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Volatile organic compounds (VOCs) removal in non-thermal plasma double dielectric barrier discharge reactor
Abstract
Non-thermal plasma (NTP) an emerging technology to treat volatile organic compounds (VOCs) present in unhygienic point source air streams. In present study, double dielectric barrier discharge (DDBD) reactors were used for the first time to evaluate the removal efficiency of VOCs mixture of different nature at constant experimental conditions (input power 16-65.8 W, VOCs mixture feeding rate 1-6 L/min, 100-101 ppm inlet concentration of individual VOC). Reactor A and B with discharge gap at 6 mm and 3 mm respectively, were used in current study. When treated at an input power of 53.7 W with gas feeding rate of 1 L/min in DDBD reactor A, removal efficiency of the VOCs were: tetrachloroethylene (100%), toluene (100%), trichloroethylene (100%), benzene (100%), ethyl acetate (100%) and carbon disulfide (88.30%); whereas in reactor B, the removal efficiency of all VOCs were 100%. Plasma-catalyst (Pt-Sn/Al2O3, BaTiO3 and HZSM-5) synergistic effect on VOCs removal efficiency was also investigated. Highest removal efficiency i.e 100% was observed for each compound with BaTiO3 and HZSM-5 at an input power 65.8 W. However, integrating NTP with BaTiO3 and HZSM-5 leads to enhanced removal performance of VOCs mixture with high activity, increase in energy efficiency and suppression of unwanted byproducts.
... At the same time, the decomposition process was hardly affected due to the non-selectivity of reactive particles. Mustafa et al. (2018) also employed a DDBD reactor to decrease the VOC mixture for the first time, and high removal efficiency (almost 100% for each VOC) was obtained at the constant operating parameters. The energy efficiency decreased with increasing input power despite an enhancement of removal efficiency due to losing more energy in VOC-molecular vibrational and electronic excitation, leading to less energy used for VOC dissociation at higher input power. ...
... Compared with single NTP method, by-products like O 3 , CO, and other organic pollutants can be significantly reduced in NTP catalysis system when the selected catalyst is suitable, which is attributed to the reactive species generated in the presence of a catalyst. Mustafa et al. (2018) used the DBD reactors for evaluating the removal efficiency of VOC mixture (VOCs with different nature) at constant experimental conditions; they found that integrating NTP with BaTiO 3 and HZSM-5 leads to an enhancement in removal efficiency, energy efficiency, and suppression of unwanted by-products resulting in improved plasma reaction. Reactive adsorption of VOC molecules would exist on the catalyst material surface. ...
... A more significant gap may have less reactive surrounding, decreasing the resultful collision between VOC molecules and reactive species in the discharge zone to a lower removal efficiency. And analogously for reactor volume, less volume owns the stronger electric field and higher electron density, facilitating better VOC removal (Mustafa et al. 2018). The increased attack of VOC molecules by free electrons makes the chemical bond easier to break within molecules, instigating VOC (like toluene) transition reactions to become faster and more thoroughly (Liang et al. 2015). ...
Volatile organic compounds (VOCs) have posed a severe threat on both ecosystem and human health which thus have gained much attention in recent years. Nonthermal plasma (NTP) as an alternative to traditional methods has been employed to degrade VOC in the atmosphere and wastewater for its high removal efficiency (up to 100%), mild operating conditions, and environmental friendliness. This review outlined the principles of NTP production and the applications on VOC removal in different kinds of reactors, like single/double dielectric barrier discharge, surface discharge, and gliding arc discharge reactors. The combination of NTP with catalysts/oxidants was also applied for VOC degradation to further promote the energy efficiency. Further, detailed explanations were given of the effect of various important factors including input/reactor/external conditions on VOC degradation performance. The reactive species (e.g., high-energy electrons, HO·, O·, N2⁺, Ar⁺, O3, H2O2) generated in NTP discharge process have played crucial roles in decomposing VOC molecules; therefore, their variation under different parameter conditions along with the reaction mechanisms involved in these NTP technologies was emphatically explained. Finally, a conclusion of the NTP technologies was presented, and special attention was paid to future challenges for NTP technologies in VOC treatment to stimulate the advances in this topic.
Graphical abstract
... Several types of NTP reactors have been developed for VOCs treatment, including dielectric barrier discharge (DBD) reactors, corona discharge reactors, and atmospheric pressure plasma jet (APPJ) reactors. [200,201] Each reactor type has its unique advantages and limitations, and the choice of reactor depends on factors such as the type and concentration of VOCs, the gas flow rate, and the desired treatment efficiency. The effectiveness of NTP treatment for VOCs removal depends on several factors, including the reactor design, the type of VOCs being treated, and the process parameters. ...
... New techniques for NTP oxidation of VOCs include packed-bed plasma reactors, dielectric barrier discharge (DBD) plasma reactors, plasma-catalytic hybrid systems, and hybrid plasma photocatalytic systems. [200,202] NTP treatment for VOCs removal faces challenges including the risk of harmful byproducts, high electricity costs, and the [197] need for optimization through research; however, with advancements, it has the promise to be an effective air purification method. The key advantages, challenges, and the key performance parameters of oxidative methods are summarized in Table 8. ...
Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed‐metal oxides, polymers, activated carbons, zeolites, metal‐organic frameworks (MOFs) and mixed‐matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent‐catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent‐catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long‐term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.
... The results of the oxidative decomposition of chlorinated hydrocarbons with the use of dielectric barrier discharge nonthermal plasma were reported [18][19][20][21]. The oxidative decomposition of DCE [18] and trichloroethylene [20] was carried out at a voltage of 10-25 kV with the formation of carbon oxides, HCl, and phosgene. ...
... The results of the oxidative decomposition of chlorinated hydrocarbons with the use of dielectric barrier discharge nonthermal plasma were reported [18][19][20][21]. The oxidative decomposition of DCE [18] and trichloroethylene [20] was carried out at a voltage of 10-25 kV with the formation of carbon oxides, HCl, and phosgene. In the absence of oxygen, the transformation of DCE (conversion, 87.9%) in dielectric barrier discharge plasma at a voltage of 16 kV led to the formation of vinyl chloride with a yield of 16.8% [22]. ...
... Under the influence of elevated electrical potential, gas discharge engenders electrons of heightened energy, which can interact with the ambient gas, generating reactive entities, or directly collide with toluene molecules, thereby leading to their decomposition. The density and energy of these highenergy electrons serve as pivotal factors in the process of toluene degradation, primarily subject to the parameters of the power supply (Mustafa et al. 2018;Jiang et al. 2018). ...
... In actual industrial applications, efficient and swift control of gas flow is crucial when dealing with pollutant gasses. Determining the optimal gas flow rate has garnered significant research attention (Mustafa et al. 2018;Vandenbroucke et al. 2011). In this section, we explore the influence of gas flow on toluene degradation, utilizing a discharge voltage of 10,000 V, a pulse frequency of 2000 Hz, and toluene concentration of 2200 mg/m 3 . ...
The objective of this investigation is to evaluate the characteristics associated with degradation of toluene through the utilization of non-thermal plasma (NTP) generated via application of a low-work-function electrode and nanosecond pulsed power supply. Initially, a comparative analysis is made between toluene removal efficiency utilizing the low-work-function electrode and that achieved with the conventional stainless-steel electrode. The outcomes demonstrate that NTP generated by the low-work-function electrode exhibits markedly superior removal efficiency for toluene in comparison to the stainless-steel electrode operating at the same voltage. Subsequently, the impacts of voltage, pulse frequency, and initial concentration of toluene on the removal efficiency and production of by-products are investigated. It is found that as the voltage and frequency increase, the removal efficiency also increases, and a maximum toluene removal efficiency of 87.2% is achieved at a voltage of 12,000 V and pulse frequency of 2000 Hz. The removal efficiency first increases and then decreases with increasing toluene initial concentration. The investigation also finds that energy yield is negatively correlated with voltage and pulse frequency and positively correlated with the initial concentration. Finally, the reaction products were subjected to quantitative analysis using GC–MS. Based on the analysis results, potential reaction pathways are inferred.
... The low-pressure NTP such as radio-frequency (RF) plasma (commonly used frequency is 13.56 MHz) and microwave discharges (typically used frequency is 2.45 GHz) are employed for surface treatments, decontamination of food and thin film coating, etc [60,61]. Atmospheric-pressure NTP, for instance, corona discharge has been investigated for electrocharging face masks and fabrics, especially in N95 mask to achieve high filtration efficiency, whereas, dielectric barrier discharge (DBD), and plasma jet have been studied in a wider range of applications such as disinfection [62], ozone generation for water treatment [63], and elimination of volatile organic compounds [64]. ...
... In addition, the use of high gas flow rates increases the production cost unreasonably. The optimal volume of the reactor (L)/H2 flow rate (L-min -1 ) for hydrogenating biodiesel in the studied DBD parallel system was 4 L/L-min -1 [63] while that for the DBD torch system was 0.35 L/L-min -1 [64]. For certain techniques such as microwave plasma which can generate higher density plasma than DBD plasma, the gas flow rate can be increased up to 8.5 L/min with the excess hydrogen recycled [66], and the volume of the reactor/H2 flow rate was 0.24 L/L-min -1 . ...
... There are many ways to generate NTP, such as glow discharge, corona discharge and dielectric barrier discharge (DBD). Among these methods, DBD can prevent the occurrence of arc discharge and avoid the corrosion of metal electrodes by covering the electrodes with barrier layers [14,15]. Therefore, DBD has been recognized as the most commonly industrial NTP. ...
... O 3 was generated from atomic O via (13), where M could be either O 2 or N 2 [35,36]. NO 2 was detected as a major NO x species, but no NO was detected in the gas treated by plasma because of the oxidization of O 3 (14) and (15) [37]. As the equations shown, O 3 and NO x are both involved in the generation and consumption of "useful" active species, such as atomic O and O 2 , which could directly oxidize VOC compounds. ...
Butene is a typical component of exhaust gas in the petrochemical industry, the emission of which into the atmosphere would lead to air pollution. In this study, a tubular multilayer dielectric barrier discharge (TM-DBD) reactor was developed to decompose 1-butene at ambient pressure. The experimental results show that a decomposition efficiency of more than 99% and COx selectivity of at least 43% could be obtained at a specific energy density of 100 J/L with an inlet concentration of 1-butene ranging from 100 to 400 ppm. Increasing the volume ratio of O2/N2 from 0 to 20% and the specific energy density from 33 to 132 J/L were beneficial for 1-butene destruction and mineralization. Based on organic byproduct analysis, it was inferred that the nitrogenous organic compounds were the main products in N2 atmosphere, while alcohol, aldehyde, ketone, acid and oxirane were detected in the presence of O2. In addition, the contents of formaldehyde, acetaldehyde, ethyl alcohol, acetic acid and propionic acid increased with an increase in specific energy density, but the contents of propionaldehyde, ethyl oxirane, butyraldehyde and formic acid decreased. Three main pathways of 1-butene destruction were proposed involving Criegee intermediates and ozonolysis of the olefins, and the following degradation could be the dominant pathways rather than epoxidation. Overall, the developed TM-DBD system paved the way for scaling up the applications of plasma technology for gaseous pollutant decomposition.
... Furthermore, the number of active electrons and internal electric field strength, which are the most effective characteristics, are proportional to the rise in input power provided to the NTP in toluene removal. In addition, these extremely active species attacked and interacted with toluene and intermediates resulting in the acceleration of the removal of toluene [28][29][30]. The increase in removal efficiency of toluene has a linear relationship with input power. ...
... It can be seen from the graph curves that when the feed gas flow rate was increased from 400 to 2400 mL min −1 , the removal efficiency of toluene declined from 91 to 54% and 20 to 3% at an input power of 44 (W) and 11 (W), respectively. Many researchers [14,29,32] have found similar trends for toluene and also for other VOCs. The reason for this is high feed flow rate decrease the retention time of toluene, which reduces the chances to collide with the reactive generated by the plasma. ...
Volatile organic compounds (VOCs) are a major class of pollutants that are hazardous to human health and environment. An emerging and successful technology for the treatment of VOC, even at low concentrations is nonthermal plasma (NTP). However, it has the disadvantages of generating undesired by-products and is less energy efficient. In this work, the NTP is combined with ferrite-based catalysts Co–Zn–Fe2O4, Co–Fe2O4, and Zn–Fe2O4 are prepared by the coprecipitation method to study the impact of input power (11–44 W), CO2 selectivity, NOx, O3, and undesired by-product generation for the degradation of toluene as representing VOC. The NTP with catalysts significantly improves the removal efficiency of toluene and suppresses by-product formation. Particularly, Co–Fe2O4 showed the highest toluene removal efficiency than Co–Zn–Fe2O4, Zn–Fe2O4, and NTP-alone. Moreover, the Co–Fe2O4 catalyst gives 66.66% higher removal efficiency of toluene than NTP-alone and reduces the generation of organic by-products. This is due to the adsorptive nature of the active sites of catalyst that prolongs residence intervals of VOCs to interact with high-energy electrons and active radicals from the plasma discharge zone. This study reveals that NTP incorporated with a catalytic system to convert VOC is truly sustainable and has great potential for future development.
Graphical abstract
... Most VOCs are regarded as major pollutants due to their volatile, diffusive, and toxic characteristics, posing a major threat to human health and the ecological [7]. And plasma technology is commonly used to degrade high-concentration VOCs into nonhazardous products [8][9][10]. ...
... The experimental design includes 17 experiments, as shown in table 1. According to equation (7), equations (8) and (9) give the best fitted models of toluene degradation efficiency and EY in terms of three operating factors. Toluene degradation efficiency (Y 1 , %): ...
This paper studied the degradation effect of high- concentration toluene in dielectric barrier discharge (DBD) plasma under different operating conditions. The degradation efficiency and energy yield (EY) were comprehensive evaluated by response surface method (RSM) under different operating parameters (discharge powers, gas flow rate, and initial concentrations) in the DBD plasma system. The results showed that EY and the degradation efficiency could reach 22.17 g/kWh and 72.3% when discharge power, initial concentration, and gas flow rate were 5.49 W, 1374.5 ppm, and 529.5 mL/min, respectively. Besides, mineralization effect was also analyzed related to different operating parameters. When the gas flow rate was 600mL/min and the initial concentration was 2500 ppm, the COx selectivity could reach 98.5%. Through the analysis of the effect of oxygen content in the background gas on high-concentration toluene degradation, it was found that oxygen content had a significant effect on the formation of oxygen-containing active substances. Emission spectra showed that normal air discharge occurred at the discharge space of DBD plasma, and nitrogen-containing active substances were generated. Therefore, active substances containing oxygen and nitrogen played an important role in DBD plasma degradation of high-concentration toluene.
... Various traditional technologies are available for VOC abatement, including absorption, adsorption, and thermal incineration [12][13][14][15][16][17]. However, each method has drawbacks, such as low efficiency, catalytic deactivation, hightemperature requirements, and longer treatment time [18][19][20][21][22]. These drawbacks limit the efficiency of VOCs degradation and new technologies are being developed for VOCs degradation [23]. ...
The feasibility and efficiency of the degradation of volatile organic compounds (VOCs) by non-thermal plasma (NTP) has been extensive investigated and proved in laboratory experiments with single target component. In practical, multicomponent VOCs are emitted during industrial production. It is urgent need to study the abatement of multicomponent VOCs to evaluate the effectiveness of NTP technology in application, and explore the impact of interactions between VOCs components on degradation efficiency. This study focused on the degradation of VOCs mixtures composed of toluene (TOL), acetone (AC), and ethyl acetate (EA) by dielectric barrier discharge (DBD) plasma in room temperature. Through changing the target gas in turn and the concentration ratio of additive gas in binary mixture, the influence of the composition and the concentration ratio of the additive gases on the target gas degradation have been investigated by comparing the decomposition of the single compound. The results showed that AC and EA had little or no inhibitory effect on degradation of TOL. When AC was added and degraded together with TOL, the degradation rate of TOL remained almost unchanged with slight fluctuations in the range of 75.3 ± 1.0% as the ratio of added AC increased. However, TOL significantly inhibited the degradation of EA and AC, and more seriously on AC. When the ratio of added TOL increased, the degradation rates of EA or AC changed from 41.1% or 34.5% to 29.8% or 12.2%, which were 11.3% or 22.3% reduced respectively. It is indicated that there was a mutual inhibitory effect between the AC and EA when they were degraded together, and a stronger inhibitory effect of EA on AC was observed. When the ratio of added AC to EA changed from 0:1 to 3:1, the degradation rate of EA decreased by 9.5%, from 49.8% to 40.3%. When the ratio of added EA to AC changed from 0:1 to 3:1, the degradation rate of AC decreased by 16.0%, from 37.9% to 21.9%.
... Commonly used techniques for acetone elimination include condensation [6], absorption [7], combustion [8], biodegradation [9], low-temperature plasma [10], and catalytic oxidation [11]. In particular, catalytic oxidation has garnered widespread attention amongst researchers due to its cost-effectiveness and high efficiency, resulting in the complete conversion of acetone into benign byproducts. ...
This study investigates the catalytic oxidation of acetone by different crystal phases of MnO2 prepared via different methods. Compared with β-MnO2 and γ-MnO2, α-MnO2 exhibited superior catalytic activity. Moreover, as replacements for traditional hydrothermal methods and air calcination, the use of microwave hydrothermal methods and N2 calcination significantly enhanced the catalytic performance of the MnO2 catalyst. The optimal catalyst, MnO2-WN (α-MnO2 synthesized via microwave hydrothermal method and N2 calcination), converted 100% of 100 ppm acetone below 150 °C, with the CO2 yields reaching 100%. Further, the stability of the catalyst and its potential for other volatile organic compounds (VOCs) were also determined. The experimental data demonstrated that its outstanding activity primarily stemmed from the improved preparation method, enhancing the specific surface area of the catalyst, optimizing the pore structure, improving the redox performance, and generating more acidic sites and active oxygen species, thereby creating a synergistic effect. Finally, the reaction pathway of acetone oxidation on the catalyst surface has been explored. This work provides a new perspective for developing economically efficient MnOx catalysts for removing VOCs.
... Common insulating dielectric materials include quartz or ceramic. [24] The majority of DBD devices now being developed are of the parallel plate and coaxial line cylinder types. High decomposition efficiency (particularly for low quantities of VOCs), a straightforward experimental setup, and stable and repeatable plasma conditions are all benefits of DBD plasma reactors. ...
Volatile organic compounds (VOCs) emissions are a factor in a number of environmental issues. To reduce the associated negative consequences, it is crucial to develop efficient VOCs removal systems. Non‐thermal plasma (NTP) co‐catalytic technology has become a popular research topic in this field as a result of its ability to reduce the activation energy of the reaction while simultaneously improving product selectivity. Despite the huge number of studies synthesising the use of metals and their oxide catalysts in the degradation of VOCs, metal‐organic frameworks (MOFs) and MOF derivatives are the subject of comparatively few studies in this area. This paper reviews the basic principles and technological progress of NTP co‐catalytic VOCs degradation, with a focus on the use of MOFs and their derivatives in plasma VOCs degradation, as well as the use of other non‐metallic carbon materials in plasma VOCs degradation. It highlights the potential future development direction of NTP catalytic synergistic treatment of VOCs by focusing on the optimization of catalytic synergism on the treatment impact. In the end, the challenges faced, the prospects, and our personal perspective on future research directions are also estimated and elucidated.
... For example, Class 1000 verticallaminar ow units commonly used in IVF laboratories cannot prevent the entry of some PMs below 1-µm diameter, SO 2 and NO 2 (Fig. 1). In addition, IVF laboratories are usually equipped with air puri cation devices (Agarwal et al. 2017; Mustafa et al. 2018) to improve indoor air quality; however, the clean air generated by the devices is easily carried away by the return air of the laminar ow units. Therefore, indoor air pollution still exists. ...
Fertilization and embryo cultures are at risk of direct exposure of germ cells to air pollutants in assisted reproductive technology. The degree of exposure of germ cells to the pollutants is different in vitro fertilization methods, conventional in vitro fertilization (c-IVF), and intracytoplasmic sperm injection (ICSI) cycles. However, there are conflicting conclusions about the effect of air pollutants on in vitro cultures. A retrospective analysis of fertilization and embryo cultures of 2689 c-IVF and 1133 ICSI cycles that underwent assisted reproductive treatment for the first time was performed. Weighted binary logistic regression models were used to investigate the correlation between air pollutant exposure and fertilization, cleavage, and embryo development. We found that D − 1 -NO 2 (adjusted odds ratios (aOR): 0.996; 95% CI: 0.992–1.000) was negatively correlated with normal fertilization, whereas D − 1 -PM 2.5 (aOR: 0.989; 95% CI: 0.982–0.995) and D 1 -O 3 (aOR: 0.998; 95% CI: 0.997–1.000) were negatively correlated with high-quality embryo formation, D − 1 -CO (aOR: 1.631; 95% CI: 1.152–2.311) and D − 1 -O 3 (aOR: 1.002; 95% CI: 1.001–1.004) were positively correlated with high-quality embryo formation. In c-IVF cycles, D 0 -SO 2 (aOR: 0.974; 95% CI: 0.953–0.995) was negatively correlated with normal fertilization, D − 1 -PM 2.5 (aOR: 0.986; 95% CI: 0.978–0.993) was negatively correlated with high-quality embryos formation, and D − 1 -CO (aOR: 1.498; 95% CI: 1.002–2.240; p = 0.049) was positively correlated with high-quality embryos formation. In ICSI cycles, D − 1 -NO 2 (aOR: 0.991; 95%CI: 0.983–0.999) was negatively correlated with normal fertilization, whereas D − 1 -CO (OR: 2.161; 95%CI: 1.068–4.373) and D − 1 -O 3 (OR: 1.004; 95%CI: 1.001–1.007) were positively correlated with high-quality embryos formation. We conclude that air pollutants affect the processes of fertilization and embryo development in vitro; however, the types and interference stages of air pollutants that affect germ cell cultures in vitro are different in c-IVF and ICSI.
... The operation cost of adsorption method is high, the regeneration of adsorbent is difficult, and it will cause secondary pollution to the environment. However, low-temperature plasma technology is rapidly developing in the application of environmental pollutant treatment and disposal, with high active material density, easy operation, high efficiency, and no secondary pollution (Judee et al., 2018;Mustafa et al., 2018;Rao et al., 2017;Wang et al., 2012). In this paper, the low-temperature plasma technology of DC corona discharge is used to degrade cooking fume. ...
A honeycomb wire-barrel type corona discharge reactor designed and assembled was used to degrade cooking fume. Firstly, the formation mechanism of oil fume and PM was analyzed. Then four edible oils, peanut oil, canola oil, soybean oil, and lard, which are mainly used by families in China, were selected for the experiment. The emission concentrations of common pollutants oil fume and PM of these four edible oils were measured respectively. Among them, vegetable oil contains higher unsaturated fatty acids, while animal oil contains less unsaturated fatty acids. Vegetable oil can produce more oil fume and PM, and canola oil has the highest emission concentration of oil fume and PM. Therefore, canola oil was selected as the research object after the experiment. In the experiment on the effect of cooking temperature on the emission concentration of oil fume and PM, the higher the temperature, the higher the concentration of oil fume and PM emissions. Then, the effects of temperature, air velocity, and discharge voltage on the removal efficiency of oil fume and PM in cooking fume were studied, and the removal mechanism of oil fume and PM was analyzed. Finally, the response surface was used to optimize the results. The experimental results show that when the voltage is 34 kV, the temperature is 127.726 °C, and the residence time is 0.011 s, the removal efficiency of oil fume and PM reach the maximum at the same time, which are 95.70% and 94.12% respectively.
... Botanical systems have shown to target VOCs and PM in the ambient air. Plant canopy is the major PM sink [58]. Characteristics like leaf shape, surface waxes, hairs and trichomes significantly affect the PM accumulation capacity [63]. ...
Every year, anthropogenic air pollution causes 7 million people to die due to various respiratory-related diseases, with indoor air quality having a significant impact on people’s health. With the emergence of the COVID-19 pandemic, clean air, and good indoor air quality have become of paramount importance. In light of the high levels of pollution that have reached unprecedented levels, the only effective solution is to implement air purifying technology. However, identifying one sustainable purifier that can perform efficiently in changing environmental conditions with a low environmental impact and is economically viable is a daunting task. This state-of-the-art review will elucidate about all the conventional physio-chemical technologies and their comprehensive comparison with advancing biotechnology-based solutions considering all the important parameters. The techno-economic and life cycle assessment of the air purifiers have been evaluated to give the situational concept of their position in air purification market, so as to understand the competition level between the two. Microalgal Air Purification Technology (MAPT) driven air purifiers are emerging as a sustainable alternative to the conventional ones with their diversity of pollutant control and versatility in applications of the produced biomass. Conversely, physio-chemical technology is more in demand on the grounds of easy availability and affordable price. Thus, this critical analysis highlights the advantages and disadvantages of each method with real-time examples of established and emerging ventures in green air purifier market.
... Long-term exposure to toluene will cause dry skin, chapping and inflammation, and even nervous system weakness and kidney failure in serious cases (Luo et al. 2019). A lot of attempts have been made to reduce the pollution caused by toluene and other harmful volatile organic pollutants by photolysis technology (Wu et al. 2021), plasma discharge (Mustafa et al. 2018), adsorption (Cheng et al. 2022), hybrid treatment (Wei et al. 2019), and catalysis . As a purification technology, catalytic combustion is considered to be an important means of effective treatment of VOCs and the most promising treatment technology, because it has a high level of purification efficiency and uses little energy and complete decomposition of toluene into CO 2 and H 2 O . ...
As an industrial solid waste produced by alumina industry, red mud was modified as support of Pd catalysts for toluene catalytic oxidation in this paper. The xPd/MRM catalysts had high activity for toluene catalytic oxidation, and the 0.3Pd/MRM catalyst showed the best catalytic performance (T50 = 175 °C and T100 = 200 °C). The results indicated that the prepared 0.3Pd/MRM catalyst had more ratio of surface-adsorbed oxygen and Fe³⁺, rather than MRM and RM, which benefitted to the toluene oxidation. The excessive Pd species and the growth of the PdO nanoparticles negatively affected the catalytic efficiency of toluene. 0.4Pd/MRM activity decreased because of PdO aggregation in the catalyst, which could be confirmed by TEM analysis. The results of XPS, H2-TPR, FT-IR, O2-TPD, and Raman examination revealed that the formation of Pd-O-Fe under the interaction between Fe in MRM and Pd (Pd²⁺ + Fe ²⁺ → Pd⁰ + Fe³⁺) increased the electron transfer and raised the mobility of surface-adsorbed oxygen. Furthermore, in situ DRIFTS and GC-MS were used to detect intermediate products of catalytic reactions, and the reaction mechanism of catalysts was also studied. The catalytic oxidation of toluene on 0.3Pd/MRM catalyst might have two reaction paths simultaneously. The first reaction path would be toluene → species benzyl → benzaldehyde → benzoic acid → long-chain aldehydes or carboxylic acids → CO2 and H2O. The second reaction path would be toluene → benzene → phenol → long-chain aldehydes or carboxylic acids → CO2 and H2O.
... Owing to this, advanced oxidation processes (AOPs) have been considered possible alternatives thanks to their extreme oxidizing capacity and their efficiency in the removal of bio-recalcitrant compounds [156]. Among these, NTP represents an innovative AOP for water treatment [157]. With respect to "thermal" plasma, the NTP system maintains at relatively low temperatures and is able to generate charge carriers. ...
Recent advances in atmospheric plasmas have led to the formation of nonthermal plasma (NTP). In recent decades, a number of novel plasma diagnostic approaches have been implemented and reported in order to better understand the physics of NTP. The use of NTP is a novel approach to producing reactive oxygen and nitrogen species. Plasma technology has many applications, including electrical device microfabrication, biomedicine, dentistry, agriculture, ozone generation, chemical synthesis, surface treatment, coating, and disease therapy. Furthermore, NTP is thought to be a successful strategy for the degradation of hazardous pollutants in the environment, making it a future hope. Recent studies showed that various operating parameters affect the yield of NTP-based technology. Especially, the presence of a catalyst, properly placed in an NTP reactor, leads to a significant increase in process performance as compared to NTP alone. Scientists have looked at using NTP in conjunction with catalysts to remove various sorts of pollutants from the environment. In this context, review articles are crucial due to the prevalence of NTP-based applications and ongoing developments. This review will describe recent advancements in NTP-based biomedical applications, bacterial inactivation, food preservation and storage, and environmental catalytic formulations. This review could be useful in providing a platform for advancements in biological applications and environmental protection through the use of NTP technology.
... Dielectric barrier discharge (DBD) is a technique that produces low-temperature non-equilibrium plasma at atmospheric pressure with a high average electron energy (9 eV). 1 Currently, this technique has extensive use in a variety of industries, including material processing, the removal of environmental pollution, biomedicine, and aerospace. [2][3][4][5] Various applications have different needs in terms of the characteristics and qualities of plasma. In particular, industrial-scale plasma surface treatments require a reduction in material processing time to under 1 s, which denotes the need for plasma with a power density of at least 10 W/cm 3 , as well as a sizable region of relatively uniform plasma. ...
Coplanar dielectric barrier discharge has a wide range of potential applications in the domains of material surface modification and other areas by producing a thin layer of diffuse plasma with high power density in the air. For a thorough examination of essential variables and discharge properties of coplanar dielectric barrier discharge plasma, an equivalent circuit model is essential. In this paper, a modified equivalent circuit for coplanar dielectric barrier discharge (CDBD) that took into account both the undischarged part and the parasitic capacitance was developed and discussed. The results showed that in the diffusion phase, the discharge area fraction grew quickly with voltage and caused a significant drop in plasma impedance and burning voltage. As the applied voltage increased, the discharge area fraction tended to saturate, the burning voltage slowly rose, and a lot of micro-discharges with greater diameters were present on the dielectric surface during the saturation phase.
... Plasma is a combination of excited components including atoms, molecules, and ions, which are associated with several active species, including electrons, positive and negative ions, and free radicals [9]. The electrons and ions' free electric charge makes the plasma electrically conductive, active, and highly reactive to electromagnetic fields [10]. By placing gas in a constant electric field existed between two electrodes charged with a direct or alternating current field, a high-frequency field, plasma can be produced. ...
Nowadays the removal of antibiotics in wastewater has become a matter of considerable interest due to their extensive usage and resistance to natural biodegradation. Among various wastewater treatment technologies, sonolysis as an advanced oxidation process has received considerable attention for the elimination and destruction of antibiotics due to its safety, operational simplicity, and environmental-friendly properties. The aim of this review is to organize the scattered available information relating to the sonochemical degradation of antibiotics for the last two decades. For this purpose, the operational variables, the degradation pathway, by-products, mineralization, the kinetics of the sonochemical antibiotic degradation as well as the mechanism of the synergistic effects in sono-based oxidation processes were critically reviewed. According to findings, most of the optimized sonolytic processes can obtain maximum removal efficiency with low antibiotic concentrations (i.e., 0.1–100 µM) and low US frequencies (i.e., 20–200 kHz) over a temperature range of 20–40 °C, though the exact recommended values vary depending on antibiotic characteristics and the sono-reactor geometry. Based on the literature, sono-based oxidation processes under optimized conditions yield significant benefits as compared to the individual processes; however, their applications at pilot and full-scale wastewater treatment are still incipient.
... Plasma is a combination of excited components including atoms, molecules, and ions, which are associated with several active species, including electrons, positive and negative ions, and free radicals [9]. The electrons and ions' free electric charge makes the plasma electrically conductive, active, and highly reactive to electromagnetic fields [10]. By placing gas in a constant electric field existed between two electrodes charged with a direct or alternating current field, a high-frequency field, plasma can be produced. ...
Treatment with non-thermal plasma is a reliable technology to oxidize chemical impurities that exist in polluted water, wastewater, and leachate, those degradation-resistant and cannot be removed by conventional treatment methods. In this study, the effective factors affecting in the formation ofreactive oxygen species in non-thermal plasma treatment process, as a new advanced oxidation process method explianed. In this manner, all associated manuscripts existed in the main databases including Google Scholar, Science Direct, PubMed, and Open Access Journal Directory from 1990 until 2022 were explored. The utilized keywords were involved non-thermal plasma, Cold plasma, Measurement, • OH, O 3 and UV. Overall, 8,813 articles were gathered and based on the relevance titles and abstracts, 18 paper were selected for further reviewing. In several studies, plasma techniques have been used to treat water, wastewater and leachate, but few studies have evaluated the factors influencing the production of ROS species by non-thermal plasma. The non-thermal plasma destroys pollutants by reactive free radicals spices (hydroxyl, hydrogen atoms, etc.) a combination effect of strong electric fields, energetically charged particles, and ultrasound. Some factors such as water vapor, hydraulic retention time, inter-electrode spacing, discharge power density, and aeration of the effluent as well as use of catalyst have direct effect on the reactive oxygen species formation. If these factors controlled within the best ranges, it will promote the oxidizing radical production and system performance. Also, high-energy electrons and oxidizing species produced in the cold plasma system can well degrade most of pollution in water and wastewater.
The generation of plasma by DBD has the advantages of low environmental requirements, simple operation, wide industrial applications, and the ability to stably generate low-temperature plasma. The high-frequency and high-voltage AC power supply is the main component of the DBD device. To achieve an adjustable frequency of the output voltage of high-frequency and high-voltage power supplies and improve the voltage stability performance of the power supply, this paper proposes a design scheme of a high-voltage and high-frequency AC power supply for DBD based on SG3525A, which introduces the system composition, control strategy, hardware circuit, simulation, and experimental results of the driving power supply in detail. The driving power supply adjusts the output voltage through a PWM signal generation circuit, an RCD absorption buffer circuit, and a power factor correction DC power supply. Under a DBD load with an equivalent capacitance of 48pF, the peak output voltage of the driving power supply is 50 kV, and the output frequency is up to 40 kHz. The experimental results show that the driving power supply meets the driving requirements of high voltage, high frequency, and excellent voltage stabilization performance for DBD.
This paper introduces the integrated Small-Scale Plant-Based Air Filtration (SPAF) system, a novel integration of air filtration and urban agriculture, specifically designed for edge computing free cooling in urban environments. The SPAF's modular design enables extensive customization to meet various air quality requirements and agricultural needs. Through evaluation across different scenarios, the system has proven its effectiveness in particulate matter reduction, with a single unit showcasing substantial initial filtration efficiency, and even greater performance when multiple units are utilised in series. Beyond its air filtration capabilities, the SPAF system also contributes to urban agriculture, expanding planting areas and supporting the growth of local produce, thereby aligning with global sustainability objectives. Despite its promising applications, challenges such as the variability in filtration performance across different plant species, external climates, and the inability to ensure complete particulate matter removal, underscore the need for further research and potential integration with other purification technologies.
Volatile organic compounds (VOCs) are harmful pollutants emitted from industrial processes. They pose a risk to human health and ecosystems, even at low concentrations. Controlling VOCs is crucial for good air quality. This review aims to provide a comprehensive understanding of the various methods used for controlling VOC abatement. The advancement of mono-functional treatment techniques, including recovery such as absorption, adsorption, condensation, and membrane separation, and destruction-based methods such as natural degradation methods, advanced oxidation processes, and reduction methods were discussed. Among these methods, advanced oxidation processes are considered the most effective for removing toxic VOCs, despite some drawbacks such as costly chemicals, rigorous reaction conditions, and the formation of secondary chemicals. Standalone technologies are generally not sufficient and do not perform satisfactorily for the removal of hazardous air pollutants due to the generation of innocuous end products. However, every integration technique complements superiority and overcomes the challenges of standalone technologies. For instance, by using catalytic oxidation, catalytic ozonation, non-thermal plasma, and photocatalysis pretreatments, the amount of bioaerosols released from the bioreactor can be significantly reduced, leading to effective conversion rates for non-polar compounds, and opening new perspectives towards promising techniques with countless benefits. Interestingly, the three-stage processes have shown efficient decomposition performance for polar VOCs, excellent recoverability for nonpolar VOCs, and have promising potential applications in atmospheric purification. Furthermore, the review also reports on the evolution of mathematical and artificial neural network modeling for VOC removal performance. The article critically analyzes the synergistic effects and advantages of integration. The authors hope that this article will be helpful in deciding on the appropriate strategy for controlling interested VOCs.
Plasma catalysis is recognized as a promising technology for the elimination of diluted volatile organic compounds (VOCs).
In this work, MOF-74 catalysts with various Co/Ni ratios obtained by hydrothermal method were prepared, and the degradation performance of various catalysts with synergistic non-thermal plasma for toluene was investigated. The addition of catalysts to NTP shown notable effects in toluene degradation and energy usage efficiency when compared to NTP alone. Notably, CoxNiy-MOF outperformed Co-MOF and Ni-MOF in terms of toluene catalytic activity. In comparison to the single plasma condition, Co2Ni3-MOF showed the maximum toluene degradation rate of 78% at the NTP discharge power of 11.66 W. SEM, BET, XRD, XPS, and FTIR were used to examine the impact of various Co/Ni ratios on the structure and redox characteristics of the samples. The interaction of Co and Ni results in many flaws and oxygen vacancies, increasing the amount of oxygen adsorbed on the surface and the reducibility of the catalyst, which is thought to be the cause of the rise in catalytic activity. Finally, based on the discovered organic compounds, the process of toluene breakdown in the plasma co-catalytic system was deduced. This work provides a novel concept for improving catalysts for the non-thermal plasma-catalyzed decomposition of toluene.
Graphical Abstract
Cobalt oxide (CoOx) is a common catalyst for plasma catalytic elimination of volatile organic compounds (VOCs). However, the catalytic mechanism of CoOx under radiation of plasma is still unclear, such as how the relative importance of the intrinsic structure of the catalyst (e.g., Co3+ and oxygen vacancy) and the specific energy input (SEI) of the plasma for toluene decomposition performance. CoOx - γ-Al2O3 catalysts were prepared and evaluated by toluene decomposition performance. Changing the calcination temperature of the catalyst altered the content of Co3+ and oxygen vacancies in CoOx, resulting in different catalytic performance. The results of the artificial neural network (ANN) models presented that the relative importance of three reaction parameters (SEI, Co3+, and oxygen vacancy) on the mineralization rate and CO2 selectivity were as follows: SEI > oxygen vacancy > Co3+ , and SEI > Co3+ > oxygen vacancy, respectively. Oxygen vacancy is essential for mineralization rate, and CO2 selectivity is more dependent on Co3+ content. Furthermore, a possible reaction mechanism of toluene decomposition was proposed according to the analysis results of in-situ DRIFTS and PTR-TOF-MS. This work provides new ideas for the rational design of CoOx catalysts in plasma catalytic systems.
Mn2O3-X catalysts (X = Cu, Fe, Ce and La) were prepared based on γ-Al2O3 for the mixture degradation of muti-component volatile organic compounds (VOCs) composed of toluene, acetone, and ethyl acetate. The catalysts were characterized, and the density functional theory (DFT) simulation of ozone adsorption on Mn2O3-X were carried out to investigate the influence of adsorption energy on catalytic performance. The results showed that the removal efficiency (RE) of each VOC component was similarly improved by Mn2O3-X catalysts, and the greatest increase in VOCs' removal efficiency was obtained (7.8% for toluene, 86.2% for acetone, and 82.5% for ethyl acetate) at a special input energy (SIE) of 700 J L-1 with Mn2O3-La catalyst. Characterization results demonstrated that Mn2O3-La catalyst had the highest content of low valence Mn elements and the greatest Oads/Olatt ratio, as well as the lowest reduction temperature. Mn2O3-La catalyst also presented superior catalytic effect in improving carbon balance (CB) and CO2 selectivity ( [Formula: see text] ). The CB and [Formula: see text] were increased by 47.7% and 12.61% respectively with Mn2O3-La at a SIE of 400 J L-1 compared with that when only γ-Al2O3 was applied. The DFT simulation results of ozone adsorption on Mn2O3-X catalysts indicated that the adsorption energy of catalyst crystal was related to the catalytic performance of the catalyst. The Mn2O3-La/γ-Al2O3 catalyst, which had the highest absolute value of adsorption energy, presented the best performance in improving VOCs' RE.
The use of plasma-activated water (PAW) as an antimicrobial agent to inactivate Salmonella Typhimurium on chilled beef during meat washing was evaluated. Two meat washing methods, spraying and immersion, were evaluated at contact times of 15, 30 and 60 s and meat storage times of 0, 1 and 7 days. The temperature of PAW was elevated to 55 °C for washing as it increased the microbial inactivation compared to ambient temperature. At the contact time of 60 s and meat storage time of 7 days, PAW spraying and immersion achieved 0.737-log10 and 0.710-log10 reductions against Salmonella Typhimurium, respectively; there were no significant differences between both washing methods, with spraying being preferred for commercial implementation. Compared to untreated and water-treated samples, meat washing with PAW alone improved the S. typhimurium inactivation and did not cause negative impacts on the lightness and hue angle values, TBARS value, water holding capacity and pH. However, PAW reduced the redness, yellowness and chroma values with the decreased oxymyoglobin values of 44.1% at the storage time of 1 day. PAW spraying at 55 °C followed by water washing at 25 °C for 60 s achieved 0.696-log10 reduction and mitigated a reduction in (i) the redness value, from 11.3 to 18.2, (ii) the yellowness value, from 9.19 to 11.1, and (iii) the chroma value, from 14.5 to 21.3, without displaying colour differences (∆E), as detected by human eyes, compared to water-treated samples. Moreover, the content of myoglobin forms was maintained by additional water washing.
Emission from diesel engine has become one of the most important sources of air pollution, which has attracted the attention of countries all over the world. Many measures have been taken to reduce diesel engine emission. In recent years, nonthermal plasma (NTP) technology has been gradually applied to the field of engine emission treatment. In this research, the authors introduced the selection of NTP generator, parameter design and electric field intensity in discharge zone were analyzed in detail. The coupling mode of NTP and catalyst, and the loading mode of catalyst were compared. Combined with the relevant experimental research, the authors analyzed the mechanism of CO, HC, PM and volatile organic compounds (VOCs) treated by NTP. Finally, the authors proposed some suggestions for the development of NTP technology.
In this paper, degradation of ciprofloxacin (CIP) in a circulating dielectric barrier discharge (DBD) plasma system with Cu-CeO2@CA composite films addition was investigated. The Cu-CeO2@CA films were synthesized through hydrothermal method, and the samples were characterized by SEM, XRD, EDS, FT-IR and Raman spectra analysis. The obtained results show that there was synergistic effect of the DBD plasma and the Cu-CeO2@CA films on the CIP degradation and mineralization. The optimal performance was obtained under the condition of 5 wt% Cu-CeO2 nanoparticles doping in the composite film. Besides the effect of the DBD plasma, the Cu-CeO2@CA films could drive the O3 decomposition, photocatalysis and then the more reactive oxygen species (ROS) formation. The presence of the main active species and their contributions to the CIP degradation were determined by electron spin resonance (ESR) analysis and radical quenching experiments. Methods of UV–vis spectrum, three-dimensional fluorescence spectrum and liquid chromatography mass spectrometry (LC-MS) were used to analyze the CIP decomposition process. The prepared Cu-CeO2@CA composite films had certain stability in the four cycles of application and the film catalyst was convenient for recycling. The toxicity evaluation results indicated the decline of the solution toxicity after treating in the Cu-CeO2@CA/DBD system.
Volatile organic compounds (VOCs) are typical pollutants that affect the air quality. Discharge plasma is thought to be a potential method that can remove VOCs from flue gas. In this experiment, pulsed corona discharge plasma combined with biological tower was carried out to remove benzene series, and toluene was selected as the typical VOCs. Results indicated that the removal efficiency of toluene by pulsed corona plasma was slightly higher than that of direct current (DC) corona plasma, while its energy efficiency was much higher than DC corona plasma. Under the optimal experimental conditions of pulse voltage 8.5 kV, initial toluene concentration 1400 mg/m3 and toluene flow rate of 12 L/h, the toluene removal efficiency reached 77.11% by the single method of pulsed corona discharge plasma, and the energy efficiency was up to 1.515 g/(kW∙h) under the pulse voltage of 4.0 kV. The trickling biofilter was constructed by using the screened and domesticated Acinetobacter baumannii, and the highest toluene removal efficiency by the pulsed corona discharge plasma combined with trickling biofilter rose up to 97.84%. Part of toluene was degraded into CO2, H2O and some intermediate products such as o-diphenol under the action of Acinetobacter baumannii. When the remaining waste gas passed through the discharge plasma reactor, the benzene ring structure could be directly destroyed by the collision between toluene and plasma. Meanwhile, O·, OH· and some other oxidizing radicals generated by the discharge also joint into the oxidative decomposition of toluene and its intermediate products, thereby further improving the removal efficiency of toluene. Therefore, the two-stage plasma-biofilter system not only showed a high toluene removal efficiency, but also had a good energy efficiency. Results of this study would provide a theoretical support and technical reference for industrial VOCs treatment.
While catalyst morphology plays an essential role in traditional thermal catalysis, the specific effects in plasma catalysis deserve further in-depth study. In the present study, hollow NiO nanospheres with a rambutan-like structure were successfully prepared by MOFs-derived method involving morphology modulation, and employed for the in-plasma catalytic oxidation of benzene. The results show an enhancement of 60% for benzene removal, while CO2 selectivity was increased by 20%. The energy consumption for 95% benzene removal efficiency (RE95%) was also reduced from 3600 J/L to 1100 J/L. Specifically, the hollow spherical shell structure is more abundant in surface oxygen species, including chemisorbed oxygen and surface lattice oxygen, which can be activated by plasma; the hollow structure also modulates the plasma discharge by shielding effect. The plasma field in turn also excites the oxidation activity of NiO, thus achieving the synergistic effect. In addition, a more comprehensive benzene decomposition pathway is proposed by analysis of the gaseous and non-gaseous intermediates (tar), where the plasma non-selectively breaks the chemical bonds of reactants and the catalyst selectively oxidizes the organic intermediates to CO2, and they promote each other to achieve synergistic effects.
The discharge characteristics of the series surface/packed-bed discharge (SSPBD) reactor driven by bipolar pulse power were systemically investigated in this study. In order to evaluate the advantages of the SSPBD reactor, it was compared with traditional surface discharge (SD) reactor and packed-bed discharge (PBD) reactor in terms of the discharge voltage, discharge current, and ozone formation. The SSPBD reactor exhibited a faster rising time and lower tail voltage than the SD and PBD reactors. The distribution of the active species generated in different discharge regions of the SSPBD reactor was analyzed by optical emission spectra and ozone analysis. It was found that the packed-bed discharge region (3.5 mg/L), rather than the surface discharge region (1.3 mg/L) in the SSPBD reactor played a more important role in ozone generation. The optical emission spectroscopy analysis indicated that more intense peaks of the active species (e.g. N2 and OI) in the optical emission spectra were observed in the packed-bed region.
This contribution attempts to establish an easy-to-apply non-thermal plasma reactor for efficient toluene removal. Derived from the already established knowledge of the so called Dielectric Barrier Discharge (DBD) Stack Reactor a new model reactor was used in this work. The DBD Stack Reactor is a multi-elements reactor but in this work only one stack element was used to investigate the efficiency and efficacy of toluene removal. In case of reliable results the scalability process for industrial application is already well known. Therefore, laboratory experiments were conducted in dry and wet synthetic air with an admixture of 50 ppm toluene. Along with the toluene removal process the electrical behaviour of the discharge configuration was investigated. It was found that the electrical capacitance of the dielectric barrier changes with variations of the operating voltage. This could be due to the changes in the area of the dielectric barrier which is covered with plasma. Additionally, it was found that the power input into the plasma, at a fixed operating voltage, is proportional to the frequency, which is in agreement with the literature.
Regarding the decomposition process, the total removal of toluene was achieved at specific input energy densities of 55 J L-1 under dry conditions and 110 J L-1 under wet conditions. The toluene removal was accompanied by the production of nitric acid (dry conditions) and formic acid (wet conditions). The latter suggested a combination of the plasma reactor with a water scrubber as an approach for total removal of pollutant molecules.
Cold Atmospheric Plasma is an ionized gas that has recently been extensively studied by researchers as a possible therapy in dentistry and oncology. Several different gases can be used to produce Cold Atmospheric Plasma such as Helium, Argon, Nitrogen, Heliox, and air. There are many methods of production by which cold atmospheric plasma is created. Each unique method can be used in different biomedical areas. In dentistry, researchers have mostly investigated the antimicrobial effects produced by plasma as a means to remove dental biofilms and eradicate oral pathogens. It has been shown that reactive oxidative species, charged particles, and UV photons play the main role. Cold Atmospheric Plasma has also found a minor, but important role in tooth whitening and composite restoration. Furthermore, it has been demonstrated that Cold Atmospheric Plasma induces apoptosis, necrosis, cell detachment, and senescence by disrupting the S phase of cell replication in tumor cells. This unique finding opens up its potential therapy in oncology.
A dielectric barrier discharge generated by flowing inert gas (helium) ionized by a high-voltage source through a cylindrical reactor working at atmospheric pressure has been studied and an electrical model characterizing this discharge is proposed. A sinusoidal voltage of up to 2 kV peak to peak with frequencies from 10 to 125 kHz has been applied to the discharge electrodes. The proposed model considers the geometry of the reactor and dielectric materials. From experimental and analytical results, a semi-empirical relation of the breakdown voltage is presented as a function of the operating frequency. The microdischarge regime is characterized by a dynamic equivalent capacitance.
In this work, the catalytic oxidation of benzene, toluene andn-hexane in air, both alone and in binary mixtures, over a commercial Pt on γ-alumina catalyst was studied. Studies have been carried out at concentrations of up to 4200 ppmV, in a laboratory fixed-bed catalytic reactor. Results for single compounds show that temperature at which 50% conversion is attained (T50) increases as concentration
increases for benzene and toluene, while the opposite behaviour is observed for n-hexane. Results for mixtures show that, while the presence ofn-hexane does not affect the conversion of benzene and toluene, the presence of benzene or toluene inhibits the combustion of hexane, and the aromatic compounds inhibits each other when are reacted together. Results obtained in absence of mass transfer limitations were fit to kinetic expressions: simple Mars–Van Krevelen kinetic expressions for single compounds, and a modified Mars–Van Krevelen mechanism, considering competitive adsorption of the hydrocarbons, for binary mixtures.
Destruction of gaseous benzene (C(6)H(6)) by dielectric barrier discharge (DBD) was studied in both laboratory-scale and scale-up DBD systems. The effects of input power, gas flow rate as well as initial concentration on benzene decomposition and energy yield were investigated. In addition, qualitative analysis on byproducts and relatively detailed discussion on mechanisms were also presented in this paper. At last, we systematically illustrated the feasibility of benzene removal with DBD on basis of three aspects: estimation of treatment cost per unit volume, comparison with other plasmas, and problems existed in DBD system. The results will help impel actual application of DBD on waste gas containing benzene.
Degradation of mechanically sorted organic fraction (MSOF) of municipal solid waste in composting facilities is among the major contributors of volatile compounds (VCs) generation and emission, causes nuisance problems and health risks on site as well as in the vicinages. The aim of current study was to determine the seasonal (summer and winter) variation and human health risk assessment of VCs in the ambient air of different processing units in MSOF at composting plant in China. Average concentration of VCs was 58.50 and 138.03mg/m(3) in summer and winter respectively. Oxygenated compounds were found to be the highest concentration (46.78-91.89mg/m(3)) with ethyl alcohol as the major specie (43.90-85.31mg/m(3)) in the two seasons respectively. Nevertheless, individual non-carcinogenic (Hazard relation i.e HR<1) and carcinogenic risk (CR<1.0E-04) of the quantified VCs were within acceptable limit except naphthalene at biofilter unit. In addition, cumulative non-carcinogenic risk exceeded from the threshold limit both in summers and winters in all units except at biofilter unit during winter. Furthermore cumulative carcinogenic risk also exceeded at same unit during the summer season. Therefore special attention should be made to minimize cumulative non-carcinogenic and carcinogenic risk as people are well exposed to mixture of compounds, not to individual.
Dry reforming of methane that converts two green-house gases (CH4 and CO2) to syngas (mixture of CO and H2) has gained a great research interests. In this research, we investigated the CO2 reforming of CH4 to syngas by the combination of dielectric barrier discharge (DBD) plasmas and zeolite catalyst particles, which was effective in converting the CO2 and CH4 into syngas. The effects of peak voltage applied to plasmas, total gas flow rate and input CO2/CH4 molar ratio on CO2 and CH4 conversions and H2 and CO selectivities were investigated. The product gases were mainly composed of H2 and CO with some generation of by-products. The conversion efficiencies of CO2 and CH4 in DBD plasmas with zeolite catalyst increased by the increase of voltage applied to plasmas. The selectivities of CO and H2 depend largely on the voltage applied to the plasmas and the ratio of CO2 to CH4, but did not depend significantly on the changes of frequency and total gas flow rate.
Mechanical-biological treatments (MBTs) of urban waste are growing in popularity in many European countries. Recent studies pointed out that their contribution in terms of volatile organic compounds (VOCs) and other air pollutants is not negligible. Compared to classical removal technologies, non-thermal plasmas (NTP) showed better performances and low energy consumption when applied to treat lowly concentrated streams. Therefore, to study the feasibility of the application of NTP to MBTs, a Dielectric Barrier Discharge reactor was applied to treat a mixture of air and methyl ethyl ketone (MEK), to simulate emissions from MBTs. The removal efficiency of MEK was linearly dependent upon time, power and specific input energy. Only 2-4% of MEK was converted to carbon dioxide (CO2), the remaining carbon being involved in the formation of byproducts (methyl nitrate and 2,3-butanedione, especially). For future development of pilot-scale reactors, acting on residence time, power, convective flow and catalysts will help finding a compromise between energy consumption, desired abatement and selectivity to CO2.
A novel dielectric barrier discharge (DBD) reactor has been designed and tested for the abatement of diluted volatile organic compounds (VOCs) of different nature. The novelty of the DBD reactor is that a metallic catalyst made of sintered metal fibers (SMF) also acts as the inner electrode. The SMF electrodes modified with oxides of Ti, Mn and Co were efficient during the destruction of toluene, isopropanol (IPA) and trichloroethylene (TCE). Total oxidation of IPA was achieved at lower specific input energy (SIE) compared to toluene and TCE. Among the catalysts studied, MnOx/SMF showed the best performance, involving the formation of active oxygen species by in situ decomposition of ozone on the catalyst surface. The selectivity to CO2 as the total oxidation product during TCE destruction was improved up to ∼70% by modifying MnOx/SMF with TiO2.
The reaction mechanism and energy efficiency analysis of non-thermal plasma assisted methane conversion are presented. Plasma catalysis is an innovative next-generation green technology that satisfies needs for energy and materials conservation, and environmental protection. Non-thermal plasma uniquely generates reactive species almost independently of reaction temperature. Those species initiate chemical reactions at remarkably lower temperatures than conventional thermochemical reactions. Low-temperature methane conversion is important because it minimizes exergy destruction accompanied by combustion of the initial feed, or production of high-temperature thermal energy, necessary for thermochemical methane reform. Non-thermal plasma has great flexibility to tune the process parameters so that energy and material consumption are minimized. This article explains aspects of plasma-assisted fuel reforming including arc plasma to non-thermal plasma. We specifically examine dielectric barrier discharge (DBD) as viable non-thermal plasma for practical fuel reforming. Second, the energy efficiency of non-oxidative methane conversion using DBD is analyzed. That energy efficiency determined by experimentation was 1%, although theoretical analysis suggested 8%, implying that DBD alone is invariably more inefficient. Finally, DBD-catalysts hybrid reaction is proposed and a synergistic effect between plasma-generated reactive species and catalysts is clarified, suggesting that vibrationally excited species are important for enhancing overall methane conversion efficiency with catalysts.
Carbon disulfide (CS2), a typical odorous organic sulfur compound, has adverse effects on human health and is a potential threat to the environment. In the present study, CS2 conversion in air by non-thermal plasma (NTP) was systematically investigated using a link tooth wheel-cylinder plasma reactor energized by a DC power supply. The results show that corona discharge is effective in removing CS2. The CS2 conversion increases with the increase of specific input energy (SIE). Both short-living (e.g. O, OH radicals) and long-living species contribute to the CS2 conversion, but the short-living species play a more important role. Both gaseous and solid products are formed during the conversion of CS2. Gaseous products mainly include CO, CO2, OCS, SO2, SO3 and H2SO4. The yields of CO and CO2 increase, the yields of OCS and SO2 follow bell curves while the sum yield of SO3 and H2SO4 remains constant as SIE increases. The solid products, consisting of CO3(2-), SO4(2-) and possible polymeric sulfur, deposit on the inner wall and electrodes of the plasma reactor.
Laboratory-scale experiments were performed to evaluate the efficiency of toluene decomposition by using a wire-plate dielectric barrier discharge (DBD) reactor with manganese oxide/alumina/nickel foam catalyst in the discharge area at room temperature and atmospheric pressure. The effects of oxygen content and gas flow rate were investigated. Under the optimal oxygen content and gas flow rate conditions, the combination effect of DBD and catalyst was observed, and the catalyst before/after discharge was structurally characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform-infrared spectroscopy (FT-IR). It has been found that combining DBD with catalyst in situ could improve the toluene removal efficiency, increase carbon dioxide selectivity and suppress byproducts formation. Whether the catalyst existed or not, the major products were carbon dioxide and carbon monoxide when oxygen was enough. The characterization of the catalyst suggested that DBD enhanced the dispersion of the active species, increased the stability as well as the activity of the catalyst, and strengthened the oxidation capability of the catalyst, therefore the removal of toluene was promoted.
This paper is aimed at investigating how the characteristics of corona and silent discharges including ozone generation are influenced by geometry of the discharge reactor. The corona discharges have been generated in coaxial wire-cylinder and wire-duct reactors stressed by dc and ac voltages. The silent discharges have been generated in the same reactors in addition to tubular reactors under ac voltage after pasting a dielectric barrier on the ground electrode of the reactors. The reactors were fed by dry air flowing at atmospheric pressure and temperature. The pulse characteristics of silent discharges are compared with those of ac corona discharges. The current-voltage and the ozone generation characteristics of silent and ac discharges are recorded. These characteristics depend significantly on the geometry of the reactor irrespective of the discharge type.
Oxidative removal of toluene in a dielectric barrier discharge reactor combined with manganese catalysts downstream was investigated. Toluene input concentration was varied in the range of 415–2227 ppm. The discharge was operated in pulsed mode, with short pulses of 23–35 kV peak voltage. At 7 W average power, toluene conversion was 60%–70%, independent on the toluene input concentration and on the total gas flow rate in the range of 110–330 SCCM (SCCM denotes cubic centimeter per minute at STP). Toluene total oxidation was favored at high residence time of the gas in the discharge zone and low toluene concentration, when the main reaction product was CO2 with selectivities of 80%–85%. The addition of the catalysts led to a 15%–20% increase in toluene conversion with respect to the values obtained in the plasma, due to oxidation with ozone on the catalyst surface.
Destruction of hydrogen sulfide using dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. Three types of DBD reactor were compared in terms of specific energy density (SED), equivalent capacitances of the gap (Cg) and the dielectric barrier (Cd), energy yield (EY), and H2S decomposition. In addition, byproducts during the decomposition of H2S and destruction mechanism were also investigated. SED for all the reactors depended almost linearly on the voltage. In general, Cg decreased with increasing voltage and with the existence of pellet material, while Cd displayed the opposite trend. The removal efficiency of H2S increased substantially with increasing AC frequency and applied voltage. Longer gas residence times also contributed to higher H2S removal efficiency. The choice of pellet material was an important factor influencing the H2S removal. The reactor filled with ceramic Raschig rings had the best H2S removal performance, with an EY of 7.30 g/kWh. The likely main products in the outlet effluent were H2O, SO2, and SO3.Highlights► Destruction of H2S using DBD plasma is studied. ► SED for all the reactors depended almost linearly on the voltage. ► ηH2S increased substantially with increasing AC frequency and applied voltage. ► The reactor filled with ceramic Raschig rings had the best H2S removal performance. ► The likely main products in the outlet effluent were H2O, SO2, and SO3.
Total oxidation of mixture of dilute volatile organic compounds was carried out in a dielectric barrier discharge reactor with various transition metal oxide catalysts integrated in-plasma. The experimental results indicated the best removal efficiencies in the presence of metal oxide catalysts, especially MnO(x), whose activity was further improved with AgO(x) deposition. It was confirmed water vapor improves the efficiency of the plasma reactor, probably due to the formation of hydroxyl species, whereas, in situ decomposition of ozone on the catalyst surface may lead to nascent oxygen. It may be concluded that non-thermal plasma approach is beneficial for the removal of mixture of volatile organic compounds than individual VOCs, probably due to the formation of reactive intermediates like aldehydes, peroxides, etc.
Silver colloids have been prepared by reducing AgNO3 in aqueous solution and embeded in alumina following a sol–gel procedure in the presence of Pluronic 84 ((EO)19(PO)39(EO)19), as surfactant. Plasma-catalytic experiments aimed at the mineralization of toluene showed that the selectivity to CO2 was significantly increased in the presence of Ag catalysts compared with results obtained using the plasma alone. In-situ studies of the ozone interaction with catalysts provide an insight into the nature of the active sites of supported silver colloids for mineralization reactions. It is noticeable that when ozone is chemisorbed on embedded Ag colloidal catalysts no change in the silver oxidation state or size is found. The population of the chemisorbed species is higher at lower temperatures, where the non-selective decomposition of ozone is smaller. The catalysts exhibit high stability, preserving the structural and textural properties after the catalytic tests, that is indeed very important in the presence of ozone.Graphical abstractHighlights► Silver colloids embedded in alumina following a sol–gel procedure in the presence of Pluronic 84 are stable catalysts in the presence of ozone. ► Plasma-catalytic experiments in the total oxidation of toluene showed a significantly increased selectivity to CO2 in the presence of Ag embedded colloids. ► In situ studies of the ozone interaction with catalysts provide an insight into the nature of the active sites of supported silver colloids for total oxidation reactions.
The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO
3pellets and porous Al
2O
3pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al
2O
3pellets. Furthermore, there was a higher selectivity to CO
2in the products from the hybrid than from a plasma reactor packed with BaTiO
3pellets alone. The presence of the Al
2O
3pellets suppressed the formation of N
2O.
Methane decomposition can be utilized to produce COX-free hydrogen for PEM fuel cells, oil refineries, ammonia and methanol production. Recent research has focused on enhancing the production of hydrogen by the direct thermocatalytic decomposition of methane to form elemental carbon and hydrogen as an attractive alternative to the conventional steam-reforming process. In this context, we review a comprehensive body of work focused on the development of metal or carbonaceous catalysts for enhanced methane conversion and on the improvement of long-term catalyst stability. This review also evaluates the roles played by various parameters, such as temperature and flow rate, on the rate of hydrogen production and the characteristics of the carbon produced. The heating source, type of reactor, operating conditions, catalyst type and its preparation, deactivation and regeneration and the formation and utilization of the carbon by-product are discussed and classified in this paper. While other hydrogen production methods, economic aspects and thermal methane decomposition methods using alternative heating sources such as solar and plasma are briefly presented in this work where relevant, the review focuses mainly on the thermocatalytic decomposition of methane using metal and carbonaceous catalysts.
Methane conversion using gliding arc plasma has been studied. The process was conducted at atmospheric pressure. Four kinds of additive gases—helium, argon, nitrogen, and CO2—were used to investigate their effects on methane conversion, as well as product selectivity, and discharged power. Methane conversion was increased with the increasing concentration of helium, argon, and nitrogen in the feed gas but decreased when CO2 concentration increased. Qualitatively, hydrogen and acetylene were the major gas products. No liquid product was produced.
Currently, hydrogen is primarily used in the chemical industry, but in the near future it will become a significant fuel. There are many processes for hydrogen production. This paper reviews the technologies related to hydrogen production from both fossil and renewable biomass resources including reforming (steam, partial oxidation, autothermal, plasma, and aqueous phase) and pyrolysis. In addition, electrolysis and other methods for generating hydrogen from water, hydrogen storage related approaches, and hydrogen purification methods such as desulfurization and water-gas-shift are discussed.
The addition of Al2O3 up to 20% (as cementing agent) in SAPO-34 support significantly integrates metal functions of Pt–Sn-based catalyst, ultimately improves catalytic performance for direct propane dehydrogenation to propylene. Superior propane conversion (initially above 40%) and propylene selectivity (around 95%) is obtained experimentally over Pt–Sn/Al2O3–SAPO-34. The results were found promising and compared with Pt–Sn/SAPO-34 under identical operating conditions. Better platinum dispersion and higher active platinum sites are characterized by TEM and hydrogen-chemisorption analysis. Moreover, the possible metal interactions with different supports were configured. Therefore, light alkane dehydrogenation to alkene was enhanced using surface modified support Al2O3–SAPO-34 for Pt–Sn-based catalysts.
Non-oxidative conversion of methane into higher hydrocarbons was studied under argon, at atmospheric pressure, in the non-equilibrium environment of the dielectric barrier discharge (DBD). In this study, two concentric dielectric barriers, a short plasma zone with a wide discharge gap have been used to investigate methane conversion in reactors employing alumina and quartz as dielectrics. As energy transfer to the plasma in a DBD system is determined by the capacitive properties of the dielectrics, discharge energy varies between quartz and alumina reactors at the same applied voltage and the conversion of methane and yield of hydrogen therefore also varies between quartz and alumina reactors. Although the dielectric strength of alumina is lower than that of quartz, this disadvantage is offset by increased dielectric permittivity resulting in greater dielectric capacity, in turn leading to increased gap voltage and associated higher conversion rates. Methane conversion was performed in a majority argon carrier. The addition of methane in low concentrations results in a modified argon discharge, one operating in the transition region between homogeneous glow and filamentary discharge regimes. Under these conditions, methane conversion rates were observed to vary with methane concentration, applied voltage and residence time. Experimental results are presented and interpreted in terms of ionization phenomena, metastable species activity and discharge power.
Different types of corona discharges, produced by DC of either polarity (+/-DC) and positive pulsed (+pulsed) high voltages, were applied to the removal of toluene via oxidation in air at room temperature and atmospheric pressure. Mechanistic insight was obtained through comparison of the three different corona regimes with regard to process efficiency, products, response to the presence of humidity and, for DC coronas, current/voltage characteristics coupled with ion analysis. Process efficiency increases in the order +DC < -DC < +pulsed, with pulsed processing being remarkably efficient compared to recently reported data for related systems. With -DC, high toluene conversion and product selectivity were achieved, CO(2) and CO accounting for about 90% of all reacted carbon. Ion analysis, performed by APCI-MS (Atmospheric Pressure Chemical Ionization-Mass Spectrometry), provides a powerful rationale for interpreting current/voltage characteristics of DC coronas. All experimental findings are consistent with the proposal that in the case of +DC corona toluene oxidation is initiated by reactions with ions (O(2)(+*), H(3)O(+) and their hydrates, NO(+)) both in dry as well as in humid air. In contrast, with -DC no evidence is found for any significant reaction of toluene with negative ions. It is also concluded that in humid air OH radicals are involved in the initial stage of toluene oxidation induced both by -DC and +pulsed corona.
The decomposition of trichloroethylene ITCE) by non-thermal plasma was investigated in a dielectric barrier discharge (DBD) reactor with a copper rod inner electrode and compared with a plasma-catalytic reactor. The particularity of the plasma-catalytic reactor is the inner electrode made of sintered metal fibers (SMF) coated by transition metal oxides. In order to optimize the geometry of the plasma reactor, the efficiency of TCE removal was compared for different discharge gap lengths in the range of 1-5 mm. Shorter gap lengths (1-3 mm) appear to be more advantageous with respect to TCE conversion. In this case TCE conversion varies between 67% and 100% for input energy densities in the range of 80-480 J/l, while for the 5 turn discharge gap the conversion was lower (53-97%) for similar values of the input energy. As a result of TICE oxidation carbon monoxide and carbon dioxide were detected in the effluent gas. Their selectivity was rather low, in the range 14-24% for CO2 and 11-23% for CO, and was not influenced by the gap length. Several other chlorinated organic compounds were detected as reaction products. When using MnOx/SMF catalysts as the inner electrode of the DBD reactor, the TCE conversion was significantly enhanced, reaching similar to 95% at 150 J/l input energy. The selectivity to CO2 showed a major increase as compared to the case without catalysts, reaching 58% for input energies above 550 J/l. (C) 2007 Elsevier B.V. All rights reserved.
This paper provides a comprehensive review regarding the application of plasma catalysis, the integration of nonthermal plasma and catalysis, on VOC removal. This novel technique combinesthe advantages of fast ignition/response from nonthermal plasma and high selectivity from catalysis. It has been successfully demonstrated that plasma catalysis could serve as an effective solution to the major bottlenecks encountered by nonthermal plasma, i.e., the reduction of energy consumption and unwanted/hazardous byproducts. Instead of working independently, the combination could induce extra performance enhancement mechanisms either in a single-stage or a two-stage configuration, in which the catalyst is located inside and downstream from the nonthermal plasma reactor, respectively. These mechanisms are believed to be responsible for the higher energy efficiency and better CO2 selectivity achieved with plasma catalysis. A comprehensive discussion on the performance enhancement mechanisms is provided in this review paper. Moreover, the current status of the applications of two different plasma catalysis systems on VOC abatement are also given and compared. The catalyst plays an important role in both configurations. Especially for the single-stage type, depositing an inappropriate active component on catalytic support would decrease the VOC removal efficiency instead. To date, no definite conclusion on catalyst selection forthe single-stage plasma catalysis is available. However, MnO2 seems to be the best catalyst for two-stage configuration because it could effectively decompose ozone and generate active species toward VOC destruction. On the other hand, although the single-stage plasma catalysis has been proved to be superior to the two-stage configuration, it does not mean that the former is always the best choice. Considering the typical VOC concentrations from different sources and the characteristics of different plasma catalysis systems, the single-stage and two-stage configurations are suggested to be more suitable for industrial and indoor air applications, respectively.
By reducing the distance between the dielectric end-fittings of a coaxial pulsed corona reactor to values on the order of millimeters, the efficiency of volatile organic compound (VOC) decontamination of atmospheric pressure air could be increased by a factor of seven over that obtained in reactors with electrode lengths in the centimeter range. The increased efficiency is attributed to the increasing effect of surface streamers with increased electron density compared to streamers in the gas space. Packing the discharge gap of the reactor with catalytically active silica gel pellets further increased the energy efficiency of VOCs decontamination by more than 50% over that obtained in the absence of any packing. Silica gel was shown to remove VOC by adsorption until it became saturated. The adsorption provides a tool for handling surplus VOCs under fluctuating input conditions. Destruction of preadsorbed organics on silica gel was also demonstrated. Aluminum oxide pellets showed no catalytic effect on destruction of VOCs under these conditions.
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