(674h) Designing an Economically Viable Process for PVC Dechlorination and Hydrogenation: Achieving Catalyst Recyclablility

Polyvinyl chloride (PVC) poses a unique challenge to waste polymer reutilization and upcycling processes, as the presence of a Cl atom in the polymer chain precludes its use in waste-to-energy processes, and also poisons heterogeneous catalysts used in upcycling. As such, reactive processes that use PVC as a feedstock require a Cl sink as part of the reaction mixture.

In our proposed tandem dechlorination and hydrogenation process, which converts PVC to a polyethylene-like wax, an amine base plays the role of a Cl shuttle, from the PVC molecule to such a chlorine sink. We demonstrate that water and strong aqueous bases can play the role of Cl sink, but with the price of catalyst deactivation via sintering, a conclusion supported by electron microscopy observations. Conversely, amines by themselves are not sufficiently basic to sequester Cl, leading to catalyst poisoning. We demonstrate that the optimal Cl sink is a heterogeneous basic material, which adsorbs Cl and prevents the deactivation of the Pt/TiO₂ catalyst. As such, the catalyst retains its activity over at least 4 cycles.

Preliminary technoeconomic analysis demonstrates that a potential process plant to convert PVC to polyethylene waxes has favorable economic metrics, achieving a payback period of 3 years, in an optimistic scenario.