Kinetics of the oxidation of methyl tert-butyl ether (MTBE) by potassium permanganate

The occurrence of the fuel oxygenate methyl tert-butyl ether (MTBE) in the environment has received considerable scientific attention. The pollutant is frequently found in the groundwater due to leaking of underground storage tanks or pipelines. Concentrations of more than several mg/L MTBE were detected in groundwater at several places in the US and Germany in the last few years. In situ chemical oxidation is a promising treatment method for MTBE-contaminated plumes. This research investigated the reaction kinetics for the oxidation of MTBE by permanganate. Batch tests demonstrated that the oxidation of MTBE by permanganate is second order overall and first order individually with respect to permanganate and MTBE. The second-order rate constant was 1.426 x 10(-6) L/mg/h. The influence of pH on the reaction rate was demonstrated to have no significant effect. However, the rate of MTBE oxidation by potassium permanganate is 2-3 orders of magnitude lower than of other advanced oxidation processes. The slower rates of MTBE oxidation by permanganate limit the applicability of this process for rapid MTBE cleanup strategies. However, permanganate oxidation of MTBE has potential for passive oxidation risk management strategies. (C) 2002 Elsevier Science Ltd. All rights reserved.

Absolute atomic oxygen density profiles in the discharge core of a microscale atmospheric pressure plasma jet

The micro atmospheric pressure plasma jet is an rf driven (13.56 MHz, ~20 W) capacitively coupled discharge producing a homogeneous plasma at ambient pressure when fed with a gas flow of helium (1.4 slm) containing small admixtures of oxygen (~0.5%). The design provides excellent optical access to the plasma core. Ground state atomic oxygen densities up to 3x1016 cm-3 are measured spatially resolved in the discharge core by absolutely calibrated two-photon absorption laser-induced fluorescence spectroscopy. The atomic oxygen density builds up over the first 8 mm of the discharge channel before saturating at a maximum level. The absolute value increases linearly with applied power.

Atomistic studies of <110] screw dislocation core structures and glide in γ-TiAl

The core structure of <110] superdislocations in L10 TiAl was investigated with a view to clarifying their dissociation abilities and the mechanisms by which they may become sessile by self-locking. A detailed knowledge of the fine structure of dislocations is essential in analysing the origin of the various deformation features. Atomistic simulation of the core structure and glide of the screw <110] superdislocation was carried out using a bond order potential for ?-TiAl. The core structure of the screw <110] superdislocation was examined, starting with initial unrelaxed configurations corresponding to various dislocation dissociations discussed in the literature. The superdislocation was found to possess in the screw orientation either planar (glissile) or non-planar (sessile) core structures. The response of the core configurations to externally applied shear stress was studied. Some implications were considered of the dissociated configurations and their response to externally applied stress on dislocation dynamics, including the issue of dislocation decomposition, the mechanism of locking and the orientation dependence of the dislocation substructure observed in single-phase ?-TiAl. An unexpectedly rich and complex set of candidate core structures, both planar and non-planar, was found, the cores of which may transform under applied stress with consequent violation of Schmid's law.

Physicochemical Characterization of Poly(ethylene glycol) Plasticized Poly(methyl vinyl ether-co-maleic acid) Films

The influence of the poly(ethylene glycol) (PEG) plasticizer content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) was investigated with tensile mechanical testing, thermal analysis, and attenuated total reflectance/Fourier transform infrared spectroscopy. Unplasticized films and those containing high copolymer contents were very difficult to handle and proved difficult to test. PEG with a molecular weight of 200 Da was the most efficient plasticizer. However, films cast from aqueous blends containing 10% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 4 : 3 and those cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 2 : 1 possessed mechanical properties most closely mimicking those of a formulation we have used clinically in photodynamic therapy. Importantly, we found previously that films cast from aqueous blends containing 10% (w/w) PMVE/MA performed rather poorly in the clinical setting, where uptake of moisture from patients' skin led to reversion of the formulation to a thick gel. Consequently, we are now investigating films cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000, where the copolymer/plasticizer ratio is 2 : 1, as possible Food and Drug Administration approved replacements for our current formulation, which must currently be used only on a named patient basis as its plasticizer, tripropylene glycol methyl ether, is not currently available in pharmaceutical grade

Extraction of cesium ions from aqueous solutions using calix[4]arene-bis(tert-octylbenzo-crown-6) in ionic liquids

Solvent extraction of cesium ions from aqueous solution to hydrophobic ionic liquids without the introduction of an organophilic anion in the aqueous phase was demonstrated using calix[4]arene-bis(tert-octylbenzo-crown-6) (BOBCalixC6) as an extractant. The selectivity of this extraction process toward cesium ions and the use of a sacrificial cation exchanger (NaBPh4) to control loss of imidazolium cation to the aqueous solutions by ion exchange have been investigated.