GB790510A - Improvements relating to the recovery of ammonia from gases - Google Patents

Abstract

<PICT:0790510/III/1> In a process for the selective recovery of ammonia values from gases which also contain weak acids, e.g. carbon dioxide, hydrogen sulphide, and/or hydrogen cyanide, the gases, after removal of suspended impurities, e.g. tar, and entrained solid particles, are passed at a temperature exceeding the dissociation temperature of the volatile ammonium compounds contained therein, e.g. above 60 DEG C. through a vessel containing a cation exchange material in the form of a porous exchange mass, and the adsorbed ammonia values are recovered during regeneration of the exchange mass after discontinuance of the gas flow. The gas from 1 passes through filter 2 to remove tar and mists and is cooled in tower 3 to about 65 DEG C. The cooled gas passes through cation exchanger column 5 where ammonia is adsorbed by less than 30 seconds contact. The cation exchange mass may be styrenemethacrylate resin or sulphonated copolymer of styrene and divinylbenzene and several exchange columns may be used. The ammonia-free gas passes by 14 through anion exchanger column 15, where H2S and HCN are adsorbed, and residual gas, presumably containing CO2, leaves at 15a for further processing. Condensates from 3, 5 are passed through 3a, 5a to separator 6, where tar is withdrawn at 7, and the collected aqueous condensates are either returned to the hot gas through 20, or passed through 20a to stripper 8. Sulphuric acid to regenerate ion exchanger in 5 is drawn from tank 13 and the acid solution of ammonium sulphate, after repeated use, is drawn from tank 12 to saturator 11. Strong ammonia water to regenerate ion exchanger in 15 is drawn from tank 16 and the solution of ammonium sulphide, or hydrosulphide, and/or ammonium cyanide, after repeated use is drawn from tank 17 to stripper 8, where it is steam distilled with the condensates. The distillate is withdrawn at 9 to waste, or as washing liquid. The distilled vapour mixture is led into saturator 11, where ammonia combines with excess acid to produce saturated ammonium sulphate solution, while the gaseous acids are withdrawn at 19 to sulphur or HCN recovery or to sulphuric acid processing. Alternatively, the cation exchanger may be regenerated with hot water and/or steam to produce ammonia gas. In all cases the cation exchanger is washed after regeneration with water as cold as possible to bring the ion exchanger to a temperature substantially below the entry temperature of the gas. Alternatively, the cation, or anion exchanger, may be regenerated by electro-dialysis to produce ammonia gas, or gaseous H2S and/or HCN. The cation or anion exchange masses may be fluidized or eddying layers. The aqueous condensates may, alternatively, be contacted with a cation exchanger.