Predictions of cation and anion effects on solubilities,selectivities and permeabilities for CO2 in ionic liquid using COSMO based activity coefficient model

The solubilities and selectivities for CO₂, N₂ and CH₄ in ionic liquid were predicted using a COSMO based activity coefficient model, COSMO-SAC method. The 1-alkyl-3-methylimidazolium cations were focused in this work. The anion species include tetrafluoroborate [BF₄], hexafluorophosphate [PF₆], triflate [OTf], dicyanamide [dca] and bis(trifluoromethane)-sulfonimide [Tf₂N]. The predicted results of the solubilities of CO₂ in the ionic liquids by COSMO-SAC method are in agreement with the experimental data within the averaged deviation of 0.0017 in mole fraction. The predicted results of selectivities for CO₂/N₂ and CO₂/CH₄ represent the effects of anion species qualitatively. Permeability through supported liquid membrane can be presented by solubility and diffusion coefficients in the liquid. The permeabilities of CO₂ through the ionic liquid membranes were also predicted by a solution-diffusion model with COSMO-SAC method. The predicted results of the CO₂ permeabilities through the ionic liquids represent the experimental data within the order of the permeabilities.     

Application of Task-specific Ionic Liquids for Intensified Separations

Summary. Ionic liquids offer tremendous opportunities to intensify reactions and separations in process technologies by tuning their physical and chemical properties. Several ionic liquids are suitable for the separation of aromatic and aliphatic hydrocarbons. CO₂ absorption behavior was influenced by the functionalized chains appended to the room temperature ionic liquid (RTIL) cation. Ionic liquids seem able to combine the chemical features of amine solutions with the characteristic advantages of the physical solvents used for CO₂ absorption.     

Study of ionic liquids by the method of voltammetry at the interface between two immiscible electrolytes

Ionic liquids were studied as the organic phase in the method of voltammetry between two immiscible electrolytes. The polarization of the interface between ionic liquid and water was studied; the dependence of the polarization range (potential window) on the solubility of ionic liquid in water was shown. It was established that the interface between H₂O and ionic liquid based on hydrophobic substituted phosphonium cation and tris(pentafluoroethyl)-trifluorophosphate anion is polarized in the range of potential of about 500 mV, which creates the possibility of determining the concentration of some union, in particular perchlorate and nitrate, even in when they are both present, as well as to measure the solubility of more hydrophilic ionic liquids in water.     

Significant Cation Effects in Carbon Dioxide–Ionic Liquid Systems

Carbon dioxide–ionic liquid systems are of great current interest, and significant efforts have been made lately to understand the intermolecular interactions in these systems. In general, all the experimental and theoretical studies have concluded so far that the main solute–solvent interaction takes effect through the anion, and the cation has no, or only a secondary role in solvation. In this theoretical approach it is shown that this view is unfounded, and evidence is provided that, similarly to the benzene–CO₂ system, dispersion interactions are present between the solute and the cation. Therefore, this defines a novel site for tailoring solvents to tune CO₂ solubility.     

Study of the solubility of CO2, H2S and their mixture in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate: Experimental and modelling

New experimental results are presented for the solubility of carbon dioxide, hydrogen sulfide in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈mim][PF₆]) at temperatures range from (303.15 to 353.15) K and pressures up to about 2 MPa. The solubility of the mixture of CO₂/H₂S in [C₈mim][PF₆] under various feed compositions were also measured at temperatures of (303.15, 323.15 and 343.15) K and the pressure up to 1 MPa. The solubility of carbon dioxide and hydrogen sulfide increased with increasing pressure and decreased with increasing temperature and the solubility of H₂S is about three times that of CO₂ in the particular ionic liquid studied. The measured data were correlated using extended Henry’s law included Pitzer’s virial expansion for the excess Gibbs energy, and the generic Redlich–Kwong cubic equation of state proposed for gas/ionic liquid systems. The correlations from the two models show quite good consistency with the experimental data for CO₂/IL and H₂S/IL binary mixtures within experimental uncertainties. For CO₂/H₂S/IL ternary mixtures, the RK model shows better correlation with the experimental values. We also studied the effect of cation alkyl chain length on the CO₂ and H₂S solubility by comparison of the experimental data of this study with those of previous reports. As the cation alkyl chain length became longer, the solubility of CO₂ and H₂S increased in the ionic liquid. Additionally, the influence of the anion on the solubility is studied by comparing the solubility of CO₂ and H₂S in [C₈mim][PF₆] with those in [C₈mim][Tf₂N]. As a result, CO₂ and H₂S have higher solubility in the IL with [Tf₂N]⁻ as the anion.     

Benzene Solubility in Ionic Liquids: Working Toward an Understanding of Liquid Clathrate Formation

The solubility of benzene in 15 imidazolium, pyrrolidinium, pyridinium, and piperidinium ionic liquids has been determined; the resulting, benzene‐saturated ionic liquid solutions, also known as liquid clathrates, were examined with ¹H and ¹⁹F nuclear magnetic resonance spectroscopy to try and understand the molecular interactions that control liquid clathrate formation. The results suggest that benzene interacts primarily with the cation of the ionic liquid, and that liquid clathrate formation (and benzene solubility) is controlled by the strength of the cation–anion interactions, that is, the stronger the cation–anion interaction, the lower the benzene solubility. Other factors that were determined to be important in the final amount of benzene in any given liquid clathrate phase included attractive interactions between the anion and benzene (when significant), and larger steric or free volume demands of the ions, both of which lead to greater benzene solubility.     

Solutions of ionic liquids with diverse aliphatic and aromatic solutes – Phase behavior and potentials for applications: A review article

This article principally reviews our research related to liquid–liquid and solid–liquid phase behavior of imidazolium- and phosphonium-based ionic liquids, mainly having bistriflamide ([NTf₂]⁻) or triflate ([OTf]⁻) anions, with several aliphatic and aromatic solutes (target molecules). The latter include: (i) diols and triols: 1,2-propanediol, 1,3-propanediol and glycerol; (ii) polymer poly(ethylene glycol) (PEG): average molecular mass 200, 400 and 2050 – PEG200 (liquid), PEG400 (liquid) and PEG2050 (solid), respectively; (iii) polar aromatic compounds: nicotine, aniline, phenolic acids (vanillic, ferulic and caffeic acid,), thymol and caffeine and (iv) non-polar aromatic compounds (benzene, toluene, p-xylene). In these studies, the effects of the cation and anion, cation alkyl chain and PEG chain lengths on the observed phase behaviors were scrutinized. Thus, one of the major observations is that the anion – bistriflamide/triflate – selection usually had strong, sometimes really remarkable effects on the solvent abilities of the studied ionic liquids. Namely, in the case of the hydrogen-bonding solutes, the ionic liquids with the triflate anion generally exhibited substantially higher solubility than those having the bistriflamide anion. Nevertheless, with the aromatic compounds the situation was the opposite – in most of the cases it was the bistriflamide anion that favoured solubility. Moreover, our other studies confirmed the ability of PEG to dissolve both polar and non-polar aromatic compounds. Therefore, two general possibilities of application of alternative, environmentally acceptable, solvents of tuneable solvent properties appeared. One is to use homogeneous mixtures of two ionic liquids having [NTf₂]⁻ and [OTf]⁻ anions as mixed solvents. The other, however, envisages the application of homogeneous and heterogeneous (PEG + ionic liquid) solutions as tuneable solvents for aromatic solutes.Such mixed solvents have potential applications in separation of the aforesaid target molecules from their aqueous solutions or in extraction from original matrices. From the fundamental point of view the phase equilibrium studies reviewed herein and the diversity of the pure compounds – ionic liquids and target molecules – represent a good base for the discussion of interactions between the molecules that exist in the studied solutions.     

Solubility of CO2 in imidazolium-based tetrafluoroborate ionic liquids

The solubility of CO₂ in imidazolium ionic liquids (ILs), 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF₄]), 1-hexyl-3-methyl imidazolium tetrafluoroborate ([hmim][BF₄]) and 1-octyl-3-methyl imidazolium tetrtafluoroborate ([omim][BF₄]) was determined at 305-25 K and pressures from 1 to 9 MPa. The influence of chain length of alkyl substituents on the imidazolium cation on the solubility of CO₂ was investigated. The differences in solubility with chain length are in the sequence [omim][BF₄] > [hmim][BF₄] > [bmim][BF₄]. The solubility data were correlated by the extended Henry's law, and enthalpy, Gibbs free energy and entropy changes were obtained.     

Application of Task-specific Ionic Liquids for Intensified Separations

Ionic liquids offer tremendous opportunities to intensify reactions and separations in process technologies by tuning their physical and chemical properties. Several ionic liquids are suitable for the separation of aromatic and aliphatic hydrocarbons. CO₂ absorption behavior was influenced by the functionalized chains appended to the room temperature ionic liquid (RTIL) cation. Ionic liquids seem able to combine the chemical features of amine solutions with the characteristic advantages of the physical solvents used for CO₂ absorption.     

Phase diagrams of ionic liquids-based aqueous biphasic systems as a platform for extraction processes

In the past few years, ionic liquid-based aqueous biphasic systems have become the subject of considerable interest as a promising technique for the extraction and purification of several macro/biomolecules. Aiming at developing guidelines for more benign and efficient extraction processes, phase diagrams for aqueous biphasic systems composed of ionic liquids and inorganic/organic salts are here reported. Several combinations of ionic liquid families (imidazolium, pyridinium, phosphonium, quaternary ammonium and cholinium) and salts [potassium phosphate buffer (KH₂PO₄/K₂HPO₄ at pH 7), potassium citrate buffer (C₆H₅K₃O₇/C₆H₈O₇ at pH 5, 6, 7 and 8) and potassium carbonate (K₂CO₃ at pH ∼13)] were evaluated to highlight the influence of the ionic liquid structure (cation core, anion and alkyl chain length), the pH and the salt nature on the formation of aqueous biphasic systems. The binodal curves and respective tie-lines reported for these systems were experimentally determined at (298 ± 1) K. In general, the ability to promote the aqueous biphasic systems formation increases with the pH and alkyl chain length. While the influence of the cation core and anion nature of the ionic liquids on their ability to form aqueous biphasic systems closely correlates with ionic liquids capacity to be hydrated by water, the effect of the different salts depends of the ionic liquid nature and salt valency.     

Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid

A new low‐energy pathway is reported for the electrochemical reduction of CO₂ to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P₆₆₆₁₄][124Triz] is able to chemisorb CO₂ through equimolar binding of CO₂ with the 1,2,4‐triazole anion. This chemisorbed CO₂ can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO₂ within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P₆₆₆₁₄][NTf₂]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.     

Poly(ionic liquid)s as new materials for CO2 absorption

A series of imidazolium‐based ionic liquid monomers and their corresponding polymers (poly(ionic liquid)s) were synthesized, and their CO₂ sorption was studied. The poly(ionic liquid)s had enhanced CO₂ sorption capacities and fast sorption/desorption rates compared with room temperature ionic liquids. The effects of the chemical structures, including the types of anion, cation, and backbone of the poly(ionic liquid)s on their CO₂ sorption have been discussed. In contrast to room temperature ionic liquids, the polymer with PF anions had the highest CO₂‐sorption capacity, while those with BF or Tf₂N^? anions had the same capacities. The CO₂ sorption and desorption of the polymers were fast and reversible, and the sorption was selective over H₂, N_2, and O₂. The measured Henry's constants of P[VBBI][BF₄] and P[MABI][BF₄] were 26.0 bar and 37.7 bar, which were lower than those of similar room temperature ionic liquids. The preliminary study of the mechanism indicated that the CO₂ sorption of the polymer particles was more absorption (the bulk) but less adsorption (the surface). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5477–5489, 2005     

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.     

Significant Improvements in CO2 Capture by Pyridine‐Containing Anion‐Functionalized Ionic Liquids through Multiple‐Site Cooperative Interactions

A strategy for improving CO₂ capture by new anion‐functionalized ionic liquids (ILs) making use of multiple site cooperative interactions is reported. An extremely high capacity of up to 1.60 mol CO₂ per mol IL and excellent reversibility were achieved by introducing a nitrogen‐based interacting site on the phenolate and imidazolate anion. Quantum‐chemical calculations, spectroscopic investigations, and calorimetric data demonstrated that multiple‐site cooperative interactions between two kinds of interacting sites in the anion and CO₂ resulted in superior CO₂ capacities, which originated from the π‐electron delocalization in the pyridine ring.     

Phase equilibria of imidazolium ionic liquids and the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a)

A number of applications with ionic liquids (ILs) and hydrofluorocarbon gases have recently been proposed. Detailed phase equilibria and modeling are needed for their further development. In this work, vapor–liquid equilibrium, vapor–liquid–liquid equilibrium, and mixture critical points of imidazolium ionic liquids with the hydrofluorocarbon refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a) was measured at temperatures of 25 °C, 50 °C, 75 °C and pressure up to 143 bar. The ionic liquids include 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf₂N]), 1-hexyl-3-methyl-imidazolium hexafluorophosphate ([HMIm][PF₆]), and 1-hexyl-3-methyl-imidazolium tetrafluoroborate ([HMIm][BF₄]). The effects of the anion and cation on the solubility were investigated with the anion having greatest impact. [HMIm][Tf₂N] demonstrated the highest solubility of R-134a. The volume expansion and molar volume were also measured for the ILs and R-134a. The Peng–Robinson Equation of State with van der Waals 2-parameter mixing rule with estimated IL critical points were employed to model and correlate the experimental data. The models predict the vapor–liquid equilibrium and vapor–liquid–liquid equilibrium pressure very well. However, the mixture critical points predictions are consistently lower than experimental values.     

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

In this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C₆(mim)]⁺_X^?, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C₆(mim)₂X₂], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl^? and Br^? anions prefer to locate almost in the plane of the imidazolium ring whereas the I^? anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl^? and Br^? anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.     

Multi‐Molar Absorption of CO2 by the Activation of Carboxylate Groups in Amino Acid Ionic Liquids

A new strategy for multi‐molar absorption of CO₂ is reported based on activating a carboxylate group in amino acid ionic liquids. It was illustrated that introducing an electron‐withdrawing site to amino acid anions could reduce the negative inductive effect of the amino group while simultaneously activating the carboxylate group to interact with CO₂ very efficiently. An extremely high absorption capacity of CO₂ (up to 1.69 mol mol^?1) in aminopolycarboxylate‐based amino acid ionic liquids was thus achieved. The evidence of spectroscopic investigations and quantum‐chemical calculations confirmed the interactions between two kinds of sites in the anion and CO₂ that resulted in superior CO₂ capacities.     

Aza‐Crown Ether Complex Cation Ionic Liquids: Preparation and Applications in Organic Reactions

Aza‐crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG‐DTA), elemental analysis and physical properties. These new and room‐temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO₂ to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel–Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza‐[18‐C‐6HK][HSO₄]₂ was the best acidic catalyst in the reactions of esterification and Friedel–Crafts alkylation under mild reaction conditions.     

Influence of the Cation on the Solubility of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript> in Ionic Liquids Based on the Bis(trifluoromethylsulfonyl)imide Anion

Experimental values for the solubility of carbon dioxide and hydrogen in three room temperature ionic liquids based on the same anion—(bistrifluoromethylsulfonyl)imide [Ntf₂]—and three different cations—1-butyl-3-methylimidazolium, [C₄mim], 1-ethyl-3-methylimidazolium, [C₂mim] and trimethyl-butylammonium, [N₄₁₁₁]—are reported between 283 and 343 K and close to atmospheric pressure. Carbon dioxide, with a mole-fraction solubility of the order of 10⁻², is two orders of magnitude more soluble than hydrogen. The solubility of CO₂ is very similar in the three ionic liquids although slightly lower in the presence of the [C₂mim] cation. In the case of H₂, noticeable differences were observed with larger mole fraction solubilities in the presence of [N₄₁₁₁] followed by [C₄mim]. All of the mole-fraction solubilities decrease with increasing temperature. From the variation of Henry’s law constants with temperature, the thermodynamic functions of solvation 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 always better than ±1%.     

Synthesis,Characterization, Thermal Analyses,and Spectroscopic Properties of Novel Naphthyl-Functionalized Imidazolium Ionic Liquids

A series of novel ionic liquids based on naphthyl-functionalized imidazolium cation have been prepared. Their structure was characterized by NMR. The thermal stabilities of the prepared liquids were studied by thermal gravimetric analysis. The new ionic liquids containing NTf^-₂ anion display significantly higher thermal stabilities (>400°C). Anion exchange to PF^-₆, BF^-₄, and Br^– decreases the thermal stabilities of such ionic liquids. Fluorescence and UV–Vis absorption spectroscopy were used to study the spectroscopic properties of the ionic liquids. Compared with common ionic liquids, the described ionic liquids provide robust fluorescence properties and remarkably increased UV–Vis absorption. This research may enrich the field of functionalized ionic liquids and provide a platform for extension of ionic liquid applications.