Chlor-alkali electrolysis

The Chlor-Alkali Electrolysis is applied for production of Caustic Soda (NaOH) or Caustic Potash (KOH), Chlorine (Cl2) and Hydrogen (H2) by electrolysis of sodium/potassium chloride brine (NaCl/KCl solution).
Modern Membrane Electrolysers are used according to the conclusion of the BREF document (Best Available Technique Reference Document) for Chlor-Alkali industry.

Feed Stock and Products

Raw materials of the Chlor-Alkali Electrolysis are Salt (NaCl or KCl) and water (H2O). Sources of salt include sea water (solar salt NaCl), mineral deposits (rock salt NaCl or KCl) or salt produced by brine evaporation (vacuum salt NaCl or KCl).

Caustic in the form of a 32 % NaOH solution or 29 % to 32 % KOH solution, Hydrogen gas and Chlorine gas are the primary products obtained in a Chlor-Alkali Electrolysis process applying membrane cells. These products can be stored into the following commercial form:

  • Hydrochloric acid (32 % - 36 % HCl)
  • 50 % caustic soda / 50 % caustic potash
  • Liquid chlorine:
    • low pressure storage e.g.: -34°C / 1 bar a or
    • high pressure storage e.g.: +20°C / 6.8 bar a

Dry and compressed chlorine gas can also be fed directly by pipeline to the chlorine consumers.

As large quantities of these products are required as key chemicals for a wide range of end products, Chlor-Alkali plants are in most cases operated in conjunction with plants from the following sectors of industry:

  • Chemical industry
  • Pulp and paper industry (supply with bleaching chemicals)
  • Industry with a high chlorine demand such as the petrochemical and plastics industry (e.g. for VCM, TDI, MDI, Trichloromethane, Epichlorohydrin)
  • Industry with a high Caustic Soda demand such as Electrowinning of Aluminium and Pharmaceutical industry and e.g. in form of Potassium Carbonate in the Glass industry

Process Technology and Electrolysers

CAC can provide electrolysers from the world leading manufacturers. Therefore specific requirements of the Chlor-Alkali plant can be met. 

Process Technology

The Chlor-Alkali Electrolysis process includes the following stages:

  1. Dissolving of rock salt, vacuum salt or solar salt
  2. Primary brine purification
  3. Brine polishing
  4. Membrane electrolysis including transformer and rectifier installation
  5. Catholyte and hydrogen treatment
  6. Anolyte and chlorine gas treatment
  7. Drying, compression, liquefaction and storage of chlorine
  8. Caustic Evaporation including filling and loading
  9. optional: NaOH (KOH) Flaking or Prilling, bagging und loading
  10. Chlorine absorption system: emergency absorption, optional with hypochlorite production
  11. Hydrochloric acid synthesis (HCl 30 % - 36 %)


  • Low energy consumption
  • No environmental pollution by mercury or asbestos
  • High product purity
  • Ease of handling and operation
  • Low investment and operating costs

References Chlor-Alkali Plants

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