Mechanisms of Low-Temperature Processes of Biomass Conversion (A Review)

Torrefaction and hydrothermal carbonization are low-temperature thermochemical procedures for the biomass conversion to biocoal, a carbon-neutral analog of fossil coal. Biocoals, compared to untreated biomass, exhibit hydrophobic properties, increased energy density, and calorific value similar to that of brown coals. The two processing methods differ essentially in that hydrothermal carbonization is performed in the presence of a large amount of water as reaction medium; hence, the biocoal formation mechanisms will be different for each process. Papers dealing with specific features of low-temperature heat treatment of biomass and with regular trends in conversion of biomass structural components (cellulose, hemicellulose, lignin) in the course of torrefaction and hydrothermal carbonization are considered in the review.

Automated summary

Torrefaction and hydrothermal carbonization are low-temperature thermochemical procedures that convert biomass into biocoal, which is a carbon-neutral alternative to fossil coal. Biocoals have hydrophobic properties, increased energy density, and similar calorific value to brown coals compared to untreated biomass. The formation mechanisms of biocoal differ between the two processes due to the presence of a large amount of water in hydrothermal carbonization. This review focuses on papers discussing specific features of low-temperature heat treatment of biomass and the conversion trends of biomass structural components (cellulose, hemicellulose, lignin) during torrefaction and hydrothermal carbonization.