Effectofadditivesonthestructureandperformanceofpol

JournalofMembraneScience348(2010)260–267ContentslistsavailableatScienceDirectJournalofMembraneSciencejournalhomepage:fibermembranesforCO2absorptionA.Mansourizadeh,A.F.Ismail∗AdvancedMembraneTechnologyResearchCentre(AMTEC),FacultyofChemicalandNaturalResourcesEngineering,UniversitiTeknologiMalaysia,81310Skudai,Johor,MalaysiaarticleinfoArticlehistory:Received11September2009Receivedinrevisedform3November2009Accepted7November2009Availableonline13November2009Keywords:AdditivesMembranestructureHollowfibermembranecontactorCO2absorptionabstractPorouspolysulfone(PSf)hollowfibermembraneswerefabricatedviaaphase-inversionmethodbyusinglowmolecularweightadditivesinthespinningdopes.Polyethyleneglycol(PEG200),ethanol,glycerolandaceticacidwereusedastheadditives.Anaqueous95wt.%1-methyl-2-pyrrolidone(NMP)solutionwasusedasneutralborefluidtofabricateinnerskinlesshollowfibersmembranes.Theprecipitationrateofthepolymerdopeswiththedifferentadditiveswasstudiedusingcloudpointmeasurement.Effectoftheadditivesontheresultingmembranestructure,surfaceporosity,poresize,criticalwaterentrypressure(CEPw)andCO2absorptionperformancewereinvestigated.Cloudpointdiagramsindi-catedthattheprecipitationrateofthepolymerdopesincreasedfollowingthetrendofglycerolaceticacidPEG200ethanol.ResultsofgaspermeationtestsshowedthatglycerolandPEG200asadditivesprovidedthemembraneswiththelargestandsmallestporesize,respectively.Moreover,alltheadditivesresultedinanincreaseinthesurfaceporosity.Thecross-sectionandinnersurfaceofthemembraneswereexaminedviaafieldemissionscanningelectronicmicroscopy(FESEM).Glycerolinthespinningdopepro-videdthemembranestructurewithathinfinger-likeandathicksponge-likelayer,whichresultedinahigherCEPwandCO2absorptionratethantheotherPSfhollowfibermembranes.©2009ElsevierB.V.Allrightsreserved.1.IntroductionRecently,porousmembraneshaveattractedconsiderableatten-tionintheareaofmembranegasabsorption[1–6].Thehighpermeabilityandhydrophobicity,lowmasstransferresistanceandexcellentchemicalresistancetovariouschemical-feedstreamsaretheessentialpropertiesofthesemembranes.Infact,long-termsta-bleoperationofthegas–liquidmembranecontactorrequiresthattheporesofmembraneremaincompletelygas-filledoverthepro-longedperiodsofoperationaltime.Therefore,usinghydrophobicmembraneswithahighresistancetowettingcanminimizethemembranemasstransferresistance.Polypropylene(PP),polyethylene(PE),polytetrafluorethylene(PTFE)andpoly(vinylidenefluoride)(PVDF)arethemostpopularhydrophobicpolymericmaterials.However,sincePE,PPandPTFEcannotbedissolvedinsolventsatlowtemperature,themembranesareusuallyfabricatedusingstretchingandthermalmethodsthatgivesymmetricstructurewithrelativelylowporosity.Inaddition,PVDFtheonlyhydrophobicpolymersolubleintheorganicsolventshasacriticalsurfacetensionandaverylowdemixingratebetweensolventandnon-solventinthephase-inversionprocess.Therefore,∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](A.F.Ismail).itisdifficulttospinhollowfibersparticularlywhenusingaveryweaknon-solventasinternalcoagulant.Asymmetrichollowfibermembraneswithlowmasstransferresistancecanbefabricatedbyincreasingtheoutersurfaceporosityandremovingtheinnerskinlayerduringspinningprocess.More-over,forthemembranehydrophobicity,despitedependingonthepropertyofthemembranematerial,itcanalsobeadjustedbythemembraneporesize,assuggestedbytheLaplace–Youngequation.Anumberofstudieshavebeencarriedouttofabricateporousmembraneswithhighpermeabilityusingdifferentadditives[7–10].However,theeffectofadditivesontheperformanceofthehollowfibermembranesforCO2absorptionisscarcelystudiedintheopenliterature.Generally,lowmolecularweightadditiveswhichcanbeusedtofabricateporousmembranesinclude:polymericadditivessuchaspoly(vinylpyrrolidone)andpoly(ethyleneglycol),organicandinorganicacidssuchasphosphoricacids,aceticacidandpropi-onicacid,weaknon-solventssuchasglycerol,ethyleneglycolanddiethyleneglycol,weakco-solventssuchasmethanol,ethanol,ace-tone,andinorganicsaltssuchaslithiumchloride(LiCl),lithiumnitrate(LiNO3)andlithiumperchlorate(LiClO4).Yeowetal.[11]havestudiedeffectsofdifferentadditivessuchaswater,glycerol,lithiumperchlorateandethanolonthePVDFmembranemorphology.Theirresultsshowedthatwithincreasingwaterintothecastingsolution,themacrovoidsbecamesmaller0376-7388/$–seefrontmatter©2009ElsevierB.V.Allrightsreserved.doi:10.1016/j.memsci.2009.11.010A.Mansourizadeh,A.F.Ismail/JournalofMembraneScience348(2010)260–267261andappearedtobemoreregular.Themembranepermeationfluxalsoincreasedasmorewaterwasadded,whereat4.6%waterinthecastingsolutionafluxincrementto1640×10−5L/m2hPa(1640L/m2hbar)wasachieved.Furthermore,glycerolinthePVDFsolutionsuppressedgelationinducedbycrystallization,whereaslithiumsaltenhancedthegelationbehavior.Han[8]fabricatedporouspolysulfone(PSf)membranesusingpropionicacidasanadditiveinthepolymersolutionandfoundthattheprecipitationrateofthepolymersolutionwasenhancedsignificantly.Theresultsrevealedthatmembranepermeability