Transesterification kinetics of soybean oil 1

Abstract

Transesterification of soybean oil (SBO) and other triglycerides with alcohols, in the presence of a catalyst, yields fatty esters and glycerol. Di‐ and monoglycerides are intermediates. Reactions are consecutive and reversible. Rate constants have been determined for each reaction with a computerized kinetic program. The effects of the type of alcohol, 1‐butanol or methanol (MeOH); molar ratio of alcohol to SBO; type and amount of catalyst; and reaction temperature on rate constants and kinetic order were examined. Forward reactions appear to be pseudo‐first order or second order depending upon conditions used. Reverse reactions appear to be second order. At a molar ratio of MeOH/SBO of 6:1, a shunt reaction was observed. Energy of activation was determined for all forward and reverse reactions under a variety of experimental conditions from plots of log k vs 1/T. Values ranged from 8–20 kcal/mol.

Biodiesel de soja: reação de transesterificação para aulas práticas de química orgânica

“…Uma série de metodologias para obtenção de biodiesel encontra-se disponível na literatura [7][8][9][10][12][13][14][15][16][17][18][19] . Nelas são discutidas as variá-veis que influenciam a eficiência do processo, bem como a qualidade do produto formado, como por ex., a quantidade de material catalítico, a razão molar álcool/óleo vegetal, a intensidade da agitação mecânica, a pureza dos reagentes, o teor de ácidos graxos livres no material de partida e o tempo reacional.…”

“…Entre os catalisadores bási-cos estão os hidróxidos de metais alcalinos, carbonatos e alcóxidos de metais alcalinos (metóxido de sódio, etóxido de sódio, propóxido de sódio e butóxido de sódio) 4 . A maior parte dos trabalhos descritos na literatura emprega catalisadores básicos, tais como KOH e NaOH onde foram observados maior rendimento e seletividade 16 . No entanto, outros catalisadores básicos não iônicos podem ser usados na transesterificação dos triacilglicerídeos, evitando a formação de subprodutos indesejáveis como os sabões, entre eles trietilamina, piperidina, guanidinas 5 .…”

Transesterification of vegetable oils: a review

“…The overall process is a sequence of three consecutive and reversible reactions, in which diand monoglycerides are formed as intermediates 26 . The stoichiometric reaction requires 1 mol of a triglyceride and 3 mol of the alcohol.…”

“…The transesterification process is catalyzed by BrØn-sted acids, preferably by sulfonic 27 and sulfuric acids 26,28,29 . These catalysts give very high yields in alkyl esters, but the reactions are slow, requiring, tipically, temperatures above 100 °C and more than 3 h to reach complete conversion 30 .…”

“…These catalysts give very high yields in alkyl esters, but the reactions are slow, requiring, tipically, temperatures above 100 °C and more than 3 h to reach complete conversion 30 . Pryde et al 26 showed that the methanolysis of soybean oil, in the presence of 1 mol% of H2SO4, with an alcohol/oil molar ratio of 30:1 at 65 °C, takes 50 h to reach complete conversion of the vegetable oil (> 99%), while the butanolysis (at 117 °C) and ethanolysis (at 78 °C), using the same quantities of catalyst and alcohol, take 3 and 18 h, respectively.…”