MOF材料

239©2012SocietyofChemicalIndustryandJohnWiley&Sons,Ltd|GreenhouseGasSciTechnol.2:239–259(2012);DOI:10.1002/ghgReviewCorrespondenceto:Hong-CaiZhou,DepartmentofChemistry,TexasA&MUniversity,CollegeStation,TX77842-3012,USA.E-mail:[e-mail]18,2012;revisedJune10,2012;acceptedJune11,2012PublishedonlineatWileyOnlineLibrary(wileyonlinelibrary.com).DOI:10.1002/ghg.1296Recentadvancesincarbondioxidecapturewithmetal-organicframeworksYangyangLiu,ZhiyongU.WangandHong-CaiZhou,TexasA&MUniversity,CollegeStation,TX,USAAbstract:Uncontrolledmassivereleaseoftheprimarygreenhousegascarbondioxide(CO2)intoatmospherefromanthropogenicactivitiesposesabigthreatandadverselyaffectsourglobalclimateandnaturalenvironment.OnepromisingapproachtomitigateCO2emissioniscarboncaptureandstorage(CCS),inwhichidealadsorbentmaterialswithhighstoragecapacityandexcellentadsorptionselectivityoverothergasesareurgentlyneeded.ForpracticalapplicationsinCO2capturefromfluegasofpowerplants,thebiggestsinglecontributorofanthropogenicCO2emission,theadsorbentmaterialsmustalsobechemicallystable,beeasytoregeneratewithminimalenergyinput,andbeeasilysynthesizedwithlowcapitalcost.Metal-organicframeworks(MOFs),highlycrystallineporousmaterialsconstructedbymetalionsandorganicligands,haveemergedasaclassofexcellentadsor-bentmaterialsforcarboncapture.GreatprogressinMOFmaterialsforCO2capturehasbeenmadeinthepastandreviewedaccordingly,butnewdiscoveriesareconstantlybeingmadeasthefieldquicklygrows.Inthispaper,weprovideashortreviewonthemostrecentadvancesinusingMOFsforCO2adsorption,storage,andseparationthataredirectlyrelatedtoCO2capture.SomeoftheimportantpropertiesofMOFadsorbentswhicharecrucialforpracticalapplicationsbutarelargelyoverlookedinresearchcarriedoutsofararediscussed.©2012SocietyofChemicalIndustryandJohnWiley&Sons,LtdKeywords:carbondioxidecapture;metal-organicframeworks(MOFs);adsorbent;fluegas;naturalgasupgradingIntroductionTheconsumptionofenergyhasbeenexplosivelygrowingwiththerapidincreaseoftheglobalpopulationandindustrialization.Duetothereadyavailabilityoffossilfuelsandmaturetechniquestoextractthem,over85%ofourcurrentglobalenergydemandissupportedbyburningfossilfuelswhichreleaseslargeamountsofCO2intotheatmosphere.1Overthelasthalf-century,researchresultshaveshownthattheCO2concentrationinatmospherehasin-creasedfromabout310ppmtoover390ppm(Fig.1);thissteepincreaseisunparalleledinhumanhistory.2Astheprimaryanthropogenicgreenhousegas,CO2couldresultintheraiseoftheaveragetemperatureoftheEarthanddisastrousglobalclimatechangeifthecurrentrateofreleaseisnotstopped.Moreover,onestudyhascorrelatedincreasingatmosphericCO2levelYLiu,ZUWangandH-CZhouReview:CO2capturewithmetal-organicframeworks240©2012SocietyofChemicalIndustryandJohnWiley&Sons,Ltd|GreenhouseGasSciTechnol.2:239–259(2012);DOI:10.1002/ghgwithhigheracidityofseawater.3AsmoreCO2isdissolvedinseawatertogeneratecarbonicacid,thesurfaceseawaterpHcoulddropfromapre-industrialvalueofabout8.2to7.8byyear2095inaworstcasescenario(Fig.2).Thiswillleadtodramaticdetrimen-talconsequencesforthebiologicalecosystemsintheupperocean.3EffectivetechniquestoreduceCO2emissionarethusurgentlyneededtomaintaintheglobalclimateandtoprotectourenvironment.Carboncaptureandstorage(CCS)isanefficientwaytoreduceCO2concentrationintheatmosphere.Itisathree-stepprocessincludingseparationofCO2fromotheremissionsbeforeenteringtheatmosphere,CO2transportation,anditspermanentstorage.Amongthem,theCO2captureisthemostchallengingkeystepinwhichnewadsorbentmaterialsneedtobedeveloped.ConventionaladsorbentmaterialsrelyoneitherchemisorptionorphysisorptiontocaptureCO2.Aminescrubbing,whichutilizesalkanolaminessuchasmonoethanolamine(MEA)inaqueoussolutionsastheadsorbent,reliesonthechemicalreactionbetweentheaminegroupandCO2togeneratecarbamateorbicarbonate.4Althoughaminescrubbinghasbeeninpracticeinindustrialsettingssuchaspowerplantsfordecades,itisstillconsideredthecurrentstate-of-the-artbecauseofitshighefficiency(upto98%capture).Thebiggestproblemwithaminescrubbing,however,isthatlargeamountsofheatareneededtoreleaseabsorbedCO2duringadsorbentregeneration,con-sumingadditionally10–30%ofthepowerplant’senergyoutput.5Moreover,theaminescrubbingsolutionsarecorrosiveandchemicallyunstableuponheating.Becauseoftheirliquidform,theyarealsodifficulttocontainandtheirhandlingisconsiderablymoredifficultthanthatofsolidadsorbents.Amine-functionalizedabsorbentssuchasmesoporousmolecularsievesinsolidformpartiallyovercomesomeoftheabovelimitations,buttheparasiticenergywasteisstillprettyhigh.6,7Incontrast,physisorptionbetweensolidadsorbentsandCO2moleculesisareversibleprocessthatrequiresmuchlessenergyfordesorption.TraditionaladsorbentssuchaszeolitesandactivatedcarbonshavebeenextensivelystudiedforCO2capture.8,9Zeolitesareporousaluminosilicatematerials.Comparedtoalkanolaminesolutions,zeolitesshowedmorerapidCO2adsorptionandlowerenergypenaltyduringdesorptioninsmall-scalepilotplants.10ButtheirusageislimitedbylowCO2adsorp-tioncapacityandinstabilityinthepresenceofwater.Figure1.AtmosphericCO2concentrationduring1958–2010