Verfahren zur vollstaendigen Entfernung von Stickstoffoxyden

摘要

1,146,625. Ammonium nitrate. HIBERNIA CHEMIE G.m.b.H., and H. PAULING. 18 May, 1966 [18 May, 1965], No. 22173/66. Heading C1A. A process for recovering nitrogen oxides in the form of an acid aqueous solution of ammonium nitrate from waste gases (which may include NO, NO 2 , N 2 O 3 and N 2 O 4 ) comprises initially adjusting the molar ratio between NO 2 and NO to about 1, then scrubbing the gas mixture with aqueous ammoniacal ammonium nitrate solution in a gas-scrubbing plant, the NH 4 OH content of this solution being such that the H 2 O : NH 3 weight ratio in the vapour phase above it is from 2 : 1 to 100 : 1, and finally reacting the NH 4 NO 2 /NH 4 NO 3 solution thus obtained with a solution of ammonium nitrate containing nitric acid. The scrubbing solution may contain 40-50 wt. per cent NH 4 NO 3 when the operating temperature is 20-30‹ C., and its NH 4 OH content is preferably such that the scrubbing plant effluent contains 0À05-0À5 wt. per cent NH 4 OH. The amount of washing solution may be so metered that the effluent contains 0À5-5 wt. per cent NH 4 NO 2 . The scrubbing may take place in a number of washing stages which are preferably arranged in series with respect to the gas flow and either in series or in parallel with respect to the scrubbing solution flow. The NO 2 : NO ratio of the gas may be readjusted to about 1 after it has traversed half or two thirds of the washing stages. In addition, three subsequent washing stages may be provided in series with respect to the gas flow, the first employing the effluent from the third (final) stage, the second employing NH 4 NO 3 /HNO 3 solution, and the third employing water. The reaction between the scrubbing plant effluent and the NH 4 NO 2 /HNO 3 solution may take place at 10-30‹ C., the latter solution preferably being used in an amount of 25 kg. thereof per kg. of NH 4 NO 2 in the effluent. The ammonium nitrate solution produced may in part be recycled to the scrubbing plant.