Investigation Of Carbon Tetrafluoride Treatment By Atmospheric Microwave Plasma

With the development of modem industry,the more and more greenhouse gases are released to the atmosphere.In all of greenhouse gases,perfluorocompounds(PFCs) have low toxic and stable chemical characters,and are widely used in industrial processes.Because of their strong infrared absorption and long atmospheric lifetimes, PFCs emission will cause the globe warming effect.Atmospheric microwave plasma, which is the new technology on decomposing PFCs from 1990,has relative high destruction and removal efficiencies and no secondary pollution in PFCs treatment.In this study,the microwave plasma device is designed to excite and maintain stable plasma on atmospheric press.The characters of plasma are diagnosed by emission optical spectroscopy.Microwave plasma is employed to decompose the CF4,which is the most difficult to be decomposed.The experiment has been done with a varity of conditions including carrier gases,microwave power,gas flow rate,initial concentration,additive gases.The products of CF4 decomposition are analysed.The process and mechanism of PFCs decomposition is certified by radicals' diagnosis and thermodynamic experiment.The combined catalysts and microwave plasma is developed to decompose PFCs.The results indicate that the atmospheric microwave plasma has relative high electron temperature and high electron density.There are kinds of actived radicals in plasma.The highest DRE of CF4 is up to 99%.The DRE is increased with the increase of microwave power,and is decreased with the increase of gas flow rate.Optimum volume of additive gases can promote the DRE,while the excessive additive gases will exhaust the electron and result in the decrease of DRE. The optimum volume of O₂ and H₂O can enhance the DRE about 20%and 10%, respectively.With O₂ exist,CO₂ and F₂ is the main products of CF₄ decomposition.The mechanism of CF₄ decomposition is that the CF₄ molecular lost one F atom each time to form CF_i by the electron collision firstly,and the O radicals was the assistance in the later reaction,to further transform CF_i to CO₂ and F₂.The thermal decomposition is not the main process in CF₄ decomposition.The DRE of CF₄ is enhanced about 10%by catalysts used,the ultraviolet radiation,high temperature and plasma all can actived the catalysts to decompose CF₄.