Exploring catalytic reactors using computational fluid dynamics: insights and limitations

Catalytic reactors are fundamental to numerous processes in the chemical industry, thus constituting the foundation for a substantial proportion of consumed products. In these reactors, reactants are converted into the desired products, while the reactions that take place are usually exothermic. Although catalytic reactors have been used extensively for over a century, our understanding of the local conditions within these reactors remains limited. However, this knowledge is essential for optimizing the processes as a whole and rendering them more economical and ecological. The field of Computational Fluid Dynamics (CFD) has emerged as a promising tool for simulating the processes in reactors with high resolution, thereby facilitating the acquisition of fundamental knowledge regarding local process conditions. Thus, the central objective of this thesis is to show the potential and the constraints of CFD in the field of reaction engineering. The work is divided into two main parts, which are built upon sequentially and differ in the type of simulations utilized.
In the first part, non-reactive CFD simulations are employed. A particular focus here is on the heat removal from the reactors, as this is an important parameter for efficient reactor operation.
The second part of this thesis focuses on the method of reactive CFD and its comparison with three-dimensional Magnetic Resonance Imaging (MRI) data. The implementation of a simplified reactor design, the integration of a novel MRI temperature measurement technique, and the utilization of ethylene hydrogenation as a model reaction allows for the quantification of three-dimensional concentration and temperature fields within the gas phase of the optically inaccessible reactor. In multi-scale CFD simulations, the reactor, including the surface-catalyzed reactions, is modeled to predict species concentrations, gas temperature, and flow field. The comparison with the MRI data demonstrates the strengths and limitations of reactive CFD, which can only qualitatively depict local conditions with high resolution.