Co-pyrolysis of biomass and plastic waste based on ReaxFF MD: Insights into hydrogen migration, radicals interactions and synergistic mechanism

The study selected cellulose (CE) and polypropylene (PP) as representatives of biomass and plastic waste, respectively, and employed reactive molecular dynamics (ReaxFF MD) simulations to investigate the properties of the products and the synergistic effects. For the first time, the dynamic migration and distribution of hydrogen in the products, along with the evolution of hydrogen-containing free radicals during the co-pyrolysis of CE and PP, were studied, revealing the synergistic mechanism behind the co-pyrolysis process. The findings indicated that the positive synergistic effect of light tar progressively strengthened as the temperature rose. This synergistic effect was mainly reflected in the inhibition of char formation and the secondary reaction of tar, thereby increasing the yield of light tar. Throughout the co-pyrolysis process, more hydrogen was transferred from gas and char to light tar, leading to a higher content of non-oxygen-containing components like aliphatic and aromatic hydrocarbons. Hydrogen free radicals and methyl free radicals produced by PP cracking participated in the formation of tar and gases such as H2O and CH4. Additionally, hydrogen radicals transferred from PP to CE, deoxidizing the oxygen-containing tar and promoting the aromatization of CE fragments, which in turn increased the yield of aromatic hydrocarbons.