Separation and Valorization of Chlorine From Tail Gas Streams.

The chemical industry generates chlorine-containing tail gas streams on a million-ton scale. Following the established linear approach, these streams are neutralized, consuming large quantities of caustic soda (NaOH), thereby producing waste streams of lower value. To overcome this unsustainable linear approach, we developed a circular process to recycle chlorine from tail gas streams. The process is enabled by an ion exchange resin [IEx]Cl that selectively adsorbs chlorine in the presence of other gases, including oxygen, nitrogen, carbon dioxide, and hydrogen, while forming the corresponding trichloride [IEx][Cl3] by halogen bonding. Upon application of heat (80°C) and reduced pressure the adsorbed chlorine is efficiently released, and the ion exchange resin [IEx]Cl is regenerated. Importantly, the adsorbed chlorine can also be directly converted with ethylene or carbon monoxide into the base chemicals 1,2-dichloroethane or phosgene, respectively. In this way, chlorine from tail gas streams can be recycled and valorized in an integrated process supporting the transformation of the chemical industry toward a more circular economy.