Catalytic Conversion of Coal and Biomass Volatiles: A Review

This paper presents a review of recent research on direct upgrading of coal/biomass volatiles into aromatics by catalytic pyrolysis and syngas by gasification with catalytic steam reforming. Coal/biomass valorization is considered an important part to fill up the depletion of modern fossil fuel resources. The catalytic pyrolysis process is a potential approach to improve coal tar/bio-oil quality by minimizing its undesirable properties (high viscosity, corrosivity, instability, etc.) and producing renewable fuels and high-value chemicals, such as aromatics (benzene, toluene, ethylbenzene, xylenes, etc.). Gasification reforming as a promising process for renewable energy utilization can produce H2-rich syngas. The produced syngas can be further synthesized to fuel and chemicals via Fischer–Tropsch synthesis. Thus, this study provides a comprehensive review of the research and development of conversion of coal and biomass volatiles in terms of technological types and catalysts. Aspects related to upgrading technology, the reactor type of catalytic pyrolysis and gasification, and the reaction mechanisms to specific products during the catalytic process are also discussed comprehensively. In particular, catalytic upgrading by fast pyrolysis involves a series of reactions, including deoxygenation, cracking, hydrocarbon pool mechanism, aromatization, and condensation, as well as desulfurization and denitrification in the gasification process. Some key points that are to be addressed for the established process of coal and biomass volatile upgrading may include finding multifunctional catalysts and reactor development for improving the efficiency. Expanding and enhancing knowledge about catalyst utilization and fundamental reaction mechanisms in the thermochemical catalytic conversion technologies of coal and biomass will play an important role in the generation of chemicals and carbon-neutral fuels.