The process has a high energy consumption, for example over 4 billion kWh per year in West Germany 1985, and produces equal (molar) amounts of chlorine and sodium hydroxide, which makes it necessary to find a use for the product with less request, usually the chlorine.
There are two production methods in use. While the mercury cell method produces chlorine free sodium hydroxide the use of several tonnes of mercury leads to environmental problems, although in normal production cycle the emission of mercury is low. The membrane and diaphragm method use no mercury, but the sodium hydroxide contains chlorine which has to be removed.
The non-permeable ion exchange membrane at the center of the cell allows the sodium ions (Na+) to pass to the second chamber where they react with the hydroxide ions to produce caustic soda (NaOH). The overall reaction for the electrolysis of brine is thus:
At higher temperatures, 333K, chlorate can be formed:
In the membrane cell, the anode and cathode are separated by an ion-permeable membrane. Saturated brine is fed to the compartment with the anode (the anolyte). A DC current is passed through the cell and the NaCl splits into its constituent components. The membrane passes Na+ ions to the cathode compartment (catholyte), where it forms sodium hydroxide in solution. The chloride ions are oxidised to chlorine gas at the anode, which is collected, purified and stored. Hydrogen gas and Hydroxide ions are formed at the cathode.
Patent Issued for Method of Concentrating an Aqueous Caustic Alkali Using a Catholyte Heat Recovery Evaporator
Dec 12, 2012; From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Davis, Anthony B. (Calvert City, KY);...
WIPO ASSIGNS PATENT TO DOLE FRESH VEGETABLES FOR "TANDEM USE OF CATHOLYTE AND ANOLYTE TO CLEAN AND SANITIZE FRUIT AND VEGETABLES" (AMERICAN INVENTORS)
Mar 26, 2011; GENEVA, March 26 -- Publication No. WO/2011/035184 was published on March 24. Title of the invention: "TANDEM USE OF...
US Patent Issued to Dole Fresh Vegetables on Oct. 9 for "Tandem Use of Catholyte and Anolyte to Clean and Sanitize Fruit and Vegetables" (Ohio, Minnesota Inventors)
Oct 11, 2012; ALEXANDRIA, Va., Oct. 11 -- United States Patent no. 8,282,974, issued on Oct. 9, was assigned to Dole Fresh Vegetables Inc....