Estimations of Enthalpies of Dissociation and Hydration Numbers of Simple and Mixed Carbon Dioxide Hydrates from Phase Equilibrium Data

In the present work, the stability conditions of simple and mixed carbon dioxide (CO2) and tetrahydrofuran (THF) hydrates are experimentally measured. Considering the difficulties of obtaining the enthalpy of dissociation data through direct measurements, the enthalpies of dissociation for these hydrates are estimated from the measured equilibrium data by applying the Clausius-Clapeyron equation. The results of the calculated enthalpy of dissociation for simple CO2 hydrates are presented and discussed. In addition, the hydration number of simple CO2 hydrate is also estimated based on the Forcrand method. It is found that the estimated enthalpy of dissociation and hydration number of simple CO2 hydrate varied from 56.85 to 75.37 kJ/mol and 5.98 to 8.54 respectively, as the temperature is reduced from 282.06 to 273.15 K. Depending on the concentration of tetrahydrofuran in the hydrate forming systems, the enthalpy of dissociation of mixed carbon dioxide and tetrahydrofuran are found to in the region of 112.37 to 152.27 kJ/mol. A rationale for this significant increase of the enthalpy of dissociation of the mixed hydrates is discussed.

Keywords: Enthalpy of dissociation, hydration number, carbon dioxide hydrate, mixed carbon and tetrahydrofuran hydrate