PHENOMENOLOGY OF ETHYLBENZENE AUTOXIDATION IN THE PRESENCE OF SURFACTANTS

The oxidation of hydrocarbons with molecular oxygen is one of the most attractive areas of petrochemical synthesis: peroxides, ketones, acids and other oxygencontaining products.On the other hand, an urgent task is the protection of organic materials, such as edible and industrial oils, fuels, cosmetics and others from thermaloxidative destruction under the influence of atmospheric oxygen.The scientific basis for controlling oxidation processes is the theory of liquid-phase oxidation, developed in relation to homogeneous and heterogeneous processes.Additions of surfactants to hydrocarbons regulate the microstructure and prevent the release of water dissolved and formed during operation.The effect of surfactants on the oxidation of hydrocarbon substrates has practically not been studied, although a priori one can expect significant effects associated with the possibility of association of surfactants and oxidation containing polar oxygen-containing groups, the involvement in these associates of inhibitors, including fragments and, consequently, changes in their reactivity and even the direction of reactions involving these compounds.In recent years, surfactants, or phase transfer catalysts (PTS) as they are often called, have been widely used in various catalytic processes, which has resulted in studies of the influence of individual PTS on the kinetics of the process.Autoxidation of ethylbenzene (RH) develops with auto-acceleration.The kinetic curves of hydroperoxide accumulation, oxygen absorption and RH consumption are described by a hydrophilic set of reactions of nucleation, continuation, degenerate branching and chain termination.Screening of surfactants and microdispersed oxides for their effect on the rate of RH oxidation showed the following: nonionic surfactants that are highly soluble in ethylbenzene-oligomeric arylpolyxethylenes and microdispersed oxides-have virtually no effect on the rate of ROOH accumulation.AOT (n-heptene-bis-(2ethyl hexyl sulfosuccinate), the molecule of which includes two hydrocarbon fragments and which forms thermodynamically stable inverted micelles in hydrocarbons, also does not affect the accumulation of ROOH.The addition of an anionic surfactant -sodium dodecyl sulfate (SDS) completely inhibits the accumulation of ROOH.Cationic surfactant-CTAB (cetyltrimethylammonium bromide) accelerates the accumulation of ROOH.Under conditions of azobisisobutyronitrile (azobisisobutyric acid dinitrile, AIBN) initiated oxidation of ethylbenzene at a constant rate of chain initiation (wi=constant), the additions of all studied surfactants did not affect the absorption rate by the possibility of association of the surfactant and oxygen.that a significant effect on the oxidation rate of RH provides ionic surfactants, i.e. sodium dodecyl sulfate and cetyltrimethylammonium bromide, and the key reaction, the rate and possibly the mechanism of which changes in the presence of a surfactant, is the decomposition of ROOH, which determines the rate of chain initiation under autoxidation conditions.