Direct conversion of methane to methanol over iron-exchanged zeolites

2022-8
Gökçe, İklim
Methane is the primary component of natural gas and the abundance of methane is increased with increased shale gas production. The extracted methane should be converted to more valuable, liquid products on site such as methanol, which is highly versatile and an important feedstock for many chemicals. Unlike the industrial conversion of methane to methanol, which is via an indirect and highly energy intensive route, alternative routes of direct conversion of methane to methanol at milder conditions are searched for. Iron loaded zeolites are promising catalysts for catalytic conversion of methane to methanol under milder conditions and should further be investigated. In this study, iron-exchanged zeolites having different frameworks such as MOR, SSZ-13 and SSZ-39 are investigated for catalytic conversion of methane to methanol. MOR, which is a large pore zeolite showed the highest methanol formation rate and selectivity. On the other hand, small pore zeolites (SSZ-13 and SSZ-39) deactivated quickly due to coke formation and even though mesopore addition improved activity for SSZ-39, Fe-MesoMOR showed better activity than Fe-MesoSSZ-39. The effect of iron content on methanol selectivity is optimized over Fe-MOR. Mesopore addition to MOR significantly promoted the methanol selectivity, especially at lower water vapor in feed, and enhanced catalyst lifetime due to shortened diffusion pathway. At the optimized reaction conditions which are 300 °C, 30% CH4, 10% N2O and 24% H2O, Fe-MesoMOR produced 330 μmol/g/h methanol with 47% selectivity. Increasing the water vapor in feed increased methanol selectivity by suppressing secondary reactions and by promoting methanol desorption from the surface and stabilized the methanol production rate. Fe-MesoMOR is compared at the optimized conditions in this study with the best performed Fe-FER and mostly studied Fe-ZSM-5 in literature. Fe-FER exhibited a better performance than Fe-MesoMOR in terms of methanol production rate and selectivity at all temperatures, 300, 320 and 340 °C. The highest methanol formation rate of 958 μmol/g/h with 41% methanol selectivity is achieved over Fe-MesoMOR at 340 °C. The characterization of active sites is carried out using DR UV–Vis spectra of N2O and CH4 treated Fe-zeolites at 300 °C.

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Citation Formats
İ. Gökçe, “Direct conversion of methane to methanol over iron-exchanged zeolites,” M.S. - Master of Science, Middle East Technical University, 2022.