Solid–Liquid Phase Equilibrium of the Ternary System NH4Cl-(NH2)2CO-H2O at Multiple Temperatures

Solid–liquid phase equilibria of the ternary system NH4Cl–(NH2)2CO–H2O at 283.15 K, 313.15 K and 353.15 K were measured by the method of isothermal solution equilibrium. Solubility data of the system were determined by volumetric and colorimetric methods; solid phases were analyzed by Schreinemaker's method of wet residues and X-ray powder diffraction. The triangle phase diagrams were drawn and the experimental data were fitted with Wilson and NRTL models. Each phase diagram includes one double salt, two eutectic points, three isothermal solubility curves, and five crystallization regions. The composition of the double salt is xNH4Cl·(NH2)2CO, the value of x reduces from 4.58 to 1.95 with the experimental temperature rising. The values of RAD and RMSD with Wilson model are 4.48% and 2.52% that with NRTL model are 4.19% and 1.77%; which indicates that the two thermodynamic models can fit the experimental data very well.