Transformation and decolorization of reactive phthalocyanine dyes

Reactive dyes are an important class of textile dyes used primarily to dye cotton and cotton blend fabrics. Phthalocyanine reactive dyes, which have a metalized ring structure, are used for blue and green shades. Currently the single most pressing environmental problem in the textile dyeing industry is the high concentration of salt and base typically used in reactive dyebaths. High salinity and base concentrations, in addition to the dye itself, complicate the management of wastewater from reactive dyeing operations. A closed-loop, spent reactive dyebath renovation and reuse system could achieve a significant decrease in the volume, as well as the load, of both salt and non-biodegradable organic compounds in wastewater produced from textile dyeing operations and could also provide significant savings from the reuse of both salt and water. Most research on the decolorization of reactive dyes has been on reactive azo dyes, while few reports exist on the biological and physico-chemical decolorization of reactive phthalocyanine dyes. Research was conducted to investigate the transformation and decolorization of commercially important reactive phthalocyanine dyes and a model phthalocyanine compound. The decolorization of reactive phthalocyanine dyes was examined in conventional microbial systems as well as in a halophilic microbial enrichment culture. Decolorization did not occur under aerobic conditions and was slow and incomplete under anoxic/anaerobic conditions. Palladium-catalyzed hydrogen reduction was also examined and found to completely decolorize the dyes tested. Such reductive decolorization was faster at the high salt and base concentrations than in the absence of both salt and base. Common products resulting from the reductive decolorization of all three dyes were detected by high performance liquid chromatography (HPLC) indicating a similar reduction mechanism for both the biological and chemical reductive decolorization of phthalocyanine dyes. Three major products—sulfophthalamide, sulfophthalamic acid and sulfophthalic acid—were identified by mass spectrometry and found to be common in solutions of all three dyes decolorized by the palladium-catalyzed hydrogen reduction process. Sonication of all three dyes resulted in complete decolorization and a significant decrease in dissolved organic carbon and chemical oxygen demand. The addition of salt decreased the rate of sonolytic decolorization for all three dyes while the presence of base increased the rate of decolorization and was successful in overcoming the negative effect of salt when both salt and base were present. (Abstract shortened by UMI.)...