Co-Pyrolysis of Biomass and Plastics: Fundamentals and Process Design for Circular Economy Applications

Biomass–plastic co-pyrolysis has emerged as a promising thermochemical route for the valorization of mixed biomass and plastic waste streams, addressing growing challenges in waste management and resource efficiency. This review summarizes current knowledge on feedstock interactions, reactor technologies, operating conditions, and resulting product distributions. The literature indicates that co-processing biomass with plastics can enhance process performance compared to single-feedstock pyrolysis. Improvements are mainly observed in liquid product quality, increased energy content of gaseous fractions, and modified char properties, although outcomes strongly depend on feedstock composition and process conditions. Beyond technical aspects, the review highlights the relevance of co-pyrolysis within circular economy systems. Oil can be considered a secondary feedstock for the refining and chemical industries, process gas can support internal energy integration, and char may be utilized in material or environmental applications, contributing to partial closure of carbon and resource loops. Despite these advantages, the transition from laboratory-scale studies to large-scale implementation remains the major challenge for biomass–plastic co-pyrolysis. This limitation is associated with feedstock heterogeneity, contamination issues, scale-up difficulties, regulatory uncertainty, and the need for downstream upgrading of products. Overall, biomass–plastic co-pyrolysis represents a promising pathway toward circular waste valorization, but its practical relevance depends on successful system-level integration rather than laboratory-scale performance alone.