Supercritical transesterification of vegetable oil and ethanol: temperature and residence time effects on phase formation and water content

Supercritical transesterification has emerged as a readily available alternative for biodiesel production since no catalyst is required, thereby generating fewer waste products. In this research, the supercritical transesterification of refined vegetable oil and aqueous ethanol was carried out at temperatures 400 to 480 °C and a 12:1 ethanol to oil molar ratio, to assess the effect of temperature and residence time in the formation of a homogeneous phase, effluent appearance and increased water content derived from glycerol etherification. The results showed that water was produced at temperatures higher than 400 °C, as expected from the occurrence of glycerol etherification, and that prolonged times resulted in gas and soot formation, indicating esters decomposition. Through water mass balances, it was possible to identify the set of operation conditions in which the water formed from glycerol etherification matched with the maximum expected according to the proposed reaction scheme.