Interpretation of ethane hydrate equilibrium data for porous media involving hydrate‐ice equilibria

Abstract

AbstractEquilibrium pressures for the dissociation of ethane hydrate confined in silica gel pores of nominal radii 7.5, 5.0 or 3.0 nm were measured over a range of temperatures. Each of these porous media contained a broad distribution of pore radii. At higher temperatures, the pressures were larger than previously reported for bulk hydrates, and generally increased with a decrease in nominal pore radius for those data where the equilibria involved liquid water. However, at the lowest temperatures (where the equilibria involved ice), the pressures were identical (within expected experimental uncertainties) for all three silica gels and the same as reported by various authors for the bulk hydrate. The lack of any dependence of the equilibrium pressure on pore size at the lowest temperatures (where the equilibrium involves ethane hydrate, ethane gas, and ice) indicates that, below the quadruple point temperature of the smallest pore in which hydrate formed, there is no detectable effects on the equilibrium pressure due to the restricted geometries of the porous media. It suggests that the interface relevant to the formation of hydrate in silica gel pores is that between the hydrate and aqueous phase (Henry et al., 1999) and that within experimental error the surface energy between the hydrate and aqueous phase can be approximated by that between ice and the appropriate aqueous phase.