UV photolysis of trichloroethylene: product study and kinetic modeling.

Direct UV photolysis of trichloroethylene (TCE) in dilute aqueous solution generated chloride ions as a major end product and several reaction intermediates, such as formic acid, di- and monochloroacetic acids, glyoxylic acid, and, to a lesser extent, mono- and dichloroacetylene, formaldehyde, dichloroacetaldehyde, and oxalic acid. Under prolonged irradiation, these byproducts underwent photolysis, and a high degree of mineralization (approximately 95%) was achieved. TCE decays through the following major pathways: (1) TCE + h nu --> ClCH=CCl + Cl; (2) TCE (H2O) + h nu --> ClCH(OH)-CHCl2; (3) TCE + h nu --> HC[triple bond]CCl + Cl2; (4) TCE + h nu --> ClC[triple bond]CCl + HCl; (5) TCE + Cl* --> Cl2HC-C*Cl2. A kinetic model was developed to simulate the destruction of TCE and the formation and fate of byproducts in aqueous solution under irradiation with polychromatic light. By fitting the experimental data, the quantum yields for the four photolysis steps were predicted as phi(1) = 0.13, phi(2) = 0.1, phi(3) = 0.032, and phi(4) = 0.092, respectively. The reaction mechanism proposed for the photodegradation of TCE accounts for all intermediates that were detected. The agreement between the computed and experimental patterns of TCE and reaction products is satisfactory given the complexity of the reaction mechanism and the lack of photolytic kinetic parameters that are provided in the literature.