A rational design of alkyl-aromatics dealkylation–transalkylation catalysts using C8 and C9 alkyl-aromatics as reactants

A catalyst has been designed to optimize the dealkylation of ethyl and propyl aromatics while producing the transalkylation of tri- and tetramethylbenzene with toluene in order to maximize xylenes and benzene when processing heavy reformate. Conversion of model ethyl-aromatics under realistic transalkylation conditions has been studied over two reference catalysts and seven different acid zeolites including topologies with channel systems containing 10 MR, 12 MR, and 10 + 12 MR. Catalytic testing was accomplished by means of a high-throughput reactor system. It has been found that zeolite structure has a direct influence on the ethyl dealkylation/transalkylation activity, increasing the ethylbenzene conversion and dealkylation selectivity when decreasing the zeolite pore volume. Moreover, Re/IM-5 and, specially, Re/ZSM-5 zeolites show an excellent dealkylation activity. Ethylbenzene undergoes different bimolecular reactions giving as primary products either benzene and diethylbenzene or toluene and ethyltoluene, each reaction involving a different biphenylic intermediate and the selectivity toward each mechanism is directly influenced by the zeolite pore size and geometry.