Emulsification of Indian heavy crude oil using a novel surfactant for pipeline transportation
Emulsification of Indian heavy crude oil using a novel surfactant for pipeline transportation
Shailesh Kumar 0
Vikas Mahto 0
0 Department of Petroleum Engineering, Indian Institute of Technology (Indian School of Mines) , Dhanbad, Jharkhand , India
The most economical way to overcome flow assurance problems associated with transportation of heavy crude oil through offshore pipelines is by emulsifying it with water in the presence of a suitable surfactant. In this research, a novel surfactant, tri-triethanolamine monosunflower ester, was synthesized in the laboratory by extracting fatty acids present in sunflower (Helianthus annuus) oil. Synthesized surfactant was used to prepare oil-in-water emulsions of a heavy crude oil from the western oil field of India. After emulsification, a dramatic decrease in pour point as well as viscosity was observed. All the prepared emulsions were found to be flowing even at 1 C. The emulsion developed with 60% oil content and 2wt% surfactant showed a decrease in viscosity of 96%. The stability of the emulsion was investigated at different temperatures, and it was found to be highly stable. The effectiveness of surfactant in emulsifying the heavy oil in water was investigated by measuring the equilibrium interfacial tension (IFT) between the crude oil (diluted) and the aqueous phase along with zeta potential of emulsions. 2wt% surfactant decreased IFT by almost nine times that of no surfactant. These results suggested that the synthesized surfactant may be used to prepare a stable oil-in-water emulsion for its transportation through offshore pipelines efficiently.
Heavy crude oil; Oil-in-water emulsion; Pipeline transportation; Sunflower oil; Rheology; Stability
In past decades, a progressive decrease in conventional oil
reserves has led to a dramatic increase in production of
heavy crude oil. However, transportation of such highly
viscous crude oil through pipelines is a major challenge for
petroleum industries especially in offshore conditions.
Heavy crude oils have viscosities of more than 1000 mPa s
at room temperature. However, viscosity of crude oil
should be less than 200 mPa s at 15 C for its
transportation through pipelines (Kessick and Denis 1982). The
flowability of crude oil at the pumping temperature is an
important factor that affects pipeline transportation. Heavy
crudes usually have higher pour points due to high content
of high molecular weight components, such as waxes,
asphaltenes and resins. In conditions where the
atmospheric temperature is below the pour point, crude oil gels
completely and causes severe transportation problems.
Especially in the cold offshore environment, waxes and
asphaltenes deposit over inner surfaces of pipelines and
eventually clog the pipelines, which further increases the
Therefore, several methods are employed by petroleum
industries to transport crude oils through pipelines,
dilution/blending of crude with lighter oil or organic solvents,
preheating of crude and subsequent heating of pipelines,
use of pour point depressants (PPDs), application of drag
reducing additives and development of core annular flow
(CAF) and in situ oil upgrading (Mart??nez-Palou et al.
2011). However, each of these methods has economic,
technical and logistical drawbacks when it comes to
transportation of heavy crude oil through offshore
pipelines. Another pipeline technique favourable for cold
offshore environments is the transportation of heavy crudes as
oil-in-water (O/W) emulsions.
Oil-in-water emulsions are thermodynamically
unstable dispersions of the oil phase in the water phase. They are
subjected to several breakdown processes like flocculation,
coalescence, Ostwald ripening and creaming (Langevin
et al. 2004). In order to make these emulsions kinetically
stable, a suitable surfactant (or mixture of surfactants) is
always added, which adsorbs at the oil/water interface and
forms a strong interfacial film (Jiang et al. 2013). However,
a particular surfactant may not be suitable for different
crude oils due to variation in physicochemical properties.
Fatty acids (FAs), derived from different vegetable oils, are
raw materials for preparation of surfactants through
esterification or polymerization. Surfactants synthesized using
vegetable oils have various advantages. They are cheaper,
biodegradable and cause no adverse effect on nature. In
this study, we used sunflower oil to synthesize a novel
surfactant. Sunflower oil is a triglyceride obtained from
pressing sunflower (Helianthus annuus) seeds. Alkaline
hydrolysis of these triglycerides produces FAs and
glycerol. Fatty acids from sunflower oil consist of 6.8%
palmitic, 5.0% stearic, 19.6% oleic and 68.6% linoleic acids
(Harrington and D?Arcy-Evans 1985). Hydrolysed
sunflower oil was esterified with a trimer of triethanolamine to
develop a new surfactant as ester and further evaluated as
emulsifier for preparation of heavy oil-in-water emulsions.
The estimated cost of the synthesized surfactant is very low
as compared to the cost of commercial surfactants.
Considering the economy, it is very important for petroleum
industries to maximize the oil content as well as minimize
the requirement of surfactant to prepare a stable emulsion
with acceptable viscosity and pour point.
The objective of current research is to synthesize a
cheap natural surfactant from sunflower oil that is
suitable for preparing an oil-in-water emulsion of an Indian
heavy crude oil to facilitate its transportation through
offshore pipelines. Oil content and the amount of surfactant
required were further optimized by investigating their
effect on pour point, viscosity, stability, droplet size
distribution, interfacial tension and zeta potential of the
Heavy crude oil sample was collected from a Rajasthan oil
field, India. Sunflower oil was procured from a local
market in Kolkata, India. Polythene ethylene glycol (PEG)
and triethanolamine (TEA) were obtained from Loba
Chemie Pvt. Ltd. (Mumbai, India). n-heptane, n-decane,
toluene, HCl and chloroform were procured from Merck
Specialties Pvt. Ltd. (Mumbai, India). Methanol, sodium
chloride, sodium carbonate, acetone, p-toluene sulphonic
acid, acetic acid, petroleum ether (40?60 C) and
acetonitrile were received from Avantor Performance
Materials India Ltd. (New Delhi, India).
2.2 Synthesis of surfactant
Hydrolysis of sunflower oil (SO) Sunflower oil (50 g) was
reacted with 10% NaOH solution (250 mL) at 150 C
under constant stirring (450 rpm) in a three-necked flask
along with gradual addition of water (400 mL) for 2 h.
After reaction, a hot solution of 30% HCl (150 mL) was
added and the mixture was kept in a water bath at 80 C
until the oily layer became clear. The oily layer was then
separated and collected as hydrolysed sunflower oil (HSO),
a mixture of several free fatty acids.
Synthesis of tri-triethanolamine TEA (149 g) was
condensed in the presence of NaOH (1.6 g) as a catalyst. The
reaction was carried at 260 C under constant stirring
(450 rpm) in a three-necked flask until 36 g of water was
collected in a Dean and Stark trap. The used catalyst was
then neutralized by washing the obtained product with 5%
acetic acid solution. To further wash out impurities, the
product was dissolved in petroleum ether (b.p. 40?60 C)
and an organic layer was separated. The remaining solvent
was distilled off using a Soxhlet apparatus to give
tri-triethanolamine (TTEA) (Hafiz and Abdou 2003).
Esterification of HSO and TTEA HSO (36 g) was
reacted with TTEA (51 g) in the presence of a catalyst,
ptoluene sulphonic acid (0.0108 g). The reaction was carried
at 150 C with continuous stirring, and water was removed
azeotropically as it was formed. The product was then
washed with a hot solution of 5% Na2CO3 to remove the
catalyst and then dissolved in petroleum ether (b.p.
40?60 C). After separating the organic layer, the solvent
was distilled off to obtain purified tri-triethanolamine
monosunflower ester (TMSE) as a desired surfactant (Hafiz
and Abdou 2003). Physical state of the surfactant is
semisolid at 25 C and brownish-black in colour. It has a
density of 1.102 gm/cm3 at 15 C.
2.3 Characterization of crude oil
Heavy crude oils are usually produced in the form of
waterin-oil emulsion (Dicharry et al. 2006), so the initial water
content in crude oil was measured using the Dean and Stark
method (ASTM D4006-11 2011). Water was then
separated with aid of a commercial demulsifier (PEG 200) and
heating to obtain pure heavy crude oil. Further, the density
(ASTM D1480-15 2015) and pour point (ASTM D5853-11
2011) of the heavy crude oil were also determined using
standard ASTM methods. SARA analysis was performed to
characterize crude into four major components: saturates,
aromatics, resins and asphaltenes (Jha et al. 2014). Wax
content was determined using the modified Universal Oil
Products (UOP) 46-64 method (Sharma et al. 2014), and
wax appearance temperature (WAT) was determined using
the viscosity method (Dantas Neto et al. 2009).
2.4 Preparation of emulsions
An aqueous phase was first prepared by dissolving the
surfactant in distilled water at 65 C. The heavy crude oil
sample was preheated to 65 C to improve its fluidity
before adding it to the aqueous phase. Emulsions were then
prepared using a Hielscher ultrasonic homogenizer with an
UP200Ht processor at a working frequency of 26 kHz and
100% amplitude for a fixed irradiation time of 10 min. In
this study, the oil content was varied in the emulsion,
keeping the volume of the surfactant constant (2wt%) with
respect to the total volume of the emulsion. Again for
specific series of experiments, at the optimized oil content,
the surfactant concentration in the emulsion was varied to
obtain an optimum surfactant concentration.
2.5 Fourier transform infrared (FT-IR)
Infrared spectra of both crude oil and the synthesized
surfactant were recorded using a Perkin-Elmer spectrum 2
spectrophotometer assisted by Spectrum-10 software to
analyse the functional groups present. Software collected
spectra, in absorbance mode, in the spectral region of from
4000 to 400 cm-1. Further infrared spectra of emulsion
systems were also recorded to compare and analyse the
2.6 Measurement of pour point and rheology
of the crude oil and emulsions
The main objective of the emulsification process is to
decrease the pour point and enhance the flowability of the
heavy crude oil. Pour points of emulsions were measured
using the ASTM method (ASTM D5853-11 2011). The
rheological flow behaviour of crude oil and emulsions was
investigated at 25 C using a Bohlin Gemini 200 rheometer
(Gemini 200 software), supplied by Malvern instruments.
Cone-plate (25-mm plate diameter, 2.5 cone angle and
70-lm gap) and parallel-plate (25-mm plate diameter at
two gaps, 750 and 500 lm) geometries were used for
measurement of rheology of the crude oil and prepared
2.7 Measurement of emulsion stability
Immediately after preparation of emulsions, each emulsion
was transferred to three separate 10-mL glass tubes
(0.1mL graduation) and tightly stoppered with a glass lid.
These three separate groups of emulsion samples were then
kept at 15, 25 and 35 C to allow separation of water over
time from these emulsion samples. The amount of water
separated at the end of six days was noted and the emulsion
stability was calculated using the following equation.
where S is the emulsion stability; Vi is the water volume in
the initial emulsion, mL; and V is the volume of water
separated from the emulsion, mL.
2.8 Interfacial tension and zeta potential
A Texas-500 spinning drop tensiometer (Data-Physics,
Model No: SVT 15 N) was used to measure interfacial
tension (IFT) between the oil and the aqueous phase at
different surfactant concentrations at 25 C. Due to the
very high viscosity of the crude oil, it was impossible to
inject a drop of oil using a microlitre syringe in the
capillary tube filled with the aqueous phase. Therefore, crude
oil had to be diluted with n-decane (40% v/v) to make it
flowable (Zhao et al. 2013). During measurement, the
capillary tube was rotated at 2000 rpm for 600 s to obtain
equilibrium IFT values.
Zeta potential of emulsions was measured using a
ZetaMeter System 4.0 (Zeta-meter, INC., Staunton, VA) to
study the charge properties of oil droplets in the emulsion
at room temperature. To prepare samples for measurement,
0.1 mL of each emulsion was diluted with 100 mL of
distilled water. At least five different particles of each
sample were tracked to obtain the average value of zeta
2.9 Measurements of oil droplet size and size
Size and distribution of oil droplets in prepared emulsions
were determined using a Zetasizer Nano S90 particle size
analyser procured from Malvern Instruments Ltd. at 25 C.
Dynamic light scattering was conducted at a 90 scattering
angle to measure particle sizes with this particle size
analyser. This instrument analyses the diffusion of particles
moving under Brownian motion by measuring the scattered
light intensity and converts this to size and a size
distribution using the Stokes?Einstein relationship. In order
to make the emulsion sample optically clear and to avoid
the effect of multiple scattering, 0.1 mL of emulsion was
diluted with 15 mL of distilled water. Tests were run three
times, and the test duration was shortened to 10 s to avoid
effect of coalescence of droplets during measurement.
3 Results and discussion
In the present investigation, a surfactant was synthesized
by extracting free fatty acids from sunflower oil and
evaluated as an emulsifier. Oil-in-water emulsions were
prepared to optimize oil content and surfactant
concentration by investigating their effects on pour point, rheology
and stability of emulsions. Effects of droplet size
distribution in emulsions on their viscosity and stability were
also examined along with discussion of interfacial
properties, IFT and zeta potentials of emulsions at various
3.1 Analysis of crude oil
The results of water content, API gravity, pour point, wax
content, WAT and SARA analysis of crude oil are reported
in Table 1. The Dean and Stark method confirmed the
presence of a large amount (45%) of dispersed water in the
crude oil (W/O emulsion) sample. API gravity of heavy
crude oil is 21.27 , so it can be classified as heavy crude oil
according to API convention. A large amount of wax is
present in heavy crude oil, which is a major factor in
resisting flow as these wax crystals start appearing at
temperature around 55 C. These wax crystals grow at
further decreasing temperatures, start to precipitate and
form a solid phase. A very high pour point (42 C) was
observed for this particular heavy crude oil which can be
Table 1 Physicochemical properties of heavy crude oil
attributed to its high wax content. As reported, the crude oil
was found to be highly asphaltinic in nature and very rich
in the resin fraction, which makes crude oil heavier and
restricts its flowability. A very high fraction of saturates
(66.5%) was present in crude oil, which provides an
asphaltene-hostile environment and assists in deposition of
asphaltenes (Alcazar-Vara and Buenrostro-Gonzalez
3.2 Infrared spectroscopic analysis
FT-IR spectra of heavy crude oil, TMSE and O/W
emulsion are shown in Fig. 1, and the observed peaks with
associated functional groups are given in Table 2.
Characteristic peaks of alkyl groups (CH3 and CH2) due to
stretching vibration and bending vibration with strong
absorbance at 2919, 2850 and 1462 cm-1 were observed
for heavy crude oil. Such high absorbance can be attributed
to high contents of saturates and wax in heavy crude oil.
Combination of the multiple bands around 1114 cm-1 and
the band at 1736 cm-1 confirms the presence of ester in the
synthesized surfactant. Presence of aromatic nuclei
observed in the crude oil may be due to the presence of
asphaltenes and resins (Quiroga-Becerra et al. 2012). Peaks
around 719 and 666 cm-1 in heavy crude oil and TMSE,
respectively, represent rocking vibration of the backbone of
carbon chains having six or more carbon atoms
(QuirogaBecerra et al. 2012). In spectra of the emulsion system, a
very strong and broad absorption band at 3443 cm-1 was
observed due to the presence of hydroxyl groups from H2O
after formation of the O/W emulsion. The absorption bands
of alkyl groups were greatly weakened, suggesting the
breaking of C?C bonds and shortening of C-chains thus
improving the flowability of heavy crude oil. Also the band
due to rocking vibration of C-chains shifted to 495 cm-1
that can also suggest that the number of C-atoms in the
chain has been reduced due to emulsion formation.
3.3 Depression in pour point
In order to avoid flow assurance problems in pipelines
under offshore conditions, the pour point of emulsions
should be very low. Ahmed et al. (1999) found the pour
point to be 6 and 9 C, respectively, for emulsions with oil
content of 60% and 70%, respectively, when the pour point
of the crude oil was 18 C. Zaki (1997) also reported a
decrease in the pour point of crude oil from 13 to 7 C after
emulsification with 70% oil content. Pour point is a very
important flow parameter, and for all the prepared
emulsions in our study, the measured pour point was found to be
remarkably low compared to the pour point of heavy crude
oil (42 C). All the emulsions prepared were flowing at
even 1 C, which is highly suitable for offshore conditions.
Fig. 1 FT-IR spectra of heavy crude oil, synthesized surfactant and prepared emulsion
Table 2 Wave number (cm-1)
Type of vibration
a Emulsion with 60% oil content and 2wt% surfactant
3.4 Rheological behaviour of heavy crude oil
and prepared emulsions
Flow behaviour of the heavy crude oil and emulsions was
investigated in a rate-controlled (CR) mode over a shear
rate range of 100?1000 s-1. The rheometer provided flow
behaviour curves as both shear stress vs. shear rate and
apparent viscosity vs. shear rate, along with respective
data. Figure 2 shows the rheological behaviour of heavy
crude oil and prepared emulsions by varying the oil content
at a constant surfactant concentration (2wt%), measured at
two gaps using parallel-plate geometry. Non-Newtonian
behaviour of the shear-thinning profile was observed for
heavy crude oil. For parallel-plate measurements at two
gaps, instead of coinciding, lower apparent viscosity values
were observed at lower gap size (at 500-lm gap) for each
emulsion over the range of shear rate studied due to
occurrence of the wall slip effect. However, all data points
from both gaps appeared to fall close to a single curve,
indicating the slight possibility of wall slip. Apparent wall
slip or wall depletion effects are observed for concentrated
emulsion systems in rheometers due to displacement of the
dispersed phase away from the solid boundaries (walls),
and this displacement of the dispersed phase is caused due
Fig. 2 Influence of oil content on the rheology of the emulsions at
2wt% surfactant, measured at 25 C. Solid and dashed lines represent
data at 750- and 500-lm gaps, respectively
to action of various physicochemical forces (Barnes 1995).
The presence of wall slip poses a special problem while
measuring actual rheological properties of emulsions.
During rheological measurement of oil-in-water emulsions,
depletion of the oil phase with an increase in shear stress
leaves the low-viscosity liquid (continuous phase) adjacent
to the boundary; thus, viscosities observed in such
conditions are much lower than the actual ones (Pal 2000).
However, during pipeline transportation of emulsions, due
to slip, dispersed particles will be displaced away (towards
centre, region of low shear) from the smooth solid wall of
pipelines and facilitate the flow; therefore, estimation of
actual rheological properties of an emulsion is important
for industries involved in pipeline transportation. Apart
from the geometry and shear rate used for measurement,
possibility of wall slip also depends on the size of dispersed
droplets in an emulsion. Lower dispersed droplet size
lessens the chances of occurrence of wall slip inside the
rheometer (Barnes 1995). All emulsions studied in this
work possessed droplet sizes lower than 400 nm, discussed
in Sect. 3.8, which also suggests lower chances of wall slip.
Zahirovic et al. (2009) utilized the parallel-plate
geometry at different gap sizes for very low apparent shear
rate up to 1.0 s-1 and the vane geometry for shear rate
further up to 100 s-1, in their study of ammonium
nitratein-diesel oil emulsion. We have considered the high shear
rate in our study because in most crude oil transportation
pipelines actual flow takes place at shear rates around
500 s-1, where the shear rate near or on the pipe wall may
be even higher (Azodi and Nazar 2013a; Johnsen and
R?nningsen 2003). Since rheological measurement carried
out at a bigger gap size is relatively less prone to wall slip
(Pal 2000), results obtained at higher gap size (750 lm) are
further discussed here. However, results obtained at both
gap sizes are comparatively presented in Table 3 as the
degree of viscosity reduction at 546 s-1 shear rate. Up to
50% oil content, emulsions showed close to Newtonian
behaviour, whereas, when the oil content further increased,
they started to behave as non-Newtonian shear-thinning
fluids. Shear-thinning behaviour suggests that the emulsion
viscosity decreased as the pumping pressure increased. At
high shear rate (546 s-1), the apparent viscosity of heavy
crude oil was found to be 5081 mPa s, whereas, after an
emulsion was formed with 40% oil content, the emulsion
viscosity reduced dramatically by 99.8% and reached
9.5 mPa s. Furthermore, an increase in the oil content led
to an increase in the emulsion viscosity. At 60% oil
content, the emulsion viscosity increased to 81.2 mPa s, where
the degree of viscosity reduction was around 98.4%.
Further increase in the oil content led to an inversion of the
O/W emulsion into a W/O emulsion. From the results
observed and considering the maximum throughput of oil
through pipelines, it is clear that the optimum volume of oil
was 60% for preparing a stable emulsion with
At 60% oil content, the optimum amount of surfactant
required to stabilize emulsions with acceptable viscosity
was determined by measuring the rheology of emulsions of
various surfactant concentrations. Figure 3 shows the
effect of surfactant concentration on the rheology of
emulsions, measured at two gaps using the parallel-plate
geometry. Results obtained at both gap sizes are
comparatively presented in Table 4, and results at 750 lm are
further discussed. As the surfactant concentration
decreased from 2wt% to 1wt%, the apparent viscosity of
emulsions also decreased. At 1wt% surfactant, the
emulsion viscosity was reduced to approximately 99.3%.
However, at higher concentrations (3wt% surfactant), the
emulsion viscosity was 98.6 mPa s, reduced by 98.0%.
This could be attributed to the fact that higher emulsifier
concentration decreases the interfacial tension between oil
and water, which leads to formation of smaller oil droplets.
As a result of a decrease in droplet sizes, the number of
droplets contacting water surface increases which
ultimately increases the emulsion viscosity (Azodi and Nazar
2013b). It is not economical to use a large amount of
surfactant. On the other hand, stability of the emulsion at
lower surfactant concentration is another important factor
to choose an optimum concentration.
3.5 Interfacial tension analysis
Surfactant effectiveness as an emulsifier is most
importantly evaluated by its ability to decrease the IFT between
crude oil and water. Figure 4 demonstrates the equilibrium
IFT values between heavy crude oil (diluted) and the
aqueous phase at various surfactant concentrations. It was
Apparent viscosity of heavy crude oil is 5081 mPa s
Fig. 3 Influence of surfactant concentration on the rheology of
emulsions of 60% oil content, measured at 25 C. Solid and dashed
lines represent data at 750- and 500-lm gaps, respectively
observed that with increasing surfactant concentration in
the aqueous phase, IFT values decreased efficiently. IFT
between diluted crude and water with no surfactant was
around 6.15 mN/m and decreased to 1.10 mN/m after
1.0 1.5 2.0 2.5
Surfactant concentration, wt%
Fig. 4 IFT between crude oil and the aqueous phase and zeta
potential as a function of surfactant concentration
0.5wt% surfactant addition. At 2wt% surfactant, the IFT
value decreased to 0.69 mN/m, whereas at 3wt%, IFT
reached to 0.37 mN/m. The decreased IFT value
contributed largely to a subsequent decrease in the drop size of
dispersed crude oil. As a result of decreased particle size
distribution, viscosity as well as the stability of the
Table 4 Viscosity reduction in emulsions of different surfactant concentrations at two gap sizes and 546 s-1 shear rate
Surfactant concentration, wt%
Apparent viscosity, mPa s
Viscosity reduction, %
Apparent viscosity, mPa s
Viscosity reduction, %
Table 3 Viscosity reduction in emulsions of different oil contents at two gap sizes and 546 s-1 shear rate
Oil content, %
Apparent viscosity of heavy crude oil is 5081 mPa s
Apparent viscosity, mPa s
Viscosity reduction, %
Apparent viscosity, mPa s
Viscosity reduction, %
3.6 Zeta potential analysis
The zeta potential measurement helps in predicting
emulsion stability by predicting the tendency of the emulsion to
coalesce or flocculate. It characterizes distance between the
emulsion droplets by calculating the electric charge on the
surface of droplets. A higher absolute value of the zeta
potential (either negative or positive) is interpreted as
meaning there is higher charge on the droplets, which
results in greater chances of them repelling each other and
avoiding coalescence and flocculation. A lesser charge on
the droplets allows them to come closer and coalesce/
flocculate (Jha et al. 2015). Figure 4 summarizes the effect
on zeta potential of O/W emulsions with increasing
surfactant concentration. It was observed that the absolute
value of zeta potential increased from 44.3 to 71.2 mV as
the surfactant concentration increased from 1wt% to 3wt%
in the emulsion. These results suggest that with an increase
in the surfactant concentration, the charge concentration on
emulsion droplets also increased which led to production of
a stable emulsion.
3.7 Stability of emulsions
Emulsion stability is a very important parameter which
depends on factors like concentrations of oil/water and
their density difference, water phase viscosity, salinity and
pH, choice and amount of surfactant, size of dispersed oil
droplets, preparation method and duration and temperature
of homogenization (Lim et al. 2015). Based on water
separation observed after 6 days at different temperatures,
the emulsion stability is plotted in Figs. 5 and 6,
respectively, against variations in oil content and surfactant
concentration. It was observed from the results that
increases in both oil content as well as surfactant
concentration led to an increase in the emulsion stability. On the
other hand, temperature also played a very important role
in the emulsion stability. Emulsion samples kept at lower
temperatures showed higher stability than at higher
temperatures. As the oil content in emulsion increased from
40% to 60% at 2wt% surfactant, the emulsion stability
increased from 51.7% to 85% at 35 C. When the
temperature decreased from 35 to 15 C, the stability of the
emulsion of 40% oil increased from 51.7% to 83.3% and
for the emulsion of oil content above 40%, 100% stability
was achieved. The effect of temperature can be explained
by the fact that a decrease in temperature leads to a
decrease in interfacial tension between oil and water. As a
result, the decrease in internal energy of the molecules may
decrease the pressure required to induce the interfacial film
thinning and ultimately increases the coalescence time
(Liyana et al. 2014).
The emulsions with 60% oil content were completely
stable at 15 C, despite variation in surfactant
concentration from 1wt% to 3wt%. However, when the temperature
increased to 25 C, the stability of emulsion with 1wt%
surfactant reduced to 82.5%, and furthermore reduced to
70% at 35 C. Again, an increase in the stability at higher
temperatures was achieved by increasing the surfactant
concentration. The emulsion with 3wt% surfactant was
found to achieve stability around 95.0% and 92.5% at 25
and 35 C, respectively. An increase in the surfactant
concentration results in an increasing number of surfactant
molecules absorbed at the oil/water interface which
provides a barrier to the coalescence of dispersed oil droplets,
thus stabilizing the emulsion (Zaki 1997). Additionally,
application of ultrasonic waves causes formation of
droplets with smaller sizes, which increases the total
interfacial area allowing more particle-to-particle interaction, and
Fig. 5 Emulsion stability as a function of oil content at different
temperatures (2wt% surfactant)
Fig. 6 Emulsion stability as a function of surfactant concentration at
different temperatures (60% oil content)
finally leads to enhancing the emulsion stability.
Considering the stability as well as viscosity of the emulsion of
60% oil content, 2wt% surfactant can be used to prepare an
efficient emulsion at 25 C. However, for lower
temperatures, the surfactant concentration can also be less than
3.8 Size distribution of oil droplets in emulsions
Droplet size distribution is one of the important parameters
that influence the rheology as well as the stability of the
emulsion. This parameter is greatly affected by oil/water
ratio, selection and concentration of surfactant and
emulsification technique. Several authors previously have
reported that the use of ultrasonic waves leads to
production of emulsion with relatively smaller dispersed phase
droplets than by a mechanical homogenizing method
(Abisma??l et al. 1999; Lin and Chen 2006). Results of the
volume droplet size distribution of O/W emulsions at
various oil content and surfactant concentration are plotted
in Figs. 7 and 8, respectively.
Figure 7 shows that as the oil content of the emulsion
increased, the size of dispersed oil droplets in the emulsion
decreased. The emulsion with 40% oil had droplet sizes in
a range of 164?342 nm in diameter, whereas, when the oil
content increased to 60%, the size range of droplets
decreased to 122?295 nm. From Fig. 8, it is clear that an
increase in the surfactant concentration allowed the
production of smaller oil droplets in the emulsion. The
emulsion with 1wt% surfactant had droplet sizes in a range
of 164 to 396 nm, whereas, when the surfactant
concentration increased up to 3wt%, the size of dispersed droplets
tended to decrease to 105?255 nm. As been discussed
previously, an increase in the surfactant concentration
Fig. 7 Droplet size distribution of emulsions as a function of oil
content (2wt% surfactant)
Fig. 8 Droplet size distribution of emulsions as a function of
resulted in a decrease in IFT between oil and water, which
further reduced the surface free energy required to increase
the interfacial area and allowed the easier production of
smaller oil droplets. A decrease in oil droplet size resulted
in an increase in emulsion stability but also increased the
emulsion viscosity, as seen in stability and viscosity
results. Many authors previously have found the same
effects of droplet size on viscosity and stability of
emulsions (Kumar and Mahto 2016; Pal 1996; Zaki 1997). It
was also noted that all the prepared emulsions had droplet
sizes less than 400 nm.
Surfactant (TMSE) synthesized using sunflower oil
was found to be a very effective emulsifying agent for
preparation of O/W emulsions, and it may be
considered for use in heavy oil transportation processes in
The emulsions prepared with TMSE were found to be
still flowing at even 1 C, which can be highly
suitable for flow in cold environments.
Flow behaviour of heavy crude oil and most of the
emulsions within the experimental range were
nonNewtonian shear thinning.
Formation of an O/W emulsion caused a tremendous
decrease in the viscosity of crude oil. All emulsions
showed viscosity lower than 200 mPa s at 25 C and
higher shear rate, which is adequate for flow in
Synthesized surfactant decreased the IFT between oil
(diluted) and the aqueous phase by the order of tenfold
and led to preparation of highly stable emulsions.
Use of ultrasonic waves led to production of emulsions
with oil droplets size less than 400 nm, which
promotes an increase in emulsion stability.
For this particular heavy crude oil, 60% oil content and
2wt% surfactant concentration were found to be
optimum values to produce a flowable and
stable O/W emulsion using the synthesized surfactant
at 25 C. For lower temperatures, a stable emulsion
can also be produced even at the surfactant
concentration less that 2wt%.
Acknowledgements Authors would like to gratefully acknowledge
the Indian Institute of Technology (Indian School of Mines), Dhanbad
for providing necessary laboratory facilities and financial support.
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appropriate credit to the original author(s) and the source, provide a
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