The chemistry of dichloromethane destruction in atmospheric-pressure gas streams by a dielectric packed-bed plasma reactor

The destruction of dichloromethane by a nonthermal plasma in atmospheric-pr essure gas streams of nitrogen with variable amounts of added oxygen has be en investigated. The identities and concentrations of the end products are determined by on-line FTIR spectroscopy, and the plasma chemistry is interp reted using a kinetic modeling scheme. Peak destructions of 20% are found f or 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 a re HCN, Cl-2 and HCl in pure nitrogen and CO, COCl2, HCl, and Cl-2 for gas streams containing oxygen. The plasma processing in streams containing oxyg en also produces significant yields of nitrogen oxides. The mechanism of di chloromethane destruction in the plasma is predominantly oxidation initiate d 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 di chloromethane. The addition of oxygen to the gas streams initially causes a dditional destruction from O and OI-I reactions, but further increase in th e oxygen concentration causes inhibition of both the atomic chlorine cycle and the formation of NOx and a consequent reduction in dichloromethane dest ruction.