Interdependencies Among Ethylene Oxidation and Chlorine Moderation Catalytic Cycles Over Promoted Ag/α-Al<sub>2</sub>O<sub>3</sub> Catalysts
K. R. Krishna Iyer, Aditya Bhan
Abstract
Ethylene epoxidation transpires with high ethylene oxide (EO) selectivity (∼90%) over promoted Ag/α-Al2O3 catalysts via the concurrent propagation of ethylene oxidation, chlorine deposition and removal, and EO degradation catalytic cycles with reactant and product species (C2H4, O2, CO2) involved in multiple reaction pathways. We resolve the interdependent kinetics of ethylene oxidation and chlorine deposition and removal catalytic cycles by measuring EO synthesis rates at constant chlorine coverages. The systematic variation in ethylene and oxygen reaction orders for ethylene epoxidation with chlorine coverage illustrates how organochloride promoters impact the kinetics of EO synthesis. EO degradation kinetics measured over promoted α-Al2O3 materials are not influenced by the chlorine promoter; however, EO degradation rates over α-Al2O3 can be as high as 3% of total EO formation rates and can contribute perceptibly to lowering net EO selectivity. We develop a reactor model that incorporates the kinetic interdependencies among the three catalytic sequences in terms of discernible changes in reaction orders for EO formation, chlorine coverage, and EO degradation rates across a packed bed and such a description, in turn, enables accurate predictions of the EO rate and selectivity over a wide range of process conditions.