PNNL

Abstract

Catalytic fast pyrolysis (CFP) has emerged as an attractive process for the conversion of lignocellulosic biomass into renewable fuels and products. Considerable research and development has focused on using circulating bed reactors with zeolite catalysts (e.g., HZSM-5) for CFP because of their propensity to form gasoline range aromatic hydrocarbons. However, the high selectivity to aromatics comes at the expense of low carbon yield, a key economic driver for this process. In this contribution, we shift away from zeolites to evaluate bifunctional metal-acid catalysts in a fixed-bed reactor configuration for an integrated CFP process to produce fuel blendstocks from lignocellulosic biomass. These experimental efforts are coupled with technoeconomic analysis (TEA) to benchmark the process and guide research and development activities to minimize costs. The results indicate that CFP bio-oil can be produced from pine with improved yield by using a bifunctional 2 wt% Pt/TiO2 catalyst in a fixed-bed reactor operated with co-fed H2 at near atmospheric pressure, as compared to H-ZSM5 in a circulating bed reactor. The Pt/TiO2 catalyst exhibited good stability over 13 reaction-regeneration cycles with no evidence of irreversible deactivation. The CFP bio-oil was effectively hydrotreated for 140 h time on stream using a single-stage system, and 84% of the hydrotreated product had boiling points in the gasoline and distillate range. The integrated biomass to blendstock process was determined to exhibit an energy efficiency of 50% and a normalized carbon efficiency of 38%, based on the experimental results and Aspen Plus process modelling. TEA of the integrated process revealed a modelled minimum fuel selling price (MFSP) of $4.34 per gasoline gallon equivalent (GGE), which represents a cost reduction of $0.85 GGE-1 compared to a value of $5.19 GGE-1 which has been reported for CFP with a zeolite catalyst. TEA also indicated that catalyst cost was a significant factor influencing the MFSP, which informed additional CFP experiments in which lower-cost Mo2C and highly-dispersed 0.5 wt% Pt/TiO2 catalysts were synthesized and evaluated. These materials demonstrated similar CFP carbon yield and oil oxygen content to the 2 wt% Pt/TiO2 catalyst, offering proof-of-concept that the lower-cost catalysts can be effective for CFP and providing a route to reduce the modelled MFSP to $3.86-3.91 GGE-1. This report links foundational science and applied engineering to demonstrate the potential of fixed-bed CFP and highlights the impact of coupled TEA to guide research activities towards cost reductions.