A custom built dynamic oxygen uptake tester was used to study the influence of nitrogen compounds on the oxidation characteristics of the saturate fractions from mineral base oils. Expermental results indicate that nitrogen compounds,especially quinoline and indole,take part in the oxidation of saturates.It is also found that indole is more active than quinoline. The latter can be oxidized partly into ketoimine,and the former is more rapidly oxidized into acylamide.The oxidation products, ketoimine or acylamide, could inhibit the oxidation of the saturates by decomposing hydroperoxide.The influences of indole and quinoline on oxidation of saturates are more complex.For lower nitrogen content, the oxidation processes were accelerated.However, at high nitrogen content, the oxidation induction peroids were increased. The oxidation characteristics of saturates were also dependent on the type of catalysts presented.
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