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How to choose Ion change membrane for producing sodium hypochlorite?
1.Three routes for producing sodium hypochlorite by electrolyzing brine:
Membrane-free method (the simplest, but with low product concentration and many impurities)
Diaphragm method (asbestos or polymer diaphragm, blocking gas but not selectively allowing ions to pass
Ion-exchange membrane method (cation exchange membrane, selectively permeating Na⁺, blocking Cl⁻ and OH⁻, with high product concentration and good purity)
2.Selection of ion-exchange membranes
The core uses Cation Exchange Membrane (CEM, Cation Exchange Membrane)
Specifically, it is a perfluoride ion-exchange membrane, that is, a perfluorosulfonic acid membrane (PFSA/Nafion type) or a perfluorocarboxylic acid/sulfonic acid composite membrane
Perfluorinated ion-exchange membranes for industrial chlor-alkali (such as DuPont Nafion, Asahi Kasei, Togo, etc.)
For the sodium hypochlorite generator scenario, research indicates that perfluorosulfonic acid ion-exchange membranes (single-layer) should be used instead of perfluorosulfonic acid-perfluorocarboxylic acid composite membranes (the latter being more prone to foaming and damage).
3.Why choose cation exchange membranes
Only Na⁺ (cations) are allowed to migrate from the anode chamber to the cathode chamber
Prevent Cl⁻ from migrating to the cathode chamber and prevent OH⁻ from reverse-migrating to the anode chamber
Prevent Cl₂ from reacting with NaOH in advance to form NaClO (if it is for the production of caustic soda, prevention is necessary, but in the production of sodium hypochlorite, it is actually Cl₂+NaOH→NaClO+NaCl+H₂O that occurs under controlled conditions).
4.Specific recommendations
Industrial grade: Perfluorocarboxylic acid/sulfonic acid composite ion-exchange membranes (such as the Nafion series composite membranes used in the chlor-alkali industry - the perfluorocarboxylic acid layer on the surface faces the anode, and the perfluorosulfonic acid layer is in the middle), this is the standard for chlor-alkali
However, for situations where sodium hypochlorite is specifically produced (unlike the production of caustic soda which requires extremely high alkali concentration), using a single-layer perfluorosulfonic acid film is actually more suitable - it has lower resistance and is less prone to foaming
For small-scale or medium-scale trials, commercial Nafion membranes (such as N117) can be used.