Optimization and Characterization of Polyphosphate Fertilizers by Two Different Manufacturing Processes.

To explore how different reaction parameters affect the major features of short-chain ammonium polyphosphate (APP) fertilizers, a batch of manufacturing experiments were conducted under two different manufacturing processes [phosphoric acid (PA)-urea and monoammonium phosphate (MAP)-urea]. The APP features including polymerization degree, polymerization rate, solubility, and N and P recovery rates were significantly varied and influenced by the molar ratio of raw materials (P:N), reaction temperature, time, and pressure under different manufacturing conditions. In the MAP-urea process, the optimized APP products were gained under the combination condition of molar ratio = 1.6:1, = 130 °C, and = 45 min, while this happened in molar ratio = 1:1.7, = 180 °C, and = 60 min in the PA-urea process. Comprehensively, the features of APP fertilizers produced by the MAP-urea process were better than those produced by the PA-urea process. Our results provide valuable references for manufacturing high-quality short-chain APP fertilizers.