Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The solubility of terephthaldialdehyde in N-methyl-2-pyrrolidone at the temperature range from T = 293.15 K to 318.15 K and the solid-liquid phase equilibrium for ternary systems of terephthalic acid + terephthaldialdehyde + N,N-dimethylformamide and terephthalic acid + terephthaldialdehyde + N-methyl-2-pyrrolidone at three temperatures T = 298.15 K, 308.15 K and 318.15 K were determined by using an isothermal saturation method under atmospheric pressure (101.2 kPa). Six isothermal ternary phase diagrams were constructed according to the measured mutual solubility data. Two pure solids were formed in the ternary systems at a certain temperature, which corresponded to pure terephthalic acid and pure terephthaldialdehyde, and were confirmed by Schreinemaker's method of wet residue and X-ray powder diffraction. Each ternary phase diagram included one cosaturated point, two boundary curves, and three crystalline regions. The crystallization region of terephthaldialdehyde was smaller than that of terephthalic acid at each temperature. Furthermore, two thermodynamic models, NRTL and Wilson were employed to correlate and calculate the solubility of terephthaldialdehyde in N-methyl-2-pyrrolidone and the mutual solubility data for the ternary terephthalic acid + terephthaldialdehyde + N,N-dimethylformamide/N-methyl-2-pyrrolidone systems. The largest value of root-meansquare deviation was 3.58x10-3, and the maximum value of relative average deviation, 1.74 %. The solid-liquid equilibrium phase diagrams and the thermodynamic models for the ternary system can provide the foundation for obtaining high purity terephthalic acid from its mixtures.