Research Article Kinetic Study of Catalytic Esterification of Butyric Acid and Ethanol over Amberlyst 15

ISRN Chemical Engineering Volume 213, Article ID 52293, 6 pages http://dx.doi.org/1.1155/213/52293 Research Article Kinetic Study of Catalytic Esterification of Butyric Acid and Ethanol over Amberlyst 15 Nisha Singh, 1 Raj kumar, 2 and Pravin Kumar Sachan 3 1 Department of Chemical Engineering, RNCET, Panipat, Haryana 13213, India 2 Department of Chemical Engineering, Bipin Tripathi Kumaon Institute of Technology, Darahat, Almora, Uttarakhand 263653, India 3 Department of Biochemical Engineering, Bipin Tripathi Kumaon Institute of Technology, Darahat, Almora, Uttarakhand 263653, India Correspondence should be addressed to Raj kumar; ranvir523@gmail.com Received 29 June 213; Accepted 5 August 213 Academic Editors: G. Bayramoglu and R. Mariscal Copyright 213 Nisha Singh et al. This is an open access article distributed under the Creative Commons Attribution License, hich permits unrestricted use, distribution, and reproduction in any medium, provided the original ork is properly cited. The esterification reaction of butyric acid ith ethanol has been studied in the presence of ion exchange resin (Amberlyst 15). Ethyl butyrate as obtained as the only product hich is used in flavours and fragrances. Industrially speaking, it is also one of the cheapest chemicals, hich only adds to its popularity. The influences of certain parameters such as temperature, catalyst loading, initial concentration of acid and alcohols, initial concentration of ater, and molar ratio ere studied. Conversions ere foundtoincreaseithanincreaseinbothmolarratioandtemperature.theexperimentserecarriedoutinabatchreactor in the temperature range of 328.15 348.15 K. Variation of parameters on rate of reaction demonstrated that the reaction as intrinsically controlled. Experiment kinetic data ere correlated by using pseudo-homogeneous model. The activation energy for the esterification of butyric acid ith ethanol is found to be 3 k J/mol. 1. Introduction Organic esters are important fine chemicals used idely in the manufacturing of flavors, pharmaceuticals, plasticizers, and polymerization monomers. They are also used as emulsifiers in the food and cosmetic industries. Several synthetic routes are available for obtaining organic esters, most of hich have been briefly revieed by Yeramian et al. [1]. Several synthetic routes have been used to make organic ester, but the most-used methodology for ester synthesis is direct esterification of carboxylic acids ith alcohols in the presence of acid/base catalysts. Esterification is used. The most acceptable method is to react the acid ith an alcohol catalyzed by mineral acids, and the reaction is reversible [2].Esterification of carboxylic acid ith alcohol in the presence of acid catalyst has been the subject of investigation of many research orkers [3]. The traditional industrial process of synthesizing esters using homogeneous acid catalyst is conveniently replaced by solid acid catalyst, ion exchange resins, clay, and so forth [4]. The ion exchange resin is a promising material for replacement of homogeneous acid catalysts. The use of ion exchange resins as solid catalyst has many advantages over homogeneous acid catalysts. They eliminate the corrosive environment; they can separate from liquid reaction mixture by filtration and have high selectivity [5]. They can also be used repeatedly over a prolonged period ithout any difficulty in handling and storing them. And the purity of the products is higher since the side reactions can be completely eliminated [6]. Fatty acid esters are used as ra materials for emulsifiers, oiling agents for foods, spin finish and textiles, lubricants for plastics, paint and ink additives and for mechanical processing, personal care emollients, and surfactants and base materials for perfumes. They are used as solvents, cosolvents, and oil carriers in the agricultural industries [7]. The esters of biobased organic acids fall into the category of benign or green solvents and are promising replacements for halogenated petroleum-based solvent in a ide range of applications [8]. The ester of butyric acid and ethanol, namely, ethyl butyrate, finds ide applications. It is commonly used as

2 ISRN Chemical Engineering artificial flavoring such as pineapple flavoring in alcoholic beverage, as a solvent in perfumery products and as a plasticizer for cellulose. Ethyl butyrate is one of the most commonchemicalsusedinflavorsandfragrances.itcanbe used in a variety of flavors: orange (most common), cherry, pineapple, mango, guava, bubblegum, peach, apricot, fig, and plum. Industrially speaking, it is also one of the cheapest chemicals, hich only adds to its popularity. Although, to the bestofourknoledge,noresearcherhasreportedthekinetics of esterification of butyric ith ethanol in the presence of Amberlyst 15, there are a number of studies related to the other esterification reactions catalyzed by solid resins. 2. Experimental 2.1. Chemicals. Ethanol of >98.5% purity (Merck) andbutyric acid of 99.8% purity (Merck) are used as the reactants. The reaction occurred in the solution of dioxane of 99.% purity (Merck). All the aqueous solutions used in the analysis are prepared ith distilled ater, sodium hydroxide (SD Fine Chemicals Ltd., Boisar, India), and phenolphthalein indicator, (Qualigens Fine Chemicals, Mumbai, India). 2.2. Catalyst. Amberlyst15(RohmandHass)isusedas catalyst. It is synthesized from styrene-divinylbenzene by suspension polymerization and finally sulfonated by sulfuric acid. The esterification reaction of butyric acid ith ethanol as studied using different catalysts. The catalytic activity of Amberlyst 15 is higher than the Amberlyst 35. It is due to Amberlyst 15 has higher surface area and pore volume than Amberlyst 35. So, Amberlyst 15 is found to be the best catalyst to generate the data. 3. Apparatus and Procedure Esterification reaction of butyric acid ith ethanol ith the initial concentrations of 1.44 mol/l and 14.84 mol/l, respectively, as carried out in three-necked flask of 5 ml capacity fitted ith a reflux condenser, a thermometer, and a magnetic stirrer. The initial volume of reaction mixture as approximately 15 ml. A reflux condenser is used to avoid the loss of volatile compounds. The ion exchange resin suspends in the reaction mixture ith the help of stirrer. Temperature inside the reactor is controlled ithin the accuracy of ±.5 K. In all the experiments, a knon amount of butyric acid and thecatalystchargedintothereactorandheatedtothedesired temperature. All of the reactants charged in the reactor are volumetrically measured. This time is considered the starting point of the reaction. Samples ere ithdran at a regular time intervals for analysis. The progress of the reaction as folloed by ithdraing small enough samples to consider them negligible compared to the volume of the reaction mixture at regular intervals. 4. Analysis All samples ere measured in measuring cylinder of 1 ml, taken periodically, and titrated against 1 N standard NaOH solution using phenolphthalein as an indicator. r A (mol/l min).7.6.5.4.3.2.1.5 1 1.5 2 C A (mol/l) Figure 1: Effect of acid concentration on initial reaction rate: (C B = 14.84 mol/l). 5. Kinetic Modeling A pseudo-homogeneous model cab as effectively applied to correlate the kinetic data of the liquid solid catalytic reaction. The esterification reactions are knon to be reversible reaction of second order. The general rate expression can be given by A+B E+W, (1) here A = butyric acid, B =ethanol,e =ethylbutyrate,and W =ater,and r A = K f (m/v) (C A C B (C E (C W /K e ))) 1+K B C B +K W C W, (2) here subscript C A and C B refer to acid and alcohol concentrations, respectively, K f isforardreactionrateconstant, K e is the equilibrium constant of the reaction, K is the adsorption equilibrium constants, m is the quality of dry resin, and V is the volume of the resin. For the initial reaction rate, ith no product present, (2) can be reduced to r A = ( K fmc B /V ) C 1+K B C A. (3) B Aplotof r A versus C A provides a straight line ith slope of (K f mc B /V(1 + K B C B )). These lines ere presented in Figure 1 at temperature 348 K. If (3) is rearranged for variables C B values, the folloing expression can be obtained: C A C B r A = V K f m +(VK B K f m )C B. (4) AplotofC A C B /( r A ) versus C B produces a straight line ith the slope of VK B /K f m and intersection of V/K f m. These lines are presented in Figure 1 at 348 K. From the slope and lines shon in Figure 2, the folloing equation can be held.

ISRN Chemical Engineering 3 C A C B / r A (mol min/l) 323 3225 322 3215 321 325 32 3195 13 13.5 14 14.5 15 C B (mol/l) Figure 2: C A C B / r A versus C B :temperature=348k;catalyst loading = 73.2 kg/m 3. r A (mol/l h).47.46.45.44.43.42.41.4.5 1 1.5 C W (mol/l) Figure 3: Effect of ater concentration on initial reaction rate: catalyst loading = 73.2 kg/m 3 ;temperature=348k. In order to evaluate the inhibiting effect of ater concentration, (2), ith no ester present initially, can be ritten as r A = K f (m/v) C A C B, (5) 1+K B C B +K W C W from hich the folloing equation can be obtained: C A C B = V(1+K BC B ) +( VK W r A K f m K f m )C W. (6) AplotofC A C B /( r A ) versus C W at constant acid and alcohol concentrations gives a straight line ith slope of VK W /K f m and intersection of V(1 + K B C B )/K f m.these lines ere presented in Figure 3. At temperature 348 K, K f mc B V(1+K B C B ) =.45, V K f m = 312.6, VK B K f m = 14.4, V(1+K B C B ) = 321.13, K f m VK W k f m = 22.18. Solving these equations by the method of averages, e found the values of K f = 4.53 1 6 L 2 /mol, K B = 4.78 1 6 L/mol, K W = 7.35 1 6 L/mol. 5.1. Integrated Rate Expression. If the reaction rate given in (3) is expressed in terms of conversion of butyric acid, the folloing equation can be obtained. Adsorption effect of alcohol and ater is neglected as discussed earlier and as alcohol is taken in far excess, so C B is taken as constant; hence, (3) becomes a pseudo-first-order rate equation: r A = K f V C BC A. (8) (7) Putting C A =C A (1 X A ), dx C A A dt dx A dt x A =K f V C BC A (1 X A ), =K f V C B (1 X A ), dx A (1 X A ) = K f V C Bdt, ln (1 X A )=K f V C Bt, here X A is the fractional conversion of A. Thus,aplot of ln(1 X A ) against time t gives a slope hich represents K. 6. Results and Discussion The esterification reaction of butyric acid ith ethanol as studiedinabatchreactorinthepresenceofacidicion exchange resin catalyst, Amberlyst 15. The kinetics of esterification of butyric acid is studied at different temperatures from 328.15 to 348.15 K ith different molar ratios and varying catalyst loading (Figure 11). A pseudo-homogeneous model has been used to describe the esterification reaction catalyzed by Amberlyst 15. The effects of temperature, catalyst loading, and molar ratio are studied. 6.1. Catalyst Performance. In Figure 5, a comparison of the behavior of the Amberlyst 15 and Amberlyst 35 catalysts is shon. Catalysts are used to access their efficacy in the esterification of butyric acid ith ethanol. Amberlyst 15 is shontobeaneffectivecatalystascomparedtoamberlyst 35. The catalytic activity of Amberlyst 15 has higher activity than Amberlyst 35. It is due to Amberlyst 15 has higher total exchange capacity, surface area, and pore volume than Amberlyst 35. So, Amberlyst 15 is found to be the best catalyst to generate the data (Table 1). 6.2. Effect of Catalyst Loading. In Figure 6 experiments ork conducted by varying the catalyst loading from 24.4 kg/m 3 (9)

4 ISRN Chemical Engineering Table 1: Characteristics of the catalysts. Property Amberlyst 35 Amberlyst 15 Acidity (eq. H + kg 1 ) 5.32 4.75 Surface area (m 2 g 1 ) 34 42 Total exchange capacity (eq/kg) 5.2 4.7 Pore volume (cm 3 g 1 ).28.36 Mean pore diameter (Å) 329 343 Skeletal density (g cm 3 ) 1.542 1.416 C A C B / r A (mol min/l) 323 3225 322 3215 321 325 32 3195.5 1 1.5 C W (mol/l) Figure 4: (C A C B / r A )versusc W :temperature=348k;catalyst loading = 73.2 kg/m 3. to 81.4 kg/m 3. Keeping butyric acid and ethanol molar ratio 1:1andandthereactiontemperature75 C. It is found that ith increase in catalyst loading, the conversion of butyric acid increased ith the proportional increase in the active sites. At higher catalyst loading, the rate of mass transfer is high, and therefore, there is no significant increase in the rate [9]. This data is once again used to plot ln(1 X A ) versus t in Figure 7 and get a straight line passing through origin, the slope of hich gives the value of K. The values of K are plotted against catalyst loading, (kg/m 3 )infigure 8, and it is observed that ith the increase in, there is a linear increase in K; thus,itvalidatesthe model. Fractional conversion 8 7 6 5 4 3 2 1 2 4 Figure 5: Variation ith type of catalyst. Amberlyst 15 ( ) and Amberlyst 35 ( ), catalyst loading = 48.8 kg/m 3,temperature=75 C, and molar ratio = 1 : 1 (butyric acid : ethanol). Fractional conversion (X A ).9.8.7.6.5.4.3.2.1 1 2 3 4 5 Figure 6: Comparison of the effect of catalyst loading ( ) 24.4 kg/m 3, ( ) 32.5 kg/m 3, ( ) 48.8 kg/m 3, ( ) 56.9 kg/m 3, ( ) 65.6 kg/m 3, (+) 73.2 kg/m 3,and( )81.4kg/m 3 on the conversion of butyric acid ith ethanol; molar ratio = 1 : 1 (butyric acid : ethanol), and temperature = 75 C. 6.3. Effect of Molar Ratio. The concentration of ethanol had an influence on the reaction rate and on the conversion. The results are given in Figure 9. It can be seen that the conversion of acid increases ith increasing the initial molar ratio of ethanol to butyric acid. For the esterification ith ethanol, the equilibrium conversion of butyric acid increases from 31% to 81% on varying ethanol to butyric acid ratio from 1 : 1 to 1 : 15 for catalyst loading 73.2 kg/m 3 at temperature 348 K (Figure 4). The result observed for the effect of initial molar ratio of ethanol to butyric acid indicated that the equilibrium conversion of butyric acid can be effectively enhanced by using a large excess of ethanol. For calculating K, thesedataareonceagainusedtoplot ln(1 X A ) versus t to get a straight line passing through origin shon in Figure 1 the slope of hich gives the value of K. The values of K are plotted against catalyst loading, (kg/m 3 ), and it as observed that ith the increase in,there as a linear increase in K;thus,itvalidatesthemodel. 6.4. Effect of Temperature. The study of the effect of temperature is very important because this information is useful in calculating the activation energy. In order to investigate the effect of temperature, esterification reactions are carried out in the temperature region from 328 to 348 K hile keeping the acid : alcohol ratio at 1 : 1 and the catalyst loading of 73.2 kg/m 3 dry resin (Figure 13). With an increase in reaction temperature, the initial reaction rate or the conversion of the butyric acid is found to increase substantially as shon in Figure 12. It shos that the higher temperature yields the greater conversion of the acid at fixed contact time.

ISRN Chemical Engineering 5 1.8 2 ln (1 X A ) 1.6 1.4 1.2 1.8.6.4.2 1 2 3 4 (ln (1 X A )) 1.8 1.6 1.4 1.2 1.8.6.4.2 Figure 7: Typical kinetic plot of comparison of different catalyst loadings: ( ) 24.4 kg/m 3,( ) 32.5 kg/m 3,( ) 48.8 kg/m 3,( ) 56.9 kg/m 3,( )65.6kg/m 3,( ) 73.2 kg/m 3,and( )81.4kg/m 3..4 1 2 3 4 Figure1:Typicalkineticplotofcomparisonofdifferentmolar ratios: ( ) 1:5,( ), 1 : 1, and ( ) 1 : 15, temperature: 348.15 K, and catalyst loading: 73.2 (kg/m 3 )..35.6 Rate constant K (min 1 ).3.25.2.15.1.5 2 4 6 8 1 Catalyst loading (kg/m 3 ) Figure 8: Effect on K ith catalyst loading. Rate constant K (hr 1 ).5.4.3.2.1 5 1 15 2 Molar ratio Figure 11: Effect of different molar ratios: rate constant (K) versus molar ratio, temperature: 348.15 K, and catalyst loading: 73.2 (kg/m 3 ). Fractional conversion (X A ).9.8.7.6.5.4.3.2.1 1 2 3 4 5 Figure 9: Comparison of the effect of molar ratio 1 : 1 ( ), 1 : 5 ( ), 1:1( ), and 1 : 15 ( ) on the conversion of butyric acid ith ethanol, ith catalyst loading of 73.2 kg/m 3 and temperature of 75 C. Fractional conversion (X A ).9.8.7.6.5.4.3.2.1 1 2 3 4 5 Figure 12: Comparison of the effect of temperature: 328 K ( ), 333 K ( ), 338 K ( ), 343 K ( ), and 348 K ( ), on the conversion of butyric acid ith ethanol, ith catalyst loading of 73.2 kg/m 3 and molar ratio of 1 : 1 (butyric acid : ethanol).

6 ISRN Chemical Engineering ln (1 X A ) 1.8 1.6 1.4 1.2 1.8.6.4.2 1 2 3 4 Figure 13: Typical kinetic plot of comparison of different temperatures: 328 K ( ), 333 K ( ), 338 K ( ), 343 K ( ), and 348 K ( ). ln (K) 6.2 6.1 6 5.9 5.8 5.7 5.6 5.5 5.4 5.3 2.85 2.9 2.95 3 3.5 3.1 1 (T) Figure 14: Arrhenius plot of ln K versus 1/T (molar ratio = 1 : 1; catalyst loading = 73.2 kg/m 3 ). Thus, 75 Cischosenasthemaximumorkingtemperature for the butyric acid esterification. Arrhenius la expresses the temperature dependency of therateconstant: K=k exp ( E RT ), (1) here k =frequencyfactor,e =activationenergy,andr = gas constant. Thisdataisonceagainusedtoplot ln(1 X A ) versus t to get a straight line passing through origin, the slope of hich gives the value of K. Equation (1), a plot of ln K versus 1/T,atconstantacid and alcohol concentrations, gives a straight line ith a slope of (E a /R)asshoninFigure 14. The study on the effect of temperature is very important for heterogeneously catalyzed reaction as this information is useful in calculating the activation energy for this reaction. An Arrhenius plot for the initial rate of reaction is given in Figure 14. The activation energy for the esterification reaction basedontheinitialrateisfoundtobe3kj/mol. 7. Conclusion The kinetics of esterification of butyric acid ith ethanol in the temperature ranging beteen 328.15 K and 348.15 K and at molar ratio 1 : 5 to 1 : 15 is investigated experimentally in a stirred batch reactor using Amberlyst 15. The optimum conditions for synthesizing ethyl butyrate have been delineated. It has also been observed that the initial reaction rate increases linearly ith acid and alcohol concentrations. And rate of reaction is found to increase ith the increase in catalyst loading, temperature, and molar ratio. Eley-Rideal model is applied to study the kinetics of the reaction. As a result, it is concluded that the acidic resin, Amberlyst 15, is a suitable catalyst for this reaction, since in the presence of it, the reaction has been found to take place beteen an adsorbed alcohol molecule and a molecule of acid in the bulk phase (Eley-Rideal model). It is also observed that ater has inhibiting effect of reaction. Temperature dependency of the kinetic constants has been found to apply Arrhenius equation. The activation energy is found to be 3 KJ/mol. References [1] A. A. Yeramian, J. C. Gottifredi, and R. E. Cunningham, Vapor-phase reactions catalyzed by ion exchange resins. II. Isopropanol-acetic acid esterification, Catalysis,vol. 12, no. 3, pp. 257 262, 1968. [2] A. Izci and F. Bodur, Liquid-phase esterification of acetic acid ith isobutanol catalyzed by ion-exchange resins, Reactive and Functional Polymers,vol.67,no.12,pp.1458 1464,27. [3] M. R. Altiokka and A. Çitak, Kinetics study of esterification of acetic acid ith isobutanol in the presence of amberlite catalyst, Applied Catalysis A,vol.239,no.1-2,pp.141 148,23. [4] K.R.Ayyappan,T.A.Pal,G.Ritu,B.Ajay,andR.K.Wanchoo, Catalytic hydrolysis of ethyl acetate using cation exchange resin (Amberlyst-15): a kinetic study, Bulletin of Chemical Reaction Engineering & Catalysis,vol.4,no.1,pp.16 22,29. [5] B. Chemseddine and R. Audinos, Use of ion-exchange membranes in a reactor for esterification of oleic acid and methanol at room temperature, Membrane Science,vol. 115,no. 1,pp.77 84,1996. [6] B. Saha and M. M. Sharma, Esterification of formic acid, acrylic acid and methacrylic acid ith cyclohexene in batch and distillation column reactors: ion-exchange resins as catalysts, Reactive and Functional Polymers, vol.28,no.3,pp.263 278, 1996. [7] A. Chakrabarti and M. M. Sharma, Esterification of acetic acid ith styrene: ion exchange resins as catalysts, Reactive Polymers,vol.16,no.1,pp.51 59,1991. [8] C. F. Oliveira, L. M. Dezaneti, F. A. C. Garcia et al., Esterification of oleic acid ith ethanol by 12-tungstophosphoric acid supported on zirconia, Applied Catalysis A, vol.372,no.2,pp. 153 161, 21. [9] S. S. Dash and K. M. Parida, Esterification of acetic acid ith n-butanol over manganese nodule leached residue, Molecular Catalysis A,vol.266,no.1-2,pp.88 92,27.

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