Naphthenic acids titration

Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

Total Acid Number—to provide an indication of the naphthenic acids content (ASTM Test Method D664, Acid Number of Petroleum Products by Potentiometric Titration). ... 

Naphthenic acid is a kind of organic acid in crude oils and has a saturated ring structure. Its content is typically measured and indirectly expressed by non-aqueous titration with potassium hydroxide (mg KOH per 100 ml for clean oils) or total acid number (TAN, as milligrams of KOH required to neutralize the acid in one gram of oil). Naphthenic acid in crude oils is a rather complex mixture. Its molecular weight ranges from 180 to 700, mainly from 300 to 400 [4]. 

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