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Lube-Tech


Figure 5. Effect on OIT of base oil Sulphur content and speciation. The samples all contain primary AO, with additional “base oil” Sulphur species of different types.


In Figure 6, the OIT is plotted against the overall Sulphur content. The strong OIT response of the sulfidic-type “base oil” Sulphur is contrasted against the absence of any effect by the addition of thiophene Sulphur.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.119 page 5


The effect of an added secondary antioxidant in the form of an additive of Dithiocarbamate type is seen in Figure 7. The response to this secondary antioxidant is far more pronounced in Nybase 150 than in the reference Group I SN 150 A base oil. The OIT was increased by a factor of five for Nybase 150, and by about 1.5 times for SN 150 A. This example shows how a more highly refined, low-sulphur base oil displays a better response to antioxidant additives, which is what is often taught in textbooks [6].


In Figure 8, the combination effect from “base oil” sulphur, primary antioxidants and a secondary antioxidant is explored. For low-sulphur doped Nybase 150, N (700 ppm S, sulfide type) the combined response of the sulphur carriers is an improved OIT by a factor of about 1.5. For the next step, increase of total sulphur to the “normal Group I level” of 3 000 ppm Sulphur, an OIT of nearly 50 minutes is reached, which more than doubles the OIT value before “base oil Sulphur” was being added. After reaching about 3 000 ppm, a saturation level effect is observed also here.


Figure 6. The effect on OIT of overall Sulphur content, and the specific effect of different Sulphur carriers.


Figure 8. The effect on OIT during incremental addition “base oil” sulphur to an oil inhibited with primary and secondary antioxidants. The OIT approached 50 minutes for the blend where the total sulphur is ca 3000 ppm. The contribution from the Dithiocarbamate additive alone at 0.1 % is ca. 200 ppm Sulphur.


Figure 7. The effect on OIT by the addition of Sulphur in the form of a Dithiocarbamate additive employed as a secondary antioxidant.


In Figure 9, a look across the base oil groups reveal that a baseline response behaviour to the combination of primary and secondary antioxidants can be observed, at an OIT of ca. 10 minutes. This value is obtained for the


36 LUBE MAGAZINE NO.148 DECEMBER 2018


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