Understanding the Differences Between Base Oil Formulations
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 a grease. But how do you know which base oil is best? Trying to choose between mineral oils and synthetics can be confusing. This article will break down the complexity between base oil distillation equipment formulations so you can make the right decision for each application.
Base Oil Categories
Lubricants can be categorized in many different ways. One of the most common classifications is by the constituent base oil: mineral, synthetic or vegetable. Mineral oil, which is derived from crude oil, can be produced to a range of qualities associated with the oil’s refining process. Synthetics are man-made through a synthesizing process and come in a number of formulations with unique properties for their intended purpose. Vegetable base oils, which are derived from plant oils, represent a very small percentage of lubricants and are used primarily for renewable and environmental interests.
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 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).
The 20th century saw a number of improvements in the refining process used for mineral oils along with the introduction of a variety of synthetics. By the early 1990s, the American Petroleum Institute (API) had categorized all base oils into five groups, with the first three groups dedicated to mineral oils and the remaining two groups predominantly synthetic base oils.
Groups I, II and III are all mineral oils with an increasing severity of the refining process. Group I base oils are created using the solvent-extraction or solvent-refining technology. This technology, which has been employed since the early days of mineral oil refining, aims to extract the undesirable components within the oil such as ring structures and aromatics.
Group II base oils are produced using hydrogen gas in a process called hydrogenation or hydrotreating. The goal of this process is the same as for solvent-refining, but it is more effective in converting undesirable components like aromatics into desirable hydrocarbon structures.
Group III base oils are made in much the same way as Group II mineral oils, except the hydrogenation process is coupled with high temperatures and high pressures. As a result, nearly all undesirable components within the oil are converted into desirable hydrocarbon structures.
