Modeling of molybdenum transport and pressure drop increase in fixed bed reactors used for selective oxidation of methanol to formaldehyde using iron molybdate catalysts

Abstract

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Alkali Earth Metal Molybdates as Catalysts for the Selective Oxidation of Methanol to Formaldehyde—Selectivity, Activity, and Stability

“…From the literature [49,54], it seemed the MoO 3 evaporation from the industrial catalyst pellets (ring shaped cylinders with outer diameter = 4.55 mm, hole diameter = 1.70 mm, and length = 4.00 mm) was a diffusion limited process, as it took much longer time for the excess MoO 3 to disappear from pellets than the sieve fraction used here (150-250 µm), under similar conditions. Additionally, a reactor model indicated that reducing MoO 3 evaporation only for the catalyst layer near the inlet might to a large extent solve the problem of increasing pressure drop [55]. In this study, the CaMoO 4 , MgMoO 4 , and Mo:Mg = 1.1 samples initially showed a smaller relative decrease of the activity than the industrial reference ( Figure 7), and much less MoO 3 per catalyst mass evaporated from them according to Raman spectroscopy.…”

A Review and Experimental Revisit of Alternative Catalysts for Selective Oxidation of Methanol to Formaldehyde

“…The model showed that increasing the pellet volume by 100% with the same dimensional ratios would decrease the volatilization by 20% over 400 h on stream [96]. The single particle model was then implemented into a dynamic model for Mo transport and pressure drop in a single tube fixed bed reactor (FBR) [97]. The FBR was modelled as a series of CSTRs and had fixed axial profiles of temperature and concentrations of MeOH and H 2 O as input from a pilot plant reactor.…”

“…Thus, both strategies could decrease the pressure drop and, thus, increase process lifetime. The model should be further developed as the changes in activity and selectivity and, thus, temperature profile over time and from the catalyst modifications were not included in the model [97].…”

“…Overall, the findings indicate that the most important factors for the deactivation and Mo volatilization include increases with high temperature, high methanol concentration, and low oxygen concentration. From these findings, the most straight forward optimization when using a FeMo catalyst may be to modify operating conditions [43,[87][88][89] and optimizing pellet size and shape [96,97].…”

Effect of particle shape on methanol partial oxidation in a fixed bed using CFD reactor modeling

“…They adjusted the constants in both sets of kinetics to reproduce axial temperature profiles obtained during the first half of the catalyst life, and used the resulting model to predict the temperature profiles during the second half of the catalyst life with good success up to 80% of the catalyst lifetime. Raun et al also investigated molybdenum volatilization and transport using a series of CSTRs model of a single reactor tube, with focus on describing the increase in pressure drop caused by the deposition of MoO 3 into the void space. Model parameters were fitted to experiments from a pilot‐plant reactor, then the model was used to simulate behavior of an industrial reactor.…”