Practical dehalogenation of automobile shredder residue in NaOH/ethylene glycol with an up-scale ball mill reactor

Abstract

Effective and efficient dehalogenation for automobile shredder residue (ASR) was successfully carried out in an NaOH/ethylene glycol solvent at 190 °C with an up-scale ball mill reactor. The element content and plastic in different fractions of ASR samples were analyzed. 1.2 ± 0.4 wt% Cl and 0.1 ± 0.1 wt% Br were measured in the fine mixture of ASR; consequently, dehalogenation was essential to mitigate the formation of hazardous compounds during thermal treatment. Sufficiently high dechlorination and debromination capacities were obtained by adjusting ball numbers and NaOH content, and the effectiveness of the treatment for throughput scale-up was confirmed. Dehalogenated ASR achieved lower than 0.1 wt% of Cl and negligible Br content, making the product suitable for feedstock recycling to recover metals and petrochemicals. We performed a life cycle assessment on the up-scale dehalogenation process and identified two beneficial impacts in comparison with the landfilling of ASR: reductions in carcinogenic effects and ecotoxicity. To mitigate impacts on climate change and resource depletion, improving dehalogenation efficiency by scaling up the throughput, enhancing the heat insulation system, and including a process for ethylene glycol recycling need to be considered.