Nitrogen dioxide formation in the gliding arc discharge-assisted decomposition of volatile organic compounds

To apply gliding arc discharge (GAD) plasma processing to volatile organic compounds (VOCs) emission control, the formation of NO2 as an undesired byproduct needs to be addressed. Comparative results of effluent temperature and product concentrations between experiment and thermodynamic equilibrium calculation show that the NO2 formation in dry air GAD is totally out of thermodynamic equilibrium. Meanwhile, obvious NO (A2∑+) and N2+ (B2∑u+) are detected as the major reactive species in the dry air GAD plasma region. These results suggest that the thermal (or Zeldovich) NOx formation mechanism is not significant in GAD system, while the energy level and the density of electrons in the plasma region will severely influence the NO2 formation. The presence of 500 ppm VOCs in the feed gases shows a limiting influence on the NO2 formation, which is in the order of aromatic hydrocarbon (C6H6 and C7H8) > straight-chain hydrocarbon (C4H10 and C6H14) > halogenated hydrocarbon (CCl4). The influences of VOCs chemical structure, supply voltage, feed gas humidity, and reactor geometry on NO2 formation are investigated, and the results correspond to above mechanism analysis. Based on the above, the possible pathways of the inhibition of NO2 formation in GAD-assisted VOCs decomposition process are discussed.