| As a novel technology for the removal of gaseous VOCs, the nonthermal plasma process has such advantages as high removal efficiency, nonselective, wide using range and so on, and exhibits promising application perspective. In this paper, the mixture of acetone, benzene, m-xylene and perchloroethylene (PCE) was chosen as the object and a bipolar pulse DBD system was set up by combining the bipolar pulse high voltage and DBD to remove the mixed VOCs in air. The feasibility and mechanism of mixed VOCs decomposition by nonthermal plasma were studied. The optimization of power supply parameters and reactor structure was investigated. Furthermore, this paper also set up a nonthermal plasma-catalysis system for mixed VOCs decomposition and investigated the synergistic effect and mechanism of this system. The main results are summarized as follows:1. The voltage waveforms, current waveforms and characteristics of input power for industry frequency alternate current DBD as well as bipolar pulse DBD had been investigated. The results showed that comparing with industry frequency alternate current DBD, the bipolar pulse DBD exhibited the advantages of short pulsed corona discharge that sharp pulse edge and narrow pulse width which led to more quantities of high-energy particles generate and better for VOCs decomposition. Under the conditions of 15 W average power,2.5 L/min flow rate and 200 ppm concentraten, the decomposition rates of acetone, benzene, PCE and m-xylene in their mixture were 23%,52%,57% and 99% for the bipolar pulse DBD, comparing with industry frequency alternate current DBD were only 10%,27%,45% and 96%。2. For the bipolar pulse DBD system, the optimization of matching the power supply and reactor was investigated by studying the effects of pulse peak voltage, pulse repetitive rate and capacitance of the pulse capacitor. Experiment results indicated that increasing the pulse peak voltage and pulse repetitive rate could improve the energy injection and promote the decomposition of VOCs. For the wire-tube DBD reactor, the appropriate match rate between the pulse capacitor and the static capacitance of reactor was 10～20 times.3. The DBD reactor configuraten was optimized at the aspect of the effective power input and spatial distribution of energy. Effects of electrode material, discharge gap, size of barrier and discharge length on the VOCs decomposition had been studied. The results showed that comparing with the stainless steel bolt, the stainless steel rod as the electrode had more uniform plasma distribution and high decomposition rates of VOCs. The reactor energy density and decomposition rates of VOCs decreased with the increased of discharge gap. At the same discharge gap, appropriate enlarging the reactor size and discharge length was helpful to the remove of VOCs.4. The interactions among the components were investigated by studied the decomposition characteristics of four kinds of mixed VOCs and analyzed the exhaust components. The results showed that there were some interactions among the components when the mixed VOCs were removed simultaneously. The component that had smaller ionization energy was priority to be decomposed to micromolecule intermediate products which will reduced the degradation efficiency of other components.5. The CO2 and CO selectivity of VOCs degradation in DBD had been studied. The results indicated that the CO2 and CO were generated by different degradation pathway that increasing the pulse peak voltage could not promote the conversion of CO to CO2.6. The degradation characteristics and mechanisms of mixed VOCs and CO2 selectivity in nonthermal plasma-catalyst system had been studied. The results suggested that DBD nonthermal plasma combining with catalysis could both enhance the decomposition rates of VOCs and CO2 selectivity. For the mixed VOCs decomposition, the catalytic capability of metal catalyst was related to the adsorption capacity of each VOC component. Adsorption capacity of VOC component in catalyst surface was stronger, the more obvious effect of catalytic degradation.
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