Yes, there is! The secret lies in the very special properties of naphthenic oils.

Naphthenics are the logical choice whenever an application can benefit from one of the following properties:

• High solvency.
• Excellent low-temperature properties.
• High compatibility to certain resins or polymers.

For the lubricants industry, perhaps the most valued property of naphthenic oils is their high solvency. In fact, the reduced solubility of highly refined API Group II and Group III paraffinic oils even strengthens the need and options for using naphthenic oils – primarily for metalworking fluids, but also for greases and industrial oils.

Where They Go

Naphthenic base oils typically serve three important markets:

• Transformer oils, which provide the cooling and insulating media in electrical transformers.
• Process oils, which are used in a great number of chemical processes due to their excellent solubility and specific chemical properties.
• Lubricating oils, including metalworking fluids, greases and industrial lubricants.

Projected market development for these varies, and growth in the lubricants industry – the focus of this article — is linked to industrial development and the Gross Domestic Product. Regions with significant industrial growth, or boom economic periods, should see an increase in demand for naphthenic oils. However, as these indicators are somewhat cyclical, the overall demand for finished lubricating oils is expected to remain flat.

Naphthenics Edge: Solvency

Among lubricant products, metalworking fluids have long been an important application for naphthenics. The two main functions of metalworking fluids are cooling and lubrication, or a balance between the two.

Without going into detail, it is generally accepted that naphthenics used in soluble oils have a higher tolerance to formulation changes than paraffinics, due to their better solvency characteristics. Superior emulsion stability and good cooling and filterability are considered as the main advantages of naphthenics in water-based fluids. As far as neat oils are concerned, naphthenics are favored over paraffinics, especially in formulations with high concentrations of additives.

The grease market is also significant. Both naphthenic and paraffinic base oils are widely used for making greases. The base fluid selected should display a moderate solvency toward the thickener being used. For greases, the viscosity of the base fluid is typically 80 centiStoke to 250 centiStoke at 40 degrees Celsius, although it is sometimes lower or higher for special applications.

In greases, lower viscosities of base oil tend to give better low-temperature properties and better heat transfer, but more bleeding, lower load capacity and higher volatility. Conversely, higher viscosities tend to give less bleeding, better load capacity and lower volatility – but worse low-temperature properties and heat transfer capabilities.

Base Oil Considerations for Grease

As you can see in Table 1, both naphthenic and solvent refined Group I paraffinic base oils have positives and negatives. Generally, a good mix of both types will have the optimum properties.

Why Is It Naphthenic?

Understanding how naphthenics and paraffinics differ begins with a look at the crude oil being processed in a refinery. Generally, crude oils having a paraffinic carbon content of less than 55 to 60 percent are called naphthenic crudes, and these are used to make naphthenic base oils. Naphthenic crudes are found in certain reservoirs around the world, from the United States East Coast to the Texas region, and following the Orinoco belt to Venezuela. They also are found in the North Sea area of Europe, Nigeria, the Middle East and Russia, and in China, Australia and Japan.

In chemical terms, naphthenics are normally wax-free, containing no N-alkanes. In the American Petroleum Institutes classification system, they belong to Group V base oils. However, to differentiate naphthenic from intermediate or paraffinic crude sources, we normally use other characteristics, such as viscosity index and aniline point (see Table 2).

Naphthenics Look Different

It is easy to look at the aromatic content of a paraffinic and a naphthenic oil, see they are the same, and assume that they have the same level of solvency. But there are several methods used to assess solvency: the aniline point, viscosity-gravity constant, and the aromatic content. When naphthenic oils are compared to paraffinic oils of identical aromatic content and viscosity, naphthenics have a lower aniline point and a higher viscosity-gravity constant, both of which indicate higher solvency powers (see Table 3).

A Question of Solvency

So aromatic content is not the only guideline for checking solvency, and these other properties should be considered when solvency is desirable.

Coming Changes

The drive towards more environmentally friendly products will continue, and more refined oils with longer lifetimes and better oxidation stability will be required.

On the technological side, we will see a drive towards the use of unconventional base oils, with less solvency power, for automotive lubricants. Consequently, there will be a need for tools to improve solvency — that is, naphthenic base stocks. Even a relatively small loss of solvency power can be critical for certain lubricant formulations, such as water-miscible metalworking fluids or neat oils with high levels of additives. Grease formulations also must be reviewed for this reason, either by increasing the naphthenic oil content or adapting the types of fatty acids used.

Another trend is globalization of specifications. Equipment manufacturers are dictating global availability of components, and its a challenge and opportunity for global suppliers to respond to this prerequisite.

Global demand for metalworking fluids, particularly metal removal fluids, will shift from straight oils to water-miscible fluids. The installation of new, faster machinery that needs more cooling increases the demand for water-soluble metalworking fluids. This trend creates great opportunities for naphthenics. The booming markets of China and Central Europe (and in India and Eastern Europe, too, which historically used mainly paraffinics) will also need more soluble oils.

The need to reduce mist formation levels in metal machining operations will have an impact on water-miscible metalworking fluids. This is another area of opportunity for naphthenics.

Finally, how will new base oil production technologies – such as very high viscosity index base oil processes and gas-to-liquid technology – impact the naphthenic market? These new production methods for making Group II and Group III base oils will create a lack of high-viscosity grades between 150 and 1,000 centiStoke. Naphthenic refining does not have these negative side-effectives, and naphthenic bright stocks will be very much appreciated, for grease production for example.

Lube Report Asia occasionally includes articles originally published in sister publications of LNG Publishing Co. This articlehas been adapted and updated from its original publication in the February 2005 issue ofLubesnGreasesmagazineunder the headline “What is a Naphthenic Oil?”

Lucien Dacraen, now retired, was global market manager, lubricants industry, for Nynas Naphthenics AB in Sweden when he wrote this article. For more information about naphthenics, visitwww.nynas.com/naphthenics.