Question

Explain Dow's process in inorganic chemistry.

Answer 1

Dow's process

• Dow's process was given by Henry Dow, it is used for the electrolytic extraction of Bromine.
• Hot brine rich in bromine ions is input to the reaction tower.
• Chlorine gas and water are introduced from the bottom of the reaction tower.

The diagram below shows the commercial preparation of bromine.

• In the reaction tower an oxidation-reduction reaction takes place, generating bromine:

$\underset{\mathrm{Bromide}\mathrm{ion}}{2{\mathrm{Br}}^{-}\left(\mathrm{aq}\right)}\underset{\mathrm{Chlorine}}{+{\mathrm{Cl}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Bromine}\mathrm{gas}}{{\mathrm{Br}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Chloride}\mathrm{ion}}{2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)}$

• The system is heated to prevent the bromine from remaining in the solution.
• Removal of the bromine from the solution (the steam carries the bromine vapors with it).
• The gas mixture containing the bromine vapours, residual chlorine, and steam rises to the top of the tower, while the liquid brine accumulates at the bottom of the tower.
• Further, the mixture undergoes condensation, separation, and drying to obtain bromine.

Thus, bromine is obtained from brine by Dow's process.