Recent progress in the direct liquefaction of typical biomass

Energy from biomass, bioenergy, is a promising source to replace fossil fuels in the future, as it is abundant, clean, and carbon dioxide neutral. Thermochemical liquefaction of biomass is widely investigated as a promising method to produce one kind of liquid biofuel, namely bio-oil. This review presents the recent research progress in the liquefaction of typical biomass from a new perspective. Particularly, this article summarizes five aspects of related work: first, the effect of solvent type on the liquefaction behaviors of biomass; second, the effect of biomass type on the liquefaction behaviors of biomass; third, the liquefaction of biomass in sub-/super-critical ethanol; fourth, the liquefaction of biomass in organic solvent–water mixed solvents; fifth, the liquefaction of sewage sludge. Meanwhile, the research advance in the migration and transformation behavior of heavy metals during the liquefaction of sewage sludge was also summarized in this review. This review can offer an important reference for the study of biomass liquefaction.