PROCESS FOR THE MANUFACTURE OF POLYPHOSPHATES

1,133,045. Polyphosphates. KNAPSACK A.G. 9 Feb., 1967 [9 Feb., 1966; 16 July, 1966], No. 6158/67. Heading C1A. Polyphosphates are produced by spraying an alkali metal or alkaline earth metal orthophosphate solution or suspension in a spray tower, in the presence of a reducing substance, especially a low-valent phosphorus compound, at 200‹ to 500‹ C., wherein said orthophosphate solution or suspension is so combined with an oxidant solution oxidizing the reducing substance and its decomposition products, that the contact time of said orthophosphate solution or suspension with the oxidant is less than 1 second, preferably 0À1 to 0.3 second, and the combined solutions are thereafter sprayed jointly. The orthophosphate solution, preferably supplied hot, may be contacted with the oxidant inside the turbulence chamber of a spray nozzle. Preferred oxidants are peroxides and alkali metal nitrates and chlorates, and the oxidant is preferably supplied at below 35‹ C. Low bulk density products may be obtained by jointly spraying an alkali metal or ammonium carbonate or bicarbonate solution with the orthophosphate. The spray tower may be heated by means of a gas containing 0 to 2000 milligrams of elementary or combined phosphorus per cubic metre, for example a gas originating from phosphorus production. The orthophosphates may be contaminated with organic compounds, preferably not more than 3% by weight on the P 2 0 5 .