Base oils are used to manufacture products including lubricating greases,

motor oil Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, deterg ...

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 The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

at various temperatures. Whether or not a

crude oil Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

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 {{Unreferenced, date=December 2009 Refining (also perhaps called by the mathematical term affining) is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, b ...

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 Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...

technology, in which

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

and

aromatics Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...

are removed using

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

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.

Official classifications

In 1993, the

American Petroleum Institute The American Petroleum Institute (API) is the largest U.S. trade association for the oil and natural gas industry. It claims to represent nearly 600 corporations involved in production, refinement, distribution, and many other aspects of the pet ...

(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.

Group I

Originating in the 1930s, the least refined type which is produced by Solvent Refining. It usually consists of conventional

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

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 I as "base stocks contain less than 90 percent saturates and/or greater than 0.03 percent

and have a

viscosity index The viscosity index (VI) is an arbitrary, unit-less measure of a fluid's change in viscosity relative to temperature change. It is mostly used to characterize the viscosity-temperature behavior of lubricating oils. The lower the VI, the more the v ...

greater than or equal to 80 and less than 120".

Group II

Originating in 1971, a better grade of

base oil, which may be partially produced by

Hydrocracking In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of ...

. 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

and have a

greater than or equal to 80 and less than 120".

Group III

Originating in 1993, the best grade of

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

and have a

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 Synthetic oil is a lubricant consisting of chemical compounds that are artificially modified or synthesised. Synthetic lubricants can be manufactured using chemically modified petroleum components rather than whole crude oil, but can also be syn ...

Group IV

Originating in 1974, consists of

s made of Poly-alpha-olefins (PAO). Group IV base oils have a

range of 125 - 200. Poly-alpha-olefins (PAO) oils have a higher oxidative stability in extreme temperatures, and also have exceptionally low

pour point The pour point of a liquid is the temperature below which the liquid loses its flow characteristics. It is defined as the minimum temperature in which the oil has the ability to pour down from a beaker. In crude oil a high pour point is generall ...

s, which makes them much more suitable for use in very cold weather (as found in northern

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

), as well as in very hot weather (as in

Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabian Peninsula, Arabia (including the Arabian Peninsula and Bahrain), Anatolia, Asia Minor (Asian part of Turkey except Hatay Pro ...

Group V

Originating in the 1940s, any type of base oil other than mentioned in the previously defined groups. They include, among others,

naphthenic oil Crude oil is extracted from the bedrock before being processed in several stages, removing natural contaminants and undesirable hydrocarbons. This separation process produces mineral oil, which can in turn be denoted as paraffinic, naphthenic or aro ...

s and

polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...

Unofficial Classifications

Unofficial base oil classifications are not recognized by the American Petroleum Institute (API), however, they are widely used and marketed for

s and

automatic transmission fluid Automatic transmission fluid (ATF) is a type of hydraulic fluid used in vehicles with automatic transmissions. It is typically coloured red or green to distinguish it from motor oil and other fluids in the vehicle. The fluid is optimized for t ...

Group II+

Originating in the 1990s, a more refined grade of

Group III base oil, produced by

Hydrotreating Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of rem ...

. Group II+ base oils have a high

at the higher end of the API Group II range. The viscosity index is 110-115 minimum.

Group III+

Originating in 2015, produced by a

gas to liquids Gas to liquids (GTL) is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons, such as gasoline or diesel fuel. Methane-rich gases are converted into liquid synthetic fuels. Two general strategies ex ...

(GTL) process. Group III+ base oils have a Very High

Viscosity Index The viscosity index (VI) is an arbitrary, unit-less measure of a fluid's change in viscosity relative to temperature change. It is mostly used to characterize the viscosity-temperature behavior of lubricating oils. The lower the VI, the more the v ...

(VHVI) at the higher end of the API Group III range. The viscosity index is 130-140 minimum.

Group VI

Consists of

s made of Poly-internal-olefins (PIO). Poly-internal-olefins (PIO) oils are similar to Poly-alpha-olefins (PAO), but use different chemicals in the synthesis process to obtain an even higher viscosity index (VI)https://patents.google.com/patent/US20140113847 High viscosity index lubricating oil base stock and viscosity modifier combinations, and lubricating oils derived therefrom

References

{{Reflist

External links

A Review of Mineral and Synthetic Base Oils

A Defining Moment for Synthetics
Petroleum products