HT Severe Hydrocracking - Clearly Superior

 

Base Oil Manufacture

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:

  • Separation of lighter boiling materials, such as gasoline, diesel, etc
  • Distillation to give desired base oil viscosity grades
  • Selective removal of impurities, such as aromatics and polar compounds
  • Dewaxing to improve low temperature fluidity
  • Finishing to improve oxidation resistance and heat stability

Generally both Solvent Refined and Hydrocracked 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, 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.

Petro-Canada's HT Severe Hydrocracking Process

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:

  • Removal of polar compounds, containing sulphur, nitrogen and oxygen
  • Conversion of aromatic hydrocarbons to saturated cyclic hydrocarbons
  • Breaking up of heavy polycyclo-paraffins to lighter saturated hydrocarbons

These reactions take place at temperatures as high as 400C , 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.

 

Hydroisomerization

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 -25C.

Petro-Canada employs Hydroisomerization dewaxing in conjunction with HT Severe Hydrocracking and as a result its base oils have the following attractive features:

  • Very High Viscosity Index (100 to 130)
  • Low Volatility
  • Superior Oxidation Resistance
  • High Thermal Stability
  • Excellent Low Temperature Fluidity
  • Low Toxicity

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

Comparison of the Products of HT Severe Hydrocracking and Solvent Refining

Base Oils

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".

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Characteristic Significant Difference
COLOUR HT Severely Hydrocracked base oils are clear and colourless
VISCOSITY INDEX HT Severely Hydrocracked base oils have higher VIs so they 'thin-out' less at high temperatures than Solvent Refined oils.
OXIDATION RESISTANCE HT Severely Hydrocracked base oils respond very well to anti-oxidants and so have superior resistance to oxidation and a longer lubricant life.
THERMAL STABILITY HT Severely Hydrocracked base oils have considerably better resistance to heat than Solvent Refined oils.
CARBON RESIDUE HT Severely Hydrocracked base oils produce lower residues than Solvent Refined oils.
DEMULSIBILITY HT Severely Hydrocracked oils separate easier from water than Solvent Refined oils
LOW TOXICITY HT Severely Hydrocracked base oils have low toxicity, due to a virtual absence of impurities.
Petro-Canada White Oils are pure enough to be used in cosmetics and pharmaceuticals.
BIODEGRADABILITY HT Severely Hydrocracked base oils biodegrade faster than Solvent Refined oils - 60% vs 30%, as measured by the CEC-L33-A-93 test.
 

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