Chlorine is produced in the Anolyte Compartment, hydrogen and caustic soda are produced in the Catholyte Compartment according to the following reaction:

NaCl is ionized into Na⁺ ion and Cl^– ion. Electric charges of chloride ion are discharged at the anode to change into chlorine gas. Meanwhile, sodium ions are transferred through the ion-exchange membrane into the Catholyte Compartment.

In the Catholyte Compartment, water changes to hydrogen gas and hydroxyl ions. Caustic soda is formed by the reaction of sodium ions with hydroxyl ions.

The above main reaction is essentially the same as that of the conventional diaphragm process. But in the membrane process, pure caustic soda can be obtained due to complete separation of electrolyte and selective permeation of sodium ions.