Degradation of a model naphthenic acid by nitrilotriacetic acid – modified Fenton process

Abstract

The degradation of cyclohexanoic acid (CHA) as a model compound of naphthenic acid (NA) was investigated in this study by a nitrilotriacetic acid (NTA) – modified Fenton process at pH 8. The optimum doses of hydrogen peroxide (H2O2) and FeIIINTA (NTA:Fe=2:1) were 4.41mM and 0.27mM, respectively. CHA degradation reached a plateau within 4h under these conditions. The degradation of CHA was influenced primarily by the dose of H2O2, while the concentration of FeIIINTA complex primarily influenced the reaction time. The second-order rate constants of hydroxyl radical (OH) with CHA and with NTA were investigated using a competition-kinetics method and obtained as 4.09±0.39×109M−1s−1 and 4.77±0.24×108M−1s−1, respectively. OH radical was the main responsible species for CHA degradation, while O2− radical played a minor role. The reaction of CHA with O2− radical generated by potassium superoxide (KO2) in dimethyl sulfoxide (DMSO)/water solution was investigated for the first time. The reaction mechanisms of the NTA-modified Fenton process were proposed and discussed based on the discovery that no FeIINTA was detected in the system.