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Research Topics Reaction Engineering

Power To X
Power-to-X Verfahren

The energy production by renewables is fluctuating which gives rise to concepts, such as Power-To-Gas (PTG) or Power-To-Liquid (PTL), which could be used to save excess energy in form of chemicals. The electrical energy is converted to hydrogen via electrolysis. Subsequently, the hydrogen, together with a carbon source, can, for instance, be converted to methane via methanation or to artificial fuels via Fischer-Tropsch synthesis (FTS). 

We use imaging techniques, such as NMR or micro-tomography, as well as computational fluid dynamics (CFD), to investigate the influence of support materials on the reaction and to intensify the process. These results could be equally transferred towards other reaction systems.

Open cell foams, often called sponges, are an ideal choice as monolithic support materials for catalysts. Their high porosity, continuous solid phase, high specific surface area, as well as the possibility for radial dispersion, make them highly suited as support for highly exothermic reactions.

We use computational fluid dynamics (CFD) as well as nuclear magnetic resonance (NMR) to predict and visualize heat and mass transfer as well as velocity, temperature and concentration profiles. The morphology of sponges is usually obtained with micro computer tomography. Our overall aim is to investigate the influence of structural parameters of the sponges on the the transport processes within them and on the efficiency of highly exothermic gas and multiphase reactions.

3d model and pressure loss across a ceramic sponge.
Vorgehen
Methodology from the ceramic sponge sample to the CFD simulation.
NMR Geschwindigkeitsfeld eines Schwammes
NMR velocimetry.

Rarefied gas flows

Many technical applications contain rarefied gas flows. A flow is rarefied when the mean free path of a molecule is in the same order of magnitude as the surrounding. In a pipe, the probability for a molecule to collide with the wall is as likely as for a molecule to collide with another molecule. As an extreme case, the probability for a molecule-molecule interaction approaches zero. The level of rarefication of a gaseous flow (obviously) depends on pressure and temperature, but also on the surrounding. Rarefieid gas dynamics are found in small pores or channels of catalyst carriers, solid oxide fuel cells (SOFCs) or micro chips but also during re-entry problems into the earth atmosphere or at ultra-high vacuum conditions (UHV). Gases under some level of rarefication behave differently from gases under regular conditions; the high level of interaction with the surrounding, e.g., the pore wall, causes the classical continuum equations to lose validity.

The relationship between mean free path and (characteristic) physical dimension is usually known as the (dimensionless) Knudsen number. Systems with large Knudsen number (rarefied gases) occur at very low pressures and macroscopic objects as well as at ambient pressures and very tiny objects. Low pressure examples are satellites in the outer atmosphere or the measurement capsule in the Fallturm. Nevertheless, we can also find high Knudsen numbers in porous gas separation membranes or chromatography columns close to atomspheric pressures. It is thus vital to study gases under this conditions to develop effective materials.