Thermodynamics and Kinetics of Adsorption of Selected Monoalkylbenzenes in H-ZSM-5

In this study, we present the first systematic investigation of the adsorption of n -propylbenzene, isopropylbenzene, and n -butylbenzene in H-ZSM-5. Both the sorption isotherms and the rate of sorption uptake were investigated at temperatures between 315 and 425 K. The adsorption isotherms are of type I and are reasonably well described by the Langmuir−Freundlich model. It is shown that the heat of adsorption of the longer sorbate molecules depends significantly on the concentration, thus indicating an increased influence of sorbate-sorbate interaction. The uptake rates are determined by Fickian diffusion. The activation energies for the diffusion process are identical for all systems (32−36 kJ/mol). The diffusivities are also in the same order of magnitude decreasing noticeably for sorbates with longer or more complex substituents. A tentative explanation based on a simple jump-rate model for intracrystalline diffusion is given.