AIChE Journal, Vol.45, No.8, 1802-1807, 1999
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 TCP 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 model for this diffusion/reaction process was used to analyze the absorption data to determine the second-order rate constant of the reaction between ozone and TCP ar 15-35 degrees C and pH 2 and 7. The kinetic data indicate that 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-tetrachlorophenol (TRCP), 4,6-dichlorocatechol (DCC), 2 6-dichlorohydroquinone (DCHQ), and 2,6-dichloroquinone (DCQ). Only DCHQ and DCQ occurred in significant concentrations. Over the pH range of 2 to 5, both DCHQ and DCQ were detected in the reacted solutions, while for pH 6 and 7 only DCHQ was detected. Carbon-13 NMR analysis shows that over longer ozone exposure times short-chain carboxylic acids are the dominant species in the reacted TCP solutions.