Avoidance of Chlorine Formation during Electrolysis at Boron-Doped Diamond Anodes in Highly Sodium Chloride Containing and Organic-Polluted Wastewater

Abstract

In the present contribution, the behavior of sodium chloride containing electrolytes at boron-doped diamond anodes are investigated. The study is focusing on industrial process water treatment and is based on half-cell measurements (active area of the working electrode: 3.14 cm2) and technical laboratory electrolysis measurements (active area: 100 cm2). It was found that the diamond electrode has a considerable overvoltage for chlorine formation (approx. 740 mV vs. RHE), regrettably not sufficient for hydroxyl radical formation before chlorine formation, regarding the electrochemical potential. Nevertheless, an operating point was identified through process parameter variation, which leads to wastewater purification at the diamond electrode without generating chlorine emissions. The application of the identified operating point is shown at the purification of real diaminodiphenylmethane-production wastewater (10 wt% sodium chloride) and artificial process water contaminated with N-(chloromethyl)-N-ethylpiperidinium chloride organic. Valuable component of both wastewaters are the high salt loads, which are reusable if the organic substances are successfully treated. The observations are confirmed by ultratrace analysis of organic products and do not show any chlorinated products at the desired operating point.