Dechlorination of Polyvinyl Chloride under Superheated Steam with Catalysts and Adsorbents

Chlorine removal from polyvinyl chloride (PVC) with the addition of catalysts, such as solid acid catalysts, and adsorbents, such as alkali and metal oxide, including a multiple one, was described using superheated steam and nitrogen as pyrolysis media in this research. The effect of the dechlorination temperature indicated that the treatment temperature was an important factor to control the carbonization and dechlorination ratio of PVC. The addition of a single metal oxide, such as TiO₂, MgO, and CoO, showed better dechlorination ability compared to β-zeolite and NaOH. CoO had a higher dechlorination ability than TiO₂ and MgO. The metal-oxide-supported adsorbent of ZnO/CoO, MgO/CoO, and NiO/CoO systems was prepared by the impregnation method to increase decomposition and chlorine capture ability of the adsorbent during dechlorination. The ZnO/CoO adsorbent achieved the highest dechlorination ratio and especially increased the dechlorination ratio of PVC at ZnO ≥ 25 wt % under a superheated steam atmosphere compared to CoO alone. CoCl₂·2H₂O was observed in the X-ray diffraction pattern of 25ZnO/CoO and 50ZnO/CoO adsorbents after PVC dechlorination. The PVC dechlorination in a nitrogen atmosphere had the same results as superheated steam with no additive and CoO adsorbent at 473 K. However, the addition of 25ZnO/CoO adsorbent at 473 K had a lower dechlorination ability than superheated steam. It is supposed to result from the formation of CoCl₂·2H₂O in a superheated steam atmosphere. To obtain a similar dechlorination ratio and solid production yield to no additive, 25ZnO/CoO and 50ZnO/CoO adsorbents were able to decrease the pyrolysis temperature from 523 to 473 K.