Standard methods (using H nuclear magnetic resonance) for the study of hydrocarbon diffusion were applied here for the first time to the diffusion of 15N2 in beds of finely powdered commercial zeolites (5A, 13X). It was found that details such as crystallite size, gradient strength, observation time, and gyromagnetic ratio were more important during the measurement of N2 self-diffusion in commercial-grade crystals. Indeed, attention had to be restricted to the measurement of long-range diffusivities. The latter were similar for both adsorbents, and varied from 3.2 x 10-6 to 1.3 x 10-8m2/s at temperatures ranging from 289 to 167K. The intercrystalline diffusivity was deduced from the measured long-range diffusivities and adsorption isotherms. The values were found to be similar to those for bulk N diffusion. The experimentally determined long-range diffusivity results were shown to compare favorably with those calculated using simple gas kinetic theory.

P.L.McDaniel, C.G.Coe, J.Karger, J.D.Moyer: Journal of Physical Chemistry, 1996, 100[40], 16263-7