Activation of methane and carbon dioxide in a dielectric-barrier discharge-plasma reactor to produce hydrocarbons—Influence of La 2O 3/γ-Al 2O 3 catalyst

Ultrafine particles (UFPs) are harmful to human beings, and their effective removal from the environment is an urgent necessity. In this study, a dielectric barrier discharge (DBD) reactor packed with porous alumina (PA) balls driven by a pulse power supply was developed to remove the UFPs (ranging from 20 to 100 nm) from the exhaust gases of kerosene combustion. Five types of DBD reactors were established to evaluate the effect of plasma catalysis on the removal efficiency of UFPs. The influences of gas flow rate, peak voltage and pulse frequency of different reactors on UFPs removal were investigated. It was found that a high total UFP removal of 91.4% can be achieved in the DBD reactor entirely packed with PA balls. The results can be attributed to the enhanced charge effect of the UFPs with PA balls in the discharge space. The UFP removals by diffusion deposition and electrostatic attraction were further calculated, indicating that particle charging is vital to achieve high removal efficiency for UFPs.

Plasma oxidation of methanol (CH3OH) in oxygen and nitrogen was investigated using two dielectric barrier discharge (DBD) reactors with or without Al2O3 as a catalyst and using a DC circle‐to‐plate (CTP) reactor. An AC power supply was used for the DBD reactors to generate corona discharges. A DC power supply, a 20‐MΩ resistor, and a 100‐pF capacitor were used to yield pulselike discharges. CH3OH was oxidized to formaldehyde (HCHO), carbon monoxide (CO), and carbon dioxide (CO2). HCHO was the main product when using DBD reactors and without Al2O3. CO was the main product when using the DBD reactor with Al2O3 and CTP reactor. Al2O3 could inhibit CH3OH further oxidation. The energy efficiency of the DBD reactors decreased with increasing power input and power density. The energy efficiency of the CTP reactor peaked with 7 g CH3OH/kWh that was three times as high as that with the DBD reactors at the same power input. Furthermore, the power density of the CTP reactor was higher than that of the DBD reactors, implying that the CTP reactor could be used for CH3OH oxidation with a small discharge space volume. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Elimination of CO in air stream using the plasma catalytic reactors was investigated. Two plasma catalytic systems were evaluated in this study, one consisting of a catalyst-bed packed in plasma zone of a dielectric barrier discharge (DBD) reactor directly (CID reactor), and the other (CAD reactor) consisting of a catalyst-bed after a DBD reactor. The examined operating parameters in this study included applied voltage, discharge power, the lengths of plasma zone and catalyst-bed, and inlet CO concentration. It was found that the glass packed DBD reactor without catalyst cannot eliminate CO in air stream effectively. When MnO x catalyst applied to DBD reactors, the removal of 1000 ppm CO can achieve to 97% by both type reactors. Under constant energy input condition, the CO removal of a CID reactor increased with the decrease of the initial CO concentration and the increase of the length of catalyst beds. In addition, the operating energy consumption of CID system was lower than that of CAD system.

This article presents the effects of different packing materials in dielectric barrier discharge (DBD) reactor on benzene removal efficiency to clarify the mechanism of combining efficiency between nonthermal plasma and catalyst over organic contaminants degradation. The influence of γ-Al2O3 and Pt/γ-Al2O3 catalysts on benzene decomposition was examined by passing gaseous benzene through two DBD reactors, each packed with one of the catalysts mentioned above. Concentrations of benzene, CO, CO2, NO2, and NO were measured and decomposition efficiency (of benzene), selectivity (of CO and CO2), and carbon balance were calculated to compare the effects of γ-Al2O3 catalyst with that of Pt/γ-Al2O3 catalyst in DBD reactors on benzene degradation. Data showed that at the same input energy density, benzene decomposition efficiency increased by about 20%, whereas the amount of CO released decreased by about 50% when using Pt/γ-Al2O3 catalyst. From the Arrhenius plot, the activation energy of Pt/γ-Al2O3 catalyst was calculated to be 3.01 kJ/mol, which turned out to be less than that of γ-Al2O3 catalyst by 57%. Further, the amounts of NO2 and NO released from the reactor when using Pt/γ-Al2O3 catalyst were only about 1/3 and 1/6 of that when using γ-Al2O3 catalyst, respectively. Therefore, Pt/γ-Al2O3 is a better catalyst because of the higher benzene decomposition efficiency, lower activation energy, and less byproducts generated when it was used in DBD reactor.

NO/sub x/ removal from a diesel engine exhaust and simulated gases was carried out using two different nonthermal plasma reactors. One is multipoints dielectric barrier discharge (DBD) reactor, the other is pulse streamer discharge (PSD) reactor. In the former reactor, the 2 mm thickness Pyrex glass plate is used as the dielectric barrier. The DBD reactor is driven by IGBT pulse modulator which can supply the 10 kV pulse voltage to the reactor with repetition rate of 2.5 kpps. The co-axial cylinder type discharge chamber is used as the PSD reactor which is driven by the pulse power generator with semiconductor opening switches (SOS). The SOS pulse generator can supply both polarity of 30 kV pulse with 300 pps repetition rate. The DBD reactor energy cost for NO removal from simulated gas (N/sub 2/:O/sub 2/=9:1, initial NO concentration = 200 ppm) is obtained to 12 g/kWh at 65% removal in 5 l/min. gas flow rate. The energy cost of the PSD reactor is almost 12 g/kWh at 25% NO removal efficiency. The DBD reactor was applied to 20 kVA diesel engine generator exhaust gas treatment. The contained NO/sub x/ (NO+NO/sub 2/) is abated from 70 to 40 ppm at no-load to the generator, and from 340 to 300 ppm. at 50 A load. The energy cost for the NO/sub x/ removal is obtained to 32 g/kWh.

Plasma-catalytic oxidation of chlorobenzene over Co-Mn/TiO2 catalyst in a dielectric barrier discharge reactor with the segmented electrodes

A novel novel negative pulse biased dielectric barrier discharge (PB-DBD) reactor was proposed, comprising a surface dielectric barrier discharge (S-DBD) reactor excited by AC voltage and a bias electrode excited by negative pulse voltage. The presence of the S-DBD plasma reduced the negative pulse voltage amplitude required to initiate volume discharge and enabled stable operation even under low-power conditions. Toluene degradation experiments further demonstrated that the PB-DBD plasma achieved markedly higher degradation efficiency (DE) than the S-DBD plasma. The DE was also increased by approximately 9%, compared with the AC-excited V-DBD plasma at a specific input energy of 350 J/L. Toluene degradation experiments in the PB-DBD reactor at different negative pulse frequencies showed that when the ratio of the negative pulse frequency to the AC frequency was 1:2 or 1:1, pronounced dips were observed in the curves of total discharge power, DE, carbon balance, CO2 selectivity, and gas temperature.

Plasma-assisted ethylene removal using silica gel and zeolite in AC dielectric barrier discharge

This project studies the conversion of CO2 into fuels and chemicals in a dielectric barrier discharge (DBD) reactor. CO2, H2 and CH4 have been used as reactants, and special attention has been paid on understanding the plasma-catalytic synergy when a catalyst is placed in a plasma discharge. CO2 and CH4 are major greenhouse gases, responsible for the global greenhouse effect and climate change. The overall aim of this project is to initiate CO2 hydrogenation and biogas reforming at ambient temperature and atmospheric pressure by using plasma-catalysis. In this project, non-thermal plasma has been generated in a DBD reactor with and without a packed-bed of catalyst, enabling the CO2 conversion to be investigated under three conditions: Plasma alone, thermal catalysis and plasma-catalysis. Transitional metal catalysts such as Cu, Co, Mn, and Ni supported on Al2O3 and SiO2 have been screened, and their performance in the CO2 hydrogenation and biogas reforming have been compared under the three conditions. The synergy between non-thermal plasma and catalysts has been clearly identified. The effects of a catalyst’s properties and operational parameters on the reactions have also been studied. The project starts by the investigation of CO2 hydrogenation with H2. Results showed that reverse water-gas shift reaction and CO2 methanation were dominant in the plasma CO2 hydrogenation process. Compared to plasma CO2 hydrogenation without a catalyst, the combination of plasma with Cu/Al2O3, Mn/Al2O3 and Cu-Mn/Al2O3 catalysts enhanced the conversion of CO2 by 6.7% to 36%. The Mn/Al2O3 catalyst showed the best catalytic activity, as it increased the CO yield by 114% and the energy efficiency of CO production by 116%. The Ni/Al2O3 was even better than the Mn/Al2O3 catalyst, while its presence in the DBD reactor has clearly demonstrated a plasma-catalytic synergy at low temperatures. In addition, the introduction of argon in the reaction has enhanced the conversion of CO2, the yield of CO and CH4 and the energy efficiency of the plasma process. The formation of metastable argon (Ar*) in the plasma has created new reaction-routes which made a significant contribution to the enhanced CO2 conversion and CH4 yield. Biogas reforming has also been initiated at ambient temperatures by non-thermal plasma. The combination of plasma with the Co/Al2O3, Cu/Al2O3, Mn/Al2O3 and Ni/Al2O3 catalysts significantly enhanced CH4 conversion and showed a plasma-catalytic synergy for CH4 conversion and overall energy efficiency of the process. The best CH4 conversion of 19.6% and syngas production have been achieved over the Ni/Al2O3 catalyst at a discharge power of 7.5 W and a gas flow rate of 50 ml min-1. Moreover, the addition of K-promoter into the catalyst has further improved the performance of the Ni/Al2O3 catalyst. A conclusion of the findings of this project and outlook for further work is presented in Chapter seven, where it is concluded that non-thermal plasma has initiated the CO2 hydrogenation and biogas reforming at lower temperatures, comparing with thermal catalytic processes. The combination of plasma and catalyst has further improved the performance of the hydrogenation processes, in terms of conversion, yield, and energy efficiency, while significant synergy between DBD plasma and catalysts has been observed. By upgrading the catalyst and adjusting the operational parameters (e.g. molar ratio of feed gas, preparation method of catalyst, composition of catalyst, and promoters), the plasma-catalytic CO2 hydrogenation and biogas reforming processes can be further optimised.

Electrode slurry coatings on the current collector of a Li-ion battery suffer from high mass loading owing to the severe floating of the binder during solvent drying. Atmospheric plasma pretreatment of the Cu current collector forms a functional group on its surface, which forms a hydroxyl bond with the binder materials. However, the Cu foil transferred to a high-speed roll-to-roll machine undergoes displacement due to wrinkling. This foil displacement deteriorates the uniformity of the process results and the discharge stability. To overcome the above-mentioned limitations, in this study, we designed an L-shaped dielectric barrier discharge (DBD) reactor as a combination of the direct-type DBD reactor with high processing speed and a jet-type DBD reactor with high discharge stability for industrial-scale current collector pretreatment. Helium gas injected between a pair of L-shaped electrodes and an electrode with bipolar high-voltage power generated stable seed electrons, which led to a homogeneous discharge between the lower part of the L-shaped electrode and the high-speed moving Cu current-collector surface. The plasma-treated Cu current collector exhibited stronger solvent adhesion and improved surface tension. In addition, the graphite anode coated on the plasma-treated current collector showed high mechanical adhesion strength with the anode materials and high-capacity retention in the half-cell test.

Manufacturing of anodic porous alumina for barriers in a dielectric barrier discharge reactor

The effect of Al2O3 and BaTiO3 packing on the plasma-enhanced NO x synthesis from air was investigated in a packed-bed dielectric barrier discharge (DBD) reactor. The discharge characteristics are significantly influenced by packing different materials into the discharge gap. Compared with the DBD without packing, the presence of Al2O3 or BaTiO3 beads in the discharge effectively enhanced the charge accumulation, average electric field, and mean electron energy, all of which contribute to the enhanced production of NO x . The lowest energy consumption of 15.9 MJ mol−1 for NO x production was achieved when placing BaTiO3 beads in the DBD, which can be attributed to the increased mean electron energy using the BaTiO3 packing, facilitating the formation of more N2 excited species in the reaction. These results suggest that choosing proper packing materials can effectively reduce the energy cost for plasma NO x synthesis using DBD.

A dielectric barrier discharge (DBD) reactor consisting of water-filled dielectric tube electrodes was used for the treatment of wastewater. The inner dielectric tube, which acted as the discharging electrode, was filled with an aqueous electrolyte solution. The outer dielectric tube, which served as the other electrode, was in contact with the wastewater, which was grounded. The present reactor system was energy-efficient for the production of ozone, not only because the perfect contact between the aqueous electrode and the dielectric surface minimized the loss of the electrical energy, but also because the DBD reactor was cooled by the wastewater. In addition, the ultraviolet (UV) light produced in the DBD reactor was able to assist in the wastewater treatment since the quartz tube used as the dielectric material was UV-transparent. The performance of the present DBD system was evaluated using a synthetic wastewater formed from distilled water and an azo dye, amaranth. The experimental parameters were the concentration of the electrolyte in the aqueous electrode, the discharge power, the initial pH of the wastewater and the concentration of hydrogen peroxide added to the wastewater. The wastewater treatment system was found to be effective for achieving decomposition of the dye.

A plate-type dielectric barrier discharge (DBD) reactor was designed and tested for removal of gaseous toluene. The DBD reactor consisted of 9 parallel plate electrodes, four of which were grounded. An AC voltage of rectangular waveform (<TEX>$5{\sim}8.5kV$</TEX>, <TEX>$60{\sim}1,000Hz$</TEX>), was applied to the other five electrodes. The gaseous toluene passed through the DBD reactor and its concentration was measured by a real-time gas analyzer. The carbon monoxide (CO) and carbon dioxide (<TEX>$CO_2$</TEX>) which were produced by decomposition of toluene in the DBD reactor, were sampled and analyzed by a micro gas chromatography. The maximum toluene removal efficiency was 51.4%.

Volatile organic compounds (VOCs) emission from anthropogenic sources has becoming increasingly serious in recent decades owing to the substantial contribution to haze formation and adverse health impact. To tackle this issue, various physical and chemical techniques are applied to eliminate VOC emissions so as to reduce atmospheric pollution. Among these methods, non-thermal plasma (NTP) is receiving increasing attention for the higher removal efficiency, non-selectivity, and moderate operation, whereas the unwanted producing of NO2 and O3 remains important drawback. In this study, a dielectric barrier discharge (DBD) reactor with wedged high voltage electrode coupled CuO foam in an in plasma catalytic (IPC) system was developed to remove toluene as the target VOC. The monolith CuO foam exhibits advantages of easy installation and controllable of IPC length. The influencing factors of IPC reaction were studied. Results showed stronger and more stable plasma discharge in the presence of CuO foam in DBD reactor. Enhanced performance was observed in IPC reaction for both of toluene conversion rate and CO2 selectivity compared to the sole NTP process at the same input energy. The longer the contributed IPC length, the higher the toluene removal efficiency. The toluene degradation mechanism under IPC condition was speculated. The producing of NO2 and O3 under IPC process were effectively removed using Na2SO3 bubble absorption.