Stable gasoil/sunflower oil fuel microemulsions prepared by using methylimidazolium based ionic liquids as surfactant

Article abstract of DOI:10.1016/j.molliq.2019.111970

The fuel microemulsions of water in a 4:1 (v:v) blend of gasoil and sunflower oil (respectively) by using of 1-dodecyl-3-methylimidazolium nitrate ([C12mim][NO₃]) and 1-butyl-3-methyl imidazolium nitrate ([Bmim][NO₃]) ionic liquids as surfactant and 1-butanol as co-surfactant. Also, the performance of 50:50 wt% blend of the mentioned ionic liquids with Span 80 as surfactant was evaluated in this work. The comparison of the phase diagrams of the samples has revealed a larger single phase region for samples prepared with ionic liquids than the conventional Span 80 surfactant or their blends with Span 80. The dynamic viscosity, and density of two samples with high oily phase content was measured according to the standards showing very close values to the net diesel fuel. DLS analysis indicated a water droplets of 9 nm (up to 70%) for [Bmim][NO₃], 3–6 nm (up to 64–82%) for [C12mim][NO₃], and 331 nm (up to 53%) for systems prepared by Span 80. Meanwhile, a very narrow size distribution was observed for the samples prepared by ionic liquids. No phase separation has been observed for the prepared samples over 6 months on the shelf.

Full text of DOI:10.1016/j.molliq.2019.111970

Journal Pre-proof
Stable gasoil/sunflower oil fuel microemulsions prepared by using methylimidazolium
based ionic liquids as surfactant
Reza Najjar, Laya Zarei-Gharehbaba, Mohand Tazerout, Sandeep R. Patil
PII:
S0167-7322(19)33351-3
DOI:
https://doi.org/10.1016/j.molliq.2019.111970
MOLLIQ 111970
Reference:
To appear in: Journal of Molecular Liquids
Received Date: 14 June 2019
Revised Date: 13 September 2019
Accepted Date: 18 October 2019
Please cite this article as: R. Najjar, L. Zarei-Gharehbaba, M. Tazerout, S.R. Patil, Stable gasoil/
sunflower oil fuel microemulsions prepared by using methylimidazolium based ionic liquids as surfactant,
Journal of Molecular Liquids (2019), doi: https://doi.org/10.1016/j.molliq.2019.111970.
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Stable gasoil/sunflower oil fuel microemulsions prepared by using methylimidazolium
based ionic liquids as surfactant
a
a
b
c
Reza Najjar *, Laya Zarei-Gharehbaba , Mohand Tazerout , Sandeep R. Patil
a
Polymer Research Laboratory, Faculty of Chemistry, University of Tabriz, 5166616471, Tabriz, Iran
Departement des Systemes Energetiques et Environnement, Ecole des Mines de Nantes, 4 Rue
b
Alfred Kastler, BP 20722, 44307 Nantes, Cedex 03, France
c
School of Engineering and Technology, Navrachana University Vadodara, Vadodara 391 410,
Gujarat, India
*
- Corresponding author: Reza Najjar, Fax: +98-41-33340191, e-mail: najjar@tabrizu.ac.ir
Abstract
The fuel microemulsions of water in a 4:1 (v:v) blend of gasoil and sunflower oil (respectively)
3
by using of 1-dodecyl-3-methylimidazolium nitrate ([C12mim][NO ]) and 1-butyl-3-methyl
imidazolium nitrate ([Bmim][NO ] ionic liquids as surfactant and 1-butanol as co-surfactant.
3
Also, the performance of 50:50 wt% blend of the mentioned ionic liquids with Span 80 as
surfactant was evaluated in this work. The comparison of the phase diagrams of the samples has
revealed a larger single phase region for samples prepared with ionic liquids than the
conventional Span 80 surfactant or their blends with Span 80. The dynamic viscosity, and
density of two samples with high oily phase content was measured according to the standards
showing very close values to the net diesel fuel. DLS analysis indicated a water droplets of 9 nm
(
upto 70%) for [Bmim][NO ], 3-6 nm (upto 64-82%) for [C12mim][NO ], and 331 nm (upto
3
3
5
3%) for systems prepared by Span 80. Meanwhile, a very narrow size distribution was observed
for the samples prepared by ionic liquids. No phase separation has been observed for the
prepared samples over 6 months on the shelf.
Keywords: Fuel microemulsion; phase diagrams; ionic liquid; gasoil; methylimidazolium;
surfactant.

1
. Introduction
Diesel engines during the last century have gained a very important place in many industries,
especially in road transportation as of their high thermal efficiency [1]. On the other hand, by the
increasing of the global concern about the high energy consumption of the world, diesel fuel has
entered into the researcher’s center of attention. This energy carrier has turned to a major source
of releasing the pollutants and suspended particles to the environment. It is believed that the
vegetable oils with a good heating power and as a renewable resource for fuel have great
potential to reduce the release of the carbon emissive [2]. But, if used directly and without any
modification, the high viscosity of these oils cause severe problems in the diesel engines, so they
need to be modified by a proper way to overcome their high viscosity problem. Blending of the
vegetable oils and diesel fuel has been introduced as a way to reduce its high viscosity problem
[3,4]. Another major approach which has been considered to resolve viscosity problem of the
vegetable oils as well as to reduce the polluting emissions from the diesel engines is to prepare
microemulsion of the diesel (or its blend with vegetable oil) and water. This technique has been
introduced as a significant approach to decrease the problems encountered by use of neat diesel
fuels [5]. The microemulsions has been very well established mixtures with a macroscopically
homogeneous appearance, which do not have a homogeneous structure in microscopic scale, and
composed of oil, water and surfactant [6]. These systems are optically clear and
thermodynamically stable and formed from two incompatible phases [7]. Regarding the relative
amount of the two phases, three type of microemulsions can be formed which include oil
dispersed in water (o/w), water dispersed in oil (w/o), and bicontinuous systems. The water in oil
(fuel or its blend with vegetable oil) microemulsions (w/o) can be used to improve the high
viscosity problem of vegetable oil [8,9] and also in many other research fields [10]. In most of
these systems, alcohols such as 1-butanol has been used as co-surfactants that help to emulsify
the water in oil as well as can function as fuel [11]. Various commercially available surfactants
such as Span 80, Tween 80 or Brij 30 have been employed in many applications [12] as well as
fuel microemulsions.
In recent decades, ionic liquids have been widely used as green solvents as well as surfactants in
many various applications [13-14]. The properties of these materials as non-conventional

solvents can be tuned by changing of the type of cation and anion, which can be investigated by
spectroscopic techniques such as fluorescent probe studies [15]. Also, having a low vapor
pressure allows these compounds to be used as a good alternative to the volatile solvents in
different applications [16]. Ionic liquids have been used as nonpolar or polar phase in
microemulsions [17]. Since ionic liquids are safe for the environment and subsequently possess
unusual solvent properties, hydrophobic ionic liquids exhibit properties similar to the oil phase
for the formation of microemulsions [18]. Microemulsions were prepared by using of
hydrophilic ionic liquids such as [Bmim][BF ] in different organic solvents as nonpolar phase
4
like toluene [19], xylene [17], triethylamine [20], cyclohexane [21] and, hydrophobic ionic
liquid [Bmim][BF6] with TX-100 (nonionic surfactant) and water [22].
Ionic liquids have been used in a large variety of applications in chemical industries, such as
electrolyte in batteries [23], lubricants [24], synthesis of polymers [25], synthesis of
nanoparticles [26], media for biological reactions [27], green solvent and catalysis in synthesis
[28-30], purification of gases [31], deep desulfurization of diesel fuel by extraction [32], as a tool
for analytical applications [15], such as chromatography [33] etc.
The use of ionic liquids in microemulsion systems is one of the most important application of
these compounds. These compounds have been extensively investigated in the role of polar and
nonpolar phase in microemulsion systems [34]. The use of ionic liquids as surfactants is gaining
a rapidly increasing attention of the researchers. The first report published in this field is related
to the use of room temperature ionic liquid (RTIL) with imidazole head as hydrophilic part and a
long hydrophobic tail for emulsion polymerization [14]. Oil recovery [35-36] and oil spill
remediation [37], are among the many other examples of applications of ionic liquids as
surfactants. The aggregation behavior of alkylimidazolium ionic liquids increases the ability of
this category to play the role of surfactant. The use of ionic liquids have exhibited some
advantages over organic surfactants in various applications. Among them one can point to the
melting points lower than 100 °C, excellent thermal and chemical stability, nonflammable
character, miscibility and solubility with many solvents, low toxicity, non-corrosive and
recyclable properties [38]. Even though, the most important feature of the ionic liquids as
surfactants is the possibility to tune their character by proper selection of the cationic and anionic
parts, and also their ability in formation of the very stable micelles without any need for
cosurfactant because of the strong interactions between their molecules. The ionic liquids with

imidazolium cation have the ability of self-aggregation and act as surfactants [39,40] and also
make aggregates such as micelles, vesicles, liquid crystals [41,42], gel and microemulsions [43].
The existence of the strong interactions between the imidazole ring and the co-surfactant
molecules is the main advantage of these compounds over the conventional surfactants. This
feature can help to immobilize the co-surfactant at the fluid/fluid interface and almost prevents its
leakage into the water phase. On the other hand, the aromatic imidazole ring head group is
strongly attractive due to the interactions of the π-π system. Finally, because of the possibility to
change the structure of ionic liquids and consequently the balance of the hydrophilic-lipophilic
parts, one can prepare the surfactants with an optimum performance in any desired application,
which is especially important in partitioning in the microemulsions [44].
The main purpose of this work is to synthesis and use some ionic liquids as surfactants for the
emulsification of the water in the diesel fuel, and compare their performance with the
conventional surfactants, Span 80. Also, the phase diagrams of the microemulsions prepared by
these ionic liquid surfactants or their mixtures with Span 80, water and diesel were investigated.
Two samples with nearly optimum compositions were selected on the phase diagrams and their
physical properties as fuel including dynamic viscosity, density and the size of water droplets
were measured according to the relevant standards and compared with the corresponding values
for neat diesel fuel.
2
. Experimental
2
.1. Materials
Gasoil was purchased from a local fuel station. The edible sunflower oil as a vegetable oil was
obtained from a local supermarket. 1-methyl imidazole (Merck, >99%), silver nitrate (BDH,
9
9%), 1-bromobutane and 1-chlordodecan (both from Merck, 98%) were used for the reactions.
The solvents used include methanol, ethyl acetate and diethyl ether has been of laboratory grade
purity >98%) and were used after distillation. 1-butanol (Merck, 99%) and Span 80 (Sigma
Aldrich Co, 97%) were used without any further purification.
(
2
.2. Methods

FT-IR spectra of synthesized ionic liquids have been measured by using of an infrared
spectrometer manufactured by Bruker, Germany, model Tensor 27. The measurements of the
FT-IR spectra of the materials has been done as KBr disks. Bruker Avance 400 MHz
1
spectrometer was used to measure the HNMR spectra of the materials. Measurement of the
1
HNMR spectrum of 1-dodecyl-3-methylimidazolium chloride ([C12mim][Cl]), 1-dodecyl-3-
3
methylimidazolium nitrate ([C12mim][NO ]) and 1-butyl-3-methylimidazolium bromide
(
[Bmim][Br]) has been performed in CDCl and DMSO-d was used as solvent for the measuring
3
6
of 1-butyl-3-methylimidazolium nitrate ([Bmim][NO ]). The dynamic light scattering (DLS)
3
analysis of the samples was performed by the DLS device model Nano ZS ZEN 3600
manufactured by Malvern, UK. The viscosity measurements of the samples were performed with
a Lovis digital viscometer device model 2000M manufactured by the Austrian company Anton
2
-1
Paar with a precision of 0.001 mm s . The density of the liquid samples was measured with a
density meter device model DSA5000, manufactured by Anton Paar, Austria, with a precision of
-6
-3
3
×10 g.cm and temperature accuracy of ±0.001 °C.
2
2
.2.1. Preparation of the ionic liquids
.2.1.1. Preparation of [Bmim][Br] and [C12mim][Cl] ionic liquids
To synthesize these ionic liquids, first 2.005 g (24.42 mmol) of 1-methyl imidazole was added
into a glass reactor equipped with magnetic stirrer and under an argon atmosphere in an oil bath.
Then, the temperature of the oil bath wan raised to 70 °C and and while stirring 26.86 mmol of
the related alkyl halide was added dropwise into the reactor via an adding funnel. After stirring
for a certain time raw product was obtained, which was then washed several times with a proper
solvent and dried in the vacuum oven at 50 °C for 6 h. the detained information regarding the
reaction times, washing solvents, physical appearance and reaction yields for each of the
prepared ionic liquids are given in Table 1.
Table 1.Detailed reaction and workup conditions for the synthesis of [Bmim][Br] and [C12mim][Cl] ionic liquids
ionic liquid
alkyl halide
reaction time washing solvent
appearance
yield

[
[
Bmim][Br]
1-butyl bro mide
1-chlorododecane
24h
72h
ethyl acetate
diethyl ether
yellow viscose oil
white waxy solid
94%
82%
C12mim][Cl]
2
3 3
.2.1.2. Preparation of [Bmim][NO ] and [C12mim][NO ]
In a 100 mL flask, 2.5 mmol of the each of ionic liquids synthesized as in the section 1.1 was
dissolved in 30 mL methanol at 20 °C. A solution of 2.5 mmol silver nitrate in 20 mL methanol
was then added dropwise to the ionic liquid solution under vigorous stirring in the darkness. The
formed silver halide was immediately appeared as precipitate. The stirring of the reaction
mixture was continued for another one hour. Then the mixture was filtered though a buchner
funnel, and the precipitate was washed with an additional 30 mL aliqout of methanol. The filtrate
was then rotaevaporated at 50 °C to remove methanol. The resultant product was further dried in
the vacuum oven at 40 °C for 24 h. The appearance of the both of ionic liquids was yellow
viscose oil. The yield of reaction for [Bmim][NO ] and [C12mim][NO ] has been 95% and 45%,
3
3
respectively.
2
.2.2. Characterization of ionic liquids
The ionic liquids were prepared via the methods already reportd in the literature with some
1
modifications [46,47], and characterized by using of HNMR and FT-IR spectra.
The FT-IR spectra of the [Bmim][Br] and [Bmim][NO ] are depicted in Fig. 1. As in Fig. 1a, the
3
-1
-1
peaks appearing in the range of 2736- 2960 cm and 3074-3142 cm are attributed to the
stretching vibrations of the aliphatic and aromatic C-H bonds, respectively. The peak related to
-1
the stretching vibrations of C = N bond in imidazole ring are appeared in 1636 cm . The peaks
-1
of stretching vibrations of C=C bonds of the aromatic imidazole ring is observed at 1568 cm .
-1
-1
The peaks appearing in the 1462 cm and 1379 cm are assigned to the bending vibrations of
-1
CH and CH groups in the butyl chains. The peak in 1168 cm could be attributed to the C-N
2
3
bond.
For the synthesis of the [Bmim][NO ] ionic liquid, the [Bmim][Br] was subjected to the ion
3
exchange reaction with silver nitrate, and the reaction completion was monitored by formation
and precipitation of the silver bromide. For comparison, the FT-IR spectra of the [Bmim][NO3]

along with the its precursor [Bmim][Br] is depicted in Fig.1. As it can be seen in the Fig.1, the
main difference between these two spectra (Fig.1a and Fig.1b) is in the peak appeared in the
-1
range of 1300-1379 cm , which can be attributed to the stretching vibrations of the NO group.
3
1
The HNMR spectra of the [Bmim][Br] is ilustrated in Fig. 2. The triplet peak at 0.96 ppm is
related to the protons of the CH of the butyl group. The multiplet peaks at 1.43 ppm and 1.88
3
ppm are related to the protons on the C2 and C3 carbons (the middle two -CH moieties) of the
2
2
butyl group. The peak of the protons in -CH -N- is appeared at 4.34 ppm with a triplet splitting
pattern. The singlet peak appearing in 4.1 ppm is related to the protons of the CH -N group. The
3
protons of the imidazole ring are produced peaks at 10.26 ppm, related to -N-CH-N- as a singlet
peak and two doublet peaks at 7.63 ppm and 7.75 ppm which are assigned to the -N-CH-CH-N-
protons.
Fig. 1. The FTIR spectra of (a) [Bmim][Br](b) [Bmim][NO3]

1
Fig. 2. The HNMR spectra of [Bmim][Br]
The FT-IR spectra of the [C12mim][Cl] and [C12mim][NO
3
] are shown in Fig. 3. As in Fig. 3a,
-1
-1
the peaks appearing in the range of 2850- 2916 cm and 3057-3144 cm are assigned to the
stretching vibrations of the aliphatic and aromatic C-H bonds, respectively. The peak related to
-1
the stretching vibrations of C = N bond in imidazole ring are appeared in 1643 cm . The peaks
-1
of stretching vibrations of C=C bonds of the aromatic imidazole ring is observed at 1572 cm .
-1
-1
The peaks appearing in the 1468 cm and 1359 cm are assigned to the bending vibrations of
-1
CH and CH groups in the dodecyl chains. The peak in 1171 cm could be attributed to the C-N
2
3
bond. For preparation of the [C12mim][NO ], the same procedure as used for [Bmim][NO ]
3
3
ionic liquid has been employed and, the [C12mim][Cl] was subjected to the ion exchange
reaction with silver nitrate. For comparison, the FT-IR spectra of the [C12mim][NO ] along with
3
the its precursor [C12mim][Cl] is depicted in Fig.3. As it can be seen in the Fig.3, similar to the
other ionic liquid the main difference between these two spectra (Fig.3a and Fig.3b) is in the
-1
peak appeared in the range of 1300-1400 cm , which can be attributed to the stretching
3
vibrations of the NO group.
1
The HNMR spectra of the [C12mim][Cl] is ilustrated in Fig. 4. The triplet peak at 0.8 ppm is
assigned to the protons of the CH group in the dodecyl chain. The multiplet peaks at 1.28-1.8
3

ppm are attributed to the protons of the methylene groups on the carbons number C2 to C11 of
the dodecyl chain. The protons of the methyl group on the N atom of the imidazole ring (CH -N)
has created a singlet peak appearing in 4 ppm. The peak of the protons on the methylene group
directly connected to the N atom of the imidazole ring (-CH -N-) is observed at 4.2 ppm which
3
2
has a triplet splitting pattern. The other two protons of the imidazole ring -N-CH-CH-N- are
produced two doublet peaks at 7.8 ppm and 7.9 ppm. The peak representing of the -N-CH-N-
proton of the imidazole ring is observed at 10.5 ppm as a singlet peak.
Fig. 3. The FTIR spectra of (a) [C12mim][Cl](b) [C12mim][NO3]

1
Fig. 4. The HNMR spectra of [C12mim][Cl]
2
.2.3. Preparation of microemulsions
The microemulsions were prepared so that to keep the mass fraction of the surfactant in the
mixture of oil and surfactant, parameter γ, at constant value of 0.05, which was calculated by Eq.
1.
ꢁ
γ =ꢀꢁ
Eq. 1
ꢂꢃ
To prepare the microemulsion system, at first the oil phase was prepared by mixing of gasoil and
sunflower oil with volume ratio of 4 to 1, which was then mixed with a certain mass of desired
surfactant to get required γ value as calculated via Eq. 1. Then, a certain amount of distilled
water as aqueous phase, was added into the oil phase (with various weights) and the mixture was
stirred at 750 rpm in room temperature for 5 min, which was then titrated with co-surfactant to
determine phase changes. Here, the conventional Span 80, 1-butyl-3-methylimidazolium nitrate,

1
-dodecyl-3-methyl-imidazolium nitrate ionic liquids and the blends of each of these ionic
liquids with Span 80 with a ratio of 50:50, were examined as surfactant.
2
.2.4. Ternary phase diagram
A ternary phase diagram is an equilateral triangle which consists of three vertices, that each one
is representing the percentage of the each of the three components [45]. The ternary phase
diagrams of the system was plotted so that the two vertices at the bottom of triangle represented
the percentage of the diesel/sunflower oil/surfactant mixture at the right side and the aqoeous
phase at the left side. Meanwhile, the upper vertex was representing the percentage of the co-
surfactant (1-butanol) phase.
3
. Result and discussion
3
.1. Phase diagram study
The solubilization of the water in the gasoil/ oil blend as two incompatible phases require the use
of an emulsifier or surfactant [48]. The surfactants facilitates the expansion of the interface
during the formation of microemulsion and stabilizes the dispersed phase in continous phase and
control the convergence of microemulsion [49]. The surfactant has also an amphipathic effect
which confines each droplet and prevents their coagulation.
One of the most important points in microemulsion studies is the used detection method for
indentifying of the phase changes, which has been done by visual inspection in this work. The
triangle diagrams was used here which is an equilateral triangle, and typically the top of that
shows co-surfactant and in its lower vertices the nonpolar phase is increased from left to right.
To ensure the same effect from the amount of surfactant in all samples, the parameter γ which
represents the mass fraction of the surfactant in oil-surfactant mixture, has been kept the same for
all samples. The mixture of gasoil and sunflower oil (sunflower oil) (80:20wt%) and surfactant
by taking into account the γ value of 0.05 was used as oil phase and distilled water as polar
phase. The all samples were prepared under the same conditions of stirring speed at the room
temperature with 1-butanol as co-surfactant, until the stable one phase system was titrated.
Samples were prepared by using of conventional surfactant, Span 80, [Bmim][NO ] and
3
3
[C12mim][NO ] ionic liquids. Also for the better investigation of the effect of ionic liquids, a

blend with a weight ratio of 50:50 of surfactant Span 80 with each of these ionic liquids by
keeping the same value of γ=0.05, were prepared and investigated here. In the Fig. 5 the phase
diagrams for microemulsion systems prepared in the presence of the conventional surfactant
Span 80, [Bmim][NO
3
] and [C12mim][NO
3
] ionic liquids, 50:50 blend of Span 80 and each of
these ionic liquids have been illustrated.
0
100
1
0
9
0
2
0
80
30
7
0
4
0
Point A
6
0
5
0
50
Point B
60
4
0
7
0
3
0
8
0
Span80
[
[
[
[
Bmim][NO3]
20
C12mim][NO3]
90
Bmim][NO3] + Span80
1
0
C12mim][NO3] + Span80
1
00
0
0
10 20 30 40 50 60 70 80 90 100
oil+surfactant
Fig. 5. The phase diagram of gasoil/sunflower oil (80:20 wt %), water, surfactant (Span 80, ionic liquids and their blends
with Span 80) and 1-butanol with γ=0.05 at room temperature and stirring speed of 750 rpm
3
.2. Stability of samples prepared with ionic liquids
The stability of the samples prepared with ionic liquids were investigated at different time
intervals, showing significant stability. These sample were stable for over 6 months without any
phase separation. After 6 months, only in one of the samples phase sepration has been observed.
Given that the ionic liquids used in this project are based on imidazolium cation, because of this,
the cation contributed to the stability of these systems which had a strong interaction between the
imidazole ring and the co-surfactant, which resulted in the stability of the formed micells and the
prevention of water leakage into the solution. Especially if the chain of ionic liquid is longer, it
can act as better surfactant and cause self-accumulation of imidazolium ionic liquids [44].

3
.3. Viscosity and Density study
The viscosity and density of the diesel fuel are among the very important parameters for its
performance. As detailed in the Table 2, the four fuel microemulsion samples of S1 to S4 were
prepared according to the compositions of the components as indicated by the two points of A
and B as marked on the phase diagram in Fig. 5. The criterion of choice for these two points has
been having the higher percentage of the oil phase, as well as the lowest co-surfactant
consumption. Indeed, these two points are chosen so that the samples prepared by these
compositions and related surfactant or ionic liquid to form one phase microemulsions. The above
four samples were differed regarding the type of materials used as surfactant or emulsifier.
Considering the phase diagram of the systems with each of the surfactants, the samples of S1, S2
and S3 were prepared according to the composition of the components in point A, while the
sample S4 was prepared as the compositions in point B. Span 80 was employed as surfactant in
3
the preparation of sample S1 and the sample S2 was prepared by using of [Bmim][NO ] ionic
liquid as emulsifier. The samples S3 and S4 are prepared by using of [C12mim][NO ] ionic
3
liquid as emulsifier. The density of the samples S1 to S4 were measured at different temperatures
and given in the Table 3.
Table 2.The general specification samples S1 to S4
Sample No
S1
S2
S3
S4
composition point
emulsifier
A
A
A
B
Span 80 [Bmim][NO3]
[C12mim][NO
]
3
[C12mim][NO3]
Table 3.The density of samples S1-S4, neat gasoil and 4:1(v:v) gasoil/sunflower oil blend at different temperatures
Temperature
°C)
S1 (A)
(g/mL)
S2 (A)
(g/mL)
S3 (A)
(g/mL)
S4 (B)
Gasoil
(g/mL)
gasoil:sunflower oil
(g/mL)
(
(g/mL)
15
20
30
40
0.841282 0.843816 0.842081 0.848774 0.837349
0.837527 0.840058 0.838501 0.845081 0.833869
0.829919 0.832475 0.830988 0.837643 0.826930
0.822204 0.824772 0.823280 0.828858 0.819895
0.853857
0.850364
0.843383
0.836412
As it is revealed by the data in Table 3, the sample S4 has indicated the highest density among
these samples. The dynamic viscosity for the samples S1 to S4 were measured at different
temperatures (15, 20, 30 and 40 °C) and plotted versus temperature in Fig. 6. As it can be seen

3
from the Fig. 6, the sample S4, which is prepared by using of [C12mim][NO ] ionic liquid as
emulsifier and composition as in the point B, exhibited a higher viscosity than other samples. As
expected, the viscosity of the samples were decreased with increasing of the temperature. Also
the difference between the viscosity of the samples S1 to S4 were reduced with increasing of the
temperature. For the samples prepared with the composition of the point A, which has different
surfactants, no significant difference in viscosities has been observed, this in indicating that these
three surfactants have imparted almost the same level of effects regarding the changes in the
viscosity of the samples, but which is a bit higher for the inonic liquid with longer length
3 3
hydrophobic chain ([C12mim][NO ]) than shorter one ([Bmim][NO ]). As expected, the viscosity
of the gasoil-sunflower oil blend has been higher than net gasoil. The microemulsification of the
water in the gasoil-sunflower oil blend has caused a significant decrease in its viscosity, but
which is still higher than the viscosity of the neat gasoil. Anyway, the viscosity of the all of fuel
microemulsions has been in the accepatable range for the diesel fuel.
S1 - Span 80 - Point A
S2 - [Bmim][NO ] - Point A
8
6
4
2
3
S3 - [C12mim][NO ] - Point A
3
S4 - [C12mim][NO ] - Point B
3
neat Gasoil
Gasoil-Sunflower oil blend
15
20
25
30
35
40
Temperature ( °C )
Fig. 6. The dynamic viscosity of the samples S1-S4 (detailed in Table 2), neat gasoil and gasoil-sunflower oil blend (4:1)
versus temperature
According to the ASTM D1298 standard, the density of diesel oil at 15 °C temperature should be
3
between 0.82 to 0.86 g/cm . Also according to the ASTM D445 the kinematic viscosity of the
2
diesel fuel at temperature of 37.5
°
C must be between 2.0 to 2.5 mm /s. Hence, the measured

data indicate that the density and viscosity of the prepared fuel microemulsion samples are in the
desirable range and near to the values for the neat diesel fuel.
3
.4. Studying the size of water droplets
In the fuel microemulsion systems, the size of water droplets and their size distribution is an
important parameter affecting the stability of these systems. The more smaller water droplets and
more narrower distribution, the greater stability will be observed for the system. The size and
size distribution of the water droplets in the prepared fuel microemulsions were measured by
using of dynamic light scattering technique (DLS). In the Fig. 7 the DLS graphs of the fuel
microemulsions prepared in this work (samples S1 to S4) are illustrated. According to the Fig. 7,
all of the samples has exhibited water droplets with a trimodal size distributions.
Table 4.The size and relative ratios of the modals of the water droplets in samples S1 to S4 measured by DLS
sample
modal 1
modal 2
mean diameter
modal 3
mean diameter
total
mean
relative
relative
relative
mean diameter
(nm)
diameter (nm)
ratio (%)
(nm)
2.3
ratio (%)
(nm)
331
—
ratio (%)
S1
S2
S3
S4
0.9
8.7
3.3
1.3
6.3
70.4
64.5
7.4
40.0
29.6
32.1
82.3
53.7
—
6.1
10.7
59
1403
935
6.1
4928
235
3.4
10.3
154
The Fig. 7 also indicate that the size and size distribution of water droplets in the systems with
the composition in point A has been 9 nm (upto 70%) for [Bmim][NO ] and 3 nm (upto 64%) for
3
3
[C12mim][NO ], also for the microemulsions with the composition in point B has been 6 nm
(
upto 82%) for systems containing [C12mim][NO ] and 331 nm (upto 53%) for systems
3
prepared by Span 80.

Fig. 7. DLS size distribution graphs of samples S1 to S4
4
. Conclusion
The synthesized ionic liquids of 1-dodecyl-3-methylimidazolium nitrate ([C12mim][NO ]) and
3
1
3
-butyl-3-methylimidazolium nitrate ([Bmim][NO ] were successfully used as surfactant for the
preparation of the fuel microemulsion of gasoil/sunflower oil (80:20), water and1-butanol as co-
surfactant. The phase diagrams of the systems indicated a wider single phase region, indicating
of the better performance of these ionic liquids compared to the conventional Span 80 surfactant.
The longer length of the hydrophobic chain on the ionic liquid imparted a bit higher viscosity on
the system, but no significant difference has been seen on the phase diagrams. The size of water
droplets formed inside of microemulsions prepared by ionic liquids with longer hydrophobic
chain has been smaller than the microemulsions of ionic liquids with shorter chains, which is
attributed to the higher stability of the micelles formed in these systems.
Acknowledgments
The financial supports from the Office of Postgraduate Studies of the University of Tabriz is
greatly acknowledged.
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Highlights
•
Methylimidazolium based ionic liquids is used as surfactant in emulsifying of water in
diesel/sunflower oil blend.
•
•
The prepared microemulsions has been stable for 9 months on the shelf.
The ionic liquids exhibited performances comparable to the commercial surfactants
such as Span80.

Declaration of interests
☒
The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐
The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: