what is chlor alkali process

The chloralkali process is an industrial process for the electrolysis of sodium chloride (NaCl) solutions, which is used to produce chlorine and sodium hydroxide (NaOH), both of which are commodity chemicals required by industry. The process is usually conducted on a brine (an aqueous solution of NaCl), in which case NaOH, hydrogen, and chlorine result. When using calcium chloride or potassium chloride, the products contain calcium or potassium instead of sodium. The chloralkali process has been in use since the 19th century and is a primary industry in the United States, Western Europe, and Japan. 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. There are three types of electrolytic processes used in the production of chlorine: the diaphragm cell process, the mercury cell process, and the membrane cell process. In each process, a salt solution is electrolyzed by the action of direct electric current that converts chloride ions to elemental chlorine. The chlorine is produced at the positive electrode (anode) and the caustic soda (NaOH) is produced at the negative electrode (cathode) . The chlorine produced at the anode is removed, and the saturated brine flows through the diaphragm to the cathode chamber. The chlorine is then purified by liquefaction and evaporation to yield a pure liquified product. The caustic brine produced at the cathode is separated from salt and concentrated in an elaborate evaporative process to produce commercial caustic soda.