Detailed Modeling of Transport-Kinetics Interactions of Ethylene Epoxidation at High Vacuum and Atmospheric Pressures

The activation of silver powder for ethylene epoxidation is investigated at vacuum and atmospheric pressure using transient response techniques based on a modified version of the TAP (Temporal Analysis of Products) reactor system. Comparisons between transient responses based on temperature programmed surface reaction and step response experiments at atmospheric pressure to those obtained at high vacuum using alternating pulses of oxygen and ethylene-d4 suggest that the activation process for silver powder is qualitatively the same in both pressure regimes. A detailed model that describes the incorporation of oxygen into the surface and subsurface sites is developed to interpret the TAP reactor data under high vacuum. Kinetic rate and transport parameters are obtained by matching the experimental and model predicted oxygen breakthrough transient responses. The results indicate that the activation process involves a concurrent filling of surface and subsurface sites, but that the latter sites are filled at a much slower rate.