Density and configuration of adsorbed CO2 near the critical point in shale nanopores

XH Ji and H Wang and L Wang and Z Meng and YJ Yuan and KQ Liu and YB Xie and CY Fan and DF Zhang and J Zou, CHEMICAL ENGINEERING JOURNAL, 519, 165425 (2025).

DOI: 10.1016/j.cej.2025.165425

In Carbon Capture, Utilization and Storage (CCUS) strategy, potentials of CO2 capture and storage are evaluated by the absolute adsorption capacity of CO2, which is inaccessible without adsorbed phase density (APD). However, the widely applied value of this density, fixed or fitted by experimental data, has been noticed to be questionable near the critical point of CO2. We got access to the APD of CO2 near the critical point in shale nanopores through molecular dynamics. Our results showed that the APD was related to mineral type, pore size, temperature, and pressure. Essentially, the ratio of the APD to the bulk phase density (BPD) was controlled by their total energy ratio. The total energy included fluid-solid (FS) and fluid-fluid (FF) interactions, and molecular potential energy related to bond length and angle. Interestingly, the adsorbed CO2 is more bent than the bulk CO2 by approximately 4 degrees, which arises from the linear and soft geometry of CO2 molecules.

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