The peculiarities of the mechanism of the direct oxidation of benzene to phenol in the barrier discharge
S. V. KUDRYASHOV, A. YU. RYABOV, A. N. OCHERED’KO
Institute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
Keywords: benzene, direct oxidation, barrier discharge, phenol, reaction mechanism
Abstract
The results of experiments on the direct oxidation of benzene to phenol using oxygen and air in a barrier discharge under the conditions of efficient removal of reaction products from the reaction zone are presented. In the case of benzene oxidation with oxygen, phenol content in the products reaches ~73 wt%, while arenediols are formed in insignificant amounts (~8 wt% as a total, mainly hydroquinone). The oxidation of benzene with air leads to an increase in the phenol content in the products to ~77 wt% and a decrease in the content of diatomic phenols to ~3 wt%. The conversion of benzene per single pass of the vapour-gas mixture through the reactor reached 0.5 wt% in oxygen and 0.4 wt% in air. The direct oxidation of benzene to phenol with air is accompanied by the formation of a precipitate. Its structure has been studied, and the mechanism of its formation has been discussed. It has been shown that the formation of the precipitate during benzene treatment with air is caused by reactions involving excited nitrogen molecules. The main stages of the mechanism of oxidation are considered in detail, and the results of calculations of electron energy losses in electron-molecular reactions occurring at the discharge initiation stage in the barrier discharge are presented. These calculations allow estimating their contribution to the mechanism of formation of intermediate active particles and stable molecules, as well as the routes of the benzene oxidation process in the barrier discharge plasma. It has been demonstrated that phenol formation occurs as a result of direct interaction between the benzene molecule and atomic oxygen. It has been shown that phenol formation occurs as a result of the direct interaction of the benzene molecule with atomic oxygen. It is demonstrated that benzene oxidation in the barrier discharge surpasses some thermocatalytic methods in terms of reaction rate and exhibits comparable results in terms of phenol formation selectivity.
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