Study of furanic compounds sorption behavior in transformers’ insulating materials

• Sorption equilibrium and kinetics of furanics in oil-paper systems were studied. • Linear adsorption isotherms adequately describe the equilibrium. • Pseudo-first and pseudo-second order models describe the kinetics of adsorption. • The model furanic compounds (FOL and FAL) exhibit different behavior. • The moisture content of transformer papers impacts the adsorption of furanics. Deterioration of electric transformers’ insulating systems can be monitored using specific markers, such as furanic compounds formed by degradation of cellulosic materials (insulating paper) impregnated with mineral oil. However, the presence of these markers in the insulating oil can be masked by their adsorption on paper, which may occur during aging tests and/or the preparation of aged oil samples for analysis. Hence, it is important to assess the partitioning of aging markers in insulating systems comprising mineral oil and paper. In this work, furfural (FAL) and furfuryl alcohol (FOL) were chosen as degradation markers to study adsorption equilibrium and kinetics of furanic compounds in oil-paper systems, at 30 °C. Two insulating papers were tested, using distinct initial moisture content and FAL/FOL mass ratio. Overall, the results showed that the partition of FAL and FOL in the oil-paper systems is influenced by the solute’s molecular structure, by the morphological surface of the paper, and by its moisture content. In the range 3.2 wt.% to 8.7 wt.% H 2 O, when the paper moisture content increases the concentration of furanic compounds in the oil is lower which means the furanic compounds migrate to the paper. Single and multicomponent equilibrium adsorption data were successfully fitted to a linear isotherm equation and kinetic data were fitted to pseudo-first and pseudo-second order models. These models are useful to plan the analysis of degradation markers in oil-paper insulating systems of electric transformers, which should consider their partition in both phases.