Base oils are used to manufacture products including lubricating greases, motor oil and metal processing fluids. Different products require different compositions and properties in the oil. One of the most important factors is the liquid’s viscosity at various temperatures. Whether or not a crude oil is suitable to be made into a base oil is determined by the concentration of base oil molecules as well as how easily these can be extracted.
Base oil is produced by means of refining crude oil. This means that crude oil is heated in order that various distillates can be separated from one another. During the heating process, light and heavy hydrocarbons are separated – the light ones can be refined to make petrol and other fuels, while the heavier ones are suitable for bitumen and base oils.
There are large numbers of crude oils all around the world that are used to produce base oils. The most common one is a type of paraffinic crude oil, although there are also naphthenic crude oils that create products with better solubility and very good properties at low temperatures. By using hydrogenation technology, in which sulfur and aromatics are removed using hydrogen under high pressure, extremely pure base oils can be obtained, which are suitable when quality requirements are particularly stringent.
Chemical substances – additives – are added to the base oil in order to meet the quality requirements for the end products in terms of, for example, friction and cleaning properties. Certain types of motor oils contain more than twenty percent additives.
In 1993, the American Petroleum Institute (API), categorized base oils into five main groups. This breakdown is based on the refining method and the base oil’s properties in terms of, among other things, viscosity and the proportion of saturates and sulfur content.
Originating in the 1930s, the least refined type which is produced by Solvent Refining. It usually consists of conventional petroleum base oils. An improvement to the refining process in the 1960s called hydro-treating made this base oil more stable, less reactive, and longer lasting than the earlier base oils.
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".
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).
Originating in the 1940s, any type of base oil other than mentioned in the previously defined groups.
Originating in the 1990s, a more refined grade of petroleum Group III base oil, produced by Hydrotreating. Group II+ base oils have a high viscosity index at the higher end of the API Group II range. The viscosity index is 110-115 minimum.
Originating in 2015, produced by a gas to liquids (GTL) process. Group III+ base oils have a Very High Viscosity Index (VHVI) at the higher end of the API Group III range. The viscosity index is 130-140 minimum.
Consists of synthetic oils made of Poly-internal-olefins (PIO).
- EUR-LEX: http://eur-lex.europa.eu/legal-content/SV/TXT/?uri=CELEX:32004D0284
- QRP OIL: http://www.qrpoil.com/site/?baseoilsn500 Archived 2016-03-04 at the Wayback Machine
- http://www.api.org/~/media/files/certification/engine-oil-diesel/publications/anne-rev-03-25-15.pdf[bare URL PDF]
- https://www.bobistheoilguy.com A Review of Mineral and Synthetic Base Oils
- "Understanding the Differences in Base Oil Groups". Archived from the original on 2016-07-02. Retrieved 2016-05-31.
- API 1509, Appendix EQRP OIL: http://www.qrpoil.com/site/?baseoilsn500 Archived 2016-03-04 at the Wayback Machine
- https://patents.google.com/patent/US20140113847 High viscosity index lubricating oil base stock and viscosity modifier combinations, and lubricating oils derived therefrom