Reactivity of triglycerides and fatty acids of rapeseed oil in supercritical alcohols.

A catalyst-free biodiesel production method with supercritical methanol has been developed that allows a simple process and high yield because of simultaneous transesterification of triglycerides and methyl esterification of fatty acids. From these lines of evidence, we expected that similar results would be attained with the use of various alcohols by the supercritical treatment. However, it still remains unclear which type of reaction, transesterification or alkyl esterification, is faster. This parameter would be important in designing the optimum reaction conditions of the supercritical alcohol method. Therefore, we studied the effect of transesterification of triglycerides and esterification of fatty acids in rapeseed oil. Reaction temperature was set at 300 degrees C, and methanol, ethanol, 1-propanol, 1-butanol or 1-octanol was used as the reactant. The results showed that transesterification of triglycerides (rapeseed oil) was slower in reaction rates than alkyl esterification of fatty acids for any of the alcohols employed. Furthermore, saturated fatty acids such as palmitic and stearic acids had slightly lower reactivity than that of the unsaturated fatty acids; oleic, linoleic and linolenic.