离子液体中木质素的溶解

GreenChemistryDynamicArticleLinksCitethis:GreenChem.,2011,13,2038†WeiyingLi,‡a,bNingSun,‡aBreenaStoner,§aXinyuJiang,¶aXingmeiLuaandRobinD.Rogers*aReceived22ndNovember2010,Accepted10thMay2011DOI:10.1039/c1gc15522aRapiddissolutionofbagasseandsouthernyellowpinehasbeenachievedintheionicliquid(IL)1-ethyl-3-methylimidazoliumacetate([C2mim]OAc)byusingadissolutiontemperatureabovetheglasstransitionoflignin(ca.150◦C).When0.5gofbagasseorpineisaddedto10gof[C2mim]OAc,completedissolutioncanbeobtainedin5–15minforbagasseatatemperatureof175–195◦C,comparedto15–16hat110◦C,andover90%ofaddedpinecanbedissolvedwithheatingat175◦Cfor30min.Uponregenerationinacetone/water,ligninandcarbohydratecanbepartiallyseparatedasligninandacellulose-richmaterial(CRM,pulp).Comparedtopublishedmethodswithlowertemperaturesandlongertimes(e.g.,110◦C,16h),processingbagassein[C2mim]OAcat185◦Cfor10minresultsinhigheryieldsofbothrecoveredlignin(31%vs.26%oftheavailablelignin)andcarbohydrate(carbohydrateyield=66%vs.63%oftheavailablecarbohydrate).Inaddition,theCRMpulprecoveredusingthehighertemperaturemethodhasmuchlowerresiduallignincontent(6%vs.20%).Similarresultswereobtainedforpine(lignincontentinCRMwithhighervs.lowertemperaturemethod=16.1%vs.23.5%).TheILwasrecycledandreusedalthoughtheefficiencydecreasedandca.15%oftheILhaddegradedafterthehighertemperatureprocess.TheselatterresultssuggestfurtheroptimizationofthechoiceofILandheatingconditionsmightbeneededtodevelopanenergyandchemicalefficientprocess.1.IntroductionWeandothershaverecentlyreportedtheabilityofcertainionicliquids(ILs)todissolvenaturalbiopolymerssuchascellulose,1,2silkfibroin,3lignin,4starch,5protein,6andchitin/chitosan,7andevennaturallignocellulosicbiomasssuchaswood.8Inoneofourrecentreports,wefoundthat1-ethyl-3-methylimidazoliumacetate([C2mim]OAc)coulddissolvesouthernyellowpinebyheatingat110◦Cfor16handpartialseparationcouldbeachievedbyreconstitutionofthewoodsolutioninspecificallyselectedsolvents.8aaCenterforGreenManufacturingandDepartmentofChemistry,TheUniversityofAlabama,Tuscaloosa,AL,35487,USA.E-mail:[e-mail]PulpandPaperEngineering,SouthChinaUniversityofTechnology,Guangzhou,510640,China†Electronicsupplementaryinformation(ESI)available.SeeDOI:10.1039/c1gc15522a‡W.LiandN.Sunmadeequalcontributionstothispaper.§Currentaddress:DepartmentofChemistry,UniversityofCentralFlorida,Orlando,FL32816,USA.¶Currentaddress:SchoolofChemistryandChemicalEngineering,CentralSouthUniversity,Changsha,410083,China.Currentaddress:InstituteofProcessEngineering,ChineseAcademyofSciences,Beijing,100190,China.Researchintoaqueouschemicalpulpinghasindicatedthatbetterdelignificationofwoodcanbeobtainedusingtemper-aturesabovetheglasstransitionoflignin(Tg=130–150◦Cdependingonthesourceoflignin).9UsinganILsystemthatdidnotdissolvecellulose,Tanetal.studiedalkylbenzenesulfonateILtoextractligninfrombiomass(bagasse)attemperaturesashighas170–190◦C.10InaPCTpatentapplication,Edye,etal.publishedexamplesofdissolutionofbagassein1-butyl-3-methylimidazoliumchloride([C4mim]Cl)and[C2mim]OAcatthesetemperaturesfollowedbyseparation,11however,wecouldnotfindfurtherdetailsofthisinthescientificliterature.SomesupportforusinghighertemperatureswhendissolvingbiomassinILscanbefoundinresultsobtainedwithswitchgrassandcorncobswherehighertemperatures(130–160◦C)wereusedtocookthemilledbiomassinattemptstoimproveenzy-maticsaccharification.12–14Highertemperaturesandincubationtimeswerefoundtoimprovethedelignificationefficiencyofthebiomassrecoveredafterregenerationindeionized(DI)waterthusfacilitatingenzymatichydrolysisofthepulp.12,13Wewerethuscurioustoknowwhetherusingsuchhightemperaturescouldfacilitatelignocellulosicbiomassdissolutionandseparationinthemethodologieswehaveemployedfordissolutionandfractionationofbiomass.8a,8fInconductingthisstudy,weagainchosetheIL[C2mim]OAcbecauseofitslowermeltingpoint,lowerviscosity,higherbiomassdissolvingpower,2038|GreenChem.,2011,13,2038–2047Thisjournalis©TheRoyalSocietyofChemistry2011DownloadedbyLibraryofChineseAcademyofScienceson23October2012Publishedon28June2011on|doi:10.1039/C1GC15522AViewOnline/JournalHomepage/TableofContentsforthisissuelowertoxicity,andlowercorrosivitythanmanyotherILsusedtodissolvebiomass.8a,15Wealsowantedtoinvestigateamoretractablelignocellulosicbiomasssourcethanourpreviouslystudiedsouthernyellowpineandsettledonsugarcanebagasse.Bagassederivesfromsugarcaneandisthefibrousresidueaftercrushingtoremovesugarfromthesugarcanestalks.16About54milliondrytonsofbagasseisharvestedworldwideeachyear,17however,itiswoefullyunder-utilized.Currently,mostbagasseisburnedinlowefficiencytopowerthesugarmills,althoughpartofitisusedinthepaperindustry.17,18Generally,bagasseiscomposedof40–45%cellulose,20–25%hemicellulose,and18–24%lignin.19Thelignincontentofbagasseislowerthansoftwood(25–35%)andsomehardwoods(18–25%).Moreover,bagassehasamoreporousstructure(ca.66%20emptyspace)comparedto