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, deterge ...

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 Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

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 chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...

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 Refining 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, but which is more useful in its pure form. For instance, most types of natural petroleum w ...

crude oil. This means that crude oil is heated in order to separate various distillates 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 Bitumen ( , ) is an immensely viscosity, viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American Engl ...

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 Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and melting poi ...

crude oil, although there are also

naphthenic In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing ...

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 catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...

technology, in which

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

and

aromatics Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...

are removed using

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

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.

Production of mineral base oils

Mineral base oils are first distilled from petroleum, and they comprise the 26-40 carbon fraction. Aromatic compounds are initially removed by solvent extraction: The distillation cut is mixed with an immiscible solvent such as phenol or furfural. This solvent preferentially dissolves aromatic compounds well, and the aromatic compounds are separated together with the solvent. Long chain alkanes form waxes that precipitate at relatively high temperature. They are removed either by crystallizing the waxes at low temperature, or they can be isomerized to branched alkanes. Various levels of hydrogenation are used thereafter to remove any remaining aromatic compounds and residual heteroatoms (in the form of nitrogen and sulfur compounds). Very generally, heteroatoms (as nitrogen and sulfur compounds) and

aromatic compound Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...

s are removed as the base oil is hydrogenated from Group I through Group III. Reduction in heteroatoms reduces formation of acids when engine oils are exposed to the combustion environment, acids being corrosive to the engine. The reduction in aromatic compounds improves the oxidative stability of the oil, delaying formation of sludge and varnish. Yet both effects lead to the oil becoming less polar, making it a poorer solvent for both the additive package of an engine oil, as well as accumulated oxidation byproducts.

API 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 extraction of petroleum, production, oil refinery, refinement, pipeline ...

(API), categorized base oils into five main groups. Chemical and physical characteristics are defined for Groups I through III that reflect how refined they are, correlating in some way to high and low-temperature viscosity, oxidative stability, volatility, and so on. Group IV oils comprise polyalphaolefins by definition, and Group V oils are those that do not fit into any previous category. The intent of such categorization is to help ensure that engine oils retain performance when different base oils are used.

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 chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

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 ...

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 ...

. 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 most refined 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".

Group IV

Originating in 1974, consists of

synthetic oil Synthetic oil is a lubricant consisting of chemical compounds that are artificially modified or synthesised. Synthetic oil is used as a substitute for petroleum-refined oils when operating in extreme temperature, in metal stamping to provide en ...

s made of polyalphaolefins (PAO). Group IV base oils have a

range of 125 - 200. Polyalphaolefin 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 generally ...

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

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

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

Middle East The Middle East (term originally coined in English language) is a geopolitical region encompassing the Arabian Peninsula, the Levant, Turkey, Egypt, Iran, and Iraq. The term came into widespread usage by the United Kingdom and western Eur ...

Group V

Originating in the 1940s, any type of base oil other than mentioned in the previously defined groups. Group V oils include

alkylated naphthalenes Alkylated naphthalenes are chemical compounds made by the alkylation of naphthalene or its derivatives with an olefin. These compounds are used as synthetic base oils, and are claimed to have improved oxidative stability over some conventional base ...

(e.g., ExxonMobil Synesstic) and esters.

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 hydraulic fluid that is essential for the proper functioning of vehicles equipped with Automatic transmission, automatic transmissions. Usually, it is coloured red or green to differentiate it from motor ...

Group II+

Originating in the 1990s, a more refined grade of

Group II base oil, produced by Hydrotreating. 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 oil refinery, 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 ...

(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 ...

(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 Lubricants

Production of mineral base oils

API classifications

Group I

Group II

Group III

Group IV

Group V

Unofficial Classifications

Group II+

Group III+

Group VI

See also

References

External links