Grease manufactures may not be asking for Group II, PetroTrends Vice President for Lubes and Fuels Wes L. Cosgriff said, but they very well could be using it now and in the future due to big-picture supply and demand issues. It may, however, require grease manufacturers to revisit grease recipes and rethink the economics of soap making.

Cosgriff said base oil refiners are producing less conventional, solvent-refined Group I base stock, and more Group II, Group II+ and Group III to accommodate the auto industry. In particular, the new GF-3 specification for passenger car motor oil lowers volatility limits in an effort to retard in-use thickening and poisoning of catalytic converters.

As a result, many engine oil blenders have switched to Group II or above base oils, which have lower aromatic contents. The unconventional base stocks have also made their way into the grease industry for at least two reasons, according to Cosgriff and coauthor Thomas F. Glenn. First, the availability of Group I oils has become less reliable as the volume produced by refiners has fallen.

Secondly, many grease makers also blend engine oil and, faced with limited tankage, let engine oil requirements dictate base oil purchases.

Unconventional base stocks may offer some advantages to grease makers, Cosgriff said. One is the ability to manufacture synthetic products at substantially lower costs than when using polyalphaolefin base stock. Greases made with unconventional base stocks may also provide better oxidative stability than those made from Group I oils.

But unconventional base stocks also pose a serious challenge because of the very characteristic driving their demand for engine oils: their lower aromatics content. Grease making involves at least two separate steps. The first is a reaction of fatty acids and known as saponification, which creates a soap thickener. Then base oil and additives are blended in to finish the grease.

As Cosgriff pointed out, aromatics improve the yield of soap during saponification, thereby reducing the need for fatty acids and alkali. Those materials make up a significant portion of the cost of grease making.

Cosgriff contended that the grease industry generally has yet to solve this problem.

What could easily be overlooked in the big picture of the switching dynamics from Group I to Group II, is that soap yields in grease are heavily dependent on the aromatic content of the base oil used during saponification, he said. Switching to Group II typically drops the aromatic content of base oils to less than 1 percent, down from nearly 10 percent in a Group I. This drop could leave grease manufacturers scratching their heads; although they had not made any perceived changes in the product or production processes, grease yields are down and additive solubility is now an issue.

Cosgriff suggested that grease makers may solve the problem by starting with pre-formed soaps. He added, however, that it will take time for grease makers to refine their formulas. He also advised careful comparison of the costs of saponification with unconventional base oils versus use of pre-formed soap.