Comparative electrochemical treatments of two chlorinated aliphatic hydrocarbons. Time course of the main reaction by-products

• Published in: Journal of hazardous materials Vol. 192; no. 3; pp. 1555 - 1564
• Main Authors: Randazzo, Serena, Scialdone, Onofrio, Brillas, Enric, Sirés, Ignasi
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.09.2011; Elsevier
• Subjects: 1,1,2,2-Tetrachloroethane; 1,2-Dichloroethane; Acetates - chemistry; acids; air; Aliphatic hydrocarbons; Anodes; Anodizing; Applied sciences; aqueous solutions; Byproducts; Chemical engineering; Chemistry Techniques, Analytical; chlorides; Chlorination; chlorine; Chlorine - chemistry; Decay; dechlorination; Dichloroacetic Acid - chemistry; Diffusion; Electro-Fenton; Electrochemical water treatment technologies; electrochemistry; Electrochemistry - methods; Electrodes; Equipment Design; Ethane - analogs & derivatives; Ethane - chemistry; ethylene dichloride; Ethylene Dichlorides - chemistry; Exact sciences and technology; hydrocarbons; Hydrocarbons, Chlorinated - chemistry; hydrogen peroxide; Hydrogen Peroxide - chemistry; iron; Mineralization; Organochlorinated pollutants; oxidation; Oxygen - chemistry; pollutants; Pollution; Reaction pathway; Reactors; Time Factors; 1,1,2,2-Tetrachloroethane; 1,2-Dichloroethane; Electro-Fenton; Organochlorinated pollutants; Electrochemical water treatment technologies; Reaction pathway; Water treatment; Hydrogen peroxide; Dehalogenation; In situ; Synergism; Dechlorination; Mineralization; Reaction mechanism; Fenton reaction; Oxidation; Diffusion; Organic compounds; Hydrocarbon; Electrochemical treatment; Chlorine; Aliphatic compound; Reaction product; Chlorates; Perchlorates; technologies; Pollutant; First order; 1, 1,2,2-Tetrachloroethane; Kinetics; Aqueous solution; Electrochemical water treatment
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.06.075

• DCA and TCA more quickly degraded by electro-Fenton with BDD than anodic oxidation. • Faster mineralization of TCA compared to DCA. • Reaction pathways include oxidative and cathodic reductive dechlorination steps. • Chloroacetic, dichloroacetic, acetic, oxalic and formic acids are major by-products. • Released Cl − is oxidized to ClO 3 − and mostly to ClO 4 − by bulk OH and BDD( OH). Acidic aqueous solutions of the chlorinated aliphatic hydrocarbons 1,2-dichloroethane (DCA) and 1,1,2,2-tetrachloroethane (TCA) have been treated by the electro-Fenton (EF) process. Bulk electrolyses were performed at constant current using a BDD anode and an air diffusion cathode able to generate H 2O 2 in situ, which reacts with added Fe 2+ to yield OH from Fenton's reaction. At 300 mA, almost total mineralization was achieved at 420 min for solutions containing 4 mM of either DCA or TCA. Comparative treatments without Fe 2+ (anodic oxidation) or with a Pt anode led to a poorer mineralization. The better performance of the EF process with BDD is explained by the synergistic action of the oxidizing radicals, BDD( OH) at the anode surface and OH in the bulk, and the minimization of diffusional limitations. The decay of the initial pollutant accomplished with pseudo first-order kinetics. Chloroacetic and dichloroacetic acids were the major by-products during the degradation of DCA and TCA, respectively. Acetic, oxalic and formic acids were also identified. The proposed reaction pathways include oxidative and reductive (cathodic) dechlorination steps. Chlorine was released as Cl −, being further oxidized to ClO 3 − and, mostly, to ClO 4 −, due to the action of the largely generated BDD( OH) and OH.