Effects of Oxygen and Water Vapor on Volatile Organic Compounds Decomposition Using Gliding Arc Gas Discharge

The combined effects of oxygen and water vapor on three typical volatile organic compounds, i.e. tetrachloromethane, n-butane and toluene, decomposition efficiency under gliding arc gas discharge conditions are studied. The electron density and the density of the reactive radicals such as O and OH are modified by addition of oxygen and water vapor. Consequently, the decomposition process can be enhanced or suppressed, depending on the involved chemical structures and reaction channels. The addition of oxygen and water vapor suppresses the tetrachloromethane decomposition which indicates that this process is mainly controlled by the electron dissociation reactions. By contrast, the n-butane and toluene decompositions are enhanced, which shows that they can be mainly ascribed to the radical induced reactions. Especially, in a moist atmosphere the OH radicals are supposed to play the most important role in the n-butane decomposition process.     

Simultaneous scission and crosslinking of polystyrene chains on irradiation by ultraviolet light in CCl4 and CHCl3 solutions

This work is the continuation of the investigations of changes in the structure of polystyrene initiated by radiation of wavelengths λ ≥ 270 nm in oxygen-free solutions in CCl₄ and CHCl₃. Coupled integral and quasielastic light scattering techniques have been applied, enabling observations of changes in the molecular weight distribution function w(M). On the basis of the experimental data and application of Saito and Inokuti's theoretical results, it is shown that in the irradiated solutions polystyrene undergoes simultaneous chain scission and crosslinking. The average number of scissions and crosslinks per macromolecule as a function of irradiation time is calculated. The effect of macromolecular mobility on both photochemical processes is also discussed.     

The Effect of Oxygen and Water Vapor on Nitric Oxide Conversion with a Dielectric Barrier Discharge Reactor

The effect of O₂ and H₂O vapor on the Nitric oxide (NO) removal rate, the NO₂ generation rate and the discharge characteristics were investigated using the dielectric barrier discharge (DBD) reactor at 1 atm pressure and at room temperature (20°). The results showed that the O₂ present in the flue gas always hampered the removal of NO and the generation of N₂O, but that the O₂ could enhance the generation of NO₂ in the NO/N₂/O₂ mixtures. Furthermore, with the increase of oxygen, the average discharge current gradually decreases in the reactor. The H₂O present in N₂/NO hindered the removal of NO and the generation of NO₂ but had no impact on the average discharge current in the reactor in the NO/N₂/H₂O mixtures in which the HNO₂ and HNO₃ was detected. The energy efficiency of the DBD used to remove the NO from the flue gas was also estimated.     

Oxidative pyrolysis of CH2Cl2, CHCl3, and CCl4-I: Incineration implications

The oxidative pyrolysis of methylene chloride, chloroform, and carbon tetrachloride has been investigated using a micro-bore, fused silica, tubular flow reactor operating under laminar flow conditions coupled to in-line GC-MS detection. Data were obtained over the temperature range 573–1273 K for the following conditions: chlorocarbon/oxygen equivalence ratios of 3.0, chlorocarbon concentrations of 2.7 ± 0.1 × 10^?5 mols/L, gas-phase residence times of 2.0 s, and reactor pressures of 1.15 ± 0.05 atm. The parent stability (defined by the temperature required for 99% destruction) was evaluated as: Chemically activated recombination of chlorinated C₁ radicals are proposed as important pathways to chlorinated ethane and olefin products. The most significant finding from analysis of product distributions containing ≥2 carbon atoms was the observation of ca. 1 mol% yields of higher-molecular-weight perchlorinated aromatic species from the decomposition of chloroform and carbon tetrachloride. Implications with respect to the controlled high-temperature incineration of these chlorinated methanes are briefly discussed.     

Clathrate formation in binary aqueous systems with CH2Cl2, CHCl3 and CCl4 at high pressures

P,T,X phase diagrams of the CH₂Cl₂-H₂O, the CHCl₃-H₂O and the CCl₄-H₂) systems have been studied by DTA in the pressure range 10^–3 to 5.0 kbar. Under pressure the cubic structure II (CS-II) hydrates forming in all the systems are replaced by hydrates with the composition M·7.3 H₂O whose stoichiometry and positive dT/dP values of melting lead us to believe that they are CS-I hydrates.In the CH₂Cl₂ and CHCl₃ systems the nonvariant point coordinates of the hydrate transformationQ ₂ ^h (l₁h17h7l₂, where l₁ and l₂ are liquid phases abundant in water and hydrate former, respectively, h₁₇ and h₇ are hydrates with hydrate numbers 17 and 7, respectively) areP = 0.6 kbar, T = –1.5°C andP =2.65 kbar,T = –10.5°C, respectively. In the CCl₄ system the 4-phaseQ ₃ ^h point (l₁h₁₇h₇s, where s is crystalline CCl₄) has coordinatesP = 0.75 kbar and T = 0.4°C.The main obstacle of the present study, the very slow achievement of equilibrium, has been eliminated by adding small amounts (0.25% by mass) of surfactants followed by ultrasonic mixing. We have shown that this accelerates the achievement of equilibrium without changing its position.     

Deactivation of I(2P1/2) by CH3Cl,CH2Cl2, CHCl3, CCl3F,and CCl4

Collisional deactivation of I(²P_1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH₃Cl, CH₂Cl₂, CHCl₃, CCl₃F, and CCl₄ are 3.1±0.3×10⁻¹³, 1.28±0.08×10⁻¹³, 5.7±0.3×10⁻¹⁴, 3.9±0.4×10⁻¹⁵, and 2.3±0.3×10⁻¹⁵cm³ molecule⁻¹ s⁻¹, respectively, at room temperature (298 K). The higher efficiency observed for relaxation by CH₃Cl, CH₂Cl₂, and CHCl₃ reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm⁻¹) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799–803, 1998     

滑动弧电极放电等离子体作用甲烷制C2烃的工艺

采用刀片式不锈钢电极放电反应器,以Ar气为稀释气,研究了等离子体作用下甲烷转化制C2烃的工艺条件。考察了CH4流量、高频电源输入电压和电极间距等参数对甲烷转化率、C2烃选择性、收率和反应表观能耗的影响。结果表明,增加CH4流量,表观能耗随之降低;当输入电压和电极间距较小时,甲烷转化率随输入电压和电极间距的增大而增大,但输入电压和电极间距过大时,C2烃收率明显下降,积碳严重。在CH4流量14 mL/min、Ar气流量60 mL/min、高频电源输入电压22 V、电流0.44 A、电极间距4 mm的优化条件下,甲烷最高转化率为43.1%,C2烃收率、选择性和表观能耗分别为40.1%、93.2%和2.41 MJ/mol。C2烃中不饱和烃的体积分数可达95%以上。     

Effect of Gliding Electric Discharge on the Oxidizing Capacity of a Water Aerosol Jet

High Energy Chemistry - The oxidizing capacity of a water aerosol jet passed through the region of pulsed gliding electric discharge has been investigated. It has been found that the action of the...     

Theoretical mechanistic study on the radical-molecule reaction of CHCl2/CCl3 with NO2

The radical-molecule reaction mechanism of CHCl(2) and CCl(3) with NO(2) have been explored theoretically at the B3LYP/6-311G(d,p) and MC-QCISD (single-point) levels. For the singlet potential energy surface (PES) of CHCl(2) + NO(2) reaction, the association of CHCl(2) with NO(2) was found to be a barrierless carbon-to-nitrogen approach forming an energy-rich adduct a (HCl(2)CNO(2)) followed by isomerization to b(1) (trans-cis-HCl(2)CONO), which can easily interconvert to b(2), b(3), and b(4). Subsequently, the most feasible pathway is the 1,3-chlorine migration associated with N-O1 bond cleavage of b(1) leading to P(1) (CHClO + ClNO). The second competitive pathway is the 1,4-chlorine migration along with N-O1 bond rupture of b(4) giving rise to P(2) (CHClO + ClON). Moreover, some of P(1) and P(2) can further dissociate to give P(6) (CHClO + Cl + NO). The lesser followed competitive channel is the 1,3-H-shift from C to N atom along with N-O1 bond rupture of b(1) to form P(3) (CCl(2)O + HNO). The concerted 1,4-H-shift accompanied by N-O1 bond fission of b(3) to product P(4) (CCl(2)O + HON) is even much less feasible. For the singlet PES of CCl(3) + NO(2) reaction, the only primary product is found to be P(1) (CCl(2)O + ClNO), which can lead to P(2) (CCl(2)O + Cl + NO) via dissociation of ClNO. The obtained major products CHClO and CCl(2)O for CHCl(2) + NO(2) and CCl(3) + NO(2) reactions, respectively, are in good agreement with kinetic detection in experiment. Compared with the singlet pathways, the triplet pathways may have less contributions to both reactions. Because the rate-determining transition state involved in the feasible pathways lie above the reactants R, the title reactions may be important in high-temperature processes. The similarities and discrepancies among the CH(n)Cl(3-n) + NO(2) (n == 0-2) reactions are discussed in terms of the substitution effect. The present study may be helpful for further experimental investigation of the title reactions.     

Abstraction of chlorine atoms from chloroalkanes. V. The liquid-phase reaction between Et3SiH radicals and CH2Cl2, CHCl3, CCl4, and CCl3CN

The kinetics of chlorine transfer from CH₂Cl₂, CHCl₃, CCl₄, and CCl₃CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1-bromopentane was used as a reference. The following Arrhenius parameters were determined: where the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et₃Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.     

The Effects of Gas Composition on Active Species and Byproducts Formation in Gas–Water Gliding Arc Discharge

The effects of gas composition on hybrid gas–water gliding arc discharge plasma reactor have been studied. The voltage cycles are characterized by a moderate increase in the tension which is represented by a peak followed by an abrupt decrease and a current peak in the half period (10 ms). Emission spectrum measurements revealed that ^•OH hydroxyl radicals are present in the discharge with feeding any gas. The H₂O₂ concentrations reach 38.0, 15.0, 10.0, and 8.0 mg/l after 25 min plasma treatment with oxygen, argon, air, and nitrogen, respectively. O₃ was produced when oxygen and air are used, but not when nitrogen and argon. The O₃ concentration reached the highest value 1.0 mg/l after 25 min plasma treatment with oxygen feeding gas, but gradually decreased to 0.2 mg/l after that. With feeding nitrogenous gas, NO₂ ⁻ and NO₃ ⁻ byproducts were formed by the plasma chemical process.     

Flowtube reactor study of the association reactions of CHCl2 and CCl3 with O2 at low pressure

The new flowtube reactor employing dissociative electron attachment to produce radicals and high-pressure photoionization in the mass spectrometric detection of radicals is described. The system has been applied to a study of the association reactions of CHCl₂ and CCl₃ with O₂ in a great excess of helium at total densities below 10¹⁷ cm^?3 over the temperature range 286 to 332 K. Both reactions display a strong negative temperature coefficient. The results can be parameterized in the form k₀(CHCl₂ + O₂) = (4.3 ± 0.2) × 10^?31(T/300)^?6.7±0.7 cm⁶ s^?1, k₀(CCl₃ + O₂) = (2.7 ± 0.2) × 10^?31(T/300)^?8.7±1.0 cm⁶ s^?1. © 1994 John Wiley & Sons, Inc.     

Degradation of 4-Chlorophenol using a Gas–Liquid Gliding Arc Discharge Plasma Reactor

The gas–liquid gliding arc discharge plasma is used directly to study degradation and dechlorination of 4-Chlorophenol (4-CP) in solution. The typical AC waveforms of discharge voltage and current revealed that the discharge behavior was not definitely periodic. The chemical oxygen demand (COD) abatement of 4-CP solution with stainless steel electrode is higher than that with aluminum or brass electrode; When air was used as carrier gas the COD abated from 1,679.2 to 190 mg/L (i.e., 88.68% abatement) after 76 min plasma treatment; Increasing gas–liquid mixing rate could also increase the degradation of 4-CP; adding appropriate amounts of Fe²⁺ or iron chips to the solution were found to be favorable for 4-CP degradation. The main intermediates of 4-CP degradation are p-benzoquinone, hydroquinone, 4-chlorocatechol, p-chloronitrobenzene, and ring cleavage products (acetic acid, glycol, propanone, and others). Furthermore, possible pathways of 4-CP degradation in solution are proposed.     

Kinetics of Low-Temperature Conversion of Carbon Monoxide with Water Vapor on Cu-Zn-Al Oxide Catalysts

Theoretical and Experimental Chemistry - According to the analysis of literature data and our experimental results, a kinetic equation for the low-temperature conversion of carbon monoxide with...     

Influence of Helium on the Conversion of Methane and Carbon dioxide in a Dielectric Barrier Discharge

We have studied the production of synthesis gas and other hydrocarbons in a dielectric barrier discharge using mixtures of helium, methane and carbon dioxide. It was found that helium has a significant influence on the discharge, decreasing the breakdown voltage and increasing the rate of conversion of CH₄ and CO₂. However it also decreases the selectivities and the range of stable operating conditions for the discharge. The main products obtained were H₂, CO, C₂H₆ and C₃H₈ but traces of other hydrocarbon, carbon deposition and the formation of condensable products were also detected. The rate of conversion and conversion abilities were obtained by fitting the conversion results to a model.