TECHNICAL PAPERS ELECTROCHEMICAL SCIENCE AND TECHNOLOGY Indirect Electrochemical Reduction of Dispersed Indigo Dyestuff

Iron-triethonolamine complexes are well suited for the indirect reduction of dispersed dyestuffs, e.g., finely dispersed indigo in a dyebath. Experiments to develop basic data for the scale-up of an electrochemical cell usable for the indirect reduction of indigo, vat dyes, and sulfur dyes are described. Planar electrodes show that the current density at the cath-ode is limited by diffusion controlled transport phenomena in the mediator system. The characterization of the iron tn-ethanolamine mediator system is performed by reduction experiments in a divided flow cell with parallel geometry. An optimization of this cell type was achieved with three-dimensional flow through electrodes, leading to high specific elec-trode areas and a good space/time yield with the investigated electrochemical system. The characterization of the differ-ent cell types was performed with electrolysis experiments using the mediator alone and in the presence of dispersed indi-go dyestuff. Infrocluction About 250,000 to 300,000 metric tons of dyestuff are produced annually for the coloration of cellulosic textiles. This amount is divided into several classes. About 120,000 metric tons of vat dyes (including indigo) and sulfur dye