Tian-Tian Meng,Hua Zhang,Fan Lü,Li-Ming Shao,Pin-Jing He
Polyvinyl chloride (PVC) is one of the most widely used plastics in the world. When PVC is heated, HCl will form, causing equipment corrosion, product quality decline, environmental pollution and other problems. Therefore, more attention is paid to recycling of PVC than other plastics. In this study, the reaction mechanisms of PVC with different metal oxides (MO x : CaO, ZnO, CuO, MgO, Fe 2 O 3 , Al 2 O 3 ) at low temperature (310 °C) were compared, with focus on chlorine capture and dehydrochlorination product (De-Cl PVC) property. The results showed that when the radius of metal ion was smaller, the extrapolated onset temperature ( T i ) of PVC-MO x pyrolysis tended to be lower, such as PVC-ZnO, PVC-CuO and PVC-Al 2 O 3 . Direct reaction of PVC and MO x was deduced for PVC-CuO and PVC-ZnO pyrolysis, based on the lower T i and peak temperature ( T max ) than that of PVC pyrolysis. MO x that did not significantly lower T max was supposed to react with HCl that dissociated from PVC. The addition of ZnO significantly reduced the release of HCl (0.5%) and captured 97.6% of chlorine as inorganic chloride salts. However, the chloride salts produced from PVC-MgO pyrolysis could decompose at low temperature, thus releasing HCl again, and the C atoms in PVC-CuO system could react with copper chloride salts and H 2 O, to form and release HCl. The capture effects of chlorine by Fe 2 O 3 and Al 2 O 3 were not good. With addition of MO x , all De-Cl PVCs were rich in C=C-H and (C) 3 C-H structures. Fe 2 O 3 , MgO and CuO reduced the release of volatile hydrocarbons, while CaO, ZnO and Al 2 O 3 increased the release of volatile hydrocarbons. Except for CaO and CuO, the other MO x increased the amount of residual hydrocarbon (De-Cl PVC).
Li-Zhi Huang,Xiang Zhan,Weiguo Chen,Changye Li,Liandong Zhu,Yitao Dai,Jia Deng
Carbon tetrachloride (CT), a common persistent pollutant in groundwater, has attracted widespread attention from environmental researchers. The dechlorination from CT to combustible hydrocarbons not only represents the removal of contaminants, but also offers the possibility of recovering carbon resources from water. In this work, we used the coprecipitation of Fe(II) and Pd(II) to synthesize Pd-Fe hydroxides for the dechlorination of CT. When Pd and Fe dosages were 0.4 and 5 mM respectively, CT with 26 µM concentration can be fast removed within 5 min, and 43.3 % of CH 4 and 11.6 % of C 2 H 6 (mol%) were generated after 110 min. The alkaline condition was more conducive to the complete dechlorination of CT comparing with acidic and neutral conditions. During the olation process, Fe(II) as electron donor transferred electrons to Pd(II) to form Pd(0) clusters. Pd(0) active sites act on the binding of CT and transfer electron to H + /H 2 O to form adsorbed atomic hydrogen (H ads •). The adsorbed CT molecules on the surface of Pd-Fe hydroxides undergo continuous dechlorination to form CH 4 and C 2 H 6 through the attack of H ads • and direct electron transfer. In real groundwater applications, CT was rapidly removed, with CH 4 and C 2 H 6 yields reaching 24.5 % and 4.6 % (mol%), respectively. Encouragingly, incomplete dechlorinated products, including chloroform and dichloromethane, did not show signs of subsequent rebound even after 60 min. Furthermore, Pd-Fe hydroxides also exhibit resistance to the oxidation effects of dissolved oxygen, which demonstrates the promising application prospects.
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