Intermittent two-phase flow study by NMR

Co-circulation of gas and liquid in a pipe can generate, depending on inlet conditions, various kinds of flow patterns. Few investigations have been performed on intermittent two-phase flows (slug flows) using classical techniques (optical probe, hot-wire anemonetry, etc.), because these techniques are difficult to apply in this flow regime. Here we show that nuclear magnetic resonance is a powerful technique to study such flows. The presented results deal with controlled isolated Taylor bubbles. In addition to a classical Pulsed Field Gradient Spin Echo (PFGSE), a magnetic field gradient was applied during the π/2)_X radio frequency pulse, which produces a selective irradiation. Thus, cutting up of the flow into slices provides the longitudinal evolution of the liquid fraction and of the velocity probability distribution in the entire region perturbed by the Taylor bubble. The existence of a recirculatory flow under the Taylor bubble is clearly demonstrated.     

Enantioselective liquid-liquid extraction of (R,S)-phenylglycinol using a bisnaphthyl phosphoric acid derivative as chiral extractant

This study demonstrates that enantioseparation by liquid-liquid extraction can be done in a continuous flow mode on both laboratory and industrial scale and is a promising technique that could become a competitive alternative for crystallization or chromatographic approaches. We studied the enantioselective liquid-liquid extraction of phenylglycinol (Pgl) using a bisnaphthyl phosphoric acid extractant. Batch experiments were performed to estimate extraction model parameters. The system was described using an extraction mechanism with homogeneous organic phase complexation. The complexation constants were very large, in the order of 10⁸-10¹⁰ L/mol in the temperature range 279<T<303 K. The developed model was then used to design a multistage countercurrent extraction process with Centrifugal Contactor Separator (CCS) equipment. This study demonstrates that high purity (70% ee) with a reasonable yield (36%) can be obtained for a moderately selective system (α=1.7) with only six extraction stages. The technology is potentially applicable to a wide range of racemates.     

Overview of cationic phthalocyanines for effective photoinactivation of pathogenic microorganisms

Phthalocyanine (Pc) dyes are photoactive compounds that can absorb and emit light in a large range of the UV–vis spectrum, with recognized potential for medical applications. Considering the low solubility of Pc macrocycles in water, it is important to use cationic symptoms on their skeleton to improve their amphiphilicity for biomedical applications. The use of suitable pyridinium groups on Pc is a good strategy to solve this drawback and make them more eff ;ective to photoinactivate microorganisms via a photodynamic inactivation (PDI) approach. This review focuses the synthesis of quaternized Pc dyes, their photophysical and photochemical properties, and their antimicrobial photoinactivation efficiency. This innovative study compares, for the first time, different cationic moieties on Pc taking into account the efficiency of singlet oxygen (¹O₂), quantum yield (Φ_Δ) generation, fluorescence quantum yield (Φ_F), (photo)stability, light irradiation type (visible/white and/or red light), maximized overlapped absorption effect of Pc (S- and/or Q-band) vs light system irradiation type, and water solubility (n-octanol/water partition coefficient, P_o/w), when these parameters are determined and provided in the multidisciplinary reports. This approach is also relevant to conjugate free-base (H₂Pc) and metalated phthalocyanines (MPc, M = Zn²⁺, Mg²⁺, In³⁺, Ga³⁺, Ge³⁺, Si⁴⁺, etc.) with aromatic or aliphatic substituents linked by N, O or S atoms on the peripheral or axial positions of the Pc structures, such as e.g. (methoxy, oxy, or thio)pyridinium, ammonium, or benzimidazolium units, etc. Here, the influence of the structural peripheral (α- and/or β-position of Pc) or axial substituents type, number and positive charge position that can affect the PDI process will be analysed. These aspects are important to design versatile molecules that can interact with pathogenic microorganisms of variable size, subcellular architecture, biochemical composition, and susceptibility to externally added chemical agents. This review highlights the important developments of several modifications of cationic Pc dyes for the PDI of microorganisms, such as pathogenic bacteria, fungi, and virus.     

MicroRaman Measurements for Nuclear Fuel Reprocessing Applications

Treatment and reuse of used nuclear fuel is a key component in closing the nuclear fuel cycle. Solvent extraction reprocessing methods that have been developed contain various steps tailored to the separation of specific radionuclides, which are highly dependent upon solution properties. The instrumentation used to monitor these processes must be robust, require little or no maintenance, and be able to withstand harsh environments such as high radiation fields and aggressive chemical matrices.Our group has been investigating the use of optical spectroscopy for the on-line monitoring of actinides, lanthanides, and acid strength within fuel reprocessing streams. This paper will focus on the development and application of a new MicroRaman probe for on-line real-time monitoring of the U(VI)/nitrate ion/nitric acid in solutions relevant to used nuclear fuel reprocessing. Previous research has successfully demonstrated the applicability on the macroscopic scale, using sample probes requiring larger solution volumes. In an effort to minimize waste and reduce dose to personnel, we have modified this technique to allow measurement at the microfluidic scale using a Raman microprobe. Under the current sampling environment, Raman samples typically require upwards of 10 mL and larger. Using the new sampling system, we can sample volumes at 10 μL or less, which is a scale reduction of over 1,000 fold in sample size.This paper will summarize our current work in this area including: comparisons between the macroscopic and microscopic probes for detection limits, optimized channel focusing, and application in a flow cell with varying levels of HNO₃, and UO₂(NO₃)₂.     

Synthesis and characterization of Ti1−2xNbxNixO2−x/2 solid solutions

Doped-rutile has been traditionally used in ceramic pigments for its intense optical properties. In this paper, we compare the classical ceramic synthesis of Ti_1−2xNb_xNi_xO_2−x/2 system with the sol-gel methodology, which allows a reduction of the anatase-rutile transformation temperature. The composition was optimised in order to obtain a unique rutile phase with the minimum amount of pollutant Ni(II) and enhanced chromatic coordinates. Incorporation of the doping ions in the rutile structure was corroborated by XRD and Rietveld refinements. The species responsible for the colour mechanism were studied by different techniques. UV-VIS spectroscopy showed the characteristic features of Ni²⁺ ions, whose existence was corroborated by EPR and magnetic measurements. From these results, (Ni,Nb)doped-TiO₂ powder samples can be now shaped as thin films, monoliths, etc. by using sol-gel methodology without modifying their properties. This study introduces new possibilities of coloured TiO₂-based solid solutions in new combined advanced applications (colouring agent and photocatalyst, etc.).     

New approaches to processing and fabrication of oxide nuclear fuels

It was shown that, in contrast to the Purex process using aggressive and environmentally hazardous 8M HNO₃ solutions for dissolving spent oxide nuclear fuel (SNF), this fuel can be easily dissolved in aqueous subacid ([H⁺] ∼0.1 M) solutions of Fe(III) nitrate (chloride) with partial separation of uranium and plutonium from fission products (FP). The low acidity of the solutions obtained (pH ∼1) allows direct application of modern technologies of finishing processing of nuclear fuel by fluoride, carbonate, oxalate, or peroxide precipitation of uranium and plutonium. It was established that U(VI) is isolated from nearly neutral nitric acid solutions as a poorly soluble uranyl hydroxylaminate complex after adding hydroxylamine. It was shown that on thermal decomposition at 200–300°C under ambient atmosphere this compound converts into uranium dioxide. A similar approach was applied to obtain mixed oxide uranium-plutonium fuel (MOX fuel).     

Toward mechanistic understanding of nuclear reprocessing chemistries by quantifying lanthanide solvent extraction kinetics via microfluidics with constant interfacial area and rapid mixing

The closing of the nuclear fuel cycle is an unsolved problem of great importance. Separating radionuclides produced in a nuclear reactor is useful both for the storage of nuclear waste and for recycling of nuclear fuel. These separations can be performed by designing appropriate chelation chemistries and liquid-liquid extraction schemes, such as in the TALSPEAK process (Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes). However, there are no approved methods for the industrial scale reprocessing of civilian nuclear fuel in the United States. One bottleneck in the design of next-generation solvent extraction-based nuclear fuel reprocessing schemes is a lack of interfacial mass transfer rate constants obtained under well-controlled conditions for lanthanide and actinide ligand complexes; such rate constants are a prerequisite for mechanistic understanding of the extraction chemistries involved and are of great assistance in the design of new chemistries. In addition, rate constants obtained under conditions of known interfacial area have immediate, practical utility in models required for the scaling-up of laboratory-scale demonstrations to industrial-scale solutions. Existing experimental techniques for determining these rate constants suffer from two key drawbacks: either slow mixing or unknown interfacial area. The volume of waste produced by traditional methods is an additional, practical concern in experiments involving radioactive elements, both from disposal cost and experimenter safety standpoints. In this paper, we test a plug-based microfluidic system that uses flowing plugs (droplets) in microfluidic channels to determine absolute interfacial mass transfer rate constants under conditions of both rapid mixing and controlled interfacial area. We utilize this system to determine, for the first time, the rate constants for interfacial transfer of all lanthanides, minus promethium, plus yttrium, under TALSPEAK process conditions, as a first step toward testing the molecular mechanism of this separation process.     

SU-8 flow field plates for a micro PEMFC

A SU-8 photoresist microfabrication process was developed for micro proton exchange membrane fuel cell flow structures for both anode and cathode flow field plates with a cross section of 5 cm² (22.5 mm×22.5 mm) and thickness (for a single cell) of about 750 µm. The new design for flow field plates would have SU-8 used as not only a photoresist but also as a microstructure material. A thickness of 30 nm Pt sputter loading deposited onto a Nafion 117 for membrane electrode assembly was made, with both scanning electron microscopy and atomic force microscopy characterization. Air flows were completed in hydrogen fuel cells with air breathing and forced air flows of low input pressure as well as low velocity. Performance tests of polarization curves and power density distribution as well as impendence measurements were conducted and discussed to examine the effects of orientation of the cathode surface with five hydrogen feeding rates as well as different airflow feeding modes.     

Nuclear, chemical, and physical characterization of nuclear materials

The goal of nuclear forensics is to establish an unambiguous link between illicitly trafficked nuclear material and its origin. The Los Alamos National Laboratory (LANL) Nuclear Materials Signatures Program has implemented a graded “conduct of operations” type analysis flow path approach for determining the key nuclear, chemical, and physical signatures needed to identify the manufacturing process, intended use, and origin of interdicted nuclear material. This analysis flow path includes both destructive and non-destructive characterization techniques and has been exercized against different nuclear materials from LANL’s special nuclear materials archive. Results obtained from the case study will be presented to highlight analytical techniques that offer the critical attribution information.     

核燃料循环中镅的氧化分离研究进展

镅离子在溶液中主要以三价形式(Am(III))存在,因其离子半径与三价镧系离子Ln(III)接近,化学特性相似,使得Am(III)与Ln(III)的有效分离被认为是核燃料循环领域最具挑战性的课题之一。利用镅的多价态特性,采用不同氧化方法可将Am(III)氧化成高价态的AmO₂⁺和AmO₂²⁺形式,再通过溶剂萃取、沉淀等方法进行分离,是实现Am与Ln分离的一种新思路。本文综述了不同氧化方法对水溶液环境中Am(III)的氧化分离研究进展,描述了相关机理,指出了不同氧化方法的优劣并展望了未来发展趋势,以期为发展新型镧系与锕系元素分离技术提供参考。     

Status of sol–gel process for nuclear fuels

Sol–gel process provides an alternate route for fabrication of ceramic nuclear fuel. The sol–gel process provides several advantages over the conventional powder pellet fabrication process by eliminating handling of radioactive powders. The sol–gel process uses only fluids or fluid like materials, thus become amenable to remote handling. The sol–gel process has been developed for the production of coated particle fuels for High Temperature Gas Cooled Reactors (HTGRs), as sphere-pac fuel for Fast Breeder Reactors (FBRs) and as SGMP fuel for Thermal Reactors. Internal Gelation Process is one of the most important routes of the sol–gel process and has been accepted as the most promising process route globally. Several countries having plutonium or ²³³U based fuel program have developed sol–gel process for nuclear fuels. In India there is special interest for the development of the sol–gel process for the thorium–uranium fuels keeping in view the large resources of thorium in India. Sol–gel process for fuel fabrication is also very attractive route for closing the nuclear fuel cycle efficiently. Author is BRNS Raja Ramanna Fellow.     

High efficiency direct methanol fuel cell based on poly(styrenesulfonic) acid (PSSA)-poly(vinylidene fluoride) (PVDF) composite membranes

semi-Interpenetrating polymer network (sIPN) composite membranes consisting of poly(styrenesuflonic) acid (PSSA) and poly(vinylidene fluoride) (PVDF) have been prepared and evaluated as proton exchange membrane electrolytes in direct methanol fuel cells (DMFCs). The membranes fabricated were evaluated in terms of their proton conductivity, methanol permeability, and their performance characteristics in direct methanol fuel cells (DMFCs). PSSA-PVDF membranes demonstrated decreased methanol crossover during operation of direct methanol fuel cells compared to state-of-art Nafion^®-H membranes, yielding improved efficiency. PSSA-PVDF membranes have been demonstrated to operate efficiently in 1 in. × 1 in. and 2 in. × 2 in. direct methanol fuel cells. Fuel cells operating with PSSA-PVDF membranes were observed to have dramatically lower crossover rates compared to Nafion^® 117 systems. Greater than 95% reduction in crossover was observed in some cases. These properties of PSSA-PVDF membranes resulted in improved fuel performance and fuel cell efficiencies for direct methanol fuel cells. It was also observed that the PSSA-PVDF membranes behave quite differently compared with Nafion^®-based systems in terms water management characteristics at the cathode. The best performance with the new membranes was observed with very low oxygen or air flow rates at the cathode which is in contrast to Nafion^®-based systems, which generally require higher flow rates due to excessive water accumulation at the cathode, resulting in flooding.     

A dynamic liquid-liquid interfacial pressure detector for the rapid analysis of surfactants in a flowing organic liquid

Design and development of a dynamic interfacial pressure detector (DIPD) is reported. The DIPD measures the differential pressure as a function of time across the liquid-liquid interface of organic liquid drops (i.e., n-hexane) that repeatedly grow in water at the end of a capillary tip. Using a calibration technique based on the Young-Laplace equation, the differential pressure signal is converted, in real-time, to a relative interfacial pressure. This allows the DIPD to monitor the interfacial tension of surface active species at liquid-liquid interfaces in flow-based analytical techniques, such as flow injection analysis (FIA), sequential injection analysis (SIA) and high performance liquid chromatography (HPLC). The DIPD is similar in principle to the dynamic surface tension detector (DSTD), which monitors the surface tension at the air-liquid interface. In this report, the interfacial pressure at the hexane-water interface was monitored as analytes in the hexane phase diffused to and arranged at the hexane-water interface. The DIPD was combined with FIA to analytically measure the interfacial properties of cholesterol and Brij^®30 at the hexane-water interface. Results show that both cholesterol and Brij^®30 exhibit a dynamic interfacial pressure signal during hexane drop growth. A calibration curve demonstrates that the relative interfacial pressure of cholesterol in hexane increases as the cholesterol concentration increases from 100 to 10,000 μg ml⁻¹. An example of the utility of the DIPD as a selective detector for a chromatographic separation of interface-active species is also presented in the analysis of cholesterol in egg yolk by normal-phase HPLC-DIPD.     

Effect of tri-n-butyl phosphate on physical properties of dodecane–nitric acid system

Extraction power of solvent depends upon the physical properties of the system. Tri-n-butyl phosphate (TBP) in dodecane is a versatile solvent used in the nuclear fuel reprocessing like PUREX process. The study of physical properties like density, viscosity, interfacial tension and solubility for TBP–nitric acid–dodecane system will be helpful in carrying out different extraction studies during PUREX process. Thus, physical properties like density, viscosity, interfacial tension and solubility have been measured for TBP–nitric acid–dodecane system using pycnometer, viscometer, pendant drop method and high performance liquid chromatography respectively. It has been observed that density and viscosity increases but interfacial tension and solubility decreases with the concentration of TBP in dodecane–nitric acid system. Physical properties of 30 % TBP–nitric acid–dodecane system have also been studied in detail. All these studies will also be useful in stripping out dissolved TBP from the nuclear waste.     

Starch - A suitable fuel in new low-temperature combustion-based synthesis of zinc aluminate oxides

Starch has been tested as single-fuel and in a two-fuel mixture, together with N-methylurea, in a new combustion-based synthesis of zinc aluminate oxides, using different fuel compositions and equivalence ratios Φ_e (Φ_e = fuel/oxidant). The combustion process has been analyzed by simultaneous thermal analysis. The corresponding oxides were characterized by X-ray diffraction analysis, UV-Vis spectroscopy, scanning electron microscopy and BET investigations. Crystal structures were refined by Rietveld method. The morphology, specific surface area and optical properties of the obtained zinc aluminate have proved to be strongly dependent on the fuel nature and composition. The lowest crystallite size (131 Å) is achieved for the oxide generated from the starch-based precursor, while the highest surface area (20.69 m²/g) has been obtained for a 3:1 N-methylurea/starch fuel composition. The non-zero value for microstrain has indicated spinelic defects in the starch-fuel corresponding oxide. UV-Vis spectroscopic analysis have confirmed the intrinsic properties of the resulted mixed metal oxide, but also shows the presence of a certain disorder degree for all the other samples. The superior values of the band gap (4.2-4.7 eV) for the obtained oxides relative to the bulk case (3.8 eV) are the result of the nanometric dimensions of the particles.     

Modeling of phase equilibria with CPA using the homomorph approach

For association models, like CPA and SAFT, a classical approach is often used for estimating pure-compound and mixture parameters. According to this approach, the pure-compound parameters are estimated from vapor pressure and liquid density data. Then, the binary interaction parameters, k_ij, are estimated from binary systems; one binary interaction parameter per system. No additional mixing rules are needed for cross-associating systems, but combining rules are required, e.g. the Elliott rule or the so-called CR-1 rule. There is a very large class of mixtures, e.g. water or glycols with aromatic hydrocarbons, chloroform-acetone, esters-water, CO₂-water, etc., which are classified as “solvating” or “induced associating”. The classical approach cannot be used and the cross-association interactions are difficult to be estimated a priori since usually no appropriate experimental data exist, while the aforementioned combining rules cannot capture the physical meaning of such interactions (as at least one of the compounds is non-self-associating). Consequently, very often one or more of the interaction parameters are optimized to experimental mixture data. For example, in the case of the CPA EoS, two interaction parameters are often used for solvating systems; one for the physical part (k_ij) and one for the association part (β^cross). This limits the predictive capabilities and possibilities of generalization of the model. In this work we present an approach to reduce the number of adjustable parameters in CPA for solvating systems. The so-called homomorph approach will be used, according to which the k_ij parameter can be obtained from a corresponding system (homomorph) which has similar physical interactions as the solvating system studied. This leaves only one adjustable parameter for solvating mixtures, the cross-association volume (β^cross). It is shown that the homomorph approach can be used with success for mixtures of water and glycols with aromatic hydrocarbons as well as for mixtures of acid gases (CO₂, H₂S) with alcohols and water. The homomorph approach is less satisfactory for mixtures with fluorocarbons as well as for aqueous mixtures with ethers and esters. In these cases, CPA can correlate liquid-liquid equilibria for solvating systems using two adjustable parameters. The capabilities and limitations of the homomorph approach are discussed.     

Preparation of 4(5)-vinylimidazole-co-acrylic acid copolymer and thermal performances related to applicability as PEM fuel cells

A series of acrylic acid and 4(5)-vinylimidazole copolymers for a non-hydrous proton transferring membrane used in polymer electrolyte membrane for fuel cell (PEMFC) are reported. The feed ratio of each monomer results in the variation of copolymer as evaluated by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (¹H-NMR). Differential scanning calorimeter and thermal gravimetric analyzer confirm the thermal properties of copolymer films with T_g at 105-177 °C and T_d above 230 °C. The simultaneous analysis of wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) suggests the thermal performance about the decrease in domain size as a consequence of the loss of moisture content in the membrane and the increase in domain size as a consequence of chain mobility after T_g. The proton conductivities under anhydrous condition of the copolymer membranes are in the range of 10⁻² S/cm even up to 120 °C.     

Anionic alkyl diglycoldiamides with covalently bonded cobalt bis(dicarbollide)(1−) ions for lanthanide and actinide extractions

Ionic diamides composed of a N,N′-dialkyl diglycolyl complexing group and two cobalt bis(dicarbollide)(1−) anions were synthesized with the aim to develop efficient extraction agents for liquid-liquid extraction of polyvalent cations, i.e. lanthanides and actinides from high-level activity nuclear waste. Compounds of general formulation [{(N,N-(8-CH₂-CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co)(N′,N′-R)NCOCH₂}₂O]Na₂, where R = n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅ and 1-C₆H₄-4-CH₃ (1-4), were prepared and characterized by combination of ¹¹B ¹H, ¹³C NMR spectroscopy, ESI-MS, HPLC and other techniques. Effects of different nitrogen substitution in the structures of 1-4 on the extraction properties were tested. The study resulted in the observation that the compounds are significantly (2-3 orders in magnitude) more efficient extractants for Eu(III) and Am(III) than synergic mixtures of organic N,N′-tetra n-octyl diglycolic acid diamide (TODGA) and chlorinated cobalt bis(dicarbollide) at the same concentrations of both groups. Low polar mixtures of n-dodecane (D) and hexyl methyl ketone (HMK) can be applied as an auxiliary solvent for extraction, replacing thus the polar and less environmentally friendly nitro-, fluoro- and chloro- solvents used in the current dicarbollide liquid-liquid extraction process.     

Liquid-liquid extraction procedure exploiting multicommutation in flow system for the determination of molybdenum in plants

A liquid-liquid extraction flow analysis procedure for the spectrophotometric determination of molybdenum in plants at μg l⁻¹ level is described. The flow network comprised a set of solenoid valves assembled to implement the multicommutation approach under microcomputer control. Radiation source (LED, 475 nm), detector (photodiode) and separation chamber were nested together with the flow cell comprising a compact unit. The consumption of reagents (potassium thiocyanate and stannous chloride) and also extracting solvent (isoamyl alcohol) were optimized to 32 mg and 200 μl per determination, respectively. Accuracy was assessed by comparing results with those obtained with ICP-OES and no significant difference at 95% confidence level was observed. Other favorable characteristics such as a linear response ranging from 25 to 150 μg l⁻¹ molybdenum (r=0.999); detection limit of 4.6 μg l⁻¹ sample throughput of 25 determinations per hour and relative standard deviation of 2.5% (n=10) were also achieved.     

Dispersive liquid-liquid microextraction for the isolation and HPLC-DAD determination of three major capsaicinoids in Capsicum annuum L.

Dispersive liquid-liquid microextraction (DLLME) was combined with high-performance liquid chromatography-diode-array detector (HPLC-DAD) for the extraction and quantitation of three major capsaicinoids (i.e. capsaicin, dihydrocapsaicin and nordihydrocapsaicin) from pepper (Capsicum annuum L.). Chloroform (extraction solvent, 100 μL), acetonitrile (disperser solvent, 1250 μL) and 30 s extraction time were found optimum. The analytes were back-extracted into 300 μL of 50 mM sodium hydroxide/ methanol, 45/55% (v/v), within 15 s before being injected into the instrument. Enrichment factors ranged from 3.3 to 14.7 and limits of detection from 5.0 to 15.0 µg g^-1. Coefficients of determination (R²) and %RSD were higher than 0.9962 and lower than 7.5%, respectively. The proposed method was efficiently applied for the extraction and quantitation of the three capsaicinoids in six cultivars of Capsicum annuum L. with percentage relative recoveries in the range of 92.0%–108.0%. DLLME was also scaled up for the isolation of the three major capsaicinoids providing purity greater than 98.0% as confirmed by liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) analysis, which significantly reduced the extraction time and organic solvent consumption.