Estimations of enthalpies of dissociation 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 and mixed CO2 and THF hydrates are presented and discussed. It is found that the estimated enthalpy of dissociation of simple CO2 hydrate varied from 56.85 to 75.37 kJ/mol, as the temperature is reduced from 282.06 to 273.15 K. Depending on the concentration of carbon dioxide and tetrahydrofuran in the hydrate forming systems, the enthalpy of dissociation of mixed carbon dioxide and tetrahydrofuran is found to be in the region of 112.37-152.27 kJ/mol. A rationale for this significant increase of the enthalpy of dissociation of the mixed hydrates is discussed. (C) 2009 Elsevier B.V. All rights reserved.