Biodiesel from wet microalgae: Extraction with hexane after the microwave-assisted transesterification of lipids

• Hexane extraction after microwave-assisted transesterification of lipids is proposed.
• FAME yield of hexane extraction from wet microalgae is increased 6-fold.
• FAME content in crude biodiesel is increased to 86.74% through hexane extraction.
• Polar pigments present in microalgae are not extracted into the crude biodiesel.

A chloroform-free novel process for the efficient production of biodiesel from wet microalgae is proposed. Crude biodiesel is produced through extraction with hexane after microwave-assisted transesterification (EHMT) of lipids in wet microalgae. Effects of different parameters, including reaction temperature, reaction time, methanol dosage, and catalyst dosage, on fatty acids methyl esters (FAMEs) yield are investigated. The yield of FAME extracted into the hexane from the wet microalgae is increased 6-fold after the transesterification of lipids. The yield of FAME obtained through EHMT of lipids in wet microalgae is comparable to that obtained through direct transesterification of dried microalgae biomass with chloroform; however, FAME content in crude biodiesel obtained through EHMT is 86.74%, while that in crude biodiesel obtained through the chloroform-based process is 75.93%. EHMT ensures that polar pigments present in microalgae are not extracted into crude biodiesel, which leads to a 50% reduction in nitrogen content in crude biodiesel.