MULTICATHODE CELL WITH FLOW-THROUGH ELECTRODES FOR THE PRODUCTION OF IRON(II)-TRIETHANOLAMINE COMPLEXES

Nonregenerable reducing agents used in dye houses for the application of indigo, vat dyes and sulfur dyes can be substituted by indirect cat hodic reduction techniques. An electrochemical cell for the indirect c athodic reduction of dispersed indigo dyestuff using an alkaline solut ion of the Fe(III/II)-triethanolamine complex as redox mediator was co nstructed and tested. The cell is built up as divided cell (cathode ar ea 5-10 m(2), catholyte volume 12 L, anolyte volume 1.5 L) with severa l three dimensional cathode units (up to 10) in the same cathode compa rtment. The cathodes were connected to a common anode and to separatel y adjustable power supplies. The catholyte was circulated through the porous cathode units parallel to the current direction. Two different electrode materials (copper and stainless steel) and cathode construct ions were tested, resulting in an optimized cell construction. The ele ctrochemical cell was characterized by a series of batch electrolysis experiments. Results are given dealing with the cell voltage drop in t he cathode, the product yield and the current efficiency at different current densities and cell current. After an optimization step the cur rent efficiency reaches 70-80% at 2 A m(-2) current density and 7.8 x 10(-3) moldm(-3) Fe(II)-complex. The cell current is 10A.