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 aromatic.
The general classification of different kinds of crude oil is based on the guidelines drawn up by American Petroleum Institute (API), in which the properties can vary depending on, for example, hydrocarbon composition and sulfur content.
Crude oil classification provides refiners with a rough guide to appropriate processing condition to reach desired products.
With the progress of the science of the petroleum, addition of physical and chemical properties has been utilized to further enhance classification of crude oils.
According to API guidelines base stocks (the lubricant component, which are obtained after the crude oil is refined) are divided into five general categories.
Development of the n-d-M method was the consequence of much preceding work relating composition refractive index (n), density (d), and molecular weight (M).
Using the given values, the percent carbons (%CA, %CN, %CP) can be derived from a correlation chart, the ASTM D2140 method.
[10] Naphthenic base oils generally have intermediate VI's and very low pour points which make them useful in the manufacture of specialty lubricants.
The pour points of naphthenic base oils, generally devoid of wax content, may be much lower (down to <−70 °C).
[14] Naphthenic oils have extraordinary low-temperature properties, high compatibility with many polymers and good solvent power.
Naphthenic oils are used in a large number of chemical processes due to their good solvent power.
These include, for example, plasticizers in polymer-based formulations, rheology modifier in printing inks and carrier oil in anti-foaming agents.