Kinetic modeling of deactivation profiles in the methanol-to-hydrocarbons (MTH) reaction: A combined autocatalytic–hydrocarbon pool approach

• Deactivation of the zeolite-catalyzed methanol-to-hydrocarbons reaction was modeled.
• An autocatalytic model considers deactivation as loss of active sites with time.
• A model based on the dual-cycle mechanism describes deactivation as coking.
• The dual-cycle model is able to reproduce experimental deactivation profiles.
• Procedures for reliable comparisons of catalyst deactivation are discussed.

Catalyst deactivation in the methanol-to-hydrocarbons (MTH) reaction was modeled using two approaches and compared with experimental data obtained over ZSM-5 and ZSM-22. In the first approach, the methanol conversion with time on stream was calculated using an autocatalytic reaction model, with the assumption that deactivation is proportional to methanol conversion. The model predicts a linear dependence of the catalyst lifetime to 50% conversion on the contact time, with a slope that characterizes the deactivation behavior. In the second model, a dual-cycle reaction mechanism was constructed, with the assumption that only reaction between methanol and aromatic species leads to coke formation. The active sites on the catalyst are gradually covered with autocatalytic species, and subsequently with coke, leading first to an induction period and later to deactivation; thereby, offering an explanation to how deactivation rates close to zero may be obtained at less than 100% initial conversion.

Modeled coke profile versus reactor coordinate and time on stream during the methanol-to-hydrocarbons reaction over a zeolite catalyst.Figure optionsDownload high-quality image (95 K)Download as PowerPoint slide