Towards the development of cavitation technology for upgrading bitumen: Viscosity change and chemical cavitation yield measurements
Towards the development of cavitation technology for upgrading bitumen: Viscosity change and chemical cavitation yield measurements
Deepak M. Kirpalani 0 1
Dipti Prakash Mohapatra 0 1
0 Energy Mining and Environment Portfolio, National Research Council of Canada , 1200 Montreal Road, Ottawa, ON K1A 0R6 , Canada
1 & Deepak M. Kirpalani
Among the different methods used for reducing viscosity of bitumen, acoustic cavitation during sonication is well recognised. Several chemical methods were used to detect the production of reactive species such as hydroxyl radicals and hydrogen peroxide during acoustic cavitation processes. However, quantification of cavitation yield in sonochemical systems is generally limited to low frequencies and has not been applied to bitumen processing. An empirical determination of the cavitation yield in midto high-frequency range (378, 574, 850, 992, and 1173 kHz) was carried out by measuring the amount of iodine liberated from the oxidation of potassium iodide (KI). Further, cavitation yield and the effects of different sonic operating conditions such as power input (16.67%83.33%) and solute concentration on cavitation yield were carried out in KI solution and sodium carboxymethyl cellulose-water mixture to obtain benchmark changes in rheology and chemistry using these two model fluids. The findings were then applied to bitumen upgrading through sonication. Through this study, it was found that the chemical cavitation yield peaked with a sonication frequency of 574 kHz. It was also found that cavitation yield and viscosity change were correlated directly in bitumen and a 38% lower bitumen viscosity could be obtained by acoustic cavitation.
Bitumen; Cavitation yield; KI solution; Viscosity correlation
Bitumen is a complex mixture of hydrocarbons of different
families (aromatics, naphthenes, and paraffin among
others), oxygen, nitrogen, and sulphur compounds as well as
trace metals. The recovery of bitumen from oil-bearing
rocks, including tar sand (also called oil sands or
bituminous sand), has become increasingly important for energy
security of the continent (Speight 2007). Due to the
growing world oil demand and scarcity of the conventional
oil reserves, increasing attention is turning towards huge
unconventional resources such as heavy oil and oil sands
deposits due to their enormous volume and worldwide
distribution. Production from these reservoirs is
challenging owing to the immobile nature of bitumen, and reducing
the in situ viscosity of the oil is considered as the main
objective of any recovery process. In order to efficiently
produce bitumen, the viscosity of the oil must be
substantially reduced. Furthermore, efficient transportation of
bitumen (e.g. by pipeline) can also be difficult unless the
viscosity of the oil is first reduced (Kariznovi et al. 2013).
Among the different methods used for reducing
viscosity of bitumen without the usage of excess energy or
changing the properties of oil, acoustic cavitation during
sonication is well recognised (Castaneda et al. 2014;
Gogate et al. 2003). It causes heating, and intense agitation
of a liquid medium or suspension, and activates chemical
processes and enhancement of heat and mass transfer
processes. Ultrasound is capable of producing
extraordinarily high transient temperature and pressure in a localised
spot within bitumen by the occurrence and collapse of
acoustic cavitation (Suslick 1990). Yan and Yaping (1996)
have studied the change in viscosity of heavy oil from the
Gudao oil field by using ultrasonic and surface active
agents. They reported that ultrasonic waves can effectively
decrease the viscosity of heavy oil and increase fluid flow
ability, which aids in producing additional oil and in
transporting heavy oil over long distances. Najafi and
Amani (2011) studied the asphaltene flocculation inhibition
with ultrasonic radiation (45 kHz frequency and 75 W
power intensity) and observed that the viscosity of heavy
oil decreases due to the disintegration of asphaltene flocs
under ultrasonic irradiation. Further, Mohammadreza et al.
(2012) studied the effect of ultrasonic irradiation on
rheological properties of asphaltenic crude oil and concluded
that ultrasonic irradiation increases the value of the yield
stress required for the flow of crude oil samples. However,
in order to understand the action of ultrasound and its effect
on the change in heavy oil viscosity, it is required to study
the effect of sonication frequency, solute concentrations,
and acoustic power intensity on cavitation yield.
Cavitation yield measurement by determining the
amount of iodine liberated during ultrasound of potassium
iodide (KI) solutions is a simple and widely accepted
method (Koda et al. 2003). The oxidation of KI is widely
regarded as a standard to calibrate sonochemical efficiency.
In addition, preparation and handling of KI solutions is
simple and easy (Koda et al. 2003). During the sonication
process, cavitation activates the generation of hydroxide
and peroxy radicals which act as oxidising agents for the
solute (KI) leading to release of iodine (Weissler et al.
1950). Entezari and Kruus (1996) reported the amount of
oxidation of iodide to iodine at sonication frequency of 20
and 90 kHz. They observed that the cavitation yield using a
900-kHz transducer was 20 times greater than that of the
20-kHz transducer. Kirpalani and McQuinn (2006)
determined the cavitation yield in a high-frequency ultrasound
system (1.7 and 2.4 MHz) by measuring the amount of
iodine liberated from the oxidation of KI solution. They
observed that the concentration of KI and temperature
affect the cavitation yield of the system such that the iodine
production is proportional to both conditions. Furthermore,
Ebrahiminia et al. (2013) studied the efficacy of different
exposure parameters on cavitation production by 1 MHz
ultrasound using iodide dosimetry and reported that with
increasing time of sonication or intensity, the absorbance is
Therefore, the following study was carried out to
determine the cavitation yield under mid- to high-range
sonication frequencies of 378, 574, 850, 992, and
1173 kHz and to investigate the effect of sonication
frequency, power input, and solute concentration on yield.
Further experiments were carried out with bitumen in order
to determine the effect of cavitation yield on the viscosity
change in heavy oil.
2 Materials and methods
Bitumen was collected from a facility at Mildred Lake near
Fort McMurray, Alberta, Canada. All the chemicals used
were of analytical grade. HPLC-grade toluene, heptane,
methanol (MeOH), dichloromethane (DCM), and acetone
used for cleaning and extraction purposes were purchased
from Fisher Scientific (Ontario, Canada). HPLC-grade
water was prepared in the laboratory using a
Milli-Q/MilliRO Millipore system (Milford, MA, USA). Nitric acid,
hydrochloric acid, and hydrogen peroxide were supplied by
Fisher Scientific (Ontario, Canada).
2.2 Sonication experiment
A mid- to high-frequency sonochemical processing system
was assembled using a broadband transducer
(Ultraschalltechnik-Meinhardt GMBH). The transducer was installed
at the bottom of a coolant-jacketed glass column reactor
with a diameter of 5 and 100 cm in height.
The ultrasound was supplied by a power amplifier
(HM8001-2) through a function generator (HM 8030-5 and
HM 8032). Sonication experiments were carried out at five
different frequencies, 378, 574, 850, 992, and 1173 kHz,
using two different broadband transducers with the same
effective diameter. The reactor was supplied with different
power inputs starting from 16.67% to 83.33%. The cooling
system was operated to maintain a constant temperature.
The experiment was carried out with a sample volume of
100 mL held within a jacked glass cooling column. A
cooling jacket with ethylene glycol as a coolant was set up
to maintain near-isotropic conditions to minimise the effect
of acoustic energy conversion to heat. The local fluid
temperature was monitored with a K-type thermocouple
and maintained between 20 ± 1 C for the duration of the
2.3 Acoustic intensity measurements based
on calorimetric determination
Experiments were carried out to determine the acoustic
intensity based on calorimetric determination at 378, 574,
860, 992, and 1173 kHz in water. Acoustic intensity based
on calorimetric determination was calculated by measuring
the temperature increase in water under ultrasound
irradiation and using Eqs. (1) and (2):
Actual power input ¼ dt CpM
Actual power input
Acoustic intensity (IÞ¼ Area of transducer tip
where ddTt is the rate of increase in the liquid temperature, Cp
is the specific heat capacity of the liquid, and M is the mass
of the liquid.
2.4 Measurement of cavitation yield
Experiments were carried out to determine the cavitation
yield at 378, 574, 860, 992, and 1173 kHz in water. Further
studies were carried out to observe the effect of these
sonication frequencies in heavy oil. Cavitation yield
measurements were taken to determine the amount of iodine
liberated when potassium iodide solutions at different
concentrations were subjected to ultrasound (Kirpalani and
McQuinn 2006). Cavitation yield was defined as the grams
of iodine liberated per unit power density during the
oxidation of potassium iodide by hydroxide and peroxy
radicals (Gedanken 2004). The amount of liberated iodine was
measured using a UV/VIS spectrophotometer at 350 nm
and quantified using a calibration curve ranging from 0 to
4 9 10-3 M of iodine for determining the cavitation yield
at various intervals of time. A calibration curve for an
iodine–water solution is presented in Fig. 1.
2.5 Measurement of viscosity
Viscosity of unsonicated and sonicated samples was
measured by using a rotational viscometer (Brookfield DVII
PRO ? (Brookfield Engineering Laboratories, Inc.,
Stoughton, MA, USA)) equipped with Rheocalc32
software. The viscosity data acquisition and analysis was
carried out using Rheocalc V2.6 software (B.E.A.V.I.S.—
Brookfield Engineering Advanced Viscometer Instruction
Set). Viscosity was measured at 50 rpm with 60% power
amplitude at controlled temperature.
3 Results and discussion
3.1 Effect of sonication frequency
A series of experiments were conducted using 0.1 and
1 wt% KI aqueous solutions in the sonication vessel in
order to establish the effect of sonication frequencies (378,
574, 850, 992, and 1173 kHz) and time (0–30 min) on
cavitation yield. The cavitation yield for oxidation of
potassium iodide solutions under different sonication
frequencies and sonication time is presented in Fig. 2
(0.1 wt% KI) and Fig. 3 (1.0 wt% KI). The results showed
that the sonication frequencies can significantly affect the
cavitation yield, and higher yield was observed at
midfrequencies as compared with high frequencies. Note that
other studies also reported the enhancement of cavitation
yield under different frequencies (Kirpalani and McQuinn
2006; Seymour et al. 1997). A comparison of two studies,
Entezari and Kruus (1996) performed at 20 and 900 kHz
and Seymour et al. (1997) at 640 kHz, showed a higher
cavitation yield at sonication frequency of 640 kHz
compared to 20 and 900 kHz. Furthermore, a study by Feng
et al. (2002) reported that when using the low MHz
frequency range, the lower the frequency used, the higher the
cavitation yield. They observed that the sound intensity of
low MHz frequency ultrasound is above 6 W cm-2, and
the cavitation yield of the combined irradiation (0.87 MHz
and 28 kHz) is more than 1.6 times of that of combined
Fig. 1 Iodine calibration
Fig. 2 Cavitation yield obtained under different conditions of
sonication frequency and time using 0.1 wt% KI solution
Fig. 3 Cavitation yield obtained under different conditions of
sonication frequency and time using 1.0 wt% KI solution
irradiation using a higher MHz frequency (1.7 MHz and
28 kHz). Formation of highly reactive free radicals due to
the formation, growth, and implosive collapse of bubbles in
a liquid is the primary mechanism of a sonochemical
reaction. The extent of radical formation in a single
cavitation bubble is a function of the following parameters:
amount of water vapour trapped in the bubble and the
temperature and pressure peak reached in the bubble during
the collapse. A mechanistic approach to the enhancement
of the yield of a sonochemical reaction showed that the
collapse of cavitation bubbles and sonochemical yield is a
complicated function of several interdependent physical
processes such as rectified diffusion, water vapour
transport, and entrapment in cavitation bubbles. Further, it was
reported that the degassing of the reaction medium
intensifies the collapse of the cavitation bubbles, resulting in
higher production of OH and other radicals, which enhance
the yield of the sonochemical reaction (Sivasankar et al.
Furthermore, higher oxidation of iodide to iodine was
observed at a sonication frequency of 574 kHz compared
to the other four frequencies 378, 860, 992, and 1173 kHz
(Figs. 2, 3). It was also observed that in case of 1 wt% KI
aqueous solutions, the cavitation yield increases with
increase in sonication time for a sonication frequency of
574 and 1173 kHz. Higher oxidation of iodide to iodine
during sonication frequency of 574 kHz was due to the
presence of more dissolved air in the medium. The
presence of dissolved air in the solution reduces the threshold
pressure during cavitation resulting in significant rise in the
number of cavities formed and consequent increase in
reaction rates. Lida et al. (2005) showed that the degree of
gas saturation, the type of gas, and the temperature of a
sonicated dosimeter solution at different sonication
frequencies play an important role in determining the
extent of inertial cavitation occurrence. Further,
Ebrahiminia et al. (2013) observed that sonication frequency
plays an important role for reactive radical generation in
the medium and showed that with increasing the sonication
frequency, the cavitation yield increased when the
frequency was greater than 250 kHz.
3.2 Effect of power supplied and KI concentration
The effect of power supplied on the oxidation of KI at
sonication frequencies of 378, 574, 992, and 1173 kHz was
observed. Figure 4 presents the cavitation yield obtained
over a power input range of 16.67% to 83.33% with
different sonication frequencies carried out for 30-min
sonication treatments on 1.0 wt% KI solutions. The results
showed that the cavitation yield increased by increasing
power input up to 50% in all the frequency level tested.
The effect of power supplied on the oxidation of KI within
a sonication frequency of 20 and 900 kHz has been studied
previously (Henglein and Gutierrez 1993; Weissler et al.
1950). A study by Entezari and Kruus (1996) showed that
at 900-kHz sonication frequency, increase in power supply
(between 8 and 76 W) leading to linearly increased
production of iodine with a cavitation threshold at
0.14 W cm-2. Merouani et al. (2010) studied the influence
of several operational parameters on the sonochemistry
dosimetry approaches such as KI oxidation, H2O2
production, and Fricke reaction using 300-kHz ultrasound.
They observed that the main experimental parameters that
showed significant effect in KI oxidation dosimetry were
initial KI concentration, pH, and acoustic power. Further,
Lim et al. (2014) studied the effects of liquid height/
Fig. 4 Cavitation yield obtained with different power inputs at
different sonication frequencies sonicated for 30 min in 1.0 wt% KI
volume, initial concentration of reactant, and acoustic
power (23, 40, and 82 W) on sonochemical oxidation.
They observed that as the liquid height/volume and the
input power changed, the power density varied from 23 to
1640 W L-1 and the maximum cavitation yields of
triiodide ion for 23, 40, and 82 W were observed as 0.05, 0.1,
and 0.2/0.3 L, respectively. They also reported that low
power was more effective for the small volume and the
large volume required high power level. However, a
previous study by Henglein and Gutierrez (1993) showed that
at large volume of KI solution, the iodine production tends
to show a nonlinear increase with an increase in power
input. Kirpalani and McQuinn (2006) established a
relationship between acoustic power and the amount of iodine
liberated by varying the power supply of 3–21 W and
8–18 W to 1.7 and 2.4 MHz transducers, respectively.
They reported that for 100 mL of KI solution, with increase
in power supply, the amount of iodine liberated increased.
Further, experiments were performed to measure the power
inputs (W) under four different sonication frequency
conditions of 378, 574, 992, and 1173 kHz with different
power inputs starting from 16.67% to 83.33%. Table 1
presents different power input settings and their measured
power output under four different sonication frequency
conditions: 378, 574, 992, and 1173 kHz. It is clear that the
power intensity and voltage at each power input level is not
constant and does not follow a particular pattern which
could be used to determine the effects of alternating
intensity levels at a different frequency. Acoustic intensity
measurements based on calorimetric determination under
different frequencies and power input are presented in
Table 2. The results showed increased cavitation yield with
increasing power input under 378 and 574 kHz sonication
frequency conditions. However, it was observed that using
a higher power input increased the amount of iodine that is
liberated, but due to the increase in power required, the
cavitation yield decreased in the system.
Furthermore, experiments were carried out to
determine the effect of KI concentration on the production of
iodine in an ultrasonic system. The yield of KI oxidation
reaction can be defined as the number of moles of iodine
liberated per unit time per unit reaction volume per unit
mole of KI per unit power input to the system (Sivasankar
et al. 2007). A decrease in cavitation yield as a result of
decreasing KI concentration was observed for all types of
sonication frequencies tested (Figs. 2, 3). Naidu et al.
(1994) also observed an increase in iodine liberation in
solutions with higher KI concentrations sonicated at
25 kHz. However, a higher cavitation yield was observed
with sonication frequency of 574 kHz in both cases of KI
concentration. Increase in cavitation yield in case of
574-kHz sonication frequency can be attributed to the
amount of hydroxyl radicals produced due to rapid
collapse of bubbles and also due to the consumption of
hydroxyl radicals by iodide ions that increase with an
increase in KI concentration.
Sonication frequency, kHz
Power input, %
Power intensity, W
Table 1 Measured power
inputs for a range of intensity
settings under different
conditions of sonication
Table 2 Acoustic power
delivered to the reaction system
at different frequencies and
power input determined using
Sonication frequency, kHz
Power input, %
Actual power, W
Acoustic intensity, W/cm2
3.3 Effect of cavitation yield on viscosity
In order to establish the effect of cavitation yield under
different sonication frequencies, 378, 574, 992, and
1173 kHz, on viscosity change, first experiments were
carried out in KI solution and sodium carboxymethyl
cellulose (CMC)–water mixture followed by application in
bitumen. CMC is used as a model fluid to describe the
behaviour of bitumen at 1000 mPa s approximately since it
is a shear-thinning fluid similar to heavy oil (Muller 1994).
Effect of cavitation yield on viscosity change under
different conditions of sonication frequency (378, 574, 992,
and 1173 kHz) and power input (16.67%–83.33%) in
0.7 wt% CMC–water sonicated for 30 min is presented in
Fig. 5. Higher viscosity changes were observed with
sonication frequencies such as 378 and 574 kHz as compared
to frequencies such as 992 and 1173 kHz. Higher viscosity
changes observed in 378- and 574-kHz sonication
frequencies were due to higher cavitation yield (Fig. 6). It was
Fig. 5 Cavitation yield and viscosity change under different
conditions of sonication frequency and power inputs in CMC–water
sonicated for 30 min
Fig. 6 Viscosity change at different sonication frequencies for
different power inputs in bitumen
also observed that with increasing power intensities leading
to higher cavitation yield results in higher viscosity change.
Chemical effects are recognised to be dominant at low
frequency (Suslick et al. 1999), while physical effects are
dominant at high frequency as it requires very high energy
input to generate cavitation at high frequencies. Change in
viscosity occurs due to intense shear or tensile force within
the fluid (Mohapatra and Kirpalani 2016). This shear is
caused by physical effects such as microconvection, and
microstreaming or microstirring. The principal physical
effect of ultrasonic cavitation is the formation of fine
emulsion droplets between immiscible phases that
eliminates the mass transfer resistance, while principal chemical
effect is the production of radicals through collapse of
cavitation bubbles, which accelerate the reaction (Kuppa
and Moholkar 2010). For all the four types of sonication
frequencies, increase in viscosity was observed with
increasing power intensity except for 378 kHz where a
decrease in viscosity change was observed after 50% power
Furthermore, the effect of five different sonication
frequency conditions, 378, 574, 860, 992, and 1173 kHz, with
different power inputs from 16.67% to 83.33% on change
in viscosity of bitumen was investigated. Typically, in oil
sands operations, bitumen is transported between unit
operations by dilution with naphtha or a paraffinic solvent
(C6–C8 paraffinics). In this work, bitumen was diluted with
naphtha to viscosity of 480 mPa s to evaluate the benefits
of acoustic cavitation for improved transportability and
reduced pumping (energy) costs. Bitumen was first diluted
with naphtha at the N/B ratio of 0.5. The diluted bitumen
sample was then centrifuged at 20 000 rpm for over 20 min
to remove the fine solids. All the experiments were carried
out at room temperature. The supernatant was then used for
preparation of a series of diluted bitumen samples by
adding more naphtha to get a viscosity of 480 mPa s.
The viscosity change in bitumen for different sonication
frequencies with different power inputs is presented in
Fig. 6. The major viscosity changes were observed to occur
at sonication frequencies of 378 and 574 kHz with
increasing power input. The highest viscosity change of
38% was observed at a sonication frequency of 574 kHz
with 83.33% power input, and lowest viscosity changes
(5%) were observed at sonication frequency of 1173 kHz
with a power input of 83.33%. However, it was observed
that the change in viscosity increases in all the five
sonication frequency conditions tested with increasing power
input. The increase in viscosity change (lower viscosity)
with increasing the power input was due to higher
disintegration of asphaltene flocs. Higher cavitation yield causes
more acoustic cavitation in the medium, which then causes
floc disintegration and cell breakage, leading to release of
intracellular materials to the aqueous phase. Cavitation
yield during different sonication frequencies and power
input conditions is a result of a series of energy conversions
(electrical energy ? mechanical energy ? acoustic
energy ? cavitation energy) that occur in the ultrasonic
processor. In case of varying frequencies, such chain of
energy conversion strongly depends on the total bubble
volume fraction in the medium which further depends on
the number of bubbles and their size distribution
(Moholkar and Warmoeskerken 2003).
Some studies report that the viscosity of bitumen
depends upon the asphaltene content (Mohammadreza
et al. 2012; Najafi and Amani 2011; Luo and Gu 2007).
Hence, during the sonication treatment of bitumen, the
dissolution of asphaltenic components occurs resulting in
the breakdown of asphaltene molecules to lighter
molecules leading to decrease in viscosity. A study by Mack
(1932) concluded that the significant viscosity increase
with the asphaltene content was due to strong aggregation
of asphaltene particles. Further, many studies also observed
ultrasonic technology as a method for reducing asphaltene
flocculation rates by changing the kinetics of aggregation
as well as for removing deposits (Mohammadreza et al.
2012; Mousavi-Dehghani et al. 2004).
Optimisation of cavitation technology including different
sonication frequencies and power intensities was carried
out in KI solution and CMC–water mixture and further
applied in bitumen heavy oil processing. This study
examines the effects of mid- to high sonication frequencies,
solute concentrations, and power intensity on cavitation
yield and viscosity changes in the medium. This study
showed that mid-range frequency levels such as 378 and
574 kHz are more effective in terms of increase in
cavitation yield and viscosity changes in bitumen heavy oil.
The highest viscosity decrease of 38% was observed at a
sonication frequency of 574 kHz with 83.33% power input,
and the lowest viscosity decrease (5%) was observed at a
sonication frequency of 1173 kHz with a power input of
83.33%. The higher viscosity change observed with the
574-kHz sonication frequency was due to a higher
cavitation yield which showed a direct relationship between
cavitation yield and viscosity change.
Different factors such as power inputs and solute
concentration affect the cavitation yield in the medium. An
optimum condition of 574 kHz sonication frequency and
83.33% power input was observed as the best method for
decreasing the viscosity of bitumen compared to other
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