Effect of eccentricity and interaction between kinetics and mass transfer on the behaviour of catalytic annular reactors: a comparison between lumped and distributed models

A numerical investigation has been carried out on an isothermal annular reactor for kinetic studies under laminar flow conditions. The scope was to investigate the effects of eccentricity in the annular reactor and the adequacy of using lumped models when modelling such cases. 1D-models were compared with the corresponding 3D-models for different values of eccentricities and for different kinetic rate laws. In the case of linear kinetics, the solutions of the lumped models agreed satisfactorily with the solutions of the distributed models for all eccentricity values investigated. However, for non-linear kinetics, especially for LHHW rate expressions, significant differences in conversion between the models were observed during a mixed chemical diffusion-control regime. The differences became progressively larger as the eccentricity was increased. An enhanced 1D-model, with compensation for those non-linear effects, was designed and gave satisfactory agreement with the 3D-models. For conditions when the 1D-model could predict multiple steady states, a higher eccentricity produced a wider temperature range over which multiplicity occurred. This was so even in the cases where the multidimensional models did not predict any multiple steady states. It is not in general possible to rely on evaluating kinetic data from an eccentric annular reactor by using a 1D-model. In order to be sure to obtain accurate data from this type of reactor, an eccentricity of less than 10% is allowed.