Quantum mechanical nanoreactor simulations reveal PVC pyrolysis pathways

Abstract

Pyrolysis, which converts macromolecules into smaller fragments in the absence of oxygen, offers a promising platform for synthetic polymer recycling. This sophisticated chemical network encompasses hundreds of reactions, yielding hundreds of molecular species and radicals as the process unfolds. We investigate the pyrolysis mechanism of polyvinyl chloride (PVC) using nanoreactor molecular dynamics simulations in tandem with the state-of-the-art semi-empirical method GFN-xTB. Our simulations reveal a complex reaction network, highlighting two competitive, energetically favorable chlorine elimination pathways: 1,2-elimination and Cl· radical-initiated hydrogen abstraction, challenging the conventional Cl/H· radical coupling mechanism. HCl elimination yields conjugated olefins, subsequently aromatizing, while hydrogen abstraction forms hydrocarbon radicals promoting cyclization. Nanoreactor simulations, driven by quantum mechanical methods of high transferability, enable the autonomous and unbiased discovery of reaction mechanisms of complex chemical processes, transcending the limitations of traditional methods that rely on pathways deduced from chemical intuition.