Biodiesel fuels from vegetable oils via catalytic

Biodieselfuelsfromvegetableoilsviacatalyticandnon-catalyticsupercriticalalcoholtransesterificationsandothermethods:asurveyAyhanDemirbas
*DepartmentofChemicalEducation,KaradenizTechnicalUniversity,PK216,Trabzon61035,TurkeyReceived8June2002;accepted23September2002AbstractVegetableoilfuelshavenotbeenacceptablebecausetheyweremoreexpensivethanpetroleumfuels.Withrecentincreasesinpetroleumpricesanduncertaintiesconcerningpetroleumavailability,thereisrenewedinterestinvegetableoilfuelsforDieselengines.Dilutionofoilswithsolventsandmicroemulsionsofvegetableoilslowerstheviscosity,butsomeengineperformanceproblemsstillexist.Thepurposeofthetransesterificationprocessistolowertheviscosityoftheoil.Pyrolysisproducesmorebiogasolinethanbiodieselfuel.SoappyrolysisproductsofvegetableoilscanbeusedasalternativeDieselenginefuel.Methylandethylestersofvegetableoilshaveseveraloutstandingadvantagesamongothernewrenewableandcleanenginefuelalternatives.Themainfactorsaffectingtransesterificationarethemolarratioofglyceridestoalcohol,catalyst,reactiontemperatureandpressure,reactiontimeandthecontentsoffreefattyacidsandwaterinoils.Thecommonlyacceptedmolarratiosofalcoholtoglyceridesare6:1–30:1.
2002ElsevierScienceLtd.Allrightsreserved.Keywords:Biodiesel;Viscosity;Pyrolysis;Soappyrolysis;Transesterification1.IntroductionAmongliquidbiofuels,biodieselderivedfromvegetableoilsisgainingacceptanceandmarketshareasDieselfuelinEuropeandtheUnitedStates.Technicalaspectsofbiodieselareap-proached,suchasthephysicalandchemicalcharacteristicsofmethylestersrelatedtoitsper-formanceincompressionignitionengines(CIEs)[1].BiodieselhasbecomemoreattractiveEnergyConversionandManagement44(2003)2093–2109*Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](A.Demirbas
).0196-8904/02/$-seefrontmatter
2002ElsevierScienceLtd.Allrightsreserved.doi:10.1016/S0196-8904(02)00234-0recentlybecauseofitsenvironmentalbenefitsandthefactthatitismadefromrenewablere-sources[2].Althoughshorttermtestsusingneatvegetableoilshowedpromisingresults,longertestsledtoinjectorcoking,moreenginedeposits,ringstickingandthickeningoftheenginelubricant.Theseexperiencesledtotheuseofmodifiedvegetableoilasafuel.AlthoughtherearemanywaysandprocedurestoconvertvegetableoilintoaDiesellikefuel,thetransesterificationprocesswasfoundtobethemostviableoilmodificationprocess[3].Transesterificationistheprocessofusinganalcohol(e.g.methanol,ethanolorbutanol),inthepresenceofacatalyst,suchassodiumhydroxideorpotassiumhydroxide,tobreakthemoleculeoftherawrenewableoilchemicallyintomethylorethylestersoftherenewableoil,withglycerolasabyproduct.Biodiesel,definedasthemono-alkylestersoffattyacidsderivedfromvegetableoiloranimalfat,inapplicationasanextenderforcombustioninCIEs(Diesel),hasdemonstratedanumberofpromisingcharacteristics,includingreductionofexhaustemissions[4].Transesterified,renewableoilshaveproventobeaviablealternativeDieselenginefuelwithcharacteristicssimilartothoseofDieselfuel.Thetransesterificationreactionproceedswithcatalystorwithoutcatalystbyusingprimaryorsecondarymonohydricaliphaticalcoholshaving1–8carbonatomsasfol-lows:TriglyceridesþMonohydricalcohol¢GlycerinþMono-alkylestersð1ÞThisstudyreviewsthepracticabilityofuseofvegetableoilsandtheirmethylandethylestersasbiodieselinCIEs.1.1.LiteraturereviewVegetableoilshavebecomemoreattractiverecentlybecauseoftheirenvironmentalbenefitsandthefactthatitismadefromrenewableresources.Morethan100yearsago,RudolphDieseltestedvegetableoilasthefuelforhisengine[5].Vegetableoilshavethepotentialtosubstituteforafractionofthepetroleumdistillatesandpetroleumbasedpetrochemicalsinthenearfuture.Vegetableoilfuelsarenotnowpetroleumcompetitivefuelsbecausetheyaremoreexpensivethanpetroleumfuels.However,withtherecentincreasesinpetroleumpricesandtheuncertaintiesconcerningpetroleumavailability,thereisrenewedinterestinusingvegetableoilsinDieselengines.TheDieselboilingrangematerialisofparticularinterestbecauseithasbeenshowntoreduceparticulateemissionssignificantlyrelativetopetroleumDiesel[6].Therearemorethan350oilbearingcropsidentified,amongwhichonlysunflower,safflower,soybean,cottonseed,rapeseedandpeanutoilsareconsideredaspotentialalternativefuelsforDieselengines[7,8].Theemergenceoftransesterificationcanbedatedbackasearlyas1846whenRochiederdes-cribedglycerolpreparationthroughethanolysisofcastoroil[9].Sincethattime,alcoholysishasbeenstudiedinmanypartsoftheworld.Othersresearchershavealsoinvestigatedtheimportantreactionconditionsandparametersonthealcoholysisoftriglycerides,suchasfishoils,tallow,soybean,rapeseed,cottonseed,sunflower,safflower,peanutandlinseedoils[10–20].Also,methylestershavebeenpreparedfrompalmoilbytransesterificationusingmethanolinthepresenceofacatalyst(KOH)inabatchreactor[21].Soybeanoilwastransesterifiedintoethylandmethylesters,andcomparisonsoftheperformancesofthefuelswithdiesel[22,23]weremade.2094A.Demirbas
/EnergyConversionandManagement44(2003)2093–2109Methyl,ethyl,2-propylandbutylesterswerepreparedfromcanolaandlinseedoilsthroughtransesterificationusingKOHa