Modeling the Solubility Behavior of CO2, H2, and Xe in [Cn-mim][Tf2N] Ionic Liquids

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 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.

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.

Physicochemical and thermodynamic characterization of N -alkyl- N -methylpyrrolidinium bromides and its aqueous solutions

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.

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

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

Promoting fluid transportation in porous media has important applications in energy, pedology, bioscience, etc. For this purpose, one effective way is to prevent swelling through surface modification; however, it is far from enough in real cases, such as ultra-low permeability reservoirs and tight oils. In this study, we considered the comprehensive effects of inhibiting clay swelling, flocculation performance, reducing water clusters and interfacial tension and developed a series of imidazole-based tetrafluoroborate ionic liquids (ILs) with different lengths of alkyl chains. Through measurements of anti-swelling rates, XRD, SEM, 17O NMR, molecular dynamics simulation, zeta potential, flocculation evaluation, interfacial tension and a core flooding experiment based on ultra-low permeability reservoirs, the relationships between the molecular structure and physicochemical properties of ILs have been revealed. Interestingly, one of the selected ILs, imidazole-based tetrafluoroborate ILs (C8-OMImBF4), shows excellent performance, which is helpful to design an effective strategy in promoting fluid transportation in narrow spaces.

Liquid–liquid extraction of caprolactam from water using room temperature ionic liquids

Separation of ethylbenzene/styrene systems using ionic liquids in ternary LLE

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.

Wetting behavior of aqueous 1-alkyl-3-methylimidazolium tetrafluoroborate {[Cn MIM][BF4] (n = 2, 4, 6)} on graphite surface

Experimental and molecular modeling studies are conducted to investigate the underlying mechanisms for the high solubility of CO2 in imidazolium-based ionic liquids. CO2 absorption isotherms at 10, 25, and 50 degrees C are reported for six different ionic liquids formed by pairing three different anions with two cations that differ only in the nature of the "acidic" site at the 2-position on the imidazolium ring. Molecular dynamics simulations of these two cations paired with hexafluorophosphate in the pure state and mixed with CO2 are also described. Both the experimental and the simulation results indicate that the anion has the greatest impact on the solubility of CO2. Experimentally, it is found that the bis(trifluoromethylsulfonyl)imide anion has the greatest affinity for CO2, while there is little difference in CO2 solubility between ionic liquids having the tetrafluoroborate or hexafluorophosphate anion. The simulations show strong organization of CO2 about hexafluorophosphate anions, but only small differences in CO2 structure about the different cations. This is consistent with the experimental finding that, for a given anion, there are only small differences in CO2 solubility for the two cations. Computed and measured densities, partial molar volumes, and thermal expansion coefficients are also reported.

Equation of state modelling of systems with ionic liquids: Literature review and application with the Cubic Plus Association (CPA) model

In the present work, wetting and interfacial properties of two new kinds of imidazolium-based ionic liquid (IL) nanodroplets, that is, dicationic IL and tricationic IL with respect to a baseline of a traditional monocationic IL on a boron nitride (BN) surface, is studied using classical molecular dynamics simulation. Calculated contact angles of all studied nanodroplets on the BN surface are lower than 90°, which demonstrate favorable wettability of the studied ILs on the BN sheet. Density profiles show an enhancement in density of both cations and anions at the BN surface for all studied droplets. Orientational analysis revealed that for monocationic ionic liquids, the imidazolium ring of cations lies parallel to the BN surface, while for multicationic ILs (dication and trication), the perfect parallel arrangement could not be observed. Identification of the truly interfacial molecule method has been used to analyze the structure and dynamics of the ions at the interface. It shows that the survival probability of cations at the interface decreases with increasing number of imidazolium moieties in the cation. The above observations signify the importance of charge and size of the cation on wetting and interfacial properties of ILs in contact with solid surfaces.