Reaction Pathways in Lubricant Degradation. 3. Reaction Model for n-Hexadecane Autoxidation

We have developed a reaction model that describes the autoxidation of n-hexadecane under severe conditions. The model rate equations were solved numerically concurrent with optimization of the reaction rate constants to yield the solution that provided the best correlation with experimental data. This numerical analysis showed that hydroperoxides were formed in the reaction step with the smallest reaction rate constants, and they decomposed in the steps with the largest rate constants. Thus, hydroperoxides were key reaction products. A comparison of the kinetics determined in this study with those reported in the literature showed that the rate constant for hydroperoxide formation during the initial stages of the autoxidation compared favorably with that determined by others. The reaction rate constants for the secondary reactions determined for the overall autoxidation under severe conditions, however, differed from those appearing in the literature for the initial stages of paraffin autoxidation. Thus, the kinetics of paraffin autoxidation appeared to depend on the extent of oxidation. An illustration of the implications of these findings to lubricant degradation is also presented.