A MOLECULAR THERMODYNAMIC MODEL FOR ADSORPTION EQUILIBRIUM FROM SUPERCRITICAL FLUIDS

Using the Bragg-Williams approximation for interaction between the molecules of a lattice gas, a phenomenological two-parameter statistical-mechanical model is studied for adsorption of pure and multi-component gases at low pressures on a variety of surfaces. The model is also used for the correlation and prediction of adsorption data from high-pressure, supercritical carbon dioxide in contact with octadecyl silica (ODS) and alumina (Alox-T), as stationary phases, respectively. The model appears to correlate and predict the data at both low and high pressures quite well, for the systems studied, and should be useful for engineering purposes. The low-pressure data were obtained from various sources in the literature while the high-pressure supercritical-fluid data came from our laboratory. The two parameters in the model characterize the adsorbate-adsorbent potential well-depth, and adsorbate-adsorbate interactions, respectively.