Isobutane diffusivities in the zeolite were measured using quasi-elastic neutron scattering and supported-membrane techniques. This was the first diffusivity measurement of a branched alkane within a zeolite of MFI-type, using a microscopic method. The self-diffusion coefficient derived from QENS was 3 x 10-12m2/s at 500K. The diffusivity obtained using the supported-membrane method was an order of magnitude larger. The comparison between quasi-elastic neutron scattering and supported-membrane data (table 62) was satisfactory. The activation energy for diffusion, determined using quasi-elastic neutron scattering, was 17kJ/mol. Because of a variation of loading due to temperature changes, an apparent activation energy (34kJ/mol) was obtained using the supported-membrane technique. In this zeolite, the diffusion of branched hydrocarbons was much slower than that of linear alkanes. The diffusion coefficient of isobutane was found to be 3 orders of magnitude lower than that of n-butane, according to quasi-elastic neutron scattering.

Diffusion of Isobutane in ZSM-5 Zeolite: a Comparison of Quasi-Elastic Neutron Scattering and Supported Membrane Results. B.Millot, A.Méthivier, H.Jobic, H.Moueddeb, M.Bée: Journal of Physical Chemistry B, 1999, 103[7], 1096-101