A new catalytic process for high‐efficiency synthesis of p‐xylene by methylation of toluene with CH₃Br

Abstract

A new catalytic process for p-xylene synthesis from the methylation of toluene with CH 3 Br was proposed. CH 3 Br was prepared from the catalytic bromination of natural gas (CH 4 ), by using H 2 O HBr O 2 as mediator over supported Rh catalyst. The methylation conditions were investigated using HZSM-5 or modified HZSM-5 catalyst. Under optimal reaction conditions, p-xylene selectivity is up to 93%, and p-xylene yield is more than 21% at 673 k over the SiP modified HZSM-5 catalyst. Compared to the processes using MeOH or dimethyl carbonate (DMC) as methylation agent, this new process is very attractive in an economic standpoint since CH 4 is much cheaper than MeOH and DMC. In addition, the process has other advantages, such as mild reaction conditions, simple operation, high-product yield, and so on. It is predicted that the process has good industrial potential for para-xylene production.Reaction conditions: T ¼ 673 K, WHSV toluene ¼ 1.5 h À1 , n(CH 3 Br):n(toluene) ¼ 2:1, the oxide content is 5 wt %, N 2 flow 10 mL/min.

Synthesis of HZSM-5@silicalite-1 core–shell composite and its catalytic application in the generation of p-xylene by methylation of toluene with methyl bromide

“…We dissolved the used catalysts with hydrouoric acid and extracted the organic compounds with carbon tetrachloride. Based on GC-MS analysis result (the deposited carbon species are mainly polyalkylbenzene and naphthalene) and our previous studies, 8,21 we deduce that CH 3 Br is rst activated on the acid sites, yielding intermediates such as CH 3 + and CH 2 , followed by methylation, oligomerization, and coking reactions. Since polyalkylbenzene and naphthalene are relatively big in size, it is hard for them to escape once they are formed inside the channels.…”

“…The procedure was described elsewhere. 8 Field emission scanning electron microscopy (FE-SEM) studies were performed on a Hitachi S-4800 emission-scanning microscope with a Schottky Emitter at an accelerating voltage of 5 kV and a beam current of 1 mA. Transmission electron microscopy (TEM) images were taken using a JEM-3010F transmission electron microscope at an accelerating voltage of 200 kV.…”

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

“…Theoretical cluster-based calculations were used to study the methylation of halomethanes (iodomethane, bromomethane, and chloromethane) with ethene, propene, and toluene, indicating only small reactivity differences among the three halomethanes, with reactivity in the order of iodomethane > bromomethane > chloromethane. 19 Ouyang et al 95 screened several modified HZSM-5 catalysts for toluene methylation with methyl bromide and reported Si−P/HZSM-5 to be the promising catalyst with regard to activity and pxylene yields up to 21%. The catalyst was observed to deactivate over a period of time, because of the CH 3 Br oligomerization and coke formation.…”

Efficient synthesis of p-chlorobenzaldehyde through liquid-phase oxidation of p-chlorotoluene using manganese-containing ZSM-5 as catalyst

“…9,10 There are reports on the selective adsorption of benzene and p-substituted benzenes over that of o-and m-substituted aromatic products on nano-sized ZSM-5 catalysts. [11][12][13] As reported, ZSM-5 zeolites modied with manganese show attractive properties and reactivity. [14][15][16][17][18] Excellent catalytic performance is ascribed to the well-isolated Mn species in the zeolite framework or those anchored on the surface.…”