Microwave radiation as a tool for process intensification in exhaust gas treatment

The present work deals with the technology transfer from basic research on the microwave-assisted heterogeneous gas-phase catalysis into pilot plant scale. This enables a direct comparison of the novel microwave-assisted catalysis technology with conventional heating systems by means of ohmic losses. The work is focused on the technology and not on the catalyst material, which represents only one possible alternative. The electromagnetic radiation of 2.45 GHz gives the opportunity to transfer energy highly efficient by volumetric dielectromagnetic heating. This results in higher heating rates and lower energy losses compared to conventionally heated systems or other heating methods. The heat flow density in microwave systems can reach up to 35,000 W m−2 [1]. Operating under those conditions the utilized catalyst has to have a high catalytic activity as well as large dielectric and magnetic loss factors. The highest potential for those properties exhibit materials based on mixed metal oxides such as perovskites and spinels. Selected compounds of these substance classes have been prepared by various synthetic methods and were characterized with respect to their catalytic activity, complex permittivity, and complex permeability [2]. The experimentally determined values built the foundation for calculation and simulation of an optimized reactor and microwave absorber design. The constructed pilot plant includes both heating systems, magnetrons for microwave-assisted and resistance heaters for conventional gas-phase catalysis, and was used for a comparison of the heating methods.