Sodium Carbonate by the Ammonia Process

The raw materials from which the sodium carbonate of commerce is manufactured are common salt, NaCl, and limestone, CaC03, but these substances do not spontaneously react with each other, rather a reaction would take place in the opposite direction, as indicated by the arrow. 

Much ingenuity has been exercised by chemists in attempts to effect this change through a series of reactions. In the older Le Blanc soda process sulphuric acid is used in the first step and coal (carbon) in another, and neither of these auxiliary substances is recovered. The soda process which is employed exclusively today is known as the Solvay or ammonia process and uses ammonia as an auxiliary substance. The ammonia is almost 100 per cent recoverable, however, and can be used over and over indefinitely. The successive steps in the process are as follows  

Heating limestone in kilns to obtain quicklime and carbon dioxide  

Passing carbon dioxide and ammonia into saturated brine in an absorption tower  

Recovery of ammonia by treating the ammonium chloride filtrate with quicklime, expelling the ammonia gas to be used again in step 2, and working up the calcium chloride left behind  

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