Similar term(s): chlor alkali plant, chlor alkali chemicals.
The term chlor-alkali refers to the two chemicals (chlorine and an alkali)
which are simultaneously produced as a result of the electrolysis of a
saltwater. The most common chlor-alkali chemicals are chlorine and sodium
hydroxide (caustic soda) but can include potassium hydroxide and muriatic acid.
There are 3 types of electrolytic processes used in the production of chlorine
and caustic soda: the diaphragm cell process, the mercury cell process, and the
membrane cell process. In the mercury cell process, chlorine and sodium
hydroxide are produced simultaneously by electrolyzing seawater (sodium
saltwater or brine) in a mercury cell. Note that when a potassium brine is used,
potassium hydroxide is produced instead of the more usual sodium hydroxide.
The mercury cell process takes place in an electrolytic cell, where liquid
mercury acts as a cathode. It attracts sodium (or potassium) cations with which
it forms an amalgam. Chlorine gas collects at the anode (graphite). When the
amalgam is added to water, the sodium (or potassium) reacts with the water to
form sodium hydroxide and hydrogen, leaving the mercury, which can then be
reused. Because mercury is highly volatile, mercury contamination occurs
throughout the process, commonly leading to both the product (caustic soda) and
the wastewater stream containing small amounts of mercury.
Français: Procédé chlore-alcali