In the past few years, the price of chlorine has skyrocketed owing to several factors, including the pandemic-inspired boom in new pool construction, the August 2020 trichlor manufacturing plant-Biolab fire, as well as numerous equipment failures at various chlor-alkali manufacturing plants.

Every few months, in fact, it seems that another chlor-alkali facility is invoking force majeure, a legal defense that frees a company from meeting the terms of their contract when an extraordinary event takes place outside of their control. This June, it was Westlake Chemical. Last April, it was Olin. In 2021, it was OxyChem.

These three companies (Olin, OxyChem, and Westlake) are the leading players in the U.S. chloralkali market, which supply the U.S. and the world with chlorine and a variety of other commodities. And every time they invoke the force majeure defense, the national supply of chlorine is threatened, which contributes to price increases.

So now seems like a good time to get a handle on what, exactly, is the chlor-alkali process.

Although it is an element, chlorine does not exist naturally on our planet, but is rather manufactured by electrolysis of saltwater.

The chlor-alkali process is the industrial process for the electrolysis of sodium chloride solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda). The chlorine and caustic soda created by this process are produced for a variety of uses.

The process is usually conducted on a solution of sodium chloride (NaCl) with water, in which case sodium hydroxide (NaOH or caustic soda), hydrogen, and chlorine result. If calcium chloride or potassium chloride is used, the products contain calcium or potassium instead of sodium.

The most common chlor-alkali process involves the electrolysis of sodium chloride in water in a membrane cell. At the anode, chloride is oxidized to chlorine, Cl2. At the cathode, water is reduced to hydroxide and hydrogen. An ionselective membrane allows sodium ions to pass across to react with the hydroxide ions to form caustic soda.

The diaphragm cell process is a lesser common method, similar to the membrane cell in that chloride ions are oxidized at the anode to produce chlorine, and at the cathode, water is split into caustic soda and hydrogen. The diaphragm prevents the reaction of the caustic soda with the chlorine. However, the caustic soda must usually be concentrated to 50% and the salt removed. Meanwhile, the chlorine contains oxygen and must often be purified.

Chlorine, the desired product made from the chlor-alkali process, is then used for a staggering number of purposes. Obviously, it can be converted to bleach, to be used for disinfection purposes. But it is also an essential component for a variety of solvents, like chloroform, methylene chloride, etc; vinyls, such as PVC; catalysts; and chlorinated isocyanurates.