Development of secondary electron emission gun for VOC's treatment

Summary form only given. Volatile organic compounds (VOCs) in the air cause photochemical oxidant formation and stratospheric ozone depletion. Non-thermal plasma technologies using electrical discharges or electron beam irradiation offer an energy- and cost- efficient approach to the decomposition of VOCs. In the present work, VOC removal using electron beam is studied. The electron beam was generated by a secondary electron emission gun (SEEG) using a wire ion plasma source (WIPS). The device has some inherent advantages over conventional ones, such as compactness in size and generation of a uniform and wide electron beam. The treatment process is based on a reaction with free radicals. These active species are produced by electron-impact dissociation and ionization of the background gas molecules. Positive ions (He+) generated in WIPS, which is a glow- discharge device using a thin wire electrode, are extracted through an ion extraction window and accelerated toward a stainless steel cathode plate biased at -100 kV in a vacuum chamber. The pressure in the vacuum chamber is 2times10-3 Torr. The WIPS uses the pulsed power system delivering an output discharge voltage of 10 kV with a pulse width in the order of a microsecond at the repetition frequency up to 10 Hz. The secondary electrons are generated in vacuum chamber by the collision of helium ions against the cathode plate and are accelerated toward an electron window made of a PET film, which separates the gas treatment chamber from the SEEG. An absorbed dose is about 3 kGy per one shot. The pressure in the treatment chamber is an atmosphere during the process and inlet gas flow rate is controlled by using a mass flow controller. Gas composition and concentration before and after the treatment are measured with a gas chromatography mass spectrometer (GCMS-QP2010, Shimadzu Co Ltd). The VOCs used in the experiment were toluene, benzene and trichloroethylene. The relationship between the absorbed dose and the decomposition rate in batch and flow system was obtained. The experimental results indicate good efficiency of VOCs removal and show that the VOCs treatment by the SEEG is a promising technology.