Interfacial properties of the hydrogen plus brine system in the presence of hydrophilic silica

XY Yao and AKN Nair and MFAC Ruslan and SY Sun and BC Yan, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 101, 741-749 (2025).

DOI: 10.1016/j.ijhydene.2024.12.417

Geological storage of hydrogen in saline aquifers can be important for a successful transition to a hydrogen economy. Molecular dynamics (MD) simulation was carried out to study the bulk and interfacial properties of the H-2+brine (NaCl), H-2+brine (KCl), and H-2+brine (CaCl2) systems. The temperature, pressure, and salt concentration for the studied systems are in the ranges of 323-423 K, 14-150 MPa, 0-5.4 mol/kg, respectively. For H(2 )solubility, the salting-out effect follows the order KCl < NaCl < CaCl2. All MD results of the interfacial tension (IFT) agree qualitatively well with the predictions of the density gradient theory. Our computed IFTs of the H2+brine (NaCl) system are also in reasonable agreement with the experimental results. The simulated fluid-fluid IFTs are obtained in the range of 45.2-80.8 mN/m for the studied systems. These IFTs are not significantly affected by pressure, and they decrease as a function of temperature. The higher the salt concentration, the higher the IFT. An important result is that the IFT values follow the order KCl < NaCl < CaCl2. A negative surface excess is found for the ions, which explains the increase of IFT with salt content. The interfacial properties of the corresponding H2+brine+silica (hydrophilic) system were also studied using MD simulation. The water CAs are obtained in the range of 42.5-72.2 degrees for the studied systems. These water CAs are not significantly affected by pressure or temperature. The water CAs seem to follow the order KCl < NaCl approximate to CaCl2. Overall, the IFT between rock and H-2 is much higher than that between rock and brine for all conditions. H-2 is negligibly adsorbed at the interface between the water droplet and the rock. The capillary pressure of the H-2+brine+silica system was found to be higher than that of the CO2+brine+silica system, indicating that CO(2 )may be used as a cushion gas to withdraw H-2 stored in saline aquifers.

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