Enzymatic production of microalgal biodiesel in ionic liquid [BMIm][PF6]

Microalgae have been taken as a sustainable energy source for biodiesel production. In this work, oils were extracted from microalgae Botryococcus braunii (two strains, BB763 and BB764), Chlorella vulgaris (CV), and Chlorella pyrenoidosa (CP). The highest lipid content was produced from CV (40.7%, w/w), whereas the lowest from CP (2.2%, w/w). The major fatty acid components of the microalgal oil from CP include myristic acid (C14:0), palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3), and their mass proportion is 1:3.9:1.9:4.2:4.3:13.8. Enzymatic production of biodiesel from the microalgal oil was investigated, catalyzed by two immobilized lipases, Penicillium expansum lipase (PEL) and Candida antarctica lipase B (Novozym 435), in two solvent systems: an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIm][PF6]) and an organic solvent (tert-butanol). The effect of the following factors on the production yield was studied for all the four reaction systems: methanol/oil molar ratio, reaction temperature, solvent volume, and water content. Under optimal conditions, both enzymes induced significantly higher yields in the IL (90.7% and 86.2%) relative to that obtained in tert-butanol (48.6% and 44.4%), while the PEL-catalyzed conversions were comparable to or slightly higher than those catalyzed by Novozym 435. These results demonstrate that ionic liquids offer a promising new type of solvent for enzymatic production of microalgal biodiesel and that PEL can be employed as an efficient catalyst for such application.