Solvation Mechanism Research Articles

Experimental and Theoretical Study of the Extraction of UO22+by Malonamides in Ionic Liquids

Solvent extraction studies of UO22+ were carried out using N,N′-dimethyl-N,N′-dibutylmalonamide (DMDBMA), N,N,N′,N′-tetrabutylmalonamide (TBMA), and N,N,N′,N′-tetraoctylmalonamide (TOMA) dissolved in three room temperature ionic liquids (RTILs) of 1-alkyl-3-methylimidazolium bis(trifluoromethane)sulfonamide ([Cnmim][Tf2N], n = 4,6,8). At lower acidity, the extraction of UO22+ carried out in RTIL was found to be much more efficient than in the conventional molecular diluents, while this advantage diminishes at higher acidity. The alkyl chain length of the RTILs plays an important role on the extraction performance. The effect of concentration of three diamides and nitric acid on extraction performance was also investigated. The extraction mechanism using RTILs as the diluent was deduced by the slope analysis and extraction experiment, and a cation-exchange mechanism at lower acidity and a neutral solvation mechanism at higher acidity were proposed. Density functional theory method was used to characterize ...

Conductivity, viscosity, and thermodynamic properties of propylene carbonate solutions in ionic liquids

Ionic liquids (ILs) are a series of stable, non-flammable, non-volatile organic compounds containing only ionic species. ILs can be used to make stable electrolyte solutions with low viscosity and high conductivity for electrochemical energy storage and conversion devices such as lithium ion batteries, fuel cells, and supercapacitors, leading to improved performance in capacity and stability. Propylene carbonate (PC) has also been used as a solvent/co-solvent to prepare electrolyte solutions for these energy storage devices. In this work, we have used a series of experimental methods such as calorimetry, gas chromatography, Fourier Transform Infrared Spectroscopy (FTIR), viscosity and conductivity measurements to characterize the properties of PC/IL solutions and the solvation mechanism. The ILs are 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI), and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI). Experimental results demonstrate that the PC/IL solutions possess lower viscosity and higher conductivity, compared with pure ILs. While the thermodynamic properties of the solutions depend on the structures of the molecular ions of the ILs.

Process for recovery of uranium from low grade SDU of phosphoric acid/D2EHPA-TBP plant origin using DHOA/n-dodecane solvent

Abstract A process is described for separation and recovery of uranium from low grade sodium diuranate (SDU) obtained from processing of phosphatic uranium with D2EHPA-TBP solvent. SDU containing impurities of rare earths mostly heavier fraction (Y, Dy, Er, Yb) and Fe, Al, Cr, Mn, Ca, etc. was dissolved in nitric acid and contacted with N,N-dihexyl octanamide (DHOA)/n-dodecane solvent for selective separation of uranium from rest of the impurities. The average separation factor of uranium with respect to the heavy rare earths and base metals was obtained was 30 and 1000 respectively. Effect of different experimental parameters like aqueous nitric acid concentration, DHOA concentration, uranium concentration, phase ratio of extraction, scrubbing and stripping was optimized to obtain high purity uranium product solution. The extraction of uranium by DHOA follows solvation mechanism, at low uranium loading the combining ratio of U to DHOA determined by slope analysis method suggests complex formation as [UO2(NO3)2·2DHOA]. A 8-stage counter current extraction of 70 g/L uranium feed solution obtained on dissolving SDU in 3 M HNO3 with 1 M DHOA/n-dodecane solvent at O/A = 1 and scrubbing with 80 g/L pure uranium solution in 3 M HNO3 at O/A = 4:1 was found appropriate to obtain uranium of purity above 99.9%.

Separation of vanadium(V) using N235 by three-phase system in concentrated HCl media

The third phase formed in the process of extracting vanadium in a N235/HCl system was usually regarded as a limit to the throughput of the plant. To have a deep insight on this problem, the formation of the third phase in the extraction of vanadium by tertiary amine N235 in the concentrated HCl system was studied. The optimum parameters of three-phase system extraction were determined, and FTIR analysis was carried out to characterize the structure of extracted complexes and analyze the mechanism of formation and elimination of the third phase. The results showed that vanadium extraction efficiency was 86.5% with 20% v/v N235 and a phase ratio (O:A) of 1:2 in 2 min at 25 °C, though an obvious third phase was found within the experimental HCl concentration range. Cl− is the participant in the process of increasing the vanadium extraction efficiency, whereas H+ has an inhibitory effect on vanadium extraction. Meanwhile, the structure of the extracted complex was confirmed as (R3N)m(HCl)m+x·([Formula: see text])·(H2O)n through a solvation mechanism with molecular association, which was further proved by FTIR spectral analysis. Furthermore, the limited solubility of the ion-extracted complexes in the nonpolar solvent kerosene made the third-phase form. The third phase disappeared when phase modifier (about 5% v/v TBP) was added into the organic phase, as the polarity of the organic phase increased.

Investigation of solvation of iron nanoclusters in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate using molecular dynamics simulations: Effect of cluster size at different temperatures

The systems composed of metal nanoclusters in ionic liquids are relevant for applications in lubrication, electrochemical devices, catalysis, and chemical processes. The mechanism of solvation and interactions of these systems are not understood at present. In this work, we have simulated iron nanoclusters with different sizes in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate [N1114][C1SO3] at two temperatures (300 and 500K) and at atmospheric pressure. We have investigated the effects of cluster size and the temperature on some of the thermodynamics, structural and dynamical properties of the systems. Our results also show that the absolute value of solvation energy increases as the nanocluster size increases. Also the absolute solvation energy increases as the temperature increases. It is also shown that the effect of the cluster size is much more than the effect of the temperature. Our structural investigations indicate at least two shells (a double layer) around the nanocluster and the anions are closer to the cluster surface than the cations. The self-diffusion coefficients of cations, anions, and iron clusters have been also presented and discussed in this work.

Structural Investigations on Lithium-Doped Protic and Aprotic Ionic Liquids.

Solutions of lithium bis(trifluoromethanesulfonyl)imide (LiNTf2), in four different [NTf2]--based ionic liquids, are extensively investigated as potential electrolytes for lithium-ion batteries. Solvation of the [Li]+ ions in the ionic liquids and its impact on their physicochemical properties are studied herein with the aid of molecular dynamics simulations. The cationic components of the investigated liquids were systematically varied so as to individually evaluate effects of specific structural changes; increase in ring size, the addition of an alkyl chain and absence of an acidic proton, on the solvation and mobility of the [Li]+ cations. The studied cations also allow for a direct comparison between solutions of [Li]+ salt in protic and aprotic ionic liquids. Emphasis is laid on elucidating the interactions between the [Li]+ and [NTf2]- ions revealing slightly higher coordination numbers for the aprotic solvent, benchmarked against experimental measurements. The study suggests that the ionic liquids largely retain their structure upon salt addition, with interactions within the liquids only slightly perturbed. The rattling motion of the [Li]+ cations within cages formed by the surrounding [NTf2]- anions is examined by the analysis of [Li]+ autocorrelation functions. Overall, the solvation mechanism of [Li]+ salt, within the hydrogen-bonded network of the ionic liquids, is detailed from classical and ab initio molecular dynamics simulations.

Pretreatment of biomass using ionic liquids: Research updates

Room-temperature ionic liquids (ILs) are molten salts at around room temperatures. The current researches of using ILs for efficient pretreatment for lignocellulosic biomass are updated in this article. The aspects of synthesis of high-performance ILs, recycling of used ILs with minimum use of utility, development of IL-tolerant enzymes, and optimization of the entire process economy were discussed. The mechanisms of IL solvation and the potential for IL-based biomass refinery are also highlighted.

Evaluation of several novel diamide based ligands for selective extraction of tetravalent plutonium

Abstract The present paper describes the selective extraction of tetravalent plutonium employing several diamide ligands containing aromatic spacer groups. The ligands containing two amide functional groups attached to a 2,4,6-tri-phenyl pyridine moiety with different substituents viz.; L I (iso-butyl), L II (n-butyl), L III (n-octyl), L IV (2-ethylhexyl) at the amidic nitrogen atom were evaluated for the extraction of Pu(IV) using their nitrobenzene solutions. The distribution ratio values of Pu(IV) with the diamide ligands followed the order: LII >LI >LIII >LIV and were significantly higher than those of metal ions such as Cs(I), Sr(II), Am(III) and Eu(III). The distribution ratio values of U(VI) were about 2–3 orders magnitude lower than those of Pu(IV). The extraction and stripping kinetics were found to be moderately fast and it took less than 30 min (less than 5 min for L I and L IV ) to obtain equilibrium D values. The extraction was found to be increasing with the aqueous phase nitric acid concentration conforming to a solvation mechanism of extraction. The extracted species contained two ligand molecules for L I and L II while monosolvates were observed for the other two extractants. The ligands showed good radiation stability up to an absorbed dose of 630 kGy.

Extraction of plutonium(IV) by diglycolamide extractants in room temperature ionic liquids

Abstract Extraction of Pu(IV) was investigated using solutions of two diglycolamide extractants viz., N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA) and its branched homolog, N,N,N′,N′-tetra(2-ethylhexyl) diglycolamide (T2EHDGA), dissolved in two imidazolium based room temperature ionic liquids viz., 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C4mim][NTf2]) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C8mim][NTf2]) from aqueous nitric acid medium. The extraction kinetics was found to be extremely slow which is reported for the first time for analogous extraction systems and took as long as 30 h to attain equilibrium D Pu values. In general, TODGA based solvents showed better extraction of Pu(IV) than the T2EHDGA based solvents, one order of magnitude higher, and though both the ionic liquids ultimately yielded comparable D Pu values, attainment of equilibrium was slower with [C4mim][NTf2]. The extracted species conformed to 1:1 for TODGA in both the ionic liquids while a mixture of 1:1 and 1:2 species was observed for T2EHDGA at 1 M HNO3 which changed to 1:1 species at 4 M HNO3. The extracted species is proposed to be (Pu(L)x 4+)IL (where, L is the extractant and x=1 or 2) at lower acidities suggesting a cation exchange mechanism which changes over to (Pu(NO3)4⋅L)IL at 4 M HNO3 conforming to a solvation mechanism for all the systems except for T2EHDGA-[C8mim][NTf2]. UV-VIS spectroscopic studies were carried out to throw light on the nature of the extracted species.

Unusual selective extraction of Pu 4+ by some novel diamide ligands in a room temperature ionic liquid

Abstract Extraction of Pu4+ was carried out from nitric acid feeds employing ionic liquid solutions of four novel diamide ligands containing an aromatic bridging group. The ligands with iso-butyl, n-butyl, n-octyl and 2-ethylhexyl groups were termed as LI, LII, LIII, and LIV, respectively and showed significantly higher extraction of the tetravalent plutonium ion as compared to the hexa-valent uranyl ion. Using 0.05 M ligands, the extraction of Pu4+ was in the range of 80–95% when 3 M HNO3 was used as the feed and followed the order: LIII > LII > LI > LIV while the UO22+ ion extraction was less than 4–5% and no particular trend could be established. The extraction of UO22+ could be partly due to the anionic nitrate complex of uranyl ion which was extracted in the absence of the ligands, while the ligand assisted extraction contributing for the remaining. Out of the other metal ions studied, Cs+ showed some extraction which was not ligand assisted while almost no extraction of metal ions such as Sr2+, Am3+ and Eu3+ was noticed. Unusually high selectivity was seen for Pu4+ ion extraction out of all the metal ions studied making the solvent systems very important for a plutonium specific separation method development. The extraction was found to be increasing with the aqueous phase nitric acid concentration conforming to a ‘solvation mechanism’ of extraction where the extracted species conforming to Pu(NO3)4·LIL for all the four diamide extractants.

Experimental and theoretical studies on extraction of actinides and lanthanides by alicyclic H-phosphonates

Abstract Three different alicyclic substituents H-phosphonates, namely, dicyclopentyl H-phosphonate, dicyclohexyl H-phosphonate and dimenthyl H-phosphonate were synthesized and used for liquid–liquid extraction of actinide elements (U, Am and Th) and lanthanide (Gd) in n-dodecane from nitric acid medium. The physicochemical properties of the extractants, such as density, viscosity, solubility were determined. At lower acidities, these H-phosphonates exhibit higher distribution values and the extraction following cation exchange mechanism through P–OH group of tri-coordinated phosphite form. At higher acidities (2N), the extraction is primarily via solvation mechanism through P=O group of penta-coordinated phosphonate form. Amongst the three H-phosphonates, examined dimenthyl H-phosphonate showed the best results for the actinide extraction. Density functional theory (DFT) calculations were applied to understand the electronic structure of the ligands and the metal complexes. The calculated large complexation energy of UO2(NO3)2·2DMnHP is in agreement with the observed trend in experimental distribution ratio data.

Influence of Fluorination on the Solubilities of Carbon Dioxide, Ethane, and Nitrogen in 1-n-Fluoro-alkyl-3-methylimidazolium Bis(n-fluoroalkylsulfonyl)amide Ionic Liquids.

The effect on gas solubilities of adding partially fluorinated alkyl side chains either on imidazolium-based cations or on bis(perfluoroalkylsulfonyl)amide anions was studied. The aim was to gain knowledge of the mechanisms of dissolution of gases in fluorinated ionic liquids and, if possible, to improve physical absorption of carbon dioxide in ionic liquids. We have determined experimentally, in the temperature range of 298-343 K and at pressures close to atmospheric pressure, the solubility and thermodynamics of solvation of carbon dioxide, ethane, and nitrogen in the ionic liquids 1-octyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide ([C8mim][NTf2]), 1-octyl-3-methylimidazolium bis[pentafluoroethylsulfonyl]amide ([C8mim][BETI]), 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-3-methylimidazolium bis[trifluoromethylsulfonyl]amide ([C8H4F13mim][NTf2]), and 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-3-methylimidazolium bis[pentafluoroethylsulfonyl]amide ([C8H4F13mim][BETI]). Ionic liquids with partial fluorination on the cation were found to exhibit higher carbon dioxide and nitrogen mole fraction solubilities but lower ethane solubilities, compared to those of their hydrogenated counterparts. Molecular simulation provided insights about the mechanisms of solvation of the different gases in the ionic liquids.

A phenomenological order approach to the volume phase transition in microgel particles.

We proposed a model to describe the volume phase transition of microgel particles, based on constitutive relations that consider the mechano-chemical coupling of deformation and solvency processes, as well as the phenomenological cooperative effect of molecular orientation of solvatable segments in the particles. We regard a nematic-isotropic like transition and define a tensor order parameter allowing analysis of the collective behaviour of water solvation mechanisms based on the Landau-De Gennes theory for liquid crystal elastomers. A complementary approach to the energy balance density is obtained with the order parameter field considering the deformation by a continuum mechanics approximation; our approach aims to extend the comprehensive understanding of the elastic behaviour and water sorption related phenomena in microgel particles. With the proposed model, we reproduce the behaviour of swelling curves through a volume phase transition of thermosensitive microgel particles by assessing characteristic parameters belonging to particular physical properties. The parameters defined within the model such as elastic and solvency related constants and characteristic temperatures were obtained by fitting of a data set mimicking the experimentally observed swelling behaviour. The obtained values of the parameters were consistent with the discussed phenomenology which shows the importance of molecular ordering interpretation as a source to describe the volume phase transition in microgel particles.

Separation of concentrated acid and salt solutions in nanoporous media as the basis for a new technology of processing of phosphorus-containing raw materials

The physical and mathematical models were used to study the method of acid retardation for separating acids from their salts in concentrated multicomponent solutions using nanoporous sorption materials. A combined mechanism of separation relies on the fact that in the sorption phase having a low dielectric permittivity, smaller-sized acid particles, namely, the molecules or strongly bound and weakly hydrated ion pairs, can penetrate the nanopores and are retained within these pores due to molecular sorption or competitive solvation forces. The dissolved salts presented by highly hydrated ions or weakly bound ion pairs can easily pass through the porous medium with a flow of concentrated solution, which is pumped through the column packed with the granulated bed of gel-type ion exchange resins or hypercrosslinked polymers. In conventional cyclic AR processes, purified acid is desorbed by water according to the mechanism of competitive solvation. However, such processes can be successfully used only when the salts separated from acids are highly soluble, as is the case with chloride and nitrate solutions free of components that may form compounds insoluble in neutral medium. At the separation in real sulfate and phosphate media, which normally contain alkaline earth metals and other components, conventional AR- based technologies proved to be unsuccessful. The new modified version of acid retardation is based on the previously discovered effect of stabilization of colloidal systems and supersaturated solutions in porous ion exchange media. A distinctive feature of the proposed technique is the use of weakly acidic aqueous solutions, instead of water, at the stages of acid displace in the cyclic AR processes. The proposed technique of WPA purification using strong-base gel-type ion exchangers in the phosphate form opens up the possibility of stable and feasible processes of acid separation and purification with simultaneous extraction of valuable components, e.g., REE concentrate.

Highly efficient and eco-friendly extraction of neodymium using, undiluted and non-fluorinated ionic liquids. Direct electrochemical metal separation

Abstract A new approach for highly efficient extraction and recovery of neodymium from acidic medium by new undiluted ionic liquids (ILs) as extractants. The distribution ratio DNd and the extraction efficiency %E was measured as a function of nitric acid concentration, extraction time, nature of the IL, concentration of the aqueous feed and molar quantity of complexing agent. DNd is higher than 105 and %E is close to 100% when the HNO3 concentration is greater than 6 M. The extraction process follows solvation mechanism, suggesting the involvement of three molecules in the extraction of one (Nd3+)-nitrate complex. The nature of bonding in the extracted complexes was investigated by various spectroscopic techniques. The recovery process, of metal was performed by direct electrodeposition from the IL phase. The electrodeposition of metal was realized by potentiostatic electrolysis at −2 V. The current efficiency evaluated from the mass change of the anode was more than 83%. The particles were obtained as small crystallite rods with various size approximately 3–70 μm and diameters range of 0.5–30 μm. The liquid-liquid extraction and the direct electrodeposition of neodymium by these H-phosphonate based ILs, are new efficient and eco-friendly process.

Au Nanoplasma as Efficient Hard X-ray Emission Source

Hard X-ray generation up to 15 keV (∼1 A) from Au nanoparticle suspensions was systematically investigated for different particle diameters ranging from 10 to 100 nm with a narrow size distribution of ±2%. Scaling law of X-ray generation is close to a 6-photon process before the onset of saturation for excitation by 40 fs laser pulses with central wavelength of 800 nm. This is consistent with bulk plasmon excitation at λpbulk ≃ 138 nm. The longitudinal E-field component due to nanoparticle focusing is responsible for the excitation of the longitudinal bulk plasmon. The proposed analysis also explains X-ray emission from water breakdown via an electron solvation mechanism at ∼6.2 eV. The most efficient emission of X-rays was observed for 40 ± 1 nm diameter nanoparticles which also had the strongest UV extinction. X-ray emission was the most efficient when induced by prechirped 370 ± 20 fs laser pulses and exhibited the highest intensity at a negative chirp.

Pressure Response of a Thermoresponsive Polymer in an Ionic Liquid

We investigated pressure effects on the lower critical solution temperature (LCST)-type phase behavior of a thermoresponsive polymer in an ionic liquid (IL) solution. The cloud point temperature of the IL solution increased monotonically with pressure, which was quite different from that of conventional aqueous polymer solutions reported in previous work, which exhibited a convex-upward-type pressure dependence. We compared the IL and aqueous systems and concluded that the difference results from their solvation mechanisms. Dynamic light scattering (DLS) measurements showed an appearance of a slow mode (corresponding to aggregation) in addition to the fast mode (corresponding to molecular dispersion) at the cloud point pressure, indicating an onset of pressure-induced phase separation. This work contributes to the fundamental understanding of the phase behavior of polymers in IL systems under high pressure.

Solvation of para-hydroxybenzoic acid and its esters (methylparaben, propylparaben) in supercritical carbon dioxide. Computer simulation

The study of solvation structures formed by para-hydroxybenzoic acid (p-HBA) and its methyl (methylparaben, MP) and propyl (propylparaben, PP) esters in methanol-modified (0.03mol fraction of methanol) supercritical carbon dioxide at the density of 0.772g/cm3 and the temperature of 328K has been made using classical molecular dynamics. It is shown that the solvation occurs through the formation of stable hydrogen bonds between the solutes and the cosolvent. Changes in solvation mechanism depending on the alkyl substituent in the sequence of p-HBA – MP – PP are considered. For p-HBA a hydrogen bond via the carboxyl hydrogen is typical, and the probability of the formation of hydrogen bonds by the hydroxyl hydrogen is much smaller. In the case of MP and PP when carboxyl hydrogen is substituted by alkyl group, the hydrogen bonds via the hydroxyl hydrogen have a much greater probability of formation and existence duration. Besides, MP and PP, unlike p-HBA, have a high probability of forming hydrogen bonds with methanol as proton acceptor via carbonyl oxygen. This feature can provide an advantage of protic compounds such as low molecular weight alcohols, by selection of cosolvent to improve parabens solubility in supercritical CO2.

Solvation free energies of nucleic acid bases in ionic liquids

The solvation free energies of five nucleic acid bases in [Cnbim]Br (where n = 2, 4, 6) ionic liquids (ILs) were computed using the Bennett acceptance ratio (BAR) method employing molecular dynamics simulations. The computed free energies using BAR were in agreement with other methods. The large and negative predicted free energies of the bases in ILs indicated that the bases were better solvated in the ILs rather than in water. Hydrogen bonding interactions between polar sites of the bases and ILs’ ions significantly contributed to the solvation mechanism.

Understanding the extraction mechanism, radiolytic stability and stripping behavior of thorium by ionic liquid based solvent systems: evidence of ‘ion-exchange’ and ‘solvation’ mechanism

The extraction efficiency for thorium followed the trend: Cyanex-923 > Cyanex-272 > DHOA > TBP. In case of TBP and DHOA the extraction proceeded via ‘solvation mechanism’ through Th(NO3)4·2L, while for Cyanex-923 and Cyanex-272 it proceeded via ‘ion exchange’ mechanism through (Th(NO3)2·2L)2+. The extraction process followed slower kinetics while change in Gibb’s energy revealed the spontaneity of the process. These ionic liquid based systems were found to be radiolytically stable, highly efficient and selective for Th. Oxalic acid was found to be suitable for almost quantitative stripping of Th from extracted ionic liquid phase.