Asbestos is chemically inert and able to effectively separate chlorine and sodium hydroxide in electrolytic cells. The chloralkali chemical production process involves the separation of the sodium and chloride atoms of salt in saltwater (brine) via electricity to produce sodium hydroxide (caustic soda), hydrogen, and chlorine. This reaction occurs in an electrolytic cell. The cell contains two compartments separated by a semi-permeable diaphragm, which is made mostly of chrysotile asbestos. The diaphragm prevents the reaction of the caustic soda with the chlorine and allows for the separation of both materials for further processing. According to the EPA, diaphragms are typically used for 1-3 years before they must be replaced.
Function of asbestos diaphragm shown. Image credit: The Essential Chemical Industry