vdWP-FL Theory for Clathrate Hydrates with Multiple Cage Occupancies

The formalism proposed by van der Waals and Platteeuw (vdWP theory) is widely used to model the thermodynamic properties of gas hydrates. Recently, an improved version of the theory called vdWP-FL was developed to account for free-energy contributions due to the vibrational and librational movement of water molecules in the hydrate lattice. The vdWP-FL theory was shown to accurately predict the dissociation temperatures and pressures of various single-occupancy gas hydrates as well as the hydrate cage occupancies, with very few fitting parameters compared to those in the original theory. In this work, we extend the vdWP-FL theory to gas hydrates of argon and nitrogen that show multiple cage occupancies. We show that the improvements seen in the vdWP-FL theory also hold for gas hydrates that have multiple cage occupancies. Finally, we parametrize the vdWP-FL theory using experimental data on nitrogen gas hydrates and compare our results with previous studies.