Experimental protocol for biodiesel production with isolation of alkenones as coproducts from commercial Isochrysis algal biomass

Authors: O'NEIL, GREGORY - Western Washington University; WILLIAMS, JOHN - Western Washington University; WILSON-PELTIER, JULIA - Western Washington University; Knothe, Gerhard; REDDY, CHRISTOPHER - Woods Hole Oceanographic Institute (WHOI)

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2016
Publication Date: 6/24/2016
Citation: O'Neil, G.W., Williams, J.R., Wilson-Peltier, J., Knothe, G., Reddy, C.M. 2016. Experimental protocol for biodiesel production with isolation of alkenones as coproducts from commercial Isochrysis algal biomass. Journal of Visualized Experiments. 112:e54189. doi: 10.3791/54189.

Interpretive Summary: Many different plant oils, but also materials such as used cooking oils and animal fats, can be used to produce biodiesel which is an alternative to conventional diesel fuel derived from petroleum. In recent years, oils obtained from algae have been receiving ever-increasing interest as potential feedstock for biodiesel. The reason is that algae may be able to produce significant amounts of oil, therefore ultimately providing more biodiesel than many other feedstocks. On the other hand, because of their composition, oils from algae have faced several issues when producing biodiesel from them. This work discusses and shows how biodiesel of improved quality, especially regarding cold flow properties, can be produced from an algal oil by removing some minor components. These minor components, called alkenones, may themselves have applications as renewable materials.

Technical Abstract: The need to replace petroleum fuels with alternatives from renewable and more environmentally sustainable sources is of growing importance. Biomass-derived biofuels have gained considerable attention in this regard, however first generation biofuels from edible crops like corn ethanol or soybean biodiesel have generally fallen out of favor. There is thus great interest in the development of methods for the production of liquid fuels from domestic and superior non-edible sources. Here we describe a detailed procedure for the production of a purified biodiesel from the marine microalgae Isochrysis. Additionally, a unique suite of lipids known as polyunsaturated long-chain alkenones are isolated in parallel as potentially valuable coproducts to offset the cost of biodiesel production. Multi-kilogram quantities of Isochrysis are purchased from two commercial sources, one as a wet paste (80% water) that is first dried prior to processing, and the other a dry milled powder (95% dry). Lipids are extracted with hexanes in a Soxhlet apparatus to produce an algal oil (“hexane algal oil”) containing both traditional fats (i.e. triglycerides, 46-60% w/w) and alkenones (16-25% w/w). Saponification of the triglycerides in the algal oil allows for separation of the resulting free fatty acids (FFAs) from alkenone-containing neutral lipids. FFAs are then converted to biodiesel (i.e. fatty acid methyl esters, FAMEs) by acid-catalyzed esterification while alkenones are isolated and purified from the neutral lipids by crystallization. We demonstrate that biodiesel from both commercial Isochrysis biomasses have similar but not identical FAME profiles, characterized by elevated polyunsaturated fatty acid contents (approximately 40% w/w). Yields of biodiesel were consistently higher when starting from the Isochrysis wet paste (12% w/w vs. 7% w/w) which can be traced to lower amounts of hexane algal oil obtained from the powdered Isochrysis product.