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 %).     

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.     

Dielectric barrier discharge plasma reactor

A dielectric barrier discharge plasma reactor has been designed and constructed. The space discharge regime has been implemented. The reactor operating conditions for the desired reaction have been calculated using the dissociation of water molecules as a model reaction. The operating conditions have been selected for the dissociation of water vapor via excitation of vibrational levels of the molecule by a single electron impact.     

Radiation-induced terpolymerization of tetrafluoroethylene with propylene and isobutylene in bulk

Terpolymerization of tetrafluoroethylene (TFE) with propylene (P) and isobutylene (iB) by γ radiation at temperatures of ?78 to 40°C, a dose rate of 5 × 10⁴?5 × 10⁵ rad/hr, and an iB/P molar ratio of 40/10?5/45 in the monomer mixture was carried out. Alternating copolymers of TFE and α-olefins, that is, P and iB, were formed at various monomer compositions. No crystalline structure was observed in the terpolymer obtained below an iB/P molar ratio of 15/35 in the monomer mixture but a partly crystalline order increased with the amounts of iB in terpolymer. The crystal lattice of the TFE–iB copolymer was affected by the introduction of P. The dose rate dependencies of the polymerization rate and inherent viscosity were 0.8 and ?0.2, respectively. The activation energy of polymerization was 2.4 kcal/mole, and the relative reactivity ratio of iB and P for a TFE radical chain end was estimated as 4.50 by the treatment of the free propagating mechanism.     

Concentrations of active species in a bulk barrier discharge in a plasmochemical reactor

The results of theoretical and experimental studies of the chemical composition of the ensemble of active species formed in a plasmochemical reactor that consists of a multicell bulk-barrier-discharge generator of active species and a working chamber are presented. To calculate the composition of the neutral species in the barrier discharge, an approach based on the averaging of the power input over the entire volume of the discharge gap was proposed. One advantage of this approach is that it involves no adjustable parameters, such as the sizes of the microdischarges, their surface density, and frequency of breakdowns. The calculations and measurements were performed using dry air (with a relative humidity of 20%) as the plasma-forming medium. The concentrations of O₃, HNO₃, HNO₂, N₂O₅, and NO₃ in the discharge gap and working chamber were measured at a mean residence time of the species in the discharge gap of τ = 0.3 s and a specific power input of 1.5 W/cm³. The best agreement between the calculation results and the experimental data was obtained when the temperature of the gas mixture in the discharge was set equal to 400–425 K, a value that coincided with the measured rotational temperature of molecular nitrogen. Generally, the calculated and measured concentrations of O₃, HNO₃, HNO₂, N₂O₅, and NO₃ in both the bulk barrier discharge and the working chamber were found to be in close agreement.     

Methane conversion into higher hydrocarbons with dielectric barrier discharge micro-plasma reactor

We reported a coaxial,micro-dielectric barrier discharge(micro-DBD)reactor and a conventional DBD reactor for the direct conversion of methane into higher hydrocarbons at atmospheric pressure.The effects of input power,residence time,discharge gap and external electrode length were investigated for methane conversion and product selectivity.We found the conversion of methane in a micro-DBD reactor was higher than that in a conventional DBD reactor.And at an input power of 25.0 W,the conversion of methane and the total C2+C3 selectivity reached 25.10% and 80.27%,respectively,with a micro-DBD reactor of 0.4 mm discharge gap.Finally,a nonlinear multiple regression model was used to study the correlations between both methane conversion and product selectivity and various system variables.The calculated data were obtained using SPSS 12.0 software.The regression analysis illustrated the correlations between system variables and both methane conversion and product selectivity.     

Removal properties of diesel exhaust particles by a dielectric barrier discharge reactor

The removal properties of diesel exhaust particles (DEP) were investigated using an engine exhaust particle size spectrometer (EEPS), field emission-type scanning electron microscopy (FE-SEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). DEP were treated using a dielectric barrier discharge (DBD) reactor installed in the tail pipe of a diesel engine, and a model DBD reactor fed with DEP in the mixture of N(2) and O(2). When changing the experimental parameters of both the plasma conditions and the engine load conditions, we obtained characteristic information of DEP treated with plasma discharges from the particle diameter and the composition. In evaluating the model DBD reactor, it became clear that there were two types of plasma processes (reactions with active oxygen species to yield CO(2) and reactions with active nitrogen species to yield nitrogen containing compounds). Moreover, from the result of a TOF-SIMS analysis, the characteristic secondary ions, such as C(2)H(6)N(+), C(4)H(12)N(+), and C(10)H(20)N(2)(+), were strongly detected from the DEP surfaces during the plasma discharges. This indicates that the nitrogen contained hydrocarbons were generated by plasma reactions.     

Glass and melting transitions of copolymers of tetrafluoroethylene with propylene and isobutylene

Copolymers of tetrafluoroethylene and propylene were prepared that contained 30–65 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and propylene-ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures, T_g, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot of T_g versus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30–56 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and isobutylene-ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained when T_g is plotted versus composition. Isobutylene-containing copolymers having 45–54 mole-% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in the polymer having two T_g.     

Photocatalytic oxidation of propylene and isobutylene over metal oxides

Theoretical and Experimental Chemistry -     

Plasma-assisted methane conversion in an atmospheric pressure dielectric barrier discharge reactor

In this paper,a cylindrical dielectric barrier discharge（DBD） reactor has been developed for the conversion of methane into hydrogen and other valuable chemicals.The effects of a wide range of processing parameters including discharge power,residence time and frequency on the performance of plasma methane conversion reaction have been investigated.The results show that the CH₄ DBD could be characterized as a typical filamentary discharge with a microdis-charge zone in each half-cycle of the applied voltage.The conversion of CH₄ reaches a maximum of 25.2%at a feed flow rate of 50 mL·min^-1,a discharge power of 45 W and an excitation frequency of 20 kHz.It is found that the residence time of methane in the discharge zone has the most significant effect on both methane conversion and hydrogen yield,which are significantly higher at higher residence time.     

填充床介质阻挡放电脱除气化燃气中苯的研究

以生物质气化焦油典型组分--苯作为模型物,采用填充床介质阻挡放电（DBD）对气化燃气氛围中的苯进行脱除。考察了燃气组成、填充物种类、反应温度及催化剂还原方式对苯脱除的影响。结果表明,反应温度200 ℃时,空气气化燃气与水蒸气气化燃气氛围内的苯脱除率比较接近,但燃气中存在少量O₂会导致脱除率明显下降。并且,提高放电能量密度,使用高介电常数、高比表面积及孔容积的填充物能提高苯脱除率。采用传统还原和等离子体还原两种方式分别制得Ni/γ-Al₂O₃（C）、Ni/γ-Al₂O₃（P）催化剂,以Ni/γ-Al₂O₃（C）为DBD填充物,反应温度在230-330 ℃时,苯脱除率随温度升高而下降,330 ℃时达到最低脱除率11.6%;温度高于330 ℃,苯脱除率随温度急剧上升且在430 ℃达到最大值85.4%。等离子体还原可制得大比表面积及高分散性的Ni/γ-Al₂O₃（P）,其苯脱除率随温度变化的趋势与Ni/γ-Al₂O₃（C）一致,但在430 ℃时达到更高的脱除率90.0%。苯脱除过程中燃气的甲烷化可提高出口燃气中CH₄浓度,但燃气的热值略有下降。     

Breakdown of a gas gap in a surface barrier discharge

The processes that occur in a surface barrier discharge in oxygen at atmospheric pressure have been studied by numerical modeling. Modeling is performed assuming the existence of local equilibrium, and the dynamics of charged particles in the gas gap is calculated using continuity equations. The configuration of the electric field in the discharge zone is determined by integration of the Poisson equation. It turns out that the breakdown of the gas gap is determined by the photoemission from the cathode surface. The appearance and development of the microdischarge channel are sustained by the cathode layer that is formed at the conducting cathode. The parameters of the cathode layer obtained in oxygen at atmospheric pressure are virtually the same as for the ordinary cathode layer of the glow discharge.     

The removal of styrene using a dielectric barrier discharge (DBD) reactor and the analysis of the by-products and intermediates

As a kind of volatile organic compound, styrene is a typical industrial pollutant with high toxicity and odorous smell. In this study, the removal of malodorous styrene simulation waste gas was carried out in a self-made wire-tube dielectric barrier discharge reactor. The decomposition efficiency of the reaction was investigated under different applied voltages and flow rates. The results showed that nearly 99.6 % of styrene could be removed with a concentration of 3,600 mg/m³ and the applied voltage of 10.8 kV. However, the selectivity of CO₂ and CO showed that the mineralization efficiency of styrene was less than 25 %. The by-products of the reaction, including O₃, NO _x and other intermediates, were also detected and analyzed under different applied voltages. The relationships between the applied voltage and the quantity of final product (CO₂) and by-products (intermediate organics, NO _x , O₃) were investigated. The reaction mechanism was also described according to the bond energy and the intermediates that formed.