Paper PS-FrM2
Atmospheric Plasma for the Degradation of Pollutants : The Promoting Effect of Water

Friday, November 13, 2009, 8:40 am, Room B2

Atmospheric plasmas have been used for a long time for the degradation of volatile organic compounds (VOC). In this study we focus on the degradation of non volatile organic compounds, like hexadecane and hexachloropropene, using an oxygen containing atmospheric plasma.

The kinetics of the reactions was followed by mass spectrometry, by tracking the m/z signal of the production of carbon dioxide.

The pollutants were degraded in a dielectric barrier discharge plasma chamber, operating at frequencies between 10 and 20 kHz, and at voltages between 1 and 4 kV. The plasma gas was either pure oxygen, or a helium/oxygen mixture. The promoting effect of water was studied by adding controlled amounts of water vapour to the gas mixture.

Optical emission spectrometry was used to characterize the plasma gas phase. More specifically, the oxygen emission lines, and the OH bands were followed, as a function of the plasma parameters.

It is shown that the degradation efficiency increases with the charge delivered in the plasma, as well as with the oxygen content.. A correlation is established between the oxygen OES emission line and the carbon dioxide production, for plasmas containing no water. For water containing plasmas, the oxygen line decreases, whereas the carbon dioxide production increases. The decrease of oxygen is interpreted in terms of consumption of the oxygen radical by water molecules to create hydroxyl groups, which are responsible for the increase of the degradation of the organic molecules. A simple global mechanism is proposed.

Acknowledgements : this work is funded by the IAP "physical chemistry of plasma-surface interactions - PSI" program from the Belgian Federal Government