Co-hydrothermal dechlorination of PVC plastic and bagasse: Hydrochar combustion characteristics and gas emission behavior

Hydrothermal treatment (HTT) of polyvinyl chloride (PVC) can efficiently remove chlorine (Cl) to produce low Cl hydrochar for solid fuel. This work performed co-hydrothermal treatment of PVC recycled plastics (PVCR) with biomass, then tried to reveal the combustion behavior and Cl migration behavior during combustion of PVC-derived hydrochar. It is shown that the hydrothermal temperature was the dominant factor affecting the degradation and dechlorination of PVCR. Treated at 220 ℃ for 60 min, the dechlorination efficiency of PVCR was 4.88 wt% and it was significantly increased to 34.09 wt%, 28.60 wt% and 32.50 wt% when PVCR was co-treated with bagasse, bagasse + high impact polystyrene (HIPS) and bagasse + acrylonitrile butadiene styrene (ABS), respectively. The substitution of Cl by hydroxyl (-OH) and elimination were two main dechlorination pathways. Bagasse could provide abundant -OH so as to promote the dechlorination of PVCR. Interestingly, in the combustion of PVCR and hydrochars, the Cl was mainly released in the form of HCl at lower temperature combustion stage but C-Cl mostly emitted at higher temperature combustion stage. The emitted Cl species strongly depends on the Cl content in hydrochar and combustion temperature, but did not show relevance to the existence form of Cl in hydrochar. Hydrothermal dechlorination could sharply reduce HCl emission.