Hydrate formation in mesoporous materials: Thermodynamic modeling and experimental investigations

Abstract

Until recently, analysis and interpretation of the equilibrium conditions of hydrate formation from water adsorbed in mesoporous materials have been carried out with the use of the Gibbs-Thomson equation. For this purpose, only the shift of equilibrium conditions due to the small size of hydrate particles formed in the confining pores was taken into account. A distribution of equilibrium temperatures of the hydrate formed in mesoporous materials was interpreted as a consequence of the existence of hydrate particles differing from each other in size. A new equation describing the equilibrium conditions for gas hydrate in thin pores of mesoporous materials is proposed in this work. This equation takes into account the size of hydrate particles together with the chemical potential of pore water in equilibrium with the hydrate. Thus, an increase in the temperature shift from the equilibrium curve causes simultaneous formation of hydrate in smaller and smaller pores, and an increase in the size of gas hydrate particles that have been previously formed in larger pores. The latter occurs due to gradual transformation into hydrate of the layer of bound water, located between the pore wall and hydrate particle being formed in the pore center. Modeling results are compared with the data obtained previously on the equilibrium conditions for the hydrate of carbon dioxide in mesoporous Al2O3 samples. It is demonstrated that experimental results are in reasonable qualitative agreement with the proposed model.