Oxidation of hydrogen chloride by nitric acid

The nitrosyl chloride route to chlorine is based on the strongly oxidizing properties of nitric acid  

The practical problems lie in the separation of the chlorine from the hydrogen chloride and nitrous gases. The dilute nitric acid must be reconcentrated. Corrosion problems are severe. Suggested improvements include (1) oxidation of concentrated solutions of chlorides, e.g., LiCl, by nitrates followed by separation of chlorine from nitrosyl chloride by distillation at 135 °C or (2) oxidation by a mixture of nitric and sulfuric acids with separation of the product chlorine and nitrogen dioxide by liquefaction and fractional distillation [205]. 

Alkali-metal chlorides, ammonium chloride, and other metallic chlorides are reacted, usually with nitric acid, to produce nitrate fertilizers [206]. Chlorine is not produced directly, but it can be obtained from the intermediate products nitrosyl chloride or hydrochloric acid. 

The chlorine gas can be cooled indirectly in a tubular titanium heat exchanger so that the cooling water is not contaminated and the pressure drop is small. The resultant condensate is either fed back into the brine system of the mercury process or dechlo-rinated by evaporation in the case of the diaphragm process. 

The chlorine gas can be cooled directly in packed towers. Water is sprayed into the top and flows countercurrent to the chlorine. This treatment thoroughly washes the chlorine however, dechlorination of the wastewater consumes a large amount of energy. The cooling water should be free of traces of ammonium salts to avoid the formation of nitrogen trichloride. 

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