Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.

Ionic Liquids-New "Solutions" for Transition Metal Catalysis.

We report here initial results that demonstrate that cellulose can be dissolved without activation or pretreatment in, and regenerated from, 1-butyl-3-methylimidazolium chloride and other hydrophilic ionic liquids. This may enable the application of ionic liquids as alternatives to environmentally undesirable solvents currently used for dissolution of this important bioresource.

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Dissolution of Cellose with Ionic Liquids

Ionic liquids are composed entirely of ions. Because of the wide range of possible binary and ternary ionic liquids, they offer a potentially wide range of solvent properties. In their Perspective,
 Rogers and Seddon
 review recent progress on developing new ionic liquid solvents for use in chemical synthesis, catalysis, fuel cells, and other applications. Ionic liquids are considered advantageous not only because of their versatility but also for their "green" credentials, although it is important to remember that not all ionic liquids are environmentally benign. One industrial process has been reported, and others may not be far behind. The authors conclude that in the next decade, ionic liquids are likely to replace conventional solvents in many applications.

http://science.sciencemag.org/content/sci/302/5646/792.full.pdf

Ionic Liquids--Solvents of the Future?

Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation

Deep Eutectic Solvents (DES) can be formed between a variety of quaternary ammonium salts and carboxylic acids. The physical properties are significantly affected by the structure of the carboxylic acid but the phase behavior of the mixtures can be simply modeled by taking account of the mole fraction of carboxylic acid in the mixture. The physical properties such as viscosity, conductivity, and surface tension of these DES are similar to ambient temperature ionic liquids and insight into the cause of these properties is gained using hole-theory. It is shown that the conductivity and viscosity of these liquids is controlled by ion mobility and the availability of voids of suitable dimensions, and this is consistent with the fluidity of other ionic liquids and molten salts. The DES are also shown to be good solvents for metal oxides, which could have potential application for metal extraction.

Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids

Metal Ion Separations in Aqueous Biphasic Systems and Using Aqueous Biphasic Extraction Chromatography

Fuel storage instability reactions of middle distillate fuel are of interest to the Department of Defense. Unlike civilian fuel, military fuel can remain in storage tanks for one or more years. As fuel is drawn from these tanks, the tanks are subsequently topped off with more recently purchased fuel, and the mixed fuel is not compatible, resulting in sediment and sludge formation. Previous research has shown that certain polar organic nitrogen functional groups involved in instability reactions are difficult and expensive to remove completely during the refining process. Therefore, this study involved the removal of these compounds by four different filtering media. An unstable fuel was treated separately with activated clay, silica gel, amorphous carbon, and iron carbon nanotubes (FeCNT) and the composition of the extracts were analyzed by GC/MS. The results of this study show that some of the media were not only more effective, but selective in removing the organic nitrogen compounds.

The Removal of Organic Nitrogen Compounds from Unstable Diesel Fuels

Metal Ion Separations in Aqueous Biphasic Systems and with ABEC™ Resins

Green Separation Science and Technology: Replacement of Volatile Organic Compounds in Industrial Scale Liquid-Liquid or Chromatographic Separations

Aqueous biphasic systems (ABS) represent wholly aqueous systems that are safe, nontoxic, nonflammable, and relatively environmentally benign as extraction media. We have studied detailed phase diagrams and partitioning data currently used in wholly aqueous solvent extraction or reactive extraction processes that may be applicable to the delignification of cellulosic materials at elevated temperature. The study results indicate that increasing the concentration of salt improves the degree of phase divergence. The partitioning results of different lignin species in PEG/salt ABS show that lignin prefers the polymer-rich phase of ABS. Four complete time-at-temperature (130-160°C) batch-cooking experiments were made using a Kraft pulping solution with and without PEG. The results for wood chips composed of a mixture of southern hardwood indicate that the use of PEG results in a pulp with lower Kappa number, lower lignin content, higher residual pulp yield, and reduced alkali consumption.

Heather D. Willauer

Papers

Metal Ion Separations in Aqueous Biphasic Systems and Using Aqueous Biphasic Extraction Chromatography

The Removal of Organic Nitrogen Compounds from Unstable Diesel Fuels

Metal Ion Separations in Aqueous Biphasic Systems and with ABEC™ Resins

Green Separation Science and Technology: Replacement of Volatile Organic Compounds in Industrial Scale Liquid-Liquid or Chromatographic Separations

Peg-based aqueous biphasic systems as improvement for kraft hardwood pulping process