Microwave-assisted pyrolysis of microalgae for biofuel production

Microwave-assistedpyrolysisofmicroalgaeforbiofuelproduction

ZhenyiDua,YecongLia,XiaoquanWanga,YiqinWana,b,QinChena,ChenguangWanga,XiangyangLina,c,YuhuanLiua,b,PaulChena,RogerRuana,b,

a

CenterforBiore ningandDepartmentofBioproductsandBiosystemsEngineering,UniversityofMinnesota,1390EcklesAve.,St.Paul,MN55108,UnitedStatesBiomassEnergyCenterandStateKeyLaboratoryofFoodScience,NanchangUniversity,Nanchang330031,Chinac

CollegeofBiologicalScienceandTechnology,FuzhouUniversity,Fuzhou350002,China

b

articleinfoabstract

ThepyrolysisofChlorellasp.wascarriedoutinamicrowaveovenwithcharasmicrowavereceptionenhancer.Theresultsindicatedthatthemaximumbio-oilyieldof28.6%wasachievedunderthemicro-wavepowerof750W.Thebio-oilpropertieswerecharacterizedwithelemental,GC–MS,GPC,FTIR,andthermogravimetricanalysis.Thealgalbio-oilhadadensityof0.98kg/L,aviscosityof61.2cSt,andahigherheatingvalue(HHV)of30.7MJ/kg.TheGC–MSresultsshowedthatthebio-oilsweremainlycom-posedofaliphatichydrocarbons,aromatichydrocarbons,phenols,longchainfattyacidsandnitrogenatedcompounds,amongwhichaliphaticandaromatichydrocarbons(accountfor22.18%ofthetotalGC–MSspectrumarea)arehighlydesirablecompoundsasthoseincrudeoil,gasolineanddiesel.Theresultsinthisstudyindicatethatfastgrowingalgaeareapromisingsourceoffeedstockforadvancedrenewablefuelproductionviamicrowave-assistedpyrolysis(MAP).

Ó2011ElsevierLtd.Allrightsreserved.

Articlehistory:

Received26October2010

Receivedinrevisedform15January2011Accepted17January2011

Availableonline22January2011Keywords:

Microwave-assistedpyrolysisMicroalgaeChlorellasp.Bio-oil

1.Introduction

Fossilfuelsareproducedfromunsustainableresourcesandtheirusescontributesigni cantlytogreenhousegas(GHG)emis-siontotheenvironment.Biomassisanabundantandpotentiallycarbon-neutralenergysourcewidelyavailableontheearth(Mo-hanetal.,2006;McKendry,2002).Biomassfeedstockcanbecon-vertedintosolid,liquid,andgaseousproductsthroughvariousthermochemicalprocessesincludingpyrolysis(Huberetal.,2006).Inpyrolysis,organicsinbiomassarethermallyconvertedtobio-oil,combustiblegases,andbiochar(BridgwaterandPea-cocke,2000;Yaman,2004).Whilemostoftraditionalslowandfastpyrolysisprocessesuse xedand uidizedbedreactorswhoseheatingisprovidedbyheatedsurface,sands,etc.(MeierandFaix,1999;CzernikandBridgwater,2004;Mohanetal.,2006),otherslookedintoalternativeheatingmethodssuchasmicrowaveheat-ing.Thenewmicrowave-assistedpyrolysis(MAP)processthatwedevelopedoffersseveraladvantagesovertraditionalprocesses,includinguniforminternalheatingoflargebiomassparticles,easeofcontrol,andnoneedforagitationor uidizationandhencelessparticles(ashes)inthebio-oil.StudiesofMAPofwood(Miuraetal.,2004),cornstover(Yuetal.,2007;Wanetal.,2009),riceCorrespondingauthorat:CenterforBiore ningandDepartmentofBioproductsandBiosystemsEngineering,UniversityofMinnesota,1390EcklesAve.,St.Paul,MN55108,UnitedStates.Tel.:+16126251710;fax:+16126243005.

E-mailaddress:ruanx001@umn.edu(R.Ruan).

0960-8524/$-seefrontmatterÓ2011ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2011.01.055

straw(Huangetal.,2010),coffeehulls(Domínguezetal.,2007),pinesawdust(Wangetal.,2009),andwheatstraw(Budarinetal.,2009)havebeenrecentlyreported,andsuggestthatMAPisahighlyscalabletechnologysuitablefordistributedconversionofbulkybiomass.

Microalgaeasanalternativebiofuelsourcehavegainedmuchattentionthesedaysbecausetheyhavenumerousadvantagescom-paredwithlignocellulosicfeedstocks:(1)theyhavehigherbiomassproduction,5–30timesofoilcropsperunitsurfacearea(Schenketal.,2008);(2)theydonotcompetewithtraditionalagriculturalresourcesastheycanbecultivatedonnon-arablelandoronwaste-water(Chenetal.,2009);(3)theyareexceedinglyrichinoil,over60%byweightofdrybiomassinsomespecies(GouveiaandOliveira,2009).Todate,variousthermochemicalconversionroutesofmicro-algaehavebeeninvestigated(Chenetal.,2009).Therearefewre-portsonpyrolysisofmicroalgae.MiaoandWu(2004)performedfastpyrolysisofautotrophicandheterotrophicChlorellaprototheco-idesandreportedbio-oilyieldsof16.6%and57.2%,respectively.Inaddition,thebio-oilsobtainedhadbetterqualitythanthosefromwoodintermsofbio-oilviscosity,densityandheatingvalue.Panetal.(2010)investigatedpyrolysisofNannochloropsissp.residuewithandwithoutthepresenceofHZSM-5catalystandobtainedbio-oilrichinaromatichydrocarbonsfromcatalyticpyrolysis.

Inthisstudy,MAPofChlorellasp.wasconductedunderdifferentmicrowavepowerlevels.Detailedcompositionalcharacterizationandcomparisonswerecarriedoutwithelemental,gaschromatog-raphy–massspectrometry(GC–MS),gelpermeationchromatogra-