Decomposition Of Naphthalene In Air By Plasma Discharge Technology At Atmospheric Pressure

With the development of industry,the content of polycyclic aromatic hydrocarbons（PAHs）in the environment has significantly increased,causing severe pollution to the environment.Among them,indoor air pollution of PAHs is one of the urgent environmental problems to be solved.Naphthalene is a typical PAHs,which is harmful to human health due to its high volatility,teratogenic and carcinogenic characteristics.In recent years,due to its high degradation efficiency,short treatment time,wide application range,and can effectively reduce the generation of adverse byproducts,the non-thermal plasma（NTP）packed-bed dielectric barrier discharge（DBD）for the decomposition of gaseous pollutants has become an essential technology for the treatment of PAHs（such as naphthalene）gas and has attracted wide attention.In this thesis,a plasma catalytic degradation device of packed bed DBD was established to study the characteristics of DBD and the degradation of naphthalene under atmospheric pressure.The main research contents are as follows:1.The characteristics of DBD plasma are studied.In this thesis,the discharge characteristics and emission spectrum of plasma are diagnosed and analyzed.It is found that the addition of the catalyst improves the uniformity of discharge,and the Ti O₂ catalyst has a stronger charge transfer ability than the other two.The primary active particles produced by discharge are N₂（C³Π_u→B³Π_g）and N₂⁺（B²Σ_u⁺→X²Σ_g⁺）in air,and the spectral emission intensity of N₂（C³Π_u→B³Π_g）is higher than that of N₂⁺（B²Σ_u⁺→X²Σ_g⁺）.The secondary diffraction of N₂（C³Π_u→B³Π_g）occurs in the 500-800 nm and overwhelms the spectral lines of N₂（B³Π_g→A³Σ_u⁺）and O(p⁵P→3s⁵₂)distributed in the band.By fitting the temperature of plasma discharge gas,it is found that when the applied voltage is 24 k V and the discharge time is 7 min,the plasma gas temperature is 750 K.2.With naphthalene as the target pollutant,three transition metal oxides（Al₂O₃,Fe₂O₃ and Ti O₂）were used as catalysts to fill the reactor,and the catalysts were characterized.The results show that the catalysts exist in the form of crystals,and have good physical properties.The surface of the Al₂O₃ catalyst is smooth,and the pore structure is less.The surface of the Fe₂O₃ catalyst is porous,and the pore structure is larger than the other two.The surface of the Ti O₂ catalyst is rough,and the pore structure is smaller than the other two.Its rough surface can enhance the amount of micro-discharge,which is conducive to enhancing the discharge of the reactor.The specific surface area of Ti O₂,pore volume and size are higher than the other two,which is beneficial to the exposure of the active site and promotes the performance of photocatalytic properties.3.The effects of different process parameters（initial naphthalene concentration-C_i,total gas flow,treatment time,discharge power and relative humidity）on the decomposition of naphthalene in air.When C_iwas 21 ppm and total gas flow was 1 L/min,the naphthalene mineralization rate in the Al₂O₃-filled reactor reached 82.2%.With the increase of treatment time and discharge power,naphthalene mineralization increases first and then becomes stable.Ti O₂ catalyst had better removal efficiency and mineralization effect on naphthalene degradation in DBD than the other two.In addition,the introduction of a small amount of water vapor can provide a large amount of hydroxyl radical（·OH）for the reaction,which promotes naphthalene mineralization and CO₂ selectivity.The effect of humidity on discharge is related to the proportion of water vapor introduced and the type of catalyst in the reactor.Through investigation and analysis of the naphthalene degradation mechanism,the possible pathway of naphthalene degradation was deduced.In the DBD reactor,naphthalene can be decomposed by collisions with electrons,nitrogen and oxygen excitation particles,and oxidation with O radicals,O atoms and O₃.When the naphthalene molecule is destroyed,the unstable intermediate products will have a variety of reactions,which further oxidation with the active particles.Finally,produce simple small-molecule compounds CO,CO₂,and H₂O.