Microwave catalytic pyrolysis of biomass: a review focusing on absorbents and catalysts

Abstract

The quest for low-carbon alternatives to fossil fuels and the carbon emissions associated with the natural degradation of biomass have accelerated the development of biomass processing technologies. Microwave catalytic pyrolysis is emerging as a technology for efficient conversion of biomass into energy, fuels and chemicals. However, due to the inherent poor dielectric properties and complex composition of biomass, two main technical challenges faced by microwave catalytic pyrolysis of biomass are efficient heating of biomass and improving the selectivity of target products. Potential solutions involve the use of microwave absorbents and catalysts, respectively. This review begins by addressing the difficulty in balancing energy efficiency and conversion efficiency by introducing microwave absorbents that play a positive role in improving heating efficiency. The principle of microwave absorbents in assisting biomass heating is revealed, and the impacts of the microwave absorbent type (related to microwave properties and physical properties) and the additive amount on the heating effect and biomass pyrolysis product distribution are discussed. Subsequently, the search for catalysts applied in biomass microwave pyrolysis for modulation of product distribution is explored. Special attention has been paid to the catalysts with microwave absorption properties, including activated carbon, zeolites, some metal oxides and metal salts. In addition, the energy efficiency, economic feasibility, and environmental impacts of this processing technology utilizing microwave absorbents and catalysts are examined based on energy analysis, techno-economic assessment, and life cycle assessment. The current scale-up challenges of microwave catalytic pyrolysis of biomass and some potential solutions to enhance the commercial feasibility of this technology are also discussed. Finally, the review provides some future development directions of this technology.