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Activatedcarbon

ActivatedcarbonFromWikipedia,thefreeencyclopedia

Activatedcarbon,alsocalledactivatedcharcoal,activatedcoal,orcarboactivatus,isaformofcarbonprocessedtohavesmall,lowvolumeporesthatincreasethesurfaceareaavailableforadsorptionorchemicalreactions.[1]Activatedissometimessubstitutedwithactive.

Duetoitshighdegreeofmicroporosity,justonegramofactivatedcarbonhasasurfaceareainexcessof500m2,asdeterminedbygasadsorption.Anactivationlevelsufficientforusefulapplicationmaybeattainedsolelyfromhighsurfaceareahowever,furtherchemicaltreatmentoftenenhancesadsorptionproperties.

Activatedcarbonisusuallyderivedfromcharcoaland,increasingly,highporositybiochar.

Contents

1Uses1.1Medicaluses1.2Adversedrugeffects1.3Analyticalchemistryapplications1.4Environmentalapplications1.5Fuelstorage1.6Gaspurification1.7Chemicalpurification1.8Soundabsorption1.9Distilledalcoholicbeveragepurification1.10Mercuryscrubbing

1.10.1DisposalintheUSAafterabsorbingmercury2Production3Classification

3.1Powderedactivatedcarbon(R1,PAC)3.2Granularactivatedcarbon(GAC)3.3Extrudedactivatedcarbon(EAC)3.4Beadactivatedcarbon(BAC)3.5Impregnatedcarbon

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3.6Polymercoatedcarbon3.7Other

4Properties4.1Iodinenumber4.2Molasses4.3Tannin4.4Methyleneblue4.5Dechlorination4.6Apparentdensity4.7Hardness/abrasionnumber4.8Ashcontent4.9Carbontetrachlorideactivity4.10Particlesizedistribution

5Modificationofpropertiesandreactivity6Examplesofadsorption

6.1Heterogeneouscatalysis6.2Absorptionrefrigeration

7Reactivationandregeneration7.1Thermalreactivation7.2Otherregenerationtechniques

8Seealso9References10Externallinks

Uses

Activatedcarbonisusedingaspurification,decaffeination,goldpurification,metalextraction,waterpurification,medicine,sewagetreatment,airfiltersingasmasksandrespirators,filtersincompressedairandmanyotherapplications.

Onemajorindustrialapplicationinvolvesuseofactivatedcarboninthemetalfinishingfield.Itisverywidelyemployedforpurificationofelectroplatingsolutions.Forexample,itisamainpurificationtechniqueforremovingorganicimpuritiesfrombrightnickelplatingsolutions.Avarietyoforganicchemicalsareaddedtoplatingsolutionsforimprovingtheirdepositqualitiesandforenhancingpropertieslikebrightness,smoothness,ductility,etc.Duetopassageofdirectcurrentandelectrolyticreactionsofanodicoxidationandcathodicreduction,organicadditivesgenerateunwantedbreakdownproductsinsolution.Theirexcessivebuildupcanadverselyaffecttheplatingqualityandphysicalpropertiesofdepositedmetal.Activatedcarbontreatmentremovessuchimpuritiesandrestoresplatingperformancetothedesiredlevel.

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Activatedcharcoalformedicaluse

Medicaluses

Activatedcarbonisusedtotreatpoisoningsandoverdosesfollowingoralingestion.Itisnoteffectiveforanumberofpoisoningsincluding:strongacidsoralkali,cyanide,iron,lithium,arsenic,methanol,ethanolorethyleneglycol.[2]

Tabletsorcapsulesofactivatedcarbonareusedinmanycountriesasanoverthecounterdrugtotreatdiarrhea,indigestion,andflatulence.

Adversedrugeffects

Incorrectapplication(e.g.intothelungs)resultsinpulmonaryaspirationwhichcansometimesbefatalifimmediatemedicaltreatmentisnotinitiated.[3]Theuseofactivatedcarboniscontraindicatedwhentheingestedsubstanceisanacid,analkali,orapetroleumproduct.

Analyticalchemistryapplications

Activatedcarbon,in50%w/wcombinationwithcelite,isusedasstationaryphaseinlowpressurechromatographicseparationofcarbohydrates(mono,ditrisaccharides)usingethanolsolutions(550%)asmobilephaseinanalyticalorpreparativeprotocols.

Environmentalapplications

Carbonadsorptionhasnumerousapplicationsinremovingpollutantsfromairorwaterstreamsbothinthefieldandinindustrialprocessessuchas:

SpillcleanupGroundwaterremediationDrinkingwaterfiltrationAirpurificationVolatileorganiccompoundscapturefrompainting,drycleaning,gasolinedispensingoperations,andotherprocesses.

In2007,UGent(GhentUniversity,Belgium)beganresearchinwatertreatmentafterfestivals.[4]AfullscaleactivatedcarboninstallationwasbuiltattheDranoutermusicfestivalin2008,withplanstoutilizethetechnologytotreatwateratthisfestivalforthenext20years.[4]

Activatedcarbonisalsousedforthemeasurementofradonconcentrationinair.

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Activatedcarbonisusuallyusedinwaterfiltrationsystems.Inthisillustration,theactivatedcarbonisinthefourthlevel(countedfrombottom).

Fuelstorage

Researchisbeingdonetestingvariousactivatedcarbons'abilitytostorenaturalgasandhydrogengas.Theporousmaterialactslikeaspongefordifferenttypesofgases.ThegasisattractedtothecarbonmaterialviaVanderWaalsforces.Somecarbonshavebeenabletoachievebondingenergiesof510kJpermol.Thegasmaythenbedesorbedwhensubjectedtohighertemperaturesandeithercombustedtodoworkorinthecaseofhydrogengasextractedforuseinahydrogenfuelcell.Gasstorageinactivatedcarbonsisanappealinggasstoragemethodbecausethegascanbestoredinalowpressure,lowmass,lowvolumeenvironmentthatwouldbemuchmorefeasiblethanbulkyonboardcompressiontanksinvehicles.TheUnitedStatesDepartmentofEnergyhasspecifiedcertaingoalstobeachievedintheareaofresearchanddevelopmentofnanoporouscarbonmaterials.Allofthegoalsareyettobesatisfiedbutnumerousinstitutions,includingtheALLCRAFTprogram,[5]arecontinuingtoconductworkinthispromisingfield.

Gaspurification

Filterswithactivatedcarbonareusuallyusedincompressedairandgaspurificationtoremoveoilvapours,odour,andotherhydrocarbonsfromtheair.Themostcommondesignsusea1stageor2stagefiltrationprincipleinwhichactivatedcarbonisembeddedinsidethefiltermedia.ActivatedcarbonisalsousedinspacesuitPrimaryLifeSupportSystems.Activatedcarbonfiltersareusedtoretainradioactivegasesfromanuclearboilingwaterreactorturbinecondenser.Theairvacuumedfromthecondensercontainstracesofradioactivegases.Thelargecharcoalbedsabsorbthesegasesandretainthemwhiletheyrapidlydecaytononradioactivesolidspecies.Thesolidsaretrappedinthecharcoalparticles,whilethefilteredairpassesthrough.

Chemicalpurification

Activatedcarboniscommonlyusedonthelaboratoryscaletopurifysolutionsoforganicmoleculescontainingunwantedcoloredorganicimpurities.

Soundabsorption

Activatedcarboncanfilterairandwater.Soundenergyisfoundwithinairandwaterandactivatedcarboncanbeusedtoabsorbthatenergy.Withthehighdegreeofporosityineachactivatedcarbongranule,soundenergyhasnumerousareastoenterintoandbeconvertedtoheat.Withtheenergychangetoheat,theprocessofsoundabsorptionoccurs.

Activatedcarboninitsgranuleformcanbeusedtoabsorbmiddleandhighfrequencyrangesprovidedtheabsorber'sdesignletsairpassthroughthecarbon.Activatedcarboncanalsobeusedinsideofdiaphragmaticabsorptiontechnologytoincreasetherateofabsorptionwithinthediaphragmaticabsorber.[6]

Distilledalcoholicbeveragepurification

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Activatedcarbonfilterscanbeusedtofiltervodkaandwhiskeyoforganicimpuritieswhichcanaffectcolor,taste,andodor.Passinganorganicallyimpurevodkathroughanactivatedcarbonfilterattheproperflowratewillresultinvodkawithanidenticalalcoholcontentandsignificantlyincreasedorganicpurity,asjudgedbyodorandtaste.

Mercuryscrubbing

Activatedcarbon,ofteninfusedwithsulfur[7]oriodine,iswidelyusedtotrapmercuryemissionsfromcoalfiredpowerstations,medicalincinerators,andfromnaturalgasatthewellhead.ThiscarbonisaspecialtyproductcostingmorethanUS$4.00perkg.However,itisoftennotrecycled.

DisposalintheUSAafterabsorbingmercury

Themercuryladenactivatedcarbonpresentsadisposaldilemma.[8]Iftheactivatedcarboncontainslessthan260ppmmercury,UnitedStatesfederalregulationsallowittobestabilized(forexample,trappedinconcrete)forlandfilling.However,wastecontaininggreaterthan260ppmisconsideredtobeinthehighmercurysubcategoryandisbannedfromlandfilling(LandBanRule).Thismaterialisnowaccumulatinginwarehousesandindeepabandonedminesatanestimatedrateof1000tonsperyear.

TheproblemofdisposalofmercuryladenactivatedcarbonisnotuniquetotheUnitedStates.IntheNetherlands,thismercuryislargelyrecovered[9]andtheactivatedcarbonisdisposedofbycompleteburning.

Production

Activatedcarboniscarbonproducedfromcarbonaceoussourcematerialssuchasnutshells,coconuthusk,peat,wood,coir,lignite,coal,andpetroleumpitch.Itcanbeproducedbyoneofthefollowingprocesses:

1. Physicalreactivation:Thesourcematerialisdevelopedintoactivatedcarbonsusinghotgases.Thisisgenerallydonebyusingoneoracombinationofthefollowingprocesses:

Carbonization:Materialwithcarboncontentispyrolyzedattemperaturesintherange600900C,usuallyininertatmospherewithgaseslikeargonornitrogenActivation/Oxidation:Rawmaterialorcarbonizedmaterialisexposedtooxidizingatmospheres(oxygenorsteam)attemperaturesabove250C,usuallyinthetemperaturerangeof6001200C.

2. Chemicalactivation:Priortocarbonization,therawmaterialisimpregnatedwithcertainchemicals.

Thechemicalistypicallyanacid,strongbase,orasalt[10](phosphoricacid,potassiumhydroxide,sodiumhydroxide,calciumchloride,andzincchloride25%).Then,therawmaterialiscarbonizedatlowertemperatures(450900C).Itisbelievedthatthecarbonization/activationstepproceedssimultaneouslywiththechemicalactivation.Chemicalactivationispreferredoverphysicalactivationowingtothelowertemperaturesandshortertimeneededforactivatingmaterial.

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Amicrographofactivatedcharcoal(R1)underbrightfieldilluminationonalightmicroscope.Noticethefractallikeshapeoftheparticleshintingattheirenormoussurfacearea.Eachparticleinthisimage,despitebeingonlyaround0.1mmacross,hasasurfaceareaofseveralsquaremetres.[11]Theentireimagecoversaregionofapproximately1.1by0.7mm,andthefullresolutionversionisatascaleof6.236pixels/m.

Classification

Activatedcarbonsarecomplexproductswhicharedifficulttoclassifyonthebasisoftheirbehaviour,surfacecharacteristicsandotherfundamentalcriteria.However,somebroadclassificationismadeforgeneralpurposebasedontheirsize,preparationmethods,andindustrialapplications.

Powderedactivatedcarbon(R1,PAC)

Normally,activatedcarbons(R1)aremadeinparticulateformaspowdersorfinegranuleslessthan1.0mminsizewithanaveragediameterbetween0.15and0.25mm.Thustheypresentalargesurfacetovolumeratiowithasmalldiffusiondistance.Activatedcarbon(R1)isdefinedastheactivatedcarbonparticlesretainedona50meshsieve(0.297mm).

PACmaterialisfinermaterial.PACismadeupofcrushedorgroundcarbonparticles,95100%ofwhichwillpassthroughadesignatedmeshsieve.TheASTMclassifiesparticlespassingthroughan80meshsieve(0.177mm)andsmallerasPAC.ItisnotcommontousePACinadedicatedvessel,duetothehighheadlossthatwouldoccur.Instead,PACisgenerallyaddeddirectlytootherprocessunits,suchasrawwaterintakes,rapidmixbasins,clarifiers,andgravityfilters.

Granularactivatedcarbon(GAC)

Granularactivatedcarbonhasarelativelylargerparticlesizecomparedtopowderedactivatedcarbonandconsequently,presentsasmallerexternalsurface.Diffusionoftheadsorbateisthusanimportantfactor.Thesecarbonsaresuitableforabsorptionofgasesandvapors,becausetheydiffuserapidly.Granulatedcarbonsareusedforwatertreatment,deodorizationandseparationofcomponentsofflowsystemandisalsousedinrapidmixbasins.GACcanbeeitheringranularorextrudedform.GACisdesignatedbysizessuchas820,2040,or830forliquidphaseapplicationsand46,48or410forvaporphaseapplications.A2040carbonismadeofparticlesthatwillpassthroughaU.S.StandardMeshSizeNo.20sieve(0.84mm)(generallyspecifiedas85%passing)butberetainedonaU.S.StandardMeshSizeNo.40sieve(0.42mm)(generallyspecifiedas95%retained).AWWA(1992)B604usesthe50meshsieve(0.297mm)astheminimumGACsize.Themostpopularaqueousphasecarbonsarethe1240and830sizesbecausetheyhaveagoodbalanceofsize,surfacearea,andheadlosscharacteristics.

Extrudedactivatedcarbon(EAC)

Extrudedactivatedcarboncombinespowderedactivatedcarbonwithabinder,whicharefusedtogetherandextrudedintoacylindricalshapedactivatedcarbonblockwithdiametersfrom0.8to130mm.Thesearemainlyusedforgasphaseapplicationsbecauseoftheirlowpressuredrop,highmechanicalstrengthandlowdustcontent.AlsosoldasCTOfilter(Chlorine,Taste,Odor).

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Amicrographofactivatedcharcoal(GAC)underscanningelectronmicroscope

Beadactivatedcarbon(BAC)

Beadactivatedcarbonismadefrompetroleumpitchandsuppliedindiametersfromapproximately0.35to0.80mm.SimilartoEAC,itisalsonotedforitslowpressuredrop,highmechanicalstrengthandlowdustcontent,butwithasmallergrainsize.Itssphericalshapemakesitpreferredforfluidizedbedapplicationssuchaswaterfiltration.

Impregnatedcarbon

Porouscarbonscontainingseveraltypesofinorganicimpregnatesuchasiodine,silver,cationssuchasAl,Mn,Zn,Fe,Li,Cahavealsobeenpreparedforspecificapplicationinairpollutioncontrolespeciallyinmuseumsandgalleries.Duetoitsantimicrobialandantisepticproperties,silverloadedactivatedcarbonisusedasanadsorbentforpurificationofdomesticwater.DrinkingwatercanbeobtainedfromnaturalwaterbytreatingthenaturalwaterwithamixtureofactivatedcarbonandAl(OH)3,aflocculatingagent.ImpregnatedcarbonsarealsousedfortheadsorptionofHydrogenSulfide(H2S)andthiols.AbsorptionratesforH2Sashighas50%byweighthavebeenreported.

Polymercoatedcarbon

Thisisaprocessbywhichaporouscarboncanbecoatedwithabiocompatiblepolymertogiveasmoothandpermeablecoatwithoutblockingthepores.Theresultingcarbonisusefulforhemoperfusion.Hemoperfusionisatreatmenttechniqueinwhichlargevolumesofthepatient'sbloodarepassedoveranadsorbentsubstanceinordertoremovetoxicsubstancesfromtheblood.

Other

Activatedcarbonisalsoavailableinspecialformssuchasclothsandfibres.The"carboncloth"forinstanceisusedinpersonnelprotectionforthemilitary.

Properties

Agramofactivatedcarboncanhaveasurfaceareainexcessof500m2,with1500m2beingreadilyachievable.[12]Carbonaerogels,whilemoreexpensive,haveevenhighersurfaceareas,andareusedinspecialapplications.

Underanelectronmicroscope,thehighsurfaceareastructuresofactivatedcarbonarerevealed.Individualparticlesareintenselyconvolutedanddisplayvariouskindsofporositytheremaybemanyareaswhereflatsurfacesofgraphitelikematerialrunparalleltoeachother,separatedbyonlyafewnanometersorso.Thesemicroporesprovidesuperbconditionsforadsorptiontooccur,sinceadsorbingmaterialcaninteract

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withmanysurfacessimultaneously.Testsofadsorptionbehaviourareusuallydonewithnitrogengasat77Kunderhighvacuum,butineverydaytermsactivatedcarbonisperfectlycapableofproducingtheequivalent,byadsorptionfromitsenvironment,liquidwaterfromsteamat100C(212F)andapressureof1/10,000ofanatmosphere.

JamesDewar,thescientistafterwhomtheDewar(vacuumflask)isnamed,spentmuchtimestudyingactivatedcarbonandpublishedapaperregardingitsadsorptioncapacitywithregardtogases.[13]Inthispaper,hediscoveredthatcoolingthecarbontoliquidnitrogentemperaturesallowedittoadsorbsignificantquantitiesofnumerousairgases,amongothers,thatcouldthenberecollectedbysimplyallowingthecarbontowarmagainandthatcoconutbasedcarbonwassuperiorfortheeffect.Heusesoxygenasanexample,whereintheactivatedcarbonwouldtypicallyadsorbtheatmosphericconcentration(21%)understandardconditions,butreleaseover80%oxygenifthecarbonwasfirstcooledtolowtemperatures.

Physically,activatedcarbonbindsmaterialsbyvanderWaalsforceorLondondispersionforce.

Activatedcarbondoesnotbindwelltocertainchemicals,includingalcohols,diols,strongacidsandbases,metalsandmostinorganics,suchaslithium,sodium,iron,lead,arsenic,fluorine,andboricacid.

Activatedcarbonadsorbsiodineverywell.Theiodinecapacity,mg/g,(ASTMD28StandardMethodtest)maybeusedasanindicationoftotalsurfacearea.

Carbonmonoxideisnotwelladsorbedbyactivatedcarbon.Thisshouldbeofparticularconcerntothoseusingthematerialinfiltersforrespirators,fumehoodsorothergascontrolsystemsasthegasisundetectabletothehumansenses,toxictometabolismandneurotoxic.

Substantiallistsofthecommonindustrialandagriculturalgasesadsorbedbyactivatedcarboncanbefoundonline.[14]

Activatedcarboncanbeusedasasubstratefortheapplicationofvariouschemicalstoimprovetheadsorptivecapacityforsomeinorganic(andproblematicorganic)compoundssuchashydrogensulfide(H2S),ammonia(NH3),formaldehyde(HCOH),mercury(Hg)andradioactiveiodine131(131I).Thispropertyisknownaschemisorption.

Iodinenumber

Manycarbonspreferentiallyadsorbsmallmolecules.Iodinenumberisthemostfundamentalparameterusedtocharacterizeactivatedcarbonperformance.Itisameasureofactivitylevel(highernumberindicateshigherdegreeofactivation),oftenreportedinmg/g(typicalrange5001200mg/g).Itisameasureofthemicroporecontentoftheactivatedcarbon(0to20,orupto2nm)byadsorptionofiodinefromsolution.Itisequivalenttosurfaceareaofcarbonbetween900m/gand1100m/g.Itisthestandardmeasureforliquidphaseapplications.

Iodinenumberisdefinedasthemilligramsofiodineadsorbedbyonegramofcarbonwhentheiodineconcentrationintheresidualfiltrateis0.02normal.Basically,iodinenumberisameasureoftheiodineadsorbedintheporesand,assuch,isanindicationoftheporevolumeavailableintheactivatedcarbonofinterest.Typically,watertreatmentcarbonshaveiodinenumbersrangingfrom600to1100.Frequently,thisparameterisusedtodeterminethedegreeofexhaustionofacarboninuse.However,thispracticeshouldbeviewedwithcautionaschemicalinteractionswiththeadsorbatemayaffecttheiodineuptakegiving

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falseresults.Thus,theuseofiodinenumberasameasureofthedegreeofexhaustionofacarbonbedcanonlyberecommendedifithasbeenshowntobefreeofchemicalinteractionswithadsorbatesandifanexperimentalcorrelationbetweeniodinenumberandthedegreeofexhaustionhasbeendeterminedfortheparticularapplication.

Molasses

Somecarbonsaremoreadeptatadsorbinglargemolecules.Molassesnumberormolassesefficiencyisameasureofthemesoporecontentoftheactivatedcarbon(greaterthan20,orlargerthan2nm)byadsorptionofmolassesfromsolution.Ahighmolassesnumberindicatesahighadsorptionofbigmolecules(range95600).Carameldp(decolorizingperformance)issimilartomolassesnumber.Molassesefficiencyisreportedasapercentage(range40%185%)andparallelsmolassesnumber(600=185%,425=85%).TheEuropeanmolassesnumber(range525110)isinverselyrelatedtotheNorthAmericanmolassesnumber.

MolassesNumberisameasureofthedegreeofdecolorizationofastandardmolassessolutionthathasbeendilutedandstandardizedagainststandardizedactivatedcarbon.Duetothesizeofcolorbodies,themolassesnumberrepresentsthepotentialporevolumeavailableforlargeradsorbingspecies.Asalloftheporevolumemaynotbeavailableforadsorptioninaparticularwastewaterapplication,andassomeoftheadsorbatemayentersmallerpores,itisnotagoodmeasureoftheworthofaparticularactivatedcarbonforaspecificapplication.Frequently,thisparameterisusefulinevaluatingaseriesofactivecarbonsfortheirratesofadsorption.Giventwoactivecarbonswithsimilarporevolumesforadsorption,theonehavingthehighermolassesnumberwillusuallyhavelargerfeederporesresultinginmoreefficienttransferofadsorbateintotheadsorptionspace.

Tannin

Tanninsareamixtureoflargeandmediumsizemolecules.Carbonswithacombinationofmacroporesandmesoporesadsorbtannins.Theabilityofacarbontoadsorbtanninsisreportedinpartspermillionconcentration(range200ppm362ppm).

Methyleneblue

Somecarbonshaveamesopore(20to50,or2to5nm)structurewhichadsorbsmediumsizemolecules,suchasthedyemethyleneblue.Methyleneblueadsorptionisreporteding/100g(range1128g/100g).

Dechlorination

Somecarbonsareevaluatedbasedonthedechlorinationhalflifelength,whichmeasuresthechlorineremovalefficiencyofactivatedcarbon.Thedechlorinationhalfvaluelengthisthedepthofcarbonrequiredtoreducethechlorinelevelofaflowingstreamfrom5ppmto3.5ppm.Alowerhalfvaluelengthindicatessuperiorperformance.

Apparentdensity

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Thesolidorskeletaldensityofactivatedcarbonswilltypicallyrangebetween2.0and2.1g/cm3(125130lbs./cubicfoot).However,alargepartofanactivatedcarbonsamplewillconsistofairspacebetweenparticles,andtheactualorapparentdensitywillthereforebelower,typically0.4to0.5g/cm3(2531lbs./cubicfoot).[15]

Higherdensityprovidesgreatervolumeactivityandnormallyindicatesbetterqualityactivatedcarbon.

Hardness/abrasionnumber

Itisameasureoftheactivatedcarbonsresistancetoattrition.Itisanimportantindicatorofactivatedcarbontomaintainitsphysicalintegrityandwithstandfrictionalforcesimposedbybackwashing,etc.Therearelargedifferencesinthehardnessofactivatedcarbons,dependingontherawmaterialandactivitylevel.

Ashcontent

Ashreducestheoverallactivityofactivatedcarbonanditreducestheefficiencyofreactivation.Themetaloxides(Fe2O3)canleachoutofactivatedcarbonresultingindiscoloration.Acid/watersolubleashcontentismoresignificantthantotalashcontent.Solubleashcontentcanbeveryimportantforaquarists,asferricoxidecanpromotealgalgrowths.Acarbonwithalowsolubleashcontentshouldbeusedformarine,freshwaterfishandreeftankstoavoidheavymetalpoisoningandexcessplant/algalgrowth.

Carbontetrachlorideactivity

Measurementoftheporosityofanactivatedcarbonbytheadsorptionofsaturatedcarbontetrachloridevapour.

Particlesizedistribution

Thefinertheparticlesizeofanactivatedcarbon,thebettertheaccesstothesurfaceareaandthefastertherateofadsorptionkinetics.Invapourphasesystemsthisneedstobeconsideredagainstpressuredrop,whichwillaffectenergycost.Carefulconsiderationofparticlesizedistributioncanprovidesignificantoperatingbenefits.

Modificationofpropertiesandreactivity

Acidbase,oxidationreductionandspecificadsorptioncharacteristicsarestronglydependentonthecompositionofthesurfacefunctionalgroups.[16]

Thesurfaceofconventionalactivatedcarbonisreactive,capableofoxidationbyatmosphericoxygenandoxygenplasma[17][18][19][20][21][22][23][24]steam,[25][26][27]andalsocarbondioxide[21]andozone.[28][29][30]

Oxidationintheliquidphaseiscausedbyawiderangeofreagents(HNO3,H2O2,KMnO4),[31][32][33]

Throughtheformationofalargenumberofbasicandacidicgroupsonthesurfaceofoxidizedcarbontosorptionandotherpropertiescandiffersignificantlyfromtheunmodifiedforms.[16]

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Activatedcarboncanbenitrogenatedbynaturalproductsorpolymers[34][35]orprocessingofcarbonwithnitrogenatingreagents.[36][37][38]

Activatedcarboncaninteractwithchlorine,[39][40]bromine[41]andfluorine.[42]

Sulfonicacidfunctionalgroupscanbeattachedtoactivatedcarbontogive"starbons"whichcanbeusedtoselectivelycatalysetheesterificationoffattyacids.[43]Formationofsuchactivatedcarbonsfromhalogenatedprecursorsgivesamoreeffectivecatalystwhichisthoughttobearesultofremaininghalogensimprovingstability.[44]

Someofthechemicalpropertiesofactivatedcarbonhavebeenattributedtopresenceofthesurfaceactivecarbondoublebond.[30][45]

ThePolyaniadsorptiontheoryisapopularmethodforanalyzingadsorptionofvariousorganicsubstancestotheirsurface.

Examplesofadsorption

Heterogeneouscatalysis

Themostcommonlyencounteredformofchemisorptioninindustry,occurswhenasolidcatalystinteractswithagaseousfeedstock,thereactant/s.Theadsorptionofreactant/stothecatalystsurfacecreatesachemicalbond,alteringtheelectrondensityaroundthereactantmoleculeandallowingittoundergoreactionsthatwouldnotnormallybeavailabletoit.

Absorptionrefrigeration

Absorptionrefrigerationandheatpumpcyclesrelyontheadsorptionofarefrigerantgasintoanadsorbentatlowpressureandsubsequentdesorptionbyheating.Theadsorbentactsasa"chemicalcompressor"drivenbyheatandis,fromthispointofview,the"pump"ofthesystem.Itconsistsofasolarcollector,acondenserorheatexchangerandanevaporatorthatisplacedinarefrigeratorbox.Theinsideofthecollectorislinedwithanadsorptionbedpackedwithactivatedcarbonadsorbedwithmethanol.Therefrigeratorboxisinsulatedandfilledwithwater.Theactivatedcarboncanadsorbalargeamountofmethanolvaporsinambienttemperatureanddesorbitatahighertemperature(around100degreesCelsius).Duringthedaytime,thesunshineirradiatesthecollector,sothecollectorisheatedupandthemethanolisdesorbedfromtheactivatedcarbon.Indesorption,theliquidmethanoladsorbedinthecharcoalheatsupandvaporizes.Themethanolvaporcondensesandisstoredintheevaporator.

Atnight,thecollectortemperaturedecreasestotheambienttemperature,andthecharcoaladsorbsthemethanolfromtheevaporator.Theliquidmethanolintheevaporatorvaporizesandabsorbstheheatfromthewatercontainedinthetrays.Sinceadsorptionisaprocessofreleasingheat,thecollectormustbecooledefficientlyatnight.Asmentionedabove,theadsorptionrefrigerationsystemoperatesinanintermittentwaytoproducetherefrigeratingeffect.

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World'slargestreactivationplantlocatedinFeluy,Belgium.

ActivatedcarbonreactivationcenterinRoeselare,Belgium.

Heliumgascanalsobe"pumped"bythermallycyclingactivatedcarbon"sorptionpumps"between4kelvinsandhighertemperatures.AnexampleofthisistoprovidethecoolingpowerfortheOxfordInstrumentsASTseriesdilutionrefrigerators.3Hevaporispumpedfromthesurfaceofthedilutephaseofamixtureofliquid4Heanditsisotope3He.The3Heisadsorbedontothesurfacesofthecarbonatlowtemperature(typically

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Otherregenerationtechniques

Currentconcernswiththehighenergy/costnatureofthermalregenerationofactivatedcarbonhasencouragedresearchintoalternativeregenerationmethodstoreducetheenvironmentalimpactofsuchprocesses.Thoughseveraloftheregenerationtechniquescitedhaveremainedareasofpurelyacademicresearch,somealternativestothermalregenerationsystemshavebeenemployedinindustry.Currentalternativeregenerationmethodsare:

Chemicalandsolventregeneration[50]

Microbialregeneration[51]

Electrochemicalregeneration[52]

Ultrasonicregeneration[53]

Wetairoxidation[54]

Seealso

CarbonblackCarbonfilteringConjugatedmicroporouspolymerKvrnerprocessOnboardrefuelingvaporrecoveryCarbocatalysisHydrogenstorage

References

1. " "PropertiesofActivatedCarbon",CPLCaronLink,accessed20080502"(http://www.activatedcarbon.com/13.html).Retrieved13October2014.

2. "Charcoal,Activated"(http://www.drugs.com/monograph/charcoalactivated.html).TheAmericanSocietyofHealthSystemPharmacists.Retrieved23April2014.

3. ElliottCG,ColbyTV,KellyTM,HicksHG(1989)."Charcoallung.Bronchiolitisobliteransafteraspirationofactivatedcharcoal".Chest96(3):6724.doi:10.1378/chest.96.3.672(https://dx.doi.org/10.1378%2Fchest.96.3.672).PMID2766830(https://www.ncbi.nlm.nih.gov/pubmed/2766830).

4. Sustainablewastewatertreatmentoftemporaryevents:theDranouterMusicFestivalcasestudy(http://www.labmeeting.com/paper/28552316/vanhulle2008sustainablewastewatertreatmentoftemporaryeventsthedranoutermusicfestivalcasestudy).Waterscienceandtechnology:ajournaloftheInternationalAssociationonWaterPollutionResearch.200858(8):16537.

5. "AllianceforCollaborativeResearchinAlternativeFuelTechnology"(http://allcraft.missouri.edu).Allcraft.missouri.edu.Retrieved20140313.

6. Foley,Dennis(2014)."BassAbsorptionWhyThePowerOfDiaphragmaticAbsorptionIsYourOnlyHope"

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Externallinks

"Imagingtheatomicstructureofactivatedcarbon"(http://www.personal.rdg.ac.uk/~scsharip/Activated_carbon_JPCM.pdf)JOURNALOFPHYSICS:CONDENSEDMATTEREngber,Daniel(Nov.28,2005)."HowDoesActivatedCarbonWork?"(http://www.slate.com/id/2131130/).Slate.

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54. ShendeRV,MahajaniVV(2002)."Wetoxidativeregenerationofactivatedcarbonloadedwithreactivedye".WasteManagement22(1):7383.doi:10.1016/S0956053X(01)000228(https://dx.doi.org/10.1016%2FS0956053X%2801%29000228).PMID11942707(https://www.ncbi.nlm.nih.gov/pubmed/11942707).