Product selectivity control and organic oxygenate pathways from partial oxidation of methane in a silent electric discharge reactor

This study of methane conversion involves the use of a glass dielectric interposed between metal electrodes and applies kilovolt AC voltage and 118-W power with frequencies in the range of 173-264 Hz. The geometry of the system is cylindrical, with gas flowing axially in the annulus between two electrodes. The partial oxidation reactions in this configuration produce methanol, formaldehyde, formic acid, methyl formate, ethane, hydrogen, water, carbon monoxide, and carbon dioxide. The outer electrode is maintained at a low temperature (12 or 15 degreesC), allowing the organic oxygenates to condense on the plate itself inside the reactor. The results show, through residence-time experiments, that methane and oxygen react to form methanol, which further reacts to form formaldehyde, methyl formate, and formic acid. Increasing the gas gap from 4.0 to 12.0 mm decreases the reduced electric field from 30 to 18 V/(cm Torr), which results in a shift in the product distribution from organic oxygenate products to ethane, ethylene, and acetylene. This is because the energy deposition directed toward oxygen dissociation decreases and the energy deposition directed toward methane and oxygen excitations increases. Finally, this work shows that increasing the pressure from 1 to 2 atm with a 1.9-mm gas gap decreases the energy consumption of the system per molecule of methane converted by 35% because the feed concentration doubles, while maintaining 46% selectivity in organic oxygenate products because the reduced electric field strength has a significant fraction of the energy directed toward oxygen dissociation under these conditions.