Method for the continuous preparation of stable aqueous ammonium polyphosphate compositions

An improved method for the continuous production of a stable aqueous ammonium polyphosphate composition comprising

• A. reacting in a pipe reactor wet-process superphosphoric acid, said acid being primarily in the orthophosphate form, and anhydrous ammonia vapor in an exothermic ammoniation to thereby ammoniate a portion of the acid and to dehydrate and convert a portion of the orthophosphate to polyphosphate in the pipe reactor by means of the heat generated by the exothermic ammoniation reaction by
• I. introducing the ammonia in the form of a single stream and exclusively into the pipe reactor and introducing the acid in the form of a single stream and exclusively into the pipe reactor along the axis of the pipe reactor and into the center of the stream of ammonia in the pipe reactor to thereby form the reaction mixture and to prevent corrosion of the pipe reactor by minimizing contact of the pipe reactor walls with the acid heated by the heat evolved in the ammoniation reaction, said streams containing the exact stoichiometric amounts of the acid and the ammonia that are required in the analysis desired for the final stable aqueous ammonium polyphosphate composition and said acid stream being introduced into said ammonia stream at a point downstream from where said ammonia stream is introduced into the pipe reactor;
• Ii. reducing the linear velocity of the combined ammonia and acid streams in the pipe reactor as they are being combined to form the reaction mixture in order to achieve efficient mixing of the combined streams within the pipe reactor;
• and
• Iii. allowing the temperature of the reaction mixture in the pipe reactor to increase in response to the heat liberated by the ammoniation reaction and without the addition or removal of heat by external means and thereby effecting the partial conversion of orthophosphate to polyphosphate in the pipe reactor;
• B. quenching the conversion reaction by removing the hot reaction mixture stream from the pipe reactor and adding to it a cooler stream consisting essentially of water, said water being at such a temperature as to lower the temperature of the reaction mixture enough to quench the conversion reaction and said water being added in the exact stoichiometric amount that is required in the analysis desired for the final stable aqueous ammonium polyphosphate composition;
• and
• C. completing rapidly the ammoniation reaction and the conversion of the reaction mixture stream to a reaction product stream in a reaction medium formed by next introducing the reaction mixture stream into a cooler stream of the desired final stable aqueous ammonium polyphosphate, said cooler stream being at such temperature as to lower the temperature of the reaction mixture below that at which loss of polyphosphate due to hydrolysis is significant;
• wherein steps A, B, and C are performed in a completely closed system, thereby eliminating additional separation steps and losses of volatile components by volatilization.