Semiempirical equations of state of H₂O/CO₂ binary mixtures in graphite nanoslits

The existence of confining walls limits the prediction accuracy of nanoconfined fluids using macroscopic equations of state (EOSs); moreover, appropriate EOSs for multicomponent mixture fluids in nanoconfined spaces are missing. Here, we derive the EOS of multicomponent mixture fluids confined in nanospaces at high temperatures and pressures, mainly considering the nano-confinement effect and the competitive adsorption effect between different components. Then, the EOSs are validated through comparison with the molecular dynamics-simulated PvT data of CO₂/H₂O mixtures in graphite nanoslits. To consider the above effects, we derive two EOSs via two modeling methods: EOS I is obtained through modification of the actual component occupation volume in the Peng-Robinson equation of state (PR EOS) by fitting the binary component interaction coefficient and the number of adsorbed molecules according to a selectivity coefficient, while EOS II is obtained by considering the decreased pressure of the fluids in PR EOS by adding an attractive term between components and walls. With the simulation results as a benchmark, the two EOSs exhibited good prediction accuracies under low CO₂ concentrations, and generally, EOS II was more accurate than EOS I. This study fills the gap in the EOSs of nanoconfined mixture fluids, and the obtained equations can help to further describe the thermodynamic properties of confined mixture fluids.