Ernie Henderson, president of K&E Petroleum Consulting, concurs with these conclusions. He told attendees at the ICIS World Base Oils and Lubricants Conference in London last February that the global supply of bright stock is being threatened primarily by changes in the automotive industry that promote the use of high viscosity index Group II and III base stocks to improve fuel economy and increase drain intervals. As a result, refiners have made significant investment to increase the capacity of these base stocks at the expense of Group I refineries.

Its Still Needed

Although overall demand for bright stock is declining, Safdari said that several applications still depend heavily on it, including certain automotive engine oils, marine engine oils, industrial engine oils, process oils, gear oils, greases, hydraulic fluids and metalworking fluids. Launching a grassroots plant to manufacture bright stock is not economically viable, he noted.

However, some plants, such as Luberef in Saudi Arabia, have considered making capacity expansions to produce bright stock output. This may be risky because bright stock demand in the automotive segment is declining due to the shift from monograde to multigrade oils and fill-for-life gear oils to meet fuel economy standards and market demand. In contrast, demand for bright stock is expected to increase in marine engine, gear oil, grease, hydraulic fluid and metalworking fluid applications because of its effectiveness in the formulation from a technical and cost standpoint.

Bright stock has long been used as a high-viscosity blending tool for lubricant formulators. Henderson noted that because of its high viscosity, it can be used to blend a wide range of ISO viscosities. Bright stock also has good solvency and color characteristics, and its polarity helps disperse soap thickeners into oil for greases, he added.

Safdari explained that bright stock is produced from the vacuum residuum of Group I refineries. The vacuum distillation process separates the atmospheric residue mixture into a series of fractions, representing different molecular weight ranges or viscosity ranges. These viscosities range from 90-100 neutral to 700 neutral and above. (The neutral number is the SUS viscosity at 100 degrees F.)

The residue contains the heavier base oils such as bright stocks (150 to 250 SUS at 210 degrees F). The vacuum residue (or bottoms) is separated from asphaltenes and resins prior to introduction into the extraction process. Safdari summarized the output form the Group I refining process as shown in the table on Page 32.

Reviewing the Options

Henderson explained that there are several alternatives to bright stock, including polyisobutene, polyalkalene glycol, polyalphaolefin, naphthenics and some viscosity modifiers. He said that each alternative has advantages and disadvantages in certain applications. Therefore, formulators need to carefully match the alternative to the product and customer needs.

In general, he explained that formulators have a couple of options. They can evaluate how a particular option improves the value proposition, thereby upgrading performance and value when the market permits and opportunities arise. They can also match the application to the cost option by determining where they must use a particular alternative vs. where they would merely like to use it.

High margin applications can use higher cost options, Henderson noted. Thus, a formulator must review technical needs and the value that bright stock brings to the formulation. When it makes sense, reformulate.

Both Henderson and Safdari provided insights into the advantages and limitations of each alternative to bright stock.

Polyisobutene (PIB) is a straight chain polymer of isobutene. It is readily available in the marketplace because it is produced on a massive scale, is priced as a commodity and has wide formulation compatibility. Production costs for PIB are lower than those for synthetic materials such as polyalphaolefin and polyalkalene glycol, Safdari said, and it is available in many different grades.

He added that PIB does not support microbial growth, an important property for metalworking fluids. It also is hydrolytically stable and burns cleanly, key properties for two-stroke engines. Finally, it can be used at lower treat rates than the other alternatives in heavy base oils.

On the downside, said Safdari, PIB has lower solvency than bright stock. It is also thick and sticky, and must be heated for transport and reheated before use. Finally, it costs more than bright stock.

Polyalphaolefin (PAO) is a synthetic base stock that has excellent low-temperature properties, high viscosity index and excellent shear stability for gear oil applications. However, PAO is more expensive than PIB, and although it comes in both high and very high viscosities, the availability of these grades is limited.

Henderson agreed that heavy PAO is a higher cost option to bright stock, but it provides improved performance that might create a quality and margin advantage. He noted that new capacity is coming on-line that may boost the opportunity to use heavy PAO as a bright stock alternative.

All producers now have heavy PAO in their portfolios, he said. And he indicated that compressor oils, industrial gear oils, oven chain oils, grease, hydraulic oils and paper machine oils might benefit from the use of PAO because it improves thermal and oxidative stability, boosts energy efficiency by reducing operating temperatures, has a wide operating range and reduces wear.

Production capacity for PAO is only about 50 percent that of PIB, said Safdari, and its decene feedstock is in short supply. PAO also must be used at higher treat rates than PIB and has a higher cost per unit of usage.

Polyalkylene glycol (PAG) is a synthetic base stock with oxypropylene (or oxyethylene) functional groups. PAG is readily available in high and very high viscosities, said Safdari, and it has excellent low-temperature properties and a high viscosity index.

PAG is suitable for rotary equipment and very low temperature applications such as turbine and compressor oils, he said, and its polar nature provides good friction reduction. Finally, PAG is available in water-soluble and water-insoluble forms.

However, PAG is more expensive than PAO and is less available than both PAO and PIB. It also has a higher mixing ratio with base oil, thus a higher cost per unit of usage comparing to PIB, he noted. PAG is also incompatible with mineral base oil and most PAOs and PIBs.

Naphthenic base oil is readily available in high and very high viscosities, and even as a bright stock. Several suppliers market naphthenic base oil, and it is a cost-effective alternative, Safdari said. It also has good low-temperature properties and good solvency.

Henderson noted that heavy naphthenic bright stocks had not been considered in the past because of their low viscosity index, oxidation stability and availability. But in many applications, viscosity index is not critical, just kinematic viscosity.

He considers grease, rolling oils, forming fluids and process oils as applications where heavy naphthenics and naphthenic bright stock can be used. In addition, naphthenic bright stock can be blended with Group I and II medium-to-heavy neutrals to improve solvency, color, oxidation resistance and low-temperature properties.

Safdari noted that in addition to naphthenics low viscosity index, only one supplier produces naphthenic bright stock with an annual output of only 100,000 metric tons. Also, the higher viscosity grades represent only about 15 percent of total output, so these viscosities are in tight supply. Finally, he concluded, Napthenics lack OEM approvals for certain applications, and they are less cost-effective; therefore, I think PIB has about 80 percent chance to replace bright stock in most applications because of its chemistry and availability.