Effects of a Matrix on Formation of Aromatic Compounds by Dehydrocyclization of n-Pentane Using ZnZSM-5-Al2O3Composite Catalysts

Abstract

In this study, the effects of the combination of a mesoporous material and Zn-exchanged ZSM-5 on the activity and selectivity of aromatic compounds in dehydrocyclization of n-pentane were investigated. A total of 65-85 wt % of ZnZSM-5 was mixed with 0-20 wt % of Al2O3 and 15 wt % of the alumina-sol binder using a conventional kneading method. Dehydrocyclization of n-pentane was performed using a fixed-bed reactor under the conditions of a H2 atmosphere and the temperature range of 450-550 °C. Conversions of n-pentane tended to increase upon increasing the amounts of zeolite content and ZnZSM/0A (85 wt % ZnZSM-5, 0 wt % Al2O3, and 15 wt % binder) exhibited the highest value. The selectivity for toluene and benzene increased with increasing temperature, while it decreased in the order ZnZSM/10A > ZnZSM/0A > ZnZSM/20A in comparison at the same temperature. Upon changing the carrier gas, the conversion decreased in the order CH4 > N2. Although the selectivity for aromatics was higher under CH4 and N2 atmospheres, the conversions decreased at 550 °C with time, suggesting that the deactivation would proceed by coke formation. Furthermore, the selectivity for aromatics of ZnZSM/10A was higher than that of ZnZSM/0A, indicating that the use of mesoporous Al2O3 as a matrix would be very effective for this reaction and draw the maximum catalytic functions. When the reaction route was estimated from the amounts of methane and C2 and C3 fractions formed, it was proposed that active Zn species would catalyze the aromatization of olefins where benzene is formed from ethene and butene, toluene from propene and butene, and xylene from 2 molecules of butene.