Prédétermination du comportement de métaux et d'enrobages pour anodes réactives

Anodic and cathodic polarization curves for zinc in presence of aqueous extracts of backfills can be used to predict the behaviour of the metal and its backfill from the point of view of their use in reactive anodes.

Zusammenfassung

Die anodischen und kathodischen Ueberspannungskurven des Zinks in Anwesenheit wässeriger Extrakte seiner Ummantelung gestatten gewisse Voraussagen über das Verhalten des Metalls und seiner Ummantelung.     

Augmentation,par régénération électrochimique du substrat,de la production d'une biomasse (thiobacillus ferrooxidans DSM 583) pour un procédé biologique de récupération de métaux

A bioelectrochemical reactor regenerates the substrate of the acidophilic bacterium Thiobacillus ferrooxidans DSM 583 (ferrous ions). This reactor uses a through-flow porous fixed bed or carbon as cathode. A linearizing non-linear regulator insures an efficient control of the intensity imposed to the electrochemical reactor. The protein concentration, correlated to the biomass concentration, is 6.4 fold increased for a 55 h growth, including a 20 h electrolysis. The metal tolerance and the metal fixation capacity of a T. ferrooxidans biomass are presented both for solutions including one or two metallic ions and an industrial waste. A bioelectrochemical process based on these characteristics is proposed for removing metal ions from wastes.     

Etude par chromatographie liquide haute pression de polyoléfines et de polyéthylènes modifiés

The high speed liquid chromatography behaviour of polyolefins with different crystallinities, of various branched chain polyolefins (high and low density polyethylene, ethylene-propylene copolymer, polypentene) as well as modified polyethylenes either in bulk (chlorination) or on the surface (chlorination, chlorophosphorylation, oxidation) was studied. The samples consisted of glass beads (44–50 μm) which were coated by deposition of the polymers. The study was carried out on one hand in an apolar mobile phase (cyclohexane) with phenol, ortho-, meta-, and para-nitrophenol as solutes, on the other hand in a polar mobile phase (water-methanol mixtures) with benzene, chlorobenzene, and orthodichlorobenzene as solutes. The influence of a swelling agent for the polymer and the temperature effect were investigated. The obtained results show the possibility of liquid chromatography to study interactions between polymers and a given solventsolute.     

Modélisation et simulation de la décomposition catalytique du méthanol dans un réacteur à lit fixe

A distributed-parameter model is presented for a tubular catalytic reactor used for the endothermic decomposition of methanol into hydrogen. The thermal and kinetic results are compared to experimental data for both transient and steady regimes, demonstrating the adequacy of the model to reproduce the behaviour of this reactor. Sensitivity analyses have highlighted the importance of certain model parameters to the calculated results.     

Etude cinétique de la déshydrtation du sulfate de cuivre par thermogravimétrie et thermogradientimétrie

A new type of thermobalance has been built, Sample temperatures have been determined by a new technique called “thermogradientimetry”. A special crucible assembly allows control of the atmosphere surrounding the sample. Kinetic results for the three successive stages in the dehydration of copper sulphate indicate that the reactions involved are of zero order. The apparent activation energy for each stage of the dehydration has been avaluated under isobaric conditions for different water vapor pressures.     

Application des chaînes de markov discrétisées à la simulation des réacteurs chimiques

Gibilaro et al have shown that Markov's time discretized process is a simple and general method for simulating unsteady flow systems. The present paper recalls briefly the main features of the original method of Gibilaro et al. It shows how to generalize this method and presents three examples with systems including time delays and systems where chemical reactions occur. Comparisons with other methods of solution (exact solution of Bernoulli's equation, numerical solution by Merson and Runge-Kutta methods indicate the accuracy of the method proposed here.     

Contribution à l'étude de la dégradation photochimique du caoutchouc chloré par la lumière ultraviolette solaire. I. Etude physicochimique de i'évolution de la masse moléculaire

The esters were prepared by the acryloylation or methacryloylation of 1-formylamino-2,2,2-trichloroethanol and 1-(N-formylmethylamino)-2,2,2-trichloroethanol and characterized by the boiling point, melting point, and the IR spectra, The temperature of spontaneous thermal decomposition, the density, limiting oxygen number for continuous combustion and the glass transition temperature of the homopolymers of the titled compounds were also determined.     

Règies de construction et d'extrapolation des réacteurs auto-agités par jets gazeux

An analysis is made of the agitation mechanism in a spherical reactor which is self-stirred by means of gas jets; it is made on the double assumption of an internal recycling and of a turbulent free jet. Extrapolation laws have been developed and verified experimentallly by means of the residence time distribution in several reactors of volumes varying between 501 and several cubic centimeters, the passage times varying from 0.6 to 7.5 seconds: the experiments involved several gases and different temperatures.     

Analyse de faisabilité, synthèse et conception des procédés de distillation réactive : état de l'art et analyse critique

A state of the art of the methods available in the literature for the feasibility analysis and the design of reactive distillation processes is presented. First, concepts and fundamental tools concerning the thermodynamics of reactive systems are introduced. Then, the different methods dedicated to the feasibility analysis, the synthesis and the design of these processes are presented and analyzed. For each method, comparative tables offer the reader a synthetic and critical vision of the existing studies. Finally, reactive distillation design in industrial practice is mentionned.     

Corrections des réponses des détecteurs placés à la sortie d'un CPG

Gel permeation chromatography only fitted with a refractometer is not sufficient for characterization of polymers. In the present study a combination of three detectors, a refractometer, a viscometer, and an IR-spectrophotometer is estimated to be necessary for analyzing polymers showing chemical and molecular heterogeneities. Unfortunately, using the crude results of these detectors for calculations leads to errors, the origins of which are identified and corrected.     

Le cyclone: Un réacteur chimique. Application à la réaction de décarbonatation de NaHCO3

The purpose of the present paper is the experimental and theoretical study of the behaviour of the cyclone working as a chemical reactor. The model reaction is the decarbonation of NaHCO₃. Thanks to the use of scale-up relationships previously determined, it is possible to derive kinetic constants in good agreement with other published values obtained under quite different conditions. The measurements are performed in a wide range of experimental conditions (particle size, residence time of particles, cyclone wall temperatures, solid flow rate). The paper emphasizes two possible fields of utilization for the cyclone: a device for the measurement of kinetic constants, a processing reactor operating with high throughput of solids.     

Étude de copolymères greffés ABS (acrylonitrile-butadiène-styrène). II. Comparaison des masses moléculaires des greffons et du copolymère san libre

A characteristic doublet and triplet growth of polyoxymethylene crystals is observed from the dilute solution in bromobenzene. The simple, but frequently observed crystal structure and its role in developing gross morphological features is illustrated. It is marked that mainly it gets multilayered by screw dislocation mechanism. Habit and orientation of secondary features so developed on the doublets are discussed.     

Influence de la quantité d'un sel de sulfonium sur la coupure des liaisons O?Si et sur la solubilité d'un mélange renfermant le sel et le poly(p-triméthylsiloxystyrène) et irradié par des UV

If coating solutions obtained by dissolving poly(p-trimethylsiloxystyrene) together with one of the salts (C₆H₅)₂(C₆H₅SC₆H₄)SSbF₆ or (C₆H₅)₃SAsF₆ in a solvent such as 3-pentanone are aged, the percentage of O? Si(CH₃)₃ bonds cleaved by irradiation at a given intensity (λ = 254 nm) and after post-annealing depends on the amount of salt introduced. The same result is observed with respect to the solubility of the resist when it is treated with the basic solvent MF-319.     

Greffage de molécules à la surface du silicium par voie électrochimique

The hydrogentated surface of silicon exhibits remarkable properties, but poor resistance to oxidation. To improve its stability, surface hydrogen has been replaced by several organic groups. Such grafting can be carried out chemically by a multi-step reaction scheme. However, an electrochemical approach allows direct reaction with the hydrogenated surface. The porous-silicon surface has been partially methoxylated by a controlled anodic dissolution. If has also been methylated using a non-destructive anodic process, with a yield of 80%, limited only by steric hindrance. The methylated surface of porous silicon exhibits a stability against oxidation increased by an order of magnitude.     

Influence du molybdène sur la cinétique des réactions de conversion du méthane en présence de H2O et CO2

An experimental study of the catalytic action of molybdenum in the reactions of methane with water vapor and carbon dioxide was performed in a fluidized bed differential reactor. In the experiments, special care was taken to isolate the homogeneous reactions which could have interfered with the catalytic effect. The ratio O₂/CH₄ in the feed and the heterogeneous reactions of oxidation and carbide Mo₂C formation, were shown to have considerable influence on the obtained yields. From kinetic results obtained on carbide and pure metal, a reaction mechanism is proposed, and a rate equation is presented for the conversion of methane by water vapor on molybdenum.