MeOH to DME in bubbling fluidized bed: Experimental and modelling

Methanol dehydration over a ZSM‐5 containing catalyst was studied in a fluidized bed reactor. At temperatures ranging from 250 to 325°C, methanol conversion varied from 30% at a contact times of 0.14 s and approached 100% of the equilibrium conversion at a contact time starting from 10 s. Sequential and parallel reactions were negligible at low temperatures while hydrocarbon formation became appreciable at 325°C. Online gas analysis by mass spectrometry provided real‐time measurements at a frequency of 4.4 Hz that allowed for fast determination of steady‐state conditions. Gas phase residence time distribution (RTD) measurements indicated that axial dispersion was essentially negligible at short contact times with a shallow bed of catalyst. With longer residence times, the flow pattern could be approximated by six continuously stirred‐tank reactors (CSTR) in series. Both the simple 1D hydrodynamic model and a detailed multi‐zone fluidized model were used to interpret the experimental data to derive a kinetic expression for the dehydration of methanol to di‐methyl ether (DME). The expression includes the reverse reaction that is most often neglected in the literature. The reaction data were best fit with the kinetics based on the 1D model. The fluidized bed is a viable reactor type for kinetic measurements of highly exothermic reactions where hotspots and radial and axial temperature gradients are problematic in fixed beds.