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Table of Contents

1Chapter 1

1O-Hydroxy benzoic acid and related compounds

1Introduction

15Chapter 2

15Process selection and description of flow sheet

15 Flow Sheet Selection

19Flow Sheet Description

21Chapter 3

21Material balance

24Chapter 4

24Energy Balance

30Chapter 5

30Design of Equipments

30 Design of CFSTR

42Flash Tank Design

52Design of Distillation Column

72Design of autoclave

96Design of Centrifuge

102Design of dryer

119Sublimation

127Chapter 6

127Instrumentation and process control

128Control scheme of distiallation column

131Chapter 7

131Basic principles of Hazop study

135Chapter 8

Potential Health Effect 121140Chapter 9

140Cost Estimation

141REFERENCES

Chapter No.1

O-HYDROXY BENZOIC ACID AND RELATED COMPOUNDSChapter 1O-HYDROXY BENZOIC ACID AND RELATED COMPOUNDSIntroduction

Compounds of the general structure

Where the hydroxy is ortho [69-72- 7], meta [99-06.9], or para [99-96-7] are commonly known as the monohydroxybenzoic acids. Of the three acids, the ortho isomer, salicylic acid, is by far the most important. The main importance of salicylic acid and its derivatives lies in their antipyretic and analgesic actions (see Analgesics, antipyretics, and anti-inflammatory agents). Natural salicylic acid, which exists mainly as the glucosides of methyl salicylate [119-38-6] and salicyl alcohol [90-01-7], is widely distributed in the roots, bark, leaves, and fruits of various plants and trees. As such, their use as preparations for ancient remedies is probably as old as herbal therapy. Hippocrates recommended the juice of poplar trees as treatment for eye diseases. Salicyl alcohol glycosides (salicin) [138-52-3) occur in Populous halsamifera (poplar) and Snlix helix (willow) trees. Methyl salicylate glucosides occur in Betula (birch) and Togas (beech) trees. A more familiar source of methyl salicylate is the leaves of Gaultheria procumbens (wintergreen) (see also hydroxy carboxylic acids).Free salicylic acid occurs in nature only in very small amounts. It has been isolated from the roots, plants, blossoms, and fruit of Spirctea ulmaria, from which its original name, acidium spiricum, was derived. Salicylic acid as well as salicyfiltes occur in tulips, hyacinths, and violets, and in common fruits, eg, oranges, apples, plums, and grapes, which explains the presence of salicylic acid in most wines (1 2).

Physical Properties. Salicylic acid is obtained as white crystals, fine needles, or fluffy white crystalline powder. It is stable in air and may discolor gradually in sunlight. The synthetic form is white and odorless. When prepared from natural methyl salicylate, it may have a lightly yellow or pink tint and a faint, wintergreenlike odor. Hydroxybenzoic acid crystallizes from water in the form of white needles and from alcohol as platelets or rhombic prisms. p-Hydroxybenzoic acid crystallizes in the form of monoclinic prisms. Various physical properties of hydroxybenzoic acids are listed in Tables 14.

Table 1Physical Properties of Hydroxybenzoic Acids

PropertyValue (Isomer)

OrthoMetaPara

Molecular weight138.12138.12138.12

Melting point, oC15920L5-203214.5 215.6

Boiling point, oC211 swub

Density

1.497

Refractive Index1.565

Flash point (Tag closed-cup), oC1.57

Ka (acid dissociation) at 25oC1.05 8.3(10-52.6(10-5

Heat of combustion, mJ/molo3.0263.0383.035

Heat of sublimation, kJ/molo95.14116.1

To convert J to cal, divide by 4.184.

Table 2Solubilities of the Hydroxybenzoic Acids in Water, Wt %

Temperature, oCIsomer

OrthoMetaPara

00.120.350.25

100.140.550.50

200.200.850.81

300.301.350.81

400.422.01.23

500.643.02.3

600.904.34.2

701.377.07.0

802.2111.012.0

Figure 1. Reactions of the carboxyl group of salicylic acid.

Reactions. The hydroxybenzoic acids have both the hydroxyl and the carboxyl moieties and, as such, participate in chemical reactions characteristic of each. In addition, they can undergo electrophilic ring substitution. Reactions characteristic of the carboxyl group include decarboxylation; reduction to alcohols; and the formation of salts, acyl halides, amides, and esters. Reactions characteristic of the phenolic hydroxyl group include the formation of salts, esters, and ethers. Reactions involving form sodium salicylate. However, if salicylic acid dissolves in the presence of alkali metals or caustic alkalies, e.g., excess sodium hydroxide, the disodium salt forms.

Salicylic acid can be converted to salicyloyl chloride by reaction with thionyl chloride in boiling benzene. However, the formation of acyl halides can be complicated by the presence of the phenolic hydroxyl. For example, the reaction with phosphorus to arid pentachlorides is not restricted to the formation of the acid chloride. Further interaction of the phosphorus halide and the phenolic hydroxyl results in the formation of the phosphoric or phosphorous esters.

The formation of amides can be accomplished by the dehydration of the ammonium salt of salicylic acid. The more common method for amides is the reaction of the ester, acylhalide, or anhydride with an amine or ammonia. Each step is fast and essentially irreversible.

Esterification is frequently carried out by direct reaction of the carboxylic acid with an alcohol in the presence of a small amount of mineral acid, usually concentrated sulfuric or hydrochloric acid. The ester of commercial importance is methyl salicylate. Direct esterification has the advantage of being a single-step synthesis; its disadvantage is the reversibility of the reaction. The equilibrium can be shifted to the right if either raw material is used in large excess, or by selective removal of one of the products. One less frequently employed technique is the transformation of the acid to the acid chloride followed by alcoholysis; each step is essentially irreversible. Another method is the reaction of the alkali salt, eg, sodium salicylate, with an alkyl or an aryl alkyl halide.

Hydroxyl. The hydroxyl group is alkylated readily by the sodium salt and an alkyl halide (Williamson ether synthesis) (see Fig. 2). Normally, only O-alkylation is ob ring substitution includes nitration, sulfonation, halogenation, alkylation, and acylation. The following reactions are illustrated only with salicylic acid; however, these reactions are characteristic of all the bydroxybenzoic acids.

Table 3 Solubilities of the Hydroxybenzoic Acids in Non aqueous Solvents, Wt %

SolventIsomer

OrthoMetaPara

Acetone at 23oC396327285

Benzene at 25 oC0.7750.0100.0035

1-butanol

Ethanol (99 wt %)

n-heptane

Methanol at 15 oC39.8740.3836.22

Carbon tetrachloride at 25 oC0.262

Chloroform (satd in H2O) at 25 oC1.84

Ethanol (abs) at 21 oC34.87

I-propanol at 21 oC27.36

Table 4 Saturated Vapor Pressure (p) of o- and p-Hydroxybenzoic Acids

Temperature,oCo-Hydroxybenzoic acidp, Pabp-Hydroxybenzoic acidp, Pab

9530.9

10048.7

10570.1

110104

115153

120220

1253223.03

1304.59

1356496.94

14010.6

14516.1

15023.9

15534.6

15947.3

B. To convert Pa to mm Hg, divide by 133.3.

Salicylic Acid

Reactions: Carboxyl. Typical decarboxylation by simple heating of a free acid occurs with only a few types of acids. However, decarboxylation of salicylic acid takes place readily because of the presence of the hydroxyl group, which is electron donating (see Fig. 1). Upon slow heating, salicylic acid decomposes to phenol and carbon dioxide; when heated rapidly, it sublimes.

Generally, the carboxyl group is not readily reduced. Lithium aluminum hydride is one of the few reagents that can reduce an acid to an alcohol. The scheme involves the formation of an alkoxide, which is hydrolyzed to the alcohol. Commercially, the alternative to direct reduction involves esterification of the acid followed by reduction of the ester.

Salicylic acid dissolves in aqueous sodium carbonate or ~odium bicarbonate to serve. However, phenolate ions are ambident nucl~ophiles and, as such and under certain conditions, as with the use of alkyl halides, the problem of C- versus O-alkylation can occur. Either reaction can be made essentially exclusive by the proper choice of reaction conditions. For example, polar solvents favor formation of the ether, whereas nonpolar solvents favor ring substitution (see Alkylation).

Figure 2. Reactions of the hydroxyl group of salicylic acid.

Esters of the phenolic hydroxyl are obtained easily by the Schotten-Baumann reaction. The reaction in many cases involves an acid chloride as the acylating agent. However, acylation can also be achieved by reaction with an acid anhydride. The single most important commercial reaction of this type is the acetylation of salicylic acid with acetic anhydride to yield acetylsalicylic acid [50-78-2] (aspirin).

Ring Substitution. In the introduction of a third group into a disnbstituted benzene, the position the group takes depends on the groups present (see Fig. 3). In the case of salicylic acid the hvdroxyl directs ortho and pan and the carboxyl directs meta substitution. It is generally accepted that if both an ortho-para and a meta director are competing for the orientation of a third group, the ortho-para director prevails since, unlike the meta director, it activates the ring. Specifically, the hydroxyl group is electron-donating which, on the basis of resonance considerations, increases the

Figure 3 Ring-substitution reactions of salicylic acid. X = halogen.

Electron density in the S and 5 positions. The electron-withdrawal nature of the car-boxyl group decreases the electron density around the 4 and C positions, which further enhances the electron density of the 3 and 5 positions. As a rule, direct substitution occurs more easily in the less sterically hindered 5 position, but most often small amounts of the 3 substituted and 3,5-disubstituted product also form. High yields of the 3-substituted salicylic acid usually can only be prepared indirectly.

Direct halogenation of salicylic acid is generally carried out in glacial acetic acid. As expected, the main product is the 5-halo-salicylic acid with small quantities of the 3-halo- and 3, 5-dihalosalicylic acids.

Reaction with cold nitric acid results primarily in the formation of 5-nitrosalicylic acid [96-97-9]. However, reaction with fuming nitric acid results in decarboxylation as well as the formation of 2, 4, C-trinitrophenol [88-89-1] (picric acid). Sulfonation with chlorosulfonic acid at 16OoC yields 5-sulfosalicylic acid [56507-30-3]. At higher temperatures (1800 C) and with an excess of chlorosulfonic acid, 3,5-disulfosalicylic acid forms. Sulfonation with liquid sulfur trioxide in tetrachloroethylene leads to a nearly quantitative yield of 5-sulfosalicylic acid (5).

Because salicylic acid contains the deactivating meta-directing carboxyl group, Friedel-Crafts reactions (qv) are generally inhibited. This effect is somewhat offset by the presence of the activating hydroxyl group. Salicylic acid also reacts with isobutyl or t-butyl alcohol in 80 wt % sulfuric acid at 750C to yield 5-t-butylsalicylic acid [16094-31-8]. In the case of isobutyl alcohol, the intermediate carbonium ion rearranges to (CH3)3C+.

Miscellaneous. The Reimer-Tiemann reaction of salicylic acid with chloroform and alkali results in the 3- and 5-formyl derivatives.

If the reaction is carried out with carbon tetrachloride, the corresponding dicarboxylic acids form.

Alkylation involving formaldehyde in the presence of hydrogen chloride is known as chloromethylation. The reagent may be a mixture of formalin and hydrochloric acid, paraformaldehyde and hydrochloric acid, a chloromethyl ether, or a formal. Zinc chloride is commonly employed as a catalyst, although many others can be used. Chloromethylation of salicylic acid yields primarily the 5-ubstituted product.

The reaction of salicylic acid with formaldehyde with catalytic amounts of acid results in the condensation product methylene-5, 5-disalicylic acid [122-25-8].

Salicylic acid, upon reaction with amyl alcohol and sodium, reduces to a ring-opened aliphatic dicarboxylic acid, ie, pimelic acid. The reaction proceeds through the intermediate cyclohexanone-2-carboxylic acid.

During certain substitution reactions, the carboxyl group is often replaced by the entering group. Au example is fuming nitric acid, which results in the formation of trinitrophenol. Another is the bromination of salicylic acid in aqueous solution to yield the tribromophenol derivative.

Salicylic acid couples with diazonium salts in the expected manner. With diazotized aniline, i.e, benzenediazonium chloride, the primary product is 5-phenylazosalicylic acid [314 7-53-3].

The close proximity of the carboxyl and the hydroxyl groups can be used for beterocyclic synthesis, as in the preparation of hydroxyxanthones (6).

USES

Approximately 60% of the salicylic acid produced in the United States is consumed in the manufacture of aspirin: this statistic has remained relatively constant for at least the last ten years. Approximately 10% of the salicylic acid produced is consumed in various applications, eg, foundry and phenolic resins, rubber retarders, dyestuffs, and other miscellaneous uses. The remaining 30% is used in the manufacture of its salts and esters for a variety of applications.

There are many foundry-resin systems in use. Salicylic acid is a small component only in the Shell process. It is used as a cross-linking agent in the phenolfornrnldehyde resin used as a sand core and mold binder and imparts higher tensile strength. More recent developments have demonstrated that higher concentrations of salicylic acid than previously used further improve cold and hot tensile strength and reduce cure and machine processing time (18). The continuing interest in energy and environmental considerations has led to the low energy processes, which typically do not use salicylic acid. Their growth has been somewhat limited because of the large capital expenditures required; however, the economics is expected to shift as the cost of energy increases. Therefore, a zero or small negative growth for salicylic acid is predicted in foundry-resin applications. Salicylic acid has also been used in other phenolic resin applications, ie, binders for grinding wheels, fiber glass, and brake linings (qv) (see Phenolic resins).

Chapter No. 2

Process Selection and Description

Of Flow Sheet

Chapter 2 Process Selection and Description of Flow SheetFIRST SYNTHESIS

Salicylic acid was first prepared by R.Piria by the fusion of salicyaldehide with the potassium hydroxide. In 1859, a synthesis method of preparing salicylic acid was discovered by treating the phenol with carbon dioxide in presence of metallic sodium. However the only commercial method of manufacturing salicylic acid until 1874 was the sponification of the methyl salicylate obtained from the leaves of the winter green or Bark of the birch.

KOLB PROCESS The first technically suitable process was introduced in 1874 by Kolb. It involves the reaction of the dry sodium phenolate with carbon dioxide under pressure and high temperature (180-200) 0C. The drawback of the process was that the yield was not more than 50% and the separation of byproducts which were in large quantity was difficult. Salicylic acid is manufactured by the reaction of phenol with caustic soda and the subsequent treatment of the sodium phenolate formed with carbon dioxide and acidifying the resultant product with the sulfuric acid .Phenol and caustic soda are charged in equomolar proportions to a mixer. The resulting solution is heated to a temperature of 1300C and further evaporated to dryness in a stirred autoclave or a heated ball mill. Dry carbon dioxide gas is absorbed and the crude product from the autoclave is dissolved in the equal amount of water and filtered. The filtrate is precipitated and dried.To obtain pure product, the crude sodium salicylate solution decolorized with the activated carbon containing the zinc dust and filtered. The clarified filtrate is acidified with the excess of sulfuric acid to precipitate the salicylic acid which is centrifuged and dried to give the high grade salicylic acid.SCHMITT

Schmitt introduced the new lower temperature ranges from 120-1400C which significantly increased the yield of the process. The reaction of the carbon dioxide on the phenol forms an intermediate phenyl carbonate which rearranges itself to give o-sodium salicylate. The Kolb-Schmitt synthesis method is still the only industrial process in use in different modifications.

More, et al

More introduced a new step process for the carbonation of dry sodium phenolate. The reaction is carried out in a stirred reactor. Carbon dioxide is passed at a temperature of 1300C until 25% of the stiochiometeric amount of the carbon dioxide is absorbed. In step 11 the temperature of the raised to 2100Cand the remaining carbon dioxide is introduced into the reactor for 5 hr. the yield of the process was 80 to 82% and for time duration the yield was 76%.

Stopp,et al

The carbonation of the sodium salicylate is carried out in a fluidized bed reactor at 1400C and pressure of 6bar until half of the phenolate is converted to salicylate. The resulting reaction mixture can be further carbonated in a subsequent stage at a temperature of 2100Cand a pressure of 10 bars. The subsequent stage may be fluidized bed reactor or stirred vessel. The yield was 85%.

Barkley et al

The sodium phenolate was cooled to 900C. The carbon dioxide was passed into the autoclave; the temperature was maintained at 1200C until the carbon dioxide adsorption was come to an end. The temperature was raised to induced rearrangement of the intermediate product. The temperature was kept 160-1700Cunder a carbon dioxide pressure 5 bar.

Jenson, et at

An improved method for the production of salicylic acid from phenol with high degree of conversion and with a significant reduction in the by products was modified by Jenson and his colleagues. The process comprises of reaction of sodium phenolate with the carbon dioxide indirect single step at a temperature above 1650C.In the Kolb carboxylation, the reaction between sodium phenolate with carbon dioxide could advantageously takes place in single step well the temperature at which sodium phenyl carbonate is ordinarily converted to sodium salicylate. More particularly instead of introducing carbon dioxide below 1500C to produce sodium phenyl carbonate which is then in second step is converted to sodium salicylate being held above 1650C.

Our contributions

The reaction of sodium phenolate and carbon dioxide is slowest reaction in whole plant so every scientist focused his attention for finding the set of thermodynamics properties that would give maximum conversion and minimum byproduct as well as cost factor would remain under considerations along with the safe operation.

I was personally interested in finding such data to improve the performance of the plant used for manufacturing of salicylic acid. The autoclave present in our department was quite unsuitable for the reaction of carbon dioxide with sodium phenolate at different temperature and pressure. But fortunately the circumstances for carrying the experiments in determination the kinetic data I was given opportunity in the chemistry department lab. I performed number of experiment at different temperature and different speed of agitation in simple conical flask.

After the result of experiment I decided batch reaction was not economical.

So I made changes in the flow diagram available in literature.

FLOW SHEET DESCRIPTION

Preparation of Sodium Phenolate

Phenol is approximately 54% is reacted with 50%caustic soda in a CFSTR. The reaction temperature is 95-990C. The reaction is exothermic; heat evolved from the reaction is utilized raising the temperature of the product to 990C. Slightly excess amount of phenol is fed into the reactor instead of caustic soda because of material of construction is greatly influenced by the strong alkali. The reaction temperature is so high that lump formation of sodium phenolate is out of question. Preparation of Sodium salicylate The product of the first reactor is fed into the flash tank where separation of water is carries out and then for any batch valve is opened and autoclave is charged and valve of the carbon dioxide is opened at the pressure of 8bars for the time of 5-6hrs. The reaction temperature is raised to about 1250C.

Almost 70% conversion is achieved; carbon dioxide released is recycled back and then utilized. Now 600Kg of phenol is added so that some sort of azeotrope is formed and when steam is provided, this mixture is vaporized leaving the thick slurry of sodium salicylate. The evaporated material is condensed and sent into the continuous distillation column where separation of phenol and sodium phenate is carried out.

Acidification tank

The product of the autoclave is thick slurry and it is diluted with the water in the dilution tank. The solution, so obtained is charged into the acidification tank where 40% sulfuric acid is reacted that comes from the storage tank of sulfuric acid. Almost two hr along with agitation gives 100 app. Conversion. In the acidification tank solid salicylic acid as well as sodium sulfate is formed

Purification from water (removal of water)

Removal of water is carried in two steps: in first step centrifuge removes the large amount of water i.e. from 66 to 16 %water content. The waste water is sent to the waste water treatment plant. The solid product that contains salicylic acid and sodium sulfate is sent to the dryer where app. All water content is removed.

Sublimation and crystallization The solid product is charged into the sublimation tank where steam is used as heating medium and vacuum is created with the help of vacuum pump. At reduced pressure the sublimation of salicylic acid is carried out at 760C. The vapors coming from the sublimation tank are injected into crystallizer where condensation of vapors takes place resulting more than 99% pure product.

Chapter No. 3

Material Balance

Chapter 3

Material Balance

Reactor-1

inputoutput

component(Kgmol)Kg%WtKgmolKg%Wt

NaOH10.65625426.2515.643750.1566.240.22902697

H2O66.480561196.6543.9181176.980561385.6550.8575665

phenol11.72161101.8340.438141.22114.684.20910456

Na-Ph00010.5121844.704302

total88.85842724.7310088.856562724.57100

FLASH TANK

inputoutput

component(Kgmol)Kg%WtKgmolKg%Wt

NaOH0.1566.240.2290270.1566.240.45868862

H2O76.980561385.6550.857571.944444352.57277271side stream

Phenol1.22114.684.2091051.07617101.167.43604822

Na-Ph10.5121844.704310.5121889.5324904water-out1350.65

88.856562724.5710013.676611360.4100total2711.05

phenol13.52

Autoclave reactor-2

Addition of CO2 and reaction

inputoutput

component(Kgmol)Kg%WtKgmolKg%Wt

NaOH0.1566.240.3259510.1566.240.36897969

H2O1.944444351.8282491.9444352.06959761

Phenol1.07617101.165.2841621.07617101.165.98172841side stream

Na-Ph10.5121863.623073.15365.421.6065991CO2231

CO212.655428.9385700

Na-Sal007.351183.3569.9730952

1914.41001691.15100

Addition of phenol and separation of azeotrope

inputoutput

component(Kgmol)Kg%WtKgmolKg%Wt

NaOH0.1566.240.2847820.1566.240.50849529

H2O1.9444351.5973351.9444352.85213707

Phenol6.395319601.1627.435820.012341.160.09452797side stream

Na-Ph3.15365.416.676170.0120691.40.11408548phenol600

CO200000Na-Ph364

Na-Sal7.351183.3554.005897.351183.3596.4307542

2191.151001227.15100

Dilution tank

inputoutput

component(Kgmol)Kg%WtKgmolKg%Wt

NaOH0.1566.240.5084950.1566.240.16949843

H2O1.9444352.852137138.29442489.367.617379

Phenol0.012341.160.0945280.012341.160.03150932

Na-Ph0.0120691.40.1140850.0120691.40.03802849side input

CO2000000water2454.3

Na-Sal7.351183.3596.430757.351183.3532.1435847

1227.151003681.45100

Acidification tank

inputoutput

component(Kgmol)Kg%WtKgmolKg%Wt

NaOH0.1566.240.169498000

H2O138.29442489.367.61738168.53063033.5566.0226652

Phenol0.012341.160.0315090.012341.160.02524642

Na-Ph0.0120691.40.0380280.0120691.40.03046982

salicylic acid0007.351014.322.0753867

Na-Sal7.351183.3532.14358000

Na2SO40003.815845541.8511.7929097

side input0

sulfuric acid362.62.450.05332219

water543.94594.71100

4587.95

Centrifuge

inputoutputside stream

component(Kgmol)Kg%WtKgmolKg%WtKgmolKg%Wt

NaOH000000000

H2O168.53063033.5566.0226716.46667296.416.0044493152.06392737.1599.79673

Phenol0.012341.160.0252460.0017020.160.008639380.0106310.03646

Na-Ph0.0120691.40.030470.0034480.40.021598450.00862110.03646

salicylic acid7.351014.322.075397.351014.354.7682622000

Na-Sal000000000

Na2SO43.815845541.8511.792913.799296539.529.13090552.35/1422.350.085681

sulfuric acid2.450.0533220.01251.2250.066145240.01251.2250.044664

4594.711001851.9851002742.725100

Drying unit

inputoutputside stream

component(Kgmol)Kg%WtKgmolKg%WtKgmolKg%Wt

NaOH000000000

H2O16.46667296.416.004450.1644442.960.1900896516.30222293.4499.53023

Phenol0.0017020.160.0086390000.0017020.160.054269

Na-Ph0.0034480.40.0215980.0034480.40.02568779000

salicylic acid7.351014.354.768267.351014.365.137815000

Na-Sal000000000

Na2SO43.8539.529.130913.8539.534.6464076000

sulfuric acid0.01251.2250.0661450000.01251.2250.415501

1851.9851001557.16100294.825100

Sublimation unit and Crystallization

inputoutputside stream

component(Kgmol)Kg%WtKgmolKg%WtKgmolKg%Wt

NaOH000000000

H2O0.1644442.960.190090.0694441.250.123365410.0951.710.345829

Phenol00000000

Na-Ph0.0034480.40.0256880000.40.080896

salicylic acid7.351014.365.137817.333333101299.87663462.30.46515

Na-Sal00000000

Na2SO43.8539.534.64641000539.5109.1081

sulfuric acid00000000

1557.161001013.25100543.91110

Chapter No.4

ENERGY BALANCE

Chapter 4

ENERGY BALANCE FOR THE PROJECT

REACTOR 1 ENERGY BALANE :

HR = Hfp - H fr

= { 10.656*(-326.6) + 10.656(-258.84)}{10.656(-165) +

10.656(-426.99)}

HR= 59.247 KJ

TOTAL HEAT RQUIRED = mCp dT + HR= (1.22*220.53KJ/Kgmol.K * 5)phenol+ (76.98*75*5)water+(10.5*243.17*5) + 0.156*78.62*5 + 59.247 KJ

H= 43099 KJ

ENERGY BALANCE OF AUTOCLAVE:

1 ST STEP : SEPARATION OF WATER

TOTAL HEAT RQUIRED = sensible heat + latent heat

= { 0.156*78*7}NaOH + { 76.98*75*7}water +{1.22*298*17}phenol+{ 10.5*243*7}Na-ph + {1350.65*2551.6}water+ { 13.52/94 *45700 KJ/Kgmol}phenol= 3513130.53 KJ

2nd STEP: ADDITION OF CO2 AND REACTIONHEAT OF REACTION = HR = HFP + HFR

LATENT HEAT REQUIRED = (12.6* 38.65*95)CO2+ 0.156*78*78)NaoH + (1.944*75*18)H2O + (1.07117*220*18)phenol +(10.5*243.17*18)Na-ph

= 99310 KJ

TOTAL HEAT RQUIRED = H = Hl + HR = 0

Hl = HR

Hl = nHfp - nHfr,

nHfr + Hl = nHfp7.35(-393.51* 1000) +7.35(-453*1000) = -7.35* X

X = 859.511 KJ/gmol

5% loss so,

X= 904.74 KJ/gmol

3rd step: addition of phenol and separation of azeotropeSIMPLE VACUUM SEPARATING THE COTENTSENERGY BALANCE OF DILLUTION TANKHeat balance:

137*75*(T-25)= {( 0.156*78*(125-T))NaOH +(1.944*75*(125-T))H2O +(0.01234*220*(125-T))phenol+(7.35*257.76*(125-T))sod.sal +(0.012069*243*(125-T))Na-phenTherefore,

1521+18228.75+339.35+236817+3665.96+256875=T{1027512.168+145.8+2.7148+1894.536+2.93)}

T =62.97 C

ACIDIFICATION TANKHR = nHfp - nHfr{-96909+(9703*44)}*1000= {3.81158*(-1384.5*1000)KJ+

7.35*(-589.5*1000)}-

{(-904*7.35)+(-811*3.69)+0.156*(-426)}*1000

HR = 93480 KJ

This much amount of heat is contained after the reaction in the system.

Now reaction temp. is 20 C

Heat balance: Heat input = Heat out put

{3.69*137.777*5}H2SO4 +{ 30.22*75*5}water+ { 0.156*78*(63-20)}NaOH +{138.2944*75*(63-20)}water + { 0.01234*220*43}phen + {0.0120*69*243.17*(63-20)}Na-phen + {7.35*257.76*43}Na-sal

= 542097.75 KJ

This much amount is contained in the system before reaction occurs.

Now the total amount of heat that must be rejected to keep the system at 20C

= 542097.75 + 93480 = 635575.73

Chapter No. 5

Design of Equipments

Chapter 5 Design of Equipments

REACTOR DESIGN

Reactor selection

I selected the CSTR

Reactor selection criteria

1- Conversion

2- selectivity

3- productivity

4- safety 5- economics

6- availability

7- flexibility

8- compatibility with processing

9- energy utilization

10- feasibility

11- investment operating cost

12- heat exchange and mixing

Kinds of impellers

A rotating impeller in a fluid imparts flow and shear to it, the shear resulting from the flow of one portion of the fluid past another. Limiting cases of flow are in the axial or radial directions so that impellers are classified conveniently according to which of these flows is dominant. By reason of reflections from vessel surfaces and

obstruction by affles and other intemals, however, flow patterns in most cases are mixed. When a close approach to axial flow is particularly desirable, as for suspension of the solids of a slurry, the impeller may be housed in a draft tube; and when radial flow is needed, a shrouded turbine consisting of a rotor and a stator may be employed. Because the performance of a particular shape of impeller

usually cannot be predicted quantitatively, impeller design is largely an exercise of judgment so a considerable variety has been put forth by various manufacturers. A few common types are illustrated on Figure 10.2 and are described as follows:

a. The three-bladed mixing propeller is modelled on the marine propeller but has a pitch selected for maximum turbulence. They are used at relatively high speeds (up to 1800rpm) with low viscosity fluids, up to about 4000cP. Many versions are available: with cutout or perforated blades for shredding and breaking

up lumps, with sawtooth edges as on Figure 10.2(g) for cutting and tearing action, and with other than three blades. The stabilizing ring shown in the illustration sometimes is included to minimize shaft flutter and vibration particularly at low liquid levels.b. The turbine with flat vertical blades extending to the shaft is

suited to the vast majority of mixing duties up to 100,000 CP or so at high pumping capacity. The simple geometry of this design and of the turbines of Figures 10.2(c) and (d) has inspired extensive testing so that prediction of their performance is on a more rational basis than that of any other kind of impeller. c. The horizontal plate to which the impeller blades of this turbine are attached has a stabilizing effect. Backward curved blades may be used for the same reason as for type e.

d. Turbine with blades are inclined 45" (usually). Constructions with two to eight blades are used, six being most common. Combined axial and radial flow are achieved. Especially effective for heat exchange with vessel walls or internal coils.

e. Curved blade turbines effectively disperse fibrous materials without fouling. The swept back blades have a lower starting torque than straight ones, which is important when starting up settled slurries. f. Shrouded turbines consisting of a rotor and a stator ensure a high degree of radial flow and shearing action, and are well adapted to emulsification and dispersion. g. Flat plate impellers with sawtooth edges are suited to emulsification and dispersion. Since the shearing action is localized, baffles are not required. Propellers and turbines also are sometimes

provided with sawtooth edges to improve shear. b. Cage beaters impart a cutting and beating action. Usually they are mounted on the same shaft with a standard propeller. More violent action may be obtained with spined blades. SHAFT

The shaft is vital component of the agitator and frequently limits its mechanical performance. In addition to transmitting torque, the shaft undergoes bending, and if not stiff enough or rigidly supported, it may vibrate badly and cause discomfort to personnel or damage to the equipment. Therefore it must be analyzed for combined torsional and bending stresses, deflection, and critical speed and must be selected to meet the limiting criteria for each. Inadequately in these respects can result in failure of the shaft by overstress, failure of the seal due to excessive shaft bending, or failure of bearings due to wear or impact Torsional and bending stresses calculation

COUPLINGS

Most agitators with long overhung shaft have rigid couplings to connect the agitator shaft and the gear reducer output shaft. The coupling facilities shipment, installation, removal and servicing of the agitators. Although it is an innocuous appearance block of metal, care in its design and fabrication can contribute significantly towards the satisfactory performance of the agitator. The reasons for this become manifest from the requirement that the rigid coupling must meet

1- the coupling must be capable of transmitting the agitator torque

2- the coupling must provide at least as much rigidity as the shaft if the critical speed of the agitator is not to be reduced .

3- the coupling must strong enough to withstand the bending moments imposed upon it by the unbalanced hydraulic and centrifugal force.

4- The coupling must provide good alignment between the shafts being connected

5- Because it must be assembled and disassembled in the field, frequently under inconvenient working condition, the coupling should be relatively easy to take apart and reassembled, and should preferably be self-aligning.

6- The coupling must be capable of taking the thrust due to weight of the agitator.

DRAFT TUBES

A draft tube is a cylindrical housing around and slightly larger in diameter than the impeller. Its height may be little more than the diameter of the impeller or it may extend the full depth of the liquid, depending on the flow pattern that is required. Usually draft tubes are used with axial impellers to direct suction and discharge

Streams. An impeller-draft tube system behaves as an axial flow pump of somewhat low efficiency. Its top to bottom circulation behavior is of particular value in deep tanks for suspension of solids.calculationsSodium hydroxide concentration calculation

NaOH added = 10.656 Kgmol = 426.25 Kg

Water added = 66.48 Kgmol = 1196.65 Kg

Density of NaOH = 1023.7 Kg/M3

Density of water = 997Kg/M3

Total volume of the mixture = V1+V2+dV

whereV1 is partial volume of NaOH

V2 is partial volume of water

dV is change in volume due to solubility

426.25 1196.65

V = ---------- + -----------

1023.7 997

= 1.617 M3

Reactor volume and dimensions calculations 10.656

= -----------

1.617

= 6.59 Kgmol/M3

CA0 = 6.59 gmol/lit

V Xa

-------- = --------- = 342 (from graph)

Fa0 - Ra

V = 0.12233*25*342

= 1.055 M3

V = 2.1 (50% reactor is filled) prove it

:

Basic equation used for calculating reactor volume =

(XA

Vf = FA0 (------------)

- rA

Vf = 1.35 m3 Vf = volume of fluid

V = 2.1 m3 (73% fill) V = volume of vessel

D = 1.2 m D = diameter of vessel

H = 1.2 m H = height of fluid

L= 1.87 m L = length of vessel

Selection and geometry of Impeller

I selected the 300 curved, square pitched turbine blade with the

Following specifications:

S-1 = Da/Dt = 0.33

S-2 = E/Dt = 0.33

S-3 = L/Da = 0.25

S-4 = W/Da = 0.20

S-5 = J/Dt = 0.0833

S-6 = H/Dt = 1.00

No. of baffles = 4 (no clearance, not twisted but adjacent with

wall of the vessel )

Power calculation:

P =Np0(Nr3)(Da)5( = Kt (Nr3)(Da)5( = 0.34 Kw =0.45 hp

= 0.55 (82 % efficiency of the motor)

SHELL THICKNESS

X=

P=Pressure of system

=Radius of shell

S=Stress of material

Ej=Efficiency of joint

Cs=Corrosion rateik

X=

=5.502 mm

HEAD THICKNESS

Pressure at the lease=(gh

=1080.46 9.8 4.43

= 46.907 KPa

Total pressure at base=827.697 KPa

t=

=

=5.84 mm

Power number, N, = Pg,/N3D5p, against Reynolds number, NRe = NDzp/p, for several kinds of impellers: (a) helical shape (Oldshue, 1983); (b) anchor shape (Oldshue, 1983); (c) several shapes: (1) propeller, pitch equalling diameter, without

baffles; (2) propeller, s = d, four baffles; (3) propeller, s = 2d, without baffles; (4) propeller, s =2d, four baffles; (5) turbine impeller, six straight blades, without baffles; (6) turbine impeller, six blades, four baffles; (7) turbine impeller, six curved blades, four baffles; (8) arrowhead turbine, four baffles; (9) turbine impeller,inclined curved blades, four baffles; (10) two-blade paddle, four baffles; (11) turbine impeller, six blades, four baffles; (12) turbine impeller with stator ring; (13) paddle without baffles (data of Miller and Mann); (14) paddle without baffles (data of White and Summerford). All baffles are of width 0.1D [after Rushton, Costich,

and Everett, Chem. Eng. Prog. 46(9), 467 (1950)l.

Specification Sheet

Identification:Item :

CFSTR ( Continuous Flow Stirred Tank Reactor)

Item no:

R-01

No.required:

01

Function:

Formation of sodium phenate from carbolic acid and caustic soda

Operation:

Continuous

Type:

Agitator cylindrical vessel

Design Data:Vessel:

Working Volume1.35 m3

Design Volume1.86 m3

Temperature (Process temperature)99C

Design Temperature109C

Working Pressure1 atm

Design Pressure1.5 atm

Dia of Vessel1.2 m

Height of vessel1.56 m

Working height1.2 m

Height to dia ratio1.3

Type of headTorispherical

Thickness of cylindrical protion

Thickness of bottom head

No. of baffle

Width of Baffle

Height of baffle

Agitator:

Following specifications:

S-1 = Da/Dt = 0.33 S-2 = E/Dt = 0.33 S-3 = L/Da = 0.25 S-4 = W/Da = 0.20 S-5 = J/Dt = 0.0833

S-6 = H/Dt = 1.00

No. of baffles = 4 (no clearance, not twisted but adjacent with wall of the vessel )

Flash tank design

The name originate from the fact that a liquid at a pressure equal to or greater than its bubble point pressure flashes or vaporizes, when the pressure is reduced below its bubble point pressure producing two phase system of liquid and vapor in equilibrium. Basic equations used in flash calculation are

L + V = 1 (material balance equation)

Ki =Yi/Xi

Where Ki equilibrium constant

Yi vapor phase composition

Xi liquid phase composition

From Raults and Henry Law

Yi(iP = XiiPisat

(I = 1 for low to moderate pressure

i = 1 assumption as no data is available in literature

Zi Ki

Yi = ----------------------

1+V(Ki 1)

Zi

Xi = -----------------------

1+V (Ki 1)

for flash calculation necessary condition

P dew < P< Pbubble

Very important equation used in flash calculation

i - idew (i - (idew P P dew

---------------- = ---------------- = --------------------

i bubble -idew (I bubble - (idew Pbubble - Pdew

V - 1

= ---------------

0 - 1

P P dew

= -----------

Pbubble - Pdew

P - P dew

V = ---------------------

P bubble P dew

P bubble = X1P1sat +X2P2sat ..

1

P dew = ------------------ Y1/P1sat+Y2/Psat Throttling Valves Globe Valve is an economical throttling valve. Its heavy duty design provides for long service life. The in-line globe design causes relatively high pressure drops, however this is a desirable valve due to its economy and reliability.

Features 1- Slow closing

2- Prevents water hammer in PVC piping

3- Heavy Duty Construction

4- Long service life

5-efficient throttling with minimum wire drawing or disk or seat erosion

6-available in multiports- short disk travel and fewer turn to operate, saving time and wear on stem and bonnet

Jet Ejector

The two most common ejectors are operated by water or steam. The liquid ejectors are used for creating a modest vacuum or for mixing liquids. The steam ejectors is important in creating and holding a vacuum in a system. Ejectors have no moving parts and operated by the action of one high pressure steam entraining and other vapors (or liquids) at low pressure into a moving stream and thereby a removing them from the process system at an intermediate pressure

Feature

Ejectors have the following features which make them good choice for continuously producing economical vacuum condition.

1- They handle wet, dry or corrosive vapor mixtures

2- They develop any reasonable vacuum needed for industrial operation.

3- All sizes are available to match any small or large capacity requirement.

4- Their efficiencies are reasonable to good.

5- Have no moving parts, hence maintenance low, operation fairly constants when corrosion is not a factor.

6- Quiet operation.

7- Stable operation within design range

8- Installation cost relatively low when compare to mechanical vacuum pumps.

9- Space requirement is small

10- Simple operation.

Types

Ejectors may be single or multi-stage. The extra stages, with or without inter stage condensing of steam; allow the system to operate at lower absolute pressure than a single stage unit. Various combinations of series of jets with no inter-condensing can be connected to jets with inter-condensers or after condensers to obtain various types of the operation and steam economy.

Material of construction

Since the ejector is basically simple in construction, it is available in many material suitable for handling corrosive vapors. Standard materials include cast iron, meehanite, cast steel, and bronze for the body and diffusers depending upon the pressure and temperature rating. The nozzle is usually stainless steel or monel. Other material of construction include porcelain, carbon graphite, impregnated graphite, synthetic resins, glass and special metal of all types

DEMISTERS OR IMPINGENT SEPARATOR

As the descriptive name suggests, the impingement separator allows the particles to be removed to strike some type of surface. This action is better accomplished in pressure system where pressure drop can be taken as a result of turbulence which necessarily accompanies the removal action. Particles removed in stream line flow is less efficient than for turbulent flow and not be effective if the path of travel is not properly well baffled.

There is basically three construction type for impingement separators.

1-wire mesh

2- Plates (curved, flat or special shaped)

3-packed impingement beds

A demister pad resembles a giant brillo pad with the soap. Many process plants have discarded demister pads lying around their scrape heaps. The theory of operation of demister is simple. Vapors and droplets of liquids strike the demister pad with a sustainable velocity. The force of this impingement velocity causes the tiny droplets. The heavier droplets of liquid to coalesce into large droplets.

For knockout drum with a demister pad it apparently must have K-value of at least

0.15 to 0.20 When a demister plugs it increases the pressure drop of the vapor, but pressure drop cannot increase a lot because the demister will break. Demister failure creates two problems.

1- The dislodged section of the demister pad are blown into down stream equipment as into suction of the centrifugal wet gas compressor

2-the failed demister promotes high localized velocities. Vapors blows through the open areas of the vessel. The remaining section of the demister pad impedes vapor flow. The resulting high localized velocities of vapors creates more entrainment than we could have without any demister

Steam trap

A steam trap is self actuating automatic drain valve in a steam distribution system that performs the following functions.

1- Removal of condensate

2-Remove air or other noncondensible gases

3- Prevents or limits the loss of steam

Condensate (water) is formed when steam condenses to release latent heat. Some heat is released in the distribution system in the form of unavoidable losses. Most of the heat is utilized in the process equipment. Once steam has condensed, the hot condensate must be removed immediately as it hinders effective heat transfer from the incoming steam. By selectively purging a steam system of its condensate and noncondensible, steam trap helps maintain high heat transfer coefficient in equipment without losing live steam

In the recent years user interest in steam trap has closely paralleled the increase in energy cost. High fuel cost associated with the malfunctioning trap cannot be ignored. Spiraling cost have highlighted the need for optimum steam trap selection and application. Experience indicates that improper selection and application are the most frequent cause of the trap failure and steam loss. The installation or the replacement of steam trap has a pay back period of as little as three to six months.

Classification of steam trap

There are three basic type of steam traps using different physical principle to distinguish between steam and condensate.

Thermostatic steam trap

These traps are actuated by the temperature sensitive which operate on the basis that the steam is hotter than condensate, air, and other noncondesibles. There are three types of thermostatic traps.

1- Liquid expansion

2- Balanced pressure

3- Bimetallic

Mechanical steam trap

These traps operate on the difference of density between steam and condensate. The two important type of mechanical steam traps are

1- ball float

2- bucket

Thermodynamic steam trap

These traps are operates on the facts that flash steam is produced when pressure is reduced on the hot condensate. The release of flash steam causes the discharge to close. There are the following further types.

1- Disk type

2- Piston type

3- Lever type FLASH CALCULATION

datafluid composision

temperature 100namecomposition

v.p.of waterKPa101.33water0.87

v.p.of phenol Kpa3.51phenol0.0137

v.p.of Na-PheKPa2.07Na-Phe0.1182

Pbubble Kpa88.45

Pdew Kpa14.36

vaporliquid

0.8563910.143609

PRESURE KpacomponentK-valuescompositioncomp. Yi Xi

25water4.0530.9755290.02206930.97860.028531

phenol0.14040.007290.0519240.0070890.061549

Na-Phe0.08280.01396880.8710020.0143610.9099

1.0284420.94511

Total mole for 25-ton per day = 88.85656*25 = 2221.4 Kgmol

Total moles in tank = 318.995 Kgmol

Total weight = 318.995(0.9*116+0.061*94+0.02818)

= 35293.41 Kg

Weight required for 1.5-batch of autoclave = 35293.41/4 = 8823.35 Kg

Average density = 0.90*1258+0.061*1023+0.028*994

= 1222.25 Kg/m3

Filled volume = 7.2174 m3 % fill = 45 %

total volume = 16 m3

L = 5m , D = 2mSome more specifications

Height of liquid =

Height of inlet pipe =

Height of demister pad =

Thickness of demister pad =

Material of demister pod =

Height of outlet =

Steam pressure =

DESIGN OF DISTILLATION COLUMNThe detailed process design of the carbolic acid column is given below. The pictorial Representation of the column is given in fig. The feed to the column is a mixture of carbolic acid and sodium phenolate. The compositions of the components are given below. The top and bottom product, both are the required products used in reactor one and in autoclave (second reactor).

I. Thermodynamics: The primary requirement while designing mass transfer contact equipment is the

Thermodynamic equilibrium data. The data required is in the Vapor-Liquid Equilibrium

(VLE) data for the carbolic acid and sodium phenolate system. The X-Y curve is shown in the fig. To

Develop the VLE data, a model was used.

yi pt = i xi Pi sat --------------------------(1)

Where,

yi = mole fraction of component i in vapor.

pt = total system pressure.

i = activity coefficient of component i in liquid.

xi = mole fraction of component i in liquid.

Pi sat = saturation vapor pressure of component i.

The equilibrium vapor pressure was evaluated using correlations given in literature. The correlation was based on the critical properties of the components. The two components carbolic acid and sodium phenolate form a highly non-ideal system. To accommodate this nonideality, an activity coefficient term was used for the liquid phase. The activity coefficient was evaluated using the UNIFAC model. Since the evaluation of the VLEdata is highly iterative, an algorithm was developed which was solved using a computer program. The gas phase was assumed to be ideal. This is a valid assumption since the column is at 1 atmosphere pressure (760 mm Hg. abs.). The boiling points of the two components require the column to be operated at 1 atmosphere. The operating pressure was chosen to be 760 mm Hg (abs).

The following questions must be answered before going into detailed design of the distillation column

1- what column is selected packed or tray column ?

Answer

Tray column would be better choice in situation facing due to the following reasons

1- stage efficiency can be determined experimentally in packed column because

=f(type and sizing of packing, fluid rates, fluid properties, column diameter, operating temperature and pressure, extent of liquid dispersion)

Where as a number of correlations are available for tray column efficiency discussed by the famous authors. Coulson and Richardson, Ludwig, Perry, Peter and Timmerhaus, conceptual design of distillation column and more..

2-tray column can be designed over a wide range without flooding

3-total dry weight of the tray column is less than the packed column

4-design information for tray column id readily available as compared to packed column. This made path of working easy for me when I decided tray column

5-if chances of foam formation are more then packed column would be given preference, but in situation facing me no foam formation (surface tension at different temperature and pressure would dictate foam formation criteria)

6- Thermal expansion chances can be easily handled with tray column instead of packed column.

7- Equilibrium Data for large compounds as well as my compound are available in literature and this data is more reliable for tray column instead of packed column

What type of tray is selected sieve tray, bubble cap, or valve tray ?

Answer

I decided sieve tray because of the following reasons

1- Manufacturing cost is low

2-operating cost is low

3-simple to construct

4-minmum entrainment as compare to bubble cap and valve tray

5-less pressure drop as compare to other

6-most commonly used

Glossary of notations used:

F = molar flow rate of Feed, gm

D = molar flow rate of Distillate, gmol/hr.

W = molar flow rate of Residue, gmol/hr.

xF = mole fraction of phenol in liquid/Feed.

yD = mole fraction of phenol in Distillate.

xW = mole fraction of phenol in Residue.

MF = Average Molecular weight of Feed, g/gmol

MD = Average Molecular weight of Distillate, g/gmol

MW = Average Molecular weight of Residue, g/mol

RRm = Minimum Reflux ratio

RR = Actual Reflux ratio

LR = Molar flow rate of Liquid in the Enriching Section, gmol/hr.

VR = Molar flow rate of Vapor in the Enriching Section, gmol/hr.LS = Molar flow rate of Liquid in Stripping Section, gmol/hr.

Vs = Molar flow rate of Vapor in Stripping Section, gmol/hr. q = Thermal condition of Feed l = Density of Liquid, kg/m3.

g = Density of Vapor, kg/m3.

ql = Volumetric flow rate of Liquid, m3/s

qv = Volumetric flow rate of Vapor, m3/s

(l = Viscosity of Liquid, cP.

Tl = Temperature of Liquid, 0K.

Tv = Temperature of Vapor, 0K.

II. Preliminary calculations:

Feed = 9915 gmol/h

xF = 0.67, MF = 101.16g/gmol.

D = 6783.89gmol/hr, xD = 0.97, MD = 94.66g/gmol.

W=3131.1gmol/hr, xW = 0.02, MW =115.56g/mol.

Basis: 1 Hour Operation.

From the graph

Rm = 1.5

Let, R= 2.1 *Rm (from trial this value is estimated )

RR= 1.52.0= 3.2

Number of Ideal trays = 17

Number of Ideal trays in Enriching Section = 8

Number of Ideal trays in Stripping Section = 9

Now, we know that,

RR = R/ D => R =RRD

i.e., R= 3.2*6783.89 = 21705gmol/h

L= Liquid flow rate on the Top tray = 21705gmol/h

VR= L + D

= (R+1)*D = 4.2*6783.89mol/hr = 28488.6gmol/h

VR = Gas flow rate in the Enriching Section = 28488.6gmol/h

Since feed is Liquid, entering at bubble point,

q= (HV-HF) / (HV-HL) = 1

Now,

Slope of q-line = q/ (q-1) = 1/ (1-1) = 1/0 = .

Now we know that,

LS = F + LR

LS = 9915+21705.6=31619.6 gmol/h

Therefore, liquid flow rate in the Stripping Section = 31619.6 gmol/h

Also, we know that,

VS = [(q-1) F] + VR

VS = [(1-1) F] + VR

VS = VR = = 28488.6gmol/h

Therefore, the flow rate of Vapor in the Stripping Section = = 28488.6gmol/h

IV. Design Specification:

Tray Hydraulics

The design of a sieve plate tower is described below. The equations and correlations are borrowed from the 6th and 7th editions of Perrys Chemical Engineers Handbook, plant design and economics by Peter and Timmerhaurse, ludwick, unit operation of chemical engineering by McCabe and Smith, Coulson and Richardsons book, separation techniques by C.G. King The procedure for the evaluation of the tray parameters is iterative in nature. Several iterations were performed to optimize the design.

The final iteration is presented here.

1. Tray Spacing, (ts):

Let ts = 457mm (18in).

2. Hole Diameter, (dh): Let dh = 5 mm.

3. Hole Pitch (lp):

Let lp = 3 dh

i.e., lp = 35 = 15 mm.

4. Tray thickness (tT):

Let tT = 0.6 dh

i.e., tT = 0.65 = 3 mm.

5. Ratio of hole area to perforated area (Ah/Ap):

Refer fig 6.3Now, for a triangular pitch, we know that

Ratio of hole area to perforated area (Ah/Ap) = (/4dh2)/ [(3/4) lp2]

i.e., (Ah/Ap) = 0.90 (dh/lp)2

i.e., (Ah/Ap) = 0.90 (5/15)2

i.e., (Ah/Ap) = 0.1

Thus, (Ah/Ap) = 0.1

6. Plate Diameter (Dc):

The plate diameter is calculated based on the flooding considerations

L/G {( g/ ( l}0.5 = 0.11

Now for,

L/G {( g/ ( l}0.5 = 0.11 and for a tray spacing of 457 mm.

We have from the flooding curve, ---------- (fig.18.10, page 18.7, 6th edition Perry.)

(Plant design and economics by Peter and Timmerhaus)

Flooding parameter, Csb, flood = 0.07 m/s.

Now, Unf = Csb, flood (/ 20) .0.2 [(( l - ( g) / ( g] 0.5---- {eqn. 18.2, page 18.6,

6th edition Perry.}

(Plant design and economics by Peter and Timmerhaus)

Where,

Unf = gas velocity through the net area at flood, m/s (ft/s)

Csb, flood = capacity parameter, m/s (ft/s, as in fig.18.10)

= liquid surface tension, mN/m (dyne/cm.)

( l = liquid density, kg/m3 (lb/ft3)

( g = gas density, kg/m3 (lb/ft3)

Now, we have,

= 28.57 dyne/cm.

l = 1023 kg/m3.

g = 2.52 kg/m3.

Therefore,

Unf = 0.07 (28.57/20)0.02 *[987-2.52)/ 2.52]0.5

i.e., Unf = 4.87 ft/s = 1.49 m/s.

Let Actual velocity, Un= 0.8Unf

i.e., Un = 1.19 m/s

Now, volumetric flow rate of Vapor

qo = 28488.6*94.5 / (36002.52*1000) = 0.3 m3/s.

Net area available for gas flow (An)

Net area = (Column cross sectional area) - (Down comer area.)

An = Ac - Ad

Thus, Net Active area, An = qo/ Un = 0.3/1.119 = 0.252 m2.

Let Lw / Dc = 0.75 Where, Lw = weir length, m

Dc = Column diameter, m

, c = 2sin-1(Lw / Dc) = 2sin-1 (0.75) = 97.180

Ac =(3.14/4) Dc2= 0.7854Dc2 , m2And, c = angle Ad = [(/4) Dc2 (c /3600)] - [(Lw/2) (Dc/2) cos (c /2)]

Ad = [0.7854 Dc2 (97.180/3600)]-[(1/4) (Lw / Dc) Dc2 cos (97.180)]

Ad = (0.2196 Dc2) - (0.1241 Dc2)

Ad = 0.0955Dc2, m2Since, An = Ac -Ad

0.252 = (0.7854Dc2) - (0.0955 Dc2)

i .e., 0.6895 Dc2 = 0.252

Dc2 = 0.252/ 0.6895 = 0.365

Dc = 0.6 mTake Dc = 0.635 m

Since Lw / Dc = 0.75,

Lw = 0.75 Dc = 0.750.635 = 0.476 m.

Therefore, Lw = 0.476 m.

Now, Ac = 0.78540.6352 = 0.316 m2 Ad = 0.08790.635 = 0.0354 m2 An = Ac - Ad

An =0.316-0.0354

An = .2806 m2

7. Perforated plate area (Ap):

Active area (Aa)

Aa = Ac - (2Ad)

Aa = 0.316- (20.0354)

Aa = 0.245 m2

Lw / Dc = 0.476/ 0.635 = 0.75

c = 97.18 0. c = angle

1=180 0 - 97.18 0 = 82.82 0 1 = angle

Acz = 2 Lw (thickness of distribution)

= 5 20% of Ac

Where Acz = area of calming zone, m2

Acz = taking 10% of Ac = 0.02833

Also,

Awz = {(/4)Dc2 (/3600)}-{/4 (Dc-0.05)2 /3600}

Where Awz = area of waste periphery, m2

i.e., Awz = 2 5 % of Ac, taking 2% of Ac,

i.e., Awz = 0.0.0057 m2

Now,

Ap = Ac - (2Ad) - Acz Awz

Ap = 0.2833 2*0.0354 - 0.02833 - 0.0.0057 =0.1784 m2Thus, Ap = 1.720 m2

8. Total Hole Area (Ah):

Since,

Ah / Ap = 0.1

Ah = 0.1 Ap

Ah = 0.1 0.1784 =0.01784m2Thus, Total Hole Area = 0.01784 m2

Now we know that,

4*Ah = nh (.dh2) Where nh = number of holes.

nh = (40.01784)/ (.3.140.0052)

nh = 909

Therefore, Number of holes = 909.

9. Weir Height (hw):

Let hw = 45 mm.

10. Weeping Check

All the pressure drops calculated in this section are represented as mm head of

liquid on the plate. This serves as a common basis for evaluating the pressure

drops.

Notations used and their units:

hd = Pressure drop through the dry plate, mm of liquid on the plate

uh = Vapor velocity based on the hole area, m/s

how = Height of liquid over weir, mm of liquid on the plate

h= Pressure drop due to bubble formation, mm of liquid

hds= Dynamic seal of liquid, mm of liquid

hl = Pressure drop due to foaming, mm of liquid

hf = Pressure drop due to foaming,

Df = Average flow length of the liquid, m

Rh = Hydraulic radius of liquid flow, m

uf = Velocity of foam, m/s

(NRe) = Reynolds number of flow

f = Friction factor

hhg = Hydraulic gradient, mm of liquid

hda = Loss under down comer apron, mm of liquid

Ada = Area under the down comer apron, m2

c = Down comer clearance, m

hdc = Down comer backup, mm of liquid

Calculations:

Head loss through dry hole

hd = head loss across the dry hole

hd = k1 + [k2 (g/l) Uh2] --------- (eqn. 18.6, page 18.9, 6th edition Perry)

where Uh =gas velocity through hole area

k1, k2 are constants

For sieve plates

k1 = 0 and

k2 = 50.8 / (Cv)2

where Cv = discharge coefficient, taken from fig. 18.14, page 18.9, 6th edition Perry).

Now,

(Ah/Aa) = 0.01784/ 0.245 m2 = 0.073also tT/dh = 3/5 = 0.60

Thus for (Ah/Aa) = 0.07993 and tT/dh = 0.60

We have from fig. edition 18.14, page 18.9 6th Perry.

Cv = 0.730

k2 = 50.8 / 0.7302 = 95.3275

Volumetric flow rate of Vapor at the top of the Enriching Section

qt = 0.3 m3/s.

Velocity through the hole area (Uh):

Velocity through the hole area at the top = Uh, = qt /Ah

= 0.3/0.01784 = 16.8 m/s

Velocity through hole area should be minimum because at low gas flow rate weeping is

observed.

Now,

hd, = k2 [g/l] (Uh )2

= 95.3275(2.91/1011) 16.82

hd, top = 85.24 mm clear liquid. -------- (minimum at top)

Head Loss Due to Bubble Formation

h= 409 [/ (ldh)] --- (eqn. 18.2.a, page 18.7, 6th edition Perry)

where surface tension, mN/m (dyne/cm)

dh =Hole diameter, mm

l = average density of liquid in the

section, kg/m3

= (987+1141)/2

= 1064 kg/m3

h=409 [17.4565 /(777.92 x5)]

h= 2.714 mm clear liquid

Height of Liquid Crest over Weir:

how = 664_)w [(q/Lw)2/3]-----------( eqn. 18.12.a, page 18.10,

6thedition Perry

q = liquid flow rate at top, m3/s

= 17747.8/ (3600788.86)

= 6.24910-3 m3/s

q = 99.05 gal/min(or GPM).

Lw = weir length = 1.425 m = 4.675 ft

q/Lw2.5 = 99.05/ (4.675) 2.5 = 2.096

now for q/Lw2.5 = 2.096 and Lw /Dc =0.75

we have from fig.18.16,

page 18.11, 6th edition Perry

Fw= correction factor =1.025

how = 1.025664[(6.24910-3)/1.425]2/3

how = 18.23 mm clear liquid.

Now,

(hd + h) = 85.24 + 2.714 = 87.95 mm ------ Design value

(hw + how) = 45 + 18.23 = 63.23 mm

Also, Ah/Aa = 0.08 and (hw + how) = 63.23 mm

The minimum value(hd + h) of required is calculated from a graph given in Perry,

plotted against Ah/Aa. we have from fig. 18.11, page 18.7, 6th edition Perry

(hd + h) min = 16.0 mm ------- Theoretical value.

The minimum value as found is 16.0 mm.

Since the design value is greater than

the minimum value, there is no

problem ofweeping.

Down comer Flooding:

hds =hw + how + (hhg /2) ------- (eqn 18.10, page 18.10, 6th edition Perry)

Where,hw = weir height, mm

hds = static slot seal (weir height minus height

of top of slot above plate floor, height

equivalent clear liquid, mm)

how = height of crest over weir, equivalent clear

liquid, mm

hhg = hydraulic gradient across the plate, height of

equivalent clear liquid, mm.

In the above equation how is calculated at bottom of the section and since the tower is

operating at atmospheric pressure, hhg is very small for sieve plate and hence neglected.

Calculation of how at bottom conditions of the section:

q = liquid rate at the bottom of the section, m3/s

= 31619*116/(3600*1258*1000)=8.1x10-4 m3/s

= (8.1x10-4)/ (6.309*10-3) = 7.7 gal/min

Lw = weir length = Lw = 0.476 m.= 1.56 ft.

q/Lw2.5 =7.7/ (1.56)2.5 = 3.14

now for q/Lw2.5 = 3.14and Lw /Dc =0.75

we have from fig.18.16, page 18.11, 6th edition Perry

Fw= correction factor =1.030

Thus, how = 1.03664[(8.1x10-4)/0.47]2.3

how = 19.33 mm clear liquid. ----- (maximum at the bottom of section).

Therefore, hds = 45 +19.33 = 64.33 mm.

Now, Fga = Ua g0.5 Where Fga = gas-phase kinetic energy factor,

Ua = superficial gas velocity, m/s (ft/s),

g = gas density, kg/m3 (lb/ft3)

Here Ua is calculated at the bottom of the section.

Ua = (Gb/g)/ Aa = (28072/2.91) /(0.245x3600) = 1.24 m/s Thus, Ua = 4.06 ft/s

g = 2.91 kg/m3 = 2.91/ (1.60184610-1) = 0.181 lb/ft3

Fga = 4.06(0.181)0.5Fga = 1.72

Now for Fga = 1.72, we have from fig. 18.15, page 18.10 6th edition Perry)

Aeration factor = (= 0.6

Relative Froth Density = (t = 0.20

Now hl= (hds ---- (eqn. 18.8, page 18.10, 6th edition Perry)

Where, hl= pressure drop through the aerated mass over and around the disperser,

mm liquid,

hl= 0.664.33 = 38.598 mm.

Now,

hf = hl/(t ------- (eqn. 18.9, page 18.10, 6th edition Perry)

hf = 38.598/ 0.20 = 192.99 mm.

Head loss over down comer apron:

hda = 165.2 {q/ Ada}2 ----- (eqn. 18.19, page 18.10, 6th edition Perry)

Where, hda = head loss under the down comer apron, as millimeters of liquid,

q = liquid flow rate calculated at the bottom of section, m3/s

and Ada = minimum area of flow under the down comer apron, m2

Now,

q = 18950.03/(3600776.98) = 6.77410-3 m3/s

Take clearance, C = 1/2 = 12.5 mm

hap = hds - C = 64.33 12.5 =51.83 mm

Ada = Lw x hap = 0.4710-3 = 24.36*10-3 m hda2

hda = 165.2[6.77410-3 / 24.36x 10-3] 2

= 12.75 mm

ht = total pressure drop across the plate (mm liquid)

= hd + hl`

= 85.24 + 38.598

= 123.838 mm

Down comer backup:

hdc = ht+ hw + how + hda + hhg ---- (eqn 18.3, page 18.7, 6th edition Perry)

Where, hdc = height in down comer, mm liquid,

hw = height of weir at the plate outlet, mm liquid,

ho =height of crest over the weir, mm liquid,

hda = head loss due to liquid flow under the down comer apron, mm liquid,

hhg = liquid gradient across the plate, mm liquid.

hdc =123.83 + 45 + 19.33 + 12.75 + 0

= 201 mm

Let (dc = average relative froth density (ratio of froth density to liquid density)= 0.5

hdc = hdc / (= 201/ 0.5 = 402 mm which is less than the tray spacing of 457 mm.

Hence no flooding in the enriching sectionV. EFFICENCIES: (AIChE Method)

A) Enriching Section:

Point Efficiency, (Eog):

Eog = 1-exp (-Nog) ----- (eqn. 18.33, page 18.15, 6th edition Perry)

Where Nog = Overall transfer units

Nog = 1/ [(1/Ng) +(/Nl)] ---- (eqn. 18.34, page 18.15, 6th edition Perry)

Where Nl = Liquid phase transfer units,

Ng = Gas phase transfer units

=(mGm)/ Lm = Stripping factor,

m = slope of Equilibrium Curve,

Gm = Gas flow rate, mol/s

Lm = Liquid flow rate, mol/s

Ng= (0.776 + (0.00457hw) (0.238Ua * g0.5)+ (104.6W))/ (NSc, g)0.5 ----- (eqn. 18.36,

page 18.15, 6th edition Perry)--- *

hw = weir height = 45.00 mm

Ua = Gas velocity through active area, m/s

Ua= (Avg. vapor flow rate in kg/hr)/ (3600Avg. vapor density active area)

= (28488.6*116/1000)/ (36000.2452.925)

Ua = 1.28 m/s

Df = (Lw + Dc)/2 = (0.635+0.47)/2 = 0.55 m

Average Liquid rate = 2040.27 kg/hr

Average Liquid Density =991 kg/m3

q = 2040.36/ (3600x991) =5.71 x 10-0.4 m3/s

W = Liquid flow rate, m3/ (s.m) of width of flow path on the plate,

= q/Df = 5.71*10-4/0.55 = 1.0410-3 m3/ (s.m)

NSc g = Schmidt number =g (gDg) = 0.66

Number of gas phase transfer units

Ng= (0.776 + (0.0045745) (0.2381.282.9250.5) + (104.61.0410-3))/(0.66)0.5

Ng = 0.744

Number of liquid phase transfer units

Nl = kl al ----- (eqn 18.36a, page 18.15, 6th edition Perry)

Where kl = Liquid phase transfer coefficient kmol/ (sm2 kmol/m3) or m/s

a = effective interfacial area for mass transfer m2/m3 froth or spray on the plate,

1= residence time of liquid in the froth or spray, s l = (hlAa)/(1000q) ---- (eqn. 18.38, page 18.16, 6th edition Perry)

q = liquid flow rate, m3/s = 5.71*10-4 m3/s

hl = hl = 38.08 mm

Aa = 0.47 m2

l = (38.080.47 )/(10005.71*10-4) =31.34 sec

kl a = (3.875108DL)0.5 ((0.40Uag0.5) + 0.17)--- (eqn. 18.40a, page 18.16,

6th edition Perry)

DL= liquid phase diffusion coefficient, m2/s

kl a = (3.8751088.0810-9)0.5 ((0.401.282.9250.5) + 0.17)

kl a = 1.832 m/s

Nl = kl al

i.e., Nl = 1.83331.34 =57.13

Slope of equilibrium Curve

mtop = 0.4375

mbottom = 0.84

Gm/Lm = 1.2

t = mt Gm/Lm =0.4375*1.2=0.525

b = mbGm/Lm = 0.84*1.2 = 1.002

= 0.76

Nog = 1/[(1/Ng_+/Nl)]

= 1/[(1/0.774) + (0.76/57.16)]

Nog = 1.6

Eog = 1-e-Nog = 1-exp (-Nog)

= 1-e-1.037 = 1-exp (-1.037)

Eog = 0.67

Point Efficiency = Eog = 0.67

2. Murphree Plate Efficiency (Emv):

Now,

Pelect number =NPe = Zl2/ (DE l)

Where Zl = length of liquid travel, m

DE = (6.675 x 10-3 (Ua)1.44) + (0.922 10 -4 hl) - 0.00562----- (eqn. 18.45, page 18.17,

6th edition Perry)

where DE = Eddy diffusion coefficient, m2/s

DE = (6.675 x 10 -3 (1.266)1.44) + (0.922 10 -4 38.08) - 0.00562

DE = 7.26510-3 m2/s

Also Zl = Dc cos (c/2)

= 0.635 cos (97.18 0/2)

= 0.46 m

NPe = Zl2/ (DE l)

= 0.462/ (7.26510-3 57.13)

NPe = 5.1

Eog = 0.76 x 0.67 = 0.502

now for Eog = 0.60 and NPe = 5.1

We have from fig.18.29a, page 18.18, 6th edition Perry

Also available in seventh edition

Emv/ Eog = 1.28

Emv = 1.28 Eog = 1.280.67 =0.81

Murphree Plate Efficiency = Emv = 0.81

3. Overall Efficiency ( EOC):

EOC = log [1 + E(- 1)]/log ----- (eqn. 18.46, page 18.17, 6th edition Perry)

Where E/Emv= 1/(1 + EMV [(/ (1-()]----- (eqn. 18.27, page 18.13, 6th edition Perry)

Emv = Murphee Vapor efficiency,

E. = Murphee Vapor efficiency, corrected for recycle effect of liquid entrainment.

(L/G) {(g/(l}0.5 = 0.039

for (L/G){g/l}0.5 = 0.039 and at 80 % of the flooding value,

We have from fig.18.22, page 18.14, 6th edition Perry

(= fractional entrainment, moles/mole gross down flow = 0.076

E = Emv 1/[1 + Emv [(/ (1- ()]]

= 0.81[(1+0.81[0.076/ (1-0.076)])]

E= 0.773

Overall Efficiency = EOC = log [1 + E(- 1)]/log

EOC = log [1+ 0.7730(0.76-1)]/log 0.76

Overall Efficiency = EOC = 0.726

Actual trays = Nact = NT/EOC = (ideal trays)/ (overall efficiency)

Where NT = Theoretical plates,

Nact = actual trays

Nact = 17/0.72623.41=25

Thus actual trays in rectifying section = 13

Thus, Actual trays in the Stripping Section = 12

Total Height of distillation column= 25ts = 25457 = 11425 mm = 11.425 m

Design of autoclave

INTRODUCTION

Autoclaves have been used in industry for many decades. As technology has progressed so has autoclave design, initially from basic riveted steam heated vessels to vessels fabricated utilizing the latest welding techniques with highly sophisticated computerized control systems

The industries that make use of autoclaves have also evolved over the years. Initially used in the textile, timber, food, sterilizing and rubber industries, autoclaves are now essential items in the advanced composites and Investment casting industries

Commercial pressure autoclaves have been in operation since mid 1950s. Historical production data suggest that these early autoclaves were originally designed with excess capacity (Bere zowsky, Collins, Kerfoot, and Torres, 1991). Process development initially consisted of tests in batch autoclaves. While in some cases this stage had been followed by continuous pilot plant tests in multi-compartment autoclaves, in many cases the batch test residence times were extended to the continuous commercial stage using some factor, resulting in an over estimation of the required autoclave volume. In some other instances the continuous stage of testing had not been performed or its results could not be interpreted as a continuation of batch tests due to differences in ore composition, grind size and reactor conditions. In such cases, it would be important to be able to scale-up the batch test data to a multi-compartment continuous mode using a sound approach that takes into account both the physical and chemical aspects of the leaching reaction as well as the reactor configuration.

For use in the production of advanced composite materials, a hot atmosphere autoclave has to achieve the following criteria:

Fail to safety, safety systems

Achieve the required internal environment (ie. heat and pressure)

Programmable temperature control and uniform temperature distribution

Programmable pressure control

Computerised process control, monitoring and data logging

Not only the autoclaves are made of a no. of different materials,but the sizea,general design and arrangement for heating are so varied that one might forgive a chemist,used only to most common forms,for failing to some of the rare types of modern apparatus as being autoclave at all.

Two particular types of autoclaves have beenselected as covering the most important ranges of high pressure work.These are

1. High pressure autoclaves

2. Low pressure autoclaves

Autoclaves can be made of Iron,steel,copper bronze or tin but some kind of the steel is by the far the most common material used in their manufacture on account of its great strength.Modern practice supports use of nickel steel and nickel chrome steel for those autoclaves designed to withstand very high pressure.

Autoclaves are made of very large size,from small labortary pieces of apparatus of few hundered cubic centimeters capacity to huge pans capable of holding a charge of twenty thousand gallons.

Autoclaves are generally cylindrical in shape,height being from 2-3 times the diameter.Bottom may be ellipsoidal or dishad bottom.In order to give strength all sharp vurves or angles axcluded from design the top of the autoclave known as cover is fixed on to flanges

Many of the different materials, are used for packing of the joints. The commonest packings are lead,copper,aluminium and asbestos.Not only does the choice of material used on type of autoclave ,but also depend on pressure.It is more common one type to fix one or more safety valves of the ordinary steam boiler type to an autoclave.But these were constantly getting chocke