Thermodynamic properties of mixtures containing ionic liquids

Thermodynamic properties of mixtures containing ionic liquids

Fluid Phase Equilibria 218 (2004) 165–175 Thermodynamic properties of mixtures containing ionic liquids Activity coefficients of aldehydes and ketone...

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Fluid Phase Equilibria 218 (2004) 165–175

Thermodynamic properties of mixtures containing ionic liquids Activity coefficients of aldehydes and ketones in 1-methyl-3-ethyl-imidazolium bis(trifluoromethyl-sulfonyl) imide using the transpiration method Sergey P. Verevkin, Tatiana V. Vasiltsova1 , Eckard Bich, Andreas Heintz∗ Department of Physical Chemistry, University of Rostock, Hermannstr. 14, D-18051 Rostock, Germany Received 8 December 2003; received in revised form 8 December 2003; accepted 16 December 2003

Abstract Vapor–liquid equilibria (VLE) of binary mixtures containing the high boiling solutes: nonan-1-al, 4-methyl-benzaldehyde, nonan-2-one, and 4-phenylbutan-2-one and the ionic liquid (IL) [EMIM][NTf2 ] were studied by using the transpiration method. VLE measurements were carried out over the whole concentration range at different temperatures between 298 and 323 K. Activity coefficients γi of these solvents in the ionic liquid have been determined from these data using the NRTL-equation. In addition vapor pressures of the pure solutes 4-methyl-benzaldehyde, nonan-2-one and 4-phenylbutan-2-one have been measured as function of temperature and their enthalpies of vaporization have been obtained. © 2004 Elsevier B.V. All rights reserved. Keywords: Ionic liquids; Mixtures; Vapor–liquid equilibria; Activity coefficient

1. Introduction Ionic liquids (IL) have gained large interest during the last years. They have no detectable vapor pressure and therefore exhibit ideal systems which can be used as solvents for new catalytic reactions and other chemical production processes as well as separation processes with respect to a “green chemistry”. The unique properties of ionic liquids open up a wide range for various applications. Ionic liquids have proved to be viable reaction media for numerous types of reactions, including, for example, Friedel–Crafts alkylations and Diels–Alder reactions [1]. Reactions such as the hydroformylation of alkenes producing aliphatic aldehydes has attracted a special attention [2,3]. Separation of aldehydes from the reaction products and the ionic liquid requires the knowledge of thermodynamic properties of such mixtures, as well as of properties of pure individual compounds. Aldehydes and ketones are very reactive and, consequently, ∗ Corresponding author. Tel.: +49-381-4986500; fax: +49-381-4986502. E-mail address: [email protected] (A. Heintz). 1 On leave from the State Academy of Refrigeration, Odessa, Ukraine.

0378-3812/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2003.12.005

are commercially important chemical intermediates. However, little accurate information is available on their physical properties. This work continues our study of thermodynamic properties of mixtures of solutes at infinite dilution in ILs [4–7]. Activity coefficients and mixing enthalpy data, covering the whole range of composition are unavailable so far for mixtures containing high boiling compounds and ionic liquids. With the present work we start to fill this gap of information on ionic liquid mixtures. Vapor–liquid equilibria (VLE) have been measured traditionally using methods such as dynamic recirculation still, static methods or headspace analysis in order to obtain information on activity coefficients in the liquid phase. An enormous body of data [8] has been accumulated in this area including a large number of components. However, all these traditional methods are generally based on the measurement of partial vapor pressures of relatively low boiling compounds. They also provide results for high-boiling compounds at elevated temperatures above 373 K. However, for the development of the separation technologies, the knowledge of thermodynamic properties of the mixtures of high-boiling compounds and ILs at ambient temperatures is of the crucial importance. A most suitable method to

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Fig. 1. Schematic diagram of the transpiration apparatus: (1) carrier gas cylinder; (2) flow valve; (3) flow meter; (4) thermostatted equilibrium cell; (5) U-shaped tube filled with the sample; (6) thermometer; (7) cooling trap at −30 ◦ C.

obtain reliable VLE data of liquid mixtures with high boiling components at ambient temperatures is the so-called transpiration method. An inert carrier gas passes a glass tube filled with glass beads which are covered by the liquid mixture of known composition consisting of IL and the high boiling substance (see Fig. 1). When the molar mass of the entrained vapor and appropriate amount of the carrier gas is known, the vapor pressure in the system can be derived from the mass of vapor condensed in a cooling trap. The method has been applied successfully in our laboratory [9] to measure vapor pressures of pure compounds and has proved to give results which are in excellent agreement with other established techniques to determine vapor pressures in the range of 0.005 to 5000 Pa. Taking into account that ILs have vanishing small vapor pressures, we decided to apply this method for the investigation of the mixtures containing a high-boiling compound (solute) and an IL (solvent). In this case, knowing the initial composition of the liquid phase xi , the composition of the vapor phase yi is governed only by the volatile solute. By an isothermal measurement of the compositions in the vapor phase and by screening the compositions of the liquid phase, i.e. mole fraction of the solute in the liquid mixture, and additionally having established the vapor pressure of the pure solute, activity coefficients γi in the mixture of solute in IL can be derived. A diversity of ionic liquids is commercially available [10]. In this work, we have performed measurements of γi of 4 solutes in the ionic liquid 1-methyl-3-ethyl-imidazolium bis(trifluoromethyl-sulfonyl) imide [EMIM][NTf2 ]. A series of mixtures of the solutes nonan-1-al, 4-methyl-benzaldehyde, nonan-2-one, and 4-phenyl-butan-2-one with the solvent—ionic liquid [EMIM][NTf2 ] has been studied in the temperature range 298–323 K. Vapor pressures of the pure individual ketones, required for the calculation of the ac-

tivity coefficients, as well as enthalpies of vaporization of these compounds, has been obtained by using the transpiration method (see Table 1). Vapor pressures of the pure nonan-1-al have been published recently [11].

2. Experimental procedure 2.1. Materials The samples of aldehydes and ketones studied were purchased from Aldrich and Merck. The degree of purity was controlled using a Hewlett Packard gas chromatograph 5890 Series II equipped with a flame ionization detector and a Hewlett Packard 3390A integrator. The carrier gas (nitrogen) flow was 726 cm3 /min. A capillary column HP-5 (stationary phase crosslinked 5% PH ME silicone) was used with a column length of 30 m, an inside diameter of 0.32 mm, and a film thickness of 0.25 ␮m. The standard temperature program of the GC was T = 333 K for 3 min followed by a heating rate of 10 K/min to T = 523 K. No impurities (greater than mass fraction 0.0005) could be detected in the samples used for the investigation. The ionic liquid [EMIM][NTf2 ] was synthesized according to the literature procedure [12,13]. Before using, the sample was dissolved in excess of methanol and filtered. Then it was subjected to vacuum evaporation at 333 K over 24 h to remove possible traces of solvents and moisture. 2.2. Vapor pressure measurements of pure component systems The vapor pressure and enthalpies of vaporization of aldehydes and ketones were determined using the method

S.P. Verevkin et al. / Fluid Phase Equilibria 218 (2004) 165–175 Table 1 g Results for the vapor pressure p and l Hm of pure aldehydes and ketones obtained by the transpiration method T (K)

m (mg)

VN 2 (dm3 )

4-Methyl-benzaldehydea 285.9 1.79 2.24 288.0 1.78 1.92 288.3 2.08 2.21 290.0 1.73 1.61 291.3 2.17 1.76 292.0 2.30 1.72 294.0 2.26 1.48 294.4 2.25 1.46 296.1 2.37 1.29 297.3 2.14 1.12 298.2 2.23 1.14 300.5 2.51 1.07 301.1 2.18 0.860 303.5 2.65 0.860 304.2 1.58 0.525 304.3 2.08 0.645 306.5 2.38 0.645 307.2 2.34 0.581 309.6 2.49 0.559 312.6 2.24 0.430 313.2 2.29 0.409 315.6 2.66 0.387 316.2 2.24 0.323 318.6 2.31 0.301 Nonan-2-oneb 305.6 3.16 308.6 3.82 311.5 4.06 314.6 4.69 317.6 4.92 320.6 5.06 323.6 4.98 326.5 4.11 332.5 4.83 335.6 4.05 338.6 4.79 344.6 7.23

0.559 0.549 0.478 0.447 0.376 0.325 0.264 0.183 0.142 0.102 0.102 0.112

4-Phenyl-butan-2-onec 293.2 0.97 296.7 1.30 302.8 1.38 305.4 1.27 308.3 1.27 311.1 1.32 313.9 1.35 316.7 1.35 317.4 2.48 319.6 1.33 322.4 1.33 325.2 1.48 328.0 1.85 330.6 1.97 330.8 3.27 333.5 1.92

4.21 3.88 2.49 1.88 1.55 1.23 1.02 0.817 1.47 0.654 0.531 0.490 0.490 0.449 0.750 0.368

g

p (Pa)

16.46 19.04 19.37 22.13 25.35 27.57 31.37 31.79 37.96 39.49 40.46 48.24 52.36 63.43 61.87 66.51 76.24 83.20 91.81 107.27 115.85 141.9 143.4 158.0 98.5 121.4 148.1 182.5 227.7 271.0 328.3 391.0 590.7 693.1 820.6 1125.9 3.86 5.62 9.26 11.26 13.63 17.96 22.18 27.72 28.22 34.00 41.84 50.57 63.23 73.26 72.99 87.21

pexp − pcalc (Pa)

g

l H m (kJ/mol)

0.0 −0.4 −0.6 −0.6 0.2 1.0 0.5 0.0 1.9 0.1 −1.6 −1.4 0.6 2.2 −2.4 1.8 1.0 4.3 −0.8 −5.5 −1.4 5.2 1.5 −6.9

54.33 54.20 54.18 54.07 53.98 53.94 53.81 53.78 53.67 53.59 53.53 53.38 53.35 53.19 53.14 53.14 53.00 52.95 52.79 52.60 52.56 52.40 52.37 52.21

1.1 0.3 −0.5 −1.5 2.5 −3.3 −4.3 −7.9 17.0 5.3 4.3 −11.1

56.90 56.62 56.35 56.06 55.78 55.50 55.22 54.95 54.39 54.10 53.82 53.26

−0.1 0.2 0.2 0.0 −0.6 0.1 0.1 0.4 −0.5 0.2 0.4 0.1 1.9 0.1 −1.1 −1.5

64.38 64.07 63.53 63.30 63.05 62.80 62.56 62.31 62.25 62.05 61.81 61.56 61.31 61.09 61.07 60.83

a  H (298.15 K) = 53.53 ± 0.51 kJ/mol. Eq. (2): a = 275.543 J/ l m g (mol K), b = −72884.138 J/mol, l Cp = 64.9 J/(mol K). b g H (298.15 K) = 57.60 ± 0.31 kJ/mol. Eq. (2): a = 320.097 J/ l m g (mol K), b = −85472.894 J/mol, l Cp = 93.5 J/(mol K). g c  H (298.15 K) = 63.94 ± 0.41 kJ/mol. Eq. (2): a = 317.568 J/ l m g (mol K), b = −90174.337 J/mol, l Cp = 88.0 J/(mol K).

167

of transpiration in a saturated N2 -stream and applying the Clausius–Clapeyron equation. About 0.5 g of the sample was mixed with glass beads (having a diameter of 1 mm) and placed in a thermostatted U-shaped tube having a length of 20 cm and a diameter of 0.5 cm. Glass beads having a diameter of 1 mm provide a surface which is sufficient for reaching the vapor–liquid equilibration. At constant temperature (±0.1 K), a nitrogen stream was passed through the U-tube and the transported amount of gaseous material was collected in a cooling trap. The flow rate of the nitrogen stream was measured using a soap bubble flowmeter and optimized in order to reach the saturation equilibrium of the transporting gas at each temperature under study. On the one hand, flow rate of nitrogen stream in the saturation tube should be not too slow in order to avoid the transport of material from U-tube due to diffusion. On the other hand, the flow rate should be not too fast in order to reach the saturation of the nitrogen stream with a compound under study. We tested our apparatus at different flow rates of the carrier gas in order to check the lower boundary of the flow below which the contribution of the vapor condensed in the trap by diffusion becomes comparable to the transpired one. In our apparatus the contribution due to diffusion was negligible at a flow rate up to 6.6 cm3 /min. The upper limit for our apparatus where the speed of nitrogen could already disturb the equilibration was at a flow rate of 49.2 cm3 /min. Thus, we carried out the experiments in the flow rate interval of 16.8–33.6 cm3 /min which ensured that the transporting gas was in saturated equilibrium with the coexisting liquid phase in the saturation tube. The amount of condensed substance was determined by GC analysis using an external standard (hydrocarbon n-Cn H2n+2 ). The saturation vapor pressure psat at each temperature T was calculated from the amount of product collected within a definite period of time. Assuming that Dalton’s law applied to the nitrogen stream saturated with the substance i is valid, values of the partial pressures psat i were calculated assuming: psat i =

mi RTa , Mi V

V = VN2 + Vi

(VN2  Vi )

(1)

where R = 8.31451 J/(K mol), mi is the mass of transported compound, Mi its molar mass and Vi its volume contribution to the gaseous phase. VN2 is the volume of transporting gas, and Ta is the temperature of the soap bubble meter. The volume of transporting gas VN2 was determined from the flow rate and time measurements. The flow rate was maintained constant with help of the high precision needle valve (Hoke, C1335G6BMM-ITA). The accuracy of the volume VN2 obtained from measurements of the flow rate was established to be (0.001 dm3 ) with help of series of a experiments, where the volume of nitrogen was measured with gas-clock or by water withdrawing from a calibrated gasometer. The experimental data psat i (T) were fitted using following equation [9]: R ln psat i =a+

b T g + l Cp ln T T0

(2)

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Table 2 g Comparison of data for the enthalpy of vaporization l Hm at 298.15 K of nonan-2-one g

Technique

T (K)

l Hm (kJ/mol)

Reference

Ebulliometr Calorimetric Calorimetric Static manometer Static manometer Transpiration

305–468 298.15 298.15 263.7–461.8 283.2–466.6 304.9–344.6

55.4 56.44 ± 0.06 56.06 ± 0.83 57.06 ± 0.10 57.36 ± 0.15 57.60 ± 0.31

[16] [19] [20] [17] [18] This work

g

were a and b are adjustable parameters and l Cp is the difference of the molar heat capacities of the gaseous and the liquid phase, respectively. T0 appearing in Eq. (2) is an arbitrarily chosen reference temperature which has been chosen to be 298.15 K. Consequently, from Eq. (2) the expression for the vaporization enthalpy at temperature T is derived: g

g

l Hm (T) = −b + l Cp T g

(3)

Values of l Cp have been derived from the isobaric molar heat capacities of the liquid, Cpl , and from values of the g isobaric molar heat capacities Cp of the gaseous species calculated according to a procedure developed by Domalski and Hearing [14]. All results together with the parameters a and b are listed in Table 1. Comparison of our results with data available from the literature is presented in Table 2.

2.3. VLE measurements of the binary mixtures (solute + IL) Activity coefficients covering the whole range of concentration in a mixture of an ionic liquid and an organic solute can be measured using a dynamic method. This method is based on the so-called transpiration technique described above which is particularly suitable in such cases where the vapor pressure of the solute is low. The principle of this method extended for mixtures is illustrated in Fig. 1. The experimental set up consists of a linear shaped glass tube having a length of 25 cm and a diameter of 0.8 cm which is kept at constant temperature by using a thermostat. The temperature inside the cell can be controlled to within of ±0.02 K and was measured by a platinum resistance thermometer PT-100 (Burster). The mixture was prepared in the following way. About 0.3 to 0.5 g of the IL was weighted in a glass flask together with a certain amount of a solute in order to obtain a desired mole fraction of the liquid phase. About 13 g of glass beads (having a size of 1 mm) were added to the content of the glass flask. Glass beads, coated with the initial mixture were placed in the transpiration tube quantitatively. A slow stream of N2 -gas flowing through the tube eluates continuously the vapor phase in the glass tubing. Due to the negligible vapor pressure of the ionic liquid the vapor phase consists exclusively of the solute and is condensed in a cooling trap. The mass of solute collected

Fig. 2. Vapor pressure diagram (top) and composition diagram (bottom) of the system n-pentanol (1) + n-decane (2) at 363.2 K. x1 , mole fraction in the liquid phase; y1 , mole fraction in the vapor phase. (䊊) Results from this work; (䊉) results from [14].

S.P. Verevkin et al. / Fluid Phase Equilibria 218 (2004) 165–175 Table 3 VLE in the system (nonan-1-al + [EMIM][NTf2 ]) exp

Table 3 (Continued )

T (K)

x1

298.6

0.000 0.079 0.149 0.239 0.314 0.434 0.563 0.673 0.718 0.879 0.938 1.000

0.000 12.50 20.20 26.13 31.44 36.63 41.01 47.14 45.25 48.59 49.77 50.05

0.000 12.58 19.88 26.64 30.99 36.76 41.82 45.19 46.30 48.85 49.58 51.39

4.020 3.109 2.598 2.166 1.923 1.650 1.445 1.306 1.254 1.082 1.029 1.000

1.391 1.134 0.955 0.773 0.654 0.501 0.368 0.267 0.226 0.079 0.028 0.000

0.000 0.071 0.130 0.153 0.221 0.412 0.552 0.665 0.712 0.875 0.937 1.000

0.00 19.18 33.15 35.67 37.66 55.06 60.39 66.17 64.86 67.76 72.10 72.35

0.00 20.13 30.71 33.85 41.42 54.53 60.71 64.34 65.54 69.20 71.09 74.48

5.040 3.831 3.174 2.978 2.513 1.779 1.476 1.298 1.236 1.062 1.019 1.000

1.617 1.343 1.155 1.091 0.921 0.576 0.389 0.261 0.212 0.060 0.019 0.000

308.6

0.000 0.053 0.060 0.104 0.137 0.204 0.280 0.388 0.541 0.657 0.705 0.871 0.935 1.000

0.00 27.19 27.45 42.51 48.40 51.29 59.13 76.79 84.60 86.35 90.70 98.96 100.84 104.11

0.00 26.70 29.06 40.24 46.12 54.96 62.57 71.59 82.43 89.19 91.53 98.11 100.94 105.79

6.826 4.747 4.555 3.646 3.181 2.547 2.113 1.745 1.441 1.283 1.227 1.065 1.021 1.000

1.921 1.557 1.516 1.294 1.157 0.935 0.748 0.557 0.366 0.249 0.205 0.063 0.020 0.000

313.6

0.000 0.042 0.050 0.120 0.184 0.258 0.363 0.525 0.647 0.697 0.865 0.933 1.000

0.00 33.23 39.87 65.29 72.90 78.76 101.52 114.10 123.11 125.91 139.59 138.00 148.08

0.00 34.58 38.71 62.19 74.04 84.16 96.59 113.59 124.22 127.79 136.36 139.38 145.39

8.073 5.649 5.343 3.571 2.767 2.246 1.830 1.487 1.320 1.261 1.084 1.027 1.000

2.089 1.732 1.676 1.273 1.018 0.809 0.604 0.397 0.278 0.232 0.080 0.027 0.000

318.6

0.000 0.031 0.038 0.160 0.235 0.337 0.510 0.688 0.860 0.931

0.00 44.19 56.23 104.42 117.00 141.67 154.01 168.03 182.76 199.96

0.00 46.28 53.10 106.90 120.07 133.89 153.86 171.36 187.02 195.29

9.667 7.126 6.723 3.235 2.474 1.921 1.460 1.204 1.052 1.014

2.269 1.964 1.906 1.174 0.906 0.653 0.379 0.186 0.051 0.014

303.6

p1

(Pa)

pNRTL (Pa) 1

169

γ1NRTL

ln γ1NRTL

T (K)

323.6

exp

x1

p1

1.000

208.30

206.72

1.000

0.000

0.000 0.022 0.028 0.132 0.212 0.310 0.494 0.679 0.929 1.000

0.00 58.91 76.64 137.82 147.10 183.02 210.39 240.56 274.00 289.93

0.00 61.71 72.76 136.78 154.55 174.59 211.49 242.17 273.69 288.73

13.585 9.639 8.855 3.597 2.529 1.952 1.482 1.235 1.020 1.000

2.609 2.266 2.181 1.280 0.928 0.669 0.393 0.211 0.020 0.000

(Pa)

pNRTL (Pa) 1

γ1NRTL

ln γ1NRTL

within a certain time interval is determined by dissolving it in a suitable solvent with certain amount of internal standard (hydrocarbon). This solution is analyzed using a gas chromatograph equipped with autosampler. Uncertainty of the solute amount determined by GC analysis was assessed to be within 1–3%. The peak area of the solute related to the peak of the external standard (hydrocarbon n-Cn H2n+2 ) is a direct measure of the mass of the solute condensed into the cooling trap provided a calibration run has been made. From these information, the partial pressure of the solute in the glass tubing can be determined, i.e. the ideal gas law can be applied provided that the vapor pressure of the substance is low enough. Real gas corrections arising from interactions of the vapor with the carrier gas turned out to be negligible. Since the method is a dynamic one extreme care has to be taken to ensure that thermodynamic equilibrium conditions have been fulfilled by adjusting the gas flow to values small enough. If the amount of solute condensed is small compared to its contents in the liquid phase inside the tubing, the change of concentration in the liquid mixture is negligible during such an experiment and the partial pressure of the solute can be assigned to the known composition of the liquid mixture being in thermodynamic equilibrium with the vapor phase. The justification of this procedure has been checked several times by calculating the change of the liquid composition from the amount of solute collected in the cooling trap. These corrections turned out to be small but they have been applied for the calculation of the true mole fraction in the liquid phase as the average value between initial and final composition. The method was checked by measuring the vapor–liquid equilibrium of the binary mixture (n-pentanol + decane), where reliable VLE data exist in the literature [15]. Studying this system both components are condensed in the cooling trap and have been analyzed providing partial pressures p1 of decane as well as of pentanol (p2 ) in the vapor liquid equilibrium. Excellent agreement with literature data was obtained. This is demonstrated in Fig. 2. Measurements of p1 covering the whole range of concentration of solute (1) + ionic liquid (2) mixtures have been performed. A series of aldehydes and ketones, mixed with

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ionic liquid has been studied. Partial pressure of the solute are presented in Tables 3–6 , the partial pressure of the ionic liquid is not detectable. We checked every system under study for repeatability of the measurements and it was governed within 1–3% by accuracy of the GC analysis.

Table 4 VLE in the system (4-methyl-benzaldehyde + [EMIM][NTf2 ]) x1

298.6

0.000 0.075 0.085 0.404 0.587 0.784 0.900 0.972 0.984 1.000

0.00 5.49 5.10 19.43 30.29 35.66 39.68 47.14 46.53 43.94

303.6

0.000 0.072 0.081 0.125 0.423 0.458 0.571 0.673 0.779 0.897 0.984 1.000

308.6

γ1NRTL

ln γ1NRTL

0.00 4.90 5.53 21.43 28.84 36.63 41.40 44.54 45.09 45.82

1.510 1.422 1.411 1.158 1.073 1.019 1.004 1.000 1.000 1.000

0.412 0.352 0.345 0.146 0.070 0.019 0.004 0.000 0.000 0.000

0.00 7.71 7.32 9.98 27.30 30.88 40.18 49.75 51.05 56.34 65.41 62.90

0.00 6.64 7.36 11.00 31.05 33.06 39.37 44.92 50.69 57.46 62.73 63.76

0.425 0.366 0.359 0.326 0.142 0.125 0.078 0.045 0.021 0.004 0.000 0.000

1.530 1.442 1.432 1.385 1.152 1.133 1.081 1.046 1.021 1.005 1.000 1.000

0.000 0.069 0.076 0.119 0.442 0.554 0.659 0.772 0.970 0.983 1.000

0.00 10.59 9.83 14.01 42.18 59.85 72.23 71.29 96.02 95.22 88.00

0.00 9.26 10.07 15.38 47.80 57.43 66.18 75.61 93.22 94.44 96.04

1.464 1.391 1.385 1.344 1.126 1.079 1.045 1.020 1.000 1.000 1.000

0.381 0.330 0.326 0.296 0.119 0.076 0.044 0.020 0.000 0.000 0.000

313.6

0.000 0.065 0.070 0.114 0.424 0.537 0.643 0.765 0.969 0.983 1.000

0.00 14.89 13.48 19.14 61.96 78.31 99.48 103.33 130.52 139.18 123.71

0.00 12.86 13.72 21.61 66.26 79.93 92.24 106.39 131.73 133.52 135.83

1.530 1.450 1.445 1.396 1.152 1.095 1.056 1.024 1.000 1.000 1.000

0.425 0.371 0.368 0.334 0.141 0.091 0.054 0.023 0.000 0.000 0.000

318.6

0.000 0.062 0.063 0.401 0.518 0.624 0.757 0.885 0.968 1.000

0.000 19.68 18.83 83.15 100.20 140.40 142.09 153.98 190.93 172.43

0.00 18.87 18.94 90.19 108.45 124.09 143.60 163.56 177.68 183.37

1.768 1.651 1.650 1.227 1.142 1.084 1.034 1.008 1.001 1.000

0.570 0.501 0.501 0.205 0.132 0.080 0.034 0.008 0.001 0.000

323.6

0.000 0.055 0.059 0.378 0.496 0.598 0.748 0.880 0.967 1.000

0.00 22.94 25.97 107.19 152.12 175.77 192.56 215.75 229.43 236.37

0.00 23.42 25.14 118.36 143.11 162.84 191.86 218.89 238.69 246.59

1.853 1.735 1.726 1.269 1.169 1.105 1.040 1.009 1.001 1.000

0.617 0.551 0.546 0.239 0.156 0.100 0.039 0.009 0.001 0.000

3. Results and discussion 3.1. Pure substances The comprehensive compilation by Stull [16] contains vapor-pressure results for pure nonan-2-one over a wide range of temperature. The origin of the data presented there is unclear, methods of measurements are unknown as well as errors of measurements and purities of compounds. In spite of this fact, we treated these results using Eqs. (2) g and (3) and calculated l Hm (298.15 K) for the sake of comparison with our results (see Fig. 3 and Table 2). However, comparison with our data remains questionable. A static apparatus was used by the research group of Jose and coworkers [17,18] for measuring vapor pressures of the pure nonan-2-one. The comparison of the experimental results with ours is given in Fig. 3 and deviations of the results are presented in Fig. 4. The data from static [17,18] and transpiration method are generally in agreement to within 1–3%. In Jose’s work, only temperature dependencies of the vapor pressure of nonan-2-one are reported, but no enthalpies of vaporization. Therefore we have treated these data by using Eqs. (2) and (3) in order to derive enthalpies of vaporization at 298.15 K. As can bee seen from the Table 2, enthalpies of vaporization derived from both methods (static and transpiration) are in very close agreement within the boundaries of their experimental uncertainties. Surprisingly, the enthalpy of vaporization of nonan-2-one, measured directly by using calorimetry [19,20] is about 1 kJ/mol lower (see Table 2). 3.2. Data correlation of binary systems using the NRTL-equation Binary mixtures of ILs with non-electrolyte components belong to the class of strong electrolyte solutions covering the whole range of composition including the pure liquid electrolyte. Since there exist no simple theoretical models for the Gibbs energy of mixing of this kind of mixtures we have tried to describe the results of activity coefficients using purely empirical expressions well known in thermodynamics of non-electrolyte mixtures. After several attempts with the simple Margules equation, the Wilson equation and the UNIQUAC equation it turned out that the NRTL-equation gives the best empirical description of the activity coefficients. Eq. (4) has been used to fit partial pressures p1 to experimental data including the vapor pressure of the pure solute: p1 = p0,1 x1 γ1NRTL

(4)

exp

T (K)

p1

(Pa)

pNRTL (Pa) 1

S.P. Verevkin et al. / Fluid Phase Equilibria 218 (2004) 165–175 Table 5 VLE in the system (nonan-2-one + [EMIM][NTf2 ]) exp

T (K)

x1

298.6

0.000 0.056 0.098 0.276 0.412 0.443 0.518 0.539 0.700 0.727 0.837 0.916 0.950 1.000

0.00 11.26 20.05 35.57 43.99 49.40 48.05 45.50 53.74 55.49 60.88 57.34 63.78 62.11

0.000 0.054 0.094 0.274 0.407 0.438 0.515 0.535 0.697 0.836 0.915 0.950 0.986 1.000

303.6

308.6

313.6

p1

pNRTL (Pa) 1

Table 6 VLE in the system (4-phenyl-butan-2-one + [EMIM][NTf2 ])

γ1NRTL

ln γ1NRTL

T (K)

x1

0.00 12.02 18.93 36.75 43.59 44.76 47.35 48.01 53.22 54.18 58.65 62.56 64.54 67.70

3.638 3.159 2.861 1.969 1.563 1.493 1.349 1.316 1.123 1.101 1.035 1.009 1.003 1.000

1.291 1.150 1.051 0.677 0.447 0.401 0.299 0.275 0.116 0.096 0.034 0.009 0.003 0.000

298.6

0.000 0.158 0.276 0.443 0.571 0.669 0.795 0.963 1.000

303.6

0.00 18.25 30.11 56.21 66.90 62.85 67.98 68.59 73.37 84.43 86.36 88.05 86.98 89.80

0.00 18.88 29.53 55.58 63.67 64.97 67.79 68.45 74.15 80.78 85.88 88.54 91.61 92.86

4.406 3.771 3.376 2.186 1.684 1.598 1.417 1.379 1.146 1.041 1.011 1.004 1.000 1.000

1.483 1.327 1.217 0.782 0.521 0.468 0.349 0.321 0.136 0.040 0.011 0.004 0.000 0.000

0.000 0.154 0.272 0.441 0.568 0.666 0.793 0.963 1.000

308.6

0.000 0.051 0.090 0.268 0.402 0.433 0.512 0.530 0.693 0.835 0.914 0.950 0.986 1.000

0.00 27.85 42.10 85.29 99.36 88.11 91.11 100.34 104.89 121.30 122.30 127.91 130.32 127.99

0.00 27.34 43.37 81.78 92.94 94.65 98.33 99.10 106.45 115.54 122.70 126.46 130.87 132.66

4.727 4.053 3.615 2.296 1.743 1.648 1.448 1.409 1.157 1.043 1.011 1.004 1.000 1.000

1.553 1.399 1.285 0.831 0.556 0.499 0.370 0.343 0.146 0.042 0.011 0.004 0.000 0.000

0.000 0.048 0.087 0.262 0.285 0.397 0.417 0.429 0.446 0.525 0.690 0.702 0.730 0.834 0.914 0.916 0.949 0.951 0.986 0.986 1.000

0.00 45.20 61.13 125.96 132.74 137.09 137.11 137.09 149.24 142.15 156.36 154.26 151.85 174.78 167.32 174.54 179.86 167.89 174.62 176.31 178.80

0.00 42.74 68.02 124.23 127.53 137.76 138.91 139.54 140.38 143.67 151.04 151.78 153.53 162.21 171.72 172.03 176.86 177.08 183.00 183.05 185.51

5.599 4.758 4.199 2.554 2.413 1.872 1.797 1.754 1.697 1.474 1.180 1.165 1.134 1.049 1.013 1.012 1.004 1.004 1.000 1.000 1.000

1.723 1.560 1.435 0.938 0.881 0.627 0.586 0.562 0.529 0.388 0.166 0.153 0.126 0.048 0.013 0.012 0.004 0.004 0.000 0.000 0.000

(Pa)

171

exp

p1

γ1NRTL

ln γ1NRTL

0.000 2.27 3.26 4.15 4.67 5.04 5.57 6.46 6.70

2.942 2.150 1.760 1.398 1.219 1.125 1.046 1.001 1.000

1.079 0.765 0.565 0.335 0.198 0.118 0.045 0.001 0.000

0.00 3.78 4.30 5.36 7.03 7.16 8.50 10.10 9.78

0.00 3.32 4.80 6.09 6.84 7.38 8.15 9.45 9.80

3.007 2.20 1.79 1.41 1.23 1.13 1.05 1.00 1.00

1.101 0.788 0.583 0.345 0.205 0.123 0.047 0.001 0.000

0.000 0.148 0.267 0.438 0.564 0.663 0.791 0.963 1.000

0.00 6.41 6.14 7.95 9.64 10.56 12.04 15.01 14.68

0.00 5.23 7.40 9.11 9.98 10.62 11.57 13.34 13.82

3.649 2.562 2.005 1.506 1.278 1.158 1.058 1.002 1.000

1.294 0.941 0.695 0.409 0.246 0.147 0.057 0.002 0.000

313.6

0.000 0.137 0.259 0.434 0.560 0.659 0.788 0.963 1.000

0.00 7.85 9.78 11.46 13.52 15.71 19.03 22.60 21.67

0.00 6.83 10.32 13.26 14.78 15.92 17.52 20.36 21.12

3.172 2.363 1.884 1.448 1.251 1.144 1.053 1.002 1.000

1.154 0.860 0.633 0.370 0.224 0.134 0.052 0.002 0.000

318.65

0.000 0.125 0.252 0.430 0.554 0.654 0.784 0.962 1.000

0.00 10.20 12.06 17.86 19.96 23.14 28.51 32.08 31.53

0.00 8.70 14.19 18.99 21.48 23.36 25.96 30.41 31.56

2.816 2.210 1.785 1.401 1.229 1.132 1.050 1.001 1.000

1.035 0.793 0.580 0.337 0.206 0.124 0.048 0.001 0.000

323.65

0.000 0.113 0.244 0.424 0.547 0.648 0.779 0.962 1.000

0.00 13.08 19.12 27.24 30.15 29.38 35.32 45.66 45.23

0.00 12.28 20.58 26.98 29.99 32.29 35.53 41.47 43.05

3.250 2.529 1.963 1.479 1.274 1.157 1.059 1.002 1.000

1.179 0.928 0.674 0.391 0.242 0.146 0.057 0.002 0.000

(Pa)

0.000 2.49 2.95 3.90 4.83 4.97 5.56 6.80 6.42

pNRTL (Pa) 1

172

S.P. Verevkin et al. / Fluid Phase Equilibria 218 (2004) 165–175

Fig. 3. Experimental data of the vapor pressures of the nonan-2-one.

Fig. 4. Experimental data of the vapor pressures of the nonan-2-one. Comparison of the data deviations. The reference line is obtained from fitting equation (Eq. (2)) adjusted to the data of [17,18].

with



ln γ1NRTL = x22 τ21



G21 x1 + x2 G21

2 +

τ12 G12 (x2 + x1 G12 )2



(5) where Gij = exp(−αij τij ) with τij = (gij −gjj )/RT and αij = αji = α (i, j = 1, 2; i = j). Table 7 contains the parameters αij and (gij − gjj ). Figs. 5–8 show the experimental partial pressures of the solutes mixed with [EMIM][NTf2 ] in comparison with the calculated results of the NRTL-model according to Eq. (4) and (5) with parameters taken from Table 7. The scattering of the experimental data is about ±5% of the maximal pressure of the pure solutes which is not

surprising considering the low values of absolute pressures obtained by the experiments. The NRTL-equation is able to fit all the results within the experimental errors. The temperature dependence of ln γ1 indicates that ln γ1 increases with increasing temperature, however, due to the relatively large scattering of the data this temperature dependence of ln γ1 is not significant enough to derive enthalpies of mixing. The concentration range where the IL is highly diluted in the organic component, i.e. where x1 approaches to unity is of special interest. Values of ln γ1 in this region should obey the Debye–Hückel limiting law. However, the scattering of our data obtained by a method not being suitable for this range of concentration is too large for testing

S.P. Verevkin et al. / Fluid Phase Equilibria 218 (2004) 165–175

Fig. 5. Partial pressure data of nonan-1-al in the mixture with [EMIM][NTf2 ] as function of x1 (nonan-1-al).

Fig. 6. Partial pressure data of 4-methyl-benzaldehyde in the mixture with [EMIM][NTf2 ] as function of x1 (4-methyl-benzaldehyde).

Fig. 7. Partial pressure data of nonan-2-one in the mixture with [EMIM][NTf2 ] as function of x1 (nonan-2-one).

173

174

S.P. Verevkin et al. / Fluid Phase Equilibria 218 (2004) 165–175

Fig. 8. Partial pressure data of 4-phenyl-butan-2-one in the mixture with [EMIM][NTf2 ] as function of x1 (4-phenyl-butan-2-one).

List of symbols g molar heat capacities of gas at constant pressure Cp

Table 7 Parameter of the NRTL equation T (K)

g12 − g22

Nonan-1-al + [EMIM][NTf2 ] 298.65 5584.58 303.55 4566.11 308.55 4559.56 313.55 5382.23 318.55 3680.87 323.55 4444.52 T (K)

g21 − g11

α

Cpl

2293.56 2618.43 3621.80 4141.88 4513.65 5569.51

0.6984 0.6288 0.7036 0.6870 0.6482 0.6784

 l Cp

g12 − g22 + g21 − g11

α

4-Methyl-benzaldehyde + [EMIM][NTf2 ] 298.65 1023.00 303.65 1072.97 308.65 978.31 313.55 1108.37 318.65 1510.14 323.65 1659.64

0.0 0.0 0.0 0.0 0.0 0.0

Nonan-2-one + [EMIM][NTf2 ] 298.65 3206.48 303.65 3743.90 308.65 3986.32 313.55 4490.70

0.0 0.0 0.0 0.0

4-Phenyl-butan-2-one + [EMIM][NTf2 ] 298.65 2679.71 303.65 2779.78 308.65 3321.71 313.65 3010.00 318.65 2742.94 323.65 3171.73

0.0 0.0 0.0 0.0 0.0 0.0

g

g

l Hm p Ta

molar heat capacities of liquid at constant pressure difference of the molar heat capacities at constant pressure for the gaseous and liquid phase, respectively molar enthalpy of vaporization vapor pressure ambient temperature

Greek letters αij interaction parameters of the NRTL equation γi activity coefficient of component i interaction parameters of the NRTL equation τij

Acknowledgements

the Debye–Hückel limiting law. This test will be performed and published in the near future using solvents with higher volatility such as methanol and a special method based on pressure difference measurements.

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