Unraveling the synergistic mechanism of lignin/polyethylene (PE) co-pyrolysis: A multi-scale exploration combining experiments, kinetics and ReaxFF-MD simulations

To address the growing challenges of energy crisis and white pollution, co-pyrolysis of lignin and plastics facilitates both biomass resource valorization and pollution mitigation. To gain deeper insight into the synergistic mechanism, this study combined experiments, kinetic analyses, and molecular simulations to systematically investigate the product distributions and bond-breaking behaviors during lignin/PE co-pyrolysis at multiple scales. The kinetic investigation demonstrated that lignin and PE interaction exhibited a positive synergistic effect, significantly lowering the activation energy. Moreover, adding PE promoted the formation of oxygen-free tar while suppressing oxygen-containing tar, consequently enhancing the fuel properties of pyrolysis tar. In parallel, ReaxFF-MD simulations provided molecular-level insights into the dynamic behaviors of chemical bonds during co-pyrolysis. The results demonstrated that lignin/PE co-pyrolysis facilitated C—C bonds breaking but inhibited C—O bonds cleavage, thereby significantly increasing the production of hydrocarbon gases. TG analysis indicated that the interaction between lignin and PE facilitated the release of volatile products. The simulations complemented experimental observations in the secondary reaction stage, demonstrating synergistic promotion of tar formation while inhibiting pyrolysis gas release. This work elucidated the synergistic mechanism of lignin/PE co-pyrolysis at multiple scales, providing theoretical support for the clean conversion and resource recovery of lignin and plastic waste.