What is Base Oil

What is Base Oil


Base oil is the name given to lubrication grade initially produced from refining crude oil, base oil is the beating heart of almost any lubricant, the crude oil is heated so that the different distillates can be separated from each other, during the heating process light and heavy hydrocarbons are separated, base oil is defined as oil with a boiling point range between 240-418°C, highly pure oils can be obtained by using hydrogenation technology in which sulfur and aromatic substances are removed using hydrogen under high pressure.

Base oils are used to manufacture products including lubricating motor oils, metal processing fluids and grease, different products require different formulations and properties, the most important factors is the viscosity of a liquid at different temperatures, whether a crude oil is suitable for conversion into a base oil is determined by the concentration of the base oil particles as well as how easily they can be extracted.

Chemicals additives are added to the base oil in order to meet the quality requirements of final products, in terms of anti-wear and performance, certain types of motor oils contain more than twenty percent of additives.


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The American Petroleum Institute (API) has categorized base oils into five categories, this breakdown is based on the refining method and base oil’s properties in terms of viscosity and proportion of saturates and sulfur content.

Group I
Group I oils have a viscosity percentage ranging from 80 to 120 and are less than 90 percent saturated and/or greater than 0.03 percent sulfur, the temperature range for these oils is from 0°C to 65°C, it’s easier to refine group i oils using solvents because it’s a less complicated procedure.

Group II
Like Group I base oils, Group II base oils are considered to be mineral oils, they contain more than 90% saturates and less than 0.03% sulfur and with a viscosity index of 80 to 120, they are manufactured by hydrocracking and have better antioxidation properties and transparent color as compared to Group I oils, Group II base oils are becoming more and more widespread on the market.

Group III
Group III described as Synthetic Technology oils or Hydrocracked (Higher Pressure and Heat), synthetic base oils contain greater than 90% saturates, less than 0.03% sulfur and have a Viscosity Index (VI) of 120 and above, these oils have been refined even further to achieve a higher quality and more pure base oil, the main difference between group II and III base oils is that the Group III base oils have a higher VI, Group III oils are becoming more prevalent.

Group IV
Unlike the first three base oil categories, which are all mineral oils, Group IV base oils are Poly-alpha-olefins synthetic base, PAOs have a much broader temperature range than Group I, II or III base oils and are therefore great for use in extreme cold conditions and high heat applications, they offer high oxidative stability, better protection at high temperature, reduce energy losses and easier starting at low temperature, Group IV base oils have a viscosity index range of 125 – 200, they will never be as widely used as the mineral base oils.

Group V
Group V base oils are classified as all other base oils, including polyesters, diesters, polyalkylene gycols, silicones, naphthenic oils, phosphate esters, biolubes, and more, these base oils are mixed with other base stocks to improve the properties, Group V oils are used as a supplement to other base oils and combined with other oils base stocks to improve the oil’s qualities, ester oils may withstand greater temperatures and provide better detergency than a synthetic PAO base oil, permitting them to be used for longer time.

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