Bulk Organic Phase Research Articles

Deuterated Malonamide Synthesis for Fundamental Research on Solvent Extraction Systems

ABSTRACT Malonamide derivatives, which are the most extensively investigated extractants for solvent extraction of lanthanides, actinides, and platinum group metal ions, were deuterated by using Pd/C and Rh/C catalysts in a D2O/2-propanol mixture. This method replaces 1H atoms in the malonamides with 2H atoms at a controllable deuteration rate. The maximum rate reached about 75%, determined by nuclear magnetic resonance and electrospray ionization – mass spectrometry. The extraction behavior of metal ions by the malonamides was unchanged by the deuteration. Deuterated malonamides are a powerful tool for fundamental research on solvent extraction systems and for structural analysis of organic phases. The large difference in the cross section of coherent neutron scattering between 1H and 2H leads to a large difference in neutron scattering length density of malonamide derivatives before and after the deuteration. Therefore, using deuterated malonamides in small-angle neutron scattering and neutron reflectivity studies may help to reveal the microscopic structure of the specific solute species in the bulk organic phase and at the liquid–liquid interface, respectively. In this paper, we report the advantage of the deuterated malonamides for a contrast-matching method in the SANS experiment. This deuteration method could be generalized and extended to a wide variety of extractant molecules.

Equilibrium & kinetic studies of reactive extraction of trans-aconitic acid using sunflower oil with tri-n-octylamine

Abstract In order to design an efficient extraction system for the separation of biochemically produced trans-aconitic acid (TAH) from fermentation broth; equilibrium and kinetics of reactive extraction of TAH from aqueous solutions was investigated using tri-n-octylamine (TOA) as an extractant and sunflower oil as a diluent. Through the equilibrium studies stoichiometry (acid, extractant) of complex formations was determined with the help of loading ratio. Formation of (1, 1), (2, 1), & (3, 1) stoichiometry complexes were observed having complexation constants values 179.73 kmol−1 m3, 9512.58 kmol−2 m6, and 614,407.02 kmol−3 m9, respectively. Kinetics experiments were performed in Lewis type stirred cell and results confirmed that reaction between TAH and TOA in sunflower oil fall in regime 1, i.e. slow reaction occurring in bulk organic phase. The overall order of reaction is pseudo first order with rate constant (K mn ) 1.78 × 10−5 (kmol m−3)−0.71 s−1 and physical mass transfer coefficient (K l ) 4.22 × 10−5 m s−1.

Behaviors of ALSEP Organic Extractants: an Atomic Perspective Derived from Molecular Dynamics Simulation

ABSTRACT Molecular dynamics simulations were performed on mixtures of N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) and 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester (HEHEHP) extractants in a dodecane-water system in order to understand the organization and interfacial behavior of extractants in the Actinide-Lanthanide Separation (ALSEP) process. The dynamic behavior and coordination environments of these extractants near the interface were investigated as a function of aqueous nitric acid concentration in the range 0–6 M HNO3. To gain a complete molecular picture of the extractants’ interfacial behaviors, the effects of varying acidity were scrutinized in the context of spatial distributions of extractants within a given phase, chemical interactions, interfacial orientation, and extractant conformation. While the composition of the interfacial solvent mixing region changed with increasing acidity, the behavior of both extractants exhibited very little response to the varying acid levels, but in their own distinct manner. HEHEHP was found to express a specific interfacial behavior marked by a stronger affinity for the interface, with the polar POOH head group being oriented toward the interface and the alkyl chains residing in a constrained conformation. The larger and more flexible extractant, T2EHDGA, is less strongly associated with the interfacial region, on average dwells deeper into the organic phase, and displays orientations and conformations that are more like those of bulk organic phase T2EHDGA molecules than the ordered HEHEHP molecules.

Does uranyl-TBP complex formation happen at the aqueous-organic interface? Revelation by molecular dynamics simulations

In addition to solvent extraction experiments, the extensive molecular dynamics simulations have been performed for aqueous (water + uranyl ion + nitrate ion + nitric acid) organic (tributyl phosphate (TBP) + dodecane) biphasic systems in order to gain molecular insights of uranium extraction process. The simulation results well corroborate with the experimental observations. An attempt has been made to uncover the location of uranyl-TBP complexation by systematically studying the distribution of the complexes at the interface, mixed phase and the bulk phases. From the distribution constant profile, the extraction of UO2+2 ions to the organic phase was predicted to increase with increase in UO2+2 ion concentration. The experimentally observed bell shaped profile of distribution constant for uranyl extraction vs. acid concentration was first time captured by the MD simulations. The interface thickness was seen to be increased with increase in uranyl concentration. On the other hand, the inverse bell-shaped curve of interfacial thickness was noticed with increasing acid concentration. The extraction of uranyl ions was predicted to be proportional to the interface thickness. Finally, the stoichiometry distribution of UO2+2ions and UO2+2-TBP complex, their hydration characteristics, and structural orientation was explored in the different zones of biphasic system. The MD results show that the UO2+2-TBP complexation happens at the interface not in the organic phase as recently reported by the vibrational sum frequency generation experiment. However, reorganization of UO2+2-TBP complex was observed while migration from interface to the bulk organic phase. More, simulations and experimental studies are needed further to resolve the issue of uranyl ion complexation at the interface.

A Telescoping View of Solute Architectures in a Complex Fluid System.

Short- and long-range correlations between solutes in solvents can influence the macroscopic chemistry and physical properties of solutions in ways that are not fully understood. The class of liquids known as complex (structured) fluids—containing multiscale aggregates resulting from weak self-assembly—are especially important in energy-relevant systems employed for a variety of chemical- and biological-based purification, separation, and catalytic processes. In these, solute (mass) transfer across liquid–liquid (water, oil) phase boundaries is the core function. Oftentimes the operational success of phase transfer chemistry is dependent upon the bulk fluid structures for which a common functional motif and an archetype aggregate is the micelle. In particular, there is an emerging consensus that mass transfer and bulk organic phase behaviors—notably the critical phenomenon of phase splitting—are impacted by the effects of micellar-like aggregates in water-in-oil microemulsions. In this study, we elucidate the microscopic structures and mesoscopic architectures of metal-, water-, and acid-loaded organic phases using a combination of X-ray and neutron experimentation as well as density functional theory and molecular dynamics simulations. The key conclusion is that the transfer of metal ions between an aqueous phase and an organic one involves the formation of small mononuclear clusters typical of metal–ligand coordination chemistry, at one extreme, in the organic phase, and their aggregation to multinuclear primary clusters that self-assemble to form even larger superclusters typical of supramolecular chemistry, at the other. Our metrical results add an orthogonal perspective to the energetics-based view of phase splitting in chemical separations known as the micellar model—founded upon the interpretation of small-angle neutron scattering data—with respect to a more general phase-space (gas–liquid) model of soft matter self-assembly and particle growth. The structure hierarchy observed in the aggregation of our quinary (zirconium nitrate–nitric acid–water–tri-n-butyl phosphate–n-octane) system is relevant to understanding solution phase transitions, in general, and the function of engineered fluids with metalloamphiphiles, in particular, for mass transfer applications, such as demixing in separation and synthesis in catalysis science.

Behavior of bifunctional phosphonium-based ionic liquids in solvent extraction of rare earth elements - quantum chemical study

The complex-forming ability of thirty different bifunctional phosphonium-based ionic liquids (IL) in solvent extraction of rare earth elements (REE) has been investigated through density functional theory (DFT) simulations. The study enabled ranking various organic-solvent-borne ionic liquids for the extraction ability of their anionic or cationic moieties towards heavy and light rare earth element aqua-complexes from the pregnant solutions. The complexation energy estimated under interfacial or bulk organic phase conditions was used as quantitative index to discriminate the best complex-forming combinations between bifunctional phosphonium-based ionic liquids and rare earth elements. Anionic moieties with P=O and P-O functional groups proved superior in terms of complex-forming ability with rare earth elements as compared with P=S and P-S containing anions. Ammonium-based cationic moieties with short alkyl chain as well as imidazolium and pyrrolidinium cationic moieties led to stronger IL-REE complexes. This strength of complexation can be promoted further with phosphonium-based ionic liquids provided pulp digestion towards pregnant solutions is carried out with nitric and hydrochloride acids instead of sulfuric acid. DFT simulations revealed that while anionic moieties of phosphonium based ionic liquids are covalently bound with rare earth elements, the IL cationic moieties are involved only through outer-sphere interactions in the IL-REE complexes. Nevertheless, these cationic moieties are shown to influence the anion electron-donor properties resulting in changes in the ionic liquid complex-forming ability.

New formulation and characterization of enhanced bulk-organic phase change materials

The main drawbacks faced by researchers to successfully implement organic-PCM as materials to improve the thermal performance of building systems are their low thermal conductivity, their high flammability, and their low thermal cycling stability. In the present work, authors present a new enhanced PCM formulations aimed to solve the stated disadvantages in organic bulk-PCM. The new enhanced PCMs were prepared by adding high thermal conductivity particles and two kinds of flame retardants into organic PCM (paraffin and fatty acid eutectic mixtures). In the first stage, the effective thermal conductivity of organic-PCM was increased by using two different methods: directly dispersion of powder graphite (PG) bulk-PCM and vacuum impregnation of PCM into expanded graphite (EG). In the second stage, the fire reaction behaviour of the thermal conductivity enhanced PCM formulations was improved by adding two kind of flame retardants: magnesium hydroxide and ammonium phosphate (APP). Their fire reaction behaviour, thermal conductivity and thermophysical properties were measured by adapting the dripping test (UNE 23727-90), the hot-wire method and Differential Scanning Calorimetry (DSC), respectively. The enhanced PCM composites show a self-extinguished behaviour in terms of fire performance mechanism. The EG working with endothermic and phosphates flame retardants improve the fire performance of PCM by acting as a synergic system and the thermal conductivity is increased. However, their thermal storage capacity is significant decreased due to the large amount of flame retardant added (up to 40%). The thermal reliability was also tested, the enhanced PCM composites were stable up to 1000 thermal cycles.

Lipid Bilayers Manipulated through Monolayer Technologies for Studies of Channel-Membrane Interplay

Fluidity and mosaicity are two critical features of biomembranes, by which membrane proteins function through chemical and physical interactions within a bilayer. To understand this complex and dynamic system, artificial lipid bilayer membranes have served as unprecedented tools for experimental examination, in which some aspects of biomembrane features have been extracted, and to which various methodologies have been applied. Among the lipid bilayers involving liposomes, planar lipid bilayers and nanodiscs, recent developments of lipid bilayer methods and the results of our channel studies are reviewed herein. Principles and techniques of bilayer formation are summarized, which have been extended to the current techniques, where a bilayer is formed from lipid-coated water-in-oil droplets (water-in-oil bilayer). In our newly developed method, termed the contact bubble bilayer (CBB) method, a water bubble is blown from a pipette into a bulk oil phase, and monolayer-lined bubbles are docked to form a bilayer through manipulation by pipette. An asymmetric bilayer can be readily formed, and changes in composition in one leaflet were possible. Taking advantage of the topological configuration of the CBB, such that the membrane's hydrophobic interior is contiguous with the surrounding bulk organic phase, oil-dissolved substances such as cholesterol were delivered directly to the bilayer interior to perfuse around the membrane-embedded channels (membrane perfusion), and current recordings in the single-channel allowed detection of immediate changes in the channels' response to cholesterol. Chemical and mechanical manipulation in each monolayer (monolayer technology) allows the examination of dynamic channel-membrane interplay.

Novel preparation of Fe3O4/styrene-co-butyl acrylate composite microspheres via a phase inversion emulsion process

A new approach to prepare the magnetic composite microspheres of Fe3O4 and copolymer of styrene-co-butyl acrylate was reported by a phase inversion emulsion technique. During the phase inversion process, the system converts from a continuous bulk organic phase to a continuous aqueous phase dispersed with organic drops composed of monomers, polymers, and Fe3O4 particles. The obtained Fe3O4/styrene-co-butyl acrylate composite microspheres were mostly spherical with a diameter in the range of a few micrometers to dozens of micrometers. Also, large amounts of Fe3O4 particles present in the interior of the microspheres and some were embedded in the surface. The results from X-ray powder diffraction indicated the crystal structure of Fe3O4 was not changed during the preparation of microspheres. According to TGA curve, the content of Fe3O4 particles in microspheres reached approximately 48%. The microspheres exhibited superparamagnetism. High-magnetic-content microspheres can be easily obtained by this method.

Photophysics of thionine in AOT and BHDC reverse micelles. Quenching of the triplet state by aliphatic amines studied by transient absorption spectroscopy

Abstract The photophysics of thionine (3,7-diamino-5-phenothiazinium) (Th + ) was investigated in reverse micelles (RMs) of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and benzyldimethylhexadecylammonium chloride (BHDC) with special emphasis on the triplet state processes. In RMs both the absorption and emission spectra of the dye present a red shift with respect to pure water. The absorption maximum wavelength and Stokes shift show a tendency towards the values in water, although do not reach them even with the higher water content examined. The photophysical parameters are more affected by the water content in BHDC than in AOT. The triplet state of Th + was investigated by the technique of laser flash photolysis. The T-T absorption spectrum presents a strong absorption band in the region between 770 and 800 nm, corresponding to the monoprotonated triplet form of the dye. This spectrum is red shifted with respect to water in the RMs. The triplet quenching by aliphatic amines was investigated. The triplet decay is well fitted by a bi-exponential function in the presence of the hydro-soluble triethanolamine (TEOA) in both RMs. This behavior is interpreted as the result of a very fast intramicellar quenching, followed by slow process that may be ascribed to an intermicellar exchange of amine molecules between RMs. The kinetic analysis showed that intermicellar exchange rate constant is two orders of magnitude more effective in BHDC than in AOT. Meanwhile, in the quenching by the hydrophobic tributylamine (TBA) the decay is mono-exponential. The amine is located preferentially in the bulk organic phase and the quenching mechanism involves the interaction of the amine with the monoprotonated triplet of dye reaching in the micellar interface. It is interesting to note that the apparent quenching rate constant by TBA is one order of magnitude lower than the exchange rate constant by TEOA.

(Invited) EIS for the Early Detection of Unexpected Corrosion Phenomena in Highly Resistive Organic Solutions: Multiple Electrical Equivalent Circuit Fitting Validated By Parametric Continuity Conditions

Unexpected corrosion phenomena caused by a priori non-corrosive organic highly resistive solutions have been identified in some industrial petrochemical plants. Due to the extremely low conductivity of this kind of non-polar solution, performing reliable and reproducible electrochemical tests remains a difficult task. In which concerns EIS, Nyquist diagrams are prone to be crippled by a strong bulk-related capacitive behavior imposed by the dielectric nature of the electrolyte. The low frequency processes at the metal interface are then often hidden or at least badly resolved. In spite of these inherent difficulties, some of these phenomena have been successfully reproduced and studied in laboratory with a two-electrode cell in which two identical large surface plates of carbon or stainless steel were assembled facing each other and separated by a gap of 1 mm. EIS was then used to detect the onset and investigate the possible causes of the corrosion phenomena. Results appeared to be related either to water contamination or to the presence of solution additives. In the case of water contamination results showed that, even below the solubility coefficient, droplets of aqueous solution are ejected from the organic matrix at the metal interface creating clusters of aggressive electrolyte yielding localized corrosion. The corresponding Nyquist diagrams after water contamination have been fitted with a two time-constants electrical equivalent circuit in which the low frequency domain was straightforwardly associated to the aqueous droplets formation and was used to monitor the onset of corrosion. In the case of additive-containing organic matrix, however, the Nyquist diagrams exhibited a time-evolving profile that required a dual electrical circuit fitting strategy to be applied. Indeed, the process time evolution was so that diagrams were alternatively fitted with two different circuits for the same system depending on the immersion duration: a 2 time-constants EEC for the first ca 36 hours and a single bulk-related time-constant after that. This fitting methodology, although mandatory from an experimental point of view due to the time evolution profile of the diagrams, brings to the forefront of the problem the question of the validity of shifting between two or more different EEC for the survey of a monotonically evolving single interface. In other words, the shift between the two different circuits must match the physical continuity of characteristic parameters. This means that the fitting results for the different elements introduced in the EEC must not show leaps or discontinuities as the EEC are changed, since they are supposed to represent the same system. This parametric continuity condition has been used throughout the study and is illustrated in Figure 1 for the time evolution of the dielectric constant of the bulk organic phase and the solution resistance as obtained from the numeric values of the fitted EEC. It can be seen that in the initial stages the modified solution showed a higher dielectric constant that was associated with corrosion processes taking place till the reactive species were depleted at the interface or till the surface was blocked by adsorbed species. The bulk phase consistently retrieved his usual dielectric constant values after ca 36 hours in the conditions of Figure 1. Figure 1

Electrochemical Insight into the Brust–Schiffrin Synthesis of Au Nanoparticles

The mechanism of the Brust-Schiffrin gold nanoparticle synthesis has been investigated through the use of ion transfer voltammetry at the water/1,2-dichloroethane (DCE) solution interface, combined with X-ray absorption fine structure (XAFS) of the reaction between [AuCl4](-) and thiol (RSH) in homogeneous toluene (TL) solution. Ion transfer calculations indicate the formation of [AuCl2](-) at RSH/Au ratios from 0.2-2 with a time-dependent variation observed over several days. At RSH/Au ratios above 2 and after time periods greater than 24 h, the formation of Au(I)SR is also observed. The relative concentrations of reaction products observed at the liquid/liquid interface are in excellent agreement with those observed by XAFS for the corresponding reaction in a single homogeneous phase. BH4(-) ion transfer reactions between water and DCE indicate that the reduction of [AuCl4](-) or [AuCl2](-) to Au nanoparticles by BH4(-) proceeds in the bulk organic phase. On the other hand, BH4(-) was unable to reduce the insoluble [Au(I)SR]n species to Au nanoparticles. The number and size of the nanoparticles formed was dependent on the concentration ratio of RSH/Au, as well as the experimental duration because of the competing formation of the [Au(I)SR]n precipitate. Higher concentrations of nanoparticles, with diameters of 1.0-1.5 nm, were formed at RSH/Au ratios from 1 to 2.

Observation of a rare earth ion-extractant complex arrested at the oil-water interface during solvent extraction.

Selective extraction of metal ions from a complex aqueous mixture into an organic phase is used to separate toxic or radioactive metals from polluted environments and nuclear waste, as well as to produce industrially relevant metals, such as rare earth ions. Selectivity arises from the choice of an extractant amphiphile, dissolved in the organic phase, which interacts preferentially with the target metal ion. The extractant-mediated process of ion transport from an aqueous to an organic phase takes place at the aqueous-organic interface; nevertheless, little is known about the molecular mechanism of this process despite its importance. Although state-of-the-art X-ray scattering is uniquely capable of probing molecular ordering at a liquid-liquid interface with subnanometer spatial resolution, utilizing this capability to investigate interfacial dynamical processes of short temporal duration remains a challenge. We show that a temperature-driven adsorption transition can be used to turn the extraction on and off by controlling adsorption and desorption of extractants at the oil-water interface. Lowering the temperature through this transition immobilizes a supramolecular ion-extractant complex at the interface during the extraction of rare earth erbium ions. Under the conditions of these experiments, the ion-extractant complexes condense into a two-dimensional inverted bilayer, which is characterized on the molecular scale with synchrotron X-ray reflectivity and fluorescence measurements. Raising the temperature above the transition leads to Er ion extraction as a result of desorption of ion-extractant complexes from the interface into the bulk organic phase. XAFS measurements of the ion-extractant complexes in the bulk organic phase demonstrate that they are similar to the interfacial complexes.

Electrochemical oxygen reduction at soft interfaces catalyzed by the transfer of hydrated lithium cations

The oxygen reduction reaction by decamethylferrocene (DMFc), triggered by hydrophilic metallic cations behaving as Lewis acids towards water molecules in a homogeneous organic phase reaction, was investigated using cyclic voltammetry at the water|1,2-dichloroethane (w|DCE) interface. Simulated CVs, prepared through a facile 1-dimensional geometry in COMSOL Multi-physics software and incorporating interfacial and homogeneous reactions, were compared to experimental ones in order to elucidate the kinetics, thermodynamics, and viability of the proposed mechanism. The predominant O2 reduction reactions were proposed to occur in bulk organic phase, or in the vicinity of the w|DCE interface; six organic phase reactions were put forward. The first step was hydrolysis made possible through polarization of the OH bond of water molecules available in the cations hydration shell. The metal ion behaves as a Lewis acid coordinating to the oxygen and weakening the OH bond, making the proton more acidic, thereby facilitating attack by decamethylferrocene (DMFc) to form DMFc-H+. DMFc-H+ then participates in dioxygen reduction, generating the O2H radical species and DMFc+. Afterwards, the radical oxidizes another equivalent of DMFc to produce O2H−, that can then abstract a proton from the metal ions hydration sphere to generate hydrogen peroxide. The disproportionation of O2H− and the ion-pair formation of Li+ and OH− make up the other two reactions. The CV analysis was based on two curve features; the DMFc+ transfer wave and the positive limit of the polarizable potential window – the edge of scan potential profile – including the metal ion return peak. The goal of this article is to determine the kinetic/thermodynamic aspects of this mechanism from the experimental electrochemical data.

Reaction and catalyst engineering to exploit kinetically controlled whole-cell multistep biocatalysis for terminal FAME oxyfunctionalization.

The oxyfunctionalization of unactivated C−H bonds can selectively and efficiently be catalyzed by oxygenase-containing whole-cell biocatalysts. Recombinant Escherichia coli W3110 containing the alkane monooxygenase AlkBGT and the outer membrane protein AlkL from Pseudomonas putida GPo1 have been shown to efficiently catalyze the terminal oxyfunctionalization of renewable fatty acid methyl esters yielding bifunctional products of interest for polymer synthesis. In this study, AlkBGTL-containing E. coli W3110 is shown to catalyze the multistep conversion of dodecanoic acid methyl ester (DAME) via terminal alcohol and aldehyde to the acid, exhibiting Michaelis-Menten-type kinetics for each reaction step. In two-liquid phase biotransformations, the product formation pattern was found to be controlled by DAME availability. Supplying DAME as bulk organic phase led to accumulation of the terminal alcohol as the predominant product. Limiting DAME availability via application of bis(2-ethylhexyl)phthalate (BEHP) as organic carrier solvent enabled almost exclusive acid accumulation. Furthermore, utilization of BEHP enhanced catalyst stability by reducing toxic effects of substrate and products. A further shift towards the overoxidized products was achieved by co-expression of the gene encoding the alcohol dehydrogenase AlkJ, which was shown to catalyze efficient and irreversible alcohol to aldehyde oxidation in vivo. With DAME as organic phase, the aldehyde accumulated as main product using resting cells containing AlkBGT, AlkL, as well as AlkJ. This study highlights the versatility of whole-cell biocatalysis for synthesis of industrially relevant bifunctional building blocks and demonstrates how integrated reaction and catalyst engineering can be implemented to control product formation patterns in biocatalytic multistep reactions.

Initial Partition and Aggregation of Uncharged Polyaromatic Molecules at the Oil–Water Interface: A Molecular Dynamics Simulation Study

Initial partitioning and aggregation of several uncharged polyaromatic (PA) molecules with the same polyaromatic core but different terminal moieties at oil-water interfaces from the bulk oil phase were studied by molecular dynamics simulation. The partition of the PA molecules between the bulk organic phase and oil-water interface was highly dependent on the terminal moiety structure of the PA molecules and aromaticity of the organic phase. The polarity ratio between the oil and water phases showed a significant influence on adsorption of the PA molecules at the oil-water interface. The presence of hydrophobic aromatic moieties in PA molecules hindered the adsorption process. Larger aromatic rings in PA molecules lowered the interfacial activity due to strong intermolecular π-π interactions and molecular aggregation in the bulk oil phase. The presence of a terminal carboxylic functional group on the side chain enhanced the adsorption of the PA molecules at the oil-water interface. The fused ring plane of the uncharged PA molecules was found to preferentially adsorb at the oil-water interface in a head-on or side-on orientation with the polyaromatic core staying in the nonaqueous phase (i.e., the principal plane of the molecule perpendicular to the oil-water interface). The results obtained from this study could provide a scientific direction for the design of proper chemical demulsifiers for PA molecule-mediated emulsions formed under specific process conditions of temperature, pressure, and pH.

Molecular Simulation of Water Extraction into a Tri-n-Butylphosphate/n-Dodecane Solution

Molecular dynamics simulations were performed to investigate water extraction into a solution of 30 vol % tri-n-butylphosphate (TBP) in n-dodecane. Our computational results indicate that the TBP electric dipole moment has a significant effect on the predicted water solubility. A larger TBP dipole moment decreases the aqueous-organic interfacial tension, leading to increased roughness of the aqueous-organic interface. Interfacial roughness disrupts the interfacial water hydrogen bonding structure, resulting in a presence of dangling water molecules at the interface. The increased interfacial roughness enhances the probability of water molecules breaking away from the aqueous phase and migrating into the organic bulk phase. By varying the atomic partial charges of the TBP molecules to reproduce a dipole moment close to the experimentally measured value, we were able to predict water solubility in close agreement with experimental measurements. In addition, our simulation results reveal the detailed molecular mechanism of the water extraction process, and the various structural forms of water molecules both at the interface and in the bulk organic phase.

Solvent extraction of La(III) with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA) by membrane dispersion micro-extractor

The conventional rare earth solvent extraction equipments have many problems such as long mixing time, low processing capacity, large factory area occupation, high energy consumption and so on. In order to solve the problems, many types of equipments were brought out. In this work, studies were carried out on the La(III) extraction process with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA) by membrane dispersion micro-extractor. Equilibrium studies showed that the initial aqueous pH value 4.15 with the saponification rate 40% was the optimal operation condition. The effects of membrane dispersion micro-extractor operational conditions such as dispersion mode, bulk flow rate and organic phase flow rate on the extraction efficiency were studied. The results showed that when the organic solution was the dispersed phase, the extraction efficiency was higher than that of others. Increasing bulk flow ratio could enhance the extraction efficiency greatly. When the ratio of organic phase flow rate to that of aqueous phase was 80:80, the extraction efficiency was over 95%. The effect of stripping phase acidity on the La(III) recovery was studied. The results showed that when the stripping phase pH was 2.0, organic phase flow rate to stripping phase flow rate was 20:80; the recovery efficiency of La(III) can reach 82%.

Lanthanide Speciation in Potential SANEX and GANEX Actinide/Lanthanide Separations Using Tetra-N-Donor Extractants

Lanthanide(III) complexes with N-donor extractants, which exhibit the potential for the separation of minor actinides from lanthanides in the management of spent nuclear fuel, have been directly synthesized and characterized in both solution and solid states. Crystal structures of the Pr(3+), Eu(3+), Tb(3+), and Yb(3+) complexes of 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe4-BTPhen) and the Pr(3+), Eu(3+), and Tb(3+) complexes of 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'-bypyridine (CyMe4-BTBP) were obtained. The majority of these structures displayed coordination of two of the tetra-N-donor ligands to each Ln(3+) ion, even when in some cases the complexations were performed with equimolar amounts of lanthanide and N-donor ligand. The structures showed that generally the lighter lanthanides had their coordination spheres completed by a bidentate nitrate ion, giving a 2+ charged complex cation, whereas the structures of the heavier lanthanides displayed tricationic complex species with a single water molecule completing their coordination environments. Electronic absorption spectroscopic titrations showed formation of the 1:2 Ln(3+)/L(N4-donor) species (Ln = Pr(3+), Eu(3+), Tb(3+)) in methanol when the N-donor ligand was in excess. When the Ln(3+) ion was in excess, evidence for formation of a 1:1 Ln(3+)/L(N4-donor) complex species was observed. Luminescent lifetime studies of mixtures of Eu(3+) with excess CyMe4-BTBP and CyMe4-BTPhen in methanol indicated that the nitrate-coordinated species is dominant in solution. X-ray absorption spectra of Eu(3+) and Tb(3+) species, formed by extraction from an acidic aqueous phase into an organic solution consisting of excess N-donor extractant in pure cyclohexanone or 30% tri-n-butyl phosphate (TBP) in cyclohexanone, were obtained. The presence of TBP in the organic phase did not alter lanthanide speciation. Extended X-ray absorption fine structure data from these spectra were fitted using chemical models established by crystallography and solution spectroscopy and showed the dominant lanthanide species in the bulk organic phase was a 1:2 Ln(3+)/L(N-donor) species.

Effect of a Phase Transfer Catalyst on the Dynamics of an SN2 Reaction. A Molecular Dynamics Study

The effect of a tetramethylammonium cation phase transfer catalyst on the benchmark Cl− + CH3Cl reaction at the water/chloroform liquid/liquid interface is investigated by a molecular dynamics-empirical valence bond (EVB) model. The effect of the catalyst on the reaction free energy profile at different interface locations and in bulk chloroform is examined. We find that, because of significant water “pollution”, activation of the nucleophilic attack is limited to the bulk organic region. The barrier height at the interface is equal to or slightly larger than the barrier in bulk water and is unaffected by the presence of the catalyst. In bulk chloroform, our calculations suggest that the barrier height, which is much lower than in bulk water, moderately increases when a few water molecules interact with the system and when the catalyst forms an ion-pair with the nucleophile. Thus, the catalyst is most effective if its role is limited to bringing the nucleophile to the bulk organic phase.