Solvation et spécificité ionique dans les milieux complexes

The object of this thesis was to create models for two applications which readily appear in separation chemistry, namely the solid-liquid and the liquid-liquid extractions. The benefit of modelling in both cases is twofold. Studying the fundamental properties of ions and their solvation properties in the complex media, and simplifying the expression for important effects, enables us to construct the framework which can be used by both chemists in the laboratory, as well as the chemical engineers in the process design. For two applications we adapted two different systems, both of which can be considered as complex. The model system to study the solid-liquid separation were TiO2 nanotubes dispersed in the aqueous solution. This system was studied by the means of Classical Density Functional Theory coupled with the charge regulation method, within the Grand-canonical ensemble. Indeed, the method proved to be successful in establishing the full description of the charge properties of TiO2 nanotubes. In this case, we were interested in obtaining the description of ion inside the charged nanotubes under influence by the electric field (exhibited by nanotubes). Calculations predicted effects such as the difference in surface charge between the outer and the inner surface, or the violation of electroneutrality inside the nanotubes. It was demonstrated that the model was in the agreement with the experimental data. Moreover, the method can be directly used to predict titration for various techniques. A simple generalization of the proposed approach can be used to study the actual adsorption efficiency of the solid-liquid separation process. The model system to study the liquid-liquid extraction process included three distinct parts. The three parts were devoted to the cases on non-ionic, acidic ion exchangers, and finally the synergistic mixtures of extractants. Simple bulk statistical thermodynamics model, in which we incorporated some of the well-established concepts in colloidal chemistry provided a soft-matter approach for the calculation of actual engineering-scale processes. Were have expanded a classical simple equilibria approach to broader, more intuitive polydisperse aggregates formation that underlines the liquid-liquid extraction. The key finding can be presented as a current opinion or newly-proposed paradigm: at equilibrium, many aggregates completely different in composition but similar in free energy coexist. With obtained polydispersity, we were equipped with a tool to study a more 'global' behavior of liquid-liquid extraction. This urged us to pass our considerations of historical extraction isotherms to extraction 'maps'. Great care was devoted to the study of synergy since it is a 60-year old ongoing question in the separation industrial and science community. To our best knowledge, the first quantitative rationalization total synergistic extraction was proposed within this thesis. Underlying effects of enthalpy and entropy control on the organic phase structuring were decoupled and studied in detail. Hopefully, this thesis demonstrated the importance of mesoscopic modelling to assist both chemists and chemical engineers in practical examples.Le but de cette thèse était de créer des modèles pour deux applications qui apparaissent couramment en chimie séparative, à savoir la séparation solide-liquide et la séparation liquide-liquide. L'avantage de la modélisation est manifeste dans les deux cas. L'étude fondamentale des propriétés des ions et de leur solvatation dans les milieux complexes, en tenant compte de façon simplifié des différents effets mis en jeu, nous a permis de construire un cadre qui utile aussi bien aux chimistes en laboratoire qu’aux ingénieurs lors de la conception des procédés. Nous avons adapté cette stratégie sur deux systèmes différents, qui peuvent tous deux être considérés comme complexes. Le premier système modèle pour étudier la séparation solide-liquide était des nanotubes de TiO2 dispersés dans une solution aqueuse. Ce système a été étudié au moyen de la Théorie de la Fonctionnelle de la Densité Classique couplée à une méthode de régulation de charge, au sein de l'ensemble Grand-Canonique. La méthode s'est avérée efficace pour établir la description complète des propriétés de charge des nanotubes de TiO2. Dans ce cas, nous nous sommes intéressés à obtenir la description de l'ion à l'intérieur des nanotubes chargés sous l'influence du champ électrique (créé par les nanotubes). Les calculs ont prédit des effets tels que la différence de charge de surface entre la surface externe et la surface interne, ou la violation de l'électroneutralité à l'intérieur des nanotubes. Il a été démontré que le modèle était en accord avec les données expérimentales. De plus, la méthode peut être utilisée directement pour prédire diverses techniques de titrage. Une simple généralisation de l'approche proposée permettra d'étudier l'efficacité d'adsorption réelle du procédé de séparation solide-liquide. Le second système modèle concerne l'étude du procédé d'extraction liquide-liquide et il comprend trois parties distinctes. Les trois parties ont été consacrées aux cas des extractants non ioniques, puis acides (échangeurs d'ions), et enfin aux mélanges synergiques d'extractants. Un modèle simple de thermodynamique statistique, dans lequel nous avons incorporé certains des concepts bien établis en chimie colloïdale, a fourni une approche de type matière molle pour calculer le processus à l'échelle de l'ingénieur. Nous avons développé une approche classique d'équilibres simples pour une compréhension plus large et plus intuitive de la formation des agrégats polydisperses dans l'extraction liquide-liquide. La principale conclusion présentée est que l’on doit proposer un nouveau paradigme pour la chimie : à l'équilibre, de nombreux agrégats de composition très différente mais similaires en énergie libre, coexistent. Avec la polydispersité obtenue, nous avons ainsi proposé un outil pour étudier un comportement plus "global" de l'extraction liquide-liquide. Cela nous a poussés à passer des considérations classiques d'isothermes d'extraction à celles plus précises des " cartes " d’extraction. Un grand soin a été apporté à l'étude de la synergie puisqu'il s'agit d'une important question depuis 60 ans dans la communauté scientifique et industrielle de la séparation. A notre connaissance, la première rationalisation quantitative de la synergie d’extraction a été proposée dans le cadre de cette thèse. Les effets sous-jacents des contrôles enthalpique et entropique sur la structuration des phases organiques ont été découplés et étudiés en détail. Nous espérons que cette thèse a démontré l'importance de la modélisation mésoscopique sur des exemples pratiques utilisés à la fois par les chimistes et les ingénieurs

From Water Solutions to Ionic Liquids with Solid State Nanopores as a Perspective to Study Transport and Translocation Phenomena

Solid state nanopores are single-molecular devices governed by nanoscale physics with a broad potential for technological applications. However, the control of translocation speed in these systems is still limited. Ionic liquids are molten salts which are commonly used as alternate solvents enabling the regulation of the chemical and physical interactions on solid-liquid interfaces. While their combination can be challenging to the understanding of nanoscopic processes, there has been limited attempts on bringing these two together. While summarizing the state of the art and open questions in these fields, several major advances are presented with a perspective on the next steps in the investigations of ionic-liquid filled nanopores, both from a theoretical and experimental standpoint. By analogy to aqueous solutions, it is argued that ionic liquids and nanopores can be combined to provide new nanofluidic functionalities, as well as to help resolve some of the pertinent problems in understanding transport phenomena in confined ionic liquids and providing better control of the speed of translocating analytes

Microstructure-efficiency relationship in liquid-liquid extraction

International audienceIt is a matter of strategic independence for Europe to urgently find processes taking account of environmental and economic issues, when mining and recycling rare earth elements. Separation and recycling of rare earths from electronic waste is important for the success of present and future carbon-free technologies. Hydrometallurgical separation based on nanoscience is one of the first technologies allowing the take-off of circular economy. Liquid-liquid extraction is a promising method for retrieving rare earths from electronic waste. However, an optimized process on an industrial scale has not been established. One major reason is the lack of fundamental knowledge, therefore designing a cost-efficient, adaptive and predictive formulation is still out of scope of possibilities. Emulsification and demulsification processes in extraction devices are only efficient when the coexisting phases are located between binodal tie-lines in the Winsor II regime. Most extraction processes are based on the combination of an extractant with a diluent. The main disadvantage of these processes is the formation of viscous emulsions known as third phase accident. This occurs when processes are intensified by increasing solute and extractant concentration. Our objective is to develop the fundamental understanding involved in the process’ complex fluids (experimental and theoretical) concerning liquid-liquid extraction of REE and furthermore to use it to design new, cost-effective and environment-friendly recycling processes.A new and promising approach has been recently proposed using Ultra Flexible MicroEmulsions (UFME) which are characterized by an Ornstein-Zernike scattering often observed for weak extractants. These surfactant-free self-assembly is based on the usage of hydrotropic co-solvents instead of the classical extractant/diluent couple. Co-solvents as well as hydrotropes quench the formation of third phases. A systematic comparison of the extracting power of a given formulation by the classical solvent-based, modifier enhanced co-solvent based and the new possible UFME route is now necessary. This requires measuring with enough precision the free energy of transfer of ions along the lines in the quaternary phase diagram. This is only achievable by using a newly developed liquid-liquid extraction microfluidic device coupled to X-ray fluorescence microanalysis. Our contribution towards a more complete understanding in this matter is the analysis and comparison of the phase behavior, extracting efficiency and selectivity of such systems as well as the correlation of these findings with the “ienaics” approach by identifying the molecular driving forces favoring or quenching the transfer