DevelopmentofSolubilitySelectiveMixedMatrixMembran

ResearchArticleDevelopmentofSolubilitySelectiveMixedMatrixMembranesforGasSeparationHeikeMushardt1,VerenaKramer2,DenizHülagü2,TorstenBrinkmann1,*,andMatthiasKraume2DOI:10.1002/cite.201300074Anewkindofgaspermeationmembraneisdevelopedtoseparatehigherhydrocarbons(C3+)frompermanentgases.Stateoftheartforsuchgaspermeationapplicationsaremembranesbasedonsolubilityselective,rubberypolymers,whichofferhighpermeancesbutrelativelylowselectivities.Thenewmembraneisdesignedtoimproveselectivity,andtherefore,significantlyreduceenergydemandandsizeofagasseparationplant.Themembraneisbasedonthemixedmatrixcon-ceptandconsistsofarubberypolymermatrixwithincorporatedactivatedcarbonparticles.Thistwophaseseparationlayerformsasolubilityselectivemixedmatrixmembranebycombiningtheadvantagesofbothmaterials.Theseparationofn-C4H10/CH4mixturesisinvestigated.Basedonexperimentalresultsanewconceptforatransportmodelformixedmatrixmembraneisintroduced.Keywords:Activatedcarbon,n-Butane/methaneseparation,Gaspermeation,Masstransportmodel,Mixedmatrixmem-braneReceived:May08,2013;accepted:October08,20131IntroductionTheseparationofgasstreamsisanimportanttaskinalmosteverybranchofindustry.Theapplicationofmembranetechnologyhasgrownrapidlysincethefirstindustrialplantsintheearly1980’sduetoitslowenergydemand,smallplantsizes,environmentalfriendlinessandeasyop-eration[1].Insomeprocessesgaspermeationisalreadywellestablished,includingnitrogenproductionfromair,separa-tionofhydrogen,CO2removalfromnaturalgas,recoveryofmonomersandsolventsinpolymerproductionorsepara-tionofvolatileorganicsfromoff-gases[2–4].Nevertheless,thetechniqueisnotcost-competitiveforallpossibleapplica-tionsasbothsufficienttransmembranefluxesandagoodselectivityarenecessarytorealizeanadequateenergyde-mandandplantsize[1].Furthermore,themembranemate-rialhastowithstandharshconditionsregardingpressure,temperatureandchemicals[5].Theseparationofcondens-able,higherhydrocarbonsfrompermanentgasstreamsisoneofthemostchallengingseparationtasksinmembrane-basedprocesses[4,6–8].Membranegasseparationcanbeanadvantageousalternativetoconventionaltechniqueslikepressureswingadsorption,cryogenicdistillationorabsorp-tion,astheseprocessesareusuallyaccompaniedbyahighenergydemand,showacomplexprocessdesign,areinher-entlydynamicincaseofadsorptionoremployseparationagentsincaseofabsorption[6].Thekeyissueforasuccessfulmembraneprocessisthemembranematerialitselfastheinteractionofgasmixturecomponentswiththematerialdeterminestheirrateoftransport[9].Almostallcommercialgasseparationsarecur-rentlybasedondensepolymericmembranes[2].Theyareeasilyproducedasthinfilmcompositemembranesonpor-oussupportstructuresorashollowfibersofferinggoodse-parationbehavioraswellasmechanicalstrength.Porousin-organicmembranesmadeofceramic,zeoliteorcarboncanprovideevenbetterseparationproperties,especiallywhenmolecularsievingcanbeachieved.Besides,theycanbeap-pliedinhightemperatureoperationsandunderharshche-micalconditions[10].Unfortunately,inorganicmembranesaredifficulttoproduceandoftenverybrittle.Theresultinghighcostsperm2andlowmechanicalstrengthavertthein-dustrialapplicationofthesemembranes[2].Theconceptofmixedmatrixmembranes(MMM)com-binestheadvantagesofinorganicandpolymericmembranematerialsbydispersinginorganicparticlesinapolymericmatrixtoformatwophaseseparationlayer[11,12].MMMChemieIngenieurTechnikChemieIngenieurTechnik2014,86,No.1–2,83–91©2014Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim–1HeikeMushardt,Dr.TorstenBrinkmann([e-mail]),Helmholtz-ZentrumGeesthacht,InstituteofPolymerResearch,Max-Planck-Straße1,21502Geesthacht,Germany;2VerenaKramer,DenizHülagü,Prof.MatthiasKraume,TechnischeUniversi-tätBerlin,ChairofChemicalEngineering,Fraunhoferstraße33–36,10587Berlin,Germany.Mixedmatrixmembrane83havebeenoflargeinterestinthelastyearsandmuchre-searchhasbeendoneregardingdifferentcombinationsofpolymeranddispersedphasematerials,optimizationofin-terfacemorphologyaswellasthedevelopmentoftransportmodels[13–16].SeveralchallengesinMMMpreparationhavetobedealtwithconcerningtheinterfacemorphology(e.g.,chainrigidification,poreblockage,lowadhesion)andthedispersionofparticleswithinthepolymericmatrix(e.g.,agglomerationorsedimentationofparticles)toformade-fect-freeseparationlayer[12].Thematerialdesignmostlyfocusesonzeolites,carbonmolecularsieves(CMS)orevenmetalorganicframeworks(MOFs)asinorganicfillerspur-suinganimprovementofsizeselectivity[12,14,17].Activatedcarbon(AC)hasbeenknownfordecadesasoneofthecheapestandveryeffectiveporoussorbentstobeusedinadsorptionprocesses[18].MMMwithactivatedcarbonin-corporatedinpolyvinylchloride(PVC)wasinvestigatedbyGarcíaetal.fortheseparationofH2/CH4[19].Theypre-paredMMMwithcarbonloadingsupto60wt%,whichshowedanincreasedgaspermeabilitybutonlylowselectiv-ity.Kusworoetal.studiedtheeffectofactivatedcarboninpolyethersulfone(PES)fortheseparationofoxygenfromni-trogenandfoundanincreaseinselectivityforupto5wt%activatedcarbon,followedbyasharpselectivitydecreaseduetoformationofdefectscausedbyparticleagglomerationathighercarbonloadings[20].A