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

The understanding of interfacial phenomena 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 nonaqueous phases. Nevertheless, 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.