Thermodynamic modeling of promoted structure II clathrate hydrates of hydrogen

This work presents a thermodynamic model of equilibrium states of binary structure II gas hydrates of hydrogen with different promoters based on the van der Waals-Platteeuw statistical thermodynamic model. Since the determination of the occupancy of the small cavities by hydrogen is still an unresolved question, the model allows for multiple occupancy of these cavities. The agreement of the predictions of the model with experimental data is satisfactory, with average absolute pressure deviations below 10%. Model results indicate that at the pressures of hydrogen hydrate formation, the small cavities of the hydrate are singly occupied by hydrogen and that at moderate pressures (P<30 MPa), hydrogen hardly displaces the promoter from the large cavities, even when the concentration of the promoter is reduced below the stoichiometric concentration. Model results are also used to optimize the conditions for hydrogen storage in the gas hydrates.