Hydrate phase equilibrium of H2/CH4/CO2 ternary gas mixtures and cage occupancy percentage of hydrogen molecules

• Hydrate phase equilibrium of H2/CH4/CO2 ternary gas mixtures in pure water system were determined.
• There exists little difference for thermodynamic model prediction if taking H2 as a former or not.
• The occupancy percentage of hydrogen molecules range from 0.3 to 2.3 percent in small cage.
• H2 molecules are indeed trapped in hydrate solid.

Hydrogen, methane, and carbon dioxide are co-existence in many cases such as vent gas from the steam reforming of hydrocarbons. For the purpose of H2 recovery and/or CO2 sequestration via separation technology based on hydrate, the hydrate phase equilibrium of four groups of H2/CH4/CO2 ternary gas mixtures in pure water system were determined using the isothermal pressure-search method in a temperature range of (274.7–284.5) K. During modeling hydrate formation conditions, there is little difference with experimental data no matter whether H2 works as a hydrate former or not. Hydrogen can be regarded as a kind of diluent gas for convenience when presetting the operation conditions. To meet the mass balance of each gas species, the cage occupancy percentages of hydrogen in hydrate have been evaluated. The result illustrates that the occupancy percentage of hydrogen molecules ranges from 0.3 to 2.3 percent in small cage and (2.16–13.6) × 10−7 percent in large cage, which deduces that H2 molecules are indeed trapped in hydrate solid.