Chemical structure of greases in a nutshell

Chemical structure of greases in a nutshell

Greases are paste-like lubricants that are generally a yield of the reaction between base oils and metal hydroxides with acids and have consistencies ranging from semi-liquid to solid and consist of emulsifying agents determined by the application area.

According to the historical records, around 1400 B.C., Egyptians prepared greases by combining olive oil with lime and used these lubricants in various vehicle wheel journals. The production of sodium (Na) greases started in the 1870s which is followed by the production of aluminum (Al) and calcium (Ca) greases in the 1880s and the lithium and complex soap greases, which rapidly came into wide use, were invented during the World War II. Patents of the first barium (Ba), lithium complex (LiX) and aluminum (Al) soap greases were registered in 1952.

Considering the sales volumes, lower amount of sales compared to other lubricants does not mean that the greases are of poor quality or not as widely used as other lubricants. On the contrary, greases entirely require extensive knowledge, research, R&D and innovation and are harder to produce than other lubricants only because they offer longer lubrication periods and shelf life.

Metal soap greases are the most commonly used grease types (80-85%) in the world. Greases that do not contain metal soaps are usually preferred for more specific sectors and processes. Nowadays, the new technology "Calcium Sulphonate Complex" greases are replacing many other grease types.

What do we expect from modern lubricating greases?

If the sector or process you work in includes;

  • High speed rolling bearings
  • Long-lasting lubrication time requirement due to the difficulty of the lubrication point
  • Rolling bearings operating at very high or low temperatures
  • Neutral against elastomer and plastic seals in your system
  • Reduction in maintenance and repair costs
  • Less labor because of the compatibility with central lubrication systems
  • Silent operation
  • And more,

grease is a must.

How are they obtained?

A metal soap is obtained through a chemical saponification process. A fatty acid reacts with a metal hydroxide. Metal soap and water are released during this reaction process. These two reaction products are both neutral, so this chemical reaction is also called the neutralization reaction.  

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Table 1. Acids used in the reaction

Fatty acids are obtained from animal or vegetable oils by chemical separation (in acid or alkaline medium). In this process, glycerol (multi-bound alcohol) emerges as a by-product and is withdrawn from the system.

Metal hydroxides used in reaction

  • Al(OH)3 = Aluminium Hydroxide
  • Ba(OH)2 = Barium Hydroxide
  • Ca(OH)2 = Calcium Hydroxide
  • LiOH       = Lithium Hydroxide
  • NaOH     = Sodium Hydroxide

Metal soap greases are classified as simple and complex soap greases. As the name suggests, production of simple soap is not as difficult as the complex soap. For production of simple soap, a fatty acid that gives a neutralization reaction with a hydroxide is used.

STEARIC ACID + LITHIUM HYDROXIDE = SIMPLE SOAP

The simple soap obtained is also called Lithium simple soap. Lithium simple soap and mineral oil (base oil) greases are the most commonly used standard greases.

Complex soap grease production, as the name suggests, is more complex, takes longer to obtain and requires deeper product know-how than simple greases. To produce complex soap grease, a hydroxide is saponified with two different fatty acids:

STEARIC ACID + ALUMINUM HYDROXIDE = COMPLEX SOAP

BENZOIC ACID

All mentioned "metals" are combined with known base oils and used in complex soap greases (Mineral, PAO, Ester, Poly Glycol, Silicone, PFPE). Thus, very specific and featured products are obtained to meet the needs for defined applications.

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Efsun ACAR

Chemical Engineer

Vario Engineering and Production Technologies Inc.

Production Coordinator

8.11.2020 12:00:00
209

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