Hydrothermal treatment of lignocellulosic biomass towards low-carbon development: Production of high-value-added bioproducts

The comprehensive and efficient utilization of lignocellulosic biomass is of great significance to humanity due to its low-carbon and sustainable characteristics. Hydrothermal treatment is a low-carbon technology for the valorization of lignocellulosic biomass toward diverse value-added bioproducts through the disintegration and conversion of lignocellulosic biomasses. This review first introduces the chemical compositions of lignocellulosic biomasses and the operating principles of hydrothermal treatment. Then, the transformation of the chemical compositions during hydrothermal treatment (<300 °C) is elucidated comprehensively. In addition, the recent advances in the hydrothermal valorization of lignocellulosic biomass into bio-oil, wood vinegar, briquette fuels, absorbents, carbonaceous electrode materials, and catalysts are introduced and discussed emphatically. The bridge between the hydrothermal treatment and the physicochemical properties and performances of the obtained value-added bioproducts is further built. The precise removal of chemical compositions and the followed directional conversion are the keys affecting the structure and physiochemical properties of the bioproducts. It is difficult to regulate the extraction and decomposition of chemical compositions in one step because of the heterogeneous structure and recalcitrant cross-linking barrier of lignocellulosic biomass. In this regard, a multi-step process is promising undoubtedly, while tailoring the specific application is necessary for industrialization due to the diversity of bioproducts. The future direction of fully efficient utilization of lignocellulosic biomass is proposed for the researches on the multipurpose valorization of high-value-added bioproducts. We believe this review would provide valuable guidance for the exploitation of biomass-derived high-value-added bioproducts through multipurpose production processes, ideally towards the achievement of a low-carbon blueprint.