TECHNOLOGY
Britain Starts Making Sodium Chlorite Laporte Industries uses German Kesting process at its Luton plant, reduces nation's dependence on imports Fast-growing Laporte Industries in Britain has started up the first sodium chlorite plant in the United Kingdom. Located at Luton, near London, the plant makes sodium chlorite from sali by the German Kesting process, licensed from Elektrochemische Werke Munchen, Munich, West Germany. Up to now, Britain has imported all of its sodium chlorite from the Continent. Laporte has not revealed how much these imports amount to, and the government does not publish statistics on the compound. But it has a wide range of uses, from treating water to bleaching natural and synthetic fibers, and is even used as a bactericide in tanning leather. How It's Made. The Kesting process has four main steps: • • • •
Electrolysis. Chlorine dioxide generation. Chlorite production and recovery, By-product recovery.
In the first step, a solution of sodium chloride and sodium chlorate is continuously recycled through electrolytic cells where some of the chloride ii oxidized to chlorate. A germanium
rectifier supplies power. The electrolyzed solution flows to a sump, returns to the main storage tanks for recycle. Make-up salt solution is bled in ahead of the cells; a small portion of the electrolyzed solution is taken off after the cells. Electrolyzed solution taken off is fed to the second step. It is acidified with hydrochloric acid, flows through a six-vessel cascade system which has a stream of air blowing countercurrently through it. The air strips chlorine and chlorine dioxide from the acidified chlorate. The chlorine and chlorine dioxide are separated, the chlorine dioxide being absorbed in one vessel while the chlorine passes through. In a second vessel, the chlorine dioxide is stripped with air. The air-chlorine dioxide mixture from the stripper passes next into a reactor, where it is treated with sodium hydroxide and hydrogen peroxide to form the chlorite. Simultaneous absorption and reduction suppresses formation of sodium chlorate; almost none appears. After absorption and reaction, the solution is spray-dried to
give the crystalline sodium chlorite. Purity is 807c, the standard industrial grade. U.S. Process. Commercial production of sodium chlorite in the U.S. has been based on reducing calcium chlorate with HC1. (However, Olin Mathieson, the only U.S. producer, won't comment on its current process.) The chlorate is reduced to C10 2 while the HC1 is oxidized to chlorine. The ClOo is reduced by powdered carbop dispersed in a solution of sodium hydroxide and lime [Ind. Eng. Cliem., 42, 2359 (1950)]. C 0 2 resulting from reduction of the CIO.» by the carbon powder precipitates the calcium as the carbonate, which is filtered off. Concentrating and drying the filtrate leaves the solid NaClOo. Laporte's Luton plant was origin all} designed to make hydrogen peroxide, but was closed down in 1958 when the company started up its autoxidation process for hydrogen peroxide at Warrington. And the sodium chlorite fits in well with the company's range of organic and inorganic peroxy compounds already used in bleaching and other industries in Britain.
How Kesting Process Makes Sodium Chlorite from Salt
Process Produces Product with 80% Purity, the Standard Industrial Grade
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C&EN
DEC. 26, 1960
