Adsorption and diffusion of n-butane/iso-butane mixtures in individual silicalite-1 crystals was investigated using infra-red microscopy. The equilibrium sorption isotherm for an equimolar gas phase mixture was calculated using configurational bias Monte Carlo simulations. A comparison between simulation results and the experimental data permitted the determination of absolute values of concentration in the infra-red experiments. The n-butane uptake in the presence of iso-butane and the  iso-butane uptake in the presence of n-butane were studied experimentally. It was shown that the n-butane counter-uptake was not limited by n-butane diffusivity, but by the availability of free sites. This was in turn determined by the mobility of iso-butane. A site-percolation threshold, given by the number of iso-butane molecules blocking the junctions of the channel network, was used to explain the occurrence of network regions which were initially inaccessible to n-butane in the counter-uptake process.

Diffusion of n-Butane/Iso-Butane Mixtures in Silicalite-1 Investigated Using Infrared (IR) Microscopy. C.Chmelik, L.Heinke, J.M.van Baten: R.Krishna: Microporous and Mesoporous Materials, 2009, 125[1-2], 11-6