Phosgene formation from the decomposition of 1,1-C₂H₂Cl₂ contained gas in an RF plasma reactor

In this study, a radio-frequency (RF) plasma system was used to decompose the 1,1-dichloroethylene (DCE) contained gas. The reactants and final products were analyzed by using an FTIR (Fourier Transform Infrared Spectroscopy). The effect of plasma operational-parameters for DCE decomposition was evaluated. In addition, the possible reaction pathways for DCE decomposition and phosgene (COCl₂) formation were built up and discussed. Both DCE decomposition efficiency and the fraction of total carbon mass converted into CO₂ and CO were decreased by the increasing DCE feeding concentration. The DCE decomposition efficiency at varied equivalence ratios, φ (stoichiometric O₂/actual O₂), was controlled by both oxidation and energy transfer efficiency. At lower equivalence ratios have an excess of oxygen, a larger amount of COCl₂ was formed due to a higher oxygen-feeding concentration. Higher input power wattage can increase both the DCE decomposition efficiency and the fraction of total-carbon mass converted into CO₂ and CO, resulting in the reduction of the COCl₂ effluent concentration. However, more soot was found in the plasma reactor when the input power wattage was higher than 60 W. Because high concentrations of C₂Cl₄, CHCl₃ and CCl₄ were detected and because copper inner-electrode might act as catalyst, the most possible pathways for the COCl₂ formation were C₂Cl₄ + OH, C₂Cl₃ + O₂, CHCl₃ + O, CHCl₂ + O, CCl₃ + O and CO + Cl₂.