Chlorine manufacture - Membrane Cell

This type of cell uses a polymer developed in the 1970s, poly(tetrafluoroethene). The polymer membrane separates the anode and cathode compartments, but only allows cations (+) to pass through. This means that the sodium ions can migrate through the membrane, but the chloride and hydroxyl ions cannot, giving much higher purity sodium hydroxide.

 

diagram: membrane cell
diagram: membrane cell diagram: membrane cell diagram: membrane cell
Some initial purification of salt is needed, adding to costs and energy use. The sodium hydroxide is produced is at about 35% strength, so some concentration is also needed to bring it to 50% strength for subsequent commercial use. Overall, however, the process is less energy intensive than the other processes, particularly as the electrolysis draws a lower current.

There are no known environmental problems associated with the use of the ion exchange membrane, and it is particularly effective at keeping the products separate, leading to high quality products.
image: The membrane process

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