(Invited) Direct Conversion of Methane to Methanol and Other Value Products in SOFC

Abstract

The direct conversion of methane to liquid fuels and chemicals is highly sought, especially at low-scale to more effectively utilize remote natural gas resources. Direct conversion has proven to be a very difficult problem, because methane is highly unreactive, though tends to over-oxidize once activated. Methanol is primarily produced today by the steam reformation of methane at high temperatures and pressures to synthesis gas (carbon monoxide plus hydrogen), followed by catalytic conversion at intermediate temperatures and high pressures. Though highly selective, this technology is not well suited for low production wellheads. The direct conversion of methane to methanol and other liquids would be a game changer, potentially leading to much lower production costs. In our presentation we will be reporting the development of the metal oxide-based electrocatalysts, which provide an oxygen activity needed for the partial oxidation of methane to liquid fuels suitable for applications in intermediate temperature fuel cells. The tests were performed at atmospheric pressure at different CH4 flow rates and different temperatures in the 200-700oC range.The product analysis was performed by online quadrupole mass spectrometer as well as by GC-MS. Methanol is the primary product of methane conversion at temperatures below 400oC. At 600-700oC, ethane, ethylene, propane, propene, n-butane, iso-butane, 2-butyne, and benzene formation was observed. In all tests the formation of carbon oxides was observed as well. Separately, the catalysts were evaluated using diffuse reflectance infrared Fourier Transform Infrared Spectroscopy (DRIFTS), TGA and in operando XRD. The kinetics of oxygen gain appeared to be slower that the oxygen loss. Somewhat longer time was needed to re-oxidize the catalyst. Kinetics are faster and conversion of CH4 was greater at higher temperatures. The post-test analysis was done using SEM and XRD. Figure 1. Methane conversion (right y-axis) and the rates of methanol, CO, and CO2 formation (left y-axis) at 300oC. Figure 2. Relative hydrocarbon distribution at 700oC. Figure 1