Direct transesterification of Botryococcus sp. catalysed by immobilized lipase: Ultrasound treatment can reduce reaction time with high yield of methyl ester

Methyl esters have been considered a promising alternative fuel for fossil fuels. However, the methyl ester production from lipase catalysed direct transesterification is a time-consuming process. It is necessary to develop the method to reduce the operating time of the lipase catalysed direct transesterification. Various operating parameters were studied such as solvent/algae ratio, catalyst addition, water addition, temperature and reaction time on the direct transesterification of Botryococcus sp. with and without ultrasound. The maximum yield, 88% methyl esters (w/w of oil) was achieved in 4 h with ultrasound treatment under optimum conditions, compared to a maximum yield of 78% methyl esters (w/w of oil), after 36 h without ultrasound. Under optimum conditions, the transesterification of Botryococcus sp. oil with dimethyl carbonate produced 2.7% glycerol carbonate and 5.7% glycerol dicarbonate (w/w of oil) with an added benefit of very low free glycerol content. The properties of methyl esters obtained were found to be within the acceptable limits. The obtained results indicate that this ultrasound assisted direct transesterification of Botryococcus sp. oil catalysed by lipase is very promising for biodiesel production using microalgae as the feedstock.