Studies On Benzene Degradation Using Surface/Packed-bed Hybrid Discharge Plasma And Combination Of Catalyst

Non-thermal plasma (NTP) has received widespread attention in VOCs abatement, showing advantages of high efficiency, high speed, and no selective to pollutions. However, single non-thermal plasma still suffers from the problems of low energy efficiency and mineralization efficiency. Therefore, surface/packed-bed hybrid discharge plasma was proposed to degrade a kind of typical VOCs-benzene in this paper. A high-voltage electrode and a ground electrode are used to generate surface discharge plasma and packed-bed discharge plasma simultaneously. The gas to be solved enters the surface discharge plasma part (part I) and the packed-bed discharge part (part II) in turn. This method can realize the sequential degradation of benzene by double-stage plasma. The main work was conducted in terms of benzene degradation characteristics, the optimization of reactor structure parameters and operational parameters, benzene degradation mechanisms, and synergistic effects between surface/packed-bed hybrid discharge plasma and catalyst for benzene degradation. The detailed work and the summarized results are as follows:1. The feasibility of surface/packed-bed hybrid discharge plasma on benzene degradation was studied. The experimental results showed that surface/packed-bed hybrid discharge plasma was an efficient and quick method for benzene degradation. The degradation efficiency, CO2selectivity, and energy yield in the surface/packed-bed hybrid discharge reactor were21%,11%, and3.9g/kWh higher, respectively, than in a surface discharge reactor and30%,21%, and5.5g/kWh higher, respectively, than in a packed-bed discharge reactor at the same specific input energy (280J/L).2. Benzene degradation characteristics were studied by evaluating the effects of reactor structure parameters, gas parameters, and electric parameters. The results showed that the reactor using the coil electrode exhibited better performance in benzene degradation than the rod electrode and bolt electrode, because the adsorption and stabilization of the reactive species Oads and Nads is favored when the coil electrode was used as the high-voltage electrode. Increasing the wire diameter of the coil electrode, the screw pitch of the coil electrode, and the inner diameter of the quartz tube in certain range could improve benzene degradation efficiency. The presence of packing materials can increase local electric fields in part II, and thus the benzene degradation efficiency enhanced. There existed optimal O2concentration and water content to obtain high benzene degradation. Increasing discharge frequency, decreasing gas flow rate, and benzene initial concentration could improve benzene degradation. Compared with AC power, bipolar pulse power had the advantages of sharp pulse edge and narrow pulse width, which was better for benzene degradation.3. By studying the role of active species on benzene degradation, and analyzing benzene degradation intermediates by FT-IR and GC-MS, benzene degradation mechanism was proposed. The attacks of energetic electrons and energetic excited molecules are the main reasons for benzene decomposition. Further degradation of benzene can be initiated by O-containing active species oxidation (such as O and OH radicals), generating hydroxylated intermediates, and then the hydroxylated intermediates were further degraded into small organic acids, CO2and H2O.4. Surface/packed-bed hybrid discharge plasma and AgxCe1-x/γ-Al2O3catalyst were combined to degrade gaseous benzene. The effect of active metal components ratio of the catalyst, catalyst placement, catalyst space velocity, and water content on benzene degradation were studied. The synergetic mechanisms were discussed by comparing the benzene degradation, mineralization, and discharge byproducts (O3and NO2) evolution in surface/packed-bed hybrid discharge plasma system and surface/packed-bed hybrid discharge plasma/AgxCe1-x/γ-Al2O3system. The results showed that more highly active oxygen atoms were generated in surface/packed-bed hybrid discharge plasma/AgxCe1-x/γ-Al2O3system, accelerating the degradation and mineralization of benzene and intermediates.