Sulfur Content

Sulfur is viewed as an index of inherent antioxidant capacity in virgin lube oil. With re-refined oils, hydrocarbons that were inherently oxidatively unstable would have 96 been oxidized during previous use. It is necessary to identify the types of sulfur content, both in virgin lube oil and used oil, in order to better understand the role that sulfur plays. Total sulfur content in an oil sample is determined by a sulfur-in-oil analyzer, Model SLFA-20/20T manufactured by Horiba Ltd., Japan. The measuring principle for this unit is the non-dispersive x-ray fluorescent (NDXRF) analysis, with a measuring range of 0-5 m/m%, repeatability of 15 ppm, and a detection limit of 20 ppm. It also uses the automatic C/H ratio compensation function to solve the problem of measurement error, which is caused by different types of oil. Any oil sample with water content more than 1v/v%, however, is not recommended to determine its total sulfur content with this instrument since noticeable deviation from actual concentration is expected to occur. Different organo-sulfur type can be determined by GC-MS. The type of sulfur compounds in lube oil may change after use and may change further after ultrasonic irradiation. It’s important, therefore, to differentiate the sulfur type as well as measure the total sulfur content. Although the total sulfur content in the used oil sample may not change after treatment, but the individual sulfur species may change. After ultrasonic treatment, some sulfur may be present in water phase as sulfate or sulfide. Sulfate concentration in water can be determined by turbidimetric method. Sulfide concentration in water can be determined by iodometric method