| The reactor design and analysis for reaction systems in which exothermic reactions, multiple reaction paths, intraphase transport resistances and catalyst deactivation are involved, are discussed.;Reactors in which highly exothermic reactions are carried out may sometimes encounter severe temperature runaway, if not carefully operated. For a single irreversible diffusion-free exothermic reaction in gas phase, simple criteria (plug flow model) are developed to determine under what operating conditions adiabatic and nonadiabatic reactors can be used safely. The criteria require minimal computations and assist one in establishing easily the safe range of operating conditions for a given set of kinetic and design parameters. Once the basic equations are derived, it is shown how their applicability can be extended to multiple reactions and reactions affected by intraphase transport resistances and catalyst deactivation. A few design alternatives are also discussed to alleviate the parametric sensitivities in these reactors.;The problem of correlating the catalyst deactivation with the reaction rates is discussed specifically for the case of the epoxidation of ethylene over silver supported on alumina. The intrinsic kinetics of ethylene oxidation reactions are experimentally studied between 421 and 489 K for 1 to 9 mole percent of ethylene in excess oxygen. The catalyst deactivation due to sintering of supported silver crystallites on alumina is also studied using oxygen chemisorption for active metal surface area measurement. It is shown that the selectivity of ethylene oxide can be related to oxygen chemisorption at any temperature for any catalyst no matter how the catalyst is prepared or sintered.;Finally, the analysis of multiple reaction systems is discussed. Generalized methods based on kinetic lumping are presented to synthesize a consistent kinetic structure for reaction mixtures with many irreversible first-order reactions. A simpler numerical scheme is developed for the solution of pellet diffusion equations to obtain the global rates for multiple reactions. |
