Jacques E. Desnoyers

Treatment of excess thermodynamic quantities for liquid mixtures

Thermodynamic data on mixtures of liquids are usually expressed as excess quantitiesYEX and analyzed with the Redlich-Kister equation. This approach can in some cases be misleading and hide strong interactions at low concentrations. In agreement with the original statement of Redlich and Kister, it is therefore better to plot such data asYEX/X2(1-X2). This quantity, which is directly related to the apparent molar quantities of both components, is often a more useful quantity and has just as much a thermodynamic significance asYEX.

Stable solvates in solution of lithium bis(trifluoromethylsulfone)imide in glymes and other aprotic solvents: Phase diagrams, crystallography and Raman spectroscopy

Lithium bis(trifluoromethylsulfone)imide (LiTFSI), a promising electrolyte for high energy lithium batteries, forms several stable solvates having low melting points in aprotic solvents. In a previous study (D. Brouillette, G. Perron and J. E. Desnoyers, J. Solution Chem., 1998, 27, 151), it was suggested, based on thermodynamic studies, that such stable solvates may persist in solution and influence their properties. To verify this hypothesis, phase diagrams and Raman spectra have been measured for solutions of LiTFSI in acetonitrile, propylene carbonate and glymes (n(ethyleneglycol) dimethyl ether or Gn), which have the chemical structure CH3–O–(CH2–CH2–O)n–CH3 for n = 1 to 4 and 10. The relative intensities of the LiTFSI and solvent Raman bands are proportional to the concentration for systems without solvates. The systems for which stable solvates were identified in the phase diagram show important changes in the relative intensities for both the LiTFSI and the solvent Raman bands at concentrations corresponding to particular stoichiometries and support the conclusion that stable solvates are present in the solutions. The structure of the crystalline G1:LiTFSI solvate was determined by X-ray crystallography. Structures for (G2)2:LiTFSI and (G1)3:LiTFSI solvates are proposed.

Apparent Molar Volume, Heat Capacity, and Conductance of Lithium Bis(trifluoromethylsulfone)imide in Glymes and Other Aprotic Solvents

Lithium bis(trifluoromethylsulfone)imide (LiTFSI) is a promising electrolyte for high-energy lithium batteries due to its high solubility in most solvents and electrochemical stability. To characterize this electrolyte in solution, its conductance and apparent molar volume and heat capacity were measured over a wide range of concentration in glymes, tetraethylsulfamide (TESA), acetonitrile, γ-butyrolactone, and propylene carbonate at 25°C and were compared with those of LiClO4 in the same solvents. The glymes or n(ethylene glycol) dimethyl ethers (nEGDME), which have the chemical structure CH3−O−(CH2−CH2−O)n−CH3 for n = 1 to 4, are particularly interesting since they are electrochemically stable, have a good redox window, and are analogs of the polyethylene oxides used in polymer-electrolyte batteries. TESA is a good plasticizer for polymer-electrolyte batteries. Whenever required, the following properties of the pure solvents were measured: compressibilities, expansibilities, temperature and pressure dependences of the dielectric constant, acceptor number, and donor number. These data were used in particular to calculate the limiting Debye-Hückel parameters for volumes and heat capacities. The infinite dilution properties of LiTFSI are quite similar to those of other lithium salts. At low concentrations, LiTFSI is strongly associated in the glymes and moderately associated in TESA. At intermediate concentrations, the thermodynamic data suggests that a stable solvate of LiTFSI in EGDME exists in the solution state. At high concentrations, the thermodynamic properties of the two lithium salts approach those of the molten salts. These salts have a reasonably high specific conductivity in most of the solvents. This suggests that the conductance of ions at high concentration in solvents of low dielectric constant is due to a charge transfer process rather than to the migration of free ions.

Aquifer washing by micellar solutions: 1: Optimization of alcohol–surfactant–solvent solutions

Abstract Phase diagrams were used for the formulation of alcohol–surfactant–solvent and to identify the DNAPL (Dense Non Aqueous Phase Liquid) extraction zones. Four potential extraction zones of Mercier DNAPL, a mixture of heavy aliphatics, aromatics and chlorinated hydrocarbons, were identified but only one microemulsion zone showed satisfactory DNAPL recovery in sand columns. More than 90 sand column experiments were performed and demonstrate that: (1) neither surfactant in water, alcohol–surfactant solutions, nor pure solvent can effectively recover Mercier DNAPL and that only alcohol–surfactant–solvent solutions are efficient; (2) adding salts to alcohol–surfactant or to alcohol–surfactant–solvent solutions does not have a beneficial effect on DNAPL recovery; (3) washing solution formulations are site specific and must be modified if the surface properties of the solids (mineralogy) change locally, or if the interfacial behavior of liquids (type of oil) changes; (4) high solvent concentrations in washing solutions increase DNAPL extraction but also increase their cost and decrease their density dramatically; (5) maximum DNAPL recovery is observed with alcohol–surfactant–solvent formulations which correspond to the maximum solubilization in Zone C of the phase diagram; (6) replacing part of surfactant SAS by the alcohol n -butanol increases washing solution efficiency and decreases the density and the cost of solutions; (7) replacing part of n -butanol by the nonionic surfactant HOES decreases DNAPL recovery and increases the cost of solutions; (8) toluene is a better solvent than D -limonene because it increases DNAPL recovery and decreases the cost of solutions; (9) optimal alcohol–surfactant–solvent solutions contain a mixture of solvents in a mass ratio of toluene to D -limonene of one or two. Injection of 1.5 pore volumes of the optimal washing solution of n -butanol–SAS–toluene– D -limonene in water can recover up to 95% of Mercier DNAPL in sand columns. In the first pore volume of the washing solution recovered in the sand column effluent, the DNAPL is in a water-in-oil microemulsion lighter than the excess aqueous phase (Winsor Type II system), which indicates that part of the DNAPL was mobilized. In the next pore volumes, DNAPL is dissolved in a oil-in-water microemulsion phase and is mobilized in an excess oil phase lighter than the microemulsion (Winsor Type I system). The main drawback of this oil extraction process is the high concentration of ingredients necessary for DNAPL dissolution, which makes the process expensive. Because mobilization of oil seems to occur at the washing solution front, an injection strategy must be developed if there is no impermeable limit at the aquifer base. DNAPL recovery in the field could be less than observed in sand columns because of a smaller sweep efficiency related to field sand heterogeneities. The role of each component in the extraction processes in sand column as well as the Winsor system type have to be better defined for modeling purposes. Injection strategies must be developed to recover ingredients of the washing solution that can remain in the soil at the end of the washing process. ©1997 Elsevier Science B.V.

Sulfamides and Glymes as Aprotic Solvents for Lithium Batteries

In view of the high reactivity of the lithium metal, lithium batteries must operate in an aprotic environment, which can either be a conducting polymer, a liquid solvent, or a mixture of them. Two families of aprotic liquids were considered as solvents for lithium bis(trifluoromethylsulfone)imide (LiCF{sub 3}SO{sub 2}NSO{sub 2}CF{sub 3} or LiTFSI). The first one is the substituted sulfamides, R{sub 1}R{sub 2}NSO{sub 2}NR{sub 3}R{sub 4}, where the R groups are either methyl, ethyl, or methoxyethyl (CH{sub 2}CH{sub 2}OCH{sub 3}), and the second one is the glymes, CH{sub 3}O(CH{sub 2}CH{sub 2}O){sub n}CH{sub 3}, for n up to 10. The phase diagrams, potential windows, conductivities, and the lithium interfacial resistances of the solutions were investigated, often as a function of temperature. The potential use of these solvents for different types of batteries is discussed.

Effect of viscosity and volume on the specific conductivity of lithium salts in solvent mixtures

As part of a study on the optimization of the electrolyte for high energy lithium batteries, the conductivity, viscosity and density of LiAsF6, LiBr, and LiClO4 were measured in aprotic solvent mixtures. The conductivity of lithium bis(trifluoromethylsulfone)imide (LiTFSI) was also obtained in a large number of mixed aprotic solvents. The solvents were chosen to verify the effect of various parameters such as viscosity, permittivity, volume, acceptor number and donor number on the conductivity. These results were used to develop a simple model for excess conductivities based on the viscosity and volume of the pure solvents. Without adjustable parameters, this model predicts the correct sign of the excess conductivities in ≈90% of the cases and the magnitude of the conductivity of the ternary mixtures within an average of 15%. Deviations from the predictions are mostly observed with solvents of low permittivity and this supports the hypothesis that a different conduction mechanism is in operation at high concentration in these solvents, and the solvating power of these solvents plays an important role in this mechanism.

Dielectric constants of acetonitrile, γ-butyrolactone, propylene carbonate, and 1,2-dimethoxyethane as a function of pressure and temperature

The dielectric constants ∈ of 1,2-dimethoxyethane, acetonitrile, γ-butyrolactone, and propylene carbonate were determined from capacitance measurements extrapolated to infinite frequency; ln ∈ are reported as a function of pressure up to 80 MPa at 15, 25, 35, 45°C and as a function of temperature in the range 10 to 50°C at 0.10133 MPa. The variation of ln ∈ with temperature or pressure can be expressed by a second order polynomial expression. The isothermal compressibilities β of the solvents were determined at 25°C from sound velocities, densities, and heat capacities. A simple correlation can be established between ∂ ln ∈/∂P and β for most aprotic solvent.

Dispersion of crude oil in seawater: The role of synthetic surfactants

Abstract Over the last two decades, the use of chemical dispersants as a countermeasure to oil spills at sea has become accepted worldwide. The recent development of more efficient and less toxic dispersants has renewed interest for basic studies on dispersant improvement and on the fate of dispersed oil in seawater. This work reports interfacial tensions and the effectiveness in oil dispersion of many synthetic, commercially available surfactants when used alone and in various blends. The results are discussed in terms of the local structure of the oil-water interface. The maximum efficiency is reached when the surfactant molecules have a structure compatibility and can form stable arrangements at the interface. An improved knowledge of interfacial phenomena responsible for the oil dispersion helps in formulating better dispersants by guiding a judicious combination of surfactants in appropriate proportions.

Correlation of the volumes and heat capacities of solutions with their solid-liquid phase diagrams

Liquid systems which have strong non-idealities, as seen from their thermodynamic properties, often show evidence of these interactions in the solid-liquid phase diagrams. This suggests that some of the structures present in the solid state can persist in the solution state, on a time average, up to temperatures much higher than the melting point. Volumes and heat capacities of typical systems were either taken from the literature or measured to illustrate this correlation with the phase diagrams. With mixtures of aprotic solvents which show nearly-ideal simple eutectic phase diagrams, the properties of the solutions are also nearly ideal. Examples of systems investigated which show strong non-idealities are ionic surfactant solutions, alcohol-water mixtures, chloroform-triethylamine mixtures and lithium salts in aprotic solvents.

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.