GB1419645A - Production of strong nitric acid - Google Patents

Abstract

1419645 Strong nitric acid E I DU PONT DE NEMOURS & CO 15 May 1973 23128/73 Heading C1A HNO 3 of concn. of at least 90% by wt., e.g. up to 100%, is prepared by continuously (a) absorbing gaseous an equilibrium NO 2 /N 2 O 4 mixture in aq. HNO 3 to form 75-85% by wt. HNO 3 , (b) reacting the HNO 3 with O 2 and H 2 O at elevated pressure to form 80-90% by wt. HNO 3 , (c) vaporizing part of the N 2 O 4 and then (d) distilling the acid to produce the strong acid. Step (a) may be carried out at a pressure of 80-120 p.s.i.g. and a temp. of 0-25‹ C. to produce the 75-85% HNO 3 containing 15-30% dissolved N 2 O 4 . Step (b) may be performed at a pressure of 300-1600 p.s.i.g. and a temp. of 40-100‹ C. The vaporization step (c) may be by depressurization to 105-155 p.s.i.g. or by bleaching with air, thereby removing 50% of the N 2 O 4 . The distillation step (d) may be operated at atm. pressure. The N 2 O 4 -containing gaseous effluent from step (a) may be scrubbed in weak HNO 3 or water to produce a weak HNO 3 which on distillation gives a distillate of concn. less than 5% HNO 3 and bottoms of concn. 55-68À5% HNO 3 , the bottoms being used as an H 2 O source in step (b). The N 2 O 4 may be obtained by the catalytic oxidation of NH 3 and oxidation of the NO formed. The cooled and separated H 2 O from the catalytic oxidation having a concn. of 35-55% HNO 3 may be distilled to give distillate of concn. <5% HNO 3 and bottoms of concn. 55-68%, one or both fractions being used as a source of H 2 O for step (b).