Solubility measurement and thermodynamics modelling for potassium dihydrogen phosphate in a water-ethanol system from 293.2 to 323.2 K

Abstract

The phase equilibrium and thermodynamic properties of potassium dihydrogen phosphate (KDP) in the binary water-ethanol system are of critical significance for the salting-out crystallization of KDP production using ethanol as anti-solvent. The solubility of KDP in water-ethanol solvent was determined by the static equilibrium method under constant pressure at temperatures ranging from 293.2 to 323.2 K, with the molar fraction of water varying between 0.3885 and 1.0. The solubility of KDP significantly decreased with the addition of ethanol and increased with rising temperature. A new group of parameters (middle-range interaction) of the mixed-solvent electrolyte model (MSE model) of KDP in the water-ethanol system were obtained by regressing all experimental solubility data. The MSE model with the newly acquired parameters was successfully used to simulate the KDP precipitation process in KH2PO4/C2H5OH/H2O systems and could predict the distribution of ion speciation and activity coefficients. This paper provides fundamental thermodynamic properties and a prediction model for the anti-solvent crystallization process for KDP production.