Ion exchange membrane
Ion exchange membrane

Ion exchange membrane

Now chlor alkali plants use membrane separation process for producing NaOH, Cl2 and H2. Ion exchange membrane is the core spare part of membrane separation process, with selective permeability. The ion exchange membrane is made from polymer material with selective permeability for ion, also called ion selective permeability membrane.
The following describes the major principles of  ion exchange membrane chlor-alkali process.
In the ion exchange membrane process for producing caustic soda, permselective cation exchange membranes are installed between cathodes and anodes.
Electrolysis is carried out while brine is circulated in Anolyte Compartment, and caustic soda through Catholyte Compartment.

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.

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