The response to antioxidants in base oils of different degrees of refining

Base oils with different compositions and different degrees of refining have been subjected to three types of oxidation stability tests in the presence of antioxidants. A higher degree of refining of base oils depletes the natural antioxidants present in oils of lower degree of refining. However, the results of the study show that oxidation stability of highly refined oils, after addition of suitable antioxidant packages, by far outperforms that of the oils of lower degree of refining. This is true regardless of the dominating hydrocarbon type in the oil, or its feedstock origin. The results also show that in general, the viscosity index of a base oil, or any other simple physical property, has no direct correlation to oxidation stability or response to antioxidants. To analyse the response to antioxidants, a concept called oxidation stability response is introduced. A novel method for determining the oxidation onset temperature in differential scanning calorimetry measurements by inverse derivatives is introduced.