Kinetics of the Esterification Reaction between Pentanoic Acid and Methanol Catalyzed by Noncorrosive Cation Exchange Resin

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1 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) 79 Kinetics of the Esterifiction Rection between Pentnoic Acid nd Methnol Ctlyzed by Noncorrosive Ction Exchnge Resin M. Shrm A. P. Toor b* nd R. K. Wnchoo b Energy Reserch Centre Pnjb University Chndigrh Indi b University Institute of Chemicl Engineering nd Technology Pnjb University Chndigrh Indi Originl scientific pper Received: July Accepted: December Methyl pentnote commonly known s methyl vlerte is the methyl ester of pentnoic cid (vleric cid) with fruity odour. Methyl pentnote is commonly used in frgrnces beuty cre sop lundry detergents t levels of %. In its very pure form (purity 99.5 %) it is used s plsticizer in the mnufcture of plstics. In the present investigtion kinetics of esterifiction of pentnoic cid with methnol ctlyzed by heterogeneous ctlyst in btch-type rector is reported. The effect of rection conditions such s temperture molr rtio ctlyst loding nd initil concentrtion of pentnoic cid nd methnol nd the inhibiting effect of wter on the kinetics hs been studied. The pentnoic cid conversion reched 93 % t K t methnol to pentnoic cid molr rtio of 10:1 with 7 % (g L 1 ) Amberlyst 15 s ctlyst. Mss trnsfer effects were found to be negligible. Observed rection rte dt ws fitted to the regression technique. Estimted Eley-Ridel kinetic model rection rte constnts were fitted to the Arrhenius type eqution with ctivtion energy E A 39.5 kj mol 1 nd pre exponentil fctor k o L 2 g 1 mol 1 h 1. Key words: Esterifiction ion exchnge resin heterogeneous kinetic kinetic modelling Amberlyst 15 Introduction The extensive demnd for clener environment is forcing the chemicl industry to use less hzrdous mterils. In this regrd solid ctlysts hve ltely ttrcted the ttention of scientists nd reserchers round the world. 1 8 By using sufficient mounts of these heterogeneous ctlysts their ctlytic ctivity for ester formtion cn be equivlent to tht of conventionl homogeneous ctlysts. Solid ctlysts hve good properties in terms of their esterifiction efficiency. 910 Amongst the wide vriety of solid ctlysts vilble ction ion-exchnge resin is widely used in esterifiction process becuse it is not corrosive nd esy to seprte from the rection mixture. 67 Mny uthors hve studied the esterifiction rections using ion exchnge resins. In spite of mny reports on the esterifiction rections over ion exchnge resins however few kinetic studies consider the effect of dsorption desorption nd prtitioning phenomenon occurring between the interior nd the exterior liquid phses with respect to the resins. For exmple Snz et l. 11 hve studied the kinetics of lctic cid esterifiction rection with methnol ctlyzed by different cidic resins. These uthors hve interpreted their results by mens of * Corresponding uthor: E-mil: ptoor@yhoo.com n Eley Ridel (ER) nd Lngmuir Hinshelwood (LH) model. Ali nd Merchnt 12 hve reported kinetic results relted to the esterifiction between cetic cid nd 2-propnol on different resins interpreting the obtined dt with vrious models: pseudo-homogeneous (PH) Eley Ridel (ER) Lngmuir Hinshelwood (LH). One of the chllenges in determining kinetic prmeters for the esterifiction over solid cid ctlysts is the proper hndling of the wter concentrtion. 13 Ylcinyuv et l. 14 demonstrted tht the phse prtitioning nd the swelling phenomen cnnot be neglected for n ccurte description of n esterifiction process involving ionic exchnge resins. In fct they hve investigted the esterifiction rection of myristic cid with isopropyl lcohol ctlyzed by Amberlyst 15 nd they hve shown tht the wter concentrtion slows down the conversion but is found to be lower thn the theoreticl vlue clculted on the bsis of the mesured cid conversion. Lee et l. 15 hve studied the kinetics of the esterifiction rection of cetic cid with methnol in the presence of Amberlyst 36 s ctlyst. According to their study the mgnitude of dsorption strengths follows the order of wter > methnol > cetic cid > methyl cette. Popken et l. 16 nd Song et l. 17 hve studied the esterifiction rection of cetic cid with methnol lso using Amberlyst 15 s ctlyst. How-

2 80 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) ever the esterifiction chrcteristics of nonnoic cid with methnol 3 cetic cid with n-butnol nd isobutnol 18 lctic cid with isopropnol 19 over Amberlyst 15 hs been investigted by our reserch group in order to gin full understnding of the reltionship between solid cid ctlysts nd wter. Here we report the esterifiction of pentnoic cid with methnol over Amberlyst 15 (Heterogeneous Ctlyst). It ws found tht Amberlyst 15 is better lternte for esterifiction rection thn cid ctlysts which re not ecofriendly. In this rticle we determined the rte equtions including inhibiting effects pplicble to the solid cidic resins. As fr s we know there hs been no ttempt to investigte the kinetics of pentnoic cid esterifiction with methnol ctlyzed by Amberlyst 15. The btch experiments were crried out in 500 ml double jcketed three-necked glss rector equipped with reflux condenser in the temperture rnge of 313 to 333 K. The rection temperture ws mintined using thermosttic wter bth (Julbo F20) within n ccurcy of ± 0.1 C. The rection mixture ws continuously stirred with n overhed stirrer fitted with motor nd speed regultor. The pentnoic cid nd the ctlyst were first chrged into the rector through peephole on the lid nd heted to the desired temperture. Therefter methnol t the sme temperture ws fed into the rector. The time t which the methnol ws dded ws considered s zero time or the strting point of the rection. Smples of 1 ml were tken every 15 minutes for the first hour nd every 30 minutes for the next 2 6 hours for nlysis. The rection prmeters re given in Tble 1. All experiments were performed t lest three times in order to ensure reproducible results. Below is the scheme of the given rection: Experimentl study Chemicls nd ctlysts Pentnoic cid (purity >99.5) methnol (purity >99) nd 1 4-dioxne were purchsed from Merck nd used without further purifiction. Gs chromtogrphy nlysis showed their respective purity vlues to be greter thn 99 %. For titrtion the lkli used ws 0.5 mol L 1 NOH volumetric-stndrd solution purchsed from Aldrich Chemicl Co. Amberlyst 15 (wet) ws obtined from Rohm nd Hss. The ctlyst ws initilly wshed four to five times with distilled wter nd dried t mbient conditions for 4 5 hours. Further the ctlyst ws wshed by dipping in n 0.1 mol L 1 HCl solution for hlf n hour. This solution ws then filtered to seprte the ctlyst nd dried t tmospheric conditions for bout 48 h. The chrcteristics of the ctlyst were listed in our previous work. 3 Apprtus nd rection procedure Anlysis For kinetic mesurements smples were tken periodiclly nd the mount of pentnoic cid ws determined by titrtion with stndrd 0.5 mol L 1 sodium hydroxide solution using phenolphthlein s n indictor. Prllel tests indicted tht the verge error of the titrtion method ws less thn 2 %. The smples were lso nlyzed by gs chromtogrph (Nucon 5765) equipped with fused silic cpillry column of 30 m 0.25 mm I.D. (Inner Dimeter of column) 0.25 μm film thickness flme ioniztion detector nd therml conductivity detector by mtching the retention time of the rection product to the retention time of methyl nonnote. Nitrogen with purity of % ws used s the crrier gs. Results nd discussion Exclusion of mss trnsfer effects For this esterifiction rection frctionl conversion of pentnoic cid ws found to be independent of externl diffusion limittions for stirrer speed of more thn 400 rpm. Four runs were crried out t molr rtio of 1 (pentnoic cid) : 10 (Meth- Tble I Rection Prmeters S.No. Temp./K Molr rtio Ctlyst loding Stirrer speed/rpm Prticle size to 333 1:10 (cid to lcohol) 57.6 g L 1 (7 % w/v) μm :10 (cid to lcohol) g L 1 to g L 1 (4 % to 8 %) μm :1 to 1:15 (cid to lcohol) 57.6 g L 1 (7 % w/v) μm : g L 1 (7 % w/v) μm : g L 1 (7 % w/v) μm μm

M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) 79 85 (2014) 81 nol) temperture: 333.15 K ctlyst loding: 57.

3 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) 81 nol) temperture: K ctlyst loding: 57.6 g L 1 by vrying stirrer speeds from rpm. Fig. 1 shows tht the frctionl conversion increses with increse in stirrer speed from 300 to 500 rpm while keeping ll other prmeters constnt but fter 500 rpm there is no significnt effect of stirrer speed. Hence n gittion speed of 500 rpm ws used for this study in order to rule out the presence of externl mss trnsfer. The effect of prticle size ws exmined by crrying out the rection using vrious prticle sizes. Fig. 2 shows tht frctionl conversion is independent of the prticle size rnging from μm. Hence from the experimentl results nd comprison with our previous work 3 on Amberlyst 15 internl mss trnsfer ws neglected. 3 gives the results for the effect of ctlyst loding on conversion of pentnoic cid. It cn be seen from Fig. 3 tht higher loding of ctlyst results in reduction of the time required to rech rection equilibrium nd t temperture condition K the use of ctlyst lodings greter thn 7 % does not pper ttrctive. All further kinetic studies were therefore conducted t this pprently optimum ctlyst loding. Fresh resin ws used for ech new run. Fig. 3 Frctionl conversion vs. time for different ctlyst loding: 4 % 5 % 6 % 7 % 8 %; Molr rtio 1:10 temperture K 500 rpm Effect of temperture Fig. 1 Percentge conversion vs rpm t K 1:10 molr rtio nd ctlyst loding 57.6 g L 1 The rection ws crried out t vrious rection tempertures rnging from to K while keeping other prmeters constnt. The effect of incresing the rection temperture is shown in Fig. 4 in the temperture region of K to K molr rtio of cid to lcohol t 1 : 10 nd ctlyst loding 7 %. In generl the ester conversion ws found to increse with incresing rection temperture. Incresing the temperture is pprently fvorble for the ccelertion of the forwrd rection. Fig. 2 Frctionl conversion vs. time (min) for different prticle sizes t K 1:10 molr rtio nd ctlyst loding 57.6 g L μm μm Effect of ctlyst loding Exmined ws the effect of vrying the ctlyst loding from 4 to 8 % (g L 1 ) on pentnoic cid esterifiction with methnol t n cid to lcohol molr rtio of 1:10 nd temperture K. Fig. Fig. 4 Frctionl conversion vs. time (min) for different temperture; K K K K K Molr rtio 1:10 Ctlyst loding 57.6 g L rpm

4 82 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) Effect of feed molr rtio Esterifiction of pentnoic cid with methnol being reversible rection is n equilibrium limited chemicl rection nd the position of equilibrium controls the mount of ester formed the use of n excess of methnol drives the equilibrium towrds the formtion of ester nd enhnces the forwrd rection. The molr rtio of methnol to pentnoic cid ws vried from 1 : 1 to 15 : 1 t temperture K 57.6 g L 1 ctlyst loding nd stirrer speed of 500 rpm. It ws observed tht cid conversion increses with the mount of methnol s shown in Fig. 5. Fig. 5 Frctionl conversion vs. time (min) for different molr rtio; 1:1 1:5 1:10 1:15 temperture K ctlyst loding 57.6 g L rpm Mthemticl model for esterifiction kinetics Initil rte of rection (r Ao = C Ao / t) defined up to conversion of 10 % ws observed using different concentrtions of pentnoic cid methnol nd wter. The concentrtions were converted to ctivities ccording to eqution 1 in order to ccount for the non-idel behvior of the rection mixtures. 3 Activity is clculted by eq. 1 given below: C i i gixi g i (1) Ct where i is ctivity of the components g i is ctivity coefficient x i is mole frction C i (mol L 1 ) is concentrtion of rectnts nd C t (mol L 1 ) is totl concentrtion of the rection mixture which is kept constnt. Activities of the chemicl compounds used in this study were clculted using UNIFAC group contribution method A generl kinetic expression for esterifiction rection ctlyzed by heterogeneous ctlysts cn be written s: r A E W kw f ct A B Ke 1K K K K A A B B E E W W n (2) where r A is the rection rte w ct weight of ctlyst in terms of the mount of dry ctlyst A B E W re pentnoic cid Methnol Methyl pentnote nd Wter respectively. K is the dsorption constnt K e is equilibrium rection rte constnt nd k f is the rte constnt where n = 0 for PH model 1 for ER model nd 2 for LHHW model. As evident from Fig. 6 rther thn producing plteu the initil rection rte is liner function of initil concentrtion of pentnoic cid giving evidence tht pentnoic cid is not dsorbed over the surfce of Amberlyst 15 beds nd t the sme time the initil rection rte increses linerly with methnol concentrtion wheres t high methnol concentrtion the rte is essentilly independent of it. Hence we cn conclude tht dsorption effect of methnol is very low t low concentrtions of methnol nd it lmost becomes constnt s the concentrtion is incresed further. Wheres Fig. 6 shows tht initil rection rte is non-liner function of concentrtion of wter nd decreses with increse in concentrtion of wter. 3 This confirms the inhibiting effect of the wter concentrtion s the rection proceeds. From this nlysis it is concluded tht the rection mechnism cn be represented by the Eley-Ridel (ER) model i.e the rection occurs between dsorbed molecules of methnol nd the molecules of pentnoic cid in the bulk solution. In ddition the wter molecules dsorbed by resin hve n inhibiting effect on the rection rte. The dsorption of solvent (dioxne) nd ester were reported in the literture to be negligible. 20 So stoichiometric nd corresponding rection rte expression in the form of Eley-Ridel (ER) model with surfce rection is the rte-determining step fter excluding the dsorption terms of cid nd ester rection eq. 2 cn be written in the ER form; Fig. 6 Effect of rectnt concentrtion shown in terms of ctivity on the initil rection rte (-r Ao ) t three different tempertures K K K. Ctlyst loding 7 % (w/v) 500 rpm; dsh-dot line ( ) : pentnoic cid double-dshed line (= = =): methnol nd solid line ( ): wter.

5 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) 83 E W kw f ct A B Ke ra (3) 1 K K B B W W A B E W re pentnoic cid methnol methyl pentnote nd wter respectively nd k f is the forwrd rection rte constnt in (L 2 g 1 mol 1 h 1 ) is o E i RT given s k i ki exp w ct is weight of ctlyst in g L 1 K is dsorption constnt nd K e is the esterifiction rection equilibrium constnt bsed on ctivity ctlyzed by Amberlyst 15. In eq. (3) ctivity rther thn concentrtion is used in the rte expression becuse it results in improved predictions of the models fitted ginst the mesured kinetic dt. Rerrnging eq. 3 for the initil rection rte with no product present cn be defined s eq. 4: AoBo 1 KB r ( k w ) k w Ao f ct f ct Bo (4) Ao Bo Plot of versus Bo results in stright rao K B line with the slope w ct nd intercept 1 wct s shown in Fig. 7. Rerrnging eq. 3 to check the inhibiting effect of wter plot of Ao Bo versus Wo results in stright line with rao K W the slope of w ct nd intercept 1 KBBo s wct shown in Fig. 8. From the slopes nd intercepts in these figures (7 nd 8) the rte constnts nd dsorption constnts k f K B K W re obtined nd their estimted vlues t three tempertures re presented in Tble 2. Fig. 8 Ao Bo r Ao versus Activtion energy nd rte constnts The temperture dependency of the rte constnt is expressed by the Arrhenius lw: i Wo o i t three different tempertures: K K K ctlyst loding 7 % w/v 500 rpm Tble 2 Kinetics nd dsorption prmeters Temp./K k f /L 2 mol 1 g 1 h 1 K B /L mol 1 K w /L mol E i RT k k exp (5) where i = f B W E i is ctivtion energy nd k i o is the frequency fctor. From eq. (5) plot of ln k f ln K B nd ln K W versus 1/T gives stright line with the slope of (E/R) nd intercept ln k io s shown in Fig. 9 versus 1/T. The ctivtion energy ws found to be 39.5 kj mol 1 in the presence of Amberlyst 15 ion-exchnge resin. The temperture dependency of the rte nd dsorption constnts cn be correlted by the following equtions: Fig. 7 Ao. Bo r Ao versus Bo t three different tempertures: K K K ctlyst loding 7 % (w/v) 500 rpm Fig. 9 Arrhenius plot of lnk B lnk f lnk W vs.1/t for ctlyst loding 7 % (w/v) 500 rpm

6 84 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) k f (L g mol h ) exp 7.5 T (6) K B (L mol ) exp T K W (L mol ) exp T Model prediction (7) (8) The observed rection rte for the esterifiction of pentnoic cid with methnol ws compred with the proposed ER model (eq. 3) using the rte consnts described by eqs. 6 8 over the whole rnge of predicted prmeters (given in Tble I). Experimentl dt ws clculted by the eqution below where C A is concentrtion of cid t is rection time nd X is conversion of cid. DCA DX ra experimentl CAo (9) Dt Dt The prity between the experimentl nd clculted vlue is given in Fig. 10. Model eq. 3 represents the dt resonbly well within ± 10 %. loding nd molr rtio ws found to increse the percent conversion of pentnoic cid. Wter hs n inhibiting effect on the conversion of cid. Non-idel behviour of the liquid mixture is tken into ccount nd UNIFAC group contribution method ws found to predict component ctivity coefficients resonbly well. On the bsis of dsorption study Eley-Ridel (ER) ws developed to interpret the obtined kinetic dt. Experimentl dt fitted the kinetic model well. Besides proving the dequcy of the tried model the obtined prity plot for clculted vs. experimentl lso proves the success of the UNIFAC model in predicting the ctivity coefficients of the components present in the system. The ctivtion energy E A for the forwrd rection ws found to be 39.5 kj mol 1 for ER model ctlyzed by Amberlyst 15. ACKNOWLEDGEMENT We grtefully cknowledge the finncil support received from UGC (Government of Indi) Project No. F.No / 2009 (S.R.). Nottions Fig. 10 Prity plot (experimentl vs. clculted rte) for dt in the ctlyst rnge of 4 % (w/v) to 8 % (w/v) molr rtio 1:1 to 1:15 temperture K to K t 500 rpm Conclusion The rection kinetics of esterifiction of pentnoic cid with methnol ws studied in temperture rnge of to K ctlyst loding 4 % to 8 % nd molr rtio of cid to lcohol 1:1 to 1:15 t stirrer speed of 400 rpm over Amberlyst 15. Experimentl findings show tht the rection is kineticlly controlled rther thn mss trnsfer effects. Under the conditions studied the increse in the ctlyst Activity E A Activtion energy kj mol 1 k o Preexponentil fctor L 2 g 1 mol 1 h 1 K e Equilibrium constnt k f Forwrd rection rte constnt L 2 g 1 mol 1 h 1 n Number of experimentl dt w ct Weight of ctlyst g L 1 T Absolute temperture K t Time x i Molr frction γ Activity coefficient ln Nturl logrithm (bse e) R J mol 1 K 1 ER Eley Ridel model UNIFAC Universl qusichemicl functionl group ctivity coefficients rpm Revolution per minute References 1. Ydv G. D. Bhgt R. D. Clen Technol. Environ. Policy 7 (2005) Ydv G. D. Thtgr M. B. Rect. Funct. Polym. 52 (2002) Shrm M. Wnchoo R. K. Toor A. P. Ind. Eng. Chem. Res. 51 (2012) Collignon F. Loenders R. Mrens J. A. Jcobs P. A. Poncelet G. J. Ctl. 182 (1999) 302.

7 M. SHARMA et l. Kinetics of the Esterifiction Rection between Pentnoic Acid nd Chem. Biochem. Eng. Q. 28 (1) (2014) Kim H. J. Kng B. S. Kim M. J. Kim D. K. Lee J. S. Lee K. Y. Stud. Surf. Sci. Ctl. 153 (2004) Ding J. He B. Li J. J. Biobsed Mter. Bioenergy 5 (7) (2011) Feng Y. He B. Co Y. Li J. Liu M. Feng Y. Ling X. Bioresour. Technol. 101 (2010) Lopez D. E. Goodwin J. G. Bruce D. A. Lotero E. Appl. Ctl. A 295 (2005) Mrchetti J. M Miguel V. U. Errzu A. F. Fuel 86 (2007) Prk Y. M. Lee D. W. Kim D. K. Lee J. S. Lee K. Y. Ctl. Tody 131 (2008) Snz M. T. Murg R. Beltrn S. Ind. Eng. Chem. Res. 41 (2002) Ali S. H. Merchnt S. Q. Int. J. Chem. Kinet. 38 (2006) Schildhuer T. J. Hoek I. Kptejin F. Moulijn J. A. Appl. Ctl. A 358 (2009) Ylcinyuv T. Deligoz H. Boz I. Gurkynk M. A. Int. J. Chem. Kinet. 40 (2008) Lee M. Tsi Y. T. Lin H. Chem. Eng. J. 171 (2011) Popken T. Gotze L. Gmehling J. Ind. Eng. Chem. Res. 39 (2000) Song W. Venimdhvn G. Mnning J. M. Mlone M. F. Doherty M. F. Ind. Eng. Chem. Res. 37 (1998) Toor A. P. Shrm M. Kumr G. Wnchoo R. K. Bull. Chem. Rect. Eng. Ctl. 6 (2011) Toor A. P. Shrm M. Thkur S. Wnchoo R. K. Bull. Chem. Rect. Eng. Ctl. 6 (2011) Fogler H. S. Elements of chemicl rection engineering 3rd ed. Prentice Hll Houston Fredenshnd A. Jones R. L. Prusnitz J. M. AIChE J. 21 (1975) Tiegs D. Gmehllng J. Rsmussen P. Fredenslund A. Ind. Eng. Chem. Res. 26 (1987) 159.

Module 2: Rate Law & Stoichiomtery (Chapter 3, Fogler)

Module 2: Rate Law & Stoichiomtery (Chapter 3, Fogler) CHE 309: Chemicl Rection Engineering Lecture-8 Module 2: Rte Lw & Stoichiomtery (Chpter 3, Fogler) Topics to be covered in tody s lecture Thermodynmics nd Kinetics Rection rtes for reversible rections