Acid, Steam Explosion, and Washing Pretreatment Impacts on Sustainable Biocrude Production via Hydrothermal Liquefaction of Canadian Lignocellulosic Residues

The impact of acid, steam explosion, and washing pretreatments on seven underutilized Canadian lignocellulosic residues was investigated via noncatalytic and catalytic hydrothermal liquefaction (HTL) for biocrude production. Washing was detrimental to biocrude production as it removed both catalytic components and those necessary for biocrude formation. Acid and steam explosion pretreatments primarily degraded hemicellulose. Acid pretreatment at 50 °C, 1 wt % H2SO4, and 4 h, with Fe+K2CO3 HTL catalyst was determined optimal with pine, observing the largest increase in biocrude yield by 13.7 wt %. While the impact on yield was moderate for lower lignin residues (−2.0 to +2.3 wt %), acid pretreatment with catalyst led to a significant oxygen reduction (up to 5.6 wt %), enhancing biocrude quality across most feedstocks. The effectiveness of steam explosion was reduced due to the loss of desirable volatile compounds during pretreatment (up to 16.0 wt %). Hydrocarbon-precursor phenols, carboxylic acids, and ketones were the major biocrude components across experiments. Although acid pretreatment improved biocrude oil production, the overall advantages were questionable due to complexity, energy, and environmental concerns. This study contributes to enhancing the viability of meeting Canadian low-carbon fuel standards through agro-forestry biocrude integration with refineries.