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

Phase diagrams determined by the cloud point method at 25 °C, including tie lines assigned from mass phase ratios according to the lever arm rule, are presented for several poly(ethylene glycol) (P...

Phase diagram data for several PEG + salt aqueous biphasic systems at 25 °C

Aqueous biphasic systems (ABSs) represent wholly aqueous systems that are safe, nontoxic, and nonflammable, and thus, they represent relatively environmentally benign extraction media. Such systems could be employed as alternatives to traditional aqueous−organic systems for the separation of, inter alia, small organic molecules, thus it is important to develop a fundamental understanding of these systems and the variables that govern solute partitioning within them. The partitioning of a series of neutral, substituted benzene compounds and neutral, aliphatic compounds in ABSs composed of different molecular weights of poly(ethylene glycol) (PEG-1000, 2000, and 3400) and formed as a result of the addition of different salt types [K3PO4, K2CO3, (NH4)2SO4, Li2SO4, MnSO4, ZnSO4, and NaOH] has been examined. The results show that the distribution of organic solutes is a function only of the degree of phase divergence of the biphasic system as expressed by the difference in polymer concentration between the pha...

Solute partitioning in aqueous biphasic systems composed of polyethylene glycol and salt: The partitioning of small neutral organic species

Several liquid-phase extraction technologies employing environmentally benign phase- or micelle-forming polymers in aqueous solution have the potential to replace volatile organic compounds in classical solvent extraction technologies. The examples reviewed here include aqueous biphasic systems, cloud-point extraction, micellar extraction, and thermoseparating polymer systems. The apparent similarities of these systems, their phase-separating properties, and their ability to solubilize a wide variety of solutes ranging from metal ions, organic compounds, and biologicals are discussed. Some comparative data from the literature whereby the solvating power of these systems may be compared to traditional solvents are presented along with new data on the polarity of the phases in typical aqueous biphasic systems. The need for additional comparative data in this area and the need to demonstrate the validity of the approach in operational processes are emphasized. A “toolbox” approach to implementing environment...

Aqueous Polymeric Solutions as Environmentally Benign Liquid/Liquid Extraction Media

The hydrogenation of CO2 using a traditional Fischer−Tropsch Co−Pt/Al2O3 catalyst for the production of valuable hydrocarbon materials is investigated. The ability to direct product distribution was measured as a function of different feed gas ratios of H2 and CO2 (3:1, 2:1, and 1:1) as well as operating pressures (ranging from 450 to 150 psig). As the feed gas ratio was changed from 3:1 to 2:1 and 1:1, the production distribution shifted from methane toward higher chain hydrocarbons. This change in feed gas ratio is believed to lower the methanation ability of Co in favor of chain growth, with possibly two different active sites for methane and C2−C4 products. Furthermore, with decreasing pressure, the methane conversion drops slightly in favor of C2−C4 paraffins. Even though under certain reaction conditions product distribution can be shifted slightly away from the formation of methane, the catalyst studied behaves like a methanation catalyst in the hydrogenation of CO2.

Influence of Gas Feed Composition and Pressure on the Catalytic Conversion of CO2 to Hydrocarbons Using a Traditional Cobalt-Based Fischer−Tropsch Catalyst

Hydrogenation of CO2 to hydrocarbons is investigated over iron-based catalysts supported on γ-alumina to produce unsaturated hydrocarbons as feedstock chemicals for jet-fuel synthesis. Over 40% conversion levels can be achieved by doping this catalyst with Mn and K, along with an olefin/paraffin ratio of over 4. The doping levels played a crucial role in the product distribution as well as CO2 conversion yields, with over doping leading to suppression of the desirable hydrocarbon products. The characterization of the catalyst showed the presence of KAlH4 as part of the catalyst's active phase, acting as a reversible H2 reservoir and as a center for H2 activation. Characterization of the catalysts by XRD, XPS, and SEM sheds light on the role each dopant had on the overall catalyst's activity and product distribution.

Heather D. Willauer

Papers

Phase diagram data for several PEG + salt aqueous biphasic systems at 25 °C

Solute partitioning in aqueous biphasic systems composed of polyethylene glycol and salt: The partitioning of small neutral organic species

Aqueous Polymeric Solutions as Environmentally Benign Liquid/Liquid Extraction Media

Influence of Gas Feed Composition and Pressure on the Catalytic Conversion of CO2 to Hydrocarbons Using a Traditional Cobalt-Based Fischer−Tropsch Catalyst

K and Mn doped iron-based CO2 hydrogenation catalysts: Detection of KAlH4 as part of the catalyst's active phase