An investigation on the solid-liquid phase equilibrium of the quaternary system KH2PO4-H3PO4-CH2OHCH2OH-H2O

The removal of HCl and the precipitation of KH2PO4 are the crucial factors to produce KH2PO4 from H3PO4 and KCl. A new process is proposed by introducing ethylene glycol to decrease the solubility of HCl and to precipitate KH2PO4. The solubility of KH2PO4 in H3PO4-CH2OHCH2OH-H2O system was studied systematically by isothermal solution saturation method. The results demonstrate that ethylene glycol is an excellent precipitant for the crystallization of KH2PO4 from the solution of KH2PO4-H3PO4-CH2OHCH2OH-H2O. The increase of ethylene glycol mass fraction brings a remarkably inhibitive effect on the dissolution of KH2PO4 in H3PO4 aqueous solution. Based on the phase equilibrium diagram of quaternary system KH2PO4-H3PO4-CH2OHCH2OH-H2O, KH2PO4 can be precipitated by cooling crystallization, evaporation crystallization or antisolvent crystallization. Focused beam reflectance measurement was used to online monitor the chord length distribution during the crystallization process. The results indicate that the particle size distribution is controllable in the process of continuous feeding antisolvent crystallization. The results provide a feasible way to separate KH2PO4 from the reaction solution of KCl and H3PO4.