Electrocatalytic Hydrogenation of Indigo

Abstract

The industrial feasibility of the electrocatalytic hydrogenation of indigo on Raney nickel electrodes as a suspension in an aqueous medium has been studied in a divided flow cell. The attempt was made to establish optimized conditions in the system, and a scale-up in indigo concentration to 10 g/L was achieved. Increasing pH can enhance the reduction rate and a maximum conversion has been found by optimizing current density and temperature. The reaction rate is clearly enhanced in the presence of ultrasonic waves and organic solvents. Methanol is among the best cosolvents and was used in concentrations of 10 vol %. With Raney nickel electrodes an optimized current efficiency of 13% could be reached at 95% conversion. This value was enhanced to 19% by using electrodes doped with platinum particles. © 2002 The Electrochemical Society. All rights reserved.