SUPERCRITICAL TRANSESTERIFICATION OF BEEF TALLOW FOR BIODIESEL PRODUCTION IN A BATCH REACTOR

^len^aSupercritical transesterification experiments of beef tallow with ethanol were carried out in a batch reactor in order to assess the effect of temperature (350 - 400°C), reactant molar ratio (9:1 - 15:1) and reaction time (8 - 40 min). Composition of the produced biofuel was assessed in terms of the percentage of peak area of the long chain Fatty Acid Ethyl Esters (FAEEs) identified, including also the decomposition products generated as a result of thermal cracking or cis-trans isomerization reactions. Thermal decomposition of FAEEs produced from beef tallow included short chain ethyl esters (C8 - C13), ethyl pentadecanoate (C15:0), heptadecanoate (C17:0), not initially present or prevalent in triglycerides sources, as well as ethyl stearate (C18:0) and n-alkanes. Glycerol decomposition reactions were also verified by the presence of glycerol ethers and water content in the produced biodiesel. The highest conversion of triglycerides was verified at 400°C, 15:1 triglycerides to ethanol molar ratio and 40-minute reaction time. At these conditions, ethyl oleate (C18:1) decomposed completely to form cis-trans isomers as well as ethyl octadecanoate (C18:0), which was attributed to double bond hydrogenation reactions. Short chain ethyl esters and glycerol decomposition products have the potential to benefit certain properties of the fuel such as viscosity and cold flow. ^les^aLos experimentos de transesterificacion supercritica de sebo vacuno con etanol se llevaron a cabo en un reactor batch con el fin de evaluar el efecto de la temperatura (350 - 400°C), relacion molar de reactantes (9:1-15:1) y tiempo de reaccion (8 - 40 min). La composicion del biocombustible producido se evaluo en terminos del porcentaje de area de picos de los esteres etilicos de acidos grasos o FAEEs (Fatty Acid Ethyl Esters) asi como los productos de descomposicion generados de reacciones de cracking o isomerizacion. La descomposicion termica de los FAEEs producidos incluyo esteres etilicos de cadena corta (C8 - C13), etil pentadecanoato (C15:0), heptadecanoato (C17:0), los cuales no proceden de acidos grasos presentes en el sebo, asi como etil estearato (C18:0) y n-alcanos. De la misma forma, se verifico la ocurrencia de reacciones de descomposicion de la glicerina por medio de la identificacion de eteres y del contenido de agua en el biodiesel. La maxima conversion de trigliceridos se verifico a 400°C, con una relacion molar de 15:1 y 40 minutos de tiempo de reaccion. A estas condiciones, el etil oleato (C18:1) se descompuso completamente para formar isomeros cis-trans asi como etil octadecanoato (C18:0). Los esteres etilicos de cadena corta y los productos de descomposicion del glicerol tienen el potencial de beneficiar ciertas propiedades del biocombustible. ^lpt^aOs experimentos de transesterificacao supercritica de sebo de bovino com etanol foram realizados em um reator batch no intuito de avaliar o efeito da temperatura (350 - 400°C), relacao molar de reagentes (9:1-15:1) e tempo de reacao (8 - 40 min). A composicao do biocombustivel produzido foi avaliada em termos de porcentagem de area de picos dos esteres etilicos de acidos graxos ou FAEEs (Fatty Acid Ethyl Esters), bem como os produtos de decomposicao produzidos pelas reacoes de cracking ou isomerizacao. A decomposicao termica dos FAEEs produzidos incluiu esteres etilicos de caida curta (C8 - C13) etil pentadecanoato (C15:0), heptadecanoato (C17:0), nao procedentes de acidos graxos presentes no sebo, bem como etil estearato (C18:0) e n-alcanos. De igual modo, verificou-se a ocorrencia de reacoes de decomposicao da glicerina atraves da identificacao de eteres e do conteudo de agua no biodiesel. A maxima conversao de triglicerides foi verificada a 400°C, com uma relacao molar de 15:1 e 40 minutos de tempo de reacao. Sob essas condicoes, o etil oleato (C18:1) decompos-se completamente para formar isomeros cis-trans, bem como etil octadecanoato (C18:0). Os esteres etilicos de cadeia curta e os produtos da decomposicao do glicerol tem o potencial de beneficiar certas propriedades do biocombustivel.