Gas content of binary clathrate hydrates with promoters.

We develop a methodology to calculate the gas storage capacity of binary hydrates stabilized by promoters. This model utilizes equilibrium experimental data of both hydrates (i.e., the hydrate of pure promoter and the binary hydrate of gas and promoter) in order to calculate the gas occupancy in the small cavities that are not occupied by the promoter. The new approach, although based on the traditional van der Waals-Platteeuw theory, has two significant advantages. The hypothetical state of an empty hydrate for the calculation of the chemical potential of water is replaced by the hydrate of the pure promoter whose properties can be determined through simple thermodynamic calculations. In addition, the computational difficulties related to the complete occupancy of the large cavities by the promoter are removed. The proposed methodology is applied to calculate the gas storage capacity of hydrates of two energy-carrier gases (methane and hydrogen) stabilized by tetrahydrofuran. Excellent agreement is observed between the proposed-model predictions and published experimental values for the gas content of hydrates.