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

Kristian Viegaard Raun, Max Thorhauge, Martin Høj, Anker Degn Jensen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

A dynamic model was developed for a single reactor tube, in which methanol oxidation to formaldehyde over an iron molybdate/molybdenum oxide catalyst takes place simultaneously with transport of MoO3 from the catalyst through the reactor. A previously developed dynamic 1D mathematical model for a single ring-shaped cylindrical catalyst pellet, in which volatilization of MoO3 takes place, was implemented in the reactor model. Known axial profiles in a pilot scale reactor with respect to MeOH and H2O concentration and temperature were used as input to the model. MeOH forms volatile Mo-species with solid MoO3 in the catalyst pellets, which diffuses to the bulk gas phase and is transported through the reactor, leading to MoO3 depleted pellets. Volatilization of MoO3 from the pellets occur at the inlet of the reactor. As MeOH is oxidized down the reactor, the volatile Mo-species decomposes via the reverse reaction that formed them. Deposition of MoO3 downstream in the reactor decreases the void space between the catalyst pellets leading to increased pressure drop. The hydraulic diameter of the catalyst pellets and the porosity of the deposited MoO3 were fitted to experimental data obtained in a pilot plant unit containing a single reactor tube. Furthermore, the model was used to simulate a tube under industrial conditions for up to two years (feed composition 8.4% MeOH, 4% H2O, 10% O2 in N2, bed length = 100 cm and a temperature of 190–346 °C). Finally, two cases where catalyst pellets with no excess MoO3 or shaped as filled cylinders are used in the initial 21 cm of the catalyst bed were simulated. The simulations show that this significantly decreases the rate at which the pressure drop increases. This model is a first step towards a useful tool to predict MoO3 transport, pressure drop increase and estimation of process life time at varying reaction conditions.
Original languageEnglish
JournalChemical Engineering Science
Volume202
Pages (from-to)347-356
ISSN0009-2509
DOIs
Publication statusPublished - 2019

Keywords

  • Methanol
  • Formaldehyde
  • Molybdenum oxide
  • Selective oxidation
  • Reactor modeling

Cite this

@article{9e760ce9fe104e6a8a12ad253f30e1f3,
title = "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 = "A dynamic model was developed for a single reactor tube, in which methanol oxidation to formaldehyde over an iron molybdate/molybdenum oxide catalyst takes place simultaneously with transport of MoO3 from the catalyst through the reactor. A previously developed dynamic 1D mathematical model for a single ring-shaped cylindrical catalyst pellet, in which volatilization of MoO3 takes place, was implemented in the reactor model. Known axial profiles in a pilot scale reactor with respect to MeOH and H2O concentration and temperature were used as input to the model. MeOH forms volatile Mo-species with solid MoO3 in the catalyst pellets, which diffuses to the bulk gas phase and is transported through the reactor, leading to MoO3 depleted pellets. Volatilization of MoO3 from the pellets occur at the inlet of the reactor. As MeOH is oxidized down the reactor, the volatile Mo-species decomposes via the reverse reaction that formed them. Deposition of MoO3 downstream in the reactor decreases the void space between the catalyst pellets leading to increased pressure drop. The hydraulic diameter of the catalyst pellets and the porosity of the deposited MoO3 were fitted to experimental data obtained in a pilot plant unit containing a single reactor tube. Furthermore, the model was used to simulate a tube under industrial conditions for up to two years (feed composition 8.4{\%} MeOH, 4{\%} H2O, 10{\%} O2 in N2, bed length = 100 cm and a temperature of 190–346 °C). Finally, two cases where catalyst pellets with no excess MoO3 or shaped as filled cylinders are used in the initial 21 cm of the catalyst bed were simulated. The simulations show that this significantly decreases the rate at which the pressure drop increases. This model is a first step towards a useful tool to predict MoO3 transport, pressure drop increase and estimation of process life time at varying reaction conditions.",
keywords = "Methanol, Formaldehyde, Molybdenum oxide, Selective oxidation, Reactor modeling",
author = "Raun, {Kristian Viegaard} and Max Thorhauge and Martin H{\o}j and Jensen, {Anker Degn}",
year = "2019",
doi = "10.1016/j.ces.2019.03.020",
language = "English",
volume = "202",
pages = "347--356",
journal = "Chemical Engineering Science",
issn = "0009-2509",
publisher = "Pergamon Press",

}

TY - JOUR

T1 - Modeling of molybdenum transport and pressure drop increase in fixed bed reactors used for selective oxidation of methanol to formaldehyde using iron molybdate catalysts

AU - Raun, Kristian Viegaard

AU - Thorhauge, Max

AU - Høj, Martin

AU - Jensen, Anker Degn

PY - 2019

Y1 - 2019

N2 - A dynamic model was developed for a single reactor tube, in which methanol oxidation to formaldehyde over an iron molybdate/molybdenum oxide catalyst takes place simultaneously with transport of MoO3 from the catalyst through the reactor. A previously developed dynamic 1D mathematical model for a single ring-shaped cylindrical catalyst pellet, in which volatilization of MoO3 takes place, was implemented in the reactor model. Known axial profiles in a pilot scale reactor with respect to MeOH and H2O concentration and temperature were used as input to the model. MeOH forms volatile Mo-species with solid MoO3 in the catalyst pellets, which diffuses to the bulk gas phase and is transported through the reactor, leading to MoO3 depleted pellets. Volatilization of MoO3 from the pellets occur at the inlet of the reactor. As MeOH is oxidized down the reactor, the volatile Mo-species decomposes via the reverse reaction that formed them. Deposition of MoO3 downstream in the reactor decreases the void space between the catalyst pellets leading to increased pressure drop. The hydraulic diameter of the catalyst pellets and the porosity of the deposited MoO3 were fitted to experimental data obtained in a pilot plant unit containing a single reactor tube. Furthermore, the model was used to simulate a tube under industrial conditions for up to two years (feed composition 8.4% MeOH, 4% H2O, 10% O2 in N2, bed length = 100 cm and a temperature of 190–346 °C). Finally, two cases where catalyst pellets with no excess MoO3 or shaped as filled cylinders are used in the initial 21 cm of the catalyst bed were simulated. The simulations show that this significantly decreases the rate at which the pressure drop increases. This model is a first step towards a useful tool to predict MoO3 transport, pressure drop increase and estimation of process life time at varying reaction conditions.

AB - A dynamic model was developed for a single reactor tube, in which methanol oxidation to formaldehyde over an iron molybdate/molybdenum oxide catalyst takes place simultaneously with transport of MoO3 from the catalyst through the reactor. A previously developed dynamic 1D mathematical model for a single ring-shaped cylindrical catalyst pellet, in which volatilization of MoO3 takes place, was implemented in the reactor model. Known axial profiles in a pilot scale reactor with respect to MeOH and H2O concentration and temperature were used as input to the model. MeOH forms volatile Mo-species with solid MoO3 in the catalyst pellets, which diffuses to the bulk gas phase and is transported through the reactor, leading to MoO3 depleted pellets. Volatilization of MoO3 from the pellets occur at the inlet of the reactor. As MeOH is oxidized down the reactor, the volatile Mo-species decomposes via the reverse reaction that formed them. Deposition of MoO3 downstream in the reactor decreases the void space between the catalyst pellets leading to increased pressure drop. The hydraulic diameter of the catalyst pellets and the porosity of the deposited MoO3 were fitted to experimental data obtained in a pilot plant unit containing a single reactor tube. Furthermore, the model was used to simulate a tube under industrial conditions for up to two years (feed composition 8.4% MeOH, 4% H2O, 10% O2 in N2, bed length = 100 cm and a temperature of 190–346 °C). Finally, two cases where catalyst pellets with no excess MoO3 or shaped as filled cylinders are used in the initial 21 cm of the catalyst bed were simulated. The simulations show that this significantly decreases the rate at which the pressure drop increases. This model is a first step towards a useful tool to predict MoO3 transport, pressure drop increase and estimation of process life time at varying reaction conditions.

KW - Methanol

KW - Formaldehyde

KW - Molybdenum oxide

KW - Selective oxidation

KW - Reactor modeling

U2 - 10.1016/j.ces.2019.03.020

DO - 10.1016/j.ces.2019.03.020

M3 - Journal article

VL - 202

SP - 347

EP - 356

JO - Chemical Engineering Science

JF - Chemical Engineering Science

SN - 0009-2509

ER -