Cette thèse a pour objectif l’étude et la mise au point d’un procédé de fabrication, par cristallisation, de sel thermal enrichi en magnésium, à partir d’eaux minérales naturelles chlorurées sodiques fortes. Un modèle dynamique a d’abord été développé pour la simulation du procédé. Ce modèle est basé sur la description des phénomènes physico-chimiques intervenant dans les équilibres thermodynamiques multiphasiques (liquide, vapeur, solides). Puis, un pilote de laboratoire a été mis en place pour vérifier la faisabilité du procédé et valider le modèle développé. Le pilote proposé est constitué de deux réacteurs en série entre lesquels est placé un système de filtration. Une étude expérimentale et par modélisation du procédé avec l’eau thermale de Salies-de-Béarn a ensuite été réalisée. Cette étude montre qu’il est possible de produire un sel thermal ou une eau-mère naturellement enrichis en magnésium. / The aim of this thesis is the study and the development of a production process, by cristallization, of thermal salt enriched in magnesium, from highly chlorinated natural waters. At first, a dynamic model was developed for the process simulation. This model is based on the description of physical-chemical phenomena occurring in multiphase thermodynamic equilibrium (liquid, vapor, solids). Then, a laboratory pilot was set up to check the process feasibility and to validate the developed model. The proposed pilot is a series of two reactors between which is placed a filtration system. Finally, an experimental and modeling study of the process has been realized with thermal water of Salies-de-Béarn as raw-material. This study shows that it is possible to produce a thermal salt or mother liquor naturally enriched in magnesium.

Values of the rate constant for the alkaline hydrolysis of methyl acetate in various aqueous-organic solvent mixtures (dimethyl sulfoxide 0<x40.2, dioxane 0 <, x., < 0.2, methyl ethyl ketone 0<x<0.06 and diglyme, i. e. ether-bis (2-methyloxethyl) 0x<0.10) have been determined for the temperatures 15 0 C, 25 0C and 35 0C conductometrically. To interpret these results the approach adapted is to experimentally determine the activity coefficient of the ester (YE ) and the activity of the water (aH20', mechanistically, at least one molecule of water is involved in the rate-determining step) and then to use the Bronsted-Bjerrum equation to determine the residual activity coefficient ratio of the participating ions, y (Yf - for Oil the transition state). Values of YE and aH 20 have been determined by a transpiration method, using gas-chromatographic analysis of the vapours of solutions of methyl acetate in aqueous-organic solvent mixtures of dir. ethyl sulfoxide, dioxane, methyl ethyl ketone and diglyme in the same composition ranges as above, tetrahydrofuran 04x org z<, 0.15, methanol, ethanol and tert-butanol in t1h6e range 04x0.20'at 25oC. These results indicate that on changing org the solvent composition YE varies by a larger factor than is predicted for the ratio YOH-/yýO_ by the Debye-Iluckel approach, and hence is the dominant factor in determining the effects of solvent composition on the rates of the hydrolysis. This is in contradiction to the assumptions of the electrostatic theories of Laidler and Eyring, and of Amis and Jaffe. The gas-chromatographic results also indicate that whilst the concentration of the water varies in each mixture studied, the activity coefficient varies in the opposite way to produce almost constant values of aý, 0* Using the transpiratioii/gas-chromatogralýlic method, the thermodynamic properties of the ternary systems, methyl acetate-water-organic Solvcat, using the organic solvents mentioned above (excepting, diglyme) have been investigated, and the results indicate that the variation of *ýE with solvent composition, for the dilute solutions of ester used, can be estimated from the thermodynamic properties of the binary water-organic solvent mixtures, using the Gibbs-Dahem equation. Single ion activity coefficients in the literature for small negative ions, to represent the OH_ ion, and for large ions, to rep-resent the transition state ion, have been used to explain the experimentally fomd variation of the residual activity coefficient -ratio with solvent composition. Hence, it is concluded that the importance of the parameters involved in the hydrolysis of esters - an ion-molecule reaction - in aqueousorganic solvent mixtures are in the order of Ymolecule > aH 20> YOH_/YM+ -> (dielectric constant), and that the nonelectrostatic effects -- thermodynamic effects - are more important in these studies than the electrostatic effects. From a preliminary investigation of the data in the literature the thermodynamic approach also yields a valid interpretation of the effect of solvent composition on the rates of the acid hydrolysis of esters.

Values of the rate constant for the alkaline hydrolysis of methyl acetate in various aqueous-organic solvent mixtures (dimethyl sulfoxide 0<x40.2, dioxane 0 <, x., < 0.2, methyl ethyl ketone 0<x<0.06 and diglyme, i. e. ether-bis (2-methyloxethyl) 0x<0.10) have been determined for the temperatures 15 0 C, 25 0C and 35 0C conductometrically. To interpret these results the approach adapted is to experimentally determine the activity coefficient of the ester (YE ) and the activity of the water (aH20', mechanistically, at least one molecule of water is involved in the rate-determining step) and then to use the Bronsted-Bjerrum equation to determine the residual activity coefficient ratio of the participating ions, y (Yf - for Oil the transition state). Values of YE and aH 20 have been determined by a transpiration method, using gas-chromatographic analysis of the vapours of solutions of methyl acetate in aqueous-organic solvent mixtures of dir. ethyl sulfoxide, dioxane, methyl ethyl ketone and diglyme in the same composition ranges as above, tetrahydrofuran 04x org z<, 0.15, methanol, ethanol and tert-butanol in t1h6e range 04x0.20'at 25oC. These results indicate that on changing org the solvent composition YE varies by a larger factor than is predicted for the ratio YOH-/yýO_ by the Debye-Iluckel approach, and hence is the dominant factor in determining the effects of solvent composition on the rates of the hydrolysis. This is in contradiction to the assumptions of the electrostatic theories of Laidler and Eyring, and of Amis and Jaffe. The gas-chromatographic results also indicate that whilst the concentration of the water varies in each mixture studied, the activity coefficient varies in the opposite way to produce almost constant values of aý, 0* Using the transpiratioii/gas-chromatogralýlic method, the thermodynamic properties of the ternary systems, methyl acetate-water-organic Solvcat, using the organic solvents mentioned above (excepting, diglyme) have been investigated, and the results indicate that the variation of *ýE with solvent composition, for the dilute solutions of ester used, can be estimated from the thermodynamic properties of the binary water-organic solvent mixtures, using the Gibbs-Dahem equation. Single ion activity coefficients in the literature for small negative ions, to represent the OH_ ion, and for large ions, to rep-resent the transition state ion, have been used to explain the experimentally fomd variation of the residual activity coefficient -ratio with solvent composition. Hence, it is concluded that the importance of the parameters involved in the hydrolysis of esters - an ion-molecule reaction - in aqueousorganic solvent mixtures are in the order of Ymolecule > aH 20> YOH_/YM+ -> (dielectric constant), and that the nonelectrostatic effects -- thermodynamic effects - are more important in these studies than the electrostatic effects. From a preliminary investigation of the data in the literature the thermodynamic approach also yields a valid interpretation of the effect of solvent composition on the rates of the acid hydrolysis of esters. / Ministry of Science and Higher Education of Iran

L’objectif de cette thèse de doctorat est le développement d’une nouvelle méthode théorique basée sur la simulation des équilibres liquide-gaz par simulations de dynamique moléculaire. Cette nouvelle m´méthode prédit les propriétés thermodynamiques telles que l’activité des solvants et les coefficients d’activité des solutés en phases aqueuses et organiques impliquées dans les systèmes d’extraction liquide-liquide. Ces propriétés thermodynamiques sont nécessaires pour les approches de modélisation thermodynamique mésoscopique permettant d’estimer l’efficacité et la s´électivité d’un système d’extraction par solvant jusqu’au une échelle industrielle. Les propriétés thermodynamiques et structurales des solutions électrolytiques aqueuses et des phases organiques, y compris les agrégats résultant des molécules d’extraction des amphiphiles, sont en bon accord avec les données expérimentales et théoriques disponibles. L’approche de dynamique moléculaire de l’équilibre osmotique fournit un nouvel outil puissant permettant d’accéder aux données thermodynamiques. / The aim of this PhD thesis is the development of a new theoretical method based on the simulation of vapor-liquid equilibria by means of molecular dynamics (MD) simulation. This new method predicts thermodynamic properties such as solvent activities and solute activity coefficients of aqueous and organic phases used in liquid-liquid extraction systems. These thermodynamic properties are required for mesoscopic thermodynamic modeling approaches estimating the efficiency and selectivity of a given solvent extraction system up to an industrial scale. Thermodynamic and structural properties of aqueous electrolyte solutions and organic solvent phase including aggregates resulting from amphiphilic extractant molecules are reproduced in very good agreement with previously available experimental and theoretical data. The osmotic equilibrium MD approach provides a new and powerful tool for accessing thermodynamic data

Methods of slab-geometry molecular dynamics computer simulation were tested, compared, and applied to the prediction of activity coefficients, interfacial electrochemistry characterization, and ion transport through a model biological channel-membrane structure. The charged-sheets, 2-D Ewald, corrected 3-D Ewald, and corrected particle-particle-particle-mesh (P3M) methods were compared for efficiency and applicability to slab-geometry electrolyte systems with discrete water molecules. The P3M method was preferred for long-range force calculation in the problems of interest and was used throughout. The osmotic molecular dynamics method (OMD) was applied to the prediction of liquid mixture activity coefficients for six binary systems: methanol/n-hexane, n-hexane/n-pentane, methanol/water, chloroform/acetone, n-hexane/chloroform, methanol/ chloroform. OMD requires the establishment of chemical potential equilibrium across a semi-permeable membrane that divides the simulation cell between a pure solvent chamber and a chamber containing a mixture of solvent and solute molecules in order to predict the permeable component activity coefficient at the mixture side composition according to a thermodynamic identity. Chemical potential equilibrium is expedited by periodic adjustment of the mixture side chamber volume in response to the observed solvent flux. The method was validated and shown to be able to predict activity coefficients within the limitations of the simple models used. The electrochemical double layer characteristics for a simple electrolyte with discrete water molecules near a charged electrode were examined as a function of ion concentration, electrode charge, and ion size. The fluid structure and charge buildup near the electrode, the voltage drop across the double layer, and the double layer capacitance were studied and were found to be in reasonable agreement with experimental findings. Applied voltage non-equilibrium molecular dynamics was used to calculate the current-voltage relationship for a model biological pore. Ten 10-nanosecond trajectories were computed in each of 10 different conditions of concentration and applied voltage. The channel-membrane structure was bathed in electrolyte including discrete water molecules so that solvation, entry, and exit effects could be studied. Fluid structure, ion dynamics, channel selectivity, and potential gradients were examined. This work represents the first such channel study that does not neglect the vital contributions of discrete water molecules.