Liquid Liquid equilibrium

1. Liquideliquid equilibrium data for (n-hexane þ ethyl
acetate þ acetonitrile) ternary system at (298.15, 308.15, and 318.15) K
Meiying Qiao a, *
, Shengkai Yang a
, Li Qu b
a
School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang, Henan, 453003, PR China
b
Xinke College, Henan Institute of Science and Technology, Xinxiang, Henan, 453003, PR China
a r t i c l e i n f o
Article history:
Received 19 January 2016
Received in revised form
6 March 2016
Accepted 7 March 2016
Available online 9 March 2016
Keywords:
LLE
n-hexane
Ethyl acetate
Acetonitrile
NRTL
UNIQUAC
a b s t r a c t
Liquideliquid equilibrium (LLE) data for ternary system (n-hexane þ ethyl acetate þ acetonitrile) have
been measured at 298.15, 308.15 and 318.15 K under atmosphere pressure. NRTL and UNIQUAC models
were used to correlate the LLE data and their model parameters were obtained. The fitting root-mean-
square deviations (RMSD) of NRTL and UNIQUAC models were both below 0.17%, which demonstrated
the successful correlations for the ternary LLE experimental data. Moreover, NRTL model gave slightly
better predict results than UNIQUAC. Simultaneously, distribution coefficient (K) and separation factor
(S) were calculated from the LLE data. Results showed that the extraction of ethyl acetate from n-hexane
with acetonitrile as solvent was feasible.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
Since Tu Youyou won the Nobel Prize in medicine for the year
2015 in terms of her extracting successfully artemisinin from
Artemisia annua with ethyl ether, the method of using solvent to
extract effective drug from plants attracted people's attention. Be-
sides ethyl ether, n-hexane and ethyl acetate are also usually used
to achieve this aim, such as extracting d-1imonene from polygo-
natum [1], extracting phenolic compound from rhodiola rosea [2]
etc. After effective drugs, i.e. D-limonene or phenolic compound,
were separated from the extraction solution, the rest discard so-
lution was mainly composed of n-hexane and ethyl acetate. Thus it
is essential to separate n-hexane and ethyl acetate mixture for
recycling.
N-hexane and ethyl acetate form azeotrope at atmospheric
pressure and cannot be separated by ordinary distillation. Some
methods have been presented to separate n-hexane-ethyl acetate
system. Batch azeotropic distillation was used to separate n-hex-
ane-ethyl acetate system with acetone [3,4] or acetonitrile [5] as
light entrainer. Extractive distillation has been used to separate n-
hexane-ethyl acetate system with N-methyl-2-pyrrolidone (NMP)
[6] or N, N-dimethylformamide (DMF) [7] as heavy entrainer.
Furthermore, solvent extraction is a desirable separation method
due to its smaller energy consumption and is used to separate n-
hexane-ethyl acetate system with acetonitrile as candidate solvent
in our project.
Solvent selection and subsequent process design of solvent
extraction need liquideliquid equilibrium (LLE) data between sol-
vents and material compositions. For the measurement of LLE data
for related components, H. Sugi and T. KATAYAMA have measured
ternary liquideliquid equilibria data for n-hexane-ethanol-aceto-
nitrile at 40 C and water-acetonitrile-ethyl acetate at 60 C [8].
In this paper, isothermal ternary LLE data for n-hexane-ethyl
acetate-acetonitrile system have been measured at (298.15, 308.15
and 318.15) K under atmosphere pressure. The thermodynamic
models of NRTL (non-random two liquid) [9] and UNIQUAC (uni-
versal quasi-chemical) [10] were then used to correlate the LLE data
with Aspen Plus physical parameter regression system. Distribution
coefficient (K) and separation factor (S) were finally calculated to
evaluate the availability of acetonitrile as solvent to extract ethyl
acetate from n-hexane.
* Corresponding author.
E-mail address: qiaomy2016@sina.com (M. Qiao).
Contents lists available at ScienceDirect
Fluid Phase Equilibria
journal homepage: www.elsevier.com/locate/fluid
http://dx.doi.org/10.1016/j.fluid.2016.03.008
0378-3812/© 2016 Elsevier B.V. All rights reserved.
Fluid Phase Equilibria 419 (2016) 84e87

2. 2. Experimental
2.1. Materials
The analytical grade chemicals n-hexane, ethyl acetate and
acetonitrile were purchased from Tianjin Kemiou Chemical Reagent
Co. Ltd. For all reagents, the purities checked by gas chromatograph
were listed Table 1. All reagents were used directly in the experi-
ment without further purification. The densities and refractive in-
dex for all reagents were also measured by a digital vibrating-tube
densimeter (DMA 4500, Anton Paar, Austria) at 298.15 K with an
uncertainty of ±0.00005 g cmÀ3
and a full automatic refract-meter
(Hanon A610, Hanon Instrument, China) with an uncertainty of
±0.0001, respectively. The densities and refractive index were also
listed in Table 1 and compared with the literature values [11e13],
with the good agreement in general.
2.2. Apparatus and procedures
The measurement methods and procedures of LLE experiments
data were similar to those described in the literature [14e16].
Firstly, a 100 mL glass container was filled up by the mixtures of
known overall composition as much as possible to avoid perhaps
appearance of additional vapor phase. Then the glass container was
stirred intensely by ultrasonic at least 1 h to make the sample mix
completely and was sealed with a glass tap. The glass container was
then placed in a cryogenic thermostatic (THD-2006, Ningbo Tian-
heng Instrument Factory, China) at constant temperatures under
atmospheric pressure. The maximum temperature fluctuations
were within 0.05 K. After almost 20 h, syringes were used to take
the samples from both phases. To cover the entire two-phase region
as far as possible, the volume for one component was usually fixed
and those for the other two were altered with one increased and
the other decreased. The change step of volume for each compo-
nent was 7e8 mL each time.
With a gas chromatograph (GC-2010 Plus from Shimadzu Co.
Ltd., Japan) with a flame ionization detector (FID), all samples for
the equilibrium phases were analyzed. The GC column is a Rtx-5
low polarity capillary column (30 m  0.25 mm  0.25 mm,
Restek Corporation, USA). The carrier gas is nitrogen with a purity
of 99.999%, with a flowrate of 30 cm3
minÀ1
and a pressure of
0.3 MPa. For each sample, the response of gas chromatography
analysis was calibrated with several standard mixtures of known
composition prepared gravimetrically over the entire composition
range. The final composition was determined from the average of
three replications. The uncertainty of the equilibrium mixture
composition is estimated to within ±0.001 in mole fraction.
2.3. Uncertainty measurement
For each variable determined experimentally, including density
(r), refractive index (nD), temperature (T), composition (x) and
pressure (p), their uncertainties were determined according to the
JCGM guidance document [17] and were shown in the respective
table footnote.
3. Results and discussion
3.1. LLE experimental data
The ternary LLE tie-line data at (298.15, 308.15, 318.15) K were
listed in Table 2 shown as mole fraction, and triangle phase dia-
grams were plotted and shown in Fig. 1 separately. According to
Treybal [18], these are Type I ternary diagrams. In other words, n-
hexane-acetonitrile system is partial miscible, while n-hexane-
ethyl acetate and ethyl acetate-acetonitrile systems both are
completely miscible with each other in the temperature range
investigated. The immiscible area in the triangle diagrams decrease
with the temperature rising from 298.15 K to 318.15 K. The positive
slope of tie-line in triangle phase graph manifests the positive
Table 1
Experimental and literature values of density r and refractive index nD, van der Waals molecular structural parameters of pure component for UNIQUAC, and mass fraction
purity w.
Chemical name ra,b
/(gcmÀ3
) nD
a,b
rc
qc
wd
Experimental Literature Experimental Literature Volume Surface area Mass fraction purity
n-hexane 0.65512 0.65507 [11] 1.3725 1.3720 [11] 4.4998 3.8560 0.9974
Ethyl acetate 0.89461 0.89460 [12] 1.3701 1.3699 [12] 3.4786 3.1160 0.9982
Acetonitrile 0.77655 0.77664 [13] 1.3413 1.3411 [13] 1.8701 1.7240 0.9978
a
The experimental values of density and refractive index are reported at 298.15 K and atmospheric pressure.
b
Standard uncertainties: u(r) ¼ ±0.00007 g cmÀ3
; u(nD) ¼ ±0.0001 and u(p) ¼ ±0.3 kPa, all with 0.95 level of confidence.
c
Taken from Aspen property databank.
d
Determined by Gas Chromatography.
Table 2
The experimental tie-line data (mole fraction) for n-hexane (1) þ ethyl acetate
(2) þ acetonitrile (3) at T ¼ (298.15, 308.15 and 318.15) K under atmospheric
pressure.a
Feed n-hexane rich
phase (I)
Acetonitrile rich
phase (II)
K1 K2 S
x1 x2 x1 x2 x1 x2
298.15 K
0.4708 0.0491 0.8601 0.0298 0.0798 0.0703 0.0928 2.359 25.43
0.4143 0.0992 0.8202 0.0696 0.1103 0.1295 0.1345 1.861 13.84
0.3797 0.1525 0.7611 0.1191 0.1305 0.1894 0.1715 1.590 9.27
0.3718 0.1842 0.7213 0.1488 0.1507 0.2189 0.2089 1.471 7.04
0.3407 0.2253 0.6614 0.1888 0.1908 0.2594 0.2885 1.374 4.76
0.3250 0.2617 0.6004 0.2291 0.2310 0.2887 0.3847 1.260 3.28
0.3055 0.2905 0.5313 0.2584 0.2724 0.3187 0.5127 1.233 2.41
0.2941 0.3103 0.4722 0.2877 0.3316 0.3189 0.7022 1.108 1.58
308.15 K
0.4958 0.0355 0.8601 0.0295 0.0904 0.0395 0.1051 1.339 12.74
0.4606 0.0690 0.8410 0.0488 0.0996 0.0901 0.1184 1.846 15.59
0.4205 0.1128 0.7900 0.0898 0.1198 0.1396 0.1516 1.555 10.25
0.3923 0.1584 0.7305 0.1293 0.1498 0.1899 0.2051 1.469 7.16
0.3675 0.1948 0.6806 0.1591 0.1818 0.2288 0.2671 1.438 5.38
0.3416 0.2312 0.6215 0.1999 0.2224 0.2589 0.3578 1.295 3.62
0.3169 0.2647 0.5404 0.2389 0.2703 0.2895 0.5002 1.212 2.42
0.3006 0.2813 0.4914 0.2685 0.3207 0.2989 0.6526 1.113 1.71
318.15 K
0.5065 0.0403 0.8498 0.0301 0.0999 0.0499 0.1176 1.658 14.10
0.4676 0.0811 0.8108 0.0594 0.1212 0.0989 0.1495 1.665 11.14
0.4448 0.1267 0.7607 0.0991 0.1406 0.1493 0.1848 1.507 8.15
0.3993 0.1572 0.7115 0.1288 0.1701 0.1797 0.2391 1.395 5.84
0.3789 0.1904 0.6607 0.1598 0.1907 0.2194 0.2886 1.373 4.76
0.3550 0.2223 0.6012 0.1989 0.2307 0.2492 0.3837 1.253 3.27
0.3392 0.2437 0.5616 0.2195 0.2601 0.2698 0.4631 1.229 2.65
0.3215 0.2632 0.4926 0.2488 0.3210 0.2791 0.6516 1.122 1.72
a
Standard uncertainties u are u(x) ¼ 0.0010, u(T) ¼ 0.05 K.
M. Qiao et al. / Fluid Phase Equilibria 419 (2016) 84e87 85

3. effect of the extraction of ethyl acetate from n-hexane with
acetonitrile as extractive solvent. In addition, the feed composition
for each tie line was also listed in Table 2 and shown in Fig. 1. Each
feed composition points in the triangle phases fall on the respective
tie line, indicating that mass balances are satisfied.
3.2. Data correlation
Here, the NRTL [9] and UNIQUAC [10] models were applied to
correlate the experimental data for the ternary systems by using an
Aspen Simulator. Van der Waals molecular structural parameters of
pure component for UNIQUAC model r and q were list Table 1 for n-
hexane, ethyl acetate and acetonitrile, respectively. The binary
interaction parameters for the two models were bij and bji and
defined as the footnote of Table 3. The regression method used in
the ASPEN simulator was the generalized least squares method
based on maximum likelihood principles and with the Deming
initialization method, the BritteLuecke algorithm [19] was
employed to obtain the model parameters. The regression conver-
gence tolerance was set to 0.0001. The values of the non-random
parameter aij for NRTL model were fixed at 0.2 for acetonitrile-n-
hexane, 0.3 for ethyl acetate-acetonitrile and 0.3 for n-hexane-
ethyl acetate according to the relative polarity of component pairs.
The interaction parameters for NRTL and UNIQUAC models were
determined by fitting all the isothermal ternary system LLE
experimental data at T ¼ (298.15, 308.15 and 318.15) K and were
reported in Table 3.
To evaluate the agreement between the measured data and the
calculated results, root-mean-square deviation (RMSD) was calcu-
lated according to the following equation:
RMSD ¼
0
B
@
PM
k¼1
P2
j¼1
P3
i¼1
xijk À xijk
2
6M
1
C
A
1=2
(1)
where M is the number of tie-line. The values of RMSD were also
listed in Table 3. From the small RMSD values, it was concluded that
LLE experimental data at T ¼ (298.15, 308.15 and 318.15) K for the
ternary system investigated could be correlated well by NRTL and
UNIQUAC models, and the former is slightly better than the latter.
3.3. Study of acetonitrile as extractive solvent
To assess the feasibility of using acetonitrile as a solvent to
extract ethyl acetate from n-hexane, the distribution coefficient (K)
and the separation factor (S) were applied, which were calculated
from the following equations:
K1 ¼
xІІ
1
xІ
1
(2)
K2 ¼
xІІ
2
xІ
2
(3)
S ¼
xІІ
2
xІІ
1
xІ
2
xІ
1
¼
K2
K1
(4)
Table 2 showed the values of K1, K2 and S in terms of each tie
line. From all the values of S which are more than 1.0 at the tem-
perature ranges investigated, it was concluded that acetonitrile can
be used as solvent to extract ethyl acetate from n-hexane. K and S
both decrease as the concentration of ethyl acetate increases,
indicating that the higher the concentration of ethyl acetate, the
Fig. 1. Ternary phase diagram for n-hexane (1) þ ethyl acetate (2) þ acetonitrile (3)
system at 298.15 K, 308.15 K and 318.15 K: (-d-) experimental data; (De e eD)
NRTL model; (,∙∙∙∙∙,) UNIQUAC model; (C) feed composition.
M. Qiao et al. / Fluid Phase Equilibria 419 (2016) 84e8786

4. lower the separation capacity of acetonitrile. It should be noted that
the distribution coefficients K2 within the temperature range
investigated are a litter more than 1.0, suggesting considerable
quantities of solvent would be required in practice.
4. Conclusions
Tie-line data for the ternary system composed of n-hexane,
ethyl acetate and acetonitrile were measured at T ¼ (298.15, 308.15
and 318.15) K under atmospheric pressure. A type I phase diagram
was found for the ternary system. With temperature increasing, the
immiscible zone in the triangle phase diagram becomes smaller.
NRTL and UNIQUAC models were applied to correlate the LLE data
and the models parameters were obtained. Two models both gave
satisfactory results and NRTL model was slightly better than UNI-
QUAC model. The works contribute to the process design of the
extraction of ethyl acetate from n-hexane with acetonitrile as
solvent.
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Table 3
NRTL and UNIQUAC binary interaction parameters (bij and bji) for the ternary system n-hexane (1) þ ethyl acetate (2) þ acetonitrile (3) valid for the temperature range
investigated.a
Components
iej
UNIQUAC parameters NRTL parameters
bij (J$molÀ1
) bji (J$molÀ1
) RMSD bij (J$molÀ1
) bji (J$molÀ1
) a RMSD
1e2 À1162.43 259.35 0.0017 3662.17 953.12 0.3 0.0014
1e3 À4347.86 À281.79 3788.39 4868.82 0.2
2e3 À5685.06 3216.78 564.65 2085.96 0.3
a
The NRTL and UNIQUAC model parameters (bij, bji) are defined as bij ¼ gij À gii and bij ¼ uij À uii, respectively.
M. Qiao et al. / Fluid Phase Equilibria 419 (2016) 84e87 87