CHEMICAL ENGINEERING THERMODYNAMICS
Chinese Journal of Chemical Engineering, 21(8) 886—893 (2013)
DOI: 10.1016/S1004-9541(13)60544-3
Measurement and Prediction of Vapor Pressure for H2O + CH3OH/
C2H5OH + [BMIM][DBP] Ternary Working Fluids*
ZHANG Xiaodong (张晓冬)1,**, HU Dapeng (胡大鹏)1 and ZHAO Zongchang (赵宗昌)2
1
2
School of Chemical Machinery, Dalian University of Technology, Dalian 116023, China
School of Chemical Engineering, Dalian University of Technology, Dalian 116023, China
Abstract The ionic liquid, 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) was prepared and the
vapor pressures of three set of binary solutions H2O(1)/CH3OH(1)/C2H5OH(1) + [BMIM][DBP](2) were measured
at different temperature and in the ILs mole fraction range from 0.1 to 0.6 with a static equilibrium apparatus. The
measured vapor pressures were correlated with Non-Random Two Liquid (NRTL) activity coefficient model and the
average relative deviations (ARD) between experimental and correlated vapor pressures for these binary solutions
were 3.19%, 2.42% and 2.95%, respectively. Then, the vapor pressures of two set of ternary solutions H2O(1) +
CH3OH(2)/C2H5OH(2) + [BMIM][DBP](3) were measured with an inclined boiling apparatus and further predicted
with NRTL activity coefficient model based on the binary interaction parameters coming from fitting the vapor
pressures of the binary solutions. The results indicated that the ternary solutions containing [BMIM][DBP] were
shown a strong negative deviation from Raoult’s Law when the mole fraction of [BMIM][DBP] was larger than 0.2,
which meant that ternary solutions could absorb the refrigerant vapors at the same or below solution temperature.
Meanwhile, the average relative deviations between experimental and predicted vapor pressures for ternary solutions
were 2.92% and 3.06%, respectively. Consequently, the NRTL active coefficient model used for non-electrolyte
solutions was still valid for predicting vapor-liquid equilibrium of binary or ternary solutions containing ILs.
Keywords ionic liquid, ternary working fluids, vapor pressure, NRTL model, absorption refrigeration
1
INTRODUCTION
The absorption refrigerator can be driven by low
grade heat sources such as solar energy and industrial
waste heat, and is widely used in industrial processes
or in heating and air-conditioning of civil buildings.
Commonly used working pairs are H2O + LiBr and
H2O + NH3. However, H2O + LiBr is easy crystallization
and corrosion to the iron-steel equipments, and H2O +
NH3 is toxic to human body and easy explosive.
Ionic liquids (ILs) are new kinds of solvent which
have unique physical and chemical properties, such as
negligible vapor pressure, non-flammability and thermal stability, low melting points, wide liquid state
range from room temperature up to 200 °C or 300 °C,
and good solubility to many organic or inorganic solvents. ILs can be used as the solvent or catalyst in
chemical reactions or as the extraction agent in separation processes [1-3].
Because of the excellent properties of ILs, it is
possible for ILs to be used as a new type of absorbent
of refrigerants in absorption cycles. Kim and co-workers
[4] measured the vapor pressure of some binary solutions containing ILs. Shiflett and Yokozeki [5-7] examined the solubility of CO2, NH3 and H2O in some
ionic liquids and calculated the coefficient of performance in absorption refrigeration cycles under the
given operation conditions.
Wang and Zheng et al. [8] and Wu and Zheng et al.
[9] measured and correlated the vapor pressures of binary
solutions water + 1,3-dimethylimidazolium chloride
[DMIM]Cl and 2,2,2,-trifluoroethanol + 1-ethyl-3methylimidazolium tetrafluoroborate [EMIM]BF4 and
water + 1,3-dimethylimidazolium
tetrafluoroborate
[DMIM]BF4.
Wang and Li et al. [10] measured and correlated
the vapor pressures of binary and ternary solutions
composed of water, methanol, ethanol and ionic
liquid 1-ethyl-3-methylimidazolium dimethylphosphate
[EMIM][DMP]. Zhao and Li et al. [11] also measured
and correlated the vapor pressures of three set of binary solutions of H2O(1)/CH3OH(1)/C2H5OH(1) +
[BMIM][DBP](2). The calculated vapor pressures
based on binary interaction parameters were in well
agreement with the experimental ones and the average
relative deviations ARD(p) were 0.46%, 0.58% and
0.24%, respectively. However, in Li and his co-workers’
research, ILs were taken as the entrainer for an azeotropic
distillation of aqueous solution of ethanol, and the IL
mole fractions were low and usually below 0.2.
Recently Li and Zheng et al. [12] measured and
correlated the vapor pressures of some ternary systems
H2O + LiBr + [DMIM]Cl or [DMIM]BF4, and found
that IL added could further reduce the pressure of the
solution H2O + LiBr. However, in this case LiBr and
ionic liquid in fact were used as the absorbent of water.
The authors [13-16] measured and correlated the
vapor pressure, excess enthalpy and specific heat capacity of some binary solutions composed of phosphoric
ionic liquids and water/ethanol/methanol, and further
simulated the thermodynamic cycle performance of
the absorption refrigerator and the absorption heat
transformer based on the thermodynamic properties of
Received 2012-08-13, accepted 2013-01-25.
* Supported by the National Natural Science Foundation of China (51076021).
** To whom correspondence should be addressed. E-mail: [email protected]
Chin. J. Chem. Eng., Vol. 21, No. 8, August 2013
887
binary working pairs containing the ionic liquid 1-ethyl-3methylimidazolium dimethylphosphate ([EMIM][DMP]).
In present research two set of ternary solutions
H2O(1) + CH3OH(2)/C2H5OH(2) + [BMIM][DBP](3)
were proposed as a new alternative working fluids for
absorption refrigeration cycle because the binary mixed
refrigerants H2O(1) + CH3OH(2) or C2H5OH(2) have
refrigeration temperature below 0 °C compared with
water, and have higher vaporization heat and conductivity compared with methanol or ethanol, while
[BMIM][DBP] was used as an absorbent of the mixed
refrigerants. As a higher IL mole fraction of 0.4 or 0.5
in binary or ternary solutions may be needed in the
absorption refrigeration cycles, it was necessary to
measure, correlate and predict vapor pressures of binary and ternary working solutions in a wider range of
IL mole fraction.
First, an appropriate amount of N-Methylimidazole
is poured into a flask with a reflux condenser and then
mixed with equimolecular of tributylphosphate. After
reacting for 10 hours at T = 423.15 K, the result mixture is cooled down to room temperature. Unreacted
agents are extracted from the result mixture with ether.
Then, the raffinate containing [BMIM][DBP] is
evaporated under the vacuum condition using a rotary
evaporator for 24 h in order to remove all volatile
components such as water and residual ether. The purity of the IL prepared was 98.9% (by mass) as determined by 1H NMR (400 MHz, D2O). The water content in ILs was 0.024% (by mass) measured by a 756
Karl Fisher coulometer.
2
In order to predict precisely vapor pressures of
ternary solutions H2O(1) + CH3OH(2)/C2H5OH(2) +
[BMIM][DBP](3), it is necessary to measure precisely
the vapor pressures of corresponding binary solutions
H2O/CH3OH/C2H5OH + [BMIM][DBP]. The static
method was adopted for measuring vapor pressure of
three set of binary systems in present study. As no
bubbles are generated in heated liquid, static method
can efficiently avoid the overheat of solution or explosive boiling, which often happens in boiling point
method at the low pressure or vacuum condition.
However, static method has also some drawbacks such
as needing a longer time to approach heat equilibrium
between the solution in the equilibrium vessel and
water or oil in the thermostat bath for each run, and
not being removed completely for non-condensed gas
in the equilibrium vessel.
The apparatus used in the static method is shown
in Fig. 1. It consists of a thermostat bath, a static equilibrium vessel, a reflux condenser, a mercury thermometer with an uncertainty of ±0.1 K, a U-tube manometer
with an uncertainty of 0.13 kPa, and two buffer vessels.
2.1
EXPERIMENTAL
Materials
N-methylimidazole (≥99%) was purchased from
Tianjin Fuchen Reagents Company. Ethanol, methanol
and tributylphosphate with purity of 99.8% were purchased from Sinopharm Chemical Reagent Company
and used without further purification. The ionic liquid,
[BMIM][DBP], was prepared according to the method
given by Zhou et al [17]. The method is briefly given
as follows:
2.2 Apparatus and procedure for vapor pressure
measurement
Figure 1 Schematic diagram of static equilibrium apparatus for vapor pressure measurement
1—thermostatic bath; 2—static equilibrium vessel; 3—condenser; 4—pressure buffer; 5—U-tube manometer; 6—vacuum control
valve; 7—vacuum pump; 8—thermometer
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Chin. J. Chem. Eng., Vol. 21, No. 8, August 2013
To ensure the measuring accuracy, vacuum silicon
grease is used at the seal fittings to prevent the air into
the static equilibrium vessel.
The procedure for measuring vapor pressure of
the binary solution containing IL is given as follows.
When the apparatus is well sealed and the pressure
increment in apparatus is below 0.13 kPa within 12
hours, the sample (~150 ml) is poured into the static
equilibrium vessel immerged into water or oil in a
thermostat bath with a given temperature. To prevent
escaping of volatile components from the equilibrium
vessel, the condenser is cooled with aqueous solution
of glycol below 0 °C. As mentioned by Zhao et al. [11],
the variation of solution concentration caused by the
holdup of volatile component in condenser is within
0.2% in the flow boiling approach. In the static approach, however, the variation of solution concentration in the bottle C may be neglected because the vapor of volatile component is sealed by the solution
between the balls A and B.
Before the vapor pressure measurement, noncondensed gases is first removed from the static equilibrium vessel by evacuating the apparatus. When the
solution temperature in the static equilibrium vessel is
in thermal equilibrium with water or oil in thermostat
bath, and then the pressure acting on the liquid surface
in small ball A is adjusted by turning the vacuum
valve or running on the vacuum pump until the liquid
surfaces in balls A and B are on the same horizontal
level. In this case the vapor pressure of solution in ball
C, pC, is the same as pB exerted on the liquid surface
in the ball B, while pB is equal to pA on the liquid surface in the ball A which can be obtained by the pressure difference in the U-tube manometer and the local
atmospheric pressure measured by a barometer in the
laboratory. Thus, a series of temperatures and corresponding vapor pressures for each binary solution can
be obtained.
The vapor pressure apparatus for ternary solutions
were shown in Fig. 2. The detailed descriptions about
them were given elsewhere [11]. This method has the
advantage that the vapor and liquid can approach to
heat equilibrium easily. and thus the experimental time
for each run can be shortened. However, it has still
drawback of explosive boiling at low pressure or higher
vacuum.
To check the reliability of the experimental apparatus, the vapor pressures of deionized water and
aqueous solution of lithium bromide (51%, by mass)
at different temperatures were measured and compared
with the calculated ones by the Antoine equation of
water [18] and by correlation equation given by Patterson and Blanco, respectively [19]. The results indicated that the experimental data were in good agreement with the calculated ones within average relative
deviations of 1.47% and 2.08% for the static equilibrium apparatus and 0.87% and 1.73% for the inclined
boiling apparatus, respectively. Thus, the experimental
apparatus are reliable and applicable for measuring the
vapor pressure of IL-containing solutions.
3
3.1
RESULTS AND CORRELATION
Binary systems
The experimental vapor pressures of three
set binary solutions H2O(1)/CH3OH(1)/C2H5OH(1) +
[BMIM][DBP](2) at different temperatures and ILs
mole fractions were shown in Figs. 3-5. Two set of
experimental vapor pressure data corresponding to the
minimum and maximum solution concentration for
each of solutions [11] were also shown in these figures.
Here −46.13, −34.29 and −41.68 in expression of abscissa for these figures are Antoine constants of water,
methanol and ethanol, respectively.
From these figures it was found that the vapor
pressure of solution was less than that of corresponding refrigerants due to the formation of hydrogen
bonds between the [BMIM][DBP] and refrigerants,
leading to obvious negative excess enthalpies of solutions [20]. The higher IL mole fraction, the lower vapor
pressure of solution. Thus, three set of binary solutions
have the ability to absorb refrigerant vapor with same
Figure 2 Schematic diagram of inclined boiling apparatus for vapor pressure measurement
1—refrigerator; 2—pressure buffer; 3—U-tube manometer; 4—vacuum pump; 5—inclined boiling kettle; 6—reflux condenser;
7—mercury thermometer
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Chin. J. Chem. Eng., Vol. 21, No. 8, August 2013
mole fractions of refrigerant i in the vapor and liquid
phases, respectively, and φi and γi are the fugacity coefficient and active coefficient of refrigerant i in vapor
and liquid phase, respectively.
As the non-volatility of [BMIM][DBP], the vapor
phase is only composed of refrigerant vapor. For binary
solutions H2O(1)/CH3OH(1)/C2H5OH(1) + [BMIM]
[DBP](2), Eq.(1) will be rewritten as follows
p = x1γ 1 p1s
Figure 3 Experimental and correlated vapor pressures of
H2O(1) + [BMIM][DBP](2)
◇ x2 = 0.099; □ x2 = 0.197; △ x2 = 0.298; ○ x2 = 0.396;
x2 =
0.488; ■ x2 = 0.013 and ◆ x2 = 0.11 coming from Ref. [11];
x2 = 0;
correlation
(2)
The saturated vapor pressure of pure refrigerant,
pis , can be calculated by the following Antoine equation:
B
(3)
T +C
where p and T are vapor pressure in kPa and temperature in K, respectively. The Antoine constants A, B and
C for water, ethanol or methanol can be obtained from
literature [18].
The vapor pressure data of binary solutions were
correlated with NRTL model, which is given as follows [21]:
ln ps = A −
{
ln γ 1 = x22 τ 21 ⎡⎣G21 ( x1 + x2G21 ) ⎤⎦ +
τ12 G12
G12 = exp ( −ατ12 )
Figure 4 Experimental and correlated vapor pressures of
CH3OH(1) + [BMIM][DBP](2)
◇ x2 = 0.100; □ x2 = 0.199; △ x2 = 0.296; ○ x2 = 0.377;
x2 =
0.504; ■ x2 = 0.023 and ◆ x2 = 0.12 coming from Ref. [11];
x2 = 0;
correlation
Figure 5 Experimental and correlated vapor pressure of
C2H5OH(1) + [BMIM][DBP](2)
◇ x2 = 0.100; □ x2 = 0.199; △ x2 = 0.298;
x2 = 0.399; x2 =
0.500; ○ x2 = 0.599; ■ x2 = 0.015 and ◆ x2 = 0.17 coming
from Ref. [11];
x2 = 0;
correlation
temperature, which is one of the fundamental feature
of working fluids in absorption cycles.
The vapor and liquid phases equilibrium can be
expressed as follows [20]:
yiϕi p = xi γ i pis
2
( x2 + x1G12 )2 }
G21 = exp ( −ατ 21 )
(4)
(5)
τ12 = a12 + b12 / T
τ 21 = a21 + b21 / T
(6)
where α, a12, b12, a21 and b21 in Eqs. (5) and (6) are the
fitted parameters and were obtained by correlating
experimental vapor pressure data as listed in Table 1.
The average relative deviations (ARD) between our
experimental and correlated vapor pressures for three
set of binary solutions were 3.19%, 2.42% and 2.95%,
respectively. Meanwhile, the experimental vapor
pressures in reference [11] were also well predicted by
binary interaction parameters from Table 1 with ARD(p)
of 1.46%, 2.10% and 4.32%, respectively. However,
when using binary interaction parameters in reference
[11] to predict our experimental vapor pressure values,
it was found that the ARD(p) were very large. For
example, the overall ARD(p) was 48.7% for H2O(1) +
[BMIM][DBP](2) in the IL mole fraction ranging
from 0.1 to 0.488. This indicated that the binary interaction parameters from present experimental data were
also suitable for predicting vapor pressure of solutions
with low IL mole fraction, but the binary interaction
parameters in reference [11] were not suitable for predicting the vapor pressure of solutions with high IL
mole fraction, because IL mole fractions in present
situation are far beyond the IL concentration range
concerned by Zhao et al [11].
3.2
Ternary systems
(1)
where p is total vapor pressure of vapor phase and pis
saturated pressure of the refrigerant i in solution at
solution temperature, respectively. yi and xi are the
The experimental vapor pressures for ternary
solutions H2O(1) + CH3OH(2)/C2H5OH(2) + [BMIM]
[DBP](3) were listed in Tables 2 and 3, and also shown
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Chin. J. Chem. Eng., Vol. 21, No. 8, August 2013
Table 1
Binary systems
ij
H2O(1) + [BMIM][DBP](2)
CH3OH(1) + [BMIM][DBP](2)
C2H5OH(1) + [BMIM][DBP](2)
H2O(1) + CH3OH(2)*
H2O(1) + C2H5OH(2)*
Parameters in NRTL model
aij
bij
α
ARD(p)/%
12
−9.9911
5103.8620
0.7979
3.19
21
−4.3169
885.8425
0.3631
2.42
0.4733
2.95
12
10.0495
−1633.3081
21
−4.7563
362.9760
12
−13.3746
7069.3460
21
−4.7945
696.7517
12
2.7322
−617.2687
21
−0.693
172.9871
12
3.4578
−586.0809
21
−0.8009
246.18
Note: the data denoted by “*” coming from ASPEN data bank. RD( pi ) =
Table 2
T/K
piexp − pical
piexp
0.3
0.3
, ARD( p) =
exp
1 N pi − pical
.
∑
N i =1
piexp
Experimental and predicted vapor pressures for ternary solution H2O(1) + CH3OH(2) + [BMIM][DBP](3)
p /kPa
exp
pcal/kPa
γ 1cal
γ 2cal
RD(p)/%
T/K
x1 = 0.4539, x2 = 0.4498, x3 = 0.0963
pexp/kPa
pcal/kPa
γ 1cal
γ 2cal
RD(p)/%
x1 = 0.4197, x2 = 0.2817, x3 = 0.2986
315.95
19.20
20.19
1.2634
0.8433
5.16
333.35
13.93
14.10
0.6980
0.3420
1.23
321.05
24.52
25.59
1.2535
0.8456
4.36
341.15
18.34
18.94
0.6723
0.3328
3.30
324.45
28.92
29.83
1.2467
0.8468
3.15
348.35
23.67
24.52
0.6505
0.3244
3.57
328.85
34.93
36.17
1.2378
0.8481
3.55
353.55
28.80
29.31
0.6357
0.3182
1.78
331.85
40.00
41.10
1.2316
0.8488
2.75
359.85
34.93
36.08
0.6189
0.3109
3.29
334.65
45.07
46.20
1.2257
0.8492
2.51
363.75
40.06
40.85
0.6089
0.3063
1.98
337.05
49.80
50.97
1.2206
0.8495
2.35
367.35
44.47
45.69
0.5999
0.3021
2.75
339.75
55.94
56.82
1.2148
0.8497
1.57
369.85
49.40
49.30
0.5938
0.2992
0.21
342.65
63.21
63.71
1.2085
0.8498
0.79
373.35
56.21
54.71
0.5854
0.2952
2.65
345.85
72.02
72.09
1.2014
0.8497
0.01
378.15
62.61
62.88
0.5741
0.2897
0.42
x1 = 0.4024, x2 = 0.3975, x3 = 0.2001
x1 = 0.2446, x2 = 0.3577, x3 = 0.3977
319.45
14.19
14.46
1.0136
0.5482
1.91
335.75
11.34
11.14
0.5755
0.2375
1.79
325.25
19.66
18.59
0.9904
0.5435
5.43
345.35
16.74
15.72
0.5455
0.2289
6.13
332.35
25.53
24.92
0.9633
0.5372
2.38
352.55
20.88
20.06
0.5256
0.2227
3.92
337.15
30.60
30.12
0.9457
0.5327
1.56
362.25
27.99
27.37
0.5017
0.2146
2.22
341.35
36.07
35.36
0.9308
0.5285
1.96
367.35
33.06
31.98
0.4903
0.2105
3.27
344.65
41.41
39.98
0.9193
0.5251
3.45
374.25
38.00
39.17
0.4760
0.2051
3.07
348.05
47.08
45.23
0.9078
0.5216
3.93
377.25
43.26
42.66
0.4700
0.2028
1.40
350.65
51.95
49.60
0.8991
0.5188
4.52
381.25
49.94
47.68
0.4623
0.1997
4.51
353.15
57.55
54.12
0.8909
0.5160
5.96
385.15
54.47
53.00
0.4550
0.1968
2.70
356.55
64.62
60.78
0.8798
0.5122
5.94
391.25
64.48
62.22
0.4439
0.1923
3.51
x1 = 0.3500, x2 = 0.35, x3 = 0.3004
x1 = 0.3041, x2 = 0.3032, x3 = 0.3927
330.25
13.93
13.62
0.7384
0.3478
2.21
338.95
11.34
11.93
0.5530
0.2344
5.22
336.95
18.34
17.64
0.7134
0.3405
3.78
346.95
16.74
15.85
0.5299
0.2270
5.32
344.65
23.67
23.39
0.6871
0.3321
1.18
353.45
20.88
19.75
0.5130
0.2211
5.41
350.15
28.80
28.35
0.6697
0.3262
1.54
363.65
27.99
27.37
0.4894
0.2122
2.22
357.45
34.93
36.19
0.6480
0.3183
3.60
369.15
33.06
32.36
0.4778
0.2075
2.14
360.75
40.06
40.26
0.6387
0.3147
0.48
375.35
38.00
38.80
0.4655
0.2024
2.09
364.75
44.47
45.65
0.6279
0.3104
2.67
380.25
43.26
44.56
0.4562
0.1984
2.99
367.35
49.40
49.45
0.6210
0.3076
0.11
383.35
49.94
48.53
0.4505
0.1959
2.82
370.35
56.21
54.14
0.6132
0.3044
3.67
386.45
54.47
52.76
0.4449
0.1935
3.14
373.95
62.61
60.21
0.6040
0.3005
3.83
392.65
64.48
62.06
0.4339
0.1887
3.75
ARD
2.92
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Chin. J. Chem. Eng., Vol. 21, No. 8, August 2013
Table 3
T/K
Experimental and predicted vapor pressures for ternary solution H2O(1) + C2H5OH(2) + [BMIM][DBP](3)
p /kPa
exp
γ 1cal
pcal/kPa
γ 2cal
RD(p)/%
T/K
pexp/kPa
pcal/kPa
γ 1cal
γ 2cal
RD(p)/%
321.65
x1 = 0.4553, x2 = 0.4456, x3 = 0.0991
19.20
19.42
1.3287
1.0249
1.15
339.55
x1 = 0.4244, x2 = 0.2784, x3 = 0.2972
14.36
14.70
0.6634
0.4181
2.42
325.85
24.52
23.78
1.3202
1.0272
3.02
348.05
20.43
20.53
0.6377
0.4126
0.49
329.25
28.92
27.89
1.3130
1.0289
3.56
354.85
25.90
26.46
0.6185
0.4085
2.16
333.05
34.93
33.17
1.3047
1.0304
5.04
358.85
30.57
30.55
0.6076
0.4061
0.07
335.95
40.00
37.73
1.2981
1.0313
5.68
364.25
36.44
36.87
0.5934
0.4028
1.19
338.65
45.07
42.44
1.2917
1.0318
5.84
366.75
41.13
40.13
0.5869
0.4012
2.55
341.05
49.80
47.02
1.2858
1.0321
5.58
370.55
46.61
45.50
0.5771
0.3986
2.46
343.75
55.94
52.21
1.2790
1.0320
6.67
374.45
51.61
51.58
0.5672
0.3957
0.05
346.45
62.21
58.80
1.2718
1.0316
5.48
377.65
57.21
57.01
0.5591
0.3932
0.35
349.55
69.02
66.58
1.2633
1.0307
3.54
380.35
64.22
61.92
0.5522
0.3909
3.72
326.75
14.19
14.81
0.9800
0.6492
4.53
339.95
11.76
12.08
0.5863
0.3505
2.72
333.85
19.66
20.28
0.9533
0.6455
3.30
347.65
16.56
16.31
0.5642
0.3459
1.60
339.95
25.53
26.25
0.9312
0.6425
2.93
356.85
22.43
22.90
0.5402
0.3409
2.09
344.85
30.60
32.03
0.9139
0.6401
4.79
362.25
28.44
27.70
0.5271
0.3382
2.71
348.95
36.07
37.64
0.8997
0.6379
4.47
367.45
34.51
33.05
0.5149
0.3355
4.46
352.15
41.41
42.56
0.8886
0.6361
2.88
371.05
38.93
37.21
0.5067
0.3335
4.65
356.65
47.08
50.32
0.8731
0.6331
6.86
375.45
44.94
42.84
0.4969
0.3310
4.92
358.85
51.95
54.51
0.8655
0.6315
4.99
381.05
52.54
50.92
0.4845
0.3274
3.18
361.35
57.55
59.60
0.8569
0.6296
3.63
385.55
61.08
58.20
0.4745
0.3242
4.91
365.05
64.62
67.79
0.8441
0.6263
4.93
388.25
67.09
62.91
0.4686
0.3221
6.55
x1 = 0.4006, x2 = 0.3986, x3 = 0.2008
x1 = 0.3981, x2 = 0.2606, x3 = 0.3413
x1 = 0.3482, x2 = 0.3519, x3 = 0.2999
14.66
0.6893
0.4187
x1 = 0.3031, x2 = 0.3069, x3 = 0.3901
338.25
14.36
2.13
347.45
20.43
21.11
0.6588
0.4131
3.36
353.15
16.56
16.83
0.4977
0.2917
1.58
353.55
25.90
26.57
0.6401
0.4097
2.60
361.45
22.43
22.65
0.4780
0.2883
0.97
357.25
30.57
30.41
0.6291
0.4076
0.57
366.95
28.44
27.35
0.4658
0.2861
3.99
362.15
36.44
36.17
0.6150
0.4048
0.79
375.35
34.51
36.01
0.4482
0.2826
4.18
365.65
41.13
40.79
0.6052
0.4027
0.86
379.15
38.93
40.57
0.4405
0.2809
4.04
369.65
46.61
46.63
0.5942
0.4001
0.05
382.05
44.94
44.34
0.4347
0.2794
1.34
372.75
51.61
51.59
0.5857
0.3980
0.04
386.65
52.54
50.85
0.4256
0.2770
3.29
376.25
57.21
57.66
0.5762
0.3954
0.78
392.05
61.08
59.36
0.4149
0.2738
2.84
379.45
64.22
63.67
0.5676
0.3929
0.87
395.65
67.09
65.57
0.4077
0.2714
2.25
ARD
3.06
in Figs. 6 and 7.
The activity coefficients of refrigerant H2O(1)
and CH3OH(2) or C2H5OH(2) in the ternary solutions
are given as follows [21].
3
ln γ i =
∑τ ji G ji x j
j =1
3
∑ Gli xl
l =1
3
⎛
∑ xrτ rj Grj
3
x j Gij ⎜
⎜
+∑ 3
τ ij − r =13
⎜
j =1
∑ Glj xl ⎜
∑ Glj xl
l =1
l =1
⎝
( i = 1, 2 )
⎞
⎟
⎟
⎟
⎟
⎠
(7)
The total vapor pressure for these ternary solutions are
as follows.
345.05
11.76
12.40
0.5189
p = p1s x1γ 1 + p2s x2γ 2
0.2955
5.26
(8)
The meaning of parameters in Eqs.(7) and (8) are the
same as those in Eqs. (2)-(6).
The total vapor pressures predicted by means of
the binary interaction parameters in Table 1 and by
Eqs. (3), (7) and (8) were also listed in Tables 2 and 3,
and shown in Figs. 6 and 7.
The results indicated that the ternary solutions
containing [BMIM][DBP] were shown strong negative deviation from Raoult’s Law when the mole fraction of [BMIM][DBP] was larger than 0.2, indicating
that the [BMIM][DBP] can obviously reduce the partial
pressures of the refrigerants in solution. Thus, these
892
Chin. J. Chem. Eng., Vol. 21, No. 8, August 2013
Figure 6 Vapor pressure of ternary solution H2O(1) +
CH3OH(2) + [BMIM][DBP](3)
□ x1 = 0.4539, x3 = 0.0963; ◇ x1 = 0.4024, x3 = 0.2001;
△ x1 = 0.3500, x3 = 0.3004; ○ x1 = 0.2446, x3 = 0.3977;
prediction
models. The average relative deviations (ARD) between experimental and correlated vapor pressures for
these binary solutions were 3.19%, 2.42% and 2.95%,
respectively.
The vapor pressures of two set of ternary systems
H2O(1) + CH3OH(2)/C2H5OH(2) + [BMIM][DBP](3)
were also well predicted with NRTL activity coefficient model based on the binary interaction parameters.
The average relative deviations between experimental
and predicted vapor pressures of the ternary solutions
were 2.92% and 3.06%.
The ternary systems containing [BMIM][DBP]
were shown strong negative deviation from Raoult’s
Law when the mole concentration of [BMIM][DBP]
was larger than 0.2. [BMIM][DBP] can effectively
reduce the partial pressures of the refrigerants. Thus,
the solutions containing the [BMIM][DBP] can absorb
the vapor of refrigerants at the same or below solution
temperature and will have possibility to be used as the
working fluids in absorption cycles.
NOMENCLATURE
Figure 7 Vapor pressure of ternary solution H2O(1) +
C2H5OH(2) + [BMIM][DBP](3)
□ x1 = 0.4553, x3 = 0.0991; ◇ x1 = 0.4006, x3 = 0.2008;
△ x1 = 0.3482, x3 = 0.2999; ○ x1 = 0.3031, x3 = 0.3901;
prediction
ternary solutions containing [BMIM][DBP] can absorb the vapor of refrigerants with or below the solution temperature, which is the fundamental thermodynamic characteristics of the working fluids in absorption cycles.
Meanwhile, it was found that the total vapor
pressures predicted by the present binary interaction
parameters were in well agreement with the experimental ones. The ARD(p) between experimental and
predicted vapor pressures were 2.92% and 3.06%,
respectively, while the ARD(p) between experimental
and predicted vapor pressures based on the binary interaction parameters [11] was 34% for H2O(1) +
C2H5OH(2) + [BMIM][DBP](3).
As binary mixed refrigerants H2O(1) + CH3OH(2)/
C2H5OH(2) may be operated below 0 °C, together
with suitable characteristics mentioned above, these
ternary solutions will have the possibility to be used in
absorption refrigeration.
4
a12
a21
b12
b21
p
pis
T
xi
yi
α
γi
φi
Superscripts
cal
exp
calculated value
experimental value
Subscripts
component ( = 1, 2, 3 )
component ( = 1, 2, 3 )
i
j
REFERENCES
1
2
3
4
CONCLUSIONS
5
The vapor pressures of three set of binary solutions H2O(1)/CH3OH(1)/C2H5OH(1) + [BMIM][DBP](2)
were well correlated by NRTL activity coefficient
fitted parameter
fitted parameter
fitted parameter
fitted parameter
total vapor pressure of vapor phase, kPa
saturated pressure of the refrigerant i at solution temperature, kPa
temperature, K
mole fraction of refrigerant i in the liquid phases
mole fraction of refrigerant i in the vapor phases
fitted parameter
active coefficient of refrigerant i in liquid phase
fugacity coefficient of refrigerant i in vapor phase
6
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