The Use of Biomass Ash as a Catalyst in the Gasification Process—A Review

Biomass plays an important role in the energy transformation aimed at carbon neutrality, with its potential estimated at 1/3rd of the entire energy mix. One of the main ways of using biomass is combustion or co-combustion, which enables the production of heat and electricity while maintaining low emissions. A promising path to utilize the combustion by-product—ash—is the possibility of using it as a natural and cheap catalyst that can effectively support the process of solid fuel gasification. This paper reviews scientific studies on the properties of biomass ash and its use to support the gasification process. The issues related to the genesis of mineral matter in plants are presented, emphasizing the importance of its transformations during biomass combustion. Particular emphasis is placed on the characterization of biomass ash, which was carried out on the basis of a comprehensive overview of the results regarding its chemical composition. An analysis of the physicochemical and surface properties relevant to the use of biomass ashes as catalysts in the gasification process was performed. In addition, a review of studies on catalytic gasification of solid fuels using biomass ash was conducted, taking into account the impact of biomass ash on the most important parameters characterizing the course of the gasification reaction, i.e., reactivity, quality of the gaseous products, and the kinetics reaction. The summary compares the most important advantages and disadvantages of using biomass ashes in the gasification process along with recommendations for future research.