DUAL-BED STRATEGIES TO IMPROVE HYDROCARBON YIELDS IN THE OXIDATIVE COUPLING OF METHANE

The performances of Li-containing catalysts have been compared in the oxidative coupling of methane (OCM), and Li/Sn/MgO was found to be superior in activity and almost equal to Li2CO3/MgO in selectivity. Using these catalysts, attempts were made to further increase the C-2+ yield of the OCM process. Blank reactor experiments on the oxidation of ethane, and catalytic OCM experiments with SiC in the pose-catalyst volume showed that the role of gas phase reactions in the formation of carbon oxides is typically minimal. However, the use of a presumably 'inert' second bed of SiC, while not increasing selectivities, can increase C-2+ yields. Ga-doped MFI zeolites are known to be good ethane dehydrogenation catalysts. The possibility of OCM using a 5 wt.-% Ga-doped ZSM-5 zeolite (MFI-5) was examined, and it was found that MFI-5 showed some OCM activity. The addition of some oxygen was necessary to convert ethane to aromatics at higher temperatures, An attempt was then made to integrate the OCM and aromatization functions in a single reactor. Intimate mixtures of Li/MgO and MFI-5 gave low activity and selectivity and no aromatization. However, using a Ga/MFI catalyst bed on top of a Li/Sn/MgO catalyst again increased overall C-2+ yields, this time accompanied by aromatics formation. Possible explanations for these phenomena are offered.