Diffusion of n-butane, isobutane and ethane in a MFI-zeolite membrane investigated by gas permeation and ZLC measurements

The diffusion of n-butane, isobutane and ethane in a composite-membrane alumina-MFI zeolite has been investigated using gas permeation and ZLC techniques. The diffusion of isobutane in the sample is faster than that of n-butane although isobutane molecule has a larger kinetic diameter, and its activation energy is comparable to the results obtained from the gas permeation and QENS measurements reported in the literature. For ethane, the diffusivity is much higher in comparison to n-butane and isobutane. When isobutane is present at a high concentration, the diffusion of ethane is remarkably hindered due to a relatively strong adsorption of isobutane in the membrane micropores. By comparing the diffusivity data obtained from the permeation and ZLC measurements, it was possible to evaluate the thickness of the zeolite membrane effective for gas permeation. (C) 2001 Elsevier Science B.V. All rights reserved.