Kinetics of Esterification of Ethylene Glycol with Acetic Acid Using Cation Exchange Resin Catalyst

Transcription

1 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) 359 Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid Using Cation Exhange Resin Catalyst V. P. Yadav, a S. K. Maity, b,* P. Biswas, a and R. K. Singh a a Department of Chemial Engineering, National Institute of Tehnology Rourkela, Rourkela , Orissa, India b Department of Chemial Engineering, Indian Institute of Tehnology Hyderabad, Ordnane Fatory Estate, Yeddumailaram-5005, Andhra Pradesh, India Original sientifi paper Reeived: Deember 8, 010 Aepted: September 18, 011 The esterifiation of ethylene glyol with aeti aid was investigated in a bath reator in presene of a strongly aidi ation exhange resin, seralite SRC-10, as atalyst in the temperature range of 333 to 363 K. The detailed kineti study was performed to understand the effet of various proess variables suh as atalyst loading, ethylene glyol to aeti aid mole ratio, and temperature on onversion of reatants and seletivity to produts. Further, two different kineti models, empirial and kineti model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) approah, were developed to orrelate the experimental onentration versus time data. The kineti parameters of the developed models were then estimated at different temperatures using non-linear regression tehnique based on modified Levenberg-Marquar algorithm. The alulated results based on the estimated kineti and equilibrium onstants at different temperatures were then ompared with the experimental values and LHHW-based model was found to fit the experimental data reasonably better ompared to empirial kineti model. The estimated rate onstants at different temperatures of LHHW-based model were then used to estimate the ativation energy and frequeny fator of the rate onstants. Key words: Reation kinetis, modeling, ethylene glyol, ethylene glyol di-aetate, ation exhange resin Introdution The growing international energy risis oupled with rising oil pries and inreasing awareness of the environment and pollution has intensified the researh on renewable fuels derived from biomass. The bio-oil produed by the proess of biomass pyrolysis is nowadays an emerging tehnology for the prodution of renewable fuels and value-added hemials. The bio-oil was first separated into aqueous and non-aqueous frations by the addition of water. The aqueous fration of bio-oils ontaining sugars, anhydrosugars, aeti aid, hydroxyaetone, furfural, and small amounts of guaiaols is a potential soure of alkanes (ranging from C 1 to C 6 ) and polyols (ethylene glyol, 1,-propanediol, 1,4-butanediol et.). 1 The ethylene glyol obtained from bio-oil fration an be utilized to produe ethylene glyol mono- and di-aetate suitable for appliation as solvent for oating, paints, and oxygenated diesel fuel additives. * Corresponding author (Dr. Sunil K. Maity): Phone: ; Fax: ; sunil_maity@iith.a.in The esterifiation proess is widely used in industry to produe esters for a wide range of appliations suh as plastiizers, solvent, perfumery, flavor hemials, preursors for pharmaeutials, agrohemials, and other fine hemials. 3 4 In reent times, several esterifiation reations with different alohols and arboxyli aids have been reported in open literature using different types of solid aid atalysts suh as zeolites (HB, HY, ZSM-5) and ation exhange resin (Amberlyst 15, Amberlyst 36, Amberlite IRA-10) The esterifiation reations are known to be atalyzed by a variety of Lewis or Bronsted aid atalysts. The homogeneous mineral aids suh as H SO 4 and p-toluenesulphuri aid are however highly orrosive to proess equipment and diffiult to separate from the reation mixture Moreover, there is an inreasing tendeny to develop proesses that should meet the requirement of generation of nearly zero waste. Thus, it would be preferable to use a safer and simpler atalyst possibly in solid state, suh as ation exhange resin. The various types of proesses inluding isomerization, dehydration, etherifiation,

2 360 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) aetylation, and esterifiation have been intensified by solid aid atalysts The study of esterifiation of ethylene glyol with aeti aid is however limited in open literature. 18 Shmid et al. 19 studied the reation using aidi ation-exhange resin, Amberlyst 36, as atalyst, and pseudo-homogeneous kineti model based on ativity was then developed using the measured thermodynami properties of ethylene glyol aeti aid reative system. 0 Suman et al. studied the entrainer-based reative distillation of ethylene glyol aeti aid system using 1,-dihloroethane (EDC) as an entrainer to enhane the onversion of reatants and seletivity to ethylene glyol di-aetate. Considering the importane of the reation, the present work was undertaken to study the kinetis of esterifiation of ethylene glyol with aeti aid in presene of a ommerial ation-exhange resin atalyst and to develop suitable kineti models for its appliation in design and simulation of reative distillation olumn. Experimental Chemials Ethylene glyol and aeti aid (99 % purity) (aldehyde free) were purhased from Merk Speialities Private Limited, Mumbai, India. The strongly aidi (hydrogen form) ation-exhange resin, seralite SRC-10 (mesh number = 0 50, ion-exhange apaity = minimum 4.5 meq g 1 dry resin, and ph range = 0 14) was proured from Siso Researh Laboratories Private Limited, Mumbai, India. Experimental set-up All kineti experiments were arried out in bath mode in a 6.5 m i.d. fully baffled, mehanially agitated glass reator with a volume of 50 m 3. A six-blade glass disk turbine impeller with.0 m diameter was used for stirring the reation mixture. The impeller was kept at a height of 1.5 m from reator bottom. The reator was kept in a onstant temperature water bath whose temperature was ontrolled within ±1 K. The reation mixture was well agitated with the help of a mehanial stirrer. To avoid the vaporization loss of reation mixture, reator setup was equipped with a ondenser. Experimental proedure In a typial experimental run, about 75 m 3 of aeti aid with known amount of atalyst (say 1 g) was harged into the reator and kept well stirred until steady-state temperature was reahed. Then the measured volume of ethylene glyol (5 m 3 ), kept separately at reation temperature, was harged into the reator and the reation started. Samples were withdrawn from reation mixture at regular intervals after stopping the stirring and allowing the atalyst to settle. The detailed study of the reation was performed in wide range of temperature ( K), atalyst loading (0.5 to 1.5 % (w/v)), and aeti aid to ethylene glyol mole ratio (0.66 to 3.13). Produt analysis The reation produt ontaining aeti aid, ethylene glyol, ethylene glyol mono-aetate (EGMA), and ethylene glyol di-aetate (EGDA) were analyzed by gas-liquid hromatography (Chemito GC 8610) using arbowax olumn. The GC equipped with a flame ionization detetor (FID) was used for analysis. The olumn temperature was programmed with an initial temperature of 333 K for one minute, inreased at a rate of 0 K min 1 up to 473 K, and maintained at 473 K for min. The nitrogen (99.99 % purity) was used as arrier gas. An FID detetor was used at a temperature of 53 K. An injetor temperature of 53 K was used during the analysis. The moles of water formed in the reation were obtained from the overall mole balane. Eah sample was analyzed three times and average value was taken for further alulation. Results and disussion The reation of ethylene glyol with aeti aid in presene of ation-exhange resin proeeds in two onseutive reversible steps as shown in Sheme 1. In the first step, ethylene glyol reats with aeti aid to produe EGMA and water. The EGMA formed in the first step reats further with aeti aid resulting in the formation of EGDA and water. The term seletivity (S) of the two produts, EGMA and EGDA, used throughout the present artile was defined as follows. S S EGMA EGDA (%) 100 (%) 100 Effet of stirring speed moles of EGMA formed mole of AA reated moles of EGDA formed mole of AA reated To determine the role of mass transfer resistanes, the effet of agitation speed on the onversion of ethylene glyol was studied. The stirring speed was varied in the range of rev min 1. The strongly aidi ation-exhange resin (seralite

3 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) 361 Sheme 1. SRC-10) of 1.5 % (w/v) was used in eah test. The variation of onversion of ethylene glyol was found to be negligible with speed of agitation as shown in Fig. 1. The external mass transfer resistane fators were therefore unimportant. Therefore, all other experiments were performed at a safe stirring speed of 1500 rev min 1. Fig. Effet of temperature on onversion of ethylene glyol. Conditions: atalyst loading = 1.5 % (w/v); aeti aid to ethylene glyol mole ratio = 3.13; stirring speed = 1500 rpm. Table 1 Effet of temperature on seletivity to EGDA a Fig. 1 Effet of speed of agitation on onversion of ethylene glyol. Conditions: Aeti aid to ethylene glyol mole ratio = 3.13; temperature = 333 K; atalyst loading = 1.5 % (w/v); mathing reation time = 5 min. Effet of temperature Temperature/K Seletivity/% to EGDA at different reation time 30 min 60 min 10 min a Conditions: Catalyst loading = 1.5 % (w/v); aeti aid to ethylene glyol mole ratio = 3.13; stirring speed = 1500 rpm. The effet of temperature on onversion of ethylene glyol and seletivity of produts was studied in the temperature range of K. The effet of temperature on onversion of ethylene glyol is shown in Fig.. The onversion of ethylene glyol was found to inrease with inrease in temperature. The effet of temperature on the seletivity to EGDA is shown in Table 1. It is observed from the table that the seletivity to EGDA is not affeted signifiantly by temperature espeially, at high reation time when the reation reahed lose to equilibrium. This is beause the standard enthalpy of reation is relatively small whih results in insignifiant temperature dependeny on the hemial equilibrium.,14,15,17 As a result, almost similar equilibrium omposition was obtained in the temperature range studied.

4 36 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) The initial rates were alulated at different temperatures and Arrhenius plot of ln (initial rate) against 1/T was made and is shown in Fig. 3. The apparent ativation energy was alulated from the slope of the best-fitted straight line as 39 kj mol 1. The high value of apparent ativation energy further onfirms that the reation system is kinetially ontrolled. Shmid et al. reported the ativation energy of 40 kj mol 1 for this reation. 19 atalyst loading on seletivity to EGDA is shown in Table. The seletivity to EGDA was found to inrease with inreased reation time as expeted. However, the seletivity to EGDA was found to be almost unaffeted by the atalyst loading. From these results, it may be onluded that with inrease in atalyst loading, the rate of both esterifiation and hydrolysis reation inreases equally keeping the seletivity to the produts unaffeted. Table Effet of atalyst loading on seletivity of EGDA a Catalyst loading/% (w/v) Seletivity/% to EGDA at different reation times 30 min 60 min 10 min 300 min a Conditions: Aeti aid to ethylene glyol mole ratio = 3.13; temperature at 333 K; stirring speed = 1500 rpm. Fig. 3 Arrhenius plot of ln(initial rate) against 1/T. Conditions: All onditions are same as in Fig.. Effet of atalyst loading The effet of atalyst loading was studied at three different atalyst loadings in the range of 0.5 to 1.5 % (w/v) of atalyst. The onversion of ethylene glyol inreases with inrease in atalyst loading as shown in Fig. 4. The effet of Fig. 4 The effet of atalyst loading on onversion of ethylene glyol. Conditions: temperature = 333 K; aeti aid to ethylene glyol mole ratio = 3.13; stirring speed = 1500 rpm. Effet of aeti aid to ethylene glyol mole ratio The effet of aeti aid to ethylene glyol mole ratio was studied at three different mole ratios of 0.66, 1.48, and 3.13, respetively, under idential experimental onditions. The aeti aid to ethylene glyol mole ratio was varied by varying the relative proportions of aeti aid and ethylene glyol keeping the total volume of the mixture onstant. With inrease in aeti aid to ethylene glyol mole ratio, the onversion of ethylene glyol was inreased as shown in Fig. 5a. This is beause of the depletion of ethylene glyol relative to aeti aid with inrease in aeti aid to ethylene glyol mole ratio. The effet of aeti aid to ethylene glyol mole ratio on EGDA seletivity is shown in Fig. 5b. For fixed onversion of ethylene glyol, seletivity to EGDA was inreased with inrease in aeti aid to ethylene glyol mole ratio as shown in Fig. 5b. With inrease in aeti aid to ethylene glyol mole ratio, the onentration of aeti aid relative to ethylene glyol was inreased whih in turn enhaned the reation of EGMA with aeti aid. As a result, the seletivity to EGDA was inreased. Similar results have been reported by Suman et al. The maximum EGDA seletivity of 70 % was observed at 80 % onversion of ethylene glyol at aeti aid to ethylene glyol mole ratio of 3.13.

5 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) 363 empirial model. The rates of formation of five different omponents involved in the reation were therefore represented by the following five ordinary differential equations (eqs.1 5). d EG k 1 k 1 (1) EG AA EGMA W daa k 1 EG AA k1egma W k k d EGMA d EGDA EGMA AA EGDA W () kegma AA kegma W (3) k k 1 EG AA 1 EGMA W k k (4) EGMA AA EGMA W dw k 1 EG AA k1egma W (5) kegma AA k EGDA W Eqs. 1 5 onstituted the developed empirial kineti model involving the four rate onstants. Fig. 5 Effet of aeti aid to ethylene glyol mole ratio on (a) ethylene glyol onversion and (b) EGDA seletivity. Conditions: temperature = 333 K; atalyst loading = 1.5 % (w/v); stirring speed = 1500 rpm. Modeling The experimental measurements were used to develop suitable kineti models for the reation of ethylene glyol with aeti aid in presene of a strongly aidi ation-exhange resin. In the present work, the two different kineti models, empirial and kineti model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) approah were developed. It was found experimentally that the reation was free from external mass transfer resistane. The kineti parameters presented here, however, inlude intraphase diffusional effets, if any. Empirial kineti model The esterifiation of ethylene glyol with aeti aid and hydrolysis as reverse reation are SN type reations (Sheme 1) and hene, the reations were onsidered as seond order in the developed Kineti model based on Langmuir-Hinshelwood-Hougen-Watson approah The kineti models were also formulated following the LHHW approah assuming ethylene glyol, aeti aid, EGMA, and EGDA were adsorbed on surfae. Sine the reation was found to be ontrolled by the kinetis only, the adsorption and desorption resistane was not onsidered and the model was developed based on surfae reation ontrolling only. Aording to this model, the rates of formation of the five omponents were given by the following five ordinary differential equations (eqs. 6 10). deg k EG AA k EGMA W 1 1 (6) daa k1eg AA k1egma W (7) kegma AA k EGDA W degma kegma AA kegma W (8) k1eg AA k 1EGMA W degda k EGMA AA k EGMA W (9) dw k1eg AA k1egma W k k EGMA AA EGDA W (10)

6 364 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) where AA, EG, EGMA, EGDA represent the fration of surfae overed by aeti aid, ethylene glyol, EGMA, and EGDA, respetively, and are given by the following equations. K AA AA AA 1 KEGEG KAA AA KEGMA EGMA KEGDAEGDA K EG EG EG 1 KEGEG KAA AA KEGMA EGMA KEGDAEGDA K EGMA EGMA EGMA 1 KEGEG KAA AA KEGMA EGMA KEGDAE GDA K EGDA EGDA EGDA 1 KEGEG KAA AA KEGMA EGMA KEGDAE GDA (11) (1) (13) (14) The developed kineti model involves four rate onstants, k 1, k, k 1, and k - and four adsorption equilibrium onstants, K AA, K EG, K EGMA, and K EGDA. Regression analysis and parameter estimation The kineti and equilibrium onstants of the developed models were estimated using the experimental data at four different temperatures, 333, 343, 353, and 363 K, by non-linear regression algorithm based on modified Levenberg Marquar. The ordinary differential equations of the developed models were integrated using fourth-order Runge-Kutta method with initial guess values of kineti and/ equilibrium onstants. The objetive funtion (F) to be minimized was then alulated based on alulated and experimental onentrations of five different omponents. The new guess values of the kineti and/ equilibrium onstants were then estimated following modified Levenberg-Marquar algorithm. This proess was repeated to minimize the objetive funtion, F, of eq. 15. F N i1 N model i N i i EG, EG, i AA, 1 EG i1 EGMA model, EGMA, i i EGMA N i1 N i1 model W, i W, i W model AA, i AA model EGDA, i EGDA, i EGDA (15) The estimated optimized rate onstants /equilibrium onstants at different temperatures are shown in Table 3 and Table 4 for empirial and LHHW-based models respetively. It was observed from the table that with inreasing temperature, the value of the rate onstants inreased as expeted. The value of adsorption equilibrium onstants of the developed LHHW-based model was found to derease with inreasing temperature. This is obvious as the adsorption is an exothermi proess. The Table 3 Kineti onstants of the empirial kineti model a Temperature/K Rate onstants/(kmol m 3 ) 1 s 1 k 1 k 1 k k Objetive funtion (F) a Conditions: Aeti aid to ethylene glyol mole ratio = 3; atalyst loading = 1.5 % (w/v). Table 4 Kineti and equilibrium adsorption onstants of the LHHW-based kineti model a Temperature/K Rate onstants/(kmol m 3 ) 1 s 1 Adsorption equilibrium onstants/(kmol m 3 ) 1 Objetive funtion (F) k 1 k k 1 k K EG K AA K EGMA K EGDA a Conditions: Aeti aid to ethylene glyol mole ratio = 3.13; atalyst loading = 1.5 % (w/v).

7 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) 365 Fig. 6 Experimental versus alulated onentration profiles at different temperatures. Conditions: atalyst loading = 1.5 % (w/v); aeti aid to ethylene glyol mole ratio = 3.13; stirring speed = 1500 rpm; (a) 333 K; (b)343 K; () 353 K; (d) 363 K. Fig. 7 The Arrhenius plot of ln(rate onstants) versus 1/T onentrations of ethylene glyol, aeti aid, EGMA, EGDA, and water were then alulated at various reation times using the estimated rate onstants at different temperatures and average relative deviation was alulated for both models. The average relative deviation of 9. % and 8.1 % was observed for empirial and LHHW-based model respetively. Therefore, LHHW-based model fits the experimental data better than empirial model. The onentration profile obtained from LHHW-based model at different temperatures was ompared with that of experimental data as shown in Fig. 6. The experimental and alulated onversion of ethylene glyol based on LHHW-based model at different temperatures were also ompared as shown in Fig. and quite a good agreement was observed between alulated and experimental results. The Arrhenius plot of ln(rate onstants) against 1/T was then made using the estimated rate onstants of the LHHW-based model at different temperatures as shown in Fig. 7. The ativation energy and pre-exponential fator were obtained from the slope and interept of the Arrhenius plot as shown in Table 5.

8 366 V. P. YADAV et al., Kinetis of Esterifiation of Ethylene Glyol with Aeti Aid, Chem. Biohem. Eng. Q. 5 (3) (011) Table 5 Ativation energy (E) and pre-exponential fator (A) of the kineti onstants of the LHHW-based model Rate onstants E, kj mol 1 A, units are onsistent with rate onstant k k k k Conlusions In the present work, the detailed kinetis of the esterifiation of ethylene glyol with aeti aid has been investigated in presene of a strongly aidi ation-exhange resin, seralite SRC-10 as atalyst. The aeti aid to ethylene glyol mole ratio was found to have enormous effet on the produt seletivity where higher mole ratio favors seletive formation of EGDA. The inrease in temperature and atalyst loading has been found to enhane the reation rate without signifiantly affeting the produt seletivity. The two different kineti models, empirial and kineti model based on LHHW approah were also developed to orrelate the experimental data. The rate onstants and equilibrium onstants of the developed kineti models were estimated using the experimental data at different temperatures using non-linear least square tehniques based on Levenberg-Marquar algorithm. The onentration of different omponents alulated based on estimated parameters were then ompared with experimental data and LHHW-based model was found to fit the experimental data better than empirial model. The ativation energies and frequeny fators of the rate onstants of the LHHW-based model were then determined from the interept and slope of the Arrhenius plot of ln(rate onstants) versus 1/T. ACKNOWLEDGMENTS Sunil K. Maity is thankful to the Department of Siene and Tehnology (DST), New Delhi, India, for funding this projet. Nomenlature A pre-exponential fator onentration, kmol m 3 E ativation energy, kj mol 1 F objetive funtion k rate onstant, (kmol m 3 ) 1 s 1 K adsorption equilibrium onstant, (kmol m 3 ) 1 T reation temperature, K N total number of experimental data Greek Letters fration of surfae overed by a partiular omponent Subsripts 1 forward reation of eq. i of sheme 1 1 reverse reation of eq. i of sheme 1 forward reation of eq. ii of sheme 1 reverse reation of eq. ii of sheme 1 AA aeti aid EG ethylene glyol EGDA ethylene glyol di-aetate EGMA ethylene glyol mono-aetate W water Supersripts Expt experimental Model model Referenes 1. Vispute, T. P., Huber, G. W., Green Chem. 11 (9) (009) Suman, T., Srinivas, S., Mahajani, S. M., Ind. Eng. Chem. Res. 48 (009) Widdeke, H., Hodge, P., Syntheses and Separations using Funtional Polymers. Wiley, New York, Yadav, G. D., Thathagar, M. B., Reat. Polym. 5 (00) Peters, A. T., Benes, E. N., Holmen, A., Keurentjes, T. F. J., Appl. Catal. A 97 (006) Lin, C. Y., Huang, J. Oean Eng. 30 (003) Lewis, R. J. Hawley s Condensed Chemial Ditionary, 14 th ed., Wiley- VCH Verlag GmbH & Co. KGaA, New York, Weinheim, Teo, H. T. R., Saha, B., J. Catal. 8 (004) Patwardhan, A. A., Sharma, M. M., Reative Polymers 13 (1990) Altkka, M. R., Citak, A., Appl. Catal. A 39 (003) Sharath, R., Kirumakki, N., Nagaraju, Narayanan, S. A., Appl. Catal. A 73 (004) Ine, E., Journal of Engineering Sienes 8 (00) Gangadwala, J., Mankar, S., Mahajani, S., Ind. Eng. Chem. Res. 4 (003) Sardin, M., Villermaux, J., Nouv. J. Chim. 3 (1979) Hashimoto, K., Adahi, S., Noujima, H., Udea, Y., Biotehnol. Bioeng. 5 (1983) Ray, A., Carr, R. W., Chem. Eng. Si. 50 (1995) Liao, X., Zhu, Y., Wang, S. G., Li, Y., Fuel Proess. Tehnol. 90 (009) Yadav, V. P., Study on esterifiation of ethylene glyol with aeti aid in the presene of seralite SRC-10 and moleular sieve 13X atalyst. M.Teh. Thesis, National Institute of Tehnology Rourkela, India, Shmid, B., Doker, M., Gmehling, J., Ind. Eng. Chem. Res. 47 (008) Shmid, B., Doker, M., Gmehling, J., Fluid Phase Equilib. 58 (007) 115.