Shape Selectivity in the Conversion of Methanol to Hydrocarbons: The Catalytic Performance of One-Dimensional 10-Ring Zeolites: ZSM-22, ZSM-23, ZSM-48, and EU-1

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Abstract

The methanol-to-hydrocarbon (MTH) reaction, a process in which low-value carbon-rich feedstocks are converted to value-added petrochemical products, is studied over one-dimensional 10-ring zeolites: ZSM-22 (TON), ZSM-23 (MTT), ZSM-48 (*MRE), and EU-1 (EUO). The latter three are little studied as MTH catalysts and were expected to display interesting product-shape-selective properties. The influence of slight differences in channel systems of the materials (size and shape) on product distribution and stability is investigated under various reaction conditions. In addition, the influence of coke deposition on product selectivity is investigated. Temperatures between 350 and 500 °C and WHSV between 2 and 6 g g–1 h–1 are investigated using a fixed bed reactor. The products are analyzed using online GC, and hydrocarbons trapped in the channels of the material during the reaction were liberated using the standard HF dissolution procedure and analyzed using GC/MS. Despite the small differences in the channel shape and dimension, the materials displayed very different product spectra. The catalysts converted comparable amounts of methanol before complete deactivation at their optimum MTH condition. Except for EU-1, all the catalysts gave high selectivity for hydrocarbons in the boiling range of gasoline fuel, C5+ fraction. Unlike ZSM-22 and ZSM-23, the EU-1 and ZSM-48 catalysts displayed notable amounts of aromatics in their C5+ fraction. Such compounds are good octane boosters. However, because of environmental problems, there are limits on aromatics in gasoline. For ZSM-22, ZSM-23, and EU-1 catalysts, the deposition of coke within the channels does not affect the selectivity. Rather, the change in selectivity with reaction time can be regarded as a change in contact time. The involvement of the 12-ring side pocket of EU-1 zeolites for the MTH reaction is indicated both by the unexpected catalytic behavior and by analysis of retained species within the pore structure.

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