Thermodynamics of 2-(1‘-Hydroxycyclohexyl)cyclohexanone:  Vaporization, Sublimation, and the Ideal Gas State Thermodynamic Properties

The thermodynamics of one of the byproducts of caprolactam production, 2-(1‘-hydroxycyclohexyl)cyclohexanone (ketol), have been studied in this work. Saturated vapor pressure for liquid and crystalline ketol was measured by the Knudsen method in the temperature ranges from (308.2 to 330.4) K and from (289.6 to 300.8) K, respectively. Additionally, the saturated vapor pressures over ketol in the undercooled state and in the liquid were measured by the transpiration method in the temperature range from (287.9 to 303.0) K and from (308.0 to 351.5) K, respectively. The enthalpy of vaporization and the enthalpy of sublimation of ketol at the average temperatures studied were obtained indirectly from the temperature dependence of the vapor pressure measured by the Knudsen method as well as by the transpiration method. Furthermore, the standard molar enthalpy of sublimation was measured directly at 303.1 K using calorimetry. The entropy of ketol in the vapor state at (320.8 and 298.2) K was derived. The thermodynamic properties for 2-(1‘-hydroxycyclohexyl)cyclohexanone in the ideal gas state were calculated from statistical mechanic calculations in the broad temperature range from (50 to 1000) K. The gaseous thermodynamic equilibrium constant <i>K</i>° (at 332.1 K) for cyclohexanone auto-condensation (side reaction of the caprolactam production) leading to 2-(1‘-hydroxycyclohexyl)cyclohexanone was assessed.