What’s the difference between base oil categories?

The most important part of any lubricant is the base oil. But are you aware how the base oil categories differ?

The two different broad base oil categories are:

1.) Mineral base oils
Modern mineral base oils are the result of a long and complex distillation and refining processes. The feedstock used is crude oil. This substance is not of uniform quality
but consists of several thousands of hydrocarbon compounds in which the elements carbon and hydrogen are present in all molecules and, in part, are bound to other elements.

2.) Synthetic Base Oil
The group of synthetic base oils covers many different substances: synthetic hydrocarbons, organic esters, polyalkyline glycols, etc.

Synthetic PAO (Polyalphaolefine) hydrocarbons are manufactured in a process that results in isoparaffins, the desired types of hydrocarbon molecules. The raw material used is reprocessed into ethene gas.

It is thus possible to produce the best possible lubricating oil, which entirely lacks the unwanted components, through chemical processes. This is the most commonly used synthetic base oil in modern engine lubricants.

API categorization of different base oils

The American Petroleum Institute (API) has categorized these into five categories:

• The first three groups are refined from crude 
• Group IV lubes are fully synthetic (polyalphaolefin). 
• Group V is for all others not included in Groups I through IV. 

Group I category base oils 

Group I lubricants are classified as less than 90 percent saturates, greater than 0.03 percent sulfur and with a viscosity-index range of 80 to 120. The temperature range for these oils is from 32 to 150 degrees F. They are solvent-refined, which is a simpler refining process. This is why they are the cheapest on the market.

Group II base oils 

Group II base stock is defined as being more than 90 percent saturates, less than 0.03 percent sulfur and with a viscosity index of 80 to 120. They are often manufactured by hydrocracking, which is a more complex process than what is used for Group I products.

Since all the hydrocarbon molecules of these are saturated, Group II category base oils have better antioxidation properties. They also have a clearer color and cost more in comparison to Group I. Still, Group II are gaining in popularity in the market today and are priced very close to Group I lubes.

Group III category base oils 

Group III are greater than 90 percent saturates, less than 0.03 percent sulfur and have a viscosity index above 120. These oils are refined even more than Group II lubricants and are generally severely hydrocracked (higher pressure and heat).

This longer process is designed to achieve a purer base oil. Although made from crude, Group III can sometimes be described as synthesized hydrocarbons. Like Group II products, these are also becoming more prevalent.

Group IV category base oils

Group IV are polyalphaolefins (PAOs). Different to the previous categories, these synthetic base oils are made through a process called synthesizing. They have a much broader temperature range and are great for use in extreme cold conditions and high heat applications.

Group V category base oils are oils that don’t fall into the above grading.

Group V include silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes, etc. These are at times mixed to enhance the properties. An example would be a PAO-based compressor oil that is mixed with a polyolester.

Esters are common Group V lubricants used in different formulations of base oils to improve the functional properties. Esters can take more abuse at higher temperatures and will provide superior detergency compared to a PAO synthetic base oil, which in turn increases the hours of use.

The changing use of these different base oils

A recent study on the use of base oils in today’s plants in comparison to a little more than a decade ago found a dramatic change has occurred. Present-day Group II lubes are the most commonly used, making up 47 percent of the capacity of plants in which the study was conducted. This compared to 21 percent for both Group II and III just a decade ago.

Currently, Group III accounts for less than 1 percent of the capacity in plants. Group I previously made up 56 percent of the capacity, compared to 28 percent of the capacity in today’s plants.

Whichever base oil you choose, just be sure it’s appropriate for the application, temperature range and conditions in your plant.

Remeber: if you’re unsure about the difference in the categories of base oils and the application of the final lubricants, you can call on the professionals. The folk at Habot Synthetic Lubricants are always available to supply you the best advice and synthetic lubricant for your requirements.