《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 2 C sotheethanolcannotbecompletelypurifiedbydistillation IndustrialusesofFractionalDistillation Oilrefinery 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 thesolubilityofasoluteinagasisusuallyrelateddirectlytothevaporpressureofthesoluteandisgenerallynegligible Thedissolutionofsolutesinsupercriticalfluidsresultsfromacombinationofvaporpressureandsolute solventinteractioneffects Theimpactofthisisthatthesolubilityofasolidsoluteinasupercriticalfluidisnotasimplefunctionofpressure AlthoughthesolubilityofvolatilesolidsinSCFsishigherthaninanidealgas itisoftendesirabletoincreasethesolubilityfurtherinordertoreducethesolventrequirementforprocessing ThesolubilityofcomponentsinSCFscanbeenhancedbytheadditionofasubstancereferredtoasanentrainer 夹带剂 orcosolvent ThevolatilityofthisadditionalcomponentisusuallyintermediatetothatoftheSCFandthesolute Theadditionofacosolventprovidesafurtherdimensiontotherangeofsolventpropertiesinagivensystembyinfluencingthechemicalnatureofthefluid Cosolventsalsoprovideamechanismbywhichtheextractionselectivitycanbemanipulated ThecommercialpotentialofaparticularapplicationofSCFtechnologycanbesignificantlyimprovedthroughtheuseofcosolvents Afactorthatmustbetakenintoconsiderationwhenusingcosolvents however isthateventhepresenceofsmallamountsofanadditionalcomponenttoaprimarySCFcanchangethecriticalpropertiesoftheresultingmixtureconsiderably