Characteristics of reactive species produced by AC plasma generated in gas bubbles (original) (raw)

2016 IEEE International Conference on Plasma Science (ICOPS), 2016

Abstract

Summary form only given. Water-treatment processes utilizing OH radicals (*OH) to decompose persistent organic compounds are called advanced oxidation processes (AOPs). *OH can be produced by the reaction of hydrogen peroxide (H₂O₂) with ozone (O₃). When O₃ was passed through a plasma-treated, highly concentrated solution of organic compounds, the processing speed and efficiency of the decomposition of the organic compounds was improved. When using a DC-voltage plasma, the production rate of H₂O₂ was high with a high energy input, whereas that of O₃ was high with a low energy input1. Multiple plasmas could be generated in parallel using an AC voltage with ballast capacitors². In this manner, if the selective production of H₂O₂ or O₃ in each plasma is achieved, AOPs can be realized without generating O₃ using an ozonizer. In this study, we investigated the characteristics of H₂O₂ and O₃ production driven by an AC voltage. The plasma reactor consisted of a high-voltage needle electrode and a ceramic plate containing a hole of 0.3 mm diameter for the generation of oxygen (O₂) gas bubbles and plasma. In addition, the reactor had a grounded electrode, immersed in Na₂SO₄ solution (40 mL) with a conductivity of 1.5 mS/cm. A square-wave AC voltage was applied through a ballast capacitor of 15-100 pF, and the plasma was generated between the needle electrode and the bubble surface. The concentrations of H₂O₂ in the solution and O₃ in the exhaust gas were measured. The power input to the reactor was increased in proportion to the frequency and the capacitance. When the source voltage was 4 kV and the frequency was 2 kHz, the power was 1.2 W at a capacitance of 15 pF; at 100 pF, the power was 5.9 W. The concentration of H₂O₂ increased, and that of O₃ decreased, as the input power increased. The molar ratio of the reactive species produced (H₂O₂/O₃) was 0.28 at a power of 1.2 W, and 4.1 at 5.9 W. Therefore, the plasma power, as well as the amounts of H₂O₂ and O₃ produced and their ratio could be controlled by varying the ballast capacitor in AC-plasma operation. AOPs with a reactor utilizing ballast capacitors to produce multiple plasmas will thus be possible.

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