Methanol Usage in Toluene Methylation over Pt Modified ZSM-5 Catalyst: Effects of Total Pressure and Carrier Gas

The present study investigates the effects of total pressure and carrier gas on toluene methylation using two modified ZSM-5 based catalysts impregnated with or without platinum. Toluene alkylation with methanol was carried out not only at different reaction pressure under nitrogen or hydrogen but also at different total pressure while the partial pressure of reactants remained constant. The amount of coke formed on the catalysts was less under hydrogen atmosphere. However, the hydrogenation reaction catalyzed by Pt modified catalyst promoted methanol conversion to undesired methane and light hydrocarbons, which in turn decreased the toluene conversion. For both carrier gases, it was found that methanol usage toward undesired byproducts increased with total pressure. Such a trend suggests that a higher total pressure results in a lower toluene and methanol adsorption complexes formation rate in the ZSM-5 pores, and therefore the toluene conversion decreased. The hydrogenation reaction and the higher total pressure simultaneously increased the selectivity of methanol converted to light hydrocarbons and methane, which led to the deteriorated catalytic performance of Pt modified catalysts at elevated reaction pressure.