Hydrotreating of biocrudes derived from hydrothermal liquefaction and lipid extraction for the high-lipid Scenedesmus
Biocrudes derived from hydrothermal liquefaction (HTL) and lipid extraction (EXT) of the high-lipid Scenedesmus were hydrotreated to investigate the influences of feedstock on the profiles of hydrotreating biofuels. As to HTL and EXT biocrudes, there were similar yields (52.87% and 49.06%, wt. %) but different fatty acid (60.53% and 66.92%), C (60.28% and 74.40%), H (9.55% and 10.96%), O (26.99% and 13.81%) and N (3.19% and 0.85%) contents (wt. %), HHV (29.19 and 38.33 MJ/kg) and chemical constituent (fatty acids and triglycerides). After hydrotreating, 0.45 g HTL and 0.42 g EXT biofuels were obtained from 1 g Scenedesmus, with different heteroatoms (9.14% and 1.01%), HHV (42.77 and 48.85 MJ/kg). However, a certain number of heavy products, such as C30+ hydrocarbons and C31+ esters were found in both biofuels. By adjusting reaction conditions including temperature and catalyst loading, the content of heavy products decreased from maximum 26.24% to minimum 1.30% at 350 °C with 50% catalyst loading. Based on hydrotreating model fatty acids and esters, the proposed reaction mechanism demonstrated that the formation of heavy products could be inhibited with EXT biocrude instead of HTL biocrude as feedstock.