Homogeneous and heterogeneous steps in catalytic methane oxidation.

摘要

One of the most important problems facing reaction engineering today concerns understanding catalytic oxidation reactors. To understand these complex processes, it is necessary to determine the contributions to the processes of homogeneous and heterogeneous chemistry. This research is useful because partial oxidation reactions may, in the future, replace industrial processes such as steam reforming and ethane pyrolysis. In this work, both theoretical and experimental research has been performed to extend our comprehension of catalytic methane oxidation chemistry and to further evaluate this chemistry as a viable alternative to current technology.;In this work, understanding catalytic oxidation reactions involves three major components: reactor seeding simulations, homogeneous-heterogeneous modeling of the partial oxidation of methane over rhodium, and the experimental determination of hydroxyl radical concentrations in gauze boundary layers. For the seeding study, we simulate the conversion of methane to synthesis gas at short contact times in a plug flow reactor (PFR) using standard chemical mechanisms for gas-phase methane oxidation. Fuel/oxygen mixtures are seeded with certain radicals and active compounds, and the effect of these seeds on ignition delay time and selectivity were examined.;Modeling both the gas-phase and surface chemistry and observing how the transfer of O·, H·, and OH· radicals between the two mechanisms affected the overall propagation of methane partial oxidation was another approach to understanding homogeneous and heterogeneous steps. The effect of radical transfer was investigated over a range of reactor dimensions, inlet temperatures, and pressures.;Finally, we employed laser-induced fluorescence spectroscopy to examine methane oxidation in air over Pt, Pt-10% Rh, and Ni gauzes. OR concentrations in the boundary layers downstream of the gauzes were measured, and the effect of the different materials on homogeneous reaction in the gauze wakes was analyzed.;The results of these theoretical models and experiments have been useful in delineating and understanding the catalytic oxidation of methane. These results will lead to the development of detailed models accounting for the coupling of heterogeneous and homogeneous chemistry in catalytic oxidation reactors. The models will assist in optimizing and scaling-up of reactors and may new reveal applications for catalytic oxidation at short contact times.