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HighlyScalableZIF-BasedMixed-MatrixHollowFiberMembranesforAdvancedHydrocarbonSeparationsChenZhang,KuangZhang,LirenXu,YingLabreche,BrianKraftschik,andWilliamJ.KorosSchoolofChemical&BiomolecularEngineering,GeorgiaInstituteofTechnology,Atlanta,GA30332DOI10.1002/aic.14496PublishedonlineMay29,2014inWileyOnlineLibrary(wileyonlinelibrary.com)ZIF-8/6FDA-DAM,aprovenmixed-matrixmaterialthatdemonstratedremarkablyenhancedC3H6/C3H8selectivityindensefilmgeometry,wasextendedtoscalablehollowfibergeometryinthecurrentwork.Wesuccessfullyformeddual-layerZIF-8/6FDA-DAMmixed-matrixhollowfibermembraneswithZIF-8nanoparticleloadingupto30wt%usingtheconventionaldry-jet/wet-quenchfiberspinningtechnique.Themixed-matrixhollowfibersshowedsignificantlyenhancedC3H6/C3H8selectivitythatwasconsistentwithmixed-matrixdensefilms.Criticalvariablescontrollingsuccessfulforma-tionofmixed-matrixhollowfibermembraneswithdesirablemorphologyandattractivetransportpropertiesweredis-cussed.Furthermore,theeffectsofcoatingmaterialsonselectivityrecoveryofpartiallydefectivefiberswereinvestigated.Toourbestknowledge,thisisthefirstarticlereportingsuccessfulformationofhigh-loadingmixed-matrixhollowfibermembraneswithsignificantlyenhancedselectivityforseparationofcondensableolefin/paraffinmixtures.Therefore,itrepresentsamajorstepintheresearchareaofadvancedmixed-matrixmembranes.VC2014AmericanInstituteofChemicalEngineersAIChEJ,60:2625–2635,2014Keywords:propylene/propane,zeoliticimidazolateframeworks,mixed-matrixmembrane,hollowfibermembrane,advancedgasseparationIntroductionPermselectivemembraneshavebeenstudiedextensivelyasenergy-efficientseparationdevicestoeitherretrofitorreplaceconventional,energy-intensivegasseparationproc-essessuchascryogenicdistillationandamine-absorption.1–3Polymermembraneswithexcellentscalabilityhavegainedmarketshareforairseparation,hydrogenrecovery,andnatu-ralgaspurificationbusinesses;4,5however,extendingpoly-mermembranestoolefin/paraffinseparationsismorechallengingduetoinsufficientseparationefficiency.6–10Mixed-matrixmembranescomprisingbothpolymersandinorganiccomponentsofferagoodcompromisetoaddresslimitationsofeitheroftheindividualcomponents.3,11Thepotentialeconomicscalabilityofmixed-matrixmembranesmakesthemattractivewhencomparedwithsupportedzeolitemembranes,metal-organicframeworks(MOFs)orzeoliticimidazolateframeworks(ZIFs)membranes,12facilitatedtransportmembranes,13,14andpotentiallyevencarbonmolec-ularsieve(CMS)membranes.15,16Researchonmixed-matrixmembranesbeguninthelate1980sandhasreceivedincreasingattention,17–24especiallywithrapidlyexpandingliteratureonMOFsandZIFssince2010.25–29Whiledevelopingmembranematerialsisaveryimportantpartofmembraneresearch,processingmembranematerialsintopracticalgeometriesconstitutesanothercriticalaspect.30Unfortunately,themajorityofpublishedresearchonmixed-matrixmembraneshasbeenfocusingonmem-branematerialsandfilmfabricationatsmallscale.Muchlesseffortshavebeenmadetoadvancemixed-matrixmem-branesintoasymmetrichollowfibers,whichisthemostpracticalmembranegeometryintermsofmembranepackingefficiency.Indeed,onlyafewarticles/patents31–34havereportedformationofmixed-matrixhollowfibers,andthesehaveonlyconsideredparticleloadingbelow20wt%.Accordingly,despiteitsexcellentscalability,mixed-matrixmembraneshaveyetevolvedintocommerciallyviabledevi-cesforlarge-scalegasseparations.First,manytechnicalchallengesmustbeaddressedtoformmixed-matrixhollowfibermembraneswithminimizedskindefectsandattractiveselectivity.Whilespinningneatpolymerhollowfibermem-branesiswell-understood,10,35aframeworkhasnotbeenestablishedtotransferintrinsicselectivityofmixed-matrixmaterials(usuallymeasuredonthickdensefilms)toasym-metrichollowfiberswithdefect-freeandultrathinselectivelayers.Additionally,beforetheinventionofhydrophobicMOFsandZIFs,mixed-matrixmembraneswerepredomi-nantlybasedonzeolitesthatrequiredsophisticatedsurfacemodificationstoadherewithglassypolymermatrices.36–38Inmostcases,moderateperformanceenhancementsofzeolite-basedmixed-matrixmembranesdidnotjustifytheintensiveeffortsrequiredtoscale-upthematerialsintohollowfibers.Inourpreviousstudy,19theparticle-matrixinterfacialadhesionproblemwassuccessfullyresolvedusinghydropho-bicZIF-8asthedispersedmolecularsieve.RemarkablyenhancedC3H6/C3H8selectivityandC3H6permeabilitywerefurtherobservedinZIF-8/6FDA-DAMmixed-matrixdenseCorrespondenceconcerningthisarticleshouldbeaddressedtoW.J.Korosatwjk@chbe.gatech.edu.VC2014AmericanInstituteofChemicalEngineersAIChEJournal2625July2014Vol.60,No.7films,whichjustifiedtheeffortsforscale-up.Inamorerecentarticle,39wereportedformationofdefect-freeneat6FDA-DAMhollowfibermembraneswithoptimizedspin-ningdopecompositionsandspinningparameters.Inthecur-rentstudy,onthebasisofsuccessfullydevelopedZIF-8/6FDA-DAMmixed-matrixdensefilmsandneat6FDA-DAMhollowfibers,wetooktheopportunitytobringmixed-matrixmembraneintoanadvancedlevelbyforminghighlyscal-able,high-loadingZIF-8/6FDA-DAMmixed-matrixhollowfibermembranes.Effortsweremadetoaddresstheinvolvedtechnicalchallengesincludingdispersionofnanoparticles,spinningdopeprocessability,andminimiz