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 int erposed 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 syst em is cylindrical, with gas flowing axially in the annulus between two elec trodes. The partial oxidation reactions in this configuration produce metha nol, formaldehyde, formic acid, methyl formate, ethane, hydrogen, water, ca rbon monoxide, and carbon dioxide. The outer electrode is maintained at a l ow temperature (12 or 15 degreesC), allowing the organic oxygenates to cond ense on the plate itself inside the reactor. The results show, through resi dence-time experiments, that methane and oxygen react to form methanol, whi ch further reacts to form formaldehyde, methyl formate, and formic acid. In creasing the gas gap from 4.0 to 12.0 mm decreases the reduced electric fie ld from 30 to 18 V/(cm Torr), which results in a shift in the product distr ibution 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 exci tations increases. Finally, this work shows that increasing the pressure fr om 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 concentra tion doubles, while maintaining 46% selectivity in organic oxygenate produc ts because the reduced electric field strength has a significant fraction o f the energy directed toward oxygen dissociation under these conditions.