pro-duction of chemicals and certain biofuels. The refined glycerol has significant application in cosmetics (37- -40%), food (23-25%), tobacco (9-10%) and pharma-ceutical products (6-8%) [11].

The present paper is an overview of the use of crude glycerol without any preparation in various chemical and biological processes in recent years. At first, the main processing steps of conventional bio-diesel production process are shortly described, pay-ing an attention to the purification of crude glycerol. Then, the chemical valorization of crude glycerol as solvent and reactant is discussed. Moreover, its util-ization in microbial fermentations for production of various products is considered. Finally, the attention is paid to the production of biogas and biohydrogen from crude glycerol.

TYPICAL BIODIESEL AND GLYCEROL PRODUCTION PROCESS

Biodiesel can be produced from various oily or fatty feedstocks and an alcohol using transesterific-ation reaction usually in the presence of a catalyst. However, most technological procedures at com-mercial scale are based on the alkali-catalyzed meth-anolysis of refined vegetable oils (Figure 1), which consists of two main stages, namely transesterific-ation reaction and separation of crude biodiesel from glycerol/methanol phase. This separation is usually performed gravitationally at a small scale or centri-fugally at a large continuous scale. The two phases are further treated in two separate technological lines. The crude biodiesel is usually washed with water to get a purified biodiesel, which is, after separating from wastewater, dried by hot air. The glycerol/methanol phase contains mainly glycerol (50–60%), methanol, water, the residual catalyst and soap [12]. The pro-cessing of the glycerol/methanol phase includes neut-

ralization (acidification) by adding a mineral acid and separation of methanol usually by vacuum flash vaporization from crude glycerol that contains about 85% of glycerol. The type and concentration of imp-urities of crude glycerol depends on the type of feed-stock and the trancesterification method employed in biodiesel production. For instance, the crude glycerol obtained from the same feedstock from alkali- and lipase-catalyzed transesterification contains different purities of glycerol [13]. Also, the use of solid cat-alysts is a good alternative to homogeneous alkaline catalysts as it improves the quality of crude glycerol. However, even in the case of heterogeneous trances-terification processes, impurities from the feedstocks accumulate in crude glycerol.

Figure 1. Biodiesel production through alkali-catalyzed

transesterification reaction.

Crude glycerol is not pure enough for direct use in many applications. To overcome this problem, pre-sent impurities must be removed by an effective, efficient purification process is needed to minimize production costs and waste. Moreover, each con-taminant requires a different removal process. The crude glycerol can be further purified to get a product with at least 95.5% of glycerol or even with more than 99.5% of glycerol for pharmaceutical use. Glycerol purification achieves up to 98% by neutralization, centrifugation, evaporation and vacuum distillation at the cost of 0.149 $/kg [14], which is shown in Figure 2. The highest-quality glycerol (greater than 99.5%) can be obtained by combining heating, evaporation, splitting, decantation, adsorption and vacuum distil-lation [15].

Chemical valorization of crude glycerol

Considering chemical valorization, crude glyce-rol can be used as a solvent and a reactant in differ-ent chemical reactions. The use of crude glycerol as a


463

solvent and a reactant in the organic reactions and the hydrogenolysis reactions are reviewed in Tables 1 and 2, respectively.

Figure 2. Purification of crude glycerol.

Glycerol as solvent

When glycerol is used as a solvent in certain homogeneous and heterogeneous catalytic reactions, the overall process is usually made greener. These reactions can be more environmentally friendly because they do not often require toxic reagents and produce fewer byproducts, resulting usually in a cleaner and simpler reaction and an easier product separation [16]. The main advantages of glycerol as solvent are polarity and very low volatility (i.e., high boiling point, 290 °C, and low vapor pressure, <1 mm Hg at 50 °C). With polar behavior, glycerol dissolves many polar organic and inorganic compounds as well as enzymes while it is immiscible with non-polar com-pounds (for instance, hydrocarbons and ethers). This property can be useful for product isolation by phase extraction. Because of its high boiling point, glycerol can easily be separated from a volatile solute and be used at higher reaction temperatures in order to

accelerate the reaction. In addition, certain reactions conducted in glycerol results in high product yields usually in shorter time [16]. In the case of crude gly-cerol originating from biodiesel production, certain reactions proceed better than in other solvents due to the presence of residual free fatty acid salts that act as a catalyst [17]. Finally, glycerol tolerates micro-wave heating, which results in many organic syn-theses in a cleaner reaction and a shorter reaction time [16]. Because of these favorable properties, gly-cerol can effectively replace many other non-green solvents. According to Gu et al. [18], glycerol behaves similarly to water in the organic synthesis and is often referred in practice to as “organic water”. On the other hand, glycerol has several drawbacks, such as high viscosity and high reactivity in acidic or basic reaction conditions [16]. The former may cause mass transfer limitation at lower reaction temperatures, while the latter requires the neutral environment in order to avoid the formation of undesired compounds. Also, certain organometallic complexes could be deactiv-ated in glycerol because of coordination problems [16]. Being low toxic, non-flammable, stable, biodeg-radable, easy available, relatively inexpensive, safe and non-mutagenic, glycerol can be an alternative, “green” solvent in accordance with the principles of green chemistry [19]. Compared to other green sol-vents, glycerol has a very low toxicity as indicated by its high lethal oral dose (LD50 = 12,600 mg/kg) [16] and shows no indications of causing gene mutations, carcinogenicity or teratogenicity [20]. Moreover, gly-cerol is not expected to accumulate in the environ-ment with use because of its high biodegradability [20]. In addition, glycerol has a very low vapor pres-sure, which means very low emissions in the environ-ment. Because of its favorable physical, chemical and biological properties, the impact of glycerol as solvent on the environment is ignorable.

Table 1. An overview on the use of crude glycerol as solvent non-catalyzed and catalyzed organic reactions; CG – crude glycerol, PG – pure glycerol, DMSO – dimethyl sulfoxide, EAA – ethylacetoacetate, acac – acetylacetonate, dmf – dymethylformamide, TFMB – trifluoro-methyl benzene, MeOH – methanol, PEG – polyethylene glycol and salen – N,N'-ethylenebis(salicylimine)

Presence of catalyst

Type of reaction Reactants Operation conditions Product yield (%)/solvent Reference

Non-catalyzed reactions

Aza-Michael addition

p-Anisidine and n-butyl acrylate

100 °C, 2 h 82/CG; 81/PG; <5/water [18]

Aniline and chalcone 150 °C, 48 h 95/PG [26]

Substituted aromatic amines and α,β-unsaturated ketones

100-150 °C, 12-96 h 68-98/PG

Michael reaction Indole and β-nitrostyrene 80 oC, 24 h 78/CG; 80/PG; 55/water [18]


464

Table 1. Continued



Non-catalyzed reactions

Electrophilic activation

4-Nitrobenzaldehyde and 2-methylindole

90 °C, 3 h <5/toluene, DMF, DMSO or n-butyl acetate; 76/water; 62-

95/PG

[31]

Condensation Benzil, benzaldehyde and ammoniumacetate

90 °C, 0.7-1.85 h 81-94/PG [27]

Benzil, benzaldehyde, ammoniumacetate and

arylamine

90 °C, 2.15-4 h 91-96/PG

Arylaldehyde, diketone and malononitrile

80 oC, 1 h 93/PG [30]

Isatin and amines 80 oC, 10-30 min 85-98/CG [24]

Vanillin and semicarbazone 65 °C, 20 min 89/CG; 72/methanol,ethanol [23]

o-Phenylenediamine and ketones

90 °C, 4.5-8 h 45-96/PG [28]

o-Phenylenediamine and aldehyde

90 °C, 0.7-6 h 84-94/PG

2-Aminothiophenols and aromatic aldehyde

Room temperature, 0.5-5 h

84-93/PG [29]

Thiole oxidation Thioles 120 °C, 15 min 74−93/PG [32]

Nucelophilic substitution

Benzyl bromide and ammonium acetate

60-100 °C, 0.5-5 h 60.3/PG; 38.1/water; 59.2/ionic liquid; 100/DMSO

[33]

Benzyl chloride and ammonium acetate

– 20/PG;14.75/water; 19.9/ionic liquid; 62.3/DMSO

Diels-Alder reaction (R)-citronellal and substituted arylamines

90 oC, 7-21 h 75-96/PG [34]

Ring-opening of p-anisidine

p-Anisidine and styrene 80 oC, 12 h 85/CG (93% selectivity); 88/water (76% selectivity)

[18]

Knoevenagel/hetero-Diels-Adler reaction

Styrene, paraformaldehyde and dimedone

110 oC, 11 h 68/PG; 14/water; <10/toluene; 33/methylnitrate

[35]

Two-step sequential reaction

Arylhydrazines, β-ketoesters, formaldehyde and styrene

110 oC, 14 h 75/CG [50]

One-pot sequential reaction

Indoles, arylhydrazine, β-ketone esters and paraformaldehyde

110 °C, 6 h 42/CG [50]

Catalyzed reactions

Aldol condensation n-Valeraldehyde 80 °C, 2 h, KOH catalyst 48/PG;49.6/PG+5% MeOH; 52.1/PG+5% water;40.8/CG

(sunflower oil); 42.5/CG (olive oil); 39.9/CG (corn oil); 43.2/CG

(canola oil); 37.2/purified CG (canola oil);

[21]

Heck coupling Iodobenzene and butyl acrylate

80 °C, 4 h, Pd catalyst 100/CG [21]

Suzuki cross coupling

Iodobenzene and phenylboronic acid.

80 °C, 1 h, Pd catalyst 66-95/CG [21]

Cross coupling Diaryl diselenides and vinyl bromides

110 °C, 3-24 h, CuI catalyst

68-96/PG [37]

Diaryl diselenides and arylboronic acids

110 °C, 30 h, CuI (5 mol)/Zn, N2

up to 95/PG [39]

110 °C, 30 h, CuI (5 mol)/DMSO,air

70-90/PG

Coupling Aryl halides with aromatic and cyclic amines

100 °C, 15 h, KOH, Cu(acac)2 catalyst

> 85/PG [38]


465

Table 1. Continued



Catalyzed reactions

β,β-diarylation of alkene

Aklylacrilate and aryliodide 120 °C, Pd nanoparticles catalyst22222

67-95/PG [40]

Multicomponent reactions under

microwave irradiation

Indole and benzaldehyde 4 min, [Fe(III)(salen)]Cl catalyst

70-95/PG [41]

Aldehyde, ethylacetoacetate and urea

7 min, [Fe(III)(salen)]Cl catalyst

Aldehyde, ethylacetoacetate and ammonium acetate

5 min, [Fe(III)(salen)]Cl catalyst

87-95/PG

Hydrothiolation 1,4-Diorganyl-1,3-butadiynes 60 °C, 1.5-3 h, KF/Al2O3

catalyst 39-98/PG; 78-97/PEG-400 [42]

Nitroarenes reduction

Nitroarenes and glycerol 100 °C, 24 h, Raney Ni catalyst

44-81/PG [44]

Nitroarenes and glycerol 80 °C, 2.5-4 h, Fe3O4-Ni monoparticles/KOH

catalyst

84-94/PG [43]

Reductive amination Primary alcohols and nitrobenzenes

130 °C, 24 h, RuCl3/PPh3/K2CO3

catalyst

70-93/(TMFB + PG, 1-2 drops) [45]

Aminolysis of epoxides

Arylamines and epoxides 35 °C,10-18 h, H3BO3 catalyst

93-100 (water + PG, 1-2 drops) [47]

Reduction Carboxylic acids 140-150 °C, 1 h, CoCl2·6H2O/KOH catalyst

90-95/PG [46]

Microwave deoxygenation

Sulfoxides 230 °C, 5 min, MoO2Cl2(dmf)2

83-94/PG or CD [22]

Pure and crude glycerol is used as a solvent in

both non-catalyzed and catalyzed organic reactions (Table 1). So far, both pure and crude glycerol has been used as solvents in comparative studies of only a few organic reactions such as the Aza-Michael addition, the Michael reaction [18], the aldol conden-sation [21] and the microwave deoxygenation [22]. In addition, crude glycerol has been employed as a sol-vent in the non-catalyzed condensation [23,24], ring- -opening of p-anisidine [18] and one- or two-step sequential reactions [25] as well as in the catalyzed Heck and Suzuki cross coupling reactions [21]. On the other hand, pure glycerol is the solvent in a num-ber of both non-catalyzed and catalyzed organic reactions, as it can be seen in Table 1.

Non-catalyzed organic reactions in glycerol

For the purpose of comparison, the non-catal-yzed Aza-Michael addition [18] and Michael reaction [18] are conducted in both pure and crude glycerol. In the Aza-Michael reaction between p-anisidine and n-butyl acrylate approximately the same product yield (82 and 81%, respectively) was achieved in 2 h in crude and pure glycerol, which was much higher than that obtained in water (5%) [18]. The Michael reaction of indole with β-nitrostyrene can be performed not

only in pure and crude glycerol but also in water. However, higher yields were obtained in crude and pure glycerol (78 and 80%, respectively) than in water (55%), which was explained by the capability of gly-cerol to form hydrogen bonds [18]. These studies demonstrate that crude glycerol can be used instead of pure glycerol in certain non-catalyzed reactions under the same conditions with the same yield.

Synthesis of Schiff bases during the catalyst-free amino-carbonyl condensation reaction can be performed in not only conventional organic solvents (methanol and ethanol) but also in crude glycerol [23,24]. The replacement of the conventional solvents with crude glycerol was done to make the process more comfortable in environmental and economic terms. High yields of the isatin derivatives (85-98%) were achieved in crude glycerol in a shorter time (5-30 min) [24]. These yields are for 3 to 13% higher than those obtained in the conventional organic sol-vents. For instance, compared to methanol and etha-nol, the reaction time for vanillin-semicarbazone syn-thesis in crude glycerol is shorter by 25 min, and yield is higher by 17% [23]. Crude glycerol as a solvent can even increase the selectivity of the reaction. The ring opening of p-anisidine with a styrene oxide is norm-


466

ally carried out in the presence of a Lewis or Brønsted acid catalyst. However, in the non-catalytic conditions, the regioselectivity of the reaction can be achieved in glycerol as a solvent [18]. Compared to water, the use of crude glycerol results in a very similar yield (88 versus 85%) but with a higher selectivity (76 versus 93%), as it can be seen in Table 1. Crude glycerol can also improve selectivity of two-step sequential reaction between arylhydrazines, β-ketoesters, form-aldehyde and styrene (yield 75%) and in one-pot sequential reaction between indoles, arylhydrazine, β-ketoneesters and paraformaldehyde [25].

Besides in Aza-Michael addition [26], the Mich-ael reaction [18] and condensation [27-30], pure gly-cerol has been used as the solvent in the electrophilic activation [31], thiole oxidation [32], nucleophilic sub-stitution [33], the Diels-Alder reaction [34] and the Knoevenagel/hetero-Diels-Alder reaction [35].

Ying et al. [26] reported the Aza-Michael add-ition of aromatic amines to electron-deficient α,β- -unsaturated ketones in pure glycerol. The reactions between aromatic amines and chalcone, 2-cyclo-hexen-1-one, 2-cyclopenten-1-one and ethyl vinyl ket-one in pure glycerol resulted in the yield of β-amino-ketones that was dependent on the reactants and the reaction conditions (68-98%). This study also shows that glycerol can be recycled and reused, which is very important for the economics of the overall process.

The activation of electrophilic aromatic aldehyde with an indole or 1,3-cyclohexanedione, is usually performed in the presence of acidic catalysts. How-ever, under the optimized conditions and catalyst free, the product can be obtained from 4-nitrobenzal-dehyde and 2-methylindole in glycerol as the solvent with the yield of 95% [31]. Also, the reaction between 4-acetamidobenzaldehida and 1,3-cyclohexanedione can be carried out without a catalyst in glycerol as a solvent to yield a product of 85%, which is higher compared to the reaction performed in water (76% relative yield) [31].

Synthesis of 2,4,5-triaryl and 1,2,4,5-tetraaryl imidazole derivatives in glycerol from different alde-hydes and arylamines was proven to be very simple, with a high yield of 2,4,5-triphenyl-1H-imidazole [27]. Since glycerol can form hydrogen bonds, it activates the carbonyl group and enhances the nucleophilic character of nitrogen, as expected [27]. High yields (higher than 90%) are also achieved in other conden-sation reactions conducted in pure glycerol [28-30], as it can be seen in Table 1. For instance, in the reaction between 2-aminothiophenols and different aromatic aldehydes, the yields of synthesized 2-aryl-benzothiazoles were 80-94%, while the products were

recovered pure from the reaction systems [29]. Also, 1H-1,5-benzodiazepines and 1,2-disubstituted benz-imidazoles were obtained in glycerol by the conden-sation reaction between o-phenylenediamine and different ketones and aldehydes. The glycerol was recovered (extraction with a mixture of hexane/ethyl acetate 95:5) and reused for four times [28]. Glycerol can also be efficiently used as a recyclable solvent in the thiole oxidation, where the yields of disulfides were 74−93% in 15 min [32], and in the nucleophilic substitution of benzyl halides and ammonium acetate [33]. Moreover, glycerol was used as a recyclable sol-vent in the one-pot Diels-Alder reaction between (R)- -citronellal and substituted arylamines, where the yield of synthesized octahydroacridines were 75-96% [34].

Besides in the ring opening of p-anisidine [18] and the sequential reactions [25], the selectivity of reaction was also reached in the subsequent Knoe-venagel/hetero-Diels-Adler reaction between styrene, paraformaldehyde and dimedone. The reaction yield in glycerol (68%) was much higher than those achieved in the conventional solvents (Table 1) as a result of the improved selectivity of the reaction [35].

Glycerol can be employed as a solvent in the non-catalyzed synthesis of heterocyclic compounds by condensation procedures. For example, one-pot three components synthesis of 4H-pyran derivatives at lower temperature (Table 1) is highly efficient in glycerol, compared to the conventional solvents, such as water, ethanol, toluene and dimethylformamide (DMF) [30].

Catalyzed organic reactions in glycerol

Glycerol can be used as a green solvent in homogeneous and heterogeneous catalytic reactions. The use of pure and crude glycerol as solvents is compared only in the case of the aldol condensation [21] and the microwave deoxygenation [22]. The KOH-catalyzed aldol condensation of n-valeraldehyde can be carried out in crude glycerol obtained from a variety of plant sources, with the product yield of 37.3- -43.2%, which is smaller than the yield achieved in pure glycerol (48%). Although the residual water and methanol in crude glycerol were thought to be res-ponsible for this, the yield of product slightly inc-reased in the mixture of pure glycerol with water (5%) and methanol (5%). Also, the yield of product was higher in crude glycerol obtained from canola oil (43.2%) than in purified glycerol (37.3%), which was attributed to the impact of present impurities [21]. The Mo-catalyzed deoxygenation of sulfoxides was per-formed in glycerol as a solvent and reducing agent. The reaction was supported with microwave heating.


467

The catalyst can be recycled, and the products were easily separated by simple extraction with hot tolu-ene. The same reaction in crude glycerol showed similar characteristics in reaction times and only slightly lower yields in comparison with the use of ref-ined glycerol [22].

Crude glycerol was employed as a solvent only in the Heck coupling of iodobenzene and butyl acryl-ate (100% product yield) and the Suzuki cross coup-ling of iodobenzene and phenylboronic (66-95%) both catalyzed by a Pd catalyst [21]. These reactions can be significantly improved ultrasonically [36].

Pure glycerol has been used in several catal-yzed organic reactions such as coupling reactions [37-39], β,β-diarylation of alkene [40], multicomponent reactions under microwave irradiation [41], hydrothio-lation [42], nitroarenes reduction [43,44], reductive amination [45] and reduction [46].

Vinyl selenides can be obtained in pure glycerol via the cross coupling reaction of diaryl diselenides with different vinylbromides, catalyzed by CuI/Zn, in significant yields (66-96%) [37]. The remaining gly-cerol/CuI/Zn are directly reused for further cross-coupling reactions up to five times. Also, the cross- -coupling of diaryl diselenides with arylboronic acids in the presence of dimethyl sulfoxide (DMSO) as a solvent can be performed in glycerol, with CuI as a catalyst, which can be recycled [39]. The corres-ponding diaryl selenides can be extracted with hex-ane/diethyl acetate (95:5 volume ratio). The copper- -catalyzed coupling reaction of amines is usually con-ducted in the presence of DMF or DMSO as solvent. However, Khatri et al. [38] performed the N-arylation in glycerol, between aryl halides and different aro-matic and cyclic amines. The products were extracted with diethyl ether in excellent yields, and the catalytic glycerol/copper system was reused for six times.

The β,β-diarylation of alkyl acrylates in the pre-sence of air-stable palladium nanoparticles can also be performed in glycerol, over the Mizoroki-Heck reaction [40]. Considering the regioselectivity of the reaction, diaryl products can be formed. Although the products can be extracted from reaction mixture, the recycle of solvent and catalyst cannot be achieved. Also, Halimehjani et al. [47] performed the aminolysis of epoxides in water with few drops of glycerol with boric acid as a catalyst. The significant regioselect-ivity of the reaction was reached, and the β-amino alcohols were obtained in excellent yields (93-100%).

The microwave synthesis of bis(indolyl)meth-anes, 3,4-dihydropyrimidines and 1,4-dihydropyri-dines were performed in glycerol with [Fe(III)-(sa-len)]Cl, and the compounds were obtained in the

excellent yield [41]. The synthesis of organylthio-enynes was performed in glycerol and PEG-400, with the basic catalyst KF/Al2O3 [42]. Although the pro-ducts were obtained in higher yields in PEG-400 than in glycerol, both catalytic systems favored the form-ation of alkenyl sulfides with Z configuration and could be reused up to three times.

The synthesis of organylthioenynes was per-formed in glycerol and in PEG-400, with the basic catalyst KF/Al2O3 [42]. Although the products are obtained in higher yields PEG-400 than in glycerol, both catalytic systems favor the formation of alkenyl sulfides with Z configuration and can be reused up to three times.

Glycerol can be used as a solvent and a hyd-rogen donor for nitroarenes reduction, with the Raney Ni [44] or Fe3O4-Ni monoparticles/KOH as a catalyst [43]. The yield of anilines was higher (84-94%) in the latter reaction.

The reductive amination of primary alcohols with nitrobenzenes was performed in a glycerol/trifluoro-methyl) benzene mixture with the RuCl3/PPh3/K2CO3 catalytic system [45]. The corresponding amines were obtained in a good yield of 70-93%. The reduction of carboxylic acids to primary alcohols with the CoCl2·6H2O/KOH catalytic system was carried out in glycerol as a solvent [48]. The corresponding alcohols were selectively formed in good yields (90-95%). The reaction was patented as an alternative for the stan-dard synthesis with H2 and NaBH4 as reducing agents.

Glycerol as reactant

Glycerol as a highly functionalized molecule with specific physico-chemical properties can be used in different reactions as a reactant or a building block [49]. Many chemical reactions such as acetalization, dehydration, esterification, etherification, aqueous phase reforming, oxidation, carboxylation and pyro-lysis can include glycerol as a reactant.

Hydrogen is an important chemical produced by glycerol via three step steam reforming (glycerol dehydrogenation, desorption and water–gas shift or methanation), partial oxidation, and auto-thermal reforming [50]. The optimum conditions for steam reforming hydrogen production are atmospheric pres-sure, 925–975 K and water/glycerol ratio of 9–12. According to the same research group, the optimum conditions for partial oxidation are: 1000-1100 K, atmospheric pressure and oxygen/glycerol ratio of 0.4-0.6, where 100% conversion of glycerol and 78.93–87.31% yield of hydrogen were achieved [51].

Acrolein can be produced from glycerol by dehydration in the presence of a catalyst. Its use as


468

intermediate in acrylic acid and acrylic acid esters are very important, such as in industry of papers and oil wells. The dehydration can be carried out with differ-ent catalysts. According to the latest investigations, the significant results are reached with the (H3[P(W2O10)4] catalyst supported on Al2O3 with a yield of 92.8% at 320 °C [52] and with HZSM-5 zeolite at 315 °C, where the glycerol conversion is 75.8% and acrolein selectivity is 63.8% [53]. Significant results were also achieved with 17NiSO4-350 as a catalyst during gas-phase dehydration of glycerol to acrolein. At 340 °C in the presence of oxygen, the sel-ectivity of acrolein is 72% with 92.5% of glycerol con-version [54]. According to Yadav et al. [55], 94% of glycerol conversion and 80% of acrolein selectivity

can be reached at 225 °C with 20 mass% DTP/HMS as a catalyst.

One of the most interesting and common util-ization of glycerol is hydrogenolysis to dioles. 1,2-pro-panediol is used for synthesis of polyethers, unsatur-ated polyester resins, hydraulic fluids, and antifreeze products [56]. The catalyst morphology and the type of metal have a significant impact on the glycerol con-version and the reaction selectivity. Table 2 shows that hydrogenolysis can undergo with different cat-alyst, such as copper, ruthenium, rhodium, palladium, platinum and nickel. However, the most efficient are copper catalysts [56], which enhance 1,2-propanediol selectivity (up to 98%) and glycerol conversion up to 100% (Table 2).

Table 2. An overview on the use of glycerol as a reactant in hydrogenolysis reactions; PG – pure glycerol and CG – crude glycerol

Product Catalyst Optimal reaction conditions Product

selectivity/yield (%)Glycerol conversion

(%)/reactant Reference

1,2-Propanediol CuO/ZnO 180 °C, 80 bar H2,90 h 93-94/19 19/PG [57]

Copper-chromite 200 oC, 200 psi, 24 h, 71.9/49.7 69.1/PG [58]

Ru/TiO2catalyst 170 °C, 3 MPa 80 80/ PG [59]

Cu/Zn/Al 200 oC, 200 psi, 24 h 76.6/30 PG; 75.6/29.8 CG

39.2/PG; 38.4/CG [60]

Raney cobalt 200 °C, 3 MPa H2 97/44 97/PG [61]

CuO/ZnO 200 °C, 3 MPa, 12 h 97.7/- 100/PG [62]

Pt/C 160-200 °C, 3 MPa, 3 h 9-17 /- 9-22/PG [63]

Pt-W/Al2O3 160 °C, 3-5.5 MPa, 3 h 4/- 20-23.3/PG

Ru/SiO2 160 °C, 8 MPa, 8 h 39/- 16.8/PG [64]

Re-Ru/SiO2 – 49.1/- 51/PG

CuO/ZnO 200 °C, 3 MPa, 12 h 93.4/- 82/PG [65]

Rh/SiO2 120 °C, 8 MPa, 5 h 38.5/- 3.3/PG [66]

Rh-ReOx/SiO2 40/- 66.7/PG

5 wt % Ru/SiO2 /glycerol ratio 0.006

240 °C, 8 MPa H2, 5 h 60.5/- 21.7/PG [67]

CuO/ZnO/MnO2 200 °C 8 MPa, 12 h 97.5/- 100/PG [68]

Alumina supp. 5 wt.% Cu/5 wt.% Cu-CrOx

160 °C, 46/- 98/PG [69]

Cu/Al 220 °C, 7.0 MPa, H2, 5 h 91/- 65/PG [70]

CuAl2O4 spinel 220 °C, 5.0 MPa, H2, 12 h 90/- 90/PG [71]

Raney nickel 200 °C, 40 bar, H2 50/- 74/PG [72]

Cu-MgO 200 °C, 40 bar, 8 h 92.3PG/-; 92CG/- 49.3/PG; 44.5/ CG [73]

Ru-Cu 180 °C, 8 MPa 78.5/- 100/PG [74]

Cu/ Al2O3 200 °C, 4MPa 24 h -/95.8 75.7/PG [56]

1Ni/3Co 220 °C, 6MPa H2, 10 h 20 wt% glycerol aqu. sol.

60.4/- 63.5/PG [75]

17.5% Ni-2.9% P/Al2O3 230 °C, 3 MPa, 15 h 84.7/- 95.7/PG [76]

Electrochemical conversion on Pt electrode

0.3 M PG, pH 1, 25 oC, 101 kPa

3.77∗/- 100/PG [77]


469

Table 2. Continued

Product Catalyst Optimal reaction conditions Product

selectivity/yield (%)Glycerol conversion

(%)/reactant Reference

1,3-propanediol Re/modified/Ir In the presence of H2SO4 67 ± 3/- 81/PG [78]

Ru/SiO2 160 °C 8 MPa, 8 h 6.4/- 16.8/PG [64]

Re-Ru/SiO2 – 8.3/- 51/PG

Pt/C 160-200 °C, 3 MPa, 3 h -/41 9-22/PG [63]

Pt-W/Al2O3 160 °C, 3-5.5 MPa, 3 h 67/- 20-23.3/PG

Rh/SiO2 120 °C, 8 MPa, 5 h 8.5/- 3.3/PG [66]

Rh-ReOx/SiO2 120 °C 8, MPa, 5 h 14.4/- 66.7/PG

Pt-sulfated ZrO2 170 oC, 7.3MPa, H2 83/55.6 66.5/PG [79]

Pt/m-WO3 180 oC, 5.5 MPa, H2, 12 h 39.2/7 18/PG [80]

Cu/ Al2O3 200 °C, 4MPa 24 h -/1.5 75.7/PG [56]

2 wt.% Pt and 10 wt.% WO3 on SBA-15

210 C, 0.1 MPa H 2 42/- 86/PG [81]

2 wt.% Pt/HM 225 °C, 0.1 MPa H2 48.6/- 94.9/PG [82]

Egg-shell RI20 130 °C, 8.0 MPa, 80 wt.% glycerol aq. sol.

31.1/- 60.9 [83]


0.3 M PG, pH 1, 25 oC, 101 kPa, 13 h

/24a 100/PG [77]


0.3 M CG, pH 1, 25 oC, 101 kPa, 14 h, 0.14 A/cm2

- 100/CGa [84]

aTotal yield of all products - 63.6%

1,3-Propanediol (1,3-PD) is mainly involved in variety of applications in the production of polymers, cosmetics, foods, lubricants and medicines [50]. It can be produced by selective hydrogenolysis with different catalysts, such as cooper, platinum, rhodium, rhenium, nickel, wolfram, etc. Hydrogenolysis is often conducted in hydrogen, and glycerol conversion and 1,3-PD selectivity depend upon the reaction condit-ions and the metal catalyst. Good glycerol conversion can be achieved with the Ni/Kieselguhr catalyst (97%) and the Pt/H–mordenite catalyst (∼95%), while 1,3-PD selectivity can be obtained with the Re/modified/Ir catalyst in the presence of H2SO4 and Pt-W/Al2O3 (∼67%, Table 2).

Crude glycerol utilization in microbial fermentation

Various biotechnological strategies have been investigated to obtain high added-value products using crude glycerol as a substrate. Bioconversion of crude glycerol provides more opportunities for the production of various chemicals that can be used as an end product or a precursor for the production of other chemicals. Glycerol represents a great sub-strate for the growth of different microorganisms [85] since the content of carbon in the crude glycerol is 24-58% depending on the feedstock used for bio-diesel production [86,87]. Crude glycerol is applied as a sole carbon and energy source in numerous mic-

robial fermentations for microbial growth and pro-duction of various products, such as 1,3-PD, citric acid, 2,3-butanediol (2,3-BD), ethanol, succinate, pro-pionic acid, glyceric acid, biosurfactants and others [88,89]. Table 3 shows high-value metabolites pro-duced at high concentration by various microorgan-isms capable to convert crude or pure glycerol, as well as the operational conditions for the conversions. However, the impurities present in crude glycerol (methanol, ethanol, salts, metals and soaps) can inhibit the growth of some microorganisms and the biological conversion of crude glycerol. Therefore, it is necessary to use the microorganisms that are tolerant to impurities in crude glycerol [90]. Clostridia are the most potent microorganisms able to utilize the gly-cerol through their unique metabolism and produce various products, such as 1,3-PD, 2,3-BD, n-butanol, ethanol and acids (acetic, butyric, succinic and lactic acid) [85].

Alcohols production

1,3-PD. Biotechnological production of 1,3-PD from crude glycerol is a promising alternative to the traditional chemical synthesis, and large number of research has focused on the microbiological con-version of crude glycerol to 1,3-PD. 1,3-PD can be used as monomer for the synthesis of various poly-esters (polypropylene terephthalate), polyurethane,


470

Table 3. Chemicals produced by microbial fermentation of crude glycerol; PG – pure glycerol, CG – crude glycerol, CGRO – crude glycerol rapeseed oil, CGSO – crude glycerol from sunflower oil, CGACH – crude glycerol from alkali-catalyzed hydrolysis, CGLCH – crude gly-cerol from lipase-catalyzed hydrolysis and DMSO – dimethyl sulfoxide

Type of product

Compound Microorganism Operation conditions

Yield, g/L ReferenceProcess Glycerol (g/L) t / °C

Alcohols 1,3-Propanediol C. butyricum CNCM 1211 Batch CG 20 37 0.62a [133]

CG 70 0.64a

C. butyricum VPI 3266 Batch PG 30 37 14.8 [99]

CG 35 16.4

C. butyricum NRRLB-23495

Anaerobic CG 20 37 9.1 [134]

C. butyricum DSP1 Fed-batch CG 50 37 71 [100]

C. butyricum AKR 102a Fed-batch, adding of fractional parts

(25 g/L)

CG 30 37 76.2 [135]

PG 30 93.7

C. freundii ATTC8090 Batch CG 20 30 0.65a [133]

CG 70 0.54a

C. freundii ATTC8090 Anaerobic CG 20 30 4.85 [136]

K. pneumoniae ATCC 25959

Batch CG 20 30 0.65a [133]

CG 70 0.55a

K. pneumoniae DSM 2026 Fed-batch PG 20 37 61.9 [13]

CGACH 20 51.3

CGLCH 20 53

E. agglomerans CNCM 1210

Batch CG 20 30 0.51a [133]

CG 70 0.64a

K. pneumoniae Fed-batch CG 65 37 36.86 [137]

Klebsiella strain HE1 Batch CG 50 35 12.5 [138]

2,3-Butanediol K. oxytoca M3 Fed-batch PG 35-40 30 115 [103]

CG 35-40 131.5

K. pneumonia G31 Fed-batch, microaerobic

CG 30 37 49.2 [102]

K. pneumonia G31 Fed- batch, aerobic CG 30 37 70 [139]

K. oxytoca FMCC-197 Anaerobic CG 20 30 4.2 [134]

C. freundii FMCC-207 Anaerobic CG 20 30 4.3

Bacillus amyloliquefaciensB10-127

Batch CG 80, beet molasses (15 g/L)

37 102.3 [140]

Klebsiella variicola SRP3 Aerobic CG 50 30 25.33 [141]

Butanol C. pasteurianum DMSZ 525

Anaerobic CG 25 37 0.280a [106]

C. pasteurianum MNO6 Anaerobic CG 25 37 0.252a

C. pasteurianum ATTC 6013

Batch CG 25 37 0.30b [105]

PG 25 0.36b

Acids Lactic acid Bacillus laevalacticus Batch PG 20 37 2.35 [142]

Lactobacillus delbrueckii Batch CG 20 37 4.37

Lactobacillus pentosus Batch CG 20 37 1.43

Lactococcus lactis subsp.la

Batch PG 20 37 2.26

E. coli AC-521 Fed-batch, aerobic CG 95 37 85.8 [110]

R. oryzae NRRL 395 Fed-batch CG 75 +crude lucerne juice

(25 g/L)

27 48 [11]


471

Table 3. Continued

Type of product

Compound Microorganism Operation conditions

Yield, g/L ReferenceProcess Glycerol (g/L) t / °C

Acids Lactobacillus sp. CYP4 Batch CG 82.95 mM 37 39.4c [108]

Lactobacillus sp. ATCC 7469

CG 39.96 mM 37 10.1c

Citric acid Y. lipolytica Wratislavia AWG7

Fed-batch PG 80-100 30 139 [142]

CG 80-100 131.5

Y. lipolytica Wratislavia K1 Fed-batch PG 80-100 30 89

CG 80-100 86.8

Y. lipolytica ACA-DC50109

Batch CG 164 28 62.5 [143]

Y. lipolytica 1.31 CG 200 30 62 [113]

Y. lipolytica 1.22 Batch CG 300 30 54 [144]

Y. lipolytica A-101 Batch CG 150 30 66.8 [145]

Y. lipolytica N15 Batch PG 170 28 98 [112]

CG 100 71

Succinic acid A. succinogenes DMSO Fed-batch CG 60 37 49.62 [146]

Y. lipolytica Y-3314 Batch CG 10% 30 45 [114]

Engineered E. coli Batch, microaerobic CG - 37 14 [115]

Propionic acid P. acidipropionici Batch CG 80 30 42 [118]

P. acidipropionici Fed-batch CG 20 30 0.79a [121]

P. freudenreichii spp. shermanii

Fer-batch CG 20 30 0.58a

Amino acid L-phenylalanine E. coli BL21(DE3) Batch CG 30 37 0.0552 [122]

Biosurfactants Mannosylerythritol U. maydis Fed-batch CG 50 30 32.1 [124]

Glycolipids Pseudozyma antarctica JCM 10317

Fed-batch CG 10% (v/v) 30 16.3 [126]

Sophorolipids C. bombicola ATTC 22214 Fer-batch CG 10% 30 40 [125]

Rhamnolipids Pseudomonas aeruginosas EM1

Batch CG 30.5 + glucose (18.1

g/L)

37 12.6 [138]

Biosurfactant Y. lipolytica Batch CG 3% 30 7.9 [147]

Antibiotics Cephalosporin C A. chrysogenum M35 Batch CG 4% (v/v) 27 7.24 [128]

Vancomycin A. orientalis XMU-VS01 Batch CG 40-60 30 7.61 [127]

Hexaene S. hygroscopicus CH-7 Batch CGSO 15 28 0.0387 [129]

CGRO 15 0.012

PG 15 0.0147

Azalomycine CGSO 15 0.0024

CGRO 15 0.0104

PG 15 0.0242 amol/mol glycerol; bg/g glycerol; cmM

lubricant, and as a precursor in pharmaceutical and chemical industries. Natural plastics that contain 1,3- -PD, showed higher biodegradability than the fully synthetic polymers [91,92].

Bacterial strains able of producing 1,3-PD belong to genera Klebsiella (Klebsiella pneumoniae), Entero-bacter (Enterobacter agglomerans), Citrobacter (Cit-robacter freundii), Lactobacillus (Lactobacillus brevis and Lactobacillus buchneri), and Clostridium (Clostri-

dium butyricum and Clostridium pasteurianum) [93- -95]. The most investigated fermentation process is the production of 1,3-PD during the cultivation of Klebsiella spp. and Clostridium spp. on crude glycerol under anaerobic conditions (Table 3). Several clos-tridial species, such as non-pathogenic anaerobic bacterium C. butyricum and C. pasteurianum [96], can use crude glycerol as a carbon source for growth and production of 1,3-PD. Facultative anaerobic mic-


472

roorganisms such as K. pneumoniae and C. freundii are also good producers of 1,3-PD from crude gly-cerol. However, these organisms are classified as pathogens, which limits their application [97]. In addi-tion, K. oxytoca [98] and Lactobacillus reuteri [97] are suitable for the production of 1,3-PD from crude gly-cerol. González-Pajuelo et al. [99] investigated the impact of different concentrations of crude and com-mercial glycerol on the production of 1,3-PD by the strain C. butyricum VPI 3266. For this study, commer-cial glycerol (87 g/100 mL) and two types of crude gly-cerol (65% and 92 g/100 mL) were used as a carbon source at two different concentrations (30 and 60 g/L). When crude glycerol fermentations were compared to the commercial glycerol fermentation, no significant differences in the maximum concentration of 1,3-PD were observed. The maximum concentration of 1,3-PD was 29.7 g/L when the strain was cultivated on the commercial glycerol (58 g/L) and 31.5 g/L of crude glycerol (62 g/L). Szymanowska-Powałowska and Białas [100] investigated the capability of C. butyricum DSP 1 to produce 1,3-PD utilizing crude glycerol in the fermenters of different volumes (6.6, 42 and 150 l). The initial concentration of crude glycerol at the start of fermentation was 50 g/L. The maximal concentration of 1,3-PD, 71 g/L for fed-batch fermentation, was received in the 6.6 l bioreactor. The concentration of 1,3-PD in the 150 l bioreactor was lower than in the 6.6 l bioreactor. During the batch cultivation the concentration was 37 g/L independent of the volume of the fermenter. Many microorganisms can metabolize crude glycerol to 1,3-PD, but strains of C. butyricum and K. pneumoniae are considered to be the best natural producers of 1,3-PD due to their significant tolerance to the substrate composition and high yield and productivity of 1,3-PD [101].

2,3-BD. 2,3-BD can be used in many chemical syntheses for the production of plastics, antifreeze and other important products. It is obtained by a chemical method from petroleum, and a microbial process from crude glycerol. The bacteria of genera Klebsiella and Bacillus were often investigated as 2,3-BD producers (Table 3).

Fermentation of crude glycerol by strains of Klebsiella spp. provides an possibility for microbial production of 2,3-BD, although the main product is 1,3-PD. A study of Petrov and Petrova [102] demon-strated that 2,3-BD may be the main product of crude glycerol fermentation by bacteria K. pneumoniae G31. The 2,3-BD production depends primarily on the com-position of the culture medium and aeration. Cho et al. [103] reported a high production of 2,3-BD from crude glycerol using the strain K. oxytoca M3.

Butanol. There is a great interest for butanol production as an alternative fuel with better physical properties compared to ethanol [104]. Studies were carried out with the bacteria C. acetobutylicum and C. beijerinckii that can produce butanol from crude gly-cerol. However, in the case of C. acetobutylicum, crude glycerol can be metabolized only in the pre-sence of glucose [105]. Also, Taconi et al. [105] studied the possibility of producing butanol (via anaer-obic fermentation) from crude glycerol by C. pasteur-anum. The results showed that, in addition to butanol, significant amounts of ethanol and 1,3-PD were pro-duced. Unlike C. acetobutylicum, which metabolized glycerol in the presence of glucose, C. pasteurianum can utilize crude glycerol as the sole carbon source and produce butanol. Until recently, C. pasteurianum has not been considered as an efficient producer of butanol. However, Jensen et al. [106] reported that C. pasteurianum can produce butanol utilizing crude and purified glycerol as a carbon and energy source.

Organic acid production

Many species of filamentous fungi, especially Rhizopus spp. and Aspergillus spp., are capable of producing large amounts of organic acids from differ-ent substrates [107]. However, with the exception of citric acid, there is limited information on the product-ion of organic acids from crude glycerol using fungi.

Lactic acid. Bioconversion of crude glycerol to lactic acid was studied in naturally isolated strain of Lactobacillus sp. CYP4 and the reference strain of Lactobacillus sp. ATCC 7469 [108]. The results showed that Lactobacillus sp. CYP4 had a higher potential for bioconversion of crude glycerol into lactic acid than the reference strain. Lactic acid may also be produced by bioconversion of crude glycerol using other microorganisms, such as Escherichia coli, Kleb-siella, Bacillus and Clostridia [96,109]. However, these strains have low productivity of lactic acid from crude glycerol. In order to increase the productivity and concentration of produced lactic acid, a strain E. coli AC-521 was isolated from soil [110]. This strain is able to use crude glycerol as a carbon source and produces lactic acid. Vodnar et al. [111] investigated the lactic acid production by Rhizopus oryzae NRRL 395 on media containing crude glycerol and crude juice of green lucerne. The maximum lactic acid con-centration (48 g/L) was obtained at the crude glycerol concentration of 75 g/L and the lucerne green juice concentration of 25 g/L.

Citric acid. Crude glycerol was not a good sub-strate for production of citric acid by Aspergillus niger (main producer of citric acid by fermentation of vari-


473

ous carbohydrates), so the studies have been dir-ected on yeast strains as a suitable substitution. This is primarily due to their resistance to high substrate concentrations and tolerance to impurities, allowing the use of low-quality substrates [112]. The high-yield organic acid production using glycerol has primarily been reported in strains of the yeast Yarrowia lipo-lytica (Table 3). The strain Y. lipolytica 1.31 was found to be the most favorable for citric acid pro-duction from crude glycerol [113]. Natural strains of Y. lipolytica achieved similar yields when cultured on crude glycerol from biodiesel production and pure glycerol. Besides citric acid, Y. lipolytica is able to produce some interesting compounds from crude gly-cerol, such as biosurfactants.

Succinic acid. It is obtained mainly by hydrogen-ation of maleic anhydride and becomes an important chemical that could be used to produce important pre-cursors for chemical synthesis such as pharmaceut-ical products (antibiotics, amino acids, and vitamins) and biodegradable plastics [107]. However, the micro-biological process based on agricultural wastes and by-products of biodiesel production is considered to be promising. For instance, Yuzbashev et al. [114] showed the possibility of biological conversion of crude glycerol into succinic acids by strains of the yeast Y. lipolytica (Table 3). The fermentative pro-duction of succinic acid from glycerol has also been investigated using a strain E. coli [115,116]. This strain was able to convert crude glycerol to succinic acid with a specific productivity of ∼4 g/(g/h) and the maximum concentration of 14 g/L [115]. Carvalho et al. [117] have shown that Actinobacillus succinogenes can produce succinic acid growing on the medium containing crude glycerol.

Propionic acid. It is used in the pharmaceutical, chemical and food industries as a preservative for animal feed and in the production of cheese and bakery products. Barbirato et al. [118] evaluated the production of propionic acid from glycerol by three bacterial strains: Propionibacterium acidipropionici, P. acnes and C. propionicum. Considering the ferment-ation time and the conversion yield, the best strain for glycerol conversion to propionic acid was P. acidipro-pionici (Table 3). Also, the strain Propionibacterum freudenreichii subsp. shermanii can produce propio-nic acid from crude glycerol [6,85,119,120]. Himmi et al. [121] investigated the effect of glucose and crude glycerol on the efficiency of the fermentation process using bacteria P. acidipropionici and P. freudenreichii subsp. shermanii. The concentration of produced pro-pionic acid was higher in both strains during the fer-

mentation of crude glycerol compared to that achieved in the fermentation of glucose.

Amino acid production, L-phenylalanine. Srinop-hakun et al. [122] investigated the possibility of using crude glycerol from biodiesel process for the growth of the bacterium E. coli BL21(DE3) and the L-phenyl-alanine production. The highest cell dry weight (3.47 g/L) and L-phenylalanine concentration (55.2 mg/L) was obtained in the medium with 30 g/L of crude gly-cerol. Also, the impurities contained in the medium of crude glycerol had positive effect to the growth of E. coli BL21(DE3).

Biosurfactant production

Interest in the production of biosurfactants inc-reases because they are non-toxic, biodegradable and have a variety of applications [123,124]. Recent studies have shown that fungi of the genera Candida, Pseudozyma and Ustilago as well as the yeast Y. lipolytica (Table 3) can produce biosurfactants glyco-lipids, including ramnolipide, sophorolipide, celobio-selipids, trehaloselipids and mannosyl erythritol lipids. Relatively high concentrations of sophorolipids from crude glycerol can be obtained by bioconversion using Candida bombicola ATCC 22214 [125]. Crude glycerol is a better substrate for the production of sophorolipids than pure glycerol since the sophoro-lipids yield on crude glycerol is over 40 g/L and only 9 g/L on pure glycerol. In addition, biosurfactant manno-sylerythritol lipids can be obtained in the fermentation of crude glycerol by the fungi Ustilago maydis [124]. The fungus growth was significantly better in crude glycerol, and the maximum concentration of mannosyl erythritol lipids under the optimized fermentation con-ditions (pH 4, 50 g/L crude glycerol, 30 °C and trace elements) was 32 g/L in 8 days of fermentation. Yeast Pseudozyma antartica may also produce biosurfact-ant glycolipids using crude glycerol and the concen-tration obtained is 16.3 g/L [126].

Antibiotic production

Recent studies indicate the possibility of using crude glycerol as a carbon source for the microbial production of antibiotics. Zeng et al. [127] investigated the possibility of using the crude glycerol to produce vancomycin the actinobacterium Amycolatopsis ori-entalis XMU-VS01. Besides glycerol, glucose, fruct-ose, maltose, sucrose, dextrin and soluble starch were also used as carbon sources in the basal medium. The results indicated that crude glycerol was the most effective carbon source for the growth of bacterium and the production of vancomycin. Crude glycerol can also be applied as an alternative carbon source in the production of cephalosporins C by Acre-


474

monium chrysogenum M35 [128]. Crude glycerol can be successfully used as an alternative to methionine, vegetable oils and other sources of carbon to inc-rease the production of cephalosporin C on the indus-trial scale [128]. In addition, the strain Streptomyces hygroscopicus CH-7 was investigated in production of antibiotics on crude glycerol from the biodiesel pro-duction from sunflower and rapeseed oil [129]. This strain S. hygroscopicus CH-7 produces different maximum concentrations of antibiotics hexaene and azalomycine depending on the carbon source [130- -132]. During the fermentation process, the maximum concentration of hexaene was obtained in the medium containing glycerol from biodiesel production from sunflower oil, which is twice higher than that achieved in the basic medium with glucose as a carbon source. Crude glycerol from biodiesel production from rape-seed oil has no a stimulating effect on the production of both antibiotics by S. hygroscopicus CH-7.

Glycerol for biogas production

The production of biogas is one of the promising possibilities of the use of crude glycerol from the bio-diesel production process [148-150]. For the pro-duction of biogas, crude glycerol can be utilized as a sole substrate or a co-substrate. The use of crude glycerol results in high production of biogas in a smaller reactor volumes and generation of low quan-tities of sludge [151].

In the production of biogas, previous pretreat-ment is often applied on crude glycerol since it can contain impurities that can be inhibitory to the anaer-

obic digestion process (methanol, higher concentra-tions inorganic salts) [86]. For instance, the presence of potassium or sodium in concentrations of 0.74 mol/l and 0.24-2.3 mol/l, respectively, can halve the pro-duction of methane [152]. Methanol is usually rem-oved by autoclaving or distillation, while alkali catalyst is removed by acidification or crystallization/precipit-ation [153]. Pretreatment of glycerol by acidification and additional rectification resulted in higher specific methane production rate compared to the pretreat-ment by acidification followed by vacuum distillation [154].

The use of crude glycerol as a solo substrate for the production of biogas depends on the organic load rate, and requires the addition of small amounts of nutrients [155,156]. According to Rétfalvi et al. [157,158], the increase of organic load rate induces higher content of volatile fatty acids and decreases the production of biogas since propionic acid can have a harmful impact to the methanogenic bacteria. Because the amount of nitrogen in the crude glycerol can be very small [86], the appropriate C/N ratio can be achieved by the addition of nitrogen, usually urea or ammonium chloride [151].

The production of biogas could be increased and accelerated in co-digestion by the addition of crude glycerol to different industrial and domestic wastes. The biogas production yield depending on co-sub-strate used, pretreatment of substrate and operating conditions is shown in Table 4.

Table 4. Co-substrate used, pre-preparation of substrate, operation conditions and production yield for biogas production from glycerol

Co-substrate (raw material) Pre-preparation

and concentration of CGa, %

Type of reactor Temperature

°C Other operation

conditions

Biogas production yield

l CH4/kg CODrem Reference

Microalgae residues from biodiesel production

- Continuously stirred tank reactor

25 C/N ratio 12.44 192b [168]

30 208b

35 295b

40 265b

25 C/N ratio 8.53 188b

30 227b

35 302b

40 308b

Glycerol-containing waste and wastewater derived from the manufacturing of biodiesel

AG Batch laboratory-scale reactor

35 310 [169]

Sewage sludge 1 Single-step anaerobic reactor

35 2.353c [161]

Granular sludge AG Batch laboratory-scale reactor

37 292 [154]

Non-granular sludge AG 288


475

Table 4. Continued

Co-substrate (raw material) Pre-preparation

and concentration of CGa, %

Type of reactor Temperature

°C Other operation

conditions

Biogas production yield

l CH4/kg CODrem Reference

Granular sludge DG 356

Sewage sludge 2 Cascade of two continuous stirred tank reactors (HRT

12.3 days)

37 114c [160]

3 139c

Cattle manure 94% + food waste 2%

4 Induced bed reactor (HRT 20

days)

55 6.92 g COD/l.day 2.43d [193]


3 6.99 g COD/l.day 2.57d


3 7.79 g COD/l.day 1.52d


2 6.91 g COD/l.day 0.65d

Cattle manure 5.6 Continuously stirred reactor

55 Organic loading rate 5.4 kg

COD/m3 day

53.2e [194]

Induced bed reactor

Organic loading rate 6.44 kg COD/m3 day

56.5e

Sewage sludge 0.63 Continuously stirred tank reactor

(50 L, HRT 20 days)

35 1.3f [195]

Canned seafood wastewater 1 Up-flow anaerobic sludge blanket

25.6 g COD/l 577b [196]

2 35.2 g COD/l 265b

3 64 g COD/l 101b

Cattle manure, ultrasonically pretreated

4 Continuously stirred reactor

35 365.4 [166]

55 228.3

6 35 335.1

55 476.4

8 35 192.3

55 409.9

Municipal wastewater sludge 1.1 Continuously stirred tank reactor

36 580c [150]

Olive mill wastewater + slaughterhouse wastewater

1 Single-stage anaerobic reactor

35 1.210c [149]

Organic fraction of municipal solid waste

2.094c

Pig manure 4 Semi-continuous stirred tank reactor

35 5.6h [148]

aCG - crude glycerol, AG - acidified glycerol, DG - distilled glycerol, COD - chemical oxygen demand and HRT - hydraulic retention time; bl CH4/kg volatile solids; cl CH4/day; dl CH4/lday; el biogas/kg wet waste; fm3/l added glycerol; gl biogas/day

Co-digestion with sewage sludge. The addition of crude glycerol and increase of the organic load rate for 25% can increase the biogas production for 82%, compared to the digestion of sewage sludge alone [159]. Also, co-digestion of sewage sludge and up to 3% of crude glycerol can improve biogas production by 3.8-4.7 times, while the addition of 4% of crude

glycerol can cause failing of the system [160]. On the contrary, according to Fountoulakis et al. [161], the addition of glycerol over 1 vol.% can reduce the bio-gas yield in the mesophilic process of biogas pro-duction in co-digestion with sewage sludge. The effect of C/N ratio in the biogas production can be considered as one of the most important factors, so


476

differences in C/N ratios can explain the disagree-ment among the previous results [162].

The addition of glycerol (1%) to the organic fraction of a municipal solid waste and a mixture of olive mill and slaughterhouse wastewaters increased the production of methane for 50 and 150%, respect-ively [149]. According to Razaviarani et al. [150], the methane production rate was increased for 80% by the addition of 1.1% of glycerol to the municipal wastewater sludge. Despite an increased interest in thermophilic anaerobic digestion of sewage sludge due to the reduction of the presence of pathogens [163], the investigation of Silvestre et al. [164] indi-cated that the increase of the biogas yield in co-dig-estion of sewage sludge and crude glycerol was much higher under the mesophilic digestion regime.

The advantages of co-digestion of animal man-ure and crude glycerol rely on the dissolution of gly-cerol due to the high content of water in the manure, stability of pH, availability of the nutrients in the man-ure which are necessary for the growth of microorg-anisms, achievement of appropriate C/N ratio and easiness of the glycerol digestion [148,151].

The almost fourfold increase in the biogas pro-duction was achieved in mesophilic co-digestion of pig manure and 4% of glycerol [148]. Promoting action of glycerol relied mostly on the higher organic load rate, but the synergy of the co-substrates and increased C/N ratio also contributed to the process. According to Amon et al. [165], glycerol can be added to pig manure in the amount lower than 6% without the disruption of the process stability. Remarkably, the safety of the use of digestate as the fertilizer is not affected by the addition of glycerol [148]. The inves-tigations of Castrillón et al. [166] showed that meso-philic and thermophilic co-digestion of cattle manure and crude glycerol differ in the optimum concentration of the added glycerol. Under the mesophilic con-ditions the highest yield was obtained with the addi-tion of 4% of crude glycerol, while in the thermophilic regime the optimum concentration of glycerol inc-

reased to 6%. In the same investigation, a positive effect of substrates pretreatment on the co-digestion process was proven, i.e., up to the eightfold increase of biogas production was achieved by applying ultra-sound. The same authors claimed that the addition of food waste can further improve the thermophilic dig-estion of the mixture of cattle manure and glycerol.

Co-digestion of biodiesel waste products and crude glycerol. It can also be applied for the biogas production. Posttransesterified microalgae residues can be a good substrate for anaerobic co-digestion with glycerol since they contain almost no lignin and lower cellulose [167]. By the addition of glycerol to this residues the C/N ration can be increased, which leads to the increase of the methane production for more than 50% [168]. Aside from this, biodiesel was-tewater can also be used as a co-substrate with gly-cerol, but with previous pretreatment (for instance, electrocoagulation) due to the high content of long-chain fatty acids which can act as an inhibitor in the process of anaerobic digestion. According to Siles et al. [169] the mixture of biodiesel wastewater and gly-cerol reduces the need for clean water supply for the glycerol dilution and provides a considerable amount of methane in the mesophilic anaerobic digestion pro-cess.

Glycerol for biohydrogen production

Crude glycerol derived from biodiesel production represents a potential carbon-rich and effective sub-strate for biohydrogen production because of the high energy content. Also, it can be utilized by the hydro-gen producing microorganisms without previous pre-treatment unlike cellulosic waste materials [153]. Hyd-rogen production yield from crude glycerol depending on the strain of microorganisms and the operational conditions for biohydrogen production is shown in Table 5. Biohydrogen can be produced by photofer-mentation (using purple non-sulfur bacteria) or by light-independent (dark) anaerobic fermentation of carbon rich substrates [170].

Table 5. Microorganisms, operational conditions and hydrogen production yield for biohydrogen production from crude glycerol (adapted from [197])

Inoculum Substratea Type of reactor Operating conditions Hydrogen production

yield, mol H2/mol glycerolReference

R. palustris CG 10 mM Glutamate 5 mM

Glass bottles, 0.5 l Photofermentation (illumination 100 W)

0.65b [173]

R. palustris CG 10mM Glutamate 4mM

Glass bottles 0.125 l

Photofermentation (illumination 50 W halogen

spotlights), 30 °C

4 [172]

CG 10mM Glutamate 6 mM

3.1


477

Table 5. Continued

Inoculum Substratea Type of reactor Operating conditions Hydrogen production

yield, mol H2/mol glycerolReference

R. palustris CG 11.4 g/L

yeast extract NaHCO3 glutamate 2 mM

Serum bottles, 0.060 l

Two stage proces: dark and photofermentation

6.42c [174]

Thermotoga neapolitana

Biodiesel waste with 10 g/L glycerol

Bottle, 0.120 l 75 °C 1.27 [198]

Thermotoga neapolitana

Pre-treated biodiesel waste with 10 g/L glycerol

(removed ethanol and/or methanol and solids)

1.97

E. aerogenes CG 21 g/L Serum bottles, 0.125 l

37 °C 0.95 [180]

E. aerogenes GBW Packed bed reactor 37 °C 1.12 [181]

E. aerogenes CG Glass flasks, 0.02 l 37 °C 0.13 [199]

E. aerogenes Slaughterhouse liquid waste 10 mg/L, crude glycerol

10 g/L


- 99.7 d [188]

Brewery waste biomass 10 mg/L

106.84d

Urea (10 mg/L) 116.41d

K. pneumoniae CG 20 g/L yeast extract 2 g/L


40 °C 0.25 [179]

K. pneumoniae Optimized medium with 20.4 g/L glycerol

Stirred tank bioreactor

37 °C 0.53 [200]

Mixed culture (E. aerogenes and C. butyricum)

Apple pomace hydrolysate 5 g/L


37 °C 26d [183]

C. pasteurianum GBW Continuous stirred tank bioreactor

35 °C 0.77 [201]

Klebsiella sp. Serum bottles 0.14

Klebsiella sp. Glycerol 11.14 g/L

KH2PO4 2.47 g/L NH4Cl 6.03 g/L


40 °C 0.26 [174]

Enterobacter ludwigii CG Glass flasks, 0,02 l 37 °C 0.35 [199]

B. amyloliquefaciens 0.50

Mixed cultures mainly consisted of Clostridium species

CG 1 g/L Serum bottles, 0.120 l

37 °C 1.1 [178]

Mixed cultures WG 22.19 g/L, sludge 7.16 g-TS/l, endo-nutrient

2.89 cm3/l


35 °C 0.0329e [190]

Mixed cultures CG 15 g/L Serum bottles, 0.125 l

37 °C 2.960f [189]

Mixed cultures WG 20.33 g/L, urea 0.16 g/L, Na2HPO4 3.97, endo-

nutrient 0.20 ml/l

Glass bottle, 1 l 55 °C 1.502g [186]

Sludge from poultry slaughterhouse

GBW Anaerobic stirred batch biofilm

reactor

30 °C 0.10 [202]

Wheat soil GBW Serum bottles, 0.5 l 30 °C 0.31 [192] aCG - crude glycerol, GBW - glycerol based wastewater, WG – waste glycerol; bl H2/g dry weight /day; cmmol H2/g COD. dmmol/ l; emol H2/l/day; fH2/ l/day; gH2/ l


478

Photofermentation. It is highly influenced by C/N ratio, illumination intensity, inoculum and design of the bioreactor [171]. Photofermentation of crude gly-cerol can lead to the biohydrogen yield on the level of 75% of the theoretical one using the non-sulfur bac-terium Rhodopseudomonas palustris [172]. The med-ium for the biohydrogen production performed by R. palustris is optimized by the addition of glutamate in the concentration 0-8 mM [170,172-174]. Higher con-centrations of glutamate, above 11 mM, can decrease the hydrogen production due to the inhibition of nitro-genase enzyme [175]. The soaps showed to be the main inhibitory component present in crude glycerol that suppressed the photofermentation performed by R. palustris [173].

In the first stage of light-independent anaerobic fermentation the produced biohydrogen can easily be collected, while the remaining product can be used for the methanogenic phase [176]. Biohydrogen product-ion is mainly under the influence of pH value, tempe-rature and the substrate concentration [177]. Com-parison of the biohydrogen yield obtained from pure and crude glycerol by mixed cultures containing mostly of Clostridium spp. indicated that 30% of methanol did not affect the biohydrogen production. The maximum production was obtained under the optimum condi-tions (1 g/L of crude glycerol, pH of 6.5 and tempera-ture of 40 °C) was 1.1 mol H2/mol glycerol (Table 5) [178]. Contrary, the process with the bacterium Kleb-siella pneumonia which was performed in quite differ-ently conditions (20 g/L of crude glycerol, 2 g/L yeast extract, pH 8.0 and temperature 40 °C) led to the pro-duction of 0.25 mol H2/mol glycerol [179].

Optimization of the fermentation by Enterobacter aerogenes indicated that optimum conditions were 7.5% oxygen in the inoculum transfer, 18% of ino-culum added and addition of Na2HPO4, FeSO4 and NH4NO3 in the concentration of 8, 0.00625 and 1.5 g/L, respectively [180]. The implementation of these optimum conditions allowed the use of relatively high concentrations of crude glycerol. The authors rep-orted the yield of 0.85 mol H2/mol glycerol for the con-centration of 15 g/L crude glycerol and 0.95 mol H2/ /mol glycerol for the substrate concentration of 21 g/L [180]. The biohydrogen production by E. aerogenes from crude glycerol can be affected by the concen-tration of NaCl and inhibited by the addition of 1% NaCl [181].

During the fermentation performed with E. coli, it was observed that the optimum concentration of gly-cerol was 10 g/L, while higher concentration caused the decrease of the biohydrogen yield and the pro-duction rate [182]. Besides biohydrogen, the ferment-

ation of crude glycerol can lead to the formation of ethanol, 1,3-PD, acetic acid and lactic acid. The addi-tion of co-substrate like apple pomace hydrolysate can shift the metabolic pathway of E. aerogenes and C. butyricum from the production of 1,3-PD to the pro-duction of hydrogen. Additionally, this co-substrate can increase the utilization of glycerol [183].

The biohydrogen production at higher tempera-ture disables the growth of mesophilic contaminants, especially those which can utilize hydrogen [184]. The efficiency of the prevention of contamination can inc-rease at a high pH value and by alkali-thermophilic bacteria (Thermobrachium celere) [185]. Thermophilic conversion of crude glycerol in concentration of 20.33 g/L with the mixed anaerobic culture predominated by Thermoanaerobacterium sp. resulted in the product-ion of 1502.84 ml H2/l [186].

Efficiency of the biohydrogen production can be increased by the modification of the substrate. Endo-nutrient containing Mg2+ and Fe2+ is often used for enhancement of the microbial growth and enzyme activity [188].

In order to analyze the production of biohydro-gen by E. aerogenes, crude glycerol in the concen-tration of 10 g/L was mixed with secondary sludge, brewery waste, starch industry wastewater, apple pomace sludge, slaughterhouse liquid wastes and urea [189]. The results indicated that the highest inc-rease of the production rate was achieved by the addition of urea in the concentration of 10 mg/L.

Municipal solid waste and wastewater can be used for biohydrogen production as a co-substrate together with crude glycerol. Production of hydrogen was increased for 114 and 75% by adding 1% of crude glycerol to the organic fraction of municipal solid waste and a mixture of olive mill wastewater and slaughterhouse wastewater, respectively [149]. Almost complete substrate degradation (97%) was achieved by using of the mixed cultures of genera Klebsiella, Escherichia/Shigella and Cupriavidus in the activated sludge with crude glycerol as the only carbon source [189].

Although sludge can often be used as inoculum for the production of biohydrogen [188,190,191] other inoculums can also be used. Comparison of biohyd-rogen production from pure glycerol inoculated with heat treated sludge, compost, tomato and wheat soil indicated that the highest yield was obtained with wheat soil, while the shortest lag phase was obtained with the compost inoculums [192].

Crude glycerol as an animal feedstuff

An especially attractive utilization of crude gly-cerol from biodiesel industry is as a feed ingredient


479

because of glycerol’s high absorption rates and good energetic value. This use is favored by the surplus of crude glycerol and the increase in the price of corn and will gain increasing attention [203]. Research works have been focused on the energetic value, fed levels and performance of crude glycerol in animal feeds. The digestible energy of crude glycerol (85%) is 14.9-15.3 MJ/kg while its metabolizable energy is 13.9-14.7 MJ/kg [204]. However, one must be aware of the presence of potential hazardous impurities in crude glycerol from biodiesel such as potassium that may result in wet litter or imbalances in dietary elec-trolyte balance in broilers [205] and methanol because of its toxicity [205,206]. In addition, excess glycerol in the animal diet may affect normal physiological meta-bolism [203].

Crude glycerol as an animal feedstuff is used in both non-ruminant and ruminant diets. Promising results have been achieved, especially for non-rumi-nant animals such as pigs, laying hens and broilers. For non-ruminants, crude glycerol is an excellent source of energy, as indicated by the metabolizable energy of broilers, laying hens, swine (15.2, 15.9 and 13.4 MJ ME/kg, respectively [207]) and growing pigs (15.9 MJ/kg nitrogen-corrected [208]). Crude glycerol added to the diets of weaned pigs up to 10% enhances the feed performance [209] while added to the diets of lactating sows up to 9% of crude gly-cerol’s performances are similar to standard corn- -soybean meal diets [210]. In broiler diets, the use of crude glycerol is effective at levels of 2.5 or 5%, but not at the level of 10% [211]. The dietary treatments of pigs had no significant effects on meat quality [212,213]. In the diets of lambs, crude glycerol, when added up to 15% dry matter, can improve feedlot per-formance, especially during the first 14 days [214]. Diets for meat goats with up to 5% of crude glycerol are beneficial [215]. Purified glycerol up to 15% of dry matter of lactating dairy cows has no deleterious effects on feed intake, milk production, and yield [216,217].

Possible uses of glycerol in biodiesel production

Both purified and crude glycerol can be used in biodiesel production in several ways such as a react-ant in esterification of free fatty acids (FFAs, termed glycerolysis) from feedstocks with a high FFA content prior to transesterification, for preparation of the deep eutectic solvents (DESs) that are employed in trans-esterification as a catalyst, an activator of another catalyst and a cosolvent or in crude biodiesel purific-ation as an extracting agent for removal of certain impurities, as well as for synthesis of the glycerol-

-based compounds (glycerolate and diglyceroxide) that are used as catalysts in transesterification.

Glycerolysis - esterification of FFAs with glycerol

A possible route to produce biodiesel from acid oil, soapstocks and deodorizer distillate originating from the refinery of various vegetable oils is con-version of FFAs to acylglycerols by glycerolysis prior transesterification [218]. In this reaction, FFAs are first esterified with glycerol to get acylglycerols, and then the reaction mixture is conventionally trances-terified. Methanol is mainly used in transesterification, while other alcohols are rarely applied. Usually batch stirred reactors are applied, although packed-bed and continuous stirred tank reactors are also employed. High reaction temperatures (up to 250 °C) are required to complete the glycerolysis reaction, and various acid, base and transition metal catalysts have been screened in order to reduce the reaction tem-perature. Higher temperatures (close to 260 °C) are not recommended because of possible glycerol decomposition. Glycerolysis can also be either enz-ymatically- or non-catalyzed. Lipases have a great catalytic potential when high regioselectivity is required [219], but they are yet too expensive for commercial scale [220]. The final product yield dep-ends on the type of feedstock and the employed process conditions such as the presence and type of catalyst, temperature and the FFA-to-glycerol molar ratio. The produced methyl esters do not satisfy the specific biodiesel standards but they can be used as a biofuel [220].

Glycerolysis reactions have rarely been studied (Table 6). In the glycerolysis reaction between acid oil and crude, neutralized glycerol carried out at 180 °C in 4 h, FFA conversion degrees of 93 and 81% were achieved using tin oxalate (1%) and dibutyl tin oxide (2%), respectively as a catalysts [221]. When this process was scaled-up using the latter catalyst, the nearly complete FFA conversion was achieved, resulting in the product with the acid value of 0.5 mg KOH/g. The glycerolysis reaction of FFAs from aci-dulated soybean soapstock over metallic zinc and zinc acetate di-hydrate as a catalyst (0.1%) resulted in the methyl ester yield of 94.7% at 200 °C within 2 h [222].The optimum reaction conditions for the glycero-lysis of palm stearin and crude glycerol derived from biodiesel production process were found to be a reaction temperature of 200 °C with a glycerol to palm stearin mole ratio of 2.5:1 and a reaction time of 20 min [223]. The yield and purity of monoacylglycerols obtained was satisfactory as compared with the pro-duct of the glycerolysis with pure glycerol. The glyce-


480

rolysis reaction of soybean oil with crude glycerol obtained from the transesterification of soybean oil with methanol produced the highest concentration of monoacylglycerols (about 42%) [224]. The reaction was very fast above 200 °C and the monoacylgly-cerols were transformed to diacylglycerols. The glyce-rolysis of nagchampa oil was significantly improved by microwave irradiation with respect to the reaction rate (six times faster) and the energy consumption (much lower), compared to the use of the conven-tional heating [225]. The FFAs of waste cooking oil with an acid value of 88.4 mg KOH/g were readily esterified with crude glycerol in the presence of the superacid SO4

2-/ZrO2–Al2O3solid catalyst [226]. The FFA conversion to acylglycerols was 98.4% under the optimal conditions (glycerol to FFA mole ratio of 1.4:1, catalyst loading of 0.3%, reaction temperature of 200 °C and reaction time of 4 h).

Mainly diacylglycerols are synthesized by lip-ase-catalyzed glycerolysis of FFAs from deodorizer distillate originating from corn, palm and soybean oils [219,227,228]. The acylglycerols yields of 70.0, 52.0 and 69.9% were achieved from the above-mentioned feedstocks in 5 , 6 and 4 h, respectively, under the optimum reaction conditions. High contents of react-ion products, especially MAG, were achieved in the ultrasound-assisted lipase-catalyzed glycerolysis of olive oil at mild irradiation) and temperature, in 2 h and low enzyme content (7.5%) [229]. The use of ultrasound irradiation in this reaction reduces the reaction time and maximizes the production of mono- and diacylglycerols [230].

Uses of glycerol-based DEPs

The use of glycerol for preparation of the deep eutectic solvents (DESs) that are employed in trans-

esterification as an activator of another catalyst and a cosolvent or in crude biodiesel purification as an ext-racting agent for removal of certain impurities (resi-dual glycerol and catalyst) has recently begun.

A glycerol-based DES with choline chloride (ChCl) can activate commercial CaO by removal of the CaCO3 and Ca(OH)2 from the surface of the solid catalyst. The ester yields of 87.3 and 95.0% were achieved in the rapeseed oil ethanolysis over calcin-ated CaO in the absence and the presence of ChCl:glycerol (1:2), respectively [231]. Moreover, non-calcinated CaO was inefficient (4.0% ester yield), while the ethyl ester yield was greatly enhanced with this DES (91.9%). In addition, the commercial CaO activated with the DES ensured the ester yield of 85.0% after the fifth cycle with no addition of the DES.

DESs are also efficient solvents in both chem-ically- and bio-catalyzed biodiesel production. Gu et al. [232] increased the ester yield in the NaOH-catalyzed transesterification of rapeseed oil in the presence of ChCl:glycerol (1:2) as a cosolvent. The same DEP was used in the Novozym 435-catalyzed soybean oil methanolysis as a cosolvent where the conversion degree of 88.0% was achieved in 24 h [233]. Also, ChCl:glycerol (1:2) and ChOAc:glycerol (1:2, 1:1 and 2:1) were efficient in producing biodiesel from Millettia pinnata seed oil with Novozym 435 [234].

Extraction of glycerol and left-over catalyst from crude biodiesel

Some glycerol-based DESs such as ChCl:gly-cerol (mole ratio 1:1), are efficient in the glycerol ext-raction form crude biodiesel produced by the KOH-catalyzed ethanolysis of rapeseed, soybean oil [235] and palm [236] oils. A DES synthesized by combining methyl triphenylphosphonium bromide (MTPB) with

Table 6. An overview on the use of crude glycerol as a reactant in glycerolysis reactions

Oily feedstock Catalyst Optimal reaction

conditions Yield of acylglycerols

% FFA conversion, % Reference

Acid oil Tin oxalate (1%) 180 °C, 4 h - 93 [221]

Dibutyl tin oxide (2%) 180 °C, 4 h - 81

Acidulated soybean soapstock

Metallic zinc and zinc acetate di-hydrate (0.1%)

200 °C, 4 h 94.7 - [222])

Palm + stearin Sodium hydroxide (2%) 200 °C, 20 h 60.8 - [223]

Soybean oil - >200 °C 42 - [224]

Waste cooking oil Superacid SO42-/ZrO2–Al2O3 200 °C, 4 h - 98.4 [226]

Corn oil Lipase 65 °C, 5 h 70 - [220]

Palm oil Lipase 65 °C, 6h 52 - [227]

Soybean oil Lipase 65 °C, 4 h 69.6 - [228]

Olive oil Lipase 65 °C, 4 h, ultrasound-assisted

>50 - [229]


481

glycerol was also successful in free glycerol removal from crude biodiesel [237]. Moreover, ChCl:glycerol and MTPB:glycerol are the most efficient in the removal of KOH, with the average removal efficien-cies of 98.59 and 97.57%, respectively [238]). Fur-thermore, these DESs reduce the amount of water in biodiesel and can be used five times with no signific-ant decrease in the efficiency.

Uses of glycerol-based compounds as catalysts in transesterification

Several glycerol compounds are tested as cat-alysts in transesterification reactions like glyceroxide (called also diglyceroxide) and glycerolate of calcium, zinc, sodium and lithium [239,240]. The performances of glycerol-based catalysts are compared in Table 7.

Table 7. The review of glycerol-based catalysts used in transesterification reactions

Feedstock Catalyst Catalyst preparation Optimal reaction condition Yield

(conversion) (%)/time (h)

ReferenceMethanol-to-oil mole ratio

Catalyst loading, % to the oil

t / °C

Soybean oil Ca(C3H7O3)2/ n-Al2O3

20% CaO/n-Al2O3, methanol and glycerol were charged to a vessel

and mixture was refluxed at 250 °C with stirring for 4 h.

9:1 3 250 82/6 [248]

Soybean oil Ca(C3H7O3)2 Prepared from CaO under reflux of methanol in the presence of

glycerol (50 vol. %) at 65 °C for 2 h.

12:1a 3.6a 65 ∼65/1 [241]

Soybean oil Ca(C3H7O3)2 CaO, obtained from limestone in He flow (900 °C, 1.5 h), was immersed

in glycerol (60 °C, N2 flow).

12:1a 3.6a 65 70/1, ∼90/2 [242]

Soybean oil CH3O-Ca-O(OH)2C3H5

CaO, obtained from limestone in He flow (900 °C, 1.5 h), was immersed in glycerol (50 vol.%) blended into

methanol under atmospheric pressure at 65 °C for 2 h.

1:2b 3.6b 60 89/2 [243]

Ca(C3H7O3)2 83/2

Soybean oil Ca(C3H7O3)2 A mixture of methanol, glycerol and CaO (calcinated at 600 °C) was

vigorously stirred at 60 °C for 8 h cooled and centrifuged. The

obtained precipitate was thoroughly washed with methanol and dried at

100 °C for 2 h.

9:1 1.3 60 82.6/2 [244]

Sunflower oil Ca(C3H7O3)2 CaO, obtained from CaCO3, was poured into methanol and glycerol, heated (50 °C, N2 atmosphere) and

agitated overnight.

14:1 0.7 60 90/3 [245]

Sunflower oil, refined

Ca(C3H7O3)2 CaO was mixed with glycerol and methanol (mass ratio of 1:4.4) and

agitated at 60 °C for 3 h.

12:1 2 60 (∼99)/6 [246]


Ca(C3H7O3)2 Synthesized by mechanochemical treatment of CaO dispersed in glycerol (1:5) for 15 min. The

mixture was centrifuged (6000 rpm, 10 min), decanted and washed with

ethanol. After several washing/centrifugation steps, the

product was dried at 60 °C for 24 h.

10:1 0.5 60 (∼95)/2 [247]

Castor oil Hydrated lime and glycerol (mole ratio 0.21), under mechanical

stirring, in the 5–180 min range and at 30, 60 and 70 °C (N2 atmosphere), centrifuged

at 5000 rpm for 15 min.

12:1 1.6 55 100/2 [249]


482

Table 7. Continued

Feedstock Catalyst Catalyst preparation Optimal reaction condition Yield

(conversion) (%)/time (h)

ReferenceMethanol-to-oil mole ratio

Catalyst loading, % to the oil

t / °C

Waste cooking oil

Ca(C3H7O3)2 A mixture of CaO, glycerol and methanol was agitated for 3 h at 60

°C under atmospheric pressure. The solid was recovered by filtration

and washed with tetrahydrofuran and dried at 60 °C for overnight

under vacuum.

9:1 1 60 93.5/0.5 (ultrasound: 22 kHz, 120 W and 50% duty cycle)

[250]

65.6/0.5 (stirring)

Jatropha oil Ca(C3H7O3)2 - 9:1 4 65 >95/1.5 [251]

Canola oil NaC3H7O3 / glycerol (1:1)

Prepared from purified crude glycerol and 50% caustic soda solution. Upon cooling to room temperature, the product was a

white crystalline solid.

9:1 1 60 - [252]

Canola oil Mixture of LiC3H7O3,

Li2(C3H6O3) and LiOH

Synthesized by heating aqueous solutions of lithium hydroxide with

glycerol under vacuum.

6:1 - (mole ratio lithium hyd-

roxide:glycerol 1:1)

120- -140

96-99/1 [253]


Ca(C3H6O3) Ca(OH)2 was mixed with glycerol (mass ratio of 1:10; 180 °C, 2 h), the solid was recovered, washed

twice with ethanol and dried overnight at 60 °C under vacuum.

12:1 2 60 (∼95)/8 [246]

Soybean oil Zn(C3H6O3) Zinc acetate dihydrate and glycerol with 2% of water was heated up to

160 °C for 1 h at 500 rpm (N2 atmosphere). The precipitate was filtered, washed with ethanol and

dried for 1 h at 40 °C

30:1 3 140 76.6 (96.8)/6 [254]

Soybean oil, refined

Ca(C3H6O3) Synthesized by mixing the respective high purity oxides with

glycerol, in a mole ratio of 1:4 (ZnO, SrO and BaO) or 1:20 (CaO) and heating at 120 °C or 60 °C for 7

days to produce mono or diglycerolate. The product was

washed and centrifuged four times with a 1:1 isopropanol:glycerol

mixture, followed by two washing/centrifugation steps with

ethyl ether and drying at 60 °C for 1 h.

50:1 2 50 62.8/2 [255]

Zn(C3H6O3) 0.8/2

Sr(C3H6O3) 99.2/2

Ba(C3H6O3) 99.0/2

Ca(C3H6O3)2 99.9/2

Soybean oil MnCO3/Zn (C3H6O3)

Solid MnCO3/ZnO and glycerol in excess were agitated at 175 °C for

2 h of mixing (200 rpm). The precipitate was separated by

filtration, washed by methanol and dried (overnight) at 50 °C.

24:1 1-2 175 81 (100)/3 [256]

aMethanol to oil ratio: 50:100 ml/ml and catalyst loading 14 mmol; bmethanol to oil ratio: 5:10 ml/ml and catalyst loading 0.4 g

Calcium diglyceroxide is the most frequently used among the glycerol-based catalysts. Glycerol is more reactive with CaO than methanol and only cal-

cium diglyceroxide is produced when CaO is immersed in methanol and glycerol under reflux [241]. When calcinated CaO is used in the synthesis of cal-


483

cium diglyceroxide, its catalytic activity is higher, while non-calcinated CaO is incompletely converted into calcium diglyceroxide [246]. There is disagree-ment between researchers on the relative activities of calcium diglyceroxide and CaO. According to Kouzu et al. [241], calcium diglyceroxide is slightly less active in the transesterification than CaO, which is attributed to the formation of another calcium com-pound, CH3O–Ca–O(OH)2C3H5, in the reaction of cal-cium diglyceroxide and methanol, which is less basic than CaO [243]. Ester yields in the presence of this calcium compound and calcium diglyceroxide within 2 h are 89 and 83%, respectively. However, some other researchers [244,245] have found that calcium digly-ceroxide is more active than CaO since the ester yield achieved over calcium diglyceroxide is higher than that obtained with CaO. Beside the presence of sur-face lipophilic CHx units, basic non-protonated O- anions at the surface of calcium diglyceroxide may be the origin of its high activity relative to CaO [246]. The main advantage of calcium diglyceroxide over CaO in is related to the initial rate of methanolysis [247]. On the other hand, it is more sensitive to the atmosphere than CaO [245]. The activity of calcium diglyceroxide supported on neutral alumina is almost the same as that of the 20% CaO/n-Al2O3 catalyst [248]. Calcium diglyceroxide is also an effective catalyst in the ultra-sound-assisted production of biodiesel from waste cooking oil [250].

Sodium glyceroxide synthesized from purified crude glycerol and 50 % caustic soda solution has been found useful not only as a generator for meth-oxide ions in situ, but also as a catalyst in the trans-esterification of canola oil into biodiesel [252]. The rate of methanolysis reaction performed with sodium glyceroxide is comparable with the same reaction wherein sodium hydroxide is catalyst. Although, the reaction catalyzed with glyceroxide is mass transfer limited, there is no visible difference in both reactions. Transesterification of canola oil with methanol was performed by using sodium methoxide (0.5 wt.%) and glycerol lithium base catalysts (0.2 wt.%) [252]. The alkoxide/hydroxide catalysts were obtained under vacuum by heating glycerol and aqueous solutions of lithium hydroxide. The yield of obtained FAME is almost 100%, The catalytic activity decreases as fol-lows 3:1 > 2:1 > 1:1 (lithium hydroxide:glycerol) and does not depend upon the composition and the pro-cess condition.

The catalytic activity of calcium glycerolate is much lower than that of calcium diglyceroxide because of its lower basic strength, basicity and spe-cific surface area [246]. In sunflower oil transester-

ification, nearly 95% conversion was achieved with calcium glycerolate within 8 h, while calcium diglycer-oxide gives an almost complete conversion within 6 h. However, calcium glycerolate is resistant to poisoning by ambient CO2 and H2O. Lisboa et al. [255] syn-thesized divalent metal glycerolates and higher con-versions to methyl esters were obtained in the soy-bean transesterification with strontium and barium monoglycerolates and calcium diglycerolate, while zinc monoglycerolate was inactive. However, at higher temperature (140 °C) zinc monoglycerolate gives higher ester yield (76.6%) and conversion of triacylglycerols (96.8%) in soybean transesterification [254]. Calcium diglycerolate was stable up to the third reuse cycle [255]. A MnCO3/Zn glycerolate catalyst gives a good activity in soybean oil transesterification with 100% conversion of tryacylglycerols and 81% ester yield with fresh catalyst, but it can give 95-100% conversion of tryacylglycerols and 62–78% ester yield after 13 repeated use of the same amount of catalyst without regeneration [256].

CONCLUSION

Crude glycerol, as cheap, safe, biodegradable and reusable, represents an excellent raw material for the production of value-added compounds. The use of glycerol as solvent gives an opportunity to make chemical reactions green, which can be performed with or without a catalyst and in the conditions of selective control of mechanism. In addition, crude glycerol can be useful as a carbon source for the microbial growth in the biotechnological production of value-added products in different fermentation pro-cesses. Moreover, the technological advancements in fuel industry justified the increase of crude glycerol involvement in biogas and hydrogen production that will give a significant contribution the economy of the biofuels industry. This review also emphasizes the opportunity for crude glycerol as a livestock feedstuff. Finally, various uses of crude glycerol in biodiesel production are considered. However, it should be emphasized that there are technical hurdles to over-come for developing practical processes to directly utilize crude glycerol from biodiesel production on commercial scale.

Acknowledgement

This work has been funded by the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project III 45001).


484

REFERENCES

[1] T. Werpy, G. Petersen, Top value added chemicals from biomass, vol. 1. US Department of Energy (2004), p. 52

[2] S. Hu, X. Luo, C. Wan, Y. Li, J. Agric. Food Chem. 60 (2012) 5915–5921

[3] European biodiesel board, http://www.ebb-eu.org/ /stats.php# (accessed 23 January 2016)

[4] M.R. Nanda, Z.Yuan, W. Qin, M.A. Poirie, X. Chunbao, Austin Chem. Eng. 1 (2014) 1-7

[5] M.R. Nanda, Z.Yuan, W. Qin, H.S. Ghaziaskar, M. Poirier, C. Xu, Fuel 117 (2014) 470-477

[6] S.S. Yazdani, R. Gonzalez, Curr. Opin. Biotechnol. 18 (2007) 213–219

[7] S.Fernando, S. Adhikari, K. Kota, R. Bandi, Fuel 86 (2007) 2806–2809

[8] G.P. Da Silva, M. Mack, J. Contiero, Biotechnol. Adv. 27 (2009) 30–39

[9] A.B. Leoneti, V. Aragão-Leoneti, S.V.W.B. de Oliveira, Renew. Energy 45 (2012) 138-145

[10] P. Dalias, P. Polycarpou, Res. Agric. Eng. 60 (2014) 17–23

[11] C. Quispe, C. Coronado, J. Carvalho Jr, Renew. Sustain. Energ. Rev. 27 (2013) 475–493

[12] M. Hajek, F. Skopal, Bioresour. Technol. 101 (2010) 3242–3245

[13] Y. Mu, H. Teng, D.J. Zhang, W. Wang, Z.L., Xiu, Bio-technol. Lett. 28 (2006) 1755-1759

[14] J.A. Posada, J.C. Higuita, C.A. Cardona, in Proceedings of World Renewable Energy Congress, Linkoping, Sweden, May 8–13, 2011

[15] W.N.R. Wan Isahak, Z.A. Che Ramli, M. Ismail, J.M. Jahim, M.A. Yarmo, Sep. Purif. Rev. 44 (2015) 250–267

[16] A. Wolfson, G. Litvak, C. Dlugy, Y. Shotland, Environ. Chem. Lett. 5 (2007) 67–71

[17] Y. Gu, F. Jérôme, Green Chem. 12 (2010) 1127-1138

[18] Y. Gu, J. Barrault , F. Jérôme, Adv. Synth. Catal. 350 (2008) 2007–2012

[19] N. Pagliaro, M. Rossi, Future of glycerol, RCS Publishing, Cambridge, 2010, p. 5

[20] S. Robertson, SIDS initial assessment report: glycerol; 56-81-5; United Kingdom (2002), http://www.inchem.org/documents/sids/sids/56815.pdf (accessed November 14, 2011)

[21] A. Wolfson, G. Litvak, C. Dlugy, Y. Shotland, D. Tavor, Ind. Crops Prod. 30 (2009) 78-81

[22] N. García, P. García-García, M.A. Fernández-Rodríguez, D. García, M.R., Pedrosa, F.J. Arnáiz, R. Sanz, Green Chem. 15 (2013) 999-1005

[23] M.B. Jovanović, S. S.Konstantinović, S.B. Ilić, V.B. Velj-ković, Adv. Technol. 2 (2013) 38-44

[24] S.S. Konstantinović, M.B. Jovanović, S.B. Ilić, I.B. Ban-ković Ilić, V.B. Veljković, Technical solution, Faculty of Technology, University of Niš, Leskovac, 2015

[25] J.N. Tan, M. Li, Z. Gu, Green Chem. 12 (2010) 908-914

[26] A.G. Ying, Q.H. Zhang, H.M. Li, G.F. Shen, W.Z. Gong, M.J. He, Res. Chem. Intermed. 39 (2013) 517–525

[27] F. Nemati, M.M. Hosseini, H. Kiani, J. Saudi Chem. Soc. (2013), http://dx.doi.org/10.1016/j.jscs.2013.02.004

[28] C.S. Radatz, R.B. Silva, G. Perin, E.J. Lenardão, R.G. Jacob, D. Alves, Tetrahedron Lett. 52 (2011) 4132–4136

[29] K.U. Sadek, R.A. Mekheimer, A.M.A Hameed, F. Elna-has, M. H. Elnagdi, Molecules 17 (2012) 6011–6019

[30] H.R. Safaei, M. Shekouhy, S. Rahmanpur, A. Shirinfes-han, Green Chem. 14 (2012) 1696-1704

[31] F. He, P. Li, Y. Gu, G. Li, Green Chem. 11 (2009) 1767- -1773

[32] D.M.L Cabrera, F.M. Líbero, D. Alves, G. Perin, E.J. Lenardão, R.G. Jacob, Green Chem. Lett. Rev. 5 (2012) 329-336

[33] A. Wolfson, H. Kimchi, D. Tavor, Asian J. Chem. 23 (2011) 1227-1229

[34] J.E.R. Nascimento, A.M. Barcellos, M. Sachini, G. Perin, E.J. Lenardão, D. Alves, R.G. Jacob, F. Missau, Tetra-hedron Lett. 52 (2011) 2571–2574

[35] M. Li, C. Chen, F. He, Y. Gu, Adv. Synth. Catal. 352 (2010) 519–530

[36] B. Banik, A. Tairai, N. Shahnaz, P. Das, Tetrahedron Lett. 53 (2012) 5627-5630

[37] L.C. Gonçalves, G.F. Fiss, G. Perin, D. Alves, R.G. Jacob, E.J. Lenardão, Tetrahedron Lett. 51 (2010) 6772– -6775

[38] P.K. Khatri, S.L. Jain, Tetrahedron Lett. 54 (2013) 2740- -2743

[39] V.G. Ricordi, C.S. Freitas, G. Perin, E.J. Lenardao, R.G. Jacob, L. Savegnago, D. Alves, Green Chem. 14 (2012) 1030–1034

[40] M. Delample, N. Villandier, J.P. Douliez, S. Camy, J.S. Condoret, Y. Pouilloux, J. Barrault, F. Jérôme, Green Chem. 12 (2010) 804–808

[41] N. Seyedi, Trans. Met. Chem. 38 (2013) 93–103

[42] D. Alves, M. Sachini, R.G. Jacob, E.J. Lenardão, M.E. Contreira, L. Savegnago, G. Perin, Tetrahedron Lett. 52 (2011) 133–135

[43] M.B. Gawande, A.K. Rathi, P.S. Branco, I.D. Nogueira, A. Velhinho, J.J. Shrikhande, U.U.R.V .Indulkar, C.A.A. Jayaram, N. Ghumman, N. Bundaleski, O.M.N.D. Teo-doro, Chem. Eur. J. 18 (2012) 12628-12632

[44] D. Tavor, I. Gefen, C. Dlugy, A. Wolfson, Synth. Com-mun. 41 (2011) 3409-3416

[45] X. Cui, Y. Deng, F. Shi, ACS Catal. 3 (2013) 808-811

[46] W.J. Chung, C. Baskar, D.G. Chung, M.D. Han, C.H. Lee, Republic Korean Kongkae Taeho Kongbo (South Korean patent), KR 2012006276 (2012)

[47] A.Z. Halimehjani, H. Gholamib, M.R. Saidi, Green Chem. Lett. Rev. 5 (2012) 1-5

[48] A.E. Díaz-Álvarez, J. Francos, P. Crochet, V. Cadierno, Curr. Green Chem. 1 (2014) 51-65

[49] A. Talebian Kiakalaieh, N.A.S. Amin, H. Heza-veh, Renew. Sustain. Energ. Rev. 40 (2014) 28–59

[50] H.W. Tan, A.R. Abdul Aziz, M.K. Aroua, Renew. Sustain. Energy Rev. 27 (2013) 118-127


485

[51] K. Wang, M.C. Hawley, S.J. Deathos, Ind. Eng. Chem. Res. 42 (2003) 2913–23

[52] A. Zsigmond, P. Bata, M. Fekete, F. Notheisz, J. Environ. Prot. 1 ( 2010) 201-205

[53] Y.T. Kim, K.D. Yung, E.D Park, Micropor. Mesopor. Mater. 131 (2010) 28-36

[54] Y. Gu, S. Liu, C. Li, Q. Cui, J. Catal. 301 (2013) 93-102

[55] G.D. Yadav, R.V. Sharma, S.O. Katole, Ind. Eng. Chem. Res. 52 (2013) 10133–10144

[56] A. Wolosniak Hnat, E. Milchert, B. Grzmil, Chem. Eng. Technol. 36 (2013) 411-418

[57] J. Chaminand, L. Djakovitch, P. Gallezot, P. Marion, Green Chem. 6 (2004) 359-361

[58] M.A. Dasaria, P.P. Kiatsimkul, W.R. Sutterlin, G.J. Suppes, Appl. Catal., A: Gen. 281 (2005) 225–231

[59] J. Feng, J. B. Wang, Y.F. Zhou, H.Y. Fu, H. Chen, X.J. Li, Chem. Lett. 36 (2007) 1274–1275

[60] L.C. Meher, R. Gopinath, S.N. Naik, K. Ajay, A.K. Dalai, Ind. Eng. Chem. Res. 48 (2009) 1840–1846

[61] Y.A Korolev, A.A. Greish, L.M. Kozlova, M.V. Kopyshev, E.F. Litvin, L.M. Kustov, Catal. Ind. 2 (2010) 287–289

[62] O. Franke, A. Stankowiak, US Patent 7.812.200, 2010

[63] N. Susuki, Y. Yoshikawa, M. Takahashi, M. Tamura M. US. Patent 7.799.957, 2010

[64] L. Ma, D. He, Catal. Today 149 (2010) 148-156

[65] J. Zhao, W. Yu, C. Chen, H. Miao, H. Ma, J. Xu, J. Catal. Lett. 134 (2010) 184-189

[66] Y. Shinmi, S. Koso, T. Kubota, Y. Nakagawa, K. Tomis-hige, Appl. Catal., B: Environ. 94 (2010) 318-326

[67] E.S. Vasiliadou, A.A. Lemonidou, Org. Process Res. Dev. 15 (2015) 925–931

[68] A. Stankowiak, O. Franke, US Patent 7.868.212, 2011

[69] A. Ševčík, A. Kaszonyi, M. Bôžik, in Proceedings of 45th International Petroleum Conference, Bratisalva, June 13th-14th, 2011

[70] R.B. Mane, A.A. Ghalwadkar, A.M. Hengne, Y.R. Sury-awanshi, C.V. Rode, Catal. Today 164 (2011) 447–450

[71] B.K. Kwak, D.S. Park., Y.S. Yun, J. Yi, Catal. Commun. 24 (2012) 90–95

[72] H.L. Hoşgün, M. Yıldız, H.F. Gerçel, Ind. Eng. Chem. Res. 51 (2012) 3863-3869

[73] M. Balaraju, K. Jagadeeswaraiah, P. S. Sai Prasad, N. Lingaiah, Catal. Sci. Technol. 2 (2012) 1967–1976

[74] H. Liu, S. Liang, T. Jiang, B. Han, Y. Zhou, Clean–Soil, Air, Water 40 (2012) 318-324

[75] T. Jiang, D. Kong, K. Xu, F. Cao, Appl. Petrochem. Res. (2015), DOI 10.1007/s13203-015-0128-8

[76] X. Li, H. Cheng, G. Liang, L. He, W. Lin, Y. Yu, F. Zhao, Catalysts 5 (2015) 759-773

[77] M. Hunsom, P. Saila, Int. J. Electrochem. Sci. 8 (2013) 11288-11300

[78] Y. Nakagawa, Y. Shinmi, S. Koso, K. Tomishige, J. Catal. 272 (2010) 191–194

[79] J. Oh, S. Dash, H. Lee, Green Chem. 13 (2011) 2004- -2007

[80] L. Longjie, Z. Yanhua, W. Aiqin, Z. Tao, Z. Chin, J. Catal. 33 (2012) 1257-1256

[81] S.S. Priya, V.P.Kumar, M.L. Kantam, S.K. Bhargava, A. Srikanth, K.V.R. Chary, Ind. Eng. Chem. Res. 54 (2015) 9104−9115

[82] S.S. Priya, P. Bhanuchander, V.P. Kumar, D.K. Dumbre, S.R. Periasamy, S.K. Bhargava, M.L. Kantam, K.V.R. Chary, ACS Sustain. Chem. Eng. 4 (2016) 1212–1222

[83] W. Luo, Y. Lyu, L. Gong, H. Du, T. Wang, Y. Ding, RSC Adv. 6 (2016) 13600-13608

[84] M. Hunsom, P. Saila, Renew. Energ. 74 (2015) 227-236

[85] G.P. Da Silva, M. Mack, J. Contiero, Biotechnol. Adv. 27 (2009) 30-39

[86] J.C. Thompson, B.B. He, Appl. Eng. Agric. 22 (2006) 261– -265

[87] Y.D. You, J.L. Shie, C.Y. Chang, S.H. Huang, C.Y. Pai, Y.H. Yu, C.H. Chang, Energ. Fuel. 22 (2008) 182–189

[88] A. André, P. Diamantopoulou, A. Philippoussis, D. Sarris, M. Komaitis, S. Papanikolaou, Ind. Crops. Prod. 31 (2010) 407–416

[89] A. Chatzifragkou, A. Makri, A. Belka, S. Bellou, M. Mav-rou, M. Mastoridou, P. Mystriot, G. Onjaro, G. Aggelis, S. Papanikolaou, Energy 36 (2011) 1097-1108

[90] R. Dobson, V.Gray, K. Rumbold, J. Ind. Microbiol. Bio-technol. 39 (2012) 217-226

[91] W.D. Deckwer, FEMS Microbiol. Rev. 16 (1995) 143-149

[92] U. Witt, R.J. Muller, J. Augusta, H. Widdecke, W.D. Deck-wer, Macromol. Chem. Phys. 195 (1994) 793–802

[93] P.F. Amaral, T.F. Ferreira, G.C. Fontes, M.A.Z. Coelho, Food Bioprod. Proc. 87 (2009) 179–186

[94] C. Dellomonaco, F. Fava, R. Gonzalez, Microb. Cell Fact. 9(3) (2010) 1-15

[95] S.S. Yazdani, R. Gonzalez, Curr. Opin. Biotechnol. 18 (2007) 213-219

[96] H. Biebl, J. Ind. Microbiol. Biotechnol. 27 (2001) 18-26

[97] R.K. Saxena, A. Pinki, S. Saurabh, I. Jasmine, Biotech-nol. Adv. 27 (2009) 805-913

[98] G. Yang, J. Tian, J. Li, Appl. Microbiol. Biotechnol. 73 (2007) 1017-1024

[99] M. Gonzalez-Pajuelo, J.C. Andrade, I. Vasconcelos, J. Ind. Microbiol. Biotechnol. 31 (2004) 442–446

[100] D. Szymanowska-Powałowska, W. Białas, BMC Micro-biol. 14 (2014) 45

[101] M. González-Pajuelo, I. Meynial-Salles, F. Mendes, P. Soucaille, I. Vasconcelos, Appl. Environ. Microbiol. 72 (2006) 96-101

[102] K. Petrov, P. Petrova, Appl. Microbiol. Biotechnol. 84 (2009) 659–665

[103] S. Cho, T. Kim, H.M. Woo, Y. Kim, J. Lee, Y. Um, Bio-technol. Biofuel. 8 (2015) 146

[104] B.G. Harvey, H.A. Meylemans, J. Chem. Technol. Bio-technol. 86 (2011) 2–9

[105] K.T. Taconi, K.P. Venkataramanan, D.T. Johnson, Environ. Prog. Sustain. Energ. 28 (2009) 100–110

[106] T.O. Jensen, T. Kvist, M.J. Mikkelsen, P. Westermann, AMB Express 2 (2012), DOI: 10.1186/2191-0855-2-44


486

[107] M. Sauer, D. Porro, D. Mattanovich, P. Branduardi, Trends Biotechnol. 26 (2007) 100–108

[108] Y. Prada-Palomo, M. Romero-Vanegas, P. Díaz-Ruíz, D. Molina-Velasco, C. Guzmán-Luna, Ciencia Tecnol. Futur. 5 (2012) 57-66

[109] M.G. El-Ziney, N. Arneborg, M. Uyttendaele, J. Debevere, M. Jakobsen, Biotechnol. Lett. 20 (1998) 913–916

[110] A. Hong, K. Cheng, F. Peng, S. Zhou, Z. Sun, C. Lui, D. Lui, J. Chem. Technol. Biotechnol. 84 (2009) 1576–1581

[111] D.C Vodnar, F.V. Dulf, O.L. Pop, C. Socaciu, Microb. Cell Fact. (2013), DOI: 10.1186/1475-2859-12-92

[112] S.V. Kamzolova, A.R. Fatykhova, E.G. Dedyukhina, S.G. Anastassiadis, N.P. Golovchenko, I.G. Morgunov, Food Technol. Biotechnol. 49 (2011) 65–74

[113] W. Rymowicz, A. Rywinska, B. Zarowska, P. Juszczyk, Chem. Pap. 60 (2006) 391–394

[114] T.V. Yuzbashev, E.Z. Yuzbasheva, T.I. Sobolevskaya, I.A. Laptev, T.V. Vybornaya, A.S. Larina, K. Matsui, K. Fukui, S.P. Sineoky, Biotechnol. Bioeng. 107 (2010) 673– -682

[115] M.D. Blankschien, J.M. Clomburgm, R. Gonzalez, Metab. Eng. 12 (2010) 409–419

[116] X. Zhang, K.T. Shanmugam, L.O. Ingram, Appl. Environ. Microb. 76 (2010) 2397–2401

[117] M. Carvalho, M. Matos, C. Roca,M. A. Reis, New. Bio-technol. 31 (2014) 133–139

[118] F. Barbirato, D. Chedaille, A. Bories, Appl. Microbiol. Biotechnol. 47 (1997) 441–446

[119] A. Zhang, S.T. Yang, Process Biochem. 44 (2009) 1346– -1351

[120] Z. Zhu, J. Li, M. Tan, L. Liu, L. Jiang, J. Sun, P. Lee, G. Du, J. Chen, Bioresour. Technol. 101 (2010) 8902-8906

[121] E.H. Himmi, A. Bories, A. Boussaid, L. Hassani, Appl. Microbiol. Biotechnol. 53 (2000) 435-440

[122] P. Srinophakun, S. Reakasame, M. Khamduang, K. Packdibamrung, A. Thanapimmetha, Chiang Mai J. Sci. 39 (2012) 59-68

[123] R.D. Ashby, D.K. Solaiman, Biotechnol. Lett. 32 (2010) 1429–1437

[124] Y. Liu, C.M.J.Koh, L. Ji, Bioresour. Technol. 102 (2011) 3927–3933

[125] R.D. Ashby, A. Nunez, D. K.Y. Solaiman, T.A. Foglia, J. Am. Oil Chem. Soc. 82 (2005) 625–630

[126] T. Morita, M. Konishi, T. Fukuoka, T. Imura, D. Kitamoto, J. Biosci. Bioeng. 104 (2007) 78–81

[127] X. Zeng, S. Wang, K. Jing, Z. Zhang, Y. Lu, Eng. Life Sci. 13 (2013) 109–116

[128] H.Y. Shin, J.Y. Lee, H.S. Choi H, J.H. Lee, S. W. Kim, J. Microbiol. 49 (2011) 753–758

[129] J. Ćirić, S. Ilić, S. Konstantinović, V. Veljković, G. Gojgić- -Cvijović, D. Savić, Adv. Technol. 2 (2012) 20-25

[130] S.B. Ilić, Ph.D. Thesis, University of Niš, Faculty of Technology, Leskovac, 2010

[131] S.B. Ilić, S. S. Konstantinović, G.Đ. Gojgić Cvijović, D.S. Savić, V.B. Veljković, Biosynthesis of antibiotics by streptomycetes in the media with different carbon and

nitrogen sources, Faculty of Technology, Leskovac, 2012 (in Serbian)

[132] S.B. Ilić, S.S. Konstantinović, G.Đ. Gojgić-Cvijović, D.S. Savić, V.B. Veljković, Med. Chem. Res. 22 (2013) 934- -937

[133] F. Barbirato, E. H. Himmi, T. Conte, A. Bories, Ind. Crops Prod. 7 (1998) 281–289

[134] M. Metsoviti, K. Paraskevaidi, A.A. Koutinas, A.P. Zeng, S. Papanikolaou, Process. Biochem. 47 (2012) 1872–1882

[135] E. Wilkens, A.K. Ringel, D. Hortig, T. Willke, K.D. Vorlop, Appl. Microbiol. Biotechnol. 93 (2012) 1057–1063

[136] T.F. Ferreira, R.R. Ribeiro, C.M.S. Ribeiro, D.M.G. Freire, M.A. Coelho, Сhem. Eng. Trans. 27 (2012) 157–162

[137] D.M. Rossi, E.A. de Souza, S.H. Flôres, M.A.Z. Ayub, Renew. Energ. 55 (2013) 404-409

[138] K.J. Wu, Y.H. Lin, Y.C .Lo, C.Y. Chen, W.N. Chen, J.S. Chang, J. Taiwan Inst. Chem. Eng. 42 (2011) 20-25

[139] K. Petrov, P. Petrova, Appl. Microbiol. Biotechnol. 87 (2010) 943–949

[140] T. Yang, Z. Rao, X. Zhang, M. Xu, Z. Xu, S.T. Yang, Microb. Cell. Fac. 14 (2015) 122

[141] M.S. Rahman, Z. Yuan, K. Ma, C.C Xu, W. Qin, J. Microb. Biochem. Technol. 7 (2015) 299-304

[142] B. Choubisa, H. Patel, M. Patel, B. Dholakiya, J. Micro-biol. Biotech. Res. 2 (2012) 90-93

[143] A. Rywińska, W. Rymowicz, B. Żlarowska, M. Wojta-towicz, Food. Technol. Biotechnol. 47 (2009) 1-6

[144] S. Papanikolaou, S. Fakas, M. Fick, I. Chevalot , M. Gali-otou-Panayotou, M. Komaitis, I. Marc, G. Aggelis, Bio-mass. Bioenerg. 32 (2008) 60–71

[145] W. Rymowicz, A. Rywinska, M. Marcinkiewicz, Biotech-nol. Lett. 31 (2009) 377–380

[146] A. Rywinska, W. Rymowicz, J.Ind. Microbiol. Biotechnol. 37 (2010) 431–435

[147] M. Carvalho, M.Matos, M.A. Reis, New Biotechnol. 25 (2014) 133-139

[148] G.C. Fontes, N.M. Ramos, P.F.F. Amaral, M. Nele, M.A. Z. Coelho, Braz. J. Chem. Eng. 29 (2012) 483–493

[149] S. Astals, V. Nolla-Ardèvol, J. Mata-Alvarez, Bioresour. Technol. 110 (2012) 63–70

[150] M.S. Fountoulakis, T. Manios, Bioresour. Technol. 100 (2009) 3043–3047

[151] V. Razaviarani, I.D. Buchanan, S. Malik, H. Katalambula, Bioresour. Technol. 133 (2013) 206–212

[152] N. Kolesárová, M. Hutňan, I. Bodík, V. Špalková, J. Biomed. Biotechnol. 2011 (2011) 1-15

[153] Y. Chen, J.J. Cheng, K.S. Creamer, Bioresour. Technol. 99 (2008) 4044–4064

[154] S.J. Sarma, S.K. Brar, E.B. Sydney, J.L. Bihan G. Buelna, C.R. Soccol, Int. J. Hydrogen Energy 37 (2012) 6473-6490

[155] J.A.S. López, M.A.M. Santos, A.F.C. Pérez, A.M. Martín, Bioresour. Technol. 100 (2009) 5609–5615

[156] I. Bodík, M. Hutňan, T. Petheöová, A. Kalina, Anaerobic treatment of biodiesel production wastes, in Proceedings of the 5th International Symposium on Anaerobic


487

Digestion of Solid Wastes and Energy Crops (M. Mahdi, Ed.), Hammamet, Tunisia, May 25–28, 2008, p. 111

[157] M. Hutňan, N. Kolesárová, I. Bodík, M. Czolderövá, Bio-resour. Technol. 130 (2013) 88–96

[158] T. Rétfalvi, A. Tukacs-Hájos, L. Albert, B. Marosvölgyi, Bioresour. Technol.102 (2011) 5270–5275

[159] Y. Wang, Y. Zhang, J. Wang, L. Meng, Biomass Bio-energy 33 (2009) 848–853

[160] S. Nartker, M. Ammerman, J. Aurandt, M. Stogsdil, O. Hayden, C. Antle, Waste Manage. 34 (2014) 2567–2571

[161] E. Athanasoulia, P. Melidis, A. Aivasidis, Renew. Energy 62 (2014) 73-78

[162] M.S. Fountoulakis, I. Petousi, T. Manios, Waste Manage. 30 (2010) 1849–1853

[163] X. Liu, H. Liu, Y. Chen, G. Du, J. Chen, J. Chem. Tech-nol. Biotechnol. 83 (2008) 1049–1055

[164] J. Mata-Alvarez, J. Dosta, M.S. Romero-Guiza, X. Fonoll, M. Peces, Renew. Sustin. Energ. Rev. 36 (2014) 412–427

[165] G. Silvestre, B. Fernandez, A. Bonmati, Bioresour. Technol. 193 (2015) 377–385

[166] T. Amon, B. Amon, V. Kryvoruchko, V. Bodiroza, V. Pötsch, W. Zollitsch, Int. Congress Ser. 1293 (2006) 217– -220

[167] L. Castrillón, Y. Fernández-Nava, P. Ormaechea, E. Mar-añón, Bioresour. Technol. 102 (2011) 7845–7849

[168] A. Vergara-Fernandez, G. Vargas, N. Alarcon, A. Vel-asco, Biomass Bioenergy 32 (2008) 338-344

[169] E.A. Ehimen, Z.A. Sun, C.G. Carrington, E.J. Birch, J.J. Eaton-Rye, Appl. Energ. 88 (2011) 3454–3463

[170] J.A. Siles, M.A. Martín, A.F. Chica, A. Martín, Bioresour. Technol. 101 (2010) 6315–6321

[171] P.C. Hallenbeck, D. Ghosh, Trends Biotechnol. 27 (2009) 287-297

[172] N. Basak, D. Das, World J. Microbiol. Biotechnol. 23 (2007) 31-42

[173] G. Sabourin-Provost, P.C. Hallenbeck, Bioresour. Tech-nol. 100 (2009) 3513–3517

[174] R.W.M. Pott, C.J. Howe, J.S. Dennis, J.S., Bioresour. Technol. 130 (2013) 725–730

[175] T. Chookaew, S.O-Thong, P. Prasertsan, Int. J. Hydrogen Energy 39 (2014) 751-760

[176] C.H. Sasikala, C.H.V. Ramana, P.R. Rao, Int. J. Hydro-gen Energ. 20 (1995) 123-126

[177] K.Y. Show, D.J. Lee, J.H. Tay, C.Y. Lin, J.S. Chang, Int. J. Hydrogen Energ. 37 (2012) 15616-15631

[178] Y. Mu, X.J. Zheng, X.Q. Yu, Int. J. Hydrogen Energ. 34 (2009) 7959–7963

[179] R. Mangayil, M. Karp, V. Santala, Int. J. Hydrogen Energy 37 (2012) 12198-12204

[180] T. Chookaew, S. O-Thong, P. Prasertsan, Int. J. Hydrogen Energy 37 (2012) 13314-13322

[181] R. Jitrwung, V. Yargeau, Int J. Hydrogen Energy 36 (2011) 9602–9611

[182] T. Ito, Y. Nakashimada, K. Senba, T. Matsui, N. Nishio, J. Biosci. Bioeng. 100 (2005) 260-265

[183] K. Trchounian, A. Trchounian, Appl. Energ. 156 (2015) 174–184

[184] V.L. Pachapur, S.J. Sarma, S.K. Brar, Y.L. Bihan, G. Buelna, M. Verma, Bioresour. Technol. 193 (2015) 297– -306

[185] C.J. Chou, F.E. Jenney Jr., W.W. Michael, M.W.W. Adams, R.M. Kelly, Metab. Eng. 10 (2008) 394–404

[186] A. Ciranna, V. Santala, M. Karp, Bioresour. Technol. 102 (2011) 8714–8722

[187] S. Sittijunda, A. Reungsang, Int. J. Hydrogen Energy 37 (2012) 15473-15482

[188] C.Y. Lin, C.H. Lay, Int. J. Hydrogen Energy 30 (2005) 285-292

[189] S.J. Sarma, S.K. Brar, Y.L. Bihan, G. Buelna, L. Rabeb, C.R. Soccol, M. Naceur, B. Rachid, Int. J. Hydrogen Energy 38 (2013) 2191-2198

[190] C. Varrone, S. Rosa, F. Fiocchetti, B. Giussani, G. Izzo, G. Massini, A. Marone, A. Signorini, A. Wang, Int. J. Hydrogen Energy 38 (2013) 1319-1331

[191] S. Sittijunda, A. Reungsang, Int. J. Hydrogen Energ. 37 (2012) 13789-13796

[192] R. Mangayil, T. Aho, M. Karp, V. Santala, Renew. Energy 75 (2015) 583-589

[193] P.A. Selembo, J.M. Perez, W.A. Loyd, B.E. Logan, Biotechnol. Bioeng. 104 (2009) 1098-1106

[194] L. Castrillón, E. Marañón, Y. Fernández-Nava, P. Orma-echea, G. Quiroga, Bioresour. Technol. 136 (2013) 73–77

[195] L. Castrillón, Y. Fernández-Nava, P. Ormaechea, E. Mar-añón, Bioresour. Technol. 127 (2013) 312–317

[196] L.D. Nghiem, T.T. Nguyen, P. Manassa, S.K. Fitzgerald, M. Dawson, S. Vierboom, Int. Biodeter. Biodegr. 95 (2014) 160-166

[197] K. Panpong, G. Srisuwan, S. O-Thong, P. Kongjan, Energ. Proc. 52 (2014) 328–336

[198] B. Danilović, D. Savić, V. Veljkovićin Proceedings of 16th International Symposium on Thermal Science and Eng-ineering of Serbia, Sokobanja, Serbia, October 22-25, 2013, pp. 199-206

[199] T.A. Ngo, M.S. Kim, S.J. Sim, Int. J. Hydrogen Energy 36 (2011) 5836-5842

[200] L. Poleto, P. Souza, F.E. Magrini, L.L. Beal, A.P.R. Tor-res, M.P. de Sousa, J.P. Laurino, S. Paesi, Int. J. Hydro-gen Energy 41 (2016) 4374-4381

[201] F. Liu, B. Fang, Biotechnol. J. 2 (2007) 374-380

[202] Y. Lo, X. Chen, C. Huang, Y. Yuan, J. Chang, Int. J. Hydrogen Energy 38 (2013) 15815-15822

[203] G. Lovato, I.S. Moncayo Bravo, S.M. Ratusznei, J.A.D. Rodrigues, M. Zaiat, J. Environ. Manage. 154 (2015) 128- -137

[204] F. Yang, M.A. Hanna, R. Sun, Value-added uses for crude glycerol – a byproduct of biodiesel production, Bio-technol. Biofuel. 5(13) (2012) 1-10

[205] M. Dasari, Feedstuffs 79 (2007)1-3

[206] S. Cerrate, F. Yan, Z. Wang, C. Coto, P. Sacakli, P.W. Waldroup, Int. J. Poult. Sci. 5 (2006) 1001-1007


488

[207] P.J. Lammers, B.J. Kerr, T.E. Weber, W.A. III Dozier, M.T. Kidd, K. Bregendahl, J. Anim. Sci. 86 (2008) 602- -608

[208] B.J. Kerr, W.A. Dozier, K. Bregendahl, in Proceedings of the 23rd Annual Carolina Swine Nutrition Conference Raleigh, NC, 2007, pp. 6-18

[209] P.J. Lammers, B.J. Kerr, M.S. Honeyman, K. Stalder, W.A. III Dozier, T.E. Weber, M.T. Kidd, K. Bregendahl, Poult. Sci. 87 (2008) 104-107

[210] M.C. Shields, E.V. Heugten, X. Lin X, J. Odle, C.S. Stark, J. Anim. Sci. 89 (2011) 2145-2153

[211] S.J. Schieck, B.J. Kerr, S.K. Baidoo, G.C. Shurson, L.J. Johnston, J. Anim. Sci. 88 (2010) 2648-2656

[212] L. McLea, M.E.E. Ball, D. Kilpatrick, C. Elliott, Br. Poult. Sci. 52 (2011) 368-375

[213] C. Kijora, R.D. Kupsch, Fett/Lipid 98 (1996) 240-245

[214] S.J. Schieck, G.C. Shurson, B.J. Kerr, L.J. Johnston, Evaluation of glycerol, a biodiesel coproduct, in grow-finish pig diets to support growth and pork quality, J. Anim. Sci. 88 (2010) 3927-3935

[215] P.J. Gunn, M.K. Neary, R.P. Lemenager, S.L. Lake, J. Anim. Sci. 88 (2010) 1771-1776

[216] K.R. Hampy, D.W. Kellogg, K.P. Coffey, E.B. Kegley, J.D. Caldwell, M.S. Lee, M.S. Akins, J.L. Reynolds, J.C. Moore, K.D. Southern, AAES Res. Ser. 55 (2008) 63-64

[217] S.S. Donkin, Rev. Bras. Zootec. 37 (2008) 280-286

[218] S.S. Donkin, S.L. Koser, H.M. White, P.H. Doane, M.J. Cecava, J. Dairy Sci. 92 (2009) 5111-5119

[219] V.B. Veljković, I.B. Banković-Ilić, O.S. Stamenković, Y.-T. Hung, in Handbook of Advanced Industrial and Haz-ardous Wastes Management, L.K. Wang, M.-H.S. Wang, N.K. Shammas, Y.-T. Hung, J.P. Chen, Eds., CRC Press Taylor and Francis Group, Boca Raton, FL, 2016

[220] S.K. Lo, B.S. Baharin, C.P. Tan, O.M. Lai, Food Bio-technol. 18 (2004) 265-278

[221] C. Echim, R. Verhe, W. De Greyt, C. Stevens, Energ. Environ. Sci. 2 (2009) 1131-1141

[222] F.J. Luxem, B.K. Mirous, in Biocatalysis and Bioenergy, C.T. Hou, J.F. Shaw, Eds., John Wiley & Sons, Inc., Hoboken, NJ, 2008, pp. 115-129

[223] P. Felizardo, J. Machado, D. Vergueiro, M.J.N. Correia, J.P. Gomes, J.M. Bordado, Fuel Process. Technol. 92 (2011) 1225–1229

[224] [P. Chetpattananondh, C, Tongurai, Songklanakarin, J. Sci. Technol. 30 (2008) 515-521

[225] D.A. Echeverri, F. Cardeno, L.A. Rios, J. Am. Oil Chem. Soc. 88 (2011) 551–557

[226] V.L. Gole, P.R. Gogate, Fuel Process. Technol. 118 (2014) 110-116

[227] Y. Wang, S. Ma, L. Wang, S. Tang, W.W. Riley, M.J.T. Reane, Eur. J. Lipid Sci. Technol. 114 (2012) 315–324

[228] S.K. Lo, B.S. Baharin, C.P. Tan, O.M. Lai, Food Sci. Tech. Int. 10 (2004) 149–156

[229] S.K. Lo, B.S. Baharin, C.P. Tan, O.M. Lai, Eur. J. Lipid Sci. Technol. 106 (2004) 218–224

[230] K.G. Fiametti, M.M. Sychoski, A. Cesaro, A. Furigo Jr., L.C. Bretanha, C.M.P. Pereira, H. Treichel, D. Oliveira, Ultrason. Sonochem. 18 (2011) 981–987

[231] K.G. Fiametti, M.K. Ustra, D. Oliveira, M.L. Corazza, A. Furigo Jr., J.V. Oliveira, Ultrason. Sonochem. 19 (2012) 440–451

[232] W. Huang, S. Tang, H. Zhao, S. Tian, Ind. Eng. Chem. Res. 52 (2013) 11943-11947

[233] L. Gu, W. Huang, S. Tang, S. Tian, X. Zhang, Chem. Eng. J. 259 (2015) 647-652

[234] H. Zhao, C. Zhang, T.D. Crittle, J. Mol. Catal., B: Enzym. 85-86 (2013) 243-247

[235] Z.-L. Huang, B.-P. Wu, Q. Wen, T.-X. Yang, Z. Yang, J. Chem. Technol. Biotechnol. 89 (2014) 1975-1981

[236] A.P. Abbott, P.M. Cullis, M.J. Gibson, R.C. Harris, E. Raven, Green Chem. 9 (2007) 868-872

[237] M. Hayyan, F.S. Mjalli, M.A. Hashim, I.M. Al Nashef, Fuel Process. Technol. 91 (2010) 116-120

[238] K. Shahbaz, F.S. Mjalli, M.A. Hashim, I.M. Al Nashef, Energ. Fuel 25 (2011) 2671-2678

[239] K. Shahbaz, F.S. Mjalli, M.A. Hashim, I.M. Al Nashef, Sep. Purif. Technol. 81 (2011) 216-222

[240] D.M. Marinković, M.V. Stanković, A.V. Veličković, J.M. Avramović, M.R. Miladinović, O.S. Stamenković, V.B. Veljković, D.M. Jovanović, Renew. Sust. Energ. Rev. 56 (2016) 1387–1408

[241] Ž. Kesić, I. Lukić, M. Zdujić, L. Mojović, D. Skala, Chem. Ind. Chem. Eng. Q. 22 (2016)391-408

[242] M. Kouzu, T. Kasuno, M. Tajika, S. Yamanaka, J. Hidaka, Appl. Catal., A. 334 (2008) 357-365

[243] M. Kouzu, M. Tsunomori, S. Yamanaka, J. Hidaka, Adv. Powder Technol. 21 (2010) 488-494

[244] M. Kouzu, J. Hidaka, K. Wakabayashi, M. Tsunomori, Appl. Catal., A 390 (2010) 11-18

[245] A. Esipovich, S. Danov, A. Belousov, A. Rogozhin, J. Mol. Catal., A: Chem. 395 (2014) 225–233

[246] I. Reyero, G. Arzamendi, L.M. Gandia, Chem. Eng. Res. Des. 92 (2014) 1519-1530

[247] L. Leon-Reina, A. Cabeza, J. Rius, P. Maireles-Torres, A.C. Alba-Rubio, M.L. Granados, J Catal. 300 (2013) 30- -36

[248] I. Lukić, Ž. Kesić, M. Zdujić, D. Skala, Fuel 165 (2016) 159–165

[249] N. Pasupulety, K. Gunda, Y. Liu, G.L. Rempel, F.T.T. Ng, Appl. Catal., A 452 (2013) 189-202

[250] M. Sánchez-Cantú, F.M. Reyes-Cruz, E. Rubio-Rosas, L.M. Pérez-Díaz, E. Ramírez, J.S. Valente, Fuel 138 (2014) 126–133

[251] A.R. Gupta, S.V. Yadav, V.K. Rathod, Fuel 158 (2015) 800–806

[252] C. Li, Z. Huang, Y. He, D. Zhou, C. Du, S. Zhang, J. Chen, Adv. Mater. Res. 666 (2013) 193-102

[253] D. Bradley, E. Levin, C. Rodriguez, P.G. Williard, A. Stanton, A.M. Socha, Fuel Process. Technol. 146 (2016) 70–75


489

[254] E. Wang, J. Shen, Y. Wang, S. Tang, S. Emami, M.J.T. Reaney, Fuel 160 (2015) 621–628

[255] D.M. Reinoso, D.E. Damiani, G.M. Tonetto, Appl. Catal., B: Environ. 144 (2014) 308–316

[256] F.daS. Lisboa, F.R. da Silva, C.S. Cordeiro, L.P. Ramos, F. Wypych, J. Braz. Chem. Soc. 25 (2014) 1592–1600

[257] X. Zhu, H. Liu, D. Skala, Chem. Ind. Chem. Eng. Q. 22 (2016) 431-443.

SANDRA S. KONSTANTINOVIĆ BOJANA R. DANILOVIĆ

JOVAN T. ĆIRIĆ SLAVICA B. ILIĆ

DRAGIŠA S. SAVIĆ VLADA B. VELJKOVIĆ

Univerzitet u Nišu, Tehnološki fakultet u Leskovcu, Bulevar oslobođenja 124,

16000 Leskovac, Srbija

PREGLEDNI RAD

VALORIZACIJA SIROVOG GLICEROLA IZ PROIZVODNJE BIODIZELA

Povećana proizvodnja biodizela kao alternativnog goriva podrazumeva istovremeni rast proizvodnje sirovog glicerola kao njenog glavnog sporednog proizvoda. Stoga, izvodlјivost i održivost proizvodnje biodizela zahteva efikasno korišćenje sirovog glicerola. Ovaj pregledni rad opisuje različite upotrebe sirovog glicerola kao potencijalnog zelenog rastvarača za hemijske reakcije, polazne sirovine za hemijske i biohemijske konverzije u hemikalije sa dodanom vrednošću, supstrata ili ko-supstrata u mikrobnim fermentacijama za sintezu vrednih hemikalija i proizvodnji biogasa i biovodonika i dodatak stočnoj hrani. Posebna pažnja je posvećena različitim upotrebama sirovog glicerola u proizvodnji biodizela.

Ključne reči: biodizel, sirovi glicerol, biokonverzija, biogas, biovodonik, rastvarač

valorization of crude glycerol from biodiesel …

Documents