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Automotive and Industrial Lubricants
Base Oils


Overview of the Process

The general principles of lubricant base oil manufacturer use a series of steps to improve certain desirable lubricant properties. These include:

  1. Viscosity Index
  2. Oxidation
  3. Heat Resistance
  4. Low Temperature Fluidity

Starting from petroleum crude oil, the typical process for making a lubricant base oil is the following:

  1. Separation of lighter boiling materials such as gasoline, jet fuel, diesel, etc.
  2. Removal of impurities including aromatics and polar compounds.
  3. Distillation to give desired base oil viscosity grades.
  4. Dewaxing to improve low temperature fluidity.
  5. Finishing to improve oxidation and heat stability.

SOLVENT REFINING PROCESS

This process which was developed in the 1920's attempts to remove the undesirable components from the feedstock by solvent extraction. Light oils such as gasoline, diesel, etc., are first separated from the crude oil by atmospheric distillation. The resulting feedstock is charged to a vacuum Distillation tower where lubricant fractions of specific viscosity ranges are produced. These fractions are treated individually in a solvent extraction tower where the solvent is mixed with the lubricant fractions. This extracts up to 80% of the aromatic hydrocarbons, and other undesirable components. After removing the aromatics, the solvent extracted lube fraction is dewaxed to improve lower temperature fluidity. Finally, the dewaxed lube fractions are finished to improve their colour and stability. One common method of finishing is mild hydrotreating. Refer to the diagram below for a graphical representation of the process.


HYDROTREATING PROCESS

This process was developed in the 1970's. Petro-Canada Lubricants currently operates a refinery in Oakville, Ontario, Canada utilizing this process.

The elimination of aromatics and impurities is accomplishes by chemically reacting the lubricant feedstock with hydrogen in the presence of a catalyst, under conditions of high temperature and pressure.

Several different reactions occur in this process, the principle 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 very high temperatures(400°C) and pressure(3000psi) in the presence of a catalyst. The hydrocarbon molecules that are formed in the process are very stable, which make them ideal for use as lubricant base oils.

Refer to the diagram below for a graphical representation of the two stage HYDROTREATING process. The first stage removes unwanted polar compounds and converts the unsaturated feedstock into a saturated waxy lube fraction. After separation into desired viscosity grades, batches of waxy base oils are dewaxed and the passed through the second stage hydrotreater for additional saturation. This maximizes base oil stability by removing the remaining traces of polar compounds and un saturates.

Lubricant Refining Process

ADVANTAGES OF HYDROTREATING VS SOLVENT REFINING

There are significant differences in certain characteristics between HydroTreated and Solvent Refined base oils. The main reason for these differences lies in the virtual elimination of aromatics(less than 0.5%) using the HydroTreating process. HydroTreated base oils may therefore be termed"99.5% Pure".In comparison, the aromatic content of Solvent Refined oils is somewhere around 20%.; so Solvent Refined oils are considered "80%Pure". The following are the characteristics and significant differences:
COLOUR
All 2-stage Hydrotreated base oils are clear and colourless.
VISCOSITY INDEX(VI)
HydroTreated base oils generally have higher VI's than Solvent Refined oils. As a result, viscosity drops off less at high temperatures than with Solvent Refined oils.
CARBON RESIDUE
Lower for HydroTreated base oils.
TOTAL ACID NUMBER(TAN)
Lower for HydroTreated base oils.
DEMULSIBILITY
HydroTreated oils will shed water better than Solvent Refined oils.
OXIDATION RESISTANCE
HydroTreated base oils, at equal levels of anti-oxidant treatment, give superior resistance to oxidation.
HIGH TEMPERATURE STABILITY
Better high temperature stability for HydroTreated oils.

SYNTHETIC LUBRICANTS

Lube oils possessing a base oil that has been manufactured from chemical constituents or by the polymerization of hydrocarbons. The three most common types of synthetic base oils are:

  1. Polyalpholefins
  2. Organic Esters
  3. Polyglycols

Synthetic lubricants have several advantages over conventional mineral oils:
  1. excellent low temperature fluidity
  2. low pour point
  3. high natural viscosity index
  4. excellent oxidation stability
  5. high flash, fire, and auto-ignition points
  6. low volatility
  7. non-corrosive and non-toxic

Synthetic lubricants have been in use for sometime in the airline industry, Arctic lubricants, and fire-resistant hydraulic fluids. These are applications which justify the high cost of these lubricants.