Selective oxidation of phenolic compounds at BDD and DSA anodes

The paper deals with the selective oxidation during galvanostatic electrolyses at Ti/RuO2 (DSA, dimensionally stable anode) or boron doped diamond (BDD) of solutions that could be representative of some agro-industrial wastewaters in which biodegradable substances, like sugars, are present along with phenolic fraction. Synthetic solutions treated in this work contain phenolic compounds (p-hydroxybenzoic acid, procatechuic acid) along with glucose selected as a model of biodegradable fraction. The experimental results have evidenced that both anodic materials are able to realise selective oxidation of the phenolic fraction from solutions containing also glucose. At BDD anodes low current densities and high mixing rates of the system allow to obtain a good selectivity of the electrochemical process. At DSA anodes, low mixing rates, high current densities and chloride concentration comprised between 1.0 and 2.5 g/l could be suitable conditions for a fast and selective removal of the phenolic fraction from solutions containing also glucose. The different experimental conditions which are requested to obtain selective oxidation of the phenolic fraction are discussed on the basis of the different reaction mechanisms that occur at BDD or DSA anodes.