Castner-Kellner method (sodium hydroxide)
The Castner-Kellner process (after Hamilton Castner and Karl Kellner ) is an electrolytic process for the production of sodium hydroxide from saline solution ( brine ). It was also developed independently by Castner and Kellner in the 1890s (also the amalgam process of chlor-alkali electrolysis ).
Procedure
The electrolysis cells on the outside (see illustration) have graphite anodes (A) and a mercury cathode (M) and contain sodium chloride solution. The sodium collects in the mercury, chlorine gas is formed as a by-product on the anodes. In the middle is another cell with a cathode made of iron (D), in which M now serves as an anode, in which sodium changes into aqueous solution and sodium hydroxide is formed (by-product is hydrogen gas). A vibrating mechanism transports the sodium amalgamated in the mercury from the outer cells to the center.
It was developed in 1892 by Castner in Birmingham and independently of Kellner in Austria and first implemented industrially in Saltville, Virginia in 1896 and by the Castner-Kellner Akali Company in Runcorn in England in 1897 and achieved great importance in the first half of the 20th century. In the 1970s, particularly in the USA and Japan, it was abandoned and replaced by diaphragm processes because of environmental concerns . In the USA, in contrast to Western Europe, after the Second World War, the focus was on improving the diaphragm process. While in the USA in 1998 over 70% of production was carried out with the diaphragm process and the Castner-Kellner process using mercury only made up just over 10%, the Castner-Kellner process was and had the dominant process in Western Europe in the 1960s still in 1998 a share of around 60%. In Japan, on the other hand, the Castner-Kellner trial was pushed back in accordance with environmental protection regulations as a result of the Minamata incident in 1956 (mercury poisoning among fishermen due to environmental contamination by an organic mercury compound from an acetaldehyde factory) in the 1970s and was no longer used until 1998 (but rather almost 90% an ion exchange membrane process). Although a link between mercury poisoning and environmental pollution from the Castner-Kellner trial has never been proven, strong public pressure led to the passage of laws (1973) that forced the chlor-alkali industry to move away from the Castner-Kellner trial (the 95% dominated in Japan) to switch to the diaphragm process. However, since the diaphragm process produced caustic soda of lower quality (and was more energy-intensive), alternatives were sought in Japan. The possibility of an alternative in the form of ion exchange membranes ( membrane process ) had been known for a long time and was quickly developed to maturity in Japan due to the new legal situation in the 1970s.
Individual evidence
- ^ Alan E. Comyns, Encyclopedic Dictionary of Named Processes in Chemical Technology, CRC Press, 4th Edition 2014, p. 58
- ↑ Masaru Yarime: Innovation of clean technology through environmental policy: Emergence of the ion exchange membrane process in the Japanese chlor-alkali industry . In: Saeed Parto, Brent-Herbert Copley (Ed.): Industrial Innovation and Environmental Regulation , United Nations University Press 2007, ISBN 978-92-808-1127-8 , p. 174