Evaluation of Fluidized-Bed Methanation Catalysts and Reactor Modeling

Abstract

The simple reactor model developed for the fluidized-bed methanator PEDU gives reasonably good parity plots for six PEDU tests using six different catalysts. This model can be used to predict the performance of the pilot plant methanator and as a building block in any computerized simulation of the BI-GAS process for process development, design or optimization purposes. Some refinements could be made to the model to accommodate changes in mode of operation and additional knowledge gained concerning the hydrodynamic properties of the catalyst bed. The kinetic model, based upon a first-order rate equation to describe the catalyst behavior in the PEDU, also appears to be satisfactory as to its utilization in the reactor model. Further refinements could be made to yield a more mechanistically accurate expression, which would include the effects of non-first-order kinetics and deactivation on CO conversion and of selectivity on product distribution. The selectivity of molybdenum-containing catalysts for the water-gas shift reaction has been shown to be significantly higher than that of cobalt-containing catalysts. This suggests that catalysts containing molybdenum might be more suitable for processes in which the water-gas shift reaction must be combined with methanation. However, this increase in selectivity appears to be coupled withmore » a reduction in overall activity. Further investigation is neededto determine whether this reduction is real or merely the result of an imbalance between particle size and pore structure of the molybdenum-containing catalyst, which has resulted in mass-transfer limitations in those catalysts tested so far.« less