Kinetics of photodegradation and ozonation of pentachlorophenol

The oxidation of 2,3,4,5,6-pentachlorophenol (PCP) has been carried out by a photodecomposition process using a polychromatic UV irradiation, and by an ozonation process. In the photodegradation process, the pH accelerated the decomposition rate and the approximate first-order rate constants were evaluated, with values between 0.16 ± 0.005 min−1 at pH=3 and 0.26 ± 0.007 min−1 at pH=9. A more rigorous kinetic study led to the determination of the quantum yields of the reaction, with values of 200 ±7 × 10−3 mol/Eins for pH=3 and 22 ± 1.1 × 10−3 mol/Eins for pH=9. In the ozonation process, the rate constants for the reaction between ozone and PCP were determined by means of a competition kinetics, with values in the range from 0.67 × 105 to 314 × 105 l/mol s. The specific rate constants for the un-dissociated and dissociated forms of PCP were also calculated. Finally, in both processes, the intermediate reaction products were identified, the most important being tetrachlorocatechol, tetrachlorohydroquinone and tetra-p-chlorobenzoquinone. Free chloride ion released, which was favored at high pHs, was also followed in both processes.