BACKGROUNDNowadays, different automotive sources generate globally large amounts of used oils. To achieve maximum energy conservation and environmental benefits, re-refining of used oil is preferable. Since removal of silicon and its chemical species is of great interest in the oil recycling industry, the aim of this study was to improve understanding of the behaviour of silicon-containing compounds at industrially relevant alkali treatment conditions.RESULTSAt industrially relevant alkali treatment conditions transformations of the model hydrogen-terminated tetramethyldisiloxane (TMDS) resulted in the formation of solid siloxanolate salts. The activation energy for TMDS transformation in the presence of 33 wt% aqueous KOH was found to be 37 kJ mol−1, which is almost two-fold lower than that for NaOH. The experimental data demonstrated that the formation of solid products undesired from an industrial point of view can be diminished by an addition of either an alcoholic solvent or dimethyl carbonate.CONCLUSIONSThe experimental results obtained can be utilized for optimization of silicon-containing used oil recycling. In particular KOH as an alkali agent is more efficient than NaOH; addition of methanol dramatically increases the reaction rate, while dimethyl carbonate introduced into the reaction mixture enhances selectivity to the liquid products.