John R. Klaehn

Selective Extraction of Minor Actinides from Acidic Media Using Symmetric and Asymmetric Dithiophosphinic Acids

The minor actinides (Am and Cm) and other transplutonium elements represent significant, long-term hazards found in spent nuclear fuel. The selective extraction of the minor actinides from the lanthanides is an important part of advanced reprocessing of spent nuclear fuel. This separation would allow the minor actinides to be fabricated into a target and recycled to a reactor and the lanthanides to be disposed. Due to the similarities in the chemical properties of the trivalent actinides and lanthanides, this separation is difficult to accomplish. The introduction of soft donor groups, such as N or S, into similarly structured ligands increases the differentiation between An(III) and Ln(III) cation coordination. Partly because of limitations imposed by synthetic methodologies, previous studies of dithiophosphinic acid (DPAH) extractants has been restricted to a comparatively small number of symmetrical dialkyl and diaryl derivatives. Research efforts at the Idaho National Laboratory have resulted in the recent development of an innovative synthetic pathway yielding new regiospecific DPAH extractants. The synthesis improves DPAH designs that can address the issues concerning minor actinide separation efficiency and extractant stability. Several new symmetric and asymmetric DPAH extractants have been prepared. The use of these extractants for the separation of minor actinides from lanthanides will be discussed. In addition, the variation in the extent of Am(III) extraction by a related series of DPAH isomers will be presented.

Synthesis and Coordination Properties of Trifluoromethyl Decorated Derivatives of 2,6-Bis[(diphenylphosphinoyl)methyl]pyridine N-Oxide Ligands with Lanthanide Ions

Phosphinoyl Grignard-based substitutions on 2,6-bis(chloromethyl)pyridine followed by N-oxidation of the intermediate 2,6-bis(phosphinoyl)methylpyridine compounds with mCPBA give the target trifunctional ligands 2,6-bis[bis(2-trifluoromethylphenyl)phosphinoylmethyl]pyridine 1-oxide (2a) and 2,6-bis[bis(3,5-bis(trifluoromethyl)phenyl)phosphinoylmethyl]pyridine 1-oxide (2b) in high yields. The ligands have been spectroscopically characterized, the molecular structures confirmed by single crystal X-ray diffraction methods, and the coordination chemistry surveyed with lanthanide nitrates. Single crystal X-ray diffraction analyses are described for the coordination complexes Nd(2a)(NO(3))(3), Nd(2a)(NO(3))(3) x (CH(3)CN)(0.5), Eu(2a)(NO(3))(3), and Nd(2b)(NO(3))(3) x (H(2)O)(1.25); in each case the ligand binds in a tridentate mode to the Ln(III) cation. These structures are compared with the structures found for lanthanide coordination complexes of the parent NOPOPO ligand, [Ph(2)P(O)CH(2)](2)C(5)H(3)NO.

Synthesis and lanthanide coordination chemistry of trifluoromethyl derivatives of phosphinoylmethyl pyridine N-oxides.

A synthetic route for the formation of 2-[bis(2-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1c) and 2-[bis(3,5-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1d) was developed and the new ligands characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The coordination chemistry of 1c was examined with Yb(NO3)3 and the molecular structure of one complex, [Yb(1c)(NO3)3(DMF)].DMF.0.5H2O, was determined by single-crystal X-ray diffraction methods. The ligand is found to coordinate in a bidentate fashion, and this is compared against lanthanide coordination chemistry observed for the related ligand, [Ph2P(O)CH2] C5H4NO.

Humidified Gas Stream Separations at High Temperatures Using Matrimid 5218

Most industrially relevant high temperature gas separations (≥150°C) of either carbon dioxide (flue gas) or hydrogen (syn-gas) must be performed in the presence of water vapor. At ambient temperatures, water vapor can permeate easily through most polymeric membranes and can influence the permeation of other gases through interaction with the polymer, such as swelling and clustering. At higher temperatures, water vapor can be destructive to polymer membranes by changing the polymer structure that can result in diminished gas separation performance. Little data has been reported on the influence of water vapor in gas separations at >100°C because most polymers are not stable at temperature. Many high performance (HP) polymers are able to endure high temperatures and aggressive chemical conditions. For example, polyimides are promising HP polymers that effectively separate permanent gases at temperatures higher than 150°C under dry conditions. In this report, the analysis of selected HP polymers in humidified gas streams (2–4 vol% water) shows that they can perform modest separations at ambient temperatures. In general, it was observed that water vapor permeability is greater than other tested gases. Additionally, the permeabilities of the analyte gases were somewhat influenced by the presence of humidity and their selectivities were significantly lower, as compared to corresponding experiments performed in the absence of water. To elucidate the role of water vapor in gas transport, energy of activation of permeation (Ep) values were obtained for Matrimid 5218 from 30–200°C in a humidified mixed gas stream, and it was found that the selectivities are nearly identical to dry gas streams at 150°C. This data suggests that water vapor functions as a gas and only slightly decreases selectivity of the other gases at elevated temperatures. As a result, economic wet gas separations may be possible using these materials if the gas stream is kept at higher temperature (≥150°C), which is assisted by the inherent stability of the membranes.

Chapter 13 – High Temperature Gas Separations Using High Performance Polymers

Abstract High performance polymers (glassy polymers) show promise for high temperature gas separations, especially for the separation of carbon dioxide and hydrogen for the water gas shift reaction. A series of polyimide (VTEC PI series) membrane materials have shown attractive gas separation performance at higher temperatures (250xa0°C). VTEC films remain robust and flexible after multiple thermal cycles (up to 400xa0°C, 10×). Many of the polyimides are highly selective for smaller kinetic diameter gases such as hydrogen and carbon dioxide; however, they have very low gas permeabilities at room temperature, and higher temperatures are needed to enhance gas fluxes. In this work, various compounds and polymers have been blended with VTEC polyimides, and some of these blends show different gas fluxes than the parent VTEC films. An interesting point is that the parent VTEC membranes show similar H 2 /CO 2 separation factors (alphas) at both 30 and 250xa0°C. A problem with glassy polymers has been shown to be entrapped water within the matrix that affects permeation behavior. Water that is entrapped within the polymer matrix (left over from processing or physisorbed) may cause the polymers fluxes and gas pair separation factor to dramatically change. Positron annihilation lifetime spectroscopy has been used to detect the presence of molecular water in the polymers void volume. Overall, several high performance polymers, including VTEC, offer gas separations that are useful for high temperature applications.

Direct synthesis of trifluoromethyl decorated diphenylphosphites. Unusual non-bonded structural features in bis-[(2-trifluoromethyl)phenylphosphite: [2-(CF3)C6H4]2P(O)H]

A direct, Grignard reagent-based route for the syntheses of [2-(CF3)C6H4]2P(O)H (1) and [3,5-(CF3)2C6H3]2P(O)H (2) has been developed and the isolation and characterization of these crystalline reagents is described. The crystal structures for 1 and 2 were determined and the structure of 1 reveals unexpected close non-bonded interaction between F-atoms of one CF3 group and the back-side of the central phosphorus atom.

Complete recovery of actinides from UREX-like raffinates using a combination of hard and soft donor ligands. II. soft donor structure variation

The feasibility of simultaneous separation of uranium, neptunium, plutonium, americium, and curium from a simulated dissolved used fuel simulant adjusted to 1.0 M nitric acid is investigated using a mixture of the soft donor bis(bis-3,5-trifluoromethyl)phenyl) dithiophosphinic acid (“0”) and the hard donor synergist trioctylphosphine oxide (TOPO) dissolved in toluene. The results reported in this work are compared to our recent demonstration of a complete actinide recovery from a simulated dissolved fuel solution using a synergistic combination of bis(o-trifluoromethylphenyl)dithiophosphinic acid (“1”) and TOPO dissolved in either toluene or trifluoromethylphenyl sulfone. While the extraction efficiency of americium was enhanced for the liquid-liquid system containing “0”, enabling to accomplish a trivalent An/Ln separation at 1.0 M HNO3, the extraction of neptunium was drastically diminished, relative to “1”. The partitioning behavior of curium was also negatively impacted, introducing an effective opportunity for americium/curium separation. Radiometric and spectrophotometric studies demonstrate that the complete actinide recovery using the solvent based upon “0” and TOPO is not feasible. In addition, the importance of radiolytic degradation processes is discussed through the comparisons of extraction properties of liquid-liquid systems based on both soft donor reagents.

Positron Annihilation Spectroscopy Of High Performance Polymer Films Under CO2 Pressure

Positron annihilation Lifetime and Doppler broadening measurements are reported for six polymer films as a function of carbon dioxide (CO2) absolute pressure ranging from 0 to 45 psi. Since the polymer films were thin and did not absorb all positrons, corrections were made in the lifetime analysis for the absorption of positrons in the positron source and sample holder using the Monte Carlo transport code MCNP. The studied polymers are found to behave differently from each other. Some polymers form positronium and others, such as the polyimide structures, do not. For those polymers that form positronium an interpretation in terms of free volume is possible; for those that don’t form positronium, further work is needed to determine how best to describe the behavior in terms of the bulk positron annihilation parameters. A few of the studied polymers exhibit changes in positron lifetime and intensity under CO2 pressure which may be described by the Henry or Langmuir sorption models, while the positron respon...

Water Transport Polymers – Structure/Property Relationships of a Series of Phosphazene Polymers

A study was undertaken to explore the water passing properties of a series of phosphazene polymers versus the attached pendant group structure. Pendant groups containing different numbers of ethyleneoxy groups were synthetically attached to the backbone of phosphazene polymers. Phosphazene polymers facilitate these types of studies because, during their synthesis, the polymer backbone is formed first and then the desired pendant groups are attached through nucleophilic substitution. For these studies, four polymer series were synthesized and tested for their water passing properties. The polymers contained different amounts of ethyleneoxy units. Two different polymer families were synthesized and compared in this work. The critical difference in the two polymer series is that one contained pendant groups with aromatic rings, in addition to the oligioethyleneoxy moieties, while the other has no aromatic rings in its structure. Polymers with phenyl group-containing pendant groups exhibited poor water permeability if they possessed fewer than six ethyleneoxy units. Polymers with more than six ethyleneoxy units inserted between the phenyl ring (tail) and the polymeric backbone exhibited reasonable water permeability. Two additional series of polymers with mixed pendant groups were synthesized and the water passing properties of the phosphazenes varied in proportion to the hydrophilic to hydrophobic balance induced by each individual pendant group. A final study of polymers with shorter pendant groups demonstrated the effect of pendant group on water permeability. These studies suggest that the polyphosphazenes may be tailored for specific water passing applications.

Comparison of Aromatic Dithiophosphinic and Phosphinic Acid Derivatives for Minor Actinide Extraction

A new extractant for the separation of actinide(III) and lanthanide(III), bis(otrifluoromethylphenyl) phosphinic acid (O-PA) was synthesized. The synthetic route employed mirrors one that was employed to produce the sulfur containing analog bis(otrifluoromethylphenyl) dithiophosphinic acid (S-PA). Multinuclear NMR spectroscopy was used for elementary characterization of the new O-PA derivative. This new O-PA extractant was used to perform Am(III)/Eu(III) separations and the results were directly compared to those obtained in identical separation experiments using S-PA, an extractant that is known to exhibit separation factors of ~100,000 at low pH. The separations data are presented and discussed in terms comparing the nature of the oxygen atom as a donor to that of the sulfur atom in extractants that are otherwise identical.