Comments on practical use of Langmuir gas adsorption isotherm model

The physical and thermodynamic characteristics of the Langmuir adsorption isotherm model for pure gas and gas mixtures as well as the constraints on the saturation adsorption capacity of the gases by this model are discussed. Arbitrary violation of these constraints, viz. temperature dependence of the saturation capacity and unequal saturation capacities for the components of a mixed gas, may lead to unrealistic heat of adsorption and unreliable predictions of mixed gas equilibria. Several physically and thermodynamically consistent analytical models for pure and mixed gas adsorption isotherms, which were developed using the Langmuir model as backbone, and which account for unequal -sized adsorbates, lateral interactions between adsorbed molecules, multi-layer adsorption, and adsorbent heterogeneity, are briefly reviewed. These models can be practically very useful to describe experimental isotherm data and for adsorptive process modeling.