Production of ammonium polyphosphate solutions

Abstract

Ammonium polyphosphate is produced in a pipe reactor by injecting a stream of ammonia countercurrent to superphosphoric acid passed axially through the reaction zone to cause vigorous backmixing of the two reactants and yield a melt of ammonium polyphosphate, and cooling the sidewalls of the pipe reactor sufficiently to form a layer of ammonium polyphosphate melt thereon to prevent formation of insoluble scale on the interior of the reactor. The resulting ammonium polyphosphate melt is then dissolved in recycled aqueous ammonium polyphosphate product solution and thereafter further diluted with water to form the product solution. In specific embodiments, minor but effective amounts of urea are added to the acid feed to diminish the tendency of insoluble scale from forming on the interior of the reaction zone, and to improve the stability and conversion of the product solution.

Dependencies are inferred from the claim text.