Molecular modeling of interfacial properties of the hydrogen+water+decane mixture in three-phase equilibrium

The understanding of geochemical interactions between H2 and geofluids is of great importance for underground H2 storage but requires further study. We report the first investigation on the three-phase fluid mixture containing H2, H2O, and n-C10H22. Molecular dynamics simulation and PC-SAFT density gradient theory are employed to estimate the interfacial properties under various conditions (temperature ranges from 298 to 373 K and pressure is up to around 100 MPa). Our results demonstrate that interfacial tensions (IFTs) of the H2-H2O interface in the H2+H2O+C10H22 three-phase mixture are smaller than IFTs in the H2+H2O two-phase mixture. This decrement of IFT can be attributed to C10H22 adsorption in the interface. Importantly, H2 accumulates in the H2O-C10H22 interface in the three-phase systems, which leads to weaker increments of IFT with increasing pressure compared to IFTs in the water+C10H22 two-phase mixture. In addition, the IFTs of the H2-C10H22 interface are hardly influenced by H2O due to the limited amount of H2O dissolved in bulk phases. Nevertheless, relatively strong enrichments and positive surface excesses of H2O are seen in the H2-C10H22 interfacial region. Furthermore, the values of the spreading coefficient are mostly negative revealing the presence of the three-phase contact for the H2+H2O+C10H22 mixture under studied conditions

Effects of impurity gases on interfaces of the hydrogen-water-decane three-phase system: A square gradient theory investigation

The effects of impurity gases on interfacial characteristics of hydrogen-water-oil three-phase systems are critical to underground H2 storage in depleted oil fields but have not been investigated yet. The square gradient theory calculations with Perturbed-chain statistical associating fluid theory equation of state are carried out to understand the effects of impurity gases (N2, CH4, and CO2) on interfaces of the H2-H2O-n-decane three-phase system under reservoir conditions. Our results obtained from the four-component three-phase systems are compared to the corresponding system without impurity gases. It is found that the all three interfaces (H2-H2O, H2O-C10H22, and H2-C10H22) are greatly influenced by impurity gases. The impurity gases accumulate in all three interfacial regions and have positive surface excesses, which leads to smaller interfacial tensions. The reduction of interfacial tensions depends on the type of impurity gas following this order: CO2 ≥ CH4 > N2. In general, the adsorption of impurity gases weakens the adsorption of other species. However, the adsorption of decane in the H2-H2O interface can be enhanced by impurity gases, which also contributes to the decrease of interfacial tensions. Moreover, the spreading coefficients are mostly negative over the studied temperature and pressure conditions indicating the existence of three-phase contact in the N2/CH4/CO2-hydrogenwater- oil three-phase systems.Document Type: Original articleCited as: Yang, Y., Wan, J., Li, J., Zhu, W., Zhao, G., Shang, X. Effects of impurity gases on interfaces of the hydrogen-water-decane three-phase system: A square gradient theory investigation. Capillarity, 2023, 9(1): 9-24. https://doi.org/10.46690/capi.2023.10.0