第四章 膜分离理论与技术1-98

第四章膜分离(membraneseparation)理论与技术4.1.1:膜及膜分离的定义:膜:狭义:如果在一个流体相或两个流体相之间有一薄层凝聚相(polymerphase,madefrompolyolefin)把流体分开,用于实现分离目的,这中间的凝聚相就叫膜.广义:一个相或多个相中间的一个不连续区间(discretemargin),用于实现分离目的.Asyntheticmembraneisaninterphasethatseparatestwophasesandrestrictsthetransportofchemicalspeciesinaspecificmanner.4.1:膜分离技术概述膜的特点:AmembranemustbeSemi-permeable:Amembranecanbe:homogeneousorheterogeneous,symmetricorasymmetricinstructure;solidorliquid;neutral,carryeitherpositiveornegativecharges,orhavefunctionalgroupswithspecificbindingorcomplexingabilities.Membranethicknessrangesfromlessthan100nmtomorethan1cm.Masstransportthroughamembranecanoccurviadiffusionofindividualmoleculesorconvectioninducedbyaconcentration,pressure,temperature,Orelectricalpotentialgradient.被膜分离的物质:Liquid,gaseous.膜分离的定义:Membraneseparationinvolvespartiallyseparatingafeedcontainingamixtureoftwoormorecomponentsbyuseofasemipermeablebarrier(themembrane)throughwhichoneormoreofthespeciesmovesfasterthananotherorotherspecies.1:按膜性质分:生物膜:细胞膜,线粒体膜,液泡膜.合成膜:有机膜,无机膜.2:按结构分:Althoughsyntheticmembranesvarywidelyinphysicalstructureandfunction,theycanbeclassifiedconvenientlyinfivegroups:microporousmembranes,Non-PorousMembranes(homogeneousmembranes),asymmetricmembranesCarrierMembranes,Liquidemulsionmembraneorwithselectivecarrierelectricallychargedbarriers,4.1.2:膜的分类Non-PorousMembranesCarrierMembranesmicroporousMembranes3:按分离过程分:Reverseosmosismembrane(ORM),Ultra-filtrationmembrane(UFM),Micro-filtrationmembrane(MFM),Nano-filtrationmembrane(NFM),Dialysismembrane(DM),Electricdialysismembrane(EDM).4.1.3:膜过程的推动力1:Pressuredriven(Pressuregap)Reverseosmosis(OR),Ultra-filtration(UF),Micro-filtration(MF),Nano-filtration(NF).Vapourizationpermeation(VP).2:Non-pressuredrivenConcentrationgradient(chemicalpotentialgradient):Dialysis(D),Potentialgradient:Electricdialysis(ED)Concentrationgradient(chemicalpotentialgradient,activetransfer):Liquidemulsiondialysis(LED).4.1.4:膜分离过程中膜的作用选择性透过:过滤;溶解-扩散;优先吸附;氢键结合;主动运输.Schematicdiagramillustratingthemodesofmasstransportinsyntheticmembranesseparatingtwohomogeneousphases:A)Passivetransport;B)Facilitatedtransport;C)ActivetransportA=componenttobetransported;B=carrier;m=chemicalpotential;superscripts(‘)and(“)indicatethetwophasesonthedifferentsidesofthemembrane.4.1.5:膜分离过程的特点及适用性1:特点:无相变,不存在平衡关系,过程简单,常温操作,能耗低,无污染,同样的过程可以解决不同的分离问题.2:适用性:化学或物理性质相似,但分子量不同的组分,如蛋白质和多肽.同分异构体,热敏性成分,酶,茶多酚,香气成分.大分子.4.2:膜及膜分离技术的发展渗透和半渗透的发现(1748年，Nollet)扩散定律(Fick),1855渗析现象(1861,Graham)渗透现象和渗透压(VantHoff)微孔过滤,超滤和反渗透1907,Backman)Donnan平衡(1911)电解质和非电解质的反渗透,1920s,Mangold膜电势1930s人工肾的发明,1940s电渗析脱盐,血液透析电渗析技术,1950sSourirajan对膜的制备苦咸水淡化技术,1960s膜分离的工业化应用1970s新型膜及膜技术的开发4.3:膜分离技术的分类4.3.1:Pressuredriven(Pressuregap)1:Reverseosmosis(OR),去除具有高渗透压的小分子,需高压(4000-8000KPa)2:Ultra-filtration(UF),去除小分子,截留大分子(300-500,000)需压力(200-2000KPa)3:Nano-filtration(NF).在RO和UF的中间状态,去除分子量大于200-500的有机分子.4:Vapourizationpermeation(VP).气体渗透的推动力为分压差，常应用于空气中氧气的分离、富集.5:Micro-filtration(MF).从液体或气体中去除0.01-10m的粒子:空气除菌.微孔过滤－DeadendMF,过滤方向与压力方向相同,build-up,batchprocess,A:Depthfiltration.B:Surface-filtrationSchematicdiagramillustratingpressure-drivenmembraneseparationprocessesa)Particles;b)Macromolecules;c)Lowmolecularmasssolutes(microsolutes);d)Solvent;e)Gas.Dead-endMF:depthfiltrationA：微孔过滤－DeadendMF,过滤方向与压力方向相同,build-up,batchprocess,A:Depthfiltration.B:Surface-filtrationDeadendMF:surfacefiltrationCrossMFB:微孔过滤－CrossMF（错流微孔过滤）,nobuild-up,continuousprocess,highfluxrateforlongperiodoftime.过滤方向与压力方向垂直.6:Gas-exchangeandseparation:Porousmembrane,根据气体分子量不同而实现分离:Gasescanbeseparatedinmicroporousaswellasinhomogeneousmembranes.TheselectivityofmicroporousmembranesisgenerallyratherlowbecauseoftheKnudsendiffusiontransportmechanism;Schematicdiagramillustratinggasseparationp=pressureNon-porousmembrane.根据气体过膜时对膜的溶解和扩散的差异而进行分离.Underthedrivingforceofahydrostaticpressuredifference,somecomponentspermeatethemembrane,andthefeedstreamissplitintoapermeateandaretentatestream.Ifthemembranehasahigherpermeabilityforoneofthecomponentsinthefeedmixturethanforothers,thiscomponentisenrichedinthepermeateanddepletedintheretentate.Significantlyhigherselectivitiescanbeobtainedinhomogeneousmembraneswheretransportisbasedonthesolutionanddiffusionofthecomponentsinthemembranephase.Masstransportinasolution–diffusionmembraneisillustratedinFigureandconsistsofthreesteps:1.sorptionofthecomponentsfromafeedmixtureaccordingtotheirpartitioncoefficientsbetweenthegasandpolymerphases;2.diffusionoftheindividualcomponentswithinthemembranephaseaccordingtotheiractivitygradients;and3.desorptionofthecomponentsfromthemembraneinthepermeablegasphase.SchematicdiagramillustratingthreeidealizedfeedandpermeateflowpatternsusedingasseparationsystemsA)perpendicularplugoffeedandpermeate;B)Cocurrentplugflowoffeedandpermeate;C)Countercurrentplugflowoffeedandpermeate***4.3.2:Non-pressuredrivenprocess:Electrodialysis:electricalpotentialLiquidemulsionseparation(LEM),Concentrationgradientandactivecarrier.Membranereactor:En