Isobaric VaporâLiquid Equilibrium for the Binary System - American

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Isobaric Vapor−Liquid Equilibrium for the Binary System (Ethane1,2-diol + Butan-1,2-diol) at (20, 30, and 40) kPa Zhen Yang, Shuqian Xia,* Qiaoyan Shang, Fangyou Yan, and Peisheng Ma School of Chemical Engineering and Technology, Tianjin University; Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China ABSTRACT: The isobaric vapor−liquid equilibrium (VLE) data were measured for the binary system (ethane-1,2-diol + butan-1,2-diol) at (20, 30, and 40) kPa using a modified dynamic recirculating still. The thermodynamic consistency of the experimental data was confirmed using the Herington and van Ness semiempirical method. The Wilson and universal quasichemical (UNIQUAC) models were used to correlate the activity coefficients with the liquid-phase composition. The average absolute deviation of the bubble-point temperature and vapor molar fraction for all of the systems obtained from the Wilson and UNIQUAC models are less than 0.18 K and 0.0011, respectively. Furthermore, the binary system (ethane-1,2-diol + butan-1,2-diol) exhibited azeotropic behavior. In addition, the data were calculated using the UNIFAC (Do) model (modified UNIFAC model) in which ethane-1,2-diol was treated as two groups (−CH2OH), and butan-1,2-diol was split to four groups (−CH2OH, −CHOH, −CH2, and −CH3). The new group-interaction parameter for CH2−CH2OH was obtained and used to estimate the VLE data for the binary system (butan-2-ol + butan-1-ol) at 101.3 kPa. The results are consistent with those of the literature data.

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INTRODUCTION Ethane-1,2-diol, commonly known as ethylene glycol (EG), is an important organic chemical. It is not only an important raw material in the production of poly(ethylene terephthalate) (PET), alkyd resins, polyester fibers, and polyester plastics, but also a commonly used high-boiling solvent. In the recent years, with the rapid development of China’s polyester industry, the consumption of EG is increasing. Because of the increase in oil price, coal is used as the raw material to produce chemicals, which has become an important direction for energy development. Moreover, it costs less to produce polybasic alcohol from coal; therefore, developing countries have begun to focus on the strategy.1 The production of EG from synthesis gas has received much attention. Although EG is obtained as the main product of the process, propane-1,2-diol and butan-1,2-diol byproducts are also produced due to excessive hydrogenation. However, butan1,2-diol and EG have similar boiling points; therefore, they cannot be separated well by the simple conventional distillation process. The vapor−liquid equilibrium (VLE) data provides the basic thermodynamic data and very important for the design of a purification process such as distillation column design. For propane-1,2-diol and butan-1,2-diol, only the saturated vapor pressure of the pure substances2 and the VLE data for the binary system (EG + butan-1,2-diol) at atmosphere pressure3 are published; the VLE data for the binary system at low pressure have not been reported yet. In this study, the isobaric VLE data for the binary system (EG + butan-1,2-diol) at (40, 30, and 20) kPa were determined. Then, the Wilson4 and universal quasichemical (UNIQUAC)5 models were used to correlate the experimental data with the liquid© 2014 American Chemical Society

phase composition. All of the experimental data were confirmed by the Herington6 and van Ness semiempirical methods. The results indicated a good thermodynamic consistency. Moreover, the UNIFAC (Do) model7 was used to correlate and estimate the VLE data for the mixtures. EG was treated as two groups (−CH2OH), and butan-1,2-diol was split to four groups (−CH2OH, −CHOH, −CH2, and −CH3). The new groupinteraction parameters for CH2−CH2OH were regressed from the VLE data. The phase equilibrium data for the binary systems (butan-2-ol + butan-1-ol) at 101.3 kPa were predicted by the UNIFAC (Do) model with this group-interaction parameter; the results are consistent with those of the literature data.

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EXPERIMENTAL SECTION Materials. EG (≥ 0.999, mass fraction) and butan-1,2-diol (≥ 0.98, mass fraction) were obtained from J&K Chemical Co., Ltd., China and used as received without further purification because no significant impurity was found by the analyses using a FL9500 gas chromatograph (GC) equipped with a thermal conductivity detector (TCD) (FuLi Analytical Instruments Co., Ltd.). The specifications of the chemicals have been given in Table 1. The physical properties8−13 of the two pure chemicals are listed in Table 2. Apparatus and Procedures. The modified dynamic recirculation still used in the VLE experiment is shown in Figure Received: November 9, 2013 Accepted: February 18, 2014 Published: February 26, 2014 825

dx.doi.org/10.1021/je400980w | J. Chem. Eng. Data 2014, 59, 825−831

Journal of Chemical & Engineering Data

Article

pressure was 0.05 kPa in a two-step automatic system; the condensed fluid was water. The compositions of the liquid and vapor phases were analyzed; furthermore, the vapor phase was analyzed when the gas condensed to liquid. All of the samples were analyzed using the same GC-9500 GC equipped with a flame ionization detector (FID). An OV-101 capillary column (30 m × 0.25 mm × 0.50 μm) was used. High-purity nitrogen (mass fraction purity 0.99999) was used as the carrier gas. The FL9500 GC workstation was used as the detector. The initial oven temperature was maintained at 363.15 K for 4 min and increased to 393.15 K by a rate of 278.15 K·min−1, then raised to 493.15 K by a rate of 303.15 K min−1 and held at 493.15 K for 2 min. The total time was ∼20 min after the oven temperature returned to the initial temperature. The injection and detector temperatures were both 523.15 K. The volume of the sample was 0.02 μL. The analysis of each sample was carried at least three times to guarantee the accuracy of the result, and the uncertainties in mole fractions were ± 0.001. The experimental system’s reliability has been tested in our previous work.14 Before the experiments of the binary system were carried out, the vapor pressures of EG and butan-1,2-diol were measured using the above-mentioned apparatus, and the experimental vapor pressures and boiling temperatures are shown in Figure 2.

Table 1. Specifications of the Chemicals Used chemical name EG (ethane-1,2diol) butan-1,2-diol a

source

mass fraction purity

analysis method

≥0.999

GCa

≥0.98

GCa

J&K Chemical Co., Ltd. J&K Chemical Co., Ltd.

Gas−liquid chromatography.

Table 2. Property Values of Molar Mass M, Refractive Indices n20, Atmospheric Boiling Temperature Tb, Critical Temperature Tc, Critical Pressure Pc, Critical Volume Vc, Density ρ, Critical Compression Factor Zc, and Acentric Factor ω of the Pure Compound EG and Butan-1,2-diol

a

properties

EG

M/g·mol−1 n20/D Tb/K (101.3 kPa) Tc/K Pc/MPa Vc/cm3·mol−1 ρ/kg·m−3(298.15 K) Zc ω

62.068a 1.4308,f 1.4310g 470.45a 645a 7.53a 191a 1134.7,b 1135.1g 0.262c 0.507c b

butan-1,2-diol 90.1222a 1.4383g 469.575d 680e 5.21e 1020.5,d 1020.1g 0.6303e c

Obtained from ref 8. Obtained from ref 9. Obtained from ref 10. Obtained from ref 11. eObtained from ref 12. fObtained from ref 13. g Obtained from experiment. , no data found in the literature. d

1. First, pure component 1 was added to the recirculation still, its temperature was measured, and then the other component was

Figure 2. Experimental saturation pressure p against temperature T of EG (w = 0.999) and butan-1,2-diol (w = 0.98) comparing with the literature values computed by the Antoine equation ln(P/kPa) = A + B/ (T/K) + C ln T + D·TE, respectively. ■, experimental vapor pressure of EG; ---, the literature values of EG computed by the Antoine equation; red ○, experimental vapor pressure of butan-1,2-diol; red , the literature values of butan-1,2-diol computed by the Antoine equation.

Figure 1. VLE experimental device. 1, heating column; 2, liquid sampling connection; 3, precise mercury thermometer; 4, condenser; 5, condensate; 6, contact with pressure-controlling devices; 7, vapor sampling connection.

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RESULTS AND DISCUSSION Pure Components. The vapor pressures of EG and butan1,2-diol are reported. The parameters of Antoine equation for EG and butan-1,2-diol were selected from the literature,15 as shown in Table 3. The vapor pressures were calculated by using the Antoine equation using the parameters, and the results were compared with the experimental data, as shown in Figure 2. The perspective of EG compared with butan-1,2-diol drawn in Figure 2 also indicates that it is hard to separate these two chemicals by convention distillation. The average deviation of the measured data in this study compared to the calculation values by the Antoine equation in

added to the still. The continuous dynamic circulation between the vapor and the liquid phases lead to intimate contact between the phases and ensures that the equilibrium can be attained rapidly. The equilibrium was presumed to be attained when the vapor temperature reaches a relatively constant value for 60 min, and the GC baseline become stabilized for 30 min in each experiment. The temperature was measured using a mercury thermometer, and the uncertainty was 0.02 K. An U-shaped differential manometer was used to determine the pressure of the system; the fluctuation was held within 0.03 kPa. The uncertainty of the 826



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Table 3. Antoine Parametersa (A, B, C, D, E) and Their Temperature Scope T Obtained from Literature

a

compounds

A

B

C

D

E

scope T/K

EGb butan-1,2-diolb

84.09 103.28

−10411 −11548

−8.1976 −10.925

1.65·10−18 4.26·10−18

6 6

260.15 to 720 220.00 to 680

ln(P/kPa) = A + B/(T/K) + C ln T + D·TE. bTaken from ref 15.

the literature15 is Δp = ∑Ni=1|(pi,exp − pi,cal)/pi,exp|/N = 0.0269, where N is the data point number. The results are consistent with those of the literature data.15 Therefore, the results of the experiments in this study are reliable. Binary Mixtures. The experimental VLE data are shown in Table 4. The plots of y−x at 40 kPa and T−x−y at three pressures of EG and butan-1,2-diol are shown in Figures 3 to 6. The experimental data were confirmed by the Herington6 method based on the Gibbs−Duhem theorem. Herington suggests that the experimental data are thermodynamically consistent if (D − J) < 10. (A+) − (A−) ·100 (A+) + (A−)

D=

Table 4. Experimental (Vapor + Liquid) Equilibrium Data for Temperature T, Liquid-Phase Mole Fraction x, and Gas-Phase Mole Fraction y, for the Binary System Ethane-1,2-diol (1) + Butan-1,2-diol (2) at (40, 30, and 20) kPaa no.

(1)

The values of “A+” and “A−”are obtained from ln(γ1/γ2) − x1 plot. J=

(Tmax − Tmin) ·150 Tmin

(2)

where Tmax and Tmin are the maximum and minimum temperatures in this study, respectively. The values of (D−J) for EG and butan-1,2-diol at (40, 30, and 20) kPa are shown in Table 5, indicating that the experimental data can meet the criteria and are verified to be thermodynamically consistent. The measured data were also confirmed using the van Ness method that is used to test the capability of a model.16 The model of mathematical activity coefficient shows that the experimental data can be reproduced accurately if they pass the test, and the equation is expressed as follows: Δy =

1 N

N

∑ Δyi = i=1

1 N

N

∑ 100|yiexp − yi cal | i=1

(3)

where N is the measured data point number; the superscript “exp” shows the measured data; and the superscript “cal” shows the values obtained using the thermodynamic model. If Δ y is < 1, the data set passes the test, and then the measured points can be considered as thermodynamically consistent. According to this calculation method, the Δy of the system was 0.11 that proved that the measured data in this study are reliable. The vapor phase was presumed to behave as an ideal gas at a low pressure. Then, the VLE equation can be expressed as eq 4. pyi = pi s γχ i i

(4) s

where p, xi, yi, and p i are the total pressure, liquid-phase mole fraction, vapor-phase mole fraction, and saturated pressure of component i, respectively. γi obtained by using eq 4 is the liquidphase activity coefficient of component i. The vapor pressures of the pure components were obtained by using the Antoine equation with the parameters listed in Table 3. The values of γi, which are listed in Table 4, are very close to 1, and most of γi values are > 1. Thus, the binary system exhibits a slight positive deviation from the Raoult’s law, indicating that the resemblance between the different molecules and the interaction forces between same molecules are slightly larger than the

a

827

T/K

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

440.15 439.95 439.47 438.95 438.45 438.20 437.70 437.60 437.50 437.55 437.70 438.00 438.20 438.45 438.65 439.80

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

431.49 430.55 430.25 430.05 429.97 429.7 429.75 429.85 429.95 430.07 430.25 430.35 430.65 431.1 432.29

1 2 3 4 5 6 7 8 9 10 11 12 13 14

420.46 419.48 419.38 419.23 418.78 418.28 417.68 417.78 418.03 418.21 418.48 418.68 419.18 420.74

x1

y1

γ1

EG (1) + Butan-1,2-diol (2) at 40 kPa 1.0000 1.0000 1.0000 0.9752 0.9645 1.0083 0.9083 0.8786 1.0030 0.8223 0.7835 1.0064 0.7377 0.7036 1.0254 0.6928 0.6643 1.0401 0.5824 0.5676 1.0761 0.5434 0.5353 1.0918 0.4995 0.4995 1.1122 0.4819 0.4843 1.1157 0.4678 0.4705 1.1105 0.4266 0.4340 1.1114 0.3991 0.4094 1.1129 0.3484 0.3664 1.1308 0.3022 0.3256 1.1503 0.0000 0.0000 EG (1) + Butan-1,2-diol (2) at 30 kPa 0.0000 0.0000 0.1663 0.1881 1.2602 0.2803 0.3054 1.2276 0.3721 0.3855 1.1760 0.4056 0.4161 1.1680 0.4919 0.4899 1.1454 0.5365 0.5302 1.1345 0.5636 0.553 1.1222 0.6224 0.6018 1.1017 0.6442 0.6203 1.0922 0.7095 0.677 1.0751 0.7498 0.7189 1.0762 0.8039 0.7698 1.0629 0.8687 0.8371 1.0519 1.0000 1.0000 1.0000 EG (1) + Butan-1,2-diol (2) at 20 kPa 0.0000 0.0000 0.2228 0.2502 1.2773 0.2596 0.2858 1.2572 0.2914 0.3197 1.2603 0.3754 0.3944 1.2288 0.4363 0.4440 1.2142 0.4650 0.4650 1.2222 0.4909 0.4871 1.2079 0.5313 0.5260 1.1932 0.5734 0.5683 1.1859 0.6418 0.6224 1.1479 0.6770 0.6515 1.1300 0.7819 0.7480 1.1012 1.0000 1.0000 1.0000

γ2

1.4718 1.3885 1.3016 1.2290 1.1993 1.1570 1.1410 1.1252 1.1180 1.1117 1.0911 1.0785 1.0576 1.0437 1.0000 1.0000 1.0593 1.0617 1.0846 1.0920 1.1273 1.1360 1.1437 1.1731 1.1819 1.2231 1.2313 1.2722 1.3222

1.0000 1.0725 1.0766 1.0780 1.1084 1.1505 1.1949 1.1990 1.1915 1.1837 1.2197 1.2384 1.2999

Standard uncertainties: u(T) = 0.02 K, and u(x1) = u(y1) = 0.002.



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Figure 5. T−x−y diagram for the EG (1) and butan-1,2-diol (2) system at 30 kPa. ■, experimental liquid-phase mole fraction x1; red ●, experimental vapor−phase mole fraction y1; , liquid-phase mole fraction x1 calculated by the Wilson equation; red ---, vapor-phase mole fraction y1 calculated by the Wilson equation.

Figure 3. Experimental vapor−liquid (y1−x1) equilibrium data for the binary system of EG (1) + butan-1,2-diol (2) at 40 kPa.



interaction forces between different ones. These two alcohols have similar physical properties; therefore, they may exhibit similar behavior in vapor−liquid phase equilibrium at a low pressure. Because of similar boiling points, the vapor and liquid lines of the two alcohols are very close, and the azeotropic point was present at the three pressures. The VLE data and azeotropic point at atmospheric pressure are also available in ref 3. However, the vapor and liquid lines are very close at the isobaric pressure when x1 < 0.4700, indicating that it is difficult to separate the two chemicals in that case. However, the distance between the vapor and liquid lines are larger at a low pressure when x1 < 0.4700, indicating that they cannot be separated. The composition and boiling point at the azeotropic point are shown in Table 6. The VLE behavior observed in this study are different from the system (EG + butan-1,3-diol) reported in ref 16. The phenomenon is caused by the molecular structural difference between butan-1,2-diol and butan-1,3-diol. The two hydroxyl groups in EG and butan-1,2-diol are adjacent, whereas they are separated by one carbon atom in butan-1,3-diol. Because of the rule of similarity, the solubility between EG and butan-1,2-diol is

Table 5. Results of (D−J) for the System EG + Butan-1,2-diol at (40, 30, and 20) kPa experimental pressure/kPa

40

30

20

D−J

−14.73

−3.67

6.02

Table 6. Azeotropic Compositions x1azo and Temperatures Tazo of the System EG (1) + Butan-1,2-diol (2) at (40, 30, and 20) kPa P/kPa

x1azo

Tazo/K

40 30 20

0.5013 0.5221 0.4809

437.55 429.74 417.68

better than EG and butan-1,3-diol. Further, the intermolecular interaction between EG and butan-1,2-diol should be larger than that between EG and butan-1,3-diol. The deviation value of γ1 to 828



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1 in the system (EG + butan-1,2-diol) is larger than that of the system (EG + butan-1,3-diol) at a low pressure, which is due to the larger polarity of butan-1,2-diol compared to butan-1,3-diol. Simultaneously, the difference in the boiling points between EG and butan-1,2-diol is < 1 K; however, the difference in the boiling point between EG and butan-1,3-diol is > 10 K at isobaric pressure. The viscosity of butan-1,3-diol is much greater than the similar viscosity between EG and butan-1,2-diol. The Wilson and UNIQUAC equations were used to correlate the experimental data of the binary systems. The objective function OF for the calculation is expressed as follows: ⎧ cal ⎪ T − Tk exp 2 OF = ∑ ⎨( k ) + ⎪ σTk k=1 ⎩ N

χ cal − χi exp 2 ⎫ ⎪ )⎬ ∑( i ⎪ σχik ⎭ i=1

Table 9. Deviations of Temperature and Vapor Mole Fraction Changesa (ΔT, Δy1) between the Calculated and Measured Values Obtained by the Wilson and UNIQUAC Equations of the System EG (1) + Butan-1,2-diol (2) at (40, 30, and 20) kPa Wilson p/kPa 40 30 20

2

r

q

2.4087 3.7568

2.248 3.324

ΔT/K

Δy1

ΔT/K

0.12 0.17 0.15 0.19 0.28 0.39

0.0009 0.0020 0.0012 0.0022 0.0016 0.0038

0.12 0.17 0.15 0.20 0.28 0.38

ΔT = |Tcal − Texp|, Δy1 = |y1,cal − y1,exp|; aver, the average absolute value; max, the maximum absolute value.

The VLE data for the systems were also calculated by using the UNIFAC (Do) model. The interaction between the groups in UNIFAC (Do) model is expressed as follows: ⎛ a + b T + c T2 ⎞ nm nm ⎟ φnm = exp⎜⎜ − nm T ⎠ ⎝

(6)

where cnm = cmn = 0; T is the equilibrium temperature, K; ψnm is the interaction energy between the groups; and anm and bnm are the interaction parameters. In this study, two group division methods were used for EG; it was treated as one group (DOH) or two groups (CH2OH). The groups for the compounds are listed in Table 10. All of the

Table 7. Values of r and q of the Compounds of EG and Butan1,2-diol in the UNIQUAC Model15 compound

Δy1 0.0008 0.0019 0.0012 0.0022 0.0015 0.0036

a

(5)

where N is the measured data number at each pressure k; i is the alcohol component in the mixture; σ is the estimated standard deviation of T and x; the superscript “cal” shows the calculated values; and the superscript “exp” shows the experimental data. The values of r and q are the molecular volume and area parameters, respectively, of the compounds in the UNIQUAC model, as listed in Table 7. The parameters of the Wilson and

EG butan-1,2-diol

aver max aver max aver max

UNIQUAC

Table 10. UNIFAC (Do) Group Type and Group Number of EG, Butan-1,2-diol, Butan-2-ol, and Butan-1-ol

UNIQUAC equations for EG and butan-1,2-diol were correlated to the experimental VLE data. The regression was carried out by using the Aspen Plus V 7.0 chemical process simulator. The interaction parameters of the Wilson and UNIQUAC models, the average absolute deviation (AAD) of temperature T, and mole fraction in vapor phase y, the percent average relative deviation (ARD %) of the activity coefficient between the experimental and calculated values are listed in Table 8. The AAD of the bubble-point temperature and vapor molar fraction obtained using the correlated parameters are less than 0.18 K and 0.0011, respectively. Therefore, both of the models can calculate the experimental data very well. The deviations in the vapor-phase mole fraction Δy1 and temperature change ΔT for the binary systems are listed in Table 9. The value of the maximum absolute deviation of temperature for all of the systems correlated to the Wilson and UNIQUAC models was 0.39 K, and all of the values the average absolute deviations of temperature were below 0.28 K. The values of the maximum and average absolute deviations of the vapor-phase compositions are 0.0038 and 0.0016, respectively.

compound

group type

group no.

EGa butan-1,2-diola

CH2OH CH2OH CHOH CH2 CH3 DOH CH2 OH CH3 CH CHOH CH2 CH3 CH2OH CH2 CH3

2 1 1 1 1 1 2 2 1 1 1 1 2 1 2 1

EGb butan-1,2-diolb

butan-2-ol

butan-1-ol

a

First group division method. bSecond group division method.

Table 8. Parameters of Molecular Interaction Energy (A12, A21) and Average Absolute Deviation (AAD) of Temperature T and Mole Fraction in the Vapor Phase y, the Percent Average Relative Deviation (ARD %) of the Activity Coefficient (γ1, γ2) between the Experimental and the Calculated Values Obtained by the Wilson and UNIQUAC Equations for the System EG (1) + Butan-1,2diol (2) at (40, 30, and 20) kPa system

A12a

A21a

AAD(T)/Kb

AAD(y)b

ARD %(γ1)c

ARD %(γ2)c

Wilson UNIQUAC

−392.80 −94.87

1726.67 640.98

0.18 0.17

0.0011 0.0011

4.320 4.300

4.700 4.700

The interaction parameters for various models: Wilson, Aij = (λij − λii)/(J·mol−1); UNIQUAC, Aij = (Uij − Ujj)/(J·mol−1). bAAD (y) = (1/N)∑Ni=1| yiexp − yical| (N, number of data points). cARD % (γi) = (100/N)∑Nj=1 (|γi,jexp − γi,jcal|/γi,jexp) (N, number of data points).

a

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parameters Rk and Qk are listed in Table 11. The CH2OH group parameters were obtained from the modified UNIFAC (Do) group parameter table,7 and the others were obtained from the UNIFAC (Do) group table.17

Table 13. Deviations of Temperature (ΔT) and Vapor Mole Fractions Change (Δy1) between the Correlated Results by the UNIFAC (Do) Model and the Experimental Data of Division Method I and Division Method II for the System EG (1) + Butan-1,2-diol (2) at (40, 30, and 20) kPa

Table 11. Volume Parameters (Rk) and Area Parameters (Qk) of Groups main group

subgroup

Rk

Qk

CH27

CH CH2 CH3 OH DOH CH2OH CHOH

0.6325 0.6325 0.6325 1.2302 2.0880 0.6311 0.4037

0.3554 0.7081 1.0608 0.8927 2.4000 0.7658 0.5378

OH7 DOH7 CH2OH16

division method I p/kPa 40 30 20

The calculation procedure using the UNIFAC (Do) model is described as follows: First, for obtaining the interaction parameters of group CH2−CH2OH, the UNIFAC (Do) model was used to correlate the experimental VLE data. The results are shown in Table 11. Simultaneously, the interaction parameters for CH2−OH, CH2−DOH, and OH−DOH were obtained from ref 7 and also listed in Table 12. The deviations between the results and the experimental data are shown in Table 13. The data in Table 13 indicate that the first group division is preferred. Second, the reliability of the interaction parameters obtained from the experimental values should be checked. The UNIFAC (Do) model and the obtained parameters (CH2−CH2OH) as listed in Table 12 were used to estimate the vapor−liquid phase equilibrium data of the binary system (butan-2-ol (1) + butan-1ol (2)) at 101.3 kPa, which were not used in the correlation. The group division method of the binary system for butan-2-ol and butan-1-ol is also shown in Table 10. The predicted T−x−y data for the binary systems were compared with the literature18 VLE data. All the deviations of the predicted results from the literature experimental data are below 0.38 K and 0.0183 for the temperature and vapor-phase compositions, respectively. The comparisons are shown in Figure 7, indicating that the results by the UNIFAC (Do) model agree well with the experimental values. The results show that the group-interaction parameters in Table 12 are reliable and can be used to estimate the VLE data for other systems containing the CH2−CH2OH group.

aver max aver max aver max

division method II

Δy1

ΔT/K

Δy1

ΔT/K

0.0007 0.0018 0.0010 0.0023 0.0014 0.0040

0.12 0.16 0.14 0.16 0.29 0.40

0.0068 0.0097 0.0069 0.0103 0.0062 0.0102

0.20 0.34 0.17 0.23 0.29 0.34

Figure 7. Experimental and calculated temperature T against mole fraction (x1, y1) for the system butan-2-ol (1) + butan-1-ol (2) at 101.3 kPa. ■, literature experimental liquid-phase mole fraction x1; red ●, literature experimental vapor-phase mole fraction y1; , liquid-phase mole fraction x1 calculated by the UNIFAC equation; red ---, vaporphase mole fraction x1 calculated by the UNIFAC equation.

thermodynamic consistency using the Herington and van Ness semiempirical methods. The Wilson and UNIQUAC models were used to correlate the experimental data. The AAD of the bubble-point temperature and vapor molar fraction obtained by using the Wilson and UNIQUAC equations were less than 0.18 K and 0.0011, respectively. The results show that both the models can calculate the experimental data well. Further, the acquired group-parameter fitted by the Dortmund (modified UNIFAC) model from the experimental data demonstrated that the Dortmund model can be applied to predict the VLE for the alcohol systems. Furthermore, the binary system (EG + butan1,2-diol) exhibited azeotropic behavior. The composition and boiling point at the azeotropic point were as follows: 0.5013 and

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CONCLUSIONS The isobaric VLE data of the binary system (EG (1) + butan-1,2diol (2)) were investigated at three different pressures: (20, 30, and 40) kPa. The vapor pressures of EG and butan-1,2-diol were measured and compared with the values calculated by using the extended Antoine equation. The equilibrium data were tested for

Table 12. Fitting Results of Group-Interaction Parameters (anm, amn, bnm, bmn, cnm, and cmn) of CH2−OH, CH2−DOH, OH−DOH, and CH2−CH2OH n−m

anm/K

CH2−OH CH2−DOH7 OH−DOH7 CH2−CH2OH 7

2777.000 897.700 499.800 −3548.04

bnm −4.674 0.000 −2.410 25.828

cnm/K−1 −2

0.155·10 0.000 0.000 0.000 830

amn/K

bmn

Cmn/K−1

1606.000 28.170 −468.800 574.468

−4.746 0.000 2.421 2.715

0.918·10−3 0.000 0.000 0.000



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437.55 K at 40 kPa; 0.5221 and 429.74 K at 30 kPa; and 0.4809 and 417.68 K at 20 kPa, respectively.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

The Tianjin Natural Science Foundation (Project No. 13JCYBJC19300) provided funding for this work. Notes

The authors declare no competing financial interest.

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REFERENCES

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