Effect of Acidity and Crystal Morphology of ZSM‐5 in Toluene Alkylation with Methyl Mercaptan

Abstract Four H‐ZSM‐5 zeolites with Si/Al ratios of 15, 25, 40, and 75 and with a number of the acid sites of 0.79, 0.65, 0.43, and 0.29 mmol NH3 g cat −1 , respectively, were evaluated in the toluene alkylation by methyl mercaptan. Due to their 3D porous structure and their medium‐sized pores, ZSM‐5 zeolites were very active and stable against deactivation in this catalytic process. This study shows that the behavior of each catalyst strongly depends on its acidity and crystal morphology, as well as on the reaction parameters. The activity increases with the increase of the concentration of acid sites in the catalysts until 0.43 mmol NH3 g cat −1 , and remains almost constant at this maximum (∼25%) for the catalysts with higher acidity. When the temperature increased from 375 to 475 °C, the reactant conversions increased, but the catalyst deactivation increased significantly. The selectivity in para ‐xylene was favored by the lower temperature and contact time, but particularly by the morphology of ZSM‐5 particles formed by a stacking of thin plate‐like shaped crystallites, most probably maximizing pore openings through sinusoidal channels, in which para ‐xylene can freely diffuse, but not meta ‐ and ortho ‐xylenes.