Isobaric VaporâLiquid Equilibria for the Binary Mixtures Composed of

Article pubs.acs.org/jced

Isobaric Vapor−Liquid Equilibria for the Binary Mixtures Composed of Ethylene Glycol, 1,2-Propylene Glycol, 1,2-Butanediol, and 1,3Butanediol at 10.00 kPa Luhong Zhang,† Weihua Wu,† Yongli Sun,*,† Lingqiao Li,† Bin Jiang,†,‡ Xingang Li,†,‡ Na Yang,† and Hui Ding†,‡ †

School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China National Engineering Research Center for Distillation Technology, Tianjin, 300072, China

‡

ABSTRACT: Isobaric vapor−liquid equilibria (VLE) data for the ethylene glycol + 1,2-propylene glycol, 1,2-propylene glycol + 1,3-butanediol, 1,2-propylene glycol + 1,2-butanediol, and ethylene glycol + 1,3-butanediol binary systems have been measured at 10.00 kPa using a VLE recirculating still. The experimental VLE data were correlated with nonrandom twoliquid (NRTL), Wilson, and universal quasichemical (UNIQUAC) activity coefficient models. The results showed that the calculated values of the vapor-phase mole fraction and boiling temperature by the NRTL, Wilson, and UNIQUAC models agreed well with the experimental data. The experimental data were checked with the Herington consistency test and Van Ness test method, which also showed thermodynamic consistency.

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INTRODUCTION As an important chemical substance, ethylene glycol is mostly used for polymer ester manufacturing and antifreezer production, with the rise of oil price, using coal as raw material instead of petroleum to produce organic chemicals has become the main research direction. Using the coal instead of the oil as material products for polybasic alcohol costs less and it is produced by using renewable resources, so more and more countries are increasingly paying attention to the strategy.1 Among these nonpetroleum processes of the EG (ethylene glycol) synthesis, the C1 chemical process based on the syngas1,2 has become the relatively efficient choice to replace petroleum process for less equipment investment, energy consumption, and materials cost. As we all know, the route for EG manufacturing based on syngas can be divided into two main steps: first, dimethyl oxalate (DMO) is synthesized by carbonization coupling of CO (carbon monoxide), and then the DMO is converted into ethylene glycol by hydrogenation. Ethylene glycol is the main product of the reaction network of the DMO hydrogenation, while the 1,2-butanediol (CAS: 584-03-2) and 1,2-propylene glycol (CAS: 57-55-6) are also generated in this process as byproducts because of the excessive hydrogenation. However, the boiling points between all these alcohols are so close that brings difficulty to separate by conventional distillation. The phase equilibrium data of alcohols are very important in the design, simulation, and optimization of the production of ethylene glycol. Amedeo et al.3 measured VLE data of ethylene glycol, 1,2-propylene glycol, and H2O with the temperatures ranged from (371.15 to © 2013 American Chemical Society

395.15) K; however, as far as we know, the isobaric vapor− liquid equilibrium relations of ethylene glycol, 1,2-butanediol, 1,3-butanediol (CAS: 107-88-0), and 1,2-propylene glycol, which are the foundation data for distillation process design, are unavailable in published literature. Therefore a major part of this work is to provide data in this field. In our work, we also added 1,3-butanediol as it is the isomeric compound for the 1,2-butanediol so that we can get the different the gas−liquid phase equilibrium behavior for these isomeric compounds. Isobaric vapor−liquid equilibrium data were measured for the four binary solutions which can be obtained from ethylene glycol, 1,2-propylene glycol, 1,2butanediol, and 1,3-butanediol. As the four chemicals have close boiling points (470.45 K, 461.15 K, 465.15 K, and 481.38 K at 101.30 kPa, respectively, in Table 2), it is advisable to separate them at a reduced pressure. We choose 10.00 kPa as VLE pressure environment since it is relatively suitable for experimental applications and our experiment condition that can also enhance the separation factors between these alcohols. We describe the nonideality of the liquid phase using the Wilson,4 nonrandom two-liquid (NRTL),5 and universal quasichemical (UNIQUAC)6 models, the vapor phases can be considered ideal because of the low pressure. The experimental VLE data were tested with the Herington Received: January 24, 2013 Accepted: April 11, 2013 Published: April 22, 2013 1308

dx.doi.org/10.1021/je400082c | J. Chem. Eng. Data 2013, 58, 1308−1315

Journal of Chemical & Engineering Data

Article

the normal boiling temperature from the experiment is 1021.40 kg·m−3 and 467.65 K, respectively, which were close to the literature values11 in Table 2. Apparatus and Procedures. The experimental apparatus for acquiring the vapor−liquid equilibrium data is a circulation VLE still as described in previous papers (a modified RoseWilliams still)14 and also shown in Figure 1. There is a feature

consistency test and Van Ness test (a point consistency method) and showed good thermodynamic consistency.

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EXPERIMENTAL SECTION Materials. The chemicals ethylene glycol (≥ 0.995, mass fraction) and 1,2-propylene (≥ 0.998, mass fraction) were supplied by J&K Chemical Co., Ltd., China, and 1,2-butanediol (≥ 0.98, mass fraction) and 1,3-butanediol (≥ 0.99, mass fraction) were supplied by TCI (Tokyo Kasei Kogyo Co., Ltd. Shanghai) Development Co., Ltd. The purity of all of the reagents was detected by gas chromatography (GC7890A, Agilent Technologies) with a flame ionization detector (FID) before the experiment. There were no impurity peaks found in ethylene glycol and 1,2-propylene glycol, so we can use them directly in the experiment without any further treatment. But the 1,2-butanediol was supplied by TCI (Tokyo Kasei Kogyo Co., Ltd. Shanghai) Development Co., Ltd. and had a minimum mass fraction purity of 0.98, through the mass spectrum, there being unknown components with molecular weight range from (90 to 150) g·mol−1. So its purity can reach 0.99 in mole fraction. From this fact we should realize that the purification of the 1,2-butanediol is a worldwide industrial issue. With the reason that the unknown component and their content are unable to be determined, it is used without additional purification either. Although it is maybe insufficient for the research to get the strict thermodynamic data, the value of the industrial application could still be considered. The specifications of the chemicals used are summarized in Table 1,

Figure 1. Experimental device for VLE measurement. 1, heating rod; 2, liquid-phase sampling port; 3, glycerol; 4, equilibrium chamber; 5, precision platinum resistance thermistor; 6, condensing coil; 7, desiccator; 8, three-way pipe; 9, buffer tank; 10, precision vacuum pump; 11, vapor-phase sampling port.

Table 1. Specifications of the Chemicals Used chemical name ethylene glycol 1,2-propylene glycol 1,2-butanediol 1,3-butanediol a

source J&K Chemical Co., Ltd. J&K Chemical Co., Ltd., China TCI Development Co., Ltd. TCI Development Co., Ltd.

mass fraction purity

analysis method

≥ 0.995 ≥ 0.998

GCa GCa

≥ 0.98

GCa

≥ 0.99

GCa

for this still that both liquid and condensed vapor phases are continuously recirculated to provide intimate contact of the phases to reach equilibrium in not a long time. The total volume was about 60 cm3 of which about 35 cm3 was occupied by the liquid solution in the still. Energy was supplied to the still by a heating rod controlled by an electric thermocouple, and a condensation stream was cooled by the cooling water to remove the heat of the rising steam from the still bottom. We use a precision platinum resistance thermistor to measure temperature. The resistance of the thermistor is evaluated with an uncertainty of ± 0.01 K on the temperature scale. The pressure of the system was monitored with a digital manometer (± 0.03 kPa) and controlled at 10.00 kPa for the experiment. A Fortin-type mercury barometer located adjacent to the experimental apparatus with an accuracy of ± 0.03 kPa was used to measure the atmospheric pressure. The thermistor and digital manometer were both calibrated before experimental measurements. During the experiments, when the leakage test for the experimental apparatus had been done, the apparatus was vacuumized by a precision vacuum pump, after reaching the desired pressure and stability, the solution would be heated. The vapor was condensed in the condenser of the still and at the same time returned to equilibrium chamber through the vapor phase sampling port in the still. In the equilibrium process, we recorded the fluctuation of the temperature and pressure, and when the fluctuation of the pressure was maintained at less than ± 0.05 % and constant experimental temperature was obtained in about (1 to 1.5) h or longer, then we consider that the equilibrium is established. Samples of vapor and liquid phase were taken out simultaneously for analysis from the sampling ports by using a micro syringe. This is done with tiny disturbances on the equilibrium since the samples (0.5 mL) is negligible, as the volume of the still is 60 cm3 as mentioned before.

Gas−liquid chromatography.

and the physical properties of these pure components are shown in Table 2.7−13 Because the purity of 1,2-butanediol is about w = 0.98 in mass fraction, here we compared its some physical properties with the literature values, the density and Table 2. Properties of the Pure Compounds compoundsa M/g·mol−1 Tb/K (101.3 kPa) Tc/K Pc/MPa Vc/cm3·mol−1 ρ/kg·m−3 (298.15 K) Zc ω

ethylene glycol

1,2butanediol

1,3butanediol

1,2-propylene glycol

62.068a 470.45a 645a 7.53a 191a 1134.7b

90.1222a 469.575d 680e 5.21e  1020.5d

90.1222a 481.38e 676e 4.02e  294.8e

76.0953a 461.15d 676.4f 5.941f  1035.6d

0.262c 0.507c

 0.6303e

 0.7053e

 0.6575g

Critical temperature: Tc, critical pressure: Pc, critical volume: Vc. : Indicating there are no data in the literature. aTaken from ref 7. b Taken from ref 8. cTaken from ref 9. dTaken from ref 10. eTaken from ref 11. fTaken from ref 12. gTaken from ref 13. a

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Table 4. Experimental Vapor Pressuresa of 1,3-Butanediol (w = 0.99)

The compositions of the liquid and vapor phases were analyzed by a gas chromatography GC-7890A supplied by Agilent Technologies Co. The column was a DB-WAX capillary column (30 m × 0.25 mm × 0.25 μm, Agilent) which is relatively suitable for analyzing the alcohols and the carrier gas was hydrogen w = 0.99999 flowing at 40 mL·min−1. The operating conditions were as following: split ratio, 50:1; injector temperature, 513.15 K; detector temperature, 553.15 K; oven temperature, started at 353.15 K, ascending at the rate of 10 K·min−1 until 503.15 K, running about 15 min totally; sample volume, 0.2 μL. The gas chromatography was calibrated with standard solutions that were prepared gravimetrically by an electronic balance (FA2004N) with an uncertainty of ± 0.0001 g. For each sample, at least three analyses were made to reduce the disturbance. The average value was recorded if the difference of the measuring value among the three samples was no more than 0.5 %.

a

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Table 3. Experimental Vapor Pressuresa of 1,2-Butanediol (w = 0.98)

a

T/K

P/kPa

T/K

P/kPa

1.89 3.33 4.96 6.36 7.66 8.81 9.90 11.39 14.09 17.27

421.49 424.91 427.57 429.92 432.76 435.37 438.52 439.97 441.78 443.55

19.63 22.54 25.06 27.24 30.39 33.36 37.30 39.30 41.90 44.75

P/kPa

T/K

P/kPa

2.43 3.60 5.03 6.26 7.72 8.54 10.48 11.87 12.54 14.63 15.84

429.75 433.71 436.29 439.65 442.45 444.75 447.01 449.80 451.70 453.10

17.09 19.96 22.24 25.30 28.15 30.78 33.36 36.78 39.45 41.39

u(T) = ± 0.01 K, and u(P) = ± 0.03 kPa.

data treatment were selected from the literature to cover the temperature range of interest in this work and are also reported in Table 5. The measured vapor pressures of 1,2-butanediol and 1,3-butanediol also compared with the results reported by Steele et al.11 were fitted by the Wagner equation in Figures 2 and 3, respectively, which showed a good fit with data from the literature. Because the boiling points between the alcohols in present study are so close that we should employ more accurate equipment to ensure the data are valid, before the VLE experiments, comparing the experimental vapor pressures with literature data is essential, which can also test and verify the reliability of the equipment and the Antoine equation in the literature at the same time. The average deviation between the experimental data and the calculated values by the Antoine equation in the literature14 is Δp = ∑k|(pexpt − pcalc)/pexpt|k/ N·100 = 0.003, where N is the number of the data points, for ethylene glycol (the vapor-pressure data are shown in Table 6), and the experiment discussed the vapor pressure under low pressure fitted the literature14 very well, thus indicating the equipment is reliable for our experiment, and this could also be seen from the vapor pressure of the 1,2-butanediol and 1,3butanediol. At the same time, the VLE data for benzene (1) + toluene (2) were measured at 101.30 kPa to test the performance of the equilibrium still. As is shown in Figure 4, the experimental data are in good agreement with those reported by Huang et al.,15 thus also verifying that our equilibrium still is reliable. Vapor−Liquid Equilibrium Data. The VLE data for the binary systems obtained at 10.00 kPa are listed in Tables 7 to 10, the binary systems are the 1,2-propylene glycol (1) + 1,3butanediol (2), ethylene glycol (1) + 1,3-butanediol (2), 1,2propylene glycol (1) + ethylene glycol (2) and 1,2-propylene glycol (1) + 1,2-butanediol (2). The activity coefficients γi for these systems were calculated from the following equation:

RESULTS AND DISCUSSION Pure Component Vapor Pressures. There are some literature data about the vapor pressure for the ethylene glycol, 1,2-propylene glycol, 1,2-butanediol, and 1,3-butanediol. Steele et al.11 measured the vapor-pressure for 1,2-butanediol and 1,3butanediol using an inclined-piston and twin ebulliometric apparatus, but they fit the measured vapor pressure data to a Wagner form vapor-pressure equation {the Wagner (1973) equation in the formulation given by Ambrose and Walton (1989) ln(p/pc) = (1/Tr)·[AY + BY1.5 + CY2.5 + DY5] where Tr = T/Tc, Y = 1 − Tr, was used}. For our experiment the purity of the ethylene glycol (w = 0.995) and 1,2-propylene glycol (w = 0.998) is high enough to meet the demand for the strict thermodynamic data, but the mass fraction of 1,2-butanediol and 1,3-butanediol is only w = 0.98 and 0.99, respectively, and there also are no Antoine equation parameters for the 1,2butanediol (w = 0.98) and 1,3-butanediol (w = 0.99) in the open literature, so the vapor pressure for these two alcohols were experimentally determined in the pressure range allowed by the still described in the Experimental Section. The pure component vapor pressures of 1,2-butanediol and 1,3butanediol were determined, and the data are shown in Tables 3 and 4. The Antoine equation was used to correlate the experimental data, and the average absolute deviation (AAD) between the measured data and those correlated by the Antoine equation was 0.039 and 0.040 kPa, respectively, as shown in Table 5 too. At the same time, the Antoine equation parameters for the ethylene glycol and 1,2-propylene glycol used for VLE

372.06 382.61 390.52 395.55 399.56 402.61 405.13 408.50 413.34 418.29

T/K 387.75 395.13 402.05 406.61 411.11 413.41 418.03 420.85 422.04 425.80 427.74

⎛ V l(p − ps ) ⎞ i i ⎟ pyi φî v = pis φisγixi exp⎜⎜ ⎟ RT ⎝ ⎠

(1)

In this equation, where yi and xi are the molar fractions of pure component i in the vapor and liquid phases, respectively, p is the total pressure, psi is the saturation vapor pressure of the pure liquid i at temperature T, φ̂ vi and φ̂ si are the fugacity coefficients of component i in the mixture vapor phase and in the pure state, γi is the activity coefficient of the component i in liquid phase, Vli is the molar volume of pure liquid i, calculated

u(T) = ± 0.01 K, and u(P) = ± 0.03 kPa. 1310



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Table 5. Antoine Parametersa of the Pure Components compounds ethylene glycolb 1,2-propylene glycolc 1,2-butanediold 1,3-butanediold a

range T/K 372.40 318 to 372.06 387.75

to 470.02 461 to 443.55 to 453.10

A

B

C

AAD(P)/kPa

15.4119 18.6034 14.9819 15.4039

3928.97002 6198.99656 3619.62165 3902.52116

−106.380 −17.940 426.356 427.259

0.039 0.040

ln(P/kPa) = A − B/(C + T/K). bTaken from refs 13 and 14. cTaken from ref 15. dAntoine parameters determined from experimental data.

Table 6. Experimental Vapor Pressuresa of Ethylene Glycol

a

T/K

P/kPa

T/K

P/kPa

386.15 389.12 389.95 390.75 395.25 400.78 402.15

3.92 4.51 4.78 4.89 6.08 7.87 8.37

405.85 406.25 409.30 411.15 411.85 413.85 416.45

9.85 10.02 11.42 12.41 12.85 13.85 15.37

u(T) = ± 0.01 K, and u(P) = ± 0.03 kPa.

Figure 2. Experimental vapor pressures of 1,2-butanediol (w = 0.98) compared with the literature values calculated from the Wagner equation.

Figure 4. y1−x1 diagram for the benzene (1) + toluene (2) system at 101.30 kPa. ■, experimental data ; □, literature data.

ideal gas for low to moderate pressure and that the four alcohols have similar properties in the measured mixtures. Then, the experimental liquid phase activity coefficient is written as follows: pyi = pis γixi

ps2x2,

When p > + it indicates that a positive deviation from Raoult’s law is shown. Then through the above equations, we can deduce that γi > 1, and on the contrary if γi > 1, it can deduce that p > ps1x1 + ps2x2 which means a positive deviation from Raoult’s law is shown for the binary system. The results reported in Tables 7 to 10 indicate that the γi of the systems is very close to 1, and most of γi is larger than 1, this can explained by the very rich molecular interactions where self-, cross-, and intramolecular associations play a dominant play a dominant role in defining the properties and equilibrium behavior of the liquid phase. Intermolecular interaction between the molecules, generally indicating positive deviation from Raoult’s law, will show when the intermolecular interaction between the same molecules is larger than that

Figure 3. Experimental vapor pressures of 1,3-butanediol (w = 0.99) compared with the literature values calculated from the Wagner equation.

from the modified Rackett equation,16 and R is the universal gas constant (8.31441 J·K−1·mol−1). Because of the low pressure, 10.00 kPa, we can consider that the exponential term is equal to 1, then the equation can be simplified as follows:

pyi φî v = pis φisγixi

(3)

ps1x1

(2)

To obtain the experimental liquid phase activity coefficient of component i, we can assume that the vapor phase behaves as an 1311



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Table 7. VLE Data of 1,2-Propylene Glycol (1) + 1,3Butanediol (2) System at 10.00 kPaa

a

T/K

x1

y1

u(x)

u(y)

γ1

398.23 399.10 400.05 401.30 402.15 403.20 404.45 404.86 405.75 406.42 406.99 407.84 408.36 408.67 409.37 411.04 412.47 413.89 416.30 416.91

1.000 0.930 0.864 0.788 0.742 0.674 0.592 0.565 0.507 0.462 0.424 0.367 0.332 0.312 0.267 0.170 0.106 0.059 0.009 0.000

1.000 0.968 0.934 0.891 0.861 0.815 0.748 0.723 0.669 0.630 0.589 0.547 0.521 0.495 0.444 0.315 0.221 0.157 0.044 0.000

0.000 0.005 0.005 0.005 0.005 0.010 0.015 0.010 0.005 0.010 0.015 0.005 0.005 0.005 0.010 0.015 0.010 0.015 0.005 0.000

0.000 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.010 0.005 0.010 0.010 0.010 0.015 0.015 0.015 0.015 0.015 0.000

1.000 1.003 1.000 0.992 0.982 0.980 0.972 0.968 0.962 0.967 0.962 0.997 1.028 1.026 1.046 1.089 1.157 1.396 2.334

Table 9. VLE Data of 1,2-Propylene Glycol (1) + Ethylene Glycol (2) System at 10.00 kPaa γ2

T/K

x1

y1

u(x)

u(y)

1.052 1.065 1.061 1.067 1.068 1.095 1.107 1.118 1.110 1.121 1.080 1.056 1.066 1.066 1.074 1.063 1.025 0.991 1.000

406.09 405.42 404.57 403.88 403.44 402.92 402.45 401.98 401.67 401.32 401.04 400.69 400.45 400.25 399.99 399.75 399.13 398.72 398.45 398.23

0.000 0.043 0.105 0.163 0.202 0.254 0.305 0.360 0.400 0.446 0.484 0.537 0.574 0.605 0.649 0.690 0.807 0.891 0.950 1.000

0.000 0.070 0.163 0.238 0.288 0.347 0.398 0.449 0.489 0.536 0.571 0.613 0.646 0.677 0.715 0.749 0.845 0.912 0.960 1.000

0.000 0.005 0.005 0.010 0.010 0.010 0.005 0.005 0.010 0.005 0.005 0.015 0.010 0.005 0.015 0.010 0.005 0.005 0.005 0.000

0.000 0.005 0.010 0.010 0.015 0.015 0.005 0.005 0.010 0.010 0.005 0.005 0.005 0.005 0.010 0.005 0.005 0.005 0.005 0.000

u(T) = ± 0.01 K, u(P) = ± 0.03 kPa.

a

Table 8. VLE Data of Ethylene Glycol (1) + 1,3-Butanediol (2) System at 10.00 kPaa

a

T/K

x1

y1

u(x)

u(y)

γ1

406.09 406.22 406.46 406.92 407.28 407.60 408.05 408.40 408.62 409.10 409.39 409.59 409.91 410.03 410.41 411.21 411.81 412.40 412.98 413.34 415.33 416.18 416.91

1.000 0.964 0.909 0.824 0.768 0.710 0.654 0.617 0.595 0.554 0.519 0.491 0.467 0.458 0.427 0.359 0.316 0.274 0.233 0.209 0.088 0.040 0.000

1.000 0.970 0.924 0.869 0.825 0.797 0.756 0.727 0.710 0.675 0.647 0.624 0.602 0.594 0.564 0.494 0.443 0.404 0.354 0.324 0.161 0.073 0.000

0.000 0.005 0.010 0.015 0.015 0.005 0.010 0.015 0.010 0.005 0.005 0.005 0.010 0.015 0.005 0.010 0.005 0.015 0.005 0.005 0.005 0.010 0.000

0.000 0.005 0.010 0.005 0.010 0.015 0.010 0.005 0.005 0.005 0.005 0.005 0.005 0.005 0.010 0.010 0.015 0.010 0.005 0.010 0.015 0.005 0.000

1.000 1.000 1.000 1.017 1.020 1.051 1.061 1.066 1.069 1.069 1.081 1.092 1.093 1.094 1.096 1.104 1.097 1.125 1.132 1.137 1.236 1.191

γ1 1.203 1.188 1.150 1.144 1.120 1.091 1.064 1.056 1.054 1.047 1.028 1.024 1.027 1.022 1.017 1.007 1.002 1.001 1.000

γ2 1.000 1.001 1.000 1.003 1.003 1.007 1.018 1.033 1.036 1.035 1.041 1.063 1.068 1.061 1.066 1.075 1.097 1.123 1.127

u(T) = ± 0.01 K, u(P) = ± 0.03 kPa.

Table 10. VLE Data of 1,2-Propylene Glycol (1) + 1,2Butanediol (2) System at 10.00 kPaa

γ2 1.357 1.345 1.173 1.169 1.068 1.054 1.048 1.042 1.037 1.031 1.028 1.024 1.021 1.019 1.020 1.023 1.004 1.004 1.002 0.987 0.997 1.000

a

T/K

x1

y1

u(x)

u(y)

γ1

398.23 398.74 399.11 399.54 399.85 400.21 400.47 400.76 400.98 401.21 401.40 401.56 401.73 401.91 402.22 402.54 403.29 404.20 405.02 405.42

1.000 0.912 0.847 0.765 0.702 0.627 0.572 0.510 0.463 0.416 0.379 0.348 0.319 0.290 0.242 0.201 0.122 0.057 0.016 0.000

1.000 0.925 0.866 0.804 0.742 0.683 0.637 0.575 0.538 0.493 0.470 0.428 0.399 0.366 0.317 0.261 0.174 0.095 0.039 0.000

0.000 0.005 0.005 0.010 0.015 0.005 0.010 0.005 0.010 0.015 0.015 0.005 0.010 0.005 0.010 0.005 0.010 0.015 0.015 0.000

0.000 0.005 0.010 0.005 0.005 0.010 0.010 0.015 0.010 0.015 0.015 0.010 0.010 0.010 0.005 0.015 0.015 0.015 0.015 0.000

1.000 0.992 0.985 0.994 0.986 1.001 1.012 1.012 1.034 1.044 1.084 1.067 1.078 1.079 1.106 1.082 1.151 1.295 1.831

γ2 1.155 1.166 1.089 1.114 1.076 1.061 1.070 1.051 1.050 1.023 1.044 1.042 1.046 1.040 1.052 1.035 1.013 0.994 1.000

u(T) = ± 0.01 K, u(P) = ± 0.03 kPa.

butanediol (2) and 1,2-propylene glycol (1) + 1,2-butanediol (2), the change of the activity coefficient of the 1,2-propylene glycol is the same (When the concentration of the 1,2propylene glycol is high, the change of activity coefficients of 1,2-propylene glycol are even), while the change of activity coefficients of 1,2-butanediol and 1,3-butanediol varies little through the whole concentrations, and the change of activity coefficients of 1,2-butanediol is relatively obvious, maybe due to the different of molecular structure (the distances between two hydroxyl groups in these two molecules are different) for the 1,2-butanediol and 1,3-butanediol. For these two mixture

u(T) = ± 0.01 K, u(P) = ± 0.03 kPa.

between different ones. The activity coefficient is close to 1, which proved that there is only a small difference in boiling point and also proved the similarity between different mixture systems. These four materials all belongs to the alcohols and also have the similar properties (high and adjacent boiling point, high viscosity etc.), so this maybe bring the similar or different gas−liquid phase equilibrium behavior at low pressure. For example, in the system of 1,2-propylene glycol (1) + 1,31312



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Table 11. Correlated Interaction Parameters, the Average Absolute Deviations (AAD), and the Percent Average Relative Deviations (ARD %) between Experimental and Calculated Values model

Aa12/K

Aa21/K

Wilson NRTL UNIQUAC

−977.5197 −507.4666 315.7809

363.8694 1039.5422 −590.8911

Wilson NRTL UNIQUAC

186.5153 500.5590 −153.3691

−393.6142 −284.7147 85.6505

Wilson NRTL UNIQUAC

−506.3657 517.1114 −82.3794

−278.8776 299.9259 −239.1655

Wilson NRTL UNIQUAC

−679.0940 −405.8736 256.7694

295.3657 749.7057 −435.0334

α

AADb(y)

AAD(T)/K

1,2-Propylene Glycol (1) + 1,3-Butanediol (2) 0.3 0.0069 0.114 0.0084 0.079 0.0077 0.075 Ethylene Glycol (1) + 1,3-Butanediol (2) 0.3 0.0029 0.045 0.0030 0.046 0.0028 0.044 1,2-Propylene Glycol (1) + Ethylene Glycol (2) 0.3 0.0031 0.004 0.0032 0.004 0.0032 0.004 1,2-Propylene Glycol (1) + 1,2-Butanediol (2) 0.3 0.0088 0.046 0.0094 0.074 0.0093 0.070

AAD(P)/kPa

ARDc% (γ1)

ARDc% (γ2)

0.003 0.002 0.002

2.22 3.71 3.43

1.78 2.26 2.17

0.001 0.001 0.001

0.83 0.94 0.84

0.01 1.17 1.23

0.001 0.001 0.001

0.79 0.80 0.81

0.92 0.94 0.93

0.001 0.002 0.016

3.16 3.40 3.38

2.34 2.73 2.71

The interaction parameters for various models: Wilson, Aij = (λij − λji)/R; NRTL, Aij = (gij − gji)/R; UNIQUAC, Aij = (Uij − Uji)/R. bAAD (y) = c N exp cal exp − ycal (1/N)∑Ni=1|yexp i i | (N, number of data points). ARD % (γi) = (100/N) ∑j=1(|γi,j − γi,j |/γi,j ) (N, number of data points).

a

systems, what they have in common is that, when the content of 1,2-propylene glycol is very small, the activity coefficient of the 1,2-propylene glycol decreased suddenly. For the systems of the ethylene glycol (2) + 1,2-propylene glycol (1) and ethylene glycol (1) + 1,3-butanediol (2), the change of activity coefficients of the ethylene glycol is monotone and obvious. For these four systems (ethylene glycol + 1,2-propylene glycol, ethylene glycol + 1,3-butanediol, 1,2-propylene glycol + 1,2butanediol, and 1,2-propylene glycol + 1,3-butanediol), the change of their relative volatilities are cord with the differences of boiling points in each system separately. At the same time, the four alcohols’ boiling points are also close enough that the distance between the vapor line and liquid line is not far, indicating that separating them is not easy work. Consistency Tests of Experimental Data. Experimental errors may cause deviation from the activity coefficients drawn from the VLE data from the Gibbs−Duhem17 equation. As you know, the purity of the 1,2-butanediol we use is w = 0.98, and these alcohols’ boiling point are also close, but we can still check the consistency test of the experimental data. The Herington consistency test18 based on the Gibbs−Duhem theorem was used to verify the experimental data. Herington suggests that, if (D − J) < 10, the experimental data are considered to be thermodynamically consistent. The values of (D − J) for the systems ethylene glycol + 1,2-propylene glycol, ethylene glycol + 1,3-butanediol, 1,2-propylene glycol + 1,2butanediol, and 1,2-propylene glycol + 1,3-butanediol at 10.00 kPa were 9.78, 2.26, 8.42, and 8.67, respectively, which indicate that the experimental data are thermodynamically consistent. Here the experimental results of the binary system could also be tested by the point consistency method of the Van Ness test,19 which is regarded as a modeling capability test.19 This test shows how a mathematical activity coefficient model can reproduce the experimental data accurately, and the equation was expressed as the following: Δp =

1 N

N

∑ Δpi = i=1

1 N

N

∑ 100 i=1

Δy =

N

∑ Δyi = i=1

1 N

N

∑ 100|yiexp − yical | i=1

(5)

where N is the number of experimental data points; the superscript exp indicates experimental data; and the superscript cal indicates values calculated by the thermodynamic model. If Δp and Δy are less than 1, the data set passes the test, and then we can consider that the experimental points are considered to be thermodynamically consistent. According to this method, the check results Δp and Δy for the systems of 1,2-propylene glycol (1) + 1,3-butanediol (2), ethylene glycol (1) + 1,3-butanediol (2), 1,2-propylene glycol (1) + ethylene glycol (2), and 1,2-propylene glycol (1) + 1,2butanediol (2) in Table 11 indicate that the experimental data were thermodynamically consistent through the Van Ness test.19 Data Regression. The experimental data were correlated with the Wilson, NRTL, and UNIQUAC modes by minimizing the objective function F:20 2 ⎛ T exp − T cal ⎞2 ⎛ p exp − p cal ⎞ j j j j ⎟ ⎜ ⎟ + F = ∑ [⎜⎜ ⎟ ⎜ ⎟ σT σp ⎠ j=1 ⎝ ⎝ ⎠ N

⎛ x exp − x cal ⎞2 j,i j,i ⎟ + + ∑ ⎜⎜ ⎟ σ x ,i ⎠ i=1 ⎝ C

⎛ y exp − y cal ⎞2 j,i ⎟ ∑ ⎜⎜ j ,i ⎟] σ y,i i=1 ⎝ ⎠ C

(6)

where N is the number of the experimental data; C is the number of components; σT, σp, σx, and σy are estimated standard deviations for T, P, x, and y, respectively. The regression was carried out using the Aspen Plus V7.2 chemical process simulator. As recommended by Renon and Prausnitz,21 the parameter α which took the nonrandomness of the solution in the NRTL equation was into account was set as 0.3 which is suitable for these polarity liquid mixture. The interaction parameters for the Wilson, NRTL, and UNIQUAC models and the average absolute deviation (AAD) and the percent average relative deviation (ARD %) between the

piexp − pical piexp

1 N

(4) 1313



Article

experimental values and the calculated values are all listed in Table 11. It can be seen from Tables 7 to 10 and Figures 5 to 8 that all of the binary systems exhibit nearly a positive deviation as we

Figure 7. T−x1−y1 diagram for the 1,2-propylene glycol (1) + ethylene glycol (2) system at 10.00 kPa: +, ×, (x1, y1) experimental data in this work; ■, □, (x1, y1) correlated results by the NRTL model; ▲, △, (x1, y1) correlated results by the Wilson model; ●, ○, (x1, y1) correlated results by the UNIQUAC model; , fitted curve by experimental data.

Figure 5. T−x1−y1 diagram for the 1,2-propylene glycol (1) + 1,3butanediol (2) system at 10.00 kPa: +, ×, (x1, y1) experimental data in this work; ■, □, (x1, y1) correlated results by the NRTL model; ▲, △, (x1, y1) correlated results by the Wilson model; ●, ○, (x1, y1) correlated results by the UNIQUAC model; , fitted curve by experimental data.

Figure 8. T−x1−y1 diagram for the 1,2-propylene glycol (1) + 1,2butanediol (2) system at 10.00 kPa: +, ×, (x1, y1) experimental data in this work; ■, □, (x1, y1) correlated results by the NRTL model; ▲, △, (x1, y1) correlated results by the Wilson model; ●, ○, (x1, y1) correlated results by the UNIQUAC model; , fitted curve by experimental data.

Figure 6. T−x1−y1 diagram for the ethylene glycol (1) + 1,3butanediol (2) system at 10.00 kPa: +, ×, (x1, y1) experimental data in this work; ■, □, (x1, y1) correlated results by the NRTL model; ▲, △, (x1, y1) correlated results by the Wilson model; ●, ○, (x1, y1) correlated results by the UNIQUAC model; , fitted curve by experimental data.

azeotropic distillation or extractive distillation maybe can be used to replace the conventional distillation to increase their relative volatility. The AAD of the vapor molar fraction, bubblepoint temperature, and pressure calculated with the correlated parameters are no more than 0.0094, 0.1139 K, and 0.0026 kPa, respectively. The ARD % for the activity coefficients of the measured binary systems are no greater than 3.71 and 2.73, respectively. As we mentioned before, from the view of industrial application, the Wilson, NRTL, and UNIQUAC models can be used to calculate the VLE of these binary systems even though the purity of the 1,2-butanediol and 1,3-

had mentioned before. The differences among the vapor phase mole fraction and boiling temperature calculated by the Wilson, NRTL, and UNIQUAC models for the 1,2-propylene glycol (1) + 1,3-butanediol (2), ethylene glycol (1) + 1,3-butanediol (2), 1,2-propylene glycol (1) + ethylene glycol (2), and 1,2propylene glycol (1) + 1,2-butanediol (2) are indistinct, indicating that their relative volatility is very low and the 1314



Article

(14) Kamihama, N.; Matsuda, H.; Kurihara, K.; Tochigi, K.; Oba, S. Isobaric Vapor-liquid Equilibria for Ethanol + Water + Ethylene Glycol and Its Constituent Three Binary Systems. J. Chem. Eng. Data 2012, 57, 339−344. (15) Huang, G. Q.; Lv, C. C. Isobaric Vapor-Liquid Equilibria for Binary Systems Comprising 1-Chloro-2-ethylhexane, 2-Ethyl-1-hexanol, p-Xylene and N-methyl pyrrolidone (NMP) at 40.0 kPa. J. Chem. Eng. Data 2013, 58, 279−284. (16) Yamada, T.; Gunn, R. D. Saturated Liquid Molar Volumes. The Rackett Equation. J. Chem. Eng. Data 1973, 18, 234. (17) Smith, J. M.; Van, N. H. C.; Abbott, M. M. Introduction to Chemical Engineering Thermodynamics, 6th ed.; McGraw-Hill: New York, 2001. (18) Herington, E. Tests for the Consistency of Experimental Isobaric Vapor-Liquid Equilibrium Data. J. Inst. Petrol. 1951, 37, 457− 470. (19) Van Ness, H. C.; Byer, S. M.; Gibbs, R. E. Vapor-liquid equilibrium: Part I. An appraisal of data reduction methods. AIChE J. 1973, 19, 238−244. (20) Prausnitz, J. M.; Anderson, F.; Grens, E.; Eckert, C.; Hsieh, R.; O’Connell, J. Computer Calculations for Multicomponent Vapor-Liquid and Liquid-Liquid Equilibria; Prentice-Hall: Englewood Cliffs, NJ, 1980. (21) Renon, H.; Prausnitz, J. M. Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures. AIChE J. 1968, 14, 135−144.

butanediol is not high enough for the strict thermodynamic data.

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CONCLUSIONS The isobaric VLE data of the binary systems ethylene glycol + 1,2-propylene glycol, ethylene glycol + 1,3-butanediol, 1,2propylene glycol + 1,2-butanediol, and 1,2-propylene glycol + 1,3-butanediol were measured at 10.00 kPa. The experimental data were checked with the Herington consistency test and the Van Ness test, which showed good thermodynamic consistency. The Wilson, NRTL, and UNIQUAC activity coefficient models were used to correlate the experimental data. The results have shown that all of the models agree well with the experimental data.

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AUTHOR INFORMATION

Corresponding Author

*Telephone no.: 86-22-27400199. Fax no.: 86-22-27400199. Email: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Sun, L.; Fu, J.-Y.; Li, W.; Zhan, X.-L.; Xiao, W.-D. Binary vaporliquid equilibrium of methyl glycolate and ethylane glycol. Fluid Phase Equilib. 2006, 09 (250), 33−36. (2) Willlian, J. B.; Charleston, W. V. Ethylene glycol by catalytic hydrogenation. U.S. Patent US 4,628,128, 1986. (3) Amedeo, L.; Dino, M.; Francesco, P. Vapor-liquid equilibria for mixtures of ethylene glycol, propylene glycol, and water between 98 and 122 °C. J. Chem. Eng. Jpn. 1996, 29, 449−455. (4) Wilson, G. M. Vapor-liquid equilibrium. XI. A New Expression for the Excess Free Energy of Mixing. J. Am. Chem. Soc. 1964, 86, 127−130. (5) Renon, H.; Prausnitz, J. M. Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures. AIChE J. 1968, 14, 135− 144. (6) Abrams, D. S.; Prausnitz, J. M. Statistical Thermodynamics of Liquid mixtures: a New Expression for the Partial Excess Gibbs Energy of Partly or Completely Miscible Systems. AIChE J. 1975, 21, 116− 128. (7) Daubert, T. E.; Damer, R. P. Physical and thermodynamic properties of pure chemicals data compilation; Hemisphere Publishing Co: New York, 1989. (8) Osvaldo, C. F.; Proust, P.; Rasmussen, P. Vapor-liquid equilibria for Glycol Ether + Water Systems. J. Chem. Eng. Data 1993, 38, 128− 131. (9) Dean, J. A. Lange’s Handbook of Chemistry; McGraw-Hill: New York, 2003. (10) Mamedov, M. K.; Piraliev, A. G.; Rasulova, R. A. Synthesis of bicyclo[2.2.1] heptyl monoethers of aliphatic diols. Russ. J. Appl. Chem. 2009, 82, 518−520 ; 524−526.. (11) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A. Vapor Pressure of Acetophenone, (±)-1,3-Butanediol, Diethylene Glycol Monopropyl Ether, 1,3-Dimethyladamantane, 2-Ethoxyethyl Acetate, Ethyl Octyl Sulfide, and Pentyl Acetate. J. Chem. Eng. Data 1996, 41, 1255−1268. (12) VonNiederhausern, D. M.; Wilson, L. C.; Giles, N. F.; Wilson, G. M. Critical-Point Measurements for Nine Compounds by a Flow Method. J. Chem. Eng. Data 2000, 45, 154−156. (13) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A. Measurements of Vapor Pressure, Heat Capacity, and Density along the Saturation Line for ε-Caporlactam, Pyrazine, 1,2-propanediol, Trirthylene Glycol, Phenyl Acetylene, and Diphenyl Acetylene. J. Chem. Eng. Data 2002, 47, 689−699. 1315


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