How it began
Ernest Solvay was born near Brussels in 1838, worked for his father, a salt refiner, and at 21 joined an uncle who managed a gasworks. Drawing on his experience with salt and coal gas, he began around 1861 to investigate making soda ash from brine with ammonia, apparently unaware of earlier attempts. He patented the process a day before his 23rd birthday.
With his younger brother Alfred he had a small experimental plant running by the end of 1861. He secured financial backing and founded Solvay & Cie at the end of 1863, and the brothers began building a full-scale plant at Couillet, near Charleroi, the following year.
Before it existed
Alkali was first obtained by leaching the ashes of certain plants, and kelp ash supported a large industry in 18th century Scotland. From 1791 the Leblanc process made soda ash from salt, limestone, sulfuric acid and coal, and it dominated production in the early 19th century. It was complicated, wasteful of raw materials and fuel, labor-intensive and severely polluting, releasing hydrogen chloride gas.
The ammonia-soda reaction was already known. Dyar and Hemming patented a version in England in the 1830s, and several producers tried and failed to commercialize it because they lost too much ammonia or used too much salt.
How it works
The process uses brine and limestone as raw materials. Concentrated brine is saturated with ammonia and then with carbon dioxide made by heating limestone. Sodium bicarbonate precipitates out of the solution and is heated to give soda ash, releasing carbon dioxide that is recycled. The ammonium chloride left behind is treated with lime to recover the ammonia, leaving calcium chloride as waste.
Solvay's contribution was engineering. The heart of his plant was a cylindrical iron carbonating tower in which rising carbon dioxide meets descending ammoniated brine, together with equipment that captured most of the ammonia for reuse instead of consuming it.
How it spread
The Couillet plant was producing by early 1865, and a second, much larger plant opened near Nancy in France in 1874. Ludwig Mond acquired rights to the process in 1872 and, with John Brunner, built a plant at Winnington in Cheshire that started up in 1874. In the United States, William Cogswell and Rowland Hazard obtained a license and formed the Solvay Process Company, whose plant at Syracuse, New York, was operating in 1884. By 1900 Solvay plants were running in France, Germany and elsewhere in Europe, and the company was among the earliest multinationals.
Who pushed back
The early plant was plagued by equipment breakdowns and problems controlling pressure and temperature, and in the fall of 1865 the main unit at Couillet blew up. The brothers rebuilt with money borrowed from their father.
The established Leblanc industry, centered in Britain, did not give way at once. A Solvay plant cost much more to build, and through the 1870s and 1880s the two processes were locked in fierce competition. Several British firms, including the leading Leblanc producer United Alkali, built ammonia-soda plants of their own, but most were short-lived and none rivaled Brunner Mond.
What changed first
Output at Couillet rose from more than a ton a day after the rebuilding to 10 tons a day by 1872. Raw materials were appreciably cheaper than for the Leblanc route, the process avoided sulfur, and its calcium chloride waste was far smaller in volume than Leblanc waste. In the 1880s the cost of making soda ash by the Leblanc method was estimated at 70 percent higher. By 1890 the Solvay process dominated world alkali production, and by 1900 about 90 percent of the nearly 2 million tons of soda ash made each year came from it.
What lasted
Cheap soda ash supplied the makers of glass and soap and the bleaching of fabrics and paper. The process made Leblanc's technology obsolete over roughly three decades and is remembered as a triumph of chemical engineering more than of chemical science. The licensees became pillars of the 20th century chemical industry: Brunner Mond became part of Imperial Chemical Industries in 1926, and the Solvay Process Company part of Allied Chemical & Dye in 1920. Ernest Solvay, by then very wealthy, gave much of his time to philanthropy in support of science and social reform. He died in Brussels in 1922.
Where it stands today
The Solvay process remains the major source of soda ash in most of the world. North America is the exception: soda ash from natural trona deposits in Wyoming, mined since the late 1940s, was cheaper, and the original Syracuse plant closed in 1986. In the 1930s the Chinese chemist Hou Debang developed a modified version that yields ammonium chloride in place of calcium chloride.
The Solvay company has announced a reworked "e.Solvay" process which it says cuts carbon dioxide emissions by 50 percent and reduces energy, water, salt and limestone use.
