Preparation Method for a Water-Insoluble Crystal Form II Ammonium Polyphosphate with High Purity and Polymerization Degrees

A preparation method for a water-insoluble crystal form II ammonium polyphosphate with high purity and polymerization degrees, comprising the following steps:

• 1) conveying crystal type-H phosphorus pentoxide and diammonium phosphate at a molar ratio of 1:1-1.5 into a malaxator with twin screw, and injecting ammonia gas into the malaxator at 20-25 m3/h while preheating the material at a temperature between 100° C. and 300° C.;
• 2) after injecting ammonia gas for 30-40 minutes, stopping to add ammonia supplying compound to the malaxator, and then injecting ammonia gas into the malaxator again at 8-15 m3/h for 4-8 hours, wherein the weight ratio of the crystal H-type phosphorus pentoxide and ammoniate is 1:0.01-0.05;
• 3) transferring the material of step 2 into another sealed container with stirring function, and adding coupling agent in when stirring, wherein the weight ratio of the crystal H-type phosphorus pentoxide and the coupling agent is 1:0.01-0.05;
• 4) keeping stirring until the temperature of the material drops below 60° C., and then transferring the material into organic solvent for washing for 30-50 mins;
• 5) transferring the material of step 4 to a filter press for filter-pressing, after that putting the material into a low temperature drying oven for drying, and then sieving the material to obtain the final product.
• wherein, the ammonia supplying compound is at least one of ammonium carbonate, biuret, semicarbazide and dicyandiamide sulfate.