Sodium
Carbonate (Ammonia-Solvay Process)
Introduction
Sodium Carbonate is an important
compound. It is manufactured by Ammonia-Solvay Process.
Raw Materials
The raw materials for the manufacture
of sodium carbonate are
1. Brine
2. Ammonia, which is made by Haber’s
Process
3. CO2, CaOH, which are obtained from
limestone.
Ammonia-Solvay Process
The Ammonia-Solvay Process consist of
the following steps.
Step I – Ammonation of Brine
In first step, ammonia gas is mixed
with brine. This process is carried in Ammonation Tower. The ammonation tower
consist of mushroom shaped buffels at short intervals. Brine is introduced from
the top and ammonia is introduced from bottom. They both flow towards each
other. Buffels control the flow of brine and ensure that they are mixed to the
point of saturation with ammonia.
Step II – Carbonation of Ammonated Brine
In this step, ammonated brine is
mixed with carbon dioxide brine is mixed with carbon dioxide in a tower called
carbonating tower or Sonvai tower. Ammonated Brine is fed from the top where as
carbon dioxide ascends from the bottom. When these two substances meet, the
following chemical reactions takes place.
2NH3 + CO2 + H2O —-> (NH4)2CO3
(NH4)2CO3 + CO2 + H2O —-> 2NH4HCO3
2NH4HCO3 + NaCl —-> NaHCO3 + NH4Cl
Sodium bicarbonate is relatively
insoluble, which is precipitated out from the solution by cooling the lower
part of the tower. Sodium bicarbonate is separated from soluble ammonium
chloride by vacuum filtration.
Step III – Production of Soda Ash
Sodium bicarbonate is heated in a
long iron tube to obtain anhydrous sodium carbonate or Soda Ash.
This carbon dioxide is recycled to
the solvay tower. This hydrated sodium carbonate is also called washing soda.
Recovery of Ammonia
Ammonia gas is recovered from the
remaining solution by treating it with Calsium Hydroxide.
2NH4Cl + Ca(OH)2 —-> CaCl2 + 2H2O
+ NH3
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