Non-thermal Plasma Technology Research Articles

Oxygen-radical pretreatment promotes cellulose degradation by cellulolytic enzymes

BackgroundThe efficiency of cellulolytic enzymes is important in industrial biorefinery processes, including biofuel production. Chemical methods, such as alkali pretreatment, have been extensively studied and demonstrated as effective for breaking recalcitrant lignocellulose structures. However, these methods have a detrimental effect on the environment. In addition, utilization of these chemicals requires alkali- or acid-resistant equipment and a neutralization step.ResultsHere, a radical generator based on non-thermal atmospheric pressure plasma technology was developed and tested to determine whether oxygen-radical pretreatment enhances cellulolytic activity. Our results showed that the viscosity of carboxymethyl cellulose (CMC) solutions was reduced in a time-dependent manner by oxygen-radical pretreatment using the radical generator. Compared with non-pretreated CMC, oxygen-radical pretreatment of CMC significantly increased the production of reducing sugars in culture supernatant containing various cellulases from Phanerochaete chrysosporium. The production of reducing sugar from oxygen-radical-pretreated CMC by commercially available cellobiohydrolases I and II was 1.7- and 1.6-fold higher, respectively, than those from non-pretreated and oxygen-gas-pretreated CMC. Moreover, the amount of reducing sugar from oxygen-radical-pretreated wheat straw was 1.8-fold larger than those from non-pretreated and oxygen-gas-pretreated wheat straw.ConclusionsOxygen-radical pretreatment of CMC and wheat straw enhanced the degradation of cellulose by reducing- and non-reducing-end cellulases in the supernatant of a culture of the white-rot fungus P. chrysosporium. These findings indicated that oxygen-radical pretreatment of plant biomass offers great promise for improvements in lignocellulose-deconstruction processes.

Effect of preliminary stresses on the resistance of Escherichia coli and Staphylococcus aureus toward non-thermal plasma (NTP) challenge

As the development of hurdle technology, cross-protection of various stresses for pathogens posed the potential risk to food safety and public health. This study tried to explore various preliminary stresses including acidity, osmosis, oxidation, heat and cold on the resistance of microbial cells toward the non-thermal plasma (NTP) exposure. The results indicated that short-term (4h) exposure of Staphylococcus aureus and Escherichia coli to acidity, osmosis, oxidation, heat and cold stresses did not lead to the resistance to the subsequent NTP treatment. On the contrary, acidity, osmosis and heat preadaptation increased the vulnerability of E. coli cells to NTP treatment. After exposing S. aureus to osmosis, oxidation, heat and cold stress for longer period (24h), the reduction level showed significantly (P<0.05) higher. Interestingly, long-term (24h) preliminary exposure of acidic stress exhibited protective effect for S. aureus against the following NTP exposure with less damage in cell membrane integrity, membrane potential and intracellular enzyme activity. It might be due to the protein production for oxidative stress response during preliminary acidic adaptation. In general, the obtained result helped to grasp better understanding of the microbial stress response to NTP treatment and provided insight for the future research in order to accelerate the development of NTP technology in food industry.

Degradation of chitosan hydrogel dispersed in dilute carboxylic acids by solution plasma and evaluation of anticancer activity of degraded products

Chitosan is a polysaccharide that has been extensively studied in the field of biomedicine, especially its water-soluble degraded products called chitooligosaccharides (COS). In this study, COS were produced by the degradation of chitosan hydrogel dispersed in a dilute solution (i.e., 1.55 mM) of various kinds of carboxylic acids using a non-thermal plasma technology called solution plasma (SP). The degradation rates of chitosan were influenced by the type of carboxylic acids, depending on the interaction between chitosan and each carboxylic acid. After SP treatment, the water-soluble degraded products containing COS could be easily separated from the water-insoluble residue of chitosan hydrogel by centrifugation. The production yields of the COS were mostly higher than 55%. Furthermore, the obtained COS products were evaluated for their inhibitory effect as well as their selectivity against human lung cancer cells (H460) and human lung normal cells (MRC-5).

Application of non-thermal plasma technology on fugitive methane destruction: Configuration and optimization of double dielectric barrier discharge reactor

Fugitive methane (CH4) from waste treatment facilities (landfill mining), power industries (oil and gas process plants) and coal mining etc. into atmosphere is an increasing environmental concern. In this study, CH4 conversion efficiency in double dielectric barrier discharge (DDBD) has been investigated at various operating parameters including input power, feed gas-mixture flow rate, CH4 initial concentrations, and discharge gap distance between two dielectrics. Increase in input power, decrease in the gas-mixture flow rate and discharge gap distance; results in increases of CH4 conversion efficiency. In plasma alone, maximum CH4 conversion efficiency of 76% was obtained using 3 mm plasma discharge gap distance at flow rates of 2 L/min, input power of 65.8 W and is limited by experimental conditions. In addition, CH4 conversion efficiency in plasma alone and plasma-catalytic is compared by introducing various catalysts includes Pt–Sn/Al2O3, BaTiO3 and HZSM-5 in single plasma discharge zone. Results revealed that plasma combined with Pt–Sn/Al2O3 showed higher CH4 conversion efficiency (84.93%) as compare to plasma alone (56.42%) using 6 mm plasma discharge gap distance at flow rates of 2 L/min, input power of 65.8 W. Moreover, maximum energy efficiency of CH4 conversion (limited by experimental conditions) was 27.24 × 10−12 mol/kJ at 32.6 W observed in plasma-catalyst. Analysis of the exhaust gas showed that DDBD is a promising alternative reactor not only to achieve high CH4 conversion efficiency, but also to overcome the drawbacks of formation of undesirable byproducts. Moreover, deposition of carbon residues on the surface of internal electrode is not observed, which is often occurred in single DBD reactors.

Promotion of the vapors from biomass vacuum pyrolysis for biofuels under Non-thermal Plasma Synergistic Catalysis (NPSC) system

Abstract Non-thermal Plasma Synergistic Catalysis (NPSC) was firstly proposed and employed in the upgrading of biomass pyrolysis vapors for preparation of biofuels. The effects of the three-way catalysis (non-thermal plasma, HZSM-5 body and modified components) on the bio-oil upgrading performance and catalyst stability were comprehensively investigated. Bio-oil yields continued to decrease, but the physicochemical properties were further improved. The contents and compositions of hydrocarbons in bio-oil were increased and improved to varying degrees. The introduction of non-thermal plasma technology enhanced performance of cracking and deoxygenation for whole catalytic process. Besides, anti-coking performance of Zn/HZSM-5 was enhanced to a certain extent, but the multiple interactions significantly improved the cracking performance when Ti species introduced, increased the coke content, and an “isomorphism” phenomenon for two kinds of coke was emerged. In general, obtained biofuels still belonged to the hydrogen-deficient fuel, lower (H/C) eff of the vapors limited substantial improvement of the fuel grade.

Effect of indirect non-thermal plasma on particle size distribution and composition of diesel engine particles

To explore the effect of the gas source flow rate on the actual diesel exhaust particulate matter (PM), a test bench for diesel engine exhaust purification was constructed, using indirect non-thermal plasma technology. The effects of different gas source flow rates on the quantity concentration, composition, and apparent activation energy of PM were investigated, using an engine exhaust particle sizer and a thermo-gravimetric analyzer. The results show that when the gas source flow rate was large, not only the maximum peak quantity concentrations of particles had a large drop, but also the peak quantity concentrations shifted to smaller particle sizes from 100 nm to 80 nm. When the gas source flow rate was 10 L min−1, the total quantity concentration greatly decreased where the removal rate of particles was 79.2%, and the variation of the different mode particle proportion was obvious. Non-thermal plasma (NTP) improved the oxidation ability of volatile matter as well as that of solid carbon. However, the NTP gas source rate had little effects on oxidation activity of volatile matter, while it strongly influenced the oxidation activity of solid carbon. Considering the quantity concentration and oxidation activity of particles, a gas source flow rate of 10 L min−1 was more appropriate for the purification of particles.

Diesel particulate filter (DPF) regeneration using non-thermal plasma induced by dielectric barrier discharge

Based on indirect non-thermal plasma (NTP) technology, an experimental study of diesel particulate filter (DPF) regeneration was implemented by a dielectric barrier discharge (DBD) reactor with different O2 flow rate strategies. Carbon deposition characteristics and parameters of the NTP injection system were discussed to facilitate further data analysis and calculation. DPF regeneration was then investigated by comparison analysis of deposit removal mass and backpressure variation. The physicochemical properties of deposit before and after NTP treatment were studied by thermogravimetric analysis (TGA). The results revealed that O3 concentration decreased with the increase of O2 flow rate, and the total output of O3 presented a completely inverse trend when the O2 flow rate was less than 10 L/min. Deposit removal mass and backpressure drop peaked at an O2 flow rate of 10 L/min. Higher O3 output contributed to a better regeneration effect at a higher O2 flow rate. The soluble organic fraction (SOF) in the deposit obviously reduced after DPF regeneration. NTP treatment enhanced the oxidative activity of particulate matter (PM) both in SOF and dry soot (DS), which could accelerate the PM oxidation later. The results demonstrated effective DPF regeneration using a DBD-type NTP reactor with oxygen source, and the favorable PM oxidation effect was obtained after NTP treatment.

Experimental Study on Purification of Diesel Particulate Matter by Non-thermal Plasma Technology

In order to investigate the effects of non-thermal plasma (NTP) on diesel particulate matter (PM), an engine test bench was built up. An engine exhaust particle sizer (EEPS) was introduced to analyze the emission concentration and size distribution of PM and a thermo-gravimetric analyzer was used to analyze the effects of NTP on the composition of the particulate matter in the exhaust gas. The results show that the size distribution interval of the particle mass concentration falls behind that of the quantity concentration under various loads. When the diesel engine operating speed is 2400 rpm and the load is 25%, after NTP, the proportions of the nucleation mode particles and the accumulative mode particles exhibit a small fluctuation while the proportion of ultrafine particles decreases by 10% due to their large quantity concentration. Under the dual effect of DPF and NTP, the particle quantity concentration decreases by 98%. In order to investigate the effect of NTP on the composition of the PM, a thermo-gravimetric analysis of the particles obtained before and after NTP was carried out. The results show that the proportion of volatile matter falls by 16.05% and solid carbon accounts for an increase of 7.29%. NTP has the ability to improve reduction activity of particles and make particles easier to be oxidized at a lower temperature.

An indoor air purification technology using a non-thermal plasma reactor with multiple-wire-to-wire type electrodes and a fiber air filter

For indoor air purification, long-term operation of the air purifier induces the growth of germs and the proliferation of molds, and results in the performance degradation of the air filter. Non-thermal plasma technology could be an effective countermeasure against these problems. Ozone generated by the electric discharge has significant germicidal power and does not produce secondary residual contaminants. Electrostatic force can enable the air filter to function as an electric precipitator. In this study, a non-thermal plasma reactor with wire-wire type electrodes and an air filter is investigated experimentally to improve the performance of the used air filter.

Non-thermal plasma technology for abatement of pollutant emission from marine diesel engine

Non-thermal plasma technology for abatement of pollutant emission from marine diesel engine

Influence of PM Size Distribution and Ingredients on DPF Regeneration by Non-thermal Plasma Technology

Experimentation was conducted to analyze the diesel particulate filters (DPF) trap under four different engine loads with particle size analysis and thermo-gravimetric analysis introduced to characterize particulate matter (PM) samples. DPF regeneration was achieved utilizing an oxygen-fed non-thermal plasma (NTP) injection system. Results indicated that accompanying the increase of engine load, the concentration of nucleation mode particles decrease while that of accumulation mode particles and the total concentration number increase at first and then decrease with the total concentration number of PM peaking at 50% load. H2O and soluable organic fraction in PM demonstrate a downward trend while dry soot exhibits an upward trend in mass fraction with the increasing load. NTP may then separate PM into CO and CO2. Size distribution and ingredients of PM trapped by DPF under different loads vary, thus the intensity of reaction between PM and radical gases produced by NTP is different. C1 (C in CO) exhibited a declining trend with the increasing of engine load, while C2 (C in CO2) and C12 (sum of C1 and C2) increase first and decrease after. Mass of PM removal maximizes at 50% load while DPF regeneration effect is the most remarkable.

Polycyclic aromatic hydrocarbon emissions of non-road diesel engine treated with non-thermal plasma technology

Non-road diesel engines are important polycyclic aromatic hydrocarbon (PAH) sources in the environment due to their high emission concentration compared to on-road diesel engines. Particle- and gas-phase PAH concentrations of a non-road diesel engine were investigated. Non-thermal plasma (NTP) as an effective after-treatment technology was used to reduce PAH emissions. The results showed that particle-phase PAH concentrations were 329.7 µg/m3, 3,206.7 µg/m3, and 1,185.7 µg/m3 without the action of NTP at three different engine loads respectively. Relatively low concentrations were measured for gas-phase PAHs. Excellent linearity was shown for particle-phase with total PAH concentrations both with, and without, NTP. The gas-phase PAH concentrations linearly increased with engine load without NTP. The five most abundant compounds of PAHs were among low molecular weight (LMW) and medium molecular weight (MMW) compounds. Total PAH cleaning efficiency was beyond 50% when treated with NTP at the three different engine loads. We hypothesized that naphthalene (Nap) concentrations increased greatly at 60% and 80% engine loads because it was produced within the plasma zone by decomposition of high molecular weight (HMW) PAHs. The PAHs content of particulate matter (PM) aggregation at 60% load was approximately three times higher than at 40% and 80% loads. High correlation values were observed for MMW PAHs with total PAH concentrations. Correlations of PAH concentration reduction could be important to clarify the PAH reduction mechanism with NTP technology.

Particle- and gas-phase PAHs toxicity equivalency quantity emitted by a non-road diesel engine with non-thermal plasma technology.

Polycyclic aromatic hydrocarbon (PAH) toxicity equivalency quantity (TEQ, denoted by benzo(a)pyrene equivalent (BaPeq) concentration) is more meaningful when evaluating the influence of non-road diesel engines PAH toxicity on environment. Particle- and gas-phase PAH BaPeq concentrations were calculated based on gas chromatography-mass spectrometer (GC-MS) results and toxic equivalency factors. A non-thermal plasma (NTP) reactor was applied to a non-road diesel engine to decrease PAH TEQ content. Only the gas-phase Nap BaPeq concentration increased slightly with the action of NTP at three different generator power outputs. BaP dominated the BaPeq concentration for 15 samples with, and without NTP except in the gas-phase at 4kW. Almost all medium molecular weight (MMW) and high molecular weight (HMW) PAH TEQs increased for particle- and gas-phases at 3kW power output compared to 2kW without the use of NTP. Particle-phase Nap, Acp, and AcPy (low molecular weight, LMW) TEQ were under detection at 3 and 4kW, while gas-phase BkF, IND, DBA, and BghiP (HMW) concentrations were below the limits of detection. The most abundant PAH TEQ compounds were MMW and HMW PAHs for gas- and particle-phase while they were BaA, CHR, BbF, BaP, and IND for PM aggregation. The total BaPeq emission factors were 15.1, 141.4, and 46.5μgm(-3) at three engine loads, respectively. Significant BaPeq concentration percentage reduction was obtained (more than 80 and 60%) with the use of NTP for particle- and gas-phases. A high TEQ content was observed for PM aggregation (38.8, 98.4, and 50.0μgkg(-1)) which may have caused secondary PAH toxicity emissions. With the action of NTP, the breakup of MMW and HMW into LMW PAHs led to reduction of some PAH concentrations.

Combining nonthermal plasma with perovskite-like catalyst for NOx storage and reduction.

A new NOx storage and reduction (NSR) system is developed for NOx removal by combining perovskite-like catalyst with nonthermal plasma technology. In this hybrid system, catalyst is mainly used for oxidizing NO to NO2 and storing them, while nonthermal plasma is applied as a desorption-reduction step for converting NOx into N2. An innovative catalyst with a high NOx storage capacity and good reduction performance is developed by successive impregnation. The catalysts prepared with various metal oxides were investigated for NOx storage capacity (NSC) and NOx conversion. Characterization of the catalysts prepared reveals that addition of cobalt (Co) and potassium (K) considerably increases the performance for NSC. Results also show that SrKMn0.8Co0.2O4 supported on BaO/Al2O3 has good NSC (209μmol/gcatalyst) for the gas stream containing 500ppm NO and 5% O2 with N2 as carrier gas. For plasma reduction process, NOx conversion achieved with SrKMn0.8Co0.2O4/BaO/Al2O3 reaches 81% with the applied voltage of 12kV and frequency of 6kHz in the absence of reducing agents. The results indicate that performance of plasma reduction process (81%) is better than that of thermal reduction (64%). Additionally, mixed gases including 1% CO, 1% H2 and 1% CH4, and 2% H2O(g) are simultaneously introduced into the system to investigate the effect on NSR with plasma system and results indicate that performance of NSR with plasma can be enhanced. Overall, the hybrid system is promising to be applied for removing NOx from gas streams. Graphical abstract ᅟ.

Experimental study of EGR cooler regeneration aided by oxygen-fed NTP and air-fed NTP

Based on non-thermal plasma (NTP) technology fed by oxygen and air as the gas source respectively, the experimental system of exhaust gas recirculation (EGR) cooler regeneration was built to do a study at different regeneration temperatures. By measuring the concentration of main active substance and COx in regeneration process, the influence of temperature on regeneration aided by oxygen-fed NTP and air-fed NTP was investigated. The experimental results indicate that EGR cooler can be regenerated both by air-fed NTP and oxygen-fed NTP at a wide temperature range of 18 °C ∼ 300 °C. By comparison of the regeneration with oxygen-fed NTP and air-fed NTP, it can be easily known that the regeneration effect is most remarkable at 150 °C with oxygen-fed NTP and at 120 °C with air-fed NTP. In addition, when the temperature is below 150 °C especially at 120 °C, the regeneration efficiency of air-fed NTP is lower than oxygen-fed NTP, nevertheless, when the temperature is above 150 °C, air-fed NTP has a superiority in regeneration and the higher the temperature is, the more obvious the superiority will be.

Non-thermal plasma technology for the development of antimicrobial surfaces: a review

Antimicrobial coatings are in high demand in many fields including the biomaterials and healthcare sectors. Within recent progress in nanoscience and engineering at the nanoscale, preparation of nanocomposite films containing metal nanoparticles (such as silver nanoparticles, copper nanoparticles, zinc oxide nanoparticles) is becoming an important step in manufacturing biomaterials with high antimicrobial activity. Controlled release of antibiotic agents and eliminating free nanoparticles are of equal importance for engineering antimicrobial nanocomposite materials. Compared to traditional chemical ‘wet’ methods, plasma deposition and plasma polymerization are promising approaches for the fabrication of nanocomposite films with the advantages of gas phase dry processes, effective use of chemicals and applicability to various substrates. In this article, we present a short overview of state-of-the-art engineering of antimicrobial materials based on the use of non-thermal plasmas at low and atmospheric pressure.

Low Temperature Diesel Particulate Filter Regeneration by Atmospheric Air Non-thermal Plasma Injection System

An experimental study of the regeneration of diesel particulate filter (DPF) was conducted through the use of a self-designed Non-thermal plasma (NTP) injection system with an experimental temperature of 20–300 °C, with atmospheric air being used as the gas source. The results revealed that the PM could be broken down into CO and CO2 by NTP, through a discharge reaction of the NTP reactor. As the temperature increases, the mass of C1 (mass of C in CO) showed an overall declining trend. Interestingly, the mass of C2 (mass of C in CO2) and C12 (the sum of C1 and C2) both showed an initial increase, followed by a decrease. The peak mass of C12 appears at 150 °C, and both axial and radial temperature gradients are less than the limit of DPF temperature gradient at this temperature. In conclusion, DPF can be regenerated by the NTP technology at a lower temperature, which can aid in the avoidance of thermal damage of DPF. The technology boasts a great advantage in adopting atmospheric air as its gas source, which can not only reduce costs, but also is convenient.

Removal of Elemental Mercury from Simulated Flue Gas by Combining Non-thermal Plasma with Calcium Oxide

Mercury emission from coal combustion has been the fourth biggest pollutant in China, following the dusts, SO2 and NOX. The technology of non-thermal plasma has been widely studied for oxidizing gaseous elemental mercury at low temperature. In this paper, a new method of combining non-thermal plasma with calcium oxide was proposed to remove elemental mercury from simulated flue gas. The effects of non-thermal plasma, input energy, combination mode of plasma and calcium oxide on Hg0 removal were investigated in a wire-cylinder non-thermal plasma reactor, whose energy was supplied by a high voltage alternating current power. The peak voltage and energy of the non-thermal plasma were measured by an oscilloscope and a high voltage probe (1000:1). The results showed that most of Hg0 was converted to oxidized mercury in simulated flue gas by non-thermal plasma treatment. The Hg0 removal efficiency of CaO was improved remarkably strengthened by the non-thermal plasma, which was closely related to input energy, and the maximum mercury removal efficiency was about 80 % at an optimal input energy. Through temperature-programmed decomposition and desorption and energy dispersive spectroscopy analysis, the majority of mercury species on CaO surface were Hg2O and HgO3 rather than HgO. Therefore, it can be concluded that O3 plays an important role in Hg0 oxidation under the condition of non-thermal plasma.

Evaluation of Residence Time on Nitrogen Oxides Removal in Non-Thermal Plasma Reactor.

Non-thermal plasma (NTP) has been introduced over the last few years as a promising after- treatment system for nitrogen oxides and particulate matter removal from diesel exhaust. NTP technology has not been commercialised as yet, due to its high rate of energy consumption. Therefore, it is important to seek out new methods to improve NTP performance. Residence time is a crucial parameter in engine exhaust emissions treatment. In this paper, different electrode shapes are analysed and the corresponding residence time and NOx removal efficiency are studied. An axisymmetric laminar model is used for obtaining residence time distribution numerically using FLUENT software. If the mean residence time in a NTP plasma reactor increases, there will be a corresponding increase in the reaction time and consequently the pollutant removal efficiency increases. Three different screw thread electrodes and a rod electrode are examined. The results show the advantage of screw thread electrodes in comparison with the rod electrode. Furthermore, between the screw thread electrodes, the electrode with the thread width of 1 mm has the highest NOx removal due to higher residence time and a greater number of micro-discharges. The results show that the residence time of the screw thread electrode with a thread width of 1 mm is 21% more than for the rod electrode.

Micro-structural and components evolution mechanism of particular matter from diesel engines with non-thermal plasma technology

The present study is about the influence of non-thermal plasma (NTP) technology on soot emissions and physico-chemical properties (morphology, particle size, chemical composition and ignition temperature) of diesel PM. Experiments have been carried out using a small direct injection diesel engine with NTP technology based on a bench test. The physico-chemical properties of PM samples were detected by GC–MS, SEM, EDX, and TGA. PM samples after NTP treatment consisted of mainly hydrocarbons with less than 18 carbon atoms and few hydrocarbons with higher than 20 carbon atoms. Analysis by SEM and EDX showed that the agglomeration degree and the mean spherule diameters were markedly reduced by NTP oxidation. TGA showed that the ending combustion temperatures of PM samples in oxygen environment were 670.03 °C and 550.54 °C before and after NTP treatment, respectively. The mean temperature difference was nearly 120 °C, which indicated that NTP technology could effectively reduce the burning combustion temperature of diesel PM emissions.