Experimental Measurement and Modeling of VaporâLiquid

Article pubs.acs.org/jced

Experimental Measurement and Modeling of Vapor−Liquid Equilibrium for the Ternary System Water + 1‑Propanol + Glycerol Lianzhong Zhang,* Wenlin Wang, Xiaoming Zhu, and Zheng Zhang Zhejiang Province Key Laboratory of Biofuel, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China ABSTRACT: Vapor−liquid equilibrium (VLE) data were reported for the ternary system water + 1-propanol + glycerol at 100 kPa. The NRTL equation was used for the modeling of ternary VLE. Binary parameters of water + glycerol were fixed as the same for water + ethanol + glycerol and were taken from the literature. The ternary VLE data, together with literature results of binary VLE data and infinite dilution activity coefficients for water +1-propanol, were used for the modeling. To extend the glycerol composition range and the temperature range, infinite dilution activity coefficients of 1-propanol in glycerol were measured in a temperature range of 313.15 to 393.15 K, and were used in the modeling. The correlation provided good agreement for all the source data. It is shown that the infinite dilution activity coefficients provide key information for reliable correlation in a wide composition range. With the addition of glycerol, the azeotrope of water + 1-propanol can be removed at a glycerol mole fraction of 0.398, indicating that glycerol is a potentially effective entrainer for the dehydration of 1-propanol by extractive distillation. Comparisons were presented for the effect of glycerol on aqueous mixtures of ethanol, 2-propanol, and 1-propanol.

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INTRODUCTION In recent years, glycerol has received considerable attention for their use in the chemical industry.1 It is also a constituent component of deep eutectic solvents, which are recognized as a new generation solvent for reaction and separation.2,3 Glycerol has many attractive features. It is nontoxic and environment compatible. Because of the large-scale production of biodiesel, glycerol is highly available and inexpensive. Under temperatures below 100 °C, the vapor pressure of glycerol is very low. In this sense glycerol has properties similar to ionic liquids, which have been widely studied for use in extractive distillation.4−6 Researches have shown that glycerol can be used in the replacement of ethylene glycol in the process of bioethanol dehydration.7,8 Souza et al.,9 Pla-Franco et al.,10 and Zhang et al.11 reported vapor−liquid equilibrium data for the ternary system water + ethanol + glycerol. Zhang et al.12 reported data for water + 2-propanol + glycerol. The mixture of water (1) + 1-propanol (2) forms a minimumboiling azeotrope at x2 = 0.43. For the removal of the azeotrope, a third component is needed for changing the nonideality of water and 1-propanol. Assuming an ideal vapor phase, the relative volatility of 1-propanol to water, α21, can be related with the activity coefficients of water and 1-propanol by α21 = (γ2/γ1)· sat sat sat (psat 2 /p1 ). The vapor pressure ratio, p2 /p1 , is usually a weak function of temperature and is mainly decided by the nature of the pure components. In comparison with those of water + ethanol and water +2-propanol, the vapor pressure ratio of water + 1-propanol is much smaller. Therefore, the removal of the azeotrope of water + 1-propanol is much more difficult and is mainly decided by the composition dependence of the activity coefficients. Various inorganic salts and ionic liquids have been studied in the literature for their performance of enhancing the © XXXX American Chemical Society

relative volatility and breaking the azeotrope. These include NaCl, NaBr, and KBr by Morrison et al.;13 NaCl and LiBr by Lin et al.;14 CaCl2 by Iliuta et al.;15 Ca(NO3)2,16 LiNO3,17 LiCl,18 and CuCl219 by Vercher et al.; 1-ethyl-3-methylimidazolium,20 1-butyl-3-ethylimidazolium,21 and 1-butyl-1-methylpyrrolidinium21 trifluoromethanesulfonate by Orchillés et al.; 1-ethyl-3methylimidazolium tetrafluoroborate,22 1-butyl-3-methylimidazolium tetrafluoroborate,22 and 1-butyl-3-methylimidazolium chloride23 by Zhang et al. In this work, we present vapor−liquid equilibrium measurements for water + 1-propanol + glycerol. To the best of our knowledge, VLE data have not been reported for the ternary system. The ternary mixtures of water + 1-propanol + glycerol and water + ethanol + glycerol have in common the binary pair water + glycerol. Model parameters for water + glycerol have been obtained in the literature11 on the basis of a wide range of data, including infinite dilution activity coefficients of water in glycerol and excess enthalpies of water + glycerol. It would be interesting to use the same binary parameters in the modeling of water +1-propanol + glycerol. Therefore, another aim of the present work is to establish a reliable activity coefficient model for water + 1-propanol + glycerol. The ternary VLE data, together with binary VLE data and infinite dilution activity coefficients for water + 1-propanol in the literature, have been used for the modeling, that is, the optimization of binary parameters of water + 1-propanol and 1-propanol + glycerol. For extending the glycerol composition range and the temperature range, infinite dilution activity coefficients of 1-propanol in glycerol were Received: November 27, 2015 Accepted: March 3, 2016

A

DOI: 10.1021/acs.jced.5b01015 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Calculated results were also provided for the liquid phase activity coefficients of water (γ1) and 1-propanol (γ2), and the relative volatility of 1-propanol to water (α21). The experimental measurements were performed at p = 100 kPa. In the calculation of the activity coefficients the vapor phase was regarded as an ideal gas and the vapor pressures of water and 1-propanol were calculated by parameters in the literature.30 The experimental results for infinite dilution activity coefficients of 1-propanol in glycerol, γ∞ 23, are listed in Table 3. The measurements were performed at five temperatures in a range of 313.15 to 393.15 K. Effects of glycerol on the vapor−liquid phase behavior of water and 1-propanol are shown in Figures 1 and 2. In Figure 1c relative volatility of 1-propanol to water is shown in relation with glycerol mole fraction at various x2′ . By the addition of glycerol, enhancement of the relative volatility can always be observed. The effect of glycerol on relative volatility can be related to, respectively, its effect on the activity coefficient of water and 1-propanol, as shown in Figure 1a,b. As described in the Introduction, α21 can be related to γ1 and γ2 by α21 = (γ2/γ1)· sat (psat 2 /p1 ). The vapor pressure ratio is only a weak function of temperature and varies in the range of 1.09 to 1.13 in the experimental temperature range. Therefore, an increase of α21 is mainly decided by the composition dependence of γ1 and γ2. With the increase of x3, γ2 generally increases. This is beneficial for the increase of α21. At the same time, γ1 decreases with the increase of x3. This will also result in the increase of α21. The opposite trends of the activity coefficients may account for the rapid increase of relative volatility with the addition of glycerol. In Figure 2a and 2b, γ1 and γ2 are also shown in relation with x′2 at various fixed w3. It can be observed that, with decreasing x′2, γ2 increases rapidly at all given w3, while γ1 decreases at w3 = 0.1 to 0.3 and tends to change much less at higher glycerol mass fractions, especially at the 1-propanol-rich end. These trends are quite similar to those for water + ethanol + glycerol11 and water + 2-propanol + glycerol.12 Because of the rapid increase of γ2, α21 increases rapidly with decreasing x2′ at all given w3, as shown in Figure 2c. The ternary vapor−liquid equilibria were modeled using the NRTL equation.31 Data of binary VLE (Gabaldón et al.,32 at 30, 60, and 100 kPa; Vercher et al.,16 at 100 kPa) and activity coefficients at infinite dilution (Kojima et al.33) for water + 1-propanol were used, together with experimental results of ternary VLE and infinite dilution activity coefficients of 1-propanol in glycerol. In the correlation, binary parameters for water + glycerol were fixed as the same for water + ethanol + glycerol and were taken from the literature.11 Energy parameters for water + 1-propanol and 1-propanol + glycerol were regarded as temperature-dependent and were optimized using the following objective function:

measured and used in the modeling. The infinite dilution activity coefficients were measured in the temperature range of 313.15 to 393.15 K.

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EXPERIMENTAL SECTION Materials. Water was double distilled. 1-Propanol (mass fraction purity 0.998) and glycerol (mass fraction purity 0.995) were supplied by Sinopharm Chemical Reagent Co. Ltd., and used without further treatment. The chemical sample descriptions are listed in Table 1. By Karl Fischer analysis, water mass Table 1. Chemical Samples Used in This Study chemical name

source

1-propanol Sinopharm Chemical Reagent Co. Ltd. glycerol Sinopharm Chemical Reagent Co. Ltd. a

mass fraction purity

purification method

analysis method

0.998

none

GCa

0.995

none

GCa

Gas chromatography.

fraction was typically 4.7 × 10−4 for 1-propanol and 6.5 × 10−4 for glycerol. Determination of Vapor−Liquid Equilibrium. Vapor− liquid equilibrium data were measured by use of an ebulliometer.24,25 The experimental procedure has been described in detail previously.11,26 For the measurement of the ternary system water (1) + 1-propanol (2) + glycerol (3), glycerol mass fraction in the liquid phase, w3, was changed from approximately 0.8 to 0.1, in an interval of 0.1, while the 1-propanol mole fraction on a glycerol-free basis, x2′ , remained approximately unchanged. When equilibrium was established, the vapor condensate was sampled and analyzed. The glycerol mass fraction in the vapor phase was analyzed by gas chromatograph (Fuli 9790J). Meanwhile, the water mass fraction was measured by Karl Fischer titration (SF-3 Titrator, Zibo Zifen Instrument, Ltd.). Vapor-phase mole fractions of water and 1-propanol were calculated. Liquid-phase compositions were obtained on the basis of mass balance.24,27 Standard uncertainties were estimated to be 0.08 K for temperature, 0.05 kPa for pressure, and 0.003 for liquid-phase glycerol mass fraction. Relative standard uncertainty for the liquid-phase 1-propanol mole fraction was estimated to be 0.01. Relative standard uncertainty for the vapor-phase mole fraction of water or 1-propanol was estimated to be 0.01. Determination of Infinite Dilution Activity Coefficients. Infinite dilution activity coefficients were measured using inverse gas chromatography. The experimental procedures and calculations have been described previously.11 Briefly, a 0.5 m length stainless steel column was packed with a stationary phase consisting of 0.396 mass fraction of glycerol on Chromosorb W AW (60/80 mesh). The retention data for 1-propanol were obtained by use of a Fuli 9790J gas chromatograph equipped with a thermal conductivity detector (TCD). Infinite dilution activity coefficients for 1-propanol (2) in glycerol (3), γ∞ 23, were calculated by the equation developed by Everett28 and Cruickshank et al.29 The relative standard uncertainty for γ∞ 23 was estimated to be 0.05.

F = Fternary +

∑ Fbinary + 0.2Finf

(1)

Fternary = 1 N

■

∑ (γ1,cal /γ1,exp − 1)2 + N

1 N

∑ (γ2,cal /γ2,exp − 1)2 N

(1a)

RESULTS AND DISCUSSION The experimental VLE data for the ternary system water (1) + 1-propanol (2) + glycerol (3) are listed in Table 2, including liquid phase mole fraction of 1-propanol on a glycerol-free basis (x2′ ), liquid phase glycerol mass fraction (w3), vapor phase mole fraction of 1-propanol (y2), and equilibrium temperature (T).

Fbinary = 1 N

∑ (γ1,cal/γ1,lit − 1)2 + N

1 N

∑ (γ2,cal/γ2,lit − 1)2 N

(1b) B



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Table 2. Experimental Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mole Fraction on Glycerol-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 System Water (1) + 1-Propanol (2) + Glycerol (3) at p = 100 kPaa x′2

w3

T/K

y1

0.1017 0.1001 0.1001 0.1000 0.1004 0.1001 0.1001 0.1004

0.8013 0.6999 0.6073 0.5014 0.4002 0.3027 0.2038 0.1003

380.92 373.24 369.17 366.29 364.51 363.30 362.41 361.71

0.5508 0.5675 0.5813 0.5913 0.6008 0.6087 0.6148 0.6196

0.2000 0.1971 0.2005 0.2003 0.2003 0.2007 0.2002 0.2002

0.7978 0.7032 0.6007 0.5009 0.4002 0.3013 0.2012 0.1001

378.46 372.17 368.18 365.79 364.15 362.94 362.03 361.30

0.4262 0.4626 0.4940 0.5214 0.5441 0.5665 0.5843 0.5990

0.4001 0.4008 0.4006 0.4005 0.4008 0.3999 0.4002 0.3990

0.7998 0.7001 0.6015 0.5013 0.4022 0.3019 0.2020 0.1006

379.02 373.32 369.88 367.39 365.49 363.89 362.56 361.38

0.2872 0.3340 0.3813 0.4257 0.4642 0.4995 0.5248 0.5519

0.6002 0.6004 0.6002 0.6005 0.6002 0.6008 0.6000 0.6001

0.8005 0.7039 0.6038 0.5014 0.4033 0.3029 0.2035 0.1020

380.55 375.69 372.51 369.96 367.90 365.99 364.18 362.43

0.1765 0.2214 0.2704 0.3168 0.3598 0.3985 0.4359 0.4734

0.8008 0.8011 0.8002 0.8004 0.8006 0.7996 0.7999 0.7994

0.7989 0.7035 0.6009 0.4990 0.4027 0.3009 0.2002 0.1003

381.92 377.95 375.33 373.09 371.25 369.34 367.32 365.27

0.9503 0.9502 0.9502 0.9502 0.9501 0.9502 0.9501 0.9504

0.8066 0.7022 0.6052 0.5016 0.4032 0.3010 0.2015 0.1041

383.56 379.77 377.61 375.91 374.44 372.93 371.33 369.63

y2

γ1

γ2

α21

0.4490 0.4324 0.4186 0.4087 0.3992 0.3913 0.3852 0.3804

0.91 0.97 1.01 1.03 1.05 1.06 1.06 1.07

5.82 5.94 5.89 5.82 5.67 5.56 5.45 5.34

7.20 6.85 6.47 6.22 5.95 5.78 5.63 5.50

0.5736 0.5373 0.5059 0.4786 0.4559 0.4335 0.4157 0.4010

0.93 0.99 1.05 1.08 1.11 1.14 1.17 1.18

4.45 4.19 3.85 3.60 3.38 3.17 3.02 2.89

5.38 4.73 4.08 3.67 3.35 3.05 2.84 2.67

0.7126 0.6659 0.6186 0.5743 0.5357 0.5005 0.4752 0.4481

0.97 1.03 1.11 1.19 1.27 1.34 1.40 1.46

3.19 2.75 2.42 2.17 1.98 1.83 1.73 1.63

3.72 2.98 2.43 2.02 1.73 1.50 1.36 1.22

0.8232 0.7785 0.7295 0.6831 0.6401 0.6014 0.5641 0.5265

0.97 1.06 1.17 1.29 1.42 1.54 1.67 1.83

2.68 2.21 1.89 1.67 1.51 1.40 1.31 1.23

3.11 2.34 1.80 1.43 1.18 1.00 0.86 0.74

0.9188 0.8902 0.8555 0.8215 0.7852 0.7526 0.7110 0.6750

0.95 1.07 1.22 1.38 1.57 1.73 2.01 2.26

2.39 1.92 1.61 1.42 1.28 1.19 1.12 1.07

2.83 2.02 1.48 1.15 0.91 0.76 0.62 0.52

0.9812 0.9729 0.9649 0.9533 0.9422 0.9280 0.9119 0.8924

0.92 1.05 1.15 1.36 1.55 1.82 2.15 2.61

2.28 1.77 1.50 1.31 1.19 1.11 1.05 1.02

2.80 1.90 1.46 1.07 0.86 0.68 0.54 0.43

x2′ = 0.1

x′2 = 0.2

x′2 = 0.4

x′2 = 0.6

a

x2′ = 0.8 0.0808 0.1094 0.1443 0.1784 0.2147 0.2473 0.2889 0.3250 x′2 = 0.95 0.0183 0.0268 0.0347 0.0465 0.0575 0.0718 0.0880 0.1076

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. C



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factor c23, which was therefore set as 0.3. For best correlation, the nonrandomness factor c12 takes a value of 0.47. This is very close to the value of 0.477 used by Vercher et al.16 Results are summarized in Table 4. Using the obtained parameters, ternary VLE data were calculated in comparison with the experimental values. Results are shown in Table 5, in which δT and δy are respectively mean absolute deviations of equilibrium temperature and vapor phase mole fraction of 1-propanol. The calculated results are in good agreement with experimental values, with δT = 0.26 K and δy = 0.0035. Calculated results for the ternary vapor−liquid equilibria are also shown in Figures 1 and 2. Generally good agreement can be observed as compared with experimental values. Relative volatility of 1-propanol to water was calculated at x2′ = 1 in relation with glycerol mole fraction, as shown in Figure 1c. The minimum amount of glycerol needed for breaking the water +1-propanol azeotrope is 0.398 in mole fraction, or 0.503 in mass fraction. The required mass fraction of glycerol for breaking the azeotrope is comparable with that of [bmim]Cl,23 which can remove the azeotrope at a mass fraction of 0.5, and is less than [emim][BF4],22 which requires a mass fraction of as much as 0.7. This indicates that glycerol is a potentially effective entrainer for

Table 3. Experimental Results for Infinite Dilution Activity a Coefficients of 1-Propanol in Glycerol, γ∞ 23 T/K

γ∞ 23

313.15 333.15 353.15 373.15 393.15

9.32 7.87 7.17 6.48 5.81

a ur(γ∞ 23) = 0.05. The infinite dilution activity coefficients have been corrected to zero pressure.

1 N

Finf = +

∞ ∞ /γ23,exp − 1)2 ∑ (γ23,cal N ∞ ∞ ∞ ∞ (γ12,cal /γ12,lit − 1)2 + (γ21,cal /γ21,lit − 1)2

(1c)

where N is the number of data points for a particular data set. In the construction of the objective function, a weighing factor of 0.2 was used for the term of infinite dilution activity coefficient (Finf). It was found that, by use of a weighing factor of 0.2, the resulting correlation was satisfactory for all the data sets. The correlation was insensitive to the choice of the nonrandomness

Figure 1. Experimental and calculated (a) activity coefficients of water, γ1, (b) activity coefficients of 1-propanol, γ2, and (c) relative volatility of 1-propanol to water, α21, in relation with glycerol mole fraction, x3, for the saturated liquid mixture water (1) + 1-propanol (2) + glycerol (3) at p = 100 kPa: ○, x2′ = 0.1; ●, x2′ = 0.2; □, x2′ = 0.4; ■, x2′ = 0.6; ◊, x2′ = 0.8; ⧫, x2′ = 0.95. Lines were calculated using NRTL parameters in Table 4: solid lines, x′2 = 0.1, 0.2, 0.4, 0.6, 0.8, and 0.95, respectively; dash line, x′2 = 1.

Figure 2. Experimental and calculated (a) activity coefficients of water, γ1, (b) activity coefficients of 1-propanol, γ2, and (c) relative volatility of 1-propanol to water, α21, in relation with 1-propanol mole fraction on solvent-free basis, x2′ , for the saturated liquid mixture water (1) + 1-propanol (2) + glycerol (3) at p = 100 kPa: ○, w3 = 0.1; □, w3 = 0.3; ◊, w3 = 0.5; ●, w3 = 0.6; ■, = 0.7; ⧫, w3 = 0.8. Lines were calculated using NRTL parameters in Table 4: solid lines, w3 = 0.1, 0.3, 0.5, 0.6, 0.7, and 0.8, respectively; dash line, w3 = 0. D



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

a

component i

component j

aij

bij/K

aji

bji/K

cij

water water 1-propanol

1-propanol glycerol glycerol

3.2932 −1.0486 −1.4800

−238.29 669.79 813.68

−1.7387 0.5754 0.5601

799.35 −527.01 268.03

0.47 0.3 0.3

τij = Δgij/RT = aij + bij/T; Gij = exp(−cijτij). The binary parameters of water + glycerol were taken from ref 11.

Table 5. Mean Absolute Deviations, δT and δy, in the Calculation of Binary VLE of Water (1) + 1-Propanol (2), and Ternary VLE of Water (1) + 1-Propanol (2) + Glycerol (3), Based on Correlation by NRTL Equation data type

source of data

data points

ternary VLE at 100 kPa binary VLE at 100 kPa binary VLE at 60 kPa binary VLE at 30 kPa binary VLE at 100 kPa

this work Gabaldón et al.32 Gabaldón et al.32 Gabaldón et al.32 Vercher et al.16

48 28 28 26 33

δT/K

δy

0.26 0.21 0.21 0.17 0.13

0.0035 0.0051 0.0038 0.0053 0.0064

Table 6. Deviations in the Calculation of Infinite Dilution Activity Coefficients, γ∞, of Water (1) + 1-Propanol (2), Based on Correlation by NRTL Equation

a

data

T/K

lit. valuea

calcd value

rel. dev.

γ∞ 12 γ∞ 21

370.35 373.15

3.39 19.35

3.26 19.85

−3.8% 2.6%

Kojima et al. (1968, cited in ref 33).

and compared with literature values (Kojima et al.33), as shown in Table 6. The calculated value of γ∞ 12 is 3.26, which is in close agreement with the literature value of 3.39. For γ∞ 21, the calculated and literature value is, respectively, 19.85 and 19.35, indicating very good agreement. Using the binary parameters of 1-propanol + glycerol, infinite dilution activity coefficients of 1-propanol in glycerol, γ∞ 23, were calculated. The calculated results show close agreement with the experimental values, as shown in Figure 4. It has been shown

dehydration of 1-propanol by extractive distillation. Calculated results in Figure 2c provide additional information. At x2′ < 0.05, α21 decreases with addition of glycerol, showing a salting-in effect. This is mainly due to the rapid decrease of γ2 with the addition of glycerol in the water-rich region, as shown in Figure 2b. Using the binary parameters of water + 1-propanol, isobaric VLE were calculated and compared with literature values, as shown in Table 5. For correlation of isobaric VLE at 30, 60, and 100 kPa, Gabaldón et al.32 used three different sets of temperature-independent binary parameters. Using a single set of temperature-dependent energy parameters, the present correlation showed relatively smaller deviations. For example, the present correlation has deviations of δT = 0.17 K and δy = 0.0053 for data at 30 kPa. This result is better than that in the original literature, with deviations of δT = 0.29 K and δy = 0.0062. For data of Vercher et al.16 at 100 kPa, the present correlation has deviations of δT = 0.13 K and δy = 0.0064. These are close to the deviations of δT = 0.19 K and δy = 0.005 in the original literature. In Figure 3, calculated boiling temperatures and vapor mole fractions were compared with literature results of Gabaldón et al.32 and Vercher et al.,16 showing good agreement. Moreover, infinite dilution activity coefficients were calculated for the binary system

Figure 4. Experimental and calculated results of infinite dilution activity coefficients of 1-propanol in glycerol, γ∞ 23: ○, experimental; solid line, calculated by use of NRTL parameters in Table 4.

previously that the binary parameters of water + glycerol are capable of reproducing infinite dilution activity coefficients of water in glycerol in a temperature range of 313.15 to 393.15 K and excess enthalpies of water + glycerol at 323.15 and 353.15 K.11 These results indicate that the present correlation may be applicable in relatively wide temperature and composition ranges. Validity of the present correlation was examined in a whole glycerol composition range, from x3 = 0 to x3 = 1, as shown in Figure 5. The calculation was carried out at T = 373.15 K. The dash line in Figure 5a presents a trend of activity coefficient of water, γ1, in relation with the glycerol mole fraction in the binary mixture of water + glycerol. For pure water, that is, x3 = 0, the activity coefficient is unity. At the other end, that is, x3 = 1,

Figure 3. T-x-y diagram for water (1) + 1-propanol (2) at p = 100 kPa: ■, □, Vercher et al. (ref 16); ●, ○, Gabaldón et al. (ref 32); solid lines, calculated by use of NRTL parameters in Table 4. E



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Figure 5. Calculated results of (a) activity coefficients of water, γ1, (b) activity coefficients of 1-propanol, γ2, and (c) relative volatility of 1-propanol to water, α21, in relation with glycerol mole fraction, x3, for the liquid mixture water (1) + 1-propanol (2) + glycerol (3) at T = 373.15 K: dash line, x′2 = 0; short dash line, x2′ = 0.2; dot line, x2′ = 0.4; dash dot line, x2′ = 0.6; dash dot dot line, x2′ = 0.8; solid line, x2′ = 1; Lines were calculated using NRTL parameters in Table 4.

Figure 6. Calculated results of (a) activity coefficients of water, γ1, (b) activity coefficients of alcohol, γ2, and (c) relative volatility of alcohol to water, α21, in relation with glycerol mole fraction, x3, for three alcohols: solid line, ethanol (ref 11); dot line, 2-propanol (ref 12); dash line, 1-propanol. Lines were calculated for the saturated liquid mixture water (1) + alcohol (2) + glycerol (3) at x2′ = 1 and p = 100 kPa.

This trend is determined by the fact that the value of γ∞ 13 (0.786) is smaller than the value of γ∞ 12 (3.21). Meanwhile, γ2 has a significant trend of increase. This is due to the fact that the value of γ∞ 23 (6.34) is greater than unity. It is a reasonable consequence that the relative volatility of 1-propanol to water increases rapidly with the addition of glycerol, as can be observed in Figure 5c. In the case of x2′ = 0, the situation is quite different. As the value of γ∞ 13 (0.786) is smaller than unity, γ1 decreases with the increase of x3. However, ∞ the value of γ∞ 21 (19.85) is much greater than the value of γ23 (6.34). Therefore, γ2 decreases significantly with the increase of x3. Because γ2 decreases more rapidly than γ1, α21 decreases with the addition of glycerol, indicating a salting-in effect. This can be observed in Figure 5c. The results in Figure 5 indicate that the infinite dilution activity coefficients are very important for reliable correlation in a wide composition range. The effect of glycerol on the quasi-binary pair water + 1-propanol was compared with those on water + ethanol11 and water + 2-propanol.12 Activity coefficients were calculated for saturated liquid mixtures of the three ternary systems at x2′ = 1 and p = 100 kPa. Results were shown in Figure 6a,b, in relation with x3. As expected, γ1 tends to have the same value for the three systems when x3 increases. This is a reasonable trend, because γ1 for the three systems will eventually coincide at the infinite dilution activity coefficient of water in glycerol at the boiling

the calculated infinite dilution activity coefficient of water is 0.786. This reproduces very well the literature value of 0.79.11 Meanwhile, the solid line shows an infinite dilution activity coefficient of water in mixtures of water and glycerol, also at T = 373.15 K. At x3 = 0, the calculated value is 3.21. This is in good agreement with the result of 3.39 at T = 370.35 K by Kojima et al.33 At x3 = 1, the solid line intersects with the dash line. In fact all the calculated lines coincide at this point, which indicates the infinite dilution activity coefficient of water in glycerol. For the other lines at x2′ = 0.2, 0.4, 0.6, 0.8, respectively, the end points at x3 = 0 are governed by the activity coefficients of water in the binary mixture of water + 1-propanol. At the same time, the trend of activity coefficient of 1-propanol, γ2, can be observed in Figure 5b. As expected, all the lines coincide at x3 = 1, having a value of 6.34 for the infinite dilution activity coefficient of 1-propanol in glycerol. This is in good agreement with the experimental value of 6.48. At x3 = 0, the calculated infinite dilution activity coefficient of 1-propanol in water is 19.85. As has been presented in Table 6, this is in good agreement with the result of 19.35 by Kojima et al.33 It is noticeable that the activity coefficient of water always decreases with the addition of glycerol, while the trend of activity coefficient of 1-propanol depends on the content of water. When water mole fraction is small, for example at x2′ = 1, γ1 decreases rapidly with increasing x3. F



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temperature of glycerol. On the other hand, γ1 for the three systems have the order ethanol < 2-propanol < 1-propanol. This is decided by the order of infinite dilution activity coefficients of water in ethanol, 2-propanol, and 1-propanol. For γ2, it is unity at x3 = 0. With the increase of x3, γ2 increases for all the three systems. For x3 < 0.3, γ2 for the three systems have almost the same value. At higher glycerol mole fractions, the activity coefficient of ethanol appears to be relatively small. As the relative volatility is decided by the ratio of activity coefficient and the ratio of vapor pressure, breaking the azeotrope of water + 1-propanol require more glycerol (x3 = 0.398), as compared with that for water + ethanol11 (x3 = 0.0473) and that for water + 2-propanol12 (x3 = 0.162). This can be observed in Figure 6c.

(7) García-Herreros, P.; Gómez, J. M.; Gil, I. D.; Rodríguez, G. Optimization of the design and operation of an extractive distillation system for the production of fuel grade ethanol using glycerol as entrainer. Ind. Eng. Chem. Res. 2011, 50, 3977−3985. (8) Navarrete-Contreras, S.; Sánchez-Ibarra, M.; Barroso-Muñoz, F. O.; Hernández, S.; Castro-Montoya, A. J. Use of glycerol as entrainer in the dehydration of bioethanol using extractive batch distillation: Simulation and experimental studies. Chem. Eng. Process. 2014, 77, 38−41. (9) Souza, W. L. R.; Silva, C. S.; Meleiro, L. A. C.; Mendes, M. F. Vapor−liquid equilibrium of the (water + ethanol + glycerol) system: Experimental and modelling data at normal pressure. J. Chem. Thermodyn. 2013, 67, 106−111. (10) Pla-Franco, J.; Lladosa, E.; Loras, S.; Montón, J. B. Phase equilibria for the ternary systems ethanol, water + ethylene glycol or + glycerol at 101.3 kPa. Fluid Phase Equilib. 2013, 341, 54−60. (11) Zhang, L.; Yang, B.; Zhang, W. Vapor−liquid equilibrium of water + ethanol + glycerol: experimental measurement and modeling for ethanol dehydration by extractive distillation. J. Chem. Eng. Data 2015, 60, 1892−1899. (12) Zhang, L.; Zhang, W.; Yang, B. Experimental measurement and modeling of ternary vapor−liquid equilibrium for water + 2-propanol + glycerol. J. Chem. Eng. Data 2014, 59, 3825−3830. (13) Morrison, J. F.; Baker, J. C.; Meredith, H. C., III; Newman, K. E.; Walter, T. D.; Massie, J. D.; Perry, R. L.; Cummings, P. T. Experimental measurement of vapor-liquid equilibrium in alcohol water salt systems. J. Chem. Eng. Data 1990, 35, 395−404. (14) Lin, C.-L.; Lee, L.-S.; Tseng, H.-C. Phase equilibria for propan-1ol + water + sodium chloride and + potassium chloride and propan-2-ol + water + lithium chloride and + lithium bromide. J. Chem. Eng. Data 1993, 38, 306−309. (15) Iliuta, M. C.; Thyrion, F. C. Effect of calcium chloride on the isobaric vapor-liquid equilibrium of 1-propanol + water. J. Chem. Eng. Data 1996, 41, 402−408. (16) Vercher, E.; Rojo, F. J.; Martínez-Andreu, A. Isobaric vapor-liquid equilibria for 1-propanol + water + calcium nitrate. J. Chem. Eng. Data 1999, 44, 1216−1221. (17) Vercher, E.; Vázquez, M. I.; Martínez-Andreu, A. Isobaric vapor− liquid equilibria for 1-propanol + water + lithium nitrate at 100 kPa. Fluid Phase Equilib. 2002, 202, 121−132. (18) Vercher, E.; Orchillés, A. V.; Vázquez, M. I.; Martínez-Andreu, A. Isobaric vapor−liquid equilibria for 1-propanol + water + lithium chloride at 100 kPa. Fluid Phase Equilib. 2004, 216, 47−52. (19) Vercher, E.; Orchillés, A. V.; Gonzalez-Alfaro, V.; MartínezAndreu, A. Isobaric vapor−liquid equilibria for 1-propanol + water + copper (II) chloride at 100 kPa. Fluid Phase Equilib. 2005, 227, 239− 244. (20) Orchillés, A. V.; Miguel, P. J.; Vercher, E.; Martínez-Andreu, A. Isobaric vapor-liquid equilibria for 1-propanol + water + 1-ethyl-3methylimidazolium trifluoromethanesulfonate at 100 kPa. J. Chem. Eng. Data 2008, 53, 2426−2431. (21) Orchillés, A. V.; Miguel, P. J.; Gonzalez-Alfaro, V.; Vercher, E.; Martínez-Andreu, A. Isobaric vapor-liquid equilibria of 1-propanol + water + trifluoromethanesulfonate-based ionic liquid ternary systems at 100 kPa. J. Chem. Eng. Data 2011, 56, 4454−4460. (22) Zhang, L.; Han, J.; Wang, R.; Qiu, X.; Ji, J. Isobaric vapor-liquid equilibria for three ternary systems: water + 2-propanol + 1-ethyl-3methylimidazolium tetrafluoroborate, water + 1-propanol + 1-ethyl-3methylimidazolium tetrafluoroborate, and water + 1-propanol + 1-butyl3-methylimidazolium tetrafluoroborate. J. Chem. Eng. Data 2007, 52, 1401−1407. (23) Zhang, L.; Guo, Y.; Deng, D.; Ge, Y. Experimental measurement and modeling of ternary vapor-liquid equilibrium for water + 1-propanol + 1-butyl-3-methylimidazolium chloride. J. Chem. Eng. Data 2013, 58, 43−47. (24) Zhang, L.-Z.; Deng, D.-S.; Han, J.-Z.; Ji, D.-X.; Ji, J.-B. Isobaric vapor-liquid equilibria for water + 2-propanol + 1-butyl-3-methylimidazolium tetrafluoroborate. J. Chem. Eng. Data 2007, 52, 199−205.

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CONCLUSIONS Isobaric vapor−liquid equilibrium data were measured for the ternary system water + 1-propanol + glycerol at 100 kPa. Infinite dilution activity coefficients of 1-propanol in glycerol were measured in a temperature range of 313.15 to 393.15 K. The NRTL equation was used for the modeling of ternary VLE. Binary parameters of water + glycerol were fixed as the same for water + ethanol + glycerol and were taken from the literature. Binary parameters of water + 1-propanol and 1-propanol + glycerol were correlated using the experimental ternary data and infinite dilution data, together with literature results of binary VLE and infinite dilution activity coefficients for water + 1-propanol. The correlation provided good agreement for all the source data. It is shown that the infinite dilution activity coefficients provide key information for reliable correlation in a wide composition range. With the addition of glycerol, the azeotrope of water + 1-propanol can be removed at a glycerol mole fraction of 0.398, indicating that glycerol is a potentially effective entrainer for dehydration of 1-propanol by extractive distillation.

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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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