Separation and recovery of chlorinated exhaust gases, a mixture of hydrogen chloride and sulfur dioxide

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When chlorination reactions are carried out using thionyl chloride, sulfonyl chloride, or chlorosulfinic acid as chlorinating agents, a large amount of mixed gas consisting of sulfur dioxide and hydrogen chloride is generated; this exhaust gas also contains a certain amount of organic vapor along with vapor of the chlorinating agents. Currently, the treatment method used in most factories involves multi-stage water absorption, followed by drying and then alkaline absorption, with the aim of converting acidic exhaust gases into by-product acids and sodium sulfite. However, this process cannot separate hydrogen chloride from sulfur dioxide satisfactorily; the large amount of by-product acid produced contains significant amounts of sulfur dioxide, and it can only be disposed of as waste acid at high cost. Sodium sulfite cannot be utilized properly due to purity issues, and in the end it can only be neutralized and treated as wastewater. The pressure swing distillation process can effectively address the separation challenges associated with such exhaust gases, enabling the production of high-purity hydrogen chloride and sulfur dioxide, while also allowing for the recovery and reuse of most of the chlorinating agents and some of the organic substances. By recovering hydrogen chloride, sulfur dioxide, and chlorinating agents from the exhaust gases, not only are valuable products obtained, but liquid alkali required in the original treatment method is also eliminated; furthermore, waste liquid generation is reduced, resulting in significant economic and social benefits. The unit consists of several components, including pretreatment, pressure swing distillation, reactor liquid recovery, hydrogen chloride charging, sulfur dioxide charging, and an emergency absorption system. For the pretreatment stage, a suitable approach must be selected based on factors such as the composition, temperature, and pressure of the exhaust gas; this step is essential in most operating conditions ； The pressure swing distillation process is the core of this unit ； The other parts can be configured as needed based on existing conditions. This process is now a mature one, with multiple units in operation; students interested in it can contact me.