Hydrodeoxygenation of microalgae oil to green diesel over Pt, Rh and presulfided NiMo catalysts

Abstract

The catalytic characteristics, activity and selectivity of 1% Pt/Al₂O₃, 0.5% Rh/Al₂O₃ and presulfided NiMo/Al₂O₃ catalysts have been investigated in the hydrodeoxygenation of microalgae (Nannochloropsis salina) oil to produce green diesel in a microreactor. Coke accumulation decreased in the order NiMo > Pt > Rh. The amount of formed coke over NiMo increased with reaction duration, while no on-stream time dependence was found over Pt and Rh. Rhodium was found to be very active for CH₄ production via hydrocracking at its freshly reduced state. The activity and selectivity of all three investigated catalysts were positively affected by increased reaction pressure, temperature, H₂/oil ratio and residence time. The selectivity of NiMo for the hydrodehydration (DHYD) route was changed to a hydrodecarbonylation/hydrodecarboxylation (DCO/DCO2) route at a reduced H₂/oil ratio and residence time, while the selectivity of Pt and Rh for the DCO/DCO2 route was not affected by the reaction conditions. The highest hydrocarbon yield, 76.5%, was obtained over 1% Pt (310 °C, 500 psig, 1000 SmL mL⁻¹ gas/oil ratio, 1.5 s residence time), which is 13.8% higher than that over NiMo (360 °C, 500 psig, 1000 SmL mL⁻¹ gas/oil ratio, 1 s residence time). The 50 °C decrease in the reaction temperature for Pt indicates possible energy saving via heat supply.