Oxygen Pathways and Carbon Dioxide Utilization in Methane Partial Oxidation in Ambient Temperature Electric Discharges

This methane conversion work studies a plasma reaction system for the production of organic oxygenates. The reactor consists of a glass dielectric interposed between the metal electrodes and a flowing gas stream through which kilovolt ac power with frequencies in the range of 100−200 Hz is applied. The geometry for this amounts to an annular system in which gas flows axially between the electrodes, with one electrode covered by a glass plate. The effect of the glass dielectric is to distribute the microdischarges across the entire electrode area and limit the duration of each microdischarge. The partial oxidation studies in this configuration produce methanol and other oxygenates (formaldehyde, formic acid, methyl formate). Selectivities for these products combined amount to 50−65%. These are the primary products when oxygen is included in the feed to the reactor. Thus far, experiments with low methane conversions have been conducted (up to around 25%) to minimize liquid condensation in the reactor. Byproducts here include significant levels of CO and CO 2, but it has been determined that CO 2 in the feed inhibits further production of CO 2 thereby eliminating net CO 2 production while increasing CO selectivity. These results show that oxygen appears to be needed in order to obtain higher methane conversions and significant oxygenated liquid organic products. CO or CO 2 does not appear to be a substitute for oxygen when trying to generate these desired oxygenated products.