Production of high-quality biofuel via ethanol liquefaction of pretreated natural microalgae

The conversion of algal lipids to fatty acid alkyl esters is a promising way for the production of high-grade biofuel, due to the lower oxygen content of lipids than that of saccharides and proteins. Herein, a catalyst-free conversion process of natural microalgae cyanobacteria was developed for biodiesel production. The conversion involved two steps: (1) pretreatment of raw microalgae by Soxhlet extraction of lipids or hydrothermal treatment for extraction of saccharides and part of proteins at 200 degrees C; (2) liquefaction of raw and pretreated samples in sub/supercritical ethanol. In the first step, a maximum lipid yield of 6.5 wt% was extracted by Soxhlet extraction, while the hydrothermal treatment dissolved saccharides and a part of proteins. The composition of biocrude obtained from raw algae was complex, containing hydrocarbons, N-containing compounds, esters, fatty acids and other oxy-compounds. The biocrude from lipid extracted algae had a poor quality, from which the degradation of proteins was facilitated. Better yet, the extraction of saccharides and part of proteins by hydrothermal pretreatment simplified the composition (mainly fatty acid ethyl esters), reduced the nitrogen content (<4%) and improved the higher heating value (-41 MJ kg(-1)) for biocrude. (C) 2019 Elsevier Ltd. All rights reserved.