2. Series Reaction Decolorization of aqueous solutions of dyes used in the textile industry may be accomplished via the use of ozone. Y.-C. Hsu, J.-T. Chen, H.-C. Yang, and J.-H.

Chen [AICHE J., 47, 169-176 (2001)] investigated the kinetics of the oxidation of Mordant Black and other dyes in a well-agitated reactor to which a gas containing ozone was fed continuously. Initially, decolorization occurs rapidly, but as the process continues, colored intermediates are formed. These intermediates are more recalcitrant to oxidation, but are destroyed as ozonation proceeds. These authors indicate that the concentration of dissolved ozone remains substantially constant so that the kinetics of this process can be treated as involving two consecutive pseudo first-order reactions: A B C where ki is the kinetic rate cons[ant of the first reaction and k2 is the kinetic rate constant of the second reaction and A represents Mordant Black, B is a lumped parameter representing several persistent colored intermediates, and C represents all of the colorless solutes. At 25°C, pH 7.0, and an initial concentration (Ao) of 200 mg/L, the values of k₁ and k₂ are 9.12 x 10-3 and 1.13 x 10-3s-1, respectively. Prepare plots of the concentrations of species A, B, and C as functions of time when no B or C is present initially. Determine the time corresponding to the maximum concentration of species B and the time at which the sum of the concentrations of species A and B is 20 mg/L. The latter time can be viewed as corresponding to removal of approximately 90% of the initial color values, thereby rendering the solution amenable to processing via more conventional waste treatment methods.