Methanol to dimethyl ether conversion over a ZSM-5 catalyst: Intrinsic kinetic study on an external recycle reactor

Molecular behaviour of methanol and dimethyl ether in H-ZSM-5 catalysts as a function of Si/Al ratio: a quasielastic neutron scattering study

“…We note from previous literature that MTH related processes such as methylation reactions are zero order with respect to methanol when co-fed with olefins 42,43 as with DME when co-fed with olefins 44 or an order of less than 0.5 with respect to methanol suggesting full surface coverage. 45 We therefore aimed to match our loadings with the archived literature for MTH/O kinetics. The samples (ca.…”

“…Several studies into the kinetics of the MTH/O process either do not specify the diffusion coefficients used 24,72 or rely on an effective diffusivity calculated by accounting for Knudsen and bulk diffusion in the zeolite pores. 45 However, QENS measurements such as those carried out in this study provide direct measurements of a self-diffusivity on a given scale which could instead be used in catalytic investigations. The use of Maxwell-Stefan equations as well as continuity equations with accurate self-diffusivity coefficients would allow for a thorough investigation of the effect of diffusion on the kinetics of MTH/O conversion.…”

“…The use of Maxwell-Stefan equations as well as continuity equations with accurate self-diffusivity coefficients would allow for a thorough investigation of the effect of diffusion on the kinetics of MTH/O conversion. Ortega et al 45 studied the conversion of methanol to DME and water in an external recycle reactor using calculated effective values of diffusion coefficients based on Knudsen and bulk diffusion coefficients. In their calculation, a derived diffusion coefficient of 3.71 × 10 −6 m 2 s −1 (taking into account bulk and Knudsen diffusivity) was used in the calculation of criteria for the absence of internal mass transfer limitations given by the Wagner-Weisz-Wheeler modulus 73 at 190°C in the catalyst grain.…”

“…We may consider that our QENS experiments which provide an effective diffusion coefficient of the order of 10 −10 m 2 s −1 (which inherently takes into account both the tortuosity/porosity of the catalyst structure) for methanol at 190°C (upon extrapolated using an activation energy of 0.58 kJ mol −1 for methanol in H-ZSM-5IJ135) listed in Table 1), may perhaps be a more accurate description of molecular mobility in the micropores in the zeolite catalysts. The difference in four orders of magnitude between the diffusion coefficients at the catalyst grain level and the intracrystalline diffusion coefficients may have implications on whether the experiments conducted by Ortega et al 45 were under intrinsic kinetic conditions (i.e. not influenced by mass transport limitations).…”

Heteropolyacid Salt Catalysts for Methanol Conversion to Hydrocarbons and Dimethyl Ether: Effect of Reaction Temperature

“…% methanol). Mass and heat transfer limitations were ruled out by theoretical calculation (see Supplementary Materials) according to the criteria in the references [52][53][54][55][56].…”