Novel Ester-Functionalized HV PAO Base Stock for Advanced Lubricant Formulations
By Mary Moon, PhD, of Presque Isle Innovations, LLC | TLT CMF Plus November 2017
Figure 1. Reaction of LAO and 9-DAME to produce WTP 40 polymers with chemically bonded ester groups.
LANXESS AG (Cologne, Germany) and Elevance Renewable Sciences, Inc. (Woodridge, IL, US), have joined forces to commercialize an innovative high viscosity base stock for industrial and transportation lubricants. Elevance Aria® WTP 40 contains polymer molecules engineered to provide advantageous performance and ease of use. The unique molecular structure of WTP 40 provides exceptional lubricant film thickness and protection against friction and wear under severe conditions including boundary lubrication. Breakthroughs in catalyst and manufacturing technologies are used to synthesize WTP 40, an ester-functionalized PAO, from esters and linear alpha olefins.
Suggested applications of WTP 40 (kinetic viscosity 40 cSt at 100 °C) range from transportation driveline and engine lubricants to industrial gear box oils, compressor oils, metalworking fluids, hydraulic fluids and lubricating greases. WTP 40 is compatible with mineral oils and many other synthetic base stocks. It is registered as an HX-1 additive for food grade lubricants. Because WTP 40 is obtained partially from bio-based materials, it can contribute to sustainability criteria for environmentally advantaged lubricants.
A New Partnership
Multinational specialty chemicals company LANXESS was formed in 2004 from the chemicals division and parts of the polymers business of Bayer AG. Effective April 21, 2017, LANXESS successfully completed the acquisition of Chemtura Corp. (Philadelphia, PA, US) and merged Chemtura’s Petroleum Additives and Bromine Solutions segments with their Rhein Chemie Additives business unit to form a new Specialty Additives segment.
One of their first strategic moves was to secure global rights to develop, create derivatives, manufacture, use and sell Elevance Aria® WTP base stock technology.
According to David Stonecipher, Strategy & Business Development Manager, Business Unit Additives, LANXESS Solutions US Inc., “Our Lubricant Additives Business offers a comprehensive line of products, from synthetic base fluids to single additives and additive packages, to fully formulated specialty lubricants, which help our customers lubricate all kinds of engines, transportation equipment and industrial machinery.
“We licensed WTP base stock technology from Elevance because we feel confident that we can help formulators experiment with this exciting new base stock chemistry and develop value-added lubricants that will set new performance benchmarks that excel beyond products based on conventional blends of PAO and ester base stocks.”
Elevance, one of the leading companies in the biochemistry industry, operates an 180,000 MT biorefinery in Gresik, Indonesia. This biorefinery processes plant-based materials and produces novel oleochemicals for use in cleaners, personal care products, coatings, oilfield chemicals, and lubricants.
New Chemical Synthesis
WTP 40 is not a mixture of separate PAO and ester base stocks. Group IV PAOs are go-to base stocks for formulators who want to develop premium lubes to meet demands for superior performance at extreme operating temperatures, viscosity that undergoes only minimum change with temperature (high viscosity index), long service life and other advantages.
Formulators frequently blend ester base stocks with PAOs to increase solvency or the ability to dissolve corrosion inhibitors, anti-wear and other additives. Synthetic esters also help balance elastomer seal compatibility of PAO base stocks.
“With WTP 40”, Stonecipher explained, “you have a new base stock with all the advantages of PAO plus improvements from built-in ester groups. Elevance converts fatty acids found in palm oil to 9-decenoic methyl ester (9-DAME) using proprietary catalyst technology. 9-DAME is a highly reactive and versatile chemical building block that we think will be very important to the future of the lubricants industry.”
“And then, LANXESS scientists and engineers apply a proprietary process to polymerize 9-DAME with LAOs (linear alpha olefins) to make ester-functionalized PAO – our WTP 40.” (Figure 1)
Why hasn’t someone manufactured ester-functionalized PAO until now?
New specialty chemicals are rare because they must satisfy rules of nature (chemical bonds, etc.) and there must be practical means to produce commercial quantities. In 2005, the Nobel Prize in Chemistry was awarded “for the development of the metathesis method in organic synthesis.”
Metathesis can be used to synthesize new chemicals that cannot be made by any other means by catalyzing reactions between molecules which exchange groups of atoms and form new molecules. Elevance uses metathesis to manufacture the 9-DAME chemistry.
Elevance Aria® WTP 40 Base Stock
WTP 40’s viscosity at 100 °C may be similar to 40 cSt PAO base stocks, but other properties differ significantly because ester groups are chemically bonded in polymer molecules of WTP 40, Table 1
Table 1. Properties of WTP 40 versus 40 cSt PAO base stocks
No Need for Ester Compatibilizers
The ester groups bonded in WTP polymer molecules significantly improve the ability of WTP 40 to dissolve chemical additives used in lubricants. The aniline point of WTP 40 is only 99 °C versus 160 °C for a typical commercial PAO with comparable viscosity (40 cSt) at 100 °C. (Figure 2
Figure 2. Aniline point for WTP 40 is substantially lower than PAO and comparable to Group 1 and Group 2 mineral base stocks.
The low aniline point of WTP 40 is an advantage over PAOs. Lower aniline point means that a base stock contains more polar molecules and is a stronger solvent and better able to dissolve many chemical additives, which tend to be polar. When formulators typically work with PAOs, they need to blend them with compatibilizers such as ester base stocks in order to dissolve polar additives. It should not be necessary to add compatibilizers to WTP 40 because ester groups are already built into polymer molecules of WTP. (Figure 3)
Figure 3. WTP 40 is bright and clear like PAO. WTP dissolves 6% of an additive package without a compatibilizer.
Also, the aniline point of WTP 40 is comparable to that of Group I and Group II base stocks. Many additives that were developed for use in Group I and Group II base stocks work well in WTP 40 formulations. Additionally, WTP 40 will be quite compatible in mixtures with these mineral oil base stocks.
Is it difficult to develop formulations based on WTP 40?
Model formulations based on WTP 40 are simpler than formulations based on PAO/ester blends. Table 2 compares two model formulations for SAE 80W-140 automotive driveline lubricants. In the conventional formula, 10% ester was blended with 90% PAOs to dissolve an additive package (6% by weight in the final formulation).
The WTP 40 formulation does not require the addition of an ester to compatibilize the additive package.
Brookfield viscosity at -26 °C for the WTP 40 formula (30,000 cP) was significantly lower than the conventional formulation (43,700 cP). Ester side chains might hinder packing of WTP molecules, which could limit viscosity increase at low temperatures. These results strongly suggest that WTP 40 could be advantageous for use in low temperature lubricant applications.
Table 2. Model 80W-140 automotive driveline lubricants formulated from a conventional PAO-ester blend versus WTP 40 base stocks
How well do simplified WTP 40 formulations perform? In laboratory tests, WTP 40 base stock shows strong potential for severe lubricant applications including boundary conditions such as equipment start-up and shut-down, slow speeds, heavy loads and shock loading.
A Mini Traction Machine (MTM) was used to compare WTP 40 with two PAO/ester blends. The coefficient of friction was 10 to 15% lower for WTP 40 than both PAO/ester blends for slide/roll ratios up to 100% at 100 °C. Wear scar diameters for WTP 40 (425+25 microns) were 5% smaller than for PAO/ester blends (450+25 microns), Figure 4. Results were similar for GL-5 75W-90 lubricants formulated with these base fluids.
Figure 4. Friction and wear data for WTP 40 are superior to PAO 40/ester and mPAO/ester blends.
Additional tests were performed to help understand the superior lubricating performance of WTP 40. Base stocks were evaluated under EHL (elastohydrodynamic lubrication) conditions. Lubricating film thickness in contact between a ¾” (19.05 mm) steel ball and glass disk was measured by optical interferometry under pure rolling conditions (0% slide/roll ratio, from 0.02 to 3 m/s entrainment speed, 40 N applied load, 100 °C). WTP 40 films were thicker than PAO at low speeds (more severe conditions) and comparable at higher speeds (less severe). Boundary lubrication of WTP 40 was better than PAO in this test. (Figure 5
Figure 5. EHL fluid film measurement data showing performance advantage of WTP 40 at slow speeds.
The superior lubricating performance of WTP 40 may be attributed to stronger and thicker adsorbed fluid films, especially under boundary conditions. The ester groups in WTP 40 enhanced film thickness relative to conventional PAOs.
WTP 40 with chemically-bound ester groups shows advantages over simple PAO/ester blends in additive compatibility, shear stability, seal compatibility, friction and wear, foam control, cleanliness and varnish control, and formulation simplicity. Thus, Elevance Aria® WTP 40 shows strong promise for use as a high viscosity base stock in formulations for demanding industrial and transportation applications, especially those where boundary lubrication conditions occur frequently.
® = registered trademark of Elevance Renewable Sciences, Inc, registered in the United States. Used under license from Elevance Renewable Sciences, Inc.