Molecular dynamics and experimental study on the solubility and diffusivity of mixed hydrogen and methane in water

This study presents an experimental and molecular dynamics analysis of the solubility and diffusivity of the (H₂ + CH₄ + H₂O) system, relevant to underground hydrogen storage in depleted gas reservoirs where hydrogen may mix with trapped methane. A range of temperatures (294–374 K) and pressures (5.3–300 bar) were investigated. Our findings demonstrate that pressure has a negligible effect on gas diffusivity in water, while the temperature dependence of diffusivity follows the Arrhenius and Stokes-Einstein equations. The diffusion coefficient of H₂ is 2–3 times higher than that of CH₄, as CH₄ interacts more strongly with H₂O. These differences are significant for applications such as gas separation, where selective diffusion is crucial. Additionally, we observe a minimum in H₂ solubility under certain conditions, which is explained in detail. The solubility and diffusivity of gases in mixed systems provide valuable insights into their behaviour under varying conditions. • Develop experimental methods for measuring mixed H 2 /CH 4 solubility in water. • The experimental and molecular dynamics methods validate each other. • Explore mixed solubility and diffusivity at a broad range of temperature and pressure. • Provide novel molecular insights into gas diffusivity in water. • Validate molecular models for reproducing experimental solubility and diffusivity.