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February 2002
Vol. 11, No. 2
pp 87–88, 90.
Chemistry Chronicles
David M. Kiefer
Soda ash, Solvay style

Introduced in the 1860s, the Solvay process for making soda ash made Leblanc’s technology obsolete.

Ernest Solvay
Ernest Solvay (1838–1922)
Throughout most of the 19th century, two processes for making soda ash (sodium carbonate) defined the world’s chemical industry. Soda ash, a key chemical for producing glass and soap and bleaching fabrics and paper, was produced by two processes, each best known by the name of its inventor: French physician Nicolas Leblanc and Belgian entrepreneur Ernest Solvay. Their success was more a triumph of skillful chemical engineering than chemical science, and during the 1870s and 1880s the two processes were locked in fierce competition. Then, over the next three decades, the Solvay process inexorably pushed aside the well-entrenched Leblanc process (see TCAW, Jan 2002, p 45).

Birth of Solvay Process
Born near Brussels in 1838, Solvay had a modest education before going to work for his father, a salt refiner. When he was 21, Solvay joined his uncle, Florimond Semet, who managed a gasworks facility in Brussels. Using his experience with salt and coal gas, he soon turned his attention to improving the manufacture of soda ash by using ammonia.

Within 20 years after the Leblanc process had been introduced in 1791, the goal of finding a better way to make soda ash began to attract the interest of chemists. The Leblanc technique had serious drawbacks. It was complicated, wasteful of costly raw materials and fuel, labor-intensive, dirty, and severely polluting.

Soda ash preparation
NaCl + NH3 + CO2 + H2O NaHCO3 + NH4Cl

2NaHCO3 Na2CO3 + CO2 + H2O

2NH4Cl + Ca(OH)2 CaCl2 + 2NH3 +2H2O

Several scientists had investigated ammonia–soda methods for preparing soda ash. Essentially, these methods involved saturating a concentrated brine solution with ammonia to form ammonium salts and then with carbon dioxide (made by burning lime). This produces ammonium bicarbonate, which reacts with the brine to form ammonium chloride and sodium carbonate. The sodium carbonate, in the presence of excess carbon dioxide, is converted to sodium bicarbonate, which precipitates out of solution and can easily be decomposed to soda ash by heating. The resulting carbon dioxide can be recycled, and the ammonium chloride treated to recover reusable ammonia. (See reaction sequence, “Soda ash preparation”.)

In 1838, Harrison Dyar and John Hemming patented such an ammonia–soda process in England. James Muspratt, a leading English producer of soda ash by the Leblanc technique, spent several thousand pounds trying to make this approach practical before giving up in 1850. Another British soda ash producer also unsuccessfully tried to commercialize an ammonia–soda process during the 1850s. A small-scale ammonia–soda plant was put into operation in France in 1858, producing >300 t of soda ash before it shut down two years later. A major drawback with all these efforts was that they wasted too much ammonia or consumed too much salt.

Solvay was apparently unaware of this earlier work when he began investigating the use of brine to make soda ash around 1861. At that time, as he pointed out years later, “there were neither so many technical publications nor such efficient patent offices.” By the end of the year, with the help of his younger brother, Alfred, he had a small experimental plant running, although it was plagued with equipment breakdowns and problems involving pressure and temperature controls. The heart of his process was a cylindrical iron-carbonizing tower in which rising carbon dioxide mixes with a spray of ammonia brine. Solvay also came up with equipment for capturing most of the byproduct ammonia thrown off in the reaction.

Solvay, Inc.
At the end of 1863, Solvay finally obtained financial backing and established the firm Solvay & Cie. The next year, the brothers began construction of a full-scale plant at Couillet, near Chaleroi, in Belgium. By early 1865, the plant was turning out 1200 to 1500 lb of soda ash a day. That fall, however, the main unit of the plant blew up. Borrowing money from their father, they rebuilt and soon were making more than a ton of product daily. By 1872, output of the works was 10 t/day. The Solvays started up a second, much larger plant in northern France, near Nancy, in 1874.

A Solvay plant cost much more to build than a Leblanc plant; however, raw materials were appreciably cheaper, and a Solvay plant avoided sulfur and used brine rather than solid salt. Ammonia initially was supplied by city gasworks facilities and later by the installation of byproduct coke ovens. Solvay, together with his cousin Louis Semet, designed coke ovens to provide his operations with ammonia in the early 1880s. Although calcium chloride was a waste, its volume was considerably less than the solid calcium sulfate waste from the Leblanc plant. In the 1880s, cost estimates for Leblanc soda ash production were 70% greater than the Solvay method production. By 1890, the Solvay process had come to dominate the world’s alkali production.

But it wasn’t until 1872 when Ludwig Mond licensed the Solvay method that the technology was introduced to the British Isles, the center of world soda ash production thanks to the Leblanc process. Mond was born in Kassel, Germany, in 1839, and studied chemistry between 1855 and 1859 under the noted German chemists Hermann Kolbe and Robert Bunsen. He worked for a few years in the blossoming German chemical industry but became concerned about what he considered the wasteful, inefficient operations of its soda ash works. He traveled to England in 1862 to find out if the British did it better. He stayed in Britain and developed a way to use a nickel catalyst for recovering sulfur from the waste calcium sulfate produced by the Leblanc plants. He failed, however, to win much success with it among British soda ash manufacturers.

Learning of the ammonia–soda process, Mond visited Solvay in Belgium and acquired rights to use the new technology. He then teamed up with John Brunner (formerly an accountant for a Leblanc soda ash firm) to form Brunner, Mond & Co. Brunner’s commercial ability complemented Mond’s technical talent. The new firm built a Solvay plant at Winnington, in Cheshire. After Mond spent much effort improving the equipment, the facility started up in 1874, initially turning out ~50 t of soda ash every month. During the next few years, the plant’s capacity greatly expanded.

Expansion to the United States
Other Solvay plants were built in Britain, including one by United Alkali Co., Britain’s leading producer of Leblanc soda ash. Most were short-lived, however, and none ever rivaled Brunner Mond. An advantage of the latter was a deal Mond had struck with Solvay that required any subsequent British licensee to pay Solvay a royalty per ton of output that was more than double that charged to Brunner Mond.

Later, Mond developed a process for refining nickel ores by treating them with carbon monoxide to form nickel carbonyl, which is easily decomposed to pure nickel. When Imperial Chemical Industries was formed in 1926, Brunner Mond became a key part of the giant chemical conglomerate.

Before 1880, demand for alkali in the United States was largely filled by imports from Europe or from potash leached from wood ashes. (Wood ashes continued to be a small-scale source of alkali in the United States west of the Allegheny Mountains until nearly the end of the 19th century.) It wasn’t until 1876, at a meeting of the American Institute of Mining Engineers in Philadelphia, that William B. Cogswell, an engineer who managed a lead mine in Missouri, heard a description of the new Solvay ammonia–soda process. He was impressed and convinced his boss, mine owner Rowland Hazard, to send him to Belgium in 1878 to talk with the Solvay brothers. At first, the Solvays were reluctant to strike an agreement, but they finally licensed Hazard and Cogswell to make soda ash in the United States.

The two formed Solvay Process Co. (in which the Solvays owned nearly half the stock) and built a plant at Syracuse, NY, where there were ample underground salt deposits and nearby limestone quarries. The facility was operating in early 1884 with a capacity of 30 t/day. Within a dozen years, capacity was expanded tenfold. After the original Solvay patents expired, several other U.S. plants based on the ammonia–soda process were started up, all told making about 350,000 t in 1900. Solvay Process and its affiliated Semet-Solvay Co., which designed, built, and operated byproduct coke ovens, became major parts of Allied Chemical & Dye Corp. when it was formed in 1920.

By 1900, several Solvay plants were operating in France, Germany, and elsewhere in Europe. Annual world production of soda ash totaled nearly 2 million t, 90% of it by the ammonia–soda method. By then very wealthy, Ernest Solvay devoted much of his time to philanthropy, especially in support of science and social reform. He died in Brussels in 1922.

Enter Caustic Soda
Also by 1900, another alkali became available in abundance to compete with soda ash. Caustic soda (sodium hydroxide) was being produced—together with chlorine—by electrolysis of salt brine. Electrolytic caustic soda did not bring about the demise of Solvay soda ash in the way that the Solvay process undercut the Leblanc process. Solvay plants, in fact, still account for a large share of the world’s alkali output.

Not in North America, though. In 1938, extensive soda ash-rich deposits of trona were found in the Green River area of Wyoming. Soda ash extracted from them, beginning in the late 1940s, was appreciably cheaper than that made in a Solvay unit. One by one, American plants were shuttered. The last to close down, in 1986, was the original one operated by Allied-Signal in Syracuse.

Just last March, an era ended when General Chemical Group stopped production at Canada’s only soda ash source, a 500,000 t/yr plant in Amherstburg, Ontario. Now all North America’s soda ash supplies—roughly 11 million t/yr—are produced from Green River and other western U.S. natural deposits.

David M. Kiefer, assistant managing editor of Chemical & Engineering News until his retirement in 1991, is a consulting editor for Today’s Chemist at Work. Send your comments or questions regarding this article to tcaw@acs.org or the Editorial Office 1155 16th St., N.W., Washington, DC 20036.

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