Experimental Measurement and Modeling of Vapor–Liquid

Jun 30, 2016 - The nonrandom two-liquid (NRTL) equation(8) has been frequently used for the calculation of activity coefficients in the liquid phase f...
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Experimental Measurement and Modeling of Vapor−Liquid Equilibrium for the Ternary Systems Water + Ethanol + Ethylene Glycol, Water + 2‑Propanol + Ethylene Glycol, and Water + 1‑Propanol + Ethylene Glycol Lianzhong Zhang,* Xiaocheng Wang, Xiaoming Zhu, and Dongping Shen Zhejiang Province Key Laboratory of Biofuel, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China ABSTRACT: The present work aims at establishing reliable activity coefficient model for the ternary systems water + ethanol + ethylene glycol, water + 2-propanol + ethylene glycol, and water + 1-propanol + ethylene glycol. Isobaric VLE data were reported for the ternary systems and for the binary system of water + ethylene glycol at 101.3 kPa. The NRTL equation was used for the modeling. Literature values of binary parameters for water + ethanol, water + 2-propanol, and water + 1-propanol, which were obtained in the modeling of the ternary systems containing glycerol, were used in this work. For the binary pair water + ethylene glycol, a unique set of binary parameters were used for all of the three ternary systems. Using the model parameters obtained, calculated results were in good agreement with the experimental values. The correlation indicated that the minimum mole fractions of ethylene glycol for breaking the azeotrope of water + ethanol, water + 2-propanol, and water + 1-propanol were, respectively, 0.072, 0.240, and 0.550. Comparisons were presented for experimental results and correlations available in the literature.

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INTRODUCTION Ethanol, 2-propanol, and 1-propanol are basic chemical materials widely applied in daily life and in industry. Separation of the aqueous mixtures of the alcohols is often demanded in their production and recovery. Because each alcohol forms with water a minimum boiling point azeotrope, the separation can not be achieved by conventional distillation. At the present stage, extractive distillation is considered as a promising technique, especially for large-scale dehydration of the alcohols. Lowering the energy demand of the distillation process has profound impact. For example, the efficient dehydration of ethanol is a key step for the cost-effective production of bioethanol. Reliable activity coefficient models are necessary for the optimal design and operation of the extractive distillation process. The use of ethylene glycol as an entrainer for alcohol dehydration has been proposed by Washall1 and has been investigated by Landisch and Dyck2 and Lee and Pahl.3 The main features of ethylene glycol are its low toxicity, low viscosity, and relatively low vapor pressure. Ternary VLE data have been reported by several authors, including Pla-Franco et al.,4 Kamihama et al.,5 and Dai et al.6 for water + ethanol + ethylene glycol and Pla-Franco et al.7 for water + 1-propanol + ethylene glycol. To the best of our knowledge, VLE data for water + 2-propanol + ethylene glycol are not available in the open literature. The nonrandom two-liquid (NRTL) equation8 has been frequently used for the calculation of activity coefficients in the liquid phase for energy evaluation and process optimization of alcohol dehydration.9,10 NRTL parameters for the three © 2016 American Chemical Society

systems are available in the database of Aspen Plus process simulator, for example, APV80 VLE-IG. Model parameters have also been proposed by Pla-Franco et al.,4 Kamihama et al.,5 and Dai et al.6 for water + ethanol + ethylene glycol and Pla-Franco et al.7 for water + 1-propanol + ethylene glycol. We have calculated VLE for the ternary system water + ethanol + ethylene glycol, using NRTL parameters of various sources in the literature. Results showed significant deviations. These would have important influence on the design of extractive distillation. The present work aims at establishing reliable activity coefficient model for the systems water + ethanol + ethylene glycol, water + 2-propanol + ethylene glycol, and water + 1propanol + ethylene glycol. New experimental data were measured for ternary VLE of the three systems and binary VLE of water + ethylene glycol. Literature values of binary parameters for water + ethanol,11 water + 2-propanol,12 and water + 1-propanol,13 which have been obtained in the modeling of the ternary systems containing glycerol, were used in the correlation and kept unchanged. For the binary pair water + ethylene glycol, a unique set of binary parameters were used for all the three ternary systems. The reliability of the correlation was evaluated in terms of activity coefficients of both ternary and binary mixtures. Received: March 24, 2016 Accepted: June 23, 2016 Published: June 30, 2016 2596

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data sets were obtained, at x2′ = 0.2 and 0.95, respectively. Calculated results are also listed in Table 2 for the liquid-phase activity coefficients and the relative volatility of the alcohol to water (α21). In the calculation of the activity coefficients, the vapor phase was regarded as an ideal gas, and the vapor pressures were calculated by parameters in the literature.17 VLE data for the binary system water (1) + ethylene glycol (3) are listed in Table 3. The ternary VLE data were examined for thermodynamic consistency using the Wisniak and Tamir18 modification of the McDermott−Ellis test.19 Results showed D < Dmax at all data points. This indicates that the ternary data can be regarded as thermodynamic consistent. The thermodynamic consistency of the binary VLE data was checked with the point test of Fredenslund et al.20 The mean absolute deviation for the vaporphase mole fraction is 0.001. This is smaller than the criterion value recommended by Fredenslund et al.,20 which is 0.01. Therefore, the binary data can be considered thermodynamically consistent. The vapor−liquid phase behavior of the ternary systems were modeled using the NRTL equation.8 Binary parameters for water + ethanol,11 water + 2-propanol,12 and water + 1propanol13 have been reported in the literature for the modeling of ternary systems containing glycerol. These parameters were used in the modeling and were kept unchanged. The three ternary systems have in common the binary pair water + ethylene glycol. It would be interesting to use the same binary parameters for all the three ternary systems. For this purpose, binary parameters of water + ethylene glycol and ethanol + ethylene glycol were optimized using binary VLE data for water + ethylene glycol in Table 3 and ternary VLE data for water + ethanol + ethylene glycol in Table 2. The objective function used for the optimization was

EXPERIMENTAL SECTION Materials. Water was double-distilled. Ethanol (mass fraction purity 0.998), 2-propanol (mass fraction purity 0.998), 1-propanol (mass fraction purity 0.998), and ethylene glycol (mass fraction purity 0.995) were supplied by Sinopharm Chemical Reagent Co. Ltd. and were used without further purification. The chemical sample descriptions are listed in Table 1. Water mass fractions for ethanol, 2-propanol, 1propanol, and ethylene glycol were typically 4.0 × 10−4, 4.6 × 10−4, 4.8 × 10−4, and 7.6 × 10−4, respectively. Table 1. Chemical Samples Used in This Study chemical name ethanol 2-propanol 1-propanol ethylene glycol a

source Sinopharm Chemical Reagent Co. Ltd. Sinopharm Chemical Reagent Co. Ltd. Sinopharm Chemical Reagent Co. Ltd. Sinopharm Chemical Reagent Co. Ltd.

mass fraction purity

purification method

analysis method

0.998

none

GCa

0.998

none

GCa

0.998

none

GCa

0.995

none

GCa

Gas chromatography.

Apparatus and Procedure. Vapor−liquid equilibrium data were measured by use of an ebulliometer.14,15 For the measurement of the ternary system water (1) + ethanol (2) + ethylene glycol (3), the experimental procedure is the same as that for water (1) + ethanol (2) + glycerol (3).11 During the measurement, the glycol mass fraction in the liquid phase, w3, was changed from high to low, while the ethanol mole fraction on a glycol-free basis, x2′, remained approximately unchanged. When equilibrium was established, the vapor condensate was sampled and analyzed. The ethylene glycol mass fraction in the vapor phase was analyzed by gas chromatograph (Fuli 9790J). The water mass fraction was measured by Karl Fischer titration (SF-3 Titrator, Zibo Zifen Instrument, Ltd.). Consequently, vapor-phase mole fractions of water and ethanol were calculated. Liquid-phase compositions were obtained on the basis of mass balance.14,16 Standard uncertainties were estimated to be 0.08 K for temperature, 0.05 kPa for pressure, and 0.003 for the liquid-phase glycol mass fraction. Relative standard uncertainties for the vapor-phase mole fraction of water and ethanol, and for the liquid-phase ethanol mole fraction were estimated to be 0.01. The same procedure was applied for the ternary systems water (1) + 2-propanol (2) + ethylene glycol (3) and water (1) + 1-propanol (2) + ethylene glycol (3). For the measurement of VLE data of water + ethylene glycol, the liquid-phase mole fractions were determined by Karl Fischer titration.

F = Fternary + Fbinary Fternary =

1 N

(1)

1 N

∑ (γ1,cal/γ1,exp − 1)2 + N

∑ (γ2,cal/γ2,exp − 1)2 N

(1a)

1 N

Fbinary =

∑ (γ1,cal /γ1,exp − 1)2 N

(1b)

where γ denotes the liquid-phase activity coefficient and N is the number of data points for a particular data set. Consequently, binary parameters of 2-propanol + ethylene glycol and 1-propanol + ethylene glycol, respectively, were optimized using ternary VLE data of water + 2-propanol + ethylene glycol and water + 1-propanol + ethylene glycol in Table 2, while the binary parameters of water + ethylene glycol were kept unchanged. The objective function was

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F=

RESULTS AND DISCUSSION The experimental VLE data for the ternary systems water (1) + ethanol (2) + ethylene glycol (3), water (1) + 2-propanol (2) + ethylene glycol (3), and water (1) + 1-propanol (2) + ethylene glycol (3) are listed in Table 2, including liquid-phase mole fraction of the alcohol on a glycol-free basis (x′2), liquid-phase glycol mass fraction (w3), vapor-phase mole fraction of water (y1), vapor-phase mole fraction of the alcohol (y2), and equilibrium temperature (T). The experimental measurements were performed at p = 101.3 kPa. For each ternary system two

1 N

∑ (γ1,cal/γ1,exp − 1)2 + N

1 N

∑ (γ2,cal/γ2,exp − 1)2 N

(2)

It was found that the correlation was insensitive to the choice of the nonrandomness factors, which were therefore set as 0.3. The energy parameters were regarded as temperatureindependent. Results are summarized in Table 4. Using the obtained parameters, ternary VLE data were calculated and compared with experimental values. Results are listed in Table 5, in which δT and δy are mean absolute deviations of, respectively, equilibrium temperature and vapor2597

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Table 2. Experimental Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mole Fraction on Glycol-Free Basis x′, Liquid-Phase Mass Fraction w, and Vapor-Phase Mole Fraction y, and Calculated Results for Activity Coefficient γ, and Relative Volatility α, for the Ternary Systems Water (1) + Ethanol (2) + Ethylene Glycol (3), Water (1) + 2-Propanol (2) + Ethylene Glycol (3), and Water (1) + 1-Propanol (2) + Ethylene Glycol (3) at p = 101.3 kPaa x2′

a

w3

0.1992 0.2004 0.2012 0.2004 0.2007 0.2000 0.2005 0.2000

0.8035 0.7012 0.6032 0.5051 0.4003 0.3018 0.2003 0.1010

0.9514 0.9502 0.9504 0.9504 0.9505 0.9500 0.9506 0.9503

0.8026 0.7038 0.6007 0.5015 0.4021 0.3021 0.2035 0.1010

0.1982 0.2007 0.2001 0.1999 0.1999 0.2000 0.2001 0.2001

0.8003 0.7016 0.6039 0.5021 0.4056 0.3040 0.2033 0.1048

0.9461 0.9503 0.9508 0.9503 0.9503 0.9503 0.9501 0.9503

0.8137 0.6992 0.6015 0.5015 0.4041 0.3015 0.2012 0.1005

0.2089 0.2032 0.1994 0.2002 0.2000 0.2002 0.2004 0.2006

0.8009 0.7017 0.5986 0.4995 0.4012 0.3019 0.2012 0.1031

0.9510 0.9502 0.9507 0.9506 0.9504 0.9511 0.9501 0.9508

0.8041 0.7220 0.6138 0.5028 0.4051 0.3040 0.2043 0.1012

T/K

y1

y2

γ1

Water (1) + Ethanol (2) + Ethylene Glycol (3), x2′ = 0.2 385.08 0.4738 0.5088 1.00 375.23 0.4673 0.5247 1.03 369.46 0.4582 0.5355 1.03 365.62 0.4548 0.5425 1.04 362.42 0.4564 0.5417 1.06 360.35 0.4552 0.5436 1.07 358.66 0.4555 0.5438 1.07 356.81 0.4624 0.5373 1.11 Water (1) + Ethanol (2) + Ethylene Glycol (3), x2′ = 0.95 380.34 0.0170 0.9607 1.07 371.85 0.0206 0.9669 1.18 366.51 0.0240 0.9663 1.28 362.83 0.0274 0.9653 1.39 359.87 0.0313 0.9636 1.54 357.22 0.0362 0.9603 1.73 355.24 0.0409 0.9568 1.93 353.24 0.0467 0.9523 2.16 Water (1) + 2-Propanol (2) + Ethylene Glycol (3), x2′ = 0.2 384.14 0.4514 0.5268 1.04 374.58 0.4492 0.5409 1.07 368.72 0.4492 0.5452 1.09 364.57 0.4541 0.5426 1.11 361.72 0.4551 0.5428 1.12 359.43 0.4570 0.5417 1.13 357.74 0.4542 0.5451 1.12 356.37 0.4561 0.5436 1.12 Water (1) + 2-Propanol (2) + Ethylene Glycol (3), x2′ = 0.95 386.39 0.0179 0.9497 1.06 377.06 0.0207 0.9613 1.15 372.18 0.0255 0.9624 1.29 368.43 0.0309 0.9599 1.43 365.35 0.0367 0.9568 1.60 362.52 0.0431 0.9524 1.80 359.84 0.0515 0.9455 2.09 357.41 0.0600 0.9384 2.40 Water (1) + 1-Propanol (2) + Ethylene Glycol (3), x2′ = 0.2 390.85 0.5488 0.4231 1.04 381.22 0.5661 0.4177 1.08 374.88 0.5787 0.4123 1.11 370.75 0.5839 0.4111 1.13 367.76 0.5889 0.4083 1.15 365.48 0.5932 0.4052 1.16 363.68 0.5979 0.4013 1.17 362.28 0.6006 0.3990 1.18 Water (1) + 1-Propanol (2) + Ethylene Glycol (3), x2′ = 0.95 399.82 0.0267 0.9129 1.09 393.00 0.0333 0.9245 1.17 387.11 0.0416 0.9306 1.30 382.76 0.0524 0.9270 1.48 379.55 0.0622 0.9218 1.64 376.47 0.0739 0.9147 1.89 373.62 0.0896 0.9033 2.19 370.74 0.1083 0.8884 2.65

γ2

γ3

α21

1.98 2.07 2.14 2.20 2.22 2.24 2.24 2.27

0.74 0.71 0.97 0.66 0.76 0.74 0.78 0.90

4.32 4.48 4.64 4.76 4.73 4.78 4.76 4.65

1.40 1.29 1.20 1.13 1.09 1.06 1.02 1.01

0.98 0.98 1.22 1.40 1.48 1.58 1.85 1.81

2.88 2.45 2.10 1.84 1.60 1.40 1.22 1.07

2.54 2.63 2.69 2.71 2.72 2.72 2.74 2.73

0.94 0.86 0.84 0.81 0.78 0.75 0.75 0.77

4.72 4.79 4.85 4.78 4.77 4.74 4.80 4.77

1.67 1.43 1.29 1.19 1.12 1.06 1.03 1.00

0.99 1.01 1.02 1.12 1.17 1.27 1.49 1.80

3.03 2.43 1.96 1.62 1.36 1.16 0.96 0.82

2.67 2.76 2.84 2.86 2.88 2.87 2.85 2.84

0.88 1.01 0.99 0.88 0.79 0.72 0.64 0.73

2.92 2.89 2.86 2.81 2.77 2.73 2.68 2.65

1.68 1.50 1.33 1.20 1.13 1.07 1.04 1.01

1.02 1.08 1.10 1.24 1.40 1.55 1.68 1.81

1.76 1.46 1.16 0.92 0.77 0.64 0.53 0.42

u(T) = 0.08 K, u(p) = 0.05 kPa, ur(x2′) = 0.01, u(w3) = 0.003, ur(y1) = 0.01, ur(y2) = 0.01. 2598

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Table 3. Experimental Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mole Fraction x, and VaporPhase Mole Fraction y, and Calculated Results for Activity Coefficient γ for the Binary System Water (1) + Ethylene Glycol (3) at p = 101.3 kPaa

a

T/K

x1

y1

γ1

γ3

424.82 415.59 407.93 402.37 397.48 388.93

0.1792 0.2468 0.3181 0.3805 0.4451 0.5845

0.8263 0.8918 0.9303 0.9496 0.9631 0.9819

0.94 0.94 0.95 0.96 0.96 0.98

1.02 0.99 0.96 0.97 0.98 0.95

Table 5. Mean Absolute Deviations in the Calculation of Isobaric VLE Data for Ternary Systems Water (1) + Ethanol (2) + Ethylene Glycol (3), Water (1) + 2-Propanol (2) + Ethylene Glycol (3), and Water (1) + 1-Propanol (2) + Ethylene Glycol (3), Based on the Correlation by NRTL Equation

water + EG water + EG water + EG water + EG water + + EG water + + EG water + + EG

u(T) = 0.08 K, u(p) = 0.05 kPa, ur(x1) = 0.01, ur(y1) = 0.01.

phase mole fraction. Results are also shown in Figures 1 to 3, in which quality of the present correlation can be visualized in terms of the relative volatility and the activity coefficients. At the same time, the effect of ethylene glycol on the phase behavior of the aqueous mixtures can be observed. The relative volatility at x′2 = 1 was calculated in relation with the glycol mole fraction, as shown in Figure 4. Comparisons are presented for literature VLE data, in Table 5, and literature correlations, in Figures 1 to 4. For the system water (1) + ethanol (2) + ethylene glycol (3), the present correlation is in good agreement with the experimental results. This can be observed in Table 5 and Figure 1. The mean absolute deviations are δT = 0.17, δy1 = 0.0024, and δy2 = 0.0023. The same system has been measured by Pla-Franco et al.,4 Kamihama et al.,5 and Dai et al.6 The present correlation presents good agreement with the results of Pla-Franco et al.4 (δT = 0.41 K, δy1 = 0.0086, and δy2 = 0.0088), and Kamihama et al.5 (δT = 0.40 K, δy1 = 0.0061, and δy2 = 0.0056). For the results of Dai et al.,6 there are significant deviations, showing δT = 0.44 K, δy1 = 0.2243, and δy2 = 0.0413. The effect of ethylene glycol on the phase behavior of water + ethanol can be observed in Figure 1c and Figure 4a, in which the relative volatility of ethanol to water, α21, is shown in relation with the mole fraction of glycol, x3. In the ethanol-rich region, that is, at x2′ = 0.95 (Figure 1c) or x2′ = 1 (Figure 4a), α21 increases with the addition of glycol. This indicates that the use of ethylene glycol may enhance the separation of water and ethanol. According to the present correlation, the azeotrope of water + ethanol is removed at x3 = 0.072, as shown in Figure 4a. Mechanism for the increase of relative volatility can be sat described by the relation α21 = (γ2/γ1)·(psat 2 /p1 ). Because the ratio of vapor pressures is independent of composition and insensitive to temperature, the effect of glycol on α21 is mainly

a

data points

δT/K

δy1

δy2

ethanol +

this work

16

0.17

0.0024

0.0023

ethanol +

38

0.41

0.0086

0.0088

33

0.40

0.0061

0.0056

ethanol +

Pla-Franco et al.4 Kamihama et al.5 Dai et al.6

27

0.44

0.2243

0.0413

2-propanol

this work

16

0.34

0.0018

0.0018

1-propanol

this work

16

0.15

0.0025

0.0024

1-propanol

Pla-Franco et al.7

21

0.48

0.0188

0.0147

systema

ethanol +

source of data

EG = ethylene glycol. p = 101.3 kPa.

decided by its effect on γ1 and γ2. As shown in Figure 1a and b, the increase of relative volatility in the ethanol-rich region results from both the decrease of γ1 and the increase of γ2. On the other hand, γ2 decreases more rapidly than γ1 with the addition of glycol in the water-rich region. This accounts for the decrease of the relative volatility at x2′ = 0.2, which can be observed in Figure 1c. NRTL parameters for VLE of water (1) + ethanol (2) + ethylene glycol (3) have been proposed by Pla-Franco et al.,4 Kamihama et al.,5 and Dai et al.6 and are available in APV80 VLE-IG. Calculated results using these model parameters are shown in Figure 1 and Figure 4a, in comparison with the present correlation. Very good agreement can be observed for the results of Pla-Franco et al.,4 which, for example, indicates the same amount of ethylene glycol that is required for breaking the azeotrope of water + ethanol. For the results of Kamihama et al.5 at x2′ = 0.95, α21 is slightly larger as compared with the present correlation. This can be attributed to the relatively smaller value of γ1. Consequently, the calculated minimum amount of ethylene glycol for removing the azeotrope is relatively small, with x3 = 0.0059. Meanwhile, significant departures can be observed for the results of Dai et al.6 and APV80 VLE-IG. The calculated minimum mole fractions of ethylene glycol are significantly small, with x3 = 0.0029 for Dai et al.6 and x3 = 0.0033 for APV80 VLE-IG. For the system water (1) + 2-propanol (2) + ethylene glycol (3), the present correlation is satisfactory. The mean absolute

Table 4. Estimated Values of Binary Parameters in the NRTL Equationa component i

component j

aij

bij/K

aji

bji/K

cij

water ethanol water 2-propanol water 1-propanol water

ethylene glycol ethylene glycol ethanol ethylene glycol 2-propanol ethylene glycol 1-propanol

0 0 13.4033 0 5.3852 0 3.2932

335.18 76.757 −4099.93 40.482 −1005.06 −54.908 −238.29

0 0 −6.1599 0 −2.5041 0 −1.7387

−303.17 161.10 2136.89 278.34 850.87 439.29 799.35

0.3 0.3 0.3 0.3 0.3 0.3 0.47

τij = Δgij/RT = aij + bij/T; Gij = exp(−cijτij). The binary parameters of water + ethanol, water + 2-propanol, and water + 1-propanol were taken from ref 11, ref 12, and ref 13, respectively. a

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Figure 1. Experimental and calculated (a) activity coefficients of water, γ1, (b) activity coefficients of ethanol, γ2, and (c) relative volatility of ethanol to water, α21, in relation with ethylene glycol mole fraction, x3, for the saturated liquid mixture water (1) + ethanol (2) + ethylene glycol (3) at p = 101.3 kPa: ○, x2′ = 0.2; □, x2′ = 0.95; Lines were calculated by model parameters: solid line, this work in Table 4; dashed line, Pla-Franco et al. (ref 4); dotted line, Kamihama et al. (ref 5); dash−dot line, Dai et al. (ref 6); dash−dot−dot line, APV80 VLE-IG.

Figure 2. Experimental and calculated (a) activity coefficients of water, γ1, (b) activity coefficients of 2-propanol, γ2, and (c) relative volatility of 2propanol to water, α21, in relation with ethylene glycol mole fraction, x3, for the saturated liquid mixture water (1) + 2-propanol (2) + ethylene glycol (3) at p = 101.3 kPa: ○, x2′ = 0.2; □, x2′ = 0.95. Lines were calculated by model parameters: solid line, this work in Table 4; dash−dot−dot line, APV80 VLE-IG.

Figure 3. Experimental and calculated (a) activity coefficients of water, γ1, (b) activity coefficients of 1-propanol, γ2, and (c) relative volatility of 1propanol to water, α21, in relation with ethylene glycol mole fraction, x3, for the saturated liquid mixture water (1) + 1-propanol (2) + ethylene glycol (3) at p = 101.3 kPa: ○, x2′ = 0.2; □, x2′ = 0.95. Lines were calculated by model parameters: solid line, this work in Table 4; short dot line, PlaFranco et al. (ref 7); dash−dot−dot line, APV80 VLE-IG.

deviations are δT = 0.34, δy1 = 0.0018, and δy2 = 0.0018. These are presented in Table 5. Good agreement can be verified in Figure 2, in terms of activity coefficients of water and 2propanol, and the relative volatility of 2-propanol to water. The effects of ethylene glycol on phase behavior of water and 2propanol are also illustrated. At x2′ = 0.95, γ1 decreases with the addition of ethylene glycol, while the increase of γ2 is observed.

Both of these effects result in rapid increase of the relative volatility. These trends are similar to those of water + ethanol + ethylene glycol. The calculation shows that the azeotrope of water + 2-propanol is removed at x3 = 0.240. NRTL parameters for the same system are available in the Aspen Plus process simulator. Results using parameters in APV80 VLE-IG are shown in Figure 2 and Figure 4b, in comparison with the 2600

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Figure 4. Relative volatility, α21, of (a) ethanol to water, (b) 2-propanol to water, and (c) 1-propanol to water, for the respective ternary mixture of water (1) + alcohol (2) + ethylene glycol (3) at p = 101.3 kPa and x′2 = 1. Lines were calculated by model parameters: solid line, this work in Table 4; dash line, Pla-Franco et al. (ref 4); dot line, Kamihama et al. (ref 5); dash−dot line, Dai et al. (ref 6); dash dot dot line, APV80 VLE-IG; short dot line, Pla-Franco et al. (ref 7).

Figure 5. (a) T−x−y diagram and activity coefficients of (b) water, γ1, and (c) ethylene glycol, γ3, in relation with water mole fraction, x1, for the binary mixture water (1) + ethylene glycol (3) at p = 101.3 kPa: ●, this work; ○, Kamihama et al. (ref 5); ■, Liu et al. (ref 21); □, Pla-Franco et al. (ref 7). Lines were calculated by model parameters: solid line, this work in Table 4; dash line, Pla-Franco et al. (ref 4); dot line, Kamihama et al. (ref 5); dash−dot line, Dai et al. (ref 6); short dot line, Pla-Franco et al. (ref 7); dash−dot−dot line, APV80 VLE-IG.

Figure 6. (a) T−x−y diagram and activity coefficients of (b) ethanol, γ2, and (c) ethylene glycol, γ3, in relation with ethanol mole fraction, x2, for the binary mixture ethanol (2) + ethylene glycol (3) at p = 101.3 kPa: ○, Kamihama et al. (ref 5); ■, Liu et al. (ref 21); △, Li et al. (ref 22). Lines were calculated by model parameters: solid line, this work in Table 4; dash line, Pla-Franco et al. (ref 4); dot line, Kamihama et al. (ref 5); dash−dot line, Dai et al. (ref 6); dash−dot−dot line, APV80 VLE-IG.

present correlation. At x2′ = 0.95 and x3 < 0.4, γ1 using APV80 VLE-IG is apparently smaller, while γ2 appears similar. As a result the calculated relative volatility is apparently higher. Based on the calculation at x2′ = 1, the mole fraction of ethylene glycol for removing the azeotrope is x3 = 0.199. At x2′ = 0.2, the value of γ2 using APV80 VLE-IG, and hence α21, is significantly lower as compared with the present correlation.

For the system water (1) + 1-propanol (2) + ethylene glycol (3) the mean absolute deviations for the present correlation are δT = 0.15, δy1 = 0.0025, and δy2 = 0.0024. These are listed in Table 5. Good agreement can also be observed in Figure 3. The effects of ethylene glycol on γ1 and γ2 are similar to those in the case of water (1) + 2-propanol (2) + ethylene glycol (3). At a given temperature, on the other hand, the vapor pressure of 12601

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Figure 7. (a) T−x−y diagram and activity coefficients of (b) 2-propanol, γ2, and (c) ethylene glycol, γ3, in relation with 2-propanol mole fraction, x2, for the binary mixture 2-propanol (2) + ethylene glycol (3) at p = 101.3 kPa: ■, Liu et al. (ref 21); △, Li et al. (ref 22). Lines were calculated by model parameters: solid line, this work in Table 4; dash−dot−dot line, APV80 VLE-IG.

Figure 8. (a) T−x−y diagram and activity coefficients of (b) 1-propanol, γ2, and (c) ethylene glycol, γ3, in relation with 1-propanol mole fraction, x2, for the binary mixture 1-propanol (2) + ethylene glycol (3) at p = 101.3 kPa: ◊, Pla-Franco et al. (ref 7); ■, Liu et al. (ref 21); ▲, Qian et al. (ref 23). Lines were calculated by model parameters: solid line, this work in Table 4; short dot line, Pla-Franco et al. (ref 7); dash−dot−dot line, APV80 VLE-IG.

literature correlations, as well as data in this work and in the literature. The literature activity coefficients were calculated by use of the literature VLE data. The binary pair water (1) + ethylene glycol (3) is a common constituent pair in all the three ternary systems. As indicated in Figure 5a, the present correlation reproduces very well the T− x−y data in this work and is in good agreement with the data reported by Kamihama et al.5 and Pla-Franco et al.7 Significant departures can be observed for the data of Liu et al.21 The correlation was further evaluated in terms of the activity coefficients, γ1 and γ3. Comparisons are shown in Figure 5b and c. The present correlation provides good agreement with the activity coefficients reported in Table 3. Generally close agreement can be observed for the data of Kamihama et al.5 and the correlations proposed by Kamihama et al.5 and PlaFranco et al.,4 while there are relatively large deviations for the data of Pla-Franco et al.7 and Liu et al.,21 and for the correlations proposed by Pla-Franco et al.,7 Dai et al.,6 and APV80 VLE-IG. For the activity coefficient of water at x2 > 0.5, results of all the data and the correlations, except the data of Liu et al.21 and the correlation of Dai et al.,6 fall in a narrow range of 0.96−1.01. Therefore, it should be concluded that the present correlation, as well as the correlations of Kamihama et al.,5 Pla-Franco et al.,4 Pla-Franco et al.,7 and APV80 VLE-IG, provide reasonable results in this composition range. It is noticeable that the correlation proposed by Pla-Franco et al.,4 which is in best agreement with the experimental results and

propanol has only about half the value of 2-propanol. It is a reasonable result that the relative volatility of 1-propanol to water, as shown in Figure 3c, has about half the value of 2propanol to water, which is shown in Figure 2c. At x2′ = 1, the calculation indicates that the azeotrope will be removed at x3 = 0.550, which can be observed in Figure 4c. The same ternary system has been measured by Pla-Franco et al.7 As shown in Table 5, the deviations calculated by the present correlation are δT = 0.48, δy1 = 0.0188, and δy2 = 0.0147. These are comparable with the deviations provided in the original literature, with δT = 0.47, δy1 = 0.0130, and δy2 = 0.0157. NRTL parameters for the same ternary system have been proposed by Pla-Franco et al.7 and are available in APV80 VLEIG. At x2′ = 0.95, the literature correlations are close to the present correlation. At x2′ = 1, the calculated minimum mole fractions for breaking the azeotrope have similar values, with x3 = 0.570 for Pla-Franco et al.7 and x3 = 0.555 for APV80 VLEIG. These can be observed in Figure 3 and Figure 4c. At x2′ = 0.2, the correlation proposed by Pla-Franco et al.7 is close to the present correlation, while APV80 VLE-IG shows relatively large deviations for γ2 and α21. Reliability of the present correlation was further evaluated by calculation of component activity coefficients and VLE data, at p = 101.3 kPa, for the four binary systems containing ethylene glycol, namely, water + ethylene glycol, ethanol + ethylene glycol, 2-propanol + ethylene glycol, and 1-propanol + ethylene glycol. Results are shown in Figures 5 to 8, in comparison with 2602

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the experimental data. Results showed that the minimum mole fraction of ethylene glycol for breaking the azeotrope of water + ethanol, water + 2-propanol, and water + 1-propanol was, respectively, 0.072, 0.240, and 0.550. The reliability of the present correlation was verified by calculation of activity coefficients of both ternary and binary mixtures. Comparisons were presented for experimental results and correlations available in the literature.

the correlation in this work, was based on ternary VLE data of water + ethanol + ethylene glycol. Meanwhile, the correlation proposed by Pla-Franco et al.7 was based on binary VLE data. However, the correlation does not match the source data very well, especially for γ3, and for γ1 in the region of x1 < 0.2. For the binary pair ethanol (2) + ethylene glycol (3), the present correlation provides T−x−y data that agree with the results of Kamihama et al.5 and Li et al.,22 as shown in Figure 6a. There are relatively large deviations for the results of Liu et al.21 For the activity coefficient of ethanol, as shown in Figure 6b, the present correlation presents similar results as compared with the data of Kamihama et al.5 and Li et al.,22 and the correlations of Pla-Franco et al.4 and Kamihama et al.5 At the same time, relatively large deviations can be observed for the correlations of Dai et al.,6 and APV80 VLE-IG. These trends are consistent with those for ternary VLE at x2′ = 0.95, which has been shown in Figure 1b. In the case of the activity coefficient of ethylene glycol, the present correlation matches the correlations of Pla-Franco et al.4 and Kamihama et al.5 There are relatively large deviations for the data of Kamihama et al.,5 Liu et al.,21 and Li et al.,22 and for the correlations of Dai et al.6 and APV80 VLE-IG. For the binary pair 2-propanol (2) + ethylene glycol (3), calculated results of T−x−y data and activity coefficients by the present correlation are shown in Figure 7. The calculation showed good agreement with the T−x−y data reported by Li et al.22 For γ2 at x2 > 0.2, the present correlation agrees with the data of Li et al.22 and the correlation of APV80 VLE-IG. The latter may account for the agreement for the ternary VLE at x2′ = 0.95, which has been observed in Figure 2b. For γ3, there are relatively large deviations. Significant deviations can be observed for the results of Liu et al.,21 in terms of T-x-y data and activity coefficients. For the binary pair 1-propanol (2) + ethylene glycol (3), the present correlation reproduces very well the T-x-y data reported by Pla-Franco et al.,7 as shown in Figure 8a. There are relatively large deviations for the VLE data of Qian et al.,23 especially for the boiling temperatures at x2 < 0.2. Significant deviations can be observed for the results of Liu et al.21 In the case of activity coefficients of 1-propanol, which is shown in Figure 8b, the present correlation agrees very well with the data and the correlation of Pla-Franco et al.7 Good agreement can also be observed for the data of Qian et al.23 and the correlation of APV80 VLE-IG at x2 > 0.3. These are consistent with the close agreement that has been observed in Figure 3b for the ternary VLE at x2′ = 0.95. In the case of γ3, as shown in Figure 8c, the present correlation shows relatively large deviations for the data of Pla-Franco et al.7 However, somewhat better agreement can be observed for the correlation of the same authors. Generally good agreement can also be observed for the data of Qian et al.23 and for the correlation of APV80 VLE-IG.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 571 88320892. E-mail: [email protected]. Funding

The authors wish to acknowledge the financial support by the National Natural Science Foundation of China (21476205). Notes

The authors declare no competing financial interest.

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REFERENCES

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CONCLUSIONS Vapor−liquid equilibrium data were measured at 101.3 kPa for the ternary systems water + ethanol + ethylene glycol, water + 2-propanol + ethylene glycol, and water + 1-propanol + ethylene glycol and for the binary system water + ethylene glycol. The NRTL equation was used for the modeling of the VLE behavior. Using literature values of binary parameters for water + ethanol, water + 2-propanol, and water + 1-propanol, which were obtained in the modeling of the ternary systems containing glycerol, and a unique set of binary parameters for water + ethylene glycol, the correlation reproduces very well 2603

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methylimidazolium acetate at low water mole fractions. J. Chem. Eng. Data 2008, 53, 1595−1601. (17) Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1987; Appendix A. (18) Wisniak, J.; Tamir, A. Vapor−liquid equilibria in the ternary systems water−formic acid−acetic acid and water−acetic acid− propionic acid. J. Chem. Eng. Data 1977, 22, 253−260. (19) McDermott, C.; Ellis, S. R. M. A multicomponent consistency test. Chem. Eng. Sci. 1965, 20, 293−296. (20) Fredenslund, A.; Gmehling, J.; Rasmussen, P. Vapor−Liquid Equilibria Using UNIFAC. A Group-Contribution method; Elsevier: Amsterdam, 1977. (21) Liu, F.; Huang, F.; Zhang, C. Ethylene glycol and diethylene glycol for alcohol-water extractive distillation, calculation and verification. Huadong-Huagong- Xue yuan-Xuebao 1993, 19, 254−262. (22) Li, J.; Chen, C.; Wang, J. Vapor−liquid equilibrium data and their correlation for binary systems consisting of ethanol, 2-propanol, 1, 2-ethanediol and methyl benzoate. Fluid Phase Equilib. 2000, 169, 75−84. (23) Qian, G.-F.; Liu, W.; Wang, L.-T.; Wang, D.-C.; Song, H. (Vapour + liquid) equilibria in the ternary system (acetonitrile + npropanol + ethylene glycol) and corresponding binary systems at 101.3 kPa. J. Chem. Thermodyn. 2013, 67, 241−246.

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