A team at the National Renewable Energy Laboratory (NREL) has demonstrated a sustainable process for converting crude extracted algal lipids to renewable diesel fuel via bleaching, deoxygenation, and hydroisomerization. A paper on their study is published in the ACS journal Energy & Fuels.
They explored the effects of bleaching (using two methods) on oil deoxygenation over Pd/C and hydroisomerization over Pt/SAPO-11 catalysts. The raw oil was completely deoxygenated and 90% denitrogenated after dilution to 25 wt % in hexanes. The bleaching operations removed 85–90% of the nitrogen and led to 95–99% nitrogen removal after deoxygenation. Oil processability was also improved by bleaching.
They found that the bulk chemistry of the deoxygenation and isomerization was not strongly affected by bleaching, as post-isomerization products with cloud points less than −10 °C and boiling ranges within or close to specification for No. 2 diesel fuel were obtained through 10 h time on stream with or without bleaching.
Lipids extracted from algal biomass have potential to be a major feedstock source for production of biofuels, but process-relevant data on refining crude algal lipids to hydrocarbon fuels is scarce. Techno-economic analyses (TEA) have demonstrated that algal biomass cost is the largest single factor affecting process economics, but the cost of hexane for lipid extraction and hydrogen for deoxygenation are the second and third largest operating costs, respectively. Thus, there is considerable motivation to gain a greater understanding of the unit operations required for refining algal lipids, which have different chemistry than either conventional crude oils or terrestrial animal or plant lipids. Generally, these operations can be categorized into oil cleanup, deoxygenation (DO), and hydroisomerization (HI).—Kruger et al.
Overall, they found that crude hexane extracts from dilute acid-pretreated algae can be converted to a diesel blendstock in overall yields approaching 60%.
Jacob S Kruger, Earl D. Christensen, Tao Dong, Stefanie Van Wychen, Gina M. Fioroni, Philip T. Pienkos, and Robert L. McCormick (2017) “Bleaching and Hydroprocessing of Algal Biomass-derived Lipids to Produce Renewable Diesel Fuel” Energy Fuels doi: 10.1021/acs.energyfuels.7b01867