Transport Process of Isopropanol Aqueous Solution by Pervaporation

Transactions ot Tanjin UniversityISSN1006-4982pp263-269Vol.13 No.4Aug.2007Transport Process of Isopropanol Aqueous Solution by PervaporationWEI Feng(魏峰), ZHANG Weijiang(张 卫江), HAN Ligno(韩莉果), ZHANG Xuemei(张雪梅)(Chemical Engincering Reeurch Center, Tnarjin Univerity, Tianjin 30020 Qina)Abstract: To study the transport process of isopropanol aqueous solution by pervaporation, thetransport model of isopropanol and that of water at 323 K in polywiny alcoho(PVA) membrane wereobtained in this paper. Theoretical predictions agreed well with the experimental results. The interac-tional parameter between water and PVA membrane is less than that between isopropanol and PVAmembrane, which shows that water is preferentially dissolved in PVA membrane. The plasticizing co-eficient and difusion coefficient at ifnite dilution of water are larger than those of isopropanol,which shows that the dissolution and permeation in PVA membrane of water are greater than those ofisopropanol. Both the interactional parameter between water and isopropanol in the membrane andthat in feed rise with the increase of isopropanol content in feed, which shows that the larger isopro-panol content is, the higher selectivity of the membrane is and the more remarkable separation effectof pervaporation is.Keywonds: model; pemeate fluX; ispropanol; water; pervaporationPeraporation(PV) is an energy eficicnt process for of isopropanol, The pilot study was crried out and a sati-the secparation of liquid mitures in the chenical processing sfactory ffeet was obtainedl0] .industry, especially for separation of aeotropie or close-In this paper, plyvinyl alcohol (PVA) pervaporationboiling liquid mixtures'". Now dehyiration of onganic sol- meabrane is employed to separate ispopan/water mix-vents is the best-developed area in PV.ure. The mss transfer model of this procese is establishedOne of the vital isues for industrial aplication of PV based on Flory Huggins theory and stutiniodifusionon modelprocses is the ability to tailor membrane matenials with to predict the geling and pervaporation properties.high PV perfomance. Anobher fundamnental ise is model-1 Experimenting pervaporative ransport to better optimixe PV process.The modelof nass tansfer through the membrane has 1.1 Swellig experimentsbeen studied extensively2) . Many models were proposed toThe PVA homnogeneous membrane used in seling ex-predict the mass transfer process ,. such 弱soutiniodifusionperiments wae provided by Bejing Megavision Meobranemodeil], Mxwell-Stefan theory4, pore flow model[s] ,Technology & Engineering Co. Lad. The thicknes of thepseudo phase change. solutin-difusion model6], resismembrane was 20 puom, avernge degree of polymerization andtance-in-series model ”and molecular simulation-the degree of alcoholysis was (1 750士50) and 98% (mo-Anmong them, slutindifusion model is most widely usedlar ratio) , repectively. And the experimental system wasin describing PV transport including sorption and difusionisopropanol/water mixture.steps. Considerable attention has been focused on the massSamples of dried PVA membrane were weighed andtransfer behavior in recent years.Isopropanol, a widely used solvent in chemical andthen immersed respectively in pure water, isopropanol andpharmaceutical industries, is known to form an azcotropethe binary mixture with diferent contents at specife temper-ature. While the sanples reached steady state, they werewith water, a characteristie that creates difculrecovery by the conventional disliltionl9l. PVt中国煤化工diatly afer caefullyly wiping out88 was repeated three times andconomical, safe and clean a means 1o achieveTYHCNMHGThedegreeofseliDs(g"Accped de:2001-17.WEI Fag, bom im 1976, dctoate suden.Corespoadence切o ZHANC Xucenei, E-mil:hneur2570@ 126. com.Transoctions of Tianjin UnierstyVol.13 No.4 2007(g membrune)-1) is as fllows: .downstream presure was kept about 2 kPa. And the pemoe-ate was ollected in trap coled with liquid nitogen,Dg=; m2- x 100%6weighed, and then analyzed by gas chromalography. Themfeed was circulated in the upper chamber of the unit to(1) eliminale he fft of concentration polarization on sepural.-where m; is the mass of dried polymer, g;m2; is the mass ing propries.of swollean polymer, g.The polyiny alcobol plylonitrile ( PVA-PAN)The extraction of the absobed prducts was perfomned compoeite membrane uged in PV experiments was providedunder vacum. The desobed vapors were cllected in tnapesby Beiing Megavision Memnbrane Technology & Engineeringcooled with liquid nimogen, and the deorbed pnoducts were Co. ud. The thickness of the PVA eparation layer was 2analyzed by gus chromnatography.pum, and that of the PAN support layer was 80 pum. The x-1.2 Pervaporation experimentsperimental systen and PVA layer were the same with thosePV experiments (Fig.1) were performed with a 500of swelling experiments.mL filter unit from Nalgene Compery ( America). The68D31/1- Qrou trenat;2 Perstatid pump:3- Flar hddes wih roirers←- Cas orndemoar; .5- -Round boteon faak; 6 Dying botle: 7-Bufe btutls; 8-Vacmm pup.Fg.1 Schemande dingn om of PV experfumeatid qplpmecotbe decribed as a product of activiy eoficient r增and vol-2 Theoretical analysisume factio虫in menbrane1. So the selling equilibrir2.1 Swelling equilibrium model in PVA mem-um is expresased bybrane for isopropanol/water mixtureWhen swelling equilibrium is reached at the interfacebetween the mixture and the polymeric membrane, thermo-(3)dynanic phase equilbrium between the mixture and the where superseripts s and m are repectively feed phaae andpolymeric membrune is established, which indicates that the membrane phase.chemical potential in both phases for component i is eaqual.y: can be calculated by Wilson equation, and the pa-Acconding t the dinition of chemical penil, the equl-. ranetes (An and Au) of Wilon equation are rspetiveiy of chemical plenial can be epresed by acivity eqi ly 0.188 65 aend 0.794 9[1]. ForHggins tern[ia ilibrium:中国煤化工activity of component i in men-al= a?MHCNMHGIn Eq. (2). al can be described as a produet of activ-Inov=hφw+(1-φw)-φη-φmπ+ity cofficient r and molar fraction对in feed, and oT can一264-WEI Feng a al: Trensport Procs of lspopanol Aqucous Solution by PenaporationVwc[ln D)+(1-0](x娟虫+ xx$x)(q; + ) - xoX溉= -(1-0)(4)(8)ln at=ln 0:+(1-虫)-中w -φm-，where 中ia volume fraction of pure component in mem-brane, which can be calculated by the degree of swelig of(x罚Ow+ xm$y)($w +φw)-pure component D'siBy Eq. (8), itractinal parameter between compo-(5) nent and membrane Xnn at 323 K (optimum operation tem-Xmnγ_peraturelto) is calculated. xwm and xnM is 0.744 and1.671, respectively. Thus it can be concluded that the in-where v is molar volume, m2 .m)-'; x is itenectional tencion betwen Wwater and the membrane i greatler than，parmeter; subscripts w, I and M are water, isopropanolthat between isopropanol and the membrane, s0 water isand PVA membrane, repectively.In Eqp.(4) and (5), Vw/V = (Mw/M)(pr1pw) =preferentially adeorbed and dissolved in PVA membrune.(1.8/6)(0.79/1) = 0.237. Due to the great langer molar2.2.2 Interactional parameter between componentsInterectional paruneter between isopropenol and watervolume of PVA membrane than that of water and isopro-in feed xn can be clculated by1m’panoi:l, Vw/Vw and V:/VM are set to zero in this paper.So selling equilibriurn model in PVA membrane for isppro-pano/water mixture can be written幽物=(Uw+*|In++)x面构"(9)墙[ - ln(0.188 65 +0.811 35墙)+(1-0.188 650.794 91where OCE is Cibe excess free energy, J. mol-1, which始(61s65+0.811 35xw1-0.205 09x.)]=can be obuained from Wilson equation;的is volume fractionof component in feed.φwexp[ 1- 9w-0.237@1+ (端中+To simplify the calculation, x简is expressed by的xuwPu)(1- Pw) -0.237xuQ.∞u]from the fllowinn equation:(6)x始=a+b0+0f + d+w!xfexp[ - ln(0.794 91 + 0.205 09xq)+(1-对)-(10)The conistants (a- -e) in Eq. (10) can be calculated0.79491+0.20509x1 1-0.811 35*) :by Eq.(9). So x的at 323 K can be deribed aspexp[1- - 4.219w + (4.219x罰$w +x简=0.712- 0.017 5折+ 1.547折-2.147唱+xmφw)(1-町) -4.219xmnφr$u]1.850v↑(7)(11)Foon Eqp.(6) and (7), it is found that seligUnder the samne conditions, the interactional panmetereuilbion in membene of component rlate如not only beheen isoparadn and water in membrane x晶cean be al-the interactional paramneter between components but alsos0 epessed by Eq,(11)[6:that between component and membrane.2.2 Interactional parametersx衢=0.712- 0.017 Su + 1.547u}-2.2.1 Interactional parameter between conponent and_ ? 147211 850u;membraneAconding to Flory-Huggins theory, it is中国煤化工(12)interactional parameter between component andime fraction of isopropanol inxov is independent of content in fd], and theEMYHCN MH Go).viscolaticity on chemical potential is igored. Thus XiMFrom Eqs.(11) and (12) it is found that both x俞can be described 8s:and x罰rise with the increase of isopmopanol content,which showg that the langer isopropanol content is, the-265一Transoctions of Tanjin UniernsityVol.I3 No.4 2007higher selling slecivity of the PVA menbrane is and the slurnifusion model. Thus,中山in Eqs.(16) and (17)nore remarkable sepuration ffect ofPV is.can be ealculated by Eqs. (6) and (7). And the membrane2.2.3 Mathematical description of difusion in membrane thickness y is 2 pm.Acording to sutindifusion moded, difusion in 2.3 Model of mass transfermembrane can be epresed by Fick's law, where m8 com- 2.3.1 Eximation of model parametercentration can be described by volune fraction Q:Inserting Egs . (6) and (7) into Eqp. (16) and (17)gives: .J=-DdC;=- p,D;dφd:d(13)Jw =0.500x 105 Dw中w°el+.*n+月中.)-1ψwφw+山中mwhere the difusion coffcient D; is assumed to be concen-(18)tation-dependent by a exponenial eletionsnip[7]. So Eq.J=0.395x 109D;中melio.*9)-1(13) can be writen酷ψπφWa + ψr中n(19)Jw=-阳D; ep(0.+..)中where墙exp[ - ln(0.188 65 + 0.811 35墙)+(1-(14)0.188 650.79491 )h=pD; exp(yOu+.)%T增)( 0.188 65+0.811 35x婚”1-0.205 09插小“(15)中mexp[1.744 - 2.488中w + (x罚- 1.377)中m +where 4 is platicing eoficient of component, dimen- (1.140- x聶)φw φ + 0.744面。+0.396配]eionless constant; D; is the difusion cofficient at infinite(20)dilution, m2.h*, which is only dependent on tempera-xex[ - ln(0.794 91 +0.205 09*i)+(1-*1).trel.The bundary condition of Eqs.(14) and (15) is(o0.79491 +0.205 09x 1 - 0.811 35xt/0.794 91)] =[z=0,更w = φw.,则=φrexp[2.67L -4.342中mw + (4.219x舜- 9.029)中w +lz=y,ow =φw,虫=中心(4.810- 4.219x蜀)中φ + 1.671配+3. 139音](21)where y is the thickness of membrane, pm; 中觀andφare volume fractions in upstream side membrane of water娟=0.712 -0.0175平+ψ+and that of isopropanol, respectively; 中w and中u are vol-φuume fractions in downstream side membrane of water and1.s7() -2.140西+∞) +that of isopropanol, respectively.Becuse of the very low preseure in downsteam side of中PV, concentration in downstream side membrane can be ne-1.850(中m +o/glected compared with that in upstream side menmbrane. Af-(22)ter integral and development, one hasEqs.(18) and (19) form a systerm of nonlinear quatermary equations, model peruneters are platicizing colf.Jπ=PwDiφw . el.o.+-1cient ψr and difusion coficient at infinite dilution Di .y.刑+ 4r中mWith definite system and ternperature, these parameters are= e.Di w.ci0.+.)-1中国煤化工im by mainm lined eti中影+ψ中CNMH Grltm ar eimnn oboninMYHGerinental data. This process iNeglecting the infuence of concentration plarizaion，camied out by Mllab, and the final result isswelling equilibrium is reached at the interface between thefeed mixture and PVA menbrane in PV process according toDW = 4.83x 10-9 m2.h-1-266-WEI Feng at ol; Tranport Proces of Iopropanod Aqueous Souion by Penaporation四= 0.531(24)Di = 1.15x 10-9 m2.h-1φm，φm in Eqs. (23) and (24) can be atained by山= 0.112Eqs.(20)- <(22).3 Results and discussionIt can be found that the plasticizing coficicnt and dif.fusion coffcient at infinite dilution of water are both langerBased on Eqs. (22)-(24), the predicted volumnethan those of isprpanol, which shows that the disoluion faction in membrane φ. and permneate flux J; are obainede.and permeation in PVA membrane of water ae both greter The changes of volume fraction of the conponent in mem-than those of isopopanol. So water permeates pelential- brane wih the ineree of molar fraction of iopopanol inly, which agrces with the result concluded from iterectional miture are demonstated in Fig.2. It shows that volumepanmeters.frnaction of water 中西gradually descend with the rise of iso-2.3.2 Model of mass transfer in PVA membraune for iso propanol content (Fig.2(a)), while that of isopropanol中:propanol/water mistureincrease and then begin to level of when罐is lurger thanIneting the valuesof Di and ψn into Eqs.(18) and 0.1 (Fig.2(b)). The avenge rlaive eror of volume frac-(19), model of mass transfer in PVA membrane for isopro- tion in membrane is 4.97% and 5.48% , respectively.pano/water misture at 323 K can be expressed byWith the similar variational trend shown in Fig.3,Fig.3 ilustrates the changes of permeate fhux of the componentwith the increase of molar fraction of isopropendl in mix--2-=1500.53510 +0.112ture .The avemage relative error of permeate fhux is 6.53%(23) and 5.73% ,repeptively.e(0.510.+0.1202)-11-0.454-0.53101 +.11200.550.070.50Celoulatin0.06Esperioent0.050.45.0.04: 0.40-， 0.030.350.02 .Caleuladom0.300.01Experineat.也0.2503 040。01020.304 ?a) Chungrs d voluse fetem ofl water(b) Chaogas olf oune feceo od spasFg.2 Changes of rolume tinetion o compoents in membrane with the inecrase of molar frnetion o isoprpanodo t itfusion ternpent-ture 323 K3Calculotion●Eperinent20.20.201.0含0.9-0.8-中国煤化工.. ClculalioEpeimert0.7-0.666.3TYHCNMHG-0一0田) Chages dlpermeste tx ofwutr(I) Changee dperneate lu od iprppedFg.3 Chunges o permeate血ot conponents im feed wh the hnorease o molar fnction of iopropsnod at feed tempenture 323 Kand domstreem pregure2 kPa一267一Transacions of Tianjin UninersityVol.13 No.4 2007The predicted volume fraction in membrane and per-φ- -volume fraction in membrane;meate flux fit well with the experimental data, which showsp-volume fructionin feed;that this model of mass transfer can be used to prediet theγ- -activity officient;swelling and PV properties and to provide a basis for四-ψ-plasicizing cofficient;houstive study of separation of isopropanolwiter mixture byD-ifusion cofficient, m?.h~';PV technology. The deviation may come from the neglect ofM- -molar mae, kg'mol-';concentration polarization and the supposed swelling equi-T- -temperature, K;librium, which maybe not actually realie in the experi-J- -permeate flux, kg:m-2h-';ment.V- -molar volume, m2' *mol-';The model esablisbed in this peper can be alo wedSuperseripts and Subscriptsto describe pervaporation proce8s of other binary system,and only the parameter in model needs 0 be modifed. So itfeed;is very convenient. Otherwise, the precision and practicn-mr membrane;bility of model may be improved if the ffte of concenra.'- -single;tion polarization and boundary layer resistance in upetream# -infrite dilution;and downstream are also considered. .i- component;d- -downstream;4 Conclusionsu upstream;(1) Based on Fory-Huggins theory and solution difu.-I一isopropanol;sion model, the model of mas transfer in PVA membraneM- memnbrane;for isopropanol/water mixture is established, The predictedW- water,volume fraction in membrune and pemeate flux are in goodagreement with the experimental data.(2) The interactinal parameter between water andReferencesPVA membrane is less than that between isopropanol n[1] Han Meng, Li Chunli, Zhao Bo. Development of perapo-PVA membrane, which shows that water is preferentiallyration for separating VOCa from water[ C]. In: Pocdingsadsorbed and dissolved in PVA membrane.of 1s Chinese National Chemical and Biochemical Engi-(3) The plasticizing colfficient and difusion coff.-nering Anrual Moeting. Nanjing: 2004. 632 (in hinese).cient at infnite diluion of water are lager than those of iso-[2] Lprizki F, Tmganlh C. Modeling of perveporation; Mode-propanol, which showg that the dissolution and permeationla to analywe and predict the mass tmanseport in pervaporationin PVA membrane of water are greater than those of ispro-[J]. Sep Purif Mehods, 2001, 30(1): 49- -125.panol. So water pempeates preferentially.[3] WjmansJ G, Baker R W. The solution difusion model:(4) Both the interactional paeraneter between waterA reiew[J]. J Membr Sai, 1995, 107(1/2): 1-21.and iopropanol in the membrane and that in the nixture [4] Schetel P, Bendjana z, VauclairC eal. Ideal andrise with the increase of isopropanol content in micture,non-ideal difusion through polymers ppicaion to pervapo-which shows that the lager isopropanol content is, theratin[J]. J Membr Sei, 2001, 191(1/2): 95- -102.higher selectivity of the membrane is and the more remark- [5] Olkeda T, Masum T. A Dew tnnapont model for pervapo-able separation efect of PV is.ration[J]. J Menbr Sei, 1991, 59(2): 133- -150.[6] Shieh JJ, Huang R Y M. A peudophase change solutiorNomenclaturedfuion model for pervaporation ( I ): Binary mistureDs- -degee of selin, g*(g membrane)-+';peetion[]. Sep Sai Technd, 1998, 33(7): 933-957.p-density, kg'm-3 ;Trmotenann R. fhenachai A, Huang R Y M. Perapora-X一interactional panmeter;中国煤化工lhanol wter mituw wih diosea- activity;( CS/HEC) conpeite meubranesu- nelative volume fraction;m- -ma88, g;MYHC N M H Gi taspor[J., JMembr Si, 2002,1办1/L1: 611- -L.x- molar fraction;[8] Hofmann D, Fitz L, Paul D. Moleular modeling of per--membane thickness, um;vwapontion Bepantion of binary mxturce with polymenicA- Wilson equation paraneter;membrane[]. J Menbr Sei, 1998， 144(1/2); 145-一268一WEI Feng e al: Transport Proces of Iopropanodl Aqueous Solution by Peraporationand preferential pemeability in pervaporaion proces[J] .[9] Dean J A. Lange' Handbooko of Chemistry [M]. 15th ed.Techanology of Fater Treatment, 1994, 20(5): 278- 283New York: McCraw-FEll Comparies Ine, 1998.(in Chinese).[10] Han Meng. Sudy on the Sparntion Pocos and the Tane- [16] Wang Hongjun. Sudy on the Sepantion Pocess and theport Mechanisem of Pereporntion in loprprn/Wwter[D].Traneport Mechunismn of Pervaporation in Ehuno/WaterTanjin; School of Chemical Engineering and Technology,Systenm[D]. Beijingn School of Chernical Engineering andHebei Univenity of Techuology, 2005(in Chinese).Technology, Beijig University of Chemical Technology,[1] Ren hihong, Jiang Chenghang. 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Data Poessing and Experinens DeigningChemical Industry Pres, 2000 in Chinse).of Chemical Technology [M]. Beijig: Hydrocarboo Pro-[15] Ni Xiuyuan, Xu Zhenliang, Shi Yajun. Separnation of孵cereing Press, 1989 (in Chinese).lerethanol by pervapontion ( I ): Prferenial sorpion中国煤化工MYHCNMHG-269-