The ozonation of the hydrolyzed and vinyl sulfone derivatives of C.I. Reactive Blue 19 and C.I. Reactive Black 5

Fiber reactive dyes are important, but a highly colored waste water results from the dyeing process. Waste water from dyeing with masked vinyl sulfone dyes, in particular, contains a mixture of the hydrolyzed and vinyl derivatives formed during the dyeing process. Two commercially important masked vinyl sulfone dyes, C.I. Reactive Blue 19 and C.I. Reactive Black 5 were chosen and their decolorization by ozonation was investigated in color concentrations representative of those found in waste water. The experimental conditions necessary to generate the hydrolyzed and vinyl derivatives of these dyes were determined, and then the ozonation efficiency of each derivative was examined at pH = 5.9 and 10.5.; The hydrolysis reaction of each dye was monitored by ion-pairing chromatography and simple kinetic models were fit to the data. Subsequently, color (by absorbance measurements between 400-700 nm), pH, and ozone consumption were monitored during the course of decolorization by ozonation. In addition, the oxidation potentials of the hydrolyzed dye derivatives were measured using cyclic voltammetry to determine if oxidation of the derivative would occur before oxidation of the water.; There were no significant differences in the rates of decolorization of solutions containing the hydrolyzed or vinyl derivatives of either dye. However, increasing the pH of the black solutions from 5.9 to 10.5 had a dramatic effect on decolorization, whereas increasing the pH of the blue solutions did not. The black solutions decolorized at a more rapid rate and consumed less ozone per unit color loss at the high pH. The differences in rate and ozone consumption may be ascribed to the deprotonation of a pendant hydroxy group on the black chromophore at the higher pH. Supporting evidence for the effect of pH on the black dye solution came from the cyclic voltammetry data.; Although the black dye consumed more ozone at the low pH, the overall ozonation of both dyes at both pH levels was very efficient in terms of moles of ozone per unit color loss.