Chemical Upcycling of Waste Chlorinated Plastics into α,ω-Dienes via Consecutive Dehydrochlorination-Hydrogenation with HCl Trapping and Metathesis

The chemical recycling of chlorinated plastics is industrially challenging due to the release of corrosive HCl and char formation. In this work, a novel upcycling route for chlorinated plastics, including polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), and chlorinated polyethylene (CPE), is developed. When ZnCl2-catalyzed dehydrochlorination (DHC) is combined with tandem DHC-hydrogenation, using a homogeneous Ru hydrogenation catalyst and metal oxides as a HCl trap, each plastic type can be selectively converted into an unsaturated polyolefin (UPO), which can be chemically split via metathesis. By rational design of reaction conditions, CPE (25 or 35 m% Cl) as a model substrate, a PVDC–PVC copolymer (66 m% Cl) and PVC (57 m% Cl) were consecutively converted into partially and fully dechlorinated UPOs. Both of these UPO products contained −CH2–CH2–sequences and up to 11 double bonds per 100 carbons. They were chemically split into α,ω-dienes using a second-generation Grubbs catalyst. Via this procedure, chlorinated plastics can be converted into valuable chemical building blocks, while the released HCl is sequestered.