Determination and modeling for solid–liquid phase equilibrium of ternary caprolactam + cyclohexanone oxime + methyl tert-butyl ether system

• Solid-liquid phase equilibrium of caprolactam + cyclohexanone oxime + methyl tert-butyl ether system were determined.
• The ternary phase diagrams were constructed at three temperatures.
• The ternary phase diagrams were correlated and calculated by NRTL model.

The solid–liquid equilibrium (SLE) for ternary system of caprolactam + cyclohexanone oxime + methyl tert-butyl ether were determined at three temperatures of (278.15, 293.15 and 308.15) K under pressure of 101.2 kPa. Three isothermal phase diagrams of the system were constructed based on the measured mutual solubility data. There were two pure solids formed in the ternary phase diagram, including pure caprolactam and pure cyclohexanone oxime, which were identified by the method of Schreinemakers' wet residue. At each temperature, the phase diagram contained three crystallization regions (which corresponded to caprolactam, cyclohexanone oxime, and a mixture of caprolactam and cyclohexanone oxime), two crystallization curves, and one co-saturated point. The crystallization field of caprolactam was larger than that of cyclohexanone oxime. The NRTL model was employed to correlate and calculate the ternary phase diagram. The calculated ternary phase diagram with the NRTL model agreed well with the experimental ones. The solid–liquid phase equilibrium and phase diagram for the ternary system of caprolactam + cyclohexanone oxime + methyl tert-butyl ether could provide basis for the purification process of caprolactam.

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