Why Is CO2 so soluble in imidazolium-based ionic liquids?

In this work, the PC-SAFT equation of state (EoS) has been used to model the solubility of acid gases (CO2 and H2S) in two imidazolium-based ionic liquids (ILs) ([C8-mim][PF6] and [C8-mim][Tf2N]). Parameters of pure ILs were estimated using experimental densities. Two strategies were considered to model densities of pure ILs. In strategy 1, ILs were modeled as nonassociating compounds and in strategy 2 ILs were considered as self-associating molecules and both association sites were assigned to each ILs. According to the results, the associating contribution should be taken into account in order to accurately correlate the properties of ILs. The solubility of CO2 and H2S in ionic liquids was then studied. In order to describe the experimental gas solubilities quantitatively, binary interaction parameters between the ILs and the gases were applied, which were allowed to depend linearly on temperature. After fitting a binary interaction parameter kij on experimental VLE data, the model was able to describe accurately the solubility of acid gases in these two ionic liquids. Using second strategy, an average deviation of less than 2.2% and 3.2% in the calculation of the mole fraction of CO2 and H2S in ILs (x2) were obtained, respectively.

The thermophysical properties (decomposition temperature, glass transition temperature, density, and viscosity) of imidazolium-based ionic liquids (ILs) paired with the tricyanomethanide ([TCM]−) anion and the bis(trifluoromethylsulfonyl)imide ([Tf2N]−) anion were studied within a wide temperature range. The effect of the ether functional group (in [Tf2N]− and [TCM]− ILs) and hydroxyl functional group (in [Tf2N]− IL) incorporated in the cation’s alkyl chain on the thermophysical behavior and carbon dioxide (CO2) solubility was evaluated by comparing their behavior to the corresponding nonfunctionalized ILs. The thermal stability was enhanced by the inclusion of hydroxyl functionalization in the cation’s alkyl chain while ether functionalization had no major effect on the thermal stability. The ether groups (one or two) resulted in an increase in the density and a decrease in the viscosity of all ILs. The hydroxyl group resulted in an increase in both properties. The CO2 solubilities were not affected by the presence of the ether groups, while the hydroxyl group led to a significant decrease in the solubility. Additionally, the electrolyte perturbed-chain statistical associated fluid theory (ePC-SAFT) equation of state was used to calculate the CO2 solubility in the ILs and the Henry’s law constant. The model showed great predictive ability. The Henry’s constants were applied to calculate the partial molar thermodynamic properties of solvation.

A comparative study on the solubility of CH3SH and H2S in imidazolium-based ionic liquids: A connectionist approach between free volume and thermodynamics

Effect of anion and methylation on the interionic interactions and reactivity of 1-butyl-2,3-dimethyl imidazolium-based ionic liquids

We present here a new model for the imidazolium-based ionic liquids (ILs) with the bis(trifluoromethylsulfonyl)imide anion [Tf(2)N](-) in the context of the soft-SAFT EoS. The model is used to predict the solubility of several compounds in these ILs, and results are compared to available experimental data. Since in the soft-SAFT EoS an associating site is used to represent a short-range and highly directional attractive force among molecules, we have used this feature to mimic the main interactions between the anion and the cation for the alkylimidazolium-[Tf(2)N] ILs. The members of the alkylimidazolium-[Tf(2)N] family are modeled as Lennard-Jones chains with three associating sites in each molecule (one "A" site and two "B" sites). An "A" site represents the nitrogen atom interactions with the cation, and a "B" site represents the delocalized charge due the oxygen molecules on the anion. Each type of associating site is identically defined, but only AB interactions between different IL molecules are allowed. Model parameters for the ionic liquids were estimated with experimental density data from different authors, following a similar approach taken in our previous work [Andreu and Vega, J. Phys. Chem. C 2007, 111, 16028]. The new set of parameters was used to study the solubility behavior of hydrogen, carbon dioxide, and xenon in these ILs over a wide range of temperature and pressure. It has been observed that no binary parameters are needed to correlate the solubility of hydrogen in [C(6)-mim][Tf(2)N] at different temperatures, and predictions up to 100 MPa are presented here. The model is able to correlate with very good agreement the experimental data for the systems [C(n)-mim][Tf(2)N] + CO(2) with only one temperature-independent mixture parameter, while two temperature-independent mixture parameters are needed to correlate the experimental solubility data for the systems IL + Xe, attaining an excellent agreement in a wide range of temperatures. The work presented here reinforces previous results, proving that a reasonable simple model for the IL within the framework of soft-SAFT is able to describe the physical absorption of different gases in ILs with good accuracy, in spite of the most complex nature of the anion, without the need of further parameters or terms. In addition, since these parameters do not depend on the particular conditions at which they were fitted, soft-SAFT is used then to analyze the solubility dependence of these gases in ILs, according to the anion nature and the alkyl chain length of the imidazolium cation by the use of the models developed within this approach.

Imidazolium-based ionic liquids (ILs) incorporating the tricyanomethanide ([TCM(-)]) anion are studied using an optimized classical force field. These ILs are very promising candidates for use in a wide range of cutting-edge technologies and, to our knowledge, it is the first time that this IL family is subject to a molecular simulation study with the use of a classical atomistic force field. The [C4mim(+)][TCM(-)] ionic liquid at 298.15 K and at atmospheric pressure was used as the basis for force field optimization which primarily involved the determination of the Lennard-Jones parameters of [TCM(-)] and the implementation of three quantum mechanical schemes for the calculation of the partial charge distribution and the identification of the appropriate scaling factor for the reduction of the total ionic charge. The optimized force field was validated by performing simulations of the 1-alkyl-3-methylimidazolium tricyanomethanide ([Cnmim(+)][TCM(-)], n = 2, 4, 6, and 8) IL family at various temperatures. The results for density, self-diffusivity and viscosity are in very good agreement with the available experimental data for all ILs verifying that the force field reliably reproduces the behaviour of the imidazolium-based [TCM(-)] IL family in a wide temperature range. Furthermore, a detailed analysis of the microscopic structure and the complex dynamic behaviour of the ILs under study was performed.

The high-pressure vapor–liquid equilibrium for the binary systems of carbon dioxide (CO2) and a series of 1-alkyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids ([CnC1pyr][NTf2] (n = 3,4,6)) are reported at 298.15, 318.15, and 338.15 K and at pressures of up to 20 MPa. Experiments were conducted using gravimetric (IGA and XEMIS microbalances) and volumetric (high-pressure view cell) methods. The solubility of CO2 in pyrrolidinium ionic liquids increases with decreasing temperature and increasing pressure. The CO2 solubility also slightly increases with increases in alkyl chain length on the pyrrolidinium cation. The molar volume and volume expansion of CO2 + IL mixtures are also reported. The Fickian diffusion of CO2 in pyrrolidinium-based ionic liquids (∼10–10 m2·s–1) was calculated at pressures of up to 2 MPa and found to be slightly lower than the diffusivity of CO2 in an imidazolium-based ionic liquid with the [NTf2] anion.

Carbon dioxide (CO2) absorption in several imidazolium-based ionic liquids (ILs), pyridinium-based ionic liquids and a tetraalkylammonium-based poly(ionic liquid) (PIL), poly[(p-vinylbenzyl) trimethylammonium hexafluorophosphate] P[[VBTMA][PF6], was studied. The trend of CO2 solubility in all of the ILs increases dramatically with decreasing absorption temperature. Based on the same bis(triflamide) [Tf2N] anion, imidazolium, pyridinium and trihexyltetradecylphosphonium-based ionic liquids all show relatively similar CO2 solubilities, which were higher than for the [ES] anion. The highest CO2 absorption was found in a poly(ionic liquid) P[[VBTMA][PF6]], however, the monomer also showed higher CO2 capacity than the other ionic liquids. The poly(ionic liquid) is remarkable in that it can adsorb 77% of its body weight of CO2 with a selectivity over nitrogen of 70 : 1. The absorbed CO2 gas can be readily desorbed from ionic liquids and poly(ionic liquid) and the selectivity for CO2 over N2 was consistent over repeated cycles. The materials can be reused several times for consecutive sorption/desorption cycles, without loss of performance in a large-scale reactor and therefore represent serious candidates for use in commercial adsorbers.

Time-resolved fluorescence spectra and fluorescence anisotropy decay of 2-aminoquinoline (2AQ) have been measured in eight room-temperature ionic liquids, including five imidazolium-based aromatic ionic liquids and three nonaromatic ionic liquids. The same experiments have also been carried out in several ordinary molecular liquids for comparison. The observed time-resolved fluorescence spectra indicate the formation of pi-pi aromatic complexes of 2AQ in some of the aromatic ionic liquids but not in the nonaromatic ionic liquids. The fluorescence anisotropy decay data show unusually slow rotational diffusion of 2AQ in the aromatic ionic liquids, suggesting the formation of solute-solvent complexes. The probe 2AQ molecule is likely to be incorporated in the possible local structure of ionic liquids, and hence the anisotropy decays only through the rotation of the whole local structure, making the apparent rotational diffusion of 2AQ slow. The rotational diffusion time decreases rapidly by adding a small amount of acetonitrile to the solution. This observation is interpreted in terms of the local structure formation in the aromatic ionic liquids and its destruction by acetonitrile. No unusual behavior upon addition of acetonitrile has been found for the nonaromatic ionic liquids. It is argued that the aromaticity of the imidazolium cation plays a key role in the local structure formation in imidazolium-based ionic liquids.

This manuscript focuses on the application of imidazolium‐based ionic liquids (ILs) 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM] + [PF 6 ] − ) and 1‐butyl‐3‐methylimidazolium bis(trifluoromethane)sulfonimide ([BMIM] + [TFSI] − ) as potential entrainers for the separation of cyclohexane/benzene and heptane/toluene utilizing gas liquid chromatography (GLC) technique. The activity coefficients at infinite dilution were obtained for 20 solutes including both polar and nonpolar in each IL at different temperatures ranging from 323.15 to 363.15 K and at pressure 101.3 kPa. The COSMO‐RS model was applied to predict experimental data and to assess the solvent–solute interactions. The results indicate that the COSMO‐RS model is an effective screening tool, offering a cost‐effective and time‐saving alternative to extensive experimental procedures. Partial molar excess enthalpies at infinite dilution, , selectivities, , and capacities, , were also determined for each of the separations studied. The extraction efficiency of the evaluated ILs was also compared with previously studied ILs and conventional solvents such as NMP and sulfolane which are available in the literature. Based on the findings, the activity coefficients and intermolecular interactions of different solutes in ILs are highly dependent on the chemical structure of the IL. Moreover, it also determines the enthalpy behavior of the binary mixture.

Evaluation of interaction between imidazolium-based chloride ionic liquids and calf thymus DNA

Anti-corrosion properties of new imidazolium-based ionic liquids as a function of cation structure

Ionic polyimides (i-PI) are a new class of polymer materials that are very promising for CO2 capture membranes, and recent experimental studies have demonstrated their enhanced separation performance with the addition of imidazolium-based ionic liquids (ILs). However, there is very little known about the molecular-level interactions in these systems, which give rise to interesting gas adsorption and diffusion characteristics. In this study, we use a combination of Monte Carlo and molecular dynamics simulations to analyze the equilibrium and transport properties of CO2 molecules in the i-PI and i-PI + IL composite materials. The addition of several different common ILs are modeled, which have a plasticization effect on the i-PI, lowering the glass transition temperature (Tg). The solubility of CO2 strongly correlates with the Tg, but the diffusion demonstrates more unpredictable behavior. At low concentrations, the IL has a blocking effect, leading to reduced diffusion rates. However, as the IL surpasses a threshold value, the relationship is inverted and the IL has a facilitating effect on the gas transport. This behavior is attributed to the simultaneous contributions of the increased i-PI plasticization at higher IL concentrations (facilitating gas hopping rates from cavity-to-cavity) and the increased IL continuity throughout the system, enabling more favorable transport pathways for CO2 diffusion.

A comparative study of ammonia solubility in imidazolium-based ionic liquids with different structural compositions

Ionic liquids containing the tetrafluoroborate anion have the best performance and stability for electric double layer capacitor applications