Diffusion of n-Butane/iso-Butane Mixtures in Silicalite-1 Investigated Using Infrared Microscopy

Zeolites of MFI-type belong to the most important zeolite structures in catalysis and are used in many shape-selective processes in petroleum refining industry, in particular for the kinetic separation of alkane isomers. Practically all important applications involve mixtures. However, due to the experimental difficulty, the number of experimental studies of mixture adsorption and diffusion is rather small compared to single components. One of the main advances of the IR microscopy technique (IRM) is the ability to differentiate between different sorbates and to allow, in this way, studies of mixture diffusion. Motivated by the practical relevance, as model system we considered a mixture of a linear and mono-branched alkane in silicalite-1 (MFI-type), viz. n-butane (nC4) and iso-butane (iC4). The primary objective was to investigate the influence of “intersection blocking” effects [1] on mixture diffusion experimentally.