Oil Acidity and Basicity

The acid-base determination of petroleum products in media of low polarity with micellar properties has not been an easy analytical problem to solve (Fox et al., 1987 and, 1991a Pawlak et al., 1989). Many lubricants for internal combustion engines contain high content calcium carbonate, calcium borate 

In petroleum oils, no ionization of acids, bases or salts takes place. Thus, the pH concept cannot be used directly (Frewing, 1962) however, the properties of base and acid mixtures in low-polar media have been studied extensively (Pawlak et al.,1989). Information from these studies has been used to overcome the difficulties inherent in analyzing petroleum products. 

High values of TAN and low values of TBN, compared to those of the fresh oil, indicate that the oil has lost some of its ability to neutralize acids. When the TBN is less than 2 (ASTM D2896), the oil reserve alkalinity is depleted when the TAN is greater than 7 (ASTM D664), the oil is acidic and may not adequately protect the engine from corrosion (Smolenski and Schwartz, 1994). 

The TBN method using 2-propanol/toluene/water as a solvent and hydrochloric acid as titrant served for a number of years. Initially presented as a tentative method in 1942, after several revisions it was published as an accepted IP method IP 177 (ASTM D-664). In 1964, however, serious discrepancies appeared when 

A positive TBN value indicates the absence of free strong acids. If free acids of the strength of sulfuric acid are present, then a TBN of zero is obtained. 

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