The problem of air cleaning from volatile organic compounds (VOC) can be solved in many cases with the use of plasma-assisted chemical decomposition method. In this paper, we present results of experiments with a recently developed barrier-discharge reactor with coaxial electrode system mounted in a duct with maximum air flow rate 250 sccm. Electrodes were separated with a dielectric layer (quartz pipe with inner diameter 9 mm) and 1.2 mm-wide air gap. The feed voltage had 3-10 kV magnitude and either 50 Hz or 2-16 kHz frequency. The input test gas mixture was produced by saturation of clean air (20 % Î2, 80 % N2) with VOC vapors, such as acetone, formic acid, hydrocarbons of white spirits, toluene and others, in 1-1000 ppm concentrations. FTIR spectroscopy and gas chromatography were used for characterization efficiency plasma cleaning and products of VOCs decomposition.
Reaction products composition varied with discharge parameters. When the applied voltage was relatively low, contamination removal process was inefficient, and reactor products included mostly HCOOH, CO, CO2, H2O, CH3NO3 and HCN. O3, N2O, HNO3 and N2O5 were the byproducts of air plasma discharge. But, as the discharge power increased, practically 100%-efficient conversion of initial VOCs into CO2, H2O and CO was achieved, with discharge byproducts NO, NO2 and N2O.
The mechanism of VOCs decomposition in low-temperature plasma at atmospheric pressure can include fragmentation of organic molecules by electron impact and a multi-stage process of oxidation of initial VOC molecules and their fragments by atomic oxygen and OH-radicals produced in the system (via intermediate stages of organic acids and aldehydes with subsequent oxidation to CO2 and H2O).
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