Basics Of Lube Oil
A lubricant usually consists of a base fluid, generally of petroleum origin, combined with additive chemicals that enhance the various desirable properties of the base fluid. Base fluids are essentially obtained from two main sources: the refining of petroleum crude oil and the synthesis of relatively pure compounds with properties that are suitable for lubricants.
Petroleum Base Oil
Petroleum lubricating oils are made from the higher boiling portion of the crude oil that remain after removal of the lighter fractions. Crude oils contain varying amounts of compounds of sulfur, nitrogen and oxygen, metals such as vanadium and nickel, water and salts. All of these materials can cause problems in refining or subsequent product applications. The manufacture of the lube base stocks from crude oil involves a series of subtractive processes to remove these undesirable components, resulting in a base oil that meets performance requirements. The manufacture of the lube base oils involves following processes. 
Vacuum Distillation Process
•    Vacuum distillation process separates the atmospheric residue mixture into a series of fractions representing different molecular weight ranges or viscosity ranges from 90-100 neutral to the 500 neutrals.(the neutral number is the SUS viscosity at 100℉) The residue contains the heavier base oils such as the bright stocks. (150 to 250 SUS at 210℉) The latter is separated from asphaltenes and resins prior to introduction into the extraction process. 
 
Purification Process 
•    Extraction process involves removal of impurities in the base oils like aromatics, polars, sulfur and nitrogen compounds. Especially, aromatics make poor quality base oils because they are among the most reactive components in the natural lube boiling range. Oxidation of aromatics can start a chain reaction that can dramatically shorten the useful life of a base oil. Conventionally, solvent(furfural) extraction was adopted as the purification process, in which aromatics are removed by feeding the raw lube distillate (vacuum gas oil) into a solvent extractor where it is countercurrently contacted with a solvent. The resulting product is usually referred to as raffinate. Hydrocracking is a more recent form of purification process. It is done by adding hydrogen to the base oil feed at higher temperatures and pressures. Feed molecules are reshaped and often cracked open into smaller molecules. A great majority of sulfur, nitrogen and aromatics are removed. This massive reforming process produces molecules that have improved viscometrics and thermal and oxidative stability than product from solvent extraction process.
 
Dewaxing Process
•    The next step in the lube base oil manufacture is the dewaxing process. Solvent dewaxing process utilizes dewaxing solvents like MEK(methyl-ethyl-ketone), which is one of the most popular ones, to be mixed with the waxy oil. The mixture is then cooled to a temperature 10 to 20 below the desired pour point. The wax crystals are then removed from the oil by filtration. More desirable alternatives to the solvent dewaxing are i) catalytic dewaxing and ii) wax hydroisomerization. Catalytic dewaxing removes long n-paraffins and waxy side chains from other molecules by catalytical cracking them into smaller molecules. The wax hydroisomerization process, more advanced form of the catalytic dewaxing process, isomerizes n-paraffins and other molecules with waxy side chains into branched molecules with very desirable quality as lube base oils rather than cracking them away.
 
Hydrofinishing  
•    The final process in the manufacturing of lube base oil is hydrofinishing to improve color and thermal/oxidative stability of base oil. In hydrofinishing process, hydrogen is added to base oil at an elevated temperature in the presence of catalyst. By reaction of hydrogen with some remained sulfur and/or nitrogen containing molecules, these sulfur/nitrogen containing compounds are decomposed into smaller molecules to improve product color and stabilities

Synthetic Base Oils
Another source of lubricant base fluids is the synthetic route. Traditionally, synthetics was defined as “A product prepared by chemical reaction of lower molecular weight materials to produce a fluid of higher molecular weight designed to provide certain predictable properties.” Currently, there are two types of synthetic base oils commercially available.(PAO and hydrocracked base oil) Until mid 1990, Polyalphaolefins(PAO) were the most widely used conventional synthetic lube base fluid in the US and Europe. They are made by combining two or more decent molecules into an oligomer, or short chain length polymer. Because PAOs are all-hydrocarbon structures and wax-free, they have low pour points, usually below -40°C, very high viscosity indexes and good thermal stability. But because of limited availability of raw material, PAO production was limited to very specific application. However, since mid 1990s, new type of synthetic base oil, hydrocracked VHVI(very high viscosity index) base stocks like S-OIL's Ultra-S, have come to use because of commercial availability. Because VHVI base oil is made by chemically converting the petroleum based molecules into a PAO-like molecular structure, it shows quite similar properties to PAO at much less cost. Hence S-OIL’s Ultra-S series will make an excellent economical alternative for PAOs for applications like crankcase engine oils, gear and power train lubricants and some industrial lubricants requiring very high quality standard and extended life.