(Liquid + liquid) phase equilibria of 1-alkyl-3-methylimidazolium methylsulfate with alcohols,or ethers,or ketones

Solubilities of binary mixtures that contain a room-temperature ionic liquid and an organic solvent – namely, 1,3-dimethylimidazolium methylsulfate, [mmim][CH₃SO₄], or 1-butyl-3-methylimidazolium methylsulfate, [bmim][CH₃SO₄] with an alcohol (hexan-1-ol, or octan-1-ol, or nonan-1-ol, or decan-1-ol), or an ether (dipropyl ether, or dibutyl ether, or methyl-1,1-dimethylethyl ether, or methyl-1,1-dimethylpropyl ether), or a ketone (pentan-2-one, or pentan-3-one, or hexan-2-one, or heptan-4-one, or cyclopentanone) – have been measured by a visual method from T = 270 K to the boiling temperature of the solvent. The (liquid + liquid) equilibria curves were predicted by the COSMO-RS method. For [bmim][CH₃SO₄], the COSMO-RS predictions correspond better with experimental results than do the predictions for [mmim][CH₃SO₄].Complete miscibility has been observed in the systems of [mmim][CH₃SO₄] with water and with alcohols ranging from methanol to octan-1-ol and that of [bmim][CH₃SO₄] with water and with alcohols ranging from methanol to decan-1-ol at the temperature T = 310 K.     

Vapor pressures and activity coefficients of binary mixtures of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with acetonitrile and tetrahydrofuran

A new apparatus for the determination of VLE has been constructed which works for absolute pressure measurements as well as for measuring differential pressures. The first results obtained are (vapor + liquid) equilibria (VLE) of binary mixtures containing acetonitrile or tetrahydrofuran and the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIm][NTf2] by using the absolute pressures method. VLE measurements were carried out over the whole concentration range at four different temperatures between 293.15 K and 313.15 K. Activity coefficients (γ₁) of the solvents in [EMIm][NTf2] and their osmotic coefficients (ϕ₁) have been determined from the VLE data.     

(Vapor + liquid) equilibria of binary mixtures containing light alcohols and ionic liquids

This work presents (vapor + liquid) equilibrium (VLE) of binary mixtures containing methanol or ethanol and three imidazolium based ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium acetate, and 1-butyl-3-methylimidazolium hydrogen sulfate. VLE measurements were carried out over the whole range of composition between (283.15 and 298.15) K using a static apparatus. Activity coefficients γ_i of these solvents in the ionic liquids have been determined from the VLE data and correlated using the NRTL model. The results show that the NRTL model can be applied successfully with systems containing ionic liquids.     

Phase behavior of {carbon dioxide + [bmim][Ac]} mixtures

Carbon dioxide solubility {(vapor + liquid) equilibria: VLE} in ionic liquid, 1-butyl-3-methylimidazolium acetate ([bmim][Ac]), has been measured with a gravimetric microbalance at four isotherms about (283, 298, 323, and 348) K up to about 2 MPa. (Vapor + liquid + liquid) equilibria (VLLE: or liquid–liquid separations) have also been investigated with a volumetric method used in our previous works, since the present analysis of the VLE data using our equation-of-state model has predicted the VLLE at CO₂-rich side solutions. The prediction for the VLLE has been confirmed experimentally. CO₂ solubilities at the ionic liquid-rich side show extremely unusual behaviors; CO₂ dissolves in the ionic liquid to a great degree, but there is hardly any vapor pressure above these mixtures up to about 20 mol% of CO₂. It indicates that CO₂ may have formed a non-volatile or very low vapor pressure molecular complex with the ionic liquid. The thermodynamic excess properties (enthalpy, entropy, and Gibbs free energy) of the present system do support such a complex formation. We have conducted several other experiments to investigate the complex formation (or chemical reactions), and conclude that a minor chemical reaction occurs but the complex formation is reversible without much degradation of the ionic liquid.     

Phase equilibria study of the binary systems (N-butyl-3-methylpyridinium tosylate ionic liquid + an alcohol)

Isothermal (vapour + liquid) equilibrium data, (VLE) have been measured by an ebulliometric method for the binary mixtures of ionic liquid (IL) {N-butyl-4-methylpyridinium tosylate (p-toluenesulfonate) [BMPy][TOS] + ethanol, 1-propanol, and 1-butanol} at T = 373.15 K over the pressure range from p = 0 kPa to p = 110 kPa. (Solid + liquid) phase equilibria (SLE) for the binary systems: ionic liquid (IL) {N-butyl-4-methylpyridinium tosylate (p-toluenesulfonate) [BMPy][TOS] + ethanol and 1-propanol} have been determined at ambient pressure. A dynamic method was used over a broad range of mole fractions and temperatures from (320 to 390) K. For the binary systems containing alcohol, it was noticed that with increasing chain length of alcohol vapour pressure of the mixture and the solubility of the IL decreases. Well-known Wilson, NRTL, and UNIQUAC equations have been used to correlate simultaneously the experimental VLE and SLE data sets with the same parameters. The excess molar Gibbs free energy, G^E function in general was negative in all systems at high temperature (VLE) and positive at low temperatures (SLE).     

Relative hydrophobicity of equilibrium phases in biphasic systems (ionic liquid + water)

Partition coefficients for a series of dinitrophenylated (DNP) amino acids in biphasic systems composed of hydrophobic ionic liquids and water were experimentally determined. The ionic liquids used were three 1-alkyl-3-methylimidazolium tetrafluoroborates, [C_nmim][BF₄], with alkyl chain substituents hexyl, octyl, and decyl. The liquid–liquid phase diagram for the system ([C₁₀mim][BF₄] + water) was experimentally determined. DNP amino acids distribute preferentially to the IL-rich phase and ([C₁₀mim][BF₄] + water) was found to be the system with the lowest partition coefficients for the solutes studied. The experimental partition coefficients decrease as the size of the alkyl side chain in the ionic liquids increases. The free energy of transfer of a methylene group between phases was calculated through the partition coefficients, which provides a measure of the relative hydrophobicity of the equilibrium phases. It was found that the system ([C₁₀mim][BF₄] + water) presents a lower free energy (and thus a lower relative hydrophobicity) than the system ([C₈mim][BF₄] + water). In order to better understand this result, the micellar behavior of the three ionic liquids was studied. Electrical conductivities of several aqueous solutions of the ionic liquids were measured to determine the critical micelle concentration (CMC) and the degree of micelle ionization, α, of the three ionic liquids. From these two properties it was possible to obtain the free energy of micellization, ΔG_mic, for the ionic liquids.     

Activity coefficients at infinite dilution of organic solutes in the ionic liquid trihexyl(tetradecyl)phosphonium tetrafluoroborate using gas–liquid chromatography at T = (313.15, 333.15, 353.15, and 373.15) K

Activity coefficients at infinite dilution have been measured by gas–liquid chromatography for 27 organic solutes (n-alkanes, 1-alkenes, 1-alkynes, cycloalkanes, aromatics, alcohols, and ketones) in the ionic liquid trihexyl(tetradecyl)phosphonium tetrafluoroborate [3C₆C₁₄P][BF₄]. The measurements were carried out at four different temperatures viz. T = (313.15, 333.15, 353.15, and 373.15) K. From the experimental data, partial molar excess enthalpy values at infinite dilution were calculated for the experimental temperature range. The selectivity values for the separation of n-hexane/benzene, cyclohexane/benzene, and methanol/benzene mixtures were determined from the experimental infinite dilution activity coefficient values. These values were compared to those available in the literature for other ionic liquids and commercial solvents, so as to assess the feasibility of employing [3C₆C₁₄P][BF₄] in solvent-enhanced industrial separations.     

Isothermal (vapour + liquid) equilibrium (VLE) for binary mixtures containing diethyl carbonate,phenyl acetate,diphenyl carbonate,or ethyl acetate

The isothermal (vapour + liquid) equilibrium (VLE) (P–T–x_i–y_i) was determined the binary systems of (ethyl acetate + diethyl carbonate) from T = (373.2 to 453.2) K, (ethyl acetate + phenyl acetate) at T = 373.2 K, and (diethyl carbonate + phenyl acetate) at T = 373.2 K, while the VLE (P–T–x_i) of three diphenyl carbonate-containing binary systems was also determined experimentally at temperatures from (373.2 to 453.2) K. The experimental results show no azeotrope formation and near ideal solution behaviour for each binary system. These new VLE (P–T–x_i–y_i) data have been passed by the point, area, and infinite dilution thermodynamic consistency tests. The Wilson-HOC, the NRTL-HOC, and the UNIQUAC-HOC models were applied to correlate the VLE results and the optimal values of the model parameters have been determined through data reduction. Comparable results were obtained from these three models.     

Use of selective ionic liquids and ionic liquid/salt mixtures as entrainer in a (vapor + liquid) system to separate n-heptane from toluene

During the last years, a large number of studies have evaluated the ability of ionic liquids (ILs) to separate aromatic from aliphatic hydrocarbons by liquid extraction. Nevertheless, in order to design a global process, a post-extraction step based on the aromatic recovery from the extract stream and the regeneration of the IL is required. Taking into account the negligible vapor pressure of the ILs, the use of separation units based on the difference of volatility among the components of the extract could be an appropriate way. However, that requires additional (vapor + liquid) equilibrium (VLE) data, which are scarce today. In this work, the isothermal VLE data for {n-heptane + toluene + 1-ethyl-3-methylimidazolium thiocyanate ([EMim][SCN])} and {n-heptane + toluene + 1-butyl-3-methylimidazolium thiocyanate ([BMim][SCN])} mixtures were experimentally measured at T = (323.2, 343.2 and 363.2) K over the whole composition range within the rich-IL miscibility region. For that, a static headspace gas chromatograph (HS-GC) was used. In addition, the non-random two liquids (NRTL) thermodynamic model was satisfactory applied to correlate the experimental VLE data.Finally, the effect of thiocyanate-based inorganic salts (AgSCN, Co(SCN)₂ and CuSCN) on the phase behavior of the above mentioned mixtures were also analyzed through the experimental determination of the isothermal VLE of the pseudo-ternary systems {n-heptane + toluene + [EMim][SCN]/salt mixture}.The obtained results show that the use of pure thiocyanate-based ILs as entrainer increases the n-heptane relative volatility from toluene whereas the addition of inorganic salts has not led to an improvement of these results.     

High-pressure phase equilibrium in the {carbon dioxide (1) + 1-chloropropane (2)} binary system

The current study reports original vapour-liquid equilibrium (VLE) for the system {CO₂ (1) + 1-chloropropane (2)}. The measurements have been performed over the entire pressure-composition range for the T = (303.15, 313.15 and 328.15) K isotherms. The values obtained have been used for comparison of four predictive approaches, namely the equation of state (EoS) of Peng and Robinson (PR), the Soave modification of Benedict–Webb–Rubin (SBWR) EoS, the Critical Point-based Revised Perturbed-Chain Association Fluid Theory (CP-PC-SAFT) EoS, and the Conductor-like Screening Model for Real Solvents (COSMO-RS). It has been demonstrated that the three EoS under consideration yield similar and qualitatively accurate predictions of VLE, which is not the case for the COSMO-RS model examined. Although CP-PC-SAFT EoS exhibits only minor superiority in comparison with PR and SBWR EoS in predicting VLE in the system under consideration, its relative complexity can be justified when taking into account the entire thermodynamic phase space and, in particular, considering the liquid densities and sound velocities over a wider pressure-volume-temperature range.     

Vapor pressures,excess enthalpies,and specific heat capacities of the binary working pairs containing the ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate

In present research the binary solutions containing ionic liquid (IL), 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM] [DMP]), are considered as new working pairs for absorption heat pumps or absorption refrigerators. The IL was synthesized in the lab and mixed with water, ethanol, or methanol. Experimental (vapor + liquid) equilibrium (VLE) of these binary systems was measured at different mole fractions ranging from 0.1 to 0.5 and was correlated by the NRTL equation within the average relative deviation of 2%, which means that the (vapor + liquid) equilibrium of these binary solutions containing ionic liquid can be predicted by traditional non-electrolyte solution model. Meanwhile these binary solutions are a negative deviation from Raoult’s law. Excess enthalpy of these binary systems was measured at the temperature of T = 298.15 K and at the pressure of 1 atm. The results indicate that the mixing processes of [EMIM] [DMP] with water, ethanol, or methanol are exothermal, which is a very important characteristic for working pairs used in absorption heat pumps or in absorption refrigerators.     

Isothermal (vapour + liquid) equilibrium and thermophysical properties for (1-butyl-3-methylimidazolium iodide + 1-butanol) binary system

Experimental isothermal (vapour + liquid) equilibrium (VLE) data are reported for the binary mixture containing 1-butyl-3-methylimidazolium iodide ([bmim]I) + 1-butanol at three temperatures: (353.15, 363.15, and 373.15) K, in the range of 0 to 0.22 liquid mole fraction of [bmim]I. Additionally, refractive index measurements have been performed at three temperatures: (293.15, 298.15 and 308.15) K in the whole composition range. Densities, excess molar volumes, surface tensions and surface tension deviations of the binary mixture were predicted by Lorenz–Lorentz (n_D-ρ) mixing rule. Dielectric permittivities and their deviations were evaluated by known equations. (Vapour + liquid) equilibrium data were correlated with Wilson thermodynamic model while refractive index data with the 3-parameters Redlich–Kister equation by means of maximum likelihood method. For the VLE data, the real vapour phase behaviour by virial equation of state was considered. The studied mixture presents S-shaped abatement from the ideality. Refractive index deviations, surface tension deviations and dielectric permittivity deviations are positive, while excess molar volumes are negative at all temperatures and on whole composition range. The VLE data may be used in separation processes design, and the thermophysical properties as key parameters in specific applications.     

Activity coefficients at infinite dilution of organic solutes in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate using gas–liquid chromatography at T = (313.15, 323.15, and 333.15) K

Activity coefficients at infinite dilution were determined for 24 solutes: n-alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, alkylbenzenes and alcohols in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate, [OMIM][PF₆], by gas–liquid chromatography at three different temperatures T = (313.15, 323.15, and 333.15) K. The partial molar excess enthalpy values at infinite dilution were calculated from the experimental data over the same temperature range. Capacities and selectivities at infinite dilution for the systems hexane/benzene and methanol/benzene were determined from the experimental data and compared to the literature values for other ionic liquids, as well as for industrial molecular solvents. The influence of the cation and anion of the ionic liquid on the activity coefficient is discussed, as well as the usefulness of [OMIM][PF₆] in separating organic liquids.     

Thermodynamic properties of {(NH4)2SO4(aq) + Li2SO4(aq)} and {(NH4)2SO 4(aq) + Na2SO4(aq)} at a temperature of 298.15 K

The water activities and osmotic coefficients of aqueous solutions of {(NH₄ )₂SO ₄ +  Li ₂SO ₄} and {(NH₄ )₂SO ₄ +  Na ₂SO ₄} have been determined at a temperature of 298.15 K with a hygrometric method, at molalities in the region 0.2 mol · kg ^− 1 to saturation of the solutes for different fractional ionic-strengthsy =  0.2, 0.5, and 0.8 of (NH ₄)₂SO ₄. The experimental results are compared with the predictions obtained from our extended compared additivity model, as well as the models reported by Zdanovskii, Stokes and Robinson, Pitzer, and Lietzke-Stoughton. From these measurements, parameters of Pitzers model have been determined. These were used to predict solute activity coefficients in the mixture and calculate the excess Gibbs function at total molalities for different y for these systems.     

A comprehensive study of {γ-butyrolactone + 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide} binary mixtures

Density, electrical conductivity and viscosity of binary liquid mixtures of γ-butyrolactone, (GBL) with 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, [pmim][NTf₂], were measured at different temperatures from (293.15 to 323.15) K and at atmospheric pressure (p = 0.1 MPa) over the whole composition range. Excess molar volumes have been calculated from the experimental densities and were fitted with Redlich–Kister’s polynomial equation. Other volumetric properties have been also calculated in order to obtain information about interactions between GBL and selected ionic liquid. All the results are compared with those obtained for binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][NTf₂], with GBL. From the viscosity measurements, the Angell strength parameter was calculated for pure ionic liquid indicating that [pmim][NTf₂] is a “fragile” liquid. Electrical conductivity results were discussed in the scope of Bahe–Varela theoretical model.     

The precise measurement of the (vapour + liquid) equilibrium properties for (CO2 + isobutane) binary mixtures

Recently, it has been suggested that natural working fluids, such as CO₂, hydrocarbons, and their mixtures, could provide a long-term alternative to fluorocarbon refrigerants. (Vapour + liquid) equilibrium (VLE) data for these fluids are essential for the development of equations of state, and for industrial process such as separation and refinement. However, there are large inconsistencies among the available literature data for (CO₂ + isobutane) binary mixtures, and therefore provision of reliable and new measurements with expanded uncertainties is required. In this study, we determined precise VLE data using a new re-circulating type apparatus, which was mainly designed by Akico Co., Japan. An equilibrium cell with an inner volume of about 380 cm³ and two optical windows was used to observe the phase behaviour. The cell had re-circulating loops and expansion loops that were immersed in a thermostatted liquid bath and air bath, respectively. After establishment of a steady state in these loops, the compositions of the samples were measured by a gas chromatograph (GL Science, GC-3200). The VLE data were measured for CO₂/propane and CO₂/isobutane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were compared with the available literature data and with values predicted by thermodynamic property models.     

Glass transition behaviour of ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H2O mixed solutions

Here, we have measured the glass transition temperature (T_g) of the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H₂O mixed solutions as a function of H₂O concentration (x mol% H₂O). The glass-forming composition region was also determined. Contrary to the results of the quaternary ammonium type of ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate–H₂O mixed solutions, we did not observed the multiple glass transition behaviour. We also measured the glassy Raman spectra of the solutions at T = 77 K. We find that the “nearly free” hydrogen bonded Raman band of water molecules in the aqueous [bmim][BF₄] solution exists up to around x = 60 mol% H₂O, even at T = 77 K.     

Cation effect of ammonium imide based ionic liquids in alcohols extraction from alcohol-alkane azeotropic mixtures

During recent last years, outstanding properties of ionic liquids such as low melting point, large liquid range and negligible volatility have turned them into possible volatile organic solvents replacers to break alcohol-alkane azeotropic mixtures. On this basis, two ionic liquids, butyltrimethylammoniumbis(trifluoromethylsulfonyl)imide, [BTMA][NTf₂], and tributylmethylammoniumbis(trifluoromethylsulfonyl)imide, [TBMA][NTf₂], were studied through ternary liquid+liquid equilibrium (LLE) of {alkane(1) + alcohol (2) + IL(3)} at T = 298.15 K and atmospheric pressure in order to consider the effect of ionic liquid cation alkyl chain length on the extraction process.The ILs capability as azeotrope breakers was determined by the calculation of parameters such as solute distribution ratio, β, and selectivity, S and this capability was compared with other bis (trifluoromethylsulfonyl)imide based ionic liquids from literature. The consistency of tie-line data was ascertained by applying the Othmer–Tobias and Hand equations. Finally, the experimental LLE were correlated by the Non Random Two Liquid (NRTL) thermodynamic model.     

STM tip-induced nanostructuring of Zn in an ionic liquid on Au(1 1 1) electrode surfaces

In this communication, the “jump-to-contact” based STM tip-induced nanostructuring is extended to BMIBF₄ ionic liquid for the first time. It is demonstrated successfully that Zn, as an example of less noble metal and being hard to deposit from aqueous solutions, can be nanostructured on Au(1 1 1) surfaces in the ionic liquid. Due to the large effective tunnel barrier in the ionic liquid, the Z-pulse required to create Zn nanoclusters in ionic liquid is about twice as large as for Cu nanoclusters of similar size in aqueous solutions. Patterns as well as large-scale arrays consisting of 100 × 100 Zn nanoclusters have been produced. The present work demonstrates the feasibility for surface nanostructuring a new category of systems that have not been possible in aqueous solutions, which could open up new opportunities for studies of nanoscopic effects from various aspects.