Shape-Selectivity of Large and Small Crystals of Zeolite ZSM-5

Abstract

The authors have shown recently that the isomer distribution in the xylene resulting from the methylation of toluene by methanol on zeolite H-ZSM-5 is independent of conversion as long as reactant methanol is not exhausted, and that it depends inter alia on the size of the unmodified zeolite crystals. The interpretation of the observed isomer distribution as resulting from intracrystalline reaction and shape-selective diffusion led to the conclusion that only that para isomer should be generated on sufficiently large crystals of the unmodified zeolite, whereas with extremely small crystals (in the hypothetical limit consisting of only one unit cell) an isomer distribution should be observed which is not influenced by subsequent diffusion and isomerization of the primary product of alkylation. The authors now report briefly the results of experiments which have been conducted to test these conclusions. 3 refs., 2 figs., 3 tabs.