title: Mineralization of naphtenic acids with thermally-activated persulfate: The important role of oxygen.
abstract: This study reports on the mineralization of model naphtenic acids (NAs) in aqueous solution by catalyst-free thermally-activated persulfate (PS) oxidation. These species are found to be pollutants in oil sands process-affected waters. The NAs tested include saturated-ring (cyclohexanecarboxylic and cyclohexanebutyric acids) and aromatic (2-naphthoic and 1,2,3,4-tetrahydro-2-naphthoic acids) structures, at 50mgL(-1)starting concentration. The effect of PS dose within a wide range (10-100% of the theoretical stoichiometric) and working temperature (40-97°C) was investigated. At 80°C and intitial pH=8 complete mineralization of the four NAs was achieved with 40-60% of the stoichiometric PS dose. This is explained because of the important contribution of oxygen, which was experimentally verified and was found to be more effective toward the NAs with a single cyclohexane ring than for the bicyclic aromatic-ring-bearing ones. The effect of chloride and bicarbonate was also checked. The former showed negative effect on the degradation rate of NAs whereas it was negligible or even positive for bicarbonate. The rate of mineralization was well described by simple pseudo-first order kinetics with values of the rate constants normalized to the PS dose within the range of 0.062-0.099h(-1). Apparent activation energy values between 93.7-105.3kJmol(-1) were obtained.
authors.affiliation: Chemical Engineering Section, University Autonoma of Madrid, Crta. Colmenar km 15, 28049 Madrid, Spain.
authors.forename: Xiyan
authors.initials: X
authors.lastname: Xu
authors.affiliation: Chemical Engineering Section, University Autonoma of Madrid, Crta. Colmenar km 15, 28049 Madrid, Spain.
authors.forename: Gema
authors.initials: G
authors.lastname: Pliego
authors.affiliation: Chemical Engineering Section, University Autonoma of Madrid, Crta. Colmenar km 15, 28049 Madrid, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Zazo
authors.affiliation: Chemical Engineering Section, University Autonoma of Madrid, Crta. Colmenar km 15, 28049 Madrid, Spain.
authors.forename: Jose A
authors.initials: JA
authors.lastname: Casas
authors.affiliation: Chemical Engineering Section, University Autonoma of Madrid, Crta. Colmenar km 15, 28049 Madrid, Spain. Electronic address: juanjo.rodriguez@uam.es.
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Rodriguez
keywords: Mineralization; Naphthenic acids; Oxygen oxidation; Persulfate oxidation; Radical reaction