GB402229A - Process for the simultaneous production of sulphuric and nitric acids - Google Patents

Abstract

Sulphuric and nitric acids are simultaneously produced by passing sulphurous and nitrous gases, of low water content and pre-cooled to temperatures not exceeding about 100 DEG C., together through an absorption system in cocurrent with a liquor containing sulphuric and nitrosyl sulphuric acids, the temperature being maintained low to avoid decomposition of the latter and to cause progressive absorption of both gases. The concentrated liquor so obtained is denitrated by heat and water vapour, concentrated nitric acid being obtained from the gaseous product and concentrated sulphuric acid from the residual liquor. The sulphurous gases may be obtained, for example, by roasting pyrites, zinc blende, or copper ores, and the nitrous gases by catalytic oxidation of ammonia, or oxidation of nitrogen in an electric arc. The relative quantities may be varied, for example in the ratio of one or more molecules of SO2 to one molecule of NO. Hot gases from pyrites furnaces are used in a Glover type tower to effect final denitration and concentration of the sulphuric acid, whereby they are cooled to about 80 DEG C., and mixed with ammonia oxidation gases cooled to about 35 DEG C. to remove most of the water. The absorption system comprises three towers irrigated with sulphuric and nitrosyl sulphuric acids, that in the first tower being relatively dilute and periodically transferred to the second, and thence to the third. The liquid is cooled to maintain a temperature of about 40 DEG C. The acid from the last tower is decomposed in a denitration column at about 130--140 DEG C. by water or dilute nitric acid, and water vapour, air being introduced at the base. 95--100 per cent nitric acid is condensed at the exit, the remaining vapours, about 40 per cent NO2, being absorbed to give 70 per cent acid which may be returned to the column. Part of the sulphuric acid withdrawn from the column is fed to the absorption system and part denitrated and concentrated in a Glover tower.