Thermodynamic consistency for binary gas adsorption equilibria

An integral and a differential thermodynamic consistency test between pure and binary gas adsorption data and three differential thermodynamic consistency tests for binary gas adsorption data alone can be formulated using the Gibbsian surface excess model of gas adsorption. These relationships originate from the Gibbs adsorption equation. It is necessary to measure the surface excess of the components of the binary gas mixture as functions of pressure at constant gas phase composition and temperature, as functions of gas phase compositions at constant pressure and temperature, and as functions of temperature at constant gas phase compositions and pressures, to apply these tests practically. The tests are very useful to check the quality of the data before they can be extrapolated for adsorptive process design using multicomponent equilibrium adsorption models. A set of pure and binary gas data for adsorption of CH4 and N-2 on a 5A zeolite was used to demonstrate the applicability of these consistency tests, and the data were found to be consistent by all tests. Some of these tests could not be applied previously because of a lack of sufficient data. A series of published pure and binary gas adsorption equilibrium data sets on various microporous adsorbents of practical interest, which passed the integral thermodynamic consistency test, is listed. They can be used to validate theoretical models for prediction or correlation of multicomponent adsorption data. The criteria for obeying the thermodynamic consistency tests by several analytical pure and multicomponent gas adsorption models (Langmuir, Nitta et al., Toth, and Martinet and Basmadjian) are derived. These models are frequently used in describing experimental data on microporous homogeneous and heterogeneous adsorbents.