Article pubs.acs.org/jced
Isobaric Vapor−Liquid Equilibrium for the Binary Systems of Methanol, Diethylamine, and N,N‑Diethylethanolamine at p = (60.0 and 101.3) kPa Changsheng Yang,* Zhenli Qin, Yali Xu, Hao Zeng, Feizhong Sun, Ping Zhang, and Yang Feng Key Laboratory for Green Chemical Technology of State Education Ministry, School of Chemical Engineering and Technology, Tianjin University, Tianjin, People’s Republic of China ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) data have been measured with a modified Rose−Williams still for the binary systems of methanol (1) + diethylamine (2), methanol (1) + N,N-diethylethanolamine (2), and N,Ndiethylethanolamine (1) + diethylamine (2) at p = (60.0 and 101.3) kPa. All of the experimental data pass the thermodynamic consistency test by the method of Herington and the point test of Van Ness. The system of methanol + diethylamine (DEA) at two pressures exhibits a maximum temperature azeotrope. The other two systems did not show that behavior. The experimental VLE data were well-correlated with the Wilson and universal quasichemical (UNIQUAC) activity coefficient models, and the average absolute deviations (AAD) of the vapor-phase mole fraction Δy between the experimental and the calculated values for all of the measured systems are less than 0.01.
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INTRODUCTION N,N-Diethylethanolamine (DEEA), which is a colorless liquid with an amine odor, is widely used in chemical and pharmaceutical industries. DEEA is commonly used as a curing agent, rust inhibitor, softener, and emulsifier agent. It also can be used as a desulfurizing agent in natural gas and acid gas absorbent. In the process of synthesizing DEEA, ethylene oxide and diethylamine (DEA) are the raw materials, and methanol is used as the catalyst. To design distillation columns correctly, accurate vapor−liquid equilibrium (VLE) data are needed. Up to now, only Aucejo et al.1 have reported the VLE data of DEA + methanol at (101.3 and 300) kPa. No VLE data are available for the other two systems. In this paper, isobaric VLE data for three binary systems of methanol (1) + DEA (2), methanol (1) + DEEA (2), and DEEA (1) + DEA (2) were measured at (60.0 and 101.3) kPa. The Herington method2 and the point test of Van Ness et al.,3 modified by Fredenslund et al.,4 which have been described by Gmehling and Onken5 were used to check all of the experimental data. In the meantime, the Wilson model6 and the univesal quasichemical (UNIQUAC) model7 was used to correlate the VLE data.
laboratory before using. The purities of all of the chemicals were checked by gas chromatography equipped with a flame ionization detector (FID, and gas chromatography (GC) failed to show any observable impurities. The water content in methanol, DEA, and DEEA were 0.05 %, 0.4 %, and 0.6 % (mass fraction) which were tested by GC equipped with a thermal conductivity detector and Porapak QS column (2 m × 3 mm). To ensure the reliability, we measured their boiling points at 101.3 kPa and compared with the literature values,8−10 which are listed in Table 1. Apparatus and Procedure. The isobaric VLE experiments were performed with a modified Rose−Williams still. The apparatus consists of a boiling chamber and a condenser. In this still, both the vapor and the liquid phases continuously circulated to provide intimate contact of the phases and to Table 1. Boiling Points (T) at 101.3 kPa of the Componentsa T/K
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EXPERIMENTAL SECTION Chemicals. Methanol (≥ 99.9 mass %) and diethylamine (≥ 99.0 mass %) were provided by Tianjin Guangfu Technology Development Co. Ltd., China. N,N-Diethylethanolamine (≥ 99.0 mass %) was purchased from Shanghai Canto Chemical Co. Ltd., China. Methanol was used without further purification. DEA and DEEA were purified by distillation in our © 2013 American Chemical Society
a
compound
experimental
literature ref
methanol diethylamine N,N-diethylethanolamine
337.82 328.67 435.94
337.85b 328.50c 435.28d
The uncertainty of T is 0.05 K. Reference 10.
d
b
Reference 8. cReference 9.
Received: November 14, 2012 Accepted: January 8, 2013 Published: January 15, 2013 482
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Table 2. Parameters of the Antoine and Extended Antoine Equations Antoine coefficients
a
component
A
B
C
ref
methanol DEA DEEA
6.76772 6.48147 C2 8653.5
1304.592 1342.957
63.608 28.358 C8 253
a a
C1 75.259
C3 0
C4 0
C5 −8.3836
C6 2.1975·10−17
C7 6
C9 592
Reference 1.
Thermodynamic Consistency Test. The isobaric VLE data for the three binary systems of methanol (1) + DEA (2), methanol (1) + DEEA (2), and DEEA (1) + DEA (2) at p = (60.0 and 101.3) kPa are listed in Tables 3 and 4 and plotted in
ensure that equilibrium could be established rapidly. To control the pressure of the system, we connected a vacuum pump to the still. The vacuum pump operated continuously by using a valve which controls the amount of the air into the system. The pressure of the system could be stable for a long time, and we measured it by using a U-shaped differential manometer whose uncertainty is 0.3 kPa. In each experiment, equilibrium was assumed when constant temperature and pressure had obtained for 30 min or more. The temperature was measured with a precision mercury thermometer whose uncertainty was 0.05 K. The reliability of the experimental system has been tested in our previous work.11−13 Analysis. The compositions of vapor (cooled to liquid) and liquid samples were analyzed by a BFRL SP-2100A GC with an FID after calibration with solutions prepared by mass using a BP210s balance reproducible to within ± 0.1 mg. The average uncertainty in the mole fraction of the mixtures was estimated to be less than ± 0.0001. The gas chromatographic column was a capillary column (30 m × 0.32 mm × 0.5 μm). High-purity nitrogen (≥ 99.999 mass %) was used as the carrier gas with a constant flow rate of 30 mL·min−1. The flow rates of hydrogen and air were (30 and 300) mL·min−1, respectively. The operation conditions of GC of three binary systems are as follows: for the system of methanol (1) + DEA (2), the column, injector, and detector temperatures are (333.15, 373.15, and 393.15) K; for the system of methanol (1) + DEEA (2), the column, injector, and detector temperatures are 403.15 K, 443.15 and 463.15 K; for the system of DEEA (1) + DEA (2), the column, injector and detector temperatures are (403.15, 443.15, and 463.15) K. The volume of each sample that was injected to the GC was 0.4 μL. Each experiment sample was analyzed at least three times to make sure that the results are reliable, and the uncertainties of vapor and liquid mole fractions were about ± 0.002.
Table 3. Experimental VLE Data of the Three Binary Systems at 101.3 kPaa
■
ln(pi0 /kPa)
Bi (T /K) − Ci
1.000 0.986 0.969 0.951 0.910 0.839 0.752 0.719 0.609
1.0000 0.997 0.992 0.984 0.950 0.867 0.750 0.711 0.542
1.000 0.853 0.712 0.685 0.536 0.420
1.000 0.999 0.993 0.991 0.975 0.953
1.000 0.928 0.815 0.767 0.697
1.000 0.401 0.143 0.101 0.065
D= (1)
C 8 i ≤ C 9i
T/K
x1
Methanol (1) + DEA (2) 337.82 0.537 338.07 0.491 338.31 0.412 338.58 0.329 339.15 0.249 339.77 0.149 340.08 0.057 340.2 0 339.33 Methanol (1) + DEEA (2) 337.82 0.359 343.04 0.224 350.01 0.105 351.51 0.046 360.71 0 369.54 DEEA (1) + DEA (2) 435.94 0.535 408.31 0.424 382.45 0.356 375.15 0.212 366.03 0
y1
T/K
0.439 0.376 0.284 0.196 0.129 0.064 0.021 0
338.55 337.89 336.45 334.64 333.05 331.18 329.55 328.67
0.923 0.833 0.616 0.365 0
374.83 389.69 408.75 422.43 435.94
0.027 0.016 0.011 0.005 0
351.79 345.15 341.95 335.45 328.67
Figures 1 to 3. In the process of measuring all of the VLE data, it is impossible to avoid the error that caused by many aspects, and this requires us to test the reliability of the VLE data that obtained by the experiment. For the binary system, the Herington method is usually used to verify the quality of all of the experimental data. The method suggested that:
Sa − S b ·100 Sa + S b
(3)
where Sa is the area of ln(γ1/γ2)−x1 above the x-axis, and Sb is the area of ln(γ1/γ2)−x1 under the x-axis.
C 2i = C1i + + C4iT /K (T /K) + C3i
+ C5i ln(T /K) + C6i(T /K)C7i
y1
a The uncertainties in T, P, x, and y were ± 0.05 K, ± 0.3 kPa, ± 0.002, and ± 0.002, respectively.
RESULTS AND DISCUSSION Pure Component Vapor Pressures. The vapor pressures of the pure component of methanol and DEA were calculated from the Antoine eq 1 and the parameters obtained from Aucejo et al.1 The DEEA was calculated from the extended Antoine eq 2 which was taken from literature.14 log(pi0 /kPa) = Ai −
x1
J = 150·
(2)
Tmax − Tmin Tmin
(4)
where Tmax and Tmin are the maximum and minimum temperatures of the system, respectively.
The Antoine parameters of the three pure components are presented in Table 2. 483
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Table 4. Experimental VLE Data of the Three Binary Systems at 60.0 kPaa x1
y1
1.000 0.963 0.893 0.793 0.744 0.731 0.665
1.000 0.981 0.929 0.813 0.742 0.720 0.613
1.000 0.895 0.796 0.561 0.539 0.417
1.000 0.999 0.997 0.986 0.983 0.963
1.000 0.910 0.876 0.770 0.699
1.000 0.320 0.230 0.093 0.056
T/K
x1
Methanol (1) + DEA (2) 324.92 0.598 325.40 0.538 326.62 0.482 327.60 0.448 327.77 0.327 327.66 0.060 327.25 0 Methanol (1) + DEEA (2) 324.92 0.310 327.93 0.233 331.79 0.093 343.17 0.051 344.31 0 352.79 DEEA (1) + DEA (2) 418.34 0.559 388.45 0.429 379.97 0.348 360.84 0.218 352.23 0
y1
T/K
0.502 0.410 0.336 0.290 0.181 0.020 0
326.51 325.56 324.32 323.81 320.71 315.24 313.64
0.924 0.872 0.631 0.455 0
361.67 369.86 391.56 402.16 418.34
0.029 0.015 0.009 0.007 0
339.34 330.72 326.51 320.76 313.64
a The uncertainty in T, P, x, and y were ± 0.05 K, ± 0.3 kPa, ± 0.002, and ± 0.002, respectively.
If (D − J) < 10, the isobaric VLE data can be considered to conform the thermodynamic consistency test. For the point-to-point test of Van Ness et al, we used a fourparameter Legendre polynomial for the excess Gibbs free energy: k
GE = x1(1 − x1) ∑ ak Lk (x1) (5) RT The value of k is 4, and a nonlinear optimization method was used to minimize the following objective function:
Figure 1. T−x1−y1 diagram of methanol (1) + DEA (2) at p = pressure: (a) p = 60.0 kPa; (b) p = 101.3 kPa; ■, experimental data for T−x1; □, experimental data for T−y1; ●, literature data for T−x1; (○), literature data for T−y1; and - - -, calculated data for T−x1 and T− y1 by the Wilson equation, respectively. · and ···, calculated data for T−x1 and T−y1 by the UNIQUAC equation, respectively.
g=
F=
∑ (Py1,cal
+ Py2,cal − P)
(6)
⎛ Aij Aji ⎞ ⎟ ln γi = −ln(xi + Aij xj) + xj⎜⎜ − xj + xiAji ⎟⎠ ⎝ xi + xjAij
Gmehling and Onken suggest that the data are probably internally consistent when the average error in vapor mole fractions is less than or equal to about 0.01. At times, a few points may not meet this criterion, but the overall set may still be of adequate quality. The results of the two methods are listed in Table 5. Azeotropic behavior was observed for the system of methanol (1) + DEA (2) at p = (60.0 and 101.3) kPa, and the data at p = 101.3 kPa was compared with the literature values1 which are shown in Figure 1. The average absolute deviations of the vapor-phase mole fraction Δy and the temperature change ΔT between our experimental values and the literature values are 0.014 and 0.55 K, respectively. As it can be seen in Table 5, the values of (D − J) of all the systems are less than 10 which indicates that this set of data can satisfy the criterion of Herington. Data Correlation. All of the experimental data of the three binary systems were correlated using the activity coefficient models (Wilson and UNIQUAC), which have introduced by our previous work.15 For the Wilson model, the mathematic forms of the activity coefficient equation are:
Aij =
vi =
⎛ λij − λii ⎞ exp⎜ − ⎟ Vi RT ⎠ ⎝
(7)
Vj
(8)
RTci τi Zci pci
(9)
τi = 1 + (1 − T /Tci)2/7
T /Tci ≤ 0.75
(10)
where γi is the activity coefficient of the component i; xi and xj are the liquid-phase mole fraction of components i and j, respectively; Aij and Aji are the Wilson parameters; Vi and Vj are the molar volumes of component i and j, respectively; λij−λii are the binary interaction energy parameters which were listed in Table 6; Tci, Pci, and Zci are the critical temperature, pressure, and compressibility factor of component i which were obtained from Aspen property data bank and listed as follows: methanol, Tci = 512.5 K, Pci = 8.084 MPa, Zci = 0.223; DEA, Tci = 496.6 K, 484
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Figure 2. T−x1−y1 diagram of methanol (1) + DEEA (2) at p = pressure: (a) p = 60.0 kPa; (b) p = 101.3 kPa; ■, experimental data for T−x1; □, experimental data for T−y1; and - - -, calculated data for T−x1 and T−y1 by the Wilson equation, respectively. · and ···, calculated data for T−x1 and T−y1 by the UNIQUAC equation, respectively.
Figure 3. T−x1−y1 diagram of DEEA (1) + DEA (2) at p = pressure: (a) p = 60.0 kPa; (b) p = 101.3 kPa; ■, experimental data for T−x1; □, experimental data for T−y1; and - - -, calculated data for T−x1 and T−y1 by the Wilson equation, respectively. · and ···, calculated data for T−x1 and T−y1 by the UNIQUAC equation, respectively.
Table 5. Results of the Thermodynamic Consistency Test for the Three Binary Systems at Two Pressures
Pci = 3.71 MPa, Zci = 0.27; DEEA, Tci = 592 K, Pci = 3.18 MPa, Zci = 0.259. For the UNIQUAC model, the mathematic forms of the activity coefficient equation are: ϕ θ ⎛Z⎞ + ⎜ ⎟qi ln i + li − i ln γi = ⎝ ⎠ xi xi 2 ϕi ϕi
∑ xjlj
− qi ln(∑ θτ j ji) + qi − qi ∑ j
area test (D − J)
point test
methanol (1) + DEA (2)
60.0 101.3 60.0 101.3 60.0 101.3
−0.54 −1.78 −3.18 −5.24 7.36 0.35
0.007 0.006 0.005 0.003 0.004 0.003
methanol (1) + DEEA (2) DEEA (1) + DEA (2)
θτ j ij ∑j θkτkj
(11) (12)
∑j qjxj
(13)
rx ϕi = i i ∑j rjxj
(14)
⎛ gji − gii ⎞ τij = exp⎜ − ⎟ ⎝ RT ⎠
(15)
θi =
p/kPa
j
Z (ri − qi) − (ri − 1) 2 qixi
li =
system
where θi and ϕi are the average area fraction and volume fraction of the pure component of i; ri and qi are constants obtained from Aspen property data bank which were listed as follows: methanol, ri = 1.431, qi = 1.432; DEA, ri = 3.684, qi = 3.172; DEEA, ri = 5.315, qi = 4.532. Z is the lattice coordination number, and its value is 10; gij is the interaction energy between the molecules i and j and gji−gii were also listed in Table 6. A nonlinear optimization method was used to optimize the binary parameters in the two activity-coefficient models (Wilson and UNIQUAC). The objective function (OF) is defined as: 485
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Journal of Chemical & Engineering Data Table 6. Results Calculated from Experimental Data with Wilson and UNIQUAC Models for the Systems of Methanol (1) + DEA (2), Methanol (1) + DEEA (2), and DEEA (1) + DEA (2) at p = (60.0 and 101.3) kPa Wilson λ12−λ11
λ21−λ22
g12−g11
g21−g22
J·mol−1
J·mol−1
J·mol−1
J·mol−1
methanol (1) + DEA (2) methanol (1) + DEEA (2) DEEA (1) + DEA (2)
−526.18 130.55 −358.74
methanol (1) + DEA (2) methanol (1) + DEEA (2) DEEA (1) + DEA (2)
−299.16 −135.28 −113.62
p = 60.0 kPa −173.31 −403.16 182.95 10.38 −412.23 509.45 p = 101.3 kPa −98.05 −309.22 −38.35 −52.84 −10.43 7.46
⎡⎛ ⎞2 ⎤ ⎢⎜ γexp − γcal ⎟ ⎥ OF = ∑ ⎢⎜ γexp ⎟⎠ ⎥ ⎣⎝ ⎦
−397.27 27.94 −625.64 −306.82 −128.37 7.46
1 N
*E-mail:
[email protected]. Fax: 022-27403389. Telephone: 022-27890907. The authors declare no competing financial interest.
(16)
■
(17)
i=1
From Table 7, we can conclude that the results are very satisfactory. Table 7. Deviations between the Calculated and the Experimental Results of the Three Systems at p = (60.0 and 101.3) kPa Using the Wilson and the UNIQUAC Equations, Temperature Change (ΔT), and Change in the Mole Fraction of the Vapor Phase (Δy1)a Wilson ΔT/K
methanol (1) + DEEA (2) DEEA (1) + DEA (2)
methanol (1) + DEA (2) methanol (1) + DEEA (2) DEEA (1) + DEA (2)
avg max avg max avg max
0.18 0.35 0.15 0.27 0.30 0.66
avg max avg max avg max
0.14 0.29 0.10 0.34 0.18 0.38
Δy1
UNIQUAC ΔT/K
p = 60.0 kPa 0.007 0.10 0.013 0.22 0.005 0.14 0.014 0.49 0.004 0.31 0.008 0.67 p = 101.3 kPa 0.004 0.15 0.010 0.31 0.003 0.19 0.010 0.28 0.003 0.50 0.010 0.83
REFERENCES
(1) Aucejo, A.; Loras, S. Phase Equilibria and Multiple Azeotropy in the Associating System Methanol + Diethylamine. J. Chem. Eng. Data 1997, 42, 1201−1207. (2) Herington, E. F. G. Tests for the consistency of experimental isobaric vapor-liquid equilibrium data. J. Inst. Petrol. 1965, 37, 457− 470. (3) 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. (4) Fredenslund, A.; Gmehling, J.; Rasmussen, P. Vapor-Liquid Equilibria Using UNIFAC; Elsevier: Amsterdam, The Netherlands, 1977. (5) Gmehling, J.; Onken, U. Vapor-Liquid Equilibrium Data Collection; DECHEMA Chemistry Data Series; DECHEMA: Frankfurt, starting 1977. (6) 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. (7) Abrams, D. S.; Prausnitz, J. M. Statistical thermodynamic of liquid mixtures: a new expression for the excess Gibbs free energy of partly or completely miscible systems. AIChE J. 1993, 14, 135−144. (8) Hao, Y. B.; Zhang, S. H. Vapor-Liquid Equilibrium for Methanol + tert-Butylamine + N,N-Dimethylformamimide and Constituent Binary Systems at Atmospheric Pressure. J. Chem. Eng. Data 2012, 57, 1244−1248. (9) Jose, M. R.; Cristina, G. S. Vapor-Liquid Equilibria of Binary Mixtures Containing Diethylamine + Diisopropylamine, Diethylamine + Dipropylamine, and Chloroform + Diisopropylamine at 101.3 kPa, and Vapor Pressure of Dipropylamine. J. Chem. Eng. Data 2000, 45, 867−871. (10) Steele, W. V.; Chirico, R. D. Measurements of Vapor Pressure, Heat Capacity, and Density alone the Saturation Line for Cyclopropane Carboxylic Acid, N,N-Diethylethanolamine, 2,3-Dihydrofuran, 5-Hexen-2-one, Perfluorobutanoic Acid, and 2-Phenylpropionaldehyde. J. Chem. Eng. Data 2002, 47, 715−724. (11) Yang, C. S.; Sun, F. Z. Organic Salt Effect on Vapor-Liquid Equilibrium of the Methanol + Water System at Subatmospheric Pressure. J. Chem. Eng. Data 2011, 57, 2696−2701. (12) Yang, C. S.; Ma, S. Y.; Yin, X. Organic Salt Effect of Tetramethylammonium Bicarbonate on the Vapor-Liquid Equilibrium of the Methanol-Water System. J. Chem. Eng. Data 2011, 56, 3747− 3751. (13) Yang, C. S.; Yin, X.; Ma, S. Y. Organic Salt Effect of Tetramethylammonium Bicarbonate on the Vapor-Liquid Equilibrium
N
methanol (1) + DEA (2)
AUTHOR INFORMATION
Notes
∑ |Uiexp − Uical|
system
■
Corresponding Author
where γexp and γcal are the experimental and calculated activity coefficients, respectively. The average absolute deviations of vapor-phase mole fraction change Δy and the temperature change ΔT of the three binary systems at two experimental pressures between the experimental values and the calculated values using the Wilson and UNIQUAC equations are listed in Table 7. The AAD was defined as: AAD =
CONCLUSIONS
In this work, isobaric VLE data for the three binary systems of methanol (1) + DEA (2), methanol (1) + DEEA (2), and DEEA (1) + DEA (2) were measured at p = (60.0 and 101.3) kPa. According to the results, the maximum boiling azeotropes were found for the system of methanol + DEA. For the other two systems, no azeotrope formation was observed. All of the experimental data pass the thermodynamic consistency test using the method of Herington and point test of Van Ness et al., and all of the systems were correlated well by the Wilson and UNIQUAC activity coefficient models, which indicates that the two models are suitable to the three measured systems.
UNIQUAC
system
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Article
Δy1 0.004 0.010 0.005 0.012 0.004 0.008 0.005 0.009 0.007 0.013 0.002 0.010
ΔTavg = (1/N)∑Ni |Ti,cal − Ti,exp|, ΔTmax = max[|Ti,cal − Ti,exp|], Δyavg = (1/N)∑Ni |yi,cal − yi,exp|, Δymax = max[|yi,cal − yi,exp|].
a
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of the Dimethyl Carbonate + Methanol System. J. Chem. Eng. Data 2012, 57, 66−71. (14) Wagner, W. New Vapor Pressure Measurements for Argon and Nitrogen and a New Method for Establishing a Rational Vapor Pressure Equation. Cryogenics 1973, 13, 470−482. (15) Yang, C. S.; Zeng, H.; Yin, X. Measurements of (vapor-liquid) equilibrium for the systems {methanol + dimethyl carbonate} and {methanol + dimethyl carbonate + tetramethylammonium bicarbonate} at p = (34.43, 67.74) kPa. J. Chem. Thermodyn. 2012, 53, 158− 166.
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