Advance in Hydrothermal Bio-Oil Preparation from Lignocellulose: Effect of Raw Materials and Their Tissue Structures

The conversion of abundant forest- and agricultural-residue-based lignocellulosic materials into high-quality bio-oil by the mild hydrothermal method has great potential in the field of biomass utilization. Some excellent research on biomass hydrothermal process has been completed, including temperature, time, catalyst addition, etc. Meanwhile, some research related to the biomass raw material tissue structure has been illustrated by adopting mode components (cellulose, hemicellulose, lignin, protein, lipid, etc.) or their mixtures. The interesting fact is that although some real lignocellulose has approximate composition, their hydrothermal products and distributions show individual differences, which means the interaction within biomass raw material components tremendously affected the reaction pathway. Unfortunately, to our knowledge, there is no review article with a specific focus on the effects of raw materials and their tissue structure on the lignocellulose hydrothermal process. In this review, research progress on the effects of model and mixed cellulose/hemicellulose/lignin effects on hydrothermal products is initially summarized. Additionally, the real lignocellulosic raw materials structure effects during the thermal process are summed up. This article will inspire researchers to focus more attention on wood fiber biomass conversion into liquid fuels or high-value-added chemicals, as well as promote the development of world energy change.