Alternatives for the Production of Biodiesel by Supercritical Technologies: A Comparative Study

On the last years, there have been proposals for using supercritical conditions to produce biodiesel fuel from vegetable oils and/or animal fats without a catalyst. Different schemes have been proposed, the most popular consisting on the use of supercritical methanol as reactant. Other alternatives involve the use of methyl acetate or acetic acid as reactants. The potential of those processes may be established in terms of their total annual cost and environmental impact. Thus, in this work, the production of biodiesel fuel by using different reactants is studied. Four processes are considered: the one step supercritical methanol process (Saka process), the two steps supercritical methanol process (Saka-Dadan process), a process with methyl acetate as reactant and a process with acetic acid as reactant. Possible flowsheets for the reaction and separation stages are proposed. The processes are analyzed and compared in terms of energy consumption, pollutant emissions and total annual costs. It has been observed that, in terms of energy, the one step methanol process has the lowest energy requirements. Nevertheless, a higher temperature for the steam supplied is required; thus, that process has high values of CO2 emissions. Furthermore, methyl esters are obtained at higher temperatures, which may have a negative impact on its quality.