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Isobaric vapor–liquid equilibrium for ternary system of ethanol, ethyl propionate and para-xylene at 101.3 kPa
Accepted Manuscript Isobaric vapor-liquid equilibrium for ternary system of ethanol, ethyl propionate and para-xylene at 101.3 kPa
Zhongpeng Xing, Yujie Gao, Hui Ding, Xianqin Wang, Lujun Li, Hang Zhou PII: DOI: Reference:
S1004-9541(17)30315-4 doi:10.1016/j.cjche.2017.10.020 CJCHE 971
To appear in: Received date: Revised date: Accepted date:
15 March 2017 9 September 2017 20 October 2017
Please cite this article as: Zhongpeng Xing, Yujie Gao, Hui Ding, Xianqin Wang, Lujun Li, Hang Zhou , Isobaric vapor-liquid equilibrium for ternary system of ethanol, ethyl propionate and para-xylene at 101.3 kPa. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Cjche(2017), doi:10.1016/j.cjche.2017.10.020
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ACCEPTED MANUSCRIPT Chemical Engineering Thermodynamics
Isobaric vapor-liquid equilibrium for ternary system of ethanol, ethyl propionate and para-xylene at 101.3 kPa 4,**
4
4
1
, Xianqin Wang , Lujun Li , Hang Zhou
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Zhongpeng Xing1, Yujie Gao2,3, Hui Ding
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
2
Tianjin Academy of Environmental Sciences, Tianjin 300191, China
3
Tianjin Huanke Environmental Planning Technology Development Company Limited, Tianjin 300191, China
4
School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
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SC
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1
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Abstract Isobaric vapor-liquid equilibrium (VLE) data for the binary system ethyl propionate (2) + para-xylene (3) and ternary system ethanol (1) + ethyl propionate (2) + para-xylene (2) at atmospheric pressure (101.3 kPa) were obtained by a VLE modified othmer still. All the experimental data passed a point to point consistency test of Van
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Ness method, which verified the data reliability. The Wilson and UNIQUAC activity coefficient models were
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employed to correlate the binary VLE data to obtain binary interaction parameters. Based on binary interaction parameters, ternary VLE data of ethanol (1) + ethyl propionate (2) + para-xylene (3) were predicted by Wilson and
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UNIQUAC models, which proved that predicted values are consistent with the experimental data. Furthermore, azeotropic phenomenon between ethanol and ethyl propionate disappears when the mole ratio of para-xylene and
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binary system of ethanol and ethyl propionate is 1:1. Therefore, this paper convinced that para-xylene is a proper extractive additive that could be used in extractive distillation to separate the binary azeotropic system of ethanol and ethyl propionate. Keywords vapor-liquid equilibrium; azeotrope; ethanol; ethyl propionate; para-xylene
______________________________ Received 2017-3-15 * Supported by the National Natural Science Foundation of China (21376166). ** To whom correspondence should be addressed. E-mail: [email protected] (H Ding).
ACCEPTED MANUSCRIPT 1 INTRODUCTION Ethyl propionate, a kind of widely-used organic synthetic raw material and solvent, is applied in the field of pharmacy, antifungal agents, edibles, plasticizers, spice, dyes and even biomass[1-2]. In industry, the traditional method of producing ethyl propionate is esterification of propanoic acid and ethanol with sulfuric acid as catalyst at 101.3 kPa, and then cut fraction from 369.15 K to
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373.15 K is collected to gain pure product in distillation[3]. However, the literature has reported
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that ethyl propionate and ethanol form an azeotrope at 101.3 kPa, which reduces the yield and purity of ethyl propionate[4]. Therefore, it is a challenge for researcher to find out a way to
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improve the purity of ethyl propionate in the operation process.
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For azeotrope or similar boiling point system, extractive distillation is an effective and widely-used process to separate the mixture[5], and entrainer needs to be added into the original
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azeotrope system to increase the relative volatility of the azeotrope. There are several reported entrainers used for breaking binary azeotrope system, such as ionic liquid[6-7], dimethyl
D
sulfoxide(DMSO)[8] and N,N-dimethylformamide (DMF)[9]. Because of high viscosity, ionic
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liquid is not widely used in extractive distillation and the extraction capacity of DMSO and DMF is lower than para-xylene in the field of separating ethanol and ethyl propionate azeotropic system[10]. Due to wide availibility, low cost, high boiling point, less causticity, good thermal
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stability and miscibility with organic solvent[11], para-xylene has been reported as an effective additive in traditional extractive distillation, especially for the separation of mixture of ethylic acid
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and water[12-13]. Zhang, H. [14] selected para-xylene as solvent of methanol and trimethoxysilane in extractive distillation and found that para-xylene can break the azeotrope. However, up to now, the utilization of para-xylene as extraction agent to separate azeotropic system of ethanol + ethyl propionate has not been reported, which may be due to the lack of VLE data. The binary system VLE data, including ethanol (1) and ethyl propionate (2) and ethanol (1) and p-xylene (3), have been reported in the literature[4, 15], but lack of VLE data of ethyl propionate (2) and p-xylene (3). In addition, the ternary system of ethanol (1) + ethyl propionate (2) + para-xylene (3) also has no VLE data reported openly. Since the lack of VLE data and its 2
ACCEPTED MANUSCRIPT preferable prospect in extractive distillation process, measurement of isobaric VLE data for binary of ethyl propionate (2) + p-xylene (3) and ternary system of ethanol (1) + ethyl propionate (2) + para-xylene (3) is meaningful. In this paper, the VLE data for binary system of ethyl propionate + para-xylene and ternary system of ethanol + ethyl propionate + para-xylene were determined at 101.3 kPa. The Wilson and
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UNIQUAC activity coefficient models were employed to correlate the binary VLE data and to
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obtain the interaction parameters, thus by use of the interaction parameters to predict the ternary VLE data.
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2 EXPERIMENTAL
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2.1 Chemicals
Three chemicals are ethanol, ethyl propionate and para-xylene, respectively, which are
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always miscible in all measurements. Their corresponding information about molecular formula, purity grade and source is listed in Table 1. The purity of all the chemicals was measured by gas
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chromatograph (GC) with a FID detector. All the reagents were used without further purification.
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Table 1 Chemical reagents information. Molecular Component name
para-xylene ①
(mass%)
instrument
C2H6O
Kewei, China
>99.3%
GC①
C5H10O2
Acros, China
≥99.8%
GC①
C8H10
Alfa, China
>99.8%
GC①
CE
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ethyl propionate
Analysis
Provider
formula ethanol
Purity
Gas chromatography.
2.2 Procedure A circulation vapor-liquid equilibrium was used to measure the isobaric VLE data of binary and ternary system[16]. The volume of the chamber was about 50 ml, of which 40 ml was taken up by liquid. A mercury thermometer below the liquid level was used to detect experimental
3
ACCEPTED MANUSCRIPT temperature. The accuracy of the mercury thermometer is ±0.1 K. And the pressure was measured by a transducer (Digiquartz 2300A) connected to a Digiuartz 740 intelligent display unit (Paroscientific) whose accuracy is 0.01%. More details about the apparatus were referred to our previous papers [17-18]. About 40 ml liquid samples were fed into the chamber during each experiment, then heated at
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101.3 kPa. The system was considered to reach equilibrium state when the temperature of the
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mercury thermometer was not change for about 1h. Then, the samples of vapor and liquid phase were collected at the same time for analysis. To minimize the effect of sample amount on the
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equilibrium, three analyses were in parallel conducted and the amounts of the analyses were taken
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at 0.1 ml.
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2.3 Analysis
Component analysis of the equilibrium vapor and liquid phase were conducted by GC2060
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with a FID detector and SE-54 column (30 m × 0.32 mm × 0.5 µm). High purity nitrogen was
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carrier gas at flow rate of 30 mL/min. The temperatures of injector, detector and oven were 473.15 K, 473.15 K and 393.15 K, respectively. Standard solutions were applied to calibrate the GC, which were prepared gravimetrically by an electronic balance (FA2004N, uncertainty of ±0.0001
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g). In addition, calibration factor of pure substance was determined ahead of time. The final composition of each sample was determined upon the average of three analyses.
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3 RESULTS AND DISCUSSION 3.1 Experimental data The VLE data for binary systems, including ethanol (1) + ethyl propionate (2) and ethanol (1) + para-xylene (3), are measured at 101.3 kPa. The activity coefficient ( i ) is determined by the following equation[19-20]：
Vi L ( P Pi s ) RT
i Py i i xi Pi s is exp
4
(1)
ACCEPTED MANUSCRIPT where xi and yi represent the liquid and vapor content of component i, respectively; Pi s , obtained according to the extended Antoine equation, is the saturation vapor pressure of pure component i;
Vi L is the liquid molar volume of pure liquid i and R is the gas constant; i and is are the fugacity coefficient of component i in the heterogeneous vapor phase and in homogeneous saturated vapor phase, separately. At low pressure, the gas phase can be regarded as ideal gas, and
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V L ( P Pi s ) is approximately equal to 1. Meanwhile, i and is are equal to 1, exp i RT
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respectively[21-22], so the activity coefficient equation can be simplified as follows:
Py i i xi Pi s
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The extended Antoine equation is defined by Eq.(3).
ln(Pi s / kPa ) C1,i C2,i / T / K C3,i C4,i T / K C5,i (ln T / K) C6,i (T / K)
(2)
C7 ,i
(3)
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where C1,i C7,i , Tmin and Tmax are pure component constants which are listed in Table 2.
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Table 2 The constants C1, i-C7, i, Tmin and Tmax for the pure components ethyl propionate
para-xylene
66.3962
98.7322
81.8122
-7122.30
-8007.00
-7741.20
0.0
0.0
0.0
0.0
0.0
0.0
C5
-7.1424
-12.4770
-9.8693
C6
2.8853*10-6
9.0000*10-6
6.0770*10-6
C7
2.00
2.00
2.00
Tmin/K
159.05
199.25
286.41
Tmax/K
514.00
546.00
616.20
C1
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C4
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C2 C3
①
ethanol
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Component
①
Taken from Aspen Plus physical properties databanks. The isobaric VLE data for ethanol (1) + ethyl propionate (2) and ethanol (1) + para-xylene (3) 5
ACCEPTED MANUSCRIPT are presented in Table 3-4. To check the stability of experimental device, the experimental VLE data were compared with literature data[4, 15], which are shown in Figs.1-2. Meanwhile, the absolute and relative errors in temperature and vapor phase mole fraction are listed in Table 5. Obviously, The experiment results show a good agreement with literature data. Therefore, it is confirmed that the experimental device and operation process are reliable.
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Table 3 VLE data and activity coefficients for the binary system of ethanol (1) + ethyl propionate (2) at 101.3 ①
kPa .
2
1.0000
-
0.9985
2.0166
0.9017
0.9984
1.9379
0.8907
0.9987
1.8753
0.8765
1.0019
1.7472
0.7723
1.1014
1.3659
0.6959
1.2048
1.1901
0.4530
0.6550
1.2702
1.1264
0.4112
0.6260
1.2970
1.1033
0.3606
0.5872
1.3252
1.0760
0.2938
0.5540
1.4500
1.0000
360.64
0.2382
0.4902
1.4523
0.9805
363.23
0.1746
0.4247
1.5602
0.9368
367.20
0.0713
0.2807
2.1870
0.9143
372.50
0
0
-
1.0000
351.41
1
1
351.52
0.9228
0.9224
351.63
0.8986
351.72
0.8839
351.90
0.8602
352.41
0.6761
353.80
0.5274
AC
358.32
CE
355.61 356.80
①
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354.80
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y1
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x1
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1
T/K
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
Table 4 VLE data and activity coefficients for the binary system of ethanol (1) + para-xylene (3) at 101.3 kPa
6
ACCEPTED MANUSCRIPT ①
.
3
y1
351.31
1
1
1.0000
-
351.63
0.9390
0.9500
1.0054
5.6269
352.70
0.8780
0.9011
0.9780
5.3447
353.45
0.8140
0.9152
1.0404
2.9243
353.79
0.7500
0.9060
1.1034
2.3749
354.28
0.5412
0.8732
354.58
0.5733
0.8790
356.39
0.4071
0.8850
357.30
0.3391
361.22
0.1862
366.03
0.1134
376.40
0.0720
400.20
0.0130
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1.7152
1.4556
1.5948
1.7974
1.1099
0.8581
2.0211
1.1882
0.8350
3.0963
0.9702
0.7850
4.0234
0.9764
0.6811
3.8267
0.9720
0.2730
4.0512
1.0030
0.0060
0.1791
5.0288
0.9844
0
0
-
1.0000
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1.4463
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410.00
PT
x1
404.93
CE
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
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①
1
T/K
Figure 1 T vs x1, y1 diagram for the ethanol (1) + ethyl propionate (2) system at 101.3 kPa (●, experimental 7
ACCEPTED MANUSCRIPT vapor phase composition y1; ■, experimental liquid phase composition x1; —, literature liquid phase
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PT
composition x1; …, literature vapor phase composition y1 [4]).
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Figure 2 T vs x1, y1 diagram for the ethanol (1) + para-xylene (3) system at 101.3 kPa (●, experimental vapor phase composition y1; ■, experimental liquid phase composition x1; —, literature liquid phase composition
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x1; …, literature vapor phase composition y1 [15]).
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Table 5 The mean absolute and relative deviations of vapor phase mole fraction and equilibrium
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temperature for system of ethanol(1)+ethyl propionate(2) and ethanol(1)+para-xylene(3) System
Mean absolute deviations ①
②
CE
ΔT /K
ethanol (1) + ethyl propionate
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(2)
ethanol (1) + para-xylene (3) ①
②
③
④
T (1 / n)
y (1 / n)
T exp i 1 i
n
i 1
y iexp y ilit
i 1
n
i 1
④
δT /K
δy
0.18
0.009
0.05%
1.45%
0.43
0.005
0.16%
0.78%
y iexp y ilit , where n is the number of data points, y is the composition of vapor phase.
Tiexp Tilit
n
③
Δy
Tilit , where n is the number of data points, T is the system temperature.
T (1 / n)
y (1 / n)
n
Mean relative deviations
Tilit
y ilit
100% , where n is the number of data points, T is the system temperature.
100% , where n is the number of data points, y is the composition of vapor phase.
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ACCEPTED MANUSCRIPT The isobaric VLE data for the binary system of ethyl propionate (2) + para-xylene (3) and ternary system of ethanol (1) + ethyl propionate (2) + para-xylene (3) were obtained at 101.3 kPa, which are listed in Table 6-7. For the ternary system, para-xylene was added into the still at a constant content (50 mol %). In Table 7, x' and y' denote the mole fraction of corresponding liquid and vapor phase on the basis of free para-xylene, respectively. The relative volatility of ethanol to
y1' / x1' y 2 ' / x2 '
(4)
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12
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ethyl propionate is determined by the following equation[23]:
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In extractive distillation, relative volatility is an important factor to evaluate the performance of extraction agent[24-25]. When the relative volatility is greater than 1, the two
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components can be separated by distillation[21]. Table 7 shows that the minimum relative
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volatility of ethyl alcohol to ethyl propionate is 3.4141 after para-xylene was added, which demonstrates the complete separation of ethanol and ethyl propionate can be achieved by extractive distillation.
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Table 6 VLE data and activity coefficients for the binary system of ethyl propionate (2) + para-xylene (3) at ①
101.3 kPa .
x2
y2
2
3
1
1
1.0000
-
0.9222
0.9780
0.9980
0.8559
0.8383
0.9498
1.0065
0.8822
379.72
0.7069
0.8932
1.0151
0.9275
382.25
0.6340
0.8540
1.0049
0.9363
383.30
0.5897
0.8245
1.0119
0.9711
387.14
0.4806
0.7470
1.0083
0.9809
390.01
0.3994
0.6795
1.0187
0.9843
393.71
0.3245
0.5945
0.9913
0.9909
T/K
374.45
AC
376.35
CE
372.25
9
ACCEPTED MANUSCRIPT 0.2414
0.4862
0.9843
0.9999
399.34
0.2051
0.4284
0.9730
1.0073
403.58
0.1268
0.2844
0.9365
1.0180
407.82
0.0580
0.1390
0.8992
1.0099
411.65
0
0
-
1.0000
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
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PT
①
397.52
①
y2
y1'
12
0.3293
0.5087
0.3930
5.3037
0.5307
0.3148
0.6277
5.6021
0.5829
0.2649
0.6875
5.5600
0.3611
0.6497
0.2151
0.7513
5.3448
0.2790
0.4345
0.6999
0.1774
0.7978
5.1341
0.2388
0.2369
0.7333
0.1425
0.8373
5.1050
359.80
0.3030
0.1565
0.6594
0.7909
0.0843
0.9037
4.8458
358.93
0.3254
0.1320
0.7114
0.8059
0.0689
0.9212
4.7448
358.44
0.3506
0.1007
0.7769
0.8226
0.0506
0.9421
4.6693
357.84
0.3857
0.0764
0.8347
0.8367
0.0412
0.9531
4.0227
357.79
0.3956
0.0412
0.9057
0.8495
0.0227
0.9740
3.8974
357.40
0.4306
0.0130
0.9708
0.8622
0.0076
0.9646
3.4141
x2
x1'
376.36
0.0585
0.4793
0.1088
369.82
0.1167
0.3878
0.2313
367.69
0.1401
0.3540
0.2835
364.70
0.1792
0.3171
362.69
0.2144
361.63
0.5020
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AC
①
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x1
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T/K
SC y1
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Table 7 VLE data for the ternary system of ethanol (1) + ethyl propionate (2)+para-xylene (3) at 101.3 kPa.
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
3.2 Data regression The acquired VLE data was correlated with the Wilson and UNIQUAC models by Aspen Plus to gain the interaction parameters of the ternary system of ethanol (1) + ethyl propionate (2) + 10
ACCEPTED MANUSCRIPT para-xylene (3)[26]. To obtain the minimizing maximum likelihood objective function, the binary VLE data was regressed, which was described as: 2 2 2 2 exp exp exp cal cal Pi Pi cal Ti exp Ti cal x1,i x1,i y1,i y1,i F P T x y i 1 N
(5)
where is the standard deviation of the corresponding parameters. The standard deviations of
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pressure P , temperature T , liquid composition x and vapor composition y used in this
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VLE data correlation are 0.1013 kPa, 0.1 K, 0.001 and 0.001, respectively.
The correlated parameters and the root-mean-square deviations (RMSD) of temperature and
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vapor phase mole fraction are given in Table 8. Meanwhile, the contradistinction between
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experimental data and calculated data is presented in Fig.3, revealing that all the values calculated by the two models fit well with the experimental data.
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Table 8 Correlated parameters and RMSD for systems of ethanol (1) + ethyl propionate (2), ethanol (1) + para-xylene (3) and ethyl propionate (2) + para-xylene (3). Correlation parameters
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Model αji
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αij
RMSD
bij
bji
T/K①
yi②
ethanol (1) + ethyl propionate (2) Wilson
③
④
11.1078
1362.00
-4062.97
0.2641
0.0060
3.0394
-1.9005
-976.88
367.37
0.2488
0.0069
2.3488
-2.1171
-1244.52
378.84
0.3393
0.0040
-3.3371
3.1186
1249.08
-1469.68
0.2368
0.0036
CE
UNIQUAC
-4.4830
Wilson
③
AC
ethanol (1) + para-xylene (3)
④
UNIQUAC
ethyl propionate (2) + para-xylene (3) Wilson
③
④
UNIQUAC
①
T 1 / n
-0.5200
-0.2846
99.6976
221.15
0.3261
0.0061
0.00959
-0.3307
133.86
-4.8281
0.2959
0.0052
n
i 1
(Tiexp
1/ 2
Tical ) 2
11
ACCEPTED MANUSCRIPT
②
yi 1 / n
③
Wilson, ln Aij aij bij / T
UNIQUAC, ij exp aij bij / T
NU
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PT
④
1/ 2
( yiexp yical ) 2 i 1 n
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Figure 3 T vs x2, y2 diagram for the ethyl propionate (2) + para-xylene (3) system at 101.3 kPa (■, □
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experimental data; …, calculated data with Wilson model; —, calculated data with UNIQUAC model).
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3.3 Consistency tests of experimental data The Van Ness test method, a point consistency method put forward by Fredenslund et al[27],
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was quoted to verify the reliability of experimental data[28]. The criterion is expressed by the
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following equation[29]:
y i (1 / n)
n
100 y
exp i
y ical
(6)
i 1
where n is the number of experimental data points; the superscript exp represents experimental data; the superscript cal represents values determined by Wilson and UNIQUAC models. If the value of yi is lower than 1, the VLE data can be confirmed to be thermodynamically consistent. Table 9 shows the results of binary and ternary systems applying the above expression, revealing that all the experimental data obtained in this work is thermodynamically consistent. Table 9 The results of thermodynamic consistency test of Van Ness method for the binary and ternary 12
ACCEPTED MANUSCRIPT systems. systems
Wilson
UNIQUAC
results
ethyl propionate (2) + para-xylene (3) 0.480
0.358
passed
△y2
0.480
0.358
passed
ethanol (1) + ethyl propionate (2) + para-xylene (3)
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△y1
0.311
0.438
△y2
0.289
0.280
passed
△y3
0.344
0.319
passed
passed
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△y1
3.4 Data prediction
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The ternary VLE data of ethanol (1) + ethyl propionate (2) + para-xylene (3) were predicted with the correlated binary parameters which were obtained by Wilson and UNIQUAC models. The
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maximum and mean absolute deviations of equilibrium temperature and vapor mole fraction for
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each system are listed in Table 10. The results illustrate that the predicted data agrees well with the experimental data, which indicate that both Wilson and UNIQUAC models can predict the experimental data accurately. A vapor-liquid residue curve map is constructed by residue in a
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simple distillation in time, which is a geometric analysis method for distillation system to explain
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the composition of an azeotropic system[30-31]. In order to further check ternary system VLE data, the residue curve of the ternary system was predicted by UNIQUAC model using correlated binary parameters, which was shown in Fig.4. The connecting lines of the vapor phase points and liquid phase points are tangent very well with the residue curves at the liquid phase points, indicating that the prediction data are coincident with experimental data[32-33]. Table10 Maximum and mean absolute deviations of equilibrium temperature and vapor-phase mole fraction for system of ethanol (1) + ethyl propionate (2) + para-xylene (3) Model
Maximum absolute deviations
Mean absolute deviations
13
ACCEPTED MANUSCRIPT ①
②
②
②
③
Δmax y1
Δmaxy2
Δmaxy3
ΔT /K
Δy1
Wilson
0.48
0.009
0.007
0.008
0.24
UNIQUAC
0.79
0.010
0.009
0.007
0.36
①
maxT maxTiexp Tical
②
max yi max yiexp yical
④
Δy i (1 / n)
n T exp i 1 i
n
i 1
④
Δy3
0.003
0.003
0.003
0.004
0.003
0.003
Tical
y iexp y ical
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ΔT (1 / n)
④
Δy2
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③
④
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ΔmaxT /K
Figure 4 Residue curves of the ternary system ethanol (1) + ethyl propionate (2) + para-xylene (3) (■,
data; …, residue curves).
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experimental liquid phase composition; ○, experimental vapor phase composition; —, pairs of VLE
To investigate the effect of with and without para-xylene on the system of ethanol (1) + ethyl propionate (2), isobaric VLE data of the binary system are presented in Fig.5. As shown in Fig.5, one can note that the azeotropic phenomenon is disappeared when the mole ratio of para-xylene and binary system of ethanol and ethyl propionate is 1:1. The reason why para-xylene can change the relative volatility of azeotrope in our work may be explained by the fact that attraction of para-xylene for alcohols is larger than that for esters[34], which demonstrates that para-xylene is a potential extraction agent for this system. 14
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ACCEPTED MANUSCRIPT
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Figure 5 x1 vs y1 diagram for the comparison of VLE behavior of binary system ethanol (1) + ethyl propionate (2) with and without para-xylene (▲, experimental VLE data without para-xylene; ●,
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experimental VLE data with para-xylene).
4 CONCLUSION
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Isobaric VLE data of the binary system ethyl propionate + para-xylene and ternary system of ethanol + ethyl propionate + para-xylene were determined at 101.3 kPa. The thermodynamic
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consistency test indicated that both binary and ternary VLE data passed the Van Ness test. Wilson
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and UNIQUAC activity coefficient models were used to correlate experimental data to obtain binary interaction parameters. The comparison between the experimental data and VLE data
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predicted by the two models reveals that predicted data fits well with experimental date. The azeotropic phenomenon vanishes when the mole ratio of the azeotrope and para-xylene is 1:1. The
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experimental and prediction results imply that para-xylene is an available additive to separate the binary system of ethanol and ethyl propionate in extractive distillation.
NOMENCLATURE ij , ji , bij , b ji
the correlated parameters of Wilson and UNIQUAC models
cal
calculated
C1,i C7,i exp
pure component constants experimental 15
ACCEPTED MANUSCRIPT F
term defined by Eq. (6)
n
the number of experimental data points saturated vapor pressure of pure component i, kPa
P
the total pressure, kPa
R
universal gas constant
T
tempreture, K
u
standard uncertainty
Vi L
liquid molar volume of pure liquid i, m3·mol-1
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Pi s
liquid and vapor content of component i, respectively
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relative volatility of ethanol to ethyl propionate
i , is
fugacity coefficient of component i in the mixture vapor phase and pure saturated vapor
liquid activity coefficient
T
root-mean-square deviations of temperature
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xi , y i
mean absolute deviations of equilibrium temperature
δT
relative deviations of equilibrium temperature
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ΔT
mean absolute deviations of vapor-phase mole fraction
y
mean relative deviations of vapor phase mole fraction
y
root-mean-square deviations of vapor phase mole fraction
the standard deviation
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Δy
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[30] Rooks, R.E., Julka, V., Doherty, M.F., Malone, M.F., Structure of distillation regions for multicomponent azeotropic mixtures, Aiche Journal, 44 (6), 1382-1391 (1998) [31] Widagdo, S., Seider, W. D., Azeotropic distillation. AIChE Journal, 42 (1), 96−130 (1996)
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[32] Zhang, X.M., Liu, Y.X., Jian, C.G., Wei, F., Liu, H.P., Experimental isobaric vapor-liquid equilibrium for ternary system of sec-butyl alcohol plus sec-butyl acetate plus N,N-dimethyl formamide at 101.3 kPa, Fluid
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Phase Equilibria, 383, 5-10 (2014) [33] Zhang, X.M., Liu, H.P., Liu, Y.X., Jian, C.G., Wang, W., Experimental isobaric vapor-liquid equilibrium for the binary and ternary systems with methanol, methyl acetate and dimethyl sulfoxide at 101.3 kPa, Fluid Phase Equilibria, 408, 52-57(2016) [34] Fredenslund, A., Gmehling, J., Rasmussen, P., Vapor-liquid equilibria using UNIFAC: A group contribution method, Elsevier, Amsterdam, 68−84, 150−155 (1977)
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Zhongpeng Xing, Yujie Gao, Hui Ding, Xianqin Wang, Lujun Li, Hang Zhou PII: DOI: Reference:
S1004-9541(17)30315-4 doi:10.1016/j.cjche.2017.10.020 CJCHE 971
To appear in: Received date: Revised date: Accepted date:
15 March 2017 9 September 2017 20 October 2017
Please cite this article as: Zhongpeng Xing, Yujie Gao, Hui Ding, Xianqin Wang, Lujun Li, Hang Zhou , Isobaric vapor-liquid equilibrium for ternary system of ethanol, ethyl propionate and para-xylene at 101.3 kPa. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Cjche(2017), doi:10.1016/j.cjche.2017.10.020
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ACCEPTED MANUSCRIPT Chemical Engineering Thermodynamics
Isobaric vapor-liquid equilibrium for ternary system of ethanol, ethyl propionate and para-xylene at 101.3 kPa 4,**
4
4
1
, Xianqin Wang , Lujun Li , Hang Zhou
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Zhongpeng Xing1, Yujie Gao2,3, Hui Ding
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
2
Tianjin Academy of Environmental Sciences, Tianjin 300191, China
3
Tianjin Huanke Environmental Planning Technology Development Company Limited, Tianjin 300191, China
4
School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China
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1
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Abstract Isobaric vapor-liquid equilibrium (VLE) data for the binary system ethyl propionate (2) + para-xylene (3) and ternary system ethanol (1) + ethyl propionate (2) + para-xylene (2) at atmospheric pressure (101.3 kPa) were obtained by a VLE modified othmer still. All the experimental data passed a point to point consistency test of Van
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Ness method, which verified the data reliability. The Wilson and UNIQUAC activity coefficient models were
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employed to correlate the binary VLE data to obtain binary interaction parameters. Based on binary interaction parameters, ternary VLE data of ethanol (1) + ethyl propionate (2) + para-xylene (3) were predicted by Wilson and
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UNIQUAC models, which proved that predicted values are consistent with the experimental data. Furthermore, azeotropic phenomenon between ethanol and ethyl propionate disappears when the mole ratio of para-xylene and
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binary system of ethanol and ethyl propionate is 1:1. Therefore, this paper convinced that para-xylene is a proper extractive additive that could be used in extractive distillation to separate the binary azeotropic system of ethanol and ethyl propionate. Keywords vapor-liquid equilibrium; azeotrope; ethanol; ethyl propionate; para-xylene
______________________________ Received 2017-3-15 * Supported by the National Natural Science Foundation of China (21376166). ** To whom correspondence should be addressed. E-mail: [email protected] (H Ding).
ACCEPTED MANUSCRIPT 1 INTRODUCTION Ethyl propionate, a kind of widely-used organic synthetic raw material and solvent, is applied in the field of pharmacy, antifungal agents, edibles, plasticizers, spice, dyes and even biomass[1-2]. In industry, the traditional method of producing ethyl propionate is esterification of propanoic acid and ethanol with sulfuric acid as catalyst at 101.3 kPa, and then cut fraction from 369.15 K to
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373.15 K is collected to gain pure product in distillation[3]. However, the literature has reported
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that ethyl propionate and ethanol form an azeotrope at 101.3 kPa, which reduces the yield and purity of ethyl propionate[4]. Therefore, it is a challenge for researcher to find out a way to
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improve the purity of ethyl propionate in the operation process.
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For azeotrope or similar boiling point system, extractive distillation is an effective and widely-used process to separate the mixture[5], and entrainer needs to be added into the original
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azeotrope system to increase the relative volatility of the azeotrope. There are several reported entrainers used for breaking binary azeotrope system, such as ionic liquid[6-7], dimethyl
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sulfoxide(DMSO)[8] and N,N-dimethylformamide (DMF)[9]. Because of high viscosity, ionic
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liquid is not widely used in extractive distillation and the extraction capacity of DMSO and DMF is lower than para-xylene in the field of separating ethanol and ethyl propionate azeotropic system[10]. Due to wide availibility, low cost, high boiling point, less causticity, good thermal
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stability and miscibility with organic solvent[11], para-xylene has been reported as an effective additive in traditional extractive distillation, especially for the separation of mixture of ethylic acid
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and water[12-13]. Zhang, H. [14] selected para-xylene as solvent of methanol and trimethoxysilane in extractive distillation and found that para-xylene can break the azeotrope. However, up to now, the utilization of para-xylene as extraction agent to separate azeotropic system of ethanol + ethyl propionate has not been reported, which may be due to the lack of VLE data. The binary system VLE data, including ethanol (1) and ethyl propionate (2) and ethanol (1) and p-xylene (3), have been reported in the literature[4, 15], but lack of VLE data of ethyl propionate (2) and p-xylene (3). In addition, the ternary system of ethanol (1) + ethyl propionate (2) + para-xylene (3) also has no VLE data reported openly. Since the lack of VLE data and its 2
ACCEPTED MANUSCRIPT preferable prospect in extractive distillation process, measurement of isobaric VLE data for binary of ethyl propionate (2) + p-xylene (3) and ternary system of ethanol (1) + ethyl propionate (2) + para-xylene (3) is meaningful. In this paper, the VLE data for binary system of ethyl propionate + para-xylene and ternary system of ethanol + ethyl propionate + para-xylene were determined at 101.3 kPa. The Wilson and
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UNIQUAC activity coefficient models were employed to correlate the binary VLE data and to
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obtain the interaction parameters, thus by use of the interaction parameters to predict the ternary VLE data.
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2 EXPERIMENTAL
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2.1 Chemicals
Three chemicals are ethanol, ethyl propionate and para-xylene, respectively, which are
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always miscible in all measurements. Their corresponding information about molecular formula, purity grade and source is listed in Table 1. The purity of all the chemicals was measured by gas
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chromatograph (GC) with a FID detector. All the reagents were used without further purification.
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Table 1 Chemical reagents information. Molecular Component name
para-xylene ①
(mass%)
instrument
C2H6O
Kewei, China
>99.3%
GC①
C5H10O2
Acros, China
≥99.8%
GC①
C8H10
Alfa, China
>99.8%
GC①
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ethyl propionate
Analysis
Provider
formula ethanol
Purity
Gas chromatography.
2.2 Procedure A circulation vapor-liquid equilibrium was used to measure the isobaric VLE data of binary and ternary system[16]. The volume of the chamber was about 50 ml, of which 40 ml was taken up by liquid. A mercury thermometer below the liquid level was used to detect experimental
3
ACCEPTED MANUSCRIPT temperature. The accuracy of the mercury thermometer is ±0.1 K. And the pressure was measured by a transducer (Digiquartz 2300A) connected to a Digiuartz 740 intelligent display unit (Paroscientific) whose accuracy is 0.01%. More details about the apparatus were referred to our previous papers [17-18]. About 40 ml liquid samples were fed into the chamber during each experiment, then heated at
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101.3 kPa. The system was considered to reach equilibrium state when the temperature of the
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mercury thermometer was not change for about 1h. Then, the samples of vapor and liquid phase were collected at the same time for analysis. To minimize the effect of sample amount on the
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equilibrium, three analyses were in parallel conducted and the amounts of the analyses were taken
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at 0.1 ml.
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2.3 Analysis
Component analysis of the equilibrium vapor and liquid phase were conducted by GC2060
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with a FID detector and SE-54 column (30 m × 0.32 mm × 0.5 µm). High purity nitrogen was
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carrier gas at flow rate of 30 mL/min. The temperatures of injector, detector and oven were 473.15 K, 473.15 K and 393.15 K, respectively. Standard solutions were applied to calibrate the GC, which were prepared gravimetrically by an electronic balance (FA2004N, uncertainty of ±0.0001
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g). In addition, calibration factor of pure substance was determined ahead of time. The final composition of each sample was determined upon the average of three analyses.
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3 RESULTS AND DISCUSSION 3.1 Experimental data The VLE data for binary systems, including ethanol (1) + ethyl propionate (2) and ethanol (1) + para-xylene (3), are measured at 101.3 kPa. The activity coefficient ( i ) is determined by the following equation[19-20]：
Vi L ( P Pi s ) RT
i Py i i xi Pi s is exp
4
(1)
ACCEPTED MANUSCRIPT where xi and yi represent the liquid and vapor content of component i, respectively; Pi s , obtained according to the extended Antoine equation, is the saturation vapor pressure of pure component i;
Vi L is the liquid molar volume of pure liquid i and R is the gas constant; i and is are the fugacity coefficient of component i in the heterogeneous vapor phase and in homogeneous saturated vapor phase, separately. At low pressure, the gas phase can be regarded as ideal gas, and
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V L ( P Pi s ) is approximately equal to 1. Meanwhile, i and is are equal to 1, exp i RT
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respectively[21-22], so the activity coefficient equation can be simplified as follows:
Py i i xi Pi s
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The extended Antoine equation is defined by Eq.(3).
ln(Pi s / kPa ) C1,i C2,i / T / K C3,i C4,i T / K C5,i (ln T / K) C6,i (T / K)
(2)
C7 ,i
(3)
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where C1,i C7,i , Tmin and Tmax are pure component constants which are listed in Table 2.
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Table 2 The constants C1, i-C7, i, Tmin and Tmax for the pure components ethyl propionate
para-xylene
66.3962
98.7322
81.8122
-7122.30
-8007.00
-7741.20
0.0
0.0
0.0
0.0
0.0
0.0
C5
-7.1424
-12.4770
-9.8693
C6
2.8853*10-6
9.0000*10-6
6.0770*10-6
C7
2.00
2.00
2.00
Tmin/K
159.05
199.25
286.41
Tmax/K
514.00
546.00
616.20
C1
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C4
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C2 C3
①
ethanol
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Component
①
Taken from Aspen Plus physical properties databanks. The isobaric VLE data for ethanol (1) + ethyl propionate (2) and ethanol (1) + para-xylene (3) 5
ACCEPTED MANUSCRIPT are presented in Table 3-4. To check the stability of experimental device, the experimental VLE data were compared with literature data[4, 15], which are shown in Figs.1-2. Meanwhile, the absolute and relative errors in temperature and vapor phase mole fraction are listed in Table 5. Obviously, The experiment results show a good agreement with literature data. Therefore, it is confirmed that the experimental device and operation process are reliable.
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Table 3 VLE data and activity coefficients for the binary system of ethanol (1) + ethyl propionate (2) at 101.3 ①
kPa .
2
1.0000
-
0.9985
2.0166
0.9017
0.9984
1.9379
0.8907
0.9987
1.8753
0.8765
1.0019
1.7472
0.7723
1.1014
1.3659
0.6959
1.2048
1.1901
0.4530
0.6550
1.2702
1.1264
0.4112
0.6260
1.2970
1.1033
0.3606
0.5872
1.3252
1.0760
0.2938
0.5540
1.4500
1.0000
360.64
0.2382
0.4902
1.4523
0.9805
363.23
0.1746
0.4247
1.5602
0.9368
367.20
0.0713
0.2807
2.1870
0.9143
372.50
0
0
-
1.0000
351.41
1
1
351.52
0.9228
0.9224
351.63
0.8986
351.72
0.8839
351.90
0.8602
352.41
0.6761
353.80
0.5274
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358.32
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355.61 356.80
①
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354.80
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y1
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x1
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1
T/K
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
Table 4 VLE data and activity coefficients for the binary system of ethanol (1) + para-xylene (3) at 101.3 kPa
6
ACCEPTED MANUSCRIPT ①
.
3
y1
351.31
1
1
1.0000
-
351.63
0.9390
0.9500
1.0054
5.6269
352.70
0.8780
0.9011
0.9780
5.3447
353.45
0.8140
0.9152
1.0404
2.9243
353.79
0.7500
0.9060
1.1034
2.3749
354.28
0.5412
0.8732
354.58
0.5733
0.8790
356.39
0.4071
0.8850
357.30
0.3391
361.22
0.1862
366.03
0.1134
376.40
0.0720
400.20
0.0130
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1.7152
1.4556
1.5948
1.7974
1.1099
0.8581
2.0211
1.1882
0.8350
3.0963
0.9702
0.7850
4.0234
0.9764
0.6811
3.8267
0.9720
0.2730
4.0512
1.0030
0.0060
0.1791
5.0288
0.9844
0
0
-
1.0000
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1.4463
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410.00
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x1
404.93
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The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
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①
1
T/K
Figure 1 T vs x1, y1 diagram for the ethanol (1) + ethyl propionate (2) system at 101.3 kPa (●, experimental 7
ACCEPTED MANUSCRIPT vapor phase composition y1; ■, experimental liquid phase composition x1; —, literature liquid phase
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composition x1; …, literature vapor phase composition y1 [4]).
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Figure 2 T vs x1, y1 diagram for the ethanol (1) + para-xylene (3) system at 101.3 kPa (●, experimental vapor phase composition y1; ■, experimental liquid phase composition x1; —, literature liquid phase composition
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x1; …, literature vapor phase composition y1 [15]).
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Table 5 The mean absolute and relative deviations of vapor phase mole fraction and equilibrium
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temperature for system of ethanol(1)+ethyl propionate(2) and ethanol(1)+para-xylene(3) System
Mean absolute deviations ①
②
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ΔT /K
ethanol (1) + ethyl propionate
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(2)
ethanol (1) + para-xylene (3) ①
②
③
④
T (1 / n)
y (1 / n)
T exp i 1 i
n
i 1
y iexp y ilit
i 1
n
i 1
④
δT /K
δy
0.18
0.009
0.05%
1.45%
0.43
0.005
0.16%
0.78%
y iexp y ilit , where n is the number of data points, y is the composition of vapor phase.
Tiexp Tilit
n
③
Δy
Tilit , where n is the number of data points, T is the system temperature.
T (1 / n)
y (1 / n)
n
Mean relative deviations
Tilit
y ilit
100% , where n is the number of data points, T is the system temperature.
100% , where n is the number of data points, y is the composition of vapor phase.
8
ACCEPTED MANUSCRIPT The isobaric VLE data for the binary system of ethyl propionate (2) + para-xylene (3) and ternary system of ethanol (1) + ethyl propionate (2) + para-xylene (3) were obtained at 101.3 kPa, which are listed in Table 6-7. For the ternary system, para-xylene was added into the still at a constant content (50 mol %). In Table 7, x' and y' denote the mole fraction of corresponding liquid and vapor phase on the basis of free para-xylene, respectively. The relative volatility of ethanol to
y1' / x1' y 2 ' / x2 '
(4)
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12
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ethyl propionate is determined by the following equation[23]:
SC
In extractive distillation, relative volatility is an important factor to evaluate the performance of extraction agent[24-25]. When the relative volatility is greater than 1, the two
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components can be separated by distillation[21]. Table 7 shows that the minimum relative
MA
volatility of ethyl alcohol to ethyl propionate is 3.4141 after para-xylene was added, which demonstrates the complete separation of ethanol and ethyl propionate can be achieved by extractive distillation.
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D
Table 6 VLE data and activity coefficients for the binary system of ethyl propionate (2) + para-xylene (3) at ①
101.3 kPa .
x2
y2
2
3
1
1
1.0000
-
0.9222
0.9780
0.9980
0.8559
0.8383
0.9498
1.0065
0.8822
379.72
0.7069
0.8932
1.0151
0.9275
382.25
0.6340
0.8540
1.0049
0.9363
383.30
0.5897
0.8245
1.0119
0.9711
387.14
0.4806
0.7470
1.0083
0.9809
390.01
0.3994
0.6795
1.0187
0.9843
393.71
0.3245
0.5945
0.9913
0.9909
T/K
374.45
AC
376.35
CE
372.25
9
ACCEPTED MANUSCRIPT 0.2414
0.4862
0.9843
0.9999
399.34
0.2051
0.4284
0.9730
1.0073
403.58
0.1268
0.2844
0.9365
1.0180
407.82
0.0580
0.1390
0.8992
1.0099
411.65
0
0
-
1.0000
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
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PT
①
397.52
①
y2
y1'
12
0.3293
0.5087
0.3930
5.3037
0.5307
0.3148
0.6277
5.6021
0.5829
0.2649
0.6875
5.5600
0.3611
0.6497
0.2151
0.7513
5.3448
0.2790
0.4345
0.6999
0.1774
0.7978
5.1341
0.2388
0.2369
0.7333
0.1425
0.8373
5.1050
359.80
0.3030
0.1565
0.6594
0.7909
0.0843
0.9037
4.8458
358.93
0.3254
0.1320
0.7114
0.8059
0.0689
0.9212
4.7448
358.44
0.3506
0.1007
0.7769
0.8226
0.0506
0.9421
4.6693
357.84
0.3857
0.0764
0.8347
0.8367
0.0412
0.9531
4.0227
357.79
0.3956
0.0412
0.9057
0.8495
0.0227
0.9740
3.8974
357.40
0.4306
0.0130
0.9708
0.8622
0.0076
0.9646
3.4141
x2
x1'
376.36
0.0585
0.4793
0.1088
369.82
0.1167
0.3878
0.2313
367.69
0.1401
0.3540
0.2835
364.70
0.1792
0.3171
362.69
0.2144
361.63
0.5020
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CE
AC
①
NU
x1
MA
T/K
SC y1
D
Table 7 VLE data for the ternary system of ethanol (1) + ethyl propionate (2)+para-xylene (3) at 101.3 kPa.
The standard uncertainty is u(T) = 0.1 K, u(P) = 0.1 kPa, and u(x1) = u(y1) = 0.004.
3.2 Data regression The acquired VLE data was correlated with the Wilson and UNIQUAC models by Aspen Plus to gain the interaction parameters of the ternary system of ethanol (1) + ethyl propionate (2) + 10
ACCEPTED MANUSCRIPT para-xylene (3)[26]. To obtain the minimizing maximum likelihood objective function, the binary VLE data was regressed, which was described as: 2 2 2 2 exp exp exp cal cal Pi Pi cal Ti exp Ti cal x1,i x1,i y1,i y1,i F P T x y i 1 N
(5)
where is the standard deviation of the corresponding parameters. The standard deviations of
PT
pressure P , temperature T , liquid composition x and vapor composition y used in this
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VLE data correlation are 0.1013 kPa, 0.1 K, 0.001 and 0.001, respectively.
The correlated parameters and the root-mean-square deviations (RMSD) of temperature and
SC
vapor phase mole fraction are given in Table 8. Meanwhile, the contradistinction between
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experimental data and calculated data is presented in Fig.3, revealing that all the values calculated by the two models fit well with the experimental data.
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Table 8 Correlated parameters and RMSD for systems of ethanol (1) + ethyl propionate (2), ethanol (1) + para-xylene (3) and ethyl propionate (2) + para-xylene (3). Correlation parameters
D
Model αji
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αij
RMSD
bij
bji
T/K①
yi②
ethanol (1) + ethyl propionate (2) Wilson
③
④
11.1078
1362.00
-4062.97
0.2641
0.0060
3.0394
-1.9005
-976.88
367.37
0.2488
0.0069
2.3488
-2.1171
-1244.52
378.84
0.3393
0.0040
-3.3371
3.1186
1249.08
-1469.68
0.2368
0.0036
CE
UNIQUAC
-4.4830
Wilson
③
AC
ethanol (1) + para-xylene (3)
④
UNIQUAC
ethyl propionate (2) + para-xylene (3) Wilson
③
④
UNIQUAC
①
T 1 / n
-0.5200
-0.2846
99.6976
221.15
0.3261
0.0061
0.00959
-0.3307
133.86
-4.8281
0.2959
0.0052
n
i 1
(Tiexp
1/ 2
Tical ) 2
11
ACCEPTED MANUSCRIPT
②
yi 1 / n
③
Wilson, ln Aij aij bij / T
UNIQUAC, ij exp aij bij / T
NU
SC
RI
PT
④
1/ 2
( yiexp yical ) 2 i 1 n
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Figure 3 T vs x2, y2 diagram for the ethyl propionate (2) + para-xylene (3) system at 101.3 kPa (■, □
D
experimental data; …, calculated data with Wilson model; —, calculated data with UNIQUAC model).
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3.3 Consistency tests of experimental data The Van Ness test method, a point consistency method put forward by Fredenslund et al[27],
CE
was quoted to verify the reliability of experimental data[28]. The criterion is expressed by the
AC
following equation[29]:
y i (1 / n)
n
100 y
exp i
y ical
(6)
i 1
where n is the number of experimental data points; the superscript exp represents experimental data; the superscript cal represents values determined by Wilson and UNIQUAC models. If the value of yi is lower than 1, the VLE data can be confirmed to be thermodynamically consistent. Table 9 shows the results of binary and ternary systems applying the above expression, revealing that all the experimental data obtained in this work is thermodynamically consistent. Table 9 The results of thermodynamic consistency test of Van Ness method for the binary and ternary 12
ACCEPTED MANUSCRIPT systems. systems
Wilson
UNIQUAC
results
ethyl propionate (2) + para-xylene (3) 0.480
0.358
passed
△y2
0.480
0.358
passed
ethanol (1) + ethyl propionate (2) + para-xylene (3)
PT
△y1
0.311
0.438
△y2
0.289
0.280
passed
△y3
0.344
0.319
passed
passed
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SC
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△y1
3.4 Data prediction
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The ternary VLE data of ethanol (1) + ethyl propionate (2) + para-xylene (3) were predicted with the correlated binary parameters which were obtained by Wilson and UNIQUAC models. The
D
maximum and mean absolute deviations of equilibrium temperature and vapor mole fraction for
PT E
each system are listed in Table 10. The results illustrate that the predicted data agrees well with the experimental data, which indicate that both Wilson and UNIQUAC models can predict the experimental data accurately. A vapor-liquid residue curve map is constructed by residue in a
CE
simple distillation in time, which is a geometric analysis method for distillation system to explain
AC
the composition of an azeotropic system[30-31]. In order to further check ternary system VLE data, the residue curve of the ternary system was predicted by UNIQUAC model using correlated binary parameters, which was shown in Fig.4. The connecting lines of the vapor phase points and liquid phase points are tangent very well with the residue curves at the liquid phase points, indicating that the prediction data are coincident with experimental data[32-33]. Table10 Maximum and mean absolute deviations of equilibrium temperature and vapor-phase mole fraction for system of ethanol (1) + ethyl propionate (2) + para-xylene (3) Model
Maximum absolute deviations
Mean absolute deviations
13
ACCEPTED MANUSCRIPT ①
②
②
②
③
Δmax y1
Δmaxy2
Δmaxy3
ΔT /K
Δy1
Wilson
0.48
0.009
0.007
0.008
0.24
UNIQUAC
0.79
0.010
0.009
0.007
0.36
①
maxT maxTiexp Tical
②
max yi max yiexp yical
④
Δy i (1 / n)
n T exp i 1 i
n
i 1
④
Δy3
0.003
0.003
0.003
0.004
0.003
0.003
Tical
y iexp y ical
RI
ΔT (1 / n)
④
Δy2
PT E
D
MA
NU
SC
③
④
PT
ΔmaxT /K
Figure 4 Residue curves of the ternary system ethanol (1) + ethyl propionate (2) + para-xylene (3) (■,
data; …, residue curves).
AC
CE
experimental liquid phase composition; ○, experimental vapor phase composition; —, pairs of VLE
To investigate the effect of with and without para-xylene on the system of ethanol (1) + ethyl propionate (2), isobaric VLE data of the binary system are presented in Fig.5. As shown in Fig.5, one can note that the azeotropic phenomenon is disappeared when the mole ratio of para-xylene and binary system of ethanol and ethyl propionate is 1:1. The reason why para-xylene can change the relative volatility of azeotrope in our work may be explained by the fact that attraction of para-xylene for alcohols is larger than that for esters[34], which demonstrates that para-xylene is a potential extraction agent for this system. 14
RI
PT
ACCEPTED MANUSCRIPT
SC
Figure 5 x1 vs y1 diagram for the comparison of VLE behavior of binary system ethanol (1) + ethyl propionate (2) with and without para-xylene (▲, experimental VLE data without para-xylene; ●,
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experimental VLE data with para-xylene).
4 CONCLUSION
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Isobaric VLE data of the binary system ethyl propionate + para-xylene and ternary system of ethanol + ethyl propionate + para-xylene were determined at 101.3 kPa. The thermodynamic
D
consistency test indicated that both binary and ternary VLE data passed the Van Ness test. Wilson
PT E
and UNIQUAC activity coefficient models were used to correlate experimental data to obtain binary interaction parameters. The comparison between the experimental data and VLE data
CE
predicted by the two models reveals that predicted data fits well with experimental date. The azeotropic phenomenon vanishes when the mole ratio of the azeotrope and para-xylene is 1:1. The
AC
experimental and prediction results imply that para-xylene is an available additive to separate the binary system of ethanol and ethyl propionate in extractive distillation.
NOMENCLATURE ij , ji , bij , b ji
the correlated parameters of Wilson and UNIQUAC models
cal
calculated
C1,i C7,i exp
pure component constants experimental 15
ACCEPTED MANUSCRIPT F
term defined by Eq. (6)
n
the number of experimental data points saturated vapor pressure of pure component i, kPa
P
the total pressure, kPa
R
universal gas constant
T
tempreture, K
u
standard uncertainty
Vi L
liquid molar volume of pure liquid i, m3·mol-1
SC
RI
PT
Pi s
liquid and vapor content of component i, respectively
12
relative volatility of ethanol to ethyl propionate
i , is
fugacity coefficient of component i in the mixture vapor phase and pure saturated vapor
liquid activity coefficient
T
root-mean-square deviations of temperature
MA
NU
xi , y i
mean absolute deviations of equilibrium temperature
δT
relative deviations of equilibrium temperature
PT E
D
ΔT
mean absolute deviations of vapor-phase mole fraction
y
mean relative deviations of vapor phase mole fraction
y
root-mean-square deviations of vapor phase mole fraction
the standard deviation
AC
CE
Δy
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