ReviewHydrothermal liquefaction of agricultural and forestry wastes: state-of-the-art review and future prospects

- Combining HTL with subsequent technologies should be an important research direction.
- Formic acid and formaldehyde are promising reagent for lignin depolymerization.
- A breakthrough is needed in the development of new materials for advanced reactor.
- Finding multifunctional catalysts is important for cutting down energy consumption.
- Novel technologies for bio-oil refining and upgrading should be developed.

Hydrothermal liquefaction has been widely applied to obtain bioenergy and high-value chemicals from biomass in the presence of a solvent at moderate to high temperature (200-550 °C) and pressure (5-25 MPa). This article summarizes and discusses the conversion of agricultural and forestry wastes by hydrothermal liquefaction. The history and development of hydrothermal liquefaction technology for lignocellulosic biomass are briefly introduced. The research status in hydrothermal liquefaction of agricultural and forestry wastes is critically reviewed, particularly for the effects of liquefaction conditions on bio-oil yield and the decomposition mechanisms of main components in biomass. The limitations of hydrothermal liquefaction of agricultural and forestry wastes are discussed, and future research priorities are proposed.