Transforming PVC plastic waste to benzene via hydrothermal treatment in a multi-phase system

Abstract

The upcycling of waste plastic to fuels, chemicals and materials is becoming more and more important, while transforming waste plastic into a single product is challenging although very attractive. Herein, a multi-phase hydrothermal treatment system (10% THF-H₂O/decane, montmorillonite K-10) was successfully developed for the transformation of polyvinyl chloride (PVC) plastic to benzene. A benzene yield of 24.8% was achieved via intramolecular cyclization reaction at 280 °C for 1 h. The biphasic solvent system of decane/water helped to extract the in situ generated benzene into the decane phase in a timely manner, preventing re-polymerization of benzene. The addition of a good solvent for PVC (tetrahydrofuran, THF) helped stretching the PVC polymer chains and the layered solid additives played a role in blocking PVC polymer chains. The latter two work together to inhibit the entanglement of polymer chains during PVC hydrothermal treatment, thus leading to a high benzene yield. The rest of the carbon was converted into carbon material with a high degree of graphitization and low Cl content after carbonization. Interestingly, it was found that the acidic nature of the solid additives did not significantly affect the yield of benzene; it is the status of polymer chains (stretching or entanglement) that determines the efficiency of PVC transformation to benzene. This work provides a new strategy for the transformation of PVC plastic waste into a single product and carbon material, which will be helpful for designing new processes for the utilization of waste plastic.