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1、GasesGases1Naturalgases2Industrialgases2Gasseparation2Dryair3CO23C2H24C3H8,C4H10andLPG5CH4andNG7Cl27HCl8He8H28NH38SF69GASESAgas(Gr.kaoz,chaos,atmosphere)isasubstanceshowingsuchalargetendencytoexpandthat,nomatterhowsmallquantitythereis,itfillstheentirecontaine
2、r(wheretheelectromagneticforcesofcontactpreventfurtherexpansion,althoughsometimesgasdiffusionthroughthewallisimportant),oritexpandsasmuchasthegravitationalforcespreventanyfurtherexpansion.Theperfectgasmodel(PGM),isthesimplestfullmodelforthethermodynamicbehavi
3、ourofagas;itcombinestheidealgasmodelpV=mRT,whichappliestoallgasesatlowpressure,andtheperfectthermalmodel,DU=mcvDT,whichisagoodapproximationfornotoolargetemperatureexcursions.Gasesmaybeprocuredbottledinseveralways:·Ascompressedgasathigh-pressure,usuallyat20MPa
4、(asforN2,O2,CH4,Ar,He,H2).·Ascompressedgasatmedium-pressure(forsmallneeds).·Asliquefiedgasesatmedium-pressure(asforcommercialbutane,propane,refrigerantfluidsandcarbondioxide).·Asrefrigeratedliquefiedgases(CO2andN2O,duetotheircriticaltemperature).·Ascryogenicl
5、iquidsatlowpressureovertheatmosphere(asforliquidN2,O2,CH4,He,H2).·Asgasesdissolvedinaliquid(acetylene,C2H2,isbottleddissolvedinacetone,CH3COCH3,soakedinporousfilling).Noticethatliquefiedgasbottlescandeliverliquidfromthebottom(insteadofgasfromabove)whenprovide
6、dwithasiphon(atubethatconnectstheheadvalvewiththeliquid;asinspraycansandsodasiphons).Liquidcanbealsodeliverbyplacingtheoutletvalveatthebottom(e.g.byholdingthebottleupsidedown,aswhenrefillingpropanegaslighters).Justforsmalllaboratorytests,in-situproductionisof
7、tenpreferable:H2andO2maybeproducedbywaterelectrolysis,CO2bydrippinganacidoveracarbonate,andCH4andC2H2bydrippingwateroverAl4C3orCa2C,respectively.Intermediategasstorageisusuallyachievedbyahydraulicsealasinagasometre.MajormanufacturersofindustrialgasesareTheLin
8、deGroup(Germany),AirLiquide(France),andPraxair(USA).NaturalgasesAllnaturalgasesaregaseousmixturesofseveralpurechemicalcomponents(sometimesholdingsolidorliquidparticlesinsuspension).Byfart
