About Base Oils
Base Oils are not fuels but are blendstocks which are used in making various lubricating oils which can be used in different engines and machinery. They are produced by extracting and treating high-viscosity material from narrow distillation cuts of vacuum gasoil or vacuum residues. This requires special processing through a number of different units comprising the lubes plant. Base oils are used to make products including lubricating greases, motor oil and metal processing fluids which require different compositions and properties in the oil basis the products. Liquid’s viscosity at various temperatures also plays an important part in this process.
Base oil is produced by refining crude oil i.e crude oil is heated to separate various distillates from one another. During the heating process, light and heavy hydrocarbons are separated. The lighter ones are used to produce petrol and other fuels and the heavier ones are used to make bitumen and base oils.
Many types of crude oils globally are used to produce base oils but the most common is a type of paraffinic crude oil, although naphthenic crude oils also create products with good properties at low temperatures. Extremely pure base oils can be obtained by using hydrogenation technology.
Additives are added to base oil to meet quality requirements for end products as per their specifications.
Sources of Base Oils
Base Oil Sources can be categorized as Mineral Oil, Synthetic Oil and Vegetable Oil.
Base Oil Characteristics
Base Oil Groups
The American Petroleum Institute (API) has categorized base oils into five main groups in 1993 based on the refining method and base oil’s properties mainly in terms of viscosity and the proportion of saturates and sulfur content. The first 3 groups are grouped for mineral oils and the 2 remaining groups contain synthetic oils predominantly.
Group I is the least refined type of Base Oil which is produced by Solvent Refining consisting of conventional petroleum base oils. API defines group I as “base stocks contain less than 90 percent saturates and/or greater than 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120”.
Group II is a better grade of petroleum base oil partially produced by Hydrocracking. All impurities will be removed from the oil leading to clearer color. API defines group II as “base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 80 and less than 120”.
Group III is the best grade of petroleum base oil, since they are fully produced by Hydrocracking, Hydroisomerization, and Hydrotreating, which make these oils purer.API defines group III as “base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur and have a viscosity index greater than or equal to 120”.This group may be described as Synthetic Technology oils or Hydro-Cracked Synthetic oil. However, some oil companies may call their products under this group as synthetic oil.
Group III consists of synthetic oils made of Poly-alpha-olefins (PAO) with a viscosity index range of 125 – 200. Poly-alpha-olefins (PAO) oils have a higher oxidative stability in extreme temperatures, and also have exceptionally low pour points, which makes them much more suitable for use in very cold weather (as found in northern Europe), as well as in very hot weather (as in Middle East).
Group V is any type of base oil other than mentioned in the previously defined groups. They include, among others, naphthenic oils and polyesters.