GB1358731A - Process for producing concentrated nitric acid - Google Patents

Abstract

1358731 Nitric acid and nitrogen oxides MONTECATINI EDISON SpA 12 Aug 1971 [13 Aug 1970] 38002/71 Heading C1A Nitric acid having a concentration higher than 68% by weight of HNO 3 -the azeotropic concentration-is prepared by freeing gases obtained by the combustion of ammonia from water in the condenser 2, oxidizing in vessel 4 to eliminate at least part of their NO content and then absorbing the resulting gases at a pressure of 2-6 atmospheres absolute by passing them through vessel 5 countercurrent to nitric acid having a concentration of 70 to 95% by wt. coming from the bottom of still 8 where acid from 5 is distilled, the N 2 O 4 emerging at 9 as a liquid which is passed to reactor 14/15 where it is mixed with an azeotropic or sub-azeotropic nitric acid (i.e. a concentration not more than 68% by wt. HNO 3 ) from fractional distillation column 19, the ratio by weight of the subazeotropic acid or azeotropic acid to N 2 O 4 being from 1 : 1À5 to 1 : 5, and the product is fractionally distilled in still 19 to give nitric acid having a concentration higher than 68% by wt. and a nitric acid having a concentration up to 60% by wt. This latter acid may be recycled to the reactor 14/15. Preferably the acid which reacts in 14 with the N 2 O 4 has the azeotropic concentration 68% by wt. The temperature in the reactor 14 may be 35‹ to 60‹ C. and in the absorber 5 it may be- 15‹ to + 10‹ C. Preferably the reactor comprises two sections the first 14 in which the N 2 O 4 reacts with the acid and the second 15 in which the N 2 O 4 is absorbed by the acid. The N 2 O 4 still dissolved in the acid having a concentration greater than 68% by weight HNO 3 may be stripped in stripper 17 using an air stream from 21. The waste gases from the reactor and the stripper may be recycled to the absorbing step to remove their N 2 O 4 content before releasing to the atmosphere.