The regenerative effect of catalyst fluidization under methanation conditions

Abstract

The regenerative effect of fluidization on catalysts in methanation reactors was shown by in situ measurements of the axial gas phase concentration profiles. The profiles prove strong carbon exchange processes between the catalyst and the gas phase. These exchange processes structure the bed into three zones: carbon deposition, predominantly by CO dissociation, at the inlet; predominant gasification of solid carbon species from the catalyst in the following zone, and predominant carbon deposition by methane dissociation in the upper part of the bed. By analyzing the carbon-balance, locally up to 20% excess carbon was found in the gas phase, mainly in form of methane. The excess methane decomposes again, forming less reactive carbon with a slow rate. Due to an intensive catalyst mixing, the build-up of unreactive carbon can be prevented by regeneration in the middle zone of the reactor. As these processes are influenced by the particle movement, conclusions about regions of up- and down-flow of the catalyst particles can be drawn.