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Isothermal vapor–liquid equilibria for methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K
Fluid Phase Equilibria 309 (2011) 201–205
Contents lists available at ScienceDirect
Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid
Isothermal vapor–liquid equilibria for methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K Chuanzhuang Feng a , Jilian Dong a , Yonghong Li a,b,∗ a b
Key Laboratory for Green Chemical Technology of State Education Ministry, Tianjin 300072, PR China National Engineering Research Center for Distillation Technology, Tianjin 300072, PR China
a r t i c l e
i n f o
Article history: Received 3 May 2011 Received in revised form 15 July 2011 Accepted 20 July 2011 Available online 26 July 2011 Keywords: Vapor–liquid equilibrium Methanol 2,3-Dimethyl-2-butene
a b s t r a c t Isothermal vapor–liquid equilibrium (VLE) data were measured for the binary system methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K, respectively. The measurements were carried out in a novel recirculation equilibrium equipment. Three activity coefficient models including Wilson, NRTL and UNIQUAC, as well as the Soave–Redlich–Kwong equation of state were used to correlate the experimental data. The correlation results showed that a good consistency between the experimental data and the Wilson model can be achieved. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The addition of ethers to gasoline to replace leaded octane enhancers and to reduce emissions of carbon monoxide and unburned hydrocarbons is well-known [1]. Although MTBE was still the most widely used fuel oxygenate, it was found to pollute the groundwater because of its high water solubility. For this reason, heavier ethers are attracting much more attention in recent years [2]. Reactive distillation is an efficient process unit that combines reaction and distillation in a single step. It has several advantages over the traditional two-step process: such as the simplification of production procedure, the reduction of unreacted reactants, and the minimization of waste discharge [3]. This technology has been applied in the ether production. Therefore, for the reliable design of such a process, accurate experimental data on vapor–liquid equilibrium (VLE) are required. The temperatures for the reaction of the higher carbon olefins with methanol are almost between 333 K and 373 K and the pressures are between 0.6 MPa and 1 MPa [4,5], this temperature and pressure ranges are the most appropriate operating conditions in the reaction zone of a reactive distillation column for manufacturing ethers. Moreover, VLE data for the mixture methanol and 2,3-dimethyl-2-butene were very scarce in the published literatures and were only measured under atmospheric pressure [6]. So the purpose of this paper is to report VLE data for the binary
∗ Corresponding author at: Key Laboratory for Green Chemical Technology of State Education Ministry, Tianjin 300072, PR China. Tel.: +86 022 27404701x8082. E-mail addresses: [email protected], [email protected] (Y. Li). 0378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2011.07.014
system methanol and 2,3-dimethyl-2-butene at various temperatures (343.15 K, 353.15 K, 363.15 K, 373.15 K) and to discuss the consistency of these experimental data with the Wilson [7], NRTL [8] and UNIQUAC [9] models as well as the Soave–Redlich–Kwong [10] equation of state. 2. Experimental 2.1. Materials for vapor–liquid equilibrium (VLE) measurements Methanol was provided by Tianjin GuangFu company and had a minimum mass fraction purity of 0.995. 2,3-Dimethyl-2-butene was purchased from Dalian chemphy Fine Chemical Co. Ltd. with a minimum mass fraction purity of 0.995. The purities of all chemical reactants were provided by the suppliers and all reactants were used without further purification expect for drying over molecular sieves (Nankai University 3A) for 24 h. We also checked the purities of all chemicals with the GC before our experiments and the results were satisfactory. 2.2. Apparatus for VLE measurements The vapor–liquid equilibrium data were measured using a new recirculation still which was designed following the general Othmer-type still [11,12]. A schematic of the apparatus is shown in Fig. 1. It consists of a stainless steel equilibrium cell and temperature and pressure measuring systems, etc. The total volume of the equilibrium cell is 196 ml and the volume of mixture needed for the measurements was approximately 120 ml. A magnetic stirrer
202
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205 Table 2 The measured and correlated vapor pressures of 2,3-dimethyl-2-butene and the deviation p.
Fig. 1. Schematic diagram of the equilibrium still. (1) Condenser, (2) observing tube of vapor condensate, (3) vapor sampling port, (4) electric heating tapes for preheating the condensate and backflow of the liquid phase, (5) oil bath, (6) equilibrium still, (7) magnetic stirrer, (8) cooling, (9) circulation pump, (10) liquid sampling port, (11) flow meter, (12) vapor rising space, (13) electric heating tapes for heating the vapor space, (14) pressure transducer and (15) thermocouple.
was used to accelerate the equilibrium process. The temperature of the equilibrium cell was maintained by a thermostated oil bath. Temperature was measured with a SME-700W-J (Yuyao Shimai Electron company) thermometer equipped with a Pt-100 resistant temperature probe with an accuracy of ±0.01 K. The uncertainty of temperature was estimated to be ±0.09 K. The total vapor pressure was measured using a pressure transducer (Beijin Weisite company, CYB-20S) when phase equilibrium was reached and maintained for at least 30 min. According to the data provided by the manufacturers of the pressure measurement devices, the pressure uncertainty was estimated to be ±0.5 kPa. The thermometers and the pressure transducer had been calibrated at the Bureau of Quality and Technical Supervision of Tianjin before experiments. In order to determine the reliability of this new vapor–liquid equilibrium still, the isothermal vapor–liquid equilibrium data for the binary system of benzene(1) + cyclohexane(2) at 403.15 K were measured and compared with the data of literature [13]. The comparison had been presented in our previous work [14] and the
T (K)
pexp (kPa)
pest (kPa)
p
336.50 338.20 340.60 342.65 344.20 346.24 347.65 350.10 353.46 355.35 357.22 362.80 365.76 368.05 370.36 373.18 375.20 376.50 379.15 381.62 383.05 384.70 386.65 388.20
73.5 77.5 84.2 90.2 94.7 101.2 105.3 113.9 125.5 133.3 140.4 164.8 179.5 190.9 202.8 218.8 230.4 238.5 255.1 271.2 281.3 292.1 306.8 318.4
73.6 77.9 84.4 90.2 94.8 101.1 105.7 114.0 126.2 133.5 141.0 165.4 179.6 191.2 203.5 219.2 231.1 238.9 255.6 271.9 281.7 292.3 307.4 319.1
0.14 0.55 0.20 0.02 0.10 0.07 0.37 0.09 0.57 0.15 0.45 0.39 0.07 0.17 0.33 0.20 0.29 0.18 0.19 0.25 0.13 0.06 0.21 0.21
P (%) =
|Pexp −Pest | Pexp
× 100.
agreement was satisfactory, which indicated that it was possible to measure good VLE data with the equipment. 2.3. Analysis and GC calibration The condensed vapor phase and liquid phase of the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) were analyzed with a FULI9790 gas chromatograph equipped with a capillary column (SGE, dimethyl polysiloxane, length 60 m, column inner diameter 0.22 mm, film thickness 0.25 m) and a flame ionization detector. Nitrogen, 99.999% pure, was used as carrier gas. The temperatures of injector and detector were both at 493.15 K. The oven was operated at programmed temperature from 353.15 K to 433.15 K at a rate of 10 K/min and then remain 5 min at the temperature of 433.15 K. Calibration curves were obtained by a set of solutions of
Table 1 Critical temperatures Tc , critical pressures pc , critical molar volumes Vc , acentric factors ω, critical compressibility factor Zc , UNIQUAC volume parameter RUNIQ , UNIQUAC area parameter QUNIQ pure-component vapor pressure equation parameters A, B, and C for the Antoine equation and recommended temperature range of the vapor pressure correlation Tmin and Tmax . Component
Methanol
2,3-Dimethyl-2-butene
Tc a (K) Pc a (MPa) Vc c (cm3 mol−1 ) ωa Zc a Ab Bb Cb RUNIQ a QUNIQ a Tmin (K) Tmax (K)
512.58 8.096 40.7 0.566 0.244 14.01 2160 −107.90 1.4311 1.4320 333.42 375.89
524.0 3.160 119.643 0.233 0.270 13.44 2473.0 −65.97 4.2649 3.8770 336.50 388.20
a b c
Ref. [15]. This work. Ref. [16].
Fig. 2. Vapor pressure for 2,3-dimethyl-2-butene: () literature [6] and () this work.
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205 Table 3 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 343.15 K. p (kPa)
x1
y1
91.5 155.5 169.5 181.2 186.4 189.3 190.0 190.3 190.8 191.2 191.4 191.1 190.4 190.3 189.3 185.4 182.9 175.3 161.1 153.1 150.8 125.3
0.000 0.068 0.109 0.183 0.253 0.326 0.416 0.433 0.448 0.528 0.605 0.621 0.652 0.659 0.739 0.810 0.852 0.898 0.948 0.964 0.969 1.000
0.000 0.419 0.473 0.519 0.543 0.549 0.559 0.560 0.562 0.570 0.578 0.580 0.583 0.584 0.593 0.616 0.638 0.677 0.759 0.807 0.826 1.000
1 7.57 5.83 4.06 3.15 2.51 2.01 1.93 1.89 1.62 1.44 1.41 1.34 1.33 1.20 1.11 1.08 1.04 1.02 1.01 1.01 1.00
203
Table 5 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 363.15 K.
2
p (kPa)
x1
y1
1
1.00 1.03 1.06 1.12 1.20 1.33 1.50 1.55 1.58 1.82 2.14 2.22 2.39 2.43 3.08 3.93 4.71 5.84 7.92 8.75 9.11
166.9 283.8 298.6 323.0 342.6 354.0 364.5 365.6 366.2 369.4 369.5 368.3 367.9 367.1 360.1 348.9 343.1 299.4 284.1 265.2 255.5
0.000 0.073 0.092 0.133 0.192 0.260 0.379 0.410 0.427 0.573 0.612 0.628 0.677 0.744 0.834 0.883 0.906 0.971 0.983 0.995 1.000
0.000 0.419 0.454 0.501 0.538 0.561 0.585 0.589 0.591 0.606 0.612 0.618 0.623 0.635 0.661 0.687 0.708 0.839 0.889 0.960 1.000
6.34 5.70 4.72 3.69 2.94 2.16 2.02 1.95 1.50 1.42 1.39 1.30 1.20 1.09 1.04 1.03 1.00 1.00 0.99 0.99
2 1.00 1.02 1.03 1.05 1.10 1.18 1.36 1.42 1.46 1.90 2.06 2.11 2.39 2.92 4.12 5.24 6.03 9.42 10.59 12.65
3. Model known compositions. The error in the determination of the liquid and vapor mole fraction was estimated to be ±0.003.
In our study, the Soave–Redlich–Kwong [10] equation of state with quadratic mixing rules in the attractive parameter and linear mixing rules in the covolume was used for the evaluation of vapor phase fugacity coefficients. Its expression is
2.4. Procedure of the VLE measurement Pure component 1 was introduced to the recirculation still, and its vapor pressure was measured. After the vapor pressure measurements, component 2 was added to the equilibrium still. In the isothermal runs, the temperature was adjusted to the desired value by adjusting the temperature of the oil bath. It took about 50 min to achieve constant temperature, the temperature was held constant for 30 min to enhance the steady-state condition before sampling. Samples of the liquid and the vapor condensate were taken manually with a cooled 1 l syringe after the steady-state condition was achieved. Every sample was analyzed 3 times, and the deviation of each analysis was less than 0.002.
Table 4 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 353.15 K. p (kPa)
x1
y1
1
124.8 216.7 242.8 253.8 263.7 266.1 266.4 267.4 268.1 268.3 268.1 267.3 266.3 265.2 254.1 245.5 231.9 196.1 180.9
0.000 0.079 0.143 0.205 0.333 0.409 0.423 0.429 0.578 0.611 0.624 0.665 0.668 0.742 0.874 0.910 0.944 0.989 1.000
0.000 0.434 0.505 0.537 0.568 0.578 0.579 0.580 0.594 0.598 0.601 0.607 0.607 0.617 0.662 0.694 0.746 0.912 1.000
6.54 4.70 3.62 2.45 2.04 1.98 1.96 1.50 1.43 1.40 1.33 1.32 1.20 1.05 1.02 1.00 1.00 1.00
2 1.00 1.03 1.07 1.13 1.29 1.44 1.47 1.49 1.95 2.10 2.15 2.37 2.39 2.98 5.17 6.38 8.11 12.11
P=
a RT − 2 V −b V + bV
(1)
a=
0.42748R2 Tc2 2 [1 + fw (1 − Tr0.5 )] Pc
(2)
b=
0.08664RTc Pc
(3)
fw = 0.315 + 1.60w − 0.166w2
(4)
Table 6 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 373.15 K. p (kPa)
x1
y1
1
219.2 343.8 407.5 447.9 471.1 488.6 490.2 492.3 496.5 497.8 498.9 498.3 497.8 496.1 488.0 472.4 460.3 453.6 447.8 415.9 400.9 387.1 353.6
0.000 0.055 0.110 0.174 0.248 0.361 0.385 0.405 0.497 0.566 0.611 0.630 0.686 0.749 0.824 0.885 0.916 0.926 0.933 0.966 0.977 0.985 1.000
0.000 0.367 0.474 0.530 0.564 0.593 0.594 0.597 0.614 0.614 0.624 0.626 0.633 0.648 0.669 0.703 0.732 0.749 0.767 0.835 0.873 0.907 1.000
6.50 4.91 3.79 2.98 2.22 2.09 2.00 1.70 1.49 1.41 1.37 1.27 1.18 1.09 1.04 1.02 1.02 1.02 1.00 1.00 1.00 0.99
2 1.00 1.01 1.03 1.08 1.15 1.30 1.35 1.39 1.59 1.84 2.01 2.10 2.42 2.91 3.84 5.12 6.17 6.50 6.63 8.77 9.46 10.20
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C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205
Fig. 3. P–x–y diagram for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 343.15 K, 353.15 K, 363.15 K, 373.15 K: (䊉) 343.15 K; () 353.15 K; () 363.15 K; () 373.15 K; solid curves were calculated from the Wilson model.
The critical temperatures, critical pressures, acentric factors, liquid molar volumes, UNIQUAC volume and area parameters used in the calculations are presented in Table 1. The liquid phase was modeled with the Wilson [7], NRTL [8] and UNIQUAC [9] equation, respectively. For the NRTL equation, the value of the parameter ˛ was fixed to be 0.3. The vapor pressure of the pure substances was calculated from the Antoine equation, Eq. (5). ln p (kPa) = A −
B T (K) + C
(5)
The vapor pressure equation parameters in Table 1 were fitted from data measured in this work. The recommended temperature ranges of the vapor pressure equations are also presented in Table 1.
Fig. 5. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 353.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
shown in Table 2. The experimental data were compared with literature data [6]. Fig. 2 shows that the agreements were satisfactory. The activity coefficients i for specie i were calculated from Eq. (6) i =
psi ˚si xi
pyi ˚vi
exp[(Vil (p − psi ))/RT ]
(6)
where yi is the molar fraction of component i in the vapor phase, p is the system total pressure, ˚vi is the fugacity coefficient of component i in the vapor phase, xi is the molar fraction of component i in the liquid phase, psi is the vapor pressure of pure component i at the system temperature, ˚si is the pure-component saturated
The vapor pressures for pure component of 2,3-dimethyl-2butene were measured in the present work and the results are
liquid fugacity coefficient at the system temperature, Vil is the component i liquid-phase molar volume at the system temperature, T is the temperature in Kelvin, and R is the universal gas constant. The measured isothermal VLE data at 343.15 K, 353.15 K, 363.15 K, 373.15 K for methanol(1) + 2,3-dimethyl-2-butene(2)
Fig. 4. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 343.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
Fig. 6. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 363.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
4. Results and discussion
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205
205
5. Conclusions The vapor pressure of 2,3-dimethyl-2-butene and the isothermal VLE data for methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K and 373.15 K were measured in this study. Three activity coefficient models had been employed to correlate the experimental data and the results showed that the Wilson model can correlate the experimental data better than the NRTL and the UNIQUAC model. The binary system showed a positive deviation from Raoult’s law and had a maximum pressure azeotrope. With the increase of temperature, the azeotropic point moved to the alcohol-rich region and the deviation from Raoult’s law increased.
Fig. 7. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 373.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
binary mixture are listed in Tables 3–6. The P–x–y diagrams and the –x diagrams are shown in Figs. 3–7, respectively. The system measured shows a positive deviation from Raoult’s law and exhibits azeotropic behavior. Azeotropic data were determined graphically from the measured values. For the correlation of the experimental data, a computer program had been developed by applying the least square method to fit an objective function. The objective function is OF =
2 NP Pexp − Pcal Pexp
i=1
+
yi
exp
− yi cal
2
Table 7 Correlation parameters of the Wilson, NRTL and UNIQUAC model, average deviation in pressure p, average deviation in vapor phase composition y, and azeotropic data for the system methanol(1) + 2,3-dimethyl-2-butene(2) at four different temperatures. 343.15 (K)
353.15 (K)
363.15 (K)
373.15 (K)
Wilson
A12 A21 p y
−639.74 −583.08 0.0033 0.0036
−586.68 −611.58 0.0021 0.0035
−550.86 −627.58 0.0025 0.0019
−516.81 −631.62 0.0063 0.0024
NRTL
A12 A21 p y
458.66 482.61 0.0133 0.0140
489.81 444.87 0.0115 0.0142
506.14 430.68 0.0125 0.0129
539.62 390.09 0.0134 0.0107
UNIQUAC
A12 A21 p y
23.05 −681.32 0.0114 0.0122
18.71 −662.10 0.0101 0.0125
18.07 −659.31 0.0110 0.0115
14.13 −640.71 0.0118 0.0094
Aze. data
xaz p (kPa) 0.12
0.5768 191.4 0.35
0.5996 268.4 0.25
0.6120 369.5 0.23
0.6282 499.1
D/%
Wilson: A12 = (12 − 22 )/R, A21 = (21 − 11 )/R; NRTL: A12 = (g12 − g22 )/R; UNIQUAC: A12 = (u12 − u22 )/R, A21 = (u21 − u11 )/R p = A21 = (g21 − g11 )/R;
NP i
|(pi exp −pi cal )/pi exp ×100%| NP
NP
; y =
i
|(yi exp −yi cal )| NP
.
Greek letters ˚i fugacity coefficient of component i i activity coefficient of the component i i interaction energy in the Wilson equation
(7)
yi exp
where NP is the number of components, p is the pressure of system. yi is the molar fraction of component i in the vapor phase. The regression results and the azeotropic data are shown in Table 7. From the data of Table 7 it can be concluded that the Wilson model agrees well with the VLE data obtained in the experiments.
Temperature
List of symbols Aij , Aji parameters of the liquid models (K) a parameter of the equation of state parameter of the equation of state b NP number of component pressure (kPa) P R gas constant (J/(mol K)) T temperature (K) interaction energy in the NRTL equation gij molar volume (m3 /mol) v Vi mole volume of pure component i (m3 /mol) uij interaction energy in the UNIQUAC equation xi liquid mole fraction of component i vapor mole fraction of component i yi
Superscripts cal calculated data exp experimental data Acknowledgments We acknowledge gratefully the financial support of the Fund of National Natural Science Foundation of China (No. 20976129), this work is also supported by the Program of Universities’ Innovative Research Terms (No. IRT0936). References [1] R.C. Everson, W. Jansen, J. Chem. Eng. Data 46 (2001) 243–246. [2] F.H. Syed, C. Egleston, R. Datta, J. Chem. Eng. Data 45 (2000) 319–323. [3] G. Bozga, A. Motelica, R. Dima a, V. Plesu, A. Toma, C. Simion, Chem. Eng. Process. 47 (2008) 2247–2255. [4] L.K. Rihko, A.O.I. Krause, Chem. Res. 35 (1996) 2500–2507. [5] R.S. Karinen, J.A. Linnekoski, A.O.I. Krause, Catal. Lett. 76 (2001) 81–87. [6] P. Uusi-Kyyny, J.P. Pokki, Y. Kim, J. Aittamaa, J. Chem. Eng. Data 49 (2004) 251–255. [7] G.M. Wilson, J. Am. Chem. Soc. 86 (1964) 127–130. [8] H. Renon, J.M. Prausnitz, AIChE J. 14 (1968) 135–144. [9] D.S. Abrams, J.M. Prausnitz, AIChE J. 21 (1975) 116–128. [10] G. Soave, Chem. Eng. Sci. 27 (1972) 1197–1203. [11] C.I. Maria, C.T. Fernand, Fluid Phase Equilibria 103 (1995) 257–284. [12] Pavlov, S. Yu, Isolation and Purification of Monomers for Synthetic Rubber (in Russian), Chimiya, Leningrad, 1987. [13] B. Wisniewska, J.S. Gregorowicz, Malanowski Fluid Phase Equilibria 86 (1993) 173–186. [14] J.L. Dong, C.Z. Feng, Y.H. Li, J. Chem. Eng. Data 56 (2011) 2386–2392. [15] C.L. Yaws, Chemical Properties Handbook, 1999. [16] T.E. Daubert, R.P. Danner, Physical and Thermodynamic Properties of Pure Chemicals: Data Compilation, Hemisphere, New York, 1989.
Contents lists available at ScienceDirect
Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid
Isothermal vapor–liquid equilibria for methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K Chuanzhuang Feng a , Jilian Dong a , Yonghong Li a,b,∗ a b
Key Laboratory for Green Chemical Technology of State Education Ministry, Tianjin 300072, PR China National Engineering Research Center for Distillation Technology, Tianjin 300072, PR China
a r t i c l e
i n f o
Article history: Received 3 May 2011 Received in revised form 15 July 2011 Accepted 20 July 2011 Available online 26 July 2011 Keywords: Vapor–liquid equilibrium Methanol 2,3-Dimethyl-2-butene
a b s t r a c t Isothermal vapor–liquid equilibrium (VLE) data were measured for the binary system methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K, 373.15 K, respectively. The measurements were carried out in a novel recirculation equilibrium equipment. Three activity coefficient models including Wilson, NRTL and UNIQUAC, as well as the Soave–Redlich–Kwong equation of state were used to correlate the experimental data. The correlation results showed that a good consistency between the experimental data and the Wilson model can be achieved. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The addition of ethers to gasoline to replace leaded octane enhancers and to reduce emissions of carbon monoxide and unburned hydrocarbons is well-known [1]. Although MTBE was still the most widely used fuel oxygenate, it was found to pollute the groundwater because of its high water solubility. For this reason, heavier ethers are attracting much more attention in recent years [2]. Reactive distillation is an efficient process unit that combines reaction and distillation in a single step. It has several advantages over the traditional two-step process: such as the simplification of production procedure, the reduction of unreacted reactants, and the minimization of waste discharge [3]. This technology has been applied in the ether production. Therefore, for the reliable design of such a process, accurate experimental data on vapor–liquid equilibrium (VLE) are required. The temperatures for the reaction of the higher carbon olefins with methanol are almost between 333 K and 373 K and the pressures are between 0.6 MPa and 1 MPa [4,5], this temperature and pressure ranges are the most appropriate operating conditions in the reaction zone of a reactive distillation column for manufacturing ethers. Moreover, VLE data for the mixture methanol and 2,3-dimethyl-2-butene were very scarce in the published literatures and were only measured under atmospheric pressure [6]. So the purpose of this paper is to report VLE data for the binary
∗ Corresponding author at: Key Laboratory for Green Chemical Technology of State Education Ministry, Tianjin 300072, PR China. Tel.: +86 022 27404701x8082. E-mail addresses: [email protected], [email protected] (Y. Li). 0378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2011.07.014
system methanol and 2,3-dimethyl-2-butene at various temperatures (343.15 K, 353.15 K, 363.15 K, 373.15 K) and to discuss the consistency of these experimental data with the Wilson [7], NRTL [8] and UNIQUAC [9] models as well as the Soave–Redlich–Kwong [10] equation of state. 2. Experimental 2.1. Materials for vapor–liquid equilibrium (VLE) measurements Methanol was provided by Tianjin GuangFu company and had a minimum mass fraction purity of 0.995. 2,3-Dimethyl-2-butene was purchased from Dalian chemphy Fine Chemical Co. Ltd. with a minimum mass fraction purity of 0.995. The purities of all chemical reactants were provided by the suppliers and all reactants were used without further purification expect for drying over molecular sieves (Nankai University 3A) for 24 h. We also checked the purities of all chemicals with the GC before our experiments and the results were satisfactory. 2.2. Apparatus for VLE measurements The vapor–liquid equilibrium data were measured using a new recirculation still which was designed following the general Othmer-type still [11,12]. A schematic of the apparatus is shown in Fig. 1. It consists of a stainless steel equilibrium cell and temperature and pressure measuring systems, etc. The total volume of the equilibrium cell is 196 ml and the volume of mixture needed for the measurements was approximately 120 ml. A magnetic stirrer
202
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205 Table 2 The measured and correlated vapor pressures of 2,3-dimethyl-2-butene and the deviation p.
Fig. 1. Schematic diagram of the equilibrium still. (1) Condenser, (2) observing tube of vapor condensate, (3) vapor sampling port, (4) electric heating tapes for preheating the condensate and backflow of the liquid phase, (5) oil bath, (6) equilibrium still, (7) magnetic stirrer, (8) cooling, (9) circulation pump, (10) liquid sampling port, (11) flow meter, (12) vapor rising space, (13) electric heating tapes for heating the vapor space, (14) pressure transducer and (15) thermocouple.
was used to accelerate the equilibrium process. The temperature of the equilibrium cell was maintained by a thermostated oil bath. Temperature was measured with a SME-700W-J (Yuyao Shimai Electron company) thermometer equipped with a Pt-100 resistant temperature probe with an accuracy of ±0.01 K. The uncertainty of temperature was estimated to be ±0.09 K. The total vapor pressure was measured using a pressure transducer (Beijin Weisite company, CYB-20S) when phase equilibrium was reached and maintained for at least 30 min. According to the data provided by the manufacturers of the pressure measurement devices, the pressure uncertainty was estimated to be ±0.5 kPa. The thermometers and the pressure transducer had been calibrated at the Bureau of Quality and Technical Supervision of Tianjin before experiments. In order to determine the reliability of this new vapor–liquid equilibrium still, the isothermal vapor–liquid equilibrium data for the binary system of benzene(1) + cyclohexane(2) at 403.15 K were measured and compared with the data of literature [13]. The comparison had been presented in our previous work [14] and the
T (K)
pexp (kPa)
pest (kPa)
p
336.50 338.20 340.60 342.65 344.20 346.24 347.65 350.10 353.46 355.35 357.22 362.80 365.76 368.05 370.36 373.18 375.20 376.50 379.15 381.62 383.05 384.70 386.65 388.20
73.5 77.5 84.2 90.2 94.7 101.2 105.3 113.9 125.5 133.3 140.4 164.8 179.5 190.9 202.8 218.8 230.4 238.5 255.1 271.2 281.3 292.1 306.8 318.4
73.6 77.9 84.4 90.2 94.8 101.1 105.7 114.0 126.2 133.5 141.0 165.4 179.6 191.2 203.5 219.2 231.1 238.9 255.6 271.9 281.7 292.3 307.4 319.1
0.14 0.55 0.20 0.02 0.10 0.07 0.37 0.09 0.57 0.15 0.45 0.39 0.07 0.17 0.33 0.20 0.29 0.18 0.19 0.25 0.13 0.06 0.21 0.21
P (%) =
|Pexp −Pest | Pexp
× 100.
agreement was satisfactory, which indicated that it was possible to measure good VLE data with the equipment. 2.3. Analysis and GC calibration The condensed vapor phase and liquid phase of the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) were analyzed with a FULI9790 gas chromatograph equipped with a capillary column (SGE, dimethyl polysiloxane, length 60 m, column inner diameter 0.22 mm, film thickness 0.25 m) and a flame ionization detector. Nitrogen, 99.999% pure, was used as carrier gas. The temperatures of injector and detector were both at 493.15 K. The oven was operated at programmed temperature from 353.15 K to 433.15 K at a rate of 10 K/min and then remain 5 min at the temperature of 433.15 K. Calibration curves were obtained by a set of solutions of
Table 1 Critical temperatures Tc , critical pressures pc , critical molar volumes Vc , acentric factors ω, critical compressibility factor Zc , UNIQUAC volume parameter RUNIQ , UNIQUAC area parameter QUNIQ pure-component vapor pressure equation parameters A, B, and C for the Antoine equation and recommended temperature range of the vapor pressure correlation Tmin and Tmax . Component
Methanol
2,3-Dimethyl-2-butene
Tc a (K) Pc a (MPa) Vc c (cm3 mol−1 ) ωa Zc a Ab Bb Cb RUNIQ a QUNIQ a Tmin (K) Tmax (K)
512.58 8.096 40.7 0.566 0.244 14.01 2160 −107.90 1.4311 1.4320 333.42 375.89
524.0 3.160 119.643 0.233 0.270 13.44 2473.0 −65.97 4.2649 3.8770 336.50 388.20
a b c
Ref. [15]. This work. Ref. [16].
Fig. 2. Vapor pressure for 2,3-dimethyl-2-butene: () literature [6] and () this work.
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205 Table 3 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 343.15 K. p (kPa)
x1
y1
91.5 155.5 169.5 181.2 186.4 189.3 190.0 190.3 190.8 191.2 191.4 191.1 190.4 190.3 189.3 185.4 182.9 175.3 161.1 153.1 150.8 125.3
0.000 0.068 0.109 0.183 0.253 0.326 0.416 0.433 0.448 0.528 0.605 0.621 0.652 0.659 0.739 0.810 0.852 0.898 0.948 0.964 0.969 1.000
0.000 0.419 0.473 0.519 0.543 0.549 0.559 0.560 0.562 0.570 0.578 0.580 0.583 0.584 0.593 0.616 0.638 0.677 0.759 0.807 0.826 1.000
1 7.57 5.83 4.06 3.15 2.51 2.01 1.93 1.89 1.62 1.44 1.41 1.34 1.33 1.20 1.11 1.08 1.04 1.02 1.01 1.01 1.00
203
Table 5 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 363.15 K.
2
p (kPa)
x1
y1
1
1.00 1.03 1.06 1.12 1.20 1.33 1.50 1.55 1.58 1.82 2.14 2.22 2.39 2.43 3.08 3.93 4.71 5.84 7.92 8.75 9.11
166.9 283.8 298.6 323.0 342.6 354.0 364.5 365.6 366.2 369.4 369.5 368.3 367.9 367.1 360.1 348.9 343.1 299.4 284.1 265.2 255.5
0.000 0.073 0.092 0.133 0.192 0.260 0.379 0.410 0.427 0.573 0.612 0.628 0.677 0.744 0.834 0.883 0.906 0.971 0.983 0.995 1.000
0.000 0.419 0.454 0.501 0.538 0.561 0.585 0.589 0.591 0.606 0.612 0.618 0.623 0.635 0.661 0.687 0.708 0.839 0.889 0.960 1.000
6.34 5.70 4.72 3.69 2.94 2.16 2.02 1.95 1.50 1.42 1.39 1.30 1.20 1.09 1.04 1.03 1.00 1.00 0.99 0.99
2 1.00 1.02 1.03 1.05 1.10 1.18 1.36 1.42 1.46 1.90 2.06 2.11 2.39 2.92 4.12 5.24 6.03 9.42 10.59 12.65
3. Model known compositions. The error in the determination of the liquid and vapor mole fraction was estimated to be ±0.003.
In our study, the Soave–Redlich–Kwong [10] equation of state with quadratic mixing rules in the attractive parameter and linear mixing rules in the covolume was used for the evaluation of vapor phase fugacity coefficients. Its expression is
2.4. Procedure of the VLE measurement Pure component 1 was introduced to the recirculation still, and its vapor pressure was measured. After the vapor pressure measurements, component 2 was added to the equilibrium still. In the isothermal runs, the temperature was adjusted to the desired value by adjusting the temperature of the oil bath. It took about 50 min to achieve constant temperature, the temperature was held constant for 30 min to enhance the steady-state condition before sampling. Samples of the liquid and the vapor condensate were taken manually with a cooled 1 l syringe after the steady-state condition was achieved. Every sample was analyzed 3 times, and the deviation of each analysis was less than 0.002.
Table 4 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 353.15 K. p (kPa)
x1
y1
1
124.8 216.7 242.8 253.8 263.7 266.1 266.4 267.4 268.1 268.3 268.1 267.3 266.3 265.2 254.1 245.5 231.9 196.1 180.9
0.000 0.079 0.143 0.205 0.333 0.409 0.423 0.429 0.578 0.611 0.624 0.665 0.668 0.742 0.874 0.910 0.944 0.989 1.000
0.000 0.434 0.505 0.537 0.568 0.578 0.579 0.580 0.594 0.598 0.601 0.607 0.607 0.617 0.662 0.694 0.746 0.912 1.000
6.54 4.70 3.62 2.45 2.04 1.98 1.96 1.50 1.43 1.40 1.33 1.32 1.20 1.05 1.02 1.00 1.00 1.00
2 1.00 1.03 1.07 1.13 1.29 1.44 1.47 1.49 1.95 2.10 2.15 2.37 2.39 2.98 5.17 6.38 8.11 12.11
P=
a RT − 2 V −b V + bV
(1)
a=
0.42748R2 Tc2 2 [1 + fw (1 − Tr0.5 )] Pc
(2)
b=
0.08664RTc Pc
(3)
fw = 0.315 + 1.60w − 0.166w2
(4)
Table 6 Experimental VLE data for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 373.15 K. p (kPa)
x1
y1
1
219.2 343.8 407.5 447.9 471.1 488.6 490.2 492.3 496.5 497.8 498.9 498.3 497.8 496.1 488.0 472.4 460.3 453.6 447.8 415.9 400.9 387.1 353.6
0.000 0.055 0.110 0.174 0.248 0.361 0.385 0.405 0.497 0.566 0.611 0.630 0.686 0.749 0.824 0.885 0.916 0.926 0.933 0.966 0.977 0.985 1.000
0.000 0.367 0.474 0.530 0.564 0.593 0.594 0.597 0.614 0.614 0.624 0.626 0.633 0.648 0.669 0.703 0.732 0.749 0.767 0.835 0.873 0.907 1.000
6.50 4.91 3.79 2.98 2.22 2.09 2.00 1.70 1.49 1.41 1.37 1.27 1.18 1.09 1.04 1.02 1.02 1.02 1.00 1.00 1.00 0.99
2 1.00 1.01 1.03 1.08 1.15 1.30 1.35 1.39 1.59 1.84 2.01 2.10 2.42 2.91 3.84 5.12 6.17 6.50 6.63 8.77 9.46 10.20
204
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205
Fig. 3. P–x–y diagram for the binary mixture methanol(1) + 2,3-dimethyl-2butene(2) at 343.15 K, 353.15 K, 363.15 K, 373.15 K: (䊉) 343.15 K; () 353.15 K; () 363.15 K; () 373.15 K; solid curves were calculated from the Wilson model.
The critical temperatures, critical pressures, acentric factors, liquid molar volumes, UNIQUAC volume and area parameters used in the calculations are presented in Table 1. The liquid phase was modeled with the Wilson [7], NRTL [8] and UNIQUAC [9] equation, respectively. For the NRTL equation, the value of the parameter ˛ was fixed to be 0.3. The vapor pressure of the pure substances was calculated from the Antoine equation, Eq. (5). ln p (kPa) = A −
B T (K) + C
(5)
The vapor pressure equation parameters in Table 1 were fitted from data measured in this work. The recommended temperature ranges of the vapor pressure equations are also presented in Table 1.
Fig. 5. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 353.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
shown in Table 2. The experimental data were compared with literature data [6]. Fig. 2 shows that the agreements were satisfactory. The activity coefficients i for specie i were calculated from Eq. (6) i =
psi ˚si xi
pyi ˚vi
exp[(Vil (p − psi ))/RT ]
(6)
where yi is the molar fraction of component i in the vapor phase, p is the system total pressure, ˚vi is the fugacity coefficient of component i in the vapor phase, xi is the molar fraction of component i in the liquid phase, psi is the vapor pressure of pure component i at the system temperature, ˚si is the pure-component saturated
The vapor pressures for pure component of 2,3-dimethyl-2butene were measured in the present work and the results are
liquid fugacity coefficient at the system temperature, Vil is the component i liquid-phase molar volume at the system temperature, T is the temperature in Kelvin, and R is the universal gas constant. The measured isothermal VLE data at 343.15 K, 353.15 K, 363.15 K, 373.15 K for methanol(1) + 2,3-dimethyl-2-butene(2)
Fig. 4. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 343.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
Fig. 6. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 363.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
4. Results and discussion
C. Feng et al. / Fluid Phase Equilibria 309 (2011) 201–205
205
5. Conclusions The vapor pressure of 2,3-dimethyl-2-butene and the isothermal VLE data for methanol and 2,3-dimethyl-2-butene at 343.15 K, 353.15 K, 363.15 K and 373.15 K were measured in this study. Three activity coefficient models had been employed to correlate the experimental data and the results showed that the Wilson model can correlate the experimental data better than the NRTL and the UNIQUAC model. The binary system showed a positive deviation from Raoult’s law and had a maximum pressure azeotrope. With the increase of temperature, the azeotropic point moved to the alcohol-rich region and the deviation from Raoult’s law increased.
Fig. 7. Activity coefficient-composition diagram for the binary mixture methanol(1) + 2,3-dimethyl-2-butene(2) at 373.15 K: () i calculated from the experimental data; (—) i predicted by the Wilson model.
binary mixture are listed in Tables 3–6. The P–x–y diagrams and the –x diagrams are shown in Figs. 3–7, respectively. The system measured shows a positive deviation from Raoult’s law and exhibits azeotropic behavior. Azeotropic data were determined graphically from the measured values. For the correlation of the experimental data, a computer program had been developed by applying the least square method to fit an objective function. The objective function is OF =
2 NP Pexp − Pcal Pexp
i=1
+
yi
exp
− yi cal
2
Table 7 Correlation parameters of the Wilson, NRTL and UNIQUAC model, average deviation in pressure p, average deviation in vapor phase composition y, and azeotropic data for the system methanol(1) + 2,3-dimethyl-2-butene(2) at four different temperatures. 343.15 (K)
353.15 (K)
363.15 (K)
373.15 (K)
Wilson
A12 A21 p y
−639.74 −583.08 0.0033 0.0036
−586.68 −611.58 0.0021 0.0035
−550.86 −627.58 0.0025 0.0019
−516.81 −631.62 0.0063 0.0024
NRTL
A12 A21 p y
458.66 482.61 0.0133 0.0140
489.81 444.87 0.0115 0.0142
506.14 430.68 0.0125 0.0129
539.62 390.09 0.0134 0.0107
UNIQUAC
A12 A21 p y
23.05 −681.32 0.0114 0.0122
18.71 −662.10 0.0101 0.0125
18.07 −659.31 0.0110 0.0115
14.13 −640.71 0.0118 0.0094
Aze. data
xaz p (kPa) 0.12
0.5768 191.4 0.35
0.5996 268.4 0.25
0.6120 369.5 0.23
0.6282 499.1
D/%
Wilson: A12 = (12 − 22 )/R, A21 = (21 − 11 )/R; NRTL: A12 = (g12 − g22 )/R; UNIQUAC: A12 = (u12 − u22 )/R, A21 = (u21 − u11 )/R p = A21 = (g21 − g11 )/R;
NP i
|(pi exp −pi cal )/pi exp ×100%| NP
NP
; y =
i
|(yi exp −yi cal )| NP
.
Greek letters ˚i fugacity coefficient of component i i activity coefficient of the component i i interaction energy in the Wilson equation
(7)
yi exp
where NP is the number of components, p is the pressure of system. yi is the molar fraction of component i in the vapor phase. The regression results and the azeotropic data are shown in Table 7. From the data of Table 7 it can be concluded that the Wilson model agrees well with the VLE data obtained in the experiments.
Temperature
List of symbols Aij , Aji parameters of the liquid models (K) a parameter of the equation of state parameter of the equation of state b NP number of component pressure (kPa) P R gas constant (J/(mol K)) T temperature (K) interaction energy in the NRTL equation gij molar volume (m3 /mol) v Vi mole volume of pure component i (m3 /mol) uij interaction energy in the UNIQUAC equation xi liquid mole fraction of component i vapor mole fraction of component i yi
Superscripts cal calculated data exp experimental data Acknowledgments We acknowledge gratefully the financial support of the Fund of National Natural Science Foundation of China (No. 20976129), this work is also supported by the Program of Universities’ Innovative Research Terms (No. IRT0936). References [1] R.C. Everson, W. Jansen, J. Chem. Eng. Data 46 (2001) 243–246. [2] F.H. Syed, C. Egleston, R. Datta, J. Chem. Eng. Data 45 (2000) 319–323. [3] G. Bozga, A. Motelica, R. Dima a, V. Plesu, A. Toma, C. Simion, Chem. Eng. Process. 47 (2008) 2247–2255. [4] L.K. Rihko, A.O.I. Krause, Chem. Res. 35 (1996) 2500–2507. [5] R.S. Karinen, J.A. Linnekoski, A.O.I. Krause, Catal. Lett. 76 (2001) 81–87. [6] P. Uusi-Kyyny, J.P. Pokki, Y. Kim, J. Aittamaa, J. Chem. Eng. Data 49 (2004) 251–255. [7] G.M. Wilson, J. Am. Chem. Soc. 86 (1964) 127–130. [8] H. Renon, J.M. Prausnitz, AIChE J. 14 (1968) 135–144. [9] D.S. Abrams, J.M. Prausnitz, AIChE J. 21 (1975) 116–128. [10] G. Soave, Chem. Eng. Sci. 27 (1972) 1197–1203. [11] C.I. Maria, C.T. Fernand, Fluid Phase Equilibria 103 (1995) 257–284. [12] Pavlov, S. Yu, Isolation and Purification of Monomers for Synthetic Rubber (in Russian), Chimiya, Leningrad, 1987. [13] B. Wisniewska, J.S. Gregorowicz, Malanowski Fluid Phase Equilibria 86 (1993) 173–186. [14] J.L. Dong, C.Z. Feng, Y.H. Li, J. Chem. Eng. Data 56 (2011) 2386–2392. [15] C.L. Yaws, Chemical Properties Handbook, 1999. [16] T.E. Daubert, R.P. Danner, Physical and Thermodynamic Properties of Pure Chemicals: Data Compilation, Hemisphere, New York, 1989.