Hydrothermal liquefaction for preparation of liquid fuels and chemicals: Solvent effects, catalysts regulation and thermochemical conversion processes

Hydrothermal liquefaction technology is an effective method for the resource utilization and energy conversion of biomass under the dual-carbon context, facilitating the conversion of biomass into liquid fuels and high-value chemicals. This paper reviews the latest advancements in the production of liquid fuels and chemicals from biomass hydrothermal liquefaction. It briefly introduces the effects of different types of biomass, such as organic waste, lignocellulosic materials, and algae, on the conversion efficiency and product yield during hydrothermal liquefaction. The specific mechanisms of solvent and catalyst systems in the hydrothermal liquefaction process are analyzed in detail. Compared to water and organic solvents, the biphasic solvent system yields higher concentrations of furan platform compounds, and the addition of an appropriate amount of NaCl to the solvent significantly enhances product yield. Homogeneous catalysts exhibit advantages in reaction rate and selectivity but are limited by high costs and difficulties in separation and recovery. In contrast, heterogeneous catalysts possess good separability and regeneration capabilities and can operate under high-temperature conditions, but their mass transfer efficiency and deactivation issues may affect catalytic performance. The direct hydrothermal catalytic conversion of biomass is also discussed for the efficient production of chemicals and fuels such as hexanol, ethylene glycol, lactic acid, and C₅/C₆ liquid alkanes. Finally, the advantages and current challenges of producing liquid fuels and chemicals from biomass hydrothermal liquefaction are thoroughly analyzed, along with potential future research directions.