Non-uniform size of catalyst particles. Impact on the effectiveness factor and the determination of kinetic parameters

Abstract

The analysis of the effectiveness factor in catalytic particles with non-uniform size, was performed. The procedure proposed by Weisz and Prater to determine the intrinsic kinetic constants from experimental results was extended to cases where the catalyst particle size distribution is considered. The approach was applied to the study of reactions with power law and Langmuir-Hinshelwood-Hougen-Watson type kinetics, the catalyst particles being spheres with volume log-normal size distribution (typical in, e.g., fluid catalytic cracking catalysts). If the catalytic effectiveness factor is calculated assuming uniform particle size Rm (Rm being the volume to area mean radius), it will be always higher than the actual effectiveness factor. If the particle size distribution is not taken into account during the assessment of the intrinsic kinetic constants by means of the Weisz and Prater method, the values of those constants will be erroneous. The higher the dispersion in the particles size distribution, the higher the error in ignoring the impact of the different sizes.