Modeling of esterification-pervaporation integrated system with ethanol

Transcription

1 Research Journal of Engneerng Scences ISSN Vol. 6(3), -5, March (27) Modelng of esterfcaton-pervaporaton ntegrated system of acrylc acd wth ethanol Abstract Ghoshna Jyot *, Amt Keshav and J. Anand Kumar Department of hemcal Engneerng, Natonal Insttute of Technology Rapur (G), Inda Avalable onlne at: Receved 3 th November 26, revsed 2 th February 27, accepted 4 th March 27 Knetc model for esterfcaton of acrylc acd wth ethanol usng sulphurc acd (H 2 SO 4 ) as a catalyst coupled pervaporaton process was establshed n ths work. The major effects of dfferent parameters such as reacton temperature, ratos of ntal molar quantty of reactants, membrane area, catalyst concentraton and membrane permeablty on the esterfcaton reacton and the permeaton knetcs of water removed by pervaporaton were taken nto consderaton n ths knetc model. The developed model equatons are solved by the ODE solver, ode45 mplemented n the MATLA. The esterfcaton of acrylc acd wth ethanol usngh 2 SO 4 was carred out at a temperature range of 5 7, catalystt concentraton of -3% of reacton mxture and ntal reactant molar rato of :-:3. The converson of acrylc acd or yeld of ethyl acrylate was enhanced n a pervaporaton reactor as compared to a conventonal reactor. The result ndcates that the esterfcaton pervaporaton ntegrated system accelerates the rate of ester formaton by removng water. Keywords: Pervaporaton, Esterfcaton, Membrane, Modelng, Acrylc acd. Introducton Nowadays, mergng reactor wth separaton unt has become a current trend n the chemcal ndustry n order to obtan more effcent processes and lower energy consumpton. Ths combnaton s advantageous for the producton of esters from esterfcaton reacton as ths reacton s thermodynamcally lmted. Pervaporaton process shfts the chemcal equlbrum towards the producton of ester by removng water contnuously. Pervaporaton (PV) s useful for dehydraton of organcchemcals 2. Moreover, PV enhances both converson and reacton rates as t can remove water smultaneously from the reactor. Mathematcal modelng of coupled reacton-membrane systems has attracted great nterest because t can provde an nsght nto the ndustral desgn and optmal operaton of theseprocesses 3. In present work the resultng ester ethyl acrylate from the esterfcaton reacton between acrylc acd and ethyl alcohol can be used as a reactve buldng block to produce coatngs and nks, adhesves, sealants, textles, plastcs and elastomers 4,5. Pervaporaton membrane reactors asssted wth esterfcaton have been studed of acrylc acd and n-butanol 6, lactc acd and so-propanol 7, acetc acd and so-propanol 8, acetc acd and soacd and ethanol. butanol 9, acetc acd and ethanol, lactc Lmted work related to esterfcaton- pervaporaton hybrd system of acrylc acd wth ethanol has been avalable on lterature 2. Truong et al used a polymer based membrane to mprove the synthess of acrylc esters and nvestgated the chemcal stablty of the membrane. In present paper experments weree conducted for esterfcaton of acrylc acd wth ethanol ntegrated wth pervaporaton and wthout pervaporaton. Modelng of the esterfcaton reacton coupled wth PV process has also been presented for the esterfcaton of acrylc acd wth ethanol. The model was valdated usng expermental data. esdes, the effect of varous process varables, such as process temperature (T), ntal mole rato of reactants (MR), and the rato of the effectve membrane area over the volume of reactng mxture (S/V),catalyst content ( ) on the performance of pervaporaton reactor for esterfcaton reacton were dscussed. Materals and methods The hydrophlc PVA membrane, used n ths work was suppled by Permoncs Membranes Pvt. Ltd., Inda. All reactants (acrylc acd, ethanol) and catalyst (sulfurc acd) were of analytcal grade wth purty hgher than 99% and obtaned from Merck. The expermental set-up used for the PV couple desterfcaton reacton was performed n stu batch operaton mode. The membrane was placed just below the reactor n a partcular cell. The effectve membrane area whchh was n contact wth the feed mxture was 78.5 cm 2. Reactants were added to the reactor along wth catalyst and heated up to the desred reacton temperature. The strrer was started at 3 rpm speed for the proper mxng of reacton mxture. A thermostat has been used to mantan the temperature wthn the accuracy of ± durng the reacton. th the help of hydrophlc membrane (PVA), water was separated from the feed mxture smultaneously. The Internatonal Scence ommunty Assocaton

2 Vol. 6(3), -5, March (27) pressure on the permeate sde was held constant at 5 mbar and chller temperature was mantaned at -5. Durng the experment samples were wthdrawn from the reactor at regular ntervals. Samples collected from the reactor and the permeate were analyzed by NUON seres 57 gas chromatograph (G) wth porapak column (d 2mm, od /8, length 2 m) hydrogen gas taken as carrer gas wth flow rate 6 ml/mn equpped wth a TD detector. Sample has njected n chromatograph wth amount of µl. To obtan accurate results, each sample was analyzed two tmes. The operatng condtons for the gas chromatograph are:. Temperature (ᵒ),. Injector: 5,. Detector: 8, v. Oven: 8. Modelng of the membranereactor: The mathematcal model of a hybrd system of a batch reactor for esterfcaton coupled wth pervaporaton s based on three aspects: (a) reacton knetcs of esterfcaton, (b) membrane perm selectvty n pervaporaton, and (c) mass balance. The esterfcaton reacton between acrylc acd (A) and ethyl alcohol () to produce ethyl acrylate (E) and water () can be represented by an elementary reversble reacton havng second order. The reacton can be wrtten as follows: + + The rate expresson for second order reversble reacton can be wrtten as: d A ra = = k A k E () dt here: A,, E, and represents the concentraton (mol/m 3 ) of acrylc acd, ethanol, ethyl acrylate, water and catalyst respectvely. k and k - are the forward and backward reacton rate constants and t s the reacton tme. The change n concentraton of acrylc acd, ethyl alcohol, ester and water can be deduced from the materal balance and can be presented as da d de d r = = = = = k A k E (2) dt dt dt dt To consder non-deal thermodynamc behavor of the reacton mxtures, the chemcal actvtes nstead of concentratons can be used n the reacton rate equaton: r = k (3) A A k here, A,, E and represent the actvty coeffcent of acrylc acd, ethanol, ethyl acrylate, water and catalyst respectvely. E E Equaton (3) can be wrtten as d( ) r = = k A A dt E E K here: the equlbrum constant, K eq can be calculated from the gven equaton below as K eq k = k EE = A A For smplfyng the mathematcal model followng assumptons can be made:. constant selectvty of the PVA membrane,. sothermal reacton and pervaporaton,. constant catalyst actvty, and v. the partal molar volume n a mxture s the same as that of a pure component 3. y combnng pervaporaton wth the esterfcaton, the change of concentraton can be wrtten as follows: d( ) S = r J (5) dt V In present work a hydrophlc PVA membrane was used so the partal fluxes of components acrylc acd, ethanol and ethyl acrylate were neglected (J Ethanol J Acd J ester ). The water balance n the PV coupled reactor can be wrtten as: d( dt ) = k A A E E K eq eq The relatonshp between flux and feed water concentraton s nonlnear and vares throughout the reacton. Hence the followng modfed relaton can be used 2. J = k k 2 PV PV 2 here: k PV and k PV2 are emprcal constants. Soluton methodology: The model equatons descrbed n the prevous secton conssts of non-lnear dfferental equatons. These ODEs along are solved by an ODE solver, ode45 n Matlab, to get the solutons of concentraton profle of reactants and product. The set of knetc parameters are estmated by a nonlnear optmzaton technque. The error between the model and expermental data serves as the objectve functon to be mnmzed by usng combnaton of optmzaton routne fmncon and Genetc Algorthm from the Matlab Optmzaton Toolbox. The objectve functon of the optmzaton problem s φ = N cal exp ( ) = 2 S V J (4) (4) (6) (7) (8) Internatonal Scence ommunty Assocaton

3 Vol. 6(3), -5, March (27) here: N s the number of expermental data ponts for concentraton of acrylc acd. The knetc parameters are obtaned by solvng the model equaton based on the successve guess values of the knetc parameters. In order to study the non-dealty assocated wth the reacton mxture, we need to consder the actvty coeffcents along wth the concentratons to determne the equlbrum constant. Here we consdered UNIFA method to determne the actvty coeffcents. The coeffcents are drectly obtaned from Aspen Plus software. Results and dscusson The man parameters whch affect the esterfcaton-pv aded process can be classfed nto three groups:. Factors affectng only the esterfcaton knetcs: catalyst concentraton, and ntal molar rato of methanol to salcylc acd.. Factors affectng only the pervaporaton knetcs: rato of effectve membrane area to volume of reacton mxture.. Factors affectng both the esterfcaton and pervaporaton knetcs: temperature. The esterfcaton reactons were carred out n annstu pervaporaton membrane reactor wth and wthout pervaporaton. The experments were carred out by changng dfferent process parameters such as temperature (5-7 o ), ntal mole rato of acrylc acd to ethanol (:-:3), catalyst concentraton (-3%) and the rato between the effectve membrane area and reacton volume ( m - ) were carred out. The results are dscussed n further secton. For the valdaton of the developed model the obtaned results are compared wth expermental data and are presented n Fgure-. The suggested model predcted results were n good agreement wth the expermental data. It was observed that the PV ntensfed the converson of acrylc acd for the PV coupled esterfcaton reacton than for the esterfcaton wthout PV. For ths experment the operatng condtons are consdered as reacton temperature of 5, molar rato of reactants of : and catalyst loadng of 3% (vol). Acrylc acd converson was ncreased from ts equlbrum value of 46% to 57.2% n 7 hr by usng PVA membrane reactor. The ncrement n the amount of the any reactant shfts the chemcal equlbrum towards the product sde. Fgure-2 presents the effect of ntal mole rato of acrylc acdto ethanol, MR, on the performance of the pervaporaton-esterfcaton coupled reactor. The smulatons were carred out under the operatng condtons as temperature of 6, of 3%, S/V of 4.3 m -. The reacton rate of esterfcaton ncreases wth an ncrease n amount of ethanol. The converson ncreased from 78% to 98.8% wth changng molar rato from : to :3. In esterfcaton catalyst concentraton s also another way to accelerate reacton rate. For the analyss, the catalyst concentraton was vared from to 3% of ntal volume of the reactng mxture. The smulaton results for converson of acrylc acd durng esterfcaton aded PV process over varous catalyst loadngs were presented n Fgure-3. It can be seen that as catalyst concentraton ncreased the converson of acrylc acd ncreases due to the avalablty of more H + ons enhancng converson. A catalyst ncreases the rate of the chemcal reacton by makng avalable a new low energy pathway for the converson of reactants to products 5. An ncrease n the temperature enhances the esterfcaton reacton because a hgher temperature favors both water removal by pervaporaton and the rate of reacton 3. Effect of temperature on the esterfcaton-pv process of acrylc acd and ethanol was studed for the fxed molar rato of acrylc acd to ethanol of : and 3% (vol) of catalyst by varyng temperature from 5 to 7. Fgure-4 shows that ncreasng n temperature ncreases the converson of acrylc acd. The acceleratng of the rate of reacton wth the ncrease of the temperature for the forward reacton was faster than the backward process..7 onverson of acd XA Seres Fgure-: Dependence of converson on tme wth and wthout PV. The sold lnes ndcate the values predcted by the knetc model. (T=5, =3%, MR=:, S/V=4.3m - ). Internatonal Scence ommunty Assocaton 2

4 Vol. 6(3), -5, March (27).2 onverson of acd XA :3 :2 : Fgure-2: Effect of change n molar rato on converson of acrylc acd (T=6, =3%, S/V=4.3m - ). onverson of acd XA Fgure-3: Effect of change n concentraton of catalyst on converson of acrylc acd (T=6, MR=:, S/V=4.3m - ). converson of acd XA Fgure-4: Effect of the reacton temperature on the converson of the PV-aded esterfcaton of acrylc acd and ethanol (MR= :, =3%, S/V=4.3m - ). % 2% 3% Internatonal Scence ommunty Assocaton 3

5 Vol. 6(3), -5, March (27) onverson of acd XA m m- 4.3 m Fgure-5: Effect of the rato between the membrane area and reacton volume on the converson of the PV coupled esterfcaton of acrylc acd and ethanol (T=6, MR= :, =3%). The larger membrane area could remove the byproduct water suffcently, and thus the esterfcaton was enhanced. Smulatons were carred out wth changng the rato of membrane area to ntal reacton volume as 4.3, 7.66 and m - and the obtaned results were presented n Fgure-5. The values for the other operatng parameters were the followng: molar rato of ntal reactant,, catalyst loadng, 3%, and reacton temperature 6. As ncreasng S/V, the water removal rate wll be more and hence leadng to enhanced converson. oncluson onverson of reversble reacton s lmted due to occurrence of chemcal equlbrum. Hence these reactons are ntegrated wth addtonal process to shft the chemcal equlbrum thereby ntensfyng the converson. In ths work, a seres of esterfcaton reacton of acrylc acd and ethanol coupled wth pervaporaton were conducted at dfferent operatng temperature, catalyst concentraton, ntal composton, etc. Moreover, dfferent ratos of the membrane area to reactng mxture volume were also studed. It was observed that these parameters have sgnfcant effect on the performance of the esterfcaton pervaporaton ntegrated reactor. Pervaporaton and reacton rate both can be ncreased wth ncrease n operatng temperature. The ester rate formaton ncreases sgnfcantly wth ncrease n catalyst concentraton. hen the A/Vo rato ncreases hgher ester conversons were obtaned. Nomenclature: A = concentraton of acrylc acd (mol/m 3 ), = concentraton of ethyl alcohol (mol/m 3 ), E = concentraton of ethyl acrylate (mol/m 3 ), = concentraton of water (mol/m 3 ), = concentraton of catalyst (mol/m 3 ), A = actvty coeffcent of acrylc acd, = actvty coeffcent of ethanol, E = actvty coeffcent of ethyl acrylate, = actvty coeffcent of water, k = forward reacton rate constant((m 3 ) 2 /kmol 2.mn), k- = backward reacton rate constant ((m 3 ) 2 /kmol 2.mn), t = reacton tme (mn), T = reacton temperature ( ), K eq = equlbrum constant, S = membrane area (m 2 ), J = total flux (gm/m 2.mn), R = rate constant (8.34 J/mol K), V = volume of ntal reacton mxture. References. Han Y., Lv E., Ma L., Lu J., hen K. and Dng J. (25). ouplng membrane pervaporaton wth a fxed-bed reactor for enhanced esterfcaton of olec acd wth ethanol. Energy onvers. Manag., 6, asewar K., Patdar S. and Agarwal V.K. (29). Esterfcaton of lactc acd wth ethanol n a pervaporaton reactor: modelng and performance study. Desalnaton, 243(-3), Yun Z.O.U., Zhangfa T., Kun L.I.U. and Xanshe F. (2). Modelng of Esterfcaton n a atch Reactor oupled wth Pervaporaton for Producton of n -utyl Acetate. hnese Journal of atalyss, 3(8), Al S.H., Tarakmah A., Merchant S.Q. and Al-Sahhaf T. (27). Synthess of esters: Development of the rate expresson for the Dowex 5 x8-4 catalyzed esterfcaton of proponc acd wth -propanol. hem. Eng. Sc., 62(2), Jyot G., Keshav A. and Anandkumar J. (26). Expermental and Knetc Study of Esterfcaton of Acrylc Acd wth Ethanol Usng Homogeneous atalyst. Internatonal Journal of hemcal Reactor Engneerng, 4(2), Internatonal Scence ommunty Assocaton 4

6 Vol. 6(3), -5, March (27) 6. Sert E. and Atalay F.S. (24). n-utyl acrylate producton by esterfcaton of acrylc acd wth n-butanol combned wth pervaporaton. hem. Eng. Process. Process Intensf., 8, Rathod A.P., asewar K.L. and Sonawane S.S. (23). Intensfcaton of esterfcaton reacton of lactc acd wth so-propanol usng pervaporaton reactor. Proceda Eng., 5, Sanz M.T. and Gmehlngb J. (26). Esterfcaton of acetc acd wth sopropanol coupled wth pervaporaton. Part II. Study of a pervaporaton reactor. hem. Eng. J., 23, Korkmaz S., Salt Y., Hasanoglu A., Ozkan S., Salt I. and Dncer S. (29). Pervaporaton membrane reactor study for the esterfcaton of acetc acd and sobutanol usng polydmethylsloxane membrane. Appl. atal. A Gen., 366(), Hasanoǧlu A., Salt Y., Keleşer S. and Dnçer S. (29). The esterfcaton of acetc acd wth ethanol n a pervaporaton membrane reactor. Desalnaton, 245(-3), Delgado P., Sanz M.T., eltrán S. and Núñez L.A. (2). Ethyl lactate producton va esterfcaton of lactc acd wth ethanol combned wth pervaporaton,hem. Eng. J., 65(2), Truong H.T., Rode S., Rozard D., Mouzon-Pelleter S. and Tretjak S. (23). Dehydraton of reactve ndustral mxtures by pervaporaton: An nnovatve approach n acrylc esters processes. Sep.Purf. Technol., 2, Altokka M.R. and Çtak A. (23). Knetcs study of esterfcaton of acetc acd wth sobutanol n the presence of amberlte catalyst. Appl. atal. A Gen., 239(), Internatonal Scence ommunty Assocaton 5