Sorption kinetics study of the diethylbenzene isomers in MFI-type zeolites

The uptake rates of the three diethylbenzene isomers in MFI-type zeolites were studied with a sorption kinetics apparatus of the barometric type. It was observed that the uptake rates depend crucially on the position of the substituted ethyl groups. While p-diethylbenzene was adsorbed with uptake rates of the same order of magnitude as benzene and the monosubstituted benzenes, diffusion of m-diethylbenzene was approximately four orders of magnitude slower. No sorption uptake was observed for o-diethylbenzene. In the experiments with H-ZSM-5, sorption kinetics were partly determined by a secondary process additional to Fickian diffusion. Comparison to the results obtained with silicalite-1 and earlier results proved that the secondary process is correlated with the existence of acidic sites inside the zeolite and can be tentatively ascribed to an isomerization reaction.