Enhancement of continuous supercritical biodiesel production: influence of co-solvent types

The aim of this work was to enhance the continuous supercritical biodiesel production process by applying the co-solvent technology. The influence of co-solvent types on the fatty acid alkyl esters (%Ester) or biodiesel content was primarily evaluated. Experiments were performed through the transesterification of palm oil and ethanol in a microtube reactor under the supercritical solvent conditions. Three different polarity levels of co-solvent including tetrahydrofuran, acetone, and iso-propanol were selected. Results indicated that each co-solvent added to the reacting system significantly enhanced the homogeneity of the mixture. The influence of co-solvent type was clearly observed and became small at high reaction temperatures and long residence time. The %Ester was higher than 80% with the addition of any types of co-solvent under the residence time of 3.5 min, co-solvent amount of 20%, reaction temperature of 350 degrees C, and alcohol-to-oil molar ratio of 23:1, whereas 65.6% of ester content was obtained in the absence of co-solvent under the same operating conditions. The use of acetone as co-solvent provided the highest %Ester, however, further studies in different perspectives such as biodiesel properties, co-solvent separation method, and economic impact should be considered to select the optimized co-solvent for improving the biodiesel production. (C) 2019 The Authors. Published by Elsevier Ltd.