XII Chemistry BIEK Topic - Sodium Carbonate (Ammonia-Solvay Process)

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