Solid−liquid phase equilibrium for the ternary system (ammonium dihydrogen phosphate + agricultural grade ammonium polyphosphate (degree of polymerization ranged from 1 to 2) + water) at (278.2 and 313.2) K

Abstract

Water-soluble ammonium polyphosphate (APP) as a promising high phosphorus fertilizer source in agricultural application can be used with ammonium dihydrogen phosphate (MAP) during fertilizer preparation and irrigation. In this work, the pH, density and solubility properties of the phase equilibrium of ternary APP-MAP-water system were systematically determined at the temperature of 278.2–313.2K. A new series of parameters of Simplified Apelblat model, empirical polynomials and Rational 2D function were used to express the solubility data of MAP, solution density and pH value, respectively. The maximum relative deviations of these three models were successively within 1.21, 0.49, and 0.54% and the corresponding model correlation coefficient R2 was close to or greater than 0.9990, which indicating the accuracy and reliability. The experimental results were further verified by observing the effect of APP on MAP supersaturated solution in OptiMax 1001 reactor and through the online detection techniques of FBRM and PVM. With the addition of water-soluble APP can significantly improve the content of P2O5 when it was combined well with MAP into fertilizer application. Therefore, APP can be better used with MAP to improve the utilization rate of phosphorus during irrigation following the basic thermodynamic data and models established in this research.

Keywords

• Ammonium polyphosphate
• Monoammonium phosphate
• Mixed dissolve
• Equilibrium of dissolved phase