En France, le traitement des combustibles nucléaires irradiés repose sur le procédé PUREX au cours duquel l'uranium et le plutonium sont extraits sélectivement par le TBP à partir d'une solution aqueuse concentrée d'acide nitrique. L'objectif de ce travail de thèse était d'aboutir à une meilleure modélisation des milieux de traitement du combustible irradié. Dans un premier temps, des mesures Raman et RMN 14N, couplées à des calculs basés sur la théorie des solutions simples et sur le modèle BIMSA, ont permis de compléter les connaissances actuelles sur la dissociation de l'acide nitrique dans des solutions binaires et dans des mélanges ternaires. Dans un deuxième temps, la spéciation de Pu(IV) dans le TBP après extraction à faible acidité a été étudiée par EXAFS et spectrophotométrie vis-NIR, ce qui a permis de mettre en évidence l'extraction d'espèces hydrolysées de Pu(IV) en phase organique. En parallèle, une nouvelle caractérisation structurale des complexes An(VI)/TBP et An(IV)/TBP a été effectuée en couplant des mesures EXAFS à des calculs de chimie quantique. Enfin, la modélisation du système Pu(IV)/HNO3/H2O/TBP 30%/dodécane a été effectuée en prenant en compte les écarts à l'idéalité dans chaque phase. La meilleure modélisation de l'extraction de Pu(IV) à l'état de trace a été obtenue en considérant l'extraction de trois complexes de plutonium : Pu(OH)2(NO3)2(TBP)2 , Pu(NO3)4(TBP)2 et Pu(NO3)4(TBP)3. / The PUREX process is a solvent extraction method dedicated to the reprocessing of irradiated nuclear fuel in order to recover pure uranium and plutonium from aqueous solutions of concentrated nitric acid. The tri-n-butylphosphate (TBP) is used as the extractant in the organic phase. The aim of this thesis work was to improve the modeling of liquid-liquid extraction media in nuclear fuel reprocessing. First, Raman and 14N NMR measurements, coupled with theoretical calculations based on simple solutions theory and BIMSA modeling, were performed in order to get a better understanding of nitric acid dissociation in binary and ternary solutions. Then, Pu(IV) speciation in TBP after extraction from low nitric acid concentrations was investigated by EXAFS and vis-NIR spectroscopies. We were able to show evidence of the extraction of Pu(IV) hydrolyzed species into the organic phase. A new structural study was conducted on An(VI)/TBP and An(IV)/TBP complexes by coupling EXAFS measurements with DFT calculations. Finally, extraction isotherms modeling was performed on the Pu(IV)/HNO3/H2O/TBP 30%/dodecane system (with Pu at tracer scale) by taking into account deviation from ideal behaviour in both organic and aqueous phases. The best modeling was obtained when considering three plutonium (IV) complexes in the organic phase: Pu(OH)2(NO3)2(TBP)2 , Pu(NO3)4(TBP)2 and Pu(NO3)4(TBP)3.

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Made available in DSpace on 2018-08-01T21:36:54Z (GMT). No. of bitstreams: 1 tese_11042_Dissertação Lucas Queiroz - FINAL APROVADA.pdf: 801845 bytes, checksum: c02d945e52f528faf6319ad6dda19507 (MD5) Previous issue date: 2017-06-14 / A Destilação é um dos processos mais importantes na caracterização do petróleo pois o separa em diferentes frações. O conhecimento da distribuição dos pontos de ebulição dos componentes do petróleo e da proporção de seus cortes é essencial para o controle e logística desse processo durante o refino, além de garantir sua qualidade e possibilitar a valoração do óleo cru. Os métodos laboratoriais mais utilizados atualmente para este fim são as ASTM D2892 (destilação atmosférica: atinge temperatura máxima de 400 ºC) e ASTM D5236 (destilação a vácuo: utiliza pressões reduzidas para destilar o resíduo atmosférico para evitar o craqueamento das moléculas). A curva PEV (curva de pontos de ebulição verdadeiros - resultado laboratorial da destilação física) é obtida através da soma dos resultados das destilações atmosférica e a vácuo. Entretanto, esses processos demandam grandes quantidades de amostra (de 5 a 40 L) e tempo (3 a 4 dias). A Destilação Simulada por cromatografia gasosa (SIMDIS, do inglês Simulated Distillation) se apresenta como uma interessante solução para contornar esses problemas. A amostra é volatilizada e a separação de seus compostos ocorre no interior de uma coluna cromatográfica sob uma variação de temperatura controlada, produzindo um cromatograma e uma curva PEV. Neste trabalho, 98 amostras de petróleo nacionais e internacionais foram analisadas e seus dados foram correlacionados em diferentes etapas. Inicialmente, cada amostra foi analisada utilizando o método ASTM D7169 (SIMDIS) no laboratório de cromatografia do LabPetro na Universidade Federal do Espírito Santo (UFES). Essa etapa gerou 4 replicatas.para cada amostra, as quais foram submetidas a uma avaliação de similaridade para determinar qual apresentou o melhor resultado. Os dados da melhor replicata foram correlacionados com os obtidos no Centro de Pesquisas e Desenvolvimento Leopoldo Américo Miguez de Mello (CENPES-Petrobras). A primeira comparação foi uma avaliação de similaridade realizada entre os resultados de SIMDIS dos dois laboratórios, realizada para 44 amostras (amostras cujos resultados de SIMDIS foram disponibilizados pelo CENPES). Em seguida, os dados de SIMDIS obtidos na UFES foram correlacionados com os da destilação convencional do CENPES-Petrobras. A correlação dos resultados se deu através da comparação dos valores de ponto de ebulição a cada 5% de recuperação em massa. A fim de obter esses valores para as duas técnicas, foi feito um ajuste polinomial de quinta ordem. Por fim, foi aplicado um teste de Viés para para avaliar a correlação dos dados. A avaliação final dos resultados evidenciou uma boa similaridade entre os resultados da destilação convencional e SIMDIS. A correlação para 13 petróleos (de um total de 15) obteve bons, não exibindo erros sistemáticos significativos.

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Aujourd’hui le combustible nucléaire usé est retraité via le procédé PUREX afin de récupérer l’uranium et le plutonium. La séparation de ces actinides des produits de fission repose sur différentes étapes d’extraction liquide-liquide avec le tri-n-butyl-phosphate (TBP) comme extractant. Un modèle a été conçu pour décrire précisément les différentes étapes du retraitement afin d’en optimiser le fonctionnement. Mais les mécanismes à l’échelle moléculaire sont encore mal décrits notamment pour le ruthénium qui est partiellement extrait et retenu en phase organique. Les études précédentes concernant le comportement du ruthénium dans le procédé ont montré que sa chimie était complexe et se sont principalement appuyées sur des données macroscopiques telles que les coefficients de distribution ou des constantes cinétiques. Des lacunes demeurent quant au mode de coordination avec le TBP, la structure et la stabilité des espèces extraites en phase organique, ou encore par rapport à la spéciation dans les conditions de faible acidité (CHNO3aq < 3 M).Une analyse de la spéciation du ruthénium en phase aqueuse et en phase organique a donc été entreprise au cours de ce travail. Elle s’appuie sur la combinaison d’outils spectroscopiques (FTIR et EXAFS) et sur l’utilisation de références solides caractérisées par DRX monocristal, FTIR et EXAFS. Cette méthodologie a été développée afin d’améliorer l’interprétation des signaux enregistrés sur les solutions aqueuses et organique de ruthénium.La méthode de couplage entre les données FTIR, les résultats de dosages potentiométriques en phase aqueuse et les informations obtenues lors de l’ajustement des spectres EXAFS nous a permis d’obtenir des structures moyennes des espèces [RuNO(NO3)x(OH)y(H2O)5-x-y]3-(x+y)+ présentes tant en phase aqueuse qu’en phase organique. Elle a permis de démontrer que dans les conditions d’extraction du procédé, les complexes identifiés en phase aqueuse sont extraits en phase organique sans modification de la sphère de coordination. L’hypothèse d’une coordination directe entre le TBP et le ruthénium a pu être exclue. L’influence de la concentration en acide nitrique ainsi qu’en ions nitrates, sur la spéciation du ruthénium dans les phases aqueuses et organiques a été mise en évidence. Différents équilibres d’extraction sont mis en œuvre selon les conditions chimiques. Pour les solutions à forte acidité (CHNO3aq = 4 M), des complexes de ruthénium non-hydrolysés avec un nombre de ligands nitrates proche de 3 ont identifiés (2 < x < 4 et z = 0). Au contraire à faible acidité (CHNO3aq = 1 M), une forme hydrolysée des complexes du ruthénium, présente en solution aqueuse, est extraite par le solvant. Cette espèce hydrolysée s’avère être un complexe bimétallique de la forme [(RuNO)2(NO3)2x(H2O)9-2x(µ-OH)](5-2x)+.Enfin l’étude du vieillissement des phases organiques a permis de mettre en évidence des échanges entre les ligands liés au ruthénium et l’acide nitrique solubilisé en phase organique. Ces processus, relativement lents pour une phase organique isolée, sont accélérés lorsque les mesures sont effectuées en présence d’une phase aqueuse, ce qui engendre une augmentation du coefficient de distribution du ruthénium. Ces échanges de ligands dans la sphère de coordination du ruthénium et les variations importantes de spéciation en fonctions des conditions chimiques (CH+ et CNO3-) pourraient être à l’origine du phénomène de rétention du ruthénium observé au sein du procédé. Finalement cette étude offre des voies d’amélioration pour une meilleure prise en compte de la diversité des équilibres impliquant le ruthénium au sein des modèles thermodynamiques, et soutient ainsi le développement de modèles prédictifs des procédés industriels de séparation. / Currently, used nuclear fuel is reprocessed using the PUREX process to isolate uranium and plutonium. Separation of these actinides is achieved through multiple steps of liquid-liquid extraction using tri-n-butyl-phosphate (TBP) as the extractant. Work aiming to develop a precise model of the fuel retreatment process in order to optimize it fails to accurately reproduce the ruthenium partial extraction and its retention in organic phase. Molecular mechanisms are still badly understood and hinder these developments. Previous studies had shown that ruthenium chemistry is complex but they mostly rely on macroscopic information as distribution coefficients or rate constants. Deficiencies remain about the coordination mode between TBP and ruthenium, about the structure and stability of extracted species or about the speciation for solutions at low acidities (CHNO3aq < 3 M).Ruthenium speciation analysis was undertaken during this work. It relies on the combination of different spectroscopic techniques (FTIR and EXAFS) and on the use of solid reference compounds fully characterized by single crystal XRD, FTIR and EXAFS. This method was developed in order to improve the interpretation of spectroscopic results for ruthenium aqueous and organic phases.This method coupling FTIR analysis, potentiometric determination in aqueous phase and fit results of EXAFS experimental data allowed us to obtain average structure for [RuNO(NO3)x(OH)y(H2O)5-x-y]3-(x+y)+ species in solution. It was demonstrated that ruthenium coordination sphere was not modified during extraction in process conditions. The hypothesis of a direct link between ruthenium and TBP was excluded. Influence of the nitric acid and nitrate concentrations was highlighted for ruthenium speciation in both aqueous and organic phases. Separate equilibria should be implemented to describe ruthenium extraction depending on chemical conditions. At high acidity (CHNO3aq = 4 M), non-hydrolyzed ruthenium complexes with an average nitrate number close to 3 were identified (2 < x < 4 et z = 0). Conversely, at low acidity (CHNO3aq = 1 M), a hydrolyzed ruthenium compound, observed in aqueous phase, is extracted into the organic phase. This compound was shown to be a bimetallic complex which could be written as [(RuNO)2(NO3)2x(H2O)9-2x(µ-OH)](5-2x)+.Finally the ageing study of organic phase allowed us to highlight exchanges between the ruthenium ligands and solvated nitric acid. These phenomena are relatively slow for isolated organic phases but are accelerated in the presence of an aqueous phase. An increase of ruthenium distribution coefficient was also observed. These ligand exchanges in ruthenium coordination sphere and the large fluctuations of speciation depending on chemical conditions (CH+ et CNO3-) may cause the ruthenium retention noticed in the process.This study offers opportunities to improve ruthenium extraction equilibria coverage in thermodynamic models and support the development of predictive models for industrial separation processes.

Na otimização do refino de petróleo é fundamental predizer a distribuição dos produtos e sua qualidade. O petróleo é uma substância muito complexa e é praticamente impossível caracterizá-lo de maneira usual, analisando a quantidade de cada um dos seus constituintes. Portanto, convencionalmente, ele é caracterizado por métodos baseados na análise da destilação, tais como o ensaio de destilação chamado de True Boiling Point (TBP) e o ensaio ASTM D86. Para predizer a distribuição dos produtos e sua relação com as condições de funcionamento, simulações em estado estacionário baseadas em primeiros princípios, em termos de balanços de massa, energia e relações de equilíbrio, são extremamente importantes. Como o número de componentes no petróleo é muito elevado a composição da mistura não pode ser utilizada diretamente. Convencionalmente, dezenas de pseudocomponentes são geradas, a fim de representar o petróleo. Mais recentemente, foi proposta a aproximação do petróleo por um conjunto reduzido de componentes reais. É esta abordagem que é estudada nesta dissertação. O principal desafio deste método é a determinação dos componentes reais e das suas quantidades, que são escolhidos para representar a mistura original. Na metodologia para a seleção da mistura substituta é necessário simular as curvas de destilação disponíveis experimentalmente. Neste trabalho simulamos as curvas de destilação TBP e ASTM D86 dentro do ambiente BatchSep da Aspentech. São apresentadas aplicações destas simulações em seis exemplos diferentes. Destes exemplos cinco se referem à simulação da TBP e um à ASTM D86. Alguns exemplos são baseados em misturas com composição conhecida, e em outros há comparações com dados experimentais de cortes de petróleo. A metodologia da mistura substituta e a dos pseudocomponentes foram comparadas na simulação de uma coluna de destilação. De maneira geral a metodologia proposta na literatura é adequada quando se quer representar a curva de temperatura apenas. Quando se dispõe de dados de densidade o método fica limitado pela disponibilidade de componentes na base de dados e pela hipótese de que os componentes saem puros, um a um, que é feita ao se adotar a metodologia convencional. Uma metodologia que leva em conta o fato de que os cortes são uma mistura de componentes deve ser implementada para que o método seja tecnicamente atraente. / In the process of optimizing petroleum refining, it is essential to predict the distribution of products and their quality. Petroleum is a very complex substance and it is practically impossible to characterize it in the usual manner, by analyzing the quantity of each single component. Therefore, conventionally, it is characterized by methods based on the analysis of distillation, such as the True Boiling Point (TBP) distillation test and the ASTM D86 test. In order to predict the distribution of products and their relationship with the operating conditions, stationary state simulations based on primary principals, in terms of fluctuations of mass, energy and relations of balance, are extremely important. As the number of components in petroleum is very high, the composition of the mixture cannot be used directly. Conventionally, dozens of pseudocomponents are created, in order to simulate petroleum. More recently the approximation of petroleum through a reduced set of real components has been proposed. This is the approach studied in this dissertation. The main challenge of this method is the determination of the real components chosen to simulate the original mixture, and their quantities. It is necessary to simulate the available distillation curves experimentally in the methodology for the selection of the substitute mixture. In this study, we simulated the TBP and ASTM D86 distillation curves in an Aspentech BatchSep environment. Applications of these simulations are presented in six different examples. Of these examples, five are TBP simulations and one is an ASTM D86 simulation. Some examples are based on mixtures with known compositions, and in others there are comparisons with experimental data from petroleum samples. The methodology of the substitute mixture and that of the pseudo-components were compared in the simulation of a distillation column. In general, the methodology proposed in literature is suitable when the only simulation that is required is a temperature curve. When density data is available, the method becomes limited by the availability of components in the data base and by the hypothesis that the components emerge pure, one by one, which is what happens when conventional methodology is adopted. A methodology that takes into account the fact that the samples are a mixture of components must be implemented so that the method is technically appealing

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