Simultaneous degradation and dechlorination of poly (vinyl chloride) by a combination of superheated steam and CaO catalyst/adsorbent

In order to explore the possibility of efficient chlorine removal from the poly (vinyl chloride) (PVC) containing waste plastics, simultaneous degradation and dechlorination of PVC at a relatively low temperature was investigated by changing the atmosphere gas and metal oxide as catalyst and/or adsorbent (catalyst/adsorbent). 5.0 g of PVC and various metallic oxides such as CaO, Fe₃O₄, SiO₂, Al₂O, Ca(OH)₂, MgO were used under the superheated steam and nitrogen atmosphere of 473 K. The degradation rate of the PVC sample was small and the chlorine conversion to inorganic chloride was not observed without catalyst/adsorbent in the presence of either superheated steam or nitrogen atmosphere. Under the superheated steam atmosphere, the CaO catalyst/adsorbent resulted in much larger rates of degradation and dechlorination than any other metal oxides such as Fe₃O₄, SiO₂, Al₂O, Ca(OH)₂, MgO compared with nitrogen atmosphere. The calcium compounds such as CaCl₂, CaClOH and Ca(OH)₂ were formed in the sample by the combination of CaO catalyst/adsorbent and superheated steam. The rates of PVC degradation and chlorine conversion to inorganic chlorides were dramatically enhanced beyond the stoichiometric CaO amount for the CaCl₂ formation reaction with PVC under the superheated steam atmosphere. The CaO addition contributed to both of the PVC degradation as a catalyst and the reactant with HCl as an adsorbent, whereas the superheated steam played a role of the sample temperature increase to promote the PVC degradation through the exothermic reaction with CaO.