Improved Selectivity toward Light Olefins in the Reaction of Toluene with Methanol Over the Modified HZSM‐5 Catalyst

Abstract

Light olefins and para-xylene were produced with high selectivity in the reaction of toluene with methanol over a modified HZSM-5 catalyst. Ordered mesoporous structure and weaker acidic sites led to significant contribution to the selectivity toward para-xylene. By means of a single-pulse reaction and the temperature-programmed surface reaction, it was confirmed that the presence of toluene and as-produced xylene shortened the reaction induction period and reduced the formation temperature of ethylene and propylene, which was beneficial to improve the selectivity toward light olefins, particularly ethylene.para-Xylene (PX) is one of the important organic materials used for the synthesis of pure terephthalic acid, which is used to make polyesters, particularly polyethylene terephathalate. In industrial processes, PX is produced from the aromatics of a naphtha catalytic reformer through complicated crystallization or adsorption separation; this method is very costly to obtain the desired purity of more than 99 %. The selective alkylation of toluene with methanol over the modified HZSM-5 catalyst has been studied extensively for decades. In general, steam treatment, [1] poison treatment of large molecules, [2] modification of Mg, [3,4] B, [5] P, [6] La, [7] Pt, [8] and so forth, and silylation method [9,10] were used to improve porous and acidic properties of the HZSM-5 catalyst to produce PX in concentrations greater than equilibrium concentrations. In addition, methanol reacted partially with toluene to produce alkylbenzenes and the rest was dehydrated to form hydrocarbons by using the methanol-to-hydrocarbon (MTH) process. [11] Some studies focused on improving the alkylation reaction as well as restraining side reactions. Thus, a high toluene/methanol molar feed ratio was often used, which would result in low conversion of toluene. However, light olefins, particularly ethylene and propylene, among hydrocarbons were not useless. They were important chemicals for the production of polyethy-lene and polypropylene, and ethylene was also a major component for the production of polyethylene terephathalate. Therefore, it would be meaningful to improve toluene conversion by using an optimum feed ratio of toluene and methanol, to restrain the formation of undesired aromatics with a designed catalyst, as well as to transform the excess methanol (unreacted with toluene) to important chemicals under the same conditions. Hence, we proposed a new mechanism to produce PX with use of extremely high-purity and high-concentration ethylene and propylene in one chemical reaction through the transformation of toluene and methanol (Scheme 1) over the modified HZSM-5 catalyst. It was also of great significance that the two materials used for the production of polyesters-PX and ethylene-could be obtained in one chemical reaction.The modified HZSM-5 catalyst for this process is expected to function in two transformations: one is the alkylation of toluene with methanol to produce PX with high selectivity and the other is the conversion ...

Direct and selective conversion of methanol to para-xylene over Zn ion doped ZSM-5/silicalite-1 core-shell zeolite catalyst

“…Then, xylenes yield increased by doping Zn, which was in accord with previous works [13,14,20,21] . these results were best on MTpX reaction in previous works [47,48] .…”

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

“…Thus, improving para-selectivity in xylene product, as an effective way to reduce the cost of para-xylene production, is the first priority for catalyst design. Commonly used techniques include impregnation with inorganic agents like boron, phosphorous or magnesium compounds [12,13,14], surface silylation by depositing teraethyl orthosilicate [9,12], tuning the crystal sizes of ZSM-5 [3] and pre-coking of ZSM-5 zeolites [5].…”

Methanol-to-hydrocarbons conversion over MoO3/H-ZSM-5 catalysts prepared via lower temperature calcination: a route to tailor the distribution and evolution of promoter Mo species, and their corresponding catalytic properties

“…The activation of the C-H bond and the resulting hydrocarbon transformation promoted by Mo based catalysts have been investigated previously. [38][39][40][41] A possible explanation is the reduction of the MoO 3 precursor by both H 2 and alkanes, resulting in molybdenum carbide formation which promotes the dissociation of the C-H connection. One study on CH 4 dehydro-aromatization with co-fed H 2 and methanol employed higher temperatures (600 C for calcination, and up to 500 C for reaction), and reported the formation of molybdenum carbide as well as its attendant well-recognized catalytic behavior in promoting the formation of aromatics and methylation on benzene-ring structure.…”