Time-resolved study of the conversion of chlorinated hydrocarbons in non-equilibrium hydrogen plasmas

Abstract

The time evolution of the decomposition of chlorinated hydrocarbons in non-equilibrium hydrogen plasmas was investigated by experiment as well as by kinetic modelling. Singly chlorinated hydrocarbons (C 2H 3Cl, C 2H 5Cl) highly diluted in hydrogen were decomposed in an electrodeless pulsed r.f. discharge sustained in a quartz glass tube. The gas-phase chemistry was also modelled by CHEMKIN computer code. In the model, the plasma was considered as weakly ionized so that the chemistry of neutral species plays the major role. It was found that the chlorinated hydrocarbons were decomposed very quickly to the main stable species HCl, CH 4 and C 2H 2. During the decomposition process, which lasts only a few milliseconds, a few chlorinated hydrocarbon radicals show up in the gas phase. Later on, the plasma is dominated by the radicals CH 3, Cl and H. CH 4, C 2H 2, and also smaller amounts of C 2H 4 and C 2H 6 are in a quasi equilibrium after the decomposition process is completed. At steady state, the concentrations of the chlorinated hydrocarbons were close to the detection limit. Experiment and modelling are in good agreement.