The transformation of silicon species contained in used oils under industrially relevant alkali treatment conditions

BACKGROUNDIn the lube oil re-refining industry silicon, coming mainly from antifoaming agents, is recognized to be a contaminant generating undesired solid deposits. The behavior of the hydrogen-terminated model compound, tetramethyldisiloxane, under base-catalyzed conditions was investigated at 100 °C in dodecane as the solvent with sodium siloxanolate as an alkali agent.RESULTSThe use of sodium siloxanolates led to high reaction rates and selectivity to the liquid products. Experiments with an industrially relevant silicon-containing substrate, namely silicone-based antifoam agent showed that its transformation in the presence of 33 wt% aqueous solution of sodium hydroxide resulted in 80% yield of solid sodium siloxanolates, whereas, when sodium siloxanolate was used as an initial alkali agent, no solid products were formed.CONCLUSIONSExperimental results demonstrated that under alkali treatment conditions silicon-containing species existing in real industrial feedstock undergo transformation reactions, with formation of solid sodium siloxanolates. It was found that the use of sodium siloxanolate as an alkali agent could significantly increase the rate of polydimethylsiloxane depolymerization reaction and completely eliminate formation of the undesired solids under industrially relevant conditions.