Dry Reforming of Methane on Ni in a Fixed-Bed Reactor: Spatial Reactor Profiles and Detailed CFD Simulations

Dry Reforming of Methane on Ni in a Fixed-Bed Reactor: Spatial Reactor Profiles and Detailed CFD Simulations

Gregor D. Wehinger¹, Matthias Kraume¹, Viktor Berg², Katharina Mette³,
Malte Behrens⁴, Robert Schlögl³, Oliver Korup², Raimund Horn²

¹ Chemical and Process Engineering, Technische Universität Berlin, Fraunhoferstr. 33-36, 10587 Berlin, Germany

² Institute of Chemical Reaction Engineering, Hamburg University of Technology, Eißendorfer Str. 38, 21073 Hamburg, Germany

³ Department of Inorganic Chemistry, Fritz Haber Insitute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

⁴ Faculty of Chemistry, Inorganic Chemistry, University of Duisburg-Essen, Universitätsstr. 7, 45141 Essen, Germany

Fixed-bed reactors are the workhorses of industrial catalysis. They are characterized by a complex interplay between physical transport processes and chemical reactions.

Current design of fixed-bed reactors is based on pseudo-homogeneous or heterogeneous reactor models in which the structure of the solid phase is not explicitly accounted for. This approach leads to unsatisfactory results in particular for small tube-to-particle-diameter ratios.

The discrete element method^[1] allows generating a random packing of catalyst particles in a single tube. Industrial multi-tubular reactors contain thousands of tubes, hence this randomly filled tube can be considered representative. For the geometry of the packing, it is possible to simulate the flow field and the transport processes of mass and heat between the bulk fluid and each individual catalyst particle. In this way the usage of lumped transport correlations can be avoided. The catalytic chemistry is implemented by detailed microkinetics.

In the present contribution we demonstrate this simulation approach for dry reforming of methane on nickel. To validate the simulations spatial reactor profiles of species concentrations and temperature were measured in a dedicated reactor^[2]. The nickel catalyst is applied as a washcoat of a Ni, Mg, Al hydrotalcite-like precursor^[3] on α-Al₂O₃ spheres of 1 mm diameter.

The conservation equations of total mass, momentum, energy, and the species balances were solved in 3D assuming laminar flow. The local temperature of the catalyst particles was set to the experimental value and the particles were considered to be isothermal. Further details on the simulation procedure can be found in Ref. ^[1].

For heat transfer only, simulation and experiment are in excellent agreement. If chemistry is included, the experimental species profiles are qualitatively reproduced by the model, but some quantitative deviations occur. This can be due to catalyst deactivation during the measurements or to inaccuracies in the microkinetics. The presented approach gives more insight into catalytic fixed-bed reactors than conventional reactor simulations treating the phases as a continuum.

Fig. 1: Top left: Reactor tube with catalyst packing. Top right: Velocity field in the bed. Bottom: Experimental species and temperature profiles.

^[1] G. D. Wehinger, T. Eppinger, M. Kraume Chem. Eng. Sci. 122 (2015) 197.

^[2] R. Horn, O. Korup, M. Geske, et al., Rev. Sci. Inst. 81 (2010) 064102.

^[3] K. Mette, S. Kühl, H. Düdder, K. Kähler, A. Tarasov, M. Muhler, M. Behrens ChemCatChem 6 (2014) 100.