Diffusivity is an important property for the design of adsorption separation systems, gas purification, and catalytic conversion processes. Porous zeolite systems are often used to perform the transport processes. The measurement of diffusivities in molecular sieve zeolites has resulted in large, unexplained differences between values determined by adsorption techniques and the nuclear magnetic resonance (NMR) method. The possible explanations for these differences are (1) failure to account for thermal effects, (2) failure to account for mass transfer resistance, (3) failure to account for a surface barrier resistance at the crystal surface, (4) differences in the crystal structure of the adsorbent, and (5) differences in the regeneration of the adsorbent. There is now the unique possibility of simultaneously measuring the diffusivities in identical systems by three independent methods. Analysis of the results will yield significant insights into the dilemma of the large differences reported in the literature, and this study may provide improved design capabilities for mass transfer processes involving gas diffusion in microporous media.
