你奈我何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.
