CO2 In Ionic Liquids Research Articles

Nanoporous copper incorporated platinum composites for electrocatalytic reduction of CO2 in ionic liquid BMIMBF4

A three-dimensional porous nanostructure electrode composed of copper skeletons and platinum shells (NPC–Pt) was prepared by electroless plating for the first time. The electrochemical behavior of this electrode for electrocatalytic reduction CO2 in ionic liquid, 1-butyl-3-methylimidazoliumtetrafluoborate (BMIMBF4), had been studied by cyclic voltammogram and electrochemical impedance spectroscopy with a reduction peak at −2.24V (vs. Ag) which was more positive 180mV than that obtained on a pure platinum electrode. The electrolyses experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, affording the dimethyl carbonate in a good yield (81%). In addition, the current for the CO2 reduction at NPC–Pt electrode was stable, with a higher current density and current efficiency (83%). Moreover, current efficiency remained after reusing it for five times.

Correlation of supercritical CO2–ionic liquid vapor–liquid equilibria with the ε*‐modified Sanchez–Lacombe equation of state

ABSTRACTThe ε*‐modified Sanchez–Lacombe equation of state (ε*‐modified SL EOS) contains a temperature‐dependent interaction energy that allows it to provide better pure component ionic liquid pressure–volume–temperature representation than the original SL EOS. In this work, we applied the ε*‐modified SL EOS to correlate available high pressure CO2–ionic liquid vapor–liquid equilibrium (VLE) data, which are important for developing viscosity correlations. Usual SL EOS mixing rules were applied with one interaction parameter, kij, which was fitted to the data. For the case of kij equal to zero, the ε*‐modified SL EOS could greatly improve the average relative deviation (ARD) of the VLE (ARD 14.6%) over that of the original SL EOS (ARD 44.0%). For the case of kij being fitted for both EOS, representation of the VLE of both equations was similar (ARD ≤ 9%). The ε*‐modified SL EOS is able to describe the vapor–liquid equilibria data over a wide range of pressures (0.1 < P < 100 MPa) and gives semi‐quantitative (ARD < 15%) representation of CO2 solubilities in many ionic liquids from knowledge of only the pure component properties. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.

Validation and Prediction of the Temperature-Dependent Henry's Constant for CO2–Ionic Liquid Systems Using the Conductor-like Screening Model for Realistic Solvation (COSMO-RS)

Henry's constant H of carbon dioxide in a number of ionic liquids (ILs) has been studied using the predictive method COnductor-like Screening MOdel for Realistic Solvation (COSMO-RS). Experimental H values for 14 CO2–IL systems spread over a temperature range of (283 to 333) K have been used to estimate the parameters λ1 and λ2 of the combinatorial term to calculate the chemical potential. The H values of CO2 in 18 other ILs have been validated and found to be in good agreement with the experimental data with a relative deviation of less than 10 %. Cation groups like imidazolium, pyridinium, ammonium, uronium, thiouronium, and phosphonium have been studied. A total of 12 anions such as L–, BF4–, EtSO4–, TFA–, OctSO4–, Tf2N–, mFAB–, eFAB–, mFAP–, eFAP–, pFAP–, and bFAP– were studied to find the most favorable cation and anion combination for high CO2 solubility. It was observed that increasing the fluorination of organic anions containing fluoro alkyl groups gave lower Henry's constant values (following th...

Prediction and Validation of Carbon Dioxide Gas Solubility in Ionic Liquids at T=298K and Atmospheric Pressure using Quantum Chemical Approach

Carbon dioxide (CO2) gas solubilities are predicted via quantum chemical calculations, which only requires molecular structure as initial information. The quantum chemical based Conductor like Screening Model for Real Solvents (COSMO-RS) has been adopted for this purpose. Predictions of gas solubility at temperatures ranging from (283.15 to 323.15 K) at 0.1 MPa were done for the IL:[EMIM][TFI]. The relative absolute deviation of around 30% shows that the quality of predictions is highly dependent on the infinite dilution activity coefficient of CO2 in [EMIM][TFI].Additionally thermodynamic parameters such as Gibb’s Energy of solvation, enthalpies and entropies have also been predicted and compared for the IL:[BMIM][BF4]. In addition, the carbon dioxide solubility in 16 ionic liquids comprising of imidazolium and pyridinium based cations was validated with reported values. The Root Mean Square Deviation (RMSD) obtained was: 3.09% [TFI], 6.5% [TFO] and 12% [PF6], respectively. Finally, the Henry’s constants of CO2 in 286 ionic liquids comprising of newer cations such as pyrrolidinium, piperidinium and morpholium were predicted at T=298.15 K. The saturated aromatic ring structure of pyrrolidinium, morpholinium and piperidinium based ionic liquids possessed low Henry’s constant values which indicates high solubility of CO2 in ionic liquids.

Measurement of CO2 Solubility in Ionic Liquids: [BMP][Tf2N] and [BMP][MeSO4] by Measuring Bubble-Point Pressure

This paper presents the bubble-point pressure data of CO2 in ionic liquids 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf2N]) and 1-butyl-1-methylpyrrolidinium methylsulfate ([BMP][MeSO4]). In our research, the high-pressure phase behavior of carbon dioxide in [BMP][Tf2N] and [BMP][MeSO4] were observed at pressure up to about 100 MPa in a temperature range from (303.15 to 373.15) K in 10 K intervals by using a high-pressure variable-volume view cell. To investigate the effect of different anion on the solubility of CO2 in the [BMP] cation based ionic liquids, we compared three [BMP] cation based systems; [BMP][Tf2N] +, [BMP][TfO] +, and [BMP][MeSO4] + CO2. In all systems, at lower mole fraction of CO2 (below 0.3), the solubility is approximately the same, however above 0.3 mol fraction, the ration between pressure and CO2 mol fraction decreases sharply. Although these experiments have used the same cation, it would appear that the ratio decreases more sharply as the alkyl group...

Thermodynamic modeling of CO2 solubility in ionic liquid ([C n -mim] [Tf2N]; n=2, 4, 6, 8) with using Wong-Sandler mixing rule, Peng-Rabinson equation of state (EOS) and differential evolution (DE) method

Environmental and safety regulations are creating increasing interest in ionic liquids which have been used as alternative solvents for a wide range of industrial applications. Knowing the phase equilibrium of these materials is very important. In this study, the solubility of CO2 in ionic liquid 1-alkyl-3 methylimidazolium bis (trifluoromethylsulfonyl) imide ([Cn-mim][Tf2N]; n=2, 4, 6, 8) was probed with the Peng-Robinson (PR) equation of state (EOS) and Wong-Sandler mixing rule and van Laar model for excess Gibbs free energy. The differential evolution (DE) optimization method was applied to optimize the binary interaction parameter and activity coefficients. Moreover, binary interaction parameters and activity coefficients were presented as mathematical correlations that for various materials have depended on temperature. Our results showed that average absolute derivations of our proposed model were less than other existing models, and by using the aforesaid method better prediction could be achieved.

EFFECTIVE NANOPOROUS COPPER FOR ELECTROCATALYTIC REDUCTION OF CARBON DIOXIDE IN IONIC LIQUID

Nanoporous copper as a robust and efficient electrocatalyst for the electrocatalytic reduction of CO2 in ionic liquid has been successfully developed due to its advantages of high surface area, open porosity and high catalysis efficiency. Nanoporous copper film was prepared by a simple dealloying method and can be directly fabricated on the surface of the electrode. The electrochemical property for electrocatalytic reduction of CO2 in ionic liquid was investigated by cyclic voltammogram (CV), showing enhanced electrocatalytic activity due to its nanoporous structure.

Effect of water in ionic liquid on the separation performance of supported ionic liquid membrane for CO2/N2

Abstract The effect of water content in 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) on CO2/N2 separation performance of polyethersulfone supported ionic liquid membrane has been investigated theoretically and experimentally. A small addition of water in [bmim][BF4] obviously improves the performance of the membrane. CO2 permeance increases from 11.5 to 13.8 GPU and CO2/N2 selectivity increases from 50 to 60, where the water molar fraction increases from 0 to 0.10 at the cross-membrane pressure difference of 0.24 MPa. The improvement of the CO2 permeance at low water content can be attributed to the increase of CO2 diffusivity due to the decrease of viscosity with increasing the water content. While, the CO2 permeance decreases at high water content because of the decreasing CO2 solubility, which is mainly caused by the hydrogen bond interaction between water and [bmim][BF4]. A corrected solubility coefficient model of CO2 in ionic liquid is proposed to evaluate the influence of water–[bmim][BF4] interaction on CO2 solubility. The comparison of CO2 permeance between theoretical values and experimental ones demonstrates that the number of water molecule bound to a [BF4]− is between 1 and 2 in the range of the water content in our research.

Measurement of CO2 Solubility in Ionic Liquids: [BMP][TfO] and [P14,6,6,6][Tf2N] by Measuring Bubble-Point Pressure

Solubility data of carbon dioxide (CO2) in ionic liquids 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([BMP][TfO]) and trihexyltetradecylphosphonium bis(trifluoro-methylsulfonyl)imide ([P14,6,6,6][Tf2N]) are presented at pressures up to about 70 MPa and at temperatures between (303.15 and 373.15) K. The solubility of CO2 in ionic liquids was measured by using a high-pressure variable-volume view cell. At high CO2 concentrations in ionic liquids, the equilibrium pressure increased very steeply. The solubility of CO2 in the ionic liquids decreased with increasing temperature. The experimental data for the CO2 + ionic liquid system were correlated using the Peng−Robinson equation of state.

The Mechanism of Absorption of CO2 in Ionic Liquids: a Computational and Raman Spectroscopy Study

Ionic liquids have the ability to solubilize various gases especially CO2, but the interaction that results in the solubility is unknown. In order to study the mechanism of solubility, a two prong approach, experimental and computational, was undertaken. Raman spectroscopy was performed on various CO2 infused ionic liquids to investigate the shift in the Raman bands which relate to the interactions between the gas and ions. In concert, a computational study was conducted to support the Raman data with possible conformations for the ion-CO2 complexes.

Supercritical CO2/Ionic Liquid Systems: What Can We Extract from Infrared and Raman Spectra?

Infrared (IR) spectroscopy has been successfully applied to study the solubility of supercritical (sc) CO2 in an ionic liquid (IL), the swelling of the IL under scCO2, the diffusion of CO2 in the IL, and the molecular interaction between the IL and scCO2 using a single defined experimental setup. The study has been performed using 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and scCO2 with a pressure of up to 150 bar at 313 K. The solubility of scCO2 in the IL was calculated via the intensity of the CO2 antisymmetric stretching mode, which was measured using the attenuated total reflection (ATR) method. This approach allowed to determine also the swelling of the IL under scCO2 using several IL bands. The knowledge gained about the solubility and swelling allowed the calculation of the molar fraction of CO2 in the IL and the attainment of similar data as previously determined by other methods. The kinetic measurement of the infrared spectra also offered the opportunity to observe the evolution of the concentration of CO2 in the IL and allowed an estimation of the diffusion coefficient of CO2 in IL under high pressure. Finally, information about the molecular interactions between the IL and scCO2 could also be gained in situ using both infrared and Raman spectroscopy.

Absorption of CO2 in the Ionic Liquid 1-n-Hexyl-3-methylimidazolium Tris(pentafluoroethyl)trifluorophosphate ([hmim][FEP]): A Molecular View by Computer Simulations

Using a computational screening methodology, we predicted (AIChE J. 2008, 54, 2717) that the anion tris(pentafluoroethyl)trifluorophosphate ([FEP]) should increase the solubility of CO2 in ionic liquids (ILs) relative to a wide range of conventional anions. This prediction was confirmed experimentally. In this work, we develop a united-atom force field for the [FEP] anion and use the continuous fractional component Monte Carlo (CFC MC) method to predict CO2 absorption isotherms in 1-n-hexyl-3-methylimidazolium ([hmim]) [FEP] at 298.2 and 323.2 K and pressures up to 20.0 bar. The simulated isotherms overestimate the solubility of CO2 by about 20% but capture the experimental trends quite well. Additional Monte Carlo (MC) and molecular dynamics (MD) simulations are performed to study the mechanisms of CO2 absorption in [hmim][FEP] and [hmim][PF6]. The site-site radial distribution functions (RDFs) show that CO2 is highly organized around the [PF6] anion due to its symmetry and smaller size, while less ordered distributions were found around [FEP] and [hmim]. However, more CO2 can be found in the first coordination shell of [FEP] compared with [PF6]. The structures of ILs, illustrated by P-P radial distribution functions, change very little upon the addition of as much as 50 mol % CO2. An energetic analysis shows that the van der Waals interactions between CO2 and ILs are generally larger than electrostatic interactions.

Measurement and correlation of supercritical CO2 and ionic liquid systems for design of advanced unit operations

Ionic liquids combined with supercritical fluid technology hold great promise as working solvents for developing compact processes. Ionic liquids, which are organic molten salts, typically have extremely low volatility and high functionality, but possess high viscosities, surface tensions and low diffusion coefficients, which can limit their applicability. CO2, on the other hand, especially in its supercritical state, is a green solvent that can be used advantageously when combined with the ionic liquid to provide viscosity and surface tension reduction and to promote mass transfer. The solubility of CO2 in the ionic liquid is key to estimating the important physical properties that include partition coefficients, viscosities, densities, interfacial tensions, thermal conductivities and heat capacities needed in contactor design. In this work, we examine a subset of available high pressure pure component ionic liquid PVT data and high pressure CO2-ionic liquid solubility data and report new correlations for CO2-ionic liquid systems with equations of state that have some industrial applications including: (1) general, (2) fuel desulfurization, (3) CO2 capture, and (4) chiral separation. New measurements of solubility data for the CO2 and 1-butyl-3-methylimidazolium octyl sulfate, [bmim][OcSO4] system are reported and correlated. In the correlation of the CO2 ionic liquid phase behavior, the Peng-Robinson and the Sanchez-Lacombe equations of state were considered and are compared. It is shown that excellent correlation of CO2 solubility can be obtained with either equation and they share some common characteristics regarding interaction parameters. In the Sanchez-Lacombe equation, parameters that are derived from the supercritical region were found to be important for obtaining good correlation of the CO2-ionic liquid solubility data.

The Mechanism of Absorption of CO2 in Ionic Liquids: a Computational and Raman Spectroscopy Study

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Influence of the enzyme concentration on the phase behaviour for developing a homogeneous enzymatic reaction in ionic liquid–CO2 media

A homogeneous enzymatic reaction in an ionic liquid (IL)–CO2 medium integrated with the separation of the product is proposed. It takes advantage of the miscibility switch phenomenon using CO2, which is able to force two immiscible phases to form one homogeneous phase to perform the reaction. After completion of the reaction the homogeneous fluid phase is split in two or three phases upon pressure decrease in order to facilitate the product recovery. For this purpose the enzymeCandida antarctica lipase B (CaL B) and the IL 1-hydroxy-1-propyl-3-methyl imidazolium nitrate (HOPMImNO3) are used. In this study the solubility of CO2 in solutions of CaL B in HOPMImNO3 was experimentally determined using the Cailletet apparatus, which operates according to the synthetic method. Concentrations of the enzyme vary from 3 to 12% by weight, and concentrations of CO2 from 5 to 20 mol% were investigated in a temperature range from 30 to 75 °C and pressures up to 12 MPa were applied. No precipitation of the enzyme was observed when dissolving CO2 in the IL. At constant CO2/IL ratios the pressure of the bubble points remained almost unchanged with the enzyme concentration. Triacetin tests showed that the reduction of the activity of the enzyme after storage for three months in liquid HOPMImNO3 was only of the order of 20%. Recovery and purification of the IL was possible by precipitation of the enzyme using isopropanol (IPA) as an anti-solvent.

Why Is the Partial Molar Volume of CO2 So Small When Dissolved in a Room Temperature Ionic Liquid? Structure and Dynamics of CO2 Dissolved in [Bmim+] [PF6-

When supercritical CO2 is dissolved in an ionic liquid, its partial molar volume is much smaller than that observed in most other solvents. In this article we explore in atomistic detail and explain in an intuitive way the peculiar volumetric behavior experimentally observed when supercritical CO2 is dissolved in 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim+] [PF6(-)]). We also provide physical insight into the structure and dynamics occurring across the boundary of the CO2 ionic liquid interface. We find that the liquid structure of [Bmim+] [PF6(-)] in the presence of CO2 is nearly identical to that in the neat ionic liquid (IL) even at fairly large mole fractions of CO2. Our simulations indicate, in agreement with experiments, that partial miscibilities of one fluid into the other are very unsymmetrical, CO2 being highly soluble in the ionic liquid phase while the ionic liquid is highly insoluble in the CO2 phase. We interpret our results in terms of the size and shape of spontaneously forming cavities in the ionic liquid phase, and we propose that CO2 occupies extremely well-defined locations in the IL. Even though our accurate prediction of cavity sizes in the neat IL indicates that these cavities are small compared with the van der Waals radius of a single carbon or oxygen atom, CO2 appears to occupy a space that was for the most part a priori "empty".

Solubilities and Diffusivities of Carbon Dioxide in Ionic Liquids: [bmim][PF6] and [bmim][BF4

Gaseous carbon dioxide (CO2) absorption measurements in l-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and l-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) were made using a commercial gravimetric microbalance at temperatures of 283.15, 298.15, 323.15, and 348.15 K and at pressures under 2 MPa. Gas solubilities were determined from absorption saturation (equilibrium) data at each fixed temperature and pressure. The experimental solubility data of CO2 in ionic liquids have been successfully correlated for the first time using a simple cubic equation of state (EOS). Some phase behaviors of CO2 and ionic liquid mixtures as well as Henry's law constants and the volume change of solutions are predicted well with the present EOS model. From time-dependent absorption data, binary diffusion coefficients of CO2 in the ionic liquids have been obtained for the first time by the use of a simple diffusion model. Magnitudes in the observed diffusion coefficients are 10-10 to 10-11 m2 s-1, which are about 10−100 times lower than typical values, found in various organic liquids.

Surprisingly high solubility of the ionic liquid trihexyltetradecylphosphonium chloride in dense carbon dioxide

For the first time an ionic liquid is observed to be appreciably miscible in dense CO2, up to about 7 mass%. The solubility in CO2 is more than one order of magnitude higher than for alkanes of similar carbon number. The investigated P–T phase behavior of four isopleths for the ionic liquid trihexyltetradecylphosphonium chloride in CO2 shows a concentration independence of the isopleths for the investigated compositions similar to the known phase behavior of organic compounds such as adamantane, octacosane and squalane in supercritical CO2 at high pressures. Overall, the results demonstrate that a single-phased ionic liquid–CO2 solvent system for chemical synthesis is conceivable.