Significance and Principle Involved in Determination of Acid Value, Saponification Value, Ester Value

Determination of Acid Value

Significance

• Oil becomes acidic with the oxidation or hydrolysis of moisture in the atmosphere leading to fatty acid formation.
• While being operated, lubricants containing a large amount of acid cause metals to corrode and form gum and sludge.

Principle

If CMM samples contain high levels of fatty acids, they may develop rancidity when stored. Fats, aldehydes, carboxylic acids, and ketones are released during decomposition. It would then impair the quality of CMM samples since they would smell distinct. The acid value is based on the quantity of potassium hydroxide required to neutralize one gram of free acid in one gram of fats, oils, or similar substances. Additionally, sodium hydroxide may be required.

Three methods are available -

• Acid value determination
• Standardization of sodium hydroxide titrant
• Reagent
• Titration of test solution
• Reagent

Determination of Saponification Value

Significance

Petroleum oils cannot be saponified, whereas oils from animals and plants can. Usually, blends of lubricating oils have a saponification value that indicates the contents of vegetable and animal oils. A change in saponification value indicates that an oil has been adulterated since blended oils have their own characteristics.

Principle

• Saponification is the process of hydrolyzing fats or triglycerides by combining them with a strong alkali in order to create glycerol and potassium salts of them.
• An excess of alcoholic KOH is refluxed with a known quantity of fat or oil.
• A titration against a standard acid determines the remaining KOH after saponification.
• Saponification number of fats or oils is determined by using the value obtained.

Determination of Ester Value

Significance

One gram of fat or oil requires a certain amount of KOH to saponify the esters. There will be a greater amount of ester in the oil sample if the number is greater. The acid number indicates the amount of potassium hydroxide that was added to neutralize one gram of oil's free fatty acid content.

Principle

Esters are saponified with potassium hydroxide when a substance has the esters of 1 gram of potassium hydroxide. Milligrams of potassium hydroxide must be added to one gram of oil sample in order to hydrolyze the esters. Separating the acid value from the saponification value is the Ester value. Molecular weight is low in high ester values, while their ester content is high.

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