Formation Characteristics and Emission Inventory of Hexachlorobutadiene in Trichloroethylene/Perchloroethylene Coproduction.

Hexachlorobutadiene (HCBD) is regulated by Stockholm Convention and United States Toxic Substances Control Act because of its toxicity and potential for long-range transport. Despite these restrictions, HCBD concentrations in the air are increasing. A major source of unintentional HCBD emissions is trichloroethylene (TCE)/perchloroethylene (PCE) coproduction. In this study, three TCE/PCE coproduction plants were investigated and their HCBD emissions were quantified. Among the plants, the plant using direct chlorination technology had a lower emission factor (0.279 g/t) than the others, which used tetrachloroethane transformation (1.20-15.1 g/t). The TCE/PCE produced was primarily used in refrigerants and detergents. Product use was identified as the main HCBD emission pathway (≥96% of total emissions), with refrigerants contributing to approximately 70% of the total emissions. Waste liquid incineration accounted for ≤4% of the total HCBD emissions. With current technology, the total unintentional emissions of HCBD from TCE/PCE coproduction plants in China and globally were estimated to be 2.97 × 103 and 3.11 × 103-5.52 × 103 kg/a. Our results show that restricting the use of TCE/PCE-containing refrigerants and developing sustainable substitutes may be effective strategies for minimizing unintentional HCBD emissions.