Decomposition Mechanism for Electron Beam Irradiation of Vaporized Trichloroethylene−Air Mixtures

Abstract

Decomposition of trichloroethylene (TCE) in electron beam irradiation was examined in order to get information on treatment of industrial off-gas. Air containing vaporized TCE was sealed into a glass vessel and irradiated with an electron beam. The concentration of TCE exponentially decreased with dose (air-absorbed energy). The doses necessary to decompose 90% of input TCE molecules had a value of 3.6 kGy independent of an initial concentrations ranging from 50 to 1800 ppmv. Between G values of decomposition and initial concentrations, the following equation was obtained: G(−TCE) [μmol J-1] = 1.5 [μmol J-1] + 0.020 [μmol J-1 ppmv-1] × conc [ppmv]. The equation shows that concentrations of Cl radicals remained constant at 6.3 × 10-4 ppmv (at 298 K and 1 bar) independent of concentrations of TCE and products under a dose rate of 2.1 kGy/s. Termination reactions in the decomposition mechanism for EB irradiation of TCE and tetrachloroethylene (PCE) were also clarified on the basis of the relation of G value of decomposition and the initial concentrations. Dichloroacetyl chloride, which was identified as a primary product, was decomposed and oxidized to give CO and CO2. Phosgene was also identified as a primary product. From the proportion of DCAC to COCl2 concentrations, a branching ratio was calculated to be 5.3 in the Cl radical chain reaction of TCE. Formation of HCl and/or Cl2 was analyzed and the collection of the products from the gas phase was examined with alkaline solution. The effect of water (400−25 000 ppmv) on decomposition efficiency was examined. The decomposition efficiencies had the same value as that in dry air.