From Biomass to Fuel Blendstocks via Catalytic Fast Pyrolysis and Hydrotreating: An Evaluation of Carbon Efficiency and Fuel Properties for Three Pathways.

Biomass was upgraded to fuel blendstocks via catalytic fast pyrolysis (CFP) followed by hydrotreating using three approaches: ex situ CFP with a zeolite catalyst (HZSM-5), ex situ CFP with a hydrodeoxygenation catalyst (Pt/TiO) and cofed hydrogen, and in situ CFP with a low-cost mixed metal oxide catalyst (red mud). Each approach was evaluated using a common pine feedstock and the same hydrotreating procedure. The oxygen contents in the CFP oils ranged from 17 to 28 wt % on a dry basis, and the carbon efficiencies for the CFP processes were in the range of 28-38%. The residual oxygen was reduced to <1 wt % during hydrotreating, which was operated for 104-140 h for each CFP oil without plugging issues. The hydrotreating carbon efficiencies were 81-93%. The CFP pathway with the hydrodeoxygenation catalyst gave the highest overall carbon efficiency from biomass to fuel blendstocks (34%) but, at the same time, also the highest cumulative hydrogen consumption during CFP and hydrotreating. The zeolite pathway produced the largest fraction boiling in the gasoline range and the highest estimated octane number due to the high aromatic content in that CFP oil. The in situ red mud pathway produced the largest fraction of diesel-range products with the highest derived cetane number. However, advances in the CFP and hydrotreating process are required to improve the fuel blendstock properties for all pathways.