Co-conversion of methanol and light alkenes over acidic zeolite catalyst H-ZSM-22: Simulated recycle of non-gasoline range products

• The ZSM-22 catalyst converts methanol into non-aromatic gasoline.
• Recycle of light alkenes to increase gasoline yields appears feasible.
• The recycle is incorporated into the regular products at high conversion.
• Recycle leads to longer catalyst lifetimes and increased methanol conversion.
• Accumulation of inert ethene might be an issue.

The zeolite-catalyzed methanol to gasoline process is one way of making synthetic transportation fuel from readily available carbon sources. In addition to the targeted chemicals, this process produces notable amounts of byproduct hydrocarbons (C2–C4). Here, we investigate the co-conversion of methanol and light alkenes (C2–C4) with aim of elucidating the effects of byproduct recycle over the ZSM-22 catalyst. ZSM-22 is a unidirectional 10-ring zeolite, which yields a C5+ product with virtually no aromatics. The addition of alkenes as co-reactants significantly improves the lifetime of ZSM-22 catalyst, and net conversion of the co-added alkenes is observed. At high methanol conversion or low partial pressure of co-reactant alkene, the product distribution is virtually unaffected compared to that found for the neat MTH reaction. However, ethene accumulation might require attention during actual process design. Using isotope-labeling experiments involving 12C-alkene and 13C-methanol, a clear tendency for methylation of the co-reactant alkene with methanol is observed with progressive deactivation of the catalyst. This investigation presents byproduct recycle as a potential route for utilization of light hydrocarbons during the MTH process over ZSM-22.

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