Ammonia-soda
Ammonia-soda : Also called the Solvay process. A process for making sodium carbonate. The basic process was invented and partially developed in the first half of the 19th century by several workers, but the key invention was made by E. Solvay in Belgium in 1861. The first plant was built at Couillet, Belgium, in 1864 and thereafter the process became accepted worldwide, displacing the Leblanc process. The raw materials are limestone and salt; calcium chloride is a waste product. The overall reaction is: CaCO3 + 2NaCl + CaCl2 + Na2CO3. When carbon dioxide is passed into a nearly saturated solution of sodium chloride containing some ammonia, ammonium bicarbonate is formed. The heart of the process is the exploitation of the equilibrium between this bicarbonate and sodium and ammonium chlorides: NH4HCO3 + NaCl NaHCO3 + NH4Cl. In this system, the least soluble component is sodium bicarbonate, so this crystallizes out. On calcination it yields sodium carbonate and the carbon dioxide is recycled. The ammonia is recovered by adding calcium hydroxide, producing calcium chloride waste and liberating the ammonia for re-use: 2NH4Cl + Ca(OH)2 + 2NH3 + CaCl2 + 2H2O. (Check source for accuracy of chemical formula)
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