|HT Severe Hydrocracking - Clearly Superior|
Before describing the Petro-Canada HT Severe Hydrocracking process and comparing it to the Solvent Refining process, we will first review the general principles of lubricant base oil manufacture. 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 fluidity.
Starting from petroleum crude oil, the typical process for making a lubricant base oil is as follows:
Generally both Solvent Refined and Hydrocracked base oils are manufactured this way, but differ in the methods employed
Developed over seventy years ago, this process attempts to remove the undesirable components from the feed, by solvent extraction. Initially, light oils such as gasoline, diesel, etc are separated from crude petroleum by atmospheric 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 dewaxed by chilling to a low temperature, which removes much of the wax and so improves the low temperature fluidity of the product. Finally, the dewaxed lube fractions are sometimes finished to improve their colour and stability, depending on the application requirements. One common method of finishing is mild hydrofinishing. This step should not be confused with Petro-Canada's HT Severe Hydrocracking process, as conditions of temperature and pressure in hydrofinishing are mild and less effective.
In Petro-Canada's modern HT Severe Hydrocracking process, the elimination of aromatics and polar compounds is achieved by chemically reacting the feedstock 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 Petro-Canada Hydrocracking process. The first one 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 base oil are dewaxed. These are then passed through a second hydrocracker for additional saturation. This final step maximizes base oil stability, by removing the last traces of aromatic and polar molecules.
In 1996, Petro-Canada completed a new base oil manufacturing plant to run in parallel with its existing base oil plant in Mississauga, Ontario. This new unit utilizes the HT Severe Hydrocracking process, but replaces the solvent dewaxing 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 VIs and improved yields, compared to previous conventional dewaxing 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 VIs ranging from 95 to 105 or unconventional base oils with VIs 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.
Petro-Canada employs Hydroisomerization dewaxing in conjunction with HT Severe Hydrocracking and as a result its base oils have the following attractive features:
These features give performance characteristics in finished lubricants very similar to synthetics, such as poly-alpha-olefins (PAO).
There are significant differences in certain characteristics between HT Severely Hydrocracked and Solvent Refined base oils. The main reason for the difference lies in the virtual elimination of aromatic molecules (less than 0.5%) in our Hydrocracking process. HT Severely Hydrocracked base oils are termed "99.5+% Pure". In comparison, the aromatics content of Solvent Refined base oils is somewhere around 20%; so Solvent Refined base oils are considered only "80% Pure".