Heat of adsorption of water vapors and benzene on high-silicon zeolite of the faujasite type

Abstract

1. The isotherms and differential heats of adsorption of water and benzene vapors on ultrahigh-silicon zeolite of the faujasite type (faujasil), obtained by the original method of substitution of Al atoms by Si atoms in the reaction of zeolite NaY with SiCl4, were investigated. 2. The isotherms and heats of adsorption indicate the existence of hydroxyl groups and a small volume of mesopores in faujasil. 3. The presence of hydroxyl groups in the zeolite masks the overall hydrophobic character of the surface of the adsorbing cavities. With the exception of the initial high heats (up to filling of 0.15 mmole/g), the entire sorption volume (17.5 mmole/g) is filled with water with almost zero “pure heat,” and the entropy of the adsorbate does not differ from the entropy of a normal liquid. 4. The pronounced bend in the benzene adsorption isotherm, the increase in the heat of adsorption with an increase in the filling, the passage of the heat through a relatively high maximum, and the deep entropy minimum in completion of sorption indicate a high degree of chemical and geometric homogeneity of the adsorbing cavities in faujasil. 5. The heats of adsorption of benzene on the basal face of graphite and on faujasil with zero filling are almost the same, ∿43 kJ/mole. Volume filling of the micropores creates favorable orientations of the molecules for the maximum adsorbate-adsorbate interaction and the heats increase to ∿60 kJ/mole, while the heats only increase to ∿45 kJ/mole in planar orientation of the molecules on graphite.