Waste from scrap tyres, due to its high volume (17 million Mg per year) and durability resulting from the physical and chemical properties, requires innovative approaches for efficient and environmentally friendly management. In many countries, the landfilling of waste tyres is banned (e.g., EU, USA, UK); however, waste tyres can be a source of valuable materials such as carbon black, pyrolysis oil, hydrogen-rich syngas, tyre char, as well as energy. The purpose of this article is to provide a synthesis of the state of knowledge regarding the thermal conversion of waste tyres by pyrolysis and gasification, taking into account the use of different measurement techniques and reactor types. These technologies are forward-looking and have a high degree of flexibility in terms of product sourcing, depending on the process conditions. The properties of waste from used tyres were analysed, i.e., the composition of the content of individual components and the main chemical substances. The results encompassed ultimate and proximate analyses of rubber from tyres, as well as the physical and chemical parameters of the tyre char obtained through pyrolysis. This article compiles available literature data regarding the impact of process and raw material parameters, such as temperature and time conditions, pressure, particle size, and catalyst addition on the pyrolysis and gasification processes. It also explores the influence of these factors on the yield and properties of the products, including pyrolysis oil, gas, synthesis gas, and tyre char.

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.