Methods for manufacturing olefins from lower alkans by oxidative dehydrogenation

This invention relates, in general, to manufacturing olefins from lower alkanes. As used herein, the term "olefins" means ethylene, propylene, butenes, pentenes, hexenes and higher olefins. The term "lower alkanes" means methane, ethane and/or propane. More particularly, the present invention relates to methods for manufacturing olefins such as ethylene and propylene from methane, ethane, and/or propane by oxidative dehydrogenation at elevated pressure, wherein the olefins are recovered from unconverted methane, ethane, and/or propane and reaction byproducts by using a complexation separation. In one embodiment of the invention, recycle of reaction byproducts is reduced or eliminated by adding an effluent containing unconverted methane, ethane, and/or propane and reaction byproducts to a methane gas transport system, such as a natural gas pipeline. The present invention provides methods for manufacturing olefins such as ethylene and propylene from lower alkanes, that is, methane, ethane and/or propane, by oxidative dehydrogenation at elevated pressure. The olefins are selectively recovered from unconverted lower alkane feed and reaction byproducts by using a complexation separation, such as an absorption separation that uses aqueous silver nitrate as the complexation agent. Catalysts are used that give high selectivity for oxidative dehydrogenation of lower alkanes to olefins at elevated pressure, such as a nonstoichiometric rare earth oxycarbonate catalyst.