Highly Durable C2 Hydrocarbon Production via the Oxidative Coupling of Methane Using a BaFe0.9Zr0.1O3−δ Mixed Ionic and Electronic Conducting Membrane and La2O3 Catalyst

Abstract

The oxidative coupling of methane (OCM) is an attractive technology for the production of ethane (C2H6) and ethylene (C2H4); and significant performance and efficiency gains as well as reduced carbon dioxide (CO2) emissions are expected when OCM takes place within mixed ionic and electronic conducting (MIEC) ceramic membrane reactors (CMRs). So far, research on OCM in CMRs has been limited to unstable and incompatible materials investigated under short-term measurements that hinder upscaling and commercial application. To this end, this work demonstrates long-term stable OCM performance enabled by a BaFe0.9Zr0.1O3−δ (BFZ91) perovskite utilized as the oxygen-ion MIEC membrane and lanthanum oxide (La2O3) used as the OCM catalyst. Experimental measurements conducted in the temperature (T) range of 750–900 °C and at inlet methane (CH4) mole fractions (XCH4in) of 0–30% revealed a highly stable performance during 23 days of continuous operation, which was further confirmed by material characterization. Under the aforementioned operating conditions, BFZ91 offers a high oxygen (O2) permeation flux (JO2) between 0.5−1.5 (μmol/cm2/s); CH4 conversion (CCH4) reached ∼35% while the selectivities to C2H6 (SC2H6) and C2H4 (SC2H4) were as high as ∼50% and ∼40%, respectively, showing a strong dependency on the operating conditions. Yields of C2H6 (YC2H6) and C2H4 (YC2H4) in the range of 1–5% and 1–7%, respectively, were measured, with more C2H4 being produced at higher T. In the absence of La2O3, CCH4 and C2 (C2H6 and C2H4) yields are lower confirming that BFZ91 does not promote CH4 oxidation, reforming, or coupling on its surface at high rates. The OCM performance of BFZ91 with La2O3 was also found to be stable under partial O2 consumption and pure CH4 conditions. Furthermore, a detailed analysis of the mixture composition allowed the identification of the primary reactions in the OCM chemistry. Our results reveal that within our reactor, CH4 full oxidation to CO2 and steam (H2O) happens simultaneously with CH4 oxidation to C2H6 and H2O (both on the La2O3 catalyst), but the production of the valuable C2H4 is primarily taking place through the C2H6 non-oxidative dehydrogenation in the gas phase; this reaction was not found to proceed on the La2O3 catalyst. Besides the promise of the investigated materials toward commercialization, the methods to study the OCM chemistry and the membrane catalyst coupling presented here are expected to promote further advances in the field of OCM.