Dissociation against oxidation kinetics for the conversion of VOCs in non-thermal plasmas of atmospheric gases

Abstract

The kinetics of four volatile organic compounds (VOCs) (propene, propane, acetaldehyde, acetone) were studied in plasmas of atmospheric gases using a photo-triggered discharge (homogeneous plasma) or a dielectric barrier discharge (filamentary plasma). It was shown for the homogeneous plasma that quenchings of nitrogen metastable states, A 3 Ʃ + u and the group of singlets a' 1 Ʃ - u , a 1 Π g and w 1 ∆ u , are important processes for the decomposition of such molecules. Recent measurements of the H 2 concentration produced in the N 2 /C 3 H 6 mixture emphasize that the hydrogen molecule can be an exit route for propene dissociation. It is also found that H 2 and CO molecules are efficiently produced following the dissociation of CH 3 COCH 3 and the subsequent chemical reactivity induced by radicals coming from acetone. Addition of oxygen to a N 2 /VOC mixture can change drastically the kinetics. However, the quenching processes of N 2 metastables by the VOC are always present and compete with oxidation reactions for the conversion of the pollutant. At low temperature, oxidations by O or by OH are not always sufficiently effective to induce an increase of the molecule decomposition when oxygen is added to the mixture. In particular, the presence of O 2 has a detrimental effect on the acetone removal. Also, as evidenced for acetaldehyde and propane, some kinetic analogies appear between filamentary and homogeneous plasmas.