Homogeneous catalytic oxidation of toluene under the ultrasonic action

Abstract

The regularities of toluene catalytic oxidation with molecular oxygen catalyzed by cobalt (II) acetate in a liquid phase under the ultrasonic action have been researched. It was found a close relationship between the temperature and pressure of the oxidation process. The relationship determines the reaction rate, the reaction products composition, and the toluene limiting conversion value. It was found that the ratio between a sonochemical reaction rate and a toluene oxidation reaction rate without ultrasonic action increases with increasing the reaction temperature both at the process initial stage and higher values of hydrocarbon conversion. Simultaneously, an increase in the rate of toluene oxidation reaction under the ultrasonic action was detected only at a temperature of 430–438 K and a pressure of 0.4 MPa. Under all other conditions the rate of sonochemical reaction is lower than the toluene oxidation rate without ultrasonic action. An extreme reaction rate dependence of the homogeneous catalytic toluene oxidation on pressure at constant temperature was revealed. It is established that the reaction rate decreases with pressure increasing under the ultrasonic action more significantly the higher the reaction temperature is. In general the sonochemical reaction rate is lower than the rate of catalytic toluene oxidation. It was shown that ultrasound affects the concentrations of all reaction products. The relationship between the product concentrations obtained in the sonochemical reaction and in the toluene oxidation reaction without ultrasonic treatment depends on temperature and pressure. It is established that the main changes in the quantitative composition of oxidation products are to increase/decrease the benzoic acid and benzyl alcohol concentrations under the ultrasonic action. The decrease in the sonochemistry reaction rate of toluene catalytic oxidation at the reaction initial stage and its simultaneous increase at higher values of hydrocarbon conversion, as well as changes in the reaction products selectivities, and the ultrasonic effect on the toluene limiting conversion indicate that the cavitation affects on the changes in the regularities of catalyst-intermediate complexes transformations.