CO-TORREFACTION OF BIOMASS AND PLASTIC WASTE: RECENT ADVANCES AND CIRCULAR ECONOMY PERSPECTIVES

Abstract

The increasing problem of biomass residues from agriculture and plastic waste presents a challenge for sustainable waste management practices, which have to tackle issues of pollution and renewable energy production at the same time. Co-torrefaction is a new thermochemical pretreatment technique which shows potential in transforming these heterogeneous waste streams into energy-dense carbon-rich solid fuels that have improved physicochemical properties. It critically analyzes recent progresses in biomass–plastic co-torrefaction, considering the feedstock characteristics, thermal degradation mechanisms, synergistic interactions, reactor technologies, optimization of the process, characterization of the products and practical applications. Special attention is given on the effect of the process parameters such as temperature, residence time, biomass-to-plastic ratio and reactor configuration on the quality of the fuel, carbon retention, hydrophobicity, energy densification, and combustion performance. The review also underscores the potential of catalytic systems, microwave-assisted torrefaction, and data-driven optimization techniques to enhance the efficiency and quality of the torrefaction process. Furthermore, the different applications of co-torrefied products as solid biofuels, as gasification and pyrolysis bio-feedstocks, as activated carbons and as advanced carbon materials are discussed in detail. Circular economy principles, life-cycle assessment and techno-economic analysis, highlight the potential of co-torrefaction for resource recovery, and for minimizing reliance on fossil fuels, while achieving environmental sustainability. Although great advances have been made, problems with feedstocks that are not completely homogeneous, scaling up the reactor, durability of the catalysts, standardization of the products, and commercialization are not solved. Intelligent process control, further development of the reactors, standardized quality assessment and integration with the new waste-to-energy technologies should be addressed in future research. In conclusion, biomass–plastic co-torrefaction is a promising and sustainable option for waste valorization, offering numerous benefits such as reduced reliance on fossil fuels and the creation of renewable energy.