Solvay process

The Solvay process or ammonia-soda process is the major industrial process for the production of sodium carbonate (soda ash, Na2CO3). The ammonia-soda process was developed into its modern form by Ernest Solvay during the 1860s. The ingredients for this are readily available and inexpensive: salt brine (from inland sources or from the sea) and limestone (from quarries). The worldwide production of soda ash in 2005 has been estimated at 42 million metric tons, which is more than six kilograms (13 lb) per year 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. This method superseded the Leblanc process. The Solvay process or ammonia-soda process is the major industrial process for the production of sodium carbonate (soda ash, Na2CO3). The ammonia-soda process was developed into its modern form by Ernest Solvay during the 1860s. The ingredients for this are readily available and inexpensive: salt brine (from inland sources or from the sea) and limestone (from quarries). The worldwide production of soda ash in 2005 has been estimated at 42 million metric tons, which is more than six kilograms (13 lb) per year 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. This method superseded the Leblanc process. 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 (K2CO3), whereas the ashes from these special plants yielded 'soda ash' and its predominant ingredient sodium carbonate (Na2CO3). The word 'soda' (from the Middle Latin) originally referred to certain plants that grow in salt solubles; 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, sulfuric 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. It has been reported that in 1811 French physicist Augustin Jean Fresnel discovered that sodium bicarbonate precipitates when carbon dioxide is bubbled through ammonia-containing brines – which is the chemical reaction central to the Solvay process. The discovery wasn't published. As has been noted by Desmond Reilly, 'The story of the evolution of the ammonium-soda process is an interesting example of the way in which a discovery can be made and then laid aside and not applied for a considerable time afterwards.' Serious consideration of this reaction as the basis of an industrial process dates from the British patent issued in 1834 to H. G. Dyar and J. Hemming. There were several attempts to reduce this reaction to industrial practice, with varying success. In 1861, Belgian industrial chemist Ernest Solvay turned his attention to the problem; he was apparently largely unaware of the extensive earlier work. His solution, a 24 metres (79 ft) gas absorption tower in which carbon dioxide bubbled up through a descending flow of brine. This, together with efficient recovery and recycling of the ammonia, proved effective. By 1864 Solvay and his brother Alfred had acquired financial backing and constructed a plant in Couillet, today a suburb of the Belgian town of Charleroi. The new process proved more economical and less polluting than the Leblanc method, and its use spread. In 1874, the Solvays expanded their facilities with a new, larger plant at Nancy, France. In the same year, Ludwig Mond visited Solvay in Belgium and acquired rights to use the new technology. He and John Brunner formed the firm of Brunner, Mond & Co., and built a Solvay plant at Winnington, near Northwich, Cheshire, England. The facility began operating in 1874. Mond was instrumental in making the Solvay process a commercial success. He made several refinements between 1873 and 1880 that removed byproducts that could slow or halt the process. In 1884, the Solvay brothers licensed Americans William B. Cogswell and Rowland Hazard to produce soda ash in the US, and formed a joint venture (Solvay Process Company) to build and operate a plant in Solvay, New York.