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The solid–liquid phase equilibrium for ternary system of 3,4-dichloronitrobenzene + 2,3-dichloronitrobenzene + methanol were determined experimentally by the method of isothermal solution saturation at temperatures of 283.15 K, 293.15 K and 303.15 K under pressure of 101.3 kPa. According to the obtained solubility data, the isothermal phase diagrams of the system were constructed. At each temperature, there were two pure solid phases formed, which were confirmed by Schreinemakers' wet residue method and corresponded to pure 3,4-dichloronitrobenzene and pure 2,3-dichloronitrobenzene. The crystallization regions of pure 3,4-dichloronitrobenzene and pure 2,3-dichloronitrobenzene increased with decreasing in temperature. The crystalline region of 2,3-dichloronitrobenzene was larger than that of 3,4-dichloronitrobenzene at the same temperature, and increased rapidly as the temperature increase. The data of solid–liquid phase equilibrium were correlated with NRTL model and Wilson model. The calculated solubility data with NRTL model agreed well with the experimental values. The mutual solubility data and ternary phase diagrams for the system were of great significance for optimizing the purification procedure of 3,4-dichloronitrobenzene and 2,3-dichloronitrobenzene.

In this work, the solid–liquid phase equilibrium data for ternary system of adipic acid + glutaric acid + ethanol were measured using an isothermal saturation method at the three temperatures of 283.15, 303.15, and 313.15 K under 101.3 kPa. Three isothermal phase diagrams were built according to the measured solubility data. There were two pure solids formed in the ternary system at a given temperature, which corresponded to pure adipic acid and pure glutaric acid, and were confirmed by Schreinemaker's method of wet residue. The crystallization region of glutaric acid was smaller than that of adipic acid at each temperature. Two thermodynamic models, NRTL and Wilson were employed to correlate and calculate the mutual solubility data for the ternary adipic acid + glutaric acid + ethanol system. Results indicated that calculated results with NRTL model agreed well than those with Wilson model. Furthermore, the densities of the equilibrium liquid phase were obtained and correlated with an empirical equation.

Solid–liquid phase equilibrium and solubility data for quaternary system of terephthalic acid + isophthalic acid + phthalic acid + N-methyl-2-pyrrolidone at 303.15 K and 313.15 K were determined by Schreinemakers’ method of wet residue under atmosphere pressure. Based on the measured solubility, the quaternary phase diagrams were constructed at the two studied temperatures according to the Janeck method. At each temperature, the quaternary phase diagram includes three crystallization regions of pure solid, three co-saturated curves and one eutectic point. The three pure solids are phthalic acid, adduct of isophthalic acid with N-methyl-2-pyrrolidone (the mole ratio of isophthalic acid to N-methyl-2-pyrrolidone is 1:2), adduct of terephthalic acid with N-methyl-2-pyrrolidone (the mole ratio of terephthalic acid to N-methyl-2-pyrrolidone is 1:2), which are confirmed by the method of Schreinemakers’ wet residue. The crystallization region of adduct of terephthalic acid with N-methyl-2-pyrrolidone is larger than those of phthalic acid and adduct of isophthalic acid with N-methyl-2-pyrrolidone. Furthermore, the quaternary solid–liquid phase equilibrium were predicted by NRTL model. The calculated quaternary phase diagrams agreed well with experimental data.