Thermodynamic evaluation of imidazolium based ionic liquids with thiocyanate anion as effective solvent to thiophene extraction

Article abstract of DOI:10.1016/j.molliq.2016.03.061

In order to have deep insight on the molecular interactions between thiophene (TS) and ionic liquids, the density, speed of sound and refractive index of binary liquid mixture of TS with 1-hexyl-3-methylimidazolium thiocyanate [HMIM][SCN], and 1-octyl-3-m

Full text of DOI:10.1016/j.molliq.2016.03.061

Journal of Molecular Liquids 219 (2016) 975–984
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Thermodynamic evaluation of imidazolium based ionic liquids with
thiocyanate anion as effective solvent to thiophene extraction
Hemayat Shekaari ⁎, Mohammed Taghi Zafarani-Moattar, Mehrdad Niknam
Department of Physical Chemistry, University of Tabriz, Tabriz, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In order to have deep insight on the molecular interactions between thiophene (TS) and ionic liquids, the density,
speed of sound and refractive index of binary liquid mixture of TS with 1-hexyl-3-methylimidazolium thiocyanate
Received 2 October 2015
Received in revised form 20 March 2016
Accepted 21 March 2016
Available online xxxx
[HMIM][SCN], and 1-octyl-3-methylimidazolium thiocyanate [OMIM][SCN] at T = (288.15 to 303.15) K and at
atmospheric pressure have been measured in dilute region of TS. Various thermophysical parameters including
0
partial molar volumes, vm;i, apparent molar volumes, V , standard partial molar volumes V
ϕ
, partial molar isentropic
, excess molar volumes, V , excess partial molar volumes,v , and molar refractions, R , have been
calculated using these data. The densitometric and refractometric non-intrinsic contributions to the partial molar
0
E
E
compressibility, κ
ϕ
D
Keywords:
Thiophene
Ionic liquid
Volumetric
Refractive index
Excess partial molar volume
Thiocyanate
m;i
d
r
volume, θ and θ have been obtained using the measured experimental data. Also, interaction volume, Vint, and
cavity volume, Vcav, have been calculated from scaled particle theory (SPT). The results demonstrate that the ionic
liquids with shorter alkyl chain length interact effectively with thiophene as according to the calculated interaction
volumes and excess partial molar volumes. One would expect that the extraction efficiency of [HMIM][SCN]
E
m;i
is slightly better than the other ionic liquid. The calculated quantities such as v and Vint can be used to predict
extraction capability of these ionic liquids to thiophene extraction from fuel.
©
2016 Elsevier B.V. All rights reserved.
1
. Introduction
coefficients at infinite dilution have been proposed as the first informa-
tion of selectivity [12,13].
The challenge of petroleum industry is to reduce the typical aromatic-
sulfur compounds that are found in fuels as thiophene, and its derivatives
1]. Deep desulfurization of fossil fuel has become an important industry
Various ionic liquids have been used to desulfurization process. Due
to high cost, high viscosity or hydrolysis and production of hazardous
substances such as HF, some of them are not appropriate for industrial
operation [14]. Recently, the use of ionic liquids with thiocyanate
anion because of low cost, low viscosity and non-hazardous hydrolysis
productions has been intensified to this process. Some studies by
COSMO-RS were conducted on systems that include [BMIM][SCN] +
TS + hexane, heptane or decane for calculating infinite dilution activity
coefficient and selectivity of the ionic liquid in the extraction of thiophene
from hydrocarbons [13]. Dibenzothiophene extraction from dodecane
by [BMIM][SCN] ionic liquid has been studied by Wilfred et al. [15].
Vapor–liquid equilibrium of binary systems including 1-ethyl-3-
methylimidazolium thiocyanate [EMIM][SCN] with thiophene or
pyridine has been studied by Khelassi-Sefaoui et al. [16]. Extract of
dibenzothiophene (DBT) from n-dodecane with [BMIM][SCN] had
been reported with extraction efficiency of more than 65% [17].
However, because there are numerous ionic liquids, it is hard and very
time consuming in practice to select appropriate IL for such processes
from liquid–liquid equilibrium. In addition, the LLE study consumes
large amounts of ionic liquid; as a result, the study will lead to more costs.
Volumetric method provides useful information about interactions
and significantly contributes to a better understanding of the interactions
between components. Volumetric properties of binary mixtures are
complex properties because they depend not only on solute–solute,
[
subject due to the new legislative regulations to reduce sulfur content in
the USA and Europe [2,3]. Nowadays, the hydrodesulfurization (HDS)
processes which are employed by refineries to remove organic sulfur
from fuels for several decades need high temperature and pressure, larger
reactor volumes, and more active catalysts [4,5].
Faced with continuing fuel quality challenges, the scientific funda-
mental research have begun to pay close attention to extraction of sulfur
compounds with ionic liquids, which have the potential for alternative
and future complementary technology for deep desulfurization [6]. It
may be industrially favorable process because of low temperature, low
use of energy and low cost [7].
So, ionic liquids (ILs) are proposed as entrainers for new alternative
technologies to the classical hydrodesulfurization process and in order
to the deep desulfurization of low level aromatic sulfur compounds.
For the application of ILs in refinery processing, the possibility of the
entrainer has to be investigated on model fuel, representing the real
feed mixtures [8]. In order to solve this problem, the ternary liquid–
liquid equilibrium (LLE) desulfurization with ILs [9–11] and activity
⁎
Corresponding author.
E-mail address: hemayatt@yahoo.com (H. Shekaari).
http://dx.doi.org/10.1016/j.molliq.2016.03.061
167-7322/© 2016 Elsevier B.V. All rights reserved.
0

976
H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
solvent–solvent, and solute–solvent interactions, but also of the structural
effects arising from interstitial accommodation due to the difference in
molar volume and free volume between components present in the
mixture [18]. Moreover, there is interest in using volumetric data to
test molecular theories or models of solution to extend our understanding
about molecular interactions between components [19] and understand
the relation between structure and property, making it easier to search
for an optimal ionic liquid for a specific application [20].
[OMIM][Cl], two naked round-bottom flask containing 1-
methylimidazole were put on a magnetic stirrer and excess amount of
1-chlorohexane/1-chlorooctane was added to the flask dropwise from
the dropper funnel in an ice bath. After completion of the haloalkane
addition, the entire system has been refluxed for 72 h under argon
atmosphere with gradually rising temperature up to 343 K [25]. The
major impurities in the thiocyanate based IL was unreacted [HMIM][Cl]
or [OMIM][Cl], NaCl and the excess NaSCN. The prepared IL was washed
then with the dry dichloromethane. The impure IL is solved in this sol-
vent, but NaSCN and NaCl salts are not soluble and separate from the so-
lution. The unreacted raw materials are evaporated under reduced
pressure using a rotary evaporator. The remaining liquid is further
dried at about T = 343 K under reduced pressure using high vacuum
pump. Since ILs are very hygroscopic compounds, to remove trace
amount of moisture, both of the obtained imidazolium based ionic liq-
uids were dried overnight at about T = 353 K under high vacuum
This work is a continuation of our studies on the extraction abilities of
chosen ILs from model fuel based on our previous fundamental thermo-
dynamic measurements from volumetric properties such as standard
0
partial molar volumes V
ϕ
, partial molar isentropic compressibility,
0
E
E
κ
ϕ
, excess molar volumes, V and excess partial molar volumes, v
,
m;i
measurements in binary systems [21,22].
Literature survey indicates that few studies have been done on the
volumetric properties of these types of systems [23]. In this study, it is
focused to study the influence of two ionic liquids with different cation
alkyl chain length on the thermodynamic properties of binary systems
that contain thiophene and ionic liquid.
To achieve this aim, in this work, volumetric, acoustic and
refractometric properties of two binary mixtures containing
thiophene + 1-hexyl-3-methylimidazolium thiocyanate and 1-octyl-
(
0.1 Pa) prior to use. Water contents of the prepared ionic liquids
were found by Karl Fischer method using a Karl Fischer titrator (751
GPD Titrino-Metrohm, Herisau, Switzerland) which was less than
1
0
.1%. The [HMIM][SCN] and [OMIM][SCN] were analyzed by H NMR
(
Brucker Av-400) and FT-IR (Brucker, tensor27) to confirm the absence
of any major impurities (supplementary content). The physical proper-
ties of pure chemicals used in this work including experimental densi-
ties, speeds of sound, and refractive indices are given in Table 2 and
compared with those values reported in the literature.
3
-methylimidazolium thiocyanate were presented in dilute region of
TS at different temperatures and at atmospheric pressure. Therefore,
density, speed of sound and refractive index data of binary studied
mixtures have been measured and some thermodynamic parameters
have been calculated. The results will help us to better understand the
influence of ionic liquids on extractive desulfurization process. A specific
experimental technique which allows a minimal consumption and loss
of IL during the experiments was adopted.
2.3. Apparatus and procedure
The density and speed of sound measurement were performed using
a vibrating tube densimeter and speed of sound analyzer (DSA5000,
Anton Paar Co.). The instrument was automatically thermostatted
−
3
(
built in Peltier method) within ± 1.0 × 10
K. The experimental
2
. Experimental
uncertainty of density and speed of sound measurements were less
−
5
−3
−1
than 3.0 × 10 g · cm and 0.1 m · s , respectively. The densimeter
includes an automatic correction for the viscosity of the sample. The
apparatus was calibrated before each series of measurements with dou-
ble distilled, degassed and deionized water and dried air at atmospheric
pressure.
2
.1. Materials
N-methylimidazole, 1-chlorohexane, 1-chlorooctane, sodium
thiocyanate, thiophene and ethyl acetate were supplied by Merck Co.
and dichloromethane was supplied by CHEM-LAB. These reagents were
used without further purification and the ionic liquids were synthesized
in our lab. The chemical name, purity in mass fraction and analysis
method of the used materials are given in Table 1.
The binary mixtures were prepared in molal base concentration
using an analytical balance (AND, GR202, Japan) with precision
−5
of ± 10
0
g. The uncertainty for molality of the solutions, m, is
−1
.0001 (mol · kg ). All the solutions were kept tightly sealed to
minimize evaporation and contamination. Measurements were
performed immediately after preparation of solutions.
2
.2. Synthesis of ionic liquids
Densities and speed of sound data of the mixtures containing TS + IL
were measured using a method to minimize the IL consumption and
loss. First, the solution with the lowest concentration was prepared by
mixing known amounts of thiophene and IL in 10 mL Hamilton gas
tight syringe containing a small magnetic stirrer for mixing the solution.
Prior to each measurement, each binary mixture degassed for half an
hour to avoid possible a bubble which would generally result in unstable
The syntheses of the ionic liquids were based on the metathesis
reaction of sodium thiocyanate with 1-hexyl-3-methylimidazolium
chloride ([HMIM][Cl]) and 1-octyl-3-methylimidazolium chloride
[OMIM][Cl]) [24].
For the synthesis of the ionic liquids, 1-hexyl-3-methylimidazolium
(
chloride, [HMIM][Cl], and 1-octyl-3-methylimidazolium chloride,
Table 1
A brief summary of the purity of the used chemicals.
Initial mass
fraction purity
Chemical name
CAS no
Abbreviation Supplier
Purification method
Mass fraction purity Analysis method
N-methylimidazole
[616-47-7]
[111-25-1]
[111-85-3]
[141-78-6]
[110-02-1]
[540-72-7]
[75-09-2]
Merck
Merck
Merck
Merck
Merck
Merck
N0.99
N0.99
N0.99
N0.99
N0.995
≥0.98
None
None
None
None
None
None
None
1
1
-Chlorohexane
-Chlorooctane
Ethyl acetate
Thiophene
Sodium thiocyanate
dichloromethane
TS
Chem.-Lab
1
1
-Hexyl-3-methyl imidazolium thiocyanate [85100-78-3] [HMIM][SCN] Synthesized
Rotary evaporator/vacuum N0.98
Rotary evaporator/vacuum N0.98
H NMR/FT-IR/KF
H NMR/FT-IR/KF
1
1-Octyl-3-methyl imidazolium thiocyanate [61545-99-1] [OMIM][SCN] Synthesized

H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
977
Table 2
D
The density (d), speed of sound (u), and refractive index (n ) of the chemicals used in this work.
1
0−3·d/(kg · m−3
)
u/(m · s−1
)
Chemical name
n
D
Exp.
Lit.
Exp.
Lit.
Exp.
Lit.
1258.2 (T = 303.15 K) [51]
1
1
278.95
258.65 (T = 303.15 K)
Thiophene
1.058556
1.05884 [4]
1.5252
1.52572 [4]
[
[
HMIM][SCN]
OMIM][SCN]
1.056845
1.008283
1.05692 [52]
1.00827 [53]
1.5524
1.5545
1669.47
1615.08
densimeter readings. Afterward, about 1.5 mL of mixture was injected to
densimeter to measure densities and speed of sound in the temperature
range from 288.15 K to 303.15 K. Afterward, the solution was carefully
recovered from the densimeter (by suction, using the same syringe as
for sampling), and the mass of the remaining solution in the 10 mL gas
tight syringe was weighed. Then, an incremental amount of thiophene
was added, and the density and speed of sound were measured after
complete dissolution and the process was repeated with a minimum IL
consumption. Each reported value is an average of three measurements.
Refractive indices of both the solvent and binary mixtures were
measured using a digital Abbe refractometer (ATAGO, Dr-A1, Japan)
V , was calculated from the density values of solution d and solvent
using the following equation [26]:
d
0
ꢀ
ꢁ
M
d
ðd−d0Þ
Vϕ ¼
−
ð1Þ
m ꢀ d ꢀ d0
where M and m are the molar mass and molality of thiophene,
respectively. The V values of the investigated mixtures at T =
(288.15, 293.15, 298.15 and 303.15) K are presented in Table 4. The V
values of thiophene in the [HMIM][SCN] and [OMIM][SCN] mixtures
are positive, increase with increase in temperature and decrease by
thiophene concentration increment. There is a linear dependence
between V and thiophene molality according to the following equation
[27]:
−
4
with an uncertainty of ± 2·10
calibrated by doubly distilled water
before each series of measurements. The temperature was controlled
with bath thermostat (HETO BIRKEROD 01 TE623, Denmark) with a
temperature stability of ± 0.1 K.
Vϕ ¼ V 0ϕ þ Sv ꢀ m
ð2Þ
3
. Results and discussion
3
.1. Volumetric properties
where V0
is the apparent molar volume at infinite dilution, that has the
ϕ
For the determination of the volumetric properties of investigated
mixtures, the experimental densities as a function of thiophene
molality m for the two binary mixtures (TS + [HMIM][SCN]) and
same meaning as the standard partial molar volume. At infinite dilution,
the solute–solute interaction is negligible and therefore, the standard
partial molar volume provides valuable information concerning the
(
TS + [OMIM][SCN]) at 288.15, 293.15, 298.15 and 303.15 K were
solute–solvent interactions and S
shows the nature of the solute–solute interactions [28]. The V
values, the corresponding standard errors and deviations are given in
v
is the experimental slope which
0
measured. The results are given in Table 3. The apparent molar
volume of thiophene in [HMIM][SCN] and [OMIM][SCN] mixtures,
ϕ v
and S
Table 3
Density (d), speed of sound (u) and refractive index (n
) data of thiophene in [HMIM][SCN] and [OMIM][SCN] binary mixtures at T = (288.15 to 303.15) K.a
D
T/K = 288.15
T/K = 293.15
T/K = 298.15
T/K = 303.15
b
3
3
3
3
m/(mol ·
10 ·d/(kg ·
u/(m ·
10 ·d/(kg ·
u/(m ·
10 ·d/(kg ·
u/(m ·
10 ·d/(kg ·
u/(m ·
−
1
−3
−1
n
D
−3
−1
n
D
−3
−1
n
D
−3
−1
n
D
kg
)
m
)
s
)
m
)
s
)
m
)
s
)
m
)
s
)
[
HMIM][SCN] + TS
0
1.062754
1.062816
1.062929
1.062995
1.063107
1.063240
1.063368
1.063512
1.063603
1.063692
1697.44
1696.43
1694.92
1694.04
1692.58
1690.88
1689.30
1687.53
1686.46
1685.47
1.5547 1.059787
1.5545 1.059834
1.5543 1.059919
1.5542 1.059971
1.5540 1.060056
1.5538 1.060162
1.5536 1.060264
1.5534 1.060385
1.5533 1.060458
1.5532 1.060533
1683.00
1682.11
1680.53
1679.62
1678.10
1676.32
1674.67
1672.83
1671.72
1670.69
1.5534 1.056845
1.5532 1.056874
1.5530 1.056928
1.5529 1.056964
1.5527 1.057019
1.5525 1.057093
1.5523 1.057163
1.5521 1.057252
1.5520 1.057305
1.5519 1.057360
1669.47
1668.60
1667.05
1666.16
1664.67
1662.92
1661.29
1659.48
1658.38
1657.34
1.5524 1.054469
1.5522 1.054462
1.5520 1.054450
1.5519 1.054443
1.5517 1.054432
1.5515 1.054421
1.5513 1.054410
1.5511 1.054399
1.5510 1.054392
1.5509 1.054386
1654.32
1652.90
1652.33
1651.89
1651.10
1650.02
1648.81
1647.26
1646.25
1644.98
1.5512
1.5510
1.5508
1.5507
1.5505
1.5503
1.5501
1.5499
1.5498
1.5497
0
0
0
0
0
0
0
0
0
.0241
.0674
.0927
.1351
.1854
.2329
.2865
.3194
.3505
[
OMIM][SCN] + TS
0
0
0
0
0
0
0
0
0
0
0
1.014075
1.014135
1.014202
1.014293
1.014470
1.014582
1.014696
1.014773
1.014957
1.015053
1.015222
1644.30
1643.76
1643.18
1642.40
1640.97
1640.12
1639.26
1638.70
1637.41
1636.74
1635.63
1.5561 1.011121
1.5559 1.011182
1.5558 1.011250
1.5557 1.011344
1.5555 1.011522
1.5554 1.011637
1.5553 1.011748
1.5552 1.011829
1.5550 1.012012
1.5549 1.012113
1.5547 1.012278
1629.31
1628.80
1628.25
1627.50
1626.15
1625.32
1624.52
1623.96
1622.73
1622.07
1620.99
1.5553 1.008283
1.5551 1.008344
1.5550 1.008411
1.5549 1.008502
1.5547 1.008676
1.5546 1.008787
1.5545 1.008903
1.5544 1.008976
1.5542 1.009161
1.5541 1.009257
1.5539 1.009421
1615.08
1614.59
1614.06
1613.35
1612.06
1611.27
1610.49
1609.97
1608.79
1608.16
1607.13
1.5545 1.005432
1.5543 1.005493
1.5542 1.005560
1.5541 1.005653
1.5539 1.005826
1.5538 1.005934
1.5537 1.006043
1.5536 1.006118
1.5534 1.006287
1.5533 1.006380
1.5532 1.006539
1601.27
1600.80
1600.29
1599.61
1598.37
1597.61
1596.88
1596.38
1595.28
1594.68
1593.70
1.5536
1.5534
1.5533
1.5532
1.5530
1.5529
1.5528
1.5527
1.5526
1.5525
1.5524
.0192
.0401
.0684
.1204
.1526
.1846
.2062
.2556
.2822
.3268
a
Standard uncertainties u for molality, density and speed of sound are u(m)= 0.0001 mol · kg−1; u(d)=3.0 × 10−5 g · cm−3 and u(u) = 0.1 m · s−1
m is the molal concentration of thiophene.
.
b

978
H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
Table 5
0
ϕ v
Standard partial molar volumes (V ), experimental slopes (S ) and standard deviations
φ
σ(V ) of thiophene in [HMIM][SCN] and [OMIM][SCN] solutions at T = (288.15 to
303.15) K.
6
0
/(m3
6
/(m3 · mol−2
6
)/(m3
T/K
10 ·V
ϕ
·
10 ·S
v
·
10 ·σ(V
φ
·
−
1
−1
mol
)
kg)
mol
)
[
HMIM][SCN] + TS
2
2
2
3
88.15 76.89 ± 0.01
−0.44 ± 0.01
−0.64 ± 0.02
−0.82 ± 0.03
−0.14 ± 0.01
0.01
0.01
0.01
0.01
93.15 77.68 ± 0.01
98.15 78.55 ± 0.01
03.15 80.06 ± 0.01
[
OMIM][SCN] + TS
288.15 79.95 ± 0.01
293.15 80.11 ± 0.01
298.15 80.36 ± 0.01
303.15 80.54 ± 0.01
−1.52 ± 0.04
−1.46 ± 0.05
−1.34 ± 0.04
−0.94 ± 0.04
0.01
0.02
0.01
0.01
Table 5. The standard deviation values have been calculated by Eq. (3)
for the concentration range studied of TS.
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ꢄ
ꢅ
2
exp
cal
ϕ
Vϕ −V
ꢂ
ꢃ
σ Vϕ
¼
ð3Þ
n−2
where n is the number of experimental data.
The S values for (TS + [HMIM][SCN])/(TS + [OMIM][SCN]) mixtures
are negative at all experimental temperature which indicates relatively
v
0
ϕ
weak TS-TS interactions in ionic liquids. The V values of TS in both
solvents are positive with the order of [HMIM][SCN] b [OMIM][SCN]
which represents the presence of stronger solute–solvent interactions
between TS and [HMIM][SCN] rather than [OMIM][SCN][29]. The increas-
0
ing V
ϕ
values of thiophene in ILs at higher temperature suggest weak
solute–solvent interactions between thiophene and ILs at higher temper-
ature. At lower temperatures, the interaction between thiophene and the
ionic liquids may be favored due to the slower molecular movement of
0
ions and thiophene that would lead to a smaller value for V
of temperature on the V
OMIM][SCN] liquid binary mixtures is depicted in Fig. 1.
Since apparent molar volumes at infinite dilution provide information
ϕ
. The effect
φ
values of thiophene in [HMIM][SCN] and
[
about solute–solvent molecular interactions, they can be used to the
development of molecular models for expression of the thermodynamic
behavior of solutions [23]. The thermodynamic features of all the solva-
tion processes of non-polar molecules are influenced by the
Fig. 1. Apparent molar volume of thiophene, V
temperatures in [HMIM][SCN]; ◊, 288.15 K, Δ, 293.15 K, ○, 298.15 K and □, 303.15 K and
OMIM][SCN]; ♦, 288.15 K, ▲, 293.15 K, ●, 298.15 K and ■, 303.15 K, \\ , calculated
from E. (1).
φ
as a function of its molality, m, at different
[

H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
979
thermodynamics of cavity creation and a suitable cavity has to be created
Table 7
0
Partial molar expansibility (E
ϕ
), isobaric thermal expansion (α) for thiophene in
for the insertion of a solute molecule. Cavity creation is studied by means
of theoretical statistical mechanical approaches and/or computer
simulations in which one of them is Scaled Particle Theory (SPT).
Based on the scaled particle theory, which assumes the solute disso-
lution as a step-wise process: creating a cavity in the solvent for the
solute molecule and allowing solute molecule to interact with surround-
ing solvent molecules, a thermodynamic model can be written in the fol-
lowing equation [30]:
[
HMIM][SCN] and [OMIM][SCN] at T = (288.15 to 303.15) K.
6
0
/(m3 · mol−1 · K−1
4
10 ·α/(K−1)
T/K
10 ·E
ϕ
)
[
HMIM][SCN] + TS
288.15
0.211
0.209
0.207
0.205
27.411
26.886
26.342
25.606
2
2
3
93.15
98.15
03.15
[
OMIM][SCN] + TS
0
288.15
0.053
0.045
0.037
0.029
6.572
5.585
4.597
3.618
V
¼ Vcav þ Vint þ kT ꢀ R ꢀ T
ð4Þ
ϕ
2
2
93.15
98.15
where Vcav is the partial molar volume of cavity formation, Vint is the
volume change due to the solute–solvent interactions, k is the coefficient
303.15
T
of isothermal compressibility of the solvent, R is the universal gas constant
and T is the absolute temperature. The cavity volume is calculated by the
relation given in Eq. (5) [31]:
where A, B and C are empirical parameters and T is the temperature. The
limiting apparent molar expansibility can be obtained by differentiating
Eq. (9) with respect to temperature at constant pressure [36],
!
2
2
3
y
−y
3 ꢀ y ꢀ z ꢀ ð1 þ zÞ 9 ꢀ y ꢀ z
π ꢀ σ2 ꢀ NA
Vcav ¼ kT ꢀ R ꢀ T ꢀ
þ
þ
þ
ð5Þ
!
2
3
0
1
6
∂V
∂
ð1−yÞ
ð1−yÞ
0
ϕ
ϕ
E
¼
:
ð10Þ
T
P
and
0
3
The calculated E values are given in Table 7. According to this table,
π ꢀ NA ꢀ σ
ϕ
1
y ¼
ð6Þ
0
we note that at each temperature, E
ϕ
values for thiophene in the studied
6
ꢀ V
mixtures are positive value and decrease with rising temperature. In
fact expansibility of solutions is greater than expansibility of solvents.
This result shows that on heating, some solvent molecules may be
released from the solvation layers. This would increase the solution
A
where N is Avogadro's constant and y is the ratio of the volume occupied
by one mole of hard sphere solute particles to the molar volume of
solvent, Eq. (6), and z is the ratio of the hard sphere diameters of solute
σ
2
and solvent σ
1
.
volume a little more rapidly than that of the solvent and so E0
ϕ
would
be positive [26].
σ2
σ1
The values of the isobaric thermal expansion coefficients of
thiophene at infinite dilution (α) can be determined using the following
equation [37] and their values are also given in Table 7.
z ¼
ð7Þ
0
The molecular volume and diameter values of thiophene and ionic
E
ϕ
α ¼
ð11Þ
liquids were calculated using an equation provided by Abraham and
Zissimos [32]. Isothermal compressibility factor for pure ionic liquids
was calculated using Equation [33]:
0
ϕ
V
The isobaric thermal expansion coefficient is basically a measure for
the response of system's volume to an increase in temperature. According
to Table 7, with increasing temperature, α decreases in all studied
mixtures.
2
α ꢀ T ꢀ V
kT ¼ kS þ
:
ð8Þ
CP
E
Excess molar volumes, V , were then calculated from density
measurements according to the following equation [38]:
P
The C values in Eq. (8) have been calculated from the equation
proposed by Ahmadi et al. [34]. Interaction volumes of TS in both ionic
liquid mixtures have negative values as shown in Table 6 and are larger
ꢆ
ꢇ
ꢆ
ꢇ
M1 ꢀ X1 þ M2 ꢀ X2
M1 ꢀ X1 M2 ꢀ X2
VE
¼
−
þ
ð12Þ
d
d1
d2
(
more negative) for the TS + [HMIM][SCN] mixture and ionic liquids
used in this study, interact effectively with thiophene. This can lead to
their good efficiency of the TS extraction. According to the values of in-
teraction, one would expect the extraction efficiency of ionic liquid with
hexyl cations alkyl chain length, is slightly more than the other one.
i i i
where x , M , d are, respectively, mole fraction, molar mass, and the
density of component i; and d is the experimental density of the binary
mixture. It can be observed from the experimental results that the
E
Considering the following relation the temperature dependence of
values for the thiophene in [HMIM][SCN] and [OMIM][SCN] mixtures
excess molar volumes V are positive over the entire studied mole
0
V
ϕ
fraction range and for a temperature range from (288.15 to 303.15) K in
[OMIM][SCN] and become more positive with increasing concentration
could be expressed as [35]:
of thiophene (Table 8), while in the [HMIM][SCN] excess molar volumes
E
V
are negative in temperature range of 288.15 to 298.15 and become
0
ϕ
2
V
¼ A þ BT þ CT
ð9Þ
slightly positive in the 303.15 K. Fig. 2 shows and compares the
E
excess molar volume of thiophene, V versus its mole fraction, x
t
, in
[
OMIM][SCN], ♦, and [HMIM][SCN], ▲, at T = 298.15 K. The positive
Table 6
Cavity volumes Vcav and interaction volumes Vint of thiophene in ([HMIM][SCN]/
values indicate a predominance of the expansive effect associated
with dissociation of the ion pairs forming the ionic liquid, rather
than a volume contraction contribution [39]. This is due to the devel-
opment of new heteromolecular interactions and the molecular
packing. The attractive interactions between [HMIM][SCN] + TS
binary system components are sufficient to cause volume contraction,
[OMIM][SCN]) solutions at T = 298.15 K.
6
10 ·Vcav/(m3 · mol−1
6
10 ·Vint/(m3 · mol−1
Systems
)
)
(
(
Thiophene + [HMIM][SCN])
Thiophene + [OMIM][SCN])
222.36
103.95
−147.31
−24.62

Table 8
E
E
m;1
Excess molar volumes (v
m
), partial molar volumes (vm;1) and excess partial molar volumes (v ) of x thiophene + (1 − x) [HMIM][SCN]/[OMIM][SCN] at T = (288.15 to 303.15) K and atmospheric pressure.
T/K = 288.15
T/K = 293.15
T/K = 298.15
T/K = 303.15
E
3
3
E
/(cm3
E
3
3
E
/(cm3
E
3
3
E
/(cm3
E
/(cm3
vm;1/(cm3
−1
E
/(cm3
·
v
m
/(cm
·
vm;1(cm
·
v
·
v
m
/(cm
·
vm;1/(cm
−1
·
v
·
v
m
/(cm
·
vm;1/(cm
−1
·
v
·
v
m
·
·
v
m;1
m;1
m;1
m;1
x
−1
−1
−1
−1
−
1
−1
−1
−1
−1
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
mol
)
[
HMIM][SCN] + TS
−0.005
0.0241 −0.009
0.0674 −0.026
0.0927 −0.036
0.1351 −0.052
0.1854 −0.072
0.2329 −0.090
0.2865 −0.111
0.3194 −0.124
0.3505 −0.137
76.71
76.42
76.26
75.98
75.65
75.33
74.98
74.76
74.55
−1.900
−2.182
−2.348
−2.628
−2.961
−3.277
−3.632
−3.849
−4.054
−0.008
−0.021
−0.029
−0.043
−0.059
−0.075
−0.094
−0.105
−0.117
77.49
77.18
77.00
76.70
76.34
75.99
75.61
75.37
75.15
−1.556
−1.862
−2.042
−2.345
−2.707
−3.050
−3.436
−3.672
−3.895
78.38
78.10
77.93
77.66
77.33
77.02
76.67
76.45
76.25
−1.119
−1.399
−1.564
−1.840
−2.170
−2.480
−2.829
−3.042
−3.243
0.001
0.002
0.002
0.003
0.004
0.004
0.005
0.005
0.006
79.38
79.43
79.46
79.50
79.55
79.59
79.63
79.65
79.67
−0.561
−0.509
−0.481
−0.438
−0.390
−0.350
−0.308
−0.285
−0.265
−0.015
−0.021
−0.031
−0.044
−0.056
−0.072
−0.081
−0.090
[
OMIM][SCN] + TS
0.004
0.0192
0.0401
0.0684
0.1204
0.1526
0.1846
0.2062
0.2556
0.2822
0.3268
0.006
0.013
0.021
0.034
0.041
0.047
0.051
0.057
0.061
0.066
79.95
79.92
79.88
79.82
79.79
79.76
79.74
79.70
79.69
79.66
1.346
1.315
1.277
1.215
1.181
1.151
1.133
1.096
1.079
1.055
0.005
0.010
0.016
0.026
0.031
0.036
0.038
0.042
0.044
0.047
80.11
80.08
80.03
79.96
79.92
79.89
79.87
79.82
79.80
79.77
1.069
1.035
0.991
0.92
0.881
0.845
0.824
0.779
0.758
0.727
80.37
80.32
80.25
80.14
80.08
80.02
79.98
79.90
79.86
79.79
0.871
0.822
0.758
0.648
0.585
0.526
0.487
0.405
0.363
0.297
0.003
0.006
0.009
0.014
0.017
0.019
0.020
0.023
0.023
0.024
80.50
80.46
80.40
80.30
80.23
80.17
80.13
80.04
80.00
79.92
0.562
0.519
0.462
0.360
0.297
0.237
0.197
0.106
0.059
−0.019
0.008
0.013
0.021
0.025
0.027
0.029
0.031
0.032
0.033

H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
981
E
m;1
[
40]. The v follows the order: [OMIM][SCN] N [HMIM][SCN]. Negative
E
m;1
v
value of [HMIM][SCN] shows that the solute–solvent interactions at
infinite dilution are comparatively strong with TS.
3
.2. Acoustic properties
Acoustic studies have been utilized to better understand the nature
of interactions in the mixture [41]. Measurement of speed of sound in
the mixture helps in clarifying the solute–solute and solute–solvent
interactions. Speed of sound values are given in Table 3. The isentropic
compressibility, κ is also computed from the Laplace–Newton's
s
equation [42]:
1
d ꢀ u
κs ¼
ð16Þ
2
where u (m · s−1) is speed of sound of the solution. The apparent molar
isentropic compressibility of thiophene, κ is computed from the
following equation based on measured speed of sound and density of
solutions [43],
ϕ
Fig. 4. Apparent molar isentropic compressibility, κ
φ
of binary mixtures of thiophene in
[
HMIM][SCN] at different temperatures ♦, 288.15 K, ▲, 293.15 K, ●, 298.15 K and ■,
03.15 K, \\ , calculated from Eq. (18) as a function of its molality, m.
3
ðκs ꢀ d−κs0 ꢀ dÞ κs ꢀ M
κϕ ¼
þ
ð17Þ
m ꢀ d ꢀ d0
d
positive with the order of [HMIM][SCN] b [OMIM][SCN]. The more
0
where κs0 and κ
s
are the isentropic compressibility of solvents
positive κ
strong repulsive interactions due to lack of solvation of thiophene. The
plot of κ versus thiophene molality at [HMIM][SCN] and [OMIM][SCN]
at T = (288.15, 293.15, 298.15 and 303.15) K is depicted in Figs. 4 and 5.
Isentropic compressibility, k , a parameter describing the elastic
properties of the medium, can be sometimes directly interpreted in
terms of the liquid structure. Ultrasonic measurements are often applied
for investigating phenomena of solvation of electrolytes, both in
aqueous and non-aqueous systems [45]. From compressibility data
one can easily determine the solvation numbers applying the idea
of Pasynski. According to it, solvation should imply a decrease of
compressibility of solution compared to that of solvent. Such
decrease is always observed in water, both in electrolytic and polar
non-electrolytic solutes [45]. Solvated molecules become less compress-
ible. If one follows the Pasynski's assumption that they are completely
non-compressible, simple derivation leads to:
ϕ
values of thiophene in [OMIM][SCN] are attributed to the
(
[HMIM][SCN] and [OMIM][SCN]) and solutions, respectively. The
values of κ
φ
for thiophene in [HMIM][SCN] and [OMIM][SCN] ionic
φ
liquid mixtures at T = (288.15 to 303.15) K are listed in Table 4. It is
observed that the κ values of thiophene solutions have the order:
HMIM][SCN] b [OMIM][SCN] and there is a linear dependence between
φ
s
[
κ
φ
and thiophene molality as the following equation:
0
κϕ ¼ κϕ þ SK ꢀ ms
ð18Þ
0
where κ
ϕ
is the apparent molar isentropic compressibility at infinite
dilution (the standard partial molar isentropic compressibility) and S
is the experimental slope. The positive values of κ are attributed to
repulsive interactions between the solute and solvent [44].
There are two factors that contribute to κ0
, (a) large molecules can
have some solvent intrinsic compressibility (positive effect) due to the
intermolecular free space that makes the solution more compressible
K
φ
ϕ
[
44], and (b) penetration (negative effect) of the solvent molecules
!
into the intra-molecular free space due to the interaction of thiophene
with the neighboring IL molecules. The solute solvation causes expanding
in the solution volume, resulting in a less compact and more compressible
medium.
n1
n2
κs
sn ¼
ꢀ
1− k
ð19Þ
0
s
The values of κ0
and S
ϕ
K
obtained for the studied solutions at the
experimental temperatures are listed in Table 9. According to this
0
ϕ
table, the values of κ in [HMIM][SCN] are positive and become more
Table 9
The values of partial molar isentropic compressibility (κ
standard deviations σ(κ ) of thiophene in [HMIM][SCN] and [OMIM][SCN] solutions
at T = (288.15 to 303.15) K.
0), experimental slope (S
) and
ϕ k
φ
4
0
14
14
T/K
101 ·κ
/
10 ·S
k
/
10 ·σ(κ
φ
)/
3
· mol · Pa−1
−1
3
(m · mol · Pa−1 · kg) (m · mol · Pa−1
−2
3
−1
(
m
)
)
[HMIM][SCN] + TS
288.15 3.720 ± 0.001
293.15 3.933 ± 0.001
298.15 4.034 ± 0.001
303.15 3.212 ± 0.009
−0.068 ± 0.004
−0.117 ± 0.005
−0.068 ± 0.004
1.484 ± 0.039
0.001
0.001
0.001
0.013
[OMIM][SCN] + TS
2
2
2
3
88.15 4.038 ± 0.001
93.15 4.074 ± 0.001
98.15 4.132 ± 0.001
03.15 4.188 ± 0.001
−0.206 ± 0.006
−0.151 ± 0.005
−0.164 ± 0.002
−0.172 ± 0.005
0.002
0.002
0.001
0.001
Fig. 5. Apparent molar isentropic compressibility, κ
φ
of binary mixtures of thiophene in
[
OMIM][SCN] at different temperatures ♦, 288.15 K, ▲, 293.15 K, ●, 298.15 K and ■,
03.15 K, \\ , calculated from Eq. (18) as a function of its molality, m.
3

982
H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
Table 10
various component molecules in the liquid mixtures [46]. The refractive
indices n for the binary mixtures of (TS + [HMIM][SCN]/[OMIM][SCN])
as a function of thiophene molality m are given in Table 3 at T =
(288.15, 293.15, 298.15 and 303.15) K. The values of the refractive indi-
ces for the studied mixtures containing TS in the ionic liquids decrease
n
Solvation number, S , values of thiophene in [HMIM][SCN] and [OMIM][SCN]
mixtures at T = (288.15, 293.15, 298.15 and 303.15) K.
D
T/K = 288.15 T/K = 293.15 T/K = 298.15 T/K = 303.15
m/(mol · kg−1)
S
n
S
n
S
n
S
n
with increasing TS. The molar refractions R
tigated mixtures using Lorentz–Lorenz equation [47]:
D
are calculated for the inves-
[
HMIM][SCN] + TS
0
0
0
0
0
0
0
0
0
.0241
.0674
.0927
.1351
.1854
.2329
.2865
.3194
.3505
−0.191
−0.179
−0.177
−0.175
−0.173
−0.171
−0.170
−0.169
−0.168
−0.188
−0.187
−0.186
−0.185
−0.184
−0.182
−0.181
−0.180
−0.179
−0.188
−0.187
−0.186
−0.185
−0.184
−0.183
−0.182
−0.181
−0.181
−0.192
−0.115
−0.109
−0.107
−0.110
−0.116
−0.123
−0.128
−0.136
ꢆ
ꢇ
2
ðnDÞ −1
xts ꢀ Mts þ x ꢀ Msol
sol
RD ¼
ꢀ
ð20Þ
2
d
ðnDÞ þ 2
D
where n is refractive index of mixture, xts and xsol are the mol fraction of
thiophene and solvent, Mts and Msol are molar mass of thiophene and
solvent respectively. The components with high molar refraction and
subsequently large polarizability should be capable of having particularly
strong dispersion forces for species with high polarizabilities [47].
Fig. 6 shows the variation of molar refraction of TS in the mixture
with [OMIM][SCN] and [HMIM][SCN] at 298.15 K.
[
OMIM][SCN] + TS
0
0
0
0
0
0
0
0
0
0
.0192
.0401
.0684
.1204
.1526
.1846
.2062
.2556
.2822
.3268
−0.123
−0.122
−0.121
−0.120
−0.119
−0.118
−0.118
−0.117
−0.116
−0.115
−0.116
−0.116
−0.115
−0.114
−0.114
−0.113
−0.113
−0.112
−0.111
−0.110
−0.112
−0.112
−0.111
−0.110
−0.109
−0.109
−0.108
−0.107
−0.107
−0.106
−0.108
−0.108
−0.107
−0.106
−0.106
−0.105
−0.104
−0.103
−0.103
−0.102
The apparent molar volumes at infinite dilution which are calculated
at the volumetric section, include 2 contributions respectively. First one
is intrinsic contribution and the other is non-intrinsic contribution. Also
according to the equation presented by Alvarado, non-intrinsic contri-
bution data can be calculated from refractometric method [48]. This
non-intrinsic contribution related to the volume, indicates solvation
shell geometry packing, as well as specific and non-specific intermolec-
ular attractive interactions. As it was explained in the mentioned study,
since the apparent molar volumes at infinite dilution contain the vol-
ume effects associated with the kinetics contribution, in this condition
this quantity is not suitable for comparison with the values obtained
from the theoretical models. In order to eliminate the effects of solute
transfer from a fixed position in a medium to fixed position in a new
medium with different density, Ben Naim standard conditions should
be considered. The corrected limiting partial molar volume, hereafter
referred as the partial molar volume at Ben-Naim standard conditions,
where n are the number of moles of solvent and solute in solution,
respectively, k is that of pure
is compressibility of the solution and k0
solvent. The calculated solvation number, S , values of thiophene in
HMIM][SCN] and [OMIM][SCN] mixtures at T = (288.15, 293.15,
1
and n
2
s
s
n
[
2
98.15 and 303.15) K are given in Table 10. Solvation number values for
TS + ionic liquid mixture are negative and with increasing concentrations
of TS, values approach to positive values. Negative values have the
physical means to weaken the local structure of the solvent in close
to solute molecules. Similar results have been reported for aqueous
mixtures [45]. In general, it can be said that the negative solvation
is equivalent to the weakening of the interaction between molecules
by adding solute.
BN
3
−1
is defined as vϕ /(cm · mol ):
BN
ϕ
0
ϕ
v
¼ v −β ꢀ R ꢀ T
ð21Þ
T
3
.3. Refractometric properties
where β
T
/kPa− is the isothermal compressibility of the solvent, R
1
The refractive index is a measure of the electronic polarizability of a
molecule and can provide beneficial information of the forces between
the gas constant and T/K the absolute temperature. Assuming the
Ben-Naim standard conditions it has been defined the densitometric
d
3
−1
non-intrinsic contribution to the partial molar volume, θ /(cm · mol ),
d
BN
θ ¼ vϕ −vi:
ð22Þ
Table 11
0
Standard partial molar volume, V
ϕ
, partial molar volume at Ben-Naim standard conditions,
BN
ϕ
d
v
, densitometric non-intrinsic contribution to the partial molar volume, θ , and refrac-
r
tometric non-intrinsic contribution to the partial molar volume, θ , of thiophene in two
studied solvents at T = (288.15, 293.15, 298.15 and 303.15) K.
6
0
6
BN
6
6
d
6
r
T/K
10 ·V
(
ϕ
/
10 ·v
ϕ
/
10 ·v
i
/
10 ·θ /
10 ·θ /
3
· mol−1)
3
3
3
3
m
(m
·
(m
·
(m
·
(m
·
mol 1)
−
mol
−1
)
mol
−1
)
mol
−1
)
[
HMIM][SCN] + TS
288.15 76.894 ± 0.003 73.397
293.15 77.678 ± 0.005 74.165
298.15 78.552 ± 0.006 75.047
303.15 80.059 ± 0.004 76.584
135.561
135.561
135.561
135.561
−62.16
−61.40
−60.51
−58.98
−71.06
−70.30
−69.47
−68.01
[
OMIM][SCN] + TS
288.15 79.946 ± 0.009 78.912
293.15 80.112 ± 0.010 79.082
298.15 80.359 ± 0.007 79.334
303.15 80.544 ± 0.008 79.514
167.092
167.092
167.092
167.092
−88.18
−88.01
−87.76
−87.58
−105.45
−105.26
−105.04
−104.85
Fig. 6. Variation of molar refractions, R
D
, of binary mixtures of (thiophene + [OMIM][SCN],
▲, + [HMIM][SCN], ■) at 298.15 K.

H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
983
[
2] L. Alonso, A. Arce, M. Francisco, A. Soto, Solvent extraction of thiophene from n-alkanes
C7, C12, and C16) using the ionic liquid [C8mim][BF4], J. Chem. Thermodyn. 40 (2008)
66–972.
They also derived a new expression for θ based on measurements of
the refraction index of solutions as a function of the concentration of the
solute under Ben-Naim standard conditions as follows:
(
9
[3] Y. Lin, F. Wang, Z. Zhang, J. Yang, Y. Wei, Polymer-supported ionic liquids: synthesis,
characterization and application in fuel desulfurization, Fuel 116 (2014) 273–280.
[4] L. Alonso, A. Arce, M. Francisco, A. Soto, Liquid–liquid equilibria of
0
1
C
ꢆ
ꢇ
4 4
([C2mim][EtSO ] + thiophene + 2,2,4-trimethylpentane) and ([C2mim][EtSO ] +
thiophene + toluene): experimental data and correlation, J. Solut. Chem. 37 (2008)
1355–1363.
∞
R
B6000 ꢀ nD
1
ψ1
∂nD
∂C2
r
2m
1
θ ¼
−@ꢄ
ꢅAꢀ
ꢀ
−v −R ꢀ T ꢀ β
ð23Þ
i
1
2
ψ1
2
C2→0
n
þ 2
D1
[5] X. Xu, S. Zhang, P. Li, Y. Shen, Desulfurization of Jet-A fuel in a fixed-bed reactor at
room temperature and ambient pressure using a novel selective adsorbent, Fuel
117, Part A (2014) 499–508.
∞
4ꢀπꢀNAꢀα2
/(cm3 · mol−1) is the dynamic apparent molar
[6] H. Gao, Y. Li, Y. Wu, M. Luo, Q. Li, J. Xing, H. Liu, Extractive desulfurization of fuel
using 3-methylpyridinium-based ionic liquids, Energy Fuel 23 (2009) 2690–2694.
[7] S. Zhang, Q. Zhang, Z.C. Zhang, Extractive desulfurization and denitrogenation of
fuels using ionic liquids, Ind. Eng. Chem. Res. 43 (2003) 614–622.
where R2
¼
m
3
2
ðn −1Þ
D1
refraction of solute, ψ ¼
2
is the specific refraction of the solvent,
1
ðn þ2Þ
D1
n
D1 and n
D
are the refraction indexes of solvent and solution, respectively
[8] Y. Nie, C. Li, H. Meng, Z. Wang, N,N-dialkylimidazolium dialkylphosphate ionic liquids:
their extractive performance for thiophene series compounds from fuel oils versus the
length of alkyl group, Fuel Process. Technol. 89 (2008) 978–983.
and α2 is the electronic polarizability of solvent and was determined by
the Hérail and coworkers method [49]. The θ quantity contains the
d
[
9] M. Francisco, A. Arce, A. Soto, Ionic liquids on desulfurization of fuel oils, Fluid Phase
volumetric contribution from the intermolecular packing (repulsive inter-
actions) and the (solute + solvent) attractive interactions. By definition,
repulsive interactions contribution to non-intrinsic volume is positive,
and attractive interactions contribution is negative. The results of
densitometric and refractometric method are given in Table 11. The
densitometric result contains information about short-range and
long-range intermolecular interactions, while the refractometric re-
sult only contains information about short-range intermolecular interac-
Equilib. 294 (2010) 39–48.
[
[
10] L. Alonso, A. Arce, M. Francisco, A. Soto, Phase behaviour of 1-methyl-3-
octylimidazolium bis[trifluoromethylsulfonyl]imide with thiophene and aliphatic
hydrocarbons: the influence of n-alkane chain length, Fluid Phase Equilib. 263
(2008) 176–181.
11] M. Rogošić, A. Sander, M. Pantaler, Application of 1-pentyl-3-methylimidazolium
bis(trifluoromethylsulfonyl) imide for desulfurization, denitrification and
dearomatization of FCC gasoline, J. Chem. Thermodyn. 76 (2014) 1–15.
[12] U. Domańska, M. Królikowska, Measurements of activity coefficients at infinite dilution
in solvent mixtures with thiocyanate-based ionic liquids using GLC technique, J. Phys.
Chem. B 114 (2010) 8460–8466.
13] R. Anantharaj, T. Banerjee, COSMO-RS based predictions for the desulphurization of
diesel oil using ionic liquids: effect of cation and anion combination, Fuel Process.
Technol. 92 (2011) 39–52.
d
tions [50]. Due to more negative values of θ for both binary systems at
lower temperatures, it can be said that the repulsive interactions between
thiophene and ionic liquids are getting stronger at higher temperature.
[
[
[
[
[
[
14] B. Rodríguez-Cabo, H. Rodríguez, E. Rodil, A. Arce, A. Soto, Extractive and oxidative-
extractive desulfurization of fuels with ionic liquids, Fuel 117, Part A (2014)
4
. Conclusions
882–889.
15] C.D. Wilfred, C.F. Kiat, Z. Man, M.A. Bustam, M.I.M. Mutalib, C.Z. Phak, Extraction of
dibenzothiophene from dodecane using ionic liquids, Fuel Process. Technol. 93
Experimental density, speed of sound and refractive index were
(2012) 85–89.
measured for the binary mixtures of (thiophene + [HMIM][SCN]) and
thiophene + [OMIM][SCN]) at different temperatures. The various
volumetric, acoustic and refractometric parameters were obtained. The
16] A. Khelassi-Sefaoui, F. Mutelet, I. Mokbel, J. Jose, L. Negadi, Measurement and correlation
of vapour pressures of pyridine and thiophene with [EMIM][SCN] ionic liquid, J. Chem.
Thermodyn. 72 (2014) 134–138.
17] C. Devi Wilfred, Z. Man, Z. Phak Chan, Predicting methods for sulfur removal from
model oils using COSMO-RS and partition coefficient, Chem. Eng. Sci. 102 (2013)
373–377.
18] K. Khanlarzadeh, H. Iloukhani, Application of ERAS-model and Prigogine–Flory–
Patterson theory to excess molar volumes for ternary mixtures of (2-chlorobutane,
butylacetate & isobutanol) at T = 298.15 K, J. Chem. Thermodyn. 43 (2011)
(
0
V
ϕ
values of thiophene in all the solutions are positive with the order of
[HMIM][SCN] b [OMIM][SCN] which represents the presence of stronger
solute–solvent interactions between thiophene and [HMIM][SCN]
E
m;1
rather than [OMIM][SCN]. Negative values of v
in TS + [HMIM][SCN]
1583–1590.
mixture would indicate that molecular interactions between different
molecules are stronger than interactions between molecules in the
same pure liquid and that attractive forces dominate the behavior of the
[
19] R.B. Tôrres, M.I. Ortolan, P.L.O. Volpe, Volumetric properties of binary mixtures of
ethers and acetonitrile: experimental results and application of the Prigogine–
Flory–Patterson theory, J. Chem. Thermodyn. 40 (2008) 442–459.
solutions. The positive vE quantities in TS + [OMIM][SCN] mixture
[20]
O. Ciocirlan, O. Croitoru, O. Iulian, Densities and viscosities for binary mixtures of 1-
butyl-3-methylimidazolium tetrafluoroborate ionic liquid with molecular solvents,
J. Chem. Eng. Data 56 (2011) 1526–1534.
m;1
are indicative of absence of considerable interactions, and enhance-
E
m;1
[21] I. Bahadur, T.M. Letcher, S. Singh, G.G. Redhi, P. Venkatesu, D. Ramjugernath, Excess
molar volumes of binary mixtures (an ionic liquid + water): a review, J. Chem.
Thermodyn. 82 (2015) 34–46.
22] J. Pires, L. Timperman, J. Jacquemin, A. Balducci, M. Anouti, Density, conductivity, viscos-
ity, and excess properties of (pyrrolidinium nitrate-based protic ionic liquid +
propylene carbonate) binary mixture, J. Chem. Thermodyn. 59 (2013) 10–19.
23] H. Shekaari, M.T. Zafarani-Moattar, N. Jabbarvand Behrooz, Volumetric, acoustic, and
refractometric properties of (thiophene + hexane/cyclohexane) solutions in the
presence of some imidazolium based ionic liquids at T = 298.15 K, J. Chem.
Thermodyn. 86 (2015) 188–195.
[24] A. Kamal, G. Chouhan, A task-specific ionic liquid [bmim]SCN for the conversion of
alkyl halides to alkyl thiocyanates at room temperature, Tetrahedron Lett. 46
(2005) 1489–1491.
25] H. Shekaari, A. Kazempour, Z. Ghasedi-Khajeh, Structure-making tendency of ionic
liquids in the aqueous d-glucose solutions, Fluid Phase Equilib. 316 (2012) 102–108.
26] H. Shekaari, S.S. Mousavi, Volumetric properties of ionic liquid 1,3-
ment of self-associated structure of TS. The v
follows the order:
E
[
OMIM][SCN] N [HMIM][SCN]. Most positive vm;1 value of [OMIM][SCN]
[
shows that the solute–solvent interactions at infinite dilution are
weakest with TS, whereas negative value of vE of [HMIM][SCN] with
m;1
[
TS shows a comparatively stronger solute–solvent interaction. Accord-
0
ing to the values of κ
ϕ
, its value in [HMIM][SCN] is positive and becomes
more positive with the order of [HMIM][SCN] b [OMIM][SCN]. The more
0
ϕ
positive κ values of thiophene in [OMIM][SCN] are attributed to the re-
pulsive interactions due to lack of solvation of thiophene. Solvation
number values are negative for TS + ionic liquid mixture and with
increasing concentrations of TS, values approach to positive values.
Negative values have the physical means to weaken the local structure
of the solvent in close to solute molecules. From interaction volumes Vint
and due to larger negative values of Vint for (TS + [HMIM][SCN])
system, it can be said that between the studied systems the attractive
interactions between [HMIM][SCN] and thiophene are more than
[
[
dimethylimidazolium methyl sulfate
(298.15–328.15) K, Fluid Phase Equilib. 291 (2010) 201–207.
27] S. Fang, D.-H. Ren, Effect of 1-ethyl-3-methylimidazolium bromide ionic liquid on
the volumetric behavior of some aqueous 1-amino acids solutions, J. Chem. Eng.
Data 58 (2013) 845–850.
+ molecular solvents at T =
[
[28] H. Zhao, Viscosity B-coefficients and standard partial molar volumes of amino acids,
and their roles in interpreting the protein (enzyme) stabilization, Biophys. Chem.
[OMIM][SCN]. Generally it can be concluded that thiophene-ionic liquid
122 (2006) 157–183.
interactions are stronger with [HMIM][SCN].
[
29] H. Shekaari, M.T. Zafarani-Moattar, M. Niknam, Thermodynamic behavior of thiophene
with octane, 1-hexyl-3-methylimidazolium bromide, or 1-octyl-3-methylimidazolium
bromide in dilute region at T = (288.15 to 303.15) K, J. Chem. Thermodyn. 97 (2016)
References
1
00–112.
30] R.A. Pierotti, Aqueous solutions of nonpolar gases, J. Phys. Chem. 69 (1965)
81–288.
[
[
1] V. Chandra Srivastava, An evaluation of desulfurization technologies for sulfur
2
removal from liquid fuels, RSC Adv. 2 (2012) 759–783.

984
H. Shekaari et al. / Journal of Molecular Liquids 219 (2016) 975–984
[
[
31] A.N. Manin, L.E. Shmukler, L.P. Safonova, G.L. Perlovich, Partial molar volumes of
some drug and pro-drug substances in 1-octanol at T = 298.15 K, J. Chem.
Thermodyn. 42 (2010) 429–435.
32] Y.H. Zhao, M.H. Abraham, A.M. Zissimos, Fast calculation of van der Waals volume as
a sum of atomic and bond contributions and its application to drug compounds, J.
Org. Chem. 68 (2003) 7368–7373.
[43] R. Sadeghi, H. Shekaari, R. Hosseini, Effect of alkyl chain length and temperature on
the thermodynamic properties of ionic liquids 1-alkyl-3-methylimidazolium bro-
mide in aqueous and non-aqueous solutions at different temperatures, J. Chem.
Thermodyn. 41 (2009) 273–289.
[44] I. Bahadur, N. Deenadayalu, Apparent molar volume and isentropic compressibility for
the binary systems {methyltrioctylammonium bis(trifluoromethylsulfonyl)imide +
methyl acetate or methanol} and (methanol + methyl acetate) at T = 298.15,
303.15, 308.15 and 313.15 K and atmospheric pressure, J. Solut. Chem. 40 (2011)
1528–1543.
[
33] I. Cibulka, T. Takagi, P–ρ–T data of liquids: summarization and evaluation. 8. Miscel-
laneous compounds, J. Chem. Eng. Data 47 (2002) 1037–1070.
[
34] A. Ahmadi, R. Haghbakhsh, S. Raeissi, V. Hemmati, A simple group contribution
correlation for the prediction of ionic liquid heat capacities at different temperatures,
Fluid Phase Equilib. 403 (2015) 95–103.
[45] A. Burakowski, J. Gliński, Solvation numbers of alcohols in n-heptane and alcohols in
n-propanol diluted liquid mixtures from the acoustic Pasynski method, Chem. Phys.
Lett. 453 (2008) 178–182.
[35] M. Vranes, S. Dozic, V. Djeric, S. Gadzuric, Volumetric properties of ammonium nitrate in
N,N-dimethylformamide, J. Chem. Thermodyn. 54 (2012) 245–249.
[46] R.G. Seoane, S. Corderí, E. Gómez, N. Calvar, E.J. González, E.A. Macedo, Á. Domínguez,
Temperature dependence and structural influence on the thermophysical properties
of eleven commercial ionic liquids, Ind. Eng. Chem. Res. 51 (2012) 2492–2504.
[47] M. Tariq, P.A.S. Forte, M.F.C. Gomes, J.N.C. Lopes, L.P.N. Rebelo, Densities and refractive
indices of imidazolium- and phosphonium-based ionic liquids: effect of temperature,
alkyl chain length, and anion, J. Chem. Thermodyn. 41 (2009) 790–798.
[48] Y.J. Alvarado, A. Ballestas-Barrientos, J. Restrepo, J. Vera-Villalobos, G. Ferrer-Amado, P.
Rodríguez-Lugo, A. Ferrebuz, M. Infante, N. Cubillán, Volume-related properties of
thiophene and furan-2-carboxaldehyde phenylhydrazone derivatives in DMSO: a
discussion about non-intrinsic contribution, J. Chem. Thermodyn. 85 (2015) 210–215.
[49] M. Hérail, M. Le Guennec, D. Le Goff, A. Proutière, Molecular weight determination
from light scattering and refraction in solutions. A new and coherent theoretical
equation, J. Mol. Struct. 380 (1996) 171–193.
[
36] X.-M. Lu, W.-G. Xu, J.-S. Gui, H.-W. Li, J.-Z. Yang, Volumetric properties of room temper-
ature ionic liquid 1. The system of {1-methyl-3-ethylimidazolium ethyl sulfate +water}
at temperature in the range (278.15 to 333.15) K, J. Chem. Thermodyn. 37 (2005)
1
3–19.
37] H. Shekaari, A. Bezaatpour, R. Elhami-Kalvanagh, Effect of an ionic liquid on the
volumetric behavior of tetradentate N
type Schiff bases in DMF at T = (308.15
[
[
[
2 2
O
to 328.15) K, J. Chem. Thermodyn. 51 (2012) 114–119.
38] M. Anouti, M. Caillon-Caravanier, Y. Dridi, J. Jacquemin, C. Hardacre, D. Lemordant,
Liquid densities, heat capacities, refractive index and excess quantities for {protic
ionic liquids + water} binary system, J. Chem. Thermodyn. 41 (2009) 799–808.
39] J. Wisniak, G. Cortez, R.D. Peralta, R. Infante, L.E. Elizalde, T.A. Amaro, O. García, H.
Soto, Density, excess volume, and excess coefficient of thermal expansion of the
binary systems of dimethyl carbonate with butyl methacrylate, allyl methacrylate,
styrene, and vinyl acetate at T = (293.15, 303.15, and 313.15) K, J. Chem.
Thermodyn. 40 (2008) 1671–1683.
[50] A. Fucaloro, Reporting molar refractions, J. Solut. Chem. 31 (2002) 601–605.
[51] A. Weissler, Ultrasonic investigation of molecular properties of liquids. IV. Cyclic
compounds, J. Am. Chem. Soc. 71 (1949) 419–421.
[
[
[
40] T. Singh, A. Kumar, M. Kaur, G. Kaur, H. Kumar, Non-ideal behaviour of imidazolium
[52] U. Domańska, M. Królikowska, M. Arasimowicz, Phase equilibria of (1-hexyl-3-
methylimidazolium thiocyanate + water, alcohol, or hydrocarbon) binary systems,
J. Chem. Eng. Data 55 (2010) 773–777.
[53] M.R. Heidari, B. Mokhtarani, N. Seghatoleslami, A. Sharifi, M. Mirzaei, Liquid–liquid
extraction of aromatics from their mixtures with alkanes using 1-methyl 3-
octylimidazolium thiocyanate ionic liquid, J. Chem. Thermodyn. 54 (2012) 310–315.
based room temperature ionic liquids in ethylene glycol at T = (298.15 to
318.15) K, J. Chem. Thermodyn. 41 (2009) 717–723.
41] P. Madhusudhana Reddy, K. Siva Kumar, P. Venkatesu, Densities and ultrasonic studies
for binary mixtures of tetrahydrofuran with chlorobenzenes, chlorotoluenes and
nitrotoluenes at 298.15 K, Fluid Phase Equilib. 310 (2011) 74–81.
42] R. Sadeghi, F. Ziamajidi, Apparent molar volume and isentropic compressibility of
trisodium citrate in water and in aqueous solutions of polyvinylpyrrolidone at
T = (283.15 to 308.15) K, J. Chem. Eng. Data 52 (2007) 1037–1044.