Long-chain phenols oxidation using a flow electrochemical reactor assembled with a TiO2-RuO2-IrO2 DSA electrode

Abstract

The electrochemical degradation of long-chain phenols present in toxic residues from the cashew-nut processing industry was systematically investigated for the first time, using a flow electrochemical reactor assembled with a Ti/TiO2-RuO2-IrO2 DSA anode. After optimizing the current density (40 mA cm−2) and chloride concentration (0.028 mol L−1) in 0.5 mol L−1 Na2SO4 supporting electrolyte, it was achieved expressive total organic carbon (TOC) removal percentage for (un)saturated cardanol and cardol, either alone (85–92%) or in association/real industrial CNSL sample (82%), over 4 h of electrolysis. Evidently, the removal rate for the mixture changes (56–88% TOC removal) according to its starting concentration (0.005–0.100% residue), showing that the system performance can improve by increasing treatment time. Chromatography coupled to mass spectrometry (GC–MS) analysis showed that the first stage of the electrooxidation process was driven towards the formation of phenoxyl radicals, followed by the formation of polymeric dimers. These intermediates were continuously oxidized by different free and chemisorbed reactive species until obtaining short-chain organic acids, CO2 and H2O. The proposed system proved to be efficient, eco-friendly, and viable to treat industrial waste containing refractory phenolic compounds.