Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 37

The acid value (sometimes referred to as the neutralization number, the acid number, or the acidity) is the amount of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of a chemical substance. It is a measure of the number of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds.

In a typical procedure, a known amount of sample dissolved in an organic solvent (often an alcohol, such as isopropanol) and titrated with a solution of potassium hydroxide (KOH) of known concentration using an indicator (such as phenolphthalein) to monitor the color change and thereby determine the neutralization point as a colour indicator (see ASTM D664. Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration).

As an example, the acid number is used to quantify the acidity of a substance such as biodiesel. As oil-fats become rancid, the triglyceride derivatives are converted into fatty acid derivatives and glycerol, thereby causing an increase in acid number. A similar observation is that of biodiesel aging through analogous oxidation processes and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester hydrolysis).

See also: Acidity and Alkalinity, Acid Number, Neutralization Number.