Wings Newsletter
Base Oil Manufacture -The Three Processes

Lubricant base oils are produced in a series of steps, which are designed to enhance certain desirable properties. These include viscosity index, oxidation resistance, thermal stability and low temperature.

Starting from petroleum crude oil, the typical process for making lubricant base oil is as follows:

Generally, both Solvent Refined and Hydro Cracked base oils are manufactured this way, but differ in the methods employed.

Solvent Refining Process

Developed over seventy years ago, this process attempts to remove the undesirable components from the feed (crude), by solvent extraction. Initially, light oils such as gasoline, diesel, etc., are separated from crude petroleum by atmosphere distillation. The resulting material is charged to a vacuum distillation tower, where lubricant fractions of specific viscosity ranges are taken off. These fractions are then treated individually in a solvent extraction tower. A solvent, e.g., furfural, is mixed with them and extracts about 80% of the aromatic material present. After reducing the aromatic content, the solvent extracted lube fraction is de-waxed by chilling to a low temperature, which removes much of the wax and so improves the low temperature fluidity of the product. Finally, the de-waxed lube fractions are sometimes finished to improve color and stability, depending on the application requirements. One common method of finishing is mild hydro finishing. This step should not be confused with the Severe Hydro Cracking process, as conditions of temperature and pressure in hydro finishing are mild and less effective.

Severe Hydro Cracking Process

In the Severe Hydro Cracking, S.H.C., process, the elimination of aromatics and polar compounds is achieved by chemically reacting the feedstock (crude) with hydrogen, in the presence of a catalyst, at high temperatures and pressures.

Several different reactions occur in this process, the principal ones being:

These reactions take place at temperatures as high as 400°C, pressures around 3000 psi and in the presence of a catalyst. The hydrocarbon molecules that are formed are very stable and this makes them ideal for use as lubricant base oils.

There are two stages in the S.H.C. process. The 1st removes unwanted polar compounds and converts the aromatic components to saturated hydrocarbons. After separation into desired viscosity grades by vacuum distillation, batches of waxy lube based oil are de-waxed. These are then passed through a second hydro cracker for additional saturation. This final step maximizes base oil for stability, by removing the last traces of aromatic and polar molecules.

Hydroisomerization

A new process which utilizes the S.H.C. process, but replaces the solvent de-waxing step with the more modern and efficient wax conversion process.... Hydroisomerization.

The Hydroisomerization wax conversion process employs a special molecular sieve, which contains a catalyst, to selectively isomerize wax (n-paraffin mixture) to high VI, low pour point, iso-paraffinic lube oil. The process yields base oils with higher VI's and improved yields, compared to previous conventional de-waxing techniques. The process is capable of giving 130-140 VI base oils, in a single pass. More usually, it is set up to produce high viscosity index base oils with VI's ranging from 95 to 105 or unconventional base oils with VI's ranging from 115 to 130. A further process feature is the flexibility it offers to produce base oils with ultra low pour points, lower than -25°C.

Base oils produced by Hydroisomerization de-waxing in conjunction with S.H.C. offer the following attractive features:

These features give performance characteristics in finished lubricants very similar to synthetics, such as poly-alpha-olefins (PAO).