Further evidence for the oxidative methylation of benzene with methane over zeolite catalysts

Abstract

We have previously shown in our previous investigations that the presence of oxygen is required for the benzene methylation with methane over zeolite catalysts in a high pressure batch reactor. Thus, a two-step mechanism involving the formation of methanol intermediate by methane partial oxidation followed by benzene methylation with methanol in the second step was postulated. This paper now presents the results of further investigation that provide more evidence that the catalytic benzene methylation with methane does occur and that the reaction is limited by the amount of oxygen. Further support is therefore given to the two-step oxidative reaction mechanism. Suggestions for further work in this area are also given.

Recent Advances in Catalytic/Biocatalytic Conversion of Greenhouse Methane and Carbon Dioxide to Methanol and Other Oxygenates

“…This observation is similar to earlier observation that the presence of small amounts of hydrocarbon additives (especially ethane) lowered the initiation temperatures of partial oxidation of methane to methanol and increased the methanol selectivity and yield (Gesser et al, 1985;Fujimoto, 1994). This observation therefore extends the significance of the oxidative methylation reaction and we had earlier suggested that this avenue could be explored further for optimisation of the conversion of methane to methanol (Adebajo et al, 2004).…”

“…The chapter also presents a discussion of the progress that has been made on the development of chemical systems like MMO that are capable of oxidizing methane at ambient conditions. One interesting observation in our previous work on catalytic oxidative methylation of aromatics with methane that is directly relevant to the conversion of methane to methanol is that it is possible to inhibit the complete oxidation of www.intechopen.com methane to carbon dioxide in the presence of an additive (Adebajo et al, 2000;Adebajo et al, 2004). This chapter also provides a brief summary of such oxidative methylation reaction and its significance to methanol conversion.…”

“…It appears that the methanol intermediate is formed homogeneously in the gas phase since it was only formed as the major product in the absence of solid catalyst. When zeolite catalysts were introduced into the reactor, the methanol was not detected but was used to methylate the aromatics reactants to produce methylated aromatic products or converted directly to aromatics in the absence of aromatic reactants (Adebajo et al, 2000;Adebajo et al, 2004). Gas phase analysis of reaction products failed to detect any CO 2 , CO, H 2 , or C 2+ non-aromatic hydrocarbon products (Adebajo, 1999;Adebajo et al, 2004).…”

“…Recent investigations in our laboratory have demonstrated the formation of methanol intermediate in the oxidative methylation of aromatics in the presence of large excess of methane in a high pressure batch reactor at 400 °C (Adebajo et al, 2000;Adebajo et al, 2004). It appears that the methanol intermediate is formed homogeneously in the gas phase since it was only formed as the major product in the absence of solid catalyst.…”

“…When zeolite catalysts were introduced into the reactor, the methanol was not detected but was used to methylate the aromatics reactants to produce methylated aromatic products or converted directly to aromatics in the absence of aromatic reactants (Adebajo et al, 2000;Adebajo et al, 2004). Gas phase analysis of reaction products failed to detect any CO 2 , CO, H 2 , or C 2+ non-aromatic hydrocarbon products (Adebajo, 1999;Adebajo et al, 2004). Thus, there appears to be no significant complete or incomplete combustion of methane due to failure to detect any CO or CO 2 deep oxidation products in the gas products.…”