《专业英语阅读》PPT课件.ppt

Unit1UnitOperations,Arp26th，2011Ying,Xiaoguang,lesson1ClassificationofUnitOperations,FluidflowThisconcernstheprinciplesthatdeterminetheflowortransportationofanyfluidfromonepointtoanother.HeattransferThisunitoperationdealswiththeprinciplesthatgovernaccumulationandtransferofheatandenergyfromoneplacetoanother.EvaporationThisisaspecialcaseofheattransfer,whichdealswiththeevaporationofavolatilesolventsuchaswaterfromanonvolatilesolutesuchassaltoranyothermaterialinsolution.DryingInthisoperationvolatileliquids,usuallywater,areremovedfromsolidmaterials,DistillationThisisanoperationwherebycomponentsofaliquidmixtureareseparatedbyboilingbecauseoftheirdifferencesinvaporpressure.AbsorptionInthisprocessacomponentisremovedfromagasstreambytreatmentwithaliquid.MembraneseparationThisprocessinvolvesthediffusionofasolutefromaliquidorgasthroughasemipermeablemembranebarriertoanotherfluid.Liquid-liquidextractionInthiscaseasoluteinaliquidsolutionisremovedbycontactingwithanotherliquidsolventwhichisrelativelyimmiscible(不混溶的)withthesolution.,Liquid-solidleaching(浸提)Thisinvolvestreatingafinelydividedsolidwithaliquidthatdissolvesoutandremovesasolutecontainedinthesolid.CrystallizationThisconcernstheremovalofasolutesuchasasaltfromasolutionbyprecipitating(沉淀)thesolutefromthesolution.MechanicalphysicalseparationTheseinvolvesseparationofsolids,liquids,orgasesbymechanicalmeans,suchasfiltration,settling,andsizereduction,whichareoftenclassifiedasseparateunitoperations.,Lesson2Fractionaldistillation,Fractionaldistillationistheseparationofamixtureofcompoundsbytheirboilingpoint,byheatingtohighenoughtemperatures.FractionalDistillationinaLaboratoryApparatus,conicalflask,1.Theapparatusisassembledasinthediagram.Themixtureisputintotheroundbottomedflaskalongwithafewantibumpinggranules(沸石),andthefractionatingcolumnisfittedintothetop.2.Asthemixtureboils,vaporrisesupthecolumn.Thevaporcondensesontheglassplatformsinsidethecolumn,andrunsbackdownintotheliquidbelow,refluxingdistillate.3.Onlythemostvolatileofthevaporsstaysingaseous(气态)formallthewaytothetop.Thevaporatthetopofthecolumnwillbealmostpureethanol.4.Thisthenpassesintothecondenser,whichcoolsitdownuntilitliquefies(液化).Theprocesscontinuesuntilalltheethanolboilsoutofthemixture.5.Thispointcanberecognizedbythesharpriseintemperatureshownonthethermometer,fromtheboilingpointofethanoltotheboilingpointofwater.,ExampleConsiderthedistillationofamixtureofethanolandwaterasanexample.Ethanolboilsat78.5oCwhilstwaterboilsat100oC.Sobygentlyheatingthemixture,theethanolwillboilofffirst.Somemixturesformazeotropes(共沸),wherethemixtureboilsatalowertemperaturethaneithercomponent.Intheethanolexample,amixtureof95%ethanoland5%waterboilsat78.2C,sotheethanolcannotbecompletelypurifiedbydistillation.,IndustrialusesofFractionalDistillationOilrefinery,Themostimportantindustrialapplicationoffractionaldistillationisthedistillationofcrudeoil.Theprocessissimilarinprincipletothelaboratorymethoddescribedaboveexceptforscale,continuousfeedandoperation,andthefactthatcrudeoilhasmanydifferentcompoundsmixedtogether.Thefractionatingcolumnhasoutletsatregularintervalsupthecolumnwhichallowthedifferentfractionstorunoutatdifferenttemperatures,withthehighlyvolatilegasescomingoutthetopmostoutletgraduatingtothelessvolatileroadtar,(bitumen沥青)comingoutatthebottom.,Lesson3Crystallization,Crystallizationisatechniquewhichchemistsusetopurifysolidcompounds.Itisoneofthefundamentalprocedureseachchemistmustmastertobecomeproficientinthelaboratory.Crystallizationisbasedontheprinciplesofsolubility:compounds(solutes)tendtobemoresolubleinhotliquids(solvents)thantheyareincoldliquids.Ifasaturatedhotsolutionisallowedtocool,thesoluteisnolongersolubleinthesolventandformscrystalsofpurecompound.Impuritiesareexcludedfromthegrowingcrystalsandthepuresolidcrystalscanbeseparatedfromthedissolvedimpuritiesbyfiltration.,Lesson4MembraneSeparation,1WhatisaMembrane?Themembranecanbedefinedessentiallyasabarrier,whichseparatestwophasesandrestrictstransportofvariouschemicalsinaselectivemanner.Amembranecanbehomogenousorheterogeneous,symmetricorasymmetricinstructure,solidorliquid,cancarryapositiveornegativechargeorbeneutralorbipolar.Transportthroughamembranecanbeeffectedbyconvectionorbydiffusionofindividualmolecules,inducedbyanelectricfieldorconcentration,pressureortemperaturegradient.Themembranethicknessmayvaryfromassmallas100microntoseveralmms.,2MembraneSeparationTechnologyAmembraneseparationsystemseparatesaninfluentstreamintotwoeffluentstreamsknownasthepermeateandtheconcentrate.Thepermeateistheportionofthefluidthathaspassedthroughthesemi-permeablemembrane.Whereastheconcentratestreamcontainstheconstituentsthathavebeenrejectedbythemembrane.,Membraneseparationprocessenjoysnumerousindustrialapplicationswiththefollowingadvantages:Appreciable(可观的)energysavingsEnvironmentallybenign(温和)CleantechnologywithoperationaleaseReplacestheconventionalprocesseslikefiltration,distillation,ion-exchangeandchemicaltreatmentsystemsProduceshigh,qualityproductsGreaterflexibilityindesigningsystems.,MembraneSeparationProcessesVarioustypesofmembraneseparationhavebeendevelopedforspecificindustrialapplications.Someofthewidelyusedprocessesarediscussedhereunder:,ReverseOsmosis(RO)Unlikewaterfiltration,thatcanonlyremovesomesuspendedmaterialslargerthan1micron,theprocessofreverseosmosis(RO)willeliminatethedissolvedsolids,bacteria,virusesandothergermscontainedinthewater.ROisessentiallyapressuredrivenmembranediffusionprocessforseparatingdissolvedsolutes.TheROisgenerallyusedfordesalinationseawaterforitsconversionintopotable(可饮用)water.Thesalient(显著)featuresoftheprocessarethatitinvolvesnophasechangeanditisrelativelyalowenergyprocess.,ROmembraneshavethesmallestporestructure,withporediameterrangingfromapproximately5-15A(0.5nm-1.5nm).TheextremelysmallsizeofROporesallowsonlythesmallestorganicmoleculesandunchangedsolutestopassthroughthesemi-permeablemembranealongwiththewater.Greaterthan95-99%ofinorganicsaltsandchargedorganicswillalsoberejectedbythemembraneduetochargerepulsion(斥力)establishedatthemembranesurface.,Nanofiltration(NF)Nanofiltrationisaformoffiltrationthatusesmembranestoseparatedifferentfluidsorions.NFistypicallyreferredtoas“loose”ROduetoitslargermembraneporestructureascomparedtothemembranesusedinRO,andallowsmoresaltpassagethroughthemembrane.Becauseitcanoperateatmuchlowerpressures,andpassessomeoftheinorganicsalts,NFisusedinapplicationswherehighorganicremovalandmoderateinorganicremovalsaredesired.,NFiscapableofconcentratingsugars,divalent(二价)salts,bacteria,proteins,particles,dyesandotherconstituentsthathaveamolecularweightgreaterthan1000Daltons(道尔顿).AnadvantageofNFoverROisthatNFcantypicallyoperateathigherrecoveries,therebyconservingtotalwaterusageduetoalowerconcentratestreamflowrate.NFisnoteffectiveonsmallmolecularweightorganics,suchasmethanol.,Ultrafiltration(UF)Ultrafiltrationismostcommonlyusedtoseparateasolutionthathasamixtureofsomedesirablecomponentsandsomethatarenotdesirable.UFissomewhatdependentonchargeoftheparticle,andismuchmoreconcernedwiththesizeoftheparticle.Typicalrejectedspeciesincludesugars,bio-molecules,polymersandcolloidalparticles.,Thedrivingforcefortransportacrossthemembraneisapressuredifferential.UFprocessesoperateat2-10barsthoughinsomecasesupto25-30barshasbeenused.UFprocessesperformfeed(锅炉给水)clarification,andistypicallynoteffectiveatseparatingorganicstreams.,Microfiltration(MF)Thisisbyfarthemostwidelyusedmembraneprocesswithtotalsalesgreaterthanthecombinedsalesofallothermembraneprocesses.Microfiltrationhasnumeroussmallapplications.Itisessentiallyasterilefiltrationwithpores(0.1-10.0microns)sosmallthatmicro-organismscannotpassthroughthem.,Microfiltrationisaprocessofseparatingmaterialofcolloidalsizeandlargerthantruesolutions.AMFmembraneisgenerallyporousenoughtopassmoleculesoftruesolutions,eveniftheyarelarge.Microfilterscanalsoheusedtosterilizesolutions,astheyarepreparedwithporessmallerthan0.3microns,thediameterofthesmallestbacterium,pseudomonas(假单孢菌).,Lesson5SupercriticalFluidExtraction,1Introductionofthephysico-chemicalpropertiesofthesupercriticalfluidsApuresupercriticalfluid(SCF)isanycompoundatatemperatureandpressureabovethecriticalvalues(abovecriticalpoint).Abovethecriticaltemperatureofacompoundthepure,gaseouscomponentcannotbeliquefiedregardlessofthepressureapplied.Thecriticalpressureisthevaporpressureofthegasatthecriticaltemperature.,Inthesupercriticalenvironmentonlyonephaseexists.Thefluid,asitistermed,isneitheragasnoraliquidandisbestdescribedasintermediatetothetwoextremes.Thisphaseretainssolventpowerapproximatingliquidsaswellasthetransportpropertiescommontogases.,Acomparisonoftypicalvaluesfordensity,viscosityanddiffusivityofgases,liquids,andSCFsispresentedinTable1.,Table1.Comparisonofphysicalandtransportpropertiesofgases,liquids,andSCFs,Thecriticalpoint(C)ismarkedattheendofthegas-liquidequilibriumcurve,andtheshadedareaindicatesthesupercriticalfluidregion.Itcanbeshownthatbyusingacombinationofisobaric(恒压)changesintemperaturewithisothermal(等温)changesinpressure,itispossibletoconvertapurecomponentfromaliquidtoagas(andviceversa)viathesupercriticalregionwithoutincurringaphasetransition.,Thebehaviorofafluidinthesupercriticalstatecanbedescribedasthatofaverymobileliquid.Thesolubilitybehaviorapproachesthatoftheliquidphasewhilepenetrationintoasolidmatrixisfacilitatedbythegas-liketransportproperties.Asaconsequence,theratesofextractionandphaseseparationcanbesignificantlyfasterthanforconventionalextractionprocesses.Furthermore,theextractionconditionscanbecontrolledtoeffectaselectedseparation.,Supercriticalfluidextractionisknowntobedependentonthedensityofthefluidthatinturncanbemanipulated(操控)throughcontrolofthesystempressureandtemperature.ThedissolvingpowerofaSCFincreaseswithisothermalincreaseindensityoranisopycnic(恒密度)increaseintemperature.InpracticaltermsthismeansaSCFcanbeusedtoextractasolutefromafeedmatrixasinconventionalliquidextraction.However,unlikeconventionalextraction,oncetheconditionsarereturnedtoambientthequantityofresidualsolventintheextractedmaterialisnegligible(可以忽略，微不足道).,ThebasicprincipleofSCFextractionisthatthesolubilityofagivencompound(solute)inasolventvarieswithbothtemperatureandpressure.Atambientconditions(25oCand1bar(1工程大气压)thesolubilityofasoluteinagasisusuallyrelateddirectlytothevaporpressureofthesolutea