Biodiesel from soybean oil in supercritical methanol with co-solvent

Abstract

Biodiesel synthesis from soybean oil using methanol was investigated at supercritical and subcritical conditions of methanol in a high pressure vessel of 250 cm 3 volume. Under the supercritical conditions, the maximum methyl ester yield exceeded 98% when the molar ratio of methanol to oil was 42:1 and the reaction temperature ranged from 260 °C to 350 °C. In order to decrease the operational temperature and pressures and increase the conversion efficiency of methanol, a novel idea was presented in which a co-solvent (hexane, carbon dioxide, KOH) was added to the reactants. The results indicated that the yield of methyl ester was improved when hexane or CO 2 was added. With CO 2 or hexane as co-solvent in the reaction system at 300 °C, there was a significant increase of the methyl esters yield. With the optimal reaction temperature of 160 °C and methanol to oil ratio of 24, a 98% yield of methyl esters was observed in 20 min at the subcritical condition with 0.1 wt% potassium hydroxide (KOH).