Extraction solutes from ionic liquid

Extraction of solutes from ionic liquids with compressed gases or... 

As an alternative to distillation, extraetion with a eo-solvent that is poorly mis-eible with the ionie liquid has often been used. There are many solvents that can be used to extract product from the ionic liquid phase, whether from a monophase reaction or from a partially miscible system. Typical solvents are alkanes and ethers (15). Supercritical CO2 (SCCO2) was recently shown to be a potential alternative solvent for extraction of organics from ionic liquids (22). CO2 has a remarkably high solubility in ionic liquids. The SCCO2 dissolves quite well in ionic liquids to facilitate extraction, but there is no appreciable ionic liquid solubilization in the CO2 phase in the supercritical state. As a result, pure products can be recovered. For example, about 0.5 mol fraction of CO2 was dissolved at 40°C and 50 bar pressure in [BMIMJPFe, but the total volume was only swelled by 10%. Therefore, supercritical CO2 may be applied to extract a wide variety of solutes from ionic liquids, without product contamination by the ionic liquid (29). 

Extraction of Solutes from Ionic Liquids with Compressed Cases or Supercritical Fluids... 

In 1999 Blanchard et al. reported a good solubility of carbon dioxide in l-butyl-3-methylimidazolium hexafluorophosphate at high pressures, while the ionic liquid did not dissolve in carbon dioxide. Therefore, supercritical carbon dioxide is suited to extract organic solutes from ionic liquids, and also continuous flow homogeneous catalysis in ionic liquids carbon dioxide systems is possible. First spectroscopic studies show that the anion dominates the interactions with carbon dioxide by Lewis acid-base interactions. However, the strength of carbon dioxide anion interactions did not correlate with carbon dioxide solubility. Thus, strong anion-carbon dioxide interactions were excluded as major cause for the carbon dioxide solubility in ionic liquids. Instead, a correlation of carbon dioxide solubility and the ionic liquid molar volume was observed. Additionally, a significant volume decrease of dissolved carbon dioxide was... 

It has recently been demonstrated that solutes can be extracted from ionic liquids by perevaporation. This technique is based on the preferential partitioning of the solute from a liquid feed into a dense, non-porous membrane. The ionic liquids do not permeate the membrane. This technique can be applied to the recovery of volatile solutes from temperature-sensitive reactions such as bioconversions carried out in ionic liquids (34). 

Figure 5.2 Schematic representation of liquid-phase microdroplet extraction setup. (1) Stir bar (2) sample solution (3) ionic liquid microdroplet (4) polytetrafluoro-ethylene (PTFE) tube (5) septum (6) microsyringe. (Adapted from Liu, J.-R, Chi, Y.-G., Jiang, G.-B., Tai, C., Peng, J.-R, and Hu, J.-T., /. Chromatogr. A, 1026,143-147, 2004.)...

A potential solution of this problem lies in the application of nanofiltration. The success of solvent extraction to remove polar or non-polar compounds from ionic liquids appears to depend strongly on the system for which it is used. While in some cases only mixed success is reported [126], in other applications solvent extraction has been shown to lead to excellent results, for example extraction with hexane [127]. 

Since the partitioning of metal ions from aqueous solutions into ionic liquids is inefficient as a result of the tendency of the metal cations to remain hydrated in the aqueous phase, additional extractants, such as crown ethers [185], calixarenes [186], dithizone [187], and others [188-214], were used. These species significantly enhance the partitioning of metal ions by forming complexes. Most of the research work has been concentrated on the extraction and separation of radioactive metals [187, 188, 191, 192, 196-213], alkali metals [185, 186, 193, 194], heavy metals [184, 192-196], and rare earth metals [197-215] and Aluminnm [216, 217]. The work reported in this field has been reviewed by Zhao et al. [190] and Chen et al. [211]. The progress made in IL extractions of metal ions (alkali, alkaline earth, heavy metals, radioactive elements, and rare earth) in recent years has been encap-snlated in Table 5.5. 

J.-M. Lee, Extraction of noble metal ions from aqueous solution by ionic liquids. Eluid Phase Equilib. 319 (2012) 30-36. 

Giridhar, P. Venkatesan, K.A. Srinivasan, T.G. Vasudewa Rao, P.R. (2005). Extraction of Uranium(VI) from Nitric Acid Medium by 1.1 M Tri-n-butylphosphonate in Ionic Liquid Diluent. J. Radioanalytical Nuc. Chem., Vol.265, pp. 31-38 Giridhar, P. Venkatesan, K.A. Srinivasan, T.G. Vasudeva Rao, P.R. (2006). Extraction of Fission Palladium by Aliquat 336 and Electrochemical Studies on Direct Recovery from Ionic Liquid Phase. Hydrometallurgy, Vol.81, pp. 30-39 Guibal, E. Gavilan, Campos, K. Bunio, P. Vincent, T. Trochimczuk, A. (2008). CYPHOS IL 101 (Tetradecyl(trihexyl)phosphonium Chloride) Immobilized in Biopolymer Capsules for Hg(II) Recovery from HCl Solutions. Sep. Sci Technol, Vol.43, No.9-10, pp. 2406 - 2433... 

Srncik, M. Kogelnig, D. Stojanovic, A. Korner, W. Krachler, R. Wallner, G. (2009). Uranium Extraction from Aqueous Solutions by Ionic Liquids. Appl. Radial Isotopes, Vol.67, No.l2, pp. 2146-2149... 

Uranium extraction from aqueous solutions by ionic liquids. Applied Radiation and Isotopes, 67,12,2146-2149, ISSN 0969-8043... 

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

THF). The authors found that the yield could be increased to 95 % by sonication of the reaction vessel, for the reaction in THF. The ionic liquid was then used to extract the manganese by-products and impurities from an ethyl acetate solution of the product [63]. 

The authors describe a clear enhancement of the catalyst activity by the addition of the ionic liquid even if the reaction medium consisted mainly of CH2CI2. In the presence of the ionic liquid, 86 % conversion of 2,2-dimethylchromene was observed after 2 h. Without the ionic liquid the same conversion was obtained only after 6 h. In both cases the enantiomeric excess was as high as 96 %. Moreover, the ionic catalyst solution could be reused several times after product extraction, although the conversion dropped from 83 % to 53 % after five recycles this was explained, according to the authors, by a slow degradation process of the Mn complex. 

Visser AE, Swatloski RP, Reichert WM, Mayton R, Sheff S, Wierzbicki A, Davis JH, Rogers RD (2001) Task-specific ionic liquids for the extraction of metal ions from aqueous solutions. Chem Commun 1 135-136... 

Visser, A.E., Swatloski, R.P., Reichert, W.M. et al. (2001) Task-Specific Ionic Liquids for the Extraction of Metal Ions from Aqueous Solutions. Chemical Communications, 1, 135-136. 

Another solution to the problem of ionic liquid loss to the organic phase is to extract the product from the ionic liquid using a supercritical fluid (See Chapter 8, Section 8.2.2.3). It has been demonstrated that this can be done continuously for a variety of reactions including the hydroformylation of long chain alkenes [20], and that neither the ionic liquid nor the catalyst are leached to significant extents. The only problem here is the high pressures involved (see section 9.8). 

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