In situ biodiesel production from wet Chlorella vulgaris under subcritical condition

The conventional base catalyzed biodiesel production process uses refined vegetable oil as feedstock oil and is not environmentally friendly. The supercritical methanol technology does not require the use of catalyst but it is energy intensive due to the high temperature and pressure required in the process. In this work, a process was developed for producing biodiesel directly from wet Chlorella vulgaris biomass (80% moisture content) using subcritical water as catalyst. Under the following conditions: The ratio of wet biomass to methanol is 1/4 (g/mL), the reaction temperature is 175 °C and after 4 h, the reaction product contained 89.71% fatty acid methyl esters (FAMEs). The yield is 0.29 g FAME per g dry biomass. This is considerably higher than the yield of 0.20 g FAME per g dry biomass obtained when the neutral lipid of C. vulgaris biomass was extracted and converted into FAME.

► The conventional biodiesel production process is not environmentally friendly.
► Biodiesel can be made directly from wet algal biomass and subcritical methanol.
► Stirring shortens the reaction time to achieve high conversion yield of FAMEs.