Effect of Hydrogen-to-Methane Concentration Ratio on the Phase Equilibria of Quaternary Hydrate Systems

Abstract

Clathrate hydrates of hydrogen are of specific interest due to their potential ability to store molecular hydrogen. In particular, structure H (sH) hydrate has a higher theoretical storage capacity in comparison with the other two more common hydrate structures (sI and sII). This paper investigates the effect of hydrogen (H2) concentration on the phase equilibria of sH hydrate in a quaternary system of water, methane, hydrogen, and methylcyclohexane. Phase equilibria and cage occupancies of the quaternary system were predicted using the van der Waals and Platteeuw (vdWP) model for different hydrogen/methane ratios ranging from 0 to 7. Model predictions for the quaternary systems were found to be in good agreement with measured experimental data. It was evident from the thermodynamic equilibrium conditions of the quaternary system (MCH + H2O + CH4 + H2) that as the H2 concentration increases (H2:CH4 ratio increased from 0 to 7), higher pressures are required to produce sH hydrates at the same temperature. It was also found that the fractional cage occupancy of CH4 in the small and medium cages of sH hydrate increases with pressure.

Hydrate phase equilibrium for CH4‐CO2‐H2O system in porous media

“…The improved model is based on the traditional thermodynamic model of van der Waals and Plateeuw, which was established based on the chemical potential of water in the hydrate phase and in the coexisting liquid phase being the same. Several thermodynamic models for calculating clathrate hydrate phase equilibrium were proposed based on this model . When a CO 2 ‐CH 4 hydrate system reaches phase equilibrium conditions, we also believe that the chemical potential of water is identical in the solid and liquid phases in this study.…”

Recent Advances in Experimental Measurements of Mixed-Gas Three-Phase Hydrate Equilibria for Gas Mixture Separation and Energy-Related Applications

“…Since the major process of interest for the particular mixture is separation, effort has been devoted in examining various hydrate promotion schemes. In particular, Khan et al 183 explored the effect that the H 2 concentration in the gas mixture has on the phase equilibria of a hydrate-forming system that contains H 2 + CH 4 + methylcyclohexane (MCH). The presence of MCH results in the formation of sH hydrate.…”

The potential of hydrogen hydrate as a future hydrogen storage medium

“…Khan et al. ( Khan et al, 2015 ) studied hydrate equilibrium condition by considering two systems with different combined promotors: one using a mixture of and methylcyclohexane and the other using a mixture of and as the promotors. The results suggested that the latter requires lower pressures for hydrate formation than the former and, hence, is preferable.…”