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.
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