In chlor-alkali industries Chlorine (Cl2), Hydrogen (H2) and Sodium Hydroxide (caustic soda - NaOH) are manufactured by means of electrolysis process.
In chlor alkali industries three types of electrolytic process are adopted for the production of caustic, chlorine, hypochlorite chemicals :
Membrane cell process (louver anode, mesh anodes)
Diaphragem cell process (box anode, perforated anode)
Mercury cell process (mesh, strip anode, rod, weir anode)
In each process salt (brine) solution is electrolyzed by the action of direct electric current, which converts the chloride ions to chlorine.
The reaction is :
2NaCl + 2H2O = Cl2 + H2 + 2NaOH
In all the methods chlorine (Cl2) is produced at the positive electrode (anode) and the hydrogen (H2) and Sodium Hydroxide (NaOH or caustic soda) are produced directly or indirectly at the negative electrode (cathode). Membrane or Diaphragm or Mercury is used to separate the anode products from the cathode products according the process adopted.