The Total Acid Number (TAN) is the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil. It is an important property of crude oil.

Value of information

The TAN value indicates to the crude oil refinery the potential of corrosion problems due to naphthenic acids. This type of corrosion is referred to as naphthenic acid corrosion or NAC, which is a problem in the 200C to 420C temperature range.

TAN is also an indication of naphthenate problems during crude oil production or desalting.


TAN value can be deduced by various methods, including

  • Potentiometric titration: The sample is normally dissolved in toluene and propanol with a little water and titrated with alcoholic potassium hydroxide (if sample is acidic). A glass electrode and reference electrode is immersed in the sample and connected to a voltmeter/potentiometer. The meter reading (in millivolts) is plotted against the volume of titrant. The end point is taken at the distinct inflection of the resulting titration curve corresponding to the basic buffer solution.
  • Color indicating titration: An appropriate pH color indicator e.g. phenolphthalein, is used. Titrant is added to the sample by means of a burette. The volume of titrant used to cause a permanent color change in the sample is recorded and used to calculate the TAN value.

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