Studies on Determination Methods for Neutralization Number of Lubricating Oils and Additives (1)

Abstract

The accuracy, precision and rapidness of several methods for determining base numbers of basic lubricating additives and blended oils were compared, since the widely used JIS K 2502 method (equivalent to the ASTM D 664) is not entirely satisfactory.While sulfuric acid-potassium hydroxide back titration in the same solvent as the JIS method and perchloric acid titration in methyl isobutyl ketone solvent were better than the JIS method, the best method was found to be perchloric acid titration in glacial acetic acid solvent (the glacial acetic acid method) proposed by Abbott and Farley.When the glacial acetic acid method was applied for used oils, the base numbers could not be determined frequently because of the lack of sharp inflection. A new technique has been developed to eliminate this defect by modifying the glacial acetic acid method to its back titration method with sodium acetate, which gave sharp inflection for used oils, thereby yielding essentially identical results with those by the forward titration method for additives and fresh oils. In order to obtain precise results by the above method, size of the sample should be so chosen that the back titration is from 30 to 70 percent of the blank.