Low-temperature microwave pyrolysis PVC to achieve modulation of elemental chlorine migration and conversion: performance evaluation of microwave absorption-catalysis-chlorine fixation trifunctional catalyst

The release of elemental chlorine in the form of HCl and the low quality of the product in the pyrolysis process of polyvinyl chloride (PVC) are constraints to its resource application. Furthermore, the regulation of chlorine migration and conversion processes also requires urgent attention. To address these shortcomings, we selected five metal oxides (M x O y ), namely MgO, CaO, Fe 2 O 3 , CuO, and ZnO, to construct an M x O y catalyst system with the functions of microwave absorption-catalysis-chlorine fixation. By discussing the composition of pyrolysis products, dielectric property analysis, oxygen vacancy (OV) defect analysis, and density functional theory (DFT) calculations under different catalyst systems, the mechanism of microwave absorption-catalysis-chlorine fixation was revealed. The results showed that ZnO had outstanding performance in microwave absorption, catalysis, and chlorine fixation: the optimal microwave absorption of ZnO increased the heating rate by 30 % (up to 19.67 °C/min) compared with the pyrolysis of PVC alone. The excellent O V content significantly catalyzed the C C bond breaking and dehydrogenation, reaction and facilitated the generation of lightweight products dominated by H 2 and CO. The chlorination reaction between ZnO and HCl had a lower reaction energy barrier, achieving a solid chlorine efficiency of 75.02 %. This work systematically evaluated and elucidated the trifunctional performance and mechanism of M x O y during low-temperature microwave pyrolysis of PVC.