Electrochemical Vat Dyeing Combination of an Electrolyzer with a Dyeing Apparatus

A standard dyeing apparatus for yarn on X-cones has been coupled to a multicathode electrolyzer for indirect reduction of dispersed oxidized vat dyes. An alkaline solution containing 0.01 M iron-triethanolamine complex was used as mediator solution. In test runs current efficiencies better than 80% were obtained at cell currents up to 10 A. The cathode was built up from 10 insulated sheets of steel fabric with a total area of 0.96 m 2 . In batch experiments cones of cotton yarn with an average mass of 900 g yarn were dyed. Different dyes were applied in light to dark shades at a dyeing temperature of 60°C. During the electrochemical dyeing process the cell must carry out different functions: reduction of dissolved oxygen, indirect reduction of dispersed oxidized vat dye, buildup of a certain reduction capacity against air oxygen, and control of redox potential in the dyeing apparatus by adjustment of cell current. A description of the concentrations of dissolved oxygen and reduced form of the mediator during electrolysis can be achieved by a simple mathematical model, which permits efficient optimization of important technical parameters for process design and scale-up.