Photooxidation of exhaust pollutants - II. Photooxidation of chloromethanes: Degradation efficiencies, quantum yields and products

Article abstract of DOI:10.1016/0045-6535(94)90073-6

The photochemical decomposition and oxidation, of CH_xCl_y (x = O-3, y = 4-x) was investigated in the gas phase by irradiation with a low pressure mercury lamp in an oxygen atmosphere. The degradation efficiency depends on the concentration of the pollutant, the power output of the UV-lamp and the irradiation time. The quantum yields for degradation at 185 nm were measured to be around 1 at low CH_xCl_y concentration in the 10^-3 range. For CH₂Cl₂ and CHCl₃ however, we observed a drastic increase of the quantum yields to values up to one hundred at high CH_xCl_y concentration in the 10^-2 range. For CH₃Cl and CCl₄ no significant increase of quantum yield with concentration was found. In addition to the main products HCl, phosgene and formyl chloride we found CO, CO₂ and formic acid. The mechanisms of their formation are discussed in detail.