Gasification of coal, natural gas, or biomass to produce methanol represents an alternative means of production of fuels and petrochemicals as methanol can be converted into a variety of hydrocarbons through a number of methanol to hydrocarbon (MTH) reactions. First reported in 1977, MTH research has expanded into three main areas: methanol to olefins (MTO), methanol to gasoline (MTG), and methanol to aromatics (MTA). Reaction conditions and catalyst determine the product distribution for methanol conversion. In this investigation, we focus on MTO on zeolites impregnated or ion-exchanged with transition metals, materials that have been shown to catalyze the oligomerization of olefins, in order to produce species heavier than currently possible. Conversion of methanol on acidic zeolites (H-[Al]ZSM-5 and H-[Al]Beta) and zinc-exchanged zeolites (Zn-[Al]ZSM-5 and Zn-[Al]Beta) was investigated. For all catalysts tested, production of hydrocarbons from methanol was not observed until the reaction temperature reached 573 K. All catalysts exhibited an induction period of approximately 1 h, which is consistent with previous reports and associated with the so-called hydrocarbon pool formation in the zeolite pores. Upon reaching maximum conversion, deactivation was observed on all samples. H-[Al]Beta and H-[Al]ZSM-5 exhibited higher consumption rates than Zn-[Al]Beta and Zn-[Al]ZSM-5. The proton form zeolites were also active for longer times than the zinc-exchanged samples. When zinc was exchanged, reaction rates decreased, but there was an increase in selectivity to olefins. For the ZSM-5 catalysts, addition of zinc resulted in a decrease in propene selectivity, but a large increase in ethene selectivity. Although there was an increase in olefin selectivity by exchanging zinc, there was a subsequent increase in aromatic production, with p-xylene being produced for Zn-ZSM-5 and hexamethylbenzene for Zn-Beta. Ion-exchange of Zn(II) on [Al]ZSM-5 and [Al]Beta, increased selectivity to olefins in the methanol to olefins reaction. Although there was an increase in olefin selectivity, there was also an increase in selectivity to aromatics. We are currently investigating the suppression of hydride transfer reactions, which will reduce aromatic formation, and addition of other transition metals to increase the yield of heavier olefins.

Conversion of methanol on zeolites containing transition metals

253rd National Meeting (2017)

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