Decomposition of Naphthalene by dc Gliding Arc Gas Discharge

Rapid Evaluation of Material Surface Modification by a Dielectric Barrier Discharge Based on Fluorescence Coloring and Image Processing Technologies

In recent years, improving the surface properties of large-scale insulation by plasma modification has attracted extensive attention with the development of power systems and high-tech industries. However, routine evaluations of the modification effect and uniformity require complicated tests after the plasma is powered off, which waste a lot of time and cannot regulate the modification effect online. In this study, a novel fluorescence-assisted dielectric barrier discharge (DBD) for fabricating a functional film is developed, and a rapid evaluation method of the modification effect and uniformity is proposed based on fluorescence coloring and image processing technologies. The results show that the addition of an organic fluorescent agent in the DBD with hexamethyldisiloxane (HMDSO) has no negative effect on the plasma discharge and modification effect, and the fluorescence-assisted DBD successfully fabricates the functional films with typical chromogenic groups (N-H and S═O) that exhibit typical fluorescence under an UV lamp. According to image processing and parameter extraction, the plasma-assisted fluorescent film is converted into a two-dimensional (2D) color map with nine color levels, and three characteristic parameters are proposed to evaluate the modification effect rapidly and directly. It shows that the warmer the color of the treated sample, the better the hydrophobicity and electrical insulating properties, where the red region represents the optimally modified surface, while the blue region represents the worst one. The area, shape, and integrity of the plasma modification are clarified quantificationally, which provides the possibility of further online evaluation of the modification effect and uniformity by the plasma treatment.

Toluene Decomposition in Plasma–Catalytic Systems with Nickel Catalysts on CaO-Al2O3 Carrier

The decomposition of toluene as a tar imitator in a gas composition similar to the gas after biomass pyrolysis was studied in a plasma–catalytic system. Nickel catalysts and the plasma from gliding arc discharge under atmospheric pressure were used. The effect of the catalyst bed, discharge power, initial toluene, and hydrogen concentration on C7H8 decomposition, calorific value, and unit energy consumption were studied. The gas flow rate was 1000 NL/h, while the inlet gas composition (molar ratio) was CO (0.13), CO2 (0.15), H2 (0.28–0.38), and N2 (0.34–0.44). The study was conducted using an initial toluene concentration in the range of 2000–4500 ppm and a discharge power of 1500–2000 W. In plasma–catalytic systems, the following catalysts were compared: NiO/Al2O3, NiO/(CaO-Al2O3), and Ni/(CaO-Al2O3). The decomposition of toluene increased with its initial concentration. An increase in hydrogen concentration resulted in higher activity of the Ni/(CaO-Al2O3) catalysts. The gas composition did not change by more than 10% during the process. Trace amounts of C2 hydrocarbons were observed. The conversion of C7H8 was up to 85% when NiO/(CaO-Al2O3) was used. The products of the toluene decomposition reactions were not adsorbed onto its surface. The calorific value was not changed during the process and was higher than required for turbines and engines in every system studied.

Collection and decomposition of oil mist via corona discharge and surface dielectric barrier discharge

Oil mist emitted during cooking is one of the major sources of atmospheric particulate matter in urban areas. A conventional electrostatic precipitator (ESP) is used in some large restaurants; it requires regular electrode cleaning to maintain particle collection performance. However, oil mist generated during cooking is viscous and difficult to clean with water. Herein, we introduce a methodology and a device for cleaning collected oil mist using surface dielectric barrier discharge (surface-DBD) plasma. Our device uses corona discharge for the collection of oil mist. Subsequently, the oil mist collected is decomposed to gas-phase species by surface-DBD plasma. A maximum collection efficiency of 93.25% (for 230 nm di-ethyl hexyl sebacate (DEHS) particle) is obtained at a flow velocity of 1.5 m/s. The maximum oil mist decomposition efficiency is 96.4%. More than 80% of the decomposed oil mist is converted to CO₂ and CO under all test conditions. Some of the byproducts other than CO and CO₂ are released as particles. Higher frequency results in higher oil mist decomposition efficiency, but also higher byproduct formation of particles. The mechanism of oil mist decomposition by surface-DBD plasma is discussed using optical emission spectroscopy data.

Prediction and evaluation of plasma arc reforming of naphthalene using a hybrid machine learning model

We have developed a hybrid machine learning (ML) model for the prediction and optimization of a gliding arc plasma tar reforming process using naphthalene as a model tar compound from biomass gasification. A linear combination of three well-known algorithms, including artificial neural network (ANN), support vector regression (SVR) and decision tree (DT) has been established to deal with the multi-scale and complex plasma tar reforming process. The optimization of the hyper-parameters of each algorithm in the hybrid model has been achieved by using the genetic algorithm (GA), which shows a fairly good agreement between the experimental data and the predicted results from the ML model. The steam-to-carbon (S/C) ratio is found to be the most critical parameter for the conversion with a relative importance of 38%, while the discharge power is the most influential parameter in determining the energy efficiency with a relative importance of 58%. The coupling effects of different processing parameters on the key performance of the plasma reforming process have been evaluated. The optimal processing parameters are identified achieving the maximum tar conversion (67.2%), carbon balance (81.7%) and energy efficiency (7.8 g/kWh) simultaneously when the global desirability index I₂ reaches the highest value of 0.65.

Investigation of mechanisms involved in seed germination enhancement, enzymatic activity and seedling growth of rice (Oryza Sativa L.) using LPDBD (Ar+Air) plasma

The study investigates the effect of LPDBD (Low Pressure Dielectric Barrier Discharge) (Ar + Air) plasma on seed germination, seedling growth and antioxidant enzyme activity of rice. Rice seeds were treated with LPDBD (Ar + Air) plasma for 2min, 4min, 6min, 8min and 10min. Seed germination rate, seedling growth, total chlorophyll content, enzymatic activity, total soluble sugar and protein concentration were increased in plants grown from the LPDBD (Ar + Air) plasma treated seeds. It was observed that the sprouting of seeds and the growth of seedlings of rice depends on the feed gases used to generate plasma and plasma processing time. In the case of plantlets germinated from the plasma-treated seeds of rice, the H₂O₂ level was increased significantly both in leaves and roots for 6min, 8min and 10min treatment respectively. No significant change was observed in Nitric Oxide (NO) concentration in seed, leaf, or root of plants grown from LPDBD (Ar + Air) plasma-treated seeds. The amount of total soluble sugar and protein increased significantly in the case of 2min, 4min, 6min, 8min and 10min seed treatment. Although plants exhibited no significant increase in APX activities, but a significant increase of CAT and SOD activity in the leaf and root was found. This study reveals that LPDBD (Ar + Air) plasma is involved in the elevation of ROS species in leaf and root of rice plants which is tightly regulated by the upregulation of CAT activity that ultimately enhances the seed germination and growth of rice plantlets.

Tar Removal by Nanosecond Pulsed Dielectric Barrier Discharge

Plasma-catalytic reforming of simulated biomass tar composed of naphthalene, toluene, and benzene was carried out in a coaxial plasma reactor supplied with nanosecond high-voltage pulses. The effect of Rh-LaCoO3/Al2O3 and Ni/Al2O3 catalysts covering high-voltage electrode on the tar conversion efficiency was evaluated. Compared to the plasma reaction without a catalyst, the combination of plasma with the catalyst significantly enhanced the conversion of all three tar components, achieving complete conversion when an Rh-based catalyst was used. Apart from gaseous and liquid samples, char samples taken at five locations inside the reactor were also analyzed for their chemical composition. Char was not formed when the Rh-based catalyst was used. Different by-products were detected for the plasma reactor without a catalyst, with the Ni- and Rh-based catalysts. A possible reaction pathway in the plasma-catalytic process for naphthalene, as the most complex compound, was proposed through the combined analysis of liquid and solid products.

Decomposition of volatile organic compounds using gliding arc discharge plasma

This work provides a systematic review on the decomposition of volatile organic pollutants in flue gas through the gliding arc (GA) plasma technology. To begin with, the basic mechanisms of GA plasma generation are summarized and three characteristic stages existed during the GA plasma generation process are revealed: gas breakdown stage, equilibrium stage, and non-equilibrium stage. Then, the types of GA reactors are comparatively illustrated. Possible destruction mechanisms of volatile organic compounds (VOCs) by GA plasma are discussed by taking chloroform, benzene, and methanol as examples. Furthermore, the effects of many operating parameters on the VOCs destruction efficiency are comprehensively analyzed. Simultaneously, the product distribution, energy cost, technical and economic during the whole decomposition process are considered. Finally, the advantages and disadvantages of GA plasma and its further development trend are concluded from the academic and industrial application of GA plasma in VOCs decomposition.Implications: This paper comprehensively describes the principle, characteristics, research progress and engineering application examples of the degradation of volatile organics by gliding arc discharge plasma, so that readers can fully understand the degradation of volatile organics by gliding arc discharge plasma and provide theoretical basis for the industrial application of the degradation of volatile organics by gliding arc discharge plasma.

Coupled Plasma-Catalytic System with Rang 19pr Catalyst for Conversion of Tar

A coupled plasma-catalytic system (CPCS) for the conversion of toluene was investigated and compared to the homogeneous system of gliding discharge plasma. Toluene was used as a model compound, which is present in tars. The study was carried out at atmospheric pressure, in a gas composition similar to the one obtained during pyrolysis of biomass. The effect of the initial toluene concentration, energy supplied to gliding discharge (GD) and the presence of a catalyst on the conversion of toluene was studied. Both the composition of outlet gas and its calorific value were monitored. Based on the obtained results it can be concluded that the conversion of toluene increases with the increase of gliding discharge power. The highest toluene conversion (89%) was received in the coupled plasma-catalytic system (catalyst: RANG-19PR) under the following conditions: CO (0.13 mol. fr.), CO₂ (0.12 mol. fr.), H₂ (0.25 mol. fr.), N₂ (0.50 mol. fr.) and 4400 ppm of toluene with a gas flow rate of 1000 Nl/h. The composition of the outlet gas in the homogeneous system and in the CPCS changed in the range of a few percents. Toluene levels were reduced tenfold. Benzene, C3 and C4 hydrocarbons, as well as acetylene, ethylene and ethane, were detected in the outlet stream in trace amounts. Carbon deposits were present in the reactor. The products of methanation of carbon oxides were detected in the both studied systems. A mechanism of toluene decomposition in the CPCS was proposed. The application of the catalyst brought about an increase in the calorific value of the outlet gas. It was above the minimal level demanded by engines and turbines.

Steam reforming of toluene and naphthalene as tar surrogate in a gliding arc discharge reactor

Steam reforming of mixed toluene and naphthalene as tar surrogate has been investigated in an AC gliding arc discharge plasma, with particular emphasis on better understanding the effect of steam and CO₂ on the reaction performance. Results show that H₂, C₂H₂ and CO are the major gas products in the plasma steam reforming of tar for energy recovery. The addition of a small amount of steam remarkably enhances the conversions of both toluene and naphthalene, from 60.4% to 76.1% and 57.6% to 67.4%, respectively, as OH radicals formed by water dissociation create more reaction pathways for the conversion of toluene, naphthalene and their fragments. However, introducing CO₂ to this process has a negative effect on the tar reforming. Optical emission spectroscopic diagnostics has shown the formation of a variety of reactive species in the plasma process. Trace amounts of monocyclic and bicyclic aromatic condensable by-products are also detected. The destruction of toluene and naphthalene can be initiated through the collisions of tar surrogates with energetic electrons, N₂ excited species, OH and O radicals etc. Further optimization of the plasma tar destruction is still needed because the complexity of the tar component in a practical gasifier could decrease the tar conversions.

Reduction of cadmium toxicity in wheat through plasma technology

Cadmium (Cd) contamination in plant-derived food is a big concern. This study examines whether and how Ar/O₂ and Ar/Air plasma techniques lead to Cd detoxification in wheat. Treatment with Ar/O₂ and Ar/Air changed the seed surface and decreased the pH of seeds as well as the cultivation media. Generally, plants subjected to Cd treatment from seeds treated with Ar/O₂and Ar/Air plasma showed considerable progress in morphology and total chlorophyll synthesis compared to Cd-treated wheat, suggesting that plasma technology is effective for Cd detoxification. Furthermore, Ar/O₂ and Ar/Air plasma treated plants showed a significant decrease in root and shoot Cd concentration, which is consistent with the reduced expression of Cd transporters in the root (TaLCT1 and TaHMA2) compared with the plants not treated with plasma in response to Cd stress. This Cd inhibition is possibly accomplished by the decrease of pH reducing the bioavailability of Cd in the rhizosphere. These observations are in line with maintenance of total soluble protein along with reduced electrolyte leakage and cell death (%) in root and shoot due to Ar/O₂ and Ar/Air treatments. Further, Cd-induced elevated H₂O₂ or oxidative damage in tissues was mainly diminished through the upregulation of antioxidant enzymes (SOD and CAT) and their corresponding genes (TaSOD and TaCAT) induced by Ar/O₂ and Ar/Air plasma. Grafting results suggest that root originating nitric oxide signal possibly drives the mechanisms of Cd detoxification due to plasma treatment in wheat. These findings provide a novel and eco-friendly use of plasma technology for the mitigation of Cd toxicity in wheat plants.

Mechanisms and Signaling Associated with LPDBD Plasma Mediated Growth Improvement in Wheat

This study investigates the effect and mechanisms of low pressure dielectric barrier discharge (LPDBD) produced with Ar/O₂ and Ar/Air technique causing biological stimulation leading to improved germination and growth in wheat. Both plasma treatments caused rougher and chapped seed surface along with noticeable improvement in seed germination in wheat. Beside this, seed H₂O₂ concentration significantly increased compared to controls subjected to Ar/O₂ and Ar/Air while this phenomenon was more pronounced due to Ar/Air plasma. Analysis of plants grown from the plasma treated seeds showed significant improvement in shoot characteristics, iron concentration, total soluble protein and sugar concentration in comparison with the controls more efficiently due to Ar/O₂ plasma than that of Ar/Air. Further, none of the plasma treatments caused membrane damage or cell death in root and shoot of wheat. Interestingly, Ar/O₂ treated plants showed a significant increase (2-fold) of H₂O₂ compared to controls in both root and shoot, while Ar/Air plasma caused no changes in H₂O₂. This phenomenon was supported by the biochemical and molecular evidence of SOD, APX and CAT in wheat plants. Plants derived from Ar/O₂ treated seeds demonstrated a significant increase in SOD activity and TaSOD expression in roots of wheat, while APX and CAT activities along with TaCAT and TaAPX expression showed no significant changes. In contrast, Ar/Air plasma caused a significant increase only in APX activity in the shoot. This suggests that Ar/O₂ plasma caused a slight induction in H₂O₂ accumulation without triggering the H₂O₂ scavengers (APX and CAT) and thus, efficiency affect growth and development in wheat plants. Further, grafting of control and Ar/O₂ treated plants showed a significant increase in shoot biomass and H₂O₂ concentration in grafts having Ar/O₂ rootstock regardless of the type scion attached to it. It indicates that signal driving Ar/O₂ plasma mediated growth improvement in wheat is possibly originated in roots. Taken together, this paper delivers new insight into the mechanistic basis for growth improvement by LPDBD technique.

Enhanced oxidation of naphthalene using plasma activation of TiO2/diatomite catalyst

Non-thermal plasma technology has great potential in reducing polycyclic aromatic hydrocarbons (PAHs) emission. But in plasma-alone process, various undesired by-products are produced, which causes secondary pollutions. Here, a dielectric barrier discharge (DBD) reactor has been developed for the oxidation of naphthalene over a TiO₂/diatomite catalyst at low temperature. In comparison to plasma-alone process, the combination of plasma and TiO₂/diatomite catalyst significantly enhanced naphthalene conversion (up to 40%) and CO_x selectivity (up to 92%), and substantially reduced the formation of aerosol (up to 90%) and secondary volatile organic compounds (up to near 100%). The mechanistic study suggested that the presence of the TiO₂/diatomite catalyst intensified the electron energy in the DBD. Meantime, the energized electrons generated in the discharge activated TiO₂, while the presence of ozone enhanced the activity of the TiO₂/diatomite catalyst. This plasma-catalyst interaction led to the synergetic effect resulting from the combination of plasma and TiO₂/diatomite catalyst, consequently enhanced the oxidation of naphthalene. Importantly, we have demonstrated the effectiveness of plasma to activate the photocatalyst for the deep oxidation of PAH without external heating, which is potentially valuable in the development of cost-effective gas cleaning process for the removal of PAHs in vehicle applications during cold start conditions.

The pyrolytic-plasma method and the device for the utilization of hazardous waste containing organic compounds

This paper is focused on the new method of waste processing. The waste, including hazardous waste, contain organic compounds. The method consists in two main processes: the pyrolysis of waste and the oxidation of the pyrolytic gas with a use of non-equilibrium plasma. The practical implementation of the method requires the design, construction and testing of the new device in large laboratory scale. The experiments were carried out for the two kinds of waste: polyethylene as a model waste and the electronic waste as a real waste. The process of polyethylene decomposition showed that the operation of the device is correct because 99.74% of carbon moles contained in the PE samples was detected in the gas after the process. Thus, the PE samples practically were pyrolyzed completely to hydrocarbons, which were completely oxidized in the plasma reactor. It turned out that the device is useful for decomposition of the electronic waste. The conditions in the plasma reactor during the oxidation process of the pyrolysis products did not promote the formation of PCDD/Fs despite the presence of the oxidizing conditions. An important parameter determining the efficiency of the oxidation of the pyrolysis products is gas temperature in the plasma reactor.

Qualitation and Quantitation on Microplasma Jet for Bacteria Inactivation

In this work, a self-made microplasma jet system was used to conduct the qualitation and quantitation of inactivation with Escherichia coli as the target bacteria. The logarithmic concentration and the size of antimicrobial rings served as the evaluation parameters, respectively. The effect of various parameters on inactivation effect was studied. The results showed that the majority of bacteria had been inactivated in 30 s. The inactivation effect enhanced and then weakened with the increase of air flow rate, and receded as the extension of treatment distance. The effect with different carrier gases showed as follows: oxygen > air > nitrogen > argon. Meanwhile, the effect of different components of microplasma was studied in the optimum conditions (The flow rate was 5 L/min; inactivation distance was 2 cm). The results showed that electrically neutral active species was the main factor of inactivation rather than heating effect, ultraviolet radiation and charged particles. Finally the experiments of thallus change proved that microplasma jet had etching effect on cell membrane. It also found that microplasma could degrade organic material like protein. Furthermore, the images of scanning electron microscope (SEM) revealed the change of cell morphology step by step in the whole process of inactivation.

Development of direct gas injection system for atmospheric-pressure in-solution discharge plasma for plasma degradation and material syntheses

We developed an in-solution discharge system with a gas injection system by utilizing a metal pipe as an electrode. Gas was directly injected into atmospheric-pressure in-solution glow discharge plasma.

Experimental study of NO2 reduction in N2/Ar and O2/Ar mixtures by pulsed corona discharge

Non-thermal plasma technology has been regarded as a promising alternative technology for NOx removal. The understanding of NO2 reduction characteristics is extremely important since NO2 reduction could lower the total NO oxidation rate in the plasma atmosphere. In this study, NO2 reduction was experimentally investigated using a non-thermal plasma reactor driven by a pulsed power supply for different simulated gas compositions and operating parameters. The NO2 reduction was promoted by increasing the specific energy density (SED), and the highest conversion rates were 33.7%, 42.1% and 25.7% for Ar, N2/Ar and O2/Ar, respectively. For a given SED, the NO2 conversion rate had the order N2/Ar>Ar>O2/Ar. The highest energy yield of 3.31g/kWh was obtained in N2/Ar plasma and decreased with increasing SED; the same trends were also found in the other two gas compositions. The conversion rate decreased with increasing initial NO2 concentration. Furthermore, the presence of N2 or O2 led to different reaction pathways for NO2 conversion due to the formation of different dominating reactive radicals.

Influence of nitrogen excited species on the destruction of naphthalene in nitrogen and air using surface dielectric barrier discharge

The destruction of naphthalene, as representative polycyclic aromatic hydrocarbons, by surface dielectric barrier discharge is investigated in air as well as dry and humidified nitrogen at ambient temperature. Naphthalene destruction efficiency is evaluated in terms of chemical change vis-a-vis energy utilization. The detected byproducts are qualitatively evaluated in order to understand the role of the active species in the destruction process. The results show that the destruction efficiency and the energy efficiency are higher in the dry nitrogen than in the humidified nitrogen, and these decrease with the increase of the humidity. Measured concentration of ozone as a byproduct qualitatively indicates the roles of oxygen and ozone in the destruction process in air. The analysis of the aerosol particles formed during the destruction process, both in the dry and humidified nitrogen, confirmed the adverse effects of the humidity on the byproducts formation and subsequently on the destruction process.