Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
reflection of the diversity and availability of raw materials that can be used in their design.
Natural esters are categorised as triglycerides and can be represented schematically as follows:
Figure 1. Schematic representation of a natural ester
The fatty acid composition is important as it is this part of the triglyceride which dictates most of the basic properties of the ester. Vegetable esters typically have kinematic viscosity at 40°C in the range of 32 – 46 mm2
stability to poor oxidative stability depending upon the degree of unsaturation in the fatty acid groups. For example, coconut and palm oils have a low degree of mono-unsaturation and poly-unsaturation and therefore have better oxidative stability properties than rapeseed oil.
The fatty acid part of vegetable and animal oils is a very important raw material in the manufacture of synthetic oleochemical esters. Fatty acids are produced by chemically splitting vegetable and
/s and from 1 to > 2000 mm2
No.100 page 2
animal oils into their constituent parts of glycerol and fatty acids using a hydrolysis process. The acids are then separated from glycerol and water, refined and chemically processed to produce raw materials which can be used in the manufacture of mono- esters, di-esters, polyol esters and polymeric esters.
Acids which can be produced through splitting, refining and additional chemical processing range from C8 – C22 mono- acids, C36 di-acids and C54 tri-acids, all very important building blocks in the manufacture of synthetic oleochemical esters.
Synthetic oleochemical esters are predominantly made by reacting mono- or poly- alcohols with one or more fatty acids, depending upon the required base fluid properties. Typical mono-alcohols would include C1 (methanol) to C18 alcohols (stearyl or isostearyl alcohol). Examples of poly alcohols include petrochemical derived neopentyl glycol, trimethyl propane, pentaerythritol, di-pentaerythritol and the naturally occurring glycerol.
Through appropriate raw material selection it is feasible to make esters with kinematic viscosity at 40°C from 2 to > 50,000 mm2
/s at 100°C. /s and can vary from good oxidative
Petrochemical esters are derived from predominantly petrochemical produced alcohols and acids. Typically petrochemical esters would be considered to have a C renewability content of 0%. Petrochemical esters are widely available and used but tend to have a much narrower viscosity range than synthetic oleochemical esters, typically ranging from 5 mm2
/s up to 460mm2 /s at 40°C.
Key Basic Properties of Esters Compared to Other Base Stocks
Listed in table 2 are some of the basic properties that are desirable for base fluids and the relative strengths of different
LUBE MAGAZINE NO.129 OCTOBER 2015
Table 2. Basic properties of a select range of base stocks 33
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