Base Oil

base-oils
base-oil-group-1-500x500

Base Oil is the name given to lubrication grade oils initially produced from refining crude oil (mineral base oil) or through chemical synthesis (synthetic base oil). Base oil is typically defined as oil with a boiling point range between 550 and 1050 F, consisting of hydrocarbons with 18 to 40 carbon atoms. This oil can be either paraffinic or napthenic in nature depending on the chemical structure of the molecules.

Almost every lubricant used in plants today started off as just a base oil. The American Petroleum Institute (API) has categorized base oils into five categories (API 1509, Appendix E). The first three groups are refined from petroleum crude oil. Group IV base oils are full synthetic (polyalphaolefin) oils. Group V is for all other base oils not included in Groups I through IV. Before all the additives are added to the mixture, lubricating oils begin as one or more of these five API groups.

Group I base oils are classified as less than 90 percent saturates, greater than 0.03 percent sulfur and with a viscosity-index range of 80 to 120. The temperature range for these oils is from 32 to 150 degrees F. Group I base oils are solvent-refined, which is a simpler refining process. This is why they are the cheapest base oils on the market.

Group II base oils are defined as being more than 90 percent saturates, less than 0.03 percent sulfur and with a viscosity index of 80 to 120. They are often manufactured by hydrocracking, which is a more complex process than what is used for Group I base oils. Since all the hydrocarbon molecules of these oils are saturated, Group II base oils have better antioxidation properties. They also have a clearer color and cost more in comparison to Group I base oils. Still, Group II base oils are becoming very common on the market today and are priced very close to Group I oils.

Group III base oils are greater than 90 percent saturates, less than 0.03 percent sulfur and have a viscosity index above 120. These oils are refined even more than Group II base oils and generally are severely hydrocracked (higher pressure and heat). This longer process is designed to achieve a purer base oil. Although made from crude oil, Group III base oils are sometimes described as synthesized hydrocarbons. Like Group II base oils, these oils are also becoming more prevalent.

Group IV base oils are polyalphaolefins (PAOs). These synthetic base oils are made through a process called synthesizing. They have a much broader temperature range and are great for use in extreme cold conditions and high heat applications.

Group V base oils are classified as all other base oils, including silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes, etc. These base oils are at times mixed with other base stocks to enhance the oil’s properties. An example would be a PAO-based compressor oil that is mixed with a polyolester. Esters are common Group V base oils used in different lubricant formulations to improve the properties of the existing base oil. Ester oils can take more abuse at higher temperatures and will provide superior detergency compared to a PAO synthetic base oil, which in turn increases the hours of use.


Typical Properties of Each Base Oil Group

 
  GroupⅠ GroupⅡ GroupⅢ Ultra-S 4,6,8 GroupⅣ
Saturates, % 65~85 93~99+ 95~99+ 99+ 99+
Aromatics, % 15~35 <1~7 <1~5 <1 <1
Sulfur, ppm 300~3000 5~300 0~30 <1 n/a
Viscosity @ 100℃, cSt 4~32 4~30 4~8 4.0~7.6 4~70
Viscosity Index(VI) 95~105 95~118 123~150 120~135 125~150
Pour point, ℃ -15 -15 -15 -22.5 ~ -15 -45

Base stocks are classified inot various grades including Neutral, Solvent Neutral, Bright Stocks, The most common names are for group I (SN: Solvent Neutral), for group II (N: Neutrals) and group III grade names refer to the viscosity (4cst, 6cst, 8cst …).


Group I – Baseoil Grades – Technical Specifications

 
Characteristic
Units
SN-150
SN-500
Bright Stock
Test Method
Kinematic viscosity at 100°C
cSt
4.4 – 5.6
9.7 – 12.0
min. 28
ASTM  D-445
Kinematic viscosity at 40°C
cSt
28 – 32
90 – 105
–
ASTM D-445
Viscosity index (VI)
–
95 – 100
95 – 100
min. 95
ASTM D-2270
Flash Point
°C
min. 195
min. 210
min. 276
ASTM D-92
Sulphur Content
%Wt
0.15 – 0.60
0.15 – 0.60
0.15 – 0.60
ASTM D-2622
Pour Point
°C
max. -6
max. -6
max. -9
ASTM D-97
Density @ 15°C
Kg/L
0.870 – 0.890
0.885 – 0.895
0.900 – 0.910
ASTM D-1298
Color
–
max. 2
max. 2
max. 2
ASTM D-1500
TAN
mg KOH/g
max. 0.05
max. 0.05
max. 0.05
ASTM D-664
Carbon Residue Content
%Wt
0.04
0.12
0.21
ASTM D-189


Group II – Baseoil Grades – Technical Specifications

 
Characteristic
Units
N-150
N-500
Test Method
Kinematic viscosity at 100°C
cSt
5.0-5.6
10.0-12.0
ASTM  D-445
Kinematic viscosity at 40°C
cSt
28-32
95-107
ASTM D-445
Viscosity index (VI)
–
95-110
95-110
ASTM D-2270
Flash Point
°C
min. 210
min. 230
ASTM D-92
Sulphur Content
%Wt
max. 0.012
max. 0.012
ASTM D-2622
Pour Point
°C
max. -12
max. -12
ASTM D-97


Group III – Baseoil Grades – Technical Specifications

 
Characteristic
Units
4cSt
6cSt
8cSt
Test Method
Kinematic viscosity at 100°C
cSt
4.1 – 4.4
5.7 – 6.5
7.6 – 8.2
ASTM  D-445
Kinematic viscosity at 40°C
cSt
19.0 – 20.0
32.0 – 37.0
43.8 – 50.1
ASTM D-445
Viscosity index (VI)
–
min. 120
min. 120
min. 120
ASTM D-2270
Flash Point
°C
min. 220
min. 220
min. 220
ASTM D-92
Sulphur Content
%Wt
0.001
0.001
0.001
ASTM D-2622
Pour Point
°C
max. -12
max. -12
max. -12
ASTM D-97