SIMULATION OF THE ISOMERIZATION OF AN ORTHO-DIETHYLBENZENE ON ZEOLITES USING A CONTINUUM APPROACH AND DIFFERENT DIFFUSION-MODELS

The overall kinetics of the isomerization of the dialkylbenzenes on ze olites such as ZSM-5 are affected by the intrinsic kinetics and, in ma ny cases, additionally by configurational diffusion inside the micropo rous zeolite. Simulation studies on the basis of a continuum model all ow a deeper insight into this complex situation. It has been shown tha t both a reactant diffusion limitation and product shape selectivity ( different diffusion rates of the products) may influence the overall k inetics (conversion/selectivity). Calculating concentration profiles i nside the crystallite gives additional details about the interrelation of diffusion and reaction. Due to the strong interaction between the diffusing molecules themselves, as well as between diffusing molecule and zeolite surface, various diffusion models have been implemented. D epending on the diffusion model used, it could be shown that at high o ccupancies, differences occurred only in the calculated conversions, b ut not in the calculated selectivities. On the basis of the simulation results a recommendation is given concerning the determination of dif fusion coefficients from measured overall kinetics. Furthermore, it wa s found that selectivity strongly depends on the chosen type of reacto r, e.g. a plug flow reactor or an ideally mixed reactor. This is impor tant for a comparison of data measured in different experimental set-u ps. (C) 1997 Elsevier Science B.V.