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Yokozeki A.,109 C Congressional Drive | Shiflett M.B.,DuPont Company
Journal of Supercritical Fluids | Year: 2010

A family of modified van der Waals equations of state (vdW EOS) is extremely useful for many industrial applications. For example, the generic Redlich-Kwong (RK) EOS or its modification by Soave (SRK EOS) and Peng-Robinson (PR EOS) are still of popular use in industry to the present day. These two most popular ("cubic") EOSs are based on modifications [1/(V2 + bV), or 1/(V2 + 2bV - b2)] of the volume dependence on the attractive part of the original van der Waals EOS [1/V2] and also modifications of the temperature dependence of the attractive "a(T)" parameter of the original EOS (constant a). It is extremely rare in actual EOS applications to use the volume dependence of the original van der Waals EOS. In the present phase equilibrium calculations, we employ such a generic vdW EOS, P = RT/(V - b) - a(T)/V2, with our well-tested mixing rule for multi-component mixtures. Using the same form of the "a(T)" parameter and the mixing rule, it has been found that all generic RK, PR, and vdW EOSs can present the phase behaviors (temperature-pressure-composition diagrams) equally well. It is shown that experimental gas solubility data (CO2, CF3-CFH2, SO2, and NH3) in room-temperature ionic liquids are well correlated with the present EOS model, and also that the phase behaviors such as LLE (liquid-liquid separations) are satisfactorily predicted. © 2010 Elsevier B.V. © 2010 Elsevier B.V. All rights reserved. Source


Shiflett M.B.,DuPont Company | Yokozeki A.,109 C Congressional Drive
Fluid Phase Equilibria | Year: 2010

We have developed a ternary equation of state (EOS) model for the CO2/H2S/1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) system in order to understand the 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. These interaction parameters have been determined using our previously measured VLE (vapor-liquid equilibrium) data for CO2/[bmim][PF6] and literature data for H2S/[bmim][PF6] and CO2/H2S. VLLE (vapor-liquid-liquid equilibrium) measurements have been made and validate EOS model predictions which suggest that the CO2/[bmim][PF6] and H2S/[bmim][PF6] systems are Type V phase behavior, according to the classifica-tion of van Konynenburg and Scott. The validity of the ternary EOS model calculations has also been checked by conducting VLE experiments for the CO2/H2S/[bmim][PF6] system. With this EOS model, isothermal ternary phase diagrams and solubility (VLE) behavior have been calculated for various (T, P, and feed compositions) conditions. The CO2/H2S gas selectivity is nearly independent of the amount of ionic liquid addition and ranged from about 3.2 to 4.0. For large CO2/H2S mole ratios (9/1) at 298.15 K, the addition of the ionic liquid increases the CO2/H2S gas selectivity from about 1.2 to 3.7. For high tempera-ture (333.15 K) and high 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. © 2010 Elsevier B.V. All rights reserved. Source


Shiflett M.B.,DuPont Company | Yokozeki A.,109 C Congressional Drive
Industrial and Engineering Chemistry Research | Year: 2010

Gaseous solubilities of sulfur dioxide (SO2) in room-temperature ionic liquids (RTILs), 1-n-butyl-3- methylimidazolium acetate and 1-n-butyl-3-methylimidazolium methyl sulfate, have been measured at four isothermal conditions (about 283, 298, 323, and 348 K) using a gravimetric microbalance. The observed pressure-temperature-composition (PTx) data have been analyzed by use of an equation-of-state (EOS) model, which has been successfully applied for our previous works. Excess thermodynamic functions and Henry's law constants have been obtained from the observed (PTx) data and our previous measurements of SO2 + 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide using the EOS correlation. All three RTILs show the chemical absorption. The classification of whether the absorption is the physical or chemical type is based on the excess Gibbs and enthalpy functions as well as the magnitude of the Henry's constant. An ideal association model has been applied in order to interpret those excess thermodynamic functions. Then, two types of the chemical associations (AB and AB2, where A is RTIL and B is SO2) have been observed with the heat of complex formations of about -6 to -19 (for AB) and from -6 to -29 (for AB 2) kJ· mol-1, respectively. © 2010 American Chemical Society. Source


Shiflett M.B.,DuPont Company | Yokozeki A.,109 C Congressional Drive
Energy and Fuels | Year: 2010

A ternary equation of state (EOS) model for the CO2/SO 2/1-butyl-3-methylimidazolium methyl sulfate ([bmim][MeSO 4]) system has been developed in order to gain further our understanding of capturing and enhanced gaseous selectivity of industrial flue gases containingCO2 and SO2 using room-temperature ionic liquids. The present model is based on a generic Redlich-Kwong (RK) EOS. The empirical binary interaction parameters have been determined using our measured vapor-liquid equilibrium (VLE) data for SO2/[bmim][MeSO4] and literature data for CO2/[bmim][MeSO4] and CO 2/SO2. The validity of the present EOS has been checked by conducting ternary VLE experiments for the present system. With this EOS, an isothermal ternary phase diagram and solubility (VLE) behaviors have been calculated for various (T, P, and feed compositions) conditions. The addition of the [bmim][MeSO4] for small and equimolar CO2/SO 2 mole ratios significantly increased the selectivity. For large CO2/SO2 mole ratios, the selectivity was high for even a small addition of ionic liquid and in certain cases showed a maximum selectivity due to preferential chemical absorption of SO2. The enhancement in CO2/SO2 selectivity using [bmim][MeSO4] was significantly higher than using 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) from our previous work and may make the simultaneous capture and separation of these acid gases practical. Copyright © 2010 American Chemical Society. Source


Yokozeki A.,109 C Congressional Drive | Shiflett M.B.,DuPont Company
Industrial and Engineering Chemistry Research | Year: 2010

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. © 2010 American Chemical Society. Source

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