Biodiesel production from microalgae by direct transesterification using green solvents

This study evaluated the production of biodiesel from the microalgae Chlorella pyrenoidosa by direct transesterification using 2-methyltetrahydrofuran or cyclopentyl methyl ether co-solvents as an alternative to chloroform. Acid-catalyzed transesterification using hydrochloric acid was developed for biodiesel production. Biodiesel was purified by column chromatography using one of the two green solvents as eluents. The highly ecological biodiesel quality was compared to the biodiesel produced using chloroform as co-solvent. A 33 factorial design was conducted to optimize the production of fatty acid methyl esters, being the independent variables investigated: solvent and catalyst volume, solvent and catalyst ratio (methanol:co-solvent:hydrochloric acid), and temperature, with a reaction time of 150 min. Biodiesel production was mainly influenced by temperature increase. The achieved yields using cyclopentyl methyl ether, 2-methyltetrahydrofuran, and chloroform were 71–92%, 67–91%, and 61–76%, respectively. The fatty acid methyl esters profile of biodiesel produced with 2-methyltetrahydrofuran and cyclopentyl methyl ether consisted of approximately 45% polyunsaturated components. The biodiesel obtained was within the ASTM D6751 and EN 14214 standards. The replacement of fossil solvents used in direct transesterification of biomass with a green solvent resulted in a further ecological biodiesel production process towards a circular bioeconomy.