Mechanisms of thermochemical biomass conversion processes. Part 3: Reactions of liquefaction

This article reviews the liquefaction mechanisms of biomass structural constituents. One pivotal study of such liquefaction processes was done in the 1970s funded by the Bureau of Mines of the United States. Liquefaction is a low-temperature, high-pressure thermochemical process using a catalyst. The process produces a marketable liquid product. In the case of liquefaction, macromolecule compounds in biomass are degraded into small molecules with or without catalyst in the aqueous medium or using organic solvent. Thus, obtained small molecules are unstable and reactive and can repolymerize into oily products with a wide range of molecular weight distribution. In the liquefaction process, the micellar-like broken-down fragments produced by hydrolysis are degraded to smaller compounds by dehydration, dehydrogenation, deoxygenation, and decarboxylation. These compounds once produced, rearrange through condensation, cyclization, and polymerization, leading to new compounds. Thermal depolymerization and decomposition of biomass, cellulose, hemicelluloses, and products were formed as well as a solid residue of charcoal.