Optimal distribution of silver catalyst in pellets for epoxidation of ethylene

The concept of optimal catalyst distribution was studied for the ethylene epoxidation reaction network on a Ag/;Chapter I. Provides background information for the ethylene epoxidation reaction, and summarizes the strategy used for catalyst performance improvement.;Chapter II. Previous work and current status of knowledge in the area of optimal catalyst distribution in a single pellet is presented.;Chapter III. Experimental design and procedural details are indicated for experiments conducted in the ethylene-lean and ethylene-rich regimes.;Chapter IV. Results from the ethylene-lean regime are described. The influence of location and width of the catalytically active layer on the conversion of ethylene, and on the selectivity and yield to ethylene oxide, as well as on the net reaction rates, is presented. It is established that pellets where the catalyst is located as a thin layer at their external surface in general show the highest selectivity, yield and net reaction rates. Further improvements, by increasing the active layer loading, were also investigated.;Chapter V. Results from the ethylene-rich regime, where there is a limited supply of oxygen are presented. The effect of active layer width on the performance of the catalyst pellets is described, and comparisons between the two regimes are made. The performance of the pellets was qualitatively similar in both regimes. Differences were due to the magnitude of intraphase transfer resistances, which were more significant in the ethylene-lean regime.;Chapter VI. Transport properties of the pellets, namely effective diffusivities and thermal conductivities were experimentally determined. Attempts to obtain the intrinsic reactivity behavior of the catalytic powder are discussed.;Chapter VII. Modeling of the experimental results was performed. The development of a diffusion-reaction model and a computational strategy based on the finite element method are described. Comparison with experimental results in general shows good qualitative agreement. Inadequacies of the model are attributed to the intrinsic kinetic expressions used.;Chapter VIII. The influence of loading on dispersion and silver surface area of the catalytic powder was experimentally established.