A STUDY OF SHAPE SELECTIVITY IN ETHYLATION DISPROPORTIONATION OF ETHYLBENZENE ON ZSM-5 ZEOLITES USING A CONTINUUM AND A MONTE-CARLO METHOD/

The ethylation and the disproportionation of ethylbenzene on ZSM-5 zeo lites yield a mixture of the three isomers ortho-, meta-and para-dieth ylbenzene. The two reaction systems were simulated on the basis of an adsorption/diffusion/reaction-model using both a continuum and a Monte Carlo approach. Para-selectivity, i.e. the fraction of the para-isome r in the isomer mixture, depended on several facto rs: the Thiele modu lus of ethylation/disproportionation, the primary product distribution , and the relative diffusivity of diethylbenzene isomers. The simulati on results obtained by both methods were in good agreement. The nature of the shape selectivity could be discussed in detail. By comparing e xperimental results from literature with these simulations, it was con cluded that in the ethylation para-selectivity can be mainly attribute d to product rather than transition state shape selectivity. On the co ntrary, for the disproportionation it is mon reasonable to ascribe the observed para-selectivity to transition state shape selectivity. On t he basis of the simulations, some suggestions to enhance the para-sele ctivity for different cases were proposed. (C) 1997 Elsevier Science L td.