GB777253A - Manufacture of alkali metal triphosphate and/or pyrophosphate - Google Patents

Abstract

Alkali metal triphosphate or pyrophosphate or mixtures thereof are prepared from polyphosphate glasses or polyphosphoric acids by treating the starting material with an alkali metal carbonate and/or hydroxide in the presence of water and spraying the resultant solution into the upper part of a tower heated to a temperature between 300 and 400 so that solid particles of the product are obtained which fall downwards through the tower. By polyphosphate glass is meant alkali metal ortho, pyro, tri, and metaphosphates having a molar ratio of P2O5 to Na2O between 1 to 0.3 and 1 to 1.3. Such a glass may contain about 10 per cent of pyrophosphate, 30 per cent of metaphosphate and the rest triphosphate. The polyphosphoric acids are mixtures of tripolyphosphoric and pyrophosphoric acid and which may also contain orthophosphoric and metaphosphoric acids, for example a mixture containing 10 per cent pyrohosphoric acid, 30 per cent metaphosphoric acid and the remainder triphosphoric acid. The treatment with alkali metal carbonate or hydroxide is preferably effected in the presence of a quantity of water which is from 1/2 to twice the quantity of the starting materials employed and the treatment is suitably effected at 50 to 60 DEG C. to produce a pH between 8 and 12; depending upon the pH triphosphate or pyrophosphate or mixtures thereof are formed. According to examles (1) aqueous sodium carbonate was added to acid sodium polyphosphate glass having a molar ratio of P2O5 to Na2O of 1 to 0.5 at a temperature between 50 and 60 DEG C. to produce a final pH of 9.4 Sodium hydroxide was then added to raise the pH to 11.4 and the resulting solution with a solids content of about 60 per cent was sprayed through a nozzle into the top of an atomizing tower heated to 300 to 400 DEG C. whereby a dry product containing 72 per cent of sodium triphosphate and 24 per cent of sodium pyrophosphate was obtained. (4) Aqueous sodium carbonate was added at 50 to 60 DEG C. to polyphosphoric acid containing 3.87 per cent of H3PO4, 6.4 per cent of H4P2O7, 47 per cent of H5P3O10 and 34 per cent of (HPO3)x, and 10 per cent of cyclic metaphosphates, to produce a final pH of 9.7. The solution containing 59 per cent solids was sprayed through a nozzle into an atomizing tower as before and a mixture containing 51 per cent of sodium triphosphate and 48 per cent of sodium pyrophosphate was obtained. Further exbox 15 and flexible connections 16. The triphosphate and sodium pyrophosphate in varying proportions.