Biocrude production via hydrothermal liquefaction of Canadian lignocellulosic residues for sustainable transportation: screening, catalytic effect, and modelling†

Abstract

Ten Canadian-grown lignocellulosic agro-forestry residues were screened for non-catalytic, catalytic, and composition effects in biocrude production via hydrothermal liquefaction. Evaluation of Canadian agricultural residue availability indicated a significant variation, with wheat straw determined to be the most abundant at 38.3 million metric tonnes annually, while flax straw and dried distillers' grains had limited availability for a hypothetical biorefinery. Comparing K₂CO₃ + Fe catalyst and non-catalytic screening revealed a pronounced catalytic effect for softwoods over straws and hardwood due to higher lignin content. Trends included increase in biocrude and oxygen content with holocellulose, while higher lignin tended to decrease oxygen content of the biocrude. Catalytically, pig manure performed poorly with the lowest biocrude yield (9.3 wt%) while dried distillers' grains was desired due to high biocrude yield (25.3 wt%) with the lowest oxygen content (10.2 wt%). Barley among straws and aspen among woods were promising based on high catalytic biocrude yields (23.3 & 26.5 wt%) and moderate oxygen content (20.8 & 21.4 wt%). Catalytic effects for both straw and wood included changes to product yields, increase in degree of degradation, energy recovery, and biocrude volatility, as well as a decrease in biocrude acidity, density, and heteroatoms. A fibre-based multiple linear regression model had a strong fit (R²_adjusted = 0.87) for catalytic biocrude yield, with positive contribution in the order of extractives > cellulose > hemicellulose > lignin, while volatile matter had the strongest individual correlation to catalytic biocrude yield (R² = 0.94). Next steps in HTL optimization and biocrude upgrading were identified to advance the feasibility of lignocellulosic biocrude production for sustainable transportation fuel production through integration with existing crude oil refineries.