Direct electrochemical reduction of vat dyes in a fixed bed of graphite granules

Abstract

Reducing agents required in the dyeing process for vat and sulphur dyes cannot be recycled and lead to problematic waste products. The application of electrochemical reduction of several vat dyes and even mixtures of them on a fixed bed cathode consisting of graphite granules has been investigated by spectrophotometric experiments in a laboratory scale pilot plant. Experiments yield information about the kinetics and show the possibility and versatility of this environmentally friendly process for production of water soluble leuco dyes. In addition to singular dyes, even dyestuff mixtures were investigated. Regarding the effect of different molecular structures on the kinetics and a preliminary understanding of the reaction mechanism, relationships between computed molecular parameters and the reduction rate are presented.