Preliminary catalyst screening for solvothermal liquefaction of biomass model compounds: Coupling experimental evaluation with techno-economic and life-cycle assessment

The conversion of organic waste into renewable fuels is increasingly explored as a strategy to reduce greenhouse gas emissions and improve resource use. Among the conversion technologies, solvothermal liquefaction (STL) has gained growing attention as a method for producing energy-dense biocrude from biomass under relatively moderate operating conditions. In this study, representative biomass model compounds were used to comparatively investigate the influence of heterogeneous catalysts during ethanol-assisted STL. Glucose, L-phenylalanine, oleic acid, and syringaldehyde were selected as representatives of carbohydrates, proteins, lipids, and lignin, respectively. Experiments were conducted at 270 °C for 30 min using Pt/Al 2 O 3 , Ni/SiO 2 -Al 2 O 3 , and CoO-MoO 3 /Al 2 O 3 catalysts. Biocrude yields varied strongly with feedstock type, with oleic acid producing the highest yield (∼56 wt%) and glucose the lowest (∼9 wt%), for the selected Ni/SiO₂-Al₂O₃ catalyst. Among the investigated systems, Ni/SiO 2 -Al 2 O 3 showed comparatively higher mean biocrude energy recovery under the investigated conditions. The experimental results were subsequently used for preliminary process simulation, techno-economic assessment, and life-cycle assessment. Aspen Plus simulations indicated minimum selling prices ranging from 3.4 to 7.25 USD/kg biocrude depending on the representative feedstock scenario, while the environmental assessment suggested comparatively lower impacts for lipid- and lignin-derived pathways than for protein-based systems. This work therefore provides a preliminary assessment of catalyst and feedstock effects during STL and highlights the importance of feedstock composition in determining process performance.