日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

The mass transport in membrane pore is of fundamental in zeolite membranes. There has been reported many studies on mass transport in zeolite single crystal, however, a few report has been reported on mass transport in zeolite membranes that shows a crystal aggregation structure. In order to design and analyze membrane performance, information on mass transport in zeolite membranes with consideration of intercrystal region is necessary. In this study we carried out ¹H pulse gradient-field spin-echo (PFG) NMR and molecular simulation to study the diffusion phenomena in polymeric membranes. PFG NMR is used to reveal the relationship of diffusion coefficient and diffusion time. We also apply a Tanner's restricted diffusion model to evaluate the structural parameters of intercrystal region. Measured diffusion coefficients show strong decay with increase in diffusion time. This means that diffusion coefficients decrease with increase in diffusion length, and suggests the existence of a diffusion barrier. This trend agrees with the MD results. Observed diffusion coefficients approach to certain values, and those values can be concluded diffusion coefficients of methane in silicalite membrane. Those are by a factor of four smaller than the diffusion coefficient in single crystal. Fitting by Tanner's equation gives 5 µm for the distance between diffusion barriers. This value corresponds with the size of crystal unit consists of the membrane revealed by scanning electronic microscopy.