Solvay process

The Solvay process or ammonia-soda process is the major industrial process for the production of sodium carbonate (soda ash). The ammonia-soda process was developed into its modern form by Ernest Solvay during the 1860s. The ingredients for this process are readily available and inexpensive: salt brine (from inland sources or from the sea) and limestone (from mines). The worldwide production of soda ash in 2005 has been estimated at 42 million metric tons, which is more than six kilograms per year (13 lb) for each person on Earth. Solvay-based chemical plants now produce roughly three-quarters of this supply, with the remainder being mined from natural deposits.

The name "soda ash" is based on the principal historical method of obtaining alkali, which was by using water to extract it from the ashes of certain plants. Wood fires yielded potash and its predominant ingredient potassium carbonate, whereas the ashes from these special plants yielded "soda ash" and its predominant ingredient sodium carbonate. The word "soda" (from the Middle Latin) originally referred to certain plants that grow in salt marshes; it was discovered that the ashes of these plants yielded the useful alkali soda ash. The cultivation of such plants reached a particularly high state of development in the 18th Century in Spain, where the plants are named barrilla; the English word is "barilla." The ashes of kelp also yield soda ash, and were the basis of an enormous 18th Century industry in Scotland. Alkali was also mined from dry lakebeds in Egypt.

By the late 18th century these sources were insufficient to meet Europe's burgeoning demand for alkali for soap, textile, and glass industries. In 1791, the French physician Nicolas Leblanc developed a method to manufacture soda ash using salt, limestone, sulphuric acid, and coal. Although the Leblanc process came to dominate alkali production in the early 19th century, the expense of its inputs and its polluting byproducts (including hydrogen chloride gas) made it apparent that it was far from an ideal solution.

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