Abstract
The ZSM-5-catalyzed transalkylation of ethylbenzene, which yields benzene and diethylbenzenes, occurs by acid-catalyzed cleavage of the ethyl group followed by addition of the ethyl group to another ethylbenzene. Xylenes transalkylate much more slowly because methyl groups are more difficult to cleave than ethyl groups due to their decreased carbonium ion stability. When a mixture of xylenes and ethylbenzene reacts, diethylbenzenes are produced preferentially to dimethylethylbenzenes if the ZSM-5 crystallites are in a size range that allows the disubstituted benzenes to diffuse out of the zeolite crystallites much faster than the trisubstituted benzenes. The dimethylethylbenzenes (produced by ethyl group addition to the xylenes) diffuse so slowly from the larger crystallites that the added ethyl group is cleaved and xylene exits, apparently unreacted.
Published Version
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