Application of Highly Selective Adsorbent in the Removal of Elemental Sulfur and Other Corrosive Sulfur Compounds From Mineral Insulating Oils

The presence of corrosive sulfur in the oil increases the risks of power transformer failures. This is very pronounced in the case of the presence of elemental sulfur (S
₈
) in the oil a compound found to be highly reactive to metals, especially to silver at lower operating temperatures causing formation of conductive silver sulfide deposits on the contacts of on-load tap changers. Highly selective adsorbent (HSA) as new mesoporous material is synthesized in the novel procedure to be applied in the removal of corrosive sulfur compounds from the oil. The removal of corrosive sulfur compounds by HSA is obtained by chemical reaction, i.e., chemisorption. The procedure for the preparation of HSA consists of deposition of silver ions on the silicon dioxide support. Both compounds added in well-defined and optimal concentration range are necessary to produce adsorbent of high efficiency in the removal of S
₈
and other corrosive sulfur compounds and to obtain good oil properties after treatment. HSA is characterized by nitrogen adsorption–desorption isotherms to define specific surface area, particle size distribution, and porosity. Since the efficiency of conventional adsorbents is found to be lowest in the case of elemental sulfur, among all corrosive sulfur compounds, the efficiency of HSA application in the removal of S
₈
is verified on lab-scale system, pilot-scale system, and on-site oil treatment on 35-kV power transformer. Adsorption kinetic study is performed in order to better understand the mechanism of sorption process and potential rate-controlling steps. The pseudo-second-order model adequately fits the S
₈
kinetic data confirming that chemisorption is the rate-limiting step.