One-path catalytic supercritical methanothermal production of fatty acid methyl ester fractions from wet microalgae Chlorella vulgaris

Abstract Biodiesel production from microalgae requires energy-intensive dewatering before lipid extraction and transesterification. In order to avoid this energy penalty, one-path direct transesterification of wet microalgae (Chlorella vulgaris) using supercritical methanol is attempted, for the first time with added heterogeneous catalysts. This methanothermal process was found to be robust, maintaining high fatty acid methyl ester (FAME) fraction yields in a wide range of water content (16–64 mol % water in methanol). Among the eight metal oxide catalysts tested, α-Al2O3 showed the best performance for the reaction, producing 1.4–1.6 times as much FAME fractions compared to non-catalytic reaction in the same moisture range. The present catalysis is found to be not affecting transesterification step, evidenced by the weak effect of surface acidity. Instead, it appears to add extra routes to produce fuel components that fall in the FAME fraction range.