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The Chlor-Alkali Process

Discover more about the history of industrial electrolysis, modern-day chlor-alkali processes and key industry associations.

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Large-scale electrolysis technology is used by industry for the manufacture of chlor alkali products such as chlorine (Cl2) and sodium hydroxide (NaOH / caustic soda), through the electrolysis of sodium chloride (NaCl).

Other uses of the process include the production of potassium hydroxide (KOH) or hydrochloric acid (HCI / muriatic) and sodium hypochlorite (bleach).

Chlor Alkali Applications

The chlor-alkali processes have been used in industrial settings since the 19th century. The resultant products offer a host of different applications and the process itself is now the principal source of all chlorine globally with territories like the United States, Western Europe, China, India, Brazil and Japan leading the globe in production capacity.

The application of the chlor-alkali process is to produce 3 main chemicals: chlorine, sodium hydroxide (caustic soda) and potassium hydroxide (caustic potash).

Primarily, chlorine is used to make chemical compounds or organic chemicals such as phosgene for polycarbonate, methyl-chloride for silicones, polyvinyl chloride (PVC), methylene chloride for adhesives, polyurethanes, sulphur chlorides for crop protection and dyes, and titanium dioxide for catalysts.

Products made from chlorine are used in a variety of sectors, which include:

  • Construction (PVC windows, water pipes, flooring, roofing materials)
  • Energy (batteries, solar panels, wind turbine blades)
  • Food (crop protection, thickening agents)
  • Health & personal care (bleaches, cosmetics, detergents, dental treatments/cements, deodorants, dry cleaning, textiles)
  • Home Care (paints, adhesives, refrigerants)
  • Paper (inks, coatings, pulp)
  • Pharmaceuticals (cancer treatment)
  • Safety (water treatment)
  • Sport (exercise equipment, clothing)
  • Technology (circuit boards, fibre-optics, semiconductors, smartphones)
  • Transportation (car parts, brake fluid, anti-freeze)

Products made from sodium hydroxide (caustic soda) are also used in many sectors, including:

  • Construction (carbon fibre, mining, metal plating)
  • Energy (oil refining, wind turbines)
  • Health & personal care (soaps, toothbrushes, anticoagulants, shampoo, vitamins)
  • Household (cooking equipment, foils, doors and windows)
  • Sport (bicycles, tennis rackets, sails)

Products made from potassium hydroxide (caustic potash) feature in sectors such as :

  • Agriculture (fertiliser)
  • Energy (batteries)
  • Food (additives, wine, chocolate)
  • Industry (steel foundry, rubber, titanium dioxide, fire suppressant, welding)
  • Transport (de-icing fluid)

Euro Chlor, a trade body that represents the European chlorine industry, features a detailed and interactive list of applications for chlorine, caustic soda and caustic potash :

History of Industrial Electrolysis

Beginning in the early 19th century, the evolution of electrolysis for chlor alkali from bench-scale experiments to industrial-scale installations developed over almost 100 years.

1800 – William Cruikshank was credited with the first formation of chlorine from brine by the method of electrolysis.

1833 – Faraday articulated the laws of electrolysis which state: The amount of substance decomposed by an electric current is proportional to the length in time and current of the electric current producing electrolysis.

1851 & 1853 – Cook and Watt obtained patents for electrolysis of chlorine from brine.

1880’s – After new inventions made the supply of high electrical current to support the process possible, two basic electrolysis methods were investigated; the “mercury cathode” and the “diaphragm” cell.

1892 - In England, Castner patented the Rocking Mercury Cell method, while in Austria, Kellner patented a mercury cell of similar design.

1893 – A large installation of diaphragm electrolytic cells was made at Rumford Falls in Canada.

1895 - Following a patent agreement with Solvay in Belgium, (who held the patent rights to the Kellner Cell) the Castner-Kellner Company was formed.

1897 - A large industrial scale electrolysis installation was erected at Weston Point, Runcorn, United Kingdom in 1897, producing chlorine, and caustic soda. To this day, INEOS maintain large scale electrolysis assets on this original site, and it remains the headquarters of INEOS Electrochemical Solutions.

1900’s – A number of Rocking Cell and diaphragm installations began to appear around the world and remained popular for many years.

1950’s – Membrane cell technology process was developed, a more energy-efficient process that doesn’t rely on the use of harmful substances.

Present day – The majority of chlor-alkali cell room installations now use the membrane cell process. Diaphragm and mercury cell processes are used to a much lesser amount due to their use of asbestos and mercury respectively, with many areas of the world using environmental legislation to close any mercury plants still in existence. Ongoing development efforts for the membrane cell process focus on reducing energy consumption even further, with key innovation in electrode coatings, optimised ‘zero-gap’ electrode designs and improved membrane materials.

Industry Associations

The chlor-alkali industry is represented at both national and international level by a number of trade organisations. Many of them host annual events, training workshops for chlorine and caustic soda applications, chlor-alkali safety guidance and best practice resources for members as well as providing stewardship to the industry. Annual chlorine and caustic production data is also often compiled by these organisations.