Effects of iron oxide minerals on the pyrolysis of polyvinyl chloride: Catalytic dechlorination, chlorine capture, and carbon sequestration

To reduce the risk of organochlorine contamination during the pyrolysis of chlorine-containing plastics, catalytic pyrolytic dechlorination of polyvinyl chloride (PVC) by iron oxides is a promising strategy. However, differences in the structural properties of various iron oxides mineral phases may lead to different catalysis activity. In this study, various characterization methods and theoretical calculations were integrated to reveal the effects of ferrihydrite (Fhy) and hematite (Hem) on the pyrolysis characteristics of PVC at 400–800 °C. Both Fhy and Hem lower the dechlorination temperature of PVC, consequently retarding the degradation of dechlorination intermediates and mitigating the emission of volatile compounds . Fhy and Hem reduced the release of chlorinated hydrocarbons and immobilized chlorine as Rokuhnite. Specifically, the yield of HCl at 400 °C decreased from 88.8% for pure PVC to 29.9%/55.8% with the additions of 30% Fhy/Hem. The surface catalytic activity of Hem is stronger than that of Fhy, resulting in better catalytic dechlorination; while Fhy has a larger specific surface area (more adsorption sites), which leads to better chlorine fixation. Fhy and Hem also facilitated the dehydroaromatisation reaction of dechlorinated PVC, increasing the residual carbon yield at 400 °C from 45.5% to 65.4% and to 75.8%, respectively. Preferably from the perspective of pollutant emission, Fhy with large specific surface area and weak crystallinity can adsorb more HCl and catalyze dechlorination as well, so the addition of Fhy (>30%) to PVC pyrolysis process can be beneficial to the control of pollutant emission and carbon sequestration. • Iron oxides can promote cleavage of chlorinated hydrocarbons during pyrolysis. • Hematite has higher catalytic dechlorination activity than ferrihydrite. • Ferrihydrite traps chlorine better owing to its greater specific surface area. • Ferrihydrite and hematite can facilitate the carbonization of polyvinyl chloride .