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About Base Oil

Almost every lubricant used in plants today started off as just a base oil. The American Petroleum Institute (API) has categorized base oils into five categories, mentioned below. The first three groups are refined from petroleum crude oil. Group IV base oils are full synthetic (polyalphaolefin) oils. Group V is for all other base oils not included in Groups I through IV. Before all the additives are added to the mixture, lubricating oils begin as one or more of these five API groups. All lubricants contain a base oil. It serves as the foundation of the lubricant before it is blended with additives or a thickener in the case of grease.

All base oils have characteristics that determine how they will hold up against a variety of lubrication challenges. For a mineral oil, the goal of the refining process is to optimize the resulting properties to produce a superior lubricant. For synthetically generated oils, the objective of the various formulations is to create a lubricant with properties that may not be achievable in a mineral oil. Whether mineral-based or synthetic-based, each base oil is designed to have a specific application.

Some of the most important base oil properties include the viscosity limitations and viscosity index, pour point, volatility, oxidation and thermal stability, aniline point (a measure of the base oil’s solvency toward other materials including additives), and hydrolytic stability (the lubricant’s resistance to chemical decomposition in the presence of water).

Present-day Group II base oils are the most commonly used base oils in plants. Currently, Group III accounts for less than 1 percent of the capacity in plants. Group I base oils previously made up 56 percent of the capacity, compared to 28 percent of the capacity in today’s plants.

Official Classifications

The American Petroleum Institute (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

The temperature range for these oils is from 32 to 150 degrees F. Group I base oils are solvent-refined, which is a simpler refining process. This is why they are the cheapest base oils on the market. It usually consists of conventional petroleum base oils. The hydro-treating refining process made this base oil more stable, less reactive, and longer lasting than the earlier base oils. Group I base oils typically range from amber to golden brown in color due to the sulphur, nitrogen and ring structures remaining in the oil. The base oils on the high end of the scale are often referred to as having a high viscosity index (HVI). This relates to how much the viscosity changes with temperature, i.e., how much it thins out at higher temperatures and thickens at low temperatures.  Group I base oils are the most common type used for industrial oils

Group II

They are often manufactured by hydro cracking, which is a more complex process than what is used for Group I base oils. Hydrogen gas is used to remove undesirable components from the crude oil.  This results in a clear and colorless base oil with very few sulphur, nitrogen or ring structures.Group II base oils have better anti oxidation properties and cost more in comparison to Group I base oils. Still, Group II base oils are becoming very common on the market today and are priced very close to Group I oils. Group II base oils are still considered to be mineral oils.  They are commonly used in automotive engine oil formulations.

Group III

These oils are refined even more than Group II base oils and generally are severely hydro cracked (higher pressure and heat). This longer process is designed to achieve a purer base oil. It is the best grade of petroleum base oil, since they are fully produced by Hydro cracking, Hydroisomerization, and Hydro treating, which make these oils purer. The resulting base oil is clear and colorless but also has a VI above 120.  In addition, it is more resistant to oxidation than Group I oils.Although made from crude oil, Group III base oils are sometimes described as synthesized hydrocarbons or Synthetic Technology oils or Hydro-Cracked Synthetic oil.

Group IV

Group IV base stocks are polyalphaolefins (PAO). PAOs fall into the category of synthetic hydrocarbons (SHCs).  They have a VI of greater than 120 and are significantly more expensive than Group III base oils due to the high degree of processing needed to manufacture them. PAO oils have a higher oxidative stability in extreme temperatures, and also have exceptionally low pour points which makes them much more suitable for use in very cold weather as well as in very hot weather.

Group V

These base oils are at times mixed with other base stocks to enhance the oil’s properties. Esters are common Group V base oils used in different lubricant formulations to improve the properties of the existing base oil. Ester oils can take more abuse at higher temperatures and will provide superior detergency compared to a PAO synthetic base oil, which in turn increases the hours of use.

About Base Oil
Offical Classifications




Official Classifications Summary
Base Stock Physical Properties
Synthetic Properties
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