Editing Chlorine (section)

==Production==
{{Main|Chlorine production}}
Chlorine is primarily produced by the [[chloralkali process]], although non-chloralkali processes exist. Global 2022 production was estimated to be 97 million tonnes.<ref>{{cite web | url=https://www.statista.com/statistics/1310477/chlorine-market-volume-worldwide/#:~:text=In%202022%2C%20the%20market%20volume,almost%20128.95%20million%20metric%20tons | title=Chlorine global market volume 2030 }}</ref> The most visible use of chlorine is in [[water disinfection]]. 35-40 % of chlorine produced is used to make [[poly(vinyl chloride)]] through [[ethylene dichloride]] and [[vinyl chloride]].<ref>{{cite web | url = https://vinyl.org.au/chlorine | title = About Vinyl: Chlorine | publisher = Vinyl Council Australia | accessdate = 2024-05-11}}</ref>  The chlorine produced is available in cylinders from sizes ranging from 450&nbsp;g to 70&nbsp;kg, as well as drums (865&nbsp;kg), tank wagons (15&nbsp;tonnes on roads; 27–90&nbsp;tonnes by rail), and barges (600–1200&nbsp;tonnes).<ref name="Greenwood796">{{harvnb|Greenwood|Earnshaw|1997|pp=796–800}}</ref>
Due to the difficulty and hazards in transporting elemental chlorine, production is typically located near where it is consumed. As examples, vinyl chloride producers such as [[Westlake Chemical]]<ref>{{cite web | url = https://www.westlake.com/chlorovinyls/chlorine | publisher = Westlake Chemical | title = Chlorine}}</ref> and [[Formosa Plastics]]<ref>{{cite web | url = https://www.fpcusa.com/products/chlor-alkali/ | publisher = Formosa Plastics | title = Chlor-Alkali | accessdate = 2024-05-11}}</ref> have integrated chloralkali assets.

===Chloralkali processes===
{{main|Chloralkali process}}
The electrolysis of chloride solutions all proceed according to the following equations:

:Cathode: 2 H<sub>2</sub>O + 2 e<sup>−</sup> → H<sub>2</sub> + 2 OH<sup>−</sup>
:Anode: 2 Cl<sup>−</sup> → Cl<sub>2</sub> + 2 e<sup>−</sup>

In the conventional case where sodium chloride is electrolyzed, [[sodium hydroxide]] and chlorine are coproducts.

Industrially, there are three chloralkali processes:
* The [[Castner–Kellner process]] that utilizes a mercury electrode
* The diaphragm cell process that utilizes an asbestos diaphragm that separates the cathode and anode
* The membrane cell process that uses an [[ion exchange]] membrane in place of the diaphragm

The Castner–Kellner process was the first method used at the end of the nineteenth century to produce chlorine on an industrial scale.<ref name="pauling">Pauling, Linus, ''General Chemistry'', 1970 ed., Dover publications</ref><ref name="lenn2">{{cite web|accessdate=2007-03-17|title=Electrolytic Processes for Chlorine and Caustic Soda|url=http://www.lenntech.com/Chemistry/electolytic-chlorine-caustic.htm|publisher=Lenntech Water treatment & air purification Holding B.V., Rotterdamseweg 402 M, 2629 HH Delft, The Netherlands}}</ref> Mercury (that is toxic) was used as an electrode to [[sodium amalgam|amalgam]]ate the sodium product, preventing undesirable side reactions.

In diaphragm cell electrolysis, an [[asbestos]] (or polymer-fiber) diaphragm separates a cathode and an [[anode]], preventing the chlorine forming at the anode from re-mixing with the sodium hydroxide and the hydrogen formed at the cathode.<ref name="Euro Chlor3">{{cite web|url=http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-produced/the-diaphragm-cell-process.aspx|title=The diaphragm cell process|publisher=Euro Chlor|access-date=2007-08-15|url-status=dead|archive-url=https://web.archive.org/web/20111111191151/http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-produced/the-diaphragm-cell-process.aspx|archive-date=2011-11-11}}</ref> The salt solution (brine) is continuously fed to the anode compartment and flows through the diaphragm to the cathode compartment, where the [[Causticity|caustic]] [[alkali]] is produced and the brine is partially depleted. Diaphragm methods produce dilute and slightly impure alkali, but they are not burdened with the problem of [[Mercury (element)|mercury]] disposal and they are more energy efficient.<ref name="Greenwood798" />

Membrane cell electrolysis employs [[Semipermeable membrane|permeable membrane]] as an [[ion exchange]]r. Saturated sodium (or potassium) chloride solution is passed through the anode compartment, leaving at a lower [[concentration]]. This method also produces very pure sodium (or potassium) hydroxide but has the disadvantage of requiring very pure brine at high concentrations.<ref name="Euro Chlor4">{{cite web|url=http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-produced/the-membrane-cell-process.aspx|title=The membrane cell process|publisher=Euro Chlor|access-date=2007-08-15|url-status=dead|archive-url=https://web.archive.org/web/20111111190719/http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-produced/the-membrane-cell-process.aspx|archive-date=2011-11-11}}</ref>
However, due to the lower energy requirements of the membrane process, new chlor-alkali installations are now almost exclusively employing the membrane process. Next to this, the use of large volumes of mercury is considered undesirable.
Also, older plants are converted into the membrane process.

[[File:Chloralkali membrane.svg|center|upright=2.75|thumb|Membrane cell process for chloralkali production]]

===Non-chloralkali processes===
In the [[Deacon process]], hydrogen chloride recovered from the production of [[organochlorine compound]]s is recovered as chlorine. The process relies on oxidation using oxygen:
: 4 HCl + O<sub>2</sub> → 2 Cl<sub>2</sub> + 2 H<sub>2</sub>O

The reaction requires a catalyst. As introduced by Deacon, early catalysts were based on copper. Commercial processes, such as the Mitsui MT-Chlorine Process, have switched to chromium and ruthenium-based catalysts.<ref name="chlorine">Schmittinger, Peter ''et al.'' (2006) "Chlorine" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH Verlag GmbH & Co., {{doi|10.1002/14356007.a06_399.pub2}}</ref>