DRIFTS Study of Kinetics of Diffusion-Limited Adsorption of Ethane from Mixtures with Hydrogen by Cationic Forms of Zeolites

The diffusion-limited adsorption of individual ethane or of ethane from mixtures with hydrogen by thin pellets of NaA, CaA and LiLSX zeolites or by thick layers of granulated zeolites was studied at room temperature. The rates of adsorption were monitored by development of the bands from the symmetry forbidden C–H stretching vibrations that were not observed for gaseous molecules. Diffusivity of individual ethane in the micropores of the thin NaA pellet obtained by this method is equal to 6 ⋅ 10⁻¹⁶ m²/s. This value agrees well with that one previously reported in literature. For adsorption of pure ethane in the larger primary micro pores of CaA or LiLSX only the lower limits of diffusivities were estimated. Diffusion-limited adsorption of ethane from mixtures with hydrogen by the thicker layers of granulated zeolites is much slower and is limited by counterdiffusion inside much larger channels between the zeolite granules. Estimation of diffusion coefficients of such counterdiffusion indicated that they are by two orders of magnitude lower than those for diffusion in gaseous mixtures of similar composition. This paper is dedicated to the memory of Professor Wolfgang Schirmer.