Selective oxidation of CH4 and C2H6 over a mixed oxygen ion and electron conducting perovskite—A TAP and membrane reactors study

In order to identify factors governing selectivity of an oxygen-conducting perovskite BaCoxFeyZrzO3−δ (BCFZ) membrane in the partial oxidation of methane and ethane, mechanistic aspects of product formation in these reactions were investigated with a millisecond time resolution using the temporal analysis of products (TAP) reactor. It was found that the selectivity depends on: (i) reduction degree of the perovskite surface; the higher the reduction degree, the higher the ethane and ethylene selectivity in methane and ethane oxidation, respectively, and (ii) contact time; short contact times favor partial selective oxidation. The influence of contact time on the ethylene selectivity in ethane oxidation at degrees of ethane conversion above 85% was experimentally proven in hollow fiber and disk membranes, which differ in the contact times.The low activity and selectivity in methane oxidation in the BCFZ perovskite membrane reactor were significantly increased, when the membrane on the hydrocarbon side was coated by a Ni-based steam reforming catalyst. This catalyst fulfils a double role: (i) it increases the oxygen transport through the perovskite membrane due to the high oxygen consumption, and (ii) it accelerates syngas production via deep methane oxidation followed by dry and steam reforming of methane. The syngas selectivity increases with an increase in the catalyst reduction degree, which is determined by the ratio of the rate of methane oxidation to the rate of oxygen permeation through the membrane.

By combining steady-state tests with transient mechanistic analysis, the selectivity-determining factors of an oxygen-conducting perovskite BaCoxFeyZrzO3−δ (BCFZ) membrane in the partial oxidation of methane and ethane to syngas and ethylene were determined. They are (i) the reduction degree of the perovskite surface; and (ii) the residence time at the catalyst surface.Figure optionsDownload as PowerPoint slide