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Vapour pressure measurement for binary and ternary systems containing water methanol ethanol and an ionic liquid 1-ethyl-3-ethylimidazolium diethylphosphate
J. Chem. Thermodynamics 39 (2007) 841–846 www.elsevier.com/locate/jct
Vapour pressure measurement for binary and ternary systems containing water methanol ethanol and an ionic liquid 1-ethyl-3-ethylimidazolium diethylphosphate Xiao-Chuan Jiang, Jun-Feng Wang, Chun-Xi Li *, La-Mei Wang, Zi-Hao Wang College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China Received 12 September 2006; received in revised form 30 November 2006; accepted 30 November 2006 Available online 12 December 2006
Abstract Vapour pressure data were measured for three binary systems containing water, methanol or ethanol with an ionic liquid (IL) 1-ethyl3-ethylimidazolium diethylphosphate([EEIM][DEP]) and for three ternary systems, i.e. (water + ethanol + [EEIM][DEP]), (water + methanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]), at varying temperature and IL-content ranging from mass fraction of 0.10 to 0.85 by a quasi-static method. The vapour pressure data of the binary systems were correlated by NRTL equation with average absolute relative deviation (ARD) within 0.0091. The binary NRTL parameters were used to predict the vapour pressure of the ternary systems (ethanol + water + [EEIM][DEP]), (water + methanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]) with an overall ARD of 0.037 and the maximum deviation of 0.1295. The results indicate that ionic liquid [EEIM][DEP] can give rise to a negative deviation from the Raoult’s law for the solvents of water, methanol and ethanol, but to a varying degree leading to the variation of relative volatility of a solvent and even removal of azeotrope for (water + ethanol). Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Vapour pressure; Measurement; Ionic liquid; NRTL equation; (Vapour + liquid) equilibrium
1. Introduction Ionic liquids (ILs) have recently attracted considerable attention for their unique attributes, e.g. negligible vapour pressure, good stability, and ionic property in contrast to the conventional molecular solvents, and some encouraging results have been achieved with respect to their utilization as a benign medium and/or solvent in a reaction and/ or separation process [1]. Vapour pressure data indicate that volatility of solvents can be changed dramatically by the addition of ionic liquid, while the variation extent is different depending on the nature of both solvent and ionic liquid involved. As a result, the relative volatility of a component is changed and even the azeotrope of a binary liquid mixture eliminated. When an IL is used as a solvent and/or salt in a salt/extractive distillation process, it might *
Corresponding author. Tel./fax: +86 10 64410308. E-mail address: [email protected] (C.-X. Li).
0021-9614/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2006.11.013
be superior to the commonly used entrainers due to its non-volatility, less causticity, and good performance in improving the separation efficiency. In contrast to the overwhelming application-oriented reports on ILs, only limited thermodynamic data on IL-containing systems have been available, for example, (liquid + liquid) equilibrium [2,3], (vapour + liquid) equilibrium [4–6], and infinite dilution activity coefficient of some organic solvents [7–10]. Vapour pressure data for IL-containing binary systems are essential for the development of thermodynamic model and calculation of (vapour + liquid) equilibrium for ILcontaining multi-component systems. However, the vapour pressure data for such systems are extremely scarce. For this reason, new vapour pressure data were measured for three IL-containing binary systems and three ternary system using quasi-static method, and the effect of ionic liquid [EEIM][DEP] on the vapour pressure lowering of water, methanol, and ethanol was investigated. The applicability of non-electrolyte NRTL equation in correlating binary
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X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846
and predicting ternary VLE data for IL-containing systems was discussed.
TABLE 1 Vapour pressure data of binary system {water (1) + [EEIM][DEP] (2)} cexp 1
cNRTL 1
x1 = 0.9929 9.230 12.310 17.044 23.556 30.842 38.632 48.476 57.141
1.0078 1.0077 1.0026 1.0001 0.9997 0.9980 0.9972 0.9981
0.9989 0.9990 0.9991 0.9991 0.9992 0.9992 0.9992 0.9993
9.352 15.336 19.706 24.119 31.311 38.853 47.442 54.915
x1 = 0.9734 9.413 15.447 19.831 24.357 31.612 39.518 48.144 55.562
0.9801 0.9806 0.9821 0.9791 0.9799 0.9731 0.9757 0.9789
0.9865 0.9877 0.9883 0.9887 0.9893 0.9898 0.9902 0.9905
322.37 328.73 334.78 340.58 346.28 350.76 355.06 359.05
9.999 13.708 18.237 23.740 30.475 36.793 43.825 51.389
x1 = 0.9392 10.467 14.328 19.056 24.793 31.791 38.402 45.803 53.889
0.8986 0.9039 0.9068 0.9096 0.9127 0.9138 0.9140 0.9151
0.9417 0.9448 0.9475 0.9499 0.9522 0.9538 0.9553 0.9597
335.67 343.03 348.57 354.81 360.40 366.55 371.31
9.576 13.588 17.498 22.917 29.158 37.269 44.949
x1 = 0.7348 9.461 13.439 17.298 22.737 28.782 36.949 44.547
0.5844 0.5978 0.6083 0.6172 0.6298 0.6372 0.6449
0.5773 0.5913 0.6014 0.6123 0.6217 0.6317 0.6392
T/K
Pexp/kPa
317.63 323.32 330.04 337.05 343.15 348.44 353.97 358.10
9.313 12.417 17.104 23.601 30.859 38.586 48.377 57.075
318.64 328.63 333.95 338.47 344.41 349.69 354.52 358.11
2. Experimental 2.1. Materials The chemical reagents used in this study were ethanol, methanol, redistilled water, and IL [EEIM][DEP]. Analytical Reagent grade methanol and ethanol with mass fraction purity of 0.998 were purchased from Beijing Red Star Reagents Company, China. The purity of reagents was checked by gas chromatogram (GC2010, Japan). The IL used was prepared and purified in the laboratory according to the literature method [11,12], and the mass fraction purity was more than 0.98 in terms of NMR analysis. Furthermore, the IL was treated before use by vacuum evaporation to remove the residual volatile impurities, and the water content was within 520 Æ 106 as measured by Karl–Fischer method (CBS-1A). 2.2. Apparatus and procedure The details of the experimental apparatus and the operation procedure were described elsewhere [12]. It was composed of a working ebulliometer and a reference one. The two ebulliometers were connected to a buffer to suppress the pressure fluctuation, and the equilibrium pressure of the system was determined by the boiling temperature of water in the reference ebulliometer in terms of the temperature–pressure relation represented by Antoine equation [13]. The equilibrium temperature of the ebulliometers was measured by 2 four-wire 25-X calibrated platinum resistance thermometers (type CST6601) with an uncertainty of 0.02 K, connected to a two-channel standard digital thermometer (CST6502). The uncertainty of the vapour pressure arising from the uncertainty of temperature measurement is estimated within ±0.04 kPa, and the vapour pressure reproducibility for a replicate sample is within ±0.07 kPa. The condensers were cooled with chilling glycol aqueous solution at 2 °C to minimize the vapour phase loss during the measurement and hence the concentration variation of the solution. The uncertainty of the mole fraction in the liquid phase is estimated within 0.002. 3. Results and discussion The vapour pressure data for three binary systems (water + [EEIM][DEP]), (methanol + [EEIM][DEP]), and (ethanol + [EEIM][DEP]) and three ternary system (water + methanol + [EEIM][DEP]), (water + ethanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]) at IL mass fraction from 0.10 to 0.85 (mole fraction from 0.0071 to 0.4849) were measured and listed in tables 1 to 6, respectively.
PNRTL/kPa
ARD(P) = 0.018, RMSD = 0.024 Pn NRTL ARDðP Þ ¼ P exp =P exp =n; i¼1 P rhffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi 2 i Pn cal exp RMSD ¼ 1 =n: i¼1 P =P
The effect of IL on the non-ideality of a solution can be expressed by activity coefficient of component i, ci, which can be calculated by the following equation [14]: ^ i P =ðxi /s P s Þ; ci ¼ y i / i i
ð1Þ
where P and P si are vapour pressures of the liquid mixture and pure component i at system temperature, respectively, and the latter can be calculated by Antoine equation with Antoine constants taken from the literature [13]. The yi and xi represent mole fraction of component i in the va^ i is the fugacity pour phase and liquid phase, respectively, / coefficient of component i in the vapour mixture, and /si is the fugacity coefficient of pure component i in its saturated state. For an IL-containing binary system, i.e. {solvent (1) + IL (2)}, the vapour phase is fully composed of solvent
X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846 TABLE 2 Vapour pressure data of binary system {methanol (1) + [EEIM][DEP] (2)}
TABLE 3 Vapour pressure data of binary system {ethanol (1) + [EEIM][DEP] (2)}
cexp 1
cNRTL 1
T/K
Pexp/kPa
x = 0.9874 17.531 21.169 25.551 30.811 36.386 43.277 50.354 58.437
0.9845 0.9856 0.9855 0.9846 0.9845 0.9848 0.9851 0.9854
0.9927 0.9931 0.9934 0.9937 0.9940 0.9942 0.9944 0.9946
309.96 314.00 319.06 323.19 327.26 330.78 334.37 337.91
14.808 18.301 23.625 28.909 35.060 41.264 48.506 56.716
17.011 19.485 23.240 28.841 34.748 41.695 49.950 57.898
x1 = 0.9530 17.166 19.680 23.448 29.124 35.089 42.066 50.342 58.381
0.9148 0.9162 0.9199 0.9224 0.9252 0.9286 0.9320 0.9336
0.9232 0.9254 0.9282 0.9315 0.9342 0.9368 0.9394 0.9414
309.80 313.92 318.49 321.24 325.40 329.03 333.54 338.72
304.41 309.04 312.75 316.39 320.25 324.51 327.72 331.26
15.977 20.320 24.418 29.051 34.773 42.231 48.525 56.515
x1 = 0.8968 15.894 20.158 24.241 28.916 34.670 42.132 48.612 56.688
0.7652 0.7766 0.7831 0.7876 0.7930 0.7995 0.8013 0.8057
0.7613 0.7704 0.7774 0.7839 0.7906 0.7977 0.8027 0.8082
330.07 335.85 341.15 346.66 351.65 356.22 361.20 366.19
14.336 18.745 23.771 29.985 37.048 44.985 54.429 65.452
x1 = 0.6052 14.311 18.732 23.767 30.169 37.167 44.720 54.407 65.779
0.3180 0.3289 0.3389 0.3471 0.3574 0.3691 0.3761 0.3829
0.3175 0.3287 0.3388 0.3492 0.3585 0.3669 0.3759 0.3848
T/K
Pexp/kPa
299.20 302.90 306.70 310.58 314.13 317.92 321.32 324.75
17.386 21.011 25.347 30.529 36.039 42.869 49.884 57.891
300.90 303.56 307.06 311.51 315.46 319.41 323.44 326.85
PNRTL/kPa
843
cexp 1
cNRTL 1
x1 = 0.9817 14.838 18.327 23.654 28.942 35.097 41.282 48.502 56.666
0.9955 0.9961 0.9964 0.9965 0.9966 0.9973 0.9978 0.9987
0.9975 0.9976 0.9976 0.9977 0.9977 0.9977 0.9978 0.9978
13.490 16.741 21.170 24.276 29.674 35.216 43.290 54.395
x1 = 0.9338 13.585 16.857 21.262 24.354 29.749 35.260 43.289 54.357
0.9617 0.9623 0.9653 0.9668 0.9679 0.9696 0.9713 0.9725
0.9685 0.9690 0.9696 0.9699 0.9704 0.9708 0.9713 0.9718
310.59 316.24 318.57 323.93 329.23 333.85 339.15 342.93
11.648 15.641 17.646 22.978 29.635 36.689 46.313 54.503
x1 = 0.8580 11.637 15.632 17.596 22.918 29.465 36.410 46.022 54.123
0.8669 0.8693 0.8724 0.8747 0.8799 0.8835 0.8845 0.8867
0.8661 0.8688 0.8700 0.8724 0.8748 0.8768 0.8790 0.8805
344.56 349.59 355.84 359.82 365.11 370.80
9.139 11.648 15.641 18.686 23.205 29.875
x1 = 0.5151 9.175 11.684 15.686 18.709 23.222 29.536
0.2382 0.2442 0.2516 0.2565 0.2622 0.2719
0.2391 0.2450 0.2523 0.2568 0.2624 0.2688
PNRTL/kPa
ARD(P) = 0.0030, RMSD = 0.0041
ARD(P) = 0.0063, RMSD = 0.0071
vapour due to the non-volatility of IL, and thus y1 = 1. Since the vapour phase composition for such a binary system and for the pure solvent are the same, and the pressure difference between them is relatively small, the fugacity coefficient correction can be cancelled out. Therefore, equation (1) can be simplified as follows: c1 ¼ P =ðP s1 x1 Þ:
ð2Þ
According to equation (2), the experimental activity coefficient of the solvent in an IL-containing binary liquid mixture can be calculated from the vapour pressure data, which were listed in tables 1 to 3, respectively. In order to correlate the experimental vapour pressure data, the NRTL equation [14] for non-electrolyte solution is used to describe the activity coefficient of the solvent as a rigorous model specific for IL-containing systems has been not available. The NRTL parameters for three binary sys-
tems, aij and (gij gjj) as listed in table 7, were obtained by fitting the experimental vapour pressure data in the whole temperature and composition range using a least square method. As shown in tables 1 to 3, the experimental vapour pressure can be well correlated by NRTL equation with average absolute relative deviation (ARD) less than 0.018 for the three binary systems studied. For the (methanol + [EEIM][DEP]) system, the variation trend of vapour pressure with temperature at different IL-content is shown in figure 1, while the T, p, x diagrams for other binary systems are not shown as they are very similar to figure 1. It is seen that the plot of the log(P/kPa) against 1/(T C) relation for a given concentration is linear over the pressure and temperature range studied, which is similar to the vapour pressure behaviour of the pure solvent and C is the corresponding Antoine constant for the pure solvent. It is apparent that ionic liquids always decrease the vapour pressure of solvent due to the strong affinity between solvents and ionic liquid, and
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X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846
TABLE 4 The experimental and predictive vapour pressure and activity coefficient of solvents for ternary system {water (1) + methanol (2) + [EEIM][DEP] (3)} T/K
Pexp/kPa
PNRTL/kPa
cNRTL 1
cNRTL 2
319.03 321.86 325.97 331.12 333.80 336.92 344.29 347.46
16.216 18.498 22.407 28.258 31.795 36.326 49.295 55.865
x1 = 0.8508, x2 = 0.1196 14.376 16.477 19.994 25.288 28.484 32.632 44.504 50.613
312.90 315.25 317.88 321.85 326.63 331.21 335.99 340.23
16.315 18.794 21.302 25.687 31.881 38.869 47.656 56.413
x1 = 0.7036, x2 = 0.2639 14.579 16.360 18.566 22.382 27.836 34.097 41.838 49.911
1.0177 1.0177 1.0176 1.0176 1.0175 1.0174 1.0173 1.0171
1.0149 1.0162 1.0177 1.0198 1.0221 1.0242 1.0262 1.0278
309.03 312.89 315.76 319.76 323.72 328.18 331.26 334.76
17.437 21.098 24.248 29.422 35.377 43.197 49.418 57.313
x1 = 0.5228, x2 = 0.4009 15.768 19.064 21.888 26.404 31.629 38.529 44.024 51.029
1.0524 1.0520 1.0517 1.0512 1.0507 1.0502 1.0498 1.0494
0.9742 0.9767 0.9785 0.9808 0.9830 0.9853 0.9868 0.9884
307.13 309.27 312.25 316.21 319.98 324.03 327.26 330.29
21.296 23.689 27.356 33.057 39.246 46.915 53.915 61.177
x1 = 0.1577, x2 = 0.7985 20.797 23.115 26.708 32.188 38.279 45.863 52.786 60.056
1.1463 1.1458 1.1450 1.1440 1.1429 1.1418 1.1409 1.1400
0.9341 0.9357 0.9378 0.9404 0.9427 0.9451 0.9470 0.9486
0.9973 0.9975 0.9977 0.9980 0.9982 0.9983 0.9987 0.9988
1.0622 1.0635 1.0653 1.0673 1.0682 1.0693 1.0715 1.0723
TABLE 5 The experimental and predicted vapour pressure data and activity coefficient of solvents for ternary system {water (1) + ethanol (2) + [EEIM][DEP] (3)} T/K
Pexp/kPa
318.19 322.00 326.20 331.03 335.94 341.98 345.69 349.53
14.564 17.518 21.573 26.931 33.593 43.663 50.996 59.606
317.10 320.63 324.60 328.64 333.33 337.06 340.80 343.73
PNRTL/kPa
cNRTL 1
cNRTL 2
x1 = 0.8830, x2 = 0.0864 14.999 18.082 22.082 27.589 34.334 44.493 51.910 60.651
1.0243 1.0243 1.0243 1.0243 1.0243 1.0242 1.0241 1.0240
3.1714 3.1402 3.1066 3.0690 3.0320 2.9879 2.9617 2.9352
16.644 19.846 24.038 29.042 36.163 42.591 50.190 56.853
x1 = 0.7650, x2 = 0.1996 16.678 19.876 24.064 29.087 35.999 42.432 49.840 56.383
1.1202 1.1194 1.1185 1.1176 1.1165 1.1156 1.1147 1.1140
2.0404 2.0316 2.0219 2.0121 2.0009 1.9921 1.9835 1.9767
316.89 321.59 323.17 325.70 329.80 333.27 336.55 341.03
18.226 22.792 24.589 27.811 33.722 39.564 45.788 56.173
x1 = 0.6038 x2 = 0.3544 17.955 22.675 24.475 27.634 33.464 39.169 45.317 55.003
1.3024 1.3003 1.2996 1.2984 1.2965 1.2948 1.2932 1.2910
1.4202 1.4171 1.4160 1.4144 1.4117 1.4095 1.4074 1.4047
316.49 319.28 321.07 324.24 328.47 332.31 336.77 340.23
19.076 21.888 23.916 27.909 34.097 40.629 49.568 57.584
x1 = 0.2193, x2 = 0.7233 19.188 22.064 24.112 28.125 34.343 40.959 49.968 58.063
1.8177 1.8192 1.8200 1.8212 1.8225 1.8232 1.8237 1.8237
1.0211 1.0209 1.0207 1.0205 1.0201 1.0198 1.0195 1.0193
ARD(P) = 0.088, RMSD = 0.096 ARD(P) = 0.011, RMSD = 0.014
the higher the IL-content, the lower the solvent vapour pressure. Moreover, the vapour pressure of solvent shows a negative deviation from the Raoult’s law as the activity coefficient of solvent is nearly always smaller than unity, as shown in tables 1 to 3. Under low pressures, the vapour phase is approximately ideal; hence, the vapour pressure for a ternary system {solvent (1) + solvent (2) + IL (3)} can be calculated by equation (3), and the vapour-phase mole fraction of component i, yi, at equilibrium can be calculated with equation (4) considering the non-volatility of IL, X2 p¼ p s x i ci ; ð3Þ i¼1 i p s xi c yi ¼ P i s i : j p j x j cj
ð4Þ
The vapour pressure for ternary systems (water + ethanol + [EEIM][DEP]), (water + methanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]) at varying liquid composition and temperature was predicted using the binary NRTL parameters listed in table 7 and compared with the experimental values as listed in tables 4 to 6. It is seen that the agreement between the experimental and the predicted values is fairly good with average deviation ARD of 0.037 and the maximum deviation of 0.1295. From the point of view of practical application, the conventional NRTL model for non-electrolyte solution is applicable for representing the (vapour + liquid) equilibrium of IL-containing multi-component systems, as indicated by Doker and Gmehling and Shi et al. [5,15]. In order to show the salt effect of ionic liquid [EEIM][DEP] on the distillation separation of three
X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846 TABLE 6 The experimental and predicted vapour pressure data and activity coefficient of solvents for ternary system {ethanol (1) + methanol (2) + [EEIM][DEP] (3)} Pexp/kPa
PNRTL/kPa
cNRTL 1
cNRTL 2
0.9882 0.9877 0.9871 0.9865 0.9859 0.9854 0.9851 0.9848
0.8265 0.8344 0.8434 0.8519 0.8605 0.8685 0.8733 0.8783
309.63 313.28 317.59 321.83 326.41 330.81 333.61 336.58
16.265 19.559 24.189 29.629 36.675 44.732 50.576 57.492
x1 = 0.6906, x2 = 0.2482 16.313 19.674 24.396 29.933 37.088 45.268 51.227 58.258
308.12 311.07 314.95 318.99 324.00 327.58 330.69
17.495 20.305 24.571 29.839 37.620 44.184 50.560
x1 = 0.4816, x2 = 0.4615 17.847 20.742 25.135 30.534 38.550 45.328 51.993
0.9748 0.9745 0.9740 0.9735 0.9729 0.9726 0.9722
0.8852 0.8899 0.8958 0.9016 0.9085 0.9131 0.9170
306.10 309.67 313.06 316.01 319.73 323.47 327.63 330.81
18.527 22.007 25.955 29.856 35.468 41.970 50.343 57.627
x1 = 0.3000, x2 = 0.6467 18.461 22.101 26.108 30.086 35.820 42.491 51.119 58.651
0.9422 0.9424 0.9426 0.9428 0.9430 0.9432 0.9435 0.9436
0.9155 0.9197 0.9235 0.9267 0.9305 0.9341 0.9379 0.9407
303.01 307.02 310.03 313.31 316.82 321.04 324.82 328.01
18.507 22.574 26.132 30.532 35.919 43.427 51.215 58.696
x1 = 0.0682, x2 = 0.8834 18.396 22.529 26.120 30.581 36.045 43.698 51.665 59.308
0.8751 0.8772 0.8787 0.8803 0.8820 0.8840 0.8857 0.8871
0.9270 0.9304 0.9328 0.9353 0.9379 0.9408 0.9433 0.9453
1.8 1.7 1.6 LogP (kPa)
T/K
845
1.5 1.4 1.3 1.2 1.1 0.0029
0.0031
0.0033 0.0035 1/{(t /˚C)+ 239.726}
0.0037
FIGURE 1. Plot of the experimental and correlative vapour pressure data against reciprocal temperature for the binary system {methanol (1) + [EEIM][DEP] (2)} at different values of mass fraction [EEIM][DEP]. Legend: - - - - pure methanol; —- calculated by NRTL equation. Symbols refer to experimental data at different values of mass fraction [EEIM] [DEP]: (j) 0.10; (m) 0.30; (d) 0.50; (D) 0.85.
of 0.5 [EEIM][DEP] were predicted in the whole concentration range. The results were plotted in figures 2 to 4, respectively, on a salt free basis for liquid composition, and compared with the VLE curves in the absence of IL. The results suggest that the salt effect of IL on the (vapour + liquid) equilibria of three binary systems is quite complex because both salting-in and salting-out effect occur in different concentration range (see table 8).
1
ARD(P) = 0.012, RMSD = 0.013
0.9 0.8 0.7 0.6
y2
binary mixtures, (water + ethanol), (water + methanol), and (ethanol + methanol), isobaric (vapour + liquid) equilibria for such mixtures in the presence of mass fraction
0.5 0.4
TABLE 7 The NRTL parameters fitted for IL-containing binary systems and taken from the literature [13] for the vapour pressure prediction of the ILcontaining ternary systems System
a12
(g12-g22)/ (J Æ mol1)
(g21g11)/ (J Æ mol1)
(water + [EEIM][DEP]) (ethanol + [EEIM][DEP]) (methanol + [EEIM][DEP]) (ethanol + water) [13] (ethanol + methanol) [13] (methanol + water) [13]
0.5317 0.1225 0.6149 0.3008 0.3053 0.3013
42.382 8431.8 56.180 510.82 1580.2 172.12
5725.8 6998.3 6104.0 5612.1 1292.9 768.56
0.3 0.2 0.1 0
0
0.2
0.4
x 2'
0.6
0.8
1
FIGURE 2. Plot of mole fraction vapour against mole fraction liquid at constant pressure to show the VLE diagram for the {water (1) + ethanol (2) + [EEIM][DEP] (3)} ternary systems at atmospheric pressure. Legend: - - - - - IL-free (water + ethanol) (j) (water + ethanol) at mass fraction of [EEIM][DEP] of 0.50.
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X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846
1 0.9
TABLE 8 Antoine vapour pressure constants of pure compounds
0.8
Component
Antoine constants A
B
C
Ethanol Methanol Water
8.1122 8.08097 8.07131
1592.864 1582.271 1730.63
226.184 239.726 233.426
0.7
y2
0.6 0.5
Antoine equation log psat = A B/(t + C) where psat is in Torr, and t is temperature in °C.
0.4 0.3 0.2 0.1 0
0
0.2
0.4
x2 '
0.6
0.8
1
FIGURE 3. Plot of mole fraction vapour against mole fraction liquid at constant pressure to show the isobaric VLE diagram for the {water (1) + methanol (2) + [EEIM][DEP] (3)} ternary systems at atmospheric pressure. Legend: - - - - - IL-free (water + methanol) (j) (water + methanol) at mass fraction of [EEIM][DEP] of 0.50.
1 0.9
0.7 0.6 y1
Acknowledgements The authors are grateful for the financial support from the National Natural Science Foundation of China (No. 20376004) that allowed the authors to accomplish the research presented herein. References
0.8
0.5 0.4 0.3 0.2 0.1 0 0
[EEIM][DEP] and the different solvents. The vapour pressure data of binary systems can be well correlated with NRTL equation, and the NRTL parameters obtained can be applied for the prediction of vapour pressure of multicomponent systems with fair accuracy.
0.2
0.4
x1'
0.6
0.8
1
FIGURE 4. Plot of mole fraction vapour against mole fraction liquid at constant pressure to show the isobaric VLE diagram for the {ethanol (1) + methanol (2) + [EEIM][DEP] (3)} ternary systems at atmospheric pressure. Legend: - - - - - IL-free (ethanol + methanol) (j) (ethanol + methanol) at mass fraction of [EEIM][DEP] of 0.50.
4. Conclusions Vapour pressure data for three binary and three ternary IL-containing systems at varying temperature and ILcontent were measured using a quasi-static method. The results indicate that ionic liquid [EEIM][DEP] can reduce the vapour pressure of water, methanol, and ethanol but to different extents due to the affinity difference between
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JCT 06-235
Vapour pressure measurement for binary and ternary systems containing water methanol ethanol and an ionic liquid 1-ethyl-3-ethylimidazolium diethylphosphate Xiao-Chuan Jiang, Jun-Feng Wang, Chun-Xi Li *, La-Mei Wang, Zi-Hao Wang College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China Received 12 September 2006; received in revised form 30 November 2006; accepted 30 November 2006 Available online 12 December 2006
Abstract Vapour pressure data were measured for three binary systems containing water, methanol or ethanol with an ionic liquid (IL) 1-ethyl3-ethylimidazolium diethylphosphate([EEIM][DEP]) and for three ternary systems, i.e. (water + ethanol + [EEIM][DEP]), (water + methanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]), at varying temperature and IL-content ranging from mass fraction of 0.10 to 0.85 by a quasi-static method. The vapour pressure data of the binary systems were correlated by NRTL equation with average absolute relative deviation (ARD) within 0.0091. The binary NRTL parameters were used to predict the vapour pressure of the ternary systems (ethanol + water + [EEIM][DEP]), (water + methanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]) with an overall ARD of 0.037 and the maximum deviation of 0.1295. The results indicate that ionic liquid [EEIM][DEP] can give rise to a negative deviation from the Raoult’s law for the solvents of water, methanol and ethanol, but to a varying degree leading to the variation of relative volatility of a solvent and even removal of azeotrope for (water + ethanol). Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Vapour pressure; Measurement; Ionic liquid; NRTL equation; (Vapour + liquid) equilibrium
1. Introduction Ionic liquids (ILs) have recently attracted considerable attention for their unique attributes, e.g. negligible vapour pressure, good stability, and ionic property in contrast to the conventional molecular solvents, and some encouraging results have been achieved with respect to their utilization as a benign medium and/or solvent in a reaction and/ or separation process [1]. Vapour pressure data indicate that volatility of solvents can be changed dramatically by the addition of ionic liquid, while the variation extent is different depending on the nature of both solvent and ionic liquid involved. As a result, the relative volatility of a component is changed and even the azeotrope of a binary liquid mixture eliminated. When an IL is used as a solvent and/or salt in a salt/extractive distillation process, it might *
Corresponding author. Tel./fax: +86 10 64410308. E-mail address: [email protected] (C.-X. Li).
0021-9614/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2006.11.013
be superior to the commonly used entrainers due to its non-volatility, less causticity, and good performance in improving the separation efficiency. In contrast to the overwhelming application-oriented reports on ILs, only limited thermodynamic data on IL-containing systems have been available, for example, (liquid + liquid) equilibrium [2,3], (vapour + liquid) equilibrium [4–6], and infinite dilution activity coefficient of some organic solvents [7–10]. Vapour pressure data for IL-containing binary systems are essential for the development of thermodynamic model and calculation of (vapour + liquid) equilibrium for ILcontaining multi-component systems. However, the vapour pressure data for such systems are extremely scarce. For this reason, new vapour pressure data were measured for three IL-containing binary systems and three ternary system using quasi-static method, and the effect of ionic liquid [EEIM][DEP] on the vapour pressure lowering of water, methanol, and ethanol was investigated. The applicability of non-electrolyte NRTL equation in correlating binary
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and predicting ternary VLE data for IL-containing systems was discussed.
TABLE 1 Vapour pressure data of binary system {water (1) + [EEIM][DEP] (2)} cexp 1
cNRTL 1
x1 = 0.9929 9.230 12.310 17.044 23.556 30.842 38.632 48.476 57.141
1.0078 1.0077 1.0026 1.0001 0.9997 0.9980 0.9972 0.9981
0.9989 0.9990 0.9991 0.9991 0.9992 0.9992 0.9992 0.9993
9.352 15.336 19.706 24.119 31.311 38.853 47.442 54.915
x1 = 0.9734 9.413 15.447 19.831 24.357 31.612 39.518 48.144 55.562
0.9801 0.9806 0.9821 0.9791 0.9799 0.9731 0.9757 0.9789
0.9865 0.9877 0.9883 0.9887 0.9893 0.9898 0.9902 0.9905
322.37 328.73 334.78 340.58 346.28 350.76 355.06 359.05
9.999 13.708 18.237 23.740 30.475 36.793 43.825 51.389
x1 = 0.9392 10.467 14.328 19.056 24.793 31.791 38.402 45.803 53.889
0.8986 0.9039 0.9068 0.9096 0.9127 0.9138 0.9140 0.9151
0.9417 0.9448 0.9475 0.9499 0.9522 0.9538 0.9553 0.9597
335.67 343.03 348.57 354.81 360.40 366.55 371.31
9.576 13.588 17.498 22.917 29.158 37.269 44.949
x1 = 0.7348 9.461 13.439 17.298 22.737 28.782 36.949 44.547
0.5844 0.5978 0.6083 0.6172 0.6298 0.6372 0.6449
0.5773 0.5913 0.6014 0.6123 0.6217 0.6317 0.6392
T/K
Pexp/kPa
317.63 323.32 330.04 337.05 343.15 348.44 353.97 358.10
9.313 12.417 17.104 23.601 30.859 38.586 48.377 57.075
318.64 328.63 333.95 338.47 344.41 349.69 354.52 358.11
2. Experimental 2.1. Materials The chemical reagents used in this study were ethanol, methanol, redistilled water, and IL [EEIM][DEP]. Analytical Reagent grade methanol and ethanol with mass fraction purity of 0.998 were purchased from Beijing Red Star Reagents Company, China. The purity of reagents was checked by gas chromatogram (GC2010, Japan). The IL used was prepared and purified in the laboratory according to the literature method [11,12], and the mass fraction purity was more than 0.98 in terms of NMR analysis. Furthermore, the IL was treated before use by vacuum evaporation to remove the residual volatile impurities, and the water content was within 520 Æ 106 as measured by Karl–Fischer method (CBS-1A). 2.2. Apparatus and procedure The details of the experimental apparatus and the operation procedure were described elsewhere [12]. It was composed of a working ebulliometer and a reference one. The two ebulliometers were connected to a buffer to suppress the pressure fluctuation, and the equilibrium pressure of the system was determined by the boiling temperature of water in the reference ebulliometer in terms of the temperature–pressure relation represented by Antoine equation [13]. The equilibrium temperature of the ebulliometers was measured by 2 four-wire 25-X calibrated platinum resistance thermometers (type CST6601) with an uncertainty of 0.02 K, connected to a two-channel standard digital thermometer (CST6502). The uncertainty of the vapour pressure arising from the uncertainty of temperature measurement is estimated within ±0.04 kPa, and the vapour pressure reproducibility for a replicate sample is within ±0.07 kPa. The condensers were cooled with chilling glycol aqueous solution at 2 °C to minimize the vapour phase loss during the measurement and hence the concentration variation of the solution. The uncertainty of the mole fraction in the liquid phase is estimated within 0.002. 3. Results and discussion The vapour pressure data for three binary systems (water + [EEIM][DEP]), (methanol + [EEIM][DEP]), and (ethanol + [EEIM][DEP]) and three ternary system (water + methanol + [EEIM][DEP]), (water + ethanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]) at IL mass fraction from 0.10 to 0.85 (mole fraction from 0.0071 to 0.4849) were measured and listed in tables 1 to 6, respectively.
PNRTL/kPa
ARD(P) = 0.018, RMSD = 0.024 Pn NRTL ARDðP Þ ¼ P exp =P exp =n; i¼1 P rhffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi 2 i Pn cal exp RMSD ¼ 1 =n: i¼1 P =P
The effect of IL on the non-ideality of a solution can be expressed by activity coefficient of component i, ci, which can be calculated by the following equation [14]: ^ i P =ðxi /s P s Þ; ci ¼ y i / i i
ð1Þ
where P and P si are vapour pressures of the liquid mixture and pure component i at system temperature, respectively, and the latter can be calculated by Antoine equation with Antoine constants taken from the literature [13]. The yi and xi represent mole fraction of component i in the va^ i is the fugacity pour phase and liquid phase, respectively, / coefficient of component i in the vapour mixture, and /si is the fugacity coefficient of pure component i in its saturated state. For an IL-containing binary system, i.e. {solvent (1) + IL (2)}, the vapour phase is fully composed of solvent
X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846 TABLE 2 Vapour pressure data of binary system {methanol (1) + [EEIM][DEP] (2)}
TABLE 3 Vapour pressure data of binary system {ethanol (1) + [EEIM][DEP] (2)}
cexp 1
cNRTL 1
T/K
Pexp/kPa
x = 0.9874 17.531 21.169 25.551 30.811 36.386 43.277 50.354 58.437
0.9845 0.9856 0.9855 0.9846 0.9845 0.9848 0.9851 0.9854
0.9927 0.9931 0.9934 0.9937 0.9940 0.9942 0.9944 0.9946
309.96 314.00 319.06 323.19 327.26 330.78 334.37 337.91
14.808 18.301 23.625 28.909 35.060 41.264 48.506 56.716
17.011 19.485 23.240 28.841 34.748 41.695 49.950 57.898
x1 = 0.9530 17.166 19.680 23.448 29.124 35.089 42.066 50.342 58.381
0.9148 0.9162 0.9199 0.9224 0.9252 0.9286 0.9320 0.9336
0.9232 0.9254 0.9282 0.9315 0.9342 0.9368 0.9394 0.9414
309.80 313.92 318.49 321.24 325.40 329.03 333.54 338.72
304.41 309.04 312.75 316.39 320.25 324.51 327.72 331.26
15.977 20.320 24.418 29.051 34.773 42.231 48.525 56.515
x1 = 0.8968 15.894 20.158 24.241 28.916 34.670 42.132 48.612 56.688
0.7652 0.7766 0.7831 0.7876 0.7930 0.7995 0.8013 0.8057
0.7613 0.7704 0.7774 0.7839 0.7906 0.7977 0.8027 0.8082
330.07 335.85 341.15 346.66 351.65 356.22 361.20 366.19
14.336 18.745 23.771 29.985 37.048 44.985 54.429 65.452
x1 = 0.6052 14.311 18.732 23.767 30.169 37.167 44.720 54.407 65.779
0.3180 0.3289 0.3389 0.3471 0.3574 0.3691 0.3761 0.3829
0.3175 0.3287 0.3388 0.3492 0.3585 0.3669 0.3759 0.3848
T/K
Pexp/kPa
299.20 302.90 306.70 310.58 314.13 317.92 321.32 324.75
17.386 21.011 25.347 30.529 36.039 42.869 49.884 57.891
300.90 303.56 307.06 311.51 315.46 319.41 323.44 326.85
PNRTL/kPa
843
cexp 1
cNRTL 1
x1 = 0.9817 14.838 18.327 23.654 28.942 35.097 41.282 48.502 56.666
0.9955 0.9961 0.9964 0.9965 0.9966 0.9973 0.9978 0.9987
0.9975 0.9976 0.9976 0.9977 0.9977 0.9977 0.9978 0.9978
13.490 16.741 21.170 24.276 29.674 35.216 43.290 54.395
x1 = 0.9338 13.585 16.857 21.262 24.354 29.749 35.260 43.289 54.357
0.9617 0.9623 0.9653 0.9668 0.9679 0.9696 0.9713 0.9725
0.9685 0.9690 0.9696 0.9699 0.9704 0.9708 0.9713 0.9718
310.59 316.24 318.57 323.93 329.23 333.85 339.15 342.93
11.648 15.641 17.646 22.978 29.635 36.689 46.313 54.503
x1 = 0.8580 11.637 15.632 17.596 22.918 29.465 36.410 46.022 54.123
0.8669 0.8693 0.8724 0.8747 0.8799 0.8835 0.8845 0.8867
0.8661 0.8688 0.8700 0.8724 0.8748 0.8768 0.8790 0.8805
344.56 349.59 355.84 359.82 365.11 370.80
9.139 11.648 15.641 18.686 23.205 29.875
x1 = 0.5151 9.175 11.684 15.686 18.709 23.222 29.536
0.2382 0.2442 0.2516 0.2565 0.2622 0.2719
0.2391 0.2450 0.2523 0.2568 0.2624 0.2688
PNRTL/kPa
ARD(P) = 0.0030, RMSD = 0.0041
ARD(P) = 0.0063, RMSD = 0.0071
vapour due to the non-volatility of IL, and thus y1 = 1. Since the vapour phase composition for such a binary system and for the pure solvent are the same, and the pressure difference between them is relatively small, the fugacity coefficient correction can be cancelled out. Therefore, equation (1) can be simplified as follows: c1 ¼ P =ðP s1 x1 Þ:
ð2Þ
According to equation (2), the experimental activity coefficient of the solvent in an IL-containing binary liquid mixture can be calculated from the vapour pressure data, which were listed in tables 1 to 3, respectively. In order to correlate the experimental vapour pressure data, the NRTL equation [14] for non-electrolyte solution is used to describe the activity coefficient of the solvent as a rigorous model specific for IL-containing systems has been not available. The NRTL parameters for three binary sys-
tems, aij and (gij gjj) as listed in table 7, were obtained by fitting the experimental vapour pressure data in the whole temperature and composition range using a least square method. As shown in tables 1 to 3, the experimental vapour pressure can be well correlated by NRTL equation with average absolute relative deviation (ARD) less than 0.018 for the three binary systems studied. For the (methanol + [EEIM][DEP]) system, the variation trend of vapour pressure with temperature at different IL-content is shown in figure 1, while the T, p, x diagrams for other binary systems are not shown as they are very similar to figure 1. It is seen that the plot of the log(P/kPa) against 1/(T C) relation for a given concentration is linear over the pressure and temperature range studied, which is similar to the vapour pressure behaviour of the pure solvent and C is the corresponding Antoine constant for the pure solvent. It is apparent that ionic liquids always decrease the vapour pressure of solvent due to the strong affinity between solvents and ionic liquid, and
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X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846
TABLE 4 The experimental and predictive vapour pressure and activity coefficient of solvents for ternary system {water (1) + methanol (2) + [EEIM][DEP] (3)} T/K
Pexp/kPa
PNRTL/kPa
cNRTL 1
cNRTL 2
319.03 321.86 325.97 331.12 333.80 336.92 344.29 347.46
16.216 18.498 22.407 28.258 31.795 36.326 49.295 55.865
x1 = 0.8508, x2 = 0.1196 14.376 16.477 19.994 25.288 28.484 32.632 44.504 50.613
312.90 315.25 317.88 321.85 326.63 331.21 335.99 340.23
16.315 18.794 21.302 25.687 31.881 38.869 47.656 56.413
x1 = 0.7036, x2 = 0.2639 14.579 16.360 18.566 22.382 27.836 34.097 41.838 49.911
1.0177 1.0177 1.0176 1.0176 1.0175 1.0174 1.0173 1.0171
1.0149 1.0162 1.0177 1.0198 1.0221 1.0242 1.0262 1.0278
309.03 312.89 315.76 319.76 323.72 328.18 331.26 334.76
17.437 21.098 24.248 29.422 35.377 43.197 49.418 57.313
x1 = 0.5228, x2 = 0.4009 15.768 19.064 21.888 26.404 31.629 38.529 44.024 51.029
1.0524 1.0520 1.0517 1.0512 1.0507 1.0502 1.0498 1.0494
0.9742 0.9767 0.9785 0.9808 0.9830 0.9853 0.9868 0.9884
307.13 309.27 312.25 316.21 319.98 324.03 327.26 330.29
21.296 23.689 27.356 33.057 39.246 46.915 53.915 61.177
x1 = 0.1577, x2 = 0.7985 20.797 23.115 26.708 32.188 38.279 45.863 52.786 60.056
1.1463 1.1458 1.1450 1.1440 1.1429 1.1418 1.1409 1.1400
0.9341 0.9357 0.9378 0.9404 0.9427 0.9451 0.9470 0.9486
0.9973 0.9975 0.9977 0.9980 0.9982 0.9983 0.9987 0.9988
1.0622 1.0635 1.0653 1.0673 1.0682 1.0693 1.0715 1.0723
TABLE 5 The experimental and predicted vapour pressure data and activity coefficient of solvents for ternary system {water (1) + ethanol (2) + [EEIM][DEP] (3)} T/K
Pexp/kPa
318.19 322.00 326.20 331.03 335.94 341.98 345.69 349.53
14.564 17.518 21.573 26.931 33.593 43.663 50.996 59.606
317.10 320.63 324.60 328.64 333.33 337.06 340.80 343.73
PNRTL/kPa
cNRTL 1
cNRTL 2
x1 = 0.8830, x2 = 0.0864 14.999 18.082 22.082 27.589 34.334 44.493 51.910 60.651
1.0243 1.0243 1.0243 1.0243 1.0243 1.0242 1.0241 1.0240
3.1714 3.1402 3.1066 3.0690 3.0320 2.9879 2.9617 2.9352
16.644 19.846 24.038 29.042 36.163 42.591 50.190 56.853
x1 = 0.7650, x2 = 0.1996 16.678 19.876 24.064 29.087 35.999 42.432 49.840 56.383
1.1202 1.1194 1.1185 1.1176 1.1165 1.1156 1.1147 1.1140
2.0404 2.0316 2.0219 2.0121 2.0009 1.9921 1.9835 1.9767
316.89 321.59 323.17 325.70 329.80 333.27 336.55 341.03
18.226 22.792 24.589 27.811 33.722 39.564 45.788 56.173
x1 = 0.6038 x2 = 0.3544 17.955 22.675 24.475 27.634 33.464 39.169 45.317 55.003
1.3024 1.3003 1.2996 1.2984 1.2965 1.2948 1.2932 1.2910
1.4202 1.4171 1.4160 1.4144 1.4117 1.4095 1.4074 1.4047
316.49 319.28 321.07 324.24 328.47 332.31 336.77 340.23
19.076 21.888 23.916 27.909 34.097 40.629 49.568 57.584
x1 = 0.2193, x2 = 0.7233 19.188 22.064 24.112 28.125 34.343 40.959 49.968 58.063
1.8177 1.8192 1.8200 1.8212 1.8225 1.8232 1.8237 1.8237
1.0211 1.0209 1.0207 1.0205 1.0201 1.0198 1.0195 1.0193
ARD(P) = 0.088, RMSD = 0.096 ARD(P) = 0.011, RMSD = 0.014
the higher the IL-content, the lower the solvent vapour pressure. Moreover, the vapour pressure of solvent shows a negative deviation from the Raoult’s law as the activity coefficient of solvent is nearly always smaller than unity, as shown in tables 1 to 3. Under low pressures, the vapour phase is approximately ideal; hence, the vapour pressure for a ternary system {solvent (1) + solvent (2) + IL (3)} can be calculated by equation (3), and the vapour-phase mole fraction of component i, yi, at equilibrium can be calculated with equation (4) considering the non-volatility of IL, X2 p¼ p s x i ci ; ð3Þ i¼1 i p s xi c yi ¼ P i s i : j p j x j cj
ð4Þ
The vapour pressure for ternary systems (water + ethanol + [EEIM][DEP]), (water + methanol + [EEIM][DEP]), and (ethanol + methanol + [EEIM][DEP]) at varying liquid composition and temperature was predicted using the binary NRTL parameters listed in table 7 and compared with the experimental values as listed in tables 4 to 6. It is seen that the agreement between the experimental and the predicted values is fairly good with average deviation ARD of 0.037 and the maximum deviation of 0.1295. From the point of view of practical application, the conventional NRTL model for non-electrolyte solution is applicable for representing the (vapour + liquid) equilibrium of IL-containing multi-component systems, as indicated by Doker and Gmehling and Shi et al. [5,15]. In order to show the salt effect of ionic liquid [EEIM][DEP] on the distillation separation of three
X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846 TABLE 6 The experimental and predicted vapour pressure data and activity coefficient of solvents for ternary system {ethanol (1) + methanol (2) + [EEIM][DEP] (3)} Pexp/kPa
PNRTL/kPa
cNRTL 1
cNRTL 2
0.9882 0.9877 0.9871 0.9865 0.9859 0.9854 0.9851 0.9848
0.8265 0.8344 0.8434 0.8519 0.8605 0.8685 0.8733 0.8783
309.63 313.28 317.59 321.83 326.41 330.81 333.61 336.58
16.265 19.559 24.189 29.629 36.675 44.732 50.576 57.492
x1 = 0.6906, x2 = 0.2482 16.313 19.674 24.396 29.933 37.088 45.268 51.227 58.258
308.12 311.07 314.95 318.99 324.00 327.58 330.69
17.495 20.305 24.571 29.839 37.620 44.184 50.560
x1 = 0.4816, x2 = 0.4615 17.847 20.742 25.135 30.534 38.550 45.328 51.993
0.9748 0.9745 0.9740 0.9735 0.9729 0.9726 0.9722
0.8852 0.8899 0.8958 0.9016 0.9085 0.9131 0.9170
306.10 309.67 313.06 316.01 319.73 323.47 327.63 330.81
18.527 22.007 25.955 29.856 35.468 41.970 50.343 57.627
x1 = 0.3000, x2 = 0.6467 18.461 22.101 26.108 30.086 35.820 42.491 51.119 58.651
0.9422 0.9424 0.9426 0.9428 0.9430 0.9432 0.9435 0.9436
0.9155 0.9197 0.9235 0.9267 0.9305 0.9341 0.9379 0.9407
303.01 307.02 310.03 313.31 316.82 321.04 324.82 328.01
18.507 22.574 26.132 30.532 35.919 43.427 51.215 58.696
x1 = 0.0682, x2 = 0.8834 18.396 22.529 26.120 30.581 36.045 43.698 51.665 59.308
0.8751 0.8772 0.8787 0.8803 0.8820 0.8840 0.8857 0.8871
0.9270 0.9304 0.9328 0.9353 0.9379 0.9408 0.9433 0.9453
1.8 1.7 1.6 LogP (kPa)
T/K
845
1.5 1.4 1.3 1.2 1.1 0.0029
0.0031
0.0033 0.0035 1/{(t /˚C)+ 239.726}
0.0037
FIGURE 1. Plot of the experimental and correlative vapour pressure data against reciprocal temperature for the binary system {methanol (1) + [EEIM][DEP] (2)} at different values of mass fraction [EEIM][DEP]. Legend: - - - - pure methanol; —- calculated by NRTL equation. Symbols refer to experimental data at different values of mass fraction [EEIM] [DEP]: (j) 0.10; (m) 0.30; (d) 0.50; (D) 0.85.
of 0.5 [EEIM][DEP] were predicted in the whole concentration range. The results were plotted in figures 2 to 4, respectively, on a salt free basis for liquid composition, and compared with the VLE curves in the absence of IL. The results suggest that the salt effect of IL on the (vapour + liquid) equilibria of three binary systems is quite complex because both salting-in and salting-out effect occur in different concentration range (see table 8).
1
ARD(P) = 0.012, RMSD = 0.013
0.9 0.8 0.7 0.6
y2
binary mixtures, (water + ethanol), (water + methanol), and (ethanol + methanol), isobaric (vapour + liquid) equilibria for such mixtures in the presence of mass fraction
0.5 0.4
TABLE 7 The NRTL parameters fitted for IL-containing binary systems and taken from the literature [13] for the vapour pressure prediction of the ILcontaining ternary systems System
a12
(g12-g22)/ (J Æ mol1)
(g21g11)/ (J Æ mol1)
(water + [EEIM][DEP]) (ethanol + [EEIM][DEP]) (methanol + [EEIM][DEP]) (ethanol + water) [13] (ethanol + methanol) [13] (methanol + water) [13]
0.5317 0.1225 0.6149 0.3008 0.3053 0.3013
42.382 8431.8 56.180 510.82 1580.2 172.12
5725.8 6998.3 6104.0 5612.1 1292.9 768.56
0.3 0.2 0.1 0
0
0.2
0.4
x 2'
0.6
0.8
1
FIGURE 2. Plot of mole fraction vapour against mole fraction liquid at constant pressure to show the VLE diagram for the {water (1) + ethanol (2) + [EEIM][DEP] (3)} ternary systems at atmospheric pressure. Legend: - - - - - IL-free (water + ethanol) (j) (water + ethanol) at mass fraction of [EEIM][DEP] of 0.50.
846
X.-C. Jiang et al. / J. Chem. Thermodynamics 39 (2007) 841–846
1 0.9
TABLE 8 Antoine vapour pressure constants of pure compounds
0.8
Component
Antoine constants A
B
C
Ethanol Methanol Water
8.1122 8.08097 8.07131
1592.864 1582.271 1730.63
226.184 239.726 233.426
0.7
y2
0.6 0.5
Antoine equation log psat = A B/(t + C) where psat is in Torr, and t is temperature in °C.
0.4 0.3 0.2 0.1 0
0
0.2
0.4
x2 '
0.6
0.8
1
FIGURE 3. Plot of mole fraction vapour against mole fraction liquid at constant pressure to show the isobaric VLE diagram for the {water (1) + methanol (2) + [EEIM][DEP] (3)} ternary systems at atmospheric pressure. Legend: - - - - - IL-free (water + methanol) (j) (water + methanol) at mass fraction of [EEIM][DEP] of 0.50.
1 0.9
0.7 0.6 y1
Acknowledgements The authors are grateful for the financial support from the National Natural Science Foundation of China (No. 20376004) that allowed the authors to accomplish the research presented herein. References
0.8
0.5 0.4 0.3 0.2 0.1 0 0
[EEIM][DEP] and the different solvents. The vapour pressure data of binary systems can be well correlated with NRTL equation, and the NRTL parameters obtained can be applied for the prediction of vapour pressure of multicomponent systems with fair accuracy.
0.2
0.4
x1'
0.6
0.8
1
FIGURE 4. Plot of mole fraction vapour against mole fraction liquid at constant pressure to show the isobaric VLE diagram for the {ethanol (1) + methanol (2) + [EEIM][DEP] (3)} ternary systems at atmospheric pressure. Legend: - - - - - IL-free (ethanol + methanol) (j) (ethanol + methanol) at mass fraction of [EEIM][DEP] of 0.50.
4. Conclusions Vapour pressure data for three binary and three ternary IL-containing systems at varying temperature and ILcontent were measured using a quasi-static method. The results indicate that ionic liquid [EEIM][DEP] can reduce the vapour pressure of water, methanol, and ethanol but to different extents due to the affinity difference between
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JCT 06-235