Catalytic upgrading of pretreated algal oil with a two-component catalyst mixture in supercritical water

Abstract

Single-component catalysts present opportunities and challenges for upgrading crude algal bio-oil in supercritical water. Herein, we report the coordination of the action of two heterogeneous catalysts to upgrade pretreated algal oil to a hydrocarbon-rich fuel. The activities of several different catalyst mixtures for hydrothermal hydrodeoxygenation and hydrodenitrogenation of pretreated algal oil at 400°C for 4h were determined in a batch reactor. The yield of upgraded oil produced using each catalyst mixture ranged from a low of 63.2wt.% in the Ru/C+Rh/γ-Al2O3-catalyzed reaction to a high of 77.2wt.% in the Ru/C+Mo2C-catalyzed reaction. Coke production was controlled in the presence of most of the two-component catalyst mixtures under these hydrothermal conditions. All the two-component mixtures exhibited excellent performance with respect to deoxygenation, denitrogenation, and, in particular, desulfurization. Ru/C+Mo2C, Ru/C+Pt/γ-Al2O3, and Ru/C+Pt/C performed best with respect to deoxygenation, denitrogenation, and desulfurization and produced upgraded oils with O, N and S contents of 0.1, 1.8, and 0.065wt.%, respectively. The upgraded oil produced with Ru/C+Mo2C retained 89.7% of the heating value of the original pretreated oil and contained 98.5% of the material boiling below 450°C. The upgraded oils consisted mainly of saturated hydrocarbons, which accounted for no less than 40% of the total peak area for the majority of the oils. Thus, we view the two-component catalyst mixture as a promising strategy for upgrading bio-oils derived from microalgae.