Thermodynamics of gas mixtures in nanoporous materials: Extension to non-ideal systems at high pressures

In this work, we developed a phenomenological approach to describe the equilibrium adsorption of nonideal gas mixtures in nanoporous adsorbents over a wide pressure range. The key point of the developed approach is an observation that the Gibbs free energy of a gas mixture is close to its ideal term. This feature, being more general than the empirical Raoult’s law in the ideal adsorbed solution theory (IAST), was combined with the distribution of elements of the adsorption volume (EAV) of the porous material over potentials in the spirit of Polanyi’s theory. We applied this approach to the adsorption of individual and binary gas mixtures of CO$_2$, CH$_4$, and N$_2$ on an activated carbon in a wide pressure range up to 13 MPa. The approach provides high accuracy in predicting the adsorption of gas mixtures based on individual adsorption isotherms and obeys the Gibbs–Duhem equation, which confirms its thermodynamic consistency.