Sodium Carbonate (Ammonia-Solvay Process)

2nd Year Chemistry Notes

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Sodium Carbonate (Ammonia-Solvay Process)



Introduction

Sodium Carbonate is an important compound. It is manufactured by Ammonia-Solvay Process.





Raw Meterials



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
filteration.



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