Preliminary Evaluation of Octyldithiobenzoic Acid as an Antioxidant in Mineral and Synthetic Oils 2004-01-3051

Organic composition such as mineral oils and lubricating compositions are subject to deterioration by oxidation and in particular are subject to such deterioration at high temperatures in the presence of air. This deterioration often leads to buildup of insoluble deposits which can foul engine parts, deteriorate performance and increase maintenance.

It is desirable that an effective inhibitor which can reduce deposit forming tendencies and improve antioxidation capacities, is employed in a lubricant oil. In our study, an oil-soluble additive octyldithiobenzoic acid compound derivative of thiosalicylic acid was synthesized. The antioxidation and deposit inhibition properties in mineral 150 SN, ester base or engine oils, were evaluated by differential scanning calorimetry (DSC), oxidation-corrosion tests, and modified micro-oxidation test respectively. In differential scanning calorimetry test, this additive can improve oxidation induction time and onset temperature of mineral oil or engine oil at high temperature, even better than commercial zinc dialkyldithiophospate (ZDDP) and dialkyldithiocarbamate derivative (BDDC) at same treat level. In the oxidation-corrosion test, in comparison to the ester oil, the additive showed a reduction in viscosity increase of about 73.7% at 0.5 wt.% concentration, an increase in the total acid number at 0.5 wt.% concentration of 41.5% less than those of the ester oil. Moreover, these results indicate that the additive shows good oxidative synergies with the arylamine antioxidant or synthetic oil FSPE. In the thin film micro-oxidation test, by means of measurement of deposit weight, the data shows that the additive can reduce deposit formed in base oil or engine oil significantly, and the behaviors of decrease in deposit weight were consistent with the result of the former two antioxidant tests.