Electrochemical reduction in vat dyeing: greener chemistry replaces traditional processes

In application of vat dyes the substitution of non-regenerable reducing agents such as Na2S2O4 by cathodically regenerable reducing agents offers great ecological advantages. In a demonstration project a 45 A multi-cathode electrolyser successfully was coupled to a dyeing apparatus for package dyeing with a capacity of 1–10 kg material. Iron-complexes with triethanolamine and Na-d-gluconate were used as cathodically regenerable reducing agents. Dyebath regeneration was performed by ultrafiltration. Substantial reduction in chemical consumption and reduction in wastewater volume, released from the dyeing process could be demonstrated. Quality of dyeings was assessed with regard to levelness and iron content analysed in the dyed samples.