GB520327A - Improvements in the purification of gases - Google Patents

Abstract

520,327. Gas-washing, plant and' processes. JOHNSON, G. W. (I. G. Farbenindustrie Akt.- Ges.). Feb. 18, 1938, Nos. 5131 and 6030. Drawings to Specification. [Class 55 (ii)] [Also in Group III] In the selective removal of sulphuretted hydrogen from gases containing both sulphuretted hydrogen and carbondioxide, the gases are washed with water in the presence of sufficient ammonia to react with the sulphuretted hydrogen, the time of contact being sufficiently short to avoid absorption of the carbon dioxide. A fraction of a second to several seconds is specified. The ammonia may be present in the gas to be purified; or' it may be added thereto before the washing operation, or it may be present in the washing liquor such as when gas liquor is used, or it may be re-cycled to the gas or washing liquor from a subsequent separation of a used washing liquor. The, ammonia is preferably introduced at a number of points before absorption of the H 2 S is complete, such as at different parts of a column. Washing temperatures of below 0‹C. to 35 ‹C. may be used, from 15 to 25‹C. being preferred. The nearly H 2 S free gas containing CO 2 and NH 3 is then scrubbed to remove the latter either with water or ammonia liquor to remove both together or with acids to selectively remove the ammonia. In the first case the foul washing liquor may be heated to drive off the mixed gases ; the latter may be separated by absorption in strong acids or acidic solutions such as sulphuric acid, nitric acid, sulphurous acid, sulphates or thionates, to form ammonium salts and freeing the carbon dioxide. In the second case, the gas is directly washed with the acids or acidic solutions referred to ; or with difficultly volatile weak inorganic or organic acids such as solutions of citric acid, amino-carboxylic acids, e.g., glycocoll, alamine, amino-sulphonic acids, or phenols, the ammonium salts of which in aqueous solution split into free ammonia and the acid on heating. The first washing liquor comprising mainly ammonium sulphide may be worked up to free H 2 S and form ammonium salts by heating the liquor and passing the gases into strong H 2 SO 4 or HC1. These washing liquors, containing NH 3 and H 2 S or the subsequent washing liquors containing NH 3 and CO 2 may be separated into NH 3 and the gaseous weak acid by treatment with strong organic bases to bind the gaseous weak acid as salts and leave the free. ammonia. Such preferred bases comprise alkylamines containing at least 3 atoms of N 2 , and the following are specified: condensation products of diamines, triaminopropane, or di-aminopropanol, NH 3 splitting off in each case, and alkyleneimine polymerization products. The latter may be used in solutions or emulsions in water or oil and at temperatures at which the salts are stable, such as 40 to 75‹C. The complex salt solutions may then be heated in a separate vessel to 100‹C. or higher, the gaseous weak acid being driven off. A column may be used having temperatures of 30-50‹C. and 90-95‹C. in its upper and lower part respectively, followed by a tower for regeneration of the bases and separation of the gaseous weak acids. The strong organic bases may be replaced by alkaline reacting salts of weak organic acids. These salts may be formed from alkalies, alkaline earths, diethanolamine, triethanolamine, ethylene diamine, or. their polymerization products combined with monohydric and polyhydric, mononuclear and' polynuclear phenols, e.g., phenol, cresols, xylenols, naphthols, chlorphenols, aminophenols, or aminocarboxylic acids, e.g., alamine, methyl- and dimethyl-alamine, or amino-sulphonic acids, e.g., taurine and its N- alkyl derivatives. The separation of NH 3 , H 2 S and CO 2 from washing liquors containing them may also be effected by boiling off the vapours and separating them by their selective solubility in water, ammonia liquor or alkali or alkaline earth salt solutions at various temperatures. NH 3 is absorbed without CO 2 or H 2 S. Solutions specified comprise ammonium nitrate, thiecyanate or sulphate, potassium nitrate, calcium chloride or nitrate, and magnesium chloride. Washing towers in which the liquid temperature rises to 70-90‹C. in'the lower part may be used. In the original washing of the coal gas &c. reduced or increased pressure may be. used, in one or more stages. The ammonia concentration may be such that the gas leaving the washihg contains as much NH 3 as the untreated gas. The concentration in the washing liquor may be from 2 to 20 times the ammonia content of the crude gas. The H 2 S removal and the subsequent washing out of NH 3 may be effected in different parts of the same column. A number of illustrative examples are'given with details of various methods for the selective separation of H 2 S, CO 2 and NH, from coke-oven gases, and a low temperature carbonization gas obtained from oil shale; in 'two of these examples the short tissue of contact for the selective removal of H 2 S is effected by using the so called Stroder washers or disintegrators.