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 x 10(-3) mol/Eins for pH = 3 and 22 +/- 1.1 X 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 x 10(5) to 314 x 10(5) 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. (C) 2003 Elsevier Science Ltd. All rights reserved.