DIFFUSION STUDIES IN ZEOLITES AND RELATED SOLIDS BY GAS CHROMATOGRAPHIC TECHNIQUES

The diffusion of inert gases (Ar, Kr, SF6) in a series of zeolites including 3A and 5A Molecular Sieves, Na and H mordenites, Na faujasite, and amorphous silica-alumina catalyst was studied by a gas chromatographic technique. Between 25° and 427° C., the flow is best described by an activated diffusion process. Activation energies increase with molecular weight of the gas and range from 2.5 to 15 kcal. per mole. For gases which can readily enter the pores, the diffusion resistance for the various solids decreases in the order: Na mordenite > H mordenite > 5A > Na faujasite > silica-alumina. The effect of molecular weight on diffusivity is much more pronounced than that expected for Knudsen diffusion. A mathematical procedure for including the effects of adsorption on the diffusion constant is described. Heats of adsorption for the various gases varied from 3 to 6 kcal. per mole. © 1969, American Chemical Society. All rights reserved.