Electrochemical control of aqueous solution pesticide: study for the degradation of 2,4-dichlorophenoxyacetic acid / Controle eletroquimico de herbicida em soluções aquosas : estudo da degradação do acido 2,4-diclorofenoxiacetico

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

In this work, the performance of the H2O2 electrogeneration process from O2 reduction on a reticulated vitreous carbon cathode was investigated. The process was also use for the oxidation of the herbicide 2,4-dichlorophenoxyacetic acid. Firstly, cyclic voltammetries were used for the identification of possible reduction reactions of the herbicide. The supporting electrolyte used was a 0,3 mol L-1 K2SO4, pH 10, nitrogen saturated solution. Then, the optimization of hydrogen peroxide electrogeneration it was carried out. As a cathode, a reticulated vitreous carbon-rotating cylinder, shaped from a 60 ppi RCV plate was used. A platinum foil was used as anode and a saturated calomel electrode was used as reference. Supporting electrolyte was always K2SO4 0,3 mol L-1, in an O2 saturated solution. The experiments were run in a 150 mL electrode cell, with a water jacket to keeping temperature in the range from 8 0C. The best potential to produce hydrogen peroxide in these conditions was -1,6 V vs. SCE. In following stage, the degradation of 2,4-D was investigated by tree different process: H2O2 electrogenerated, H2O2/UV and photo electro-Fenton being the last at pH 2,5. The degradation of 2,4-D was followed by HPLC, moreover TOC and COD analyses. The most efficient process was the catalyzed UV/Fe2+ process that presented a TOC reduction of 69 %. In a sequence, a pilot scale reactor was mounted for hydrogen peroxide electrogeneration. The reactor is formed by two anolytes and one catholyte compartments, separated by a N424 Nafion® membrane. The reactor was optimized considering three different parameters: the applied potential, oxygen flow and the electrolyte flow. Best operational parameters electrogeneration rate of hydrogen peroxide in a K2SO4 0,3 mol L-1 electrolyte support were: -1,6 V vs. Pt, 500 L h-1 of electrolyte flow and 6 L s-1 of oxygen flow. Considering these results, the experiments for the degradation of 2,4-D were conducted with the optimized reactor. In this new series of experiments, six different processes were tested. In alkaline medium, the degradation occurred only with H2O2 and H2O2, catalyzed by UV radiation. Four processes were used in acidic medium: H2O2, H2O2 catalyzed by UV radiation, Fe2+ (electro Fenton process) and H2O2 with Fe2+ catalyzed by UV radiation (photo-electro Fenton process). In catalyzed experiments in acidic medium, degradation rates were higher TOC decay presented a pseudo-first order kinetic. The differences between electro Fenton and photo-electro Fenton processes appeared only when TOC reduction was considered. A greater degree of organics combustion was observed for the last process, with 95 % of TOC was eliminated

ASSUNTO(S)

reatores quimicos advanced oxidative process 2 agua oxigenada eletrodo de carbono hydrogen peroxide 4-dichlorophenoxyacetic acid celulas eletroliticas fenton reagent electrochemical reactor

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