Understanding the effects of feedstock blending and catalyst support on hydrotreatment of algae HTL biocrude with non-edible vegetable oil

Abstract

The performance of cobalt-molybdenum (CoMo) on hydrotreating of algae HTL biocrude and carinata oil was investigated. Commercial CoMo/Al2O3 (CoMo/Al) and synthesized CoMo supported on Douglas fir biochar (CoMo/DF), sulfided or unsulfided catalysts, were compared for hydrodeoxygenation (HDO), hydrodenitrogenation (HDN), hydrodesulfurization (HDS) and hydrodemetallization (HDM) reactions. Results showed that there lies a synergistic effect when HTL algae biocrude and carinata oil blends are hydrotreated. The yield of the upgraded blend (UB) oils retrieved over alumina catalyst was higher than the individual hydrotreated parent oils. For example, a 9% and 5% increase in yield was noted compared to the average of individual hydrotreated parent oils. The UB produced from sulfided CoMo/Al exhibited superior HDO activity primarily by decarbonylation. This was apparent in increased heating value, carbon addition, higher octane number, and lower total acid number than the oils obtained from the biochar-supported catalysts. Sulfided CoMo/DF catalyzed cracking reactions which lowered the viscosity, followed by high HDN and HDS activity compared to the commercial catalyst. The two supports showed different sorption behaviors. Interestingly, CoMo/DF had an effective sorption mechanism that helped in higher metal removal from the oil. Additionally, presulfiding and DF support exhibited positive results in term of less coke formation. In brief, biochar supports have higher acidic sites, inorganic mineral oxides, ion exchange capacity, high surface area, pore structure and connectivity. All of these make a substantial contribution to its unique catalytic behavior.