Construction d'un enthalpimetre adapte a l'etude des equilibres solide-liquide multiconstitues

In order to study solid-liquid equilibria in multicomponent systems, an enthalpimeter has been built and perfected. Measurements can be carried out between —100 and +150°. During the thermal analysis, samples are continually stirred and heated, or cooled, at constant flow rate.In these conditions, reproducible and accurate results are obtained and very closed temperature phenomena may be separated. As an illustration, the ternary system waterstrontium choride-barium chloride has been studied at low temperature and the polythermic diagram is described up to 100°.

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Zusammenfassung Für die Untersuchung von fest-flüssig-Gleichgewichten in Multikom-ponentensystemen wurde ein Enthalpiemeter gebaut und verbessert. Darin können Messungen zwischen –100 und + 150°C durchgeführt werden. Während der Thermoanalyse werden die Proben bei konstanter Duchsatzgeschwindigkeit ständig gerührt und erhitzt oder gekühlt. Unter diesen Bedingungen werden reproduzierbare und sehr genaue Ergebnisse erzielt und sehr eng beieinanderliegende Temperatur-phänomene können getrennt werden. Als Beispiel wurde das ternäre System Wasser-Strontiumchlorid-Bariumchlorid bei niederen Temperaturen untersucht und ein polythermisches Diagramm bis 100°C erstellt.

     

Etude Experimentale et Modelisation des Equilibres Solide—Liquide du Systeme Binaire H2O—UO2(NO3)2

The binary system H₂O—UO₂(NO₃)₂ was studied by solubility measurements and constant heat flow thermal analysis. Temperature and composition of the eutectic transformation between ice and uranyl nitrate hexahydrate were accurately defined. A new hydrate with 24 molecules of water decomposes at –21°C according to the peritectoid reaction<UO₂(NO₃)₂·24H₂O> <UO₂(NO₃)₂·6H₂O> + 18<H₂O>The quasi-ideal model was applied to the solid—liquid equilibria, using the following reaction hypothesis:((UO ₂ ²⁺ )) + 2((NO ₃ ^– ))+ h((H₂O)) ((UO₂OH⁺aq)) + ((H₃O⁺aq + 2((NO ₃ ^– aq))A complete calculation of the binary system was carried out with a global ionic hydration number h equal to 9 in the aqueous solutions. It allowed to the melting enthalpies of uranyl nitrate hydrates.

This revised version was published online in November 2005 with corrections to the Cover Date.     

From the dilute solution to the pure compound: Extraction strategy based on a multi-stage process of phase separation

It is very rare that a one-step process of extraction leads to the pure compound with a high degree of purity specified by an industrial application. The various stages of a synthesis process and possible secondary reactions may lead to the synthesis of more or less complex and highly diluted solutions. In this work, the rationale and strategy for extraction and purification of a high added value compound are discussed. All the thinking is based on the knowledge and the exploitation of phase diagrams and then developed for different unit operations of the process. The most significant research tools are the experimental data and the modelling of phase equilibrium to estimate the yield of each step of extraction. The significant example chosen involves all the basic methods of phase separation, starting with liquid-vapour equilibrium: stripping of high volatility components and then more or less complex distillation are classically employed. The theoretical plateau number can be deduced from the equilibrium equation curves. The second step is based on the study of the liquid-liquid equilibrium and is an intermediate step for enrichment of the solution when distillation is not possible. A final step based on solid-liquid equilibrium consists of the selective crystallization of the pure product at low temperature, in order to satisfy the requirements of purity and safety imposed by industrial use. The conclusion includes all isolation operations in the form of a general extraction and purification scheme.

     

Solvation phenomena and revision of solid–liquid equilibria in aqueous solutions of two precursors of mixed oxides, the hydrates of cobalt and nickel nitrates

The hydrates of cobalt and nickel nitrates are highly relevant as precursors for the preparation of mixed ceramics. In order to verify the numerous bibliographical data, systematic solubility measurements in aqueous medium under atmospheric pressure and a critical evaluation have been undertaken. By taking solvation phenomena into account, it has proved possible to correlate all the phenomena observed, to obtain equations representative of the liquidus curves, and to refine and extrapolate the experimental curves. The whole stable and metastable coordinates of the invariant transformations in both binary systems have been calculated or more accurately determined.     

High-performance liquid chromatographic analysis of the unusual pathway of oxidation of L-arginine to citrulline and nitric oxide in mammalian cells

A very unusual pathway of the oxidation of L-arginine to citrulline and nitric oxide has been discovered recently in cytotoxic macrophages. In an attempt to detect molecules generated through this metabolic pathway, a fast radio high-performance liquid chromatographic method was developed to analyse the whole set of radiolabelled L-arginine-derived metabolites produced by mammalian cells after appropriate induction. A new intermediate which might be NG-hydroxy-L-arginine was found.     

Synthesis of 1‐amino‐2‐methylindoline by Raschig process: Parallel reactions,modeling, and optimization

The reaction between chloramine and 2‐methylindoline was studied at pH 12.89, T = 40°C, and for different initial concentrations of reactants. The interaction includes two concurrent bimolecular mechanisms leading to 1‐amino‐2‐methylindoline and 2‐methylindole. The rate laws were determined at the first moments of the reaction by using a differential method. By considering the totality of the reactions that occur in the medium, an appropriate mathematical model was developed. It permits to follow the evolution of the system over time and to calculate the final yields of reaction products. An optimization in terms of the initial contents of 2‐methylindoline and chloramine was performed. It indicated that the maximum yield of 1‐amino‐2‐methylindoline does not exceed 56%. The results show the limit of the Raschig process for the synthesis of indolic hydrazines in aqueous medium. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 575–584, 2002