污控ch6.1等离子体 1class

Chapter6.1

PlasmatechniqueforPollutionControlChemistryonPollutionControl等离子体等离子体是处于电离状态的气体，是美国科学家Langmuir于1927年在研究低气压下汞蒸汽中放电现象时命名的。等离子体由大量的电子、离子、中性原子、激发态原子、光子和自由基等组成，但整体表现出电中性。等离子体又称物质第四态，它是包含足够多的正负电荷数目近于相等的带电粒子的非凝聚系统。

WhatisPLASMA?“FourthState”ofmatterIonizedgasathightemperaturecapableofconductingelectricalcurrentLightningisanexamplefromnature等离子体催化

等离子体催化净化技术是利用高能电子射线激活、电离、裂解废气中各组分，从而使其发生一系列复杂的物理变化和化学反应，而随后的催化剂将促进副产物的转化，并降低反应的活化能，把有害物转化为无害的或有用的物质加以回收。低温等离子体催化技术解决了传统的净化方法所不能解决的问题。利用该技术来处理废气始于20世纪70年代，有的已进入应用阶段。低温等离子体催化可以处理废气，如VOCs，还原脱硫、联合脱硝等。Whenanelectricfieldisappliedtoavolumeofgas,highlyenergeticelectronsaregenerated.Highlyenergeticelectronsrapidlycollidewithgasmoleculesinitiatingasuccessionofchemicalreactions.‘Active’plasmaspeciesisformed,includingfreeradicals,ions,excitedmolecules.Inthecaseofaplasmaformedinamixtureofmethaneandcarbondioxide,newgasmoleculessuchasH2

isformed.Dry:CH4+CO2=2CO+2H2Withwater:CH4+2H2O=CO2+4H2AppliedCatalysisB:Environmental94(2010)19–26Prepr.Pap.-Am.Chem.Soc.,Div.FuelChem.2004,49(1),180Processesofplasma

Non-thermalPlasmasElectricalProperties&ChemistryElectricalpropertiesDependingonreactortypePulsedcorona–largevolume/surfaceratio,largedischargegapDielectricbarrier–largesurface/volumeratio,smalldischargegap;barrierproperties;frequency(capacitivecoupling)Dielectricpackedbed–intermediatesurface/volumeratio&dischargegap;dielectricpackedbeproperties;frequency(localcapacitivecoupling)ChemistryFastradical&ionformation(E/n)inactivedischargeregionPulsedcorona–streamerheadDielectricbarrier–μ-discharges;ionizationwaves;fullydevelopedstreamers;AtmosphericPressureGlowDischargeSlowvolumechemistry(chainreactions)Plasma-CatalyticReactorConcepts1-stagereactor(plasmaincontacttocatalyticsurfaces)Example:DPBreactorDielectricpropertiesofcatalystneedtofittoapplicationDirectinteractionofplasma&catalystenabled2-stagereactor(nodirectplasma–catalystcontact)Example:DBD&catalystelectricalconductivityofthecatalystdoesn’tplayarolecatalyticreactionsinitiatede.g.bymetastableintermediateproductsPlasmaActivationofCatalyticReactionsPhysical/chemicaleffectsGasheatingCatalystheatingElectricfieldsVibrationalexcitationDissociationIonizationUVradiationIntermediateproductformationApplicationofplasmacatalysisCatalyticNOXremovalCatalyticmethaneconversionCatalyticVOCsdegradationCatalyticCO2reductionCatalystpreparation,regenerationApplicationPlasmaPlasma-CatalyticHybridProcessesforGasCleaningPlasmainduced/enhancedselectivecatalyticNOx-reductionforautomotiveexhaustgases(SAG,Ford,Chrysler,LLNL,PNNL,...)oxidationduetodielectricbarrierdischarge(DBD)pretreatmentnon-preciousmetalcatalyst&urea/fuelasareducingagentNOx-reductioninanoxidizingatmospherecatalyticactivityextendedtolowtemperaturessulfurtolerantPlasmaassistedcatalyticoxidationofVOCsforthedecontaminationofgroundwaterofindustrialsites(IUT)extractionofVOCsfromgroundwaterbyairstripping:largegasflows,lowgastemperatureefficientplasmapre-treatmentusingdielectricbarrierdischargescatalyticoxidationoftheVOCsatlowtemperature(<100°C)Sorption&plasmaassistedoxidationofVOCsusingoxygenplasma(AIST)SorptionofVOCfromoff-gasRegenerationofcatalyticsorbentbyoxygenplasmaIncreasedefficiencycomparedtodirectplasma-catalyticconversionCH4+CO2=2CO+2H2Fig.

Plasma

reactor.1–gasinlet2–highvoltage electrode3–

discharge

gap4–electricheater5–grounded electrode6–gasoutletAThereagentactivationbyelectronimpactorbyreactionswithatomicandmolecularactivespecies:CH4

+

e

=

CH3

+

H

+

eCH4

+

e

=

CH2

+

H2

+

eCH4

+

e

=

CH

+

H2

+

H

+

eCO2

+

e

=

CO

+

O

+

eBFasthomogeneousreactionsproceedinthegasphasebetweentheshortlivingactivespeciesCReactionsinducedbythesolidsurfacestakeplaceonelectrodesurfacesandinsidethe

discharge

volume.ThreestagesofPlasmacatalytic

reactionAppliedCatalysisB:Environmental94(2010)19–26ApplicationofplasmacatalysisApplicationofplasmacatalysisPlasmacatalytichybridprocessescansuccessfullybeappliedfortheabatementofodorous&noxiouscompoundsfromoff-gasesHybridprocessesweredemonstrated(PlasmaenhancedselectivecatalyticNOxreduction;PlasmaenhancedcatalyticoxidationofHCs&VOCs)Goodenergyefficiency,lowoperationcostscanbeexpected.Plasma-catalytichybridreactor&powersupplyconceptsareavailableSorptionpropertiesofcatalystareimportantCatalystneedstobetailoredforapplication(intermediateproductgeneratedbyplasma,plasmaregenerationofcatalyst,...)ApplicationofplasmacatalysisElectroncollisiondissociationofoxygenRadicalattackofHCsOxidationofNONO-Reductione+O2→e+O+OO+C2H4→HCO+CH3+HCH3+O2

→CH3O2H+O2

→HO2RO2+NO→NO2+ROO+NO+M→NO2+MO+NO2

→NO+O2NO+N→N2+OO2+N

→NO+OAdvantagesandshortcomingsofplasmacatalysis等离子体催化技术的优点用该项技术处理有机废气具有以下优点：能耗低，可在室温下与催化剂反应，无需加热,极大地节约了能源;使用便利，设计时可以根据风量变化以及现场条件进行调节；不产生副产物，催化剂可选择性地降解等离子体反应中所产生的副产物；不产生放射物;尤其适于处理有气味及低浓度大风量的气体。CatalystCatalysisToday,2002,72:173–184Agoodcatalystmusthavecertaincharacteristics:provideasufficientlyhighreactionrateunderthespecificreactiveconditions;sustainitsactivityoveralongperiodoftime;exhibitlowsensitivitytopoisons,suchassulfurcompounds;havegoodmechanicalstrength;showselectivity,itshouldacceleratethedesiredreactiononly;bereducedbeforeusesincemostofcatalystsareproducedasoxides.

Thereductionperiodshouldbeasshortaspossibleinordertoavoidadecreaseintheproductionefficiency.等离子体催化中的催化剂等离子体催化净化技术采用的催化剂包括几类：铁电体材料；分子筛；贵金属催化剂；金属氧化物及其金属盐催化剂；光催化剂；多性能颗粒／混合物等。CatalystpreparationCatalysisToday,2002,72:173–184Maintrends:plasmachemicalsynthesisofultrafineparticlecatalysts;plasmaassisteddepositionofcatalyticallyactivecompoundsonvariouscarriers,especiallyplasmasprayingforthepreparationofsupportedcatalysts;plasmaenhancedpreparationorplasmamodificationofcatalysts.

Advantages:ahighlydistributedactivespecies;reducedenergyrequirements;enhancedcatalystactivation,selectivity,andlifetime;shortenedpreparationtime.Catalystpreparation,regenerationPlasma-chemicalsynthesisandregenerationofcatalystsCatalysisToday,2002,72:213–2211:electric-arcdcplasmatron;1a:thoriatedtungstencathode;1b:copperwater-cooledanode;1c:plasticadjustingring;2:CWPCR;3:quenchingdevice;4:copperwater-cooledsectionsforthequenchingdevice;5:powder-trappingchamber;6:filter;7:vibrationpowder-feeding;8:currentrectifier;9:flow-meters;10:bottleswithplasma-forming,powdercarryingandquenchinggases;T1:temperatureofinletwater;T2:temperatureofoutletwater.Schematicdrawingoftheplasma-chemicalinstallationforsynthesisandregenerationofcatalysts.Catalystpreparation,regenerationPlasma-chemicalsynthesisandregenerationofcatalystsCatalysisToday,2002,72:213–221Electronmicroscopephotographofsamplesphericalinshapeequivalentdiametersfellwithintherangeof10–30nmPlasma-chemicalsynthesisiseffectiveforregeneratingspentindustrialcatalysts.CatalysisToday,2002,72:173–184(a)glowdischarge;(b)microwaveplasma;(c)plasmaspraying.SchematicallyrepresentativesofelectrodeconfigurationsofdischargephenomenaappliedforcatalystpreparationDevicesforcatalystpreparationCommercialPlasmaTorchPlasmatorchinoperationPlasmaassisteddepositionofcatalyticallyactivecompoundsonvarioussupportsCatalysisToday,2002,72:173–184CatalystPlasmaMetalandmetaloxidesofFe,Ni,Cr,Cu,Au:supportedonasupportsPlasmaplatingFe–CrorFe–Cr–Ni/supportPlasmasprayedalloyCoandCuoxidesonAl2O3fibersheetPlasmavapordepositionPtsupportedonporousNi–CralloyThermalplasmasprayingDual-layerceramiccoatedsurfacePlasmadepositionHoneyPtsupportplasma,coatedwithPdPlasmadepositionCatalystforcombustion(Pt,Au)Plasmasprayingonametalsupportα-Al2O3andγ-Al2O3supportedonNi,Ti,Co–LaElectric-arcplasmatorchNicatalystforhydro-treatingHighfrequencyplasmaCo–FePlasmasprayingTable.IllustrativecatalystspreparedusingplasmasprayingCatalysisToday,2002,72:173–184ThermalplasmaColdplasmaPressureAtmosphericorhigherLow(<0.1bar)formostcasesAppearanceFilamentaryinhomogeneousHomogeneousTemperaturesHighelectrontemperatureHighelectrontemperatureHighgas(bulk)temperatureLowgastemperatureDe-excitationrateingasphaseHighLowTypesPlasmajet;dccoronatorch;arcGlow;radiofrequency;microwaveUsesUltra-fineparticlesspraying;sputteringModificationortreatmentofcatalystsurfaceTable.CharacteristicsofthermalandcoldplasmasusedforcatalystpreparationCatalystregenerationSurfaceofCatalysttreatedbydischargeplasmaCatalysisToday,2006,115:205–210Theschematicrepresentativeofsetupforglowdischargecatalysttreatment.CatalystregenerationSurfaceofCatalysttreatedbydischargeplasmaCatalysisToday,2006,115:205–210Thecatalystpreparedbyplasmatreatmentshowsanimprovedlow-temperatureactivityandanenhancedstability.Comparedtothereportedwork,methaneconversionovertheplasmatreatedcatalysthasaca.20%increaseatthesamereactiontemperature.Theplasmatreatedcatalystpossessesabetteranti-carbondepositperformanceforcarbondioxidereformingofmethane,comparedtothereportedwork.Theplasmatreatmentfollowedbycalcinationthermallyinducesagenerationofspecificnickelparticlesonthesupport.Highlydispersedmetalspecieswouldinducebetterlow-temper