Does Group II Get the Heavy-duty Gold?
Many industry experts agree that Group II base stocks have taken over from Group I as the new “workhorse” grade. Used to formulate a variety of different kinds of lubricants, Group II base stocks offer improved oxidative properties over Group I base stocks as well as an ability to yield products that demonstrate lower viscosity, lower volatility, higher viscosity index and increased fuel efficiency. Group II base stocks can deliver lower additive treat rates to meet sludge and deposit requirements, and they also have the ability to handle soot in diesel engines.
Very simply put, Group II base stocks are created by using a hydrocracking process in which large hydrocarbon molecules are broken down into smaller ones. The end product of this process is a clear and colorless base oil with very few sulfur, nitrogen or ring structures.
As defined by the American Petroleum Institute, Group II has saturates greater than 90%, sulfur less than 0.03% and a viscosity index between 80 and 120.
A number of factors go into base stock selection, including the type of lubricants to be made, their performance properties, raw material costs, storage tank availability and the proximity of suppliers.
So what might lead a lubricant blender to select Group II base stocks for its formulations?
As a result of many factors spurred on by the COVID-19 pandemic and severe weather in key base oil producing regions, Group II oils have been more easily accessible than their Group I counterparts in recent months. They have also generally been less expensive than Group I and Group III base oils. (Check out Base Oil Editor Gabriela Wheeler’s Base Oil Report: Pricing column on Page 8 for more information on base oil pricing.)
Because they possess a range of desirable traits—listed at the beginning of this column—Group II base stocks can be and are often used to formulate various types of heavy-duty and passenger car engine oils. Najib Aragrag, Europe, Middle East and Africa base stocks technical adviser with ExxonMobil, said in a webinar hosted by the company that the lubricants market in Europe has been developing in such a way that the door has been opened for lower-viscosity engine oil formulations to thrive.
“SAE 15W-40 has been the principal grade in Europe until recent years,” Aragrag said. “The rapid demand for low-SAPS—low-SAPS means low sulfated ash, phosphorous and sulfur—lubricants reflected a strong growth in SAE 10W-40 viscosity grades.”
What grades of base oils are required to formulate these popular low-viscosity heavy-duty engine oils?
“The 15W-40 oils are typically formulated with Group I base stocks, whereas the 10W-40 oils are formulated with Group II-Group III base stock blends or entirely with Group III,” Aragrag said.
However, he also noted that Group II base stocks can be “used in these viscosity grades, replacing completely or partially Group III base stocks.”
What might be the benefits of choosing Group II base stocks to formulate heavy-duty engine oils?
“Not only can this bring savings to the total formulation cost without compromising on performance and quality, but it may also allow you to reduce the number of base stocks in your blending plants,” Aragrag said.
To illustrate that Group III base stocks are not always needed to craft lubricants with high performance capabilities, Aragrag pointed to a 10W-40 heavy-duty engine oil formulation made with 94% ExxonMobil EHC 50 Group II base oil mixed with 6% EHC 120 Group II base oil. The test formulation—which ExxonMobil said was representative of a commercially available lubricant—was found to meet ACEA E6 requirements while also demonstrating lower volatility.
Furthermore, the company sought to prove that its EHC Group II base stocks also show similar oxidation resistance to Group III base stocks, as oxidation resistance is dependent on the performance of the base oil. Using the CEC L-109 Biodiesel Oxidation bench test, researchers at ExxonMobil tested three ACEA E6 10W-40 engine oils—one formulated with 100% EHC Group II base stocks, one with a mixture of Group III and EHC Group II base stocks, and the last with a mixture of Group II and Group III base stocks.
The additive packages were removed from each engine oil formulation, with the only additive being left in the formulations being an antioxidant, Aragrag said.
All three base oil blends yielded similar results for kinematic viscosity at 100 degrees Celsius. “People would expect that the Group II would thicken earlier than the Group II-Group III blend, but this is not the case,” Aragrag said. “We see similar results.”
The Mini-Rotary Viscometer results did offer some differentiation, though. The 100% EHC Group II formulation yielded similar results as the Group II-Group III blend, while the EHC Group II-Group III formulation demonstrated the lowest percent change.
Sydney Moore is managing editor of Lubes’n’Greases magazine. Contact her at Sydney@LubesnGreases.com