Improving carbon dioxide solubility in ionic liquids

Previously we showed that CO2 could be used to extract organic molecules from ionic liquids without contamination of the ionic liquid. Consequently a number of other groups demonstrated that ionic liquid/CO2 biphasic systems could be used for homogeneously catalyzed reactions. Large differences in the solubility of various gases in ionic liquids present the possibility of using them for gas separations. More recently we and others have shown that the presence of CO2 increases the solubility of other gases that are poorly soluble in the ionic liquid phase. Therefore, a knowledge and understanding of the phase behavior of these ionic liquid/CO2 systems is important. With the aim of finding ionic liquids that improve CO2 solubility and gaining more information to help us understand how to design CO2-philic ionic liquids, we present the low- and high-pressure measurements of CO2 solubility in a range of ionic liquids possessing structures likely to increase the solubility of CO2. We examined the CO2 solubility in a number of ionic liquids with systematic increases in fluorination. We also studied nonfluorinated ionic liquids that have structural features known to improve CO2 solubility in other compounds such as polymers, for example, carbonyl groups and long alkyl chains with branching or ether linkages. Results show that ionic liquids containing increased fluoroalkyl chains on either the cation or anion do improve CO2 solubility when compared to less fluorinated ionic liquids previously studied. It was also found that it was possible to obtain similar, high levels of CO2 solubility in nonfluorous ionic liquids. In agreement with our previous results, we found that the anion frequently plays a key role in determining CO2 solubility in ionic liquids.     

Electrospray ionization mass spectrometry of ionic liquids and determination of their solubility in water

Electrospray ionization mass spectrometry is used to detect both the cations (C⁺) and the anions (A^–) of ionic liquids (CA). In this study, the ionic liquids are diluted with aqueous methanol before injection. In addition to the main peaks of the parent ions, fragmentation products are observed upon increasing the cone voltage, whereas aggregates of the parent ion with one or more ionic liquid molecules (e.g., C(CA)_n⁺, A(CA)_n^–) are observed upon decreasing the cone voltage. The ions of several ionic liquids in a mixture are also detected and the ratios of their concentrations estimated. A method is developed to determine quantitatively the concentration of an ionic liquid in solution by using the cation and anion of another ionic liquid as internal standards. By using this method, the solubilities in water at room temperature (22±1 °C) of three typical hydrophobic ionic liquids have been determined: 0.70±0.08 g L^–1 for methyltributylammonium bis(trifluoromethylsulfonyl)imide (MeBu₃NNTf₂), 6.0±0.5 g L^–1 for butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyrNTf₂), and 18.6±0.7 g L^–1 for 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆).     

Measurement of SO2 solubility in ionic liquids

Measurements of the solubility of sulfur dioxide (SO(2)) in the ionic liquids 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf(2)N]) and 1-n-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide ([hmpy][Tf(2)N]) at temperatures from 25 to 60 degrees C and pressures up to 4 bar indicate that large amounts (up to 85 mol %) of SO(2) dissolve in ionic liquids by simple physical absorption.     

Anion effects on gas solubility in ionic liquids

This work presents the results of solubility measurements for a series of gases in 1-n-butyl-3-methyl imidazolium tetrafluoroborate and 1-n-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide. The gases considered include benzene, carbon dioxide, nitrous oxide, ethylene, ethane, oxygen, and carbon monoxide. Carbon dioxide and oxygen solubilities are also reported in methyl-tributylammonium bis(trifluoromethylsulfonyl) imide, butyl-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide, and tri-isobutyl-methyl phosphonium p-toluenesulfonate. We report the associated Henry's constants and enthalpies and entropies of absorption. In general, benzene, followed by carbon dioxide and nitrous oxide, have the highest solubilities and strongest interactions with the ionic liquids, followed by ethylene and ethane. Oxygen had very low solubilities and weak interactions. Carbon monoxide had a solubility below the detection limit of our apparatus. Ionic liquids with the bis(trifluoromethylsulfonyl) imide anion had the largest affinity for CO(2), regardless of whether the cation was imidazolium, pyrrolidinium, or tetraalkylammonium. These results suggest that the nature of the anion has the most significant influence on the gas solubilities.     

Using XPS to determine solute solubility in room temperature ionic liquids

X-Ray Photoelectron Spectroscopy (XPS) was used to quantify the amount of bromide ions present in two samples of [C(4)mpyrr]Br dissolved in the room temperature ionic liquid (RTIL) [C(4)mpyrr][N(Tf)2]. One sample was of a known concentration (0.436 Br atom%); the other was a saturated solution. The results obtained from quantitative XPS analysis indicated that the saturated sample had a concentration, or solubility, of 0.90 Br atom% (746 mM) at 298 K, which was then independently confirmed by potential-step chronoamperometry of the same solution.     

Biphasic hydroformylation in ionic liquids: interaction between phosphane ligands and imidazolium triflate, toward an asymmetric process

Biphasic hydroformylation of dec-1-ene and styrene, at commercially competitive rates, can be successfully performed in imidazolium triflate ionic liquids; the ionic liquid network forms 'inclusion complexes' with the phosphane ligands used to modify the rhodium catalyst.     

色谱分析中离子液体的应用及其测定

离子液体作为一种优良的溶剂越来越受到人们的关注。由于离子液体特殊的物理化学性质使其在色谱分析中也得到了较广泛的应用。本文综述了离子液体在气相色谱、高效液相色谱和毛细管电泳中的应用,其中包括离子液体作为气相色谱的固定相、高效液相色谱的固定相及流动相添加剂和毛细管电泳的电解质添加剂等,并对离子液体的色谱分离检测作了详细介绍。     

Thermodynamic analysis for solubility of pimelic acid in ionic liquids

Based on the solubilities of pimelic acid in ionic liquids [EMIM][HSO₄], [PMIM]Br, [i-PMIM][HSO₄], [BMIM]Br, and [BMIM][HSO₄], dissolution enthalpy and dissolution entropy at different temperatures have been calculated. The experimental data of solubilities are correlated with the modified Apelblat equation. The thermodynamic properties of pimelic acid in ionic liquids were discussed. The solubilities correlated by the model are in good agreement with experimental data.     

The molecular characteristics dominating the solubility of gases in ionic liquids

This critical review provides a critical discussion of the current state of knowledge of the key factors influencing the solubility of gases in ionic liquids (ILs), including sample purity, experimental methodology, "molecular" characteristics of ILs, temperature and pressure. The review starts with a brief introduction to the current developments and the existing problems in the studies of the gas solubility in ILs. Then, the experimental, computational and theoretical developments in conformational equilibria of ions, in nanosegregated polar and nonpolar domains in ILs, and in the mechanisms for dissolution of gases in ILs are discussed and subsequently collaborated together with our freeze-fracture transmission electron microscopic and Raman measurements to propose the new microscopic mechanism for dissolving the gases in ILs. Next, a critical and quantitative analysis of the influences of the sample purity and the experimental methodology on the gas solubility is made so that the "real" relationships between structure and solubility property can be revealed. In addition, a systematic and deeper understanding of how the "molecular" features of the ILs, the temperature, and the pressure influence the gas solubility is provided at the molecular level. In the section of concluding remarks, the comments are made on the molecular criteria for the future design of the ILs to enhance the gas solubility by specifically optimizing the molecular characteristics of the ILs (265 references).     

Low pressure solubility and thermodynamics of solvation of oxygen,carbon dioxide,and carbon monoxide in fluorinated liquids

The solubility of oxygen, carbon dioxide, and carbon monoxide in three fluorinated liquids – perfluorohexylethane, perfluorooctane and bromoperfluorooctane – is presented. Mole fraction solubilities were calculated from new experimental Ostwald coefficient data for CO₂ and CO, and from previously published values for O₂, associated with original values of density and vapour pressure for the pure solvents. Carbon dioxide is the most soluble gas with mole fraction solubilities of the order of 10⁻². Oxygen and carbon monoxide are one order of magnitude less soluble. The measurements were done as a function of temperature between (288 and 313) K and from the variation of the calculated Henry’s law constants with temperature, the thermodynamic properties of solvation such as the Gibbs free energy, the enthalpy and the entropy were calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry’s law constants from appropriate smoothing equations is of 1% for carbon dioxide and oxygen and of 3% for carbon monoxide. The data obtained here are judged accurate to within ±5%.     

Carbon dioxide induced separation of ionic liquids and water

Both hydrophobic and hydrophilic room-temperature ionic liquids can be separated from aqueous solutions with relatively low-pressure gaseous carbon dioxide.     

A novel dicationic phenoxaphosphino-modified Xantphos-type ligand: a ligand for highly active and selective, biphasic, rhodium catalysed hydroformylation in ionic liquids

A highly active and regioselective catalyst obtained from a novel dicationic ligand (1) and Rh(CO)2(acac) for hydroformylation of 1-hexene and 1-octene in ionic liquids is reported. Optimisation studies of various reaction parameters led to an unprecedentedly active (TOFs > 6200 mol mol(-1) h(-1), T= 100 degrees C), selective (l/b ratios > 40) and stable hydroformylation procedure. No catalyst leaching (Rh-loss < 0.07% of initial rhodium intake, P-loss < 0.4% of the initial phosphorus intake) or losses in performance could be measured during 1-octene hydroformylation recycle experiments in 1-butyl-3-methylimidazolium hexafluorophosphate. At low catalyst loadings activities and regioselectivities competitive with one-phase catalysis in conventional solvents were observed. At high catalyst loadings the system is extremely stable and has a long shelf-life as a result of the formation of stable, if inactive rhodium dimers.     

Description of the pVT behavior of ionic liquids and the solubility of gases in ionic liquids using an equation of state

A molecular thermodynamic model developed previously for fluids of chain-like molecules has been extended to correlate the pVT behavior of ionic liquids and the solubilities of gases such as CO₂, C₃H₆, C₃H₈, C₄H₁₀ in various ionic liquids. The relative deviation between the calculated molar volume and experimental data is less than 0.2%. It is shown that this equation of state can be used to correlate the solubility of CO₂ in ionic liquids with only one temperature-independent adjustable interaction parameter, and the accuracy of the correlation can be further improved using two temperature-independent adjustable parameters. The water content of ionic liquids has a large influence on the calculated results. For systems with water content lower than 0.1%, the average relative deviations of bubble point pressure are 3.14 and 4.90% using two parameters and one parameter, respectively. For systems containing C₃H₆, C₃H₈ and C₄H₁₀ two temperature dependent adjustable parameters are needed to obtain a good fit, and the corresponding deviation of the gas solubility is less than 2%, except for C₃H₈.     

Ideal gas solubilities and solubility selectivities in a binary mixture of room-temperature ionic liquids

This study focuses on the solubility behaviors of CO2, CH4, and N2 gases in binary mixtures of imidazolium-based room-temperature ionic liquids (RTILs) using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][Tf2N]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) at 40 degrees C and low pressures (approximately 1 atm). The mixtures tested were 0, 25, 50, 75, 90, 95, and 100 mol % [C2mim][BF4] in [C2mim][Tf2N]. Results show that regular solution theory (RST) can be used to describe the gas solubility and selectivity behaviors in RTIL mixtures using an average mixture solubility parameter or an average measured mixture molar volume. Interestingly, the solubility selectivity, defined as the ratio of gas mole fractions in the RTIL mixture, of CO2 with N2 or CH4 in pure [C2mim][BF4] can be enhanced by adding 5 mol % [C2mim][Tf2N].     

Mechanistic studies on the formation of Pt(II) hydroformylation catalysts in imidazolium-based ionic liquids

The kinetics of the formation of the active species cis-[Pt^II(PPh₃)₂Cl(SnCl₃)] and cis-[Pt^II(PPh₃)₂(SnCl₃)₂] from the hydroformylation catalyst precursor cis-[Pt^II(PPh₃)₂Cl₂] in the presence of SnCl₂, was studied in two different imidazolium-based ionic liquids. A large range of different chlorostannate melts consisting of 1-butyl-3-methyl-imidazolium cations and [Sn_xCl_y]^{(−y + 2x)} anions with varying molar fraction of SnCl₂, were prepared and characterized by ¹H and ¹¹⁹Sn NMR. The observed chemical shifts point to major changes in the composition of the anionic species within the melt. The second ionic liquid employed, viz., 1-butyl-3-methyl-imidazolium-bis(trifluormethylsulfonyl)amide was prepared in a colorless quality that enabled its application in kinetic studies. The concentration and temperature dependence of the substitution of Cl⁻ by [SnCl₃]⁻ to yield cis-[Pt^II(PPh₃)₂Cl(SnCl₃)], could be studied in detail. Theoretical (DFT) calculations were employed to model the reaction progress and to resolve the role of the ionic liquid in the activation of the catalyst. The available results are presented and a plausible mechanism for the formation of the catalytically active species is suggested.     

Protic pyridinium ionic liquids: Synthesis, acidity determination and their performances for acid catalysis

Three new protic ionic liquids based on 2-methylpyridinium were prepared and characterized. Their catalytic activities for the tert-butylation of phenol and the esterification of cyclic olefins with acetic acid were examined and satisfactory results were obtained over 2-methylpyridinium trifluoromethanesulfonate ([2-MPyH]OTf). Hammett method was used to determine the acidity order of these ionic liquids and the results are consistent with the catalytic activities observed in the acid-catalyzed probe reactions.     

Stochastic structure determination for conformationally flexible heterogenous molecular clusters: Application to ionic liquids

We present a novel method that enables accurate and efficient computational determination of conformationally flexible clusters, “Kick³” This method uses stochastically generated structures in combination with fast quantum mechanical methods. We demonstrate the power of this method by elucidating the structure of ionic liquid (IL) ([xMIM⁺][ clusters (x = E, B, D, n = 1–10,15). Dispersion‐corrected, third‐order self‐consistent‐charge density‐functional tight‐binding (DFTB3) is shown to be a computationally efficient, yet reliable approximation to density functional theory for predicting and understanding IL structure and stability. The presented approach, therefore, enables the accurate and efficient screening of ILs with high potential toward practical applications, without recourse to more expensive quantum chemical methods. © 2013 Wiley Periodicals, Inc.     

Method for the determination of the solubility of gases in liquids

A rapid and experimentally simple method for the determination of the solubilities of oxygen or hydrogen in liquids is presented The method employs a membrane-enclosed amperometric detector of the well known Clark type to measure the partial pressure of the gas when distributed at equilibrium between the liquid and a gas space for a series of internal volumes of the system. The amounts of all substances and the temperature are maintained constant throughout the series although the internal pressure changes as a result of the volume changes. The glass apparatus is water jacketed for temperature control, has inlet and outlet ports for gas, and the amperometric sensor is mounted in a gas-tight sliding fitting for effecting the volume changes. The liquid content is vigorously stirred by a magnetic bar during measurements. Equations for the interpretation of results at different internal volumes take into account the conservation of the solvent and of the gas, the dependence of the volume of the liquid on the concentration of dissolved gas and Henry's law describing the distribution of the gas between gas and liquid phases at equilibrium. The solution of these equations yields an equation for the dependence of the measured partial pressure on volume, which includes the Henry's law constant H as a parameter. Conditions can usually be arranged to give a straight line dependence of volume on the reciprocal of partial pressure. The method has been applied to several common liquids, and has been shown to produce results which agree with literature solubilities to within about ±5%. Examples which have been studied include oxygen in water (H=4.039 × 10⁶ kPa at 20°C), in acetone (1.25 × 10⁵ kPa at 20°C), in ethanol (1.758 × 10⁵ kPa at 20°C) and in toluene (1.05 × 10⁵ kPa at 20°C) as well as hydrogen in water (6.89 × 10⁶ kPa at 20°C).