Iraqi Journal of Chemical and Petroleum Engineering 

 Vol.15 No.2 (June 2014) 39- 48  

ISSN: 1997-4884 

 
 
 
 

Viscosity Reduction of Sharqi Baghdad Heavy Crude Oil Using 

Different Polar Hydrocarbons, Oxygenated Solvents  

 
Hussein Qasim Hussein and Saja Abdul-wahhab Mohammad  

Chemical Engineering Department, College of Engineering, University of Baghdad 

 
Abstract 

This work studied the facilitation of the  transportation of Sharqi Baghdad heavy 

crude oil characterized with high viscosity 51.6 cSt at 40 °C, low API 18.8, and high 

asphaltenes content 7.1 wt.%, by reducing its viscosity from break down asphaltene 

agglomerates using different types of hydrocarbon and oxygenated polar solvents 

such as  toluene, methanol, mix xylenes, and reformate. The best results are obtained 

by using methanol because it owns a high efficiency to reduce viscosity of crude oil to 

21.1 cSt at 40 °C. Toluene, xylenes and reformate decreased viscosity to 25.3, 27.5 

and 28,4 cSt at 40 °C, respectively. Asphaltenes content decreased to 4.2 wt. % by 

using toluene at 110 °C. And best improvement in API of the heavy crude oil is 26.1 

at 40 °C by using xylenes.   
 

Keywords: Heavy crude oil; transportation; asphaltene content; viscosity reduction 

 

Introduction 

Petroleum transportation has become a 

complex and highly technical 

operation. One of the major difficulties 

in the pipeline transportation is the 

high viscous fluids that require 

efficient and economical ways to 

transfer the heavy crude. Heavy crude 

oils have a density approaching or even 

exceeding that of water. They are 

usually extremely viscous, with a 

consistency ranging from that of heavy 

molasses to solid at room temperature. 

Heavy crude oils are not pumped easily 

through the pipelines because of the 

high concentrations of sulfur and 

several metals, particularly nickel and 

vanadium. Crude oils are complex 

fluids that can cause a variety of 

difficulties during the production, 

separation, transportation and refining 

of oil [1, 2]. 

Heavy crude is high viscosity ,and high 

specific gravity as well as heavy 

molecular composition.  It is dense and 

viscous due to the high presence of 

naphthenes and paraffines [3]. Heavy 

crude oil contains greater proportions 

of higher-boiling constituents such as 

(lubricating oil motor oils, lubricants, 

engine oil, cylindrical oil, and gear 

oil),greases and wax, and residue  

(residual  fuel  oils,  coke,  tar  and  

asphalt).In addition,  more  aromatic,  

and heteroatom  containing (N, O, S 

and metals) are contained in heavy 

petroleum than light petroleum [4]. 

Such asphalting is considered as a 

ruthless problem within the petroleum 

industry due to their various costy 

problems in terms of production loss 

Iraqi Journal of Chemical and 
Petroleum Engineering 

 

University of Baghdad 
College of Engineering 



Viscosity Reduction of Sharqi Baghdad Heavy Crude Oil Using Different Polar Hydrocarbons, 

Oxygenated Solvents   

40                                        IJCPE Vol.15 No.2 (June 2014)               -Available online at: www.iasj.net 
 

and transport difficulties. Heavy crudes 

account for a large fraction of the 

world’s potentially recoverable oil 

reserves. The viscosities of those 

crudes at room temperature vary from 

100mPas to more than 10
5
 mPas. 

Generally, crude oil with viscosity 

<400 mPas is the classical maximum 

desired pipeline viscosity [5-7]. 

The high viscosity of heavy oil is a 

crucial factor that strongly affects its 

up-stream recovering, down-stream 

surface transporting and refining 

processes. A better understanding of 

the origination of its high viscosity can 

greatly help to find more effective and 

economical methods for recovering the 

heavy oil and reducing the related 

capital and/or operating costs [8]. 

Therefore, different methods are used 

in order to reduce the viscosity of the 

heavy crude for the pipeline 

transportation. For instance, upgrading, 

dilution with lighter crudes or alcohols, 

heating, and the use of surfactants to 

stabilize emulsions are some of those 

common methods, oxidation and drag 

reduction. Heating is a common 

method utilized to overcome the above 

noted problems of transporting heavy 

oil by pipeline [1]. 

Another way to transport heavy oil is 

to heat the oil as the viscosity 

decreases very rapidly with increasing 

temperature. The basis for this method 

lies in the fact that as heavy oil is 

heated, the viscosity of the heavy oil is 

reduced and thus made easier to pump. 

Therefore, it is important to heat the oil 

to a point where the oil has a 

substantially reduced viscosity. A 

principle drawback to the use of heated 

pipelines is the high capital and 

operational cost of such a heated 

pipeline over long distances [5]. In 

addition, underwater pipeline 

transportation of heavy oil through a 

heated pipeline is very difficult due to 

the cooling effect of the surrounding 

water and the practical difficulty of 

maintaining pumping stations and 

heating stations [9, 10].  

Several experimental studies have 

shown that heavy oil viscosity is 

strongly dependent on the volume 

fraction, chemical structures, and 

physicochemical properties of its 

asphaltenes, which are the most polar 

and/or heaviest components in heavy 

oil [11, 12]. 

Petroleum asphaltenes are defined as a 

solubility class of the heavy 

components in crude oil which are 

insoluble in nonpolar solvents. 

Asphaltenes exist in the form of 

colloidal dispersions stabilized by 

other constituents of the crude oil. 

These naturally occurring dispersions 

can be easily disturbed by a variety of 

mechanical and physicochemical 

conditions involved in oil field 

recovery and production. Changes in 

temperature and pressure, 

commingling of crude and condensate 

streams, and especially the use of 

enhanced recovery techniques can 

result in asphaltene destabilization, 

precipitation, and eventual deposition. 

Once deposited, asphaltenes pose a 

multitude of problems for crude oil 

producers
 
[13]. 

Studies have shown that asphaltenes 

exhibit properties similar to colloids. 

These colloids exist in the heavy oil 

matrix in a micelle form. Since the 

mole fraction of resins is higher than 

asphaltenes in petroleum, micelles are 

richer in resins. Asphaltenes also 

exhibit properties of colloidal systems 

such as the ‘critical micelle 

concentration’ (CMC) at which 

aggregates begin to form. The breaking 

down of asphaltenes upon the addition 

of polar solvents can be rationalized in 

terms of a reduction in the solubility 

parameter or the polarity of the 

hydrocarbon medium [14-16]. 

The formation of micelles is believed 

to be primarily due to the interaction 

between asphaltene species or 



Hussein Qasim Hussein and Saja Abdul-wahhab Mohammad 

 

-Available online at: www.iasj.net                      IJCPE Vol.15 No.2 (June 2014)                                 41 
 

asphaltene-resin fractions. The nature 

of the intermolecular or intramolecular 

forces that cause the formation of 

asphaltene micelles is not clear at 

present. It has been suggested that a 

number of forces may be involved 

including Van der Waals attraction, 

dipole-dipole interaction, hydrogen 

bonding, electron-transfer or charge 

transfer between aromatics (𝜋-𝜋 
bonding), and porphyrin interaction

 

[17-18].
  

The aim of the present work is to study 

the reduction viscosity of heavy crude 

oil using different polar hydrocarbons 

and oxygenated solvents (toluene, 

methanol, mix xylenes and reformate) 

at different concentration (4, 8, 10 and 

12 wt.%) and different temperature (40 

°C and boiling point for each solvents 

except reformate at 100 °C) on the 

efficiency of viscosity reduction 

systems.  

 
Experimental 

Feedstock  
The feedstock in this study was Sharqi 

Baghdad crude oil, obtained from 

Baghdad east oil fields. The properties 

of the crude are given in Table 1. 

 
Table 1: Physical properties of Sharqi Baghdad 

crude oils 

Test 
Crude oil from 

east of Baghdad 

Viscosity at 40°C 51.6 (cSt) 

API at 60°F 18.8 

Asphaltene content 7.1 wt.% 

Sulfur content 5.0 wt.% 

Vanadium 88 ppm 

Iron 25 ppm 

Nickel 38 ppm 

Saturate compounds 42.2 ppm 

Naphthene compounds 23.8 wt.% 

 

Light Naphtha 

Light naphtha was supplied from Al-

Doura refinery, with viscosity and 

density 6.76*10
7
(stock) and  0.65 g 

cm
-3

, respectively. 

 

Reformate 

Reformate was supplied from Al-

Doura refinery, with boiling point   

225 °C. 

 
Toluene Solvent (C7H8) 

Toluene was supplied from 

(GCC.Gainland chemical company). 

With molecular weight, boiling point 

and density are (92.14 kg/mole, 110 °C 

and 0.87 g/cm
3
 ), respectively. 

  

Methanol Solvent (CH3OH) 

Methanol was supplied from (POCH 

SA) company. With molecular weight, 

density and boiling point are 32.04, 

0.79 g cm
-3

 and 65 °C, respectively. 

 
Xylenes Mixture (C8H10) 

Xylenes mixture of isomers, extra 

pure, is supplied from Al-Doura 

refinery. With molecular weight, 

density and boiling point are 106.17, 

0.68 g cm
-3

 and 137.76 °C, 

respectively. 

 
Distillation Stage 

Two liters of Sharqy Baghdad heavy 

crude oil were subjected to the 

distillation using computerized 

laboratory apparatuse (according 

ASTM 5236) (PIGNAT COMPANY, 

FRANCE) that consists of distillation 

flask, heating mantle, distillation 

column, condenser, thermometer and 

fraction collector as shown in Fig. 1. 

Distillation was carried out to remove 

naphtha from crude oil to obtain 

stripped crude oil; the initial boiling 

point was 75 °C to the end point of 

distillation was 175 °C. Distillated 

naphtha was represented 17% vol. 

based on crude oil. 

 



Viscosity Reduction of Sharqi Baghdad Heavy Crude Oil Using Different Polar Hydrocarbons, 

Oxygenated Solvents   

42                                        IJCPE Vol.15 No.2 (June 2014)               -Available online at: www.iasj.net 
 

 
Fig. 1: Schematic diagram of the labrorty 

distillation unit 

 

Solvent Stage 

1. Mixing 
A 250 ml two-necked flat bottom flask 

was equipped with high efficiency 

condenser from one neck and with the 

sensor of controlled hot plate magnetic 

stirrer (Stuart) from another. A chiller 

(Gallenham) was used for providing 

cold water for condenser as shown in 

Fig. 2. A 100 g of stripped crude oil 

was poured into the mixing flask for 

each run. Mixing was carried out with 

two temperatures, 40 °C and normal 

boiling point of each solvent with 

various solvent concentrations 4,8,10 

and 12 wt.% based on crude oil. The 

sample of stripped crude oil was heated 

to the temperature of treatment and 

then a specific concentration of solvent 

was added; the duration of mixing was 

1h. 

 

 
Fig. 2: Schematic diagram of the mixing unit 

 

2. Evaporation 
Treated stripped crude oil was exposed 

to the evaporation to ensure a 

recovering not less than 90% of 

solvent from treated samples of 

stripped crude oil with solvent. 

Temperature of evaporation was varied 

according to the boiling point of each 

solvent.  

 

3. Blending 
The evaporated sample of treated 

stripped crude oil was blended with 

distilled naphtha recovered from 

distillation stage. Constant blending 

percentage (vol. 17%) of naphtha was 

blended to ensure converting 

evaporated treated stripped crude oil to 

treated crude oil. 

 

Results and Discussions 

The results obtained in the present 

investigation for viscosity reduction of 

Sharqi Baghdad heavy crude oil by the 

breakdown of asphaltenes using 

different polar solvents at different 

temperatures and concentrations are as 

follows: 

 



Hussein Qasim Hussein and Saja Abdul-wahhab Mohammad 

 

-Available online at: www.iasj.net                      IJCPE Vol.15 No.2 (June 2014)                                 43 
 

Effect of Solvent Type on Asphaltene 

Content 

Figures 3, 4, 5 and 6 show the effect of 

different types of polar solvents with 

different concentration on the 

asphaltene content.  The feedstock is 

exposed to different solvents at 

different concentrations and 

temperatures. These solvents reduced 

asphaltenes content affected by 

temperature and the action of polar 

solvents to disperse asphaltene 

agglomerates. From Figures 3, 4, 5 and 

6, the higher reduction in asphaltene 

content is obtained with toluene 4.3638 

wt.% at 40°C, while 5.0071 wt.% 

asphaltenes is obtained with reformate, 

5.0381 wt.%, and 5.0392 wt.% 

asphaltene content is obtained with 

xylenes and methanol, respectively. 

It is well known that special types of 
compounds have the ability to break 

down aspaltene agglomerates. The 

presence x of electrons in the ring of 

solvents may play a role in the 

interaction between the compounds 

added and the n electrons in the 

polyaromatic systems of the asphaltene 

agglomerates. The compounds kept to 

one ring to keep the size of the 

molecules allow for a greater diffusion 

through the crude oil matrix and 

penetration into the asphaltene 

agglomerates. 

 

 
Fig. 3: Effect of toluene weight fraction on 

asphaltene content of crude oil 

 
Fig. 4: Effect of xylene weight fraction on 

asphaltene content of crude oil 

 

 
Fig. 5: Effect of methanol weight fraction on 

asphaltene content of crude oil 

           

 
Fig. 6: Effect of reformate weight fraction on 

asaphaltene content of crude oil 

Solvent wt.%

A
s
p
h
a
lt
e
n
e
 
C

o
n
t
e
n
t

4.4

4.6

4.8

5.0

5.2

5.4

5.6

5.8

3 5 7 9 11 13

Asphaltene at 40 
o

C

Asphaltene at 110 
o
C

Solvent wt.%

A
s
p
h
a
lt
e
n
e
 
C

o
n
t
e
n
t

5.0

5.2

5.4

5.6

5.8

6.0

6.2

6.4

6.6

3 5 7 9 11 13

Asphaltene at 40 
o

C

Asphaltene at 138 
o
C

Solvent wt.%

A
s
p
h
a
lt
e
n
e
 
C

o
n
t
e
n
t

4.8

5.0

5.2

5.4

5.6

5.8

6.0

6.2

6.4

6.6

3 5 7 9 11 13

Asphaltene at 40 
o
C

Asphaltene at 65 
o
C

Solvent wt.%

A
s
p
h
a
lt
e
n
e
 
C

o
n
t
e
n
t

4.8

5.2

5.6

6.0

6.4

6.8

3 5 7 9 11 13

Asphaltene at 40 
o

C

Asphaltene at 100 
o
C



Viscosity Reduction of Sharqi Baghdad Heavy Crude Oil Using Different Polar Hydrocarbons, 

Oxygenated Solvents   

44                                        IJCPE Vol.15 No.2 (June 2014)               -Available online at: www.iasj.net 
 

Effect of Solvent Type on Viscosity 

The effect of solvent concentration at 

different temperature on viscosity 

reduction of Sharqi Baghdad heavy 

crude oil was studied. Figures 7, 9, 11 

and 13 show the effect of different 

concentrations of toluene, methanol, 

xylenes, and reformate on viscosity of 

crude oil at different temperatures, 

respectively. The viscosity decreased 

with increasing solvent concentration. 

The heavy crude oil viscosity 

decreases maximally from 51.6 cSt to 

21.7 cSt at 110 °C by using toluene, 

and to 21.1, 27.5, and 28.4 cSt at 40 °C 

by using methanol, xylenes, and 

reformate, respectively.  

It is widely assumed that the 

asphaltene molecules in oil 

agglomerate to form micelle-like 

cluster. Interactions between these 

clusters contribute towards the 

viscosity of the oil. By breaking these 

agglomerates apart, viscosity will be 

reduced. So, increasing polar solvent 

concentration had an essential role on 

increasing and acceleration of breaking 

down the asphaltene agglomerates, and 

thus achieved deeper viscosity 

reduction [19].   

The addition of a polar solvent acted 

on the colloidal structure of the 

asphaltenes and the viscosity 

decreased. The higher the polarity 

parameter or the hydrogen bonding 

parameter of the solvent was, the 

greater the viscosity reduction was 

[20].   

To access the extent of the viscosity 

reduction, the percentage of viscosity 

reduction VR % was introduced and it 

was calculated by Eq. 1[21]. 

 

    
(     )

  
                        …(1) 

 

Where    and    are the reference and 
corresponding viscosities of crude oil 

in cSt at 40°C. Figures 8, 10, 12, and 

14 show the viscosity reduction 

percentage vs. solvent concetration at 

different temperatures for different 

solvents. Figs. 7 and 8 show that 

toluene gave best viscosity reduction at 

110 °C; toluene is a strong solvent that 

owns a high ability to disperse the 

asphaltene agglomerates. 

 

 
Fig. 7: Effect of toluene weight fraction on 

viscosity of crude oil 

 

 
Fig. 8: Effect of toluene weight fraction on 

viscosity reduction percentage of crude oil 

 

If partial solubility or phase separation 

is occurring such as methanol, then a 

lower than expected viscosity 

measurement will be recorded.  This is 

because when phase separation occurs, 

then the more fluid phase, the additive 

compound, may tend to concentrate 

around the spindle of the viscometer, 

and thus lower apparent viscosity [22].             

Solvent wt.%

V
is

c
o
s
it
y
 (

c
S

t
)

21.5

22.5

23.5

24.5

25.5

26.5

27.5

3 5 7 9 11 13

Viscosity at 40 
 o

C

Viscosity at 110 
 o

C

Solvent wt.%

V
is

c
o
s
it
y
 
r
e
d
u
c
t
io

n
 
%

48

50

52

54

56

58

60

3 5 7 9 11 13

Viscosity at 40 
 o

C

Viscosity at 110 
 o

C



Hussein Qasim Hussein and Saja Abdul-wahhab Mohammad 

 

-Available online at: www.iasj.net                      IJCPE Vol.15 No.2 (June 2014)                                 45 
 

Methanol owns high polarity more 

than the other solvent used in this 

study. So the lowest crude oil viscosity 

was achieved by this solvent. The 

effect of methanol concentration on 
viscosity is better at low temperature 

40 °C than at its boiling point or high 

temperature, and this is more 

economical point of work as shown in 

Figure 9. Figure 10 clarify VR% of 

methanol. 
 

 
Fig. 9: Effect of methanol weight fraction on 

viscosity of crude oil 
 

 
Fig. 10: Effect of methanol weight fraction on 

viscosity reduction percentage of crude oil 
 

Xylenes mixture gives good results on 

reducing the viscosity of heavy crude 

oil. Pure isomers of xylenes are  more 

efficient at low temperature, 40 °C, 

than high temperature, 138 °C, as 

shown in Figure 11; Figure 12 clarifies 

VR%. 

Figure 13 shows the effect of using 

reformate to reduce viscosity in crude 

oil at different concetrations and 

different temperature; viscosity of the 

crude at 40 °C is better than  100 °C.  

Figure 14 clarifies VR% of reformate . 
 

Fig. 11: Effect of xylenes weight fraction on 

viscosity of crude oil 
 

 
Fig. 12: Effect of xylenes weight fraction on 

viscosity reduction percentage of crude oil 

 

 
Fig. 13: Effect of reformate weight fraction on 

viscosity of crude oil 

Solvent wt.%

V
is

c
o
s
it
y
 
(
c
S

t
)

21

22

23

24

25

26

27

28

3 5 7 9 11 13

Viscosity at 40 
o
C

Viscosity at 65 
o
C

Solvent wt.%

V
is

c
o
s
it
y
 r

e
d
u
c
ti
o
n
 %

46

48

50

52

54

56

58

60

62

3 5 7 9 11 13

Viscosity at 40 
 o

C

Viscosity at 65 
 o

C

Solvent wt.%

V
is

c
o
s
it
y
 (

c
S

t)
27.4

27.8

28.2

28.6

29.0

29.4

29.8

30.2

3 5 7 9 11 13

Viscosity at 40 
 o 

C

Viscosity at 138 
 o  

C

Solvent wt.%

V
is

c
o
s
it
y
 r

e
d
u
c
ti
o
n
 %

 

42

43

44

45

46

47

3 5 7 9 11 13

Viscosity at 40 
 o 

C

Viscosity at 138 
 o  

C

Solvent wt.%

V
is

c
o
s
it
y
 (

c
S

t)

28

29

30

31

32

33

3 5 7 9 11 13

Viscosity at 40 
 o 

C

Viscosity at 100 
 o  

C



Viscosity Reduction of Sharqi Baghdad Heavy Crude Oil Using Different Polar Hydrocarbons, 

Oxygenated Solvents   

46                                        IJCPE Vol.15 No.2 (June 2014)               -Available online at: www.iasj.net 
 

 
Fig. 14: Effect of reformate weight fraction on 

viscosity reduction percentage of crude oil 

 

API Gravity 

The API of heavy crude oil was 

increased with increasing solvent 

concentration at different temperatures. 

Figures 15, 16, 17 and 18 show the 

effect of solvents concentration on 

improvement of API values at 

difference temperatures. 

It is clear that the breaking down of 

asphaltenes agglomerates and reducing 

presence of micelle-like clusters had an 

essential role in the improvement of 

API for heavy crude oil, where the 

polar solvents played on dispersion of 

asphaltenes molecules, reduction of 

their molecular size, and decreasing of 

asphaltenes content,  which led to the 

increasing of API of heavy crude oil. 

 

 
Fig. 15: Effect of toluene weight fraction on 

API of crude oil 

 
Fig. 16: Effect of methanol weight fraction on 

API of crude oil 

 

 
Fig. 17: Effect of xylenes weight fraction on 

API of crude oil 

 

 
Fig. 18: Effect of reformate weight fraction on 

API of crude oil 

 

 

Solvent wt.%

V
is

c
o
s
it
y
 r

e
d
u
c
ti
o
n
 %

36

37

38

39

40

41

42

43

44

45

3 5 7 9 11 13

Viscosity at 40 
 o 

C

Viscosity at 100 
 o  

C

Solvent wt.%

A
P

I
 
a
t
 
(
6
0
/
6
0
)
 

o
F

19

20

21

22

23

24

25

3 5 7 9 11 13

API at 40 
 o 

C

API at 110 
 o  

C

Solvent wt.%

A
P

I
 
a
t
 
(
6
0
/
6
0
)
 

o
F

20.5

21.5

22.5

23.5

24.5

25.5

26.5

3 5 7 9 11 13

API at 40 
 o 

C

API at 65 
 o  

C

Solvent wt.%

A
P

I 
a
t 

(
6
0
/6

0
)
 

o
F

22.5

23.0

23.5

24.0

24.5

25.0

25.5

26.0

26.5

27.0

3 5 7 9 11 13

API at 40 
 o 

C

API at 138 
 o  

C

Solvent wt.%

A
P

I
 
a
t
 
(
6
0
/
6
0
)
 

o
F

22.0

22.6

23.2

23.8

24.4

25.0

3 5 7 9 11 13

API at 40 
 o 

C

API at 100 
 o  

C



Hussein Qasim Hussein and Saja Abdul-wahhab Mohammad 

 

-Available online at: www.iasj.net                      IJCPE Vol.15 No.2 (June 2014)                                 47 
 

Conclusion 

From rheological and structure 

measurements heavy oils can be 

described as aggregation of 

agglomeration asphaltenes particles; 

heavy viscosities of this type of crudes 

are due to the entanglement of solvated 

asphaltene particles. Some ways that 

will limit the entanglement will likely 

reduce the viscosity. 

According to the results obtained from 

this study, the following conclusions 

are obtained: 
1. Treatment of the heavy crude oil 

with different polar solvents gave 

high reduction in viscosity and 

asphaltene content; methanol owned 

a high efficiency to reduce viscosity 

of crude oil to 21.109 cSt at 40 

°C.Toluene, xylenes and reformate 

decreased viscosity to 25.37, 27.510 

and 28.407 cSt at 40 °C, 

respectively.  

2. API of heavy crude oil improved to 
26.193 at 40 °C by using xylenes, 

toluene, methanol and reformate 

improvement API to 23, 25.374 and 

24.753 at 40 °C, respectively.  

3. Asphaltenes content decreased to 
4.259 wt. % by using toluene at  

110 °C. Methanol, xylenes and 

reformate decreased asphaltene 

content to 5.0392, 5.0381 and 

5.0071 wt. % at 40 °C, respectively.  

4. Crude oil viscosity decreased with 
decreasing asphaltenes content. 

5. Crude oil viscosity was decreased 
with increasing polar solvent 

concentration. 
 

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Viscosity Reduction of Sharqi Baghdad Heavy Crude Oil Using Different Polar Hydrocarbons, 

Oxygenated Solvents   

48                                        IJCPE Vol.15 No.2 (June 2014)               -Available online at: www.iasj.net 
 

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