Studies on the Physical Adsorption Equilibria of Gases on Porous Solids over a Wide Temperature Range Spanning the Critical Region—Adsorption on Microporous Activated Carbon

Adsorption equilibria of nitrogen and methane on microporous ( < 2 nm) activated carbon were measured for a wide temperature range (103-298 K) spanning the critical region. Information relating to Henry constants, the isosteric heat of adsorption, and the amount of limiting adsorption were evaluated. All isotherms show type-I features for both sub- and supercritical temperatures. A new isotherm equation and a consideration for the importance of the effect of the adsorbed phase volume allow this kind of isotherms to be modeled satisfactorily. The model parameter of the saturated amount of absolute adsorption (n⁰_t) equals the limiting adsorption amount (n^itm), leaving the physical meaning of the latter clarified, and the exponent parameter (q) proves to be an appropriate index of surface heterogeneity.