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

Abstract

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.

A Facile Strategy to Prepare Shaped ZSM-5 Catalysts with Enhanced Para-Xylene Selectivity and Stability for Toluene Methylation: The Effect of In Situ Modification by Attapulgite

“…In order to test its applicability, a Si-P-Mg modified ZSM-5 catalyst (M-ZSM-5) was extruded with attapulgite as binder. According to our previous investigations, the combined modification by Si, P and Mg with a proper sequence can efficiently reduce external surface acid sites and simultaneously narrow the catalyst pore openings, which lead to a higher para-selectivity [9,37,38]. Figure 11 shows the catalytic performance in toluene alkylation with methanol over M-ZSM-5 and the corresponding extrudate catalysts (MZ-atp).…”

“…The resulting extrudates were dried at 120 °C for 12 h and calcined in air at 540 °C for 4 h. The obtained catalysts using attapulgite and boehmite as binders were coded as HZ-atp and HZ-bo. For further investigations, H-ZSM-5 was modified with 6 wt% SiO 2 , 5 wt% P 2 O 5 and 3 wt% MgO according to procedures described in our previous work [9,38], coded M-ZSM-5. The extrudate obtained by the above-mentioned procedure using M-ZSM-5 and attapulgite was coded MZ-atp.…”

Process Design Strategies To Produce p-Xylene via Toluene Methylation: A Review

“…It is suggested that increasing the total pressure decreases the toluene concentrations in the catalyst pores, leading to lower conversion due to reduced methanol usage for toluene methylation. 41 Li et al observed a decreasing trend of toluene conversion and para-selectivity with increasing pressure from atmospheric to 40 bar. 85 Increased methylation reactor pressure was found to suppress the catalyst deactivation (see Table S1 in the Supporting Information), which extends the catalyst life and decreases the catalyst regenerations.…”

Novel Short Process for p-Xylene Production Based on the Selectivity Intensification of Toluene Methylation with Methanol

“…It was speculated that pressurization was not conducive to the desorption of the preferentially generated PX, which would accelerate the isomerization reaction. 31 Therefore, a low reaction pressure was more conducive for improving PX selectivity.…”