(335w) Extension of a Clausius - Clapeyron Model for Predicting the Dissociation Heat of Gas Hydrates

Gas hydrates are solid crystalline compounds stabilized by the inclusion of suitably sized gas molecules inside cavities, of different sizes, formed by water molecules through hydrogen bonding. They resemble ice in appearance, but unlike ice, they may form at temperatures well above the ice point. Gas hydrates can occur in staggering abundance in cold sub-sea, sea floor and permafrost environments where temperature and pressure conditions ensure their stability. The natural gas trapped in these deposits represents a potential source of energy many times all known natural gas reserves. To exploit methane from natural gas hydrates in deep-ocean sediments or the permafrost region, it is necessary to possess many information on thermal properties as well as phase equilibria of gas hydrates. Unfortunately, only a few experimental measurements for thermal properties of gas hydrates have been reported in the literature. Most of the previous investigations on gas hydrates have been limited to the crystalline structure and phase equilibria such as pressure-temperature behavior. For practical applications, one of the most important thermal properties of gas hydrates is the heat of dissociation (or the enthalpy of dissociation). The Clausius-Clapeyron model is traditionally used for predicting the heat of dissociation of gas hydrates. However, the conventional Clausius-Clapeyron based models do not take into account the heat of dissolution of guest component(s) in water and the change in volume between gas hydrate and ice (or water) phases as well as the difference in compressibility by phase transition and therefore may not predict satisfactorily the heat of dissociation of gas hydrates, especially for carbon dioxide and hydrogen sulfide hydrates. In this work, the conventional Clausius-Clapeyron based model for predicting the dissociation heat of gas hydrates is extended to take into account the latter factors. It is found that the effects of these factors on the predicting the dissociation heat of gas hydrates are not negligible.