[H-SC05] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC05-03] Wettability of CO₂/Water/Mineral Systems: Comparison of Water-wet and CO₂-wet systems by thermodynamics and molecular dynamics

*Masashige Shiga^1,2, Masaatsu Aichi¹, Masao Sorai² (1.The University of Tokyo, 2.AIST)

Keywords:wettability, interface, contact angle, thermodynamics, molecular dynamics

CO₂ capture and storage (CCS) is expected to be one of the important methods for reducing CO₂ emissions into the atmosphere. In CCS, the wettability of CO₂/water/mineral system is an important physical property that directly affects the storage potential and sealing performance. The contact angle is commonly used as an evaluation index of wettability. Therefore, many experimental measurements and simulations have been performed so far. The contact angle is modeled by Young's equation based on the balance of the energy of the three interfaces (CO₂/water interfacial tension, water/mineral interfacial energy, CO₂/mineral interfacial energy).
On the other hand, since it is not easy to measure and calculate the energy of the solid-liquid interface, it is difficult to make quantitative discussions such as estimating the value of the contact angle and identifying the influential factors. A better understanding of the structure and energy of solid-liquid interfaces is necessary to improve the model.
In this study, we focused on differences of these structure and energy between water-wet system and CO₂-wet system. We performed molecular dynamics simulation to analyze the structure of the solid/fluid interface and calculate the adsorption free energy. As a result, the presence or absence of an adsorption film of the wetting phase was mentioned as a remarkable difference in the interfacial structure, and it was shown that the crucial factor was the salvation forces (structural forces) of the mineral surface.