Application and modi

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JournalofMembraneScience463(2014)145–165

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JournalofMembraneScience

journalhomepage:http://wendang.chazidian.com/locate/memsci

Applicationandmodi?cationofpoly(vinylidene?uoride)(PVDF)

membranes–Areview

Guo-dongKangn,Yi-mingCaonn

DalianNationalLaboratoryforCleanEnergy(DNL),DalianInstituteofChemicalPhysics(DICP),ChineseAcademyofScience(CAS),457ZhongshanRoad,

Dalian116023,China

articleinfo

Articlehistory:

Received2January2014

Receivedinrevisedform

20March2014

Accepted20March2014

Availableonline30March2014

Keywords:

PVDFmembrane

Application

Hydrophilicity

Hydrophobicity

Modi?cationabstractPoly(vinylidene?uoride)(PVDF)membraneshavebeenextensivelyappliedtoscienti?cresearchandindustrialprocessduetoitsoutstandingpropertiessuchashighthermalstability,goodchemicalresistanceandmembraneformingproperties.Thisarticleprovidesanoverviewofrecentprogressontheapplicationandmodi?cationofPVDFmembranes.Theapplicationsincludewatertreatment,membranedistillation,gasseparation,pollutantsremoval,bioethanolrecovery,separatorforlithiumionbattery,supportforpreparingcompositemembranes,etc.Subsequently,onthebasisoftwomajorproblemsofPVDFmembranesinapplications,i.e.,membranefoulingandmembranewetting,thehydrophilicmodi?cationandhydrophobicmodi?cationmethodsarecomprehensivelyreviewed.Finally,thekeyissuesassociatedwiththemodi?cationofPVDFmembranesforactualapplicationsarediscussed.ThispapermayprovideaninsightforthedevelopmentofPVDFmembranesinfuture.&2014ElsevierB.V.Allrightsreserved.Contents

1.

2.Introduction........................................................................................................ApplicationsofPVDFmembranes.......................................................................................

2.1.Filtrationmembraneforwatertreatment..........................................................................

2.1.1.MF..................................................................................................

2.1.2.UF...................................................................................................

2.1.3.MBR.................................................................................................

2.2.Membranecontactorprocess....................................................................................

2.2.1.Membranedistillation...................................................................................

2.2.2.Acidgasesabsorption...................................................................................

2.2.3.Acidgasesdesorption...................................................................................

2.2.4.Boronremoval.........................................................................................

2.2.5.Pollutantsremovalfromwater............................................................................146146146146147147147147148151151151

Abbreviations:PVDF,poly(vinylidene?uoride);PSF,polysulfone;PES,poly(ethersulfone);PAN,polyacrylonitrile;PTFE,polytetra?uoroethylene;DMAc,N,N-dimethylacetamide;DMF,dimethylformamide;NMP,N-methyl-2-pyrrolidone;NIPS,non-solventinducedphaseseparation;TIPS,thermallyinducedphaseseparation;VIPS,vaporinducedphaseseparation;THF,tetrahydrofuran;DMSO,dimethylsulfoxide;DMP,dimethylphthalate;DBP,dibutylphthalate;MF,micro?ltration;UF,ultra?ltration;MBR,membranebioreactor;RO,reverseosmosis;COD,chemicaloxygendemand;MWCO,molecularweightcut-off;PVP,poly(vinylpyrrolidone);BSA,bovineserumalbumin;NF,nano?ltration;VOCs,volatileorganiccompounds;DEA,diethanolamine;TCA,1,1,1-trichloroethane;TFC,thin-?lmcomposite;MWCNTs,multi-walledcarbonnanotubes;PDMS,polydimethylsiloxane;PEBA,poly(etherblockamide);SPPO,poly(2,6-dimethyl-1,4-phenyleneoxide);IEC,ionexchangecapacity;PVA,polyvinylalcohol;PEG,polyethyleneglycol;PS-b-PEGMA,polystyrene-b-poly(ethyleneglycol)methacrylate;PDMAEMA,poly(N,N-dimethylamino-2-ethylmethacrylate);PACMO,polyacryloyl-morpholine;PEO,poly(ethyleneoxide);PPO,propyleneoxide;SBMA,sulfobetainemethacrylate;ATRP,atomtransferradicalpolymerization;PEGDA,polyethyleneglycoldiacrylate;l-CO2,liquidcarbondioxide;AIBN,azobisisobutyronitrile;PDOPA,polydopamine;HEMA,2-hydroxyethylmethacrylate;DMAEMA,2-(dimethylamino)ethylmethacrylate;FTIR-ATR,attenuatedtotalre?ectance–Fouriertransforminfraredspectroscopy;PMAA,poly(methacrylicacid);PVDF-HFP,poly(vinylidene?uoride-co-hexa?

uropropylene)

nCorrespondingauthor.Tel.:þ8641184379329;fax:þ8641184379329.

nnCorrespondingauthor.Tel.:þ8641184379053;fax:þ8641184379329.

E-mailaddresses:kangguod@http://wendang.chazidian.com(G.-d.Kang),ymcao@http://wendang.chazidian.com(Y.-m.Cao).

http://wendang.chazidian.com/10.1016/j.memsci.2014.03.055

0376-7388/&2014ElsevierB.V.Allrightsreserved.

146G.-d.Kang,Y.-m.Cao/JournalofMembraneScience463(2014)145–165

2.3.Recoveryofbiofuelsviapervaporation.............................................................................2.4.Supportforpreparingcompositemembranes.......................................................................2.5.Separatorforlithiumionbattery.................................................................................2.6.Otherapplications.............................................................................................3.Hydrophilicmodi?cationofPVDFmembranes............................................................................

3.1.Improvementofmembranepreparationprocess.....................................................................

3.1.1.Introductionofpolymermaterials.........................................................................3.1.2.Introductionofinorganicnanoparticles.....................................................................

3.2.Surfacehydrophilicmodi?cationofexistingPVDFmembranes.........................................................

3.2.1.Physicalmodi?cation....................................................................................3.2.2.Chemicalmodi?cation...................................................................................

4.Hydrophobicmodi?cationofPVDFmembranes...........................................................................

4.1.Improvementofphaseseparationprocess..........................................................................4.2.Introductionofper?uorinatedpolymers...........................................................................

http://wendang.chazidian.comeofcopolymer.......................................................................................

4.3.Surfacehydrophobicmodi?cationofexistingPVDFmembranes........................................................

4.3.1.Physicalmodi?cation....................................................................................4.3.2.Chemicalmodi?cation...................................................................................

5.Conclusionsandrecommendations.....................................................................................Acknowledgments.......................................................................................................References.............................................................................................................153153154154155155155156157157158159159160160160160161161161162162

1.Introduction

Membranetechnologyhasgraduallybecomeapopularsepara-tiontechnologyoverthepastfewdecades.Therearemanysig-ni?cantadvantagesofusingmembranesforindustrialprocesses,forexample,nophasechangesorchemicaladditives,modularwhichiseasytoscaleup,simpleinoperation,relativelylowenergyconsump-tion,etc.Therefore,membranetechnologyhasbeenwidelyappliedtovarious?eldssuchaswatertreatment[1,2],gaspuri?cation[3],foodprocessing[4],pharmaceuticalindustry[5]andenvironmentalprotection[6].

Themembraneisthekeyofthemembraneseparationtechnol-ogy,anditdirectlyaffectsprocessef?ciencyandpracticalapplicationvalue.Atpresent,almostallmembranesforindustrialprocessesaremadefrominorganicmaterialsand/ororganicpolymers,andthelatterdominatestheexistingmembranemarket.Examplesoforganicpolymersincludepolysulfone(PSF),poly(ethersulfone)(PES),poly-acrylonitrile(PAN),polyamide,polyimide,poly(vinylidene?uoride)(PVDF)andpolytetra?uoroethylene(PTFE).Therein,PVDFisoneofthemostusedmembranematerialsandhasbeenpaidmuchattentionbyresearchersandmanufacturersinrecentyears[7].

PVDFisasemicrystallinepolymerwithrepeatedunitof–(CH2CF2)n–.Itexhibitshighmechanicalstrength,goodchemicalresistanceandthermalstabilityaswellasexcellentagingresistance,whichareveryimportantfortheactualapplicationofseparationmembranes.Moreover,PVDFshowsgoodprocessabilitytoprepare?atsheet,hollow?berortubularmembranes.PVDFissolubleinsomecommonsolventssuchasN,N-dimethylacetamide(DMAc),dimethylformamide(DMF)andN-methyl-2-pyrrolidone(NMP).Consequently,PVDFmembranescanbeproducedbyconventionalnon-solventinducedphaseseparation(NIPS)process.Thermallyinducedphaseseparation(TIPS)wasatechniquedevelopedinthe1980s[7]andithasbecomeanotherfrequentlyusedmethodforthepreparationofporousPVDFmembranes.TheparallelcomparisonofthesetwomajortechnologiesissummarizedinTable1.Inaddition,thePVDFmembranescanbealsofabricatedbyvaporinducedphaseseparation(VIPS),solutioncasting,electro-spinning,etc.Thepre-parationmethodsandin?uencingparametersofPVDFmembraneswerediscussedindetailinarecentreview[7].

Sofar,therehavebeenanumberofarticlesreportingontheapplication?eldsofPVDFmembranes,includingmicro?ltration(MF),ultra?ltration(UF),membranebioreactor(MBR),membrane

distillation,gasseparationandstripping,pollutantsremovalfromwater(e.g.,boron,volatileorganiccompoundsandammonia),recoveryofbiofuels,separatorforlithiumionbattery,ionexchangeprocessandothers.Moreover,manycommercialmembranesinthemarketarealsofabricatedwithPVDFmaterials.TheapplicationsofPVDFmembranes,however,arelimitedbytwomajorproblems:foulinginwatertreatmentandwettinginmembranecontactors.Foulingandwettingwillreducethemembraneef?ciencyanddegradetheperformance,consequentlyincreasingtheoperationcostandevencausingfailure.Thesuitablehydrophilicorhydro-phobictreatmentsofPVDFmembranesareeffectiveinimprovingthefoulingorwettingresistance,andhaveattractedextensiveattention.

Thisarticle?rstprovidesanoverviewofapplicationsofPVDFmembranes,includingwatertreatment,membranecontactorprocess,recoveryofbiofuels,supportforpreparingcompositemembranes,separatorforlithiumionbattery,andotherareas.Subsequently,thehydrophilicandhydrophobicmodi?cationmethods,whichwereusedtocorrespondinglysolvefoulingandwettingproblemsofPVDFmembranesinapplications,werecomprehensivelydiscussed.ThispapermayprovideareferencetotheresearchersandmanufacturerswhoengageinthedevelopmentofPVDFmembranes.

2.ApplicationsofPVDFmembranes2.1.Filtrationmembraneforwatertreatment

WatertreatmentisamajorapplicationareaofPVDFmem-branesnowadays.Therehavebeenmanyarticlespublishedreportingonthepreparation,characterizationandapplicationsofPVDFmembranesinwatertreatmentsuchasMF,UF,MBR,etc.Moreover,somemembranemanufacturersalsodevelopedavari-etyofPVDFmembraneproductsforwaterpuri?cationinrecentyears.Forexample,somecommercialproductsofPVDFmem-branesfromAsahiKaseiChemicals,GE,MerckMillipore,KochMembraneSystems,Hy?uxandSiemensWaterTechnologiesarelistedinTable2.

2.1.1.MF

Generally,MFmembraneseparatesorrejectsparticlesfromabout0.05–0.1μmto1.0μm,andistypicallyavailableforthe

G.-d.Kang,Y.-m.Cao/JournalofMembraneScience463(2014)145–165147

removalofprotozoaandbacteria.MFmembraneisalsoaneffectivewaytoremovesuspendedsolidstoreducewaterturbid-ity[2].Forexample,Xiaoetal.investigatedthefeasibilityofusingPVDFhollow?berMFmembraneforthereuseofsecondarymunicipalef?uentpriortoreverseosmosis(RO)[8].ThePVDFMFmembranespreparedbytheTIPSmethodexhibitedexcellentmechanicalstrength.Thepilot-scalestudyresultsindicatedthatthetreatedwaterfromMFsystemhadstablequalitywithlowturbidity,15-minsiltdensityindexandchemicaloxygendemand(COD),whichcouldcompletelymeetthequalityrequirementofROfeedwater.Moreover,themembranepermeabilitycouldbeeasilyrecoveredbychemicalenhancedback-washataloweffectivechorineconcentration.Similarly,http://wendang.chazidian.comedacommercial?at-sheetPVDFMFmembranesystem(AmiconCorporation,USA)forwastewaterreuse[9].Intheirstudy,however,thepretreatmentprocess(i.e.,coagulation–?occulationandozonation)wasrecom-mendedtoimprovethedeclineofpermeate?ux.

withenvironmentsensitivity.Themembranesobtainedweresuitableforproteinseparation.Moreover,Zhaoetal.preparedhigh?uxUFmembranesbycrosslinkingchitosanonelectrospunnano?brousPVDFscaffolds[14].Themembranesdevelopedexhibitedagood?uxrate,highrejectionef?ciencyandlowfoulingtendencyinbovineserumalbumin(BSA)?ltrationtests.

2.1.3.MBR

MBRcombinestheconventionalbiologicalwastewatertreatmentwithmembraneseparation.Itisanattractivealternativetotheconventionalactivatedsludgetreatmentusingsecondarysedimenta-tion[15].Thetypesofmembranesusedaredifferentdependingonthesizecontaminantscontactingduringthetreatmentprocess.Basically,membranesemployedinMBRaretypicallyUForMFmembranes[16].Forexample,http://wendang.chazidian.comedcommercialPVDFUFmembranesforthetreatmentoftextilewastewatertowardsreusebyMBRtechnology[17,18].Thisprocessshowedsuperiorperformancecomparedtootherbiologicaltreatmentsystems.Nevertheless,apost-processingsuchasnano?ltration(NF)wasrecommendedbytheauthorstotreattherecalcitrantCODandcolorcomponents.Recently,http://wendang.chazidian.comparedmembranefoulinginMBRwitharti?cialsewagefeedcontaining30%protein[19].ItwasfoundthatthePVDFmembranecoatedwithPEBAX(apolyetherblockamide)showedbetterantifoulingperformancethanthatofuncoatedpolyetherimidemembrane.

2.2.Membranecontactorprocess

“Membranecontactor”isusedtoidentifymembranesystemsthatareemployedto“keepincontact”twophases.Contrarytothetraditionalideaofmembranesasmediaforperformingsepara-tions,thankstotheirselectivity,membraneonlyactsasabarrierbetweentwophasesinvolvedinmembranecontactorprocess.Thespeciesaretransferredfromonephasetoanotherbydiffu-sion[20].Duetothehighhydrophobicity,PVDFmembraneshavebeenwidelystudiedforuseinmembranecontactors,includingmembranedistillation,acidgasesabsorptionandstripping,andremovalofpollutantsfromwatersuchasboron,volatileorganiccompounds(VOCs),ammonia,etc.

2.2.1.Membranedistillation

Membranedistillationisamembraneseparationprocessappliedfordesalinationofseawaterandbrackishwater.Atpresent,mem-branedistillationisstillintestingstagesandnotfullyimplementedinindustry.However,itisconsideredasapromisingtechnologyforsomespecialareas,suchasdesaltinghighlysalinewaters,the

2.1.2.UF

UFmembraneshaveaporesizerangeof0.01–0.1μm,andareusuallycharacterizedbytheirmolecularweightcut-off(MWCO).UFprocessisusuallyusedtoremoveviruses,emulsi?edoils,metalhydroxides,colloids,proteins,andotherlargemolecularweightmaterialsfromwaterandothersolutions.Forexample,Morãhttp://wendang.chazidian.comedcommercialPVDFUFmembranewithanMWCOof100KDforthetreatmentoffermentationbrothsofdemethyl-chlortetracycline[10].

Atpresent,PVDFUFmembranesarecommonlypreparedbytheNIPSmethod.Khayetetal.investigatedthepreparationandcharacterizationofPVDFUFhollow?bermembranes[11].DMAcandethyleneglycolwereusedassolventandnon-solventaddi-tives,respectively.TheMWCOofPVDFmembraneswastestedbyUFexperimentsusingpolyethyleneglycolandethyleneoxidesofdifferentmolecularweightsassolutes.Yietal.preparednano-sizedTiO2/Al2O3modi?edPVDFUFmembranes,whichwerethenusedforthetreatmentofoil/wateremulsion[12].Duetotheenhancedhydrophilicity,themodi?edPVDFmembranesexhibitedbetterantifoulingpropertyunderthesameoperationalconditions.

Inaddition,theUFmembranescanbealsopreparedbasedonPVDFMFmembranesorelectrospunnano?bers.Lietal.developedanovelPVDFUFmembranewithcontrollableselectivity[13].Poly(vinylpyrrolidone)(PVP)was?rstlycross-linkedon/inthePVDFhollow?berMFmembranesurfaceandporestoattractmoresulfobetainemonomeradjacenttomembraneforthesubsequentgraftingpolymerization.TheformedthicksulfobetainepolymerlayeronPVDFmembranesubsurfaceactedasthesievinglayer

Table1

ParallelcomparisonofNIPSandTIPSmethodsforthepreparationofPVDFmembrane.Item

Solventsordiluentsused

In?uencingparametersformembranefabricationProcessingtemperature

MinimumporesizeofmembranePoresizedistributionofmembrane

TypicalmicrostructureofPVDFmembrane

prepared

NIPSmethod

TIPSmethod

Triacetin,sulfolane,dimethylphthalate(DMP),dibutylphthalate(DBP),etc.LessHigherLargerNarrower

DMAc,DMF,NMP,tetrahydrofuran(THF),dimethylsulfoxide(DMSO),etc.MoreLowerSmallerWider

MechanicalstrengthofmembraneAntifoulingpropertyMajordisadvantageWeakerBetter

Dif?cultrecoveryofsolventStrongerLower

Highenergyconsumption

148G.-d.Kang,Y.-m.Cao/JournalofMembraneScience463(2014)145–165

Table2

SomecommercialproductsofPVDFmembranesforwatertreatment.Manufacturer

Productname

Membranetype

Molecularweightcut-offID/OD/thickness

(mm)(MWCO)/nominalporesize(μm)

AsahiKaseiChemicalsGE

MicrozaZeeWeed500

ZeeWeed1000ZeeWeed1500

Hollow?berHollow?ber

0.1/0.2/0.45/0.650.040.020.02

0.1/0.22/0.45/0.65/0.8/5.00.03

ID:0.7/1.1/1.4/2.6http://www.asahi-kasei.co.jp/membrane/

microza/en/index.htmlID/OD:0.8/1.9ID/OD:0.47/0.95ID/OD:0.66/1.1Thickness:0.125OD:2.6ID/OD:0.6/1.2ID/OD:0.6/2.1–

http://wendang.chazidian.comWebsite

MerckMillipore

KochMembraneSystemsHy?ux

HydrophilicDuraporeFlatsheetPVDFmembranePURONs

KristalsK2000TKristalsK2000T3

Hollow?ber

http://wendang.chazidian.com/http://wendang.chazidian.comhttp://www.hy?http://wendang.chazidian.com/http://wendang.chazidian.com

Hollow?ber150,000MWCOHollow?ber(tri-bore)200,000MWCOHollow?ber

0.04

SiemensWaterTechnologiesMemcors

combinationwithsolarenergyandwasteheat,etc.Inmembranedistillationprocess,theporousmembranemustbehydrophobicthatallowsthepassingthroughofonlyvapormoleculesbutnotbulkwater[21].Inaddition,themembraneshouldhavegoodthermalstabilityinextremetemperatureandlowthermalcon-ductivitytopreventheatlossacrossthemembrane.PVDFisanavailableandcommonmaterialincurrentresearchesofmembranedistillation.Somearticlesreportingonthedesalinationbymem-branedistillationusingPVDFmembranesarelistedinTable3.

Besidesoperationconditions,thedistillationperformanceisalsocloselyrelatedtothecharacteristicsofPVDFmembranessuchasporesizeandporosity.Althoughlargeporesizeandhighporosityareadvantageoustowaterpermeation?ux,itwillalsoincreasetheriskofmembranewetting.Generally,theappropriateporesizeandporosityareabout0.1–0.5μmand50–80%,respec-tively.Moreover,duetothelargeporesandhighporosityinbothbulkandsurfaces,themembranesoftensufferfromweakmechanicalpropertiesintermsoftensilerigidityatbothaxialandradialdirections.Duringamembranedistillationprocess,themechanicalpropertiesdiminishfurtherduetotheelevatedopera-tiontemperature[33].TheweakmechanicaldurabilityofPVDFmembraneisoneofthemajorproblemsduringlong-termopera-tionstomaintainperformancestability.Recently,Wangetal.[33]developedalotus-root-likemulti-borePVDFhollow?bermem-brane.Themechanicalrigidityandelasticityweresigni?cantlyimproved.Consequently,thefabricatedmembranesexhibitedsuperiorstabilityintermsofvaporpermeation?uxandsaltrejectionduringthecontinuousDCMDexperimentwithrobustoperationalconditions.

NIPSprocess,whichistherelativelymaturemethod,isthemainapproachtopreparePVDFmembranesformembranedistillation,especiallyintheearlystages.However,theelectro-spunPVDFnano?bershavebeenpaidmoreandmoreattentioninrecentfewyearssincethe?rstreportin2008[29–32,34,http://wendang.chazidian.comparedtotheNIPSmethod,electrospunmembranesexhibitseveralattractiveattributessuchashighvoidvolumefraction,interconnectedopenstructure,highsurface-to-mass(orvolume)ratio,highlyorderedpolymerchains,morecontrollablestructureand,mostimportant,morehydrophobicsurface[31].Forexample,thecontactangleofthePVDFnano?bermembranewasusuallyhigherthan1301whilethatofthedensePVDF?at?lmpreparedbysolventevaporationatroomtemperaturewasonlyabout831[29].Infuture,electro-spinningmaybeapromisingmethodtopreparePVDFmembraneswithbetterstructureandperfor-manceformembranedistillation.

ApartfromNIPSandelectro-spinningprocesses,porousPVDFmembranescanalsobefabricatedbytheTIPSmethod.Actually,

therehavebeensomerelevantreports[36–41].TIPSprocessisawaytoobtainmembraneswithcontrolledmorphology,andhasseveralwell-documentedadvantages,includingaverylowtendencyfordefectformation,andhigheroverallporosity,bettermechanicalstrength,andnarrowerporesizedistribution[37,42].Sofar,however,theporousPVDFmembranespreparedbyTIPSprocesshavenotbeenappliedtothemembranedistillation.Bycombiningwithsuitablemodi?cationmethodstoenhancemembranehydrophobicity,thismaybeapotentialresearchdirectioninfuture.

2.2.2.Acidgasesabsorption

Theremovalofacidgasesfromgaseousstreamsisanessentialprocessinindustrialoperations,e.g.,thecaptureofCO2from?uegasandthesweeteningofnaturalgas.Theconventionalmethodisabsorptiontowerusingalkanolaminesandalkalinesolutionsasabsorbents.However,therearesomedisadvantagessuchas?ood-ing,foaming,entrainingandchannelingphenomenaaswellashighspaceoccupancyandoperatingcosts[43].Toovercometheaforementionedproblems,membranecontactortechnologyforacidgasesabsorptionhasbeenproposedasapromisingalter-native[http://wendang.chazidian.comparedtotheconventionalabsorbers,themem-branecontactorleadstoareductioninsize,height,weightandcapitalcost.Moreover,theliquidandgas?owsareindependent,whichmakestheavailablesurfaceareaundisturbedathighandlow?owrates.Membranecontactorprocessisinsensitivetomotion,whichiscriticalforoffshoreapplication.Finally,itismodular,sothescaleupisstraightforward.

TheschematicofacidgasesabsorptionmechanismthroughporousPVDFmembranecontactorisshowninFig.1.Todate,alotofpublicationsreportedinthepastdecadeonacidgasesabsorp-tionusingPVDFmembraneswerededicatedtoCO2/N2mixtures,CO2/CH4mixtures,H2S/N2mixtures,SO2/N2mixtures,etc.Table4summarizessomeresearchesontheacidgasesabsorptioningas-liquidPVDFmembranecontactors.

ThesestudiesdemonstratedthattheabsorptionofacidgasesfromgaseousstreamscouldbeachievedusingPVDFmembranecontactorswithappropriatemicrostructure(suchasporesize,porosity,etc.).Itprovidesanalternativeprocessfortheacidgasremovalinfuture.Membranewettingbyabsorbents,especiallychemicalabsorbents,however,isaproblemthatcannotbeignoredforPVDFporousmembranesatthesametime[58].Actually,wettingphenomenonisacommonprobleminallmembranecontactoroperationsincludingmembranedistillation[59,60].Membranewettingcanleadtotheincreaseintotalmasstransferresistanceandthustoareductioninabsorptionef?ciency[44].

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