Download Water + Propionic Acid + Cyclohexanol

THERMODYNAMICS AND CHEMICAL ENGINEERING DATA
Chinese Journal of Chemical Engineering, 19(4) 565—569 (2011)
Salt Effect on the Liquid-Liquid Equilibrium of (Water + Propionic
Acid + Cyclohexanol) System at T = (298.2, 303.2, and 308.2) K
Bahram Ghalami-Choobar*, Ali Ghanadzadeh and Shahram Kousarimehr
Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box: 19141, Rasht, Iran
Abstract Effects of salt and temperature on the liquid phase equilibrium of the (water + propionic acid + cyclohexanol) system were investigated. The liquid-liquid equilibrium data in the presence of KCl for various salt ionic
strength of 0.5, 1.0, 1.5, 2.0, and 2.5 mol·dm−3 and in absence of the salt at T = (298.2, 303.2, and 308.2) K were
determined. The experimental results were correlated based on the Othmer-Tobias equation and Pitzer ion-interaction
model. Thermodynamic properties such as distribution coefficients and activity coefficients of propionic acid in
water + cyclohexanol were determined. In addition, the separation factor, S, of the chosen solvent was obtained for
the investigated system.
Keywords liquid-liquid equilibrium, salt effect, propionic acid, distribution coefficient
1
INTRODUCTION
Separation of carboxylic acids from dilute aqueous solutions is an important operation in many industrial processes [1]. Propionic acid is one of the important carboxylic acid widely used as mold inhibitor in
baking and esterifying agent in the production of
thermoplastics and in the manufacture of flavors and
perfume bases [2, 3]. Liquid-liquid extraction is one of
the practical separation processes. Liquid-liquid extraction using aqueous two-phase systems (ATPS) has
been demonstrated to be a highly efficient separation
technique for small organic species [4, 5]. The addition
of a salt or a non-volatile solute in a solvent mixture
and temperature can significantly change two-phase
equilibrium composition. Adding salt to an aqueous
solution of an organic acid can result in either a decrease (salting out) or an increase (salting in) in solubility of the organic acid. The concentration of a
component in a liquid-liquid system increases if the
component is salted-in and decreases if it is salted out
of the liquid phase [6-8]. This salt effect has been advantageously used in distillation, separation and solvent extraction. The salt effect is also important in
biological separation processes such as purification of
proteins, enzymes, nucleic acids, and others [9].
In recent years, the liquid-liquid equilibrium
(LLE) [10] and salt effect on the liquid-liquid equilibrium systems [11, 12] have been studied. The LLE data
of (water + propionic acid + solvents) ternary systems
are important in chemical industry. Propionic acid
obtains by chemical reactions or by fermentation with
bacteria of the genus propionibacterium. Several solvents have been tested to improve the recovery of
propionic acid from aqueous solutions [13-16]. However, salt effect on the thermodynamic data of our investigated system (water + propionic acid + cyclohexanol)
has not been reported in literature. In this work, effects
of salt and temperature on the liquid-liquid equilibrium
data of water + propionic acid + cyclohexanol system
were investigated.
To obtain LLE data, the most common methods
include titration, Karl-Fisher titration and gas chromatograghy methods. In this work, the experimental
measurements were performed with the potetiometric
titration and Karl-Fisher methods. The experimental
results were correlated based on the Othmer-Tobias
equation and the Pitzer ion-interaction model, in
which a small number of adjustable parameters were
applied. The Pitzer parameters represent the measure
of the interactions between ions and solvent molecules.
In addition, separation factor value, S, of the chosen
solvent was evaluated for the investigated system.
2
2.1
EXPERIMENTAL
Materials
Propionic acid, cyclohexanol, and potassium
chloride were purchased from Merck. The mass fraction purities of the compounds were 0.99, 0.99, and
0.995, respectively. The chemicals were used without
further purification. Double distilled water was used
throughout all experiments.
2.2 Apparatus and procedure
A 0.02 dm3 of aqueous solution of potassium
chloride, for adjusting the ionic strength at the desired
value, was shaken with 0.02 dm3 of cyclohexanol and
the known amount of propionic acid at constant temperature T = (298.2, 303.2, and 308.2) K and then were
stirred vigorously for at least 2 h, then it was settled
down for 4 h. All these procedures were completed in
a double-wall container thermostated with water from
a Model GFL circulation system. After that propionic
acid concentration in each phase was determined by
Received 2010-08-01, accepted 2011-04-27.
* To whom correspondence should be addressed. E-mail: [email protected]
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Chin. J. Chem. Eng., Vol. 19, No. 4, August 2011
titration with a standard solution of sodium hydroxide.
Then, acid analysis was checked according to mass
balance equations. The potassium chloride concentration in the organic and aqueous phases was evaluated
by potentiometric titration method using Cl− indicator
electrode. All of the potentiometric measurements
were made using digital multimeter (Martini instruments Mi180) with 0.1 mV resolution. The output of
the multimeter was connected to a personal computer
by the RS232 connector for data acquisition. The
Mi5200 software and Microsoft Excel (Office 2007)
software were used for data acquisition and calculations. The water mole fractions in the organic phase
were also measured by Karl-Fisher (Dl-18 model mettler Toledo) method. The solubility curves were determined by using the method based on detection of
the cloud point.
3
3.1
Figure 1 Phase diagram of water + propionic acid + cyclohexanol ternary system at T = 298.2 K
Table 1 Experimental solubility data for water (1) +
propionic acid (2)+ cyclohexanol (3) ternary system
at T = 298.2 K
RESULTS AND DISCUSSION
LLE measurements
Figure 1 shows the binodal curve prior to addition of salt for ternary system of (water + propionic
acid + cyclohexanol) at 298.2 K. The composition of
mixtures on the binodal curve and the mutual binary
solubility of water and the alcohol are given in Table 1,
where xi denotes the mole fraction of the ith component. After salt addition, the experimental results
(tie-lines) for various ionic strength (0.5, 1.0, 1.5, 2.0,
and 2.5 mol·dm−3) were evaluated and are presented in
Tables 2 to 4 at T = (298.2, 303.2, and 308.2) K, respectively. Although the data deal with quaternary
system, use of free-salt mole fractions makes the representation easier.
Distribution coefficient, D2, of propionic acid,
and separation factor, S, of the chosen solvent were
calculated as follows [17]:
x
D2 = 23
(1)
x21
x
S = D2 11
(2)
x13
where x23 and x21 are propionic acid mole fractions in
solvent-rich and water-rich phases, respectively, and
Table 2
I/mol·dm−3
x1
x2
x3
0.0040
0.0000
0.9961
0.0098
0.0499
0.9404
0.0116
0.0565
0.9319
0.0184
0.0658
0.9158
0.0390
0.0954
0.8656
0.0630
0.1202
0.8167
0.0919
0.1508
0.7573
0.1249
0.1637
0.7114
0.1729
0.1878
0.6393
0.2348
0.1871
0.5782
0.3485
0.1630
0.4885
0.5391
0.1197
0.3412
0.6742
0.0000
0.3259
x13 and x11 are the water mole fractions in solvent-rich
and water-rich phases, respectively. The values of distribution coefficient and separation factor for each aqueous solution containing potassium chloride are summarized in Table 5 at T = (298.2, 303.2, and 308.2) K.
Figs. 2 to 4 show the distribution coefficients for
Experimental tie-line data of (water + propionic acid + cyclohexanol) ternary system
in the presence of salt at T = 298.2 K
Aqueous phase
Organic phase
x11
x21
x31
x13
x23
x33
0
0.9599
0.0013
0.0388
0.3680
0.0188
0.6131
0.5
0.9742
0.0012
0.0246
0.3245
0.0199
0.6557
1
0.9806
0.0011
0.0182
0.3087
0.0213
0.6700
1.5
0.9833
0.0010
0.0156
0.3018
0.0237
0.6745
2
0.9852
0.0010
0.0014
0.2973
0.0231
0.6796
2.5
0.9599
0.0013
0.0388
0.3680
0.0188
0.6131
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Chin. J. Chem. Eng., Vol. 19, No. 4, August 2011
Table 3
Experimental tie-line data of (water + propionic acid + cyclohexanol) ternary system
in the presence of salt at T = 303.2K
Aqueous phase
I/mol·dm−3
Organic phase
x11
x21
x31
x13
x23
x33
0
0.9781
0.0014
0.0206
0.3683
0.0183
0.6133
0.5
0.9830
0.0012
0.0158
0.3465
0.0184
0.6352
1
0.9831
0.0011
0.0158
0.3243
0.0188
0.6569
1.5
0.9873
0.0010
0.0116
0.3013
0.0214
0.6773
2
0.9913
0.0010
0.0076
0.2830
0.0225
0.6946
2.5
0.9781
0.0014
0.0206
0.3683
0.0183
0.6133
Table 4
Experimental tie-line data of water + propionic acid + cyclohexanol) ternary system
in the presence of salt at T = 308.2K
Aqueous phase
I/mol·dm−3
Organic phase
x11
x21
x31
x13
x23
x33
0.0
0.9784
0.0014
0.0202
0.3633
0.0189
0.6177
0.5
0.9896
0.0013
0.0091
0.3451
0.0199
0.6350
1.0
0.9916
0.0012
0.0072
0.3293
0.0206
0.6502
1.5
0.9955
0.0011
0.0034
0.3037
0.0216
0.6747
2.0
0.9861
0.0010
0.0129
0.3015
0.0215
0.6770
2.5
0.9784
0.0014
0.0202
0.3633
0.0189
0.6177
Table 5
Concentration
/mol·dm−3
The values of ionic strength, distribution coefficients for propionic acid, and
separation factor at T = (298.2, 303.2, and 308.2) K
298.2 K
I/mol·kg
−1
303.2 K
I/mol·kg
−1
308.2 K
D2
S
D2
S
D2
S
0.0
0
2.99
24.07
0
3.76
31.00
0
3.94
33.17
0.5
0.50
4.56
38.87
0.50
3.81
35.51
0.52
3.92
37.38
1.0
1.01
4.66
50.88
1.04
4.07
42.42
1.05
4.17
45.37
1.5
1.57
5.17
62.29
1.57
4.28
49.00
1.61
4.41
51.61
2.0
2.14
4.81
65.86
2.13
5.21
67.25
2.18
4.85
64.76
2.5
2.77
6.05
78.41
2.72
5.31
76.01
2.74
5.54
70.95
Figure 2 Distribution coefficient of propionic acid, D2,
plotted against the mole fraction of propionic acid in the
aqueous phase at T = 298.2 K
propionic acid in different temperatures. It can be concluded that propionic acid concentration in the aqueous phase decreases with increase of salt ionic strength.
The effectiveness of extraction of propionic acid by
the solvent is given by its separation factor, S, which
I/mol·kg
−1
Figure 3 Distribution coefficient of propionic acid, D2,
plotted against the mole fraction of propionic acid in the
aqueous phase at T = 303.2 K
is an indication of the ability of solvent to separate
propionic acid from water. Fig. 5 shows the separation
factor for the propionic acid at T = (298.2, 303.2, and
308.2) K. As it can be seen, separation of propionic
acid from water in the presence of the salt is possible.
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Chin. J. Chem. Eng., Vol. 19, No. 4, August 2011
Table 6 Values of Othmer-Tobias parameters for
water + propionic acid + cyclohexanol system
at T = (298.2, 303.2, and 308.2) K
Figure 4 Distribution coefficient of propionic acid, D2,
plotted against the mole fraction of propionic acid in the
aqueous phase at T = 308.2 K
3.3
T/K
A
B
R2
298.2
0.4142
0.2821
0.9614
303.2
0.9287
0.3749
0.8932
308.2
0.1411
0.1590
0.9624
Pitzer model
The Pitzer ion-interaction model was also used to
correlate and calculate the activity coefficients of
propionic acid. The Pitzer equation for the natural
logarithm of the activity coefficient of a neutral species, N, is [19]:
ln γ N = 2∑ λcN mc + 2∑ λcN ma + ∑∑ μcaN mc ma (4)
c
Figure 5 Separation factor plotted against the mole fraction of propionic acid in aqueous solution containing potassium chloride at different temperatures
T/K: ◆ 298.2; ■ 303.2; ▲ 308.2
3.2
where x11 is the mole fraction of water in the waterrich phase, x33 is the mole fraction of alcohol in the
solvent-rich phase. A and B are constant which depend
on the degree of immiscibility of components in systems. Fig. 6 shows the plot of ln[(1−x33)/x33] versus
ln[(1−x11)/x11]. The linearity of the plots indicates the
consistency of experimental data. The values of parameters A and B and the corresponding correlation
coefficient values (R2) are given in Table 6. It indicates that Eq. (3) can be satisfactorily used to correlate
the tie-line data of the investigated system.
K=
c
K
K0
(5)
morg
(6)
maq
where K and K0 are the molality ratio of propionic
acid for the organic phase and the aqueous solution, in
the presence and in absence of the salt, respectively.
The Pitzer ion-interaction parameters (λ and μ) were
obtained by combining Eqs. (4) and (5) using an iterative minimization procedure employing the Microsoft
Excel (solver) program. The KCl second and triply
virial coefficients found for investigated system are
illustrated in Table 7. Fig. 7 shows the calculated activity coefficients of propionic acid versus the ionic
strength of salt in aqueous solutions. It can be seen
that the activity coefficient of propionic acid increases
with ionic strength, but it decreases as temperature
increases. It can be concluded that the addition of
this salt decreases the solubility of propionic acid in
the aqueous phase. In addition, the salt effect on the
solubility of propionic acid is more important at lower
temperatures.
Table 7
Figure 6 Othmer-Tobias plots of water + propionic acid +
cyclohexanol ternary system at T = 298.2 K
c
ln γ N = ln
Othmer-Tobias correlation
The consistency of experimental tie-line data can
be determined by applying the Othmer-Tobias correlation [15-18] as shown in the following equation
1 − x33
1 − x11
ln
= A + B ln
(3)
x33
x11
c
where the sums are over cations c and over anions a,
mi is the molality of species i, λ the second virial coefficient, and μ the triple virial interactions coefficients.
Besides, the experimental activity coefficients were
determined by the following equations [20]:
The values of Pitzer ion-interaction parameters
at different temperatures
T/K
λ
μ
298.2
0.7417
−0.2249
303.2
0.0420
0.0382
308.2
0.0092
0.0411
Chin. J. Chem. Eng., Vol. 19, No. 4, August 2011
4
5
6
Figure 7 The plot of activity coefficients for propionic acid
versus total ionic strength of salt in aqueous solution containing potassium chloride at T = (298.2, 303.2, and 308.2) K
◆ 298.2 K; ■ 303.2 K; ▲ 308.2 K
4
CONCLUSIONS
The LLE results for the system of (water + propionic acid + cyclohexanol) were reported at T = (298.2,
303.2 and 308.2) K. The distribution coefficients and
activity coefficients of the propionic acid were determined in different media. It was found that the addition of potassium chloride decreases the solubility of
propionic acid in the aqueous phase for the investigated system. Also, the solubility of water in cyclohexanol decreases as the salt concentration increases.
It can be concluded from the distribution coefficient
and selectivity data that it is possible to separate
propionic acid from water in the presence of salt by
extraction with cyclohexanol.
7
8
9
10
11
12
13
14
ACKNOWLEDGEMENTS
15
We gratefully acknowledge the graduate office of
University of Guilan for supporting this work.
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