SF₆ Hydrate Formation in Various Reaction Media: A Preliminary Study on Hydrate-Based Greenhouse Gas Separation

Abstract

SF₆ hydrate formation behaviors in various reaction media, such as bulk water, porous silica gel, and hollow silica, were investigated for hydrate-based SF₆ separation with a primary focus on thermodynamic stability and formation kinetics. The measured three-phase (H-L_W-V) equilibria demonstrated that the types of reaction media used in this study had no effect on the thermodynamic stability of SF₆ hydrates. The dissociation enthalpy (Δ<i>H</i>_d) of SF₆ hydrate was measured using a high-pressure micro-differential scanning calorimeter, and it corresponded well with estimates from the Clausius-Clapeyron equation. The unstirred porous silica gel system showed a larger gas uptake and a higher growth rate at the early stage of SF₆ hydrate formation. However, the gas uptake and growth rate of SF₆ hydrates in stirred bulk water and unstirred hollow silica were significantly increased at a larger temperature driving force or in the presence of sodium dodecyl sulfate. The experimental results obtained in this study will be very helpful for a better understanding of the thermodynamic and kinetic characteristics of SF₆ hydrate formed in various reaction media and in surfactant-added solution, and are expected to contribute to further development of the hydrate-based SF₆ separation process.