GB442528A - Improvements in or relating to the manufacture of alkali metal cyanides - Google Patents

Abstract

Alkali metal cyanides are obtained by reacting hydrogen cyanide or ammonium cyanide with an anhydrous alkali metal carbonate at elevated temperature, treating the resulting gaseous mixture to remove water vapour and/or carbon dioxide and preferably also ammonia, and either reintroducing the gases resulting from such treatment into the reaction zone or bringing them into contact with a fresh quantity of anhydrous alkali metal carbonate at elevated temperature. According to a modification, formamide is employed as a starting material, ammonia as well as water vapour and/or carbon dioxide being removed from the resulting gases before their further treatment. Temperatures of 200--500 DEG C. may be employed. If desired, a plurality of carbonate containing reaction vessels connected in series may be used, the gases being passed through the entire series with intervening removal of water vapour and/or carbon dioxide. When the carbonate in the first reaction vessel has been sufficiently converted into cyanide, the hydrocyanic acid gas may be led directly into the second vessel while the exit gases from the last reaction vessel after dehydration are passed into a fresh charge of carbonate. According to an example, formamide vapour and nitrogen are passed through finely divided anhydrous sodium carbonate at 415--435 DEG C. The ammonia is removed from the exit gases by means of dilute sulphuric acid and the water vapour by means of calcium chloride, the exit gases from the calcium chloride tube containing hydrocyanic acid being passed through a second reaction vessel containing finely divided anhydrous sodium carbonate heated to 445--455 DEG C. The exit gases from the second reaction vessel are passed through sodium hydroxide solution to absorb residual hydrocyanic acid.