Kinetics of the aqueous-phase reaction between ozone and 2,4,6-trichlorophenol

A wetted-sphere absorber was used to measure absorption rates of ozone into aqueous-buffered solutions of 2,4,6-trichlorophenol (TCP). Gas consisting of approximately 2.5% ozone in oxygen was contacted with aqueous-buffered T CP solution flowing over a sphere in a laminar liquid film. Absorption data were obtained by measuring the change in the liquid-phase concentration of TCP from the inlet to the outlet of the absorber. A rigorous numerical mod el for this diffusion/reaction process was used to analyze the absorption d ata to determine the second-order rate constant of the reaction between ozo ne and TCP ar 15-35 degrees C and pH 2 and 7. The kinetic data indicate tha t the rate-limiting step for the reaction of aqueous TCP with ozone is the same at pH 2 and 7. Four reaction products that occur early in the reaction of ozone with aqueous TCP were identified by GCMS, including: 2,3,4,6-tetr achlorophenol (TRCP), 4,6-dichlorocatechol (DCC), 2 6-dichlorohydroquinone (DCHQ), and 2,6-dichloroquinone (DCQ). Only DCHQ and DCQ occurred in signif icant concentrations. Over the pH range of 2 to 5, both DCHQ and DCQ were d etected in the reacted solutions, while for pH 6 and 7 only DCHQ was detect ed. Carbon-13 NMR analysis shows that over longer ozone exposure times shor t-chain carboxylic acids are the dominant species in the reacted TCP soluti ons.