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Concept
Chloralkali process
Summary
The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are commodity chemicals required by industry. Thirty five million tons of chlorine were prepared by this process in 1987. The chlorine and sodium hydroxide produced in this process are widely used in the chemical industry.
Usually the process is conducted on a brine (an aqueous solution of NaCl), in which case sodium hydroxide (NaOH), hydrogen, and chlorine result. When using calcium chloride or potassium chloride, the products contain calcium or potassium instead of sodium. Related processes are known that use molten NaCl to give chlorine and sodium metal or condensed hydrogen chloride to give hydrogen and chlorine.
The process has a high energy consumption, for example around of electricity per tonne of sodium hydroxide produced. Because the process yields equivalent amounts of chlorine and sodium hydroxide (two moles of sodium hydroxide per mole of chlorine), it is necessary to find a use for these products in the same proportion. For every mole of chlorine produced, one mole of hydrogen is produced. Much of this hydrogen is used to produce hydrochloric acid, ammonia, hydrogen peroxide, or is burned for power and/or steam production.
The chloralkali process has been in use since the 19th century and is a primary industry in the United States, Western Europe, and Japan. It has become the principal source of chlorine during the 20th century. The diaphragm cell process and the mercury cell process have been used for over 100 years but are environmentally unfriendly through their use of asbestos and mercury, respectively. The membrane cell process, which was only developed in the past 60 years, is a superior method with its improved energy efficiency and lack of harmful chemicals.
Official source
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