Nicholas J. Bridges

Separations of metal ions using ionic liquids: The challenges of multiple mechanisms

Ionic liquids are a distinct sub-set of liquids, comprising only of cations and anions, often with negligible vapor pressure. As a result of the low or non-volatility of these fluids, ionic liquids are often considered in liquid/liquid separation schemes where the goal is to replace volatile organic solvents. Unfortunately, it is often not yet recognized that the ionic nature of these solvents can result in a variety of extraction mechanisms, including solvent ion-pair extraction, ion exchange, and simultaneous combinations of these. This paper discusses current ionic liquid-based separations research where the effects of the nature of the solvent ions, ligands, and metal ion species were studied in order to be able to understand the nature of the challenges in utilizing ionic liquids for practical applications.

Direct, Atom Efficient, and Halide-Free Syntheses of Azolium Azolate Energetic Ionic Liquids and Their Eutectic Mixtures, and Method for Determining Eutectic Composition

We report i) the successful halide free, efficient syntheses of azolium azolates by reaction of 1,3-dimethylimidazolium2-carboxylate with neutral azoles, ii) the development of a facile, low sample demand method for ready determination of the eutectic point compositions of mixtures of these salts, and iii) the application of the new synthetic techniques for the direct preparation of the eutectic mixtures. This work is illustrated here with the synthesis of 1,3-dimethylimidazolium 4,5-dinitroimidazolate and 1,3-dimethylimidazolium 4nitro-1,2,3-triazolate (via a one-pot synthesis with an easy to remove byproduct (CO2(g)), thus avoiding halide and metal impurities) and the determination of their eutectic composition and its direct synthesis. The ever growing list of applications for the unique physical, chemical, and biological property sets available from ionic liquids (ILs) calls for an increased emphasis on the preparation of ILs in more elegant and, more importantly, cleaner ways. The specifications needed for many new applications (e.g., energetic materials, catalysis, and pharmaceuticals) often require synthetic products free of inorganic salts and other impurities which are commonly observed in current IL preparation techniques such as metathesis reactions. At the same time it is readily apparent that ILs may require formulation with other ionic or molecular components to achieve the often stringent physical properties these applications require. With the introduction of dialkylsulfates and dialkylcarbonates, and more recently the use of alcohols in Mitsunobu alkylation reactions and alkanesulfonates as alkylating agents for the synthesis of alkylated imidazolium salts, halide-free IL materials were successfully prepared. These salts, though halide free, were then typically used as precursors for further ion-exchange reactions. Ideally, in order to obtain pure IL salts, the synthesis would have to be carried out directly with routes that are byproduct-free or that allow facile removal of byproducts by their evaporation, rather than by extraction. The zwitterionic dialkylimidazolium-2-carboxylate, for example, can be decarboxylated with a protic acid to form pure imidazolium salts with only CO2(g) as byproduct. 12] Our group, as well as others, have been interested in transferring the synthetic techniques demonstrated for the dialkylimidazolium-based ILs to the azolate class of anions in the development of energetic azolium azolate materials. The structural similarity to the azolium cations used in many ILs, suggested that similar degrees of functionalization in azolate anions would lead to a diverse new range of ILs with interesting physical and chemical properties. To that end, we demonstrated that the combination of the 1butyl-3-methylimidazolium cation ([1-Bu-3-MeIm]) with a variety of azolate anions resulted in the formation of low melting salts with glass transitions as low as 82 8C (for [1Bu-3-MeIm][tetrazolate]) and no observable melting point. Moreover the thermal stabilities of these new salts are high which can be beneficial for many IL applications. Others have also reported the utilization of azolate-based anions in attempts to form ILs, with the majority of these salts prepared via ion exchange, or by protonation of neutral azoles (when differences in the pKa values of the substrates permitted) via Brønsted acid–base neutralization reactions. 18] The only exception to this approach was presented by Ohno and co-workers, where the azolate salts were formed by the reaction of a hydroxide precursor with neutral azoles. Unfortunately, this latter approach is limited to cations that are stable as hydroxide salts. [a] Dr. M. Smiglak, Dr. N. J. Bridges, Dr. M. Dilip, Prof. R. D. Rogers Department of Chemistry/Center for Green Manufacturing The University of Alabama, Tuscaloosa, AL 35487 (USA) [b] Prof. R. D. Rogers School of Chemistry & Chemical Engineering/QUILL The Queen s University of Belfast Belfast BT9 5AG, Northern Ireland (UK) Fax: (+44) 28-9097-4606 E-mail : r.rogers@qub.ac.uk Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200801811.

Can Kosmotropic Salt/Chaotropic Ionic Liquid (Salt/Salt Aqueous Biphasic Systems) be Used to Remove Pertechnetate From Complex Salt Waste?

Abstract Aqueous solutions of water‐structuring, kosmotropic salts (e.g., salts of PO4 3−, HPO4 2−, CO3 2−) will salt‐out water‐destructuring chaotropic ionic liquids (ILs) (e.g., 1‐butyl‐3‐methylimidazolium chloride, ([C4mim]Cl)) forming salt/salt aqueous biphasic systems (ABS). The chaotropic pertechnetate (TcO4 −) anion will partition without the use of an extractant into the IL‐rich phase. These complex salt/salt ABS are not unlike the complex and salt‐rich Hanford tank waste, and thus have been used here as a simple model to show effectiveness in the partitioning of TcO4 − from such tank waste into an IL‐rich phase.

Effects of gamma radiation on electrochemical properties of ionic liquids

Abstract The electrochemical properties of ionic liquids (ILs) make them attractive for possible replacement of inorganic salts in high temperature molten salt electrochemical processing of nuclear fuel. To be a feasible replacement solvent, ILs need to be stable in moderate and high doses of radiation without adverse chemical and physical effects. Here, we exposed seven different ILs to a 1.2 MGy dose of gamma radiation to investigate their physical and chemical properties as they related to radiological stability. The azolium-based ILs experienced the greatest change in appearance, but these ILs were chemically more stable to gamma radiation than some of the other classes of ILs tested, due to the presence of aromatic electrons in the azolium ring. All the ILs exhibited a decrease in their conductivity and electrochemical window (at least 1.1 V), both of which could affect the utility of ILs in electrochemical processing. The concentration of the irradiation decomposition products was less than 3 mol. %, with no impurities detectable using NMR techniques.

Enhanced Thermal Performance of Ionic Liquid-Al2O3 Nanofluid as Heat Transfer Fluid for Solar Collector

Next generation Concentrating Solar Power (CSP) system requires high operating temperature and high heat storage capacity heat transfer fluid (HTF), which can significantly increase the overall system efficiency for power generation. In the last decade several research going on the efficacy of ionic liquids (ILs) as a HTF in CSP system. ILs possesses superior thermophysical properties compare to currently using HTF such as Therminol VP-1 (mixture of biphenyl and diphenyl oxide) and thermal oil. However, advanced thermophysical properties of ILs can be achieved by dispersing small volume percentage of nanoparticles forming nanofluids, which is called Nanoparticle Enhanced Ionic Liquids (NEILs). In the present study NEILs were prepared by dispersing 0.5% Al2O3 nanoparticles (spherical and whiskers) in N-butyl-N, N, N-trimetylammonium bis(trifluormethylsulfonyl)imide ([N4111][NTf2]) IL. Viscosity, heat capacity and thermal conductivity of NEILs were measured experimentally and compared with the existing theoretical models for liquid–solid suspensions. Additional, the convective heat transfer experiment was performed to investigate thermal performance. The thermal conductivity of NEILs enhanced by ∼5%, heat capacity enhanced by ∼20% compared to the base IL, which also gives 15% enhancement in heat transfer performance.Copyright

Heat Transfer and Flow Behavior of Nanoparticle Enhanced Ionic Liquids (NEILs)

Experimental investigations were carried out to characterize forced convection behavior of Nanoparticle Enhanced Ionic Liquids (NEILs). 1-butyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl} imide ([C4mim][NTf2]) was used as the base ionic liquid (IL) with 0.5% (weight%) loading of Al2O3 nanoparticles. Flow experiments were conducted in a circular tube in the laminar flow regime. Convection results from IL without nanoparticles were used as the base line data for comparison with convection results with NEIL. Viscosity and thermal conductivity of the NEIL and base IL were also measured. NEIL displayed superior thermal performance compared to the base IL. An average of 13% enhancement in heat transfer coefficient was found for the NEIL compared with that of the base IL. Probable reasons of these enhancements are discussed in the paper.Copyright

Ionic Liquid-Based Routes to Conversion or Reuse of Recycled Ammonium Perchlorate

New, potentially green, and efficient synthetic routes for the remediation and/or re-use of perchlorate-based energetic materials have been developed. Four simple organic imidazolium- and phosphonium-based perchlorate salts/ionic liquids have been synthesized by simple, inexpensive, and nonhazardous methods, using ammonium perchlorate as the perchlorate source. By appropriate choice of the cation, perchlorate can be incorporated into an ionic liquid which serves as its own electrolyte for the electrochemical reduction of the perchlorate anion, allowing for the regeneration of the chloride-based parent ionic liquid. The electrochemical degradation of the hazardous perchlorate ion and its conversion to harmless chloride during electrolysis was studied using IR and (35)Cl NMR spectroscopies.

EXPERIMENTAL INVESTIGATION OF NATURAL CONVECTION HEAT TRANSFER OF IONIC LIQUID IN A RECTANGULAR ENCLOSURE HEATED FROM BELOW

This paper presents an experimental study of natural convection heat transfer for an Ionic Liquid. The experiments were performed for 1-butyl-2, 3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, ([C{sub 4}mmim][NTf{sub 2}]) at a Raleigh number range of 1.26 x 10{sup 7} to 8.3 x 10{sup 7}. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of thermophysical properties of [C{sub 4}mmim][NTf{sub 2}] such as, density, viscosity, heat capacity, and thermal conductivity. The results show that the density of [C{sub 4}mmim][NTf{sub 2}] varies from 1.437-1.396 g/cm{sup 3} within the temperature range of 10-50 C, the thermal conductivity varies from 0.105-0.116 W/m.K between a temperature of 10 to 60 C, the heat capacity varies from 1.015 J/g.K - 1.760 J/g.K within temperature range of 25-340 C and the viscosity varies from 18cp-243cp within temperature range 10-75 C. The results for density, thermal conductivity, heat capacity, and viscosity were in close agreement with the values in the literature. Measured dimensionless Nusselt number was observed to be higher for the ionic liquid than that of DI water. This is expected as Nusselt number is the ratio of heat transfer by convection to conduction and the ionic liquid has lower thermal conductivity (approximately 18%) than DI water.

Electrochemical degradation of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide for lithium battery applications

Ionic liquids (ILs) are being considered as electrolytes for lithium ion batteries due to their low volatility, high thermal stability, and wide electrochemical windows which are stable at the strongly reducing potentials present in Li/Li+ batteries. Lithium metal deposition occurs under strongly reducing conditions and the effect that Li metal and any overpotential has on the stability of ILs is important in furthering the application of ILs in lithium based batteries. Here, N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide was exposed to various potential differences in order to collect and characterize the volatile products. The IL produced more volatile products when exposed to strong reducing potentials which included reactive products such as hydrogen, alkanes, and amines. Water is a known contributor to hydrogen production in reducing environments, but the IL is also a source of hydrogen. If Li+ was present, the preferred pathway of reduction was plating of the lithium onto the working electrode, thus decreasing the reaction rate of degraded ILs.

Natural Convection in Rectangular Cavity With Nanoparticle Enhanced Ionic Liquids (NEILs)

A systematic natural convection heat transfer experiment has been carried out of nanoparticle enhanced ionic liquids (NEILs) in rectangular enclosures (lengthxwidthxheight, 50×50×50mm and 50×50×75mm) heated from below condition. In the present experiment NEIL was made of N-butyl-N-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl} imide, ([C4mpyrr][NTf2]) ionic liquid with 0.5% (weight%) Al2O3 nanoparticles. In addition to characterize the natural convection behavior of NEIL, thermophysical properties such as thermal conductivity, heat capacity, and viscosity were also measured. The result shows that the thermal conductivity of NEIL enhanced ∼3% from the base ionic liquid (IL), heat capacity enhanced ∼12% over the measured temperature range. The natural convection experimental result shows consistent for two different enclosures based on the degrading natural convection heat transfer rate over the measured Rayleigh number range. Possible reasons of the degradation of natural convection heat transfer may be the relative change of the thermophysical properties of NEIL compare to the base ionic liquid.Copyright