GB362908A - Improvements in and relating to the production of nitric acid - Google Patents

Abstract

Highly concentrated nitric acid is produced by absorbing oxidized nitrous gases in nitric acid of about 90 per cent concentration, diluting to a concentration of not less than 80 per cent, and treating the mixture with oxygen under pressure. Nitrous gases containing water, produced by denitration of nitrous sulphuric acid in a vessel A, pass to a cooler B, when nitric acid of about 40 per cent concentration condenses, part of which is returned to A. The gases are supplied with an excess of oxygen and pass through a cooler C to an absorption plant D1, D2, where the nitrogen tetroxide is dissolved in nitric acid of about 90 per cent, which may contain about 5 per cent dissolved tetroxide. Cooling water having a temperature even exceeding 20 DEG C. may be used. Residual gases may be absorbed in water. The <PICT:0362908/III/1> acid leaving the absorption plant, preferably containing about 20 per cent tetroxide, is mixed in E with dilute acid from the condenser B sufficient to supply the water required for conversion into nitric acid by treatment with oxygen in a pressure vessel F, at a temperature of about 40 to 50 DEG C. The oxygen is supplied by a compressor K2 at about 5 to 10 atmospheres or more, and part is discharged through a valve V2 and added to the nitrous gases. The discharge acid, preferably of the same composition as the absorption acid, passes to a vessel I, from which part is supplied to the vessel D2 and the rest to a bleaching plant G. The expelled tetroxide is returned, and the bleached acid distilled in H to give acid of, for example, 98 per cent, while the remaining acid of about 70 per cent is led to the vessel E. By maintaining the liquid level here constant it is only necessary to control the quantity of acid flowing from the vessel I to the distillation plant. Specification 131,642, [Class 1 (ii), Inorganic compounds, other than &c.], is referred to.