N. Karpel Vel Leitner

Oxidation of Methyl tert-Butyl Ether (MTBE) and Ethyl tert-Butyl Ether (ETBE) by Ozone and Combined Ozone/Hydrogen Peroxide

Abstract The aim of this work was to study the reaction of ozone and combined ozone/hydrogen peroxide on oxygenated additives such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) in dilute aqueous solution using controlled experimental conditions. Experiments conducted in a semi-continuous reactor with MTBE and ETBE in combination (initial concentration: 2 mmol/L of each) showed that ETBE was better eliminated than MTBE with both ozone and combined O3/H2O2. Batch experiments led to the determination of the ratio of the kinetic constants for the reaction of OH°-radical with MTBE and ETBE [kOH°/ETBE/kOH°/MTBE = 1.7). Tert-butyl formate and tert-butyl acetate were identified as the ozonation byproducts of MTBE and ETBE, respectively, while tert-butyl alcohol was found to be produced during the ozonation of both compounds.

Effects Of Catalysts During Ozonation Of Salicylic Acid, Peptides And Humic Substances In Aqueous Solution

Abstract The oxidation of two model molecules (salicylic acid and a peptide) and humic substances in aqueous solution was studied using ozone in the presence of various catalysts. Experiments were performed in reactors operated either in batch (TOCo = 2.5 mg C.L−1) or in semi-continuous flow mode (TOCo = 42 mg C.L−1).

Destruction of pollutants in industrial rinse waters by advanced oxidation processes

Recycling process water is a growing need for a variety of industries faced with increasing water costs and environmental constraints. Metal finishing activities such as printed circuit board (PCB) manufacturing generate large volumes of rinse water slightly contaminated with inorganic chemicals and organic additives. While the former can be removed with proven technologies, there is a need for effective processes for elimination of trace organics in order to allow recycling of rinse water without negative impact on process bath quality. A cooperative research project started recently to study a water recycling process adapted to this need, able to remove 95% of the Chemical Oxygen Demand (COD) of the rinse water by combining proven membrane separation with an innovative chemical oxidation. Two types of advanced oxidations based on the conjunction of heterogeneous catalysts with oxidants will be specifically investigated. In a preliminary stage of the project, the experimental tests were performed with a set of model compounds, selected from among the chemicals most frequently used in the plating processes, namely chelating agents, surfactants and corrosion inhibitors. These compounds were oxidized comparatively by ozone and catalytic ozonation. The differences between standard oxidation and catalytic oxidation are presented and discussed.

Modeling the oxidation of atrazine by H2O2/UV. Estimation of kinetic parameters

Abstract A kinetic model for the oxidation of atrazine by H2O2/UV in dilute aqueous solutions ([Atrazine]0 < 2 μM) has been tested in a batch reactor. In this model, direct photolysis and oxidation by hydroxyl radicals are assumed to be the main reactions in the decomposition of atrazine by H2O2/UV. The data showed that the model can be used to predict the effects of some parameters (hydrogen peroxide dose, pH, bicarbonate alkalinity, …) and to estimate values of quantum yield of photolysis, rate constants for the reaction of hydroxyl radicals with atrazine and of the scavenging term (SkiSi) of natural waters.

A new photochemical reactor design for the treatment of absorbing solutions

The recent developments in the field of Advanced Oxidation Processes (AOP) require improvements in reactor design. Indeed, light-induced procedures cannot be used for the removal of micropollutants in strong absorbing solutions. In this work, the technical design concept for mixing in a cylindrical reactor has been approached in a rational way for the treatment of compounds in highly absorbing solutions. The new photochemical reactor perfected in our laboratory consists of an annular reactor with one UV lamp in axial position. However, this reactor differs from classical ones since the rotation of the quartz sleeve protecting the lamp associated with the flux of the solution establishes a Couette-Taylor type flow. This means that toroical eddies are formed between the two surfaces of the cylindrical reactor and thus, periodically, each fraction of liquid comes near the UV source. Three photochemical processes with irradiation at 254 nm have been examined: direct photolysis, H 2 O 2 /UV and TiO 2 /UV for the removal of organic micropollutants such as atrazine and aliphatic acids in strongly absorbant solutions. Para-nitrophenol in the concentration range 1.0 to 2.3 mmol.L −1 (3.0-6.4 cm −1 ) has been added to the water to be treated as a product that absorbs the 254 nm light. The overall effect simulates that of an inner filter absorbing incident photons. In several experiments, para-nitrophenol was replaced by a mineral component bentonite. Experiments showed that under these experimental conditions, for the three photochemical systems, the yield of oxidation was significantly increased as a result of the rotating movement of the central cylinder. This new design will be able to improve the efficiency of commonly used industrial reactors.

Kinetics and mechanisms of the photolytic and OH° radical induced oxidation of fluorinated aromatic compounds in aqueous solutions

Abstract Laboratory experiments with H 2 O 2 /UV oxidation processes and photolysis at 253.7 nm wavelength have been carried out on dilute aqueous solutions (C o = 0.1 to 3.0 mM) of trifluorobenzene derivatives (1,3,5-trifluorobenzene, 1,2,3 and 1,2,4-trifluorobenzene) and of α,α,α-trifluorotoluene in the presence and in the absence of dissolved oxygen. The analyses of fluoride ions content during the oxidation experiments showed that the first steps lead to the production of about 2 mol of F-/mol of trifluorobenzene decomposed and of 1 mol of F − /mol of trifluorotoluene decomposed. Kinetic studies lead to the determination of the quantum yield for the photolysis of 1,3,5-trifluorobenzene, 1,2,3 and 1,2,4-trifluorobenzene ( Φ = 0.011, 0.010 and 0.015 respectively), and of trifluorotoluene ( Φ = 0.015). The rate constants for the reaction of hydroxyl radicals with these molecules, determined under specific experimental conditions, were found to range from 3.7 10 9 to 4.9 10 9 M −1 .s −1 ). GC/MS analyses carried out on extracts at different irradiation time (UV, H 2 O 2 /UV) lead to the identification of numerous by-products from trifluorobenzene and trifluorotoluene. They consist mostly in hydroxylated and dehalogenated compounds. Dimers have also been observed during photolysis. Moreover, experiments carried out under oxygen limiting conditions revealed the formation of other compounds. For each case studied, a detailed mechanism involving radical intermediates and the different reaction sequences is proposed.

Degradation of Formic Acid in Different Oxidative Processes

Abstracts—The decomposition of formic acid by OH radicals produced upon UV irradiation of hydrogen peroxide or in a spark corona discharge between solid electrodes and water surface was studied. Experimental data for both processes are rationalized in terms of the same scheme of transformation of formic acid and various schemes of interaction of active species. The degradation yields in these processes are compared with those obtained in a radiation-chemical process. The yields with reference to the efficiency of the devices were shown to be close in value in all cases.