Co-pyrolysis of biomass and plastic waste into carbon materials with environmental applications: a critical review†

The urgent need for global energy transformation and environmental protection, combined with widespread plastic contamination, has stimulated research into the co-pyrolysis of biomass and plastic waste. This approach challenges traditional resource utilization methods and opens new pathways for sustainable energy generation and waste management. The reaction processes and mechanisms of both biomass pyrolysis and various plastic wastes are comprehensively examined. The influences of co-processing parameters on the composition, content, and product characteristics are analysed, providing a solid theoretical foundation for the large-scale production and application of co-pyrolysis. Besides the potential problems related to plastic co-pyrolysis, the enhancement of carbon materials’ properties by plastic waste in co-pyrolysis is also explored, which is significant for the functionalization of carbon materials. The reaction mechanism, reaction process, reaction conditions, and products generated from the co-pyrolysis of biomass and plastic waste are discussed. In the co-pyrolysis of biomass (especially lignocellulosic biomass) and plastic waste, PET, PU, and PVC are more conducive to the production of carbon materials, while PP, PE, and PS are more favourable for the generation of bio-oils. The interaction between the hydroxyl radicals provided by biomass and the hydrogen radicals provided by plastic waste enhances the reaction. Slow co-pyrolysis at 500 °C, a feedstock ratio of 3 : 1 (biomass to plastic waste), and a suitable catalyst (such as zeolites) are more beneficial for carbon materials in terms of the yield, porosity, and production rate. Co-pyrolysis carbon materials possess superior hydrophobicity and adsorption properties compared to conventional carbon materials and can be enriched in elements often absent from the original carbon materials, such as nitrogen. These potential advantages of co-pyrolyzing plastics with biomass open new prospects beyond waste management, such as enhanced material development for a range of environmental and agricultural applications.