Once formulators try alkylated naphthalenes, they never go back to esters again.
So says John Filak, vice president of specialty products at Houston-based J.A.M. Distributing. ANs have so many advantages, theyre so easy to use, theyre often a drop-in for an ester, and the prices are very comparable.
Just as the iconic Leatherman offers a tool for almost every purpose, so ANs offer solutions for nearly any lubrication problem.
Only two companies in the world, ExxonMobil Chemical Co. and King Industries Inc., manufacture these bright, light-colored synthetic base stocks. King specializes in niche markets, producing customized viscosity grades ranging from 3.8 to 19.8 cSt, and handles its own distribution. ExxonMobil Chemical manufactures two viscosity grades, 5 and 12 cSt, which it says meet the needs of most users. It handles most bulk shipments directly, while its distributors, including J.A.M., focus on customers needing drums, totes and compartmentalized bulk containers. Every company professes a concentrated focus on the specific needs of its customers.
What product volumes are involved? Filak admits only to plenty, adding that it amounts to somewhere between a lot and a whole lot. Michel Hourani, vice president for commercial development at King Industries in Norwalk, Conn., is equally close-mouthed, saying, We are always working with customers to see what physical and performance characteristics they require, and then we try to develop specific ANs for them. We tend to be focused on customers and niches, not necessarily volumes. Regardless, everyone claims easy availability, quick delivery, and ready-to-go ability to upgrade capacity when its needed.
Compared to esters, ANs were once the high-priced alternative and not widely used; today its a different story. According to Filak, the price of esters has risen with the cost of the adipic acid and alcohol precursors; meanwhile the price of AN (made by reacting naphthalene and alphaolefins, and manufactured primarily on the East Coast, away from Gulf Coast hurricanes) remains stable. That, he says, makes AN an easy choice.
We focus on the value proposition, says Sandra Mazzo-Skalski, ExxonMobil Chemicals performance products specialist in Paulsboro, N.J. I can take a blend of PAO [polyal-phaolefin] with AN and show performance that will justify a higher price than a mineral oil. Many customers use AN as a blend stock, typically at a concentration of 10 to 30 percent, while some use AN as a base stock, particularly for compressor fluids and some greases.
Sometimes nature can fool us and give us something economical that works very well, comments Hourani. Some companies have applications that reach 230 to 300 degrees C, and the alkylated naphthalene allows their base oil to perform. Weve seen other cases where ANs cured solubility problems and stability issues.
Perhaps the two key features of alkylated naphthalenes, according to sources, are that they resist oxidation at high temperatures, and they do it even in the presence of moisture. You can get a lot of the properties you need from esters, but you cant get the hydrolytic stability, Mazzo-Skalski says.
ExxonMobil Chemical and King point to a variety of oxidation tests that show how ANs stack up against fluids such as API Group III mineral oils, PAOs, and synthetic and vegetable based esters. In one example (a bulk oxidation test run for 72 hours at 160 degrees C), the viscosity of Kings 13.5 cSt AN showed almost no increase, long after the alternatives had shot skyward by anywhere from 300 to 900 percent (Figure 1, page 42).
Another crucial property is additive solubility and improved additive effectiveness. This matters because Group III mineral oils and most synthetic base stocks are non-polar and have a hard time holding additives in solution. To optimize additive concentrations, you need a polar blend stock – and esters are more polar than Ans.
But what looks like an ester advantage actually turns out to be a disadvantage, says Hourani. Its all relative. Esters are extremely polar, and alkylated naphthalenes are less polar. But the polarity of esters is so strong that instead of just solubilizing additives, they end up competing with the additives for the surface of the metal youre trying to protect. The AN is not too polar and not too non-polar – its just right, and it does not compete. As a result, additives of all types tend to more effective and often can be used in smaller concentrations.
Mazzo-Skalski concurs that AN hits the sweet spot in solubility, saying, If youre relying on additive chemistry to be the major player in wear protection, you could find a significant advantage using AN. (See Figure 2.) She goes on to highlight another performance advantage of ANs: The oxidation stability of ANs prevents deposit precursors from forming, and when they do form, ANs enhance their solubility, which further improves sludge and varnish performance.
Wear and Seal Properties
Both King and ExxonMobil Chemical have performed extensive tests on the anti-wear characteristics of ANs. In high-speed zones with relatively mild loads and temperatures – like automotive applications – ANs play well, Hourani says. They give you very good film thickness, especially compared to polyol esters. This means lubricants built with AN are better able to resist shearing and maintain their viscosity under a load.
When it comes to base stock impact on elastomer seals, he continues, you want a slight swelling without loss of physical properties. Shrinkage creates leaks, and with too much swelling you start losing physical properties like tensile strength, compressive strength and hardness. Every seal should be tested individually because there are so many seals and possible combinations. Hourani and Mazzo-Skalski agree that ANs are, in most cases of seal compatibility, a drop-in replacement for esters.
Some see viscosity index as ANs Achilles heel, the principal area where esters outperform them. Exxon-Mobils Synesstic brand 12 cSt, for example, has a V.I. of 124, while the 5 cSt musters just 74 V.I. But according to Mazzo-Skalski, thats typically not an issue. A lot of customers use a PAO/AN blend or a Group III/AN blend, and the V.I. issue surprisingly doesnt have as big an impact on low-temperature properties as the mineral oils.
Mazzo-Skalski notes that ANs also provide good performance in compressor lubricants, which often face issues of hydrolytic stability, as well as compatibility issues with the gases or liquids being compressed. ExxonMobil Chemical also focuses on automotive applications, both gasoline and diesel, industrial applications and greases.
Used in the latter, she adds, AN enhances the solubility of grease thickeners and disperses them better, reducing the amount of thickener needed. That helps low-temperature properties and improves other properties as well. And you save on the cost of thickener. In FE9 high-temperature bearing tests, AN greases were able to show more than a six-fold improvement in high-temperature bearing life compared to PAO greases, she points out. (See Figure 3.)
We see tremendous growth in the use of alkylated naphthalenes going into the future, says Andy Winter, senior market planner at ExxonMobil Chemical in Houston. Were especially excited about the opportunities for alkylated naphthalenes in food-grade lubricants and greases. They are good in any environment that is moist and hot.
Having received NSF H-1 and HX-1 registration for its Synesstic ANs in 2009 (for use in lubricants for incidental food contact), Exxon- Mobil Chemical this year began strongly promoting their use in food-processing applications. This is a growing market, Winter says. As food regulations continue to tighten and companies put in more automated equipment, the need for lubricants approved for incidental food contact will expand. That equipment represents a huge investment, and theres a big emphasis now on using higher quality lubricants.
Privately held King Industries has held food-grade registration for its KR line of ANs since 2007, and considers food processing as one of many important niche markets. Tom Pane, global sales and marketing manager, says these molecules are strategically important to his company.
Alkylated naphthalene finds uses in all product areas any time youre looking for longer life and better performance, whether that be hydraulic oils, industrial oils, compressor oils, automotive engine oils, gear oils, greases, food-grade lubricants, transformer oils – whatever, he says. With the range of viscosities we have, I would say there are not many areas where ANs wouldnt have some application.
Hourani adds, Our success, besides solving problems, has been where we have allowed a customer to formulate an advanced lubricant or develop a new system.
ExxonMobil Chemical has its eye on new markets too, says Carolyn Moore, global marketing manager for synthetics in Houston. Were always testing. Sandy [Mazzo-Skalski] goes out and talks to customers, and when customers have a need, we decide if we believe AN can meet it. Thats how we got into the food-grade registration. Its really a focus on customer needs and the value we believe we can bring.
Not everyone needs a Leatherman on their belt. But if youre a lubricant formulator, AN could belong in your toolbox.