Membrane cell process for chlor alkali production

The process makes use of brine and a membrane cell with positive and negatively charged electrodes. The anode (negative charge) oxidizes the chloride ion, which loses an electron to become free chlorine gas. The hydrogen ions are pulled at the cathode and form hydrogen gas. The semi-permeable membrane of the cell allows for the sodium ions to travel to a second chamber, where they react with water to produce sodium hydroxide.

To explain it a bit more in detail we’ll have to take a look at Fig. 2 which describes the basic membrane cell used in the electrolysis of brine,

At the anode (A), chloride (Cl⁻) is oxidized to chlorine. The ion-selective membrane (B) allows the counterion Na+ to freely flow across, but prevents anions such as hydroxide (OH⁻) and chloride from diffusing across. At the cathode (C), water is reduced to hydroxide and hydrogen gas.

The chemical reactions that take place are as follows,

(A) Saturated brine is passed into the first chamber of the cell where the chloride ions are oxidised at the anode, losing electrons to become chlorine gas,

2Cl- → Cl2 + 2e-

(C) Positive hydrogen ions pulled from water molecules are reduced by the electrons provided by the electrolytic current, to hydrogen gas, releasing hydroxide ions into the solution

2H2O + 2e- → H2 + 2OH-

(B) Sodium ions (Na+) pass to the second chamber where they react with the hydroxide ions to produce caustic soda (NaOH)

The overall reaction for the electrolysis of brine is,

2NaCl + 2H2O → Cl2 + H2 + 2NaOH

Industrial salt (NaCl) contains impurities which can affect the membrane cell process, like sulfate which can accumulate in the membrane cell when it is not removed from the recycled brine. Please check our pages for more information:

Removal of sulfate from chlor alkali brine by nano filtration

Removal of Sulphates from Chlor Alkali Brine

Lenntech can access and provide you the best solution for chlor alkali brine treatment.

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