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.     

Effets de certains additifs sur i'extrudabilité du polypropylène

A polymer which is to be processed must always be combined with some stabilization agents in order to control its chemical and mechanical degradation. This paper concentrates on the influence of some stabilizer systems, namely phosphits thiophosphits and hindered phenolics, on melt flow properties and molecular characteristics of polypropylene. The resins were extruded several times at 250°C. Extrudates were cut up and analyzed by Gel Permeation Chromatography and capillary viscometry. The results reveal the influence of the nature and concentration of the different stabilizer systems on the control of degradation. A combination of a phosphite or a thiophosphite with a phenolic, prevents totally the degradation of the resin after submission to five extrusions.     

Influence de léagitation mécanique sur les transferts thermiques en fluidisation homogène

It is possible, through the use of an agitator with a particular shape which renews in a rapid sequence the matter contacting the column walls, to increase significantly the intensity of the thermal transfer between a liquid fluidized layer and the walls. It is shown experimentally that the rotative speed of the agitator has an important effect on the transfer. The whole results are qualitatively interpreted within the framework of a transiant-state mechanism.     

Influence des copolymères greffés sur les propriétés mécaniques des alliages de polyéthylène avec polystyrène

The use of graft copolymers polyethylene-graft-polystyrene (P(E-g-S)) in blends of low-density polyethylene and polystyrene is studied. The copolymers P(E-g-S) are prepared by polymerisation of styrene in the presence of hydroperoxylated polyethylene. Addition of 2,5 wt.-% P(E-g-S) to polyethylene-polystyrene blends considerably increases its breaking strength σ_R but much less so its elongation at break ε_R. A comparison of graft and block copolymers used as emulsifiers in polyethylene-poly-styrene blends at present shows that P(E-g-S) is intermediate between the former graft and block copolymers with regard to their influence on the mechanical properties of blends. Photographs of fractures in the blends show a tenfold smaller phase size upon adding P(E-g-S) to the blends.     

Préparation et etude de copolymères triséquencés isoprène et méthacrylate de méthyle

A convenient method is described for the synthesis of ABA triblock copolymers having a high vinyl polyisoprene as center block and poly(methyl methacrylate) as end blocks. Dynamic mechanical properties of these copolymers as a function of temperature are compared for different compositions (100%, 85%, 70%, 60%, 50%, and 30% of rubber) using solvent-casting methods. Since the morphology is dependent on the method of preparation of the samples, five solvents of different solubility parameters were tested for the same copolymer (i.e., 70% polyisoprene by weight) to show their influence on mechanical behavior.     

Étude cinétique du greffage de polystyrène anionique sur les silices. Contraction des macromolécules sur la surface solide

The kinetic study of the grafting reaction of anionic polystyrene on silica has been investigated in order to control the surface coverage model described previously. The amount of polymer fixed, or the grafting ratio, is related to the physicochemical characteristics of the silica as well as to the properties of the anionic polymer solution. The influence of the surface area(S), the silica concentration (Cs) and the surface concentration (A = S · Cs) has been followed. In dilute solution, the grafting ratio is proportional to the surface area if A is kept constant. This result is in favour of the proposed model. In concentrated solution, the grafting ratios are mostly dependend on the properties of the polymer solution, such as concentration, molecular weight and nature of the solvent. From the experimental results, it is possible to obtain informations about the contraction of the statistical coil fixed on the solid surface.     

Fractionnement des mélanges de protéines par électrophorèse convective

A new apparatus is proposed which allows the fractionation of protein mixtures by convective electrophoresis. The cell is arranged as a stack of elementary units, each of which consists of two compartments bounded by semi-permeable membranes and separated by a permeable cotton diaphragm. The solutions are circulated by forced convection, either co-current or eounter-current. The development of transport equations has made it possible to define which parameters control separation. An experimental study has been carried out to show the effect of these parameters (potential difference, rate of convection, number of elementary units) on the concentration of proteins from dilute solutions and on the fractionation of binary mixtures. Finally, predictive calculations are attempted in order to define the optimum operating conditions, and in order to scale-up the apparatus used.     

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.     

Stabilité de V2O5 supporte sur SiO2, comme photocatalyseur de l'oxydation du cyclohexane

The activity of Vanadium pentoxide supported on silicagel for the photocatalytic oxidation of cyclohexane has been studied. It was found that this catalyst presents a stable activity after an or decrease depending on the surface concentration of VOshrd initial unsteady state period during which the activity might increase or decrease depending on the surface concentration of V₂O₅. An interpretation is proposed for the two phenomena affecting the activity during the unsteady state period.     

La réduction de l'oxyde de nickel par l'hydrogène

The kinetic study of the isothermal reduction by hydrogen of powdered and compressed pellets of nickel oxide, has revealed the influence of the Curie transition of the oxide on the rate of reduction. Between 180 and 250°C, the reduction rate exhibits a sharp maximum and the activation energy is 26.3 kcal./mole. Above 250°C, the rate of reduction is constant during 70% of the reduction process. Between 250 and 300°C, the activation energy is 11.3 kcal./mole. Above 300°C, the kinetics is almost independent of temperature. Subsequent experiments have shown that water vapor strongly inhibits the reaction above 250°C.     

Étude de l'hydrogénation sélective du cyclopentadiène sur l'aérogel Cu/Al2O3 fluidisé

This work was conducted to evaluate the use of Cu/Al₂O₃ aerogel for the selective hydrogenation of the cyclopentadiene. Aerogel particles belonging to the C group of Geldart's classification, fluidize via a discrete clustering process above a minimum superficial velocity of 0.04 m/s. A kinetic study of the cyclopentadiène hydrogenation was performed on an integral reactor. The kinetic data suggest that the rate model can be represented by an equation corresponding to the Rideal—Eley mechanism. The reaction between gaseous hydrogen and the cyclopentadiène adsorbed on the catalyst surface is, in this mechanism, the controlling step. Because of the low activity of the catalyst, several reactor models (homogeneous and heterogeneous) were able to describe the experimental conversion rates observed in a small pilot fluidized bed reactor. However, the single phase plug flow model, which conforms more to the pseudo-homogeneous behaviour of the bed, was the most appropriate based on statistical discrimination.     

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.     

Modélisation du traitement de purification de l'acide phosphorique de voie humide par la méthylisobutylcétone

The present paper reports results for the purification of phosphoric acid by liquid—liquid extraction with methylisobutylketone. The simultaneous effect of some operating parameters, namely concentration of the feed acid, massic ratio of solvent to feed, temperature and number of theoretical stages, on the performances of the extraction step has been examined using a factorial design 2⁴. The established models allowed us to forecast the experimental conditions required to obtain a given yield of P₂O₅ and/or a well‐defined quality of the stripped acid. The optimal conditions have been determined by using a desirability function.     

Détermination du facteur d'efficacité et du coefficient de tortuosité d'un catalyseur au vanadium pour l'oxydation du dioxyde de soufre

An experimental study of the reaction rate for SO₂ oxidation on a vanadium catalyst under atmospheric pressure is presented. Different particles size are used (0,04–0,05 cm, 0,0115–0,02 cm, 0,15–0,16 cm, 0,2–0,21 cm, 0,3 cm) to determine catalyst effectiveness as a function of conversion and temperature. Effective diffusivity of SO₂ is then determined on the basis of a gas phase diffusion model. These values and the tortuosity of the catalyst are compared with results obtained by Kadlec et al⁽⁸⁾ and Livbjerg et al⁽⁹⁾.     

Estérification de l'acide stéarique par des alcools légers: Catalyse homogène par les titanates

Stearic acid estérification with low boiling alcohols using alkyl titanate compounds is performed in a semi-continuous reactor. The kinetic study of the reaction at high temperature (for which titanates are more efficient) requires to include the uncatalyzed reaction. The significance of the catalyst is specified; the nature of the active species, depending on rapid exchange reactions is also discussed.     

Etude des propriétés viscoélastiques de quelques mélanges polybutène-1 – polypropène

Viscoelastic properties of polybutene-1—polypropene blends were investigated in the β-relaxation range. Those blends show only òne relaxation peak and are assumed to be compatible in the amorphous phase. These results permit to corroborate our former assumption concerning the influence of the relative length of the alkyl group in polyolefin blends.     

Une application de l'oxydation humide à la récupération du mercure

The Canadian “Couplan Process” uses the absorptive capacity of sphagnum (peat) moss to remove heavy metal contaminants from aqueous effluents. Disposal of the peat moss is accomplished through incineration, which then permits metal recovery. Wet air oxidation (WAO) is a possible alternative to incineration for reducing the volume of peat moss wastes and recovering the metal. The objective of this study was to assess the feasibility of WAO for recovering mercury from pcat moss. Studies were performed by preparing samples of peat moss slurrics (up to 25% water added to air-dried peat moss) and exposing them for two hours to stoichiometric excess oxygen in a stirred autoclave at temperatures reaching 500°F. Mercury-free samples were studied, as well as those containing 3% by weight of HgS to simulate the saturated moss. The reduction in solids volume was almost 100%; about 5% by weight of the original peat moss was converted to acetic acid; ash residues amounted to 3 to 4% of the initial peat moss, and consisted of about 50% mercury by weight; about 2% of the original mercury was present in the final solution. It was concluded that wet air oxidation represents a possible alternative to incineration in the Couplan process.     

Etude de la viscosité dynamique complexe de quelques mélanges de polybutène-1 et de polypropène

Studies have been made on the dynamic oscillation and static properties in the molten state of blends from polybutene-1 and polypropene. Measurements were made with a balance-rheometer system Dr. Kepes and a capillary viscosimeter. Three experimental parameters, η₀, τ₀ and h have been determined. Steady shear and oscillatory shear viscosity data have been compared. A plot of intrinsic viscosity vs. composition of blends shows a minimum. Variation of η₀ and τ₀ with temperature follow the Arrhenius law but h does not depend on temperature.