Article pubs.acs.org/jced
Organic Salt Effect on Vapor−Liquid Equilibrium of the Methanol + Water System at Subatmospheric Pressure Changsheng Yang,* Feizhong Sun, Shengyong Ma, Xia Yin, and Hao Zeng 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) for methanol (1) + water (2) + tetramethylammonium bicarbonate (TMAB) has been measured at pressures of 66.52 kPa and 37.60 kPa. The binary data for methanol + water were correlated by the Wilson model at subatmospheric pressures. All of the experimental results of the binary system passed the thermodynamic consistency test by the area test of Redlich−Kister and the point test of Van Ness et al. The Ohe’s preferential solvation model was used to correlate the VLE data of the ternary system. The experimental results of the ternary system show that TMAB has a salt-out effect on methanol, and this effect enhances with increasing the concentration of TMAB.
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INTRODUCTION
Tetramethylammonium hydroxide (TMAH) is extensively used as a developer for photoresists in a printed circuit board and ultrapure cleaning reagent for the chemical mechanical polishing (CMP) technology process. Ultrapure TMAH was prepared by electrolysis of tetramethylammonium bicarbonate (TMAB).1 In the process of preparing TMAB, methanol was used as a solvent and the byproduct. Vapor−liquid equilibrium (VLE) data for the methanol + water has been widely studied at atmospheric pressure, but few studies involved the VLE data of methanol + water containing organic salts at low pressures. The VLE of the methanol + water + sodium nitrate at 760 ± 3 mmHg has been determined by Natarajan and Srinivasan.2 The isothermal and isobaric VLE data of methanol + water + ethanol were reported by Kiyofumi.3,4 Yang and Lee5 studied the VLE data of methanol + water + sodium chloride, potassium chloride, and sodium bromide at 298.15 K. Kurzin et al.6 studied the VLE data of a methanol + water system containing ammonium bromide. Iliuta et al.7 correlated and predicted vapor−liquid−solid equilibrium of a methanol− water system containing nonelectrolytes. In our previous work,8 we studied the VLE data of methanol + water + TMAB at atmospheric pressure. Because the electrolysis process had a strict requirement with the percent of methanol, simultaneously, considering that TMAB is prone to decompose at about 393.15 K slowly, vacuum distillation was designed to rectify the mixture containing methanol, water, and TMAB. Therefore, we measured the VLE data of methanol + water, as well as the methanol + water containing TMAB system at subatmospheric pressure.
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Figure 1. Rose-Williams VLE device: (1) heating column, (2) liquid sample connection, (3) vapor sample connection, (4) condenser, (5) U-tube manometer, (6) vacuum pump, (7) buffer tank (20 L), (8) needle value, (9) a precision mercury thermometer.
Tianjin, China), deionized water, the purity of solvents was checked by GC (SP2100, Tianjin, China), and tetramethylammonium bicarbonate (mass fraction is greater than 0.980, the mass fraction of impurity tetramethylammonium carbonate and water were less 0.005 and 0.015, respectively) were used;8 the mass fraction of TMAB was analyzed by back-titration,9 and the Karl Fisher method was used to measure the water in the TMAB. The salt was dried in a vacuum oven at 383.15 K at least for 48 h, until a constant mass was reached and then stored in a desiccator.
EXPERIMENTAL SECTION
Received: May 8, 2012 Accepted: August 30, 2012 Published: September 18, 2012
Chemicals. Methanol (mass fraction ≥ 0.999 GC grade, supplied by Tianjin Guangfu Technology Development Co. Ltd., © 2012 American Chemical Society
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Table 1. VLE Data and Activity Coefficients (γ) for a Binary System of Methanol (1) + Water (2) at p = (66.52 and 37.60) kPaa x1
y1
γ1
T/K
x1
y1
T/K
γ1
0.332 0.289 0.246 0.160 0.075 0.039 0.020 0
0.706 0.674 0.638 0.538 0.366 0.235 0.139 0
339.77 341.06 342.54 346.11 352.16 355.88 358.06 361.51
1.285 1.341 1.409 1.597 1.857 2.156 2.305
0.337 0.292 0.248 0.169 0.075 0.025 0.011 0
0.713 0.685 0.653 0.568 0.376 0.169 0.084 0
325.90 327.30 328.98 332.45 338.48 343.76 345.73 347.16
1.272 1.329 1.390 1.537 1.801 1.982 2.079
66.62 kPa 1.000 0.948 0.819 0.707 0.620 0.536 0.449 0.393
1.000 0.983 0.935 0.888 0.849 0.816 0.769 0.744
327.45 328.20 330.31 331.93 333.76 335.03 336.93 338.16
1.000 0.950 0.819 0.709 0.621 0.544 0.450 0.394
1.000 0.983 0.938 0.897 0.862 0.832 0.785 0.754
313.55 315.19 317.14 318.86 320.37 321.75 323.64 324.93
1.000 1.008 1.037 1.050 1.110 1.157 1.219 37.60 kPa 0.999 1.012 1.034 1.061 1.100 1.155 1.199
x1, the mole fraction of methanol in the liquid phase; y1, the mole fraction of methanol in the vapor phase; γ1, the activity coefficient of methanol; γ2, the activity coefficient of water; T, equilibrium temperature; p, equilibrium pressure. Uncertainties in T, P, x, and y are ± 0.1 K, ± 0.13 kPa, ± 0.01, and ± 0.01, respectively. a
Table 2. Results of Thermodynamic Consistency Test for the Binary System of Methanol + Watera
a
system
p/kPa
area test
methanol (1) + water (2)
66.52 37.60
−5.03 + −7.41 +
Table 3. Results of the Correlation with the Wilson Model for the System of Methanol (1) + Water (2) at p = (66.52 and 37.60) kPa
point test, Δyave 0.004 0.007
+ +
Wilson
“+” (consistent) and “−” (not consistent).
Apparatus and Procedure. The equilibrium apparatus was a modified Rose-Williams still; the equipment is shown in Figure 1. The still was connected with a vacuum pump and a buffer tank with a volume of 20 L to adjust the pressure. The vacuum pump operated continuously, and the needle valve was used to regulate the amount of the air into the system slowly and that could control the pressure to the setup of reduced pressure conditions. The ethanol was used as the coolant in the condenser, and its working temperature was 273.15 K to prevent the water in the vapor phase from freezeing. Furthermore, it could ensure the methanol and water from being lost. Mixture solutions were prepared gravimetrically by an electronic balance which has an uncertainty of ± 0.1 mg. Each experiment was kept at a constant vapor temperature for more than 30 min to ensure a stationary state. In our previous work,10 we have checked the reliability of the experimental system. The mole fractions of methanol and water were analyzed by GC. All samples were directly injected into the GC without any pretreatment. The glass linear GC was filled with glass wool which can trap the TMAB and protect the GC column. The GC was equipped with a thermal conductivity detector (TCD) and a Porapak QS column (2 m × 3 mm). The carrier gas was hydrogen flowing at 40 mL·min−1. The GC conditions were as follows: the column temperature of 353.15 K, the injector and detector temperatures of 393.15 K and 423.15 K, respectively. A combining titration method11 was used to analyze the concentrations of TMAB. We calculated the concentrations of methanol and water by calibration curves: at least five times were measured for each sample to ensure the accuracy, abandoning
λ12−λ11 λ21−λ22 Δy ΔT/K
66.52 kPa
37.60 kPa
806.5 1808.5 0.005 0.36
548.5 1768.4 0.003 0.18
Figure 2. Experimental T, x, y diagram of methanol + water: ■, □, T−y1 and T−x1, respectively, at 67.38 kPa; ●, ○, experimental T−y1 and T−x1, respectively, at 66.52 kPa; ▲, △, experimental T−y1 and T−x1, respectively, at 37.60 kPa.
the maximum and minimum numbers. In this case, the uncertainty of mole fraction of methanol and water in the liquid and vapor phase of samples was ± 0.01. The uncertainty of equilibrium temperature was ± 0.1 K. The equilibrium pressure of the whole system was measured by a u-tube manometer which has an uncertainty of ± 0.13 kPa. 2697
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RESULTS AND DISCUSSION
mole percent are both less than 0.01, and those of the system pressures are less than 1.01 kPa at pressures of 66.52 kPa and 37.60 kPa. All the experimental data at the two pressures meet the thermodynamically consistency test, which indicates that the VLE data for methanol + water are reliable. Figure 2 shows the comparison of the VLE data for the system methanol + water on the basis of the experimental data at 66.52 kPa in our work and the literature values17 at 67.38 kPa. As can be seen in Figure 2, a reasonable agreement between the experimental and the literature VLE data was obtained. Correlation of the Binary Data. At low or moderate pressure, the vapor phase is regarded as an ideal gas, and the liquid is regarded as nonideal mixture; then the equilibrium equation can be expressed as
Experimental Results and Consistency Test. The VLE data for the binary system at pressures of 66.52 kPa and 37.60 kPa are listed in Table 1. The Redlich−Kister method12,13 was used to ensure the quality of the methanol + water experimental data. Besides, the point test of Van Ness et al.,14 in the version of Fredenslund et al.,15,16 is also used to verify the thermodynamic consistency of VLE data of methanol + water. Fredenslund et al. report that the excess Gibbs energy GE/RT can be expressed as a Legendre polynomial expansion and then the calculated value of the composition of the vapor phase and system pressure can be obtained by the vapor−liquid equation. If the deviation of the calculated vapor-phase mole fraction to the experimental value is less than 0.01 and that of the system pressure is less than 1.01 kPa, then the experimental data pass the thermodynamics consistency test. The results of thermodynamic consistency test are given in Tables 2 and 3; as can be seen in these tables, the deviations of
yP = Pi0γixi i
Vapor pressures Pi were calculated with the Antoine equation:
Table 4. Antoine Coefficients A, B, and C
ln(Pi0/kPa) = A +
Antoine coefficients component
T/K
A
B
C
ref
water methanol
284 to 441 257 to 364 353.4 to 512.63
16.2886 16.5725 16.4831
−3816.44 −3626.55 −3614.17
−46.13 −34.29 −34.85
a a c
a
(1) 0
B (T /K) + C
(2)
where Pi0 is the vapor pressure of solvent i at equilibrium temperature, which can be calculated with Antoine equation; Antoine constants (A, B, C) obtained from Albert et al.18 and Ambrose et al.19 are summarized in Table 4, where xi and yi are the mole fractions of component i in the liquid and vapor
Reference 15. cReference 16.
Table 5. VLE Data for Temperature T, Pressure P, Liquid Mole Fraction of Methanol x1′ on a Salt-Free Basis, Vapor Mole Fraction of Methanol y1, and Liquid Mole Fraction of TMAB x3 at 66.62 kPa and 37.60 kPaa
a
T/K
x1′
378.65 374.82 371.37 366.19 361.70 357.92 355.85 351.98 348.05 346.24 344.30 341.85
x3 = 0.159 0.000 0.020 0.053 0.103 0.143 0.200 0.250 0.333 0.500 0.667 0.800 1.000
0.000 0.308 0.506 0.659 0.732 0.798 0.824 0.869 0.911 0.937 0.958 1.000
371.85 367.01 363.25 357.45 354.55 351.65 348.75 346.64 343.15 340.38 338.69 336.25
366.65 362.32 355.71 348.45 343.93 340.48 337.55 334.57 331.94 329.93 328.95 327.15
x3 = 0.159 0.000 0.019 0.051 0.103 0.143 0.200 0.250 0.333 0.500 0.667 0.800 1.000
0.000 0.314 0.531 0.695 0.759 0.809 0.845 0.885 0.920 0.949 0.968 1.000
356.57 352.41 348.76 341.26 337.87 334.88 333.17 331.05 327.25 324.84 323.18 321.43
y1
T/K
x1′ 66.52 kPa x3 = 0.114 0.000 0.019 0.049 0.106 0.146 0.203 0.250 0.333 0.500 0.667 0.800 1.000 37.60 kPa x3 = 0.114 0.000 0.018 0.043 0.106 0.149 0.205 0.256 0.333 0.500 0.667 0.800 1.000
y1
T/K
x1′
y1
0.000 0.237 0.433 0.629 0.699 0.751 0.794 0.826 0.878 0.924 0.949 1.000
366.65 363.11 359.02 352.50 348.88 346.10 343.76 341.36 338.46 336.35 334.78 332.15
x3 = 0.076 0.000 0.020 0.050 0.100 0.143 0.200 0.250 0.333 0.500 0.667 0.800 1.000
0.000 0.202 0.366 0.574 0.647 0.702 0.757 0.811 0.871 0.909 0.941 1.000
0.000 0.242 0.428 0.654 0.723 0.779 0.801 0.839 0.898 0.935 0.961 1.000
351.95 348.11 343.96 337.27 334.34 331.65 329.49 327.52 324.47 322.24 320.05 318.25
x3 = 0.076 0.000 0.018 0.047 0.105 0.147 0.203 0.255 0.333 0.500 0.667 0.800 1.000
0.000 0.208 0.378 0.577 0.647 0.717 0.759 0.801 0.863 0.915 0.947 1.000
Uncertainty in T, P, x, and y are ± 0.1 K, ± 0.13 kPa, ± 0.01, and ± 0.01, respectively. 2698
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phases, respectively, and P is the equilibrium pressure. The nonlinear least-squares method is used to optimize the Wilson20 parameter, the following objective function was minimized during optimization of the Wilson parameters. ⎡⎛ ⎞2 ⎤ ⎢⎜ γexp − γcal ⎟ ⎥ OF = ∑ ⎢⎜ γexp ⎟⎠ ⎥ ⎣⎝ ⎦
mole fraction, respectively. The experimental results are listed in Table 5. As suggested in our previous works, the Ohe’s preferential solvation model21 was used to correlate the experimental VLE data in this work. x1a =
(3)
x1 − Sx3 (x1 − Sx3) + x 2
(4)
where x1a represents the actual composition of methanol in liquid phase, S represents the preferential solvation number. Since x1 = x1′ (1 − x3), x2 = x2′ (1 − x3), and x1′ + x2′ = 1, eq 4 is rewritten as follows:
Binary interaction parameters of the Wilson equation and the absolute deviation of mole fraction in vapor phase and temperature at each experimental pressure are listed in Table 3. As can be seen, absolute deviations Δy are 0.005 and 0.003 at 66.52 kPa and 37.60 kPa, respectively; absolute deviations ΔT are 0.36 K and 0.18 K at 66.52 kPa and 37.60 kPa, respectively. The correlated results are very satisfactory. VLE Data for Ternary Systems. Isobaric VLE data for the system (methanol + water + TMAB) have been measured at pressures of 66.52 kPa and 37.60 kPa. The TMAB concentrations added to the system were 0.076, 0.114, and 0.159
′ = x1a
x1′(1 − x3) − Sx3 (1 − x3) − Sx3
(5)
From eq 5, we can obtain S=
′ 1 − x3 x1′ − x1a ′ x3 1 − x1a
(6)
where S was calculated by determining x′1a. x1 x1a = x1 + (x 2 − Sx3) ′ = x1a
S=
(7)
x1′(1 − x3) (1 − x3) − Sx3
(8)
′ − x1′ 1 − x3 x1a ′ x3 x1a
(9)
The relation of the ln(s/x′2) and x3 as follows: ln(S /x 2′) = A − B x3
The parameters A and B at the two pressures can be calculated by Figure 3, and their values are listed in Table 6. The deviations of temperature and vapor-phase composition ΔT and Δy are listed in Table 7. The y1−x1′ diagram of methanol (1) + water (2) + TMAB (3) at pressures of 66.52 kPa and 37.60 kPa are shown in Figures 4 and 5. The two figures indicated that the higher the mole fraction of TMAB in the liquid phase, the higher the mole fraction of methanol in the vapor phase, which means the salt-out effect will enhance with the increasing of concentrations of TMAB. Moreover, the concentration of methanol in the vapor phase increases with the decline of pressure at the same concentrations of TMAB.
Figure 3. Relationship of solvated number and salt concentrations: ■, 66.52 kPa; ●, 37.60 kPa.
Table 6. Correlated Parameters with the Ohe’s Preferential Solvation Model 66.52 kPa
37.60 kPa
A
B
A
B
−2.927
2.497
−3.294
2.711
(10)
Table 7. Correlation Deviations in Equilibrium Temperature and Vapor-Phase Composition for the Ternary System Using Ohe’s Modela 66.52 kPa
37.60 kPa
mole fraction of TMAB
Δyave
Δymax
ΔTave
ΔTmax
Δyave
Δymax
ΔTave
ΔTmax
x3 = 0.159 x3 = 0.114 x3 = 0.076
0.012 0.021 0.017
0.024 0.047 0.027
0.55 1.25 0.65
1.25 1.75 0.95
0.015 0.009 0.022
0.023 0.017 0.041
0.85 0.78 1.29
1.54 1.35 1.85
a N
ΔTave = (1/N )∑ |Ti ,cal − Ti ,exp|
ΔTmax = max[|Ti ,cal − Ti ,exp|]
i
N
Δyave = (1/N )∑ |yi ,cal − Ti ,exp|
Δymax = max[|yi ,cal − yi ,exp |]
i
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: 022-27403389. Telephone: 022-27890907. Funding
This research is financially supported by the Programme of Introducing Talents of Discipline to Universities (No. B060006). Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Yagi, O.; Shimizu, S. Synthesis of Tetramethylammonium Hydroxide Solution Free from Chloride Ion by Electrolysis of Its Formate. Denki Kagaku 1993, 22, 443−445. (2) Natarajan, T. S.; Srinivasan, D. Effect of Sodium Nitrate on the Vapor-Liquid Equilibria of the Methanol-Water System. J. Chem. Eng. Data 1980, 25, 218−221. (3) Kiyofumi, K.; Tsuyoshi, M.; Kouichi, T.; Kazuo, K. Isothermal Vapor−Liquid Equilibria for Methanol + Ethanol + Water, Methanol + Water, and Ethanol + Water. J. Chem. Eng. Data 1995, 40, 679−684. (4) Kiyofumi, K.; Mikiyoshi, N.; Kazuo, K. Isobaric Vapor−Liquid Equilibria for Methanol + Ethanol + Water and the Three Constituent Binary System. J. Chem. Eng. Data 1993, 38, 446−449. (5) Yang, S. O.; Lee, C. S. Vapor-Liquid Equilibria of Water + Methanol in the Presence of Mixed Salts. J. Chem. Eng. Data 1998, 43, 558−561. (6) Kurzin, A. V.; Evdokimov, A. N.; Antipina, V. B.; Pavlova, O. S. Measurement and Correlation of Isothermal Vapor-Liquid Equilibrium Data for the System Methanol + Water + Ammonium Bromide. J. Chem. Eng. Data 2005, 50, 2097−2100. (7) Iliuta, M. C.; Thomsen, K.; Rasmussen, P. Extended UNIQUAC model for correlation and prediction of vapour-liquid-solid equilibria in aqueous salt systems containing non-electrolytes. Part A. Methanolwater-salt systems. Chem. Eng. Sci. 2000, 55, 2673−2686. (8) 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. (9) Levitin, G.; Myneni, S.; Hess, D. W. Reactions Between CO2 and Tetramethylammonium Hydroxide in Cleaning Solutions. Electrochem. Solid-State Lett. 2003, 6, 101−104. (10) Yang, C. S.; Yin, X.; Ma, S. Y. Organic Salt Effect of Tetramethylammonium Bicarbonate on the Vapor-Liquid Equilibrium of the Dimethyl Carbonate + Methanol System. J. Chem. Eng. Data 2012, 57, 66−71. (11) Fu, J. Q. Isobaric Vapor Liquid Equilibrium for the Methanol + Ethanol + Water + Ammonium Bromide System. J. Chem. Eng. Data 1998, 43, 403−408. (12) Wisniak, J. A new test for the thermodynamic consistency of vapor−liquid equilibrium. Ind. Eng. Chem. Res. 1993, 32, 1531−1533. (13) Redlich, O.; Kister, A. T. Algebraic Representation of Thermodynamic Properties and the Classification of Solutions. Ind. Eng. Chem. 1948, 40, 345−348. (14) Van Ness, H. C.; Byer, S. M.; Gibbs, R. E. Vapor Liquid Equilibrium. I. Appraisal of data Reduction Methods. AIChE J. 1973, 19, 238−244. (15) Fredenslund, A.; Gmehling, J.; Rasmussen, P. Vapor-Liquid Equilibrium Using UNIFAC; Elsevier: Amsterdam, 1977. (16) Gmehling, J.; Onken, U. Vapor-Liquid Equilibrium Data Collection, Chemistry Data Series; DECHEMA: Frankfurt, 1977. (17) Soujanya, J.; Satyavathi, B.; Vittal Prasad, T. E. Experimental (vapor + liquid) equilibrium data of (methanol + water), (water + glycerol) and (methanol + glycerol) systems at atmospheric and subatmospheric pressures. J. Chem. Thermodyn. 2010, 42, 621−624.
Figure 4. Equilibrium vapor−liquid composition diagram of methanol + water + TMAB at TMAB mole fractions (■, 0.159, ●, 0.114, ▲, 0.076, ▼, 0.000) at 66.52 kPa, solid lines, correlated using Ohe’s equation.
Figure 5. Equilibrium vapor−liquid composition diagram of methanol + water + TMAB at TMAB mole fractions (■, 0.159, ●, 0.114, ▲, 0.076, ▼, 0.000) at 37.60 kPa, solid lines, correlated using Ohe’s equation.
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CONCLUSION New VLE data for the binary system (methanol + water) and the ternary system (methanol + water + TMAB) have been measured at pressures of 66.52 kPa and 37.60 kPa. The VLE data for the binary system were well correlated by the Wilson models. All of the experimental results of methanol + water passed the thermodynamic consistency test. The VLE data of the ternary system were correlated by Ohe’s preferential solvation model. Absolute deviations Δy were 0.012, 0.021, and 0.017 at 66.52 kPa, and 0.015, 0.009, and 0.022 at 37.60 kPa, respectively; absolute deviations ΔT were all less than 1.5 K. Experimental studies showed that TMAB has a salt-out effect on methanol, and this effect enhanced with increasing the concentration of TMAB and the decline of pressure. Furthermore, the temperatures of the ternary system at different concentrations of TMAB and different pressures were all less than the decomposed temperature of TMAB; these results will be used for the distillation design in the near future. 2700
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(18) Albert, M.; Hahnenstein, I.; Hasse, H.; Maurer, G. Vapor-liquid and Liquid-Liquid Equilibria in Binary and Ternary Mixtures of Water, Methanol, and Methylal. J. Chem. Eng. Data 2001, 46, 897−903. (19) Ambrose, D.; Sprake, C. H. S.; Townsend, R. Thermodynamic Properties of Organic Oxygen Compounds. XXXVII. Vapour Pressures of Methanol, Ethanol, Pentan-1-ol, and Octan-1-ol from the Normal Boiling Temperature to the Critical Temperature. J. Chem. Thermodyn. 1975, 7, 185−190. (20) 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. (21) Ohe, S. Prediction of Salt Effect in Vapor-Liquid Equilibrium: A Method Based on Solvation. Adv. Chem. Ser. 1976, 155, 53−74.
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