Entrance of straight and branched chain compounds from their bulk liquid phase into H-ZSM-5 zeolite

Abstract

Intra-crystalline mass transfer in H-ZSM-5 for the entry of n-butylamine, n-butanol, iso-butanol, tert-butanol, n-hexanol, n-octanol, 2,3 dimethyl butane and iso-octane from their bulk liquid phase has been studied by measuring their initial rate of sorption. The entry of the sorbate molecules into the zeolite channels is strongly influenced by the critical size of the molecules, but much more strongly by their configuration. The influence of both the critical size and configuration may very well be explained by the Shuttlecock-Shuttlebox model for the sorption of bulky molecules in medium-pore zeolites. The activation energy for the entry of n-butanol, iso-butanol and higher n-alcohols is found to be quite different from that of their overall sorption/diffusion from the liquid phase into the same zeolite. For the entry and overall sorption/diffusion, the steric hindrance of bulky sorbate molecules is a common factor deciding the activation energy, but the other factors for the two cases are different. For the first case, only physical sorbate-zeolite interactions are involved but for the second case, both the physical and chemical sorbate-zeolite interactions and also sorbate-sorbate interactions are involved. Also, the entry of sorbate molecules into the zeolite channels from liquid phase differs from their entry to channels from the gas phase, as an additional energy barrier exists for the former case.