Preparation of biodiesel from soybean oil using supercritical methanol and CO2 as co-solvent

Transesterification of soybean oil in supercritical methanol has been carried out in the absence of catalyst. A co-solvent was added to the reaction mixture in order to decrease the operating temperature, pressure and molar ratio of alcohol to vegetable oil. With CO2 as co-solvent in the reaction system, there was a significant decrease in the severity of the conditions required for supercritical reaction. It was demonstrated that, with an optimal reaction temperature of 280 °C, methanol to oil ratio of 24 and CO2 to methanol ratio of 0.1, a 98% yield of methyl esters (biodiesel) was observed in 10 min at a reaction pressure of 14.3 MPa, which makes the production of biodiesel using supercritical methanol viable as an industrial process. Furthermore, the production process is environmentally friendly.