Non-ideal characteristics in a micro packed-bed reactor: A coupled reaction-transport CFD analysis for propane dehydrogenation

Abstract

Kinetic experiments can be significantly influenced by fluidic effects and transport limitations within reactors, particularly for strongly exo- and endo-thermic reactions. This paper describes the influence non-uniform physical fields, e.g. temperature, velcocity and species concentration, on the determination of kinetic parameters for endothermic systems with propane dehydrogenation (PDH) as a model process, which was analyzed using computational fluid dynamics (CFD) method based on the porous media model. Propane conversions calculated from 3-D porous media model at various conditions have discrepancies from the reported experimental data and 1-D numerical regression. This is due to the application of kinetic parameters obtained from 1-D plug flow assumption to the 3-D model with inhomogeneous temperature distributions. In the kinetic analysis, it is found that the low space velocity may lead to backward diffusion but can be a preference to minimize the temperature gradients within the catalyst bed. On the other hand, the commonly used higher space velocity may enlarge the temperature inhomogeneity. The sensitivity of temperature distribution with various reaction conditions is further analyzed. In addition, with respect to the packed bed properties, a high thermal conductivity and low loading of catalysts can reduce the non-uniformity of temperature distribution. Therefore, it is proposed that a mixed packing scheme with lower catalyst concentration and higher thermal conductivity could effectively suppress temperature gradients in kinetic analysis. This study exemplifies the necessity to consider the non-ideal distribution of physical fields for the kinetic study of reactions with strong thermal effects.