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Abstract

In this contribution the relationship between the reaction kinetics of the disproportionation of ethylbenzene and the pore structure of the zeolite catalyst is discussed. Earlier studies of the kinetics revealed that over large-pore zeolites at low temperatures the reaction rate is significantly but reversibly retarded by the product diethylbenzene. In contrast, with medium-pore zeolites no product inhibition was observed. As a possible explanation it was suggested that the difference between the adsorption constant of the inhibiting product and that of the feed is more strongly pronounced in large- than in medium-pore zeolites. This proposal is supported by some further dissimilarities in the catalytic behavior of these zeolites. Thus, both the evaluation of the deficit of the product diethylbenzene compared with the product benzene during the induction period of the reaction, and transient experiments, in which the feed flow rate was suddenly changed, indicate a stronger accumulation of the diethylbenzene in faujasite than in H-ZSM-5. In agreement with these results different reaction networks for the dealkylation of ethylbenzene and diethylbenzene over large- and medium-pore zeolites were observed at higher temperatures. Sorption measurements with pure ethylbenzene and diethylbenzene on H-ZSM-5 and Y-zeolites confirmed the assumption that with decreasing pore-size the product is no longer sorbed more strongly in the zeolite than the feed.