Manufacture of water-insoluble ammonium polyphosphate

Claim 1

A continuous process for the production of crystalline, water-insoluble ammonium polyphosphate of a pH ranging from about 4.5-6.5 which comprises (1) admixing either a. a condensed phosphoric acid of P 2 O 5 /H 2 O mole ratio of at least about 0.155 and a combined ammoniating and condensing agent at a mole ratio of about 1.0-3.0 moles of agent per mole of acid, or b. urea phosphate and a combined ammoniating and condensing agent at a ratio of about 0.5-1.05 moles of agent per mole of phosphate, 2. heating the resultant admixture to from about 75°-90°C. to form a melt, 3. contacting the resultant melt with a clean endless moving belt which is preheated to a temperature of from about 150°-200°C. to immediately foam the melt, 4. passing the belt having the resultant foam thereon through a zone heated to from about 180° to about 360°C. to cause ammonia gas to evolve therefrom, 5. venting off said ammonia gas at a rate controlled by the measured pH of the resultant ammonium polyphosphate and 6. recovering the resultant crystalline, water-insoluble ammonium polyphosphate of the above pH.