Co-pyrolysis of biomass and plastic wastes: A review on reactants synergy, catalyst impact, process parameter, hydrocarbon fuel potential, COVID-19

Unprecedented growth in mixed plastic and biomass wastes such as plastic bags, drinking water bottles, agro-and-forestry-waste, along with COVID-19 driven waste (facemask, gloves, PPE kits, surgical masks) have obliged the scientific community to look for technologies that can process and convert both biomass and plastic wastes together into useful end-products. The co-pyrolysis of biomass and plastic would be promising as it may produce a high-quality liquid fuel (hydrocarbon-rich bio-oil) because of the synergy between the two reactants. Notably, the addition of catalysts in a co-pyrolysis process facilitates multiple parallel reactions such as depolymerization, dehydration, deoxygenation, hydrogenation, hydrodeoxygenation, aromatization, and condensation. As a result, hydrocarbon-rich bio-oil, suitable for direct use/blend in the existing fuel, is produced. This review critically discussed the progress and opportunities of co-pyrolysis for the processing of biomass and plastics wastes. Synergistic effects of biomass and plastic during co-pyrolysis, with and without catalyst, are discussed and correlated with the final product yields. Several commercial, naturally occurring metal salts, and anthropogenic catalysts affecting bio-oil yield and composition are reviewed. The mechanistic insight into biomass/plastic thermal decomposition is presented and compared with those under the catalytic environment. Finally, the process parameters and techno-economic analysis of the biomass and plastic co-pyrolysis, including COVID-19 waste handling, are discussed. Co-pyrolysis advised as a promising route for biomass and COVID-19 waste processing and hence management.