Understanding the pyrolysis mechanism of polyvinylchloride (PVC) by characterizing the chars produced in a wire-mesh reactor

The study aims to understand the fundamental mechanism of the pyrolysis of polyvinylchloride (PVC) by investigating the chars produced in a wire-mesh reactor, where the interactions of evolving volatiles and pyrolysing PVC particles as well as the secondary reactions of the volatiles are minimized. The initiation of PVC pyrolysis can start at a temperature as low as 200 °C on the surface of PVC particles via dehydrochlorination, as confirmed by the surface color change and the X-ray photoelectron spectroscopy (XPS) results. However, significant dehydrochlorination reaction mainly starts at ∼300 °C, leading to the formation of conjugated polyene sequences. The results also suggest that the cyclization/aromatization reaction may take place at the early stage of the dehydrochlorination process, as the hydrocarbon release already starts (i.e., at ∼350 °C with a Cl loss of ∼80%) before the termination of the dehydrochlorination process. The initial released hydrocarbons have an H/C atomic ratio close to 1, more likely via intramolecular cyclization/aromatization reaction. However, the contribution of the hydrocarbon release to weight loss is small at low temperatures (<450 °C), and the majority of the weight loss is caused by the dehydrochlorination.