Editing Sodium carbonate (section)

==Production==
The initial large-scale chemical procedure was established in England in 1823 to manufacture soda ash.<ref name="Himmel" />

===Mining===
[[Trona]], also known as [[sodium sesquicarbonate|trisodium hydrogendicarbonate dihydrate]] (Na<sub>3</sub>HCO<sub>3</sub>CO<sub>3</sub>·2H<sub>2</sub>O), is mined in several areas of the US and provides nearly all the US consumption of sodium carbonate. Large natural deposits found in 1938, such as the one near [[Green River, Wyoming]], have made mining more economical than industrial production in North America. There are important reserves of trona in Turkey;<ref>{{cite news |date=2021-08-09 |title=Ciner Weighs Sale of Stake in $5 Billion Soda Ash Unit |language=en |work=Bloomberg.com |url=https://www.bloomberg.com/news/articles/2021-08-09/ciner-said-to-weigh-sale-of-stake-in-5-billion-soda-ash-unit |access-date=2023-12-04}}</ref> two million tons of soda ash have been extracted from the reserves near Ankara.

===Barilla and kelp===
Several "[[halophyte]]" (salt-tolerant) plant species and seaweed species can be processed to yield an impure form of sodium carbonate, and these sources predominated in Europe and elsewhere until the early 19th century. The land plants (typically [[glasswort]]s or [[saltwort]]s) or the seaweed (typically ''[[Fucus]]'' species) were harvested, dried, and burned. The ashes were then "[[Leaching (chemistry)|lixivated]]" (washed with water) to form an alkali solution. This solution was boiled dry to create the final product, which was termed "soda ash"; this very old name derives from the Arabic word ''soda'', in turn applied to ''[[Salsola soda]]'', one of the many species of seashore plants harvested for production. "Barilla" is a commercial term applied to an impure form of [[Pearlash|potash]] obtained from coastal plants or [[kelp]].<ref>{{cite book |last1=Hooper |first1=Robert |author-link1=Robert Hooper (physician) |title=Lexicon Medicum |date=1802 |publisher=Longman |location=London |pages=1198–9 |edition=1848|oclc= 27671024}}</ref>

The sodium carbonate concentration in soda ash varied very widely, from 2–3 percent for the seaweed-derived form ("[[kelp]]"), to 30 percent for the best [[barilla]] produced from [[saltwort]] plants in Spain. Plant and seaweed sources for soda ash, and also for the related [[alkali]] "[[potash]]", became increasingly inadequate by the end of the 18th century, and the search for commercially viable routes to synthesizing soda ash from salt and other chemicals intensified.<ref name="Clow52">
Clow, Archibald and Clow, Nan L. (June 1952). ''Chemical Revolution''. Ayer. pp. 65–90. {{ISBN|0-8369-1909-2}}.</ref>

===Leblanc process===
{{Main|Leblanc process}}
In 1792, the French chemist [[Nicolas Leblanc]] patented a process for producing sodium carbonate from salt, [[sulfuric acid]], [[limestone]], and coal. In the first step, sodium chloride is treated with sulfuric acid in the [[Mannheim process]]. This reaction produces [[sodium sulfate]] (''salt cake'') and [[hydrogen chloride]]:
{{block indent|2NaCl + H<sub>2</sub>SO<sub>4</sub> → Na<sub>2</sub>SO<sub>4</sub> + 2HCl}}

The salt cake and crushed [[limestone]] ([[calcium carbonate]]) was reduced by heating with [[coal]].<ref name=Ullmann>{{cite encyclopedia|author=Christian Thieme|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|location=Weinheim|year=2000|doi=10.1002/14356007.a24_299|isbn = 978-3527306732|chapter = Sodium Carbonates}}</ref> This conversion entails two parts. First is the [[carbothermic reaction]] whereby the coal, a source of [[carbon]], [[Redox|reduces]] the [[sulfate]] to [[sulfide]]:
{{block indent|Na<sub>2</sub>SO<sub>4</sub> + 2C → Na<sub>2</sub>S + 2CO<sub>2</sub>}}

The second stage is the reaction to produce sodium carbonate and [[calcium sulfide]]:
{{block indent|Na<sub>2</sub>S + CaCO<sub>3</sub> → Na<sub>2</sub>CO<sub>3</sub> + CaS}}
This mixture is called ''black ash''. The soda ash is extracted from the black ash with water. Evaporation of this extract yields solid sodium carbonate. This extraction process was termed [[Leaching (chemistry)|lixiviating]].

The hydrochloric acid produced by the [[Leblanc process]] was a major source of air pollution, and the [[calcium sulfide]] byproduct also presented waste disposal issues. However, it remained the major production method for sodium carbonate until the late 1880s.<ref name="Clow52"/><ref name="Kiefer">{{cite journal |last1=Kiefer |first1=David M. |date=January 2002 |url=http://pubs.acs.org/subscribe/journals/tcaw/11/i01/html/01chemchron.html |title=It was all about alkali |journal=Today's Chemist at Work |volume=11 |issue=1 |pages=45–6}}</ref>

===Solvay process===
{{Main|Solvay process}}

In 1861, the [[Belgium|Belgian]] industrial chemist [[Ernest Solvay]] developed a method for making sodium carbonate by first reacting [[sodium chloride]], [[ammonia]], water, and carbon dioxide to generate [[sodium bicarbonate]] and [[ammonium chloride]]:<ref name=Ullmann/>

{{block indent|NaCl + NH<sub>3</sub> + CO<sub>2</sub> + H<sub>2</sub>O → NaHCO<sub>3</sub> + NH<sub>4</sub>Cl}}

The resulting sodium bicarbonate was then converted to sodium carbonate by heating it, releasing water and carbon dioxide:

{{block indent|2NaHCO<sub>3</sub> → Na<sub>2</sub>CO<sub>3</sub> + H<sub>2</sub>O + CO<sub>2</sub>}}

Meanwhile, the ammonia was regenerated from the ammonium chloride byproduct by treating it with the lime ([[calcium oxide]]) left over from carbon dioxide generation:

{{block indent|2NH<sub>4</sub>Cl + CaO → 2NH<sub>3</sub> + CaCl<sub>2</sub> + H<sub>2</sub>O}}

The Solvay process recycles its ammonia. It consumes only brine and limestone, and [[calcium chloride]] is its only waste product. The process is substantially more economical than the Leblanc process, which generates two waste products, [[calcium sulfide]] and [[hydrogen chloride]]. The Solvay process quickly came to dominate sodium carbonate production worldwide. By 1900, 90% of sodium carbonate was produced by the Solvay process, and the last Leblanc process plant closed in the early 1920s.<ref name=Ullmann/>

The second step of the Solvay process, heating sodium bicarbonate, is used on a small scale by home cooks and in restaurants to make sodium carbonate for culinary purposes (including [[pretzels]] and [[alkali noodles]]). The method is appealing to such users because sodium bicarbonate is widely sold as baking soda, and the temperatures required ({{convert|250|F|C}} to {{convert|300|F|C}}) to convert baking soda to sodium carbonate are readily achieved in conventional kitchen [[oven]]s.<ref name="McGee"/>

===Hou's process===
This process was developed by Chinese chemist [[Hou Debang]] in the 1930s. The earlier [[steam reforming]] by-product carbon dioxide was pumped through a saturated solution of [[brine|sodium chloride]] and ammonia to produce sodium bicarbonate by these reactions:

{{block indent|[[methane|CH<sub>4</sub>]] + 2[[water|H<sub>2</sub>O]] → [[carbon dioxide|CO<sub>2</sub>]] + 4[[hydrogen|H<sub>2</sub>]]}}
{{block indent|3[[hydrogen|H<sub>2</sub>]] + [[nitrogen|N<sub>2</sub>]] → 2[[ammonia|NH<sub>3</sub>]]}}
{{block indent|[[ammonia|NH<sub>3</sub>]] + [[carbon dioxide|CO<sub>2</sub>]] + [[water|H<sub>2</sub>O]] → [[ammonium bicarbonate|NH<sub>4</sub>HCO<sub>3</sub>]]}}
{{block indent|[[ammonium bicarbonate|NH<sub>4</sub>HCO<sub>3</sub>]] + [[sodium chloride|NaCl]] → [[ammonium chloride|NH<sub>4</sub>Cl]] + [[sodium bicarbonate|NaHCO<sub>3</sub>]]}}

The sodium bicarbonate was collected as a precipitate due to its low solubility and then heated up to approximately {{Convert|80|C|}} or {{Convert|95|C|}} to yield pure sodium carbonate similar to last step of the Solvay process. More sodium chloride is added to the remaining solution of ammonium and sodium chlorides; also, more ammonia is pumped at 30–40&nbsp;°C to this solution. The solution temperature is then lowered to below 10&nbsp;°C. Solubility of ammonium chloride is higher than that of sodium chloride at 30&nbsp;°C and lower at 10&nbsp;°C. Due to this temperature-dependent solubility difference and the [[common-ion effect]], ammonium chloride is precipitated in a sodium chloride solution.

The Chinese name of Hou's process, ''lianhe zhijian fa'' ({{zh|c=联合制碱法|labels=no}}), means "coupled manufacturing alkali method": Hou's process is coupled to the [[Haber process]] and offers better [[atom economy]] by eliminating the production of calcium chloride, since any ammonia generated gets used by the reaction. The by-product ammonium chloride can be sold as a fertilizer.