Gas Solubility In Ionic Liquids Research Articles

Rapid screening of gas solubility in ionic liquids using biased particle insertions with pre-sampled liquid trajectories

ABSTRACTWe present an efficient, general-purpose variant of the Widom test particle insertion method for computing chemical potentials of gaseous solutes in fluids or porous solids. The method is implemented in the Monte Carlo molecular simulation engine Cassandra, but receiving phase configurations are independent of this process and may be pre-sampled by other molecular simulation engines such as molecular dynamics codes. Efficiency enhancements present in this method include configurational biasing and accelerated atomic overlap detection. When applied to the estimation of Henry's law constants of atomistic difluoromethane and pentafluoroethane in ionic liquids, the accelerated overlap detection results in a speedup of more than an order of magnitude compared to conventional methods without sacrificing accuracy. We found good agreement between this method and Hamiltonian replica exchange (HREX) for Henry's law constant and absorption isotherm estimation. This embarrassingly parallel method is especially well suited for screening Henry's law constants of many small gases in the same solvents, since a liquid trajectory can be reused for as many solutes as desired.

Thermodynamic modeling of gas solubility in ionic liquids using equations of state

This work aimed at the thermodynamic modeling of gas solubility in ionic liquids (ILs) using the Soave-Redlich-Kwong (SRK), cubic-plus-association (CPA), and perturbed-chain statistical associating fluid theory (PC-SAFT) equations of state. Wherefore, the routines were developed for the parameterization of ILs. Then, the ILs were implemented in the Aspen plus simulator to evaluate the equations of state and explore the phase equilibrium data with the predictive equations and the correlation of the binary interaction parameter. Hence, it was verified the correlation of the density and speed of sound curves presented limitations to correcting the slope of the curves of pure ILs. Nonetheless, the PC-SAFT with the 4C associative scheme demonstrated a better fit for the thermophysical properties. As for the prediction of phase equilibrium for the [EMIM][TfO], the PC-SAFT with the 2B scheme showed a better fit with CO2, while the CPA with the 2B scheme presented the best result for H2S. For [OMIM][NTf2], the PC-SAFT with the 1A scheme showed better results with CO2, and the CPA with the 2B scheme showed the lowest deviation with H2S.

Solubility of gaseous hydrocarbons in ionic liquids using equations of state and machine learning approaches

Ionic liquids (ILs) have emerged as suitable options for gas storage applications over the past decade. Consequently, accurate prediction of gas solubility in ILs is crucial for their application in the industry. In this study, four intelligent techniques including Extreme Learning Machine (ELM), Deep Belief Network (DBN), Multivariate Adaptive Regression Splines (MARS), and Boosting-Support Vector Regression (Boost-SVR) have been proposed to estimate the solubility of some gaseous hydrocarbons in ILs based on two distinct methods. In the first method, the thermodynamic properties of hydrocarbons and ILs were used as input parameters, while in the second method, the chemical structure of ILs and hydrocarbons along with temperature and pressure were used. The results show that in the first method, the DBN model with root mean square error (RMSE) and coefficient of determination (R2) values of 0.0054 and 0.9961, respectively, and in the second method, the DBN model with RMSE and R2 values of 0.0065 and 0.9943, respectively, have the most accurate predictions. To evaluate the performance of intelligent models, the obtained results were compared with previous studies and equations of the state including Peng–Robinson (PR), Soave–Redlich–Kwong (SRK), Redlich–Kwong (RK), and Zudkevitch–Joffe (ZJ). Findings show that intelligent models have high accuracy compared to equations of state. Finally, the investigation of the effect of different factors such as alkyl chain length, type of anion and cation, pressure, temperature, and type of hydrocarbon on the solubility of gaseous hydrocarbons in ILs shows that pressure and temperature have a direct and inverse effect on increasing the solubility of gaseous hydrocarbons in ILs, respectively. Also, the evaluation of the effect of hydrocarbon type shows that increasing the molecular weight of hydrocarbons increases the solubility of gaseous hydrocarbons in ILs.

An electrochemical setup designed for carbon dioxide solubility measurements in ionic liquids.

An electrochemical setup was designed and built to evaluate carbon dioxide solubility in ionic liquids. The setup can simultaneously measure amounts of CO2 in the gas and in the ionic liquid phase, making it very useful for in situ electrochemical measurements. The home-built glass cell is able to withstand high vacuum allowing the ionic liquid samples to be properly evacuated before characterization and kept free of contaminants during experiments. A pressure gauge attached to the setup enables continuous monitoring of gas added to the system. This kind of configuration can measure gas solubility in ionic liquids expressed as Henry's constants determined from generated plots of dissolved gas concentration in the ionic liquid vs headspace gas pressure. It also serves as a more economical alternative to other gas solubility measurement techniques, as it is predominantly made of glass, and requires minimal sample amounts. The setup can be useful in determining the solubility of various gases in ionic liquids.

Monte Carlo Simulations of Pure and Mixed Gas Solubilities of CO2 and CH4 in Nonideal Ionic Liquid–Ionic Liquid Mixtures

The knowledge of mixed gas solubility in ionic liquids at high pressures, which becomes relevant in applications such as tertiary oil recovery and landfill gas utilization, is critical for the desi...

Rapid Measurement of Gas Solubility in Ionic Liquids with a Simple Tube-in-Tube Reactor

Here, we present a strategy for rapid measurement of gas solubility in ionic liquids based on a simple configuration of tube-in-tube reactor. Ionic liquids can be rapidly saturated without direct c...

Assessment of carbon dioxide solubility in ionic liquid/toluene/water systems by extended PR and PC-SAFT EOSs: Carbon capture implication

Recently, there has been a growing interest in CO2 capture using ionic liquids (ILs). To determine the CO2 absorption potential of ILs and their selectivity in the presence of other gaseous components in the mixture, the solubility of ILs at various operating conditions and the influence of impurities/additives such as water and toluene should be evaluated. Carbon capture capacity of the ILs can be examined using various methods such as experiments, thermodynamic approaches including Equations of State (EOSs), and molecular-based modeling. In this research work, the extended Peng–Robinson (PR) and Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) EOSs are utilized to assess the solubility and selectivity of CO2 in ILs through comparing the modeling results with experimental data. PC-SAFT and PR parameters are determined by employing the experimental density data. Modeling results reveal that the solubility values estimated by the PC-SAFT due to considering the association effects have a lower deviation (or a better performance) than PR EOS based on the magnitudes of Absolute Average Deviation (AAD %). The AAD (%) for [bmim][BF4], [bmim][PF6], [bmim][Tf2N], [hmim][Tf2N], [hmim][FAP], and [hmim][FAP] are calculated using PR EOS and PC-SAFT EOS, which are 2–5.7% and 3–7.5%, respectively. Furthermore, ternary systems of CO2 + ILs + water and CO2 + ILs + toluene are modeled to determine the effect of water and toluene on the gas solubility in ILs and viscosity of ILs with PC-SAFT EOS. Based on the results, low concentrations of water (0.1 wt%) have a negligible influence on the CO2 solubility in ILs. However, with increasing the water concentration, the solubility of water reduces significantly. On the other hand, the viscosity of ILs is reduced with increasing the water concentration. Viscosity reduction in the hydrophilic ILs is significant. It seems promising to add water up to 10 wt% to hydrophilic ILs, since a decrease in the viscosity to an amount close to the viscosity of water and a decrease in solubility by 9% are experienced. Finally, the selectivity of [hmim][Tf2N] in separation of CO2 from mixtures containing H2S, SO2, CH4, and H2 are reported. Based on the results, [hmim][Tf2N] is not appropriate for separation of CO2 from streams with a high concentration of H2S and SO2 gases.

Application of COSMO-RS and UNIFAC for ionic liquids based gas separation

In recent years, due to their advantages on good stability, non-volatility, tunable viscosity and tailor-made properties, ionic liquids (ILs) have been regarded as novel potential solvents and alternative media for gas separation. However, the various cations and anions representing the ILs, together with limited experimental data, make it challenging to predict gas solubility in ILs and identify the optimal IL for a specific gas separation. In this work, a comprehensive Henry’s law constants database is first established for gas-IL which supplements an already established extensive gas solubility database. Because of the insufficient experimental data for both IL-C2H4 and IL-C2H6 systems, the COSMO-RS model is used after validation to generate additional pseudo-experimental data. Then, together with the sufficient experimental data of CO2-IL and CH4-IL systems, UNIFAC-IL is developed for the prediction of four-component shale gas (CH4, C2H4, C2H6, CO2) solubility in ILs. A relatively good agreement between the model predicted and the experimental solubility data is observed. Moreover, the developed UNIFAC-IL model can be used to predict the solubility of gases in new ILs that are not included in parameter fitting due to its group contribution basis. For this reason, the model represents a very useful tool for task-specific design of ionic liquids for gas separations.

Data‐Driven Modelling of Gas Solubility in Ionic Liquids Using Principal Properties as Orthogonal Descriptors

AbstractPrincipal properties for gases and ionic liquids (ILs) were used as descriptors to model gas solubility in ILs by means of data‐driven approaches such as partial least squares (PLS) and orthogonal PLS (OPLS). Satisfactory PLS predictions, spanning above 3 log units, can be easily achieved using a nine parameters equation, while disjoint OPLS models for different gases, namely hydrocarbons, neutral and acidic ones, allow more accurate predictions.

Prediction of Gas Solubility in Ionic Liquids Using the Cosmo-Sac Model

Abstract Thermodynamic principles for the dissolution of gases in ionic liquids (ILs) and the COSMO-SAC model are presented. Extensive experimental data of Henry’s law constants for CO2, N2 and O2 in ionic liquids at temperatures of 280-363 K are compared with numerical predictions to evaluate the accuracy of the COSMO-SAC model. It is found that Henry’s law constants for CO2 are predicted with an average relative deviation of 13%. Both numerical predictions and experimental data reveal that the solubility of carbon dioxide in ILs increases with an increase in the molar mass of ionic liquids, and is visibly more affected by the anion than by the cation. The calculations also show that the highest solubilities are obtained for [Tf2N]ˉ. Thus, the model can be regarded as a useful tool for the screening of ILs that offer the most favourable CO2 solubilities. The predictions of the COSMOSAC model for N2 and O2 in ILs differ from the pertinent experimental data. In its present form the COSMO-SAC model is not suitable for the estimation of N2 and O2 solubilities in ionic liquids.

Influence of Ion Diffusivity and Gas Solubility in Ionic Liquids on Li-Air Battery Performance

Owing to its extreme high theoretical energy density1, the non-aqueous Li-air battery has received remarkable attention in recent years as a promising candidate for electric vehicle applications. Ionic Liquids (ILs), molten salts that are liquid at room temperature, have been investigated as potential electrolytes in Li-air batteries due to their negligible vapor pressure, good thermal stability, and wide electrochemical windows.However, comparing to conventional organic electrolytes, for example, ethylene carbonate (EC), ILs generally have higher viscosity and consequently lower ionic conductivity and ion diffusivity. Therefore, two low viscosity ILs, [Pyrr12O1][TFSI], N-methoxyethyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide, and [PP12O1][TFSI], N-methoxyethyl-N-methyl piperidinium bis(trifluoromethanesulfonyl)imide, and their mixture with Li[TFSI], were investigated.In this work, the diffusivity of the cation and anion of the IL, as well as the diffusivity of the Li+ cation, were measured with pulsed-field-gradient spin-echo (PFG-SE) NMR Spectroscopy. In addition, the I-V performances of the two ILs were characterized in a Li-O2 battery and compared with a non-ether-functionalized IL, [PP13][TFSI]2. Physical properties of the ILs and IL-Li[TFSI] mixtures, including densities, viscosities, ionic conductivities, and electrochemical windows are reported. An additional property that can affect Li-O2 battery performance, the solubility of O2 in the ILs and IL-Li[TFSI] mixtures, was also measured, using a gravimetric microbalance.

Influence of Ion Diffusivity and Gas Solubility in Ionic Liquids on Li-Air Battery Performance

Owing to their extremely high theoretical energy density, non-aqueous Li-air batteries have received remarkable attention in recent years. Ionic Liquids (ILs), molten salts that are liquid at room temperature, have been investigated as potential electrolytes in Li-air batteries due to their negligible vapor pressure, good thermal stability, and wide electrochemical windows. However, compared to conventional organic electrolytes, ILs generally have higher viscosity and, consequently, lower ionic conductivity and ion diffusivity. Therefore, we have selected eight low-viscosity ILs containing the bis(trifluoromethanesulfonyl)imide ([TFSI]-) anion, and their physical properties were characterized. The diffusivities of the cation and anion of the ILs were measured with pulsed-field-gradient spin-echo (PFG-SE) NMR Spectroscopy. In addition, the I-V performances of three characteristic ILs were tested in a Li-O2 battery. The solubility of O2 in the ILs and IL-Li[TFSI] mixtures, an additional property that can affect Li-air battery performance, was also measured using a gravimetric microbalance.

Evaluation of imidazolium-based ionic liquids for biogas upgrading

The conceptual processes for biogas upgrading using three imidazolium-based ionic liquids ([hmim][Tf2N], [bmim][Tf2N] and [bmim][PF6]) were simulated in Aspen Plus to study the effect of properties of ionic liquids (ILs) on the process performance. To conduct the process simulation, each IL was input into Aspen Plus as a pseudo component, their critical properties were estimated by group contribution method, and their thermo-physical properties were correlated from the available experimental data by semi-empirical equations. The gas solubility in ILs was modeled with the non-random two-liquid model and Redlich–Kwong equation of state. Among the studied ILs, the simulation results show that the amount of recirculated solvents and the total energy consumption for upgrading process using ILs follow: [bmim][Tf2N]<[bmim][PF6]<[hmim][Tf2N]. The effects of density and viscosity of ILs on pressure drop and diameter of the absorber as well as the effects of operational pressures and temperatures on the process efficiency were investigated. It is found that the energy consumption increases with increasing pressure and temperature in the absorber and decreases with increasing pressure in the first flash tank. The ILs-based technology was further compared with water scrubbing and aqueous choline chloride/urea scrubbing, and the comparison shows that the total energy consumptions follow: 50%ChCl/Urea-water<[bmim][Tf2N] scrubbing<water scrubbing.

1-Ethyl-3-methylimidazolium trifluoromethanesulfonate와 1-Butyl-1-methylpyrrolidinium trifluoromethanesulfonate 이온성 액체에 대한 황화수소와 메탄의 용해도

동일한 음이온을 가진 두 가지 종류의 이온성 액체인 1-ethy-3-methylimidazolium trifluoromethanesulfonate ([emim][TfO])와 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([bmpyr][TfO])를 대상으로 약 303 K로부터 약 343 K의 온도 범위와 약 30 MPa까지의 압력 범위에서 이온성 액체에 녹는 황화수소(<TEX>$H_2S$</TEX>)와 메탄(<TEX>$CH_4$</TEX>)의 용해도를 측정하였다. 가변부피투시창이 장착된 고압용 상평형 장치를 사용하여 온도를 변화시키면서 여러 가지 조성을 갖는 기체 + 이온성 액체 혼합물의 기포점 압력을 측정함으로써 이온성 액체에서의 기체의 용해도를 결정하였다. 이온성 액체에 대한 <TEX>$H_2S$</TEX>의 용해도는 압력이 증가함에 따라 증가하였으며 온도가 증가함에 따라 감소하였다. 반면에 이온성 액체에 대한 <TEX>$CH_4$</TEX>의 용해도는 압력이 증가함에 따라 크게 증가하였으나 온도의 영향은 거의 없었다. 동일한 음이온을 갖는 이온성 액체인 [emim][TfO]와 [bmpyr][TfO]에 대하여 <TEX>$H_2S$</TEX>의 용해도는 몰랄 농도 기준으로 온도 및 압력 조건에 관계없이 거의 유사하였다. 이온성 액체[emim][TfO]에 대한 <TEX>$H_2S$</TEX>와 <TEX>$CH_4$</TEX>의 용해도를 비교한 결과, <TEX>$H_2S$</TEX>의 용해도가 <TEX>$CH_4$</TEX>의 용해도보다 훨씬 컸다. 동일한 종류의 이온성 액체에 대하여 본 연구를 통해 얻은 <TEX>$H_2S$</TEX>와 <TEX>$CH_4$</TEX>의 용해도 데이터를 문헌으로부터 얻은 <TEX>$CO_2$</TEX>의 용해도 데이터와 비교하였다. 같은 압력 및 온도 조건에서 비교할 때, <TEX>$CO_2$</TEX>의 용해도는 <TEX>$H_2S$</TEX>와 <TEX>$CH_4$</TEX>의 용해도의 사이에 있었다. Solubility data of hydrogen sulfide (<TEX>$H_2S$</TEX>) and methane (<TEX>$CH_4$</TEX>) in two kinds of ionic liquids with the same anion: 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][TfO]) and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([bmpyr][TfO]) are presented at pressures up to about 30 MPa and at temperatures between 303 K and 343 K. The gas solubilities in ionic liquids were determined by measuring the bubble point pressures of the gas + ionic liquid mixtures with various compositions at different temperatures using a high-pressure equilibrium apparatus equipped with a variable-volume view cell. The <TEX>$H_2S$</TEX> solubilities in ionic liquid increased with the increase of pressure and decreased with the increase of temperature. On the other hand, the <TEX>$CH_4$</TEX> solubilities in ionic liquid increased significantly with the increase of pressure, but there was little effect of temperature on the <TEX>$CH_4$</TEX> solubility. For the ionic liquds [emim][TfO] and [bmpyr][TfO] with the same anion, the solubility of <TEX>$H_2S$</TEX> as a molality basis was substantially similar, regardless of the temperature and pressure conditions as a molar concentration basis. Comparing the solubilities of <TEX>$H_2S$</TEX> and <TEX>$CH_4$</TEX> in the ionic liquid [emim][TfO], the solubilities of <TEX>$H_2S$</TEX> were much greater than those of <TEX>$CH_4$</TEX>. For the same type of ionic liquid, the solubility data of <TEX>$H_2S$</TEX> and <TEX>$CH_4$</TEX> obtained in this study were compared to the solubility data of <TEX>$CO_2$</TEX> from the literature. When compared at the same pressure and temperature conditions, the <TEX>$CO_2$</TEX> solubility was in between the solubility of <TEX>$H_2S$</TEX> and <TEX>$CH_4$</TEX>.

High pressure solubility of CH4, N2O and N2 in 1-butyl-3-methylimidazolium dicyanamide: Solubilities, selectivities and soft-SAFT modeling

The society and industry commitment to progressively reduce Green House Gases (GHGs) emissions forged important challenges that conventional gas separation processes are unable to overcome. Ionic liquids (ILs) have been attracting an outstanding attention during the last decade as a promising class of viable solvents to capture pollutants and for gas separation processes. Being the IL-based membranes gas separation controlled by the gas solubility in the IL rather than by its diffusivity, the solubility of gases in ILs stands as highly relevant input for their application in liquid membranes. As part of a continuing effort to develop an IL based process for high pressure capture of GHGs, the phase equilibria of nitrous oxide (N2O), methane (CH4) and nitrogen (N2) were investigated in this work. Experimental gas–liquid equilibrium data for N2O, CH4 and N2 in [C4C1im][N(CN)2] were determined in the (293 to 363) K temperature range, for pressures up to 70MPa and gas mole fractions up to 35 %.Unfavorable interactions towards the studied gases, with positive deviations to ideality, were observed for all the studied gases, placing the studied IL among those with the lowest selectivities reported. The observed behavior highlights that a delicate balance between the solvent polarity and its molar volume must be ascertained when a highly selective solvent for N2 or CH4 separation is envisaged. The soft-SAFT EoS successfully described the high pressure phase behavior data using the molecular model and parameters sets reported in previous works. A good description of the binary systems studied, including the small CH4 temperature dependency and the N2 reverse temperature dependency on the solubility were achieved using just one binary interaction parameter. This reinforces the use of soft-SAFT as an accurate model to describe the behavior of gases in ILs for different applications.

Multiple headspace extraction for gas detection in ionic liquids

In this study multiple headspace extraction was used for the first time to measure the saturation concentration of carbon monoxide and oxygen in various ionic liquids (ILs). Many processes in ILs involve the reaction of gases so that the reactant solubility is not a mere characteristical parameter, but understanding the solubility of gases in ILs is required for assessing the feasibility of possible applications. Multiple headspace extraction has proofed to be a powerful tool to obtain solubilities in good accordance with literature data. The measured saturation concentration for carbon monoxide and oxygen in ILs based on rarely researched tetracyanoborates and other anions was in the range of 1.5–6.5mmol/L. The great advantage of multiple headspace extraction is that it is a nonexpensive method that can be realised in most analytical laboratories by combination of a simple gas chromatograph and an eligible headspace injector.

Development of a simple method for predicting CO2 enhancement of H2 gas solubility in ionic liquids

The solubility of hydrogen in an ionic liquid (IL) is important for hydrogenolysis and hydrogenation used in biomass transformations. In this work, we formulate an enhancement ratio (ER) for H2–CO2–IL systems that is defined in terms of the ternary system H2 molality, the binary H2 molality at constant temperature and the isofugacity condition. Literature data were used to demonstrate the utility of the definition for ER and to develop a predictive model for ionic liquids that dissolve cellulose. The ER is greater than one when CO2 can be used to increase H2 solubility in the IL. Although the solubility of H2 in many IL can be enhanced by CO2, for some ILs the presence of CO2 reduces H2 solubility in the IL. The ER for [hmim][Tf2N] was found to be less than one at low CO2 concentrations. Temperature affected the ER of ionic liquids in different ways with some IL exhibiting maximum hydrogen solubility ([bmim][PF6]) and others having an ER that monotonically increased with temperature ([Tf2N]-containing IL). Correlation of the ER with literature data is proposed in terms of Henry's constant of H2 and CO2 and the solubility parameter of the ionic liquid. The correlation was applied to six ionic liquids at conditions of 313–453K and at CO2 molalities up to 5mol/kg to give a sum of squares of the residuals of 1.4×10−3 in ΔmH2. Solubility enhancement ratios for H2 gas by CO2 for ionic liquids that dissolve cellulose were estimated with the predictive model to be as high as 1.2 per unit molality CO2 in the IL. Vapor–liquid equilibrium measurements of mixed gases (H2–CO2, CO–CO2, O2–CO2) with ionic liquids that dissolve biomass are urgently needed to promote development of methods for transforming biomass into biofuels and chemicals.

Modeling imidazolium-based ionic liquids with ePC-SAFT. Part II. Application to H2S and synthesis-gas components

ePC-SAFT was used to model the gas solubility in ionic liquids (ILs). The gases under consideration were CO, H2, H2S and O2, and the imidazolium-based ILs studied were [Cnmim][Tf2N], [Cnmim][PF6] and [Cnmim][BF4] (n=2, 4, 6 and 8). For the ePC-SAFT modeling, each IL was considered to be completely dissociated into a cation and an anion. Each ion was modeled as a non-spherical species exerting repulsive, dispersive and Coulomb forces. CO, H2 and O2 were modeled as non-spherical molecules exerting repulsive and dispersive forces, and H2S was modeled as a non-spherical, associating molecule. ePC-SAFT reasonably predicts the gas solubility in the considered gas/IL mixtures. In order to describe the experimental gas solubilities quantitatively in a broad temperature and pressure range, one ion-specific binary interaction parameter between the IL-anion and the gas was applied, which was allowed to depend linearly on temperature.

Gas Solubility in Ionic Liquids

Gas Solubility in Ionic Liquids

High pressure phase behaviour of mixtures of hydrogen and the ionic liquid family [cnmim][Tf2N

The high-pressure solubility of hydrogen gas in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)amide ([emim][Tf2N]) was measured experimentally in an equipment based on the synthetic technique. Measurements were carried out within a temperature range of 310–450K and pressures up to 15MPa. Hydrogen solubility was shown to be low in this ionic liquid, reaching a maximum concentration of about 6mole percent at the highest temperatures and pressures investigated. Hydrogen solubility showed an “inverse” temperature effect, indicating increased solubility at higher temperatures in contrast to other commonly investigated gas solubilities in ionic liquids, such as carbon dioxide. Within the temperature and pressure range investigated, solubility isotherms on a pressure–concentration diagram approximated linear behaviour. It was also shown that the solubility of hydrogen increases as the alkyl side chain of the cation increases in size within the homologous family.