Solubility behavior and thermodynamic properties of caprolactam in four pure solvents and two cosolvent mixtures

Abstract

The purpose of this work is to study the dissolution behavior of caprolactam in different solvents and to provide solid-liquid equilibrium data for the design and operation of crystallization and purification process for production and recovery of caprolactam. The mole fraction solubility of caprolactam was investigated in four pure solvents (benzene, ethyl acetate, cyclohexane, acetonitrile) and two cosolvent mixtures (ethyl acetate + cyclohexane, benzene + cyclohexane) by gravimetric method at atmospheric pressure from 277.65 K to 323.65 K. At the same temperature, the order of solubility of caprolactam in the selected pure solvents is: benzene > acetonitrile > ethyl acetate > cyclohexane. In the selected cosolvent mixtures, the solubility increases with increasing temperature and the content of good solvent. A series of thermodynamic models were used to fit the experimental solubility data. Finally, the thermodynamic properties of caprolactam in selected solvents were studied using the van't Hoff equation. From this analysis, it was concluded that the dissolution of caprolactam in the selected solvents is a heat-absorbing and entropy-increasing process.