Coupling carbon dioxide and magnetite for the enhanced thermolysis of polyvinyl chloride

To valorize plastic wastes, pyrolysis of polyvinyl chloride (PVC) was conducted as a case study. In an effort to build the more sustainable pyrolysis platform for PVC, CO2 was particularly employed as a reactive gas medium, and magnetite (Fe3O4) was used to explore the feasibility of enhancing CO2-assisted PVC pyrolysis. The favorable effect of Fe3O4 on syngas generation from pyrolysis of PVC was apparent to yield highest concentration of H2 (0.28 mol% at 590 °C) and CO (4.34 mol% at 800 °C) in the presence of 0.1 g Fe3O4/1 g PVC. The GC-TOF analysis of tar generated from thermal decomposition of PVC evidenced more breakdown of PVC hydrocarbons in the presence of Fe3O4, which led to the enhanced production of syngas. In the presence of 0.01 g Fe3O4, the evolution of CO was observed at lower temperature (7.1 mol% at 680 °C) than the case without Fe3O4, and further addition of Fe3O4 up to 0.5 g gradually increased the CO level in the latter stage of pyrolysis (up to 4.5 mol% at 900 °C), which is attributed to the enhanced Boudouard reaction. Good adsorption ability of biochar products was also demonstrated in the removal of methylene blue. Collectively, the use of Fe3O4 in CO2-assisted pyrolysis of plastics could open the possibility of utilizing waste plastics in thermo-chemical process for energy recovery and environmental application.