Search

We have developed a ternary equation of state (EOS) model for the N2O/CO2/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) system in order to understand separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a generic RK (Redlich−Kwong) EOS, with empirical interaction parameters for each binary system. The interaction parameters have been determined using our measured VLE (vapor−liquid equilibrium) data for N2O/[bmim][BF4] and CO2/[bmim][BF4] and literature data for N2O/CO2. The binary EOS models for the N2O/[bmim][BF4] and CO2/[bmim][BF4] systems correctly predicted the liquid−liquid phase separation found in VLLE experiments. The validity of the ternary EOS model has been checked by conducting VLE experiments for the N2O/CO2/[bmim][BF4] system over a range in temperature from 296 to 315 K. With this EOS model, solubility (VLE) behavior has been calculated for various (T, P, and feed compositions) conditions. For both large and small N2O/CO2feed ratios, the N2O/CO2gas selectivity [αN2O/CO2= (yN2O/xN2O)/(yCO2/xCO2)] is α = 1.4−1.5, compared with (α = 0.96−0.98) in the absence of ionic liquid. While the concentration of the ionic liquid does not affect the selectivity, the addition of an ionic liquid provides the only practical means of separating CO2and N2O. [ABSTRACT FROM AUTHOR]

We have developed a ternary equation of state (EOS) model for the CO2/H2S/1-butyl-3-methylimidazolium methylsulfate ([bmim][MeSO4]) system to understand separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a modified RK (Redlich−Kwong) EOS, with empirical interaction parameters for each binary system. The interaction parameters have been determined using our measured VLE (vapor−liquid equilibrium) data for H2S/[bmim][MeSO4] and literature data for CO2/[bmim][MeSO4] and CO2/H2S. Due to limited VLE data for H2S/[bmim][MeSO4], we have also used VLLE (vapor−liquid−liquid equilibrium) measurements to construct the EOS model. The VLLE for H2S/[bmim][MeSO4] is highly asymmetric with a narrow (mole fraction H2S between 0.97 and 0.99) LLE gap which is the first such case reported in the literature and exhibits Type V phase behavior, according to the classification of van Konynenburg and Scott. The validity of the ternary EOS model has been checked by conducting VLE experiments for the CO2/H2S/[bmim][MeSO4] system. With this EOS model, solubility (VLE) behavior has been calculated for various (T, P, and feed compositions) conditions. For large (9/1) and intermediate (1/1) CO2/H2S feed ratios, the CO2/H2S gas selectivity is high (10 to 13, compared with <4.5 in the absence of ionic liquid) and nearly independent of the amount of ionic liquid added. For small CO2/H2S mole ratios (1/9) at 298.15 K, increasing the ionic liquid concentration increases the CO2/H2S gas selectivity from about 7.4 to 12.4. For high temperature (313.15 K) and large CO2/H2S feed ratios, the addition of the ionic liquid provides the only means of separation because no VLE exists for the CO2/H2S binary system without the ionic liquid. [ABSTRACT FROM AUTHOR]

The absorption cooling cycle has been in use for more than 100 years. Although the vapor compression cycle is now used for most air-conditioning and refrigeration applications, the well-known refrigerant−absorbent systems (water−LiBr and ammonia−water) are still being used for space cooling and industrial refrigeration. Recently, absorption cooling cycles using water + room-temperature ionic liquids (RTILs) have been proposed as a replacement for the water + LiBr system. There have been a few reports in the literature since about the year 2000 on the solubility of water in RTILs, and some of the hydrophilic RTILs show extremely high mutual solubility with water, indicating formation of chemical complexes. Almost all solubility data have been correlated with the use of activity (or solution) models. In the present report, we apply an equation of state (EOS) model in order to understand the solubility characteristics, as well as the chemical complex formation, consistently with the same thermodynamic model. Also, such a model is convenient for estimating the performance of the absorption cooling cycle, as we have demonstrated in the past for the absorption cycle performance of various hydrofluorocarbons (HFCs) + solvents and ammonia + RTILs. The present purpose is to examine the feasibility of using water and RTILs in an absorption cooling cycle and to show some promising results for this application. [ABSTRACT FROM AUTHOR]

Liquid−liquid equilibria in binary mixtures of substituted benzenes (toluene, ethylbenzene, propylbenzene, xylene isomers, trimethylbenzene isomers, aniline, nitrobenzene, phenol, and benzaldehyde) with ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]), have been measured using a mass–volume technique over a temperature range from about (293 to 373) K. Trends in both the polarity and molecular size of the solute with the immiscibility gap were discovered for the alkyl-substituted benzenes. In general, as the polarity increased and the molecular size decreased, the immiscibility gap became smaller. The nonalkyl-substituted benzenes containing functional groups (−NH2, −NO2, −OH, and −CHO) were completely soluble in [emim][Tf2N] over the composition and temperature range studied. The excess molar volumes for the ionic liquid-rich side solutions range from (−1 to −5) cm3·mol−1, and the magnitudes are somewhat larger than those of ordinary liquid solutions. Observed LLE are well correlated by use of the nonrandom two liquid (NRTL) solution model. [ABSTRACT FROM AUTHOR]

Liquid−liquid equilibria in binary mixtures of halogenated benzene (chlorobenzene, bromobenzene, and iodobenzene) with ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]), have been measured using a volumetric method over a temperature range from about (293 to 373) K. A general trend between the molecular size of the solute (monohalogenated benzene) and the immiscibility gap was discovered; the larger the size, the wider the gap. No correlation with the dipole moment exists, although other intermolecular interactions (higher-order moments, π-electron effects, and hydrogen bonding) may also play a role. The excess molar volumes range from (−1 to −5) cm3·mol−1; the magnitudes are larger than those of ordinary liquid solutions. Observed LLE are well correlated by use of the nonrandom two liquid (NRTL) solution model. [ABSTRACT FROM AUTHOR]

The solubility (vapor−liquid equilibria) of carbon dioxide (CO2) has been measured in ionic liquids, 1-ethyl-3-methylimidazolium acetate ([emim][Ac]), 1-ethyl-3-methylimidazolium trifluoroacetate ([emim][TFA]), and a mixture containing a fixed mole ratio of 49.98 ([emim][Ac])/50.02 ([emim][TFA]) using a gravimetric microbalance at three temperatures (298.1, 323.1, and 348.1) K and pressures up to about 2 MPa. The [emim][Ac] strongly (chemically) absorbed CO2with hardly any vapor pressure above the mixture up to about 20 % mole fraction of CO2at 298.1 K. The [emim][TFA] did not show the same behavior and physically absorbed CO2. The ionic liquid mixture containing equimolar amounts of [emim][Ac] and [emim][TFA] showed a combination of both chemical and physical effects, and the CO2solubility was well predicted at a fixed pressure using either a molar average of the pure component solubilities or a model based on linear isobaric lines in the ternary phase diagram. The binary pressure−temperature (PTx) data at 298.1 K have also been analyzed by use of an equation-of-state (EOS) model, and predictions at higher temperatures and of the ternary system are reasonable. [ABSTRACT FROM AUTHOR]

A binary system of benzene and hexafluorobenzene is known as a system with famous double azeotropes (minimum-and-maximum pressure azeotropes at the isothermal VLE (vapor−liquid equilibrium)). In order to understand how these azeotropic behaviors will be affected by interactions with an ionic liquid, solubility experiments for benzene + ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [emim][Tf 2N], and hexafluorobenzene + [emim][Tf 2N] systems have been carried out at temperatures of about 283, 298, and 318 K. Both binary systems show immisciblity gaps with concentration ranges from about 77 to 100 and from about 66 to 100 mol % for benzene and hexafluorobenzene systems, respectively. The observed solubility data have been used to develop equation-of-state (EOS) models (with a generic Redlich−Kwong cubic equation) for these binary systems. As for the binary system of benzene and hexafluorobenzene, VLE data in the literature have been employed to develop the EOS model. Thus, binary and ternary phase diagrams for the present three components have been constructed using the present binary interaction parameters. Then, extractive separations of the azeotropes are discussed based on the present EOS model. [ABSTRACT FROM AUTHOR]

Solubilities of hydrofluorocarbon-4310mee (threo-2,3-dihydrodecafluoropentane and erythro-2,3-dihydrodecafluoropentane) as well as their deuterated species in room-temperature ionic liquids (RTILs) have been studied. RTILs used here are 1-butyl-3-methylimidazolium hexafluorophosphate, bmimPF6, 1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4, and 1-ethyl-3-methylimidazolium tetrafluoroborate, emimBF4. All systems showed limited miscibility, and the liquid−liquid phase equilibria (LLE) have been investigated with the volumetric and cloud-point methods. It was found that the threo-isomer is more soluble than the erythro-isomer in the present RTILs, and the LLE curves of the threo-isomers in the RTILs possess lower critical solution temperatures (LCSTs). The deuterated isotope effect on the solubility was found to be minor, but the deuterated isomers did show slightly better miscibility than the nondeuterated isomers. This trend of the isotope effect is qualitatively consistent with the case of alcohol RTIL mixtures in the literature, although the LLE behavior is different (LCSTs vs upper critical solution temperatures (UCSTs)). [ABSTRACT FROM AUTHOR]

Solubility behaviors of binary HFC-125 (CF 3−CF 2H), HFE-125 (CF 3−O−CF 2H), HFC-143a (CF 3−CH 3), and HFE-143a (CF 3−O−CH 3) systems with room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf 2N]) have been studied using a gravimetric microbalance method from (283 to 348) K and/or volumetric and cloud-point methods. Vapor–liquid equilibrium (VLE) data for HFC-125 + [emim][Tf 2N] and HFE-125 + [emim][Tf 2N] systems have been well correlated with our equation-of-state (EOS) model, which predicted vapor–liquid–liquid equilibria (VLLE) for both of these binary systems, and the VLLE have been experimentally proved. As for the binary systems of HFC-143a + [emim][Tf 2N] and HFE-143a + [emim][Tf 2N], only VLLE experiments have been made, and partial miscibility (temperature and composition: VLLE− Tx) data are well correlated with the NRTL (nonrandom two-liquids) activity model. While the immiscibility gap of the HFC-125 binary system is smaller than that of the HFE-125 system, the immiscibility behaviors for the HFC-143a and HFE-143a systems are opposite; the HFE-143a system is more soluble. [ABSTRACT FROM AUTHOR]

Binary liquid−liquid equilibria (LLE) in mixtures of five hydrofluoroethers and room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, have been measured for the first time using the volume−mass method. All five binary systems show large immiscibility gaps. The ionic liquid-rich side solutions become increasingly more soluble in HFE (hydrofluoroether) as the HFE normal boiling point decreases. Observed LLE are well correlated by use of the nonrandom two liquid (NRTL) solution model. The excess molar volumes of the HFE and ionic liquid rich side solutions are small and similar to ordinary binary mixtures which is opposite to what we have previously reported with hydrofluorocarbons (HFCs) in ionic liquids. Therefore, the insertion of an ether oxygen has changed the liquid structure of HFEs vs HFCs in ionic liquids. [ABSTRACT FROM AUTHOR]

Solubility behaviors of CFC-113 (CFCl2−CF2Cl), CFC-113a (CCl3−CF3), CFC-114 (CF2Cl−CF2Cl), CFC-114a (CFCl2−CF3), HCFC-123 (CHCl2−CF3), HCFC-123a (CHClF−CF2Cl), HCFC-124 (CHFCl−CF3), HCFC-124a (CHF2−CF2Cl), HFC-134 (CHF2−CHF2), and HFC-134a (CH2F−CF3) in room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (emimTf2N) have been investigated using a gravimetric microbalance method from (283 to 348) K or volumetric and cloud-point methods. In the case of the perhalogenated compounds (CFC-113, CFC-114, and their isomers), the solubility behavior between isomers in the ionic liquid is practically identical with large immiscibility gaps. This suggests that the (present) ionic liquid cannot be used for these isomer separations. However, the monohydrogen substituted halocarbons (HCFC-123, HCFC-124, and their isomers) begin to show some difference (liquid−liquid immiscibility gap) in the ionic liquid. The isomer effect on the solubility in the ionic liquid becomes significant for the dihydrogen-substituted halocarbons (HFC-134 and HFC-134a), and these isomers can be separated using emimTf2N as an entrainer in an extractive distillation. This observation is consistent with our earlier findings for various HFCs in ionic liquids. [ABSTRACT FROM AUTHOR]

Binary liquid−liquid equilibria (LLE) in mixtures of 1,3-propanediol and three ionic liquids have been measured using the volumetric and cloud-point methods. The room-temperature ionic liquids studied are 1-butyl-3-methylimidazolium hexafluorophosphate bmimPF6, 1-butyl-3-methylimidazolium tetrafluoroborate bmimBF4, and 1-ethyl-3-methylimidazolium tetrafluoroborate emimBF4. All three binary systems show upper critical solution temperatures (UCSTs), with about 299 K for bmimBF4, about 310 K for emimBF4, and about 360 K for bmimPF6. The limited solubility behaviors with UCSTs are similar to the cases of various monoalcohols with ionic liquids reported in the literature. Observed LLE are well correlated by use of the nonrandom two liquid (NRTL) solution model. [ABSTRACT FROM AUTHOR]

Solubility measurements of carbon dioxide in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide have been performed with a gravimetric microbalance at temperatures of about 282, 297, 323, and 348 K and pressures up to about 2 MPa. Two different sources for the ionic liquid are examined in this work:  an ultrapure sample from NIST (the IUPAC task force sample) and a commercially available sample. Both samples show nearly identical solubility behaviors, being undistinguishable within experimental uncertainties. Solubility (pressure−temperature−composition) data have been well correlated with an equation-of-state (EOS) model used in our previous works. The EOS model calculations are compared with experimental solubility data for the same system in the literature. The present EOS has predicted partial immiscibility at the CO2-rich side solutions. To prove this prediction, vapor−liquid−liquid equilibrium experiments have been made, and our predictions have been confirmed. [ABSTRACT FROM AUTHOR]

The solubilities of ammonia in the room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), 1-hexyl-3-methylimidazolium chloride (hmimCl), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (emimTf2N), and 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) have been measured for the first time. New static phase equilibrium cells have been constructed for the present experiment. Isothermally fixed temperatures are ∼283, 298, 323, 348, and 355 K, and six mixture compositions are prepared (from ∼10 mol % to 85 mol % ammonia) at the ambient temperature. The observed solubilities are high:  in fact, they are among the highest ever reported in the literature for room-temperature mixtures that contain ionic liquids. Observed pressure−temperature−composition (PTx) data have been successfully correlated with our previous equation of state (EOS) model. Possible applications of the present systems to the absorption cooling/heating cycle have been discussed, in comparison to the traditional ammonia−water system. [ABSTRACT FROM AUTHOR]

In this article, we investigate vapor−liquid−liquid equilibria (VLLE) of binary systems using a simple volumetric method. Being different from the usual cloud-point method for the determination of liquid−liquid separation boundaries, the present volumetric method is able to determine the direct VLLE properties, such as equilibrium compositions, as well as molar volumes of the two liquid phases, by measuring only weights and volumes of liquid samples. The theory behind this method is described, and detailed error analyses for our simple apparatus are discussed by using well-established systems in the literature:  water 2-butanol and 1-butanol 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). Then, results for mixtures of bmimPF6 and pentafluoroethane (R-125) are provided, as well as those of the test systems above. As predicted in our earlier work, this binary system shows liquid−liquid separations in the R-125-rich side solutions with a lower critical solution temperature. In addition, we have found very large negative excess molar volumes in this system. [ABSTRACT FROM AUTHOR]