Microwave-assisted pyrolysis of microalgae for biofuel production(4)

Z.Duetal./BioresourceTechnology102(2011)4890–48964893

wasobtained.Beyond750Wthedecreaseinoilyieldandincreaseingasyieldmaybecausedbythesecondarycrackingofoilvaporsintoincondensablegases.Inaddition,constantcharyieldinthepowerrangeof750W-1250Wispossiblyarisingfromthefactthatthedecompositionofthesamplewascompleteortherewasabal-ancebetweendecompositionofsolidsandformationofchar-likecarbonaceousmaterialthroughrepolymerization.Thewaterphaseyieldremainedvirtuallyconstantatabout21%inthestudiedpowerrange.AsshowninFig.3,therewasatradeoffbetweenheatingrateandpyrolysistemperature.Lowerpowerwithlowerheatingratealwaysledtotheformationofhigheryieldofchar(WilliamsandBesler,1996),whilehigherpowerwithhigherpyro-lysistemperaturefavoredgasi cationreactionswhichthusde-creasedtheyieldofbio-oil.Theseresultsaresimilartothosereportedintheliterature(Sßensözetal.,2006;Panetal.,2010;Is-lametal.,2010).Thevariationsaremainlyduetothecomposi-tionaldifferencesoffeedstockandthespeci ccharacteristicsofthemicrowavepyrolysissystem.Inthisstudy,750Wwastheopti-mumpowertoobtainbio-oilproductfromMAPofChlorellasp.3.3.Analysisofbio-oils

3.3.1.Physicalpropertiesandelementalanalysisofbio-oil

Thecharacteristicsofthealgalbio-oilincomparisonwithwoodbio-oilsanddieselfuelareshowedinTable3.Thebio-oilfromChlorellasp.hadaloweroxygencontent,highercarbon,hydrogencontentandHHVthanbio-oilproducedfromlignocellulosicmate-rials.ThesevaluesareclosetotheresultsofMiaoandWu(2004).Algalbio-oilhasalowerdensitythanlignocellulosicbio-oil,andaviscosityinthetypicalrangeofwoodbio-oil.Thepresenceofnitro-genbases,includingindole,pyridine,amides,ammonia,etc.,ren-deredthealgalbio-oilpHalkaline(9.7),whichisverydifferentfromthatforlignocellulosicbio-oil(typically2–3).However,theelementalcompositionandHHVofthebio-oilfromChlorellasp.arestillnotcomparableto(quitedifferentfrom)thoseoffossiloil.3.3.2.GC–MScharacterizationofbio-oil

Theidenti edcompoundswerecategorizedintothefollowinggroups:aliphatichydrocarbons,aromatichydrocarbons(includingbenzeneandbenzenealkylderivatives),nitrogenatedcompounds(includingnitriles,amidesandN-heterocycliccompounds),phe-nols,polycyclicaromatichydrocarbons(PAHs),andothers(suchasfattyacids,alcoholsandesters).Asemi-quantitativeanalysiswasperformedbycalculatingtherelativepercentageofareaofthechromatographicpeakswithresultsshowninTable4.Among

Table4

Relativeproportions(area%)ofthemaincompoundsofbio-oilobtainedunder750Wmicrowavepower.CategoriesAliphatics

Bicyclo[3.1.1]heptane,2,6,6-trimethyl-,(1.alpha.,2.beta.,5.alpha.)-2-Hexadecene,3,7,11,15-tetramethyl-,[R-[R ,R -(E)]]-Dodecane,2,6,10-trimethyl-1-Tridecene

Aromatics

Toluene

EthylbenzeneStyreneo-XyleneBenzene

Nitrogenatedcompounds

Indole

HexadecanamidePentadecanenitrile1H-Pyrrole,3-methyl-Phenols

Phenol,4-methyl-Phenol

Phenol,2-ethyl-PACs

NaphthaleneAnthracene

Others

n-HexadecanoicacidOleicAcid

Hexadecenoicacid,Z-11-9,12-Octadecadienoicacid,methylester

Unidenti ed

Compounds

Area/%15.192.021.830.550.496.992.341.020.910.720.5228.392.241.811.721.116.202.591.670.553.380.610.4817.905.044.732.090.1121.95

thesecompounds,hydrocarbonsarevaluablecomponentsinbio-oilfromthepointofviewoffuelapplication.Speci cally,aromatichydrocarbonsserveasimportantindustrialchemicalsandtrans-portationfueladditivestoincreaseoctanenumber.Table4showsthatbothaliphaticandaromatichydrocarbonswerehigherthanthoseobtainedfromotherbiomasses(Adametal.,2006;Wangetal.,2009;Zhangetal.,2009).Thismightresultfromthelargeramountoflipidsinmicroalgaebeingcrackedintohydrocarbonsduringpyrolysis.Phenolanditsalkylatedderivatives,whichareofgreatcommercialimportance,represented6.20%ofthebio-oil.N-containingcompoundsformedduringthedecompositionofproteinsinalgaecells,andtheymayaccountforpotentialNOx

Table3

ComparisonamongNo.2dieselfuel,bio-oilfromMAPofChlorellasp.andotherlignocellulosicfeedstocks.Properties

Bio-oilsChlorellasp.

Elementalcomposition(wt.%)CHNO

HHV(MJ/kg)fDensity(kg/L)pH

Viscosity,at40°C(cSt)

abcdefg

No.2dieselfueld

Pinechips(slowpyrolysis)a54.766.030.0939.1222.0–––

Wheatstraw(MAP)b58.96.851.1533.224.81.2––

Wood(fastpyrolysis)c56.46.20.137.316–191.22–3

25–1000

86.3113.27––430.83–

2.5–3.2

65.47.8410.2816.48e30.70.98g9.761.2

DerivedfromthereferenceSßensözandCan(2002).DerivedfromthereferenceBudarinetal.(2009).

DerivedfromthereferenceBridgwaterandPeacocke(2000).DerivedfromthereferenceTatandVanGerpen(1999).Calculatedbydifference.

Calculatedusingtheequation(Friedletal.,2005)HHV(MJ/kg)=(3.55ÂC2À232ÂCÀ2230ÂH+51.2ÂCÂH+131ÂN+20600)Â10À3.at30°C.

搜索“diyifanwen.net”或“第一范文网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，第一范文网，提供最新高等教育Microwave-assisted pyrolysis of microalgae for biofuel production(4)全文阅读和word下载服务。