Adsorption equilibria of single gas and gas mixture on homogeneous surfaces: A unified approach based on statistical thermodynamics developments. Part I: Single gas adsorption

Theoretical description of single gas and gas mixture adsorption equilibria can be achieved in many different ways depending on the kind of approach (microscopic or macroscopic) and on the physical assumptions related to the nature of the adsorbent-adsorbate systems studied as well as temperature and pressure conditions. In this paper, a detailed statistical thermodynamics development is presented. It leads to a generalized expression of adsorption isotherms for pure gases on homogeneous surfaces. The non-ideality of both gas and adsorbed phases are taken into account using the Redlich-Kwong equations of state (EOS) which is adapted for two-dimension phases. Such an approach leads to a symmetrical treatment of both phases resulting in similar expressions of their EOS and of their fugacity coefficients. It allows an easy extension to gas mixtures adsorption equilibria. We present adsorption isotherms calculated using our model, the influence of the non-idealities are presented and discussed.