生物分离工程第二章-过滤-PPT

Chapter2Filtration第二章过滤APretreatment预处理1、Heating加热2、Coagulationandflocculation凝聚和絮凝3、Adsorptiononfilteraids助滤剂上的吸附BGeneralTheoryforFiltration1、Darcy’sLaw达西方程2、IncompressibleCakes不可压缩滤饼t＝(μαρo/(2△P))*(V/A)23、Compressiblecake可压缩的滤饼CContinuousRotaryFilter连续旋转式过滤机DEquipmentforConventionalFiltration传统的过滤设备Filtrationseparatessolidfromaliquidbyforcingtheliquidthroughasolidsupportorfiltermedium.Thisisastraightforwardprocedureforwelldefinedcrystals.过滤是将料液通过固体支持或者过滤介质时，使得固体物质从溶液中分离，对于好的定形的晶体，这是一种最直接的步骤。滤饼传统的过滤cakeConventionalfiltrationfilterfilterfilterfiltratesolidsrecoveryuponbackflushFigure2.1SchematicrespresentationodsfilterpressConceptualrepresentationofplateandframefilterunderFlowsheetforcontinuousrotaryvacuumfiltrationwashspraysAirconnectioncakeContinuosrotaryfilterWashwaterpumpWashFiltratepumpMoisturetrap30'AiroutDryvacuumpumpBarometricsealVacuumreceiversFigure2.2FlowsheetforcontinuousrotaryvacuumfiltrationHoweverthesmallsizeofmicroorganismsmakefiltrationoffermentationbeersorotherbiologicalsolutionsconsiderablymorecomplicated.但对微小而形状多变的微生物细胞，发酵液和其它生物溶液的过滤就变得复杂了。Generally,fermentationbeersandotherbiologicalsolutionsarenotoriouslyhardtofilter.Theyareoftenhardtofilterbecauseofhighnon-Newtonianviscosityorhighlycompressiblecakes.Thatistosay,wemustmodifytheseproceduresforbio-separations.一般，由于料液通常都是高的非牛顿粘度流体或者是高度可压缩滤饼，发酵液和其它生物溶液是极其难以过滤的，也就是说，我们必须对这些生物分离程序进行修改。APretreatment预处理1、Heating加热2、Coagulationandflocculation凝聚和絮凝3、Adsorptiononfilteraids助滤剂上的吸附Thesetreatmentsarealsousefulforcentrifugationandsedimentation.这些方法也适用于对于离心和沉淀过程。1、Heating加热Thesimplestpretreatmentandtheleastexpensivemethodistoheatthefeed.Suchheatingcannotonlyimprovethefeed’shandlingcharacteristics,butalsomaypasteurizeit.Thechiefconstraintofthisapproachisthethermalstabilityoftheproduct.(leadtoirreversiblereaction).最简单、最经济的预处理方法是加热，加热不仅可以增加料液的操作特性，也可以对其进行灭菌。但加热变性的方法只适合于对热稳定性的产物。2、Coagulationandflocculation凝聚和絮凝Thesecondpretreatmentmethodistheadditionofelectrolytestopromotecoagulationandflocculationintheinitialsolution.Usefulagentsrangfromsimpleelectrolytesthroughacidsandbasestosyntheticpolyelectrolytes.第二种预处理方法是通过电解质的加入促进原始溶液的凝聚和絮凝，试剂有简单的电解质、酸、碱、合成的聚合电解质。Simpleelectrolytesactbyscreeningtheelectrostaticrepulsionwhichcommonlyexistsbetweencolloidalparticles.Whenthiselectrostaticrepulsionisreduced,attractiveLondon-vanderwaalsforcespredominate.Thecolloidscanthencoagulateaslarger,denseparticleswhicharemoreeasilyfiltered.简单电解质降低了胶体粒子间的排斥电位，从而使得范德华引力起主导作用，聚合成较大的胶粒，粒子的密度越大，越易分离。18pH3.8pH2.8TheeffectonfiltratevolumeofpHpH值对过滤体积的影响00200400600612pH4.6pH4.2FiltrateVolume(cm)3Time(min)Time(min)181%filteraidinfeed2%3%5%00100400600612FiltrateVolume(cm)3Theeffectonfiltratevolumeoffilteraid助滤剂对过滤体积的影响Simpleacidsandbases（简单的酸或碱）Alum（明矾）Ferricchloridecrystals（三氯化铁）Syntheticpolyelectrolytesaddedaspretreatmentscanbothreduceelectrostaticrepulsionandadsorbonadjacentparticles,formingbridgesbetweenthem.Asaresult,thecolloidalparticlesflocculateaslarge,lessdenseaggregateswhicharemoreeasilyfiltered.Thesepolyelectrolytescanbeanionic,cationicornonionic.预处理时加入合成聚合电解质既能降低排斥电位，又吸附了周围的微粒，形成桥架作用，促使胶粒形成粗大，密度低的絮凝团。这些絮凝团很容易被过滤得到。Polyacrylamides（聚丙烯酰胺）Polyethylenimines（聚乙烯亚胺）Polyaminederivatives（多聚胺衍生物）（1）、Diatomaceousearths硅藻土Diatomaceousearthsaretheskeletalremainsofthetinyaquaticplantsdepositedcenturiesago.硅藻土是百年前水生植物沉淀下来的遗骸。（2）、Perlites珍珠岩Theperlitesarevolcanicrockprocessedtoyieldanexpandedform.珍珠岩是处理过的膨胀火山岩。3、AdsorptiononFilterAids助滤剂上的吸附Table2.1.TypicalpropertiesofFilterAidsB.GeneralTheoryforFiltrationNowweturntothemathematicaldescriptionoffiltration.现在我们对过滤过程进行数学描述。Darcy方程－－fluidmechanicsforfiltrationDarcy’slaw：1、forincompressiblecake,simplestcase适用于不可压缩和简单的可压缩滤饼2、forcompressiblecake,commonforbio-separations适用于可压缩滤饼，普遍使用于生物分离过程Darcy’slaw（达西定律）Darcy’slawrelatestheflowratethroughaporousbedofsolidstothepressuredropcausingthatflowDarcy定律把流速与通过固体多孔床产生的压降联系起来。v=k△P/μl(2.1)vdirectlyproportionalto△P流速正比于压降vinverselyproportionaltol/k流速反比于阻力l/kvisthevelocityoftheliquidv–流体流速k：proportionalityconstant,usuallycalledtheDarcy’slawpermeabilityofthebedk－比例常数,通常叫达西方程参数△P:thepressuredropacrossthebedofthickness△P－通过厚度为l的床产生的压降μ:viscosityoftheliquidμ－液体粘度·Darcy’slawholdsonlywhenRe5当Re5时达西定律才成立Re=dvρ/μ(1-ε)(2.2)d-particlesizeorporediameterinthefiltercake滤饼粒子的大小或孔的直径ε-thevoidfractioninthecake滤饼空隙率ρ-theliquiddensity液体的密度visthevelocityoftheliquid流体流速Re–Reynoldsnumber雷诺准数Forbatchfiltration,thevelocityis对于板框式过滤,速率方程为：v=(1/A)*dV/dt(2.3)A–filtrationarea过滤面积V–thetotalvolumeoffiltration过滤液体积t–thefiltrationtime过滤时间Theresistancetoincludeexplicitlythecontributionsofcakeandfiltermedium.滤饼和过滤介质所产生的阻力：l/k=Rm+Rc(2.4）Rmtheresistanceofthefiltermedium过滤介质的阻力Rctheresistanceofaccumulatecakebio-mass滤饼的阻力CombiningE.q.(2.1)(2.3)(2.4)wefinddifferentialequationforbatchfiltrationattheconstantpressuredrop：我们发现板筐式过滤压降是一个常数(1/A)*dV/dt=△P/μ(Rm+Rc)(2.5)Rmisaconstantindependentofthecake；Rm是常数，与滤饼无关；RCthecake’sresistancevarieswithtotalvolumeoffiltration；Rc与滤液总体积有关；Theexactnatureofthisvariationdependsonwhetherthecakeisincompressibleornot.Rc的