| In recent years, air pollution is worsening, severe regional air quality issues such as photochemical pollution, ozone depletion and severe haze adversely affect human health and ecological environment, and has attracted wide attention of scholars at home and abroad. Air pollution control in China is mainly focused on dust removal, desulfurization and denitrification for a long time and some progresses have been achieved. However, the volatile organic compounds (VOCs) pollution still need to be solved urgently. The study on Non-thermal Plasma technology in the field of low concentration VOCs control has achieved remarkable results. But there are some problems with this technology like high energy consumption, the formation of hazardous and toxic by-products. Studies have shown that plasma-catalytic technology could significantly improve the efficiency of VOC degradation, with advantages of low energy consumption and fewer byproducts. Early research of plasma-catalytic technology mainly focuses on traditional hydrocarbon compounds, while study on the stench of sulfur-containing organic waste is less.In this paper, the line-tube type dielectric barrier discharge reactor is used. Firstly, the discharge characteristics of plasma reactors and the degradation characteristics of methyl sulfide with different packing materials and different temperatures were investigated. And then we studied the effects of discharge parameters, V2O5 loading, gas flow rate, initial concentration and temperature on the plasma-V2O5-WO3/TiO2 system to removal methyl sulfide. And analyzed the structure-activity relationship of the catalyst by XRD, BET, H2-TPR characterizations. After tested and analyzed the by-product, this paper proposed reaction pathway of plasma -catalytic removal of dimethyl sulfide process. On the basis of small scale experiments above, the scaling up experiments of plasma-catalytic removal of industrial organic waste gas have been taken and researched. The main conclusions are as follows:(1) We investigated the discharge characteristics of plasma reactors and the degradation characteristics of methyl sulfide with different packing materials (glass pellets, Al2O3 and TiO2) and different temperatures. The dielectric constant of the packing materials had great influence on the discharge characteristics and the degradation characteristics of methyl sulfide. Under the same discharge voltage, discharge power and the degradation efficiency of dimethyl sulfide are all in the order: TiO2> Al2O3> glass pellets. Under the same discharge voltage, the discharge power increases with the increase of the temperature. Compared with surface area, relative dielectric constant of packing materials has a more important effect on the degradation efficiency of methyl sulfide. Temperature is an important factor affecting the degradation efficiency of methyl sulfide. At the same discharge energy density, when the temperature is increased from 25 ℃ to 200 ℃, the degradation efficiency of methyl sulfide was improved by 30%-40% in the packed TiO2 reactor.(2) Plasma-catalytic removal of dimethyl sulfide are examed. At normal temperature, the V/W/Ti catalyst has a significant promotion effect on the oxidation of methyl sulfide in plasma environment, and the removal efficiency and energy efficiency of methyl sulfide increased with the increase of the load of V2O5. When the mass fraction of V2O5 is 0.6% and the energy density is 788 J/L, the removal efficiency of dimethyl sulfide was 91.6%, which was improved by 40% compared with plasma only, and energy efficiency was 6.54 g/(kWh), one times increased compared with the plasma only. With the increase of V2O5 loading, the catalyst specific surface area decreased, while the oxidation and reduction of the catalyst was improved. The comparison with dimethyl sulfide degradation effect showed that oxidation-reduction of catalyst itself than its physical structure played a more important role in the plasma catalytic reactions.(3) The byproducts in the process of plasma-catalytic removal of methyl sulfide are mainly SO2, HCHO, CO, CO2, etc. With the increase of discharge energy density, CO, CO2 concentration gradually increased, HCHO firstly increased and then decreased, some HCHO further decomposed into CO and CO2, SO2 firstly increased and then gradually kept stable. In addition to the above byproducts, there may also exist dimethyl sulfoxide (DMSO2), dimethyl disulfide (DMDS) and other sulfur-containing organic compounds.(4) This paper compared catalytic oxidation, plasma oxidation and plasma-catalytic removal of dimethyl sulfide under different temperature conditions. The results showed that the removal efficiency of dimethyl sulfide was greater increased when combine plasma with V/V/Ti catalyst than V/V/Ti catalyst oxidation. The catalytic activity of the V0.9W/Ti catalyst was only 1.3%, when combine with 12 W plasma, dimethyl sulfide removal efficiency was 92.6%. The active temperature range of the catalyst was reduced with the introduction of plasma, and it was achieved to removal methyl sulfide more efficiently at low temperature. We analyzed the chemical kinetic of the reaction process. It showed that the activation energy of V0.9W/Ti catalytic oxidation of methyl sulfide was 74.6 kJ/mol, while plasma-V0.9W/Ti with discharge power of 12 W was 5.94 kJ/mol. The catalytic reaction was activated by the addition of plasma, which promoted the degradation of methyl sulfide.(5) The results of scale-up experiments showed that at the condition of air flow rate of 100 m3/h, the initial concentration of toluene of 40 ppm, the discharge center frequency of 3 kHz and the discharge power of 2 kW, the removal efficiency of the plasma-catalytic system was 90.7%, and the energy efficiency was 7.3 g/kWh. In the two-component VOCs, toluene and methyl sulfide are competitive. Under the same conditions, since the C-S bond energy within dimethyl sulfide is less than that of C-C bond between benzene rings and methyl and the C-H bond of the methyl within toluene, methyl sulfide is more easily oxidized than toluene in two-component of toluene/methyl sulfide. |
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