Comparing the effects of different metal oxides on low temperature decomposition of PVC

Abstract

Polyvinyl chloride (PVC) is one of the most widely used plastics in the world. When PVC is heated, HCl will form, causing equipment corrosion, product quality decline, environmental pollution and other problems. Therefore, more attention is paid to recycling of PVC than other plastics. In this study, the reaction mechanisms of PVC with different metal oxides (MOx: CaO, ZnO, CuO, MgO, Fe2O3, Al2O3) at low temperature (310 °C) were compared, with focus on chlorine capture and dehydrochlorination product (De-Cl PVC) property. The results showed that when the radius of metal ion was smaller, the extrapolated onset temperature (Ti) of PVC-MOx pyrolysis tended to be lower, such as PVC-ZnO, PVC-CuO and PVC-Al2O3. Direct reaction of PVC and MOx was deduced for PVC-CuO and PVC-ZnO pyrolysis, based on the lower Ti and peak temperature (Tmax) than that of PVC pyrolysis. MOx that did not significantly lower Tmax was supposed to react with HCl that dissociated from PVC. The addition of ZnO significantly reduced the release of HCl (0.5%) and captured 97.6% of chlorine as inorganic chloride salts. However, the chloride salts produced from PVC-MgO pyrolysis could decompose at low temperature, thus releasing HCl again, and the C atoms in PVC-CuO system could react with copper chloride salts and H2O, to form and release HCl. The capture effects of chlorine by Fe2O3 and Al2O3 were not good. With addition of MOx, all De-Cl PVCs were rich in C=C-H and (C)3C-H structures. Fe2O3, MgO and CuO reduced the release of volatile hydrocarbons, while CaO, ZnO and Al2O3 increased the release of volatile hydrocarbons. Except for CaO and CuO, the other MOx increased the amount of residual hydrocarbon (De-Cl PVC).