Effect of CO2/N2 addition to supercritical methanol on reactivities and fuel qualities in biodiesel production

Addition of the third component to supercritical methanol has been studied in the literature for biodiesel production in order to reduce reaction temperature without deteriorating the reaction rate. However, effect of pressure had often been neglected in the discussion. In this paper, therefore, effect of pressure was examined with hexane, carbon dioxide (CO2) and nitrogen (N2) as one of the third components, using batch-type and flow-type reactors. As a result, it was found that an addition of the third component did not contribute to better product yield at constant reaction pressure. Furthermore, the reaction rate was found to be determined by pressure and concentration of the reactants involved in transesterification, not by the function of so-called co-solvent. Additionally, N2 addition was found to contribute to improvement in oxidation stability and reduction of the total glycerol content, thus offering high-quality biodiesel production.