OCM Reactors and Modes of Operation

1) Cofeeding ofCH4 and 02- In this case, CH4 and O2 are mixed together and fed to the reactor where the OCM reaction takes place. 

2) Alternating feeding of CH4 and 02- In this mode of operation, O2 (reoxidation of reduced catalyst) and CH4 (oxidative coupling to ethane by lattice oxygen of oxidized catalyst) are separately fed to the reactor. The possibility to use air instead of pure O2 eliminates the expensive oxygen separation from air. 

3) 02-conducting membrane reactors. O2 and CH4 are also separated from each other, when OCM is performed in membrane reactors. The membranes applied control the oxygen supply via either simple diffusion of gas-phase O2 or via oxygen ionic transport as 0 . The latter option is more preferable because air can be used as oxidizing agent 

Depending on the mode of feeding of methane and oxidant, different catalytic materials are applied. When the OCM reaction is performed with cofed CH4 and O2, nonreducible metal oxides show higher C2 selectivity than reducible metal oxides. Promoting with alkaline earth and alkali metal oxides significantly enhances the selectivity to C2 hydrocarbons of reducible and nonreducible metal oxides [8,10-12]. Very recently, Ivanov et al. [22] demonstrated that MgO and SrO formed under reaction conditions and stabilized on the surface of Mg-, A1-, 

or Pb-substituted perovskite-like SrTiOs and Sr2Ti04 samples performed superior to pure MgO and SrO. The positive role of perovskite was unfortunately not explained. Taking into account such effect of reaction conditions on restructuring of doped perovskites, the effect of promoting of the BaSr-TiOs perovskite with Mg, Li, or Na in a previous study of Fakhroueian et al. [23] can also be explained. Those authors reported the yield of C2 hydrocarbons of 24% over the Na-promoted perovskite. 

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