Diminution du temps de préchauffage d'un réacteur isothermique

The kinetic study of a reaction performed in a high pressure batch reactor equipped with an inefficient heating device has led to the design of an efficient and inexpensive heating system for that autoclave. The electrical heating mantle has been replaced by a constant temperature oil bath. A stirrer coupled to the electrical motor by means of a leakproof mercury shaft seal, ensured uniform temperature within the oil bath. The theoretical preheating time of the improved reactor is much less than the original one, and the errors in the evaluation of the reaction rate due to the preheating period can almost be eliminated.     

Étude de la déshydratation des ethers de glycol comme une nouvelle voie de synthèse des vinyl-ethers

A study has been made to determine the basic conditions to develop an economical manufacturing process for vinyl glycol ethers. To achieve the aforesaid purpose, the synthesis of the above-mentioned products by means of glycol ether dehydration has been experimentally investigated; the most suitable way to achieve it has been found to be an indirect dehydration (pyrolysis of the corresponding acetates). After having found the best way of synthetizing the vinyl glycol ethers, a determination has been made of the parameters which have a significant influence on the reaction carried out, in the gaseous phase, in a glass tubular reactor under normal pressure. An optimization study has enabled to develop a model from which the maximum response area has been found, selectivity being the objective function.     

Etude de l'oxydation du pentachlorophénol dans différentes géométries de réacteurs à ultrasons de haute fréquence

The determination of the key geometric parameters used for high-frequency sonoreactor modeling has been studied. The methodology allowing the characterization of the different reactors built in our laboratory has been defined. The methods are: calorimetry, determination of the residence time distributions, the observation of the chemiluminescence of luminol and the degradations of a prototype molecule: pentachlorophenol. After characterization of the studied reactors, it seems that volumetric power, with equivalent emitting system, is the major parameter of the reactor's performance.     

Dispositif de déposition de couches de suspensions de céramiques appliqué à la stéréolithographie

A system to coat uniform layers of ceramic suspensions has been developed for rapid prototyping applications. The metering system is made of a gas injection nozzle which height, angle of attack and pressure can be adjusted. The coated layer homogeneity and the process reproducibility have been studied. The effect of each parameter on the coated layer thickness has been characterized using a design of experiments approach and a reliable mathematical model is proposed to optimze the coating system.     

Propriétés rédox de fullerènes fonctionnalisés

The C₆₀ physical chemistry properties make it possible to use it an elemental base for the synthesis of new materials. As the functionalization of fullerenes modify these properties, the modifications of their physical chemistry properties, in particular their electrochemical properties have been studied for a series of highly functionalized fullerenes. This article presents the results obtained with the electrochemical studies of fullerenes C₆₀ mono- and polyfunctionalized covalently. Our objective was to analyze the possible correlations between the redox properties of fullerenes and the degree, shape and natue of the functionalization. A series of functionalized fullerenes on positions [6, 6] was synthetised to carry out the investigation. This unique series of mono- and poly-functionalized fullernes provides an effective study of the modifications of the physical chemistry and electrochemical properties vs. the degee, shape and nature of the functionalization. The results obtained have been compared with literature data.     

Matériaux composites à base de bois rétifié, III. Etude de l'influence de la granulométrie des charges lignocellulosiques

Different composite materials, with retified or natural poplar and polyester resin were prepared by molding. The influence of the filler granulometry on certain physicochemical (density, humidity, hardness) or mechanical properties of the materials was studied. The density and the increase of mass in humid atmosphere were always found to be less when the wood was thermally treated. On the other hand, the hardness of the composites made from natural poplar was much higher. The mechanical properties were found to be weak when the wood was retified. When the wood was thermally treated, it was possible to optimise the three parameters, namely, density, water retention capacity and mechanical properties. The optimal granulometry of poplar was determined between 0.75 and 1.5 mm. The results obtained are discussed considering the physico-chemical properties of the different varieties of wood studied and the interactions which exist between the polar resin and the wood.     

Modélisation de l'efficacité de filtration d'un échangeur cyclone

This work is a modelling of the Aireco® filtration system. This heat exchanger, with particle catching capabilities, is made of a cyclonic body which contains refrigerated coils. The water vapour contained in the gas to be treated condensed on the coils surface. Our modelling considers two main capture surfaces: the entry zone in which particles are collected by inertial impaction and the cyclonic body in which particles diffused by centrifugal force is the main phenomena. We found that these considerations explain our experimental results with an accuracy more than 90%, when the Aireco® is on a normal point of working.     

Modélisation d'un four de calcination du coke de pétrole: II. Simulation du procédé

A one-dimensional steady-state mathematical model has been developed to simulate the process of calcination of petroleum coke in a rotary kiln. A simulation is made to reproduce the operating conditions prevailing during a normal working day, in order to validate the model, and to study the effects of the main process control variables. It has been found that of the energy provided by combustion, 59.5 % comes from hydrogen, 14.6 % from the carbon of the coke bed, 13.8 % from coke dust, 11.3 % from methane and 0.8 % from tar. A comparison with existing models is made to identify eventual similarities between the various kilns under study. It appears that maximum coke temperature occurs at 45 to 55 % of kiln length, while volatile matters evolution takes place between 5 and 60 % of kiln length, measured from feed end.     

Cinétique de la calcination du coke de pétrole en atmosphères neutre et oxydante

A devolatilization kinetic study of oil coke samples under conditions close to those of industrial calcination furnace is presented. The effects of the surrounding conditions (neutral or oxydizing medium), the heating rate and the percentage of oxygen in an oxydizing environment are analyzed. Experiments are carried out in an induction oven and involved thermogravimetric and chromatographic analyses. Results show that, under certain conditions, the nature of the environment influence the devolatilization process. A slow heating rate and a low content in volatiles promote the coke degradation by oxygen in an oxydizing medium. The reactive schemes are derived by tracking the concentration of CH₄, H₂, CO and CO₂. In regions where the coke is not degraded, a kinetic model is used to compare the parameters describing the develotilization phenomena in the two media (neutral and oxydizing), i.e.: the reaction order, the activation energy and the pre-exponential factor. It is shown that the oxydizing medium promotes an increase in the activation energy.     

Etude des propriétés rhéologiques de mélanges fondues de polybutène-1 et de polypropène à des cisaillements élevés

The viscoelastic behaviour of polybutene-1-polypropene blends has been studied in the molten state with respect to temperature, shear stress and shear rate. The corrections of experimental data have been carried out and the influence of the radius of capillary on these corrections was studied. The elasticity was investigated by means of Barus factor and the variation of viscosity versus composition of blends shows a minimum which might be interesting for the technology of plastic materials.     

Modélisation de la cinétique de biodégradation de phénol par granules aérobies

This work describes a model of the biodegradation of phenol carried out by aerobic granules. These granules were obtained by culturing an activated sludge supernatant in a sequencing batch reactor fed with a synthetic waste water and subsequently, by acclimation to phenol (100 mg/L). The kinetics of phenol biodegradation by the aerobic granules was investigated over a wide range of initial phenol concentrations (40–1112 mg/L) in shake‐flask cultures. A Haldane‐type model was adjusted to the experimental results, which depicts successfully the phenol biodegradation profiles in the entire range of initial concentrations studied by using only one set of parameters. It is our view that the proposed model could contribute to the knowledge about the ability of aerobic granular systems to biodegrade toxic, inhibitory compounds such as phenol.     

Propriétés photocatalytiques de Ta2O5/SiO2

The photocatalytic properties of deposited tantalum oxide (Ta₂O₅) on silica, in the reaction of photocatalytic oxidation of cyclohexane by oxygen, have been studied. The properties of this catalyst were compared with those of the previously studied system V₂O₅/SiO₂, and it was concluded that the mobilities of V⁺⁵ and Ta⁺⁵ ions on the surface of silica under radiation arc verymuch different. This study was completed by an analysis of the diffuse reflectance spectra and a thermogravimetric analysis of the used catalysts. The conclusion was that the site active in the photocatalytic reaction, is hydrated during the oxidation of cyclohexane.     

Étude de l'étirage à froid des fibres de polymères synthétiques dans les agents organiques

The cold drawing of synthetic polymers is generally carried out through necking at a short collar between the drawn part and the undrawn part of the fiber; if the drawing is carried out in certain organic liquids, the lengthening is realized through thousands of simultaneous necks which permit the fiber to be penetrated by a dye dissolved in the liquid. The stress–strain curves for the drawing in liquid show an important decrease in the force at the time the multiple necking are produced. This decrease is the result of an increase in the mobility of the macromolecular chains through the penetration of the organic liquid to the level of the shoulder of the necks. A morphological study has been carried out through the observation of cuts by optical microscopy, along with a utilization of the techniques of x-ray diffraction, IR spectroscopy, and electron microscopy. It was found that the liquid penetrates t?he fiber to the level of the necking via a rupture of the interchain bonds which takes place during the change of structural following the drawing. The bonds are maintained ruptured as long as the liquid is not squeezed out by the aligning of the chains; they reform later to produce a new highly crystalline structure.     

Influence du dodecyl sulfate de sodium sur la tension interfaciale du système biphasé butanol-eau

Interfacial tension between the two phases formed by the partially miscible system composed of butanol-1 and water has been investigated. Using the method of drop volume tensiometry, the effect of a surface-active agent, sodium dodecyl sulfate, on interfacial tension was investigated. Addition of surfactant to the butanol-rich phase, which forms the droplet, has been found to bring about a decrease in interfacial tension the magnitude of which was influenced by the time of contact. When the surfactant was added to the aqueous (bulk) phase, the decrease in interfacial tension was greater and it was equal to that observed when the surfactant was added to both phases. It is concluded that the orientation of phases in the instrument has an important effect on the apparent interfacial tension observed.     

Récupération sélective du vanadium dans l'effluent d'un procédé de fabrication du blanc de titane

The selective recovery of vanadium from an effluent of a manufacturing process for titanium white (oxide) has been made. The process retained is based on the partial neutralization of the effluent by means of calcium carbonate and on the separation of metal hydroxides from calcium sulfate and the solution. The hydroxides are thereafter calcined in the presence of a sodium salt, so that sodium vanadate may then be extracted by washing with water. Vanadium is finally precipitated by the addition of ammonium chloride or pH adjustment. The experimental results obtained in the laboratory study of the effluent neutralization, the calcination and leaching of the hydroxides and the vanadium precipitation are presented and discussed. The yields obtained in the various stages and their interdependance are also discussed.     

Caractéristiques rhéologiques des suspensions de tourbe

The flow of peat suspensions in water has been studied in the concentration range of 0.75 to 2.25% by weight on a dry basis; the fibre size was below 3 mesh. The pressure drop has been measured, for an extensive range of flow rates (the Reynolds numbers varying from 10³ to 10⁵), in 3 horizontal tubes, the internal diameter of which was 50.8, 38.1 and 25.4 millimeters, respectively. The results have shown that the deviation from the new-tonian behaviour increased with the concentration and the tube diameter. A comparison with dilute pulp slurries has indicated that the behaviour of both suspension had the same characteristics. The fibre suspensions are non-homogeneous fluids and the conventional rheological models cannot describe their behaviour. The annular ring model, which implies the presence, in a laminar flow, of an entangled-fibre network, explains the experimental results obtained. A size analysis of the particles has shown that the type of pump used had an effect on the fibre degradation.     

Etude numérique et paramétrique de la combustion de particules d'aluminium

Several numerical models have been investigated to study the reactivity of aluminium particles coming from the combustion of solid propellants in spatial launchers. The Law model has been rapidly selected as it yields a continuous model from an aluminium drop to an oxide drop. The model also gives the residue size at the end of the combustion process. This could explain the scaling observed in the rocket engines. In order to study the coupling between the flow and the combustion, the combusion of aluminium drops has been widely analyzed with 0D computation. The main mechanisms of the combustion process have been identified.     

Plastification sélective dans le cas d'alliages de polymères II) Systèmes ternaires — Rôle de l'adhésion interfaciale

Polymerization of methly methacrylate (MMA) was carried out in the presence of nylon-6 with different content of amino end groups and water. The more the content of amino end groups of the nylon molecule, the lower is the conversion of MMA. The rate of polymerization, R_p, is proportional to the amount of nylon. However, as for the amount of MMA, the rate increased at first amount of MMA, but then became independent of the amount of MMA. These kinetical behaviours suggest a model of an enzyme-like reaction. MICHAELIS -MENTEN'S equation was found to be able adequately to be applied. The polymerization was confirmed to proceed through a radical mechanism. By the activation analysis, it was found that the nylon used here contained a slight amount of copper (5 – 8 · 10^?7 g Cu/g fiber). When the nylon was dissolved in formic acid and reprecipitated by adding hot water, the nylon was found to lose the activity for the polymerization. However, when a trace of CuCl₂ was absorbed on the nylon, the nylon was confirmed to regain the activity. As a conclusion, an assumed mechanism similar to an enzymatic reaction in which nylon plays as enzyme and copper as coenzyme was proposed. In the second part of the present paper, a study on the polymerization in the presences of carbon tetrachloride was made. Regardless of the content of the NH_2? end groups, the conversion was always near to quantitative yield. The mechanism was found to be a radical one. An initiation mechanism, in which a complex of nylon, CCl₄, H₂O and MMA is formed, was proposed.     

Modèles cinétiques et mécanisme de l'oxydation catalytique. Du propene en présence de molybdate de fer

The kinetic study of propylene oxidation to acrolein over a ferric molybdate catalyst has been performed on a differential reactor. Among models derived on the assumptions of Langmuir Hinshelwood kinetic rate or on Mars and Van Krevelen oxido-reduction mechanism, a discrimination method has been realized. The discrimination leads on one hand to the conclusion that acrolein is obtained either from oxygen of the oxide lattice or from absorbed dissociated oxygen. On the other hand carbon dioxide is formed both by acrolein degradation and by a mechanism excluding dissociation of oxygen.     

Matériaux composites à base de bois retifié II. Etudes des propriétés mecaniques de differents mélanges

Different composite materials, with retified pine wood as base, were prepared. Their mechanical properties were compared with composite materials prepared using mineral (zinc oxide, talc, glass) or organic (powdered pine wood) constituents and polar (PVC, ABS) or non-polar (PP) resins. The behaviour of the mixtures varied with the nature of the polymer. An improvement in the mechanical properties was observed when retified wood and polar resins were used. Based on the fibre/matrix interactions, a general interpretation of the differences observed in the behaviour, has been proposed. Results obtained from the tests done on the extent of swelling and the gain in weight of the composite materials in humid atmospheres confirm the need in the use of retified wood as an additive of polar resins.