Influence d'une agitation rotative sur le mélange en retour dans une colonne pulsée à plateaux perforés

The efficiency of a pulsed perforated plate extraction column can be improved, particularly at low values of A.f, by superimposing a rotary agitation. The hold up and the Peclet number have been measured in such a column in order to calculate the coefficient of backmixing of the continuous phase. A comparison of the results with those for a conventional pulsed column has indicated that the improved performance is due to an increase in hold up and not, as might have been supposed, to reduced backmixing.     

Synthese du furyl-2 oxiranne en milieu hétérogène solide-liquide faiblement hydrate: Determination du régime de production,expression de la loi cinétique

Optimum conditions for scaling up the synthesis of furyl-2 oxyrane from furfural have been determined. A continuous stirred tank reactor proved the most efficient configuration for the production of the oxirane. The kinetic model makes it possible to predict the yields of epoxide per unit volume and unit time.     

Adsorption de surfactants sur le dechet lainier de carbonisage surfactant adsorption on the wool carbonizing waste

Although wool carbonizing waste is available in large amounts (8.000 tonnes per year, in France), no process has been developed for its valorization. Wool carbonizing waste is made up of chemically modified short-sized wool fibres and of plant material particles which are considered as sulphuric lignins. Owing to the physical structure as well as to the polar and apolar characteristics of its macromolecules, wool carbonizing waste was likely to be a suitable material for the adsorption of ionic organic solutes. The adsorption of various surfactants on wool carbonizing waste was therefore investigated so as to assess the optimal conditions of use of this substrate in water pollution control. The adsorption isotherms of anionic (SDS; Figs 1 and 2). cationic (CPC; Figs 3 and 4), and non-ionic (NPPO; Fig. 5) surfactants were drawn, for various pH and temperature conditions, so as to determine the adsorption mechanisms involved as well as the adsorption capacity of the carbonizing waste and the optimal adsorption conditions. The adsorption was shown to be enhanced by temperature as a result of changes in adsorbent structure. Wool carbonizing waste is therefore liable to be used for the purification of hot effluents. The processing of anionic surfactant solutions by wool carbonizing waste requires acidic media (pH < 3), whereas alkaline media are more suitable for effluents containing cationic surfactants. Ionic bonding is involved in both cases. The adsorption rates of SDS and CPC range from 15 to 26% and from 35 to 55%, respectively, depending on the temperature, and are thus markedly higher than that of NPPO (7%) of which adsorption proceeds mainly through hydrophobic bonding. Although these adsorption rates are lower than those of ion-exchange resins, they are higher than those of charcoals (Table 3). The L-shape of the adsorption isotherms corroborates the successive involvement of ionic and hydrophobic interactions in the case of ionic surfactants. The models of Langmuir and Freundlich (Tables 1 and 2) were used for the modelization of water processing units. Besides, the column processing of a SDS solution showed the effect of pH on the efficiency of the operation (Fig. 6) as well as the beneficial effect of temperature (Fig. 7). The processing of industrial effluents in a stirred reactor corroborated the outstanding ability of wool carbonizing waste to adsorb cationic surfactants (Table V). Furthermore, these tests showed that the removal of non-ionic surfactants is improved when they are mixed with anionic surfactants (Table 4).     

Étude des isothermes d'Adsorption de surfactants ioniques et non ionique sur des fibres de laine carbonisée

The adsorption isotherms of the three main types of surfactant have been plotted against various pH's and temperatures. It has thus been possible to propose new ways of insuring adsorption and determining the importance of the ionic links and hydrophobic interactions involved in the various-medium conditions considered. The presentations by Lauginuir and Freundlich have permitted to develop the adsorption equations corresponding to each case. Finally, the isotherm plotting in a series of low concentrations has permitted to predict the maximum volume of an effluent purified per kilogram of substrate, in the case of the concentrations frequently found in the waste waters.     

Effects of surface-active agents on mass transfer inside drops

The transfer of iodine from a drop of carbon tetrachloride falling in water has been studied in the presence of two surface-active agents, Teepol and sodium dodecylsulfate.The presence of Teepol is found to decrease the drop's terminal velocity more than that of sodium dodecylsulfate, this effect being more pronounced for larger drops.Small amounts of these surfactants reduce the internal circulation and consequently the mass transfer rates. Efficiencies can even fall below those for rigid spheres when the surfactant concentration is high. The maximum reduction for the individual mass transfer coefficient is about 77% with both surface-active agents.Results are compared with the model of Vermeulen and the model of Calderbank and Korchinski. These results are also expressed using the Galileo number and diffusivity effective factor $\text{R}$.     

Influence of mass transfer direction on efficiency of a pulsed perforated plate column

The purpose of this paper is to give a complete analysis of the influence of mass transfer direction on the performance of a pulsed perforated plate-column.The ternary system studied was water—iodine—carbon tetrachloride. Both mass transfer directions were considered, i.e. iodine transfering from continuous aqueous phase to dispersed organic phase and vice versa.Parameters considered are overall efficiency, hold up, true number of transfer units, Peclet number for both phases, drop size, interfacial area and overall mass transfer coefficient.     

Recovery of aconitic and lactic acids from simulated aqueous effluents of the sugar‐cane industry through liquid–liquid extraction

The recovery of aconitic and lactic acids from dilute aqueous effluents of the sugar‐cane industry by a solvent extraction technique has been investigated in order to reduce environmental pollution and in view of the possible uses of pure solutes in the field of foods and pharmaceuticals. Reactive extraction of carboxylic acids with tributylphosphate dissolved in dodecane was examined. Experiments were performed at 25 °C for three extractant concentrations of 50%, 60% and 70% (mass %) in dodecane. The decrease of specific gravity and viscosity of solvent resulting from the presence of an inert diluent was favourable to the phase settling and the mass transfer. The percentage of acids recovered in the organic phase for a volumetric solvent ratio varying from 0.5 to 5.0 was determined. Taking into account the difference between the partition coefficients for the carboxylic acids under consideration, the selectivity of solvent with regard to aconitic acid also was quantified. Moreover, owing to its water‐insolubility, its availability and its low cost, tributylphosphate can be considered as a promising extractant for large‐scale applications. © 2000 Society of Chemical Industry     

Piloting the spanning tree protocol in home?networks using a?multi-agent system

Broadband access to the Internet at home was the first step in the emergence of so called Home Networks. In a close future, the number of appliance connected will rise and the network will become the home backbone. Its architecture has to evolve to tackle those new challenges. After a study of the network requirements, this paper introduces a complete system to pilot the forwarding ensuring a proper QoS. This is achieved by a knowledge plane composed of agents embedded on devices, which are optimizing the Ethernet layer.