Mechanism research on the co-pyrolysis of PVC and cellulose through ReaxFF MD combined with DFT simulation

Abstract

Co-pyrolysis of waste plastic and biomass presents great perspectives for sustainable and clean waste recycling. Unifying the distribution and generation mechanism of co-pyrolysis products of polyvinyl chloride (PVC) and cellulose (CE) solely through macroscopic experiments is challenging. In this study, the synergetic effect mechanism of co-pyrolysis of PVC and CE was comprehensively analyzed through reactive force field molecular dynamics (ReaxFF MD) combined with density functional theory (DFT) at the molecular level. PVC provides sufficient ·H radicals for the co-pyrolysis system, which promotes biomass degradation and the decarboxylation and dehydroxylation reactions of oxygen-containing groups. Co-pyrolysis limits the release of HCl, and the inhibition diminishes with increasing temperature. The quality of oil and char improves as their oxygen content declines. The dehydroxylation reaction of the CE monomer is most likely to occur under the catalysis of HCl at the C4 site, accompanied by a minimum reaction energy barrier of 23.87 kJ/mol. The alcoholization of furfural compounds is enhanced by ·H radicals. In co-pyrolysis, the biomass-derived activated intermediates release CO₂ and CO through hydrogenation, oxidation, hydrogen capture, and cracking. The conjunction of ReaxFF MD and DFT effectively exposes the co-pyrolysis mechanism of PVC and CE at the microlevel, which provides a theoretical supplement for resource utilization of solid waste to generate renewable energy.