Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
2.4 Esters are designed Synthetic esters are produced from defined, mostly pure raw materials. These alcohols and acids may be chosen from a variety of available compounds. This ultimately means that: • Synthetic esters are mostly pure materials. The chemical structures are usually well defined and they are composed of a very limited number of compounds, if not one single molecule. There is not any undesirable material in the base fluid, and properties and the behaviour of synthetic esters remain very consistent in operation, thus ensuring optimum performance.
• Mineral or organic impurities may have a significant impact on the performance of the base fluid. Synthetic esters are clean products, which means they do not contain impurities or other compounds not introduced deliberately that may be detrimental to quality – provided the manufacturing process is optimized that way.
• The chemical structure of synthetic esters can be chosen. Trade-offs do exist with synthetic esters, and one may choose to maximize some properties over others, and minimize undesirable features. This can be achieved through careful design of the structure to match, as closely as possible, lubricating needs. This gives some precious flexibility to formulators.
• Whilst most neopolyols derive from petroleum industry (even though biosourced alcohols are coming up), fatty acids may be chosen from vegetable sources, thus allowing the production of esters showing high contents of renewable carbon. This content may be as high as 100% but typically revolves around 70 to 80%.
Synthetic esters constitute a large family of compounds, which may be very different in performance from one another. However, most of them will offer a unique combination of high performance features, including low volatility, high viscosity indices, low pour points, excellent thermo-oxidative stability and low propensity to deposit formation, excellent lubricity, whilst showing a very good environmental profile.
3 Esters in modern, challenging lubricating applications
3.1 Tougher requirements in modern lubrication Market drivers are clearly changing the world of lubrication by promoting: • higher power density, • higher energy efficiency, • increased durability, • lower environmental impact, • more sustainability, • improved safety.
This translates into new legislation prompting OEMs to issue specifications that reflect this in simple terms: added power density, energy efficiency, and durability, whilst environmental impact should be minimized.
LUBE MAGAZINE NO.131 FEBRUARY 2016 33 Figure 9. Comparison between 4 mm2 /s synthetic fluids
The Micro-Coking Test clearly demonstrates improved deposit formation features with the oils that contain the ester (Figure 10).
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From the lubricant manufacturer’s point of view this translates into: • stronger oxidative stress on lubricants, • reducing friction, possibly by reducing viscosity, • keeping volatility at a low level, • harmless, biodegradable and renewable lubricants.
The following is a number of examples of how synthetic esters may contribute to developing such modern – or future – lubricants.
3.2 Latest generation Passenger Car Motor Oil The future 4-stroke engine oils will have to be: • thinner, for fuel economy improvement; • submitted to higher temperatures, for longer times, for better energy efficiency and durability;
• submitted to the increasing presence of biofuels.
Therefore 4-stroke engine oils will have to show lower volatilities, higher thermo-oxidative stabilities, and improved cleanliness features. This is typically what high performance esters should be able to deliver.
A laboratory experiment was conducted, in which 5W-30 oils, one being ILSAC GF-5 compliant, and the other ACEA C1-2012 compliant, were modified by replacing 20% of PAO 4 by a neopolyol ester of equivalent viscosity. Looking at the neopolyol ester properties (Figure 9), improved cleanliness, weaker deposit formation, and lower volatility are expected with this change.
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