| Volatile organic pollutants(VOCs)have extensive sources and complex components,which are harmful to the environment and human health.As a promising VOCs treatment technology,NTP has attracted extensive attention from researchers,which dielectric barrier discharge(DBD)is one of the most commonly used ways of adsorption followed by discharge catalytic oxidation of VOCs,which has the advantages of uniform discharge,stable process and high energy efficiency.In the industry,VOCs exist in a variety of components at the same time.However,most studies focus on the removal of a single component,and different catalysts are applicable to different VOCs.So the catalysts that can efficiently remove multi-component VOCs at the same time need to be further explored.In this study,toluene and ethyl acetate were selected as the target pollutants,suitable catalysts were screened out,and the catalysts were characterized by SEM,BET,H2-TPR,XPS and GC-MS.The main research conclusions are as follows(1)The results of the study on the degradation of adsorbed toluene by DBD combined with 13X and ?-Al2O3 and supported by Fe,Mn,Ag and Mo,respectively,showed that:The mineralization effect of ?-Al2O3 on adsorbed toluene is relatively good,about 10%higher than 13X.Among the four active components,Fe oxidizes toluene with the highest COx concentration and the best mineralizationt.Mn has the strongest decomposition ability to the by-products O3 and N2O.Although the mineralization of 13X was less than that of ?-Al2O3,the COx yield of Fe/13X oxidized toluene was higher than that of Fe/?-Al2O3,up to 65%.This is due to the presence of more oxidized Fe3+ and adsorbed oxygen on the surface of Fe/13X.In addition,mixing Fe/13X with equivalent amount of ?-Al2O3 was beneficial to its mineralization effect of adsorbed toluene,and COx yield reached the highest,which was 69%(2)The results of the study on the degradation of adsorbed ethyl acetate by DBD combined with the above catalysts showed that:The mineralization rate of adsorbed ethyl acetate by ?-Al2O3 was 40%,which was 13.6%higher than 13X.Mn of the four active components had the best effect on the mineralization of ethyl acetate and the inhibition of the by-product.The synergistic effect of Mn and 13X was better,and the COx yield was higher than Mn/?-Al2O3,up to 61.5%.This is because:1)specific surface area of Mn/13X catalyst is larger than Mn/?-Al2O3,and there are more active sites.2)there were more highly oxidized Mn4+ and adsorbed oxygen content on the surface of Mn/13X.When the mixing ratio of Mn/13X and ?-Al2O3 is 1:1,the COx yield of its oxidative adsorbed ethyl acetate can be increased by about 3%,and the emission of by-product is also the least.(3)The results of the study on the degradation of adsorbed toluene and ethyl acetate by DBD combined with 13X,Fe and Mn screened showed that:there was a competitive adsorption relationship between toluene and ethyl acetate at the adsorption stage.Ethyl acetate was adsorbed until penetration,and then toluene was adsorbed,toluene was difficult to adsorb.When toluene is adsorbed until penetration and then ethyl acetate is adsorbed,the toluene that was adsorbed will be replaced;When toluene and ethyl acetate were adsorbed at the same time,toluene began to penetrate after 80 min.Therefore,when the two pollutants exist simultaneously,the adsorption time should be less than 80 min.Mn/13X-Fe/13X-?-Al2O3 has the best effect on the mineralization of two-component pollutants among the several mixing methods of catalysts,Catalyst mixed with a mechanical catalyst of equal mass of ?-Al2O3 after loading Mn and Fe respectively on 13X.The effects of adsorption capacity,discharge voltage and humidity on two-component VOCs oxidation of Mn/13X-Fe/13X-?-Al2O3 on DBD combined mixed catalyst are as follows:1)the increase of the initial adsorption amount leads to the decrease of the collision probability between individual VOC molecules and active particles,which is not conducive to the oxidation of adsorbed VOCs;2)as the voltage increases,the electric field strength increases,so that more active species can be formed to facilitate the oxidation of adsorbed VOCs;3)the increase of humidity is not conducive to the mineralization of adsorbed toluene and ethyl acetate.On the one hand,the electronegativity of water limits the energy of electrons,leading to the quenching of the active species.On the other hand,due to the competitive adsorption of water vapor and pollutants,VOCs in adsorption state are replaced.The Mn/13X-Fe/13X-?-Al2O3 catalyst has stable performance after 5 adsorption-discharge cycles,COx yield remains unchanged,and CO2 selectivity decreases slightly.(4)The mechanism of degradation of adsorbed VOCs by DBD combined catalyst shows that there are three main ways to degrade adsorbed toluene:1)toluene is directly bombarded by high-energy electrons into phenyl and methyl radicals,and then the active groups generated by the decomposition of O3 are further oxidized to form CO2 and H2O;2)toluene molecules react directly with free radicals in the gas phase to produce benzyl alcohol,which is further oxidized to benzaldehyde and benzoic acid,followed by ring-opening reaction,which is further mineralized into CO2 and H2O;3)toluene molecules are hit by high-energy electrons to generate methyl,phenyl,phenyl and other groups,which can be directly integrated to produce polymers.The degradation path of ethyl acetate is also divided into three parts:1)high-energy electrons generated in the discharge directly bombards ethyl acetate into fragments;2)the active particles formed by the collision of high-energy electrons with air(N2 and O2)directly participate in the oxidation of ethyl acetate;3)ROS generated by the decomposition of O3 on the catalyst surface participate in the oxidation of the adsorbed ethyl acetate.When toluene and ethyl acetate were degraded at the same time,the organic intermediates decreased,but not significantly.In addition,the organic by-products degraded by toluene were significantly higher than that of ethyl acetate,because the bond energy of benzene ring was larger and it was difficult to open,and benzene ring substances such as benzaldehyde o-xylene and 4-methyl-diphenylmethane were easily formed. |
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