Hydrothermal dechlorination of polyvinyl chloride for solid fuel: A heterogeneous model based on in situ sampling and cross-section characterization

The high chlorine content within polyvinyl chloride (PVC) has long posed a predicament in waste management. Chlorine-induced pollution and corrosion of equipment during thermal treatment have severely impeded the disposal and recycling of PVC wastes. Hydrothermal treatment is a promising method to remove chlorine from PVC wastes to prepare clean solid fuel, a heterogeneous process often oversimplified by the Homogeneous Model (HM). This study proposed in situ sampling to advance the study of heterogeneous kinetics based on the Shrinking Core Model (SCM). The SCM could fit the process data of three types of PVC much better than the HM, with the coefficient of determination 0.9707, 0.9601, and 0.9922, respectively. The initiation stage of the treatment was controlled by chemical reaction and liquid film diffusion. At this stage, the SEM and XPS showed that the pores started to evolve on the surface of PVC particles by dehydrochlorination-induced HCl release. At the propagation stage, the dechlorination was controlled by product layer diffusion. The agglomeration of particles and collapse of pores restricted the internal diffusion and dechlorination. Adding NaCl could enhance the structured porous channels, strongly reducing the diffusion resistance within hydrochars, and improving dechlorination efficiency (DE) from 77 % to 95 %. This research underscores the importance of integrating kinetic analysis with characterization to provide a comprehensive understanding of PVC hydrothermal dechlorination dynamics, offering valuable insights for future process optimization and contributing to converting waste PVC plastics into energy. [Display omitted] •The real-time behavior of chlorine migration was investigated by in situ sampling.•A heterogeneous kinetic model for hydrothermal dechlorination of PVC was built.•Mass transfer resistance in the product layer is the main hindrance to dechlorination.•The mechanism of PVC hydrothermal dechlorination was verified and updated based on the heterogeneous model.