Description
The term ‘lubricating oil’ refers to a wide range of products that
are characterized by hundreds of base chemicals and additives.
Lubricating oils may be either mineral-based or synthetic. The
mineral-based are more widely used than the synthetic oils.
This article focuses on petroleum-based lubricating oils, which
are composed of 80–90% of petroleum hydrocarbon distillates
and 10–20% of additives. Additives are necessary to impart
specific properties to the oil for specific applications and
include among others ‘extreme pressure additives,’ antiwear
additives, corrosion inhibitors, oxidation inhibitors, viscosity
index improvers, or demulsifiers.
Lubricating oils are a complex combination of hydrocarbons
obtained from solvent extraction and dewaxing processes. It consists predominantly of saturated
hydrocarbons having carbon numbers in the range C15
through C50, with the heavier distillates having higher
percentages of the higher carbon number compounds. The
mineral-based oils are produced from heavy-end crude oil
distillates and they contain hundreds to thousands of hydrocarbon
compounds, including a substantial fraction of
nitrogen- and sulfur-containing compounds. The hydrocarbons
are mainly mixtures of straight and branched chain
hydrocarbons (alkanes), cycloalkanes, and aromatic hydrocarbons.
PAHs (polycyclic aromatic hydrocarbons), alkyl PAHs,
and metals are important components of motor oils and
crankcase oils. Lubricating oil composition changes under the
use conditions of heat and friction and, if appropriate, exposure
to exhaust gases of internal combustion engines. Used
lubricating oils or crankcase oils generally have higher
concentrations of PAHs than unused oils and they are considered
to be more toxic. Used lubricating oils are not specifically
addressed in this article.
The petroleum hydrocarbon distillate generally consists of
paraffinic or naphthenic compounds. The exact composition of
mineral-based lubricating oil as petroleum products varies
depending upon (1) the source of the crude oil (crude oil is
derived from underground reservoirs which vary greatly in their
chemical composition) and (2) the refining practices used to
produce the product. All the lubricating oils listed in Table 1
have been classified in Europe on the basis of the Global
Harmonized System (GHS) as carcinogen category 1B (known
or presumed to have carcinogenic potential for humans based
primarily on animal evidence) with the hazard statement of
H350 may cause cancer.
Uses
Lubricating oils are used for lubrication of various internal
combustion engines. The uses of mineral oils include applications
such as engine oils, automotive and industrial gear oils,
transmission fluids, hydraulic fluids, circulating and hydraulic
oils, bearing oils, and machine oils. Other uses are as machinetool
oils, compressor and refrigerator oils, textile machine oils,
air tool oils, steam engine oils, and metalworking oils.
Mineral oils have also medicinal and food uses; they are
used as ingredients in various pharmaceutical and cosmetic
preparations and as a vehicle for drugs, and in fungicides,
chemical and plastics industries (e.g., processing medium,
extenders, plasticizers), and animal feed products. Two chemical
classes (paraffin waxes, CAS 8002-74-2 and petrolatum,
CAS 8009-03-8) are considered generally recognized as safe
food ingredients by the Food and Drug Administration (FDA).
Uses
Lubricating oils are based on aliphatic hydrocarbon molecules containing 17 or more carbon atoms. The wide array of lubricating oil mixtures are used to reduce the friction and heat produced when mechanical parts come into contact with one another. Similar to cutting oils, there are two major classifications: (1) mineral, which are made from refined petroleum, and (2) synthetic, which are made from other oil sources. The exact composition of lubricating oils varies, as lubricating oils are complex mixtures that contain small amounts of aromatic and polycyclic substances and a broad variety of dissimilar materials known collectively as additives. Additives serve a variety of functions, including inhibiting corrosion or oxidation, preserving integrity of the oil film, altering the viscosity of the mixture, suppressing bacterial growth within the mixture, or acting as a detergent. The presence of the additives determines the toxicity and possible adverse health outcomes of lubricating oils.
Flammability and Explosibility
Non flammable
Environmental Fate
The physical–chemical properties of mineral oils depend on
their composition in terms of carbon number distribution,
and this is defined by the source of crude oil.
It shows the physical–chemical properties of both lubricating
oil in general and the most relevant substances present in
lubricating oils.
Generally, they are viscous fluids with brown to black color.
The higher the carbon number, the higher the viscosity of the
fluid. They are insoluble in water and alcohol, but are soluble
in benzene, chloroform, ether, carbon disulphide, and petroleum
ether. Lubricating oils are photodegraded by sunlight at
1 000 000 molecule m
-3.
Toxicity evaluation
The mechanism of lubricating oil toxicity is mediated through
its irritant effects, which after sufficient exposure duration and
concentration result in tissue hyperplasia. Chronic hyperplasia
leads to subsequent loss of tissue integrity and damage, and
cancer in some animal models.
