The destruction of dichloromethane by a nonthermal plasma in atmospheric-pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the end products are determined by on-line FTIR spectroscopy, and the plasma chemistry is interpreted using a kinetic modeling scheme. Peak destructions of 20% are found for a deposited energy of 66 J L -1 . The maximum dissociation is found for a carrier gas that contains 1-3% O 2 , and the dissociation is greater in pure nitrogen than in an air stream. The major end products of the processing are HCN, Cl 2 , and HCl in pure nitrogen and CO, COCl 2 , HCl, and Cl 2 for gas streams containing oxygen. The plasma processing in streams containing oxygen also produces significant yields of nitrogen oxides. The mechanism of dichloromethane destruction in the plasma is predominantly oxidation initiated by atomic chlorine that is produced by collisions of dichloromethane with electronically excited nitrogen atoms and molecules. Because of low cross sections, electron attachment does not play a role in the destruction of dichloromethane. The addition of oxygen to the gas streams initially causes additional destruction from O and OH reactions, but further increase in the oxygen concentration causes inhibition of both the atomic chlorine cycle and the formation of NO x and a consequent reduction in dichloromethane destruction.
It has been demonstrated that a dielectric packed pellet-bed plasma reactor operating on a mixture of NO 2 in air at atmospheric pressure can be used as an efficient method for the synthesis of dinitrogen pentoxide, N 2 O 5 . The reactor is packed with glass beads and operates at high frequency (10-13 kHz) and high voltage (V pk−pk < 30 kV). Typically, the energy density is 38 J l −1 and 45 ppm of NO 2 is converted into 53 ppm of N 2 O 5 . The synthesis of N 2 O 5 is found to be plasma-assisted in the sense that sources of nitrogen in addition to the initial NO 2 are converted into N 2 O 5 by the plasma. There is an energy cost of ∼180 eV for every molecule of N 2 O 5 produced. The possible role played by surface and heterogeneous effects in the pellet bed reactor is considered.
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