Comparison of Hydrometallurgical Parameters of N,N‐Dialkylamides and of Tri‐n‐Butylphosphate

Straight‐chain N,N‐dihexyloctanamide (DHOA) and branched‐chain N,N‐di(2‐ethylhexyl)isobutyramide (D2EHIBA) have been identified as promising alternatives to tri‐n‐butylphosphate (TBP) for the reprocessing of spent uranium based fuels, and selective extraction of ²³³U from irradiated thorium fuels, respectively. The present work deals with the effects of different hydrodynamic parameters such as viscosity, density, and interfacial tension (IFT) on the phase‐separation time (PST) under uranium and thorium loading conditions. The IFT values have been determined under varying experimental conditions such as the aqueous nitric acid concentration, n‐dodecane purity, ligand concentration, and thorium/uranium loading conditions. These studies have suggested that the quality of n‐dodecane affects the IFT values of different solutions. The IFT values of D2EHIBA changed marginally (23.3 ± 0.9 mNm^?1) against THOREX feed solution for the wide range of D2EHIBA concentration (0.1–1.0 M). However, IFT, viscosity, and PST values increased with uranium loading of 1.1 M DHOA. These studies suggested that a lower phase‐disengagement rate with increased uranium loading was mainly due to the increased viscosity of the loaded 1.1 M DHOA solution.     

Palladium,Gold, and Gold–Palladium Nanoparticle-Supported Carbon Materials for Cyclohexane Oxidation

Transition metal supported porous carbon materials have become a promising aspirant in energy storage, solid catalysis, and material chemistry. Palladium, gold, and gold–palladium anchored carbon composites (CPC-25/170, CGC-25/170, and CGPC-25/170) with two different sized carbon cages (～25 and 170 nm) were constructed using nano-silica ball (NSB) as the template and a pyrolysis fuel oil (PFO) based pitch residue as the carbon source. The Pd, Au, and Au–Pd doped carbon nanoreactors were characterized by various physicochemical analysis methods. The developed materials were used as heterogeneous catalysts for the oxidation of cyclohexane to cyclohexanol and cyclohexanone using H₂O₂ at room temperature (25°C) and atmospheric pressure. The most active catalyst CGC-170 showed combined cyclohexanol and cyclohexanone yield of 7.7% after 4 h reaction time. The conversion of 2.4%, 0.05%, and 0.32% was achieved using CGC-25, CGPC-25, and CGPC-170 catalysts, respectively. Recyclability of the catalysts maintains no observable loss of performance during catalytic oxidation reaction.     

Hydrothermal deactivation of Ce‐ZSM‐5, Ce‐beta, Ce‐mordenite and Ce‐Y zeolite deNOx catalysts

The hydrothermal stability of Ce³⁺ zeolite catalysts used for selective catalytic reduction of NO _x was investigated. Aging of Ce‐ZSM‐5, Ce‐beta, Ce‐mordenite and Ce‐Y catalysts consisted of steaming in 10 or 12 vol% water at 600°C for 3–99 h. Ce‐ZSM‐5 (Si/Al ratios: Si/Al = 17.1, 22.6 and 146.6) and Ce‐mordenite (Si/Al = 6.4, IE = 77.2%) showed fast deactivation. Ce‐beta (Si/Al = 12, IE = 68.4%) and Ce‐Y (Si/Al = 2.8, IE = 122%) are significantly more stable zeolite catalysts, Ce‐beta being the most active of these two. Ce‐beta and Ce‐ZSM‐5 catalysts – both having high initial activities – were characterized with ²⁹Si‐NMR and ²⁷Al‐NMR. Especially Ce‐ZSM‐5 showed an increase of non‐framework Al, meaning that the zeolite suffered from dealumination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of the Steric Hindrance,Ligand Hydrophobicity,and DN of solvents on Structure and Extraction of Cu(II) Complexes of 1‐Alkyl‐2‐Ethylimidazoles

Abstract

Formation of Cu(II) complexes of 1‐alkyl‐2‐ethylimidazoles (where alkyl=propyl, butyl, pentyl, hexyl, and octyl) has been studied by using the liquid‐liquid partition method, at 25°C and a fixed ionic strength of the aqueous phase (I=0.5; (HL)NO₃, KNO₃). The complexes were extracted with 2‐pentanone, 2‐butanol, isoamyl alcohol, 2‐ethyl‐1‐hexanol, dichloromethane, trichloromethane, and toluene. The length of the 1‐alkyl group and the nature of solvent have been shown to influence the extraction process. Extraction curves (log D_M vs. pH) are displaced towards lower pH's with increasing chain length of the 1‐alkyl substituent and donor number of the solvents. Stability constants of the complexes in aqueous solution were determined as well as their partition ratios between the aqueous and organic phase. The stability of the Cu(II) complexes increased with increasing 1‐alkyl chain length. The stability constants are comparable with β_n ones for the Cu(II) complexes of 1‐alkyl‐2‐methylimidazoles, but smaller than those of the Cu(II)–1‐alkylimidazole counterparts. The P_c‐partition ratios of the 1‐alkyl‐2‐ethylimidazole complexes with Cu(II) are high, and increased with increasing 1‐alkyl chain length and the donor number of the solvents. Both the strong steric effect of the ethyl substituent at position 2 and the bulkiness of the 1‐alkyl‐2‐ethylimidazole molecules as well as the strong electron‐donating properties of the solvent molecules have an effect on the change of the coordination number of Cu(II) from 6 to 4. The 4‐coordinate Cu(II) complexes (distorted tetrahedron) are more readily extractable by organic solvent than are the 6‐coordinate ones and for this reason their partition constants, P_c, are high. This finding offers the possibility of extraction of the Cu(II) ions from a mixture cations.     

15N solid state NMR study of the reactions of propane or propene, 15NO and oxygen on Na‐, H‐, and CuZSM‐5

Ni- and Co-based catalysts derived from NiAl- and CoAl-layered double hydroxides were tested in four kinds of reactions of methanol, namely decomposition of methanol (DCM), partial oxidation of methanol (POM), steam reforming of methanol (SRM), and oxidative steam reforming of methanol (OSRM), for the purpose of H₂ production for fuel cells. H₂, CO and/or CO₂ were the predominant products with minor amounts of dimethyl ether (DME) and CH₄ depending on the reaction temperature. Among the four kinds of reactions tested, the OSRM reaction was found to be more effective in terms of MeOH conversion and H₂ selectivity over these catalysts. Higher selectivity of H₂ and CO₂ with only traces of CO could be obtained at about 100% methanol conversion around 300 °C in the OSRM reaction over the catalyst derived from CoAl-LDH. Substitution of a part of Al by Sn in the NiAl- and CoAl-LDH systems was found to be inhibiting the methanol conversion. On the other hand, the selectivities to DME and CH₄ were declined with a consequent increase in the selectivity to H₂. In addition, considerable amount of formaldehyde was also noticed, especially over the catalyst derived from CoAlSn-LDH at lower reaction temperatures. The observed difference in the catalytic performance upon Sn incorporation was attributed to an improved redox capability of the Ni- and Co-based oxide catalysts, as determined by temperature-programmed reduction (TPR) experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Extraction of Palladium(II) from Nitric Acid Solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea

The extraction of palladium (II) from HNO₃ solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea (Ia) and several monodentate thiourea derivatives in 1,2‐dichloroethane has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant in the organic phase on the Pd(II) extraction is considered. The stoichiometry of the extracted complexes has been determined. The increasing number of thioamide groups in the molecule of Ia increases its extraction efficiency towards Pd(II). The potentialities of a polymeric resin impregnated with compound Ia for selective extraction of Pd(II) from nitric acid solutions are demonstrated.     

Dependence of Synergetic Effect of Palladium–Manganese-Hexaaluminate Combustion Catalyst on Nature of Palladium Precursor

A synergetic effect in the methane oxidation activity of palladium and manganese hexaaluminate was studied over Pd-modified manganese-hexaaluminate catalysts, prepared by incipient wetness impregnation and calcined at 1,200?°C. The magnitude of the synergetic effect is found to be depends on the palladium precursor: it is higher for palladium nitrate and palladium acetate than for tetrachloropalladic acid. The Pd/MnLaAl₁₁O₁₉ catalysts were characterized by X-ray diffraction, X-ray microanalysis, transmission electron microscope and temperature-programmed reduction with hydrogen. These data were compared with the properties of Pd/Al₂O₃ catalysts. At variation of Pd-precursors, a minor trend to the decrease of the Pd particle size was observed at transition from the ex-chloride Pd/MnLaAl₁₁O₁₉ catalyst with uniform Pd-distribution profile to the ex-nitrate and ex-acetate catalysts with egg-shell Pd-distribution. Slightly smaller size of metal palladium particles in the ex-nitrate and ex-acetate catalysts leads to the formation of larger amount of PdO dispersed on their surface during oxygen-pretreatment in H₂-TPR experiments (Pd/PdO atomic ratio was 1/4) and under methane-oxidation mixture in comparison with ex-chloride catalysts (Pd/PdO?=?4/1). The palladium addition to manganese-hexaaluminate changes strongly its redox properties, as result Mn³⁺ reduction to Mn²⁺ take place about 100?°C below that of pure hexaalunimate. The latter indicate probably on the higher oxygen mobility in Pd-modified manganese-hexaaluminate. A higher PdO/Pd ratio formed in the ex-nitrate and ex-acetate Pd-modified manganese-hexaaluminate catalysts together with the high oxygen mobility provide the synergetic effect in methane oxidation activity at light-off temperature region. The high catalytic activity of manganese-hexaaluminate ensures methane combustion efficiency of the Pd-modified manganese-hexaaluminate catalysts at temperature above 700?°C.     

Studies on the Sorption of Palladium using Cross‐Linked Poly (4‐Vinylpyridine‐Divinylbenzene) Resins in Nitric Acid Medium

Various cross‐linked (4, 8, and 12%) gel‐type weak‐base poly(4‐vinylpyridine) (PVP) resins were studied for palladium recovery from nitric acid medium. The sorption of palladium was found to decrease with an increase in cross‐linkage of the resin. 8 and 12% PVP resins exhibited maximum D _Pd(II) values at 2–6 M HNO₃, whereas 4% PVP resin showed maximum D _Pd(II) values at lower acidities (0.1 M HNO₃). FT‐IR, SEM, and XPS techniques were used for the characterization of palladium‐loaded resins. Detailed studies were carried out with the resin of modest cross‐linkage i.e., 8% PVP resin. The sorption isotherm studies revealed that the maximum palladium loading approaches the theoretical capacity of the resin, presuming the sorption of palladium as divalent anion at 4 M HNO₃. The pseudo‐second order kinetics model yielded the best fit for the experimental data of sorption kinetics. An increase in temperature accelerates the rate of palladium extraction and also the addition of chloride ions increases the palladium uptake. Column studies were performed using 4 and 8% PVP resins in 2 and 4 M nitric acid concentrations. The loaded palladium could be eluted efficiently with acidic thiourea solution.     

Comparison of the catalytic properties of Al‐ZSM‐22 and Fe‐ZSM‐22 in the skeletal isomerization of 1‐butene

The catalytic activities of Al‐ZSM‐22 (Al in the framework) and Fe‐ZSM‐22 (Fe in the framework) were compared in the skeletal isomerization of 1‐butene to isobutene. The catalysts synthesized in the laboratory were characterized by means of XRD, FTIR spectroscopy, SEM and surface area measurements. The activity of the zeolites was investigated using a fixed‐bed microreactor system. Al‐ZSM‐22 demonstrated higher activity in 1‐butene transformation compared to Fe‐ZSM‐22, while the selectivity to isobutene, on the other hand, was higher over Fe‐ZSM‐22. Coke formation was monitored using a microbalance and the results showed that the weight gain of Fe‐ZSM‐22 was slightly higher compared to Al‐ZSM‐22. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Hydrogen Storage Properties of Palladium Nanoparticle–Organic Frameworks

We report a simple synthesis of aggregates of individual Pd colloidal nanoparticles linked by bridging ligands that may be used to advance the strong hydrogen storage properties of palladium nanoparticles. The aggregates were characterized by transmission electron microscopy and infrared spectroscopy. The bridged aggregates showed up to 1.0 wt% hydrogen absorption, about 6.7 times that of pristine isocyanide-protected Pd nanoparticles.     

Ring‐expansion of methylcyclopentane to cyclohexane and ring‐contraction of cyclohexane to methylcyclopentane on silica‐supported 12‐tungstophosphoric acid and stoichiometric and nonstoichiometric microporous silver 12‐tungstophosphate

Methylcyclopentane is ring‐expanded to cyclohexane and cyclohexane is ring‐contracted to methylcyclopentane on 12‐tungstophosphoric acid (HPW) supported on silica and on stoichiometric microporous silver 12‐tungstophosphate. The conversions of the two reactants increase with the loading of HPW on SiO₂ while achieving significantly higher values on silver 12‐tungstophosphate which pass through a maximum as the Ag/H⁺ preparative ratio increases. The ring‐expansion and ring‐contraction processes on the supported HPW and the microporous AgPW are catalyzed by the acidic protons in the solid acid and the residual protons in the silver salt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synergistic Extraction of Lanthanides(III) by Mixtures of N‐p‐Methoxybenzoyl‐N‐phenylhydroxylamine and 1,10‐Phenanthroline

Abstract

We conducted a study on the equilibrium extraction behavior of the trivalent lanthanide ions (M³⁺), La, Pr, Eu, Ho, and Yb, from tartrate aqueous solutions into chloroform solutions containing N‐p‐methoxybenzoyl‐N‐phenylhydroxylamine (Methoxy‐BPHA, HL) and 1,10‐phenanthroline (phen). The synergistic species extracted was found to be {ML₂(phen) (HL)}⁺(1/2)Tar^2?, where Tar^2? is tartrate ion. The extraction constants were calculated. The extraction separation behavior and extractability of lanthanides are discussed in comparison with the self‐adducted chelate, ML₃(HL)₂, which was extracted in the absence of phen, and synergistic extraction by mixtures of other extractants such as 2‐thenoyltrifluoroacetone, and neutral donors.     

Characterization of Extraction of Chromatographic Materials Containing Bis(2‐ethyl‐1‐hexyl)Phosphoric Acid, 2‐Ethyl‐1‐Hexyl (2‐Ethyl‐1‐Hexyl) Phosphonic Acid,and Bis(2,4,4‐Trimethyl‐1‐Pentyl)Phosphinic Acid

Abstract

This work describes the uptake of a wide range of metal ions, including alkaline earths, transition metals, post‐transition metals, lanthanides and actinides, from acidic nitrate and chloride media on extraction chromatographic resins prepared from three different acidic organophosphorus compounds: bis(2‐ethyl‐1‐hexyl) phosphoric acid (HDEHP), 2‐ethyl‐1‐hexyl(2‐ethyl‐1‐hexyl)phosphonic acid, (HEH[EHP]) and bis(2,4,4‐trimethyl‐1‐pentyl)phosphinic acid (H[DTMPP]). The data is plotted in a format allowing for the easy comparison of the uptake of all metal ions under a given condition. Additionally, examples of several novel separations using the three extraction chromatographic materials are discussed.     

Extraction of Actinide(III,IV, V,VI) Ions and TcO4 − by N,N,N′,N′‐Tetraisobutyl‐3‐Oxa‐Glutaramide

Abstract

The extraction behavior of U(VI), Np(V), Pu(IV), Am(III), and TcO₄ ^? with N,N,N′,N′‐tetraisobutyl‐3‐oxa‐glutaramide (TiBOGA) were investigated. An organic phase of 0.2 mol/L TiBOGA in 40/60% (V/V) 1‐octanol/kerosene showed good extractability for actinides (III, IV, V VI) and TcO₄ ^? from aqueous solutions of HNO₃ (0.1 to 4 mol/L). At 25°C, the distribution ratio of the actinide ions (D _An) generally increased as the concentration of HNO₃ in the aqueous phase was increased from 0.1 to 4 mol/L, while the D _Tc at first increased, then decreased, with a maximum of 3.0 at 2 mol/L HNO₃. Based on the slope analysis of the dependence of D _M (M=An or Tc) on the concentrations of reagents, the formula of extracted complexes were assumed to be UO₂L₂(NO₃)₂, NpO₂L₂(NO₃), PuL(NO₃)₄, AmL₃(NO₃)₃, and HL₂(TcO₄) where L=TiBOGA. The enthalpy and entropy of the corresponding extraction reactions, Δ_r H and Δ_r S, were calculated from the dependence of D on temperature in the range of 15–55°C. For U(VI), Np(V), Am(III) and TcO₄ ^?, the extraction reactions are enthalpy driven and disfavored by entropy (Δ_r H<0 and Δ_r S<0). In contrast, the extraction reaction of Pu(IV) is entropy driven and disfavored by enthalpy (Δ_r H>0 and Δ_r S>0). A test run with 0.2 mol/L TiBOGA in 40/60% 1‐octanol/kerosene was performed to separate actinides and TcO₄ ^? from a simulated acidic high‐level liquid waste (HLLW), using tracer amounts of ²³⁸U(VI), ²³⁷Np(V), ²³⁹Pu(IV), ²⁴¹Am(III) and ⁹⁹TcO₄ ^?. The distribution ratios of U(VI), Np(V), Pu(IV), Am(III) and TcO₄ ^? were 12.4, 3.9, 87, >1000 and 1.5, respectively, confirming that TiBOGA is a promising extractant for the separation of all actinides and TcO₄ ^? from acidic HLLW. It is noteworthy that the extractability of TiBOGA for Np(V) from acidic HLLW (D _Np(V)=3.9) is much higher than that of many other extractants that have been studied for the separation of actinides from HLLW.     

Synthesis,Characterization, and Evaluation of Gel‐Type Poly(4‐Vinylpyridine) Resins for Plutonium Sorption

Abstract

Three different cross‐linked (4, 8, and 12%) gel‐type strong‐base poly(4‐vinylpyridine) resins (PVP) have been synthesized and characterized by elemental analysis, IR, exchange capacity, and moisture content. The uptake of plutonium and uranium was measured as a function of nitric acid concentration using all the three PVP resins. Plutonium sorption and elution kinetics experiments were also performed on all three PVP resins and compared with the benchmark, a gel‐type quarternary ammonium type anion‐exchange resin. The plutonium sorption rate decreases with the increase in cross‐linkage of the resin. All the three PVP resins exhibit better elution kinetics compared to the benchmark. The results on kinetic experiments performed on all three‐gel‐type resins indicated 8% gel‐type PVP resin with 50–100 mesh as a better candidate for plutonium processing or purification. Radiation degradation studies were carried out on the 8% PVP resin by gamma irradiation up to 200 MRad. The irradiated resins were characterized by IR, TGA, and SEM.

The exchange capacity, moisture content, and plutonium uptake were also evaluated for the irradiated PVP resins in comparison with the benchmark. The results indicated a better radiation stability for PVP resin over the benchmark.     

Cobalt‐catalyzed amination of 1,3‐cyclohexanediol and 2,4‐pentanediol in supercritical ammonia

The onestep procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixedbed reactor. Application of supercritical NH₃ as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8–10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via ,unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3propanediol.     

Characterization and catalytic activities of MoMCM‐41

Catalysts consisting of molybdenum incorporated into MCM‐41 mesoporous molecular sieves (MoMCM‐41) were synthesized and characterized by XRD, N₂ adsorption/desorption, ESR, FTIR, and UV‐vis analysis techniques. The MoMCM‐f41 catalysts were synthesized by addition of Na₂MoO₄·2H₂O as molybdenum source at the initial step of synthesis; the framework Mo in MoMCM‐41 catalysts could be confirmed by ESR, FTIR and UV‐vis. As the molybdenum content is increased, the structure of MoMCM‐41 changed from hexagonal to amorphous. Molybdenum loading up to ca. 10% was a maximum concentration that was obtained in this study. The MoMCM‐41 catalysts showed a catalytic activity for propylene oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stereoselective Formation of 1,4‐Anhydro‐2‐C‐carboxytetritols in the Degradation of 1,5‐Anhydroribitol and 1,5‐Anhydroxylitol with Oxygen in Aqueous Alkali

Abstract

In addition to other acid products, degradation of 1,5‐anhydroribitol (5) and 1,5‐anhydroxylitol (6) with oxygen in 1.25 M NaOH produced diastereomeric 1,4‐anhydro‐2‐C‐carboxy‐D‐erythritol (7) and 1,4‐anhydro‐2‐C‐carboxy‐D‐threitol (8) and their enantiomers as major products. However, the ratio of the diastereomers differed for the two reactants. Thus, their formation could not proceed solely by benzilic acid‐type rearrangements through α‐dicarbonyl intermediates as typically proposed for formation of alkyl C‐carboxyfuranosides from alkyl glycopyranosides in similar reactions. The α‐dicarbonyl species that can form from 5 and 6 are identical. Potential mechanisms to account for stereoselective formation of 7 and 8 are presented.     

Effect of Anions on the Extraction of Lanthanides (III) by N,N′‐Dimethyl‐N,N′‐Diphenyl‐3‐Oxapentanediamide

Abstract

The extraction of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y by N,N′‐dimethyl‐N,N′‐diphenyl‐3‐oxapentanediamide (DMDPhOPDA) in 1,2‐dichloroethane from aqueous media containing ClO₄ ^?, PF₆ ^?, (CF₃SO₂)₂N^? anions or by DMDPhOPDA in 1,2‐dichloroethane in the presence of 1‐butyl‐3‐methylimidazolium bis[(trifluoremethyl)sulfonyl]imide ([C₄mim][Tf₂N]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) from HNO₃ solutions has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes has been determined. The addition of HPF₆ and (CF₃SO₂)₂NH or their salts to the aqueous HNO₃ or HCl solutions leads to an enchancement of lanthanides (III) extraction by DMDPhOPDA. A considerable synergistic effect was observed in the presence of ionic liquids (IL) in the organic phase containing DMDPhOPDA. This effect is connected with the hydrophobic nature of the IL anion. The distribution of ILs between the equilibrium organic and aqueous phases can govern the extractability of lanthanides (III) in DMDPhOPDA‐IL systems.     

Quasi‐Homogeneous and Pseudospin Modes of Zirconium‐Wire Combustion in Air

A novel experimental technique is proposed for examining the transition mechanism from quasihomogeneous to heterogeneous combustion — burning of a variablepitch spring. Depending on the pitch of aircombustible zirconium springs, two combustion modes are possible. Quasihomogeneous (layerbylayer) combustion is observed in the case of smallpitch springs; as the spring pitch increases, quasihomogeneous combustion transforms into heterogeneous (pseudospin) combustion. Conditions for the occurrence of various combustion modes, depending on the spring diameter and pitch, are studied.