Bridging the gap for CO2 fluid modelling: a new multi-scale molecular liquid state theory – BAC2MOL

CO2 fluids are crucial in eco-friendly technologies, from geological storage to industrial processes (separation, extraction). Their development necessitates a clear understanding of the structure and thermodynamics of CO2 fluid across various scales, pressures, temperatures, and complex environments (mixtures, confinement, solvation). Currently, no single method exists to encompass this multi-scale modelling challenge. The macroscopic data are aptly described by empirical cubic equations of state (EoS), widely used in industry, or by the statistical associating fluid theory, a microscopic coarse model. Both methods fall short however in capturing the molecular scale, where anisotropic interactions between CO2 and its surroundings are critical. Conversely, molecular dynamics model the microscopic interactions to provide the structure, thermodynamics, and transport properties., but their computational costs limit their applicative uses. Finally, liquid state theories provide efficiently the structure, but fail to reproduce the thermodynamics and are usually limited to spherical particles. To develop CO2 fluid-based technologies a new multi-scale modelling approach is imperative, characterized by accuracy, efficiency, and versatility. Our project BAC2MOL aims to bridge the gap between the microscopic and the macroscopic modelling by merging state-of-the-art molecular liquid state theories with EoS. This strategy combines the efficiency and molecular-level accuracy of new, anisotropic liquid state theories with the EoS exact thermodynamics. We plan to establish first a reference theory for hard-rod fluid. We will then incorporate the exact EoS, with special care in the near-critical region. Two realistic applications will be provided: CO2 fluid confined in sub-nanopores and its solvation properties near the critical point. The project BAC2MOL will provide an innovative tool to unlock the potential of CO2-fluid application toward more sustainable technologies.