CRUDE OIL TO BASE OIL - Part 2
Once completed in the distillation process, each of the compounds extracted can be further refined to achieve their intended purpose. With base oil, the further refining is done for a number of reasons, colour, viscosity index, oxidation resistance, thermal stability, carbon residue, demulsibility & biodegradability. In addition the distilled crude oil contains varying amounts of compounds of sulphur, 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 refining process for the crude oil involves a series of subtractive processes to remove & control the above components, resulting in a base oil that meets performance requirements.
The basic four stages:
Vacuum Distillation Process
Purification Process
Dewaxing Process
Hydrofinishing
Vacuum Distillation Process
This process involves the separation of the atmospheric residue mixture into a series of fractions representing different molecular weight ranges or viscosity ranges.
Purification Process
This Extraction process involves removal of impurities in the base oils like aromatics, polars, sulphur 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.
Dewaxing Process
The next step in the lube base oil manufacture is the dewaxing process. Dewaxing is done to improve low-temperature fluidity. 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. Other dewaxing methods like Catalytic dewaxing & hydroisomerization can be used to produce high quality results.
The process for creating Base stock can finish here, but one more process can be done to make a premium product.
Hydrofinishing
Hydrofinishing changes the polar compounds in the oil by a chemical reaction involving hydrogen. After this process, an observer would notice a lighter-colored product and an improved chemical stability. The final quality of the base oil is determined by the severity of the application of temperature and pressure in the hydrofining process.
Next week we will go through the differences of the classifications of Base Oil.