SORPTION KINETICS OF P-ETHYLTOLUENE IN NAH-ZSM-5 CRYSTALS - SIMULTANEOUS EFFECT OF INTRACRYSTALLINE DIFFUSION AND A MASS-TRANSPORT RESISTANCE WITHIN THE CRYSTAL-SURFACE

Adsorption equilibrium and sorption uptake data have been measured for the system p-ethyl-toluene/NaH-ZSM-5 zeolite under constant volume/va riable pressure condition at elevated ambient temperature of 343 K. Th e equilibrium data are described by a superposition of two Langmuir is otherms. The uptake curves observed in the present paper revealed deva tions from the second Fick law behaviour. The experimental uptake curv es are compatible with rate mechanism involving Fickian diffusion supe rimposed by a surface barrier. The evaluation of the model parameters was carried out by simulation of the kinetic curves that include both the interactions of the system with the apparatus and the intrinsic so rption kinetics. The dependence of the fitted model parameters on sorb ent amount and pressure, respectively, is consistent with Langmuir sor ption kinetics at crystal surface on one side and with the concept of molecule jumps on a system of fixed positions in the crystal bulk on t he other.