Study On Toluene Removal From Waste Gas By Array Double Dielectric Barrier Discharge With Catalysis

VOCs are the important precursors of PM2.5 and 03,which not only exacerbate the occurrence of haze,but also endager human health due to its a large amount of emisions.VOCs removal from waste gas by dielectric barrier discharge has the advantages of high energy electrons and strong universality,but there are still some problems such as high energy consumption,low energy utilization rate and many uncontrollable by-products.On the contrary,the method of catalysis can just make up for the lack of dielectric barrier discharge because of its the advantages of high efficiency and less by-products.Therefore,VOCs removal from waste gas by dielectric barrier discharge with catalysis has become hotspot.However,most of the studies on VOCs removal by dielectric barrier discharge with catalysis are only in the laboratory stage and the gas flow rate of treatment is small,which can not truly reflect the removal efficiency of VOCs in the industry.In this paper,we propose and adopt a new type of reactor of array double dielectric barrier discharge(DDBD)with catalysis to remove toluene from the large volume of waste gas.We studied the discharge characteristics of the reactor,inspected the influence factors and by-products(NOx and O3)of toluene removal by discharge with catalysis and analyzed the surface products of the catalyst and by-products from the exhaust gas,tried to derive the possible pathway of toluene removal by discharge with catalysis.The main conclusions are as follows:(1)When the output peak voltage exceeded 9 kV,the energy output efficiency of the high voltage power could reach more than 95%.When the discharge peak voltage of the reactor of double dielectric barrier discharge with catalysis was higher than 9 kV,a significant discharge phenomenon could be observed,and a uniform and stable discharge phenomenon could be obtained when the discharge peak voltage was 12.5 kV.When the discharge peak voltage was 12.5 kV,the influence of different ventilation gas flow rate on the discharge of the reactor is small,however,the high humidity could significantly reduce the discharge of the reactor,and the generated ultraviolet light was also weaker.The discharge peak current of the reactor increases with the increase of discharge peak voltage,and the higher the peak voltage,the greater the growth rate.The indoor air relative humidity can affect the discharge peak current of the reactor of double dielectric barrier discharge with catalysis,and the effect is more obvious when the discharge peak voltage is high.(2)The removal efficiency of toluene from waste gas by DDBD with catalysis and the single DDBD decreases with the increase of the initial concentration of toluene and the ventilation gas flow rate.When the indoor air relative humidity was 55%,the removal efficiency of toluene from waste gas was better than that of relative humidity by 85%.The removal efficiency of toluene from waste gas by DDBD with catalysis and the single DDBD increases with the increase of the specific energy density,in contrast,the energy yield of toluene removal from waste gas by DDBD with catalysis and the single DDBD decreases with the increase of the specific energy density.In general,the removal efficiency of toluene from waste gas is as follows:Ti02/Al2O3 catalyst>Co/activated carbon catalyst>DDBD.The maximum removal efficiency of toluene from waste gas by DDBD with the TiO2/Al2O3 catalyst was 98.5%,and the energy yield was 8.64 g/kWh,the corresponding working conditions were as follows:the indoor air relative humidity was 55%,the ventilation gas flow rate was 100 m3/h,the initial concentration of toluene was 50 mg/m3,the discharge plate space was 400 mm,and the specific energy density was 21.6 J/L.(3)The concentration of ozone and nitrogen dioxide decreases with the increase of the initial concentration of toluene and the ventilation gas flow rate,but increases with the increase of the specific energy density.When the catalyst was used,the catalyst could significantly reduce the concentration of ozone and nitrogen dioxide,in which Co/activated carbon catalyst had the most significant effect in reducing the concentration of ozone and nitrogen dioxide.When the initialconcentration of toluene was 300 mg/m3,the indoor air relative humidity was 55%and the ventilation gas flow rate was 100 m3/h,the removal of toluene from waste gas by DDBD with the Co/activated carbon catalyst produced the lowest ozone concentration of 8.6 ppm.When the initial concentration of toluene was 50 mg/m3,the indoor air relative humidity was 85%and the ventilation gas flow rate was 100 m3/h,the removal of toluene from waste gas by DDBD with the Co/activated carbon catalyst produced the lowest nitrogen dioxide concentration of 12.7 ppm.(4)The results of XPS analysis showed that the surface of the used TiO2/Al2O3 catalyst contained many kinds of reactive oxygen species(O22-,O-and O2-),and there were many chemical bonds(C-N,C=N,H-O,C-O,C=O,C-Al,C-H or C-O-Al,etc.).The results of FT-IR analysis showed that the surface of the used TiO2/Al2O3 catalyst might contain benzyl alcohol,benzaldehyde,phenol,aniline and other alcohols,esters,aldehydes or amides.The results of GC-MS analysis showed that the main intermediates were phenol,benzaldehyde,benzyl alcohol,benzoic acid,N-benzyl formamide,dimethyl terephthalate,dimethyl isophthalate and other substances.