Question

What is Chloro-Alkali process?

Answer 1

Chloro-Alkali process:

• When electricity is passed through an aqueous solution of sodium chloride $\left(\mathrm{NaCl}\right)$ (called brine), then it decomposes its constituent elements which then react with water to give sodium hydroxide $\left(\mathrm{NaOH}\right)$.
• The process is known as the Chloro-Alkali process due to the formation of “chloro” for chlorine and “alkali” for sodium hydroxide as a product.
• The chloro-alkali process is an industrial process for the electrolysis of sodium chloride solutions.

Chemical Reaction:

• For the electrolysis of brine, a basic membrane cell is used.
• Chloride $\left({\mathrm{Cl}}^{-}\right)$ is converted to chlorine $\left({\mathrm{Cl}}_2\right)$ at the anode.
• In contrast to anions like hydroxide $\left({\mathrm{OH}}^{-}\right)$ and chloride, the ion-selective membrane does not permit the free passage of the counterion $\left({\mathrm{Na}}^{+}\right)$.
• Hydroxide and hydrogen $\left({\mathrm{H}}_2\right)$ gas are formed by the reduction of water at the cathode.

• The cathode and anode reaction is as follows:

$$\begin{gathered} \mathrm{Anode}:2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\to {\mathrm{Cl}}_2\left(\mathrm{g}\right)+2{\mathrm{e}}^{-} \\ \mathrm{Cathode}:2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2\left(\mathrm{g}\right) \end{gathered}$$

• In the end, sodium hydroxide and chlorine gas are produced by the electrolysis of an aqueous solution of sodium chloride.
• The corresponding chemical reaction is as follows:

$2\mathrm{NaCl}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{\mathrm{Electricity}}{\to }2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Diagram of Chloro-Alkali process