ABSTRACT
Most of today’s industrial oils use either a mineral or synthetic base oil. These base oils are categorized into five groups according to their refining or manufacturing process. Groups I, II, and III (see table 15.1 - Base Oil Groups) represent conventional mineral based lubricants while groups IV and V are reserved for man made synthetic base oils.
Group I base oils are known as “conventional” base oils made from solvent refined crude stock and have a Viscosity Index of between 80 to 120. Their sulfur content is above 0.03% and their saturated hydrocarbon levels are less than 90%.
Group II base oils are refined using a hydro processing method known as “Hydrotreating” designed to add hydrogen to the base oil at temperatures above 600F. This is performed using a catalyst and by applying moderate pressure over 500psi to convert the base stock and reduce its sulfur content to less than 0.03% and increase its hydrocarbon saturation to levels of 90% and above.
Group III base oils are known as “bright stock” and are primarily manufactured using a severe hydro processing conversion method known as “hydrocracking” that employs a catalyst at a temperature above 650F combined with pressure exceeding 1000psi to take out undesirable elements such as sulfur and nitrogen and replace them with hydrogen to attain a more stable base oil with a VI - viscosity index above 120 and a low pour point. In addition, remaining wax compounds are often removed to reduce the pour point even further. Due to this more complex refining process, Group III base oils perform in a similar manner to Group IV pure synthetic base oils and in most countries around the world, including North America, are allowed to be classified as a synthetic lubricant, even though it is hydrocarbon based.
Group IV base oils are reserved for Polyalphaolephin – (PAO for short) synthetically manufactured base oils made up of very small, synthesized hydrocarbon molecules.
Group V base oils represent all other synthetic base oil configurations
