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页数:11页
时间:2020-11-23
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1、Molecularsieve李瑞琦应化01PrincipleAmolecularsieveisamaterialwithverysmallholesofpreciseanduniformsize.Theseholesaresmallenoughtoblocklargemoleculeswhileallowingsmallmoleculestopass.ApplicationManymolecularsievesareusedasdesiccants.SomeexamplesincludeActivatedcharcoalandsilicagel.Activatedcha
2、rcoalSilicagelMaterialsMolecularsievescanbemicroporous,mesoporous,ormacroporousmaterial.Microporousmaterial(<2nm)Zeolites、Porousglass、Activecarbon、ClaysMesoporousmaterial(2-50nm)SilicondioxideMacroporousmaterial(>50nm)Mesoporoussilica、ZeoliteLTAPoresizePropertiesMolecularsievesareusedasa
3、dsorbentforgasesandliquids.Moleculessmallenoughtopassthroughtheporesareadsorbedwhilelargermoleculesarenot.Itisdifferentfromacommonfilterinthatitoperatesonamolecularlevelandtrapstheadsorbedsubstance.Forinstance,awatermoleculemaybesmallenoughtopassthroughtheporeswhilelargermoleculesarenot,
4、sowaterisforcedintotheporeswhichactasatrapforthepenetratingwatermolecules,whichareretainedwithinthepores.Becauseofthis,theyoftenfunctionasadesiccant.Amolecularsievecanadsorbwaterupto22%ofitsownweight.DifferentsfromtheSize-exclusionchromatographyTheprincipleofadsorptiontomolecularsievepar
5、ticlesissomewhatsimilartothatofsizeexclusionchromatography,exceptthatwithoutachangingsolutioncomposition,theadsorbedproductremainstrappedbecause,intheabsenceofothermoleculesabletopenetratetheporeandfillthespace,avacuumwouldbecreatedbydesorption.Size-exclusionchromatography(SEC)isachromat
6、ographicmethodinwhichmoleculesinsolutionareseparatedbytheirsize,andinsomecasesmolecularweight.ApplicationsMolecularsievesareoftenutilizedinthepetroleumindustry,especiallyforthepurificationofgasstreamsandinthechemistrylaboratoryforseparatingcompoundsanddryingreactionstartingmaterials.They
7、arealsousedinthefiltrationofairsuppliesforbreathingapparatus,forexamplethoseusedbyscubadiversandfirefighters.Insuchapplications,airissuppliedbyanaircompressorandispassedthroughacartridgefilterwhich,dependentontheapplication,isfilledwithmolecularsieveand/oractivatedcarbon,
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