Study On The Degradation Of Toluene Using Asymmetric Rod-type Dielectric Barrier Discharge (DBD) And Its Combination With Catalyst

With the rapid development of human industrial processes,the problem of air pollution caused by fossil energy consumption has become increasingly serious,which has aroused widespread concern in the international community.Volatile organic compounds?VOCs?are one of the causes of air pollution,causing serious harm to human health and the ecological environment.Unlike traditional VOCs end-processing techniques,low-temperature plasma?NTP?technology is an emerging processing technology for processing VOCs in point source gas streams,where dielectric barrier discharge?DBD?technology is mild due to its discharge conditions,high field strength,and processing.The advantages of good effect and simple device are the most widely used NTPs for VOCs processing.The conventional symmetric DBD electrode structure has the disadvantages of high discharge starting voltage,large thermal effect,and easy accumulation of discharge intermediate products.In this paper,an asymmetric dielectric barrier discharge electrode structure is proposed.The metal rod with a small radius of curvature such as a thread and a fin is used as a high voltage electrode,and the insulating medium filled with a conductive material is used as a ground electrode to form an asymmetric electrode structure.It can produce a stable and uniform filamentary streamer discharge.This asymmetric electrode structure generates an inhomogeneous electric field in the discharge region,so that the aerosol molecules generated during the discharge treatment are polarized and moved toward the strong electric field to deposit on the electrode.The position of the groove is separated from the deposition area by the discharge area,thereby ensuring uniform discharge gap and making the discharge more stable.The research contents and conclusions are as follows:?1?Comparing the discharge characteristics of the asymmetric electrode structure with the conventional smooth rod electrode structure and the toluene degradation characteristics,the results show that the discharge of the smooth rod electrode is distributed over the entire smooth rod and is more uniform,while the threaded rod and the fin The rod electrode discharge is distributed on the thread and fin structure and has greater discharge intensity;the degradation efficiency and energy efficiency of the smooth rod electrode are relatively high,but the mineralization effect of the fin rod is better,and the ozone concentration at the outlet is lower.The detection and analysis of the discharge-degraded toluene product showed that o-nitrotoluene and 3-methyl-5-nitrophenol were the main gas phase and solid phase organic by-products respectively,and the presence of intermediate organic by-products was lower in the carbon balance of toluene degradation.One of the reasons.Long-term discharge aerosol deposition experiments show that the fin electrode is more stable than the smooth rod electrode discharge,and the effect of aerosol deposition on its discharge power,toluene degradation efficiency and energy efficiency is relatively small.?2?By optimizing the electrode structure parameters and gas phase parameters,the results show that more arrangement of dielectric electrodes can accumulate more charge on the surface of the medium,thereby increasing the discharge power;at the same voltage,copper powder is used as the electrode material.Compared with iron powder and carbon powder,it is more conducive to the degradation efficiency of toluene;when the fin thickness is 1.0 mm,the fin spacing is 2 mm,the groove depth is 1.0 mm,the discharge spacing is 3mm,and the initial concentration of toluene is At 100 ppm,the total flow rate of 0.5 L/min,the fin-type DBD discharge reactor has the highest degradation efficiency of toluene.?3?Comparing the research on the degradation of toluene by different power supply?high-frequency unmodulated power supply and modulation power supply?,the results show that the unmodulated power supply is a continuous discharge,and the modulated power supply is a discontinuous discharge.The discharge intensity of the modulated power supply during the discharge phase of the same voltage is required.It is larger than the unmodulated power supply;the toluene degradation efficiency of the modulated power supply at a higher voltage is close to that of the unmodulated power supply,and the modulated power supply can significantly reduce the heat loss caused by the discharge to improve the energy efficiency of toluene degradation.The higher the frequency of the high-frequency unmodulated power supply,the lower the initial discharge voltage,but at the same energy input density,the higher the power frequency,the higher the degradation efficiency of toluene,the lower the energy efficiency of toluene.The ratio of the air ratio and the modulation frequency is proportional to the energy input density.The greater the duty cycle and modulation frequency at the same voltage,the greater the degradation efficiency of toluene,the lower the energy efficiency,and the higher the temperature inside the reactor chamber.?4?Combining the finned rod DBD reactor with Mn/Ce catalyst,the addition of Mn/Ce catalyst improves the degradation efficiency and mineralization effect of toluene and reduces the formation of by-products such as ozone.When the Mn/Ce ratio is 3:1,the toluene removal rate and CO₂ selectivity are the highest,80%and 55%,respectively,and the outlet ozone concentration is 0.19 mg/L.As the catalyst space velocity decreases,the toluene removal efficiency increases and the ozone concentration decreases.