Chemistry – Oil Splitting and Oil Emulsification – Part 2

“Splitting” of oil from a surface as described in a preceding blog is a part of nearly any oil removal process.

Note – Even cleaning chemistry that is generally classified as an “emulsifier” has ingredients to promote the initial “splitting” of the oil from the surface being cleaned.  These ingredients are often called “surface active agents.”

The difference between a chemistry that only “splits” and one that also “emulsifies” emerges when we look at what happens to the oil after it is removed from the surface being cleaned.  In the case of splitting chemistries, the removed oil simply floats to the surface of the tank where it can be collected and removed for disposal or re-use.  In the case of an emulsifying chemistry, the removed oil becomes disbursed in the cleaning chemistry to form what is called an “emulsion.”  In most cases, oil and water that are in an emulsion maintain their original properties but are allowed to mix by the action of micelles (my-cells).

Micelles are molecules of groups of molecules which have the unique property of having one end that is “oil loving” while the other is “water loving.”  In basic terms, a micelle has the ability to “glue” oil and water together.

Emulsifiers, surfactants and other chemicals that promote the emulsification of oil and water are comprised of micelles.  Micelles have been discussed in the blogs Cleaning Chemistry – Water Based Chemistry – Neutral and Emulsions and Cleaning – Soluble Contaminants – “Solvents”.  In most cases, agitation of some sort is required to mix the oil, water and the micelles to cause emulsification to occur.  Of course in automated cleaning systems, agitation is usually present in the form of spraying, turbulation, ultrasonics, etc. so this isn’t a problem.  Once an emulsion is formed, depending on the interaction of the components it can be permanent or, over time, separate back into the original components by gravity separation (assuming, of course that one component has a specific gravity different from the other).

The important difference between splitting and emulsifying chemistries in use is that a splitting chemistry, ideally, only serves to remove the oil from the surface being cleaned.  It does not interact chemically and, therefore, can be used indefinitely without replacement or replenishment.  An emulsifying chemistry, on the other hand has only a limited number of micelles available to allow oil and water molecules to c0-exist.  Once all of the micelles are busy acting as intermediaries between oil and water molecules, no more oil can be emulsified.  Additional oil will simply float to the top of the solution.

When an emulsifying chemistry is used for cleaning, the drag out from the cleaning stage to the rinse will be comprised of oil emulsified with water.  Thorough rinsing, therefore, is required to make sure that emulsified oil does not remain on cleaned surfaces but, rather, remains emulsified in the rinse.  In some cases this may mean that a low concentration of an emulsifying agent be used in at least the first rinse.  Chemistries that are called “free rinsing” usually include ingredients that assure that this won’t happen.

Because of their differences in properties, splitting chemistries are appropriate in applications where there is a large quantity of oil to be removed from a part.  Oil splitting chemistry is commonly used in pre-cleaning applications prior to a more thorough cleaning using an emulsifying chemistry.

–  FJF  –