Hydrogen storage in sH clathrate hydrates: thermodynamic model

A thermodynamic model of equilibrium states of structure sH clathrate hydrates of hydrogen with methyl tert-butyl ether, methyl cylohexane, or 1,1-dimethyl cyclohexane is presented. The model uses the van der Waals-Platteeuw statistical-thermodynamical model to represent the hydrates and the cubic-plus-association equation of state to represent the fluid phases. Good agreement between experimental and calculated phase equilibrium data has been obtained, with average absolute pressure deviations between experiments and calculations ranging from 1.2 to 2.1% depending on the promoter. The model has also been used to estimate the occupancy of the cavities of the hydrate by hydrogen and the promoter, as well as the hydrogen storage capacity of the hydrate. This capacity has been found to vary between 0.85 and 1.05% of hydrogen by weight at the conditions of formation of the sH hydrates (270-280 K and 60-100 MPa).