Regenerative Behaviors of Cokes-Deposited Ferrierite Zeolite during Gas-Phase Fluidized-Bed DME Carbonylation Reaction

Gas-phase dimethyl ether (DME) carbonylation to methyl acetate (MA) is prone to be deactivated by coke depositions on Brønsted acid sites (Si-OH-Al groups) of ferrierite zeolite, and those inevitable coke depositions on the active sites, especially in eight-membered ring (8-MR) channels, are required to be regenerated through in situ removal of coke precursors in a circular fluidized-bed reactor (FBR) for its stable operation. The bench-scale FBR system was applied to verify optimal regenerative treatment conditions and to study behaviors of spray-dried FER zeolites ∼60 μm in size after regeneration. Those inactive coke precursors were effectively removed with small structural disintegrations of the FER zeolite under an air environment at 500 °C at a slow ramping rate of 1 °C/min among the tested range of 1–25 °C/min. Although the high regeneration temperature (∼500 °C) compared to the lower regeneration temperature of 300–400 °C caused slight decreases of Si-OH-Al sites assigned to Brønsted acid sites, the catalytic activity was almost recovered at those optimal regeneration conditions with an almost complete removal of coke precursors. The stable maintenance of active sites and original sphere shapes was clearly observed during 5 successive cycles of gas-phase DME carbonylation reaction at 240 °C and regenerative treatment at ∼500 °C at a fixed pressure of 5.0 MPa, which were attributed to the appropriate removal of surface coke precursors in the 8-MR channels without any significant structural disintegration.