GB702003A - Process for the production of chlorine - Google Patents

Abstract

<PICT:0702003/III/1> In the preparation of pure chlorine by heating chlorides, e.g. of alkali or alkaline earth metals or hydrogen, with nitric acid, the resulting gas-vapour mixture comprising chlorine, nitrogen oxides, nitric acid vapour, and water vapour is treated with sulphuric acid of 82-100 per cent. concentration to remove water vapour, so as to obviate the formation of nitrosyl chloride, and then concentrated nitric acid vapour, dry chlorine, and nitrogen oxides are individually separated. Chloride and excess nitric acid are heated to boiling in reactor 50 and the resultant gases pass up through column 51 countercurrent to the sulphuric acid introduced at 41. The sulphuric acid is reduced to 70 per cent. concentration and heated to 170 DEG C. in column 51 so that it does not retain any chlorine, nitrogen peroxide, or nitric acid vapour. The dried gases pass through heat exchanger 52 to cooling coil 53 where the concentrated nitric acid is liquefied and returned to reactor 50 through heat exchanger 52. The remaining gases pass up through absorption column 54 countercurrent to dilute nitric acid (55-65 per cent.), which may be the make-up acid for the process, added at 22 to absorb the nitrogen oxides, and then up through column 55 countercurrent to concentrated sulphuric acid (70-88 per cent.) introduced at 18 to decompose nitryl chloride and absorb the nitrogen oxides produced, and pure chlorine is withdrawn at 19. The dilute nitric acid from the base of absorption column 54 flows down through column 57 countercurrent to air or free oxygen-containing gas added at 24 to desorb the nitrogen oxides, and thence through heat exchanger 52 to column 51 at 28, where it is concentrated (to 80-99 per cent.) and passes out with the vapours to be condensed in coil 53 before passing to reactor 50 for treatment of further chloride. The nitrogen peroxide gases from column 57 pass to regenerator 58 where they are converted, by water added at 30, to nitric acid, which is also passed to column 51 at 28 for concentration. If hydrogen chloride is used then reactor 50 is eliminated and hydrogen chloride gas is passed into the base of tower 51 see Fig. 2 (not shown).