Different diffusivities of xylene isomers in BaX zeolite measured by the neutron spin echo technique

The neutron spin echo (NSE) technique has been used for measuring the transport diffusivities of xylene molecules in BaX zeolite in the temperature range 470-650 K. The NSE technique pushes down the lower limit of diffusion coefficients accessible by neutron methods by two orders of magnitude. Diffusivities in the range 10^-1²-10^-13 m²s^-1 could thus be measured, p-xylene diffusing about three times faster than m-xylene. This suggests that (i) microporous diffusion could be rate limiting, and (ii) diffusion can influence the separation in the industrial process.