Advances in Effects of Torrefaction Pretreatment on Catalytic Copyrolysis of Biomass and Plastics: A State-of-the-Art Review

Amid rising energy scarcity and ecological challenges, catalytic copyrolysis of biomass and plastic waste is now considered a key strategy to transform solid residues into clean fuels and high-value chemicals. However, the inherent limitations of raw biomass hinder the synergistic effects and industrial viability of this process. Torrefaction, a mild thermochemical pretreatment conducted at 200–300 °C, serves as a critical enabling step for optimizing catalytic copyrolysis. This review summarizes recent advances in understanding how torrefaction influences the catalytic copyrolysis of biomass and plastics, focusing on the effects of torrefaction alone and of coupled torrefaction–catalytic treatments on reaction behavior, synergistic effects, product distribution, and product quality. The mechanisms by which torrefaction enhances copyrolysis and interacts with catalysts are also elucidated. It is concluded that torrefaction significantly strengthens the synergistic effect in copyrolysis, and the coupled torrefaction–catalysis approach further improves the selectivity toward high-value-added products while mitigating catalyst deactivation. Finally, considering current research gaps, future research directions are proposed to guide the optimization, scale-up, and widespread adoption of this technology.