Article pubs.acs.org/jced
Vapor−Liquid Equilibrium for Ternary and Binary Mixtures of Tetrahydrofuran, Cyclohexane, and 1,2-Propanediol at 101.3 kPa Zhigang Zhang, Peng Jia, Donghao Huang, Ming Lv, Yan Du, and Wenxiu Li* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang 100142, China ABSTRACT: Vapor−liquid equilibrium (VLE) data of the binary systems tetrahydrofuran + cyclohexane, tetrahydrofuran + 1,2-propanediol, and cyclohexane + 1,2-propanediol were reported at 101.3 kPa, as well as the ternary system tetrahydrofuran + cyclohexane + 1,2-propanediol. The results showed that the 1,2-propanediol was a good solvent which can break the binary azeotrope and effectively improve the relative volatility for the system of tetrahydrofuran and cyclohexane. Then, the equations of nonrandom twoliquid (NRTL), universal quasichemical (UNIQUAC), and Wilson were used to correlate the activity coefficients, and the results indicate that the NRTL model provides the best description of the phase equilibrium data.
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INTRODUCTION Up to now, tetrahydrofuran and cyclohexane are the most widely used as a solvent, polar additive, dilution initiator, structure regulator, and active additive in the synthesis of medicine, copolymer, resin, and rubber. Tetrahydrofuran and cyclohexane are of importance as an organic synthesis assistant; especially tetrahydrofuran has the reputation of an “alcahest”. Tetrahydrofuran and cyclohexane are the main ingredients among medicine and chemical waste liquid. Therefore, recovery of the waste liquid will have been linked to a host of positive effects. However, the separation of tetrahydrofuran and cyclohexane is a specific problem due to a minimum boiling point azeotrope will appear at 338.74 K with the composition of tetrahydrofuran at 93 % (wt %),1 and it is difficult or impossible to separate by conventional distillation, so we choose extractive distillation which is commonly applied in industry to separate close boiling mixtures. In extractive distillation, a third component (solvent or entrainer) is added to the binary mixture to increase the relative volatility of the original mixture.2 In this study, some entrainers have been selected according to the molecular characters of tetrahydrofuran and cyclohexane. 1,2-Propanediol has been chosen as a possible entrainer because the hydrogen bond is formed easily with tetrahydrofuran after the experiment. The vapor−liquid equilibrium (VLE) data for the binary system tetrahydrofuran (1) + cyclohexane (2) were reported by different researchers. Prasad et al.3 measured the isobaric VLE data, while Wu and Sandler,4 Deshpande and Oswal,5,6 Arm and Bankay,7 Cabani et al.,8 and Lepori and Matteoli9 measured the isothermal VLE data. However, the VLE data for the binary systems tetrahydrofuran (1) + cyclohexane (2), tetrahydrofuran (1) + 1,2-propanediol (3), and cyclohexane (2) + 1,2propanediol (3) and the VLE data for the ternary system © 2013 American Chemical Society
tetrahydrofuran (1) + cyclohexane (2) + 1,2-propanediol (3) at 101.3 kPa have not yet been reported. It is significant to measure the VLE data of these systems at atmospheric pressure because of its importance for the separation of tetrahydrofuran and cyclohexane with the entrainer 1,2-propanediol. For the reason above, in this work we measured the VLE data for these systems. In addition the VLE data were correlated by the universal quasichemical (UNIQUAC), Wilson, and nonrandom two-liquid (NRTL) equations.
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EXPERIMENTAL SECTION Chemicals. The specifications of the used chemicals, that is, tetrahydrofuran, cyclohexane, and 1,2-propanediol, which were purchased from Sinopharm Group Co. Ltd., are summarized in Table 1. The purity of the reagents is checked by gas chromatography, and they failed to exhibit any significant impurities. The densities of the pure components were measured at 298.15 K using a vibrating tube density meter (M196028, China), and the refractive indexes were measured at Table 1. Specifications of Chemical Samples chemical name
source
tetrahydrofuran
Sinopharm Group Sinopharm Group Sinopharm Group
cyclohexane 1,2-propanediol
initial mass fraction purity
purification method
0.9950
none
0.9950
none
0.9950
none
Received: May 23, 2013 Accepted: October 15, 2013 Published: October 30, 2013 3054
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Table 2. Density ρ, Refractive Index n3, and Normal Boiling Point T of Pure Components11 ρ/(g·cm−3) (298.15 K)
nD (298.15 K) component a
tetrahydrofuran cyclohexanea 1,2-propanediola a
T/K (101.3 kPa)
exptl
lit.
exptl
lit.
exptl
lit.
1.4061 1.4265 1.4335
1.4040 1.4262 1.4329
0.8886 0.7779 1.0420
0.8892 0.7785 1.0381
339.25 354.01 460.65
339.15 353.87 460.45
Standard uncertainties u are u(ρ) = 0.0002 g·cm−3, u(nD) = 0.0002, and u(T) = 0.05 K.
Table 3. Experimental Vapor Pressures of Tetrahydrofuran, Cyclohexane, and 1,2-Propanediol at Different Temperatures tetrahydrofurana
cyclohexanea
p/kPa
a
1,2-propanediola
p/kPa
p/kPa
T/K
exptl
lit.
Δp/p(%)
T/K
exptl
lit.
Δp/p(%)
T/K
exptl
lit.
Δp/p(%)
290.03 292.45 294.92 297.35 299.83 302.25 304.72 307.15 309.62 312.05 314.57 316.95 319.43 321.85 324.31 326.75 329.21 331.65 334.15 336.55 339.06
14.68 16.28 18.84 20.89 23.05 25.92 28.41 31.35 34.95 38.73 42.19 46.56 50.86 55.60 61.11 66.49 72.47 78.78 85.92 93.33 100.72
14.89 16.67 18.65 20.79 23.17 25.71 28.53 31.55 34.87 38.42 42.40 46.45 51.01 55.79 61.01 66.57 72.58 78.96 85.94 93.11 101.10
1.43 2.40 1.01 0.51 0.54 0.79 0.42 0.63 0.22 0.79 0.49 0.24 0.28 0.33 0.16 0.12 0.14 0.22 0.02 0.24 0.38
290.00 293.19 296.37 299.56 302.74 305.93 309.12 312.30 315.49 318.67 321.86 325.05 328.23 331.42 334.60 337.79 340.98 344.16 347.35 350.53 353.72
8.85 10.50 12.14 13.69 15.76 18.19 20.79 23.78 26.79 30.85 34.27 38.60 43.35 48.95 54.55 60.86 67.63 74.58 82.34 91.27 100.58
8.94 10.39 12.04 13.89 15.97 18.29 20.89 23.79 27.00 30.55 34.48 38.80 43.55 48.75 54.45 60.66 67.42 74.77 82.74 91.37 100.69
1.01 1.03 0.86 1.45 1.27 0.57 0.50 0.02 0.77 0.95 0.60 0.53 0.46 0.41 0.19 0.34 0.30 0.26 0.48 0.11 0.11
390.26 393.53 397.06 400.59 404.12 407.65 411.18 414.71 418.24 421.77 425.30 428.83 432.36 435.89 439.42 442.95 446.48 450.01 453.54 457.07 460.60
6.90 8.30 9.69 11.37 12.67 14.62 17.44 19.97 22.93 26.36 29.70 34.19 38.68 43.90 49.71 56.37 63.53 71.46 80.23 89.60 100.36
7.01 8.13 9.50 11.08 12.87 14.92 17.23 19.86 22.82 26.15 29.89 34.08 38.77 44.00 49.82 56.29 63.46 71.39 80.15 89.81 100.43
1.68 2.11 1.88 2.54 1.61 2.04 1.19 0.56 0.50 0.82 0.63 0.32 0.25 0.23 0.22 0.14 0.11 0.10 0.09 0.23 0.07
Standard uncertainties u are u(T) = 0.15 K and u(p) = 0.3 kPa.
298.15 K using an Abbe refractometer (DR-A1, China). The uncertainties in density and refractive index measurements are 0.01 g·cm−3 and 0.0002, respectively. The purity of components was compared their normal refractive indices, densities, and boiling points with values10 of the corresponding literature as shown in Table 2. Apparatus and Procedure. In the present study, the VLE for the ternary mixture tetrahydrofuran (1) + cyclohexane (2) + 1,2-propanediol (3) and for the binary systems tetrahydrofuran (1) + cyclohexane (2), tetrahydrofuran (1) + 1,2-propanediol (3), and cyclohexane (2) + 1,2-propanediol (3) were measured with an all-glass dynamic recirculating still (NGW, Wertheim, Germany) at 101.3 kPa, which is described by Hunsmann.12 The mixture in the equilibrium still was maintained in the constant boiling temperature for about 30 min; then samples were taken every 20 min, from the vapor and liquid phase of the system, respectively. The samples were taken until the standard deviation of the last five samples was less than 0.0015 for both vapor and liquid phasea to verify the equilibrium state. The sampling process could ensure that the vapor and liquid phases are in equilibrium state after the total sampling process lasted for about 2 h. In each VLE experiment, the pressure was kept at 101.3 ± 0.05 kPa. The system pressure and the temperature were determined by high accuracy pressure controller (MKS, USA) and quartz thermometer (HP model
2804A, USA), respectively. The solutions for VLE measurement were prepared gravimetrically using an electronic balance (AcculabAlcb210.4) with a standard uncertainty of 0.0001 g. The conditions of them were described by Zhang et al.13 Analysis. Compositions of the liquid and condensed vapor were analyzed by an Agilent 7890A gas chromatograph equipped (GC). A flame ionization detector was used together with a 30 m, 0.25 mm i.d., and 0.25 μm capillary column HP-1. The gas chromatography response peaks were integrated using an Agilent Chemstation. Injector, detector, and column temperatures were (472, 553, and 313) K, respectively. Each vapor and liquid composition should make at least three analyses. The standard deviation in the mole fraction was usually less than 0.001.
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RESULTS AND DISCUSSION
Vapor Pressure. The pure component vapor pressures for tetrahydrofuran, cyclohexane, and 1,2-propanediol, P0i , are listed in Table 3, and they were compared with these calculated by the Antoine equation. The Antoine constant parameters14 are listed in Table 4. The measured vapor pressures were correlated using the Antoine equation, and the results shown in Figure 1 demonstrate that the vapor pressure matched well with the Antoine equation. 3055
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Table 4. Antoine’s Coefficients for Pure Components
a
components
A
B
C
tetrahydrofurana cyclohexanea 1,2-propanediola
16.143 15.965 19.594
2782.4 2889.5 5357.1
−46.522 −44.278 −47.543
Table 5. Experimental VLE Data for the Tetrahydrofuran (1) + Cyclohexane (2) System at 101.3 kPaa
Parameters obtained in ref 14.
ln(pi0 /mmHg) = Ai −
Bi T /K + Ci
(1)
T/K
x2
y2
339.15 339.11 339.08 339.05 339.04 339.04 339.07 339.15 339.19 339.35 339.65 339.81 340.15 340.71 341.51 342.44 343.55 345.51 346.42 348.44 351.31 353.83
0.000 0.021 0.043 0.058 0.070 0.081 0.111 0.128 0.158 0.220 0.272 0.309 0.339 0.419 0.500 0.579 0.639 0.732 0.799 0.851 0.944 1.000
0.000 0.023 0.040 0.062 0.070 0.078 0.095 0.125 0.150 0.184 0.201 0.245 0.276 0.319 0.379 0.438 0.499 0.577 0.644 0.729 0.875 1.000
γ1 1.751 1.488 1.712 1.602 1.543 1.370 1.559 1.513 1.326 1.160 1.238 1.257 1.154 1.119 1.084 1.079 1.023 1.016 1.014 1.004 1.003
γ2 0.999 0.998 1.004 0.998 1.002 1.006 1.019 1.002 1.007 1.038 1.079 1.068 1.059 1.113 1.150 1.200 1.204 1.288 1.405 1.356 1.526
a
The uncertainties of composition and temperature, that is,u(p) and u(T), with a 0.95 level of confidence, are listed. The maximum expanded uncertainties of the composition and temperature measurements were below 0.005 mole fraction and 0.06 K. The uncertainty of pressure is 0.3 kPa.
Figure 1. Variation of the pure component vapor pressure with temperature: ●, experimental data for tetrahydrofuran; ▲, experimental data for cyclohexane; ■, experimental data for 1,2-propanediol. The solid line was calculated from the Antoine equation.
Table 6. Experimental VLE Data for Tetrahydrofuran (1) + 1,2-Propanediol (3) System at 101.3 kPaa
Binary Systems. The VLE data of tetrahydrofuran (1) + cyclohexane (2), tetrahydrofuran (1) + 1,2-propanediol (3), and cyclohexane (2) + 1,2-propanediol (3) are listed in Tables 5 to 7 and plotted in Figures 2 to 4. The results of test measurements for the tetrahydrofuran (1) + cyclohexane (2) system at 101.3 kPa were found to be in good agreement with the result of Wang.15 All of the VLE data were correlated by the equations of NRTL, Wilson, and UNIQUAC. The activity coefficient γ of pure liquid i was calculated with the activity coefficient equation: γi =
ϕiPyi Pi0xiϕis
exp[υiL(P − Pi0)/RT ]
(2)
where yi and xi are the vapor mole fraction and liquid mole fraction, ϕi and ϕsi are the vapor-phase fugacity coefficient and vapor-phase fugacity coefficient at saturation, P0i are the pure component vapor pressures, νiL16 are the liquid molar volumes for component i. Vapor-phase fugacity coefficients, ϕi, ϕsi , were calculated from the Soave−Redlich−Kwong (SRK) equation of state,17 where the binary interaction parameter, kij, was set to 0. According to the activity coefficients exhibited in Tables 6 and 7, the tetrahydrofuran (1) + 1,2-propanediol (3) system presents positive deviations from ideal behavior, and the cyclohexane (2) + 1,2-propanediol (3) system presents a minor deviation from ideal behavior. The thermodynamic consistency of the binary experimental data had been passed by the method of Fredenslund18 test and Herington19 test. The details and statistics of pertinent
T/K
x1
y1
460.87 454.04 449.32 444.75 440.35 435.13 431.10 424.27 420.18 410.83 403.69 389.53 386.94 372.07 368.31 363.71 353.10 349.31 344.63 342.08 340.39 339.15
0.000 0.011 0.022 0.029 0.040 0.051 0.060 0.071 0.090 0.111 0.161 0.212 0.252 0.343 0.403 0.505 0.653 0.688 0.788 0.895 0.953 1.000
0.000 0.233 0.357 0.457 0.545 0.601 0.667 0.738 0.799 0.853 0.906 0.948 0.958 0.979 0.985 0.990 0.992 0.993 0.996 0.998 0.999 1.000
γ1 1.450 1.203 1.265 1.182 1.124 1.143 1.218 1.128 1.182 1.008 1.105 0.999 1.090 1.031 0.938 0.984 1.048 1.060 1.014 1.006 0.999
γ3 1.000 0.965 0.955 0.947 0.933 0.995 0.969 0.994 0.910 0.986 0.898 0.986 0.945 1.109 1.058 1.085 2.230 2.704 3.008 3.550 4.404
a
The uncertainties of composition and temperature, that is, u(p) and u(T), with a 0.95 level of confidence, are listed. The maximum expanded uncertainties of the composition and temperature measurements were below 0.007 mole fraction and 1.50 K. The uncertainty of pressure is 0.3 kPa.
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Table 7. Experimental VLE Data for Cyclohexane (2) + 1,2Propanediol (3)System at 101.3 kPaa T/K
x2
y2
460.87 455.62 449.62 443.81 438.34 433.20 428.39 423.92 418.76 414.89 411.30 406.37 401.93 396.66 390.92 385.95 380.78 374.92 369.96 363.75 358.62 353.83
0.000 0.019 0.041 0.062 0.083 0.101 0.124 0.141 0.161 0.181 0.202 0.232 0.262 0.303 0.353 0.478 0.564 0.645 0.712 0.858 0.915 1.000
0.000 0.115 0.222 0.318 0.385 0.471 0.541 0.632 0.700 0.741 0.789 0.809 0.848 0.890 0.925 0.957 0.976 0.985 0.990 0.996 0.998 1.000
γ2 0.603 0.598 0.629 0.628 0.696 0.715 0.802 0.864 0.882 0.908 0.903 0.925 0.947 0.968 0.835 0.822 0.844 0.878 0.871 0.949 1.003
γ3 1.000 1.066 1.166 0.998 0.967 0.975 0.953 0.876 0.885 0.785 0.802 0.823 0.835 0.782 0.726 0.736 0.689 0.697 0.589 0.509 0.567
Figure 3. Experimental VLE data for the tetrahydrofuran (1) + 1,2propanediol (3) system at 101.3 kPa: ●, experimental data; , calculated by the NRTL equation; ---, calculated by the Wilson equation; ···, calculated by the UNIQUAC equation. The equation parameters of NRTL, Wilson, and UNIQUAC are given in Table 9.
a
The uncertainties of composition and temperature, that is, u(p) and u(T), with a 0.95 level of confidence, were listed. The maximum expanded uncertainties of the composition and temperature measurements were below 0.006 mole fraction and 0.07 K. The uncertainty of pressure is 0.3 kPa.
Figure 4. Experimental VLE data for the cyclohexane (2) + 1,2propanediol (3) system at 101.3 kPa: ●, experimental data; , calculated by the NRTL equation; ---, calculated by the Wilson equation; ···, calculated by the UNIQUAC equation. The equation parameters of NRTL, Wilson, and UNIQUAC are given in Table 9. N
OF =
⎛ T exptl − T calcd i i
∑ ⎜⎜ i=1
⎝
Tiexptl
⎞ + |yiexptl − yicalcd |⎟⎟ ⎠
(3)
which are shown in Table 9, as well as the relevant statistics of each VLE. The equilibrium temperatures of each binary system were correlated with the function proposed by Wisniak and Tamir:23
Figure 2. Experimental VLE data for the tetrahydrofuran (1) + cyclohexane (2) system at 101.3 kPa: ●, experimental data; , calculated by the NRTL equation; ---, calculated by the Wilson equation; ···, calculated by the UNIQUAC equation. The equation parameters of NRTL, Wilson, and UNIQUAC are given in Table 9.
k=0
T = xiTi + xjTj + xixj ∑ Ck(xi − xj)k m
consistency are listed in Table 8. It could be seen that the Fredenslund test has passed since the consistency criteria (AAD y < 0.1) was achieved using a two-parameter Legendre polynomial. Also the Heringon test passed due to |D − J| < 10. The equations of Wilson,20 NRTL,21 and UNIQUAC,22 were used to correlate the activity coefficients. The parameters of the models determined by minimizing the objective function (OF) as follows:
(4)
where i and j are the pure component, Ti and Tj are the boiling temperatures, m is the number of binary parameters and Ck is the binary coefficient of the system. All of the parameters were obtained by the least-squares method. The average absolute deviation (AAD) and the root-mean-square deviation (rmsd) are summarized in Table 10. The experimental data listed in Tables 5 to 7 were correlated with the models, and they are shown in Figures 2 to 4. 3057
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Table 8. Consistency Test Statistics for the Binary Systems Fredenslund test
Herington test
system i+j
A1a
A2a
AADyib
AADpc/kPa
Dd
Jd
1+2 1+3 2+3
0.4263 0.6624 0.3785
0.2682 0.2523 0.1042
0.0022 0.0024 0.0042
0.316 0.535 0.367
2.96 46.90 41.67
6.49 53.83 45.38
a
Legendre polynomial parameters. bAverage absolute deviation in vapor-phase composition. cAverage absolute deviation in pressure. dParameters were calculated according to ref 18.
Table 9. Experimental VLE Data Reduction with the Wilson, NRTL, and UNIQUAC Models model c
Wilson
NRTL
UNIQUACe
Aij
Aji
system i+j
J·mol−1
J·mol−1
1 1 2 1 1 1 2 1 1 1 2 1
−350.26 492.51 456.58
5718.31 4384.54 −1548.48
+ + + + + + + + + + + +
2 3 3 2 + 3d 2 3 3 2 + 3d 2 3 3 2 + 3d
3754.52 −2587.60 −2754.21 −2727.58 −2754.13 −1419.58
rmsd a
954.52 3021.5 −3541.25
0.3 0.3 0.3
−1193.35 −1088.99 2024.63
AADTa
AADy1b
0.85 0.57 0.54 0.75 0.25 0.24 0.52 0.12 0.47 0.33 0.51 0.41
0.0012 0.0049
AADy2b
0.0058 0.0054 0.0045 0.0047 0.0081 0.0023 0.0062
0.0045 0.0084
0.0054 0.0058
0.0036 0.0075
a
Average absolute deviation in temperature. bAverage absolute deviation in vapor-phase composition. cMolar liquid volumes of pure components from ref 16. dTernary prediction from binary parameters. eVolume and surface parameters from DECHEMA.15
Table 10. Coefficients, Average Deviation, and rmsd in the Correlation of Boiling Points by the Tamir−Wisniak Equations system i+j 1 1 2 1 a
+ + + +
2 3 3 2+3
C0
C1
C2
C3
A
−19.76 −148.83 −148.83
−6.35 101.73 120.69
−4.92 −121.76 −31.50
−4.35 76.34 −73.35
C
AADTa/K
rmsdb/K
7.43
0.09 0.11 0.15 0.18
0.03 0.05 0.02 0.09
B
−15.36
−31.71
b N exptl 2 0.5 Average absolute deviation in temperature: 1/N∑Ni=1|Texptl − Tcal − Tcal i i |. rmsd: 1/N {∑i=1(Ti i ) } .
According to these figures, we found that all of the models can predict the VLE data successfully, but for tetrahydrofuran (1) + cyclohexane (2) system, the NRTL model was better than others. Ternary System. The VLE data for ternary system tetrahydrofuran (1) + cyclohexane (2) + 1,2-propanediol (3) at 101.3 kPa are reported in Table 11. The ternary data were found to be thermodynamically consistent by the Wisniak and Tamirmodification of the McDermott−Ellis24 test (D < Dmax at all data points) and the Wisniak L−W test25 (0.92< Li/Wi < 1.10). For the ternary systems, the VLE data have been estimated by using the Wilson, NRTL, and UNIQUAC models with the binary interaction parameters obtained from the regression of binary data. The mean absolute deviations of vapor phasemole fractions between experimental and calculated are shown in Table 9. The three models represent the data successfully. Thus, the models can be used to calculate boiling points from liquid phase compositions at the system pressure. The equilibrium temperatures of the ternary system were with the equation suggested by Wisniak and Tamir:
3
T=
3
∑ xiTi + ∑ [xixj ∑ Ck(xi − xj)k ] + x1x2x3 i=1
k=0
·[A + B(x1 − x 2) + C(x1 − x3)]
(5)
where Ti is the boiling temperature, Ck is the binary coefficient, m is the number of binary parameters, and A, B, and C are the ternary parameters. All of the parameters and their correlation statistics are summarized in Table 10. The residue curve map which illustrate in Figure 5 is simulated by Aspen Plus at 101.3 kPa. It used the NRTL model. As can be seen from the residue curve map, all of the residue curves begin from the tetrahydrofuran−cyclohexane binary azeotrope point and terminate to the tetrahydrofuran1,2-propanediol face, which means that the tetrahydrofuran and 1,2-propanediol mixture will be obtained in the bottom and cyclohexane in the distillate. The behavior of binary systems can be expected via these features. Figure 6 shows the (y2−x2) equilibrium diagram of the ternary system. It can be observed that 1,2-propanediol produces a strong solvent effect on tetrahydrofuran (1) + cyclohexane (2) system. When the mole fraction of 1,2propanediol is about 0.3, the azeotrope has already been broken. 3058
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Table 11. Experimental VLE Data for Tetrahydrofuran (1) + Cyclohexane (2) + 1,2-Propanediol (3) at 101.3 kPaa T/K
x1
y1
x2
y2
γ1
γ2
γ3
343.75 344.29 345.01 345.25 346.26 346.68 346.79 347.44 347.54 347.87 348.03 348.72 349.02 349.19 349.23 349.27 349.39 349.48 350.25 350.89 351.00 351.60 352.24 353.33 353.36 354.40 354.56 355.27 360.12 362.67
0.733 0.640 0.201 0.544 0.231 0.705 0.585 0.114 0.541 0.496 0.736 0.366 0.106 0.360 0.029 0.337 0.331 0.312 0.547 0.252 0.425 0.094 0.170 0.148 0.147 0.598 0.086 0.068 0.463 0.435
0.133 0.224 0.204 0.318 0.209 0.068 0.172 0.342 0.181 0.213 0.019 0.198 0.384 0.363 0.428 0.312 0.117 0.504 0.085 0.544 0.100 0.868 0.489 0.634 0.581 0.013 0.604 0.740 0.018 0.013
0.806 0.703 0.158 0.609 0.194 0.846 0.661 0.083 0.610 0.548 0.948 0.377 0.080 0.388 0.020 0.344 0.362 0.373 0.694 0.303 0.520 0.180 0.172 0.185 0.168 0.930 0.093 0.095 0.835 0.849
0.193 0.296 0.837 0.390 0.800 0.152 0.336 0.910 0.387 0.449 0.050 0.618 0.912 0.607 0.971 0.650 0.633 0.621 0.302 0.690 0.475 0.815 0.818 0.804 0.821 0.066 0.894 0.890 0.157 0.142
0.947 0.931 0.653 0.921 0.670 0.944 0.886 0.558 0.864 0.839 0.973 0.761 0.556 0.785 0.496 0.742 0.791 0.863 0.896 0.832 0.845 1.291 0.672 0.805 0.733 0.970 0.673 0.848 0.954 0.960
2.003 1.784 5.425 1.602 4.846 2.796 2.435 3.250 2.603 2.540 3.233 3.664 2.755 1.934 2.621 2.405 6.189 1.412 3.977 1.392 5.190 1.008 1.761 1.291 1.437 4.962 1.452 1.155 7.308 8.164
1.295 1.648 1.288 2.131 1.328 1.241 1.728 1.717 1.444 1.515 0.974 1.382 1.924 2.202 2.028 1.855 1.140 3.460 1.118 3.781 1.129 13.223 2.850 4.780 3.881 0.971 3.919 6.707 0.984 0.980
a The uncertainties of composition and temperature, that is, u(p) and u(T), with a 0.95 level of confidence, are listed. The maximum expanded uncertainties of the composition and temperature measurements were below 0.009 mole fraction and 0.07 K. The uncertainty of pressure is 0.3 kPa.
Figure 6. Isobaric VLE data on a solvent-free basis for tetrahydrofuran (1) + cyclohexane (2) + 1,2-propanediol (3) system at 101.3 kPa: , x3 ≈ 0.0; ■, x3 ≈ 0.1; ●, x3 ≈ 0.2; ▲, x3 ≈ 0.3; ○ , x3 ≈ 0.4.
Figure 5. Residual curve map for the ternary system tetrahydrofuran (1) + cyclohexane (2) + 1,2-propanediol (3).
α=
Figure 7 shows the relative volatility of cyclohexane to tetrahydrofuran at different mole fractions of 1,2-propanediol. The relative volatility is calculated by the following equation:
y2 /x 2 y1 /x1
(6)
where y1 and y2 are the mole compositions of tetrahydrofuran and cyclohexane based on solvent free in the vapor phase, and 3059
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Figure 7. Relative volatility α of cyclohexane to tetrahydrofuran with the cyclohexane mole fraction x2 at 101.3 kPa for different mole fractions of 1,2-propanediol: ---, x3 ≈ 0.0; ■, x3 ≈ 0.1; ●, x3 ≈ 0.2; ▲, x3 ≈ 0.3; ○, x3 ≈ 0.4.
x1 and x2 are the mole compositions in the liquid phase. In Figure 7, we can see that 1,2-propanediol improves the relative volatility of cyclohexane effectively.
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CONCLUSIONS In our study, the VLE data for the binary systems tetrahydrofuran (1) + cyclohexane (2), tetrahydrofuran (1) + 1,2-propanediol (3), and cyclohexane (2) + 1,2-propanediol (3) and the ternary system tetrahydrofuran (1) + cyclohexane (2) + 1,2-propanediol (3) at 101.3 kPa were obtained. All of the VLE data were correlated with the NRTL, UNIQUAC, and Wilson models, and the NRTL model showed better results than the others. From the experimental results, 1,2-propanediol was a good solvent because the azeotrope was broken and the relative volatility was improved effectively for the system of tetrahydrofuran and cyclohexane.
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AUTHOR INFORMATION
Corresponding Author
*Fax: 86-24-89383736. E-mail:
[email protected]. Funding
The authors acknowledge the National Science Foundation of China (project no. 21076126) and Program for Liaoning Excellent Talents in University (project no. 2012013) for partial financial support of this project. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Bai, P.; Tan, K.; Shao, X. Determination of Atmospheric VLE for the Ternary System of Cyclopentane-Tetrahydrofuran-Cyclohexane. Huaxue Gongcheng 2009, 26 (1), 54−56. (2) Treybal, R. E. Mass-Transfer Operations; McGraw Hill: New York, 1955. (3) Prasad, T. E. V.; Raj, E. D. A.; Maheedhar, G.; Reddy, M. S.; Kumar, V.; Garapati, S.; Patanjali, V.; Prasad, D. H. L. BubbleTemperature Measurements on Some Binary Mixtures Formed by Tetrahydrofuran or Amyl Alcohol with Hydrocarbons, Chlorohydrocarbons, or Butanols at (94.6 or 95.8) kPa. J. Chem. Eng. Data 2004, 49 (4), 746−749. 3060
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