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Transesterification of Vegetable Oils a Review

Transesterification of Vegetable Oils a Review -...

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Unformatted text preview: Transesterification of Vegetable Oils: a Review Ulf Schuchardt a , Ricardo Sercheli a , and Rogério Matheus Vargas* b a Instituto de Química, Universidade Estadual de Campinas, C.P. 6154, 13083-970 Campinas - SP, Brazil b Instituto de Química, Universidade Federal da Bahia, Campus de Ondina, 40170-290 Salvador - BA, Brazil Received: May 9, 1997 A transesterificação de óleos vegetais com metanol, bem como as principais aplicações de ésteres metílicos de ácidos graxos, são revisadas. São descritos os aspectos gerais desse processo e a aplicabilidade de diferentes tipos de catalisadores (ácidos, hidróxidos, alcóxidos e carbonatos de metais alcalinos, enzimas e bases não-iônicas, como aminas, amidinas, guanidinas e triamino(imino)fosforanos). Enfoque especial é dado às guanidinas, que podem ser facilmente heterogeneizadas em polímeros orgânicos. No entanto, as bases ancoradas lixiviam dos polímeros. Novas estratégias para a obtenção de guanidinas heterogeneizadas mais resistentes à lixiviação são propostas. Finalmente, são descritas várias aplicações para ésteres de ácidos graxos, obtidos por transesterificação de óleos vegetais. The transesterification of vegetable oils with methanol as well as the main uses of the fatty acid methyl esters are reviewed. The general aspects of this process and the applicability of different types of catalysts (acids, alkaline metal hydroxides, alkoxides and carbonates, enzymes and non-ionic bases, such as amines, amidines, guanidines and triamino(imino)phosphoranes) are described. Special attention is given to guanidines, which can be easily heterogenized on organic polymers. However, the anchored catalysts show leaching problems. New strategies to obtain non-leaching guanidine-containing catalysts are proposed. Finally, several applications of fatty acid esters, obtained by transesterification of vegetable oils, are described. Keywords : transesterification, fatty acid methyl esters, non-ionic bases, heterogenization General Aspects of Transesterification Transesterification is the general term used to describe the important class of organic reactions where an ester is transformed into another through interchange of the alkoxy moiety. When the original ester is reacted with an alcohol, the transesterification process is called alcoholysis (Scheme 1) 1 . In this review, the term transesterification will be used as synonymous for alcoholysis of carboxylic esters, in agreement with most publications in this field. The transesterification is an equilibrium reaction and the trans- formation occurs essentially by mixing the reactants. How- ever, the presence of a catalyst (typically a strong acid or base) accelerates considerably the adjustment of the equi- librium. In order to achieve a high yield of the ester, the alcohol has to be used in excess....
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