Discharge Plasma Reactor Research Articles

Degradation of phenolic compounds by dielectric barrier plasma: Process optimization and influence of phenol substituents

The degradation of a series of phenolic compounds in a novel dielectric barrier discharge (DBD) plasma reactor was studied in this paper. The effect of various parameters, such as applied voltage, water flowrate, initial concentrations of organics, solution conductivity and pH, was investigated to achieve a high removal efficiency for phenolic compounds. The complete degradation of p-CH3 could be achieved within 32 min, and the highest energy yield was about 3.5 g/kWh. Electron paramagnetic resonance analysis and radical quenching experiment indicated that OH played an important role in phenols degradation, along with ozone molecules. O2− and 1O2 also possibly contributed to phenols degradation. Substituted phenols were more easily degraded, especially nitrophenol with strong electron withdrawing groups, originating from OH and O2− attack. The intermediates of different phenolic compound generated in the degradation process were identified by Mass spectroscopy (MS) and the corresponding mechanism were proposed to strengthen the understanding of mechanism. A DBD plasma and activated carbon combined technique is further proposed to promote the conversion of oxygen into ROS (reactive oxygen species) and enhance the mineralization rate of substituted phenols.

Industrial Application of Non-thermal Plasma (NTP) for Mercury and Dioxin Removal in Flue Gas

At present, there is an urgent demand for mercury and dioxin pollution control technology, internationally. It is necessary to find a solution other than the activated carbon adsorption process. In recent years, our self-developed low temperature plasma coupling system has been applied for mercury and dioxin removal in the flue gas, the system is composed of corona discharge plasma reactor and ceramic nano-material adsorption tank. The parameters of the plasma are 35-40kV, 400-450A, 1000Hz. The saturated adsorption capacity of ceramic nano-materials for Hg2+ is more than 5156μ g(Hg2+)/g. Pilot plant testes have been conducted in several industries, including collaborative disposal of cement kiln, medical waste incineration, recovery of waste mercury catalyst, recycling of waste fluorescent tubes, and achieved ideal result (Hg removal efficiency > 95%). It is expected to be an economical and efficient technology for mercury and dioxin removal, with great promotion value and social significance.

Catalytic DBD plasma reactor for low temperature partial oxidation of methane: Maximization of synthesis gas and minimization of CO2

In this study, room temperature synthesis gas production from partial oxidation of methane through a dielectric barrier discharge plasma reactor was investigated experimentally. In this case, operating conditions including applied voltage and Ar flow rate were evaluated to obtain the best operating conditions for the purpose of enhancing CH4 conversion and selective synthesis gas production. In addition, plasma alone system was compared with the catalytic system (NiO–CaO/Al2O3), revealing great improvement of synthesis gas selectivity through utilization of the catalyst. The maximum CH4 conversion of 99.9% with the synthesis gas module of 1.84 and energy efficiency of 3.2% was gained in the catalytic system where the applied voltage was 10 kV. Besides, synthesis gas module of almost 2, which is in favor of commercial applications including methanol production, was achievable at the applied voltage of 8 kV in the catalytic system. Finally, the obtained results were compared with the similar previous studies.

Plasma-Enhanced Catalytic Synthesis of Ammonia over a Ni/Al2O3 Catalyst at Near-Room Temperature: Insights into the Importance of the Catalyst Surface on the Reaction Mechanism.

A better fundamental understanding of the plasma-catalyst interaction and the reaction mechanism is vital for optimizing the design of catalysts for ammonia synthesis by plasma-catalysis. In this work, we report on a hybrid plasma-enhanced catalytic process for the synthesis of ammonia directly from N2 and H2 over transition metal catalysts (M/Al2O3, M = Fe, Ni, Cu) at near room temperature (∼35 °C) and atmospheric pressure. Reactions were conducted in a specially designed coaxial dielectric barrier discharge (DBD) plasma reactor using water as a ground electrode, which could cool and maintain the reaction at near-room temperature. The transparency of the water electrode enabled operando optical diagnostics (intensified charge-coupled device (ICCD) imaging and optical emission spectroscopy) of the full plasma discharge area to be conducted without altering the operation of the reactor, as is often needed when using coaxial reactors with opaque ground electrodes. Compared to plasma synthesis of NH3 without a catalyst, plasma-catalysis significantly enhanced the NH3 synthesis rate and energy efficiency. The effect of different transition metal catalysts on the physical properties of the discharge is negligible, which suggests that the catalytic effects provided by the chemistry of the catalyst surface are dominant over the physical effects of the catalysts in the plasma-catalytic synthesis of ammonia. The highest NH3 synthesis rate of 471 μmol g–1 h–1 was achieved using Ni/Al2O3 as a catalyst with plasma, which is 100% higher than that obtained using plasma only. The presence of a transition metal (e.g., Ni) on the surface of Al2O3 provided a more uniform plasma discharge than Al2O3 or plasma only, and enhanced the mean electron energy. The mechanism of plasma-catalytic ammonia synthesis has been investigated through operando plasma diagnostics combined with comprehensive characterization of the catalysts using N2 physisorption measurements, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), NH3-temperature-programmed desorption (TPD), and N2-TPD. Four forms of adsorbed NHx (x = 0, 1, 2, and 3) species were detected on the surfaces of the spent catalysts using XPS. It was found that metal sites and weak acid sites could enhance the production of NH3 via formation of NH2 intermediates on the surface.

Structural modifications of calcium based catalysts by non-thermal plasma in the CO2 reforming of CH4 and the influence of water

Calcium oxide, calcium hydroxide and calcium carbonate were tested for the CO2/CH4 reaction in a dielectric barrier discharge plasma reactor under humid conditions. It appeared that the presence of water in the gas stream enhanced slightly the selectivity to CO and H2 syngas on each support (2–5 %), contrary to the selectivities to CxHy that decreased (0.5 to 2%). The water showed little effect on oxygenates selectivities (in the order of 0.1%) compared to dry treatment. The three materials were characterized by thermogravimetric analysis and infrared spectroscopy prior and after, dry and humid, plasma treatments. Addition of humidity in the plasma gas stream led to the formation of calcium hydroxide on the surface of CaO and enhanced the carbonation of Ca(OH)2. We showed that the carbonation of Ca(OH)2, H2O proceeded through simultaneous CO2 capture and H2O release, highlighting an oscillating behavior.

Decomposition of Heptane by Dielectric Barrier Discharge (DBD) Plasma Reactor Having the Segmented Electrode: Comparison of Decomposition Mechanisms to Toluene

The effect of the structure of VOC and the exposed surface area on the decomposition of VOCs adsorbed on the zeolite by dielectric barrier discharge plasma were investigated. The decomposition mechanisms of heptane and toluene, which are chosen as a model reaction for alkane and aromatic VOC, respectively, were compared each other at the same experimental conditions in the plasma reactor having the segmented electrode. The comparison was discussed in terms of mineralization, CO2 selectivity, ozone consumption, by-products, and energy yield. Also, the exposed surface area was expected to have a close relationship with the ozone consumption. The segmented electrode reactor could accelerate the dehydrogenation reaction at the low temperature as well as the atmospheric pressure without any support of catalyst. In each decomposition mechanism, the formation of hydrocarbon radical was considered as a key stage for decomposition of VOCs. The hydrocarbon radicals in the heptane decomposition were formed by the dehydrogenation, but that in the toluene decomposition were formed by the ring cleavage. The formation of hydrocarbon radicals could increase the active spots which could be attacked by the ozone, leading to the increased use efficiency of ozone. In conclusion, the toluene was decomposed easily when the similar energy was applied because the number of hydrogen atom was fewer.

Degradation of Methylene Blue via Dielectric Barrier Discharge Plasma Treatment

The degradation of methylene blue (MB) using an upgraded dielectric barrier discharge (DBD) plasma reactor was investigated in this paper. Air plasma was generated in the glass bead packed bed in the reactor, which was propagated into MB solution through a microporous diffuser plate. Microdischarge phenomenon can be observed on the interface of MB solution and the diffuser plate, where plasma active species were generated. The effects of air flow rate, initial solution concentration, initial solution pH, and initial solution conductivity on MB degradation were examined. Experimental results indicated that the proposed plasma reactor was effective for MB degradation. No obvious change in MB degradation efficiency was obtained for solution with various initial pH and conductivities, which suggested the potential of the reactor in actual wastewater treatment. The possible mechanism of the generation of plasma active species for MB degradation was proposed. In addition, the total organic carbon removal and chemical oxidation demand removal after 30 min treatment were 38.5% and 48.3%, which was higher than that obtained by ozone. The energy yield for MB degradation reached up to 9.3 g/kWh. Finally, a possible degradation pathway of MB solution was proposed.

Cold plasma treatment to improve the adhesion of cassava starch films onto PCL and PLA surface

Since starch hydrophilicity makes it difficult to be used as packaging material, its combination with synthetic biodegradable polymers is an alternative of interest. In this work, atmospheric air cold plasma was used as an adhesion improver between polycaprolactone (PCL) or poly(lactic acid) (PLA) and starch layers, in order to produce multilayer films. For this, a barrier dielectric discharge plasma reactor was used, at ambient temperature and atmospheric pressure. The treatment of PCL and PLA films resulted in increase of the surface roughness and decrease of the water contact angle. Multilayer films (PCL-, PLA-starch) were produced after plasma treatment. Adhesion of starch films onto both PCL and PLA surfaces was improved with plasma treatment, and the delamination resistance increased with treatment time. The best adhesion was obtained for PLA-starch film with 10 min of plasma treatment, resulting in no delamination. The water vapor barrier of the multilayer films was significantly higher than of starch films, while the mechanical properties were similar to those found for PCL/PLA films, showing that these multilayer films are promising for package applications.

PLASMA-ETCHING AND MODIFICATION OF POLYETHYLENE FOR IMPROVED SURFACE STRUCTURE, WETTABILITY AND OPTICAL BEHAVIOR

In the present paper, the surface modification of low-density polyethylene (LDPE) polymer is done by plasma-etching to tune its surface structure, wettability and optical behavior to make it useful for technical applications. For this purpose, two gasses (N[Formula: see text] and (O[Formula: see text] are used as the discharge precursors in a home-built plasma reactor. The plasma-treated LDPE surface etch-rate (control other surface properties) is high at the beginning and slows down as the treatment time increases due to surface restructuring. The etched surfaces are analyzed by scanning electron microscopy (SEM), which indicate greater surface changes due to O2plasma compared to that of N2. Also, the surface hardness is slightly low at the first treatment time and increases rapidly at higher exposure durations. Besides, the friction coefficient is significantly changed by plasma treatment, suggesting the formation of cohesive surface skin. The obtained X-ray diffraction (XRD) patterns show that the plasma-treated LDPE samples suffer disordering and structural changes which increase with raising the treatment duration. Surface restructuring is attributed to the combined effects of active species (from plasma) bombardments and surface oxidation. Also, the surface chemistry changes are evaluated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy which reveals chain scission after N2plasma treatment. Whereas, the O2plasma-treated samples suffer surface oxidation and formation of polar groups which offer some surface oxidation coatings. Furthermore, the surface wettability has been determined by the sessile drop method and shows enhancement upon plasma treatment due to the combined influence of surface chemistry and morphology. Also, the surface free energy (SFE) and adhesion are found to increase with the plasma exposure time due to surface activation. The optical behavior of LDPE is studied using ultraviolet–visible (UV–Vis) spectrophotometer which indicates that the optical bandgap performance depends on the amorphous or crystalline nature of the polymer. Also, the conjugated carbon atoms were examined and correlated to the reduced bandgap. In conclusion, the studied home-built glow discharge plasma reactor could be utilized efficiently to tune polymer surface properties to be used in high technology applications.

Hierarchically Porous Nanostructured Nickel Phosphide with Carbon Particles Embedded by Dielectric Barrier Discharge Plasma Deposition as a Binder-Free Electrode for Hybrid Supercapacitors

Three-dimensional (3D) metal phosphides are promising superior electrode components for supercapacitors. In this study, 3D porous nickel phosphide nanoarrays are successfully enrooted on the surface of nickel foam (Ni2P/NF) by low-temperature hydrothermal treatment. Subsequently, a nanocarbon was embedded over Ni2P@NF by efficient utilization of the environmental pollutant ethylene gas via a dielectric barrier discharge plasma reactor. This nanocarbon was deposited on porous Ni2P/NF nanoarrays (Ni2P-C/NF) as a positive electrode sandwiched with peanut shell-derived porous activated carbon (PNS-AC) as a negative electrode for the fabrication of a hybrid supercapacitor device. The hybrid supercapacitor device (Ni2P-C/NF//PNS-AC) delivers an enormous amount of areal and gravimetric capacities values at a 1 A g–1 current density of 318.8 μAh cm–2 and 106.2 mAh g–1, respectively. Moreover, the hybrid supercapacitor device achieved outstanding energy and power density with excellent cyclic durability (90.1%) even after 5000 cycles at 7 A g–1, which are 108.1 Wh kg–1 at 1 A g–1 and 14,370.4 W kg–1 at 15 A g–1, respectively. These results evidenced that the novel nanostructured Ni2P/NF with embedded carbon nanoparticles has excellent potential as the supercapacitor electrode material.

CO2 hydrogenation to lower hydrocarbons over ZSM-5-supported catalysts in a dielectric-barrier discharge plasma reactor

ZSM-5-supported metal catalysts, including Fe/ZSM-5, Co/ZSM-5, Ni/ZSM-5, Cu/ZSM-5 and Mo/ZSM-5, were tested for the plasma-induced CO2 hydrogenation in a dielectric-barrier discharge (DBD) plasma reactor. A significant synergy between DBD plasma and the catalyst was found. Without catalyst, CO2 was converted solely to CO at a conversion level of 8.1% in the plasma. The supported metal catalysts enhanced CO2 conversion and promoted the hydrocarbon formation. Co/ZSM-5 exhibited the best performance with a C2-C4 selectivity of 13.7% at 45.0% CO2 conversion. Powder XRD studies revealed that the stable active phase was Co metal particles in the Co/ZSM-5 catalyst.

Enhancement of plasma-assisted catalytic CO2 reforming of CH4 to syngas by avoiding outside air discharges from ground electrode

This work presents the effects of the insulation of ground electrode and operating parameters on CO2 reforming of CH4 to syngas in a coaxial-cylindrical dielectric barrier discharge (DBD) plasma reactor coupled with Ni/α-Al2O3 catalyst. For the conventional plasma reactor, abnormal outside discharge inevitably ignites and develops from the ground electrode, giving rise to the formation of harmful substances (e.g., NOx) and the waste of energy. The power dissipation for the conventional reactor therefore includes both that used for the dry reforming reactions and the loss of energy due to the air discharge. The new finding of this work is that by covering the ground electrode with an insulating oil jacket, not only the NOx formation is prevented but also the conversion rates, product selectivity and energy efficiency are largely enhanced by roughly 30, 10 and 100% at a specific energy input of about 47 kJ, respectively. The results are associated with the extinguishment of the discharge occurring outside the reactor, which is usually neglected when designing DBD reactors.

Experimental investigation of hydrogen production by CH4–CO2 reforming using rotating gliding arc discharge plasma

Hydrogen produced from CH4–CO2 reforming by an optimized rotating gliding arc discharge plasma reactor is investigated in this study. The effect of CH4/CO2 ratio (mole ratio), total input flow rate, discharge gap, voltage, and discharge frequency are analyzed. The results show that H2 yield increases with the increase of CH4/CO2 ratio. Arc can be stretched effectively by increasing total input flow rate, then the discharge region is enlarged. Increasing discharge gap can enlarge the discharge region, but the reaction of the gas mixture would be suppressed if the discharge region was excessively large. The discharge region decreases with the increased discharge frequency to a certain degree. Based on the experimental results, the optimal experimental condition is concluded as applied voltage 60 V, discharge frequency 20 kHz, and minimum discharge gap 3 mm. It is anticipated that the results would serve as a good guideline to the application of hydrogen production from hydrocarbon fuels by plasma reforming onboard.

Post-discharge DBD plasma treatment for degradation of organic dye in water: A comparison with different plasma operation methods

Dielectric barrier discharge (DBD) plasma reactor is an innovative advanced oxidation technology for degradation of organic dye in water. In this study, the crystal violet (CV) solution was exposed to a post-discharge DBD plasma in which O2 was used as the feed gas. In this mode, the liquid target is isolated from the plasma medium and the plasma effluent gas is bubbled across the liquid target to increase mass transfer between reactive species and the solution. The influence of operating parameters including applied power and gas flow rate was studied. It was shown that increasing reactor temperature resulted in the reduction of CV removal. Dilution of the plasma forming gas (pure O2) with Ar enhanced the CV removal up to 44%. The kinetic model of CV bleaching was shown to follow a first-order reaction. In the most suitable experimental condition after one minute treatment, the CV decolorization of 100% was achieved, and the total organic carbon (TOC) dropped to zero. Preliminary investigation into the byproducts through UV-VIS, TOC and GC-MS were done which showed the disappearance of the aromatic rings. This work also outlines current operation methods for plasma treatment of organic dyes in water and compares their performance in terms of energy efficiency, degradation rate constant and formation of main reactive species. The interesting results of post discharge treatment which can be compared quite favorably with those achieved by other operation methods, are the degradation rate constant of 4.37 (1/min) and energy efficiency of 12.2 (g/kWh).

Enhanced reforming of mixed biomass tar model compounds using a hybrid gliding arc plasma catalytic process

Abstract Plasma-catalytic steam reforming of mixed tar model compounds (toluene and naphthalene) from biomass gasification has been carried out in a gliding arc discharge (GAD) plasma reactor. The influence of three catalysts (15Ni, 7.5Ni7.5Co and 15Co) on the performance of the plasma reforming of toluene and naphthalene has been evaluated including the conversion, the energy efficiency, the yield/selectivity of gaseous products and the formation of by-products. A plasma-catalysis synergy was generated when introducing the catalysts to the plasma tar reforming process. The highest toluene conversion of 95.7% and naphthalene conversion of 83.4% were achieved when the 7.5Ni7.5Co catalyst was integrated with the GAD plasma at a total tar concentration of 16.0 g/Nm3 and a discharge power of 75 W. The corresponding energy efficiency for the conversion of toluene and naphthalene was 38.0 g/kWh and 2.3 g/kWh, respectively, giving the highest total tar conversion of 95.1% and overall energy efficiency of 40.3 g/kWh. The coupling of GAD with the 7.5Ni7.5Co catalyst also showed the highest yield of H2 (42.3%) and CO (37.3%) and the highest CO selectivity of 40.1%. In addition, the combination of the GAD plasma with 7.5Ni7.5Co reduced the carbon deposition on the catalyst surfaces and the formation of by-products in the plasma-catalytic tar reforming process. The enhanced reducibility and NiCo alloy formation of the 7.5Ni7.5Co catalyst contribute to the enhanced conversion of mixed tar compounds and the formation of the plasma-catalysis synergy in the hybrid plasma-catalytic tar reforming process.

The comparison of ozone production with dielectric barrier discharge plasma reactors series and parallel at atmospheric pressure

Ozone that was generated by using dielectric barrier discharge plasma (DBDP) reactor has been investigated. In this study, we compared ozone production with reactor series and parallelled at atmospheric pressure. The reactor used models of a wire mesh - aluminum foil configuration. The first reactor uses a series circuit with two reactors and the second reactor uses a parallel circuit with two reactors. Ozone was produced by DBDP reactor using AC high Voltage. Oxygen that source of ozone has been taken from the pure oxygen and natural gas. Some analysis conducted including the variation of voltage, the flow rate of gas and type of source gas which affect produced concentration. Some parameters varied including voltage from 0 - 10 kV and the flow rate of gas 4 - 12 L / min. The results showed that ozone concentration in the series reactor is higher than that of the parallel reactor. The series reactor could produce ozone with a concentration of 348 ppm at a voltage of 10 kV. Then the parallel reactor of ozone could produce with a concentration of 240 ppm at a voltage of 10 kV. We found that series reactor could produce more high ozone concentration at the same voltage.

Oxidative Decomposition of Adsorbed Toluene Using Ozone Concentrated by Nonthermal Plasma Flow

Toluene decomposition is performed using an adsorbent and a nonthermal plasma (NTP) induced radical flow system that consists of a surface discharge and circulation flow. The liquid toluene is vaporized in the circulation channel connected to a blower and the surface discharge plasma reactor in series, and the toluene gas is adsorbed by the adsorbent. In order to accelerate the oxidative decomposition of the adsorbed toluene, two techniques are tested. In the first technique, concentrated ozone injection is utilized and the adsorbed toluene is decomposed using the NTP flow. This occurs after introducing the concentrated ozone in advance, through the bypass channel connected in parallel with the adsorbent. In the other technique, toluene decomposition occurs under the reduced pressure of the adsorbent chamber during the decomposition process, because accelerated toluene decomposition on the surface of the adsorbent is expected. This reduced pressure is in the range of −3 to −7 kPa and is achieved by regulating the ball valve located upstream of the adsorbent chamber. When the concentrated ozone is introduced into the circulation channel, the adsorbent temperature increases drastically and the conversion ratio of toluene to $\text{CO}_{x}$ (CO and CO2) increases by a factor of 2.0 in comparison with that without the concentrated ozone injection. In addition, the energy efficiency of the conversion increases by a factor of 1.9, even when the energy required for the concentrated ozone is included. However, there was no noticeable effect of the reduced pressure on the toluene decomposition under experimental conditions.

Optimation of ozone capacity produced by DBD plasma reactor: dedicated for cold storage

The optimation of ozone production generator that used for cold storage has been done. Ozone generator was constructed by using Dielectric Barrier Discharge Plasma Reactor with single pyrex dielectic. Plasma was generated by HV AC with voltage from 0.5 kV to 11 kV, and frequence of 1 kHZ. This research was conducted in two treatment namely control treatment and ozone treatment by tuna fish, milkfish and shrimp. Ozone treatment are stored into Cold Storage (2 m x 2 m x 2.5 m), temperature (2°C-8°C) with average concentration of ozone distributed into the cold storage for 24 points is 6.2 ppm ± 0,14 ppm. The result showed that the optimum to generate ozone by using variations of power input, air flow rate. we obtained that the highest efficiency of 320 grams / kWh and ozone capacity of 65 grams / hour at 15 L / min flow rate with an input power of 210 watts. The concentration of dissolved ozone in the water containing fish and shrimp is almost the same that is equal to 2 ppm ozone flow for 60 minutes with ozone generator production capacity of 65 gram/hour. We test proximate of milkfish, tuna fish, and white shrimp that storaged in cold room (2°C-8°C), and we found that until days 15 still meet SNI 01-2729.1-2006, as fresh fish and shrimp.

Development and characterization of an atmospheric pressure plasma reactor compatible with spatial ALD

Dielectric Barrier Discharges (DBD) are widely used for atmospheric pressure plasma generation. The possibility of their adaptation in custom-made configurations makes them potential candidate to assist deposition processes. In fact, the increased need of high-quality thin films forces to improve the deposition techniques. New processes should be able to work in less constrained conditions such as atmospheric pressure rather than vacuum and to have faster deposition rates while respecting the same high quality of the deposited films. In this paper we present the development of a surface dielectric barrier discharge plasma reactor to assist an atmospheric spatial atomic layer deposition process. The reactor was fabricated with 3D printing and the plasma was generated by a surface dielectric barrier discharge powered by a microsecond pulsed high voltage power supply. The dissipated power was measured for different configurations, and thanks to the micro discharges imaging, it was observed that the thickness and the shape of the dielectric barrier influenced the micro discharges distribution on the dielectric surface. The plasma reactor exhaust gas was chemically analyzed by FTIR spectroscopy and micro gas chromatography. The ozone concentration was determined as function of frequency of the power supply.

Practical Design of a High-Voltage Pulsed Power Supply Implementing SiC Technology for Atmospheric Pressure Plasma Reactors

Non-thermal plasma reactors offer numerous advantages and are used in a wide variety of applications. Exemplary fields of use include exhaust gas or water quality improvement, surface processing, agriculture, or medical processes. Two of the most popular discharge chamber constructions are dielectric barrier discharge (DBD) and pulsed corona discharge (PCD, barrierless) plasma reactors. Various power supply constructions are presented in the literature with varying complexity and operating principles. A simple, power electronic, pulsed power supply construction is presented in this work, implementing resonant power switch operation, modern silicon carbide (SiC) power semiconductors and a Tesla coil-like transformer design. The power supply construction is immune to short circuits in the reactor and can be used for both types of reactor constructions. The principles of operation, simulation results, and prototype test verifications are presented with main power supply characteristics.