P 08/02


Mass transport in graded monolithic catalysts during gas and multiphase reactions

Ceramic sponges, also known as open-cell foams, combine high permeabilities and large volumetric surface areas with exceptional heat and mass transport properties. This unique combination distinguishes them as promising monolithic catalyst supports in fixed-bed reactors for exothermic processes such as CO2-methanation, Fischer-Tropsch synthesis (FTS), and selective oxidations. In previous projects we demonstrated that the porosity of sponges can be tuned locally to control axial and radial temperature profiles during CO2-methanation and thus increase space-time-yield significantly. In this project we now like to extend the concept of graded sponges to mass transport related reaction problems. In a first step we focus on gaseous mass transport. Therefore, available reactor models will be adapted to a chosen model reaction that suffers from mass transport limitations. A comparison of the calculated concentration profiles to local concentration maps measured in-situ with NMR-based (Nuclear Magnetic Resonance) techniques shall allow assessing the quality of the model predictions and giving insight into the influence of the sponge structure on gas-phase mass transport. In addition, local temperature profiles and integral analysis of the fluid composition from bench-scale experiments will provide further validation. The model can then be used to predict a sponge with graded pore size that will lead to intensified mass transport and hence to improved process performance.

In a second step we like to investigate liquid-phase transport in solid sponges which is highly important for FTS as the developing liquid phase increases gaseous diffusion within the reactor. Again, model predictions will help to estimate the potential of liquid phase control during FTS, and guide the development of tailored sponge structures. Non-invasive imaging techniques such as Micro X-Ray Computer Tomography (µCT) allow to visualize the liquid phase distribution in solid sponges to further understand the influence of specific structure features. In combination, the model predictions and the µCT visualizations will permit to deduce design rules for advanced liquid control during FTS.

Contact: Thöming , (Kirsch) , since 08/2017 Sadeghi