Thermal degradation of PVC: A review

This review summarized various chemical recycling methods for PVC, such as pyrolysis, catalytic dechlorination and hydrothermal treatment, with a view to solving the problem of energy crisis and the impact of environmental degradation of PVC. Emphasis was paid on the recent progress on the pyrolysis of PVC, including co-pyrolysis of PVC with biomass/coal and other plastics, catalytic dechlorination of raw PVC or Cl-containing oil and hydrothermal treatment using subcritical and supercritical water. Understanding the advantage and disadvantage of these treatment methods can be beneficial for treating PVC properly. The dehydrochlorination of PVC mainly happed at low temperature of 250-320 degrees C. The process of PVC dehydrochiorination can catalyze and accelerate the biomass pyrolysis. The intermediates from dehydrochlbrination stage of PVC can increase char yield of co-pyrolysis of PVC with PP/PE/PS. For the catalytic degradation and dechlorination of PVC, metal oxides catalysts mainly acted as adsorbents for the evolved HCl or as inhibitors of HCl formation depending on their basicity, while zeolites and noble metal catalysts can produce lighter oil, depending the total number of acid sites and the number of accessible acidic sites. For hydrothermal treatment, PVC decomposed through three stages. In the first region (T<250 degrees C), PVC went through dehydrochiorination to form polyene; in the second region (250 degrees C < T<350 degrees C), polyene decomposed to low-molecular weight compounds; in the third region (350 degrees C < T), polyene further decomposed into a large amount of low-molecular weight compounds. (C) 2015 Elsevier Ltd. All rights reserved.