Effect of crystal size on the kinetics of alkane adsorption on NaCaA zeolites

Abstract

1. Study has been made of the effect of the crystal size (2R=1.5–45 μm) on the kinetics of the adsorption of ethane, propane, and n-butane on NaCaA zeolites (75% exchange) at −80°C and 23°C. Measurements were made by a constant-pressure gravimetric method, and by a constant volume, decreasing pressure, adsorption method, the working conditions being so chosen as to eliminate the possibility of effects from intercrystalline diffusion. 2. Effective diffusion coefficients calculated for an assumed intracrystalline transfer mechanism were found to be closely dependent on the crystal size. From this it was concluded that these effective values were not true coefficients for diffusion within the zeolite crystal. The relation in question here could be interpreted as indicating the existence of diffusional barriers on the crystal surface.