Experimental Study On VLE of Ternary Systems of Cn-Ionic Liquid Using HS Chromatography
Experimental Study On VLE of Ternary Systems of Cn-Ionic Liquid Using HS Chromatography
Experimental Study On VLE of Ternary Systems of Cn-Ionic Liquid Using HS Chromatography
J. Chem. Thermodynamics
journal homepage: www.elsevier.com/locate/jct
a r t i c l e i n f o a b s t r a c t
Article history: (Vapor + liquid) equilibrium (VLE) data for ternary systems of (hexane + benzene), (hexane + cyclohex-
Received 18 December 2011 ane), (benzene + cyclohexane), (1-hexene + cyclohexane), and (1-hexene + benzene) with an ionic liquid
Received in revised form 19 February 2012 were measured by headspace gas chromatography. The applied ionic liquid 1-methyl 3-octylimidazolium
Accepted 24 February 2012
thiocyanate, [Omim][SCN], acts as an entrainer. The comparison of the measured VLE data with the equi-
Available online 5 March 2012
librium data for the binary mixtures without ionic liquid show that [Omim][SCN] signicantly improves
the separation factor of these systems. The NRTL thermodynamic model is applied for correlating the
Keywords:
experimental data. The modeling results show the NRTL model can correlate the experimental data with
Ionic liquid
(Vapor + liquid) equilibria
a good accuracy.
Headspace gas chromatography 2012 Elsevier Ltd. All rights reserved.
NRTL model
0021-9614/$ - see front matter 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jct.2012.02.032
78 B. Mokhtarani et al. / J. Chem. Thermodynamics 51 (2012) 7781
In the present research, the VLE data for the mixtures of (hex- determined carefully. For this purpose, a mathematical relation
ane + benzene), (hexane + cyclohexane), (benzene + cyclohexane), for the volume of the liquid was derived as a function of the height
(1-hexen + benzene), and (hexane + 1-hexene) with 1-methyl 3- of the liquid in the vial. The volume of the liquid phase can then be
octylimidazolium thiocyanate [Omim][SCN] is investigated by determined by measurement of the height of liquid phase. Then,
using headspace gas chromatography. To our knowledge, there is the density of the liquid phase was measured using an Anton Paar
no report on the experimental VLE data for this type of IL in DMA-5000 digital densitometer with an uncertainty of less than
literature. The NRTL thermodynamic model was then used for 4.105 g cm3. Afterward, the mass of liquid phase was calcu-
correlating the experimental data. lated, from which the mass of vapor phase was determined by sub-
tracting the total initial mass and the mass of liquid phase. By
using the mass fractions in the vapor phase, the mass fraction of
2. Experimental each component in the vapor and liquid phase were then deter-
mined. The experimental uncertainty for the liquid mole fraction
2.1. Chemicals was 0.002.
K i yi =xi
2.2. Apparatus and procedure aij ; 1
K j yj =xj
The concentrations of vapor contents in the VLE of ternary where Ki is the ratio of mole fraction of component i in the vapor (yi)
systems were determined by headspace gas chromatography. to that in the liquid phase (xi).
The term of headspace refers to the vapor space above the As the results show, the separation factors in all theses systems
liquid sample placed in a vial [6]. The apparatus consists of a are higher than 1, which means that the IL can act as an appropri-
headspace sampler (HS-sampler) from Perkin Elmer Company ate entrainer for these systems.
(turbo matrix 40), a gas chromatograph (Varian, cp 3800), and a
computer where a FID detector and capillary column (Chrompack,
25 m 0.32 mm 1.2 lm) were used for GC analysis. TABLE 2
Experimental equilibrium data of liquid mole fraction (xs1 ) and vapor mole fraction
The ternary mixtures of hydrocarbons and IL were prepared by
(ys1 ) based on solvent free basis and separation factors a12 for the system of {hexane
mass using a laboratory balance with the precision of 104 g. The (1) + benzene (2)} in the presence of 80 mol% [Omim][SCN] at 323.2 K.
mole fraction of the [Omim][SCN] was xed at 0.8 in each mixture.
xs1 ys1 a12
This mole percent was selected because the mixture of the hydro-
carbon and ionic liquid is not homogeneous in mole fraction less 0.048 0.210 5.27
than 0.75, and a two-phase system is observed. The mixtures were 0.109 0.325 3.94
0.145 0.436 4.56
transferred into 20 cm3 vials and the vials were closed tightly with 0.255 0.558 3.68
the cap and septum. The vials were inserted in the oven of head- 0.328 0.634 3.55
space sampler and heated to the specied temperature. After 3 h, 0.437 0.676 2.69
when the equilibrium conditions were attained in the vials, a sam- 0.601 0.762 2.12
0.673 0.836 2.48
ple of the vapor phase was taken by the headspace sampler and
0.800 0.900 2.24
analyzed by the gas chromatography. Since the vapor pressure of 0.872 0.968 4.42
the IL is negligible, the vapor phase consists of hydrocarbons. 0.904 0.996 26.84
Therefore, in order to measure, the compositions of the vapor
phase; calibrations for the binary systems were required. The
samples of the binary hydrocarbons with compositions within
the entire range of concentrations were prepared and injected TABLE 3
directly into the gas chromatograph. The experimental uncertainty Experimental equilibrium data of liquid mole fraction (xs1 ) and vapor mole fraction
(ys1 ) based on solvent free basis and separation factors a12 for the system of {hexane
for the vapor phase mole fraction was less than 0.001.
(1) + cyclohexane (2)} in the presence of 80 mol% [Omim][SCN] at 323.2 K.
In order to determine the composition of the liquid phase, the
volume of the liquid phase at equilibrium conditions was xs1 ys1 a12
0.009 0.091 11.05
0.028 0.170 7.12
TABLE 1 0.100 0.300 3.86
The purities and suppliers of the chemicals. 0.214 0.441 2.90
0.294 0.517 2.57
Chemical name Supplier Mass fraction purity
0.378 0.611 2.58
Hexane Merck >0.99 0.491 0.702 2.45
Benzene Merck >0.99 0.603 0.789 2.46
Cyclo hexane Merck >0.99 0.672 0.856 2.90
1-Hexene Fluka >0.99 0.818 0.948 4.07
[Omim][SCN] Prepared in lab >0.99 0.915 0.985 6.13
B. Mokhtarani et al. / J. Chem. Thermodynamics 51 (2012) 7781 79
TABLE 4 Dg ij g ij g jj : 5
Experimental equilibrium data of liquid mole fraction (xs1 ) and vapor mole fraction
(ys1 ) based on solvent free basis and separation factors a12 for the system of In order to correlate the experimental data, the following equa-
{cyclohexane (1) + benzene (2)} in the presence of 80 mol% [Omim][SCN] at 323.2 K. tion is used as an objective function:
xs1 ys1 a12 exp
Pn y1 ycal
1
0.045 0.105 2.52 F ; 6
i1 yexp
1 i
0.093 0.204 2.50
0.204 0.340 2.01
0.323 0.445 1.68 where n is the number of data points, y is the vapor mole fraction,
0.467 0.576 1.55 and superscripts of exp and cal referred to experimental and calcu-
0.503 0.603 1.50 lated values, respectively.
0.587 0.687 1.54 The experimental data were correlated by the Microsoft Excel
0.710 0.780 1.45
program (Solver). The solver program minimizes the objective
0.851 0.896 1.51
0.940 0.975 2.51 function through changing the interaction parameters of the NRTL
0.943 0.991 6.58 model with trial and error. The method of the solution is based on
the newton method. At the minimum point the nal NRTL interac-
tion parameters are determined. The nonrandomness parameter, a,
TABLE 5 in NRTL model was set to 0.3 for all the systems and the interaction
Experimental equilibrium data of liquid mole fraction (xs1 ) and vapor mole fraction parameters are reported in table 7. The root mean square deviation
(ys1 ) based on solvent free basis and separation factors a12 for the system of {1-hexene
is dened as follows:
(1) + cyclohexane (2)} in the presence of 80 mol% [Omim][SCN] at 323.2 K.
1=2
xs1 ys1 a12 P
n
exp 2
rmsd yexp
1 ycal
1 =y 1 i =n 1 100: 7
0.026 0.124 5.41 i1
0.054 0.304 7.61
0.101 0.402 6.00 As seen in table 7, the NRTL model can correlate the VLE data
0.179 0.468 4.04 with a good accuracy.
0.295 0.570 3.18 The experimental results and the literature data [1821] for the
0.421 0.666 2.74 hydrocarbon binaries are compared with the correlated data by the
0.546 0.771 2.80
0.654 0.849 2.97
NRTL model on the solvent free basis in gures 1 to 4. As the g-
0.723 0.878 2.76 ures show, adding [Omim][SCN] as the entrainer improves the sep-
0.839 0.948 3.47 aration factor of these systems. The gures also show that the
0.934 0.976 2.80 correlated data by the NRTL model represent good agreements
with the experimental data.
In order to evaluate the performance of [Omim][SCN] as the en-
TABLE 6 trainer for these binary systems, the experimental VLE data and
Experimental equilibrium data of liquid mole fraction (xs1 ) and vapor mole fraction separation factors can be compared with those obtained by using
(ys1 ) based on solvent free basis and separation factors a12 for the system of {1-hexene other ILs reported in a previous work [8]. The comparison of the
(1) + benzene (2)} in the presence of 80 mol% [Omim][SCN] at 323.2 K.
VLE data with those obtained by using [Omim][BTI] for the binary
xs1 ys1 a12 systems of (hexane + benzene), (hexane + cyclohexane), and
0.071 0.201 3.30 (cyclohexane + benzene) are shown in gures 1 to 3. From gure
0.084 0.240 3.44 1, it can be seen that the [Omim][BTI] is a more suitable entrainer
0.142 0.368 3.53
0.341 0.646 3.52
0.369 0.701 4.02 TABLE 7
0.441 0.779 4.47 The interaction parameters (Dg) for NRTL model obtained by correlating VLE data and
0.486 0.821 4.85 the root mean square deviation (rmsd).
0.591 0.889 5.54
0.743 0.943 5.70 Component ij NRTL parameter rmsd
Dgij (kJ mol1) Dgji (kJ mol1)
{Hexane (1) + benzene (2) + [Omim][SCN] (3)}
4. Thermodynamic correlation 12 85.108 105.080
13 4.806 11.972 2.28
The experimental VLE data were correlated using the Non 23 16.700 3.327
Random Two Liquid (NRTL) model [13]. This model has been {Hexane (1) + cyclohexane (2) + [Omim][SCN] (3)}
widely used in modeling both (vapor + liquid) and (liquid + liquid) 12 16.372 13.102
equilibria [1417]. In this model, the activity coefcients are calcu- 13 11.986 29.446 1.58
23 5.657 30.038
lated as follows:
Pn Pn
s
j1 ji xj Gji P
n xj Gij m1 smi xm Gmi
{Cyclohexane (1) + benzene (2) + [Omim][SCN]} (3)
ln ci Pn Pn sij P n ; 2 12 1.162 568.904
k1 xk Gki j1 k1 xk Gkj k1 xk Gkj 13 76.105 3.983 2.10
23 4.011 20.951
where
{1-Hexene (1) + cyclohexane (2) + [Omim][SCN]} (3)
Gij expa sij ; 3 12 3.625 568.904
13 76.049 17.138 1.83
Dg ij 23 2.562 18.425
sij ; 4
RT {1-Hexene (1) + benzene (2) + [Omim][SCN]} (3)
where x is the mole fraction, R is the gas constant, a is the nonran- 12 9.458 3.120
13 4.775 6.072 0.73
domness parameter, and Dg ij is the energy parameter which is
23 11.321 1.999
dened as:
80 B. Mokhtarani et al. / J. Chem. Thermodynamics 51 (2012) 7781
1 1.0
0.8 0.8
0.6 0.6
y1
y1
0.4 0.4
0.2 0.2
0 0.0
0 0. 2 0. 4 0. 6 0. 8 1 0. 0 0. 2 0. 4 0. 6 0. 8 1.0
x1 x1
FIGURE 1. Mole fraction of vapor against mole fraction of liquid (IL-free basis) for FIGURE 4. Mole fraction of vapor against mole fraction of liquid (IL-free basis) for
the ternary system of {hexane (1) + benzene (2) + 80 mol% IL} at T = 323.2 K, () the ternary system of {1-hexene (1) + benzene (2) + 80 mol% [Omim][SCN]} at
ternary system with [Omim][SCN]; (j) binary system without IL [14]; (N) ternary T = 323.2 K, () ternary system with [Omim][SCN]; (j) binary system without IL at
system with [Omim][BTI] at T = 322.8 K [8]; and () NRTL correlation. T = 313.1 K [17]; and () NRTL correlation.
and compared with the VLE data of the systems with [Omim][BTI]
0.4
as the entrainer. The comparison indicates that both ILs are appro-
priate entrainer for binary systems of hydrocarbons but [Omim][B-
0.2
TI] is a more suitable entrainer for (hexane + benzene) and
(cyclohexane + benzene) systems. For the binary system of (hex-
0.0
ane + cyclohexane), the inuence of [Omim][SCN] on the VLE is
0. 0 0. 2 0. 4 0. 6 0. 8 1.0
more than that of [Omim][BTI]. It seems that more experimental
x1 data are required for the inuence of the different ILs on the VLE
of the hydrocarbon systems over the entire concentration range.
FIGURE 3. Mole fraction of vapor against mole fraction of liquid (IL-free basis) for
the ternary system of {cyclohexane (1) + benzene (2) + 80 mol% IL} at T = 323.2 K,
() ternary system with [Omim][SCN]; (j) binary system without IL [16]; (N) References
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