Calorimetric and DTA studies of 1,3-dioxolane hydrate and (1,3-dioxolane) 1−x(tetrahydrofuran) x mixed hydrates

Abstract

The heat capacities of 1,3-dioxolane clathrate hydrates (DXL·17H 2O) doped with potassium hydroxide ( x = 1.8 × 10 −4 and 1.8 × 10 −3 to water) were measured with an adiabatic calorimeter in the temperature range between 13 and 300 K. A glass transition due to freezing of the water reorientation appeared at 43 K in both samples. The relaxation time of the reorientational motion of the water molecule was obtained from the enthalpy relaxation data and the corresponding activation enthalpy was determined to be about 8 kJ mol −1 for both samples. A eutectic melting between DXL hydrate and KOH hydrate occurred at 216 K in the sample richer in KOH ( x = 1.8 × 10 −3), indicating that the solubility limit of KOH to DXL hydrate is around x = 1.8 × 10 −4. Differential thermal analyses of (1,3-dioxolane) 1− x (tetrahydrofuran) x mixed hydrates doped with KOH ( x = 1.8 × 10 −4) were performed in the temperature range between 20 and 100 K. The transition temperature reported in tetrahydrofuran hydrate ( T trs = 62 K) decreased with increase in x and the transition did not occur for x < 0.6 owing to the slowing down of the transition rate. This result indicates that the ordering transition of the water and guest molecules did not occur in DXL hydrate because the hypothetical transition temperature is lower than the freezing temperature of the water reorientation.