Patent GB-636073-A (GB)
Title: A process for the recovery of hydrocarbon-substituted ammonium nitrites and the like
Filed: 1947-10-16
Abstract: Hydrocarbon-substituted ammonium nitrites such as di-isopropylammonium nitrite, or other compounds of an acid and an organic base, are recovered from a multi-component liquid system by evaporating the other components from the system after adding thereto a relatively non-volatile stabilizer which has a lower dissociation constant than the base, and which maintains the pH of the system near but not below 7.  The recovery of di- and tri-methyl, di- and tri-ethyl, di-n- and di-isopropyl, di-n-and di-sec.-butyl, and bis-1,3-dimethyl-butyl, ammonium nitrites is referred to. Triethanolamine, sodium bicarbonate and potassium bicarbonate are suitable stabilizers.  In an example, a crude solution containing 40 per cent by weight of di-isopropylammonium nitrite, water (32 per cent) and isopropyl alcohol (25 per cent), is evaporated at a pressure between 3 and 6 inches of mercury in the presence of 0.5 per cent by weight, based on the weight of nitrite present, of triethanolamine.  When the temperature in the evaporation kettle is about 59 DEG  C., additional crude nitrite solution containing added triethanolamine is fed into the kettle at a rate adjusted to maintain this temperature as the evaporation proceeds, until the kettle capacity is reached.  The feed is then stopped and the evaporation is continued until crystals start to form in the solution.  The kettle residue is then emptied into a crystallizer, cooled to 20 DEG  C. and the di-isopropylammonium nitrite crystals filtered or centrifuged out, and washed with isopropyl alcohol.  The recovery of di-isopropylammonium nitrite from a crude solution by using benzene as entrainer, and di-isopropylamine as stabilizer, was carried out but found to be disadvantageous; for the di-isopropylamine passes over in the distillate, and some of the nitrite is converted into the corresponding nitrosoamine.ALSO:Hydrocarbon-substituted ammonium nitrites, or other compounds of an acid and an organic base, are recovered from a multi-component liquid system, e.g. a crude aqueous-alcoholic solution containing the product of the reaction between an amine sulphate and sodium nitrite, by evaporating the other components from the system after adding thereto a relatively non-volatile stabilizer which has a lower dissociation constant than the base, and which maintains the pH of the system near but not below 7.  In the preparation of hydrocarbon-substituted ammonium nitrites, the requisite amine is reacted successively with sulphuric acid and sodium nitrite.  The other reaction product-sodium sulphate-is removed by precipitation with alcohol, followed by filtration. Di-isopropylammonium nitrite is prepared from di-isopropylamine, and since the latter often contains water, isopropyl alcohol, acetone, and isopropylamine as impurities, the resulting nitrite also contains these impurities.  They are removed by evaporation after the nitrite has been stabilized against conversion to the corresponding nitrosoamine.  The recovery of di- and tri-methyl, di- and tri-ethyl, di-, n- and di-isopropyl, di-, n- and di-secbutyl, and bis-1,3-dimethyl-butyl, ammonium nitrites is referred to. Triethanolamine, sodium bicarbonate and potassium bicarbonate are suitable stabilizers.  In the evaporation of a crude solution containing 40 per cent of di-isopropylammonium nitrite, 0.5 per cent by weight of triethanolamine, based on the weight of nitrite present, is added.