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.