Group I base oils are crude or petroleum fractions that are solvent-refined. It undergoes physical and/or mechanical processes by which impurities such as waxes, sulfur, and aromatics are removed. Group II base oils on the other hand, while still extracted from crude, undergoes a hydrogen finishing process to remove impurities further. In this process, hydrogen reacts chemically with the crude fraction to improve on the properties of the Group I base oils.
Group II base oils exhibit the following advantages:
- Higher Viscosity Indices – up to 120, as opposed to <100 with Group I, allowing better lubrication at higher application temperatures,
- Lesser Aromatic Content (less than 10%), allowing for better thermal stability, and thus, less volatility,
- Lower Sulfur Level, improving on the anti-corrosion and anti-oxidation performance of a lubricant
For most industrial applications, such as with hydraulic systems and gearboxes, Group I mineral-based oils have found widespread use due to its availability and affordability. In most cases, the properties of Group I base oils, though somewhat inferior as against Group II and higher lubricant bases, are sufficient for the ‘regular applications’.
In prior years, the use of Group II base oils have been confined to more demanding applications, such as with engine oils, as well steam turbine oils. However, as the pricing of Group II base oils are now nearly aligned with Group I pricing, it is not surprising anymore to find the use of Group II is gaining popularity.
In summary, lubricants utilizing Group II base oils offer an advantaged alternative nowadays, especially considering its improved characteristics, and relative affordability. Know your base oils before making lubricant selection!