Effectofsurfactantadditiononthemorphologyandpervap

JournalofMembraneScience176(2000)97–103EffectofsurfactantadditiononthemorphologyandpervaporationperformanceofasymmetricpolysulfonemembranesH.A.Tsaia,L.D.Lia,K.R.Leeb,Y.C.Wangb,C.L.Lib,J.Huangc,J.Y.Laia;aMembraneResearchLaboratory,DepartmentofChemicalEngineering,ChungYuanUniversity,ChungLi32023,TaiwanbDepartmentofChemicalEngineering,NanyaInstituteofTechnology,ChungLi32034,TaiwancDepartmentofChemistry,ChungYuanUniversity,ChungLi32023,TaiwanReceived29October1999;receivedinrevisedform24March2000;accepted31March2000AbstractInthepresentwork,theseparationofaqueousalcoholsolutionthroughwet-phaseinversionpreparedpolysulfone(PSf)membranewasinvestigatedbyusingthepervaporationprocess.Theroleplayedbysurfactant(Span-80)intheformationofPSfmembranewasalsostudied.Additionofsurfactantinthecastingsolutioncansuppressmacrovoidsinpolymericmembrane.TheformationofasymmetricPSfmembraneswasdiscussedintermsofthepresenceofsurfactantinthecastingsolutionandthePSfconcentration.ThesurfacepropertiesoftheasymmetricPSfmembraneswerecharacterizedbyscanningelectronmicroscopy(SEM).Theeffectsofpolymerconcentration,surfactantcontent,feedcomposition,andfeedsolutiontemperatureonthepervaporationperformancewereinvestigated.Theseparationfactortowardswaterandthepermeationratefora10wt.%aqueousethanolsolutionthroughtheasymmetricPSfmembranewitha15wt.%Span-80were16and240g/m2h,respectively.©2000ElsevierScienceB.V.Allrightsreserved.Keywords:Asymmetric;Surfactant;Macrovoidsuppress;Polysulfone;Pervaporation1.IntroductionSeparationofazeotropicmixtures,closeboilingpointmixturesorisomers,andfortheremovalorrecoveryoftracesubstancesbytheuseofpervapora-tionmembraneseparationprocesshasbeengaininggreaterinterestinrecentyears,sincethepervapora-tiontechniqueisconsideredtobeanenergysavingprocess[1,2].Thepervaporationisaseparationtech-niquebasedonaselectivetransportthroughadenselayassociatedwithanevaporationofthepermeate.TheefficiencyofthepervaporationprocessdependsmainlyontheintrinsicpropertiesofthepolymersCorrespondingauthor.Tel.:C886-3-4563-672;fax:C886-3-4563-672.usedtopreparethemembrane.Therefore,designingmembranestructurewithahighpermeationrateandseparationfactorisanimportantissue.Thesepara-tionofaqueousalcoholmixturebyapervaporationtechniqueusingadensehomogeneouspolymermem-branehasrecentlybeengivenmuchattention[3,4].Oneofthedisadvantagesofadensehomogeneousmembraneforthepervaporationseparationisthelowpermeationrate,especiallywithhighlyselectivemembranematerials.Severalmethodsofmembranepreparationmaybeusedtoimprovetheseparationperformancessuchas:surfacemodification,blending,copolymerization,andgraftingaselectivespeciesontoaninertfilm[5–7].Thus,weattemptedtoprepareasymmetricmembraneswithhigherpermeationrate,whileretainingtheselectivitysame.Wetphaseinver-0376-7388/00/$–seefrontmatter©2000ElsevierScienceB.V.Allrightsreserved.PII:S0376-7388(00)00435-X98H.A.Tsaietal./JournalofMembraneScience176(2000)97–103sionisthemostwidelyusedtechniqueforpreparingtheasymmetricmembranes.Theasymmetricmem-braneisformedbyexchangeofsolventandcoagula-tionmedium[8].LoebandSourirajanwerethefirsttoprepareasymmetrichyperfiltrationmembrane[9].PinnauandKorosmadeintegrallyskinnedasymmet-ricgasseparationmembranefrompolycarbonateandpolyimidepolymer[10].Aseriesofmembranefor-mationmechanismandmass-transfermodelshasbeenreportedbySmolderetal.,Radovanoricetal.andRouvers[11–13].Recently,manyresearchesindicatethatmembraneswithmacrovoidstructureareusefulinosmoticdrugdeliveryandultrafiltration[11,14].KimandLeeinvestigatedtheeffectofPEGadditiveasapore-formeronthestructureformationofPSfmembranes[15].Theinfluenceoftheadditionofin-organicsaltsandthesurfacetensiononthemembraneformationwerereportedbyKrausetal.[16]andDar-covichandKutowy[17],respectively.Nevertheless,itisnotsuitableforpervaporationprocessbecauseofthelowerselectivity.Therefore,understandingtheformationmechanismofmacrovoidsandthencon-trollingtheformationofmacrovoidsisofgreatimpor-tance.Themainpurposeofthisworkistoinvestigatetheeffectofsurfactantaddition,themorphologyofasymmetricPSfmembranesandthepervaporationperformances.Inaddition,thesurfacepropertiesoftheasymmetricPSfmembraneswascharacterizedbyscanningelectronmicroscopy(SEM).2.Experimental2.1.MaterialsPolysulfone(PSf)usedinthisstudywassuppliedfromAMOCOPerformanceProductsInc.(Ridgefield,CT,USA)underthetradenameofUdelP-3500.Thesolvent,N-methylpyrrolidinone(NMP)wasofreagentgradeandusedwithoutfurtherpurification.Distilledwaterwasusedasthenonsolvent.Thesurfactant(Sor-bitanmonooleate,Span-80,HLBD4.3)usedinthisstudywaspurchasedfromSHOWAChemicalsInc.,Japan2.2.MembranepreparationSurfactant(Span-80)wasaddedinNMPtoacon-centrationof0–17.5wt.%.PSfwasdissolvedintheabovesolventmixturetoformacastingsolutionatroomtemperature.Thedegassedcastingsolutionwascastonaglassplatetoapredeterminedthicknessof300mmbyaGardnerknife,andthenimmersedintoadistilledwatercoagulationbathovernight.Theob-tainedmembraneswerepeeledoffanddriedinair.2.3.SEManalysisThemembranestructureswereexaminedbyaHi-tachi(ModelS570)SEM.Themembranesampleswerefractured