Removal of volatile organic compounds in atmospheric pressure air by means of direct current glow discharges (original) (raw)
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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.
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...
2008
Major sterilization mechanisms are related to atoms and radicals, charged parti-cles, excited molecules, ozone, and UV radiation. The ROS (Reactive Oxygen Species) are well known as evildoers. These species are easily created in ambient air and water and they live long enough to reach the cell and attack the organic matter. Test molecules conversion in dry and wet air is studied using Dielectric Barrier Discharge (DBD) and Gliding Arc Reactors (GAR). The effects of tem-perature and energy deposition into the media on the active species production and then on the organic compounds degradation are presented for two non thermal plasma reactors: DBD and GAR. Main production species investigated are OH, O3, NOx, CO and CxHyOz by-products. It is shown from experiment analysis that the reactive species production is quite different from one reactor to another. GAR and pulsed DBD are two chemical processing ways in which the temperature of heavy species in ionized gas is determinant. By reviewing the species production obtained from both reactors, a discussion is open about plasma decontamination.
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.
Plasma Sources Science and Technology, 2011
The conversion of methane to value-added chemicals and fuels is considered to be one of the challenges of the 21st century. In this paper we study, by means of fluid modeling, the conversion of methane to higher hydrocarbons or oxygenates by partial oxidation with CO 2 or O 2 in a dielectric barrier discharge. Sixty-nine different plasma species (electrons, ions, molecules, radicals) are included in the model, as well as a comprehensive set of chemical reactions. The calculation results presented in this paper include the conversion of the reactants and the yields of the reaction products as a function of residence time in the reactor, for different gas mixing ratios. Syngas (i.e. H 2 + CO) and higher hydrocarbons (C 2 H x ) are typically found to be important reaction products.
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.
Environmental Science & Technology, 2008
A novel, multistage, dielectric, packed-bed, plasma reactor has been developed and is used to efficiently destroy environmental pollutants, such as volatile organic compounds (VOCs). A three cell plasma reactor, operated at ambient pressure and low temperatures, is found to be an effective technology for complete VOC remediation in air. The combination of plasma cells in series can significantly improve the efficiency of VOC decomposition, but the combined destruction rate is not simply an additive effect, there is a synergistic enhancement related to the effect on the plasma chemistry of sequential processing in the three cells. At the same time, the formation of byproduct such as NO x is strongly suppressed, and it is possible to remediate toluene and ethylene in air, with no detectable formation of NO x or nitric acid.
Effects of a pulsed operation on ozone production in dielectric barrier air discharges
We have performed an experimental investigation of ozone production in a pulsed dielectric barrier discharge (DBD) reactor. Measurements of ozone in the gas-phase as a function of the power level show that in continuous mode a maximum concentration is achieved before a decrease presumably connected with gas-phase heating. When the reactor is employed in pulsed mode, by applying a definite duty cycle, a strong increase in ozone concentration is generally observed, with a maximum which happens at quite reduced duty cycles, thus requiring reduced power compared to the continuous mode.