One-pot co-crystallization of beta and pentasil nanozeolites for the direct conversion of a heavy reformate fraction into xylenes

Abstract Upgrading of the heavy reformate fraction (HR), containing mainly C 9+ aromatics, is usually performed by dealkylation or by transalkylationwith added benzene and/or toluene to obtain the more valuable xylenes. However, when the costs related to the use of benzene and toluene are considered, the one-step dealkylation/ transalkylationof the C 9+ alkylaromatics to xylenesbecomes economically attractive. Thus, in a first step, ethylmethylbenzenes (EMB) will have to be dealkylated to toluene, which will then react with the trimethylbenzenes(TMB) present in the HR feed to produce xylenesby transalkylation. Medium pore zeolites will favor dealkylation, whereas large pore zeolites will be more adequate for carrying out the transalkylationreaction. In this work, we present the one- pot synthesisof beta-pentasil aggregates with tunable ratios of the large pore beta to the medium pore component. We show that the close proximity of the beta and pentasil nanocrystals obtained by one-pot co-crystallization synthesis, results in a highly efficient catalyst for the consecutive dealkylation/ transalkylationprocess. The bifunctional catalystbased on the co-crystallized aggregate is more active and selective to xylenesthan a catalyst based on a physical mixture of equivalent beta and pentasil nanozeolites synthesized following an analogous procedure. The small crystallite sizes of the co-crystallized zeolites provide the additional advantage of a lower deactivation rate as compared to a reference benchmark catalyst. Results are shown on both, model molecules and industrial HR feed.