Methylbenzene Chemistry on Zeolite HBeta:  Multiple Insights into Methanol-to-Olefin Catalysis

Abstract

The reactions of 1,2,4-trimethylbenzene, 1,2,4,5-tetramethylbenzene (durene), pentamethylbenzene, hexamethylbenzene (HMB), ethylbenzene, and cumene were studied on large-pore zeolite HBeta catalysts, either alone or with co-injection of methanol-13 C. The reactivity of the methylbenzenes alone increased with increasing methyl substitution, as did selectivity for propene over ethylene. Disproportionation occurred for all methylbenzenes studied; in the case of HMB, pentamethylbenzene was a major volatile product, and we inferred that the heptamethylbenzenium cation also formed and remained in the catalyst. Substantially higher yields of olefins were obtained when methylbenzenes were co-reacted with methanol-13 C. Ethylbenzene alone was unreactive at 350 °C, but when injected with five equivalents of methanol-13 C, ethylbenzene formed ethylene-12 C 2 with very high selectivity. These and other experiments led to a detailed description of the hydrocarbon pool mechanism for MTO chemistry with side-chain methylation as the predominant route to olefins and the paring reaction as a possible minor pathway.

Effect of magnesium modification over H-ZSM-5 in methanol to propylene reaction

“…From the data ranged from 2005 to 2013, the apparent consumption of raw petroleum increased year by year, the world's industrial production depended heavily on fossil fuels for energy, such as coal, petroleum and natural gas. Due to the increasing price of crude oil and the demand for light olefins, as well as the larger demand for propylene than ethylene, a growing number of researchers were dedicating to developing the non-oil route for producing low carbon olefins, in especial, propylene [1][2][3][4][5][6][7][8]. The development of methanol-to-olefins (MTO) process can effectively reduce the dependence on oil resources in the propylene industrial [1,4,5].…”

“…In recent years, synthetic erionite, offretite, mordenite, SAPO-34 and ZSM-n were applied in MTO process [3][4][5][6][7]. On the basis of previous research findings in the past few years, SAPO-34 and ZSM-5 zeolites standed out from zeolite molecular sieves and non-zeolite molecular sieves [4,[6][7][8][9].…”

Methylation of benzene by methanol: Single-site kinetics over H-ZSM-5 and H-beta zeolite catalysts

“…The large-pore structure allows direct feeding of even larger species than in H-ZSM-5, making H-beta an ideal candidate for the study of mechanistic aspects, the activity of larger hydrocarbon pool species and the formation of coke precursors [14,[23][24][25]. However, because of its largepore structure, MTH-conversion in H-beta results in a product stream consisting predominantly of larger components such as hexamethylbenzene.…”

A Complete Catalytic Cycle for Supramolecular Methanol‐to‐Olefins Conversion by Linking Theory with Experiment

“…[1] Instead of plainly following direct routes, [2][3][4][5] the MTO process has been found to proceed through a hydrocarbon pool mechanism, in which organic reaction centers act as co-catalysts inside the zeolite pores, adding a whole new level of complexity to this issue. [6][7][8][9] Therefore, a detailed understanding of the elementary reaction steps can best be obtained with the complementary assistance of theoretical modeling. Several experimental observables add to the theoreticians challenge: any full catalytic cycle should not only provide low-energy pathways towards olefin formation, but it should also explain the zeolite-specific product distribution.…”