Papers by Alexandre CHAGNES
Langmuir, 2004
Original and versatile new materials for the electrocatalytic hydrogenation of organic compounds ... more Original and versatile new materials for the electrocatalytic hydrogenation of organic compounds were designed. The materials consist of reticulated glassy carbon cathode electrodes in which the modified silica particles (average diameter 40-63 microm) were dynamically circulated. The modification of the silica surface is 2-fold. First, the silica is surface-modified using organic functions such as -OSi(CH3)2(CH2)3OCH2CH-(OH)(CH)2OH (SiO2-Diol), -OSi(CH3)2(CH2)7CH3 (SiO2-C8), and -OSi(CH3)2C6H5 (SiO2-Phenyl). Second, these silica particles were further modified by vapor phase deposition of nickel nanoaggregates (used as sites for hydrogen atoms and electric contacts with the electrode material), which does not destroy or alter the organic functionalization as demonstrated by thermogravimetric analysis-mass spectrometry and Raman, diffuse reflectance IR Fourier transform, and Auger electron spectroscopies. The new concept stems from relative adsorption and desorption properties of the organic molecules and their corresponding reduced products into the organic functionalization of the surface-modified silica. In this work, the electrocatalytic hydrogenation cyclohexanone was used to test the concept. The performances (amount of cyclohexanol vs time of generated electrolysis at constant current) are measured and compared for the various bonded organic functions of the silica surface listed above, along with the unmodified silica particles (but still containing nickel nanoaggregates) and the presence or absence of methanol in solution. The measurements of the adsorption isotherms of cyclohexanone, and the calculations of the interaction energies (MM3 force field) between the chemisorbed organic functions and the substrates, corroborate perfectly the electrocatalysis results.
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Canadian Journal of Chemistry-revue Canadienne De Chimie, 2004
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Solvent Extraction and Ion Exchange, 2012
Relationships between metal chelate stability, ligand basicity, and metal ion acidity are reviewe... more Relationships between metal chelate stability, ligand basicity, and metal ion acidity are reviewed and the general applicability is illustrated by linear correlations between aqueous stability constants and ligand pKa values for 35 metals with 26 ligands. The results confirm that most individual ligands of this type exhibit a stability ordering that correlates with the Lewis acidity of the metal ion. It is concluded that the general metal ion selectivity exhibited by liquid-liquid oxoacid extractants such as carboxylic acids, β-diketones, and organophosphorus acids reflects the intrinsic affinity of the metal ion for the negative oxygen donor ligand.
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Applied Surface Science, 2011
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Hydrometallurgy, 2011
... Liquidliquid extraction is a well-established technique for the production of both base and ... more ... Liquidliquid extraction is a well-established technique for the production of both base and strategic metals (Cote, 2000). ... III) in the reprocessing of used nuclear fuels but which were found to be fragile against degradation under chemical and radiolytical stresses (Drew et al ...
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Solvent Extraction and Ion Exchange, 2012
The kinetics of degradation of a mixture of tri-n-octylamine (extractant) and various alcoholic p... more The kinetics of degradation of a mixture of tri-n-octylamine (extractant) and various alcoholic phase modifiers in n-dodecane in contact with acidic aqueous sulfate solutions containing vanadium (V) has been investigated. The nature of the modifier influences the kinetics of degradation and an improvement of the resistance against the chemical degradation is obtained when secondary alcohol (2-nonanol) or tertiary alcohols such as 9-octyl-9-heptadecanol are used as phase modifiers instead of 1-tridecanol. For instance, the kinetic constant of degradation is divided by one half when 9-octyl-9-heptadecanol is used as phase modifier instead of 1-tridecanol. On the contrary, the alcohols containing aromatic substituents or fluorine atoms are responsible for an increase of the chemical degradation of the extraction solvent.
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Journal of Chemical Technology and Biotechnology, 2009
BACKGROUND: The extractants used in solvent extraction processes undergo degradation under therma... more BACKGROUND: The extractants used in solvent extraction processes undergo degradation under thermal, chemical and radiolytical stresses. In the case of uranium plants, tri-n-octylamine, used as an extractant, slowly degrades into di-n-octylamine. Such degradation causes a gradual depletion of the uranium extraction isotherms and as a result, of the efficiency of uranium recovery from feed solutions. The present work highlights a new route to delay this depletion of the extraction efficiency, merely by optimizing the flow-sheets involved in the process. Five flow-sheets have been compared for uranium recovery from acidic sulfate media by a solution of 0.146 mol L−1 tri-n-octylamine in kerosene modified with 5% w/w 1-tridecanol and stripping with a 199 g L−1 Na2CO3 solution. These five flow-sheets include the classical counter-current flow-sheet with four mixers–settlers in extraction and three mixers–settlers in stripping and four unusual combined solvent extraction flow-sheets with two independent extraction stripping loops and with one or two feed inlets.RESULTS: Computer simulation supplied evidence of the strong influence of the studied flow-sheets on the sturdiness of the process. More precisely, the unusual combined solvent extraction flow-sheets appeared to be significantly more efficient than the classical counter-current one and it is shown that an advantage of this can be to delay the negative impact of gradual degradation of tri-n-octylamine on uranium recovery efficiency from acidic sulfate media.CONCLUSION: The replacement of classical counter-current flow-sheets with a unique extraction-stripping loop in unusual combined flow-sheets with two or more independent extraction-stripping loops and with one or more feed inlets is a fruitful approach to delay the periodic addition of fresh tri-n-octylamine necessary for counter-balancing the progressive degradation of the extraction solvent and, as a result, to delay the gradual depletion of the efficiency of uranium recovery. Copyright © 2009 Society of Chemical Industry
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Hydrometallurgy, 2010
The speciation of vanadium (V) extracted from acidic sulfate media by protonated trioctylamine in... more The speciation of vanadium (V) extracted from acidic sulfate media by protonated trioctylamine in n-dodecane modified with 5% (wt) 1-tridecanol has been investigated by Fourier transformed infrared spectroscopy (FTIR) and 51V nuclear magnetic resonance spectroscopy (51V NMR). In aqueous sulfate solutions, vanadium (V) exists both as VO2+ and VO2SO4− ions. The FTIR spectra of 0.2molkg−1 protonated trioctylamine in n-dodecane modified
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Physical Chemistry Chemical Physics, 2011
Density functional theory calculations were performed on uranyl complexed with nitrate and monoam... more Density functional theory calculations were performed on uranyl complexed with nitrate and monoamide ligands (L) [UO(2)(NO(3))(2)·2L]. The obtained results show that the complex stability is mainly governed by two factors: (i) the maximization of the polarizability of the coordinating ligand and (ii) the minimization of the steric hindrance effects. Furthermore, the electrostatic interaction between ligands and uranium(vi) was found to be a crucial parameter for the complex stability. These results pave the way to the definition of (quantitative) property/structure relationships for the in silico screening of monoamide ligands with improved extraction efficiency of uranium(vi) in nitrate acidic solution.
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Journal of Chemical Technology and Biotechnology, 2009
BACKGROUND: A series of nine conventional and non-conventional flow-sheets have been considered f... more BACKGROUND: A series of nine conventional and non-conventional flow-sheets have been considered for the recovery of uranium from acidic sulfate solution by liquid–liquid extraction with 0.146 mol L−1 Alamine® 336 in kerosene modified with 5% w/w 1-tridecanol and stripping with a 199 g L−1 Na2CO3 solution. The reference flow-sheet was a classical counter-current configuration with four mixers–settlers in the extraction stage and three mixers–settlers in the stripping stage. The others flow-sheets possessing a total of eight mixers–settlers are unusual combined solvent extraction flow-sheets with one or two independent extraction stripping loops and with one or two feed inlets.RESULTS: The configuration of the flow-sheets strongly influences the extraction performance of the process depending on the working conditions (feed, stripping and solvent flow rates). The presence of two independent extraction–stripping loops may allow the delay of the saturation phenomenon encountered in the conventional flow-sheet and thus, to operate at higher feed flow rates without loss of performance, as far as the residual fraction in the raffinate and the concentration factor in the stripping solution are concerned. Furthermore, the presence of a modification in the non-conventional flow-sheets with two independent extraction–stripping loops and two feed inlets leads to interesting configurations for uranium recovery from less concentrated solutions, such as heap leach solutions.CONCLUSION: The use of non-conventional flow-sheets is interesting as it allows the process of uranium (VI) recovery by liquid–liquid extraction to be improved. Copyright © 2009 Society of Chemical Industry
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Journal of Power Sources, 2006
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Journal of Power Sources, 2005
... concerns the research of performant electrolytes for low or high temperature applications suc... more ... concerns the research of performant electrolytes for low or high temperature applications such as military, space applications or electric vehicle. ... Ionic liquid may an alternative to classical electrolytes for lithium batteries owing to their low vapor pressure, their non-flammability ...
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Journal of Applied Electrochemistry, 2003
γ-Butyrolactone-ethylene carbonate (BL-EC) mixtures have been investigated as electrolytes for Li... more γ-Butyrolactone-ethylene carbonate (BL-EC) mixtures have been investigated as electrolytes for Li-ion batteries using LiPF6 and LiBF4 as lithium salt. The thermal stability of the electrolytes in a large range of temperatures (−90 °C to 40 °C) have been studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). From the results of these experiments, the phase diagram of the BL-EC system has been determined. It is characterised by a eutectic point at −56.3 °C and a molar fraction in EC: x EC = 0.1. A metastable compound has been demonstrated below −90 °C at x EC = 0.4. Conductivity measurements of BL-EC solutions, in the presence of LiPF6 and LiBF4, indicate that LiPF6 in the eutectic mixture is the most conducting electrolyte in the range of temperatures investigated (−30 °C to room temperature). Nevertheless, at low temperature, LiBF4 based electrolytes compete well with LiPF6, especially when the amount of EC in the mixture is as high as x EC = 0.5. Moreover, recrystallisation of the salt below −20 °C is avoided when LiBF4 is used as salt. A large increase in viscosity of the solvent mixture is observed when a salt is added, but the increase is lower for LiBF4 than LiPF6. When EC is added to BL at constant salt concentration (1 M), the conductivity of LiPF6 solutions decreases more rapidly than LiBF4 solutions. This has been attributed, at least partially, to the dissociating power of EC. The electrochemical windows of BL-EC (equimolar) mixtures in the presence of LiPF6 and LiBF4 are comparable but it is shown that the solvents oxidation rate at high potentials is lower when LiBF4 is used.
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Chemphyschem, 2003
An algorithm is proposed for calculating the energy of ion–dipole interactions in concentrated or... more An algorithm is proposed for calculating the energy of ion–dipole interactions in concentrated organic electrolytes. The ion–dipole interactions increase with increasing salt concentration and must be taken into account when the activation energy for the conductivity is calculated. In this case, the contribution of ion–dipole interactions to the activation energy for this transport process is of the same order of magnitude as the contribution of ion–ion interactions. The ion–dipole interaction energy was calculated for a cell of eight ions, alternatingly anions and cations, placed on the vertices of an expanded cubic lattice whose parameter is related to the mean interionic distance (pseudolattice theory). The solvent dipoles were introduced randomly into the cell by assuming a randomness compacity of 0.58. The energy of the dipole assembly in the cell was minimized by using a Newton–Raphson numerical method. The dielectric field gradient around ions was taken into account by a distance parameter and a dielectric constant of ε=3 at the surfaces of the ions. A fair agreement between experimental and calculated activation energy has been found for systems composed of γ-butyrolactone (BL) as solvent and lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as salts.
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Journal of Chemical Thermodynamics, 2002
Thermodynamic data on liquid mixtures are usually expressed as excess quantities and analysed wit... more Thermodynamic data on liquid mixtures are usually expressed as excess quantities and analysed with the Redlich–Kister equation. Excess molar volume, excess viscosity, excess dielectric constant, and excess Gibbs energy of activation flow are calculated for γ-butyrolactone (BL) and dimethylcarbonate (DMC) mixtures at T=298.15K and atmospheric pressure over the complete composition range. All these excess thermodynamics functions shows that DMC is
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Journal of Solution Chemistry, 2004
The shear viscosities of ionic fluids composed of ethylammonium nitrate (EAN) and methanol (MeOH)... more The shear viscosities of ionic fluids composed of ethylammonium nitrate (EAN) and methanol (MeOH) have been investigated as a function of the shear rate, the composition of the mixtures (quoted as x, the mole fraction of EAN), and the temperature (T) in the range 293–328 K. At low content of EAN (0.2 ≤ x ≤ 0.4), the solutions exhibit a non-Newtonian and a non-Arrhenius behavior. The viscosities of these solutions increase with the temperature when T > 313 K, but they are independent of the temperature at x = 0.6 and decrease for x > 0.6. Excess viscosities and excess Gibbs energies for the viscosity give evidence of the formation of strong hydrogen bonded complexes in solution for x < 0.6 and T > 318 K. For these systems, any increase in temperature favors the formation of hydrogen bonds between EAN and MeOH.
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Electrochimica Acta, 2001
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Journal of Power Sources, 2005
γ-Butyrolactone (BL) has been mixed to the room temperature ionic liquid (RTIL) 1-butyl 3-methyl-... more γ-Butyrolactone (BL) has been mixed to the room temperature ionic liquid (RTIL) 1-butyl 3-methyl-imidazolium tetrafluoroborate (BMIBF4) (ratio: 3/2, v/v) in the presence of lithium tetrafluoroborate (LiBF4) for use as electrolyte in lithium-ion batteries. This mixture exhibits a larger thermal stability than the reference electrolyte EC/DEC/DMC (2/2/1)+LiPF6 (1M) and can be considered as a new RTIL as no free BL molecules
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Journal of Power Sources, 2002
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Papers by Alexandre CHAGNES