Adsorption of water vapors and the micropore structure of carbon adsorbents. Communication 2. Features of adsorption of water vapors by ultramicroporous activated carbons

Abstract

1. The isotherms of physical adsorption of water vapors by ultramicroporous active carbons (AC) are reversible in the entire range of relative pressures. For AC with a high concentration of primary adsorption sites, the adsorption isotherms are convex in a wide range of relative pressures. 2. Preliminary evacuation of the AC at 673°K significantly alters the shape of the isotherm. The quasi-equilibrium physical adsorption isotherm acquires the S-shape with “open” adsorption-desorption hysteresis characteristic of the water vapor adsorption isotherms for AC, since a slower process of chemisorption of water molecules takes place simultaneously with physical adsorption. 3. The isosteric heats of adsorption of water vapors by ultramicroporous AC in the region of small degrees of filling are lower than the heats of condensation of water vapor and increase with an increase in the adsorption value.