Article pubs.acs.org/jced
Isobaric Vapor−Liquid Equilibrium Data for the Binary System of Water + 2‑Methylpyridine at 101.3, 60.0, and 20.0 kPa Ying Yang, Kaigong Fan, Peng Bai, and Xianghai Guo* Department of Pharmaceutical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China Key Laboratory of Systems Bioengineering, Ministry of Education, Tianjin University, Tianjin 300350, China S Supporting Information *
ABSTRACT: Isobaric vapor−liquid equilibrium (VLE) data for the binary system of water + 2-methylpyridine were determined by using Fisher VLE 602 equipment at 101.3, 60.0, and 20.0 kPa to assist with the design of the separation process by distillation. All of the binary data at different pressures were considered to be thermodynamically consistent according to Wisniak’s area and point test. The results showed that the binary system at all three pressures formed the minimum boiling azeotropes and exhibited a positive deviation from Raoult’s law. The binary VLE data were correlated by using NRTL-HOC, UNIQUAC-HOC, and Wilson-HOC models with minor deviations, and the result showed that all three models were in good agreement with the experimental data. The azeotropic temperatures and compositions at 101.3, 60.0, and 20.0 kPa were determined by the NRTLHOC model, respectively, which showed that the azeotropic composition of 2-methylpyridine tended to decrease with the decline in system pressure.
1. INTRODUCTION 2-Methylpyridine, also known as α-methylpyridine or 2picoline, is an important reagent that is widely used in chemical and pharmaceutical production processes. For example, it could be used as a raw material for the synthesis of rubber, dye, resin, and so on. For the processes in which 2-methylpyridine is involved, it is indispensable to find suitable and efficient techniques to recover it from residual liquor, especially from its aqueous solution.1−3 As a common recycling method, a special distillation process is widely used, and its rational design relies on the accurate vapor−liquid equilibrium data of the 2methylpyridine−water system. On the basis of the literature, 2-methylpyridine is miscible with water in any proportion at all temperatures,4 and few data for vapor−liquid equilibrium have been tested or collected by well-known databank NIST. Gierycz reported vapor−liquid equilibrium data and activity coefficients at infinite dilution for the aqueous solution of 2-methylpyridine at T = 373.15 K.5 Abe measured the vapor pressures of the binary system at 298.15, 308.15, and 318.15 K over the whole composition range by a static method.6 It had also been reported that 2-methylpyridine and water formed the minimum-boiling azeotrope. Vriens © 2017 American Chemical Society
measured the VLE data over the range of 6.6 to 95.5 mass % of 2-methylpyridine for the binary system with a modified Othmer still at 101.32 kPa and reported that the azeotropic values are 94.8 °C, 53.3 mass % of 2-methylpyridine.7 Jiang et al. measured the VLE data of the binary system with a modified Rose still at 1 atm, and they reported that the azetropic temperature and composition were 94.5 °C, 52.5 mass % of 2methylpyridine.8 However, the correlated results of VLE data in the above-mentioned literature were that there existed an immiscible phenomenon near the azeotropic area, which is in contradiction with reality. And the data are incomplete or do not check the thermodynamic consistency. Therefore, it is imperative to strictly remeasure the experimental VLE data of the binary system. In this article, the VLE data for the binary system of water + 2-methylpyridine at 101.3 kPa were first measured with Fisher VLE equipment. To confirm the feasibility of the pressureswing distillation process for the separation of this azeotrope, Received: August 10, 2016 Accepted: January 11, 2017 Published: January 23, 2017 684
DOI: 10.1021/acs.jced.6b00713 J. Chem. Eng. Data 2017, 62, 684−690
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Table 1. Normal Boiling Point (Tb), Density (ρ), and Refractive Index (nD) of Pure Componentsa,b purity (mass%) component 2-methylpyridine water
GC 0.9996 none
ρ (298.15 K) (g·cm−3)
Tb (101.3 kPa) (K) c
exp
402.20 373.25
lit
d
exp
402.45 373.15
0.9405 1.0010
lit 12
0.9410 1.002914
nD (293.15 K) exp
lit
1.4985 1.3322
1.499413 1.330015
Standard uncertainties are u(Tb) = 0.1 K, u(ρ) = 2.0 × 10−5 g·cm−3, and u(nD) = 0.00001. bStandard uncertainties of experimental pressure and temperature are u(T) = 0.1 K and u(p) = 0.1 kPa. cExperimental value. dLiterature value. a
reached. If the vapor temperature was constant for a period of 15 to 30 min (temperatures might change by 0.1 K in this period), then equilibrium was assumed and the first samples were able to be collected for analysis. Samples were taken via sample valves, and switch actuation should be done within a split second in order to minimize the sample volume. At least three analyses were made for each sample. 2.3. Methods of Analysis.16 The compositions of vapor and liquid phases were determined by an Evolution 300 ultraviolet spectrophotometer produced by the Thermo Electron Corporation. A pair of 1 cm quartz cells were used throughout, and the solutions in the cells were kept at a constant temperature by using the temperature control block to guaranteed precision. The scanning method was used over the wavelength range from 190 to 1100 nm to determine the maximum absorption wavelength of the binary mixture of water and 2-methylpyridine, and a wavelength of 262 nm was chosen. The fixed method at 262 nm was then used to make the working curve and measure the composition of each sample. Each sample was analyzed three times, and the measured absorbance value was converted to mole fraction by the working curve from the law of Lambert−Beer. With repeated measurements, the standard uncertainty in composition was estimated to be 0.001 in mole fraction.
which would avoid the introduction of the additional impurities and the necessary cost of recycling the entrainer or extractant resulting from the use of azeotropic or extractive distillation, this article also measured the VLE data for the binary system at two other pressures, 60.0 and 20.0 kPa, in terms of the frequent range of operating pressure. The thermodynamic consistency of all of the experimental VLE data were checked out under the rule of Wisniak’s area test and Wisniak’s point test. The experimental data were correlated with activity coefficient models NRTL-HOC,9 UNIQUAC-HOC,10 and WilsonHOC.11 Then, the correlated parameters of these models and the average absolute deviations were compared and discussed. The azeotropic temperatures and compositions of the binary system at all pressures were determined by the best-fit NRTLHOC model.
2. EXPERIMENTAL SECTION 2.1. Materials. All of the analytical reagents used in this study were prepared by Adamas Reagent, Ltd. and supplied by Shanghai Taitan Scientific Co., Ltd., China. 2-Methylpyridine was further purified with batch distillation, and the purity was checked with a gas chromatogram (GC) equipped with a flame ionization detector (FID) and was found to be greater than 99.90 mass %. The reagents were further verified by comparing their physical properties with the corresponding literature values, as shown in Table 1. The normal boiling point was measured with Fisher VLE 602 equipment with a standard uncertainty of 0.1 K. The density of the reagents was measured at 298.15 K using a KEM DA-510 density meter, and the refractive index was measured at 293.15 K using an ATAGO RX-5000 Abbe refractometer. The uncertainties in density and refractive index measurements were 2.0 × 10−5 g·cm−3 and 0.00001, respectively. 2.2. Apparatus and Procedure. The measurements of vapor−liquid equilibria were performed with the VLE 602 apparatus from i-Fischer Engineering GmbH, Waldbüttelbrunn, Germany. The operation procedure is based on the principle of the circulation method. The apparatus was an all-glass dynamic recycling still equipped with a Cottrell pump, which ensures that liquid and vapor phases were in intimate contact during the boiling process. The equilibrium temperature was measured with a PT-100 precise glass temperature sensor with a standard uncertainty of 0.1 K. A Fisher M101 control system was used to control and measure the pressure and heating power, and a single-stage rotary vane vacuum pump and an electrovalve activated by an on−off controller were used to minimize the pressure deviation from the setting value. The standard uncertainty of the pressure is 0.1 kPa. For each experiment in the binary system, the pressure was fixed, the immersion heater and stirring system of the liquid mixture were turned on under the proper operating conditions, and the minimum temperature difference between cooling water and vapor was 60 K. The system was operated under constant conditions for about 30 min until equilibrium was
3. RESULTS AND DISCUSSION 3.1. Experimental Data. The isobaric vapor−liquid equilibrium data for the binary system of water (1) + 2methylpyridine (2) were measured at 101.3, 60.0, and 20.0 kPa, as listed in Tables 2−4 and plotted in Figures 1−3, respectively. The result showed that the binary system formed a minimumboiling azeotrope at all three pressures. The azeotropic composition under each pressure could be determined by using y1 − x1 versus x1 diagrams at y1 − x1 = 0, and the azeotropic temperature could be determined by the T versus x1, y1 diagrams at the location corresponding to the azeotropic composition.17 3.2. Vapor−Liquid Equilibrium Model. In this work, the nonideality of the vapor phase was taken into consideration. Therefore, the activity coefficients were calculated from the following equation18 ⎧ [(B − V L)(p − ps ) + (1 − y 2 )]pδ ⎫ yp ii i ij ⎪ i i i ⎪ ⎬ ⎨ γi = s⎪ ⎪ xipi ⎩ RT ⎭
(1)
with
δij = 2Bij − Bii − Bjj
(2)
where yi is the mole fraction of component i in the vapor phase, xi is the mole fraction of component i in the liquid phase, p and T are the system pressure and temperature, γi is the activity coefficient of component i in the liquid phase, R is the gas constant, and psi is the saturation vapor pressure of pure 685
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Table 2. Experimental Vapor−Liquid Equilibrium Data and Activity Coefficients for the Binary System of Water (1) + 2Methylpyridine (2) at 101.3 kPaa
Table 4. Experimental Vapor−Liquid Equilibrium Data and Activity Coefficients for the Binary System of Water (1) + 2Methylpyridine (2) at 20.0 kPaa
p (kPa)
T (K)
x1
y1
γ1
γ2
p (kPa)
T (K)
x1
y1
γ1
γ2
101.3
372.34 371.16 368.62 368.40 368.20 368.18 368.18 368.18 368.18 368.19 368.39 369.43 370.25 372.80 378.03 383.47 392.31 396.01 401.11
0.9990 0.9970 0.9829 0.9270 0.8910 0.8500 0.8130 0.7770 0.7540 0.6920 0.6010 0.4490 0.3416 0.2913 0.2170 0.1474 0.0616 0.0356 0.0054
0.9740 0.9331 0.8426 0.8120 0.7950 0.7920 0.7910 0.7910 0.7900 0.7900 0.7850 0.7650 0.7185 0.6851 0.6140 0.5058 0.2941 0.1913 0.0350
1.0038 1.0048 1.0088 1.0395 1.0669 1.1150 1.1643 1.2182 1.2538 1.3657 1.5514 1.9500 2.3399 2.3921 2.4055 2.4389 2.5743 2.5952 2.7035
66.2992 58.9618 26.3386 7.4084 5.4409 4.0135 3.2346 2.7124 2.4704 1.9725 1.5477 1.1810 1.1484 1.0943 1.0215 1.0093 1.0088 1.0086 1.0074
20.00
333.08 332.86 332.52 332.06 331.95 330.99 330.52 330.41 330.38 330.38 330.39 330.47 330.56 331.70 334.81 336.50 338.03 339.42 341.98 346.68 350.57
0.9985 0.9957 0.9912 0.9836 0.9811 0.9571 0.9254 0.8915 0.8571 0.8228 0.7723 0.7137 0.6834 0.5435 0.4322 0.3639 0.3128 0.2645 0.1987 0.0933 0.0322
0.9925 0.9798 0.9608 0.9335 0.9257 0.8743 0.8462 0.8361 0.8330 0.8318 0.8296 0.8243 0.8200 0.7829 0.7291 0.6739 0.6243 0.5740 0.4838 0.2927 0.1197
1.0002 1.0002 1.0008 1.0010 1.0027 1.0127 1.0364 1.0685 1.1088 1.1534 1.2250 1.3123 1.3576 1.5459 1.5701 1.5977 1.6089 1.6459 1.6532 1.7482 1.7684
11.4315 10.8409 10.4295 9.6816 9.4302 7.3252 5.2597 3.8719 2.9992 2.4360 1.9195 1.5683 1.4469 1.1493 1.0049 1.0029 1.0022 1.0011 1.0007 1.0005 1.0002
a
Standard uncertainties are u(T) = 0.1 K, u(p) = 0.1 kPa, and u(x1) = u(y1) = 0.001. a
Standard uncertainties are u(T) = 0.1 K, u(p) = 0.1 kPa, and u(x1) = u(y1) = 0.001.
Table 3. Experimental Vapor−Liquid Equilibrium Data and Activity Coefficients for the Binary System of Water (1) + 2Methylpyridine (2) at 60.0 kPaa p (kPa)
T (K)
x1
y1
γ1
γ2
60.00
358.70 358.11 357.97 357.11 356.80 355.76 355.64 355.39 355.26 355.26 355.28 355.44 355.46 355.49 355.54 357.69 363.17 367.33 377.47
0.9971 0.9925 0.9911 0.9806 0.9750 0.9517 0.9256 0.8867 0.8608 0.8459 0.8130 0.7794 0.7328 0.6756 0.5746 0.4266 0.3023 0.2122 0.0685
0.9819 0.9565 0.9502 0.9091 0.8929 0.8493 0.8294 0.8213 0.8210 0.8205 0.8203 0.8201 0.8197 0.8193 0.8015 0.7461 0.6591 0.5542 0.2583
1.0003 1.0015 1.0018 1.0018 1.0017 1.0170 1.0263 1.0714 1.1089 1.1278 1.1722 1.2147 1.2903 1.3973 1.6043 1.8508 1.8746 1.9291 1.9604
15.2481 14.4589 14.0161 12.0874 11.1692 8.4356 6.2210 4.3174 3.5371 3.2039 2.6412 2.2280 1.8421 1.5189 1.2689 1.1092 1.0015 1.0004 1.0003
Figure 1. Plot of experimental data and correlated data for the binary system of water (1) + 2-methylpyridine (2) at 101.3 kPa. Black ●, experimental vapor and liquid-phase composition; green ⧫, Jiang’s experimental VLE data; pink ▲, Vriens’ experimental VLE data; black solid line, calculated vapor and liquid phase composition from the NRTL-HOC model; red dashed line, calculated vapor and liquid phase composition from the UNIQUAC-HOC model; blue dotted line, calculated vapor and liquid phase composition from the Wilson-HOC model.
a
Standard uncertainties are u(T) = 0.1 K, u(p) = 0.1 kPa, and u(x1) = u(y1) = 0.001.
component i. Variables Bii and Bjj are the second virial coefficients of pure components i and j, respectively, and Bij is the cross second virial coefficient. All of the second virial coefficients were estimated from the Hayden and O’Connell (HOC) model with the critical properties, acentric factors, and dipole moments tabulated in Table 5. VLi is the liquid molar volume of component i at equilibrium temperature, which was obtained from the Rackett equation modified by Yamada and Gunn,18 which particularly applies to the estimate of saturated
liquid molar volume when the reduced temperature is less than 0.99 and also applies to polar compounds with high accuracy. The saturation vapor pressure of pure component i can be calculated by the extended Antoine equation, and parameters A1 to A9 can be obtained from Aspen Plus V8.6, as listed in Table 6. The equation for the extended Antoine vapor pressure is 686
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system of water (1) + 2-methyloyridine (2) showed a positive deviation from Raoult’s law at all three pressures. 3.3. Thermodynamic Consistency Test of the Experimental Data. To test the reliability and reasonability of the experimental data, the thermodynamic consistency test of the VLE data was checked by means of Wisniak’s L−W area test and point test.19,20 The former checks the thermodynamic consistency of the VLE data on the whole, and the latter conducts the point-to-point test. In Wisniak’s L−W area test, the values of integrals L and W should be approximately identical, and a deviation factor D is defined, with D < 3−5 indicating thermodynamic consistency. For the point-to-point test, the ratio of Li to Wi for the binary system should all approach the value of 1 (0.92 < Li/Wi < 1.10) at all points.21−23 The test can be described by the following equations Figure 2. Plot of experimental data and correlated data for the binary system of water (1) + 2-methylpyridine (2) at 60.0 kPa. ●, experimental vapor and liquid phase composition; black solid line, calculated vapor and liquid phase composition from the NRTL-HOC model; red dashed line, calculated vapor and liquid phase composition from the UNIQUAC-HOC model; blue dotted line, calculated vapor and liquid phase composition from the Wilson-HOC model.
Li =
∑ Tk◦xk Δsk◦ ∑ xk Δsk◦ − T
Wi =
RT ⎛ ⎜∑ xk ln γk − ∑ xk Δsk◦ ⎝
D = 100 ×
(4)
1
1
1
1
∑ xk ln
yk ⎞ ⎟ xk ⎠
(5)
∫0 Li dx1 − ∫0 Wi dx1 ∫0 Li dx1 + ∫0 Wi dx1
where γk is the activity coefficient of component k in the liquid phase, Tk° is the boiling point of pure component k; xk and yk are the mole fractions of component k in the liquid phase and vapor phase, respectively, and Δsk° is the molar entropy of vaporization of component k, which can be obtained from Aspen Plus V8.6 by using the Clausius−Clapeyron equation. The results of the thermodynamic consistency test listed in Table 7 indicate that the experimental data passed the area test, and the values of Li/Wi at all points plotted in Figure 4 indicate that the experimental data passed the point-to-point test. 3.4. Correlation of VLE Data. Taking the nonideality of both the vapor phase and liquid phase into consideration, the experimental data for the binary system of water (1) + 2methylpyridine (2) at 101.3, 60.0, and 20.0 kPa were correlated with the NRTL-HOC, UNIQUAC-HOC, and Wilson-HOC models by Aspen Plus V 8.6 to obtain the interaction parameters. In the regression calculation, the maximum likelihood objective function (F) was adopted,24 and it is expressed as
Figure 3. Plot of experimental data and correlated data for the binary system of water (1) + 2-methylpyridine (2) at 20.0 kPa. ●, experimental vapor and liquid phase composition; black solid line, calculated vapor and liquid phase composition from the NRTL-HOC model; red dashed line, calculated vapor and liquid phase composition from the UNIQUAC-HOC model; blue dotted line, calculated vapor and liquid phase composition from the Wilson-HOC model.
2 ⎛⎛ exp ⎛ pexp − pest ⎞2 Ti − Tiest ⎞ i ⎟ ⎜ F=∑ ⎜ ⎟ + ⎜⎜ i ⎟ ⎜⎝ σ σ ⎠ ⎝ ⎠ T p i=1 ⎝ n
⎛ ⎞ A2 ln(pis ) (kPa) = A1 + ⎜ ⎟ + A4 T (K) ⎝ T (K) + A3 ⎠ + A5 ln T(K) + A 6T(K)A 7 A8 ≤ T (K) ≤ A 9
(6)
2 ⎛ xiexp − xiest ⎞2 ⎛ yiexp − yiest ⎞ ⎞ ⎟⎟ ⎟ +⎜ ⎟ + ⎜⎜ σx σ ⎝ ⎠ ⎝ ⎠ ⎟⎠ y
(3)
(7)
where n is the number of data points, x and y are the mole fractions of the liquid phase and vapor phase, T and p are the
In this way, the activity coefficients were calculated with eq 1, as listed in Tables 2 to 4. The results indicated that the binary Table 5. Physical Properties of Pure Componentsa
a
compound
Tc (K)
pc (kPa)
Vc (cm3 mol−1)
Zc
μ (D)
ω
water 2-methylpyridine
647.1 621.0
22 064 4600
55.9 335.0
0229 0.298
1.8497 2.0386
0.3449 0.2990
Taken from the Aspen Plus physical properties databank. 687
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Table 6. Parameters for the Extended Antoine Equation component
A1
A2
A3
A4
A5
A6
A7
A8
A9
water 2-methylpyridine
66.7412 84.3652
−7258.2 −7841.2
0 0
0 0
−7.3037 −10.216
4.17 × 10−6 6.21 × 10−6
2 2
273.16 206.44
647.10 621.00
the equilibrium temperature and mole fraction of water in the vapor phase. The comparisons of experimental VLE data with calculated values by all three models are illustrated graphically in Figures 1−3. And the relationship between activity coefficients γ1 and γ2 and liquid phase mole fraction x1 is illustrated graphically in Figure 5. According to Table 8, most of the RMSDs of the vapor phase composition of water are less than 0.01, and it suggested that these three models showed good agreement with the experimental values. The NRTLHOC and UNIQUAC-HOC models showed better fits than did the Wilson-HOC model. The reason is that the binary system comes about as close to separating into two phases as is possible without actually doing so at the boiling point,7 whereas the Wilson model is appropriate only for the miscible system. From Figures 1 to 3, the binary system of water (1) + 2methylpyridine (2) formed a minimum-boiling azeotrope at all three pressures and the azeotropic temperature and composition of water were determined with the best-fit NRTL-HOC model, respectively, as listed in Table 9. The azeotropic composition of 2-methylpyridine tends to decrease with the decline in system pressure. From Figure 5, the activity coefficient of 2-methylpyridine increased rapidly with increasing dilution at low concentrations. The binary systems showed a positive deviation from Raoult’s law at all three pressure. The experimental VLE data from Jiang and Vriens were also plotted in Figure 1, and there are some differences between the results in the literature and this work. However, all of the VLE data in this work have passed the thermodynamic consistency test and show good agreement with the simulation result, which means that the VLE data in this work are more reliable. The azeotropic temperature and composition of the binary system at 101.32 kPa were compared with the literature values, and the absolute deviations of the azeotropic temperature (ΔTaz = |Tazexp − Tazlit|) and the mole fraction of water in the
Table 7. Thermodynamic Consistency Test Results for the Binary System at 101.3, 60.0, and 20.0 kPa Wisniak’s L−W area test pressure (kPa)
L
W
D
101.3 60.0 20.0
13.87 10.41 7.01
13.08 9.76 6.69
2.94 3.26 2.38
Figure 4. Plot of the point-to-point test result for the binary system at different pressures: (●) 101.3, (▲) 60.0, and (■) 20.0 kPa.
equilibrium temperature and pressure, σ is the standard deviation of the indicated data, and superscripts exp and est denote the experimental and estimated values. The correlated binary interaction parameters of the NRTLHOC, UNIQUAC-HOC, and Wilson-HOC models are listed in Table 8, together with the root-mean-square deviations (RMSDs) and the maximum absolute deviations (MADs) of
Table 8. Correlation Parameters, Root Mean Square Deviations (RMSDs), and Maximum Absolute Deviations (MADs) for the Binary Systems correlation parameters models
aija
ajia
Water (1) + 2-Methylpyridine (2) at 101.32 kPa −3.5486 −2.7624 NRTLe UNIQUACf 2.1769 −0.1380 Wilsong 5.4487 3.1879 Water (1) + 2-Methylpyridine (2) at 60.00 kPa NRTL −9.0295 −2.4252 UNIQUAC 2.8929 0.0211 Wilson 6.1818 20.9089 Water (1) + 2-Methylpyridine (2) at 20.00 kPa NRTL −17.6919 −1.0984 UNIQUAC 2.8154 0.6180 Wilson 5.6046 18.6082
RMSDs
MADs
bij
bji
σy1b
σT1c
Δmaxy1d
ΔmaxT1
2383.0733 −789.1930 −2156.6914
1012.5070 −225.1766 −2696.1441
0.0055 0.0050 0.0110
0.4478 0.4599 0.5181
0.0129 0.0129 0.0207
1.3137 1.3423 1.5209
4376.5147 −1104.0356 −2277.3208
715.6383 −101.3262 −8467.2266
0.0019 0.0035 0.0131
0.2423 0.2600 0.4342
0.0059 0.0077 0.0290
0.7091 0.7265 1.2134
6962.6254 −1016.6972 −1846.5704
155.2745 −237.5711 −7062.3449
0.0051 0.0061 0.0121
0.3510 0.3733 0.5418
0.0118 0.0134 0.0242
0.8729 0.8284 1.1997
exp 2 n est exp 2 1/2 c 1/2 d Binary interaction parameter. bσy1 = (∑i n= 1((yest 1,i − y1,i ) /n)) . σT1 = (∑i = 1((T1,i − T1,i ) /n)) . Δmaxy and ΔmaxT are the maximum vapor phase composition and temperature deviation, respectively. eNRTL, τij = aij + (bij/T), with αij fixed at 0.3 for the binary system. fUNIQUAC, τij = exp(aij + (bij/T)). gWilson, ln Aij = aij + (bij/T). a
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Figure 5. Plot of γ1, γ2 versus x1 for the binary system at 101.3, 60.0, and 20.0 kPa. ●, Experimental activity coefficient of 2-methylpyridine; ○, experimental activity coefficient of water; black solid line, calculated activity coefficients from the NRTL-HOC model; red dashed line, calculated activity coefficients from the UNIQUAC-HOC model; blue dotted line, calculated activity coefficients from the Wilson-HOC model.
Table 9. Azeotropic Data at Different Pressuresa ΔTaz (K)
Δxaz (mol % water)
0.01 0.31
0.0300 0.0347
az
pressure (kPa)
Taz (K)
x (mol % water)
101.32 this work Vriens Jiang et.al. 60.00 20.00
367.96 367.95 367.65 355.27 330.52
0.7892 0.8192 0.8239 0.8212 0.8381
azeotropic temperatures and compositions are 367.96 K, 0.7892 mol % of water at 101.3 kPa; 355.27 K, 0.8212 mol % of water at 60.0 kPa; and 330.52 K, 0.8381 mol % of water at 20.0 kPa, respectively. The experimental VLE data were correlated with three different activity coefficient models: NRTL-HOC, UNIQUACHOC, and Wilson-HOC. The correlated results were in good agreement with the experimental data. The azeotropic temperature and composition of the binary system at all three pressures were determined with the NRTL model, which showed the least deviation from the experimental values. The results of azeotropic compositions at different pressures showed that the concentration of 2-methylpyridine tended to decrease with the decline in system pressure, which would assist in the design of the separation process by distillation.
a
Standard uncertainties are u(p) = 0.1 kPa, u(Taz) = 0.1 K, and u(xaz) = 0.001.
azeotropes (Δxaz = |xazexp − xazlit|) between the experimental values and the literature values are listed in Table 9.
4. CONCLUSIONS Isobaric vapor−liquid equilibrium (VLE) data for the water + 2-methylpyridine binary system were measured at 101.3, 60.0, and 20.0 kPa with Fisher VLE 602 equipment. Thermodynamic consistency was tested for the binary system using Wisniak’s L−W area test and point test, and all of the experimental VLE data points passed the test. The results showed that the binary system formed a minimum-boiling azeotrope at all three pressures and had a positive deviation from Raoult’s law. The
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00713. Explanation of the Table of Contents graphic (PDF) 689
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AUTHOR INFORMATION
Corresponding Author
*Tel: +86 022 27406186. E-mail:
[email protected]. ORCID
Xianghai Guo: 0000-0002-1519-4050 Funding
This work was supported by the Independent Innovation Foundation of Tianjin University (2016XZC-0071) and the Natural Science Foundation of Tianjin (16JCYBJC20300). Notes
The authors declare no competing financial interest.
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DOI: 10.1021/acs.jced.6b00713 J. Chem. Eng. Data 2017, 62, 684−690
