Chemical Structure Bases for Oxidation Stability of Neutral Base Oils

A statistical approach was used to evaluate the oxidation stability of neutral base oil blends in terms of their chemical structure. Different oxidation bench methods were, therefore, applied to follow deterioration of the oils through the initial, breakdown, and final oxidation stages. For the initial stage, a statistical blocking of data was used in terms of the absence or presence of diaromatics to improve the derived correlations. Mathematical equations were derived for zero diaromatic oils by simple linear curve fitting while the application of multiple linear regression gave meaningful models for the diaromatics-containing oils. In the breakdown and final oxidation stages, significant models were obtained by multiple linear regression using five different chemical structure independent variables. To check the statistical validity of the derived models, the “F” values and correlation coefficients “R2” were calculated where their values proved the validity with a minimum of 95 percent confidence. The derived models indicate that, in the evaluation of oxidation stability for neutral base oils, not only sulfur content and saturates should be considered, but also the aromatic-type distribution.