This paper describes a new alkylation technology that is very effective at synthesizing structurally different alkylated diphenylamine chemistries relative to those currently available to lubricant formulators. Examples are provided showing how this technology can be used in a practical way to produce a variety of chemically modified nonylated diphenylamine types. One example is also provided illustrating the preparation of a higher molecular weight dodecylated diphenylamine. Engine oil performance data utilizing pressurized differential scanning calorimetry (PDSC), the thermo-oxidation engine oil simulation test, and a bulk oil oxidation test demonstrate that subtle changes in alkylated diphenylamine chemical composition can result in significant oxidation and deposit control performance enhancements or losses. Examples of similar performance responses in industrial oils are demonstrated utilizing PDSC and the rotating pressure vessel oxidation test. These performance changes are directly related to specific structural changes in the modified products.

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The current turbine oil oxidation bench tests have been in place for many years. Recently, however, the basestocks used to formulate these lubricants have changed significantly. Traditional basestocks, containing high levels of aromatics and sulfur, have been substantially displaced by more highly refined basestocks, which have very low levels of aromatics and almost no sulfur. Over time it has become clear that the oxidation performance of the different basestock classes is quite different. One key question, however, remains unanswered. “What modifications are required in current bench tests to adequately mimic oxidation processes in modern turbine lubricants?” In order to adequately address this critical question, the fundamentals of lubricant oxidation and stabilization will be discussed. Data will be presented on the oxidation of different basestocks under varying conditions of temperature, metal catalysts and antioxidant type, using model bulk oil oxidation tests. The data highlights the fundamental oxidation mechanisms that can occur in turbine oil systems and new test methods are proposed.

Using simple turbine oil formulations, we studied the effects of different antioxidant systems on oxidation behaviour. Fourier transform infrared was used as a sensitive probe to monitor the depletion of different antioxidant types present in turbine oils based on Group II, III and IV base stocks. It was found that the depletion of alkylated diphenylamine antioxidants from turbine oil systems is generally slower when hindered phenolics are present in the formulation. Furthermore, the type of hindered phenolic used in the formulation is critical for preserving this amine activity, with the bis-phenolic 4,4-methylenebis(2,6-di-tert-butylphenol) showing superior performance over a phenolic ester of approximately the same molecular weight. This effect was explained by the higher hindered phenolic activity of the bis-phenolic relative to the phenolic ester. The ability of the bis-phenolic to preserve or protect the amine antioxidant, combined with its higher hindered phenolic activity, was shown to improve the oxidation resistance of turbine oils. The results also showed a surprisingly high oxidation stability for turbine oils formulated with Group III base stock, with the oxidation resistance of the Group III systems exceeding that of the equivalent Group II and Group IV systems.

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