ULTRASONIC DECOLORIZATION OF REACTIVE PHTHALOCYANINE DYES

The objective of the work presented here was to assess the sonolytic decolorization of two reactive phthalocyanine textile dyes (Reactive Blue 7, RB7; Reactive Blue 21, RB21) and the compound Cu-phthalocyanine tetrasulfonic acid (PhTSA). Sonications were performed in a 515-ml sonocell with a 640 kHz transducer and a power output of 250 W. The dye solutions were recirculated with in-line oxygen sparging. Sonications were performed with RB21 to test the effect of salt (90 g/L Na2SO4), base (3 g/L Na2CO3 and 1 g/L NaOH), and the combined effect of salt and base, conditions typically found in phthalocyanine-containing, reactive textile dyebaths. Addition of salt decreased the rate of sonolytic decolorization. However, base addition (Na2CO3 and NaOH) completely offset the decreased decolorization rate due to salt. The negative effect of high salt concentration on the sonolytic decolorization rate was overcome with the addition of base at both low and high dye concentrations. The pseudo-first order rate constant decreased with increasing RB21 concentration in the range of 50 to 500 mg/L. Sonication of RB7 and RB21 solutions with both salt and base at concentrations typically found in spent reactive dyebaths, resulted in 52 to 53% decrease in chemical oxygen demand and 45 to 52% decrease in nonpurgable organic carbon in about 102 h of sonication. Therefore, in addition to decolorization, a significant degree of mineralization of phthalocyanine dyes takes place during sonication.