But the comparison is not quite that simple, as a Rhein Chemie official explained during a presentation at the ICIS Middle Eastern Base Oils & Lubricants Conference in October. Some of the properties that make Group II perform better in some ways can detract from other performance parameters. That need not prohibit the use of Group IIs, Technical Manager Frank Bongardt said, but it does require adjustment in formulation.

Group I oils are the dominant category of base stocks, accounting for roughly three quarters of worldwide demand. For the past two decades, though, the industry has trended toward Group II and Group III oils, which are produced through more intensive refining and which have higher viscosity indices, less sulfur and nitrogen and lower levels of aromatic hydrocarbons. As Bongardt noted, both qualities were highly valued for automotive lubricants, which make up approximately half of the total market.

Those factors lead to longer lubricant life times and drain intervals, he said. They also have environmental impacts like reductions [in emissions] of sulphur and aromatics. And there are commercial benefits because the price premiums [over Group I] are low, but they save blending costs by allowing lower additive treat rates.

The drawback is this: Reduced sulfur levels and more uniform composition of hydrocarbons means Group II oils have fewer molecules that are prone to bond; they do a poorer job of dissolving additives.

Additives which have good solubility and performance in Group I base oils, may have only a limited solubility in modern base fluids… due to the non-polar, paraffinic structure and the absence of aromatic compounds, Bongardt said.

To illustrate the effects, he showed results of tests that Rhein Chemie conducted on samples of hydraulic oils, some formulated with Group I base stocks, others with Group II, some using additive pack-ages that contained zinc, some zinc-free.

All combinations passed tests that measure high-temperature performance and hydrolytic stability, the Mannheim, Germany-based chemical company found, and hydraulic oils with zinc-containing additives passed filterability tests whether they contained Group I or Group II base stocks. Filterability is important because hydraulic systems have filters to remove contaminants. The filters should not remove components of the lubricant.

The zinc-free samples made with Group I stocks also passed the filterability test, Bongardt said, but those made with Group II failed. The reason was clear and not very surprising, he added. The zinc-free additives did not dissolve as well in Group II.

The problem can be addressed, Bongardt said, by adjusting formulas to make the additives more soluble in Group II. And this, he said, is clearly the most sensible route, because the other advantages of Group II oils make such adjustments worthwhile.

He concluded with a prediction.

Demand for Group II oils will grow in the future worldwide and in the Middle East, he said. The technical advantages provided by Group II oils are obvious and will lead to longer lifetime of specific industrial and automotive lubes. The shift from Group I to high-quality Group II oils does not require new complete additive technology. But modifications in respect to solubility of packages… are unavoidable.