Hydrotreatment Upgrading of Hydrothermal Liquefaction Biocrude toward Advanced Fuels: A State-of-the-Art Review

Abstract

The nonrenewable resource depletion and associated environmental concerns have intensified research into advanced biofuel technologies. Biomass-derived biofuels present a promising solution for meeting energy needs while supporting a circular economy and reducing carbon emissions. Among the various conversion methods, hydrothermal liquefaction (HTL) has attracted significant attention due to its ability to process both wet and dry biomass feedstocks into a liquid biocrude product. Although this biocrude exhibits improved characteristics compared with raw biomass, it still requires further upgrading prior to its use as a fuel or refinery intermediate. Catalytic hydrotreating is a crucial process for upgrading HTL biocrude, improving its stability, reducing the oxygen content, and enhancing overall fuel quality. Recent research has focused on optimizing hydrotreating processes using both batch and continuous-reactor systems. This Review provides a comprehensive overview of current advancements in HTL biocrude upgrading through catalytic hydrotreatment. It examines various biomass feedstocks to understand how their compositions affect hydrotreatment efficiency and final product outcomes. Additionally, it discusses commonly used catalysts and evaluates the influence of key operating conditions, such as temperature, pressure, and reaction time, on the product quality. By compiling and analyzing existing experimental data, this Review aims to fill the gap in dedicated literature on HTL biocrude upgrading. Ultimately, it offers practical guidelines and a technological assessment to support future research and development in sustainable biofuel production.