1. 300r 2010 American Chemical Society pubs.acs.org/EF
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m
Published on Web 12/14/2010
Investigation on Asphaltene and Heavy Metal Removal from Crude Oil Using
a Thermal Effect
M. Ashtari,†
M. Bayat,*,‡
and M. Sattarin‡
†
Department of Chemical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran, and
‡
Research Institute of Petroleum Industry (RIPI ), Post Office Box 14665-137, Tehran, Iran
Received July 29, 2010. Revised Manuscript Received November 6, 2010
Removal of asphaltenes and heavy metals, using asymmetric ceramic monolith membranes with pore sizes
of 0.2 μm and 50 nm, was investigated for three Iranian crude oils. The experiments were conducted in a
batch filtration unit at a pressure gradient of 200 kPa and temperature range of 75-190 °C based on
the amount of crude oil asphaltene contents. The investigated crude oils consisted of 1-10 wt % asphaltene
contents. During heating of crude oils to specified temperatures, nanometer particles of asphaltene
aggregated to micrometer size and then micrometer particles were separated smoothly using the
membranes. The obtained results illustrated that asphaltene separation reached 60-87 wt % based on
the asphaltene content of crude oils. In addition, the separation of asphaltene and heavy metals, such as
nickel and vanadium, increased using the membrane of a smaller pore size. Besides, densities and viscosities
of crude oils showed a sufficient decline after filtration through the membrane.
1. Introduction
Recently, heavy and extra-heavy crude oil reservoirs have
being explored in Iran. Low American Petroleum Institute
(API) gravity and high asphaltene and heavy metal contents
are the greatest disadvantages of heavy and extra-heavy
crudes, which may be a cause to reduce their worth seriously.
The asphaltenes and resins are the major polar fractions in
crude oil. These largeand polarcomponents havea condensed
polyaromatic structure containing alkyl chains, heteroatoms
(such as O, S, and N), and some metals.1
The asphaltenes are
defined as a solubility class, namely, the fraction of the crude
oil precipitating in light alkanes, such as pentane, hexane, or
heptane. The asphaltene is soluble in aromatic solvents, such
as toluene and benzene,2
while the resins are soluble in higher
molecular-weight normal alkanes and insoluble in lower
molecular-weight alkanes. The resin molecules attach to the
asphaltene with their polar head, form a layer around asphal-
tenes, and stabilize the asphaltene micelles. As long as the
asphaltenes are kept stable in the micelles, no precipitation
occurs.3
Variations of temperature, pressure, composition,
flow regime, and electrokinetic effect cause the asphaltene
precipitation and deposition during petroleum production,
transportation, refining, and processing. Asphaltene precipi-
tation makes oil production more arduous and costly because
of the partial plugging in the oil well, pipeline, and equipment.
The asphaltene precipitation may further decrease recovery
efficiency or even stop oil production.4
Asphaltene precipita-
tion was postulated to occur in the following steps: (1) molec-
ular self-association into dimer- or trimer-like molecules, (2)
micellization with resins and aromatic compounds, and (3)
aggregation of micelles into precipitates.5
It is of great importance to know under which conditions
that the asphaltenes precipitate and to what extent precipi-
tated asphaltenes can be redissolved. In other words, to what
extent the processofasphalteneprecipitationisreversiblewith
respecttothechangeinthermodynamicconditions.Thesubject
of asphaltene precipitation has been studied greatly by re-
searchers, but there are still some controversies and disagree-
ments between researchers. The content of disagreements is
about the nature of asphaltene in crude oil. There are two
different models that describe the nature of asphaltene in
solution. The first approach is the solubility model, which
considers asphaltene to be dissolved in a true liquid state and
asphaltene precipitation to be a thermodynamically reversible
process. The second approach is the colloidal model, in which
asphaltenes are considered to be solid particles that are sus-
pended colloidally in the crude oil and are stabilized by large
resin molecules and the precipitation of asphaltene is consid-
ered to be irreversible. The validity of each of these models
depends upon whether the precipitation process is reversible or
not.6,7
Andersen and Stenby studied the effect of the temperature
on asphaltene precipitation/dissolution in crude oil. They
*To whom correspondence should be addressed. E-mail: bayatm@
ripi.ir.
(1) Mohamed, R. S.; Loh, W.; Ramos, A.; Delgado, C.; Almeida, V.
Reversibility and inhibition of asphaltene precipitation in Brazilian
crude oils. Pet. Sci. Technol. 1999, 17 (7), 877–896.
(2) Orangi, H. S.; Modarress, H.; Fazlali, A.; Namazi, M. H. Phase
behavior of binary mixture of asphaltene þ solvent and ternary mixture
of asphaltene þ solvent þ precipitant. Fluid Phase Equilib. 2006, 245,
117–124.
(3) Al-Sahhaf, T. A.; Fahim, M. A.; Elkilani, A. S. Retardation of
asphaltene precipitation by addition of toluene, resins, deasphalted oil
and surfactants. Fluid Phase Equilib. 2002, 194-197, 1045–1057.
(4) Zewen, L.; Ansong, G. Asphaltenes in oil reservoir recovery. Chin.
Sci. Bull. 2000, 45, 682–688.
(5) Kyeongseok, O.; Terry, A.; Milind, D. Asphaltene aggregation in
organic solvents. J. Colloid Interface Sci. 2004, 271, 212–219.
(6) Jamialahmadi, M.; Soltani, B.; M€uller-Steinhagen, H.; Rashtchian,
D. Measurement and prediction of the rate of deposition of flocculated
asphaltene particles from oil. J. Heat Mass Transfer 2009, 52 (19-20),
4624–4634.
(7) Peramanu, S.; Singh, C.; Agrawala, M.; Yarranton, H. Investiga-
tion on the reversibility of asphaltene precipitation. Energy Fuels 2001,
15, 910–917.

2. 301
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m Ashtari et al.
used a mixture of toluene and n-heptane and performed
solvent reversibility runs at 24, 50, and 80 °C. Although the
reversibility of precipitation with the temperature was not
explicitly investigated, the results showed that asphaltenes
partially redissolve with an increase in the temperature.8
Buckley et al. showed that asphaltene precipitation occurs
by not only adding alkanes as a solvent but also increasing the
temperature. According to this research, the size of precipi-
tated particles as a result of the increasing temperature was
less than 10 μm and this size was much smaller than the
precipitated particles as a result of adding solvent.9
Peramanu et al. reported that solvent treatments can be an
effective method for redissolving asphaltenes in crude oil,
when there is sufficient turbulence to break up the asphaltene
particles, but temperature treatments in the n-dodecane/
asphaltenesystem may not be the best method for redissolving
asphaltenes.7
Mousavi-Dehghani et al. showed that asphaltene precipita-
tion in crude oil increases with an increase of the temperature
and asphaltene precipitation is an irreversible process.10
Ashoori et al. reported that asphaltene precipitation is
reversible with respect to the temperature and composition.11
Bayat et al. developed a correlation that predicts the
asphaltene precipitation onset temperature of crude oil using
the crude oil refractive index (RI).12
In this work, the asphaltene precipitation and precipitation
reversibility were investigated relating to the temperature
effect in crude oils with low, mild, and high asphaltene
contents. The precipitation onset temperature was identified
using Bayat et al. correlation.12
The asphaltene separation
experiments were performed in a batch system using a ceramic
membrane. All experiments were performed without adding
solvents.
2. Experimental Section
2.1. Chemicals and Materials. Three crude oils with different
asphaltene contents were selected. Their physical properties
and metal contents are demonstrated in Tables 1 and 2. Merck
toluene and n-heptane were used for rinsing. Nitrogen, at 99.5%
purity, was used for blanketing and drying the system.
2.2. Apparatus. The batch filtration unit included a 19-
channel, ceramic monolith membrane placed in stainless-steel
housing, a feed pump, and two pressure gauges.
The19-channel,ceramic monolithmembrane(length,1016 mm;
outside diameter, 30 mm; and inside diameter of each channel,
4 mm) was secured in the housing by two special o-rings, resisted
to organic solvents and high temperatures, located on ferrules
glued to either end of the ceramic membrane. Feed entered the
housing on the tube side, and permeate was collected from the shell
side through a ball valve located near the bottom of the membrane
housing. The crude oil, fed from a pressure vessel using the feed
pump, entered the recycle loop. A portion of crude oil was bled
back to the feed tank. A reflux condenser has been used to prevent
light end evaporation.
The crude oil feed vessel included several electrical heating
elements, which maintained the heavy oil at an elevated tem-
perature. The capacity of the feed pump was 10 L/min at a
maximum differential pressure of 10 bar. It was driven by a
0.75 kW alternating current (AC) motor. The graphite mechan-
ical seal of the pump withstands high temperatures near 200 °C
in the presence of organic solvents. The flow stream was con-
trolled by bypassing some portion of the stream to the feed
vessel. The over pressure of the system was controlled by a
pressure safety valve over the feed vessel. The temperature and
pressure indicators were installed as thermocouples and pres-
sure gauges. The permeate flow was also measured every 2 min
for up to 4-5 h.
2.3. Experimental Procedures. At first, 5 L of crude oil was fed
to the feed vessel, and then electrical heaters were turned on. The
system was purged with nitrogen to remove trapped air com-
pletely. Then, the feed pump was turned on, and the feed was
routed in the loop line. The pressure of filtration in the system
was regulated by V-6 valve, and the full open condition of this
valve allowed the fluid to circulate to its greatest extent. The
light hydrocarbon vapors after depressurizing through the shell
side of the filter housing condensed in the provided condenser
E-4. The cooling fluid in the condenser was chilled water at a
temperature of 5 °C. The experiments were performed in tem-
peratures between 75 and 190 °C, and nitrogen was purged into
the system to prevent cracking of heavy hydrocarbons during
heating. Thus, the pressure changed rarely while the tempera-
ture increased. The permeate stream was sampled periodically
and weighed to determine the mass flux. The schematic of the
separation system was illustrated in Figure 1.
2.4. Analytical Methods. 2.4.1. Asphaltene Analysis. The
asphaltene contents of feed and permeate, defined as n-heptane
insoluble, were determined using a full automatic asphaltene
analyzer, model APD-500A, whose operation is based on
the measurement of absorbance of two wavelengths of asphal-
tene particles. This method had a strong correlation to ASTM D
6560 and IP 143/01 methods.13
2.4.2. Metal Analysis. The metal contents of feed and perme-
ate, defined as vanadium, nickel, iron, and sodium contents of
crude oil, were determined using an atomic absorption spectro-
meter according to the ASTM D 5863 standard.14
Table 1. Crude Oil Characterization
crude oil place asphaltene content (wt %) density (g/cm3
) viscosity at 10 °C (cP) viscosity at 40 °C (cP)
LabSefid Khuzestan Province 1.50 0.858 19.51 5.46
Foruzan Khark Island 4.36 0.876 35.26 10.58
Nowruz Khark Island 9.51 0.933 599.4 103.6
Table 2. Metal Analysis
crude oil vanadium (ppm) nickel (ppm) iron (ppm) sodium (ppm)
LabSefide 41 11 9.5 5.7
Foruzan 62 14 1 12
Nowruz 122 21 3.7 16
(8) Andersen, S. I.; Stenby, E. H. Thermodynamics of asphaltene
precipitation and dissolution investigation of temperature and solvent
effects. Fuel Sci. Technol. Int. 1996, 14, 261–287.
(9) Buckley, J. S.; Hirasaki, G. J.; Liu, Y.; Von Drasek, S.; Wang,
J. X.; Gill, B. S. Asphaltene precipitation and solvent properties of crude
oils. Pet. Sci. Technol. 1998, 16 (3-4), 251–285.
(10) Mousavi-Dehghani,S.A.;Riazi,M.R.;VafaieSefti,M.;Mansoori,
G. A. An analysis of methods for determination of onsets of asphaltene
phase separations. Pet. Sci. Eng. 2003, 42, 145–156.
(11) Ashoori, S.; Jamialahmadi, M.; M€uller Steinhagen, H.; Ahmadi,
K. Investigation of reversibility of asphaltene precipitation and deposi-
tion for an Iranian crude oil. Iran. J. Chem. Chem. Eng. 2006, 25 (3),
41–47.
(12) Bayat, M.; Sattarin, M.; Teymouri, M. Prediction of self-pre-
cipitation in dead crude oil. Energy Fuels 2008, 22, 583–586.
(13) UIC, Inc. www.uicinc.com/AsphalteneAnalyzer.htm; UIC, Inc.:
Joliet, IL, 2009.
(14) American Society for Testing and Materials (ASTM). ASTM D
5863-00a, Standard Test Methods for Determination of Nickel, Vana-
dium, Iron, and Sodium in Crude Oils and Residual Fuels by Flame Atomic
Absorption Spectrometry; ASTM: West Conshohocken, PA, 2005.

3. 302
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m Ashtari et al.
2.4.3. Density and Viscosity. The crude oil density was mea-
sured by a digital density analyzer, model FP-6000, according
to the ASTM D 4052 standard.15
Furthermore, the crude oil
viscosity was measured using glass capillary viscometers in a water
bath at10 and40 °C, according tothe ASTMD 445-06 standard.16
3. Results and Discussion
The asphaltene molecular weight is extended from 1000 to
2 000 000 in different crude oils.17
The parameters that affect
molecular weight of asphaltene components are nearly un-
known, but it may be hypothesized that crude oils with
different asphaltene contents consist of different molecular
weights of asphaltene. The temperature effect on three kinds
of crude oils with different asphaltene contents have been
investigated regarding the probability of the molecular-weight
effect on asphaltene precipitation and redissolving behavior.
The asphaltene separation using a ceramic membrane was
evaluated as permeate mass flux and asphaltene rejection. The
“permeate mass flux” was calculated by dividing the mass of
the permeate sample to the interval of time. The asphaltene
rejection (R) is calculated using eq 1
R ¼ ð1 - Cp=Cf Þ Â 100 ð1Þ
where Cp and Cf are asphaltene contents in permeate and
feed, respectively.
3.1. Asphaltene Precipitation in Crude Oil with a Low
Asphaltene Content. The Labsefide crude oil, consisting of
1.5 wt % asphaltene, was selected as a low-asphaltene-
content sample. Asphaltene rejection via the temperature is
shown in Figure 2 for two different pore sizes of membranes.
The rejection asphaltene maxima are detected at 44 and 60%
for the membranes with 0.2 and 0.05 μm pore sizes, respec-
tively, at 105 °C. Consequently, this temperature is consid-
ered as the optimum temperature for separating asphaltene
in this crude oil. When the temperature increases over
105 °C, the asphaltene separation reduces and the asphal-
tenes redissolve in the crude oil. In fact, at first, when the
temperature increases, resin layers are dissolved gradually
Figure 1. Schematic of the separation process system.
Figure 2. Asphaltene rejection versus the temperature for the membrane at Δp = 200 kPa and Cf = 1.5 wt %.
(15) American Society for Testing and Materials (ASTM). ASTM D
5002-96, Standard Test Method for Density and Relative Density of
Liquids by Digital Density Meter; ASTM: West Conshohocken, PA, 2002.
(16) American Society for Testing and Materials (ASTM). ASTM D
445-06, Standard Test Method for Kinematic Viscosity of Transparent
and Opaque Liquids; ASTM: West Conshohocken, PA, 1990.
(17) Mansoori, G. A. A unified perspective on the phase behaviour of
petroleum fluids. Int. J. Oil, Gas Coal Technol. 2009, 2 (2), 141–167.

4. 303
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m Ashtari et al.
and, then, at the optimum temperature, the resin layers are
dissociated from the asphaltenes molecules. Hence, the
asphaltene particles can aggregate better and form micropar-
ticles. After optimum temperature, if the temperature increase
continues, the kinetic energy of asphaltene particles will in-
crease; consequently, the asphaltene aggregation will break,
and the microparticles will convert to nanoparticles again.
Figure 2 illustrates the variation trend of asphaltene
rejection at different temperatures, which is only 10% for
low asphaltene crude oil. As seen, most asphaltenes are
rejected at 105 °C. Equation 2 shows the RI correlation of
this crude oil. Measurements of the RI at the onset of
precipitation have shown that, for each oil-precipitant
combination, the onset occurs at a characteristic RI of
1.42-1.44 and is independent of the crude oil asphaltene
content.9
According to eq 2, the RI of this crude oil reaches
1.42 at a temperature of 124 °C. This temperature is almost
close to the experimental temperature in the presented work.
RI ¼ 1:4944 - 0:0006T ð°CÞ ð2Þ
Figure 3 illustrates a comparison of the permeate flux versus
time in different temperatures, using a 0.2 μm membrane
pore size. The maximum flux, as seen, belongs to 120 and
130 °C, while the minimum asphaltene separation is ob-
served at both temperatures. In fact, the precipitation rever-
sibility was observed to a little extent at the mentioned
temperatures. Furthermore, other temperatures had a simi-
lar flux trend that can be explained by a little difference
between asphaltene rejection values.
According to Figures 2 and 3, the optimum temperature
for the separation process is 105 °C, because most asphaltene
is separated at this temperature.
The densities, viscosities, and metal contents of the perme-
ate samples at 105 °C, in different membrane pore sizes, are
compared in Tables 3 and 4. The second column in Table 3
specifies the asphaltene content in the permeate samples. The
densities are reported at a standard temperature (15.56 °C),
and the viscosities are reported at 10 and 40 °C. As shown in
Table 3, the asphaltene content has an important role in the
viscosity value. In fact, although the viscosity value is deter-
mined by both asphaltene and resin contents of crude oil,18
the asphaltene content plays a basic role in determining the
viscosity and its reduction can remarkably reduce the vis-
cosity value. The viscosity reduction is more obvious in
heavy crude oils, which have higher asphaltene contents. In
addition, the asphaltene contents influence the crude oil
density, and their reduction decreases the density value;
however, a direct relation does not exist between them.19
Furthermore, the asphaltene separation causes a reduction
of the crude oil metal contents, such as nickel and vanadium.
The deleterious effects of metals in petroleum have appeared
as product contamination, catalyst poisoning, and equip-
ment corrosion. They also tend to form particulate emissions
in the sub-micrometer range.20
According to Table 4, the
vanadium and nickel contents were reduced in permeate
samples in both membrane pore sizes. However, the iron
content increased after the separation process, and this
Figure 3. Permeate flux versus time for the membrane at Δp = 200 kPa and Cf = 1.5 wt %, with a membrane pore size of 0.2 μm.
Table 3. Characteristics of the Permeate Sample in Low-Asphaltene-Content Feed (LabSefid, Khuzestan Province)
pore size (μm) asphaltene content (wt %) density (g/cm3
) viscosity at 10 °C (cP) viscosity at 40 °C (cP)
0.2 0.83 0.854 14.85 4.38
0.05 0.59 0.853 10.06 3.84
Table 4. Metal Analysis of the Permeate Sample in Low-Asphaltene-Content Feed (LabSefid, Khuzestan Province)
temperature (°C) pore size (μm) vanadium (ppm) nickel (ppm) iron (ppm) sodium (ppm)
105 0.05 7 8.3 3.4 3.7
105 0.2 11 11 3.6 7
(18) Hinkle, A.; Shin, E. J.; Liberatore, M. W.; Herring, A. M.; Batzle,
M. Correlating the chemical and physical properties of a set of heavy oil
from around the world. Fuel 2008, 87, 3065–3070.
(19) Evdokimov, I. N. Bifurcated correlations of the properties of
crude oils with their asphaltene content. Fuel 2005, 84, 13–28.
(20) Farhat Ali’, M.; Abbas, S. A review of methods for the deme-
tallization of residual fuel oils. Fuel Process. Technol. 2006, 87 (7), 573–
584.

5. 304
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m Ashtari et al.
phenomenon could be as a result of corrosion of the filtration
equipment.
3.2. Asphaltene Precipitation in Crude Oil with a Mild
Asphaltene Content. The second crude oil, Foruzan, with
4.36 wt % asphaltene content, was selected as a mild-
asphaltene-content crude oil. Figure 4 shows the asphaltene
rejection via the temperature for two different pore sizes of
membranes. The asphaltene rejection maxima, 61 and 81%,
are observed at 120 °C for 0.2 and 0.05 pore size membranes,
respectively. Consequently, the optimum temperature for
asphaltene separation from Foruzan crude oil is 120 °C,
higher than the optimum temperature of the previous crude
oil, because this crude oil includes more asphaltene content
and precipitation of them occurs at higher temperatures.
Similar to the former case, the asphaltene participates are
redissolved when the temperature increases over 120 °C, but
the precipitation reversibility in this case is shown more.
According to Figure 4, the variation trend of asphaltene
rejection in different temperatures is approximately 30%,
while this variation trend was detected at 10% for the lighter
crude oil. Because, in the second crude oil, asphaltene
particles exist more, they can form larger accumulations that
cannot pass from the filter. Therefore, the separation value
increases regarding the first case. Equation 3 correlates the
RI of Foruzan crude oil. According to this equation, the RI
of Foruzan crude oil reaches 1.42 at 126.8 °C (onset tem-
perature of asphaltene precipitation), which is close to the
experimental temperature of 120 °C.
RI ¼ 1:4961 - 0:0006T ð°CÞ ð3Þ
In Figure 5, the permeate flux versus time is compared at
different temperatures using a 0.2 μm membrane pore size.
As seen, the maximum flux belongs to 160 °C, and the highest
precipitation reversibility is observed at this temperature,
while the minimum flux is detected at the optimum tempera-
ture of 120 °C.
The densities and viscosities of the permeate samples at
120 and 140 °C for both membrane pore sizes are reported in
Table 5. The second column specifies the asphaltene contents
in the permeate samples. The densities are reported at the
standard temperature (15.56 °C). Also, the viscosities are
Figure 4. Asphaltene rejection versus temperature for the membrane at Δp = 200 kPa and Cf = 4.36 wt %.
Figure 5. Permeate flux versus time for the membrane at Δp = 200 kPa and Cf = 4.36 wt %, with the membrane pore size of 0.2 μm.

6. 305
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m Ashtari et al.
reported at 10 and 40 °C. Because most asphaltenes sepa-
rated at 120 °C, the viscosity and density decreased con-
siderably in this temperature. In Table 6, the metal contents
of the permeate samples at 120 °C are reported. As seen, the
vanadium contents in permeate samples reduced 39 and
28 ppm regarding the feed, using membranes with 0.05 and
0.2 μm pore sizes, respectively. Furthermore, nickel contents
decreased 7 and 3 ppm using membranes with 0.05 and
0.2 μm pore sizes, respectively. However, the iron content
increased after the separation process, and this phenomenon
could most likely be as a result of the corrosion of the
filtration equipment.
3.3. Asphaltene Precipitation in Crude Oil with a High
Asphaltene Content. In the third case, Nowruz crude oil,
with 9.51 wt % asphaltene content, was selected as a high-
asphaltene-content sample. Figure 6 shows the asphaltene
rejection via the temperature for two different pore sizes of
membranes. The asphaltene rejection maxima, 57 and 87%,
are observed at 140 °C for 0.2 and 0.05 pore size membranes,
respectively. Consequently, the optimum temperature for
asphaltene separation from this crude oil is 140 °C, higher
than the previous crude oil, and as explained before, heavier
crude oils include more asphaltene content and these parti-
cles agglomerate at higher temperatures with respect to
lighter crude oils. In addition, the redissolving of asphaltene
participates occur in this crude oil too, when the temperature
increased over 140 °C. During the experiments, complete
precipitation reversibility was not observed in any cases.
According to Figure 6, the variation trend of asphaltene
rejection in different temperatures is 40%. The RI correlation
of Nowruz crude oil is determined on the basis of eq 4.
According to this equation, the RI of Nowruz crude oil
reaches 1.42 at 188.5 °C (onset temperature of asphaltene
precipitation), which is higher than the experimental tem-
perature.
RI ¼ 1:5331 - 0:0006T ð°CÞ ð4Þ
In Figure 7, the permeate flux versus time was compared in
different temperatures using a 0.2 μm membrane pore size for
heavy crude oil. As shown, the minimum flux belongs to 140
°C, as long as the maximum asphaltene separation was
detected at this temperature. In addition, the maximum flux
was observed at 100 °C.
The densities and viscosities of the permeate samples at
140 and 120 °C in different membrane pore sizes are reported
in Table 7. As shown, at 140 °C, the best quantities of
viscosity and density are obtained. It is clear, because the
highest asphaltenes are separated at this temperature; thus,
the viscosity and density decrease significantly.
In Table 8, the metal contents of the permeate samples
are reported at 140 °C. As seen, the vanadium contents in
permeate samples reduced 82 and 51 ppm regarding feed,
using membranes with 0.05 and 0.2 μm pore sizes, respec-
tively. Furthermore, nickel contents decreased 6 and 4 ppm
using membranes with 0.05 and 0.2 μm pore sizes, respec-
tively. Although the separation process could significantly
reduce the metal contents of particularly heavy crude oil, the
iron content increased after the separation process. This
phenomenon could most likely be as a result of corrosion
Table 5. Characteristics of the Permeate Sample in Mild-Asphaltene-Content Feed (Foruzan, Khark Island)
temperature (°C) pore size ( μm) asphaltene content (wt %) density (g/cm3
) viscosity at 10 °C (cP) viscosity at 40 °C (cP)
120 0.2 1.69 0.882 27.10 9.11
140 0.2 2.98 0.884 34.19 10.17
120 0.05 0.73 0.870 19.17 5.73
140 0.05 1.01 0.880 29.20 10.09
Table 6. Metal Analysis of the Permeate Sample in Mild-Asphaltene-Content Feed (Foruzan, Khark Island)
temperature (°C) pore size ( μm) vanadium (ppm) nickel (ppm) iron (ppm) sodium (ppm)
120 0.05 23 7 4.3 11
120 0.2 34 11 6.1 12
Figure 6. Asphaltene rejection versus temperature for the membrane at Δp = 200 kPa and Cf = 9.51 wt %.

7. 306
Energy Fuels 2011, 25, 300–306 : DOI:10.1021/ef100986m Ashtari et al.
of the filtration equipment. In fact, the increasing iron con-
tent is more evident in the last experiments in relation to the
initial experiments, and this phenomenon can confirm the
assumption of corrosion of the filtration equipment.
4. Conclusion
The temperature effect was investigated on asphaltene
separation from crude oil, using a 19-channel, ceramic mono-
lith membrane. The experiments were performed on crude oils
with different asphaltene contents. In all cases, the maximum
asphalteneseparation occurred at theasphaltene precipitation
onset temperature. Then, when the temperature was increased,
the asphaltene separation decreased, because of the precipita-
tion reversibility. In fact, increasing the temperature causes the
resin layers to dissolve, which enclosed asphaltene molecules.
Then, at the optimum temperature, the resin layers are dis-
sociated from the asphaltene molecules. Therefore, the asphal-
tene particles can aggregate better and form microparticles.
Consequently, the separation percentage reaches a maximum
at the optimum temperature. If the temperature increase
continues after the optimum temperature, the kinetic energy
of asphaltene particles will increase, and this phenomenon will
cause the asphaltene aggregates to break and convert to nano-
particles; as a result, the separation percentage declined.
Increasing the asphaltene content of crude oil causes an
increase of the temperature of asphaltene precipitation onset.
Furthermore, the variation range is wider in heavier crude oil,
because more asphaltene particles are presented and can form
larger aggregations stuck behind the filter. Also, the density,
viscosity, and heavy metal contents of permeate, including
nickel and vanadium, decrease as a result of removing asphal-
tenes in the feed content.
Acknowledgment. The authors gratefully acknowledge the
support of this by the Research Institute of Petroleum Industry
of Iran.
Nomenclature
Cf = feed asphaltene content (wt %)
Cp = permeate asphaltene content (wt %)
Δp = pressure difference (bar)
R = asphaltene rejection (wt %)
RI = refractive index
T = temperature (°C)
Figure 7. Permeate flux versus time for the membrane at Δp = 200 kPa and Cf = 9.51 wt %, with the membrane pore size of 0.2 μm.
Table 7. Characteristics of the Permeate Sample in High-Asphaltene-Content Feed (Nowruz, Khark Island)
temperature (°C) pore size ( μm) asphaltene content (wt %) density (g/cm3
) viscosity at 10 °C (cP) viscosity at 40 °C (cP)
120 0.2 7.65 0.934 571.70 94.82
140 0.2 5.52 0.933 245.10 58.31
120 0.05 2.10 0.909 113.22 28.30
140 0.05 1.21 0.877 89.80 20.01
Table 8. Metal Analysis of the Permeate Sample in High-Asphaltene-Content Feed (Nowruz, Khark Island)
temperature (°C) pore size ( μm) vanadium (ppm) nickel (ppm) iron (ppm) sodium (ppm)
140 0.05 40 10 8.3 14
140 0.2 71 12 5.7 13