Electron-Impact Ionization of Air Molecules and its Application to the Abatement of Volatile Organic Compounds (original) (raw)
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The European Physical Journal Applied Physics, 2016
The kinetics of four volatile organic compounds (VOCs) (propene, propane, acetaldehyde, acetone) were studied in plasmas of atmospheric gases using a photo-triggered discharge (homogeneous plasma) or a dielectric barrier discharge (filamentary plasma). It was shown for the homogeneous plasma that quenchings of nitrogen metastable states, A 3 Σ + u and the group of singlets a 1 Σ − u, a 1 Πg and w 1 Δu, are important processes for the decomposition of such molecules. Recent measurements of the H2 concentration produced in the N2/C3H6 mixture emphasize that the hydrogen molecule can be an exit route for propene dissociation. It is also found that H2 and CO molecules are efficiently produced following the dissociation of CH3COCH3 and the subsequent chemical reactivity induced by radicals coming from acetone. Addition of oxygen to a N2/VOC mixture can change drastically the kinetics. However, the quenching processes of N2 metastables by the VOC are always present and compete with oxidation reactions for the conversion of the pollutant. At low temperature, oxidations by O or by OH are not always sufficiently effective to induce an increase of the molecule decomposition when oxygen is added to the mixture. In particular, the presence of O 2 has a detrimental effect on the acetone removal. Also, as evidenced for acetaldehyde and propane, some kinetic analogies appear between filamentary and homogeneous plasmas.
Destruction of Vocs Using Non-Thermal Plasmas
2000
Volatile organic compounds (VOCs) emitted to the atmosphere can cause adverse effects on human health and participate in photochemical smog formation reactions. Title III of the 1990 Clean Air Act Amendments (CAAA) requires that the U.S. EPA promulgate emission standards for 188 hazardous air pollutants (HAPs) associated with about 300 major source categories. Many DOE and industrial facilities throughout the U.S. will need pollution abatement systems for HAPs in order to comply with the 1990 CAAA. Nonthermal plasmas are an excellent source of gas-phase free radicals (O•, OH•, H•) and other active species useful for destroying pollutants. While there has been extensive research on using plasma-based air pollution control technologies to remove gas-phase species such as SO 2 and NOx, research on destroying VOCs with plasmas is in its early stages. This research uses a cylindrical dielectric barrier discharge (DBD) plasma reactor to destroy HAPs, such as benzene and methly-ethyl keton...
Electron-impact ionization of ozone
International Journal of Mass Spectrometry and Ion Processes, 1995
Partial electron ionization cross-sections of ozone for incident electron energies from 40 to 500 eV have been determined using time-of-flight mass spectrometry. The cross-sections are derived by identifying the contribution of ozone to the ion signals recorded following ionization of a mixture of 02 and 03. Only one previous determination of these crosssections, for energies up to 100 eV, is available in the literature. The cross-sections derived in the present study at these lower electron energies are in good agreement with the previous determination.
Removal of Volatile Organic Compounds in Atmospheric Pressure Air
A nonthermal plasma with an electron density on the order of 10 12 cm 3 and a gas temperature of 2000 K was generated in atmospheric pressure air, using a microhollow cathode discharge as plasma cathode. The plasma was sustained in a 1 mm 3 micro reactor, by a voltage of 470 V between the plasma cathode and a planar anode, and at currents ranging from 12 to 22 mA. This direct current glow discharge has been used to study the remediation of methane and benzene, two of the most stable volatile organic compounds (VOCs). The removal fraction for 300-ppm methane in atmospheric pressure air, flowing through the 0.5-mm thick plasma layer, with a residence time of the gas in the plasma of less than 0.5 ms, was measured at 80% with an energy density of 4 kJ/L. For benzene, the remediation rate is as high as 90%, comparable to results obtained with low pressure glow discharges. The energy efficiency for benzene remediation is 0.9 g/kWh, higher than that obtained for benzene remediation in low pressure glow discharges in noble gases. However, the VOC fraction remaining was found to be limited to values of approximately 0.1 and 0.05 for methane and benzene, respectively. In addition to experimental studies, the VOC dissociation mechanism in a VOC/dry air mixture plasma was modeled using a zero-dimensional plasma chemistry code. The modeling results have shown that atomic oxygen impact reactions are the dominant dissociation reactions for VOC destruction in this kind of glow discharge. Diffusion of atomic oxygen to the dielectric walls of the reactor is assumed to cause the observed limitation in the VOC destruction rate and efficiency.
Please cite this article as: Schiavon M, Scapinello M, Tosi P, Ragazzi M, Torretta V, Rada EC, Potential of non-thermal plasmas for helping the biodegradation of VOCs released by waste management plants, Abstract 3 This paper investigates the feasibility of exploiting a non-thermal plasma (NTP) to treat the gaseous 4 effluents released by the mechanical-biological treatments (MBTs) of waste and overcome the 5 typical disadvantages of biofilters, whose removal efficiency is limited during acclimatization of 6 bacteria, peaks of pollutant concentration or unstable airflow rates. A dielectric barrier discharge 7 was applied to two mixtures of volatile organic compounds (VOCs) and air. Ethanol and ethyl 8 acetate (Mixture 1) and benzene, toluene and octane (Mixture 2), in addition to being typical 9 constituents of the waste air released by MBTs of waste, also represent real emissions from two 10 specific sectors that use biofiltration for air pollution control (APC): the printing (Mixture 1) and 11 the petrochemical industries (Mixture 2). At the highest specific energy densities applied to the 12 discharge (900-2520 J L -1 ), all the initial VOCs were removed by 95-100%. With respect to ethyl 13 acetate, the maximal CO 2 selectivity and the maximal energy yield resulted in 62-70% and 6-11 g 14 kW -1 h -1 , respectively; with regards to benzene, the same parameters resulted in 52-90% and 0.17-15 0.72 g kW -1 h -1 , respectively. At medium-low energy, acetaldehyde and acetic acid were detected as 16 the main byproducts of Mixture 1, while several trace compounds were found as the byproducts of 17 Mixture 2. Interestingly, the byproducts generated are more polar than the initial compounds and, 18 thus, their solubility in water is higher. Therefore, NTPs can be considered as a promising 19 technology to help the biodegradation of VOCs in facilities where biofilters are used as APC 20 systems.
IEEE Transactions on Plasma Science, 2005
A nonthermal plasma with an electron density on the order of 10 12 cm 3 and a gas temperature of 2000 K was generated in atmospheric pressure air, using a microhollow cathode discharge as plasma cathode. The plasma was sustained in a 1 mm 3 micro reactor, by a voltage of 470 V between the plasma cathode and a planar anode, and at currents ranging from 12 to 22 mA. This direct current glow discharge has been used to study the remediation of methane and benzene, two of the most stable volatile organic compounds (VOCs). The removal fraction for 300-ppm methane in atmospheric pressure air, flowing through the 0.5-mm thick plasma layer, with a residence time of the gas in the plasma of less than 0.5 ms, was measured at 80% with an energy density of 4 kJ/L. For benzene, the remediation rate is as high as 90%, comparable to results obtained with low pressure glow discharges. The energy efficiency for benzene remediation is 0.9 g/kWh, higher than that obtained for benzene remediation in low pressure glow discharges in noble gases. However, the VOC fraction remaining was found to be limited to values of approximately 0.1 and 0.05 for methane and benzene, respectively. In addition to experimental studies, the VOC dissociation mechanism in a VOC/dry air mixture plasma was modeled using a zero-dimensional plasma chemistry code. The modeling results have shown that atomic oxygen impact reactions are the dominant dissociation reactions for VOC destruction in this kind of glow discharge. Diffusion of atomic oxygen to the dielectric walls of the reactor is assumed to cause the observed limitation in the VOC destruction rate and efficiency.
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Electrical Insulating Materials (or Dielectrics) are materials in which electrostatic fields can remain almost indefinitely. These materials thus offer a very high resistance to the passage of direct currents. However, they cannot withstand an infinitely high voltage. When the applied voltage across the dielectric exceeds a critical value the insulation will be damaged. The dielectrics may be gaseous, liquid or solid in form.
Towards a Consistent Chemical Kinetic Model of Electron Beam Irradiation of Humid Air
2009
A chemical kinetic model has been assembled based upon previous literature to assist in developing a better understanding of the mechanism behind the electron beam irradiation of humid air. Thermodynamic determination of the feasibility of particular product sets was used to eliminate certain reactions proposed previously, dynamical models were used to guide the choice of product sets, and updated rate constants were obtained from the current literature. Tracers were also used to determine significant sources and sinks of hydroxyl radical, an important species in the irradiation process. Modeling results for selected species have been presented for 1 atm of air at 298.15 K and 50% relative humidity, at doses of 1, 5, 10, 25, and 50 kGy delivered over 0.8 s. The concentrations of the most abundant ions, radicals, and stable reaction products have been included, as well as the calculated major sources and sinks of hydroxyl radical.