An improved Clapeyron model for predicting liquid water–hydrate–liquid hydrate former phase equilibria

Determination of pressure–temperature phase diagram for the liquid water–hydrate–liquid hydrate former region is a challenge considering this diagram at these conditions is a strong function of temperature. The Clapeyron model is traditionally used for this purpose. However, the conventional Clapeyron model does not take into account the effect of pressure on the hydrate molar volume as well as the heat of dissolution of hydrate former in water and therefore cannot predict satisfactorily the gas hydrate phase diagram. In this work, the conventional Clapeyron model is extended to take into account the aforementioned factors as well as the change in the slope of the pressure–temperature phase diagram when increasing the temperature. Three hydrate formers, i.e. carbon dioxide, hydrogen sulfide and ethane, are studied. It is found that the effect of these factors on the determination of the gas hydrate phase diagram is not negligible.