Continued from page 18
In addition, EEB has a very high viscosity index, exhibits excellent shear stability and good low temperature properties. Therefore, EEB is an excellent choice for formulating energy efficient lubricants, for example gear oils or compressor fluids.
High viscosity esters Esters are the most flexible and thus most diverse class of base oils as all important properties can be modified by a clever selection of raw materials used for ester synthesis. Of course, properties cannot be modified independently of each other, so normally the best possible compromise of properties and costs needs to be achieved.
The most flexible way to make high viscosity esters is the complex ester route. Complex esters are made by a combination of a polyol, a di-acid and a mono acid - alternatively also a mono-alcohol. The resulting products are mixtures of different oligomeric or polymeric ester species.
Market standard complex esters predominantly are made of oleochemical raw materials and fall into two generic groups: unsaturated or fully saturated systems. Saturated complex esters are often built around C8-C10 acid or isostearic acid. These raw materials are expensive with pronounced price fluctuations and issues around supply. Unsaturated systems are built around unsaturated mono-acids like animal or vegetable derived oleic acid. Oleic acid is a readily available raw material at reasonable cost, which is a main advantage of the resulting esters.
Unsaturated esters combine a set of excellent properties including lubricity, very good low temperature properties and high biodegradability. One major deficiency of unsaturated esters is oxidative stability, limiting the applicability under severe conditions. In such cases, saturated systems are the better choice as they
generally exhibit excellent oxidative stabilities. Thus, the selection of unsaturated or saturated ester is often a trade-off between cost and stability.
A promising way to reduce cost of fully saturated esters is to change the raw material basis to pure petrochemical raw materials. Better supply security is often an additional benefit.
Pure petrochemical derived esters of course lack any renewable content, but in terms of performance such esters match or even outperform market standard saturated high-viscosity esters and they come at only a slight premium compared to unsaturated systems.
Figure 6: Performance profile of an optimised petrochemically derived complex ester in comparison with market standard unsaturated and saturated technologies
Summary
High viscosity base oils are key components for formulating industrial oils and a wide range of established as well as innovative technologies is available. High viscosity base oils are often a key cost driver in formulations. Therefore, it is very important to select a technology with an appropriate cost-performance ratio.
Each technology has individual strengths and limitations. The final selection depends on the target performance and the requirements of a given application.
LINK
www.basf.com
Figure 5: Esters – Most flexible and diverse class of base oils 20 LUBE MAGAZINE NO.153 OCTOBER 2019
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