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

Abstract

AbstractA 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 at 15–35°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.