Multiscale mechanistic study into cellulose pyrolysis and Co-pyrolysis with polyethylene via ReaxFF molecular dynamics and experimental validation

Understanding the molecular mechanism of biomass–plastic co-pyrolysis is critical for optimizing mixed-waste conversion into clean fuels. This study integrates rapid Py-GC/MS experiments (400–700 °C) with ReaxFF molecular dynamics simulations (2000–2600 K) to unravel temperature-dependent reaction pathways during the pyrolysis of cellulose and its co -pyrolysis with polyethylene (CELL:PE = 3:1). Increasing temperature suppressed light-tar fractions and enhanced heavy-tar and coke yields, trends consistently reproduced by simulations. ReaxFF-MD revealed that elevated temperatures accelerate secondary condensation and cross-linking, intensifying agglomeration and promoting H₂ and H₂O formation through synergistic dehydrogenation and dehydration. Co-pyrolysis reduced inorganic-gas evolution (≈ 2.5–20%) relative to cellulose alone (≈ 20–65%), stabilized organic-gas production, and increased the H₂/H₂O ratio. Sequential radical evolution—H₂O → CO → H₂ → CO₂—and charge transfer analyses indicated progressive oxidation and coke maturation (declining H/C and O/C ratios). The combined simulation–experiment framework identifies temperature windows that minimize inorganic gas penalties while enriching H₂-containing gases, offering actionable guidance for temperature-programmed biomass–plastic conversion reactors.