the extraction of some metallic bromides from aqueous solutions with methyl ethyl ketone and methyl iso-butyl ketone

The extraction of the following metals from aqueous solutions containing excess bromide with methyl ethyl ketone (MEK), and methyl isobutyl ketone MIBK has been investigated:—Cu(I), Cu(II), Zn(II), Ni(II), Co(II), Fe(II), Fe(III), Al(III), Mn(II), Sn(II) and Sn(IV). The use of MEK was found to be strictly limited by its solubility in acidic aqueous solutions. Determinations of the formulae of the extracted compounds were attempted in two cases but were found to be not wholly satisfactory and were discontinued. An interesting reaction between the cupric bromide complex and the solvents was noticed. Separations of Fe(IIl) from Mn(II), Fe(III) from Al(III), Fe(III) from Co(Il) and Fe(III) from Ni(II) could be achieved under suitable conditions.     

Crystallization of isotactic polystyrene from dilute solutions

The overall rate of crystallization of isotactic polystyrene from dilute solutions, 1% by weight, in trans-decalin and benzyl alcohol was studied as a function of temperature using dilatometry. These solvents were chosen because the dissolution temperatures of crystalline isotactic polystyrene are practically the same in both solvents. The overall rate of crystallization as a function of crystallization temperature showed a maximum in both solvents at about 50°C. At lower crystallization temperatures the rate of crystallization is much lower. The overall rate of crystallization of isotactic polystyrene in benzyl alcohol is far larger than in trans-decalin at the same undercooling throughout the temperature range, which is in apparent contradiction to present crystallization theories. At very large undercooling (T_c lower than about 0°C) the solutions of isotactic polystyrene in both solvents quickly become “rigid” gels. Surface replicas of freeze-etched gels indicate that a fringed micelle type of crystallization takes place at these low temperatures. The transition from folded chain crystallization to fringed micelle crystallization may be due to a stiffening of the polymer chain below about 50°C, with a reduced rotational mobility of the phenyl groups on the chain. If very dilute solutions, below 0.5% by weight, are crystallized at these low temperatures no gels were formed but fibrous crystals are produced which could be observed under the polarizing microscope.     

TheLangmuir-Freundlich equation in adsorption from dilute solutions on solids

Correlation between parameters obtained from the signle-solute and bisolute adsorption data by means of theLangmuir-Freundlich equation has been studied.     

Kinetics and hazards of thermal decomposition of methyl ethyl ketone peroxide by DSC

Differential scanning calorimetry (DSC) was applied to analyze thermal decomposition of methyl ethyl ketone peroxide (MEKPO). Thermokinetic parameters and thermal stability were evaluated. MEKPO decomposes in at least three exothermic decomposition reactions and begins to decompose at 30–32 °C. The total heat of decomposition is 1.26 ± 0.03 kJ g⁻¹. Thermal decomposition of MEKPO can be described by a model of two independent reactions: the first is decomposition of a less stable isomer of MEKPO, followed by decomposition of the main isomer, after which an exothermic reaction of the reaction products with the solvent, dimethyl phthalate. The results can be applied for emergency relief system design and for emergency rescue strategies during an upset or accident.     

Global non-ideality effects in adsorption of organic substances from dilute aqueous solutions on activated carbon

Summary A method for the quantitative estimation of the global non-ideality of the adsorption of weak organic electrolytes on activated carbon from dilute aqueous solutions is presented. The method is based on the analysis of aGraham plot which reflects the adsorption isotherm deviations from ideality. Averaging these deviations over the whole range of adsorption, one gets a single value representing the global non-ideality of a system. The method also allows to estimate the contributions of heterogeneity and interactions in the adsorbed phase to the global non-ideality effect. The theoretical considerations are illustrated by some model calculations. The usefulness of the method is tested for experimental data of benzoic and salicyclic acid adsorption over a wide range ofpH and concentrations.

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Globaler Effekt der Nicht-Idealität bei der Adsorption organischer Substanzen aus verdünnten wässerigen Lösungen an Aktivkohle

Zusammenfassung Es wird eine Methode zur quantitativen Abschätzung der globalen Nicht-Idealität für die Adsorption schwacher organischer Elektrolyte aus verdünnten wässerigen Lösungen an Aktivkohle vorgestellt. Diese Methode basiert auf der Analyse der bekanntenGraham-Abhängigkeit, die die Abweichung der Adsorptionsisotherme von der Idealität zeigt. Bei Errechnung des Durchschnittwertes dieser Abweichung über den ganzen Asorptionsbereich erhält man einen Wert, der die globale Nicht-Idealität für ein Adsorptionssystem charakterisiert. Die Methode erlaubt auch, den Beitrag der Heterogenität und der Wechselwirkungen in der Adsorptionsphase zum globalen Effekt der Nicht-Idealität abzuschätzen. Die theoretischen Erörterungen werden an Hand von Modellberechnungen illustriert. Die Nutzbarkeit der Methode wurde mit experimentellen Daten der Benzoe- und Salicylsäureadsorption in einem weiten Bereich vonpH und Konzentration getestet.

     

Chemiluminescence in the course of methyl ethyl ketone oxidation by ozone in acidic aqueous solutions

Chemiluminescence in the visible spectral region is observed in the course methyl ethyl ketone oxidation by ozone in neutral and acidic aqueous solutions. The spectral composition of the chemiluminescence is studied. On going from neutral to acidic aqueous solutions of methyl ethyl ketone, the initial intensity of the signal increases and the kinetics of a decrease in the chemiluminescence intensity changes. A radical scheme of the process is proposed to explain the results obtained.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 829–835.Original Russian Text Copyright © 2004 by Zimin, Gusmanov, Khursan.     

Degradation on freezing dilute polystyrene solutions in p-xylene

Chain scission was observed during the crystallization of p-xylene in dilute polystyrene solutions. Degradation yields were determined by gel permeation chromatography, as a function of the number of freeze-and-thaw cycles, polymer concentration, and initial polymer molecular weight (M). The rate constant for chain scission K_c increases with the polymer chain length, from 0.021%/cycle at M = 110·10³ to 4.7%/cycle at M = 8.5·10⁶. Over the two decades range of investigated molecular weights, K_c follows an empirical scaling law of the form K_c ～ (M ? M_lim)^1.17578, where M_lim is a limiting molecular weight ? 29,000 g. mol^?1 below which no degradation could be induced. Some propensity for midchain scission was detected, although this tendency was much weaker in comparison to flow-induced degradation. A chain scission model based on crack propagation failed to reproduce the experimental results. To explain the observed dependence of K_c with the square of the radius of gyration, an interfacial stress transmission mechanism between the crystallization fronts and the polymer coil has been proposed. © 1994 John Wiley & Sons, Inc.     

Conformation analysis of freeze-dried isotactic polystyrene from dilute solutions

Fourier transform infrared spectra of freeze-dried samples of isotactic polystyrene (i-PS) from dilute solutions were analyzed. The 698, 1452, 1493 and 1601 cm⁻¹ bands increased in sharpness and intensity as the solution concentration decreased, indicating that the freeze-dried sample is in a more dilated state. When the freeze-dried i-PS was annealed at 100°C, all aforementioned bands broadened and their heights depressed, accompanied with a significant change of the bands at 981 and 906 cm⁻¹.     

Determination of airborne methyl ethyl ketone peroxide

Summary A new method for the determination of airborne methyl ethyl ketone peroxide (MEKP) is based on the reaction of peroxides with 4-tert-butyl catechol, in which the peroxide radicals oxidize the catechol to the corresponding benzoquinone. The yellow colour generated is measured at 395 nm. Sampling from factory air can be performed by aluminium oxide sampling tubes. Glacial acetic acid is used as a solvent and for the desorption of the peroxide from the aluminium oxide. The detection limit (0.05 mg/m³ for 4 h samples) for the MEKP in air is well below the current hygienic reference value (1.5 mg/m³). The method was used for MEKP determinations during lamination applications in the production of reinforced unsaturated polyester plastics, where the airborne concentrations of the peroxide were well below the current hygienic reference values.     

Kinetics of adsorption from micellar solutions

Previous studies on surfactant adsorption mostly deal with dilute systems without aggregation in the bulk phase. At the same time, micellar solutions can be more important from the point of view of applications. If one attempts to estimate the equilibrium adsorption, neglecting the influence of micelles can lead to reasonable results. The situation differs for non-equilibrium systems when the adsorption rate can increase by an order of magnitude at the increase of the surfactant concentration beyond the CMC. A critical survey of various models describing the influence of micelles on adsorption kinetics at the liquid-gas interface is given and the theoretical results are compared with existing experimental data. The theories proposed for the case of large deviations from the equilibrium are usually based on some unjustifiable assumptions and can describe the kinetic dependencies of adsorption in only a limited number of situations. Consequently, only rough estimates of the kinetic coefficients of micellization can be obtained from experimental data on dynamic surface tension. More rigorous equations can be derived if the system only deviates slightly from equilibrium. In the latter case, the agreement between theoretical and experimental results is essentially better and measurements of the dynamic surface elasticity of micellar solutions allow us to study the micellization kinetics.     

Effect of the carbon surface layer chemistry on benzene adsorption from the vapor phase and from dilute aqueous solutions

We present a complex study of benzene adsorption on chemically modified commercial activated carbons. The porosity of studied carbons is almost the same, whereas the chemical composition and the acid-base properties of surface layers differ drastically from amphoteric (initial de-ashed carbon D43/1, Carbo-Tech, Essen, Germany) and acidic (carbon modified with concentrated HNO3 and fuming H2SO4) to strongly basic (carbon modified with gaseous NH3). Benzene adsorption isotherms measured from aqueous solution at three temperatures (298, 313, and 323 K) and at the neutral pH level are reported. They are supported by studies of water and benzene adsorption from the gaseous phase (volumetric and calorimetric data) and the data of benzene temperature-programmed desorption (TPD). Moreover, the data of the enthalpy of immersion in water and benzene are also presented. Obtained data of benzene adsorption from the gaseous phase are approximated by applying the method of Nguyen and Do (ND) and the Dubinin-Astakhov (DA) equation. The data of adsorption from solution are described by the hybrid DA-Freundlich (DA-F) model. We show that there are similarities in the mechanisms of benzene adsorption from the gaseous phase and from aqueous solutions and that the pore-blocking effect is the main stage of the adsorption mechanism. This effect strongly depends on the polarity of the carbon surface. The larger the ratio of the enthalpy of carbon immersion in water to the enthalpy of immersion in benzene, the larger the reduction in adsorption from solution, compared to that in the gaseous phase, that is observed.     

Kinetics and mechanism of oxidation of acetone,ethyl methyl ketone and diethyl ketone with chloramine-T in hydrochloric acid medium

The kinetics of oxidation of aliphatic ketones (acetone, ethyl methyl ketone and diethyl ketone) by chloramine-T in presence of hydrochloric acid (0.1 to 0.3M) have been investigated at 30 °C. The rate of disappearance of chloramine-T has been found to be first order each with respect to oxidant, ketone and [H⁺], in the range of the acid concentrations studied. The thermodynamic and kinetic parameters have been evaluated by determining the rate constants at different temperatures. The products of the reaction have been identified as chloroketones by their NMR spectra. The solvent isotope effect has been studied in the case of the oxidation of acetone and ethyl methyl ketone. A mechanism has been proposed.     

Diffusion in glassy polymers. IV. Diffusion of methyl ethyl ketone in atactic polystyrene above the critical concentration

Integral absorption and desorption of methyl ethyl ketone in atactic polystyrene were studied as functions of film thickness at 25 and 45°C. with concentrations above the critical concentration of the system. In all cases investigated, the reduced absorption and desorption curves for films of different thicknesses did not give a single curve, though the individual absorption and desorption curves appeared to have the shape expected from the Fickian diffusion mechanism. The initial slopes of the reduced curves increased with increasing film thickness for both absorption and desorption. The quantity R₀, the value of the reciprocal of the half-time for absorption or desorption extrapolated to zero concentration increment, provides a measure of absorption rate at a given initial concentration. The dependence of R₀, on film thickness was almost unaltered in the concentration region concerned at both temperatures. The values of the mutual diffusion coefficient D of the system were calculated by assuming absorption and desorption processes for hypothetical film of infinite thickness to be controlled by the purely Fickian mechanism. The values of D evaluated by this method agreed quite well with those deduced by Kishimoto from steady-state permeation measurements.     

Non-newtonian behavior of associations of macromolecules in dilute solutions

The shear-thickening of dilute of flexble macromolecules of high molecular weight is explained theoretically assuming the existance of one-to-one reversible, concentration and shear rate dependent association between the macromolecules. The theoretical curves obtained are in fairly good agreement with the experimental results.     

Viscosimetric study of polystyrene polymacromonomer dilute solutions

The viscosimetric behaviour of poly(ω-norbornenyl polystyrene) polymacromonomers is studied in dilute solutions as a function of the degree of polymerisation and the branch molar mass. We emphasise the fact that the exact molar mass characterisation using scattering techniques is illusory, owing to a strong intermolecular contribution in the scattering distribution, as evidenced by neutron scattering. Two characteristic behaviours are evidenced in the viscosimetric dependence versus molar mass of the polymacromonomer and are attributed to their global conformation when they could be considered as spherically or cylindrically symmetric. Moreover for the branch of higher molar mass used an unexplained deviation appears between the two behaviours. Received: 6 May 2000 Accepted: 6 September 2000