Couplage Flux-Expert / Fluent : application à la modélisation 3D d'un électrolyseur à production d'hydrogène

Les électrolyseurs à production d'hydrogène de type Westinghouse sont des dispositifs électrochimiques constitués d'un empilement de compartiments cathodiques et anodiques séparés par une membrane. Ils abritent un ensemble de phénomènes physiques couplés. Pour modéliser ces installations nous avons développé un couplage entre les logiciels Fluent® (volumes finis) et Flux-Expert® (éléments finis). Le premier est utilisé pour la résolution de la partie thermo-hydraulique du problème, le second pour la partie électrocinétique avec surtensions d'activation. Leur couplage met en œuvre un processus itératif dans lequel chacun calcule des grandeurs physiques et les transmet à l'autre. Ces interpolations de grandeurs d'un maillage sur l'autre nécessitent une localisation des points de calcul sur des régions volumiques ou surfaciques 3D. Une librairie de passation de messages simple et robuste permet aux deux codes de communiquer

Modélisation d'une colonne d'extraction à effet Taylor-Couette

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Self-Regulated Ion Permeation through Extraction Membranes

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Tantalum and Niobium Selective Extraction by Alkyl-Acetophenone

A study has been carried out on Ta and Nb recovery by a liquid-liquid extraction process using 4-methylacetophenone (4-MAcPh) as the organic phase. The 4-MAcPh was compared to methyl isobutyl ketone (MIBK) with respect to extraction efficiencies (D values) at different concentrations of H2SO4 in the aqueous phase. The results showed a similar extraction of Nb for both solvents. However, for Ta, extraction efficiency is increased by a factor of 1.3 for 4-MAcPh. In addition, the MIBK solubilized completely after 6 mol∙L−1 of H2SO4 against only a loss of 0.14–4% for 4-MAcPh between 6 and 9 mol∙L−1 of H2SO4. The potential of 4-MAcPh has also been studied to selectively recover Ta from a model capacitor waste solution. The results showed a selectivity for Ta in the presence of impurities such as Ag, Fe, Ni and Mn. The 4-MAcPh also presents the advantage of having physicochemical properties adapted to its use in liquid-liquid extraction technologies such as mixer-settlers

Effects of porous media on extraction kinetics: Is the membrane really a limiting factor?

International audiencePorous media in extraction and especially pertraction are often suspected to add unnecessary diffusive resistance and considerably slow down extraction kinetics. This work presents a miniaturized pertraction device and simulation of diffusive and reactive solute transport. Kinetics are experimentally observed and numerically fitted. Reaction rates – or solute transfer rates – are estimated via this fit on a numerical basis. The work shows that the diffusive resistance created by a porous medium is prevalent only at low distribution coefficients. At high distribution coefficients as is the case of quasi all industrial processes, the porous membrane does not interfere with overall kinetics. Instead, the diffusive resistance is shared between the feed and extraction phases, and the interface transfer, depending on the value of the transfer rate. Overall, this work can be generalize as enabling the measurement of solute transfer rates at the liquid-liquid interface, a key parameter in pertraction and membrane separation which is difficult to measure using classic methods of extraction

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

Mass transfer efficiency in rare earth extraction using a hollow fiber pertraction device

International audienceExtraction of neodymium by N,N-dibutylacetamide (DBAc) has been investigated using a single hollow porous fibre pertraction device. It consists of a polypropylene hydrophobic fibre maintained in a cylindrical glass calender. The Nd loaded aqueous phase flows inside the porous fiber. The organic phase flows outside in the calender and fills the pores of the membrane. Neodymium is extracted by DBAc, transported through the membrane by molecular diffusion and collected in the solvent flow. DBAc was chosen because of its low variation of viscosity with metal concentration. Accurate measurements of diffusion coefficient of neodymium in the solvent by Taylor Dispersion Analysis (TDA) confirmed the low influence of the neodymium concentration on its diffusivity. These results, combined with the determination of the distribution coefficient of Nd in DBAc, gave good agreement between experimental and simulated data of pertraction test. Nevertheless, the results showed a high resistance of mass transfer mainly due to the diffusion in membrane. A possible explanation was that the distribution coefficient of Nd was not high enough to ensure a sufficient gradient of concentration along the thickness of the membrane filled by the solvent. To prove it, a second pertraction experiment was performed using HDEHP at 1 mol L-1 in n-dodecane as extractant. In this case, the distribution coefficient of Nd is 3 times higher than for DBAc. Good fitting of experimental data with simulated extraction of neodymium has been obtained and confirm the aforementioned hypothesis: high mass transfer rate requires high distribution and diffusion coefficients

The free energy of transfer in metal-extracting water-poor microemulsions as the crucial molecular driving force

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