GB256137A - Improvements in the manufacture and production of di-ammonium phosphate - Google Patents

Abstract

256,137. Johnson. J. Y., (I. G. Farbenindustrie Akt.-Ges.). Feb. 22, 1926. Ammonium phosphate.-In the production of di-ammonium phosphate by the interaction of ammonia and phosphoric acid a ratio of 1 molecule of phosphoric acid to 1.5-2 molecules of ammonia is maintained, the further additional quantity of ammonia when required being introduced during or after cooling the solution. Phosphoric acid may be added to a solution of diammonium phosphate until the ratio of 1 molecule of phosphoric acid to 1.5 molecules of ammonia is obtained and ammonia and phosphoric acid and then introduced in the same ratio. Water is evaporated owing to the heat of neutralization and when the solution is sufficiently concentrated it is withdrawn continuously or at intervals. After cooling, ammonia is added to precipitate the di-ammonium phosphate. When stronger phosphoric acid is used, to avoid too high a temperature aqueous ammonia may be introduced with the phosphoric acid. Heat may be supplied when weak acid is used, and to facilitate evaporation reduced pressure may be employed. In a second example, dilute crude phosphoric acid obtained by decomposing rock phosphate by means of sulphuric acid is treated with ammonia until the ratio of 1 molecule of phosphoric acid to 1.5 molecules of ammonia is obtained. A mother liquor containing di-ammonium phosphate from a subsequent step is then added. After evaporation a further quantity of ammonia is introduced in order to give the di-ammonium phosphate, which separates in the crystalline condition, leaving a mother liquor for re-use. Before the final treatment with ammonia, impurities such as iron and aluminium compounds may be removed by filtration.