光催化氧化技术.doc

【精品文档】如有侵权，请联系网站删除，仅供学习与交流光催化氧化技术.精品文档.92GRANULAR ACTIVATED CARBON12.Gullick,R.W.,Grayman,W.M.,Deininger,R.A.,andMales,R.M.(2003).Designofearlywarningmonitoringsystemsforsourcewaters.J.Am.WaterWorksAssoc.95:5872.13.Ropp,S.L.,Jin,Q.,Knight,J.C.,Massung,R.F.,andEspos-ito,J.J.(1995).PCRstrategyforidenticationanddiffer-entiationofsmallpoxandotherorthopoxviruses.J.Clin.Microbiol.33:20692076.14.Peruski,A.H.andPeruski,L.F.,Jr.(2003).Immunologicalmethodsfordetectionandidenticationofinfectiousdiseaseandbiologicalwarfareagents.Clin.Diagn.Lab.Immunol.10:506513.15.Tims,T.B.andLim,D.V.(2004).RapiddetectionofBacillusanthracissporesdirectlyfrompowderswithanevanes-centwaveber-opticbiosensor.J.Microbiol.Methods59:127130.16.Kijek,T.M.,Rossi,C.A.,Moss,D.,Parke,R.W.,andHen-chal,E.A.(2000).Rapidandsensitiveimmunomagnetic-electrochemiluminescentdetectionofstaphylococcalentero-toxinB.J.Immunol.Methods236:917.17.Firmani,M.A.andBroussard,L.A.(2003).Moleculardiag-nostictechniquesforuseinresponsetobioterrorism.ExpertRev.Mol.Diagn.3:605616.defmw1702mw166GRANULAR ACTIVATED CARBONDINESHMOHANKUNWARP.SINGHGomtiNagar,Lucknow,UttarPradesh,IndiaActivatedcarbonisthegenerictermusedtodescribeafamilyofcarbonaceousadsorbentswithahighlycrystallineformandextensivelydevelopedinternalporestructure.ActivatedcarbonisdistinguishedfromAmongthemostcommonlyusedrawmaterials,precursorsfortheproductionofcommerciallyactivatedcarbonsarewood(130,000tons/year),coal(100,000tons/year),lignite(50,000tons/year),coconutshell(35,000tons/year),andpeat(35,000tons/year)(4,5).TYPES OF ACTIVATED CARBONSBasedonthephysicalproperties,activatedcarbonscanbeclassiedintothefollowingbroadcategories:Powdered Activated Carbon (PAC)Theseactivatedcarbonsaremadeinthepowdersornegranulesaccordingtotherequirement.Powderedactivatedcarbonshaveadiameterbetween15and25 µm.Thesecarbonsprovidealargeinternalsurfacewithasmalldiffusiondistance.Granular Activated Carbon (GAC)Granularactivatedcarbon(GAC)iscommonlyusedforthepuricationofliquidsandgases.Granularactivatedcarbonadsorbsavastvarietyofdissolvedorganicmate-rials,includingmanythatarenonbiodegradable.GACremovesorganiccontaminantsfromwater/wastewaterbytheadsorptionprocessoftheattractionandaccu-mulationofonesubstanceonthesurfaceofanother.Granularactivatedcarbonstypicallyhavesurfaceareasof5002000m2/g,withsomereportedashighas3000m2/g.MuchofthesurfaceareaavailablefortheadsorptioningranularactivatedcarbonparticlesisfoundintheporeswithinthegranularcarbonparticlescreatedduringTable1.SourceMaterialsUsedforthePreparationofActivatedCarbonselementalcarbonbytheremovalofallnoncarbonimpuritiesandtheoxidationofthecarbonsurface(1).Activatedcarbonhasthehighestvolumeofadsorbingporosityofanysubstanceknowntohumans(5gramsofactivatedcarboncanhavethesurfaceareaofafootballeld).Itcanbedenedas(2):Activatedcarbonisacrudeformofgraphite,witharandomoramorphousstructure,whichishighlyporous,overabroadrangeofporesizes,fromvisiblecracksandcrevices,tocracksandcrevicesofmoleculardimensions.Theuseofactivatedcarbonisnotnew.TheEgyptiansusedcarbonizedwoodaround1500B.C.asanadsorbentformedicinalpurposesaswellasapurifyingagent.TheancientHindusinIndiausedcharcoalforltrationofdrinkingwater.However,thebasisforindustrialpro-ductionofactivecarbonswasestablishedin19001901inordertoreplacebonecharinthesugarreningprocess(3).Activecarbonscanbepreparedfromawiderangeofcarbonaceousmaterials,whichincludecoconutshells,woodchar,lignin,petroleumcoke,bonechar,peat,sawdust,carbonblack,ricehulls,sugar,peachpits,sh,fertilizerwaste,andwasterubbertire.(Table1).Therangeofrawmaterialsisdiverseandwidespreadandgreatlyinuencedbytheneedtoproducelow-costcarbon.BagasseBarkBeat-sugarsludgeBloodBluedustBonesCarbohydratesCerealsCoalCoconutcoirCoconutshellCoffeebeansCornCobsandcornstalksCottonseedhullsDistillerywasteFertilizerwasteslurryFishFruitpitsFullersearthGraphiteHumanhairsJutestickKelpandseaweedLeatherwasteLigninLigniteLampblackLeatherwasteMolassesMunicipalwasteNewspaperNutshellsOilshaleOlivestonesPalmtreecobspeatPetroleumacidsludgePetroleumcokePotassiumferrocynideresiduePulp-millwasteRefnationearthRenerywasteRicehullsRubberwasteSawdustScraptiresSpentFullersearthSunowerseedsSugar-beetsludgeTealeavesRubberTiresWheatstrawWoodGRANULAR ACTIVATED CARBON93theactivationprocess.GAChaverelativelylargerparti-clesixesthanpowderedactivatedcarbonandthereforeprovideasmallerexternalsurface.Thesecarbonsarepre-ferredforallthesorptionofgasesandvapors.GACarealsousedinwater/wastewatertreatment,deodorization,decol-orization,andseparationofcomponentsinowsystems.Spherical Activated Carbon (SAC)Thesecarbonsarepreparedfromsmallsphericalballswhereinpitchismeltedinthepresenceofnaphthaleneortetorlinandconvertedintospheres.Thesespheresarethencontactedwithnapthasolution,whichextractsnaphthaleneintroducedintotheporousstructure.Theseporousspheresarethenheatedbetween100and400 Cinthepresenceofanoxidizingagent.Theoxidizedspheresarethenheatedbetween150and700 CinthepresenceofammoniatointroducenitrogenintospheresfollowedbyactivationinsteamorCO2.Impregnated Activated Carbon (IAC)Inchemicalactivation,acatalystmaybeimpregnatedintothefeedstock.ThemostcommonlyusedchemicalactivantsincludeZnCl2,H3PO4,H2SO4,KOH,K2S,andKCNS.Inthisprocess,anear-saturatedsolutionofcatalyst-impregnatedfeedstockisdriedtoinuencepyrolysisinsuchawaythattarformationandvolatilizationcanbekeptataminimum.Theresultingproductisthencarbonized.Silverimpregnatedactivatedcarbonsareusedforpuricationofdomesticwater.Polymer Coated Activated Carbons (POAC)Inthisprocess,porouscarboncanbecoatedwithbiocompatiblepolymersresultinginasmoothandpermeablecoatwithoutblockingthepores.Itiswelldocumentedinliteraturethatactivatedcarbonspossessahighlydevelopedporoussystem.Theseporesareproducedduringtheactivationprocessofcarbonizedresiduewhenspacesbetweenelementarycrystallineareclearedofcarbonaceouscompoundsandnonorganizedcarbon.Theprecursorsusedfortheproductionofactivatedcarbonshavealargeeffectontheporesizedistribution,surfacearea,andotherphysicalandchemicalproperties.Table2sumsupsomeofthebasicdifferencesbetweentherawmaterialsusedfortheproductionofsomeimportantactivatedcarbons,whereasthepropertiesofsomecommerciallyavailablecarbonswiththeirsourcesascollectedfromliteraturearepresentedinTable3.METHODS FOR ACTIVATED CARBON DEVELOPMENTThemethodsforthedevelopmentofactivatedcarbonsarenearlyaswidespreadastheirpotentialusesandsourcematerials(6).However,thebasicstepsmostcommonlyusedinthepreparationofactivatedcarbonsareprecursormaterialpreparation,palletizing,low-temperaturecarbonization,followedbychemicalorphysicalactivation(Fig.1).Anumberofmethodswereusedforthepreparationofactivatedcarbonsfromwastematerialsfromtimetotimeusingdifferentactivationparameters.Differentsteps/activationparametersusedforthepreparationofsomeoftheactivatedcarbonsarepresentedinTable4.Althoughthelistisnotcomplete,itwillprovideageneralideaofthedifferentmethodsusedfortheproductionofactivatedcarbons.Raw MaterialsTheselectionofanappropriaterawmaterial(Table1)forthedevelopmentofgranularactivatedcarbonisthemostimportantaspect.Thefollowingpointsmustbeconsideredbeforeselectinganyrawmaterialfortheproductionofactivatedcarbons:1.Industriallyinexpensivematerialswithhighcar-bonandlowinorganiccontentshouldalwaysbepreferred.2.Theimpuritiesinrawmaterialsshouldbekeptataminimumbecauseaftertheactivationprocess,manyofthesemaybepresentinthecarbonathigherconcentrationsthantheprecursorsmaterials.3.Importanceshouldbegiventotheprecursorshavinghighdensityandsufcientvolatilecontent.Thevolatileresultsinporouschar,whereashighdensityfavorstheenhancementofstructuralstrengthofthecarbonneededtowithstandexcessiveparticlecrumbleduringuse.4.Therawmaterialshouldbeavailableinabun-dancelocally.Therawmaterialsusedforthepreparationofactivatedcarbonsvarywiththeirapplications.AcomparisonofsomeoftherawmaterialsispresentedinTable2.Table2.BasicDifferencesinPrecursorMaterialsUsedfortheProductionofActivatedCarbonsPercentRawPercentVolatileAshDensityActivatedMaterialsHardwoodSoftwoodNutshellsCarbon404240454045Matter556055605560Percent0.251.20.251.00.400.60(kg/m3)0.500.80.400.501.4CarbonTextureSoftwithlargeporevolumeSoftwithlargeporevolumeHardwithlargemultiporeApplicationsLiquidphaseadsorptionLiquidphaseadsorptionVaporphaseadsorptionvolumeLigniteSoftcoal5070608025402530562121.01.401.251.50HardwithsmallporevolumeMediumhardwithmediumLiquidphaseadsorptionLiquidandvaporphasemicroporevolumeadsorptionSemihardcoalHardcoal707585951155105152151.451.502.0HardwithlargeporevolumeHardwithlargeporevolumeVaporphaseadsorptionVapourphaseadsorption94GRANULAR ACTIVATED CARBONTable3.PropertiesofSomeSelectedActivatedCarbonsGatheredfromtheLiteratureTotalMoistureSurfacePoreIodineasTypesofRawArea,BETVolumeNumberAshUniformityPackedEffectiveApparentCarbonsMaterial(m2/g)(ml/g)(mg/g)CoefcientpHzpcSize,mmDensityF-100F-200BituminouscoalBituminouscoal8509007148508502.11.99.08.2220.81.00.550.75F-300F-400F-816F-820CentaurHSVNucharSNNucharSANucharWHD-4000DracoKBNoritGAC840RBituminouscoalBituminouscoalBituminouscoalBituminouscoalBituminouscoalWoodWoodWoodLignitecoalHardwoodReactivated9501501050120014001800140018001400160062515000.850.940.931.8900100090090080090090090064780095.49736362322.11.91.41.51.449.810.404.04.022224101010820.81.00.5g/cc0.550.75271.31.51.01.20.56g/cc337369(kg/m3)337369(kg/m3)240305(kg/m3)0.740.40g/ml0.45g/cc0.48g/ccCarbonNoritPAC20BHD-CCoalLignitecoal556800500340.51g/ccNoritGAC1240coal11000.9510201.820.50g/ccBarnebey&Coconutshell11001200105023SutcliffeSEBarnebey&Coconutshell11001200105023SutcliffePEBarnebey&Coconutshell115050.48g/ccSutcliffeKEBarnebey&Coconutshell1150550.40.8g/ccSutcliffeUUPicaPOU/POECoconutshell70022001150550.450.54g/ccGX203carbonPicaPOU/POENCCoconutshell70022001100430.410.45g/cc506carbonCameronPACarbResinouswood500830.45g/cccharcoalSelectoABA40003005000.350.55LCWitco517Petroleum105010000.51.410.890.52g/ccCarbonizationCarbonization,sometimescalledcharring,convertstheorganicmaterialintoprimarycarbon,whichisamixtureofash,tars,amorphouscarbon,andcrystallinecarbon.Incarbonization,thematerialisheatedslowlyintheabsenceofair.Inthisprocess,mostofthenoncarbonelements,hydrogen,andoxygenarerstremovedingaseousformbypyrolyticdecompositionofthestartingmaterials.Theimportantparameters,whichdeterminethequalityandquantityofthecarbonizedproduct,are(a)rateofheating,(b)naltemperature,and(c)soakingtime.ActivationTheactivationiscarriedoutbasicallytoenlargethediametersofthepores,whicharecreatedduringthecarbonizationprocess,andtocreatesomenewporosity,whichresultsintheformationofawell-denedandreadilyaccessibleporestructurewithlargeinternalsurfacearea.Duringtheactivationprocess,thespacesbetweentheelementarycrystallitesbecomeclearedorlessorganizedlooselyboundcarbonaceousmaterial.Theresultingchannelsthroughthegraphiticregions,thespacesbetweentheelementarycrystallites,togetherwithssureswithinandparalleltothegraphiteplanesconstitutetheporousstructure,withlargeinternalsurfacearea(24).Therearetwotypesofactivation,whichareusedtoimpartaporousstructurewithinastartingmaterialofrelativelylowsurfacearea,namelythermal/physicalorchemicalactivation.Physical or Thermal Activation.Physicalorthermalactivationoccursafterinitialtreatmentandpalletizing;itinvolvescarbonizationat500600 CtoeliminatethebulkofthevolatilematterfollowedbypartialgasicationusingmildoxidizinggassuchasCO2,steam,orfuelgasat8001000 Ctodeveloptheporosityandsurfacearea(25).Anexampleincludesthegasicationofthecarbonizedmaterialwithsteam,andcarbondioxideoccursbythefollowingendothermicreactions:C +H2O CO +H2 (29kcal)C +CO2 2CO (39kcal)PrecursormaterialsGRANULAR ACTIVATED CARBON95ReconstitutionPretreatmentCarbonizationGrinding/Classifying/SizingPACGrindingActivationPhysicalChemicalSieveanalysisGACFigure1.Variousstepsusedintheactivatedcarbonproduction.CO +H2O CO2 +H2 (10kcal)TheH2OmoleculeissmallerthantheCO2moleculeandthusdiffusesfasterintotheporesofthecarbon.Consequently,areactionwithsteamisfasterthanthatofCO2.IthasbeenreportedinliteraturethatadecreaseinthereactionratewithCO2activationoncarbon-containingwastesisnearlytwotimeslessthanthatofsteam.Whenairoroxygenisusedasanactivatingagent,problemsdevelopbecauseoftheexothermicnatureofthereactionsofcarbonwithair(oxygen),andthusitisdifculttocontrol.Despitetheseproblems,severalresearchershaveusedthesamefortheactivationoftheirproducts.Chemical Activation.Thesecondtypeofactivationinvolvestheincorporationofinorganicadditivesormetallicchlorides,suchaszincchlorideorphosphoricacid,intotheprecursorbeforethecarbonization(6).Ithasbeenreportedthatcarbonswithwell-developedporousstructure,mainlymesoandmicroporous,canbeproducedbyZnCl2incorporation.KOHactivationhasalsobeenshowntosuccessfullyincreasethesurfaceareaandporevolumeofactivecarbons(20,26)Manyotherchemicals,suchasammoniumsalts,borates,calciumoxide,ferricandferrouscompounds,manganesedioxide,nickelsalts,hydrochloricacid,nitricacid,andsulfuricacid,havealsobeenusedfortheactivationpurpose.Thebasicdifferencebetweenphysicalandchemicalactivationisthenumberofstagesrequiredforactivationandthetemperatureatwhichtheactivationtakesplace.Chemicalactivationisaone-stepprocess,whereasphysicalactivationisatwo-stepprocess,includingcarbonizationandactivation.Thetemperaturerequiredinphysicalactivation(8001000 C)ishigherthanthatofchemicalactivation(200800 C).96GRANULAR ACTIVATED CARBONTable4.SomeChemicalActivant-FeedstockCouplesExtendedFormof(4)FeedstockCoconutshellActivantCon.H2SO4Conditions1.5partsbyweightH2SO4for24hrsat140160 C:steamReference7activationat1Kg/m2pressurefor30min.AgriculturalbyproductssuchasHeatinginCO2at1123K8almondshell,olivestonesandpeachston