GB321982A - Improvements in or relating to the purification of industrial gases with the recovery of by-products - Google Patents

Abstract

321,982. Carpmael, A., (I. G. Farbenindustrie Akt.-Ges.). Aug. 23, 1928. Materials for purifying.-Industrial gases are washed with a liquor comprising ammonium polythionate and ammonium thiosulphate and sufficient ammonia completely to absorb hydrogen sulphide and fix the hydrogen cyanide. In most cases the ammonia content of the gas requires supplementing for this purpose and owing to the excess of ammonia which is required to effect the reaction between ammonia and hydrogen sulphide, additional sulphur is also necessary for conversion of all the ammonia into ammonium sulphate. This is preferably supplied in the form of sulphur dioxide during regeneration of the liquor. To obtain ammonium sulphate and thiocyanate the wash liquor is boiled and after filtration from the separated sulphur is subjected to fractional evaporation. Ammonium sulphate is thereby separated almost completely from the ammonium thiocyanate solution. In an example crude coal gas containing 1.2 per cent of ammonia, 0.8 per cent of hydrogen sulphide and 0.1 per cent of hydrogen cyanide is treated with the wash liquor. 0.74 per cent of ammonia and 0.22 per cent of sulphurous acid being added. The two-stage process described in Specification 292,669 may be utilized by removing in the first stage an additional quantity of hydrogen sulphide corresponding to the hydrogen cyanide content of the gas so that the ammonia available in the second stage completely suffices for combining with the remainder of the hydrogen sulphide and the hydrogen cyanide.