S. V. Kudryashov

Oxidation of hydrocarbons in a barrier discharge reactor

The oxidation of n-hexane, cyclohexane, cumene (isopropylbenzene), and cyclohexene in a barrier discharge reactor under conditions ensuring effective product transport out of the discharge zone was studied. It was shown that hydrocarbon oxidation reactions can be carried out in barrier discharge plasma reactors with a fairly high selectivity. The oxidation of n-hexane, cyclohexane, and cumene primarily yields the hydroxy and carbonyl compounds alcohols, aldehydes and ketones. The major product of cyclohexene oxidation is epoxycyclohexane (~62 wt %).

Study of the products of benzene transformation in the presence of argon, hydrogen, and propane-butane mixture in barrier discharge

The conversion of benzene in a medium of Ar, H2, and propane-butane mixture in a dielectric-barrier discharge reactor, accompanied by polymerization yielding liquid and solid compounds, has been investigated. The amount of polymerization products reaches 79.7 wt %. Addition of H2 to benzene reduces the amount of benzene-soluble polymer-like compounds in the products to ∼61 wt % and precludes the formation of solid polymerization products. The transformation of benzene with a propane-butane mixture yields alkylbenzenes (up to 38.5 wt %) and liquid alkanes (to 20.5 wt %, mainly with a branched structure). It has been found that an increase in benzene flow rate from 0.08 to 0.4 cm3/min in the case of benzene conversion with the propane-butane mixture can significantly reduce the amount of polymerization products from 56.7 to 9.1 wt %.

Transformations of benzene-argon mixture in barrier discharge

The transformation of a benzene-argon mixture in dielectric-barrier discharge (DBD) was studied. Benzene-soluble polymeric compounds (76.5 wt %), biphenyl (7.6 wt %), and phenylcyclohexadienes (9 wt %) are the major products. Monoalkylbenzenes, cyclohexadienes, and ethynylbenzene are in trace amounts in the reaction mixture. The benzene conversion per pass through the discharge zone was 5.5 wt %. The possible mechanism of the benzene transformation in DBD was suggested on the basis of experimental data and theoretical calculations.

Transformations of n-Hexane and Cyclohexane by Barrier Discharge Processing in Inert Gases

The conversion of n-hexane and cyclohexane by barrier discharge treatment in He, Ar, Kr, or Xe was studied. The action of a barrier discharge on n-hexane vapor primarily results in the formation of branched-chain hydrocarbons (93.48 wt %). Bicyclohexyl is the main reaction product of cyclohexane; alkyl and alkenyl substituted cyclohexanes (48.12 wt %) are also formed. Using n-hexane as an example, it was demonstrated that the energy consumption increased from 1.30 to 2.17 keV per hydrocarbon molecule converted in the following order of inert gases: He, Ar, Kr, and Xe.

Oxidative conversion of cyclohexane in discharge plasma maintained with different high-voltage power sources

The influence of the pulse parameters of supply voltage in a barrier discharge reactor on the yield of incomplete oxidation of cyclohexane was studied. It was shown that the voltage pulse parameters have an insignificant effect on both the product composition of cyclohexane oxidation and on selectivity for the products cyclohexanone (40.8%), cyclohexanol (49.5%), and water (9.7%). The lowest power consumption for the conversion of cyclohexane was achieved with the use of a sine wave generator operating at a frequency of 50 Hz (3.0 kWh kg−1) and a harmonic generator with a pulse duration of 15.3 μs and a pulse repetition frequency of 980 Hz (3.5 kWh kg−1). The space mode of barrier discharge was realized with the use of a generator of microsecond (53 μs) alternating voltage pulses.

Simulation of the Kinetics of Cyclohexane Oxidation in a Barrier Discharge Reactor

The kinetics of cyclohexane oxidation in a barrier discharge reactor was simulated for a single voltage pulse. A significant difference between the yields of O3 obtained experimentally (not detected) and theoretically (15.5 wt %) suggests that O3 was absent from the reaction mixture because of a fast reaction between O(3P) and an excited cyclohexane molecule. This hypothesis was indirectly supported by experimental data on the oxidation of a mixture of n-hexane and cyclohexene (50 : 50 wt %). The integrated rate constant of the reaction of O(3P) with n-hexane was 1.4 × 10–12 cm3/s, which is an order of magnitude higher than the published value 1.2 × 10–13 cm3/s.

Oxidation of propylene with air in barrier discharge in the presence of octane

Oxidation of propylene with air in barrier discharge was studied. The effect exerted on the propylene conversion and on the selectivity of propylene oxide formation by replacement of oxygen with air in the course of propylene oxidation was examined.

Oxidation of Cyclohexene in the Presence of Alkanes in a Barrier Discharge Plasma

The oxidation of cyclohexene mixtures with hexane, octane, decane, and cyclohexane was studied in a dielectric-barrier discharge reactor. It was shown that a decrease in the partial pressure of cyclohexene in the mixture resulted in a significant increase in the yield of cyclohexene oxide to ∼75%, with the composition of oxidation products being the same as in the oxidation of individual compounds. A plausible mechanism of the reaction is proposed.

Matrix IR Study of Benzene Transformations in a Pulsed Glow Discharge in the Absence and the Presence of Oxygen

Matrix FTIR study of products of benzene transformations in a pulsed glow discharge at low pressure in highly diluted mixtures of benzene with argon in the presence and absence of small oxygen additions has been carried out. Formation of the following hydrocarbon species has been established: acetylene, butadiyne, fulvene, benzvalene, methane, ethylene, phenyl, ethynyl and butadiynyl radicals. It has been shown that oxygen additions mainly result in deep oxidation of benzene to CO2, CO and H2O, although some products of intermediate oxidation have been detected. Those are formaldehyde, formyl radical, ketene, ketenyl radical, propadiene-1,3-dione, propadien-3-on-1-ilyden and hydroperoxyl radical. At the same time, it has unexpectedly been found that oxygen additions strongly increase the yield of butadiyne. Possible pathways, leading to formation of the listed species have been discussed on the basis of the obtained data and results reported in the literature.

Conversion of hydrocarbon gases in dielectric barrier discharge in the presence of water

The conversion of C1–C4 hydrocarbons into gaseous and liquid products in a dielectric barrier discharge plasma in the presence of water has been studied. The formation of a deposit on the electrode surface is prevented by introducing water in the liquid state into a gaseous hydrocarbon stream, a finding that has been confirmed by IR spectroscopic study of the electrode surface. Hydrogen and C2+ hydrocarbons have been detected among the gaseous products of conversion, the liquid products being represented by C6–C10+ alkanes. The total liquid products have amounted to 13.4, 26.0, or 36.6% for the methane, propane, or n-butane conversion, respectively. A 10% propane or butane admixture to methane increases the yield of the liquid products to make 22.0 and 31.7% for the methane–propane and the methane–butane mixture, respectively.