A NONEQUILIBRIUM SURFACE-BARRIER FOR SORPTION KINETICS OF P-ETHYLTOLUENE ON ZSM-5 MOLECULAR-SIEVES

Adsorption equilibrium and kinetic data were measured for the system p-ethyltoluene/Na,H-ZSM-5 zeolite at 343 K. The equilibrium data can be described by the superposition of two Langmuir isotherms. The kinetic data follow a complex mechanism of Fickian diffusion superimposed on the penetration of a surface barrier. The evaluation of the model parameters were carried out by simulation of sorption uptake curves including interactions of the system with both the apparatus and the intrinsic sorption kinetics. The dependence of fitted model parameters with respect to loading and pressure, respectively, is consistent with mechanistic understanding of the mobility within the crystal interface layer and in the crystal bulk.