Prediction of effectiveness factor using one-dimensional approximations for complex pellet shapes and abnormal kinetics expressions

Abstract

This contribution undertakes the evaluation of one-dimensional (1D) models to approximate the behavior of actual three-dimensional (3D) catalyst pellets, in the case of abnormal kinetics and close to the limit of steady state multiplicity. Two 1D models are tested: a one parameter model, called generalized cylinder (1D-GC) and a three parameter model termed the variable diffusivity (1D-VD) model. A representative set of shapes presented by commercial catalytic pellets was selected to study the performance of the models to predict effective reaction rates. Kinetics expressions covering typical cases of thermal and self-inhibition effects have been considered. Predictions of effectiveness factor using 1D-GC and 1D-VD models are compared with numerical results obtained from the Comsol Multiphysics environment for the 3D pellets. The simpler 1D-GC model can lead to maximum errors exceeding 40%, while the 1D-VD model reduces them to a level of 10%.