Chlorine by electrolysis

The third reaction product, hydrogen, is usually not utilized in chlor-aUcali electrolysis. Current annual world production of chlorine by electrolysis is over 30 that of alkali is 35 megatons, and it increases by 2 to 3% per year. This industry consumes about 100 billion kilowatthours of electrical energy per year. 

Griesheim (1) An early process for producing chlorine by electrolysis, developed by Chemische Fabrik Griesheim-Elektron, in Germany, and commercialized in 1890. The electrolyte was saturated potassium chloride solution, heated to 80 to 90°C. The byproduct potassium hydroxide was recovered. The process was superseded in the United States by several similar electrolytic processes before being ousted by the mercury cell, invented by H. Y. Castner and K. Kellner in 1892. See Castner-Kellner. 

Sodium hydroxide is manufactured together with chlorine by electrolysis of sodium chloride solution. Various types of electrolytic cells are used commercially. They include the mercury cell, the diaphragm cell, and the membrane cell. 

The Niagara River has one of the largest concentrations of chlorine chemical industries in North America. It was attractive historically because of the availability of inexpensive electricity for making chlorine by electrolysis of brine, and the abundance of process water. Four chlorine-producing facilities in the Niagara River area were identified by Mumma and Lawless [52], EPA has developed fact sheets on five sites which may have contributed PCDD/Fs contamination to the Niagara River. These are discussed in Sect. 4.4 on sources in the Niagara River. 

FIG. 14—2. A cell used for making sodium and chlorine by electrolysis of fused sodium chloride. 

The annual production of chlorine in the United States is approximately 150,000 tons. Assuming no loss, how many faradays of electricity and how many tons of sodium chloride would be required to produce this much chlorine by electrolysis If the cells are operated at 2.4 volts, what fraction of the total hydroelectric power of the country, 20,000,000 kilowatts, would be required to produce the chlorine ... 

The resulting milk of magnesia—which could indeed be used as a laxative—is converted to magnesium chloride. The metal is then separated from the chlorine by electrolysis. The final product is metallic magnesium, which is only one-fourth as heavy as iron and widely used in the aircraft industry. 

The hydrochloric arid produced during the cracking of ethylene dichloride can be converted to chlorine by electrolysis. Bayer, De Nora, Dow, HoccksifUhde, eta use a technique of this type. However, the method proposed more generally involves the catalytic oxidation of hydrochloric acid by the following overall reaction ... 

Some variants on the simple template-directed chlorination were also developed. For example, a steroid carrying a tethered iodophenyl group was chlorinated by electrolysis of a solution carrying chloride ion [54]. In this case, the electrolysis furnished CI2 in solution to carry a radical relay process and electrolysis also initiated the radical process by one-electron oxidation of the iodophenyl group. As another variant, the radical relay mechanism requires that it be a chlorine atom that attaches to the iodine or pyridine or sulfur to abstract hydrogen, since a complexed bromine atom is not reactive enough, but the new bond to the substrate does not have to be a carbon-chlorine link. That bond is formed by untemplated attack of the substrate carbon radical on a reagent in solution and, with an appropriate sequence of tandem reactions, other atoms can be linked to the substrate. 

Table 16.5 Checklist for manufacture of caustic soda and chlorine by electrolysis...

Recent developments in cell technology include the use of ion-exchange membranes instead of diaphragms [29] and the use of oxygen-depolarized cathodes [30]. Section 11.2.2.2C discusses the latter as an alternative to the standard cathode that reduces the reversible potential by about 1.23 V. Section 17.2.2.2 identifies these cathodes as an important emerging technology. A commercial plant for production of about 24,000 tons of chlorine by electrolysis of HCl with depolarized cathodes was recently announced [31]. 

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