Non-uniform catalyst distribution in fixed-bed reactors to improve dehydrogenation processes

Abstract

In the design and operation of industrial dehydrogenation reactors, loss of selectivity and catalyst deactivation caused by undesirable by-products are two critical issues. The hypothesis explored in this work has been that it is possible to address these matters by distributing the catalyst non-uniformly in the reactors. However, these constraints are characteristics of large reactors and only observable in that scale, thus testing the proposed hypothesis by experiments in the laboratory would be of limited value. A practical approach is to study the validity of this idea by process simulation. This method allows exploring a varied range of parameters and reveals the qualitative trends when experimenting with large-scale reactors is not feasible. In this study, a comprehensive process simulator is developed for dehydrogenation reactors, allowing the implementation of several catalyst distributions. The simulator includes options for both dissociative and non-dissociative dehydrogenation, with detailed reaction steps, key modes of species mass transfer, and the capability for parametric studies with a wide range of non-uniform patterns that are needed for optimization of catalyst distribution for a specific case. The simulator is also used for exploring other options such as the use of segmented beds with gaps in packing, or the introduction of hydrogen at various locations in the reactor. Results show that it is possible to improve the reactor yield and enhance the catalyst life by using a preferred non-uniform distribution of catalyst. Simulation results also show that the use of hydrogen injection into the segmented catalyst bed is an effective technique for improving the reactor performance and catalyst life, but the injection needs to be at a location inside the reactor and not at the inlet.