(743c) Direct Methane Conversion to Ethylene and Ethane By Oxidative Coupling in Packed Bed and Membrane Reactors

The abundance of methane makes it an attractive raw material for chemical production. However, current industrial routes for converting methane to valuable chemicals typically involve a synthesis gas (CO and H₂) production step which is complex and expensive. Direct methane conversion can reduce the need for syngas production and is potentially more suitable for converting methane released from small scale sources, which is typically flared resulting in greenhouse gas emissions. Oxidative coupling of methane (OCM) is a direct route for converting methane into ethylene and ethane (C₂). Ethylene, one of the target products of OCM, is a widely-used feedstock in the petrochemical industry. However, OCM is yet to be commercialized due to the low C₂yields obtained, particularly in conventional packed bed reactors (PBRs).

It has been demonstrated that a reactor with distributed oxygen feed (i.e. an O^2- conducting membrane reactor) can give much higher C₂ selectivity and yield compared to a PBR. However, the relatively few membrane reactors that have been studied in OCM literature give C₂ yields that are still below the commercial viability targets^1,2. The low performance of OCM membrane reactors is partly due to the limited oxygen flux through the membranes and low membrane surface area. Another reason for the low performance of some of these membrane reactors is the absence of a selective OCM catalyst. The integration of such catalyst in the reactor should facilitate methane activation, leading to improvements in C₂ yields. Ideally, the integrated catalyst should be ionically conductive to accept O^2- from the membrane, and compatible with the membrane material at the high temperatures used in fabrication and testing^1,3

In this work, we use PBR experiments to identify O^2- conducting catalysts that are selective for OCM. These catalysts include lanthanum and barium containing perovskite oxides. We test these catalysts in membrane reactors that consist of a dense O^2- conducting membrane and a porous O^2-conducting layer to aid methane activation. We present our results and discuss our efforts to further improve the OCM performance of these membrane systems by increasing the membrane surface area and oxygen flux.

(1) Farrell, B. L.; Igenegbai, V. O.; Linic, S. ACS Catal. 2016, 6, 4340−4346.

(2) Wang, B.; Albarracín-Suazo, S.; Pagán-Torres, Y.; Nikolla, E. Catal. Today 2017, 1–12.

(3) Farrell, B.; Linic, S. Catal. Sci. Technol. 2016, 6, 4370–4376.