In situ detection of coke deposits on fixed-bed catalysts by a radio frequency-based method

The aim of this work is to study whether a contactless radio frequency-based method is suitable to monitor both coking and regeneration (coke burn-off) of industrial fixed-bed catalysts directly and in operando. The tubular steel reactor serves as an electromagnetic cavity and two waveguide feeds (coaxial antennas) are used to impress and receive electromagnetic waves between 1 and 20 GHz. Shifts of the resonance frequencies mirror the coke loading in the lowly loaded state and strongly decreasing power transmission over the entire frequency range goes along with increasing coke load at higher coke loadings. Both the locally homogeneously distributed coking process and the coke burn-off process that starts in the reactor front and moves through the reactor can be observed by the radio frequency-based method.