生物柴油-产品与质量-ASTM-D6751

BiodieselProductionandQualityLastupdatedApril26,2007Theproductionprocessesforbiodieselarewellknown.Therearethreebasicroutestobiodieselproductionfromoilsandfats:*Basecatalyzedtransesterificationoftheoil.*Directacidcatalyzedtransesterificationoftheoil.*Conversionoftheoiltoitsfattyacidsandthentobiodiesel.Mostofthebiodieselproducedtodayisdonewiththebasecatalyzedreactionforseveralreasons:*Itislowtemperatureandpressure.*Ityieldshighconversion(98%)withminimalsidereactionsandreactiontime.*Itisadirectconversiontobiodieselwithnointermediatecompounds.*Noexoticmaterialsofconstructionareneeded.Thechemicalreactionforbasecatalyzedbiodieselproductionisdepictedbelow.Onehundredpoundsoffatoroil(suchassoybeanoil)arereactedwith10poundsofashortchainalcoholinthepresenceofacatalysttoproduce10poundsofglycerinand100poundsofbiodiesel.Theshortchainalcohol,signifiedbyROH(usuallymethanol,butsometimesethanol)ischargedinexcesstoassistinquickconversion.Thecatalystisusuallysodiumorpotassiumhydroxidethathasalreadybeenmixedwiththemethanol.R',R'',andR'''indicatethefattyacidchainsassociatedwiththeoilorfatwhicharelargelypalmitic,stearic,oleic,andlinoleicacidsfornaturallyoccurringoilsandfats.TheBiodieselReactionCH2OCOR'''CH2OHR'''COOR|Catalyst|CH2OCOR''+3ROH------CH2OH+R''COOR||CH2OCOR'CH2OHR'COOR100pounds10pounds10pounds100poundsOilorFatAlcohol(3)GlycerinBiodiesel(3)TheNationalBiodieselBoarddoesnotgetinvolvedwithcommercialbiodieselproductionorthedesignandconstructionofbiodieselfacilities,butwehaveprovidedanexampleofasimpleproductionflowchartalongwithashortexplanationofthestepsinvolvedtoacquaintthereaderwiththegeneralproductionprocess.MethanolCatalystCatalyst-MixingTransesterificationVegetableOils,UsedCookingOil,AnimalFatsNeutralizationPhaseSeparationRe-neutralizationMethanol-RecoveryPurificationMethanol-RecoveryQualityControlGlycerinPurificationNeutralizingAcidCrudeBiodieselMethylMethylEsterEsterCrudeCrudeGlycerinGlycerinPharmaceuticalPharmaceuticalGlycerinGlycerinBiodieselProductionProcessRecycledMethanolIfdesiredThebasecatalyzedproductionofbiodieselgenerallyoccursusingthefollowingsteps:Mixingofalcoholandcatalyst.Thecatalystistypicallysodiumhydroxide(causticsoda)orpotassiumhydroxide(potash).Itisdissolvedinthealcoholusingastandardagitatorormixer.Reaction.Thealcohol/catalystmixisthenchargedintoaclosedreactionvesselandtheoilorfatisadded.Thesystemfromhereonistotallyclosedtotheatmospheretopreventthelossofalcohol.Thereactionmixiskeptjustabovetheboilingpointofthealcohol(around160°F)tospeedupthereactionandthereactiontakesplace.Recommendedreactiontimevariesfrom1to8hours,andsomesystemsrecommendthereactiontakeplaceatroomtemperature.Excessalcoholisnormallyusedtoensuretotalconversionofthefatoroiltoitsesters.Caremustbetakentomonitortheamountofwaterandfreefattyacidsintheincomingoilorfat.Ifthefreefattyacidlevelorwaterlevelistoohighitmaycauseproblemswithsoapformationandtheseparationoftheglycerinby-productdownstream.Separation.Oncethereactioniscomplete,twomajorproductsexist:glycerinandbiodiesel.Eachhasasubstantialamountoftheexcessmethanolthatwasusedinthereaction.Thereactedmixtureissometimesneutralizedatthisstepifneeded.Theglycerinphaseismuchmoredensethanbiodieselphaseandthetwocanbegravityseparatedwithglycerinsimplydrawnoffthebottomofthesettlingvessel.Insomecases,acentrifugeisusedtoseparatethetwomaterialsfaster.AlcoholRemoval.Oncetheglycerinandbiodieselphaseshavebeenseparated,theexcessalcoholineachphaseisremovedwithaflashevaporationprocessorbydistillation.Inotherssystems,thealcoholisremovedandthemixtureneutralizedbeforetheglycerinandestershavebeenseparated.Ineithercase,thealcoholisrecoveredusingdistillationequipmentandisre-used.Caremustbetakentoensurenowateraccumulatesintherecoveredalcoholstream.GlycerinNeutralization.Theglycerinby-productcontainsunusedcatalystandsoapsthatareneutralizedwithanacidandsenttostorageascrudeglycerin.Insomecasesthesaltformedduringthisphaseisrecoveredforuseasfertilizer.Inmostcasesthesaltisleftintheglycerin.Waterandalcoholareremovedtoproduce80-88%pureglycerinthatisreadytobesoldascrudeglycerin.Inmoresophisticatedoperations,theglycerinisdistilledto99%orhigherpurityandsoldintothecosmeticandpharmaceuticalmarkets.MethylEsterWash.Onceseparatedfromtheglycerin,thebiodieselissometimespurifiedbywashinggentlywithwarmwatertoremoveresidualcatalystorsoaps,dried,andsenttostorage.Insomeprocessesthisstepisunnecessary.Thisisnormallytheendoftheproductionprocessresultinginaclearamber-yellowliquidwithaviscositysimilartopetrodiesel.Insomesystemsthebiodieselisdistilledinanadditionalsteptoremovesmallamountsofcolorbodiestoproduceacolorlessbiodiesel.ProductQualityandRegistration.Priortouseasacommercialfuel,thefinishedbiodieselmustbeanalyzedusingsophisticatedanalyticalequipmenttoensureitmeetsASTMspecifications.Additionally,allbiodieselproducedmustberegisteredwiththeUnitesStatesEnvironmentalProtectionAgencyunder40CFRPart79.Themostimportantaspectsofbiodieselproductiontoensuretroublefreeoperationindieselenginesare:*CompleteReaction*RemovalofGlycerin*RemovalofCatalyst