Catalytic Hydroconversion of HTL micro-algal bio-oil into biofuel

RMN+CATREN+BMG:RCE:CLO:PAF:DLA:CGEInternational audienceThe main compounds present in the HTL micro-algal bio-oil were C16 and C18 carboxylic acids from triglycerides hydrolysis. Fatty amides, and cyclic aromatics nitrogen and oxygen compounds formed from the decomposition of carbohydrates and proteins were also found. The N and O content were, respectively 2.6 wt. % and 11.7 wt. %.The experiment performed with nickel phosphide showed the same conversion as an experiment without catalyst, indicating that, even though phosphides have been reported in the literature as a potential candidate to replace sulfide catalysts, more advances should be done to increase the activity of this active phase.However, the sulfide and nitride catalysts permitted to reduce the number of contaminants and improved the quality of bio-oil. The main compounds formed after the upgrading step were C15, C16, C17, and C18 from carboxylic acids hydrogenation (HDO) or decarboxylation/decarbonylation (DCO). More than 60% of upgraded bio-oil eluted on the diesel range, which corroborates the potential of microalgae as a feedstock for biofuel production. The degree of deoxygenation and denitrogenation were, respectively, 91% and 67% for sulfide catalyst, 93% and 46% for nitride catalyst, and 84% and 6% for phosphide. Therefore, NiWS/Al2O3 had a higher hydrodenitrogenation (HDN) ability than NiMoN and Ni2P/Al2O3 catalysts. GCxGC-MS/FID analysis revealed that fatty amides were first converted into nitriles and then in alkanes. The experiments performed over Ni2P/Al2O3 and without catalyst showed a family of nitriles that are completely converted with nitride and sulfide systems. Besides, it was also observed that NiWS/Al2O3 converted more cyclic nitrogen compounds, such as, pyrroles, indoles, and carbazoles than NiMoN which is associated with a higher hydrogenation ability of this catalyst, since these nitrogen molecules should be hydrogenated before the HDN reaction. These results were also corroborated by GPC-DAD analyses which indicate a lower absorbance for the upgraded bio-oil over sulfide catalyst which is associated with a lower degree of aromaticity of this sample.The HHV increased from 36 MJ/kg in the HTL micro–algal bio-oil to 47 MJ/kg in the upgraded bio-oil over sulfide catalyst, and the average molar mass reduced from 363 to 265 g/mol indicating that heavy molecules were converted during the upgrading step