16.2 Manufacture of Sodium Carbonate by Solvay's Process

Principle of Solvay's process lies in the low solubility of sodium bicarbonate at low temperature i.e. at $15^{\circ}C$ . When ${\mathrm{C}\mathrm{O}}_2$$\mathrm{CO}_{2}$ is passed through an ammonical solution of NaCl called ammonical brine only ${\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}\mathrm{O}}_{3(\mathrm{s})}$$\mathrm{NaHCO}_{3(\mathrm{s})}$ precipitates.

16.2.1 Raw Materials

The raw materials needed for this process are cheap and easily available. They are in abundance, such as,

(i) Sodium chloride (NaCl) or brine. (ii) Limestone (CaCO3). (iii) Ammonia gas $({\mathrm{N}\mathrm{H}}_3)$$(\mathrm{NH}_{3})$ .

Basic Reactions

The process consists of the following steps:

(i) Preparation of ammonical brine:

First of all, ammonical brine is prepared by dissolving ammonia gas in sodium chloride solution (brine).

(ii) Carbonation of ammonical brine:

Ammonical brine is fed into carbonating tower and carbon dioxide is passed through it. Following reactions take place in the carbonating tower.

The temperature of the mixture is lowered to $15^{\circ}C$ and precipitates of $\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}{\mathrm{O}}_3$$\mathrm{NaHCO_3}$ are obtained.

(iii) Filtration of precipitates:

The milky solution from the carbonating tower is filtered to get sodium bicarbonate. It is used as a baking soda.

(iv) Calcination: