Transformation behavior and fate of chlorine in polychloroprene (PCP) during its pyrolysis

Polychloroprene (PCP) rubber is mostly mixed in industrial solid waste (ISW) as the main source of chlorine element. Whereas, the products formation and chlorine behavior during the pyrolysis are insufficiently illustrated for this typical chlorinated polymer, which is not conducive to the chlorine regulation of ISW pyrolytic products. In order to investigate the chlorine transformation behavior, the PCP pyrolysis under the influence of a wide range of heating rates (3-600 degrees C/min) was conducted to explore the chlorine distribution properties as well as its migration mechanism in the present study. Importantly, 30-65 wt% chlorine was found to be migrated to gas and tar, respectively. Compared with PVC, the differences of chlorine distribution between PCP and PVC may be attributed to the easier cyclization with a longer molecular chain. Also, the release temperature of HCl acted as main component determines its availability for the subsequent formation of chlorinated hydrocarbons. In details, the conversion pathway from chlorinated limonene to Cl-aromatic hydrocarbons was confirmed and the reaction was found to be enhanced at higher temperature and heating rate. By analyzing the content of tar components (especially at low heating rate), it was found that the major formation pathway of aromatic hydrocarbons was supposed to be the direct Diels-Alder reaction of monomer rather than the dechlorination of intermediate chlorinated limonene. Our findings discussed the effect mechanism of heating rate and temperature on chlorine behavior during PCP pyrolysis, providing guidance for the chlorine regulation of ISW pyrolytic products.