A Membrane-Free and Energy-Efficient Three-Step Chlor-Alkali Electrolysis with Higher-Purity NaOH Production.

Conventional chlor-alkali processes are energy-consuming and environmentally unfriendly. To deal with this problem, we developed a three-step electrolysis (TSE) for a cleaner, energy-saving, and lower-cost chlor-alkali process. This new chlor-alkali process consists of three independent steps: a NaOH-production step in a Na0.44MnO2/oxygen-depolarizing cathode cell (step I), a Na+ and CI- extraction step in a Ag/Na0.44-xMnO2 cell (step II), and a CI2-production step in a graphite/AgCl cell (step III). This technology avoids the use of expensive ion-exchange membrane and toxic electrode materials, providing a great prospect to create a cleaner, energy-saving, and lower-cost chlor-alkali electrolysis process. This electrochemical ion coupling/decoupling technology can also be extended to other salt solutions (Na2SO4/NaNO3) to produce corresponding alkali (NaOH) and acid (H2SO4/HNO3), which has potential significance in the chlor-alkali industry.