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. 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.
Mineral Base Oil
Modern mineral base oils are the result of a long and complex distillation and refining processes. The feedstock used is crude oil. This substance is not of uniform quality but consists of several thousands of hydrocarbon compounds in which the elements carbon and hydrogen are present in all molecules and, in part, are bound to other elements.
The hydrocarbons can be divided into three main groups: paraffinic, naphthenic and aromatic. Paraffinic hydrocarbons can be further divided into two subgroups: normal paraffinic and iso- paraffinic.
Paraffinic hydrocarbons are the best lubricants. The distillation process in the refinery separates the hydrocarbons contained in the crude into cuts based on the molecule size.
Furthermore, as many unwanted substances as possible are removed in the process, such as sulphur, aromatic hydrocarbons, paraffin wax, etc. In other words the mineral oil production process is physical cleaning and the end product is so-called paraffinic base oil.
Most of the hydrocarbons in the base oil are paraffinic, but it also contains naphthenic and aromatic molecules. When the finished lubricant, such as motor oil, is made of these, several additive compounds are used to improve the base oil properties.
The final outcome can also be so-called naphthenic base oil, where most of the hydrocarbons are naphthenic. Their cold properties are excellent.
Groups of Base oils
Group I - Group 1 base oils are the least refined of all the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications.
Group I base stocks contain less than 90 percent saturates and/or greater than .03 percent sulfur and have viscosity index greater than or equal to 80 and less than 120.
Group II - Group II base oils are common in mineral based motor oils currently available on the market. They have fair to good performance in lubricating properties such as volatility, oxidative stability and flash/fire points. They have only fair performance in areas such as pour point; cold crank viscosity and extreme pressure wear .
Group II base stocks contain greater than or equal to 90 percent saturates and less than or equal to .03 percent sulfur and have viscosity index greater than or equal to 80 and less than 120.
Group III - Group III base oils are subjected to the highest level of mineral oil refining of the base oil groups. Although they are not chemically engineered, they offer good performance in a wide range of attributes as well as good molecular uniformity and stability. They are commonly mixed with additives and marketed as synthetic or semi-synthetic products. Group III base oils have become more common in America in the last decade.
Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to .03percent sulfur and have viscosity index greater than or equal to 120.
Group IV - Group IV base stocks are polyalphaolefins (PAO) and are chemically engineered synthetic base stocks.
Poly Alpha Olefins (PAO's) are a common example of a synthetic base stock. Synthetics, when combined with additives, offer excellent performance over a wide range of lubricating properties. They have very stable chemical compositions and highly uniform molecular chains. Group IV base oils are becoming more common in synthetic and synthetic-blend products for automotive and industrial applications
Group V - Group V base stocks include all other base stocks not included in Group I, II, III, and IV. Group V base oils are used primarily in the creation of oil additives. Esters and polyolesters are both common Group V base oils used in the formulation of oil additives. Group V oils are generally not used as base oils themselves, but add beneficial properties to other base oils.
Note that the additives referred to in the Group V description are not aftermarket type oil additives. The additives referred to be used in the chemical engineering and blending of motor oils and other lubricating oils by the specific oil company that produces the finished product.
Production Flow Chart
• Feedstock is separated into distillates and vacuum gas oils
• Vacuum gas oil is sent through the hydro-cracker for conversion
• To saturate the molecules and remove impurities such as nitrogen, sulfur, oxygen and heavy metals, Hydrogen is introduced.
• Under extreme temperature and pressure in the presence of a catalyst, hydro-cracking converts aromatics molecules into saturated Paraffin.
• This process yields stock with lighter in color since the absence of contaminants.
• Long waxy paraffin molecules are restructured into shorter ones, so-Paraffin that resist gelling and improve low temperature pump-ability.
• Hydrogen is introduced again to clean up the remaining and impurities thus enhancing the oxidation and thermal stability of the final product.
Remember, whichever base oil you choose, just be sure it is appropriate for the application, temperature range and conditions in your plant.