Patent GB-975325-A (GB)
Title: Concentrating nitric acid
IPC: C01B21/084
Filed: 1960-12-21
Abstract: 975,325. Production of chlorine and sodium or potassium nitrate. AMERICAN METAL CLIMAX Inc. Dec. 21, 1960 [Dec. 24, 1959], No. 46890/63. Divided out of 975,324. Heading C1A. In the reaction of nitric acid with the chlorides of sodium, potassium or hydrogen to produce chlorine and nitrogen dioxide with or without sodium or potassium nitrate, the reaction is effected in two stages, the first being effected with relatively dilute nitric acid and the vapours produced being then passed to a secondary reaction zone, where they are contacted countercurrently with down-flowing strong nitric acid, some of which is recycled from the system. Gaseous products including chlorine and NO 2  are withdrawn overhead and the weak nitric acid solution from the first reaction zone is passed to a distillation zone and then distilled in the presence of potassium nitrate, present as a result of the use of KCL in the starting material or added as such before the distillation stage. The presence in the result of potassium nitrate changes the azeotropic composition and results in a stronger nitric acid being produced on distillation, such acid being recycled to wash the upflowing gases in the second, reaction zone. As shown in Fig. 1, potassium chloride and nitric acid pass to a first reaction zone 11 optionally having passed through a pre-reaction zone 9, the vapours effluent from 11 are fed to the superjacent reactor 14 where they are contacted with down-flowing strong nitric acid (85% HNO 3 ) in the presence of nitrous gases re-cycled from later stages of the process and from the pre-reaction zone 9 if used. Liquid flow is indicated by single lines and vapour flow by double lines. Chlorine and NO 2  reaction products are withdrawn through a condenser 18 and passed to a fractionator 19 from which the chlorine is withdrawn overhead and the NO 2  recovered as such and passed to a NO 2  fractionator 21 from which NO 2  is withdrawn at 51, condensed and removed at 52 as product or sent to HNO 3  production zone 22. Dilute nitric acid withdrawn from the base of the first reaction zone 11 is sent to a water removal column 26. (If hydrogen chloride or sodium chloride had been the initial reactant, potassium chloride would be added at some point preceding the admission of the nitric acid to the column 26.) Water is removed overhead and the bottoms from column 26 now consisting of 80% HNO 3  with potassium nitrate crystals with or without sodium nitrate, then passes to a crystallizer 32, from which nitric acid vapours are withdrawn overhead to condenser 33 and recycled to the second reaction zone 14. The crystal slurry withdrawn from the bottom of crystallizer 32, passes to a filter 36, and product KNO 3  is withdrawn. Aqueous dilute nitric acid, potassium nitrate fines and sodium nitrate in solution is withdrawn from the upper part of crystallizer 32, sodium nitrate is crystallized and removed at 35 and the liquid then passed to an evaporator 38 from which nitric acid vapours are withdrawn and recycled and from which a nitric acid solution containing potassium nitrate in solution is re-cycled to a point preceding the water removal column 26.