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Phase equilibria of water + methanol + hexyl acetate mixtures
FLglDPHAS[ EQUIUBRIA ELSEVIER
Fluid Phase Equilibria 128 (1997) 261-270
Phase equilibria of water + methanol + hexyl acetate mixtures Alberto Arce *, Antonio Blanco, Ana Soto, Isabel Vidal Department of Chemical Engineering, University of Santiago, E-15706 Santiago de Compostela, Spain
Received 4 November 1995; accepted 22 February 1996
Abstract
Liquid-liquid equilibrium data at 25, 35 and 45 °C, and isobaric vapour-liquid equilibrium data at 101.32 kPa, were determined for the ternary system water + methanol + hexyl acetate. The data were correlated using the Wilson, NRTL and UNIQUAC models and were predicted using the UNIFAC and ASOG methods. Keywords: Liquid-liquid equilibrium; Vapour-liquid equilibrium; Correlation; Prediction 1. Introduction
Solvent extraction is an important technique for separation of liquid mixtures that has been widely examined in chemical engineering. Post-extraction recovery of the extractant is usually achieved by distillation of the extract phase. In this work, we examined the separation of methanol-water mixtures by extraction with hexyl acetate, and subsequent recovery of the ester by distillation. Isobaric vapour-liquid equilibrium (VLE) data for the binary system methanol + hexyl acetate have been published already [1]. Here we report VLE and liquid-liquid equilibrium (LLE) data for the ternary mixtures at 101.32 kPa, which as far as we are aware are not available in the literature. These experimental data were correlated using the NRTL [2] and UNIQUAC [3] equations. The VLE data were also correlated with the Wilson equation [4]. The data were compared with those predicted by group contribution methods: the UNIFAC [5] method was used for both equilibria, and the ASOG [6] and U N I F A C - L y n g b y [7] methods were used only for VLE. 2. Experimental
2.1. Materials Water was triple distilled. Methanol (Merck) and hexyl acetate (Aldrich) had nominal purities > 99.8 and > 99.5 mass% respectively. Table 1 lists their measured densities, refractive indices and boiling points, together with published values for these parameters [8].
* Corresponding author. 0378-3812/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved. PH S 0 3 7 8 - 3 8 1 2 ( 9 6 ) 0 3 0 4 7 - 6
262
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
Table 1 Physical properties of the pure components
Water Methanol Hexyl Acetate Hexyl Acetate b
Density at 25 °C (g cm 3)
Refractive index at 25 °C, n D
Boiling point at 760 mm Hg (°C)
Exp.
Lit. a
Exp.
Lit. a
Exp.
Lit. a
0.99702 0.7866 0.8686
0.99705 0.78637 0.8681
1.3324 1.3264 1.4069 1.4092 b
1.33250 1.32652
100.03 64.60 170.90
100.00 64.546 170.50
1.4096 b
a Ref. [8]. b At 20 °C.
2.2. Procedure
The liquid-liquid equilibrium data were determined by a published method [9]. Firstly, solubility curves were constructed from cloud-point data for a series of mixtures. Then the compositions of the Table 2 Phase composition data (mole fractions) for the system water ( 1 ) + m e t h a n o l ( 2 ) + h e x y l acetate(3) at equilibrium at three different temperatures Aqueous phase x I (mol.f.) t = 25 °C 0.9999 0.9204 0.8850 0.8182 0.7853 0.7325 0.7014 0.6453 0.5211 t = 35 °C 0.9999 0.8898 0.8362 0.7872 0.7135 0.6736 0.6108 0.5440 t = 45 °C 0.9999 0.8612 0.7795 0.7302 0.6727 0.5695
Organic phase x 2 (mol.f.)
xl (mol.f.)
x~ (mol.f.)
0.0000 0.0795 0.1149 0.1817 0.2112 0.2589 0.2973 0.3340 0.4389
0.0323 0.0754 0.0811 0.0912 0.1016 0.1113 0.1172 0.1286 0.1713
0.0000 0.0433 0.0661 0.1110 0.1287 0.1690 0.2003 0.2468 0.3652
0.0000 0.1101 0.1637 0.2122 0.2844 0.3235 0.3840 0.4389
0.0345 0.0839 0.0810 0.1049 0.1189 0.1419 0.1661 0.2049
0.0000 0.0706 0.1026 0.1560 0.2079 0.2625 0.3195 0.3872
0.0000 0.1387 0.2144 0.2567 0.3040 0.3894
0.0302 0.0939 0.1070 0.1231 0.1547 0.1868
0.0000 0.1033 0.1621 0.2029 0.2624 0.3466
263
A. Arce et a l . / Fluid Phase Equilibria 128 (1997) 261-270
METHANOL 10
METHANOL
0
0.2
WATER
0.4
0.6
0.8
1
0
0.2
0.4
WATER
HEXYL ACETATE
0.6
0.8
i
HEXYL ACETATE
METHANOL
o
0.2
WATER
0.4
0.6
0.8
I
HEXYL ACETATE
Fig. 1. Binodal curves and tie-lines for the liquid-liquid equilibrium of the system water + methanol-t- hexyl acetate at 25, 35 and 45 °C. Compositions in mole fraction.
conjugate phases of mixtures lying in the immiscible region were determined by gas chromatography in a Hewlett Packard 5890 Series II chromatograph equipped with a thermal conductivity detector. Calibration was by the internal standard method; quantification was precise to within _ 0.0004 mole fraction. The LLE data obtained at 25, 35 and 45 °C (compositions of the ends of the tie-lines) are listed in Table 2, and Fig. 1 shows the experimental binodal curves and tie-lines. The VLE data were determined in a Labodest distillation apparatus that recycles both liquid and vapour phases (Fischer, Germany). The inert atmosphere in this distillation apparatus was argon, which was maintained at a constant pressure of 101.32 kPa. The compositions of the equilibrium vapour and liquid phases were determined by densimetry and refractometry in an Anton Paar DMA 6 0 / 6 0 2 digital vibrating tube densimeter and an ATAGO RX-1000 refractometer, respectively. These
264
A. Arm
et d./Fluid
Phusr Equilibria
I28 (1997) 261-270
Table3 Isobaric VLE dataforthesystemwater(l)+methanol(2)+hexyl acetate(3) at 101.32 kPa x, (m0l.f.)
x2 (mol.f.1
y, (m0l.f.)
y, (m0l.f.)
t (“a
0.1516 0.2258 0.3354 0.3365 0.3894 0.4075 0.4399 0.4902 0.2104 0.2134 0.2131 0.2095 0.0119 0.0135 0.1752 0.1742 0.2956 0.0057 0.0157 0.0163 0.0079 0.0223 0.0382 0.0908 0.0801 0.1436 0.0215 0.0374 0.0548 0.0493 0.0507 0.0374 0.0681 0.1253 0.1607 0.1626 0.1609 0.1584 0.2941 0.2893 0.1952 0.1669 0.1411 0.1079 0.0762 0.0037 0.0090
0.8062 0.7249 0.6047 0.601 1 0.5672 0.5245 0.5281 0.4870 0.7048 0.6746 0.6465 0.6076 0.9784 0.9355 0.7825 0.7427 0.6340 0.0177 0.0483 0.0921 0.0057 0.2198 0.3340 0.4443 0.5605 0.5839 0.3307 0.4531 0.5993 0.7201 0.7967 0.8592 0.8328 0.7672 0.7186 0.6812 0.6303 0.5620 0.5764 0.5358 0.4502 0.3753 0.3308 0.2474 0.1862 0.0115 0.0509
0.0737 0.1128 0.1804 0.1807 0.1948 0.2221 0.2143 0.2343 0.1182 0.1286 0.1369 0.1521 0.0050 0.0063 0.0851 0.0967 0.1624 0.1461 0.2373 0.2394 0.0588 0.1279 0.1070 0.1431 0.0923 0.1372 0.0877 0.0773 0.0644 0.0414 0.0348 0.0221 0.0411 0.0818 0.0993 O.IIIX 0.1263 0.1481 0.1879 0.2096 0.2153 0.2527 0.2663 0.2947 0.3237 0.0751 0.2035
0.9209 0.8783 0.8043 0.8062 0.7912 0.7619 0.7711 0.7497 0.8710 0.8594 0.8496 0.8337 0.9940 0.9897 0.9083 0.8933 0.8248 0.3366 0.5604 0.6778 0.0937 0.8269 0.8665 0.8363 0.8909 0.8464 0.8863 0.9023 0.9200 0.9472 0.9563 0.9708 0.9515 0.9087 0.8893 0.8755 0.8585 0.8346 0.7960 0.7730 0.7649 0.7246 0.7084 0.6758 0.6385 0.1709 0.5750
68.28 69.87 72.45 72.44 72.88 73.93 73.60 74.36 70.36 70.91 71.38 72.07 65.03 65.91 68.78 69.64 71.77 148.48 121.55 99.47 164.12 86.91 78.31 74.58 72.18 72.36 78.35 74.31 71.40 69.43 68.32 67.27 67.85 69.16 69.99 70.67 71.54 72.60 72.95 73.71 74.82 76.49 77.69 80.35 85.11 159.76 123.97
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A. Arce et a l . / Fluid Phase Equilibria 128 (1997) 261-270
Table 3 (continued) x I (mol.f.)
x 2 (mol.f.)
y] (mol.f.)
Y2 (mol.f.)
t (°C)
0.0351 0.0110 0.0171 0.0400 0.0066 0.0091 0.0300 0.1320 0.1929 0.1955
0.0725 0.5385 0.6567 0.6015 0.1314 0.1035 0.1699 0.3703 0.4695 0.4935
0.3247 0.0226 0.0187 0.0519 0.1120 0.1543 0.1983 0.2270 0.2047 0.1977
0.5673 0.9625 0.9689 0.9343 0.8188 0.7637 0.7501 0.7498 0.7750 0.7829
107.10 72.49 70.24 71.29 96.57 100.59 90.49 76.51 74.43 74.09
data w e r e d e t e r m i n e d in a p r e v i o u s s t u d y [10]. T h e isobaric V L E data for the ternary s y s t e m are given in T a b l e 3, and Fig. 2 s h o w s the isotherms for the h o m o g e n e o u s region o f the ternary s y s t e m at equilibrium.
3. C o r r e l a t i o n
of equilibrium
data
T h e e x p e r i m e n t a l L L E data w e r e correlated using the N R T L e q u a t i o n [2] at values o f the n o n - r a n d o m n e s s factor, a , o f 0.1, 0.2 and 0.3, and also using the U N I Q U A C e q u a t i o n [3], for w h i c h
METHANOL 100 .
0
80 /~~ '
°/-
60 /
345
..........
__~_34~ ___
\
____~
:,----
4
~49___~ 60 "".\
353
20/
0
//
~
0 WATER
I 20
I
I 40
i
t 60
i
I 80
z-a,- 100 100
HEXYL ACETATE
Fig. 2. Isotherms (K) in the homogeneous region for the vapour-liquid equilibrium of the system water+ methanol + hexyl acetate at 101.32 kPa. Compositions in mole fraction.
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
266
Table 4 N R T L and U N I Q U A C binary interaction parameters for correlation o f the LLE data of the system w a t e r ( l ) + m e t h a n o l ( 2 ) + hexyl acetate(3) t = 25 °C
t = 35 °C
t = 45 °C
i- j
aij
aji
aij
aji
aij
aji
N R T L ( a = 0.1) 1-2 1-3 2-3 N R T L ( a = 0.2)
-826.86 3024.9 201.63
673.44 - 262.61 - 171.62
- 1509.1 4001.5 220.18
1348.7 - 212.52 -549.66
- 1160.7 2999.7 -73.432
621.99 - 207.58 -356.40
758.44 2078.0 796.83
-603.10 439.53 - 321.84
681.15 2657.6 881.35
-632.67 555.30 - 426.19
918.71 1840.4 1084.8
-677.97 505.72 - 485.47
- 233.45 1917.3 618.04
- 58.776 763.49 -318.32
- 508.11 2014.0 745.46
- 127.93 839.71 -661.36
72.335 1668.4 667.72
- 164.95 817.59 -250.26
806.14 150.07 - 61.167
- 369.75 604.32 398.64
1158.5 224.20 - 58.543
- 424.36 593.82 338.48
201.02 15.948 62.563
- 250.73 814.89 209.86
1-2 1-3 2-3 N R T L ( c~ = 0.3) 1-2 1-3 2-3 (UNIQUAC) 1-2 1-3 2-3
Structural parameters (area and volume)
Water Methanol Hexyl acetate
r 0.9200 1.431 6.1762
q 1.400 1.432 5.276
the structural parameters r and q (Table 4) were obtained from the literature [11,12]. The binary interaction parameters for each equation were optimized using the procedure described by S0rensen and Arlt [13], and are included in Table 4. Table 5 shows the corresponding deviations of these models from the experimental LLE data in terms of the residual function F, which is the r.m.s.
Table 5 Root mean square (r.m.s.) deviation in F and A/3 for N R T L and U N I Q U A C equations fitted to the liquid-liquid equilibrium data Equation N R T L ( ~ = 0.1 ) N R T L ( ce = 0.2) N R T L (or = 0.3) UNIQUAC
F A/3 F ,5/3 F A/3 F A/3
t = 25 °C
t = 35 °C
t = 45 °C
0.81 2.8 0.57 3.1 0.56 2.5 0.46 8.7
0.84 4.0 0.63 3.8 0.75 4.3 0.50 3.4
0.83 3.0 0.52 3.4 0.50 2.7 0.49 2.9
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
267
Table 6 Antoine's coefficients A, B a n d C (for P in kPa and t in °C) Compound
A
B
C
Reference
Water Methanol
7.23255 7.20519 6.46060
1750.286 1581.993 1688.630
235.000 239.711 208.766
[ 15] [8] [ 1]
H e x y l acetate
deviation of the calculated composition from the experimental composition, and A/3, the r.m.s. relative error in the solute distribution ratio.
F= 100 ]~
/
(1)
Y'~(Xi;k--Xijk) / 6 M
k
"
j
^
2
Aft= 100 ~[(]3 k- ]3k)/]3k] / M k
7
(2)
For correlation of the VLE data, the equilibrium condition to be satisfied was
(3)
Yi P = Yi Xi P i s
where x i and Yi a r e the mole fractions of component i in the liquid and vapour phases respectively, Yi is the activity coefficient of component i in the liquid phase, P is the total pressure of the system and Pis is the saturated vapour pressure of component i as calculated from Antoine's equation using the coefficients A, B and C given in Table 6. The activity coefficients, Yi, were calculated using the Wilson equation [4] and the NRTL and UNIQUAC equations, in the latter case using the structural parameters, r and q, recommended by Gmehling et al. [14]. Correlation of the VLE data used least-squares regression (Simplex method) performed by a computer program. The objective function minimized was
OF= E E('~ik--Xik) 2 k
(4)
i
Table 7 Binary interaction parameters (cal m o l - 5 ) and mean deviations (m.d.) in temperature ( t ) and vapour phase composition ( y i ) for correlation of the VLE data of the system w a t e r ( l ) + methanol(2)+ h e x y l acetate(3) by the indicated models
Model
Parameters
Wilson
A 3.12 = A3.2j = A 3.31 = A g 12 = A g2J =
N R T L ( a = 0.1 )
UNIQUAC
604.36 194.76 2431.8 969.24 - 425.52 Ag31 ~ - - 1114.7 Aul2 = 358.10 Au2~ = -- 233.16 Au31 = 8 1 2 . 2 4
A 3.13 = 2 4 9 8 . 4 A3.23 = 1096.2 A 3. 32 = - - 213.00 A g 13 = 4763.2 A g23 = 2372.5 Ag32 = - - 1230.5 Au13 = 406.79 Au23 = -- 97.941 Au32 = 801.20
m.d. t (°C)
m.d. Yl
m.d. Y2
1.49
0.0272
0.0277
1.22
0.0211
0.0214
0.98
0.0180
0.0151
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A. Aree et al. / Fluid Phase Equilibria 128 (1997) 261-270
Table 8 Mean deviations (m.d.) between experimental and predicted temperature t and mole fractions Yi of each component i in the vapour phase, for the water(l) + methanol(2) + hexyl acetate(3) system at equilibrium Method
m.d. t (°C)
m.d. Yl (tool. f.)
m.d. Y2 (tool. f.)
m.d. Y3 (mol. f.)
ASOG UNIFAC UNIFAC-Lyngby
9.71 3.43 3.67
0.0294 0.0448 0.0454
0.0346 0.0345 0.0268
0.0557 0.0586 0.0546
The resulting binary interaction parameters and r.m.s, deviations in temperature and vapour phase composition are listed in Table 7.
4. Prediction of equilibrium data The LLE data were predicted by means of the UNIFAC group contribution method [5] using group interaction parameters taken from Ref. [10]. The deviations of the predictions from the experimental data were calculated as F residuals using Eq. (1). These residuals were 2.19, 2.42 and 2.29% for the data at 25, 35 and 45 °C, respectively. The VLE data were predicted using the UNIFAC method mentioned above, and also the ASOG [6] and modified UNIFAC [7] group contribution methods. The mean deviations of the predicted data from the experimental VLE data are listed in Table 8 for all three methods.
5. Conclusions The experimental liquid-liquid equilibrium data for the system water + methanol + hexyl acetate at 25, 35 and 45 °C, and the vapour-liquid equilibrium data for the range of homogeneous mixtures of this ternary system at 101.32 kPa, were determined. These data confirm hexyl acetate to be a suitable extractant for separation of methanol from methanol-water mixtures, the separated alcohol being easily recovered by subsequent distillation. Both NRTL and UNIQUAC equations proved suitable for correlation of the experimental LLE data for the ternary system. At 25 and 45 °C, it was the NRTL model (with a = 0.3) that afforded the smallest mean deviations from the experimental data, whereas at 35 °C it was the UNIQUAC equation. For correlation of the VLE data, the UNIQUAC equation afforded smaller deviations from the experimental data than both the Wilson equation and the NRTL equation, for which the optimum value of a was nonetheless 0.1. The UNIFAC predictions of the LLE data at 25, 35 and 45 °C were good, as was evidenced by the low F residuals obtained. Similarly, the UNIFAC methods afforded better predictions of the VLE data than the ASOG method, for which deviations in temperature were rather large.
6. List of symbols a
A,B,C
NRTL or UNIQUAC binary interaction parameters, K Antoine's coefficients
A. Arce et a l . / Fluid Phase Equilibria 128 (1997) 261-270
269
density, g c m - 3 r.m.s, deviation in composition, % NRTL binary interaction parameters, cal molnumber of tie-lines number of moles in the mixture refraction index pressure, kPa UNIQUAC area parameter UNIQUAC volume parameter temperature, °C UNIQUAC binary interaction parameters, cal molexperimental composition of liquid phase, mole fraction calculated composition of liquid phase, mole fraction experimental composition of vapour phase, mole fraction
d F g M H nD
~p q r
t u x
2 Y
Greek letters a /3 /3 A A/3 h T
NRTL non-randomness parameter solute distribution ratio calculated solute distribution ratio increment r.m.s, relative error in solute distribution ratio, % Wilson binary interaction parameters, cal mol-l activity coefficient
Subscripts i j k 1, 2, 3
ith component jth component, jth phase kth tie-line component identification
Superscripts S
saturation
Acknowledgements This work was partly financed by the D.G.I.C.Y.T. (Spain) under Project PB94-0658.
References [1] [2] [3] [4] [5] [6]
A. Arce, A. Blanco, J. Martinez-Ageitos and A. Soto, J. Chem. Eng. Data, 40 (1995) 515-518. H. Renon and J.M. Prausnitz, AIChE J., 14 (1968) 135-144. D.S. Abrams and J.M. Prausnitz, AIChE J., 21 (1975) 116-128. G.M. Wilson, J. Am. Chem. Soc., 86 (1964) 127-130. A. Fredenslund, J. Gmehling and P. Rasmussen, Vapor-Liquid Equilibria using UNIFAC, Elsevier, Amsterdam, 1977. K. Kojima and K. Tochigi, Prediction of Vapor-Liquid Equilibrium by the ASOG Method, Kodansha Ltd., Elsevier, Tokyo, 1979.
270 [7] [8] [9] [10] [11] [12]
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
B.L. Larsen, P. Rasmussen and A. Fredenslund, Ind. Eng. Chem. Res., 26 (1987) 2274-2286. J.A. Riddick, W.B. Bunger and T.K. Sakano, Organic Solvents, 4th edn., Wiley, New York, 1986. J.M. Correa, A. Blanco and A. Arce, J. Chem. Eng. Data, 34 (1989) 415-419. A. Arce, A. Blanco, J.C. P~rez and A. Soto, J. Chem. Eng. Data, 39 (1994) 95-97. T. Magnussen, P. Rasmussen and A. Fredenslund, Ind, Eng. Chem. Process Des. Dev., 20 (1981) 331-339. J.M. Prausnitz, R.N. Lichtenthaler and E.G. Azevedo, Molecular Thermodynamics of Fluid-Phase Equilibria, PrenticeHall, Englewood Cliffs, NJ, 1986. [13] J.M. S~rensen, and W. Arlt, Liquid-Liquid Equilibrium Data Collection, Vol. V, Part 2, Dechema Chemistry Data Series, Frankfurt/Main, Germany, 1980. [14] J. Gmehling, P. Rasmussen and A. Fredenslund, Incl. Eng. Chem. Process Des. Dev., 21 (1982) 118-127. [15] M. Hirata, S. Ohe and K. Nagahama, Computer Aided Data Book of Vapor-Liquid Equilibria, Elsevier, Tokyo, 1975.
Fluid Phase Equilibria 128 (1997) 261-270
Phase equilibria of water + methanol + hexyl acetate mixtures Alberto Arce *, Antonio Blanco, Ana Soto, Isabel Vidal Department of Chemical Engineering, University of Santiago, E-15706 Santiago de Compostela, Spain
Received 4 November 1995; accepted 22 February 1996
Abstract
Liquid-liquid equilibrium data at 25, 35 and 45 °C, and isobaric vapour-liquid equilibrium data at 101.32 kPa, were determined for the ternary system water + methanol + hexyl acetate. The data were correlated using the Wilson, NRTL and UNIQUAC models and were predicted using the UNIFAC and ASOG methods. Keywords: Liquid-liquid equilibrium; Vapour-liquid equilibrium; Correlation; Prediction 1. Introduction
Solvent extraction is an important technique for separation of liquid mixtures that has been widely examined in chemical engineering. Post-extraction recovery of the extractant is usually achieved by distillation of the extract phase. In this work, we examined the separation of methanol-water mixtures by extraction with hexyl acetate, and subsequent recovery of the ester by distillation. Isobaric vapour-liquid equilibrium (VLE) data for the binary system methanol + hexyl acetate have been published already [1]. Here we report VLE and liquid-liquid equilibrium (LLE) data for the ternary mixtures at 101.32 kPa, which as far as we are aware are not available in the literature. These experimental data were correlated using the NRTL [2] and UNIQUAC [3] equations. The VLE data were also correlated with the Wilson equation [4]. The data were compared with those predicted by group contribution methods: the UNIFAC [5] method was used for both equilibria, and the ASOG [6] and U N I F A C - L y n g b y [7] methods were used only for VLE. 2. Experimental
2.1. Materials Water was triple distilled. Methanol (Merck) and hexyl acetate (Aldrich) had nominal purities > 99.8 and > 99.5 mass% respectively. Table 1 lists their measured densities, refractive indices and boiling points, together with published values for these parameters [8].
* Corresponding author. 0378-3812/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved. PH S 0 3 7 8 - 3 8 1 2 ( 9 6 ) 0 3 0 4 7 - 6
262
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
Table 1 Physical properties of the pure components
Water Methanol Hexyl Acetate Hexyl Acetate b
Density at 25 °C (g cm 3)
Refractive index at 25 °C, n D
Boiling point at 760 mm Hg (°C)
Exp.
Lit. a
Exp.
Lit. a
Exp.
Lit. a
0.99702 0.7866 0.8686
0.99705 0.78637 0.8681
1.3324 1.3264 1.4069 1.4092 b
1.33250 1.32652
100.03 64.60 170.90
100.00 64.546 170.50
1.4096 b
a Ref. [8]. b At 20 °C.
2.2. Procedure
The liquid-liquid equilibrium data were determined by a published method [9]. Firstly, solubility curves were constructed from cloud-point data for a series of mixtures. Then the compositions of the Table 2 Phase composition data (mole fractions) for the system water ( 1 ) + m e t h a n o l ( 2 ) + h e x y l acetate(3) at equilibrium at three different temperatures Aqueous phase x I (mol.f.) t = 25 °C 0.9999 0.9204 0.8850 0.8182 0.7853 0.7325 0.7014 0.6453 0.5211 t = 35 °C 0.9999 0.8898 0.8362 0.7872 0.7135 0.6736 0.6108 0.5440 t = 45 °C 0.9999 0.8612 0.7795 0.7302 0.6727 0.5695
Organic phase x 2 (mol.f.)
xl (mol.f.)
x~ (mol.f.)
0.0000 0.0795 0.1149 0.1817 0.2112 0.2589 0.2973 0.3340 0.4389
0.0323 0.0754 0.0811 0.0912 0.1016 0.1113 0.1172 0.1286 0.1713
0.0000 0.0433 0.0661 0.1110 0.1287 0.1690 0.2003 0.2468 0.3652
0.0000 0.1101 0.1637 0.2122 0.2844 0.3235 0.3840 0.4389
0.0345 0.0839 0.0810 0.1049 0.1189 0.1419 0.1661 0.2049
0.0000 0.0706 0.1026 0.1560 0.2079 0.2625 0.3195 0.3872
0.0000 0.1387 0.2144 0.2567 0.3040 0.3894
0.0302 0.0939 0.1070 0.1231 0.1547 0.1868
0.0000 0.1033 0.1621 0.2029 0.2624 0.3466
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A. Arce et a l . / Fluid Phase Equilibria 128 (1997) 261-270
METHANOL 10
METHANOL
0
0.2
WATER
0.4
0.6
0.8
1
0
0.2
0.4
WATER
HEXYL ACETATE
0.6
0.8
i
HEXYL ACETATE
METHANOL
o
0.2
WATER
0.4
0.6
0.8
I
HEXYL ACETATE
Fig. 1. Binodal curves and tie-lines for the liquid-liquid equilibrium of the system water + methanol-t- hexyl acetate at 25, 35 and 45 °C. Compositions in mole fraction.
conjugate phases of mixtures lying in the immiscible region were determined by gas chromatography in a Hewlett Packard 5890 Series II chromatograph equipped with a thermal conductivity detector. Calibration was by the internal standard method; quantification was precise to within _ 0.0004 mole fraction. The LLE data obtained at 25, 35 and 45 °C (compositions of the ends of the tie-lines) are listed in Table 2, and Fig. 1 shows the experimental binodal curves and tie-lines. The VLE data were determined in a Labodest distillation apparatus that recycles both liquid and vapour phases (Fischer, Germany). The inert atmosphere in this distillation apparatus was argon, which was maintained at a constant pressure of 101.32 kPa. The compositions of the equilibrium vapour and liquid phases were determined by densimetry and refractometry in an Anton Paar DMA 6 0 / 6 0 2 digital vibrating tube densimeter and an ATAGO RX-1000 refractometer, respectively. These
264
A. Arm
et d./Fluid
Phusr Equilibria
I28 (1997) 261-270
Table3 Isobaric VLE dataforthesystemwater(l)+methanol(2)+hexyl acetate(3) at 101.32 kPa x, (m0l.f.)
x2 (mol.f.1
y, (m0l.f.)
y, (m0l.f.)
t (“a
0.1516 0.2258 0.3354 0.3365 0.3894 0.4075 0.4399 0.4902 0.2104 0.2134 0.2131 0.2095 0.0119 0.0135 0.1752 0.1742 0.2956 0.0057 0.0157 0.0163 0.0079 0.0223 0.0382 0.0908 0.0801 0.1436 0.0215 0.0374 0.0548 0.0493 0.0507 0.0374 0.0681 0.1253 0.1607 0.1626 0.1609 0.1584 0.2941 0.2893 0.1952 0.1669 0.1411 0.1079 0.0762 0.0037 0.0090
0.8062 0.7249 0.6047 0.601 1 0.5672 0.5245 0.5281 0.4870 0.7048 0.6746 0.6465 0.6076 0.9784 0.9355 0.7825 0.7427 0.6340 0.0177 0.0483 0.0921 0.0057 0.2198 0.3340 0.4443 0.5605 0.5839 0.3307 0.4531 0.5993 0.7201 0.7967 0.8592 0.8328 0.7672 0.7186 0.6812 0.6303 0.5620 0.5764 0.5358 0.4502 0.3753 0.3308 0.2474 0.1862 0.0115 0.0509
0.0737 0.1128 0.1804 0.1807 0.1948 0.2221 0.2143 0.2343 0.1182 0.1286 0.1369 0.1521 0.0050 0.0063 0.0851 0.0967 0.1624 0.1461 0.2373 0.2394 0.0588 0.1279 0.1070 0.1431 0.0923 0.1372 0.0877 0.0773 0.0644 0.0414 0.0348 0.0221 0.0411 0.0818 0.0993 O.IIIX 0.1263 0.1481 0.1879 0.2096 0.2153 0.2527 0.2663 0.2947 0.3237 0.0751 0.2035
0.9209 0.8783 0.8043 0.8062 0.7912 0.7619 0.7711 0.7497 0.8710 0.8594 0.8496 0.8337 0.9940 0.9897 0.9083 0.8933 0.8248 0.3366 0.5604 0.6778 0.0937 0.8269 0.8665 0.8363 0.8909 0.8464 0.8863 0.9023 0.9200 0.9472 0.9563 0.9708 0.9515 0.9087 0.8893 0.8755 0.8585 0.8346 0.7960 0.7730 0.7649 0.7246 0.7084 0.6758 0.6385 0.1709 0.5750
68.28 69.87 72.45 72.44 72.88 73.93 73.60 74.36 70.36 70.91 71.38 72.07 65.03 65.91 68.78 69.64 71.77 148.48 121.55 99.47 164.12 86.91 78.31 74.58 72.18 72.36 78.35 74.31 71.40 69.43 68.32 67.27 67.85 69.16 69.99 70.67 71.54 72.60 72.95 73.71 74.82 76.49 77.69 80.35 85.11 159.76 123.97
265
A. Arce et a l . / Fluid Phase Equilibria 128 (1997) 261-270
Table 3 (continued) x I (mol.f.)
x 2 (mol.f.)
y] (mol.f.)
Y2 (mol.f.)
t (°C)
0.0351 0.0110 0.0171 0.0400 0.0066 0.0091 0.0300 0.1320 0.1929 0.1955
0.0725 0.5385 0.6567 0.6015 0.1314 0.1035 0.1699 0.3703 0.4695 0.4935
0.3247 0.0226 0.0187 0.0519 0.1120 0.1543 0.1983 0.2270 0.2047 0.1977
0.5673 0.9625 0.9689 0.9343 0.8188 0.7637 0.7501 0.7498 0.7750 0.7829
107.10 72.49 70.24 71.29 96.57 100.59 90.49 76.51 74.43 74.09
data w e r e d e t e r m i n e d in a p r e v i o u s s t u d y [10]. T h e isobaric V L E data for the ternary s y s t e m are given in T a b l e 3, and Fig. 2 s h o w s the isotherms for the h o m o g e n e o u s region o f the ternary s y s t e m at equilibrium.
3. C o r r e l a t i o n
of equilibrium
data
T h e e x p e r i m e n t a l L L E data w e r e correlated using the N R T L e q u a t i o n [2] at values o f the n o n - r a n d o m n e s s factor, a , o f 0.1, 0.2 and 0.3, and also using the U N I Q U A C e q u a t i o n [3], for w h i c h
METHANOL 100 .
0
80 /~~ '
°/-
60 /
345
..........
__~_34~ ___
\
____~
:,----
4
~49___~ 60 "".\
353
20/
0
//
~
0 WATER
I 20
I
I 40
i
t 60
i
I 80
z-a,- 100 100
HEXYL ACETATE
Fig. 2. Isotherms (K) in the homogeneous region for the vapour-liquid equilibrium of the system water+ methanol + hexyl acetate at 101.32 kPa. Compositions in mole fraction.
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
266
Table 4 N R T L and U N I Q U A C binary interaction parameters for correlation o f the LLE data of the system w a t e r ( l ) + m e t h a n o l ( 2 ) + hexyl acetate(3) t = 25 °C
t = 35 °C
t = 45 °C
i- j
aij
aji
aij
aji
aij
aji
N R T L ( a = 0.1) 1-2 1-3 2-3 N R T L ( a = 0.2)
-826.86 3024.9 201.63
673.44 - 262.61 - 171.62
- 1509.1 4001.5 220.18
1348.7 - 212.52 -549.66
- 1160.7 2999.7 -73.432
621.99 - 207.58 -356.40
758.44 2078.0 796.83
-603.10 439.53 - 321.84
681.15 2657.6 881.35
-632.67 555.30 - 426.19
918.71 1840.4 1084.8
-677.97 505.72 - 485.47
- 233.45 1917.3 618.04
- 58.776 763.49 -318.32
- 508.11 2014.0 745.46
- 127.93 839.71 -661.36
72.335 1668.4 667.72
- 164.95 817.59 -250.26
806.14 150.07 - 61.167
- 369.75 604.32 398.64
1158.5 224.20 - 58.543
- 424.36 593.82 338.48
201.02 15.948 62.563
- 250.73 814.89 209.86
1-2 1-3 2-3 N R T L ( c~ = 0.3) 1-2 1-3 2-3 (UNIQUAC) 1-2 1-3 2-3
Structural parameters (area and volume)
Water Methanol Hexyl acetate
r 0.9200 1.431 6.1762
q 1.400 1.432 5.276
the structural parameters r and q (Table 4) were obtained from the literature [11,12]. The binary interaction parameters for each equation were optimized using the procedure described by S0rensen and Arlt [13], and are included in Table 4. Table 5 shows the corresponding deviations of these models from the experimental LLE data in terms of the residual function F, which is the r.m.s.
Table 5 Root mean square (r.m.s.) deviation in F and A/3 for N R T L and U N I Q U A C equations fitted to the liquid-liquid equilibrium data Equation N R T L ( ~ = 0.1 ) N R T L ( ce = 0.2) N R T L (or = 0.3) UNIQUAC
F A/3 F ,5/3 F A/3 F A/3
t = 25 °C
t = 35 °C
t = 45 °C
0.81 2.8 0.57 3.1 0.56 2.5 0.46 8.7
0.84 4.0 0.63 3.8 0.75 4.3 0.50 3.4
0.83 3.0 0.52 3.4 0.50 2.7 0.49 2.9
A. Arce et al./Fluid Phase Equilibria 128 (1997) 261-270
267
Table 6 Antoine's coefficients A, B a n d C (for P in kPa and t in °C) Compound
A
B
C
Reference
Water Methanol
7.23255 7.20519 6.46060
1750.286 1581.993 1688.630
235.000 239.711 208.766
[ 15] [8] [ 1]
H e x y l acetate
deviation of the calculated composition from the experimental composition, and A/3, the r.m.s. relative error in the solute distribution ratio.
F= 100 ]~
/
(1)
Y'~(Xi;k--Xijk) / 6 M
k
"
j
^
2
Aft= 100 ~[(]3 k- ]3k)/]3k] / M k
7
(2)
For correlation of the VLE data, the equilibrium condition to be satisfied was
(3)
Yi P = Yi Xi P i s
where x i and Yi a r e the mole fractions of component i in the liquid and vapour phases respectively, Yi is the activity coefficient of component i in the liquid phase, P is the total pressure of the system and Pis is the saturated vapour pressure of component i as calculated from Antoine's equation using the coefficients A, B and C given in Table 6. The activity coefficients, Yi, were calculated using the Wilson equation [4] and the NRTL and UNIQUAC equations, in the latter case using the structural parameters, r and q, recommended by Gmehling et al. [14]. Correlation of the VLE data used least-squares regression (Simplex method) performed by a computer program. The objective function minimized was
OF= E E('~ik--Xik) 2 k
(4)
i
Table 7 Binary interaction parameters (cal m o l - 5 ) and mean deviations (m.d.) in temperature ( t ) and vapour phase composition ( y i ) for correlation of the VLE data of the system w a t e r ( l ) + methanol(2)+ h e x y l acetate(3) by the indicated models
Model
Parameters
Wilson
A 3.12 = A3.2j = A 3.31 = A g 12 = A g2J =
N R T L ( a = 0.1 )
UNIQUAC
604.36 194.76 2431.8 969.24 - 425.52 Ag31 ~ - - 1114.7 Aul2 = 358.10 Au2~ = -- 233.16 Au31 = 8 1 2 . 2 4
A 3.13 = 2 4 9 8 . 4 A3.23 = 1096.2 A 3. 32 = - - 213.00 A g 13 = 4763.2 A g23 = 2372.5 Ag32 = - - 1230.5 Au13 = 406.79 Au23 = -- 97.941 Au32 = 801.20
m.d. t (°C)
m.d. Yl
m.d. Y2
1.49
0.0272
0.0277
1.22
0.0211
0.0214
0.98
0.0180
0.0151
268
A. Aree et al. / Fluid Phase Equilibria 128 (1997) 261-270
Table 8 Mean deviations (m.d.) between experimental and predicted temperature t and mole fractions Yi of each component i in the vapour phase, for the water(l) + methanol(2) + hexyl acetate(3) system at equilibrium Method
m.d. t (°C)
m.d. Yl (tool. f.)
m.d. Y2 (tool. f.)
m.d. Y3 (mol. f.)
ASOG UNIFAC UNIFAC-Lyngby
9.71 3.43 3.67
0.0294 0.0448 0.0454
0.0346 0.0345 0.0268
0.0557 0.0586 0.0546
The resulting binary interaction parameters and r.m.s, deviations in temperature and vapour phase composition are listed in Table 7.
4. Prediction of equilibrium data The LLE data were predicted by means of the UNIFAC group contribution method [5] using group interaction parameters taken from Ref. [10]. The deviations of the predictions from the experimental data were calculated as F residuals using Eq. (1). These residuals were 2.19, 2.42 and 2.29% for the data at 25, 35 and 45 °C, respectively. The VLE data were predicted using the UNIFAC method mentioned above, and also the ASOG [6] and modified UNIFAC [7] group contribution methods. The mean deviations of the predicted data from the experimental VLE data are listed in Table 8 for all three methods.
5. Conclusions The experimental liquid-liquid equilibrium data for the system water + methanol + hexyl acetate at 25, 35 and 45 °C, and the vapour-liquid equilibrium data for the range of homogeneous mixtures of this ternary system at 101.32 kPa, were determined. These data confirm hexyl acetate to be a suitable extractant for separation of methanol from methanol-water mixtures, the separated alcohol being easily recovered by subsequent distillation. Both NRTL and UNIQUAC equations proved suitable for correlation of the experimental LLE data for the ternary system. At 25 and 45 °C, it was the NRTL model (with a = 0.3) that afforded the smallest mean deviations from the experimental data, whereas at 35 °C it was the UNIQUAC equation. For correlation of the VLE data, the UNIQUAC equation afforded smaller deviations from the experimental data than both the Wilson equation and the NRTL equation, for which the optimum value of a was nonetheless 0.1. The UNIFAC predictions of the LLE data at 25, 35 and 45 °C were good, as was evidenced by the low F residuals obtained. Similarly, the UNIFAC methods afforded better predictions of the VLE data than the ASOG method, for which deviations in temperature were rather large.
6. List of symbols a
A,B,C
NRTL or UNIQUAC binary interaction parameters, K Antoine's coefficients
A. Arce et a l . / Fluid Phase Equilibria 128 (1997) 261-270
269
density, g c m - 3 r.m.s, deviation in composition, % NRTL binary interaction parameters, cal molnumber of tie-lines number of moles in the mixture refraction index pressure, kPa UNIQUAC area parameter UNIQUAC volume parameter temperature, °C UNIQUAC binary interaction parameters, cal molexperimental composition of liquid phase, mole fraction calculated composition of liquid phase, mole fraction experimental composition of vapour phase, mole fraction
d F g M H nD
~p q r
t u x
2 Y
Greek letters a /3 /3 A A/3 h T
NRTL non-randomness parameter solute distribution ratio calculated solute distribution ratio increment r.m.s, relative error in solute distribution ratio, % Wilson binary interaction parameters, cal mol-l activity coefficient
Subscripts i j k 1, 2, 3
ith component jth component, jth phase kth tie-line component identification
Superscripts S
saturation
Acknowledgements This work was partly financed by the D.G.I.C.Y.T. (Spain) under Project PB94-0658.
References [1] [2] [3] [4] [5] [6]
A. Arce, A. Blanco, J. Martinez-Ageitos and A. Soto, J. Chem. Eng. Data, 40 (1995) 515-518. H. Renon and J.M. Prausnitz, AIChE J., 14 (1968) 135-144. D.S. Abrams and J.M. Prausnitz, AIChE J., 21 (1975) 116-128. G.M. Wilson, J. Am. Chem. Soc., 86 (1964) 127-130. A. Fredenslund, J. Gmehling and P. Rasmussen, Vapor-Liquid Equilibria using UNIFAC, Elsevier, Amsterdam, 1977. K. Kojima and K. Tochigi, Prediction of Vapor-Liquid Equilibrium by the ASOG Method, Kodansha Ltd., Elsevier, Tokyo, 1979.
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B.L. Larsen, P. Rasmussen and A. Fredenslund, Ind. Eng. Chem. Res., 26 (1987) 2274-2286. J.A. Riddick, W.B. Bunger and T.K. Sakano, Organic Solvents, 4th edn., Wiley, New York, 1986. J.M. Correa, A. Blanco and A. Arce, J. Chem. Eng. Data, 34 (1989) 415-419. A. Arce, A. Blanco, J.C. P~rez and A. Soto, J. Chem. Eng. Data, 39 (1994) 95-97. T. Magnussen, P. Rasmussen and A. Fredenslund, Ind, Eng. Chem. Process Des. Dev., 20 (1981) 331-339. J.M. Prausnitz, R.N. Lichtenthaler and E.G. Azevedo, Molecular Thermodynamics of Fluid-Phase Equilibria, PrenticeHall, Englewood Cliffs, NJ, 1986. [13] J.M. S~rensen, and W. Arlt, Liquid-Liquid Equilibrium Data Collection, Vol. V, Part 2, Dechema Chemistry Data Series, Frankfurt/Main, Germany, 1980. [14] J. Gmehling, P. Rasmussen and A. Fredenslund, Incl. Eng. Chem. Process Des. Dev., 21 (1982) 118-127. [15] M. Hirata, S. Ohe and K. Nagahama, Computer Aided Data Book of Vapor-Liquid Equilibria, Elsevier, Tokyo, 1975.