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 (PVC R ) 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 PVC R . Treated at 220 ℃ for 60 min, the dechlorination efficiency of PVC R was 4.88 wt% and it was significantly increased to 34.09 wt%, 28.60 wt% and 32.50 wt% when PVC R 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 PVC R . Interestingly, in the combustion of PVC R 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.
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.
Weichen Yang,Xing Cao,Qiushi Zhang,Rui Ma,Lin Fang,Shiwei Liu
To improve the degradation efficiency of persistent organic pollutants (POPs) in municipal solid waste incineration fly ash (MSWIFA), as well as to overcome the difficulties of subsequent hydrothermal liquid and hydrothermal slag treatment, a two-step treatment strategy of microwave hydrothermal degradation coupled with geopolymer immobilization was proposed. Results showed that the optimal process parameters for microwave hydrothermal dechlorination were a temperature of 220 °C, a time of 1 h, and NaOH addition of 10 wt%. Microwaves accelerated the OH − mediated hydrolysis reactions and promoted the breaking of C Cl bonds, leading to dechlorination. The compressive strength of the 20 % MSWIFA-based geopolymers reached 75.79 MPa, and the immobilization rate of the heavy metals (HMs) and Cl − surpassed 90 %. Alkaline environment provided by microwave hydrothermal promoted the formation of Ca(OH) 2 , which subsequently formed Friedel's salt (3CaO•Al 2 O 3 •CaCl 2 •10H 2 O) with Cl − in the geopolymer. The charge density difference and density of states (DOS) of Friedel's salt were analyzed by first-principles calculations, confirming that the existence of strong interactions between Ca-s, Al-p, O-p, and Cl-p states was the chemical mechanism of Cl − immobilization. The Friedel's salt and HMs were encapsulated by geopolymers with dense silica-alumina tetrahedral frameworks, achieving the solidification/stabilization (S/S) of HMs and Cl − . This work provided a new approach for the environmentally sound and resourceful treatment of MSWIFA.
危险品化学品经营许可证（带存储）