Experimental Study On The Degradation Of CH₃SH By Double Dielectric Barrier Discharge Plasma Coupled With Catalysis

Methyl mercaptan（CH₃SH）,as a typical sulfur-containing volatile organic pollutant,is the key object to be solved in the prevention and control of air pollution.In recent years,non-thermal plasma technology has become one of the most active research fields at home and abroad due to its high degradation efficiency and easy management.However,the problems of high energy consumption and toxic by-products have always plagued its further development.In this paper,a separate coaxial double dielectric barrier discharge reactor is first used to study the degradation of CH₃SH.The discharge characteristics of the reactor were investigated,and the influence of process parameters such as discharge voltage,discharge frequency,inlet concentration,gas flow,O₂content,humidity on the degradation effect of CH₃SH was determined.Secondly,in response to the existing problems of non-thermal plasma technology,Ni O/γ-Al₂O₃,Mn O₂/γ-Al₂O₃and Ce O₂/γ-Al₂O₃catalysts withγ-Al₂O₃pellets as the carrier were prepared.The effect of filling the dielectric barrier discharge space with four catalysts includingγ-Al₂O₃compared with the empty tube reactor was investigated in terms of CH₃SH degradation rate,reactor energy consumption control,by-product suppression and CH₃SH mineralization degree.Then the optimal catalyst was selected,and the influence of the active component loading and the calcination temperature on its catalytic oxidation activity was determined.Finally,by means of XPS,FT-IR and GC-MS,the intermediate products in the reaction were inferred,the possible reaction pathways of CH₃SH under the synergistic effect of the two technologies were given,and the reaction mechanism was analyzed.The main conclusions are as follows:（1）Study on the degradation of CH₃SH by a single dual dielectric barrier discharge plasmaThe coaxial double dielectric barrier discharge reactor device belongs to resistive-capacitive load.When the voltage is 15 k V,an obvious discharge phenomenon can be observed in the reactor.As the voltage increases,the discharge light intensity increases,and the energy density and O₃output also increase.The degradation rate of CH₃SH can increase rapidly with the increase of voltage,but the increase of voltage will also increase energy consumption.In the experiment,the degradation rate of CH₃SH can reach the highest when the discharge frequency is 8.01k Hz.The increase of CH₃SH inlet concentration and gas flow rate will reduce the degradation rate of CH₃SH,which is more obvious at lower voltage.A certain range of O₂content and humidity will have a positive effect on the degradation of CH₃SH.In this experiment,the most suitable O₂content is 10%,and the most suitable humidity range is 60%to 70%.（2）Study on the degradation of CH₃SH by double dielectric barrier discharge plasma coupled with catalysisWhen the catalyst is filled in the discharge area of the reactor,the discharge of the reactor is advanced.Compared with empty tube reactors,the presence of catalysts can increase the energy density of the reactor,thereby increasing the degradation rate of CH₃SH to varying degrees.The order of the catalytic oxidation activity of each catalyst for CH₃SH is Ni O/γ-Al₂O₃>Mn O₂/γ-Al₂O₃>Ce O₂/γ-Al₂O₃>γ-Al₂O₃.The existence of catalysts can reduce the energy consumption of the reactor.When the voltage is 16 k V,the energy efficiency of the empty tube reactor is 4.21 g/k Wh.After the catalyst is filled,the energy efficiency of the reactor is increased by 2.7%to17.6%.In addition,the catalysts can also inhibit the formation of by-products such as O₃,NO_x,SO₂,and promote the deep oxidation of CH₃SH.When the voltage is 16 k V,the mineralization rate of CH₃SH in the empty tube reactor is 43.8%,and the mineralization rate of CH₃SH is increased by 8.7%to 24.0%after the catalyst is filled.Comprehensive degradation effect analysis shows that the Ni O/γ-Al₂O₃catalyst calcined at 450°C with an active component loading of 10 wt%has the highest CH₃SH degradation activity.（3）Study on the degradation mechanism of CH₃SH in the double dielectric barrier discharge plasma synergistic catalytic systemAnalyzed by XPS,FT-IR and GC-MS technology,the intermediate product of the reaction may be 4-hydroxybutan-2-one,butan-1-amine,dimethyl disulfide,ethyla-mine,thiodiglyco,3-hydroxybutyraldehyde,1,2-Diaminopropane,isopropylamine,1,1-bis（methylsulfanyl）ethane and propionamide.It is speculated that the mechanism of synergistic degradation is as follows:high-energy electrons break down the gas in the electric field to generate a large amount of active oxygen species that act on pollutant molecules and promote their deep oxidation.High-energy electrons stimulate the oxidation activity of the catalyst.The catalyst uses its own lattice oxygen to oxidize the captured pollutant molecules,and the formed oxygen vacancies are supplemented by the O₃in the decomposition system.