Causticization

from Wikipedia, the free encyclopedia

The causticizing (Ätzendmachung) is an old method of the technical chemistry for the preparation of caustic sodium hydroxide and potassium hydroxide . It is also known as the soda-lime process for the production of sodium hydroxide.

General

Before the introduction of electrochemical synthesis processes for the production of alkali metal hydroxides ( chloralkali electrolysis ), causticization was used. For example, a soda solution with calcium hydroxide (slaked lime) was implemented.

Since calcium hydroxide is considerably more soluble than the by-product calcium carbonate , an almost complete precipitation reaction took place . The supernatant sodium hydroxide solution could be concentrated to solid sodium hydroxide (caustic soda) by evaporation .

Potassium hydroxide (caustic potash) was produced in an analogous manner from potash . At that time the caustic alkalis were mainly needed for the production of soap . Soap boilers made sodium hydroxide themselves from soda; industrial production only gained importance in the 19th century.

Large-scale procedure

The soda solution was diluted and reacted directly with quicklime in large iron kettles . The extinguishing heat released in the process contributed to the heating. In addition, heating was carried out by introducing steam. The soda came from the Leblanc process at the time and was accordingly contaminated with sulfate , sulfide , sulfite and thiosulfate . Sulphide and sulphite caused a bad odor. To clean the resulting caustic soda, air was blown in or saltpetre added, which oxidized many impurities. The solution was then concentrated and most of the salts were allowed to crystallize out.

literature

  • H. Ost: Textbook of technical chemistry . Published by Robert Oppenheim, Berlin 1890, pp. 82–83.

Individual evidence

  1. Detlef Gysau: Fillers Basics and Applications . Vincentz Network GmbH & Co KG, 2006, ISBN 978-3-87870-337-2 , p. 54 ( limited preview in Google Book search).