The adsorption isotherms with each saturation vapor pressure factor (cs1, cs2 or cs3) for two groups of sites in two cases of the multilayer and for three groups of sites in one case of the multilayer are derived statistically in heterogeneous non-porous solid adsorbents without interactions among the adsorbed molecules. When some sites of BET isotherm are substituted by less energetic sites, the two-group isotherm obtained by substitution, shows less adsorption over the whole range of relative pressure than the BET isotherm prior to the substitution, at any combined values of f1 with M1 of the two-group isotherm with the same saturation vapor pressure factor. A method to get the monolayer sites (vm) from the ratios of the experimental isotherm to the theoretical isotherm at the whole relative vapor pressure minimizing the standard error is suggested. Our two-or three-group isotherms calculated through many experimental adsorption isotherm data selected appropriately provide larger values of vm than those obtained from BET isotherm. Differential heat vs. v/vm and Bose-Condensation heat are mentioned.
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