Тұзdan карбонат натрий өндірудің бұрынғы өнеркәсіптік процесі

Former industrial process for producing sodium carbonate from salt

The Leblanc process was an early industrial process for making soda ash (sodium carbonate) used throughout the 19th century, named after its inventor, Nicolas Leblanc. It involved two stages: making sodium sulfate from sodium chloride, followed by reacting the sodium sulfate with coal and calcium carbonate to make sodium carbonate. The process gradually became obsolete after the development of the Solvay process.

The sodium chloride is initially mixed with concentrated sulfuric acid and the mixture exposed to low heat. The hydrogen chloride gas bubbles off and was discarded to atmosphere before gas absorption towers were introduced. This continues until all that is left is a fused mass. This mass still contains enough chloride to contaminate the later stages of the process. The mass is then exposed to direct flame, which evaporates nearly all of the remaining chloride. The coal used in the next step must be low in nitrogen to avoid the formation of cyanide. The calcium carbonate, in the form of limestone or chalk, should be low in magnesia and silica. The weight ratio of the charge is 2:2:1 of salt cake, calcium carbonate, and carbon respectively. It is fired in a reverberatory furnace at about 1000 °C. Sometimes the reverberatory furnace rotated and thus was called a "revolver". The black ash product of firing must be lixiviated right away to prevent oxidation of sulfides back to sulfate. The first British soda works using the Leblanc process was built by the Losh family of iron founders at the Losh, Wilson and Bell works in Walker on the River Tyne in 1816, but steep British tariffs on salt production hindered the economics of the Leblanc process and kept such operations on a small scale until 1824. Following the repeal of the salt tariff, the British soda industry grew dramatically. The Bonnington Chemical Works was possibly the earliest production, and the chemical works established by James Muspratt in Liverpool and Flint, and by Charles Tennant near Glasgow became some of the largest in the world. Muspratt's Liverpool works enjoyed proximity and transport links to the Cheshire salt mines, the St Helens coalfields and the North Wales and Derbyshire limestone quarries. By 1852, annual soda production had reached 140,000 tons in Britain and 45,000 tons in France. In 1863, the British Parliament passed the Alkali Act 1863, the first of several Alkali Acts, the first modern air pollution legislation. This act allowed that no more than 5% of the hydrochloric acid produced by alkali plants could be vented to the atmosphere. To comply with the legislation, soda works passed the escaping hydrogen chloride gas up through a tower packed with charcoal, where it was absorbed by water flowing in the other direction. The chemical works usually dumped the resulting hydrochloric acid solution into nearby bodies of water, killing fish and other aquatic life. The Leblanc process also meant very unpleasant working conditions for the operators. It originally required careful operation and frequent operator interventions (some involving heavy manual labour) into processes giving off hot noxious chemicals. Sometimes, workmen cleaning the reaction products out of the reverberatory furnace wore cloth mouth and nose gags to keep dust and aerosols out of the lungs. This improved somewhat later as processes were more heavily mechanised to improve economics and uniformity of product. By the 1880s, methods for converting the hydrochloric acid to chlorine gas for the manufacture of bleaching powder and for reclaiming the sulfur in the calcium sulfide waste had been discovered, but the Leblanc process remained more wasteful and more polluting than the Solvay process. The same is true when it is compared with the later electrolytical processes which eventually replaced it for chlorine production.

In 1861, the Belgian chemist Ernest Solvay developed a more direct process for producing soda ash from salt and limestone through the use of ammonia. The only waste product of this Solvay process was calcium chloride, and so it was both more economical and less polluting than the Leblanc method. From the late 1870s, Solvay based soda works on the European continent provided stiff competition in their home markets to the Leblanc based British soda industry. Additionally the Brunner Mond Solvay plant which opened in 1874 at Winnington near Northwich provided fierce competition nationally. Leblanc producers were unable to compete with Solvay soda ash, and their soda ash production was effectively an adjunct to their still profitable production of chlorine, bleaching powder etc. (The unwanted by products had become the profitable products). The development of electrolytic methods of chlorine production removed that source of profits as well, and there followed a decline moderated only by "gentlemen's' agreements" with Solvay producers. By 1900, 90% of the world's soda production was through the Solvay method, or on the North American continent, through the mining of trona, discovered in 1938, which caused the closure of the last North American Solvay plant in 1986. The last Leblanc based soda ash plant closed in the early 1920s.