GB407089A - Improvements in or relating to the manufacture and production of concentrated nitric acid - Google Patents

Abstract

Nitric acid is concentrated by exposing a down-flowing-mixture of the weak acid and a dehydrating agent, in a fractionating column <PICT:0407089/III/1> or tower, to a counter-current of weak nitric acid vapours from the distillation of the effluent collected at the base of the column, and exposing the partially denitrated effluent in a second fractionating column to a counter-current of steam, whereby denitration is completed. Weak acid mixed with a dehydrating agent, for example sulphuric acid, is fed from vessel 1 to the fractionating tower 3. A preheater 14 may be used. Strong acid vapours are evolved at 5 and the effluent liquid enters externally heated vessels 6, the vapours produced passing back into the tower, and the residual liquid entering a second tower 8 supplied with steam from a pipe 9. The weak nitric acid vapours pass to the tower 3. The liquid leaving tower 8 may be passed to a further externally heated vessel and the steam produced therein employed in tower 8. The towers may be superposed and the heating vessels built into them. The vessels 6 are arranged in series, each at a lower level than the preceding one, and may consist of jacketed tubes heated by steam or liquid, or of tubes or stills set in a furnace. Alternatively, the tower 3 may be so constructed that a portion thereof can be heated. The vapours from the top of the tower 8 may be led directly to the bottom of tower 3, or scrubbed in counter-current with cold water and the dilute acid obtained fed to the top of tower 3.