Properties of the material spontaneously formed in interfacial layer of system at extraction of rare-earth elements

The wetting ability of the material formed spontaneously in the interface layer of an aqueous solution of a rare-earth element (REE) salt/solution of di-(2-ethylhexyl)phosphoric acid (D2EHPA) extraction system adhered onto a glass plate is investigated. It is found that its properties depend on the natures of the REE and the solvent, and the initial concentrations of the REE and the extracting reactant. It is shown that the material formed at the interface and adhered onto a glass plate has controlled wetting ability. The difference between the properties of interface REE formations for yttrium and cerium subgroups is established. The electric conductivity of interphase formations in the same systems is measured and shown to display an extreme dependence on time in systems with heptane but a monotonically increasing one in systems with toluene. It is shown that the electric conductivity of interphase formations diminishes sharply with an increase in the ratio of the initial concentrations of REE salt and D2EHPA. It is concluded that an increase in the relative gain of the average molar mass of interphase formations indicates coagulation and the formation of polymers.     

Asymmetric orientation of toluene molecules at oil-silica interfaces

The interfacial structure of heptane and toluene at oil-silica interfaces has previously been studied by sum frequency generation [Z. Yang et al., J. Phys. Chem. C. 113, 20355 (2009)]. It was found that the toluene molecule is almost perpendicular to the silica surface with a tilt angle of about 25°. Here, we have investigated the structural properties of toluene and heptane at oil-silica interfaces using molecular dynamics simulations for two different surfaces: the oxygen-bridging (hydrophobic) and hydroxyl-terminated (hydrophilic) surfaces of quartz (silica). Based on the density profile, it was found that both heptane and toluene oscillate on silica surfaces, with heptane showing more oscillation peaks. Furthermore, the toluene molecules of the first layer were found to have an asymmetric distribution of orientations, with more CH(3) groups pointed away from the silica surface than towards the silica surface. These findings are generally consistent with previous experiments, and reveal enhanced molecular structures of liquids at oil-silica interfaces.     

Properties of the material of interphase formations based on lanthanide Di-(2-ethylhexyl)phosphate

The structural, optical, and electrical properties of the material of interphase formations arising spontaneously in the interface region of an extraction system consisting of an aqueous solution of a rare-earth element (REE) salt (a solution of di-(2-ethylhexyl)phosphoric acid (D2EHPA) in an organic solvent) are investigated. The structure of lanthanide di-(2-ethylhexyl)phosphate is determined and its lattice constants are estimated. It is shown that the electric conductivity and optical density of the material of interphase formations transferred onto a glass plate correlate with the accumulation of REEs in the interfacial layer of the extraction system. The difference between the properties of the material of interphase formations based on REEs of the yttrium and cerium subgroups is established.     

Structuring in Interphase Layer of Extraction System

The results of a study of the rheological properties of the interphase layer formed when an aqueous phase containing HCl and PrCl₃ is brought in contact with a solution of an extracting agent (nonoxymethylphosphonic acid) in toluene at varied content of the components in the system are presented.     

Effect of interfacial rheology on model emulsion coalescence I. Interfacial rheology

Interfacial elasticity and "dynamic" surface pressure isotherms were measured for interfaces between a dispersed water phase and a continuous phase of asphaltenes, toluene, and heptane. The interfacial modulus is a function of asphaltene concentration and in all cases reached a maximum at an asphaltene concentration of approximately 1 kg/m(3). The modulus increased significantly as the interface aged and slightly as the heptane content increased to a practical limit of 50 vol%. The modulus was approximately the same at 23 and 60 degrees C. The modulus correlated with the inverse of the initial compressibility determined from surface pressure isotherms. The surface pressure isotherms also indicated that a phase transition occurred as the interface was compressed leading to the formation of low compressibility films. Crumpling was observed upon further compression. The phase transition shifted to a higher film ratio with an increase in heptane content and interface age. Asphaltene concentration and temperature (23 and 60 degrees C) has little effect on the surface pressure isotherms. The surface pressure and elasticity measurements are consistent with the gradual formation of a cross-linked asphaltene network on the interface.     

Effect of mechanical vibrations on the reextraction kinetics in the toluene-HNO3-H2O system

The kinetics of reextraction through a vibrating interface in systems containing di-(2-ethylhexyl)phosphoric acid (D2EHPA) is studied. When mechanical vibrations are excited in the interface layer, the mass transfer rate increases. It is established that mechanical vibrations promote reextraction by means of three factors: an increase in the interphase surface area, a decrease in the diffusion layer thickness, and the process of dispersion. It is demonstrated that an increase in the amplitude of vibrations results in an increase in the effective mass transfer coefficient, with its dependence on the squared amplitude being linear over the range covered. It was established how extractant adsorption, a phenomenon that influences the mass transfer of D2EHPA and nitric acid, influences the process.     

Lactone cleavage reaction kinetics of rhodamine dye at liquid/liquid interfaces studied by micro-two-phase sheath flow/two-photon excitation fluorescence microscopy

Two-photon excitation fluorescence microscopy was combined with the two-phase microflow system in order to measure the fast interfacial reaction rate at liquid/liquid interfaces. The lactone cleavage kinetics of octadecylrhodamine B (C(18)RB) at the toluene/water and heptane/water interfaces was studied by this new method. The organic solution containing the nonfluorescent lactone of C(18)RB was made to flow as an inner flow with an aqueous outer sheath flow. The diameter of the inner flow was <20 microm. A focused fundamental beam of a Ti:sapphire pulse laser of 780 nm was irradiated to the interface, and emitted fluorescence from the fluorescent product was detected by a charge-coupled device (CCD) camera or a streakscope. The increase in the concentration of the fluorescent form of C(18)RB was measured along the interface of the inner flow of the toluene/water and heptane/water systems for 80 micros just after the contact of two phases. The analysis made by the time-dependent Langmuir adsorption model with the aid of the digital simulation method gave the cleavage reaction rate constants of the lactone form of C(18)RB at the liquid/liquid interfaces.     

Effect of external factors on the increase in the extraction rate in a vibration treatment on the dynamic interfacial layer

Vibration treatment of a dynamic interfacial layer in the extraction system constituted by an aqueous solution of a salt of a rare-earth element and a solution of di-(2-ethylhexyl)phosphoric acid in heptane (toluene) results in an increase in the process rate. This increase is characterized by an acceleration coefficient defined as the ratio between the lanthanide concentrations in the organic phase after equal intervals of time in systems with and without vibrations. It is shown that the acceleration coefficient depends on the concentration of the extractive agent, initial concentration of an element being extracted, solution pH, and phase contact duration. The observed behavior is explained in terms of the process model suggested by the authors. According to this model, the effect depends on the relative contributions made by a number of interfacial phenomena accompanying the extraction of a lanthanide with solutions of di-(2-ethylhexyl)phosphoric acid in diluents and, in particular, by the spontaneous surface convection and structuring in the interfacial layer.     

Polymerization behavior of propene with [t-BuNSiMe2Flu]TiMe2: effects of solvents and cocatalysts

The titanum complex [η¹:η³tert-butyldimethylfluorenylsilyl]-amido)dimethyltitanum ([t-BuNSiMe₂Flu]TiMe₂, Cat.A) was synthesized by an alternatively quicker one pot procedure. Polymerization of propene in the presence of [t-BuNSiMe₂Flu]TiMe₂/dried pure methylaluminoxane (d-PMAO) system at 0 °C was investigated in toluene and heptane. A strong enhancement of productivity was observed in toluene compared to heptane. Polymerization of propene was also investigated with Cat.A in heptane, with different cocatalysts, d-PMAO and dried pure modified methylaluminoxane (d-MMAO), which was prepared from the mixture of trimethylaluminum (TMA) and triisobutylaluminum (TIBA). A 10-fold higher number average molecular weight (M_n) and broad molecular weight distribution (MWD) was obtained with d-PMAO in heptane, even though kinetic features and other parameters signified the living nature of the polymerization process. However, the broadening of MWD was attributed to the poor insolubility of d-PMAO in heptane.     

Effects of Cetyltrimethylammonium Bromide and Heptane on the Surface Properties and CO2 Adsorption of Zeolite NaX

Zeolite X was synthesized by the gelation method for use as a CO₂ adsorbent. The zeolite was prepared from a sodium silicate solution and Al(OH )₃ as silicon and aluminum source, respectively. The effects of cetyltrimethylammonium bromide (CTAB ) and heptane addition on surface properties, morphology, and CO₂ adsorption capacities were investigated. The CO₂ adsorption capacity of the synthesized zeolite with the addition of CTAB and heptane increased as demonstrated by the higher CO₂ uptake (3.00 mmol/g), which was due to the higher surface area and pore volume. Interaction between CTAB micelles and sodium cations with aluminosilicate anions led to an increase in the nucleation rate and smaller crystalline sizes. The addition of heptane resulted in higher positively charged CTAB micelles and improved the affinity between the micelles and aluminosilicate anions.     

(Liquid + liquid) equilibrium for the ternary systems {heptane + toluene + 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide} and {heptane + toluene + 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide} ionic liquids

The (liquid + liquid) equilibrium (LLE) data for two systems containing heptane, toluene, and 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide ([mpim][Tf₂N]) or 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([amim][Tf₂N]) ionic liquids (ILs) were determined at T = 313.2 K and atmospheric pressure. The effect of a double bond in an alkyl side chain in the imidazolium cation was evaluated in terms of selectivity and extractive capacity. The results show a decrease of the amount of toluene and heptane dissolved in the IL with the allyl group. Thus, the distribution ratios of toluene and heptane of [mpim][Tf₂N] IL are higher than those of [amim][Tf₂N] IL. On the other hand, the separation factor of the [amim][Tf₂N] IL increases comparing to [mpim][Tf₂N] IL. The NRTL model was used to correlate satisfactorily the experimental LLE data for the two studied ternary systems.     

Membrane extraction for separation of copper cations from acid solution using polypropylene hollow fibre membrane

The membrane extraction of copper ions was carried out using hydrophobic poly(propylene) (PP) hollow fiber membrane modules and kerosene solutions containing organic extractant. The influences of different extractant on the extraction yield, mass transfer performance and mass transfer mechanism were studied. Compared with 2‐ethylhexyl phosphoric acid (2EHPA) and 2‐methyl‐5‐sulpho benzaldoxime (2M5SB), di‐(2‐ethylhexyl)phosphoric acid (D2EHPA) extractant system with high distribution coefficient exhibited higher extraction yield of 99.7%. The extraction equilibrium time, the final extraction yield and the total mass transfer coefficient were independent of the flow rates of two phases. The extraction equilibrium time and the final extraction yield at different flow rates of two phases were 80 min and near 99.5%, respectively. A mass transfer model of a complexation reaction describing the overall mass transfer resistance was controlled by interfacial reactions rather than the aqueous and organic boundary layer which could explain the effect of flow rate on the final extraction yield and the total mass transfer coefficient. This model showed that the mass transfer resistance and mass transfer coefficient were independent of Cu²⁺ when copper ion concentration was more than 0.06 g/L. However, when copper concentration was less than 0.06 g/l, the mass transfer resistance increased as Cu²⁺ concentration decreased, and the mass transfer coefficient decreased as Cu²⁺ concentration decreased. Extractant entrainment in the aqueous phase and membrane fouling were investigated primarily. It was found that the solvent entrainment could reduce to 10 ppm much lower than 200 ppm of the classic liquid–liquid extraction, and that the cleaning of contaminated membranes was not complete. However, it can be still concluded from this research that the membrane extraction in PP hollow fibre with D2EHPA extractant would be an effective and promising processing means for Cu²⁺ separation from aqueous solution. Copyright © 2005 John Wiley & Sons, Ltd.     

Control of various morphological changes of poly(meth)acrylate microspheres and their swelling degrees by SPG emulsification

Crosslinked poly(meth)acrylate polymers with a variety of morphologies were synthesized with two steps. In the first step, a microporous glass membrane (Shirasu Porous Glass, SPG) was employed to prepare uniform emulsion droplets by applying an adequate pressure to the monomer phase, which was composed of the ADVN initiator, solvent of toluene or heptane or their mixture, and a mixture of (meth)acrylate monomers. The droplets were formed continuously through the membrane and suspended in the aqueous solution, which contained a PVA‐127 suspending agent, SLS emulsifier, and NaNO₂ inhibitor to suppress the nucleation of secondary particles. SPG pore sizes of 0.90, 5.25, and 9.25 μm were used. Then the emulsion droplets were polymerized at 343 K with a rotation rate 160 rpm for 24 h. The (meth)acrylate monomers 2‐ethylhexyl acrylate (2‐EHA), 2‐ethylhexyl methacrylate (2‐EHMA), cyclohexyl acrylate (CHA), methyl methacrylate (MMA), lauryl acrylate (LA), and lauryl methacrylate (LMA) were used in this research. The influences of the ratios of the monomer and crosslinking agent EGDMA, the amount of diluents, the monomer type on the polymer particle morphology, the swelling degree, and the polymer particle size were investigated. It was found that an increase in the concentrations of EGDMA and heptane resulted in higher coarse porous spheres and smaller polymer particle sizes. A coefficient with a variation close to 10%, or a standard deviation of about 4, was obtained. The capacity of these spheres as solvent absorption materials was examined. The highest swelling degrees of heptane and toluene were obtained when LA was employed as the monomer with 30% (by weight) of EGDMA and 70% (by weight) of heptane as an inert solvent. The highest capacity of the solvent absorption was obtained when using a polymer particle size of 4.81 μm, as prepared by SPG pore size 0.9 μm. The polymer particles were able to absorb aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and a mix of aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents, such as toluene and heptane. The capacity of solvent absorption for the aromatic hydrocarbon solvents was higher than for the aliphatic hydrocarbon solvents. In addition, the particles did not rupture or collapse after absorption in solvents. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4038–4056, 2000     

Adsorption of lanthanides(III) from aqueous solutions by fullerene black modified with di(2-ethylhexyl)phosphoric acid

Fullerene black (FB) - a product of electric arc graphite vaporization after extraction of fullerenes - was modified with the di(2-ethylhexyl)phosphoric acid (D2EHPA). The distribution of D2EHPA between FB and aqueous HNO₃ solutions has been studied. The effect of HNO₃ concentration in the aqueous phase and that of D2EHPA concentration in the sorbent phase on the adsorption of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y nitrates from HNO₃ solutions by D2EHPA-modified FB are considered. The stoichiometry of the sorbed complexes has been determined by the slope analysis method. The efficiency of lanthanides’ adsorption increases with an increase in the element atomic number. A considerable synergistic effect has been observed upon the addition of the neutral bidentate tetraphenylmethylenediphosphine dioxide ligand to D2EHPA in the sorbent phase.      

Swelling of <Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam-dodecyl methacrylate gel in {heptane + toluene} mixtures

A copolymer gel has been synthesized from N-vinylcaprolactam and dodecyl methacrylate in ethanol using the free radical cross-linking polymerization method. Characterizations of the gel were performed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA) techniques. Swelling behavior of the gel was investigated in heptane, toluene, and their binary mixtures with different compositions. Swelling value in toluene is higher than that in heptane and swelling value increases with the increasing initial content of toluene in the binary mixture with heptane. The swelling values are correlated by the first- and second-order differential equations, and the best model correlating the experimental results is a second-order one. Diffusion coefficients have also been calculated for heptane and toluene at each concentration by power-law and first-order equations. While the diffusion mechanism of the gel in heptane is a Fickian one, the gel swelled in toluene exhibits a non-Fickian character. Diffusion mechanisms of the gels in binary mixtures are much more complicated. Because of the higher swelling degree in toluene compared to that in heptane, selectivity of the gel in different {heptane + toluene} mixtures with selectivity close to 1 has also been taken into consideration.     

Extraction of Lanthanide Nitrates in Multicomponent Aqueous-Organic Two-Phase Systems with D2EHPA

Lanthanum nitrate distribution in three-component aqueous-organic systems with D2EHPA from acetate or acetic acid–acetate solutions has been studied, it has been shown that variation in sodium acetate concentration or composition of CH₃COONa–CH₃COOH mixture can affect metal distribution ratios. It has been found that extraction in three-component mixture of 1: 1: 1 composition (aqueous solution Ln(NO₃)₃ + CH₃COONa + CH₃COOH–D2EHPA in hexane–isopropyl alcohol) can provide lanthanide separation, which is dependent on the ratio of sodium acetate and acetic acid in aqueous phase and on D2EHPA concentration in organic phase. Lanthanide–lanthanum separation factors have been calculated for the extraction of lanthanide nitrates from acetic acid–acetate solutions.     

二(2-乙基己基)磷酸萃取亮氨酸平衡研究

萃取平衡;二乙基己基磷酸;二(2-乙基己基)磷酸萃取亮氨酸平衡研究     

Degradation of parathion methyl by reactive sorption on the cerium oxide surface: The effect of solvent on the degradation efficiency

A simple and easily scalable “wet” procedure was used to prepare nanocrystalline cerium oxide capable of destroying the toxic organophosphate pesticide parathion methyl. The synthetic procedure consists of the direct precipitation of cerous salt with aqueous ammonia in the absence of CO₂. The prepared cerium oxide was able to decompose the organophosphate compounds both in nonpolar (e.g., heptane) and polar aprotic (e.g., acetonitrile) solvents. However, in solvents with hydrogen-bond donating ability, the –OH groups on the cerium oxide surface were solvated and inactivated. The preferential solvation model was used to express the experimental dependencies of the cerium oxide degradation efficiency on the composition of the water-acetonitrile mixture. In certain solvent systems, some empirical polarity scales, such as the alpha-scale or the Dimrodth-Richardt parameter ET(30), may be correlated with the degradation efficiency of cerium oxide.     

Molecular mass ranges of coal tar pitch fractions by mass spectrometry and size‐exclusion chromatography

A coal tar pitch was fractionated by solvent solubility into heptane‐solubles, heptane‐insoluble/toluene‐solubles (asphaltenes), and toluene‐insolubles (preasphaltenes). The aim of the work was to compare the mass ranges of the different fractions by several different techniques. Thermogravimetric analysis, size‐exclusion chromatography (SEC) and UV‐fluorescence spectroscopy showed distinct differences between the three fractions in terms of volatility, molecular size ranges and the aromatic chromophore sizes present. The mass spectrometric methods used were gas chromatography/mass spectrometry (GC/MS), pyrolysis/GC/MS, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and laser desorption time‐of‐flight mass spectrometry (LD‐TOFMS). The first three techniques gave good mass spectra only for the heptane‐soluble fraction. Only LDMS gave signals from the toluene‐insolubles, indicating that the molecules were too involatile for GC and too complex to pyrolyze into small molecules during pyrolysis/GC/MS. ESI‐FTICRMS gave no signal for toluene‐insolubles probably because the fraction was insoluble in the methanol or acetonitrile, water and formic acid mixture used as solvent to the ESI source. LDMS was able to generate ions from each of the fractions. Fractionation of complex samples is necessary to separate smaller molecules to allow the use of higher laser fluences for the larger molecules and suppress the formation of ionized molecular clusters. The upper mass limit of the pitch was determined as between 5000 and 10 000 u. The pitch asphaltenes showed a peak of maximum intensity in the LDMS spectra at around m/z 400, in broad agreement with the estimate from SEC. The mass ranges of the toluene‐insoluble fraction found by LDMS and SEC (400–10 000 u with maximum intensity around 2000 u by LDMS and 100–9320 u with maximum intensity around 740 u by SEC) are higher than those for the asphaltene fraction (200–4000 u with maximum intensity around 400 u by LDMS and 100–2680 u with maximum intensity around 286 u by SEC) and greater than values considered appropriate for petroleum asphaltenes (300–1200 u with maximum intensity near 700 u). Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of organic acid on lauroamide propyl betaine surface dilatational modulus and foam performance in a porous medium

The purpose of this work was to study the effect of surface tension and surface dilatational modulus on foam performance in high-salinity water in a porous medium. In order to clarify the role of the surface dilatational property in foam flow in a porous medium, three systems were established: a system with low surface dilatational modulus and high surface tension, a system with low surface dilatational modulus and low surface tension, and a system with high surface dilatational modulus and low surface tension. Measurement of dilatational modulus and surface tension showed that lauroamide propyl betaine (LAB) could not reduce surface tension and that surface dilatational modulus was low. The addition of lauric acid (LCOOH) to LAB could not achieve high surface dilatational modulus; however, it could reach lower surface tension. The addition of myristic acid (MCOOH) to LAB could achieve high surface dilatational modulus and lower surface tension. Unlike the other two systems, the results of a dilatational modulus comprised of a mixture of MCOOH and LAB were not a constant, as demonstrated by varied surface area deformation outcomes. With the increase of deformation, surface dilatational modulus decreased. Results of foam flow tests showed that among the two lower surface dilatational modulus systems, LAB foam had higher flow resistance regardless of flow rate. Among the two systems of similar lower surface tension, the mixture of LAB and MCOOH showed higher flow resistance than the mixture of LAB and LCOOH. However, with the increase of flow rate, pressure differences between the two systems became smaller, which corresponded to the decrease of surface dilatational modulus with an increase of deformation.