Elemental sulfur (S8) is a corrosive sulfur compound which was found to be extremely reactive to silver, causing intensive silver sulfide (Ag2S) deposition on on-load tap changer (OLTC) contacts in power transformers. A highly selective adsorbent (HSA), called Tesla’Ssorb, for the removal of S8 from mineral insulating oils was prepared from raw material (RM) using the novel procedure. In this study, the adsorption properties of HSA for the removal of S8 from the oil were determined. RM and HSA were characterized using various techniques, such as field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The performance of HSA was determined by adsorption equilibrium, thermodynamic, and kinetic study through batch experiments, at various temperatures and initial concentrations of S8. The obtained results were analyzed by Langmuir and Freundlich adsorption isotherms and it was found that equilibrium data were fitted better with the Langmuir isotherm model. The maximum adsorption capacity was 4.84 mg of S8/g of HSA at 353 K. Thermodynamic parameters, such as enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°), were calculated and it was found that the sorption process was spontaneous (ΔG° < 0) and endothermic in nature (ΔH° > 0). It was found that the adsorption of S8 follows pseudo-second-order kinetic model, and the activation energy indicated the activated chemisorption process.

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Most power transformer failures are associated with the presence of corrosive sulfur compounds in mineral insulating oil, of which dibenzyl disulfide (DBDS) is the best known and most widespread corrosive sulfur compound. The oil of failed transformers usually contained DBDS, a compound with a pronounced affinity for the formation of copper (I) sulfide (Cu2S). Copper (I) sulfide is a compound that does not dissolve in oil, conducts electricity, and can be deposited on the paper insulation or copper conductor of the transformer. Created conductive paths between the windings can initiate turn-to-turn breakdown and failure of the transformer. Several technological procedures have been developed as a solution to oil corrosivity. The application of desulfurization technology developed by the Electrical Engineering Institute "Nikola Tesla" enables the efficient removal of DBDS and aging products from mineral insulation oils.