Evolution and speciation transformation of chlorine during automobile shredder residue pyrolysis.

[Display omitted] • The evolution and speciation of chlorine during ASR pyrolysis are studied. • Org-chlorine can be converted to InO-chlorine and remain in char. • Up to 12% and over 64% of chlorine are migrated to HCl and char, respectively. • Rising temperature promotes the conversion from Org-chlorine to inorganic in char. • Calcium-based compounds in ASR play a predominant role in the capture of chlorine. Disposal of automobile shredder residue (ASR) via pyrolysis enables the recovery of valuable products; however, the production of hazardous pollutants and low-value products is inevitable due to its high chlorine content. In this work, chlorine evolution behavior and the conversion mechanism during ASR pyrolysis between 480 and 600 °C were systematically studied. The experimental results for organic chlorine (Org-Cl) showed that released chlorinated gases were complex, and HCl only accounted for 35% of the gas phase products, while short-chain hydrocarbons with carbon atoms between two and four accounted for 52%. Chlorine was predominantly retained in the char, and Org-Cl was the primary contributor to the residual chlorine, accounting for over 50% of the char. The content of inorganic chlorine (InO-Cl) was low in the raw sample but significantly increased in the char. Through the distinction between organic and inorganic chlorine content in char, it was confirmed that Org-Cl could be converted to InO-Cl due to complex secondary reactions with metallic compounds. The conversion was favored by increasing the Org-Cl content and the temperature. Our findings clarified the evolution mechanism of chlorine and the transformation from Org-Cl to InO-Cl, thus providing guidance for chlorine regulation and the efficient recycling of metal resources. [ABSTRACT FROM AUTHOR]