(370d) Exploring Strategies to Improve Yields of Oxidative Coupling of Methane in a Chemical Looping System

Direct conversion of methane to value added products such as hydrocarbons has been a grand challenge for many decades. Although there are several strategies and technologies for converting methane, oxidative coupling of methane (OCM) is a promising pathway which is the focus of this study. Under chemical looping mode, methane is oxidized by a metal oxide, instead of molecular oxygen as done in the traditional co-feed OCM to produce higher hydrocarbons as the desired product. The metal oxide thus serves as a catalytic oxygen carrier (COC), which provides lattice oxygen to oxidize hydrogen and oxygen vacancies to serve as active sites for methyl radical formation and desorption. Previously, a detailed energy analysis was performed on the chemical looping OCM process over a proprietary Mg₆MnO₈ based COC, which gave a hydrocarbon yield of 23.2%. The objective of this study is to intuitively develop COCs which can achieve high yields in OCM by modifying the base COC.

This study would focus on using density functional theory (DFT) calculations to screen for different metal oxide dopants which are potential candidates that can increase the OCM hydrocarbon yield. This computational tool will be accompanied by experimental screening to develop an optimal COC configuration. Thermogravimetric analysis (TGA) will investigate the reactivity of these COC’s under methane reduction. TGA would also help in investigating the recyclability of the COC over several redox cycles. These results will be combined with fixed bed tests of the COCs, which would provide gas-composition data as the reduction proceeds. A fourier transform infrared (FTIR) gas analyzer along with a gas chromatography analyzer will be used for this purpose. Changes in the COC will be characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. These results will be fit into a microkinetic model, which would be developed from the experimental and theoretical calculations. Results from this study would provide key insights into the development of such COCs for chemical looping application.