Decomposition Of VOCs Mixture By Multi-needle-mesh Corona Discharge Combining With Pulsed High-voltage

Nowadays, the volatile organic compounds (VOCs) are widely used in industries. The emission of VOCs from these industries has led to serious atmospheric pollution and indoor air pollution. Therefore, the removal of VOCs is extremely urgent. Among the various VOCs removal technologies, plasma discharge process (PDP) is regarded as a promising technology for the effective removal of VOCs. PDP can be operated at room temperature and atmospheric pressure, with low energy consumption, simple structure, easy to operate and so on.In this paper, high-voltage pulsed corona discharge plasma technology for the removal of mixed VOCs was investigated. The self-made multi-needle-mesh reactor was adopted in this study, and benzene and m-xylene were selected as the target pollutants. By examining the effects of electrode configuration, electrical parameters (including the high-voltage power supply, pulse forming capacitor, pulse repetition rate) and gas parameters on the pollutant decomposition characteristics, the relationships of pollutants decomposition characteristics and the factors, such as power input, energy density, the react mode of plasma and pollutant molecules, have been investigated. Furthermore, the effects of oxygen content and the application of transition metal catalyst on the decomposition characteristics of mixed VOCs, carbon balance and CO₂ selectivity have been examed, and then the mechanism of degradation of pollutants have been discussed. The results of this study are as follows:(1) Compared to the DC high-voltage power supply, the average power input of pulsed high-voltage power supply is smaller, while the pulse effective power is much higher. So the energy efficiency of pulsed high-voltage power supply is higher than that of DC high-voltage power supply. Considering the general effect of energy input and the decomposition efficiency of benzene, the optimal electrode configuration set as needle-needle distance of 10 mm and needle-mesh distance of 10 mm. It was found that optimizing the pulse forming capacitor is helpful to improve the discharge characteristics and the decomposition efficiency of pollutants. The optimal pulse forming capacitor is 253 pF in this study. The results also showed that the backward gas flow could enhance the gaseous turbulence level, which results in a better interaction of benzene molecules and plasma. Therefore, the backward gas flow could enhance the decomposition rate of pollutants.(2) Compared to the decomposition characteristics of single component benzene and m-xylene, the decomposition characteristics of benzene in mixture and m-xylene in mixture are different. The maximum decomposition rate of benzene decreased from 51.5% of single component to 35.7% of mixed component. While the decomposition rate of m-xylene had a slight increase, which increased from 85.1% of single component to 89.6% of mixed component.(3) The oxygen content in the background gas has a major impact on the composition of active particles generated in the process of discharge, and then it could affect the decomposition characteristics of VOCs. The research results revealed that different types of free radicals have different selectivities of the reaction with benzene and m-xylene. Benzene is more easily to react with nitrogen radicals, while m-xylene is more easily to react with oxygen radicals. It was also found that the increase of oxygen content is helpful to improve carbon balance and CO₂ selectivity.(4) The combination of pulsed corona discharge and transition metal catalysts is helpful to improve selectivity of CO₂. MnO_x catalyst is better than NiO_x catalyst for improving the decomposition efficiency. Both of MnO_x catalyst and NiO_x catalyst have better catalytic effect on benzene than that on m-xylene.