Continuous contraction in API Group I production always raises the issue of where the bright stock will come from. But equally important is the question of how the process oil market, currently heavily skewed to Group I, will be kept supplied.

Group I once was the default option for most process oil applications, but with a better understanding of base oil composition and performance, it has become obvious that using Group I also provides quite distinct technical advantages. This is especially true as the limitations of Group II and III in this arena have become more obvious.

Process oils utilize not only Group I finished base oils, but also deliberately under-processed versions, so-called medium extracted solvates (MES) as well as the by-products of base oil production, including both extracts and waxes. Process oils, especially for rubber manufacture, exploit not only Group I derived MES but also two very high solvency extracts that are by-products of Group I manufacture. These are broadly termed unmodified distillate aromatic extracts (DAEs) from distillate Group I base oil manufacture – the SN-150 to SN-600 viscosity range.

Today, DAEs require further treatment before sale in the European Union and United States to ensure health, safety and environmental requirements are met for polycyclic aromatic (PCA) content. This gives rise to the safer subclass of more readily saleable treated distillate aromatic extracts (TDAEs). There is still significant DAE manufacture, but it tends to be used only as a feedstock for TDAE or for sale in countries with more relaxed health and environmental requirements.

The other type of aromatic extract is residual aromatic extract (RAE), associated with residual base oil production; that is, Group I bright stock. RAE has the advantage of being intrinsically better with respect to health and safety performance, even without post-treatment, for reasons that have to do with the sheer size of the molecules. But the future of RAE is inextricably linked to that of solvent extracted bright stock production, which is the principal process under threat due to Group I production efficiency limitations. Hydroprocessed bright stocks produce no extracts, so are no help.

Recently, process oils based on Group II and III base oils have been developed for certain metalworking fluids such as quenching oils. These products exploit the tendency of high-saturate base oils to leave fewer deposits on metal surfaces than Group I-derived equivalents.

White oils are another subset of process oils. Because of their end uses in consumer products, they normally require very low to trace PCA content, requiring either clay finishing or severe hydrofinishing in their manufacture. They are classed as technical white oils or medicinal white oils, depending on their residual PCA content.

For these oils, it makes more sense to use base oils with inherently low aromatic content as feedstocks in the first place, such as Group II and III. As a result, the contraction in Group I will not really affect this segment of the process oil market.

An area where Group I based process oils have a distinct technical advantage is as heat transfer fluids. While Group I oils tend to have lower specific heat capacities than Group II or III base stocks grade-for-grade, they have an inherent stability advantage in this application. The residual sulfur that solvent extracted Group I stocks possess provides a significant boost to uninhibited (natural) antioxidancy performance. This is especially important in the continuous high-temperature environments of heat transfer fluids where runaway oxidation can have explosive consequences.

Essentially sulfur-free Group II stocks need a synthetic antioxidant to maintain their integrity and should never be used neat as heat transfer fluids. But even a simple synthetic antioxidant treatment can be exhausted, potentially leaving the heat transfer fluid unstable. Therefore, much more careful product development is needed for Group II based heat transfer fluids. Antioxidant exhaustion is a much more gradual, less time critical process with Group I stocks by virtue of the type of antioxidancy they possess.

So, as Group I production continues its inevitable decline, for economic as much as technical reasons, more and more work will be done to formulate better process oils with the newer types of base stocks. But for those players in the Group I market that run well-maintained and maximally efficient Group I plants, there will be good and potentially profitable outlets as process oils for the foreseeable future.