Synergistic effects of biomass building blocks on pyrolysis gas and bio-oil formation

Abstract

Before biobased fuels can replace fossil fuels, several key issues must be addressed. Bio-oils derived through pyrolysis of lignocellulosic material have high acidity and viscosity, and poor energy density and stability. To address these issues, this paper examines the individual and combined behavior of lignocellulosic feedstock components to shed light on the potential to generate preferential biofuel properties through biomass mixing. Dry lignocellulosic biomass is mostly composed of cell wall polysaccharides (cellulose, hemicellulose, lignin), which vary widely in type and concentration across biomasses. This heterogeneity leads to increased unpredictability in biobased fuel formation during pyrolysis. Using derivative thermogravimetric (DTG) analysis, gas chromatography-mass spectroscopy, and residual gas analysis, this work explores the synergistic interactions of lignocellulosic biomass components during pyrolysis to manipulate bio-oil and gas product composition based on desired compound classes. Cellulose, xylose, xylan, and lignin were blended at different ratios to determine the extent of synergistic effects during pyrolysis. For each mixture, an ‘expected’ outcome was developed by summing the individual behavior (e.g. mass loss rate, H2 gas evolution, etc.) of the individual components based on mass fraction present. Mixtures containing lignin and/or xylan yield peak DTG mass loss rates at lower temperatures than predicted with corresponding reductions in biochar yield suggesting synergistic interactions that promote devolatilization. By itself, lignin produces large amounts of hydrogen gas, and when mixed with other biomasses promotes dehydrogenation. Lignin increases CO2 formation, resulting in lower oxygen concentrations in the bio-oil and biochar. While suppressing bio-oil generation, the presence of lignin – even at low concentrations – increases the number of phenol compounds produced, while decreasing the yield of furans. The synergistic interactions between different polysaccharides could be exploited depending on the desired biorefinery products – allowing for targeted selection of lignocellulosic biomass mixes to fine-tune resulting fuels.