Biodiesel fuel from rapeseed oil as prepared in supercritical methanol

Transesterification reaction of rapeseed oil in supercritical methanol was investigated without using any catalyst. An experiment has been carried out in the batch-type reaction vessel preheated at 350 and 400°C and at a pressure of 45–65 MPa, and with a molar ratio of 1:42 of the rapeseed oil to methanol. It was consequently demonstrated that, in a preheating temperature of 350°C, 240 s of supercritical treatment of methanol was sufficient to convert the rapeseed oil to methyl esters and that, although the prepared methyl esters were basically the same as those of the common method with a basic catalyst, the yield of methyl esters by the former was found to be higher than that by the latter. In addition, it was found that this new supercritical methanol process requires the shorter reaction time and simpler purification procedure because of the unused catalyst.