Voltammetric behavior of triethylamine trihydrofluoride and anisole in acetonitrile as a first approach of studies for electro-fluorination of some adducts

This work focuses on kinetic studies of anisole and triethylamine trihydrofluoride (fluorinating agent) on platinum electrode and acetonitrile as solvent, in order to get a better understanding of their anodic behavior. Results show that both compounds can be oxidized and some kinetic parameters are calculated: the diffusion coefficient within the working media, the anodic electronic transfer coefficient and the apparent intrinsic heterogeneous electronic transfer constant. An unusual variation of these parameters occurs within the chosen reaction conditions, particularly by varying the triethylaminetrihydrofluoride concentration. Preliminary experiments for anodic fluorination of dimethoxy ethane (DME) and anisole were carried out and even if results show a possible electrofluorination for the DME (classically used as solvent), there is no fluorination of anisole when electrochemical microreactor was used

Electrochemical oxidation of oxalic acid and hydrazinium nitrate on platinum in nitric acid media

Several studies in the literature have investigated the electrochemical effects of oxalic acid and hydrazine on various materials in neutral (pH buffered to 7), basic or weakly acidic media (pH 6). The present work proposes electrochemical techniques that allow for the study of the electrochemical behavior, on a Pt electrode, of oxalic acid and hydrazinium nitrate to better understand their oxidation mechanisms in a nitric acid medium at a pH below 1; in addition, some experiments were carried out to define an electrochemical method that would allow for the simultaneous detection of these species when present within process effluent in very acidic solutions. Some physical data regarding oxalic acid and hydrazinium nitrate were also determined: anodic oxidation of hydrazinium nitrate and oxalic acid were observed at 0.2 V and 0.7 V (vs. Ag/AgCl), respectively. The diffusion coefficients of hydrazinium nitrate and oxalic acid were found to be 5.2 × 10−6 and 2.9 × 10−7 cm2 s−1, respectively. An experimental design approach demonstrated the influence of nitric acid concentrations on the diffusion coefficients of these species

Electrochemical study in both classical cell and microreactors of flavin adenine dinucleotide as a redox mediator for NADH regeneration

The electrochemical reduction of flavinadeninedinucleotide (FAD) is studied in a classical electrochemical cell as well as in two types of microreactors: the first one is a one-channel reactor and the other one, a multichannel filter-press reactor. The ultimate goal is to use the reduced form of flavin (FADH2), in the presence of formate dehydrogenase (FDH), in order to continuously regenerate the reduced form of nicotinamide adeninedinucleotide (NADH) for chiral syntheses. Various voltammetric and adsorption measurements were carried out for a better understanding of the redox behavior of the FAD as well as its adsorption on gold. Diffusivity and kinetic electrochemical parameters of FAD were determined

Scalable synthesis of ionic liquids: comparison of performances of microstructured and stirred batch reactors

A range of alkylpyridinium bromide ionic liquids have been synthesized in a stirred reactor at multigram scale and characterized by physical methods (viscosity, conductivity, melting point, electrochemical window, and water content). One ionic liquid, octylpyridinium bromide, was chosen to be synthesized in both macro and reduced scale reactors, in order to compare its performance and to afford evidence of the advantages of a cross channel micro reactor (channel width = 1 mm) compared to a stirred reactor

Acoustic bubbles microstreaming-induced fragmentation of ramified iron electrodeposits in a microchannel

We report on the use of a high aspect ratio microchannel (Hele-Shaw’s cell) in which ramified iron deposits are electrochemically formed and next subjected to acoustic vibrations in order to fragment them into fine particles. Both the electrodes and a piezoelectric element are integrated in the microchannel. High speed visualization allows to highlight the key role of the co-produced H2 bubbles (during the electrodeposition step) which generate microstreaming when subjected to vibrations. The resulting flow pattern sets in motion the ramified iron branches and bring them to bubbles surfaces where they are fragmented into submicrometric particles of iron

Conception et réalisation de microréacteurs électrochimiques (application à la régénération électroenzymatique de NADH et potentialités en synthèse)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Multi-parametric device with innovative all-solid-state electrodes for long term monitoring of pH, redox and conductivity in reconstituted anaerobic water of a future nuclear waste disposal

International audienceNuclear waste disposal are being installed in deep excavated rock formations in some places in Europe to isolate and store radioactive waste. To ensure long term safety and to provide reliable data for future decision making process, it is necessary to implement long-term monitoring sensors. Thereby, robust, sustainable, reliable and autonomous sensors (no-maintenance required) have to be developed to measure the most important physical and chemical parameters.This study aims at developing and optimizing a multi-parametric device composed of all-solid-state electrodes for the long term monitoring of pH, redox potential (ORP) and ionic conductivity. The multi-parametric device consists of a limited number of inert or/and weakly alterable electrodes, allowing auto-controlled and redundant open circuit potential differences measurements in semi-continuous way.Based upon the reversible interfacial redox processes involving H+, Sb2O3/Sb system has been regarded among the most promising technologies to be devoted to the monitoring of pH into the underground components of nuclear disposal due to its physical and chemical stability, with regards to temperature, pressure and aggressive environments1. For redox potential measurements, platinum wires (Pt-Ir alloy; 90-10%) were selected among the “inert” conductive material presenting physical and chemical stability properties. All-Solid-state AgCl/Agcoated/Ag was selected for the development of non-conventional reference electrodes since its potential only depends on Cl- concentration and because the on-site Cl- concentration should remain relatively stable on the long term2.Performance and reliability were examined by potentiometric measurements in various pH buffer solutions at 25°C, under atmospheric conditions as well as in an “oxygen free” gloves box (99% N2, 1% CO2 and [O2]<2ppm). Investigations were limited in pH, ranging from 5.5 to 13.5, close to those encountered in the environment of the nuclear repositories. Robustness was then investigated over six months in a synthetic solution whose composition in major elements and pH was representative of the Callovo-Oxfordian (COx) pore water. For conductivity measurements, both platinum wires as well as AgCl/Agcoated-Ag electrodes were used. The Galvanostatic Electrochemical Impedance Spectroscopy (GEIS) was used, which consisted in applying a known alternating current (AC) between the two most distant electrodes and to measure the induced potential between two other electrodes. The Sb-electrode proved to be reliable for pH measurements. In the absence of any redox couple, except O2/H2O, the platinum electrode showed a linear potentiometric response to pH variations. The all-solid-state AgCl/Agcoated-Ag electrode showed a stable potentiometric response over several months even when subjected to pH variations. According to our results, the long-term monitoring of pH and ORP via the multi-parametric device is feasible. Further investigations are in progress regarding: (i) the influence of redox species such as S(VI)/S(II) or Fe(III)/Fe(II) and (ii) corrosion rates of each electrode materials in order to estimate electrodes lifetime and therefore of the device

A Multi-Parametric Device with Innovative Solid Electrodes for Long-Term Monitoring of pH, Redox-Potential and Conductivity in a Nuclear Waste Repository

International audienc

Détermination du mécanisme de déchloration réductrice de l'hexachlorobutadiène et de l'hexachloroéthane par des particules bimétalliques Pd/Fe à l'aide d'un suivi indirect de la corrosion du fer

International audienceCette étude est dédiée à la compréhension du mécanisme de déchloration réductrice de l'hexachlorobutadiène (HCBD, C4Cl6) et de l'hexachloroéthane (HCA, C2Cl6) par des particules bimétalliques Pd/Fe en suspension dans un mélange de polymères et d'oligomères d'acide lactique (PLA). Elle est basée sur l'utilisation d'un suivi indirect en continu de la corrosion du fer par mesure du pH, du potentiel d'oxydo-réduction et de la conductivité de la solution, en plus des analyses chromatographiques permettant la quantification des composés organiques chlorés. Les essais ont été réalisés en réacteur fermé selon différentes conditions expérimentales visant à déterminer l'influence de la quantité de particules Pd/Fe, de la concentration initiale en polluant, de la quantité de PLA et de la température. L'inter-comparaison des résultats a permis de mettre en évidence le mécanisme de déchloration des deux polluants. La corrosion aqueuse du fer entraîne la génération d'hydrogène atomique au niveau du palladium, permettant l'hydrodéchloration des polluants. Durant le traitement, seul le PCE a été quantifié lors de la réduction de HCA ; ainsi, aucune accumulation de sous-produits chlorés toxiques en solution tels que le TCE et le chlorure de vinyle n'a été observée. Les variations au cours du temps du pH, du potentiel redox et de la conductivité ont permis de comprendre l'effet de chacun des paramètres étudiés sur la corrosion des particules. Les résultats ont montré la bonne corrélation entre l'évolution des paramètres, la cinétique de corrosion des particules et la déchloration réductrice de HCBD et HCA dans les différentes conditions expérimentales, démontrant l'intérêt de ce type de suivi en continu. L'avantage de ce dernier est qu'il peut être facilement implémenté sur site pour obtenir des informations sur l'évolution des conditions géochimiques des eaux souterraines durant le traitement par réduction chimique

SILPHES – Investigation of chemical treatments for the remediation of recalcitrant chlorinated solvents: at the roots the development of an innovative in situ eco-friendly process

International audienceThis study is accomplished within the framework of SILPHES financed by ADEME, the French Environment and Energy Management Agency (AMI 2013 program). SILPHES is a "technology demonstrator" project which aims at developing innovative solutions for in situ remediation of a mixture of recalcitrant chlorinated solvent, mainly composed of hexachlorobutadiene, hexachloroethane, PCE, TCE and hexachlorobenzene. SILPHES is organized around two fundamental and complementary tasks:-The remediation of chlorinated solvents point source pollution. This part is devoted to the optimization of the treatment of the point source, which includes physical, chemical and thermal treatments, associated with diagnostic and monitoring;-The remediation of chlorinated solvents plume. This part is devoted to the improvement of environmental diagnosis and the design and monitoring of natural attenuation, bioremediation or chemical treatment.This paper only covers a part of the first point stated above, i.e. the remediation of the residual phase of chlorinated solvents remaining after pumping