INFLUENCE OF THE FRAMEWORK DENSITY AND THE EFFECTIVE ELECTRONEGATIVITY OF SILICA AND ALUMINOPHOSPHATE MOLECULAR-SIEVES ON THE HEAT OF ADSORPTION OF NONPOLAR MOLECULES

The influence of the framework density, the chemical composition, and derived from those the influence of the effective electronegativities of silica and aluminophosphate molecular sieves on the adsorption prop erties have been investigated experimentally and theoretically. By usi ng the electronegativity equalization method (EEM), the average effect ive electronegativities have been determined. A correlation of the ini tial heats of adsorption (as measured by calorimetry) of nonpolar mole cules such as ethane, n-hexane, and benzene is found with the framewor k density as well as with the effective electronegativity of the uncha rged frameworks. An increasing density of the microporous solids and a corresponding decrease of the effective electronegativity results in an increase of the initial heats of adsorption. Because of a compensat ion effect of the entropy, the free enthalpy of adsorption increases l ess with rising framework densities than the enthalpy of adsorption do es.