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1、Lesson6FractionalDistillationFractionaldistillationistheseparationofamixtureofcompoundsbytheirboilingpoint,byheatingtohighenoughtemperatures.FractionalDistillationinaLaboratoryApparatus·roundbottomflask·conicalflask·Liebigcondenser·anti-bumpinggranules·thermometer·rubberbungs(unlessquickfitapparatu
2、sisused)MethodAsanexample,considerthedistillationofamixtureofethanolandwater.Ethanolboilsat78.5°Cwhilstwaterboilsat100°C.Sobygentlyheatingthemixture,theethanolwillboilofffirst.Somemixturesformazeotropes,wherethemixtureboilsatalowertemperaturethaneithercomponent.Intheethanolexample,amixtureof95%etha
3、noland5%waterboilsat78.2°C,sotheethanolcannotbecompletelypurifiedbydistillation.Theapparatusisassembledasinthediagram.Themixtureisputintotheroundbottomedflaskalongwithafewantibumpinggranules,andthefractionatingcolumnisfittedintothetop.Asthemixtureboils,vaporrisesupthecolumn.Thevaporcondensesonthegl
4、assplatformsinsidethecolumn,andrunsbackdownintotheliquidbelow,refluxingdistillate.Onlythemostvolatileofthevaporsstaysingaseousformallthewaytothetop.Thevaporatthetopofthecolumnwillbealmostpureethanol.Thisthenpassesintothecondenser,whichcoolsitdownuntilitliquefies.Theprocesscontinuesuntilalltheethano
5、lboilsoutofthemixture.Thispointcanberecognizedbythesharpriseintemperatureshownonthethermometer,fromtheboilingpointofethanoltotheboilingpointofwater.IndustrialusesofFractionalDistillation——OilrefineryThemostimportantindustrialapplicationoffractionaldistillationisthedistillationofcrudeoil.Theprocessi
6、ssimilarinprincipletothelaboratorymethoddescribedaboveexceptforscale,continuousfeedandoperation,andthefactthatcrudeoilhasmanydifferentcompoundsmixedtogether.Thefractionatingcolumnhasoutletsatregularintervalsupthecolumnwhichallowthedifferentfractionstorunoutatdifferenttemperatures,withthehighlyvolat
7、ilegasescomingoutthetopmostoutletgraduatingtothelessvolatileroadtar,(bitumen)comingoutatthebottom.Words&Phrasesazeotrope共沸混合物,恒沸物bitumen沥青liquefy(使)溶解,(使)液化thermometer温度计,体温计volatile挥发物anti-bumpinggranules防
