(207b) Tuning Selectivity of Dimethyl Ether-to-Hydrocarbons On H-MFI by Changing the Composition of the Hydrocarbon Pool

The dehydrative conversion of methanol-to-hydrocarbons over acidic zeolite catalysts has been extensively studied, showing that different classes of hydrocarbons, such as olefins of gasoline-range hydrocarbons, can be formed as a result of the shape selective nature of zeolites. Recent studies have shown that the conversion of methanol/dimethyl ether (DME) proceeds through a dual hydrocarbon pool mechanism, where light olefins are produced from polymethyl benzene intermediates and can subsequently enter another cycle in which subsequent methylation reactions produce larger olefins and alkanes. In this work, DME was reacted over H-MFI at 548 K, using propene and toluene as co-feeds to determine the effect of the hydrocarbon pool composition on product selectivities. Species entrained within the zeolite during reaction were also examined by dissolving the spent catalyst in HF, followed by organic extraction with dichloromethane. The organic extract was analyzed using GC-MS. When 65 kPa DME was co-fed with 4 kPa propene, C4 hydrocarbons, resulting from propene methylation, were the most abundant products. Under these conditions, the species entrained within the zeolite were predominantly penta- and hexamethyl benzenes. In contrast, when 4 kPa toluene was co-fed with DME, ethene, propene, and arenes were the major products. These conditions resulted in a greater concentration of tri- and tetramethyl benzenes entrained within the zeolite. Co-feeding 65 kPa DME with 2 kPa propene and 2 kPa toluene resulted in a product distribution in between the two single co-feed cases. These results show that product selectivity of DME reactions over H-MFI can be tuned by varying the composition of the hydrocarbon pool, and thus controlling the extent of olefin and arene methylation. The effects of varying the arene:olefin ratio as well as the effect of varying the identity of the arene and olefin components of the hydrocarbon pool will also be discussed.