GB492392A - Improvements in the manufacture and production of concentrated nitric acid and ammonium sulphate - Google Patents

Abstract

Concentrated nitric acid and ammonium sulphate are obtained by subjecting the dilute sulphuric acid, obtained in the concentration of aqueous nitric acid by means of concentrated sulphuric acid, while it is still hot to a partial or complete neutralization with ammonia, and supplying the vapours thus formed to the concentration or denitration apparatus instead of corresponding amounts of fresh steam. The ammonia may be introduced directly into the lower part of the concentration or denitration apparatus, or alternatively, the hot effluent dilute sulphuric acid may be treated with ammonia outside the column, the vapours formed being supplied to the column. It may be necessary to neutralize only a part of the sulphuric acid with ammonia, the remainder of the acid being branched off before the neutralization for other uses. Or the whole of the sulphuric acid may be neutralized in stages, the vapours necessary for the nitric acid being produced in the first stage and the vapours produced in the second stage being otherwise used, e.g. for the preliminary concentration of dilute nitric acid or for the evaporation of the ammonium sulphate solution. When only a proportion of the ammonia necessary to neutralize the sulphuric acid is supplied directly to the lower part of the concentration apparatus, the solution of ammonium bisulphate or polysulphate in sulphuric acid may be completely neutralized to ammonium sulphate outside the tower. Alternatively, the acid solution may be freed from bisulphate and polysulphate by cooling and filtration, the resulting salts only being completely neutralized and the dilute sulphuric acid being used for other purposes.