Development of a model system to study fuel autoxidation in supercritical media: decomposition kinetics of 2,2′-azobis(isobutyronitrile) in supercritical carbon dioxide

A high pressure reactor has been constructed and used for in situ spectroscopic measurements of reaction kinetics in supercritical fluids. The thermal decomposition of 2,2′-azobis(isobutyronitrile) (AIBN) in supercritical carbon dioxide (SC-CO2) was studied as part of an effort to characterize free-radical autoxidation of hydrocarbon fuels under supercritical conditions. The findings show that AIBN decomposes both thermally and photochemically in SC-CO2 to form the 2-cyano-2-propyl free radical which dimerizes to form tetramethylsuccinic dinitrile and dimethyl-N-(2-cyano-2-propyl) ketenimine. Examination of the decomposition kinetics of the ketenimine revealed that it was photochemically stable in the kinetic reactor, but decomposed thermally to form the dinitrile.