Packed-bed Dielectric Barrier Discharge Research Articles

Effect of packing materials on the decomposition of tetrafluoroethane in a packed-bed dielectric barrier discharge plasma reactor

The performance of 1,1,1,2-tetrafluoroethane or HFC-134a decomposition and the formation of byproducts in a dielectric barrier discharge plasma reactor were studied with different packing systems such as α-Al2O3 (porous and nonporous), γ-Al2O3 (porous) and ZrO2 (nonporous). Experimental variables such as reactor temperature, initial HFC-134a concentration and oxygen levels were chosen for the performance analysis. Among the packing systems, the porous γ-Al2O3 and α-Al2O3 decomposed HFC-134a much more effectively than the nonporous α-Al2O3 and ZrO2. The combination of the plasma with the porous γ-Al2O3 was found to cover a wide range of initial concentration. The decomposition efficiency tended to increase with the addition of oxygen up to 2 %, but further increase in the oxygen led to a decrease. As well as carbon oxides (CO2 and CO), significant amounts of unwanted byproducts such as COF2 and CF4 were also identified in the effluent gas with the nonporous α-Al2O3 and ZrO2. On the contrary, with the porous γ-Al2O3 and α-Al2O3, such unwanted byproducts were considerably suppressed, enhancing the formation of CO2 and CO.

Experimental study of acetone removal by packed-bed dielectric barrier discharge reactor

In this study, a packed-bed dielectric barrier discharge (DBD) reactor was developed for acetone removal. The effects of packing materials were investigated in terms of discharge characteristics, removal efficiency and byproducts formation. The identification of organic byproducts was conducted. The results indicated the presence of packing materials enhanced the energy density and exhibited a positive effect on acetone removal, while high oxygen concentration inhibited the removal of acetone. The formations of byproducts were significantly reduced in the presence of packing materials. The degradation pathways and mechanisms were discussed, showing CH3 radicals played a crucial role in the acetone degradation process.

Decomposition Treatment of SO2F2 Using Packed Bed DBD Plasma Followed by Chemical Absorption

The technology of packed bed dielectric barrier discharge (DBD) plasma followed by a chemical absorption has been developed and was found to be an efficient way for decomposition treatment of sulfuryl fluoride (SO2F2) in simulated residual fumigant. The effects of energy density, initial SO2F2 concentration, and residence time on the removal efficiency of SO2F2 for the DBD plasma treatment alone were investigated. It was found that the SO2F2 could be removed completely when initial volume concentration, energy density, and residence time were 0.5%, 33.9 kJ/L, and 5.1 s, respectively. The removal mechanism of SO2F2 in the packed bed DBD reactor was discussed. Based on the detailed analysis of SO2F2 molecular stability and its exhaust products in the DBD plasma reactor, it was concluded that the energetic electrons generated in the packed bed DBD reactor played a key role on the removal of SO2F2, and the major decomposition products of SO2F2 detected were SO2, SiF4, and S (Sulfur). Among these products, SiF4 was formed by the F atom reacted with the filler-quartz glass beads (SiO2) in the packed bed DBD reactor. Aqueous NaOH solution was used as the chemical absorbent for the gaseous products of SO2F2 after plasma pretreatment. It was found that the gaseous products in the plasma exhaust could be absorbed and fixed by the subsequent aqueous NaOH solution.

Combination of non-thermal plasma and heterogeneous catalysis for methane and hexadecane co-cracking: Effect of voltage and catalyst configuration

Co-cracking of methane and n-hexadecane is investigated over Mo–Ni/Al2O3 catalyst in a packed bed dielectric barrier discharge (DBD) plasma reactor. The effects of applied voltage and plasma-catalyst configuration are experimentally studied in terms of process energy efficiency and product composition. Hydrogen and gaseous hydrocarbon (methane, C2, C3 and C4 components) are obtained as the cracking product. Results show that combination of catalyst and plasma improves energy efficiency of hydrocarbons plasma conversion. The applied voltage has dominant effect on the catalytic-plasma cracking process and in-plasma catalysis configuration is more efficient compared with post-plasma catalysis. The highest energy efficiency is achieved the value of 194.44l/kWh for in-plasma configuration under highest applied voltage condition (11kV). In these conditions, the production rate and mole percent of hydrogen are obtained 107.66ml/min and 63.7%, respectively. The effect of catalyst deactivation is also investigated on the process variables.

Removal of formaldehyde by adsorption and plasma treatment of mineral adsorbent

Formaldehyde is a harmful ambient air pollutant which can be produced by incomplete combustion processes, e.g. in power plants or automobiles. In this work a cycled adsorption and discharge process using mineral granulate in a packed bed dielectric barrier discharge plasma reactor was applied for formaldehyde (99 ppm) removal from gas streams. The mineral granulate used consisted of 80% halloysite and showed a good adsorption capacity for formaldehyde. In the discharge step, the adsorbed formaldehyde molecules were decomposed to COx and hydrocarbons in a N2 plasma at a low input discharge power of 2.2 W. The decomposition performance on adsorbed formaldehyde molecules was studied depending on space–time, a specific oxygen fraction of the carrier gas and the influence of temperature. With rising N2 space times in the discharge area, the total amount of decomposed formaldehyde molecules increased and the decomposition reaction mechanism shifted to CO2 formation. An oxygen fraction in the carrier gas further raised the oxidized amount of formaldehyde to CO2. The mineral granulate showed satisfied regeneration ability during the cycled plasma process.

Hydrogen production from hydrogen sulfide in a packed-bed DBD reactor

The effect of different reactor packing materials on the nonthermal plasma (NTP) assisted decomposition of hydrogen sulfide (H2S) in a coaxial dielectric barrier discharge (DBD) reactor has been described in the present investigation. The packing materials studied include ceramic beads, glass material with different geometries like spherical (glass beads), hollow cylinder (glass tubes) and honeycomb (glass wool), and for comparison the reaction was carried out in the absence of any packing material. The packing material studied in the present work do not exhibit any catalytic activity in the traditional sense; however, they do have different dielectric constants and morphologies that may influence the plasma discharge behavior and may also affect the residence time of the gas molecules in the discharge zone. From the experimental results, it has been found that the ceramic pellets and hollow cylindrical glass material packed reactor showed better performance for H2S decomposition into H2 and S.

Packed Bed DBD Discharge Experiments in Admixtures of N2 and CH4

The physical, chemical and electrical properties of a coaxial Dielectric Barrier Discharge (DBD) fed by various mixtures of N2 and CH4 at atmospheric pressure and ambient temperature has been studied. FTIR spectral measurements of the products formed in the discharge have shown that the main chemical products are C2H2, HCN and C2H6 produced by dissociation of CH4, with small but significant traces of NH3.such a chemical transformation may provide some insight into the chemical processes prevalent in the atmosphere of Titan. During operation of the discharge a solid brown-yellowish deposit was formed on the central rod electrode and the dielectric pellets. Such a deposit is similar to that observed in other N2:CH4 discharges and is believed to be an analogue of the aerosol and dust observed in Titan’s atmosphere being composed of chemical species commonly known as ‘tholins’.

Formaldehyde removal from gas streams by means of NaNO2 dielectric barrier discharge plasma

Destruction of formaldehyde by means of NaNO2 ferro-electric packed bed dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. The difference among four kinds of NaNO2 ferro-electric reactors was compared in terms of specific energy density (SED), energy yield (EY), and HCHO decomposition. In addition, by-products during the decomposition of HCHO and destruction mechanism were also investigated. The removal efficiency of HCHO increased by means of NaNO2 DBD plasma significantly and enhanced with increasing SED distinctly. More amount of NaNO2 contributed to higher HCHO removal efficiency in the reactors. Reactor C had the highest HCHO removal efficiency among the reactors. As an important by-product, ozone concentration increased with higher SED. The possible main products in the outlet effluent were CO, CO(2) and H(2)O.

Abatement of toluene from gas streams via ferro-electric packed bed dielectric barrier discharge plasma

Destruction of gaseous toluene via ferro-electric packed bed dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. The difference among three kinds of reactors was compared in terms of specific energy density (SED), energy yield (EY), toluene decomposition. In order to optimize the geometry of the reactor, the removal efficiency of toluene was compared for various inner electrode diameters. In addition, qualitative analysis on by-products and particular discussion on toluene abatement mechanisms were also presented. It has been found that ferro-electric packed bed DBD reactor could effectively decompose toluene. Toluene removal efficiency enhanced with increasing SED. With respect to toluene conversion, 1.62 mm electrode appeared to be superior to 1.06 mm electrodes. BaTiO 3 reactor had the highest toluene removal efficiency among the reactors. For NaNO 2 reactor, the highest EY could reach 17.0 mg/kWh to a certain extent.

Destruction of Styrene in an Air Stream by Packed Dielectric Barrier Discharge Reactors

This study presents the decomposition rates of styrene vapors with non-packed and packed bed dielectric barrier discharge reactors. The concentrations of intermediate byproducts at various plasma operation conditions were evaluated. The results showed that although styrene vapors could be almost completely removed at low styrene inlet concentration of 132 ppm, the selectivity of CO2 as the major product was rather low in a non-packed bed reactor. It was found that solid carbon containing compound was the major byproduct. An increase in the styrene inlet concentration tended to reduce the styrene removal efficiency, it also led to increase in the solid byproduct. The reactors that packed with glass, Al2O3 or Pt–Pd /Al2O3 pellets could improve the styrene decomposition efficiency and reduce the formation of intermediate products, of which the best oxidation of styrene to CO2 could be achieved with a Pt–Pd /Al2O3 packed bed reactor. The carbon byproducts could also be reduced if the rector length was increased. The concentrations of ozone formed during the plasma process were also evaluated for the non-packed and packed bed reactors. The plasma reactor that packed with Pt–Pd /Al2O3 pellets was proved to have the lowest O3 concentration.

Removal of formaldehyde from gas streams via packed-bed dielectric barrier discharge plasmas

Formaldehyde is a major indoor air pollutant and can cause serious health disorders in residents. This work reports the removal of formaldehyde from gas streams via alumina-pellet-filled dielectric barrier discharge plasmas at atmospheric pressure and 70 °C. With a feed gas mixture of 140 ppm HCHO, 21.0% O2, 1.0% H2O in N2, ∼92% of formaldehyde can be effectively destructed at GHSV (gas flow volume per hour per discharge volume) of 16 500 h−1 and Ein = 108 J l−1. An increase in the specific surface area of the alumina pellets enhances the HCHO removal, and this indicates that the adsorbed HCHO species may have a lower C–H bond breakage energy. Based on an examination of the influence of gas composition on the removal efficiency, the primary destruction pathways, besides the reactions initiated by discharge-generated radicals, such as O, H, OH and HO2, may include the consecutive dissociations of HCHO molecules and HCO radicals through their collisions with vibrationally- and electronically-excited metastable N2 species. The increase of O2 content in the inlet gas stream is able to diminish the CO production and to promote the formation of CO2 via O-atom or HO2-radical involved reactions.

Influences of Reactor Geometry on Ozone Production with Dielectric Barrier Discharges: Experimental and Simulation Studies

AbstractThis study developed a model to simulate ozone synthesis in dry oxygen streams with a coaxial dielectric barrier discharge (DBD) reactor. Analyzing ozone synthesis chemistry, we found that fast quenching metastable species seems favorable for ozone production. This interpretation was successfully confirmed by the experiment conducted with a packed-bed DBD reactor. Ozone concentration generated by the packed-bed DBD reactor was significantly enhanced compared to non-packed one. Model simulations were carried out to elucidate the effects of reactor geometries on ozone synthesis. Parameters in the simulation include radii of inner and outer electrodes, dielectric thickness, dielectric constant, and discharge gap. More details regarding their effects were extensively discussed in the paper. In brief, a DBD reactor with a thinner dielectric thickness and/ or a greater dielectric constant could achieve higher ozone yields.

Gas-phase removal of acetaldehyde via packed-bed dielectric barrier discharge reactor

The effectiveness of applying packed-bed dielectric barrier discharge(PBDBD) technology for removing acetaldehyde from gas streams wasinvestigated. Operating parameters examined in this study include appliedvoltage, oxygen content, and gas-flow rate. Experimental results indicatethat the destruction efficiency of acetaldehyde predominantly depends onthe applied voltage. Removal of 99% of acetaldehyde has been achieved forgas streams containing 1000 ppmv acetaldehyde, 5% oxygen, with nitrogen asthe carrier gas. The oxygen content in the gas stream plays an importantrole in removing acetaldehyde within PBDBD. A higher CH3CHO removalefficiency is achieved for the gas stream containing less oxygen, since itwill dissipate energy due to its electronegative property. Carbon dioxideis the major end product, which is less hazardous to the environment and tohuman health. However, undesirable products, e.g., NO2 and N2O,CH3OC2H5, CH3COOH, CH3NO2,HCN, CH3NO3, and CH3OH, are detected as well.

Plasma Assisted Oxidation of Propene

AbstractNon-thermal plasma processing is an innovative technique for pollutant abatement. This approach involves the use of electrical energy for the production of free radicals which then react with the pollutant molecules. We have studied the oxidation of propene as a prototype hydrocarbon using a packed bed dielectric-barrier discharge reactor to generate the non-thermal plasma. We report the effect of three different types of material filling the reactor: glass, zirconia, and titania. The titania filled reactor shows the greatest selectivity for producing CO