Vol.9 No.3 (September 2008) 

 

 
Iraqi Journal of Chemical and Petroleum Engineering 

 Vol.9 No.3 (September 2008) 51-57 
ISSN: 1997-4884 

 

Viscosity Index Improvement of Lubricating Oil Fraction (SAE – 30)  

Abdul-Halim Abdul-Karim Mohammed
*
and Amal Khalid Shehab Al – Rubai  

*
Chemical Engineering Department - College of Engineering - University of Baghdad – Iraq 

 

Abstract 

An investigation was conducted for the improvement of viscosity index of a lubricating oil fraction (SAE – 30) 

obtained from vacuum distillation unit of lube oil plant of Daura Refinery, using solvent extraction process. In this study 

two type of extraction solvents were used to extract the undesirable materials which reduce the viscosity index of raw 

lubricating oil fraction, the first solvent was furfural which is un use today in the Iraqi refineries and the second was 

NMP (N-methyl, 2, pyrrolidone) which is used for the first time in this work to extract the lubricating oil fraction 

produced from Iraqi crude oils. The studied effecting variables of extraction are extraction temperature range from 70 

to 110 oC for furfural and NMP extraction, solvent to oil ratio range from 1:1 to 5:1 (wt/wt) for furfural extraction and 

from 0.5:1 to 2:1 (wt/wt) for NMP extraction. The results of this investigation show that the viscosity index of 

lubricating oil fraction increases with increasing extraction temperature and increasing the solvent to oil ratio and 

reaches 83 for NMP extraction at extraction temperature 110 oC and solvent to oil ratio 2:1, while the viscosity index 

reaches to 80 for furfural extraction at the same extraction temperature and solvent  oil ratio. Higher viscosity index of 

lubricating oil fraction is obtained by using NMP instead of furfural under the same operating variables (extraction 

temperature and solvent to oil ratio). Further more, the results show that the viscosity, refractive index, and percentage 

yield of raffinate decreased as the extraction temperature or solvent to oil ratio increases for furfural and NMP 

extraction. 

                                                                                                                               

 

 

Introduction 

With the increasing demands for high quality lubricating 

oils to withstand the severe operating conditions of the 

modern gasoline and diesel engines, it become apparent 

that the selected crudes were no longer sufficient in either 

quantity or quality to supply the demand. Therefore, it 

was obvious that the petroleum industry would have to 

resort to some means for separation of the desirable and 

undesirable component of lubricating oil stocks. Other 

than the heavy asphaltic materials and the normally solid 

paraffin waxes, which be removed by precipitation or by 

filtration at reduced temperatures, the undesirable 

components comprise those aromatic type hydrocarbons 

which possess low oiliness, low viscosity index, poor 

oxidation stability, high carbon residue, and poor color 

[1]. Solvent treating is the most widely used method of 

refining lubricating oils. These processes yield products 

that meet the requirements of a modern lubricant by 

removing from the charge material those undesirable 

constituents. The solvent – treated lubricating oils have 

higher viscosity indexes, greater resistance to gum and 

sludge formation by oxidation, and increased 

susceptibility to further improvement by addition of 

selective additives [2]. Although no solvent meets all of 

the requirements of the ideal extraction solvents have 

been proposed and used commercially. The major 

solvents in use today are N – methyl – 2 – pyrrolidone 

and furfural, with phenol and liquid sulfur dioxide being 

used to a lesser extent [3]. The present work deals with 

viscosity index improvement of lubricating oil fraction 

SAE – 30 obtained from vacuum distillation unit of lube 

oil plant of Daura Refinery, by extremely selective 

solvent extraction process using furfural and N – methyl 

– 2 – pyrrolidone solvents. This work includes the study 

of the effects of extraction temperature and solvent to oil 

University of Baghdad 

College of Engineering 
Iraqi Journal of Chemical 

and Petroleum Engineering 

 



 Viscosity Index Improvement of Lubricating Oil Fraction (SAE – 30) 

52 
Vol.9 No.3 (September 2008) 

ratio on the physical properties and the percentage yield 

of the produced lubricating oil.  

Experimental Work 

Feed Stock 
A distillate lube oil fraction (SAE – 30 distillate) 

obtained from vacuum distillation unit of lube oil plant of 

Daura Refinery was used in this work. Atmospheric 

residue produced from mixed Iraqi crude oil (60 % of 

Basrah crude, 30 % of Kirkuk crude, and 10 % of Sharki 

– Baghdad crude) was the feed stock for vacuum 

distillation unit. Table (1) shows the  properties of the 

lube oil fraction.  

Table 1 Properties of lube oil fraction 

No. Specification 
Lube Oil 

Fraction 

1 Specific Gravity @ 60/60 
o
F 0.91705 

2 Viscosity, Cst, @ 40 
o
C 118.00 

3 Viscosity, Cst, @ 100 
o
C 9.39 

4 Viscosity Index 26 

5 COC Flash Point, 
o
C 242 

6 Pour Point, 
o
C 25 

7 Color ASTM – D 1500, @ 50 
o
C 5.5 

8 Sulfur Content, % wt. 3.073 

Solvents 

Two solvents were used in this work. These solvents are 

furfural (Liaosin private limited company, China) and 

NMP (Fluka chemicals AG, Germany). Table (2) shows 

the measured properties of these solvent. 

Table 2 Properties of furfural and NMP 

No. Specification Furfural NMP 

1 
Density (

25

4
d ), g/cm3 

1.1563 1.0270 

2 Boiling Point, 
o
C 161 202 

3 
Refractive Index (

25

D
n )  

1.5235 1.4690 

4 COC Flash Point, 
o
C 68 95 

5 Freezing Point, 
o
C  -36.5 -24 

6 Viscosity, cps, @ 25 
o
C 1.49 1.65 

 

Extraction Experiments 

Figure (1) shows the schematic diagram of the 

laboratory batch extraction unit. This unit consists of a 

bench scale jacketed glass column extraction apparatus 

with 50 mm ID, 700 mm length, 80 mm jacket ID and 2 

mm wall thickness. The jacketed extractor was heated 

and controlled by circulating hot oil through the jacket. 

The solvent was stripped from the raffinate using 

distillation with nitrogen. 

 

 

 

 

 

 

 

 

 

 

 

 

Fig.1: The schematic diagram of the laboratory 

batch extraction unit 

Figure (1) shows the schematic diagram of the laboratory 

batch extraction unit. This unit consists of a bench scale 

jacketed glass column extraction apparatus with 50 mm 

ID, 700 mm length, 80 mm jacket ID and 2 mm wall 

thickness. The jacketed extractor was heated and 

controlled by circulating hot oil through the jacket. The 

solvent was stripped from the raffinate using distillation 

with nitrogen. 

 

Extraction Experiments Conditions 

In the present work, the experiments that applied on the 

extraction of lube oil distilled fraction were classified in 

to two categories. The first one was applied on furfural as 

extraction solvent. The operating conditions are 

extraction temperature range from 70 to 110 oC, solvent 

Mixer 

Heating 

Bath 

Circular Pump 

• 



 Abdul-Halim Abdul-Karim Mohammed*and Amal Khalid Shehab Al – Rubai 

 

53 
Vol.9 No.3 (September 2008) 

to oil ratio from 1:1 to 5:1 (wt. / wt.), and using 

atmospheric pressure. The second set of experiments 

applied on NMP as the extraction solvent. The extraction 

temperature was the same as for the first set but the 

solvent to oil ratio were reduced to 0.5:1 to 2:1 because 

of the higher solvent power of NMP than furfural [4]. 

 

Test Methods 

1 - Viscosity 

The viscosity of feed stock, and raffinate were 

determined by capillary U-tube viscometer according to 

ASTM D-445 [5].  

2 - Viscosity Index 

The raffinate viscosity index was determined by 

measuring the raffinate refractive index and from the data 

relating the refractive index to viscosity index  tabulated 

in Table (3) (6), The refractive index was determined 

according to ASTM  D-1747 [5].  

The feed stock has a color greater than No. 4 according to 

ASTM color – D1500, therefore the viscosity index can 

not be determined by measuring the refractive index. 

Also the viscosity at 40 oC of waxy feed can not be 

measured, therefore The viscosity of the feed stock was 

measured at 80 and 100 oC to obtain the viscosity at 40 

oC using the viscosity – temperature charts of liquid 

petroleum products according to ASTM – D341 (5).. The 

viscosity index of the feed stock fraction was calculated 

according to ASTM – D2270 (5) by applying the 

procedure for oils of zero to 100 VI. In this procedure 

Equation (1) was used. 

 

100
HL

UL
VI 






                                               (1) 

 

Where 

U :kinematic viscosity at 40 °C of the oil whose viscosity 

index to be calculated (cst). 

L : kinematic viscosity at 40°C of an oil of zero viscosity 

index having the same kinematic viscosity at 100°C as 

the oil whose viscosity index is to be calculated (cst). 

H :kinematic viscosity at 40 °C of an oil of 100 viscosity 

index having the same kinematic viscosity at 100 °C 

as the oil whose viscosity index is to be calculated 

(cst). 

 

 

 

Table 3 Raffinate refractive index and viscosity index [6] 

RI VI RI VI 

1.4560 103 1.4690 86 

1.4565 102 1.4700 85 

1.4570 101 1.4708 84 

1.4575 100 1.4715 83 

1.4580 99 1.4720 82 

1.4590 98 1.4730 81 

1.44600 97 1.4740 80 

1.4610 96 1.4745 79 

1.4625 94 1.4765 77 

1.4630 93 1.4770 76 

1.4640 92 1.4780 75 

1.4650 91 1.4790 74 

1.4655 90 1.4795 73 

1.4665 89 1.4805 72 

1.4675 88 1.4815 71 

1.468 87 1.4820 70 

 

Results and Discussion 

Effect of Operating Variables and Solvent Type on 

Raffinate Viscosity 

The viscosity of lubricating oil fraction is a very 

important factor in the manufacturing of lubricating oils, 

and the correct operation of the equipment depends upon 

the appropriate viscosity of the lubricating oil being used. 

  

 

In the present work the effect of extraction temperature 

and solvent to oil ratio on raffinate kinematic viscosity at 

100 oC were studied.  

 Figures (2 and 3) show the effect of extraction 

temperature on raffinate viscosity for furfural and NMP 

extraction respectively, while Figures (4 and 5) show the 

effect of solvent to oil ratio on raffinate viscosity for 

furfural and.  

 In general, the viscosity of raffinate produced 

from furfural or NMP extraction decreased with 

increasing the extraction temperature or increasing the 

solvent to oil ratio and that is due to the extraction of 

aromatic materials especially polycondensed aromatics 

from the raw lubricating oil fraction.  

 The aromatics have the higher viscosity among 

the hydrocarbons that presented in raw lubricating oils 

and the extraction of these materials decrease its content 

in the produced raffinate and increase the paraffins 

content which have a viscosity relatively lower than that 

of aromatics as mentioned by Kosters [7]. 



 Viscosity Index Improvement of Lubricating Oil Fraction (SAE – 30) 

54 
Vol.9 No.3 (September 2008) 

 Figures (2 and 3), clearly indicate that the 

extraction temperature slightly affect the viscosity of 

raffinate produced from furfural and NMP extraction for 

a given solvent to oil ratio. Figures (4 and 5) show that 

the increase in solvent to ratio for a given extraction 

temperature have higher effect in decreasing the raffinate 

viscosity obtained by furfural and NMP extraction. The 

viscosity of the raffinate produced from NMP extraction 

is slightly lower than that produced from furfural 

extraction using the same operating variables, because of 

the higher activity and high solvent power of NMP than 

furfural [4].  
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig.2: Effect of extraction temperature on raffinate 

viscosity at different solvent to oil ratio for furfural 

extraction 
 

 

 

Figure (4) Effect of solvent to oil ratio on raffinate 

viscosity at various extraction temperature for furfural 

extraction 
 

 

 

 

 

 

Fig.4: Effect of solvent to oil ratio on raffinate viscosity 

at various extraction temperature for furfural extraction 

 

Fig.5: Effect of solvent to oil ratio on raffinate viscosity 

at various extraction temperature for NMP extraction 
 

 

Effect of Operating Variables and Solvent Type on 

Raffinate Viscosity Index  
 

The viscosity index of lubricating oil reflects the ability 

of lube oil viscosity to vary with temperature. 

 Figures (6 and 7) show the effect of extraction 

temperature on raffinate viscosity index for furfural and 

NMP extraction respectively at various solvent to oil 

ratio.  

 Figures (8 and 9) show the effect of solvent to 

oil ratio on raffinate viscosity index for furfural and NMP 

extraction respectively at various extraction temperature.  

 The increase in extraction temperature will 

encourage the solubility of undesirable materials 

especially polycondensed aromatics (which reduce the 

viscosity index of lubricating oil) in extraction solvent. It 

is obvious from Figures (6 and 7) that the viscosity index 

of lubricating oil fraction increase with increasing the 

extraction temperature. The increase of extraction 

temperature 10 oC will increase the viscosity index one 

Temperature ,         o C

Visc
osity

 , cst
.

8.2

8.4

8.6

8.8

9.0

9.2

9.4

65 75 85 95 105 115

  1:1  
  2:1  
  3:1  
  4:1  
  5:1  

Temperature ,          o C

 Visc
osity

 , cst
.

7.8

8.2

8.6

9.0

9.4

9.8

65 75 85 95 105 115

0.50:1  
0.72:1   
1.25:1  
1.78:1  
2.00:1  

Solvent to Oil Ratio , wt/wt

Visc
osity

 , cs
t.

8.2

8.4

8.6

8.8

9.0

9.2

9.4

1:1 2:1 3:1 4:1 5:1

70 
o
 C

80 
o
 C

90 
o
 C

100  
o
 C

110  
o
 C

Solvent to Oil Ratio ,wt/wt

 Visc
osity

 ,cst.

7.8

8.2

8.6

9.0

9.4

9.8

0.5:1 0.72:1 1.25:1 1.78:1 2.0:1

70  
o
 C

76  
o
 C

90  
o
 C

104   
o
 C

110   
o
 C



 Abdul-Halim Abdul-Karim Mohammed*and Amal Khalid Shehab Al – Rubai 

 

55 
Vol.9 No.3 (September 2008) 

point for a given solvent to oil ratio using furfural and 

NMP as extraction solvents. 

 Figures (8 and 9) indicate that the increasement 

in solvent to oil ratio has a high effect on increasing the 

viscosity index of lubricating oil fraction compared with 

extraction temperature in furfural and NMP extraction. In 

case of using furfural as extraction solvent, the significant 

solvent to oil ratio is higher than 1:1 because of the 

constancy of the viscosity index on a fixed value using 

different extraction temperatures and that is due to the 

saturation of this amount of furfural with undesirable 

materials. 

 The increase in raffinate viscosity index related 

to the reduction in naphthene – aromatic and polar 

aromatic content and the increase in saturates content in 

the produced raffinate.  

 The higher solvent power of NMP compared 

with furfural gave higher viscosity index using the same 

operating variables. These results are in agreement with 

those obtained by Sequeira and Sherman (4) which 

approved that the solvent power is better (solvent to oil 

ratio is lower) for NMP than for furfural.  

Fig.6:  Effect of extraction temperature on raffinate 

viscosity index at various solvent to oil ratio for furfural 

extraction 

 

Fig.7: Effect of extraction temperature on raffinate viscosity 

index at various solvent to oil ratio for NMP extraction 
 

Fig .8: Effect of solvent to oil ratio on raffinate viscosity 

index at various extraction temperatures for furfural 

extraction 
 

Fig .9: Effect of solvent to oil ratio on raffinate viscosity 

index at various extraction temperatures for NMP 

extraction 

 
 

 

Effect of Operating Variables and Solvent Type on 

Raffinate Yield 
 

 

Many factors controlling the convential operating 

conditions of solvent extraction. One of these important 

factors affecting the overall process performance is the 

lubricating oil yield.    

 Figures (10 and 11) show the effect of extraction 

temperature on raffinate yield at various solvent to oil 

ratio for furfural and NMP extraction. It appears from 

these figures that the yield percentage decreases as the 

extraction temperature increased but that effect is some 

what little in comparison with the effect of solvent to oil 

ratio.  

 Figures (12 and 13) show the effect of 

increasing solvent to oil ratio on decreasing the raffinate 

yield percentage at various extraction temperatures for 

furfural and NMP extraction respectively. 
 

Temperature,       o C

 Vis
cosi

ty In
dex

68

72

76

80

84

88

92

65 75 85 95 105 115

 1:1
 2:1
 3:1
 4:1
 5:1

Temperature ,        o C

 Visc
osity

 Inde
x

50

56

62

68

74

80

86

65 75 85 95 105 115

0.50:1 
0.72:1 
1.25:1 
1.78:1 
2.00:1 

Solvent to Oil Ratio ,wt/wt

 Vis
cosi

ty In
dex

68

72

76

80

84

88

92

1:1 2:1 3:1 4:1 5:1

70 
o
 C

80 
o
 C

90 
o
 C

100 
o
 C

110 
o
 C

Solvent to Oil Ratio ,wt/wt

Visco
sity I

ndex

50

56

62

68

74

80

86

0.5:1 0.72:1 1.25:1 1.78:1 2.0:1

70  
o
 C

76  
o
 C

90  
o
 C

104   
o
 C

110   
o
 C

Temperature,        o C

Yiel
d ,%

wt

52

56

60

64

68

72

76

80

84

65 75 85 95 105 115

1:1 
2:1 
3:1 
4:1 
5:1 

Solvent to Oil Ratio ,wt/wt

Yield
,%wt

66

70

74

78

82

86

90

0.50:1 0.72:1 1.25:1 1.78:1 2.00:1

70  
o
 C

76  
o 
C

90  
o 
C

104   
o
 C

110   
o
 C



 Viscosity Index Improvement of Lubricating Oil Fraction (SAE – 30) 

56 
Vol.9 No.3 (September 2008) 

Solvent to Oil Ratio , wt/wt

 Yiel
d , %

wt

52

56

60

64

68

72

76

80

84

1:1 2:1 3:1 4:1 5:1

70 
o
C

80 
o
C

90 
o
C

100 
o
C

110 
o
C

Solvent to Oil Ratio,wt/wt

Visco
sity I

ndex

68

70

72

74

76

78

80

82

1.00:1 1.25:1 1.75:1 2.00:1

NMP 
FURF 

Figure (10) Effect of extraction temperature on raffinate 

yield at various solvent to oil ratio for furfural extraction 
 

 

 

Figure (11) Effect of extraction temperature on raffinate 

yield at various solvent to oil ratio for NMP extraction 
 

 

 

 

Figure (12) Effect of solvent to oil ratio on raffinate yield 

at various extraction temperatures for furfural extraction 
 

 

 

Figure (13) Effect of solvent to oil ratio on raffinate yield 

at various extraction temperatures for NMP extraction 

 

Comparison of Furfural and NMP Extraction 

For the purpose of selecting the most efficient solvent for 

the extraction of undesirable materials presented in raw 

lubricating oil fraction used in this study, a comparison 

between the viscosity index and percentage yield of 

raffinates produced from furfural and NMP extraction 

process were included in this investigation.  

 The comparison was taken place at extraction 

temperature of 90 oC and solvent to oil ratio in the range 

1:1 to 2:1 for furfural and NMP extraction. 

 Figure (14) show the effect of increasing the 

solvent to oil ratio on raffinate viscosity index for furfural 

and NMP extraction at 90 oC, while Figure (15) shows 

the effect of increasing solvent to oil ratio on raffinate 

yield for furfural and NMP extraction at 90 oC.  

 Figure (14) indicates that the raffinate viscosity 

index produced from furfural extraction is slightly higher 

than that produced from NMP extraction in solvent to oil 

ratio lower than 1.5:1, above this ratio the viscosity index 

of NMP becomes higher than that of furfural extraction 

and reaches 80 for NMP raffinate and 77 for furfural 

raffinate at 2:1 solvent to oil ratio. 

 Figure (15) show that the raffinate yield 

produced from furfural extraction is higher than that 

produced from NMP extraction but at solvent to oil ratio 

2:1 an equivalent yield was obtained from furfural and 

NMP extraction. 

 If the extraction temperature increase to 110 oC, 

the raffinate yield for NMP extraction becomes higher 

than that for furfural extraction at solvent to oil ratio 

above 1.5:1 and the raffinate viscosity index reaches to 

83 for NMP extraction and 80 for furfural extraction at 

2:1 solvent to oil ratio. 

 From the above mentioned discussion it may be 

concluded that NMP was the most efficient solvent for 

the extraction of lubricating oil fraction used in this study 

because of the following: 

Low solvent to oil ratio can be used to produce the same 

raffinate viscosity index. 

An equivalent or higher raffinate yield obtained from 

NMP extraction at solvent to oil ratio higher than 2.0:1.0. 

Low solvent toxicity. 

Better heat stability because of high boiling point. 

 

Figure (14) Effect of solvent to oil ratio on raffinate 

viscosity index for furfural and NMP extraction at 90 oC 

Temperature,          o C

Yield
,%wt

66

70

74

78

82

86

90

65 75 85 95 105 115

0.50:1 
0.72:1 
1.25:1 
1.78:1 
2.00:1 



 Abdul-Halim Abdul-Karim Mohammed*and Amal Khalid Shehab Al – Rubai 

 

57 
Vol.9 No.3 (September 2008) 

 

Figure (15) Effect of solvent to oil ratio on raffinate yield 

for furfural and NMP extraction at 90 oC 

 

CONCLUSIONS 

1. the viscosity index of lubricating oil fraction 
increases from 26 to 71 as a minimum for furfural 

extraction at 70 oC and 1:1 solvent to oil ratio 

and reaches 90 as a maximum at 110 oC and 5:1 

solvent to oil ratio. 

2. the viscosity index of lubricating oil fraction 
increases to 54 as a minimum for NMP extraction 

at 70 oC and 0.5:1 solvent to oil ratio and reaches 

83 as a maximum at 110 oC and 2:1 solvent to oil 

ratio.  

3. The raffinate viscosity index produced from NMP 
extraction was higher than that produced from 

furfural extraction at the solvent to oil ratio 

higher than 1.5:1 and reaches 83 and 80 for NMP 

and furfural extraction respectively at 2:1 solvent 

to oil ratio and 110 oC extraction temperature, 

while the raffinate yield is 68.69 % wt. and 65.66 

% wt. for NMP and furfural extraction 

respectively using the same operating variables. 

A compromise should be performed between the 

desired viscosity index and lubricating oil yield.  

4. The solvent to oil ratio has the higher influence 
on increasing the raffinate viscosity index and 

decreasing yield, viscosity, and refractive index 

for furfural and NMP extraction than extraction 

temperature. 

 

REFERENCE 

1. Kemp, L. C. et al., Industrial and Engineering 
Chemistry, Vol. 40, No. 2, p.p. 65 – 73, 1948. 

2 Bland and Davidson, Petroleum Processing Hand 
Book, Mc Graw Hill, New York, 1967.  

3 Mc Ketta, Encyclopedia of Chemical Processing 
and Design, Vol. 28, Marcel Dekker, Inc., New 

York, 1988. 

4 Sequeira, A., Sherman, P. B., J. V., and Mc 
Bride, E. O., Hydrocarbon Processing, Vol. 58, 

No. 9, p.p. 155 – 160, 1979. 

5 Annual book of ASTM Standards, Vol. 05.01, 
1994. 

6 Daura Refinery, Internal report, 1972.  
7 Kosters, W. C. G., Chemistry and Industry, Vol. 

15, No. 2, p.p. 220 – 223, 1977. 

 

 

 

 

 

 

 

 

 

 

 

 

Solvent to Oil Ratio,wt/wt

Yield
,%wt

68

70

72

74

76

78

80

82

84

1.00:1 1.25:1 1.75:1 2.00:1

NMP 
FURF