TEMPERATURE-DEPENDENT AND OCCUPANCY-DEPENDENT DIFFUSION OF N-BUTANE THROUGH A SILICALITE-1 MEMBRANE

The permeation flux of n-butane through a silicalite-1 (MFI) membrane as a function of the partial feed pressure at 300 K and as a function of the temperature at 0.5 bar partial pressure is excellently described by a Maxwell-Stefan diffusion model in the temperature range 300-630 K, which takes into account the occupancy dependency. The Maxwell-Stefan diffusivity is independent of the occupancy over the whole temperature range and is consistent with an activated process having an activation energy of nearly 30 kJ/mol. The Fickian diffusivity increases strongly with increasing occupancy. The obtained diffusivity values compare well with frequency response and square wave values, but deviates from nuclear magnetic resonance (NMR) and quasi-elastic neutron scattering (QENS) values, especially with respect to the stronger temperature dependency.