Water Vapor Plasma Research Articles

Comparative study between the simulation and experimental results of H<sub>2</sub> production from water vapour plasmolysis

In the present study, the kinetics of hydrogen production from water vapour using dielectric barrier discharge (DBD) plasma in a cylindrical reactor were analyzed. The simulation analysis was carried out for both models with and without the dissociative attachment reaction to predict and compare the concentration of produced hydrogen gas from water vapour. The effect of water vapour input temperature ranges of 523–623 K and plasma voltage in the range of 12–14 kV were investigated. It was revealed that the hydrogen concentration increased with the input water vapour temperature and plasma voltage increased in both the simulation models. It was seen that the H2 concentration results of the simulation model with the dissociative attachment reaction (H-) were nearly same as the H2 concentrations of the water vapour plasmolysis experimental results. Moreover, it can be concluded that the dissociative attachment reaction was controlled the H2 generation from water vapour plasmolysis. It was remarkable that the conversion rates of the simulation model included the dissociative attachment reaction has more acceptable results to the experimental data compared to the simulation model deselecting the dissociative attachment reaction (H-). Also, it was seen as the main reason for the difference between simulation and experimental results.

Remediation of organochlorine pesticides contaminated soil using thermal plasma

Organochlorine pesticides have been used widely in agriculture for effective pest control. However, organochlorine pesticides such as dichloro-diphenyl-trichloroethane (DDT) contaminate soil, groundwater and cause carcinogenic effects, reproductive disorders for birds, humans and other mammals. Consequently, the use of DDT in agriculture has been gradually forbidden since 1972. Nevertheless, due to the long halflife of DDT (~36 years), its residues are still present in the soil. Therefore, there is a need to find a method for the treatment of this dangerous contaminant in the soil. This experimental research is aimed to analyse thermal air and water vapour plasmas eligibility to remediate soil contaminated by organochlorine pesticides (mainly DDT). Hence, parameters of the polluted soil were investigated before and after the treatment with thermal plasma using scanning electron microscopy (SEM), an optical microscope, a photo camera, energy dispersive X-ray spectroscopy (EDX) and gas chromatography-mass spectrometry (GC-MS). SEM analysis revealed that interaction of polluted soil with thermal air plasma or water vapour plasma caused structural changes of the soil. EDX data demonstrated complete removal of chlorine after the soil cleaning with plasmas. Moreover, the measurements performed with GCMS confirmed that organochlorine pesticides concentrations in the soil were reduced noticeably after the soil cleaning with thermal plasmas. Thus, experimental results indicate that contaminated soil treatment using thermal air or water vapour plasma has satisfactory pesticides degradation capacity.

Gasification of Waste Cooking Oil to Syngas by Thermal Arc Plasma

The depletion and usage of fossil fuels causes environmental issues and alternative fuels and technologies are urgently required. Therefore, thermal arc water vapor plasma for a fast and robust waste/biomass treatment is an alternative to the syngas method. Waste cooking oil (WCO) can be used as an alternative potential feedstock for syngas production. The goal of this experimental study was to conduct experiments gasifying waste cooking oil to syngas. The WCO was characterized in order to examine its properties and composition in the conversion process. The WCO gasification system was quantified in terms of the produced gas concentration, the H2/CO ratio, the lower heating value (LHV), the carbon conversion efficiency (CCE), the energy conversion efficiency (ECE), the specific energy requirements (SER), and the tar content in the syngas. The best gasification process efficiency was obtained at the gasifying agent-to-feedstock (S/WCO) ratio of 2.33. At this ratio, the highest concentration of hydrogen and carbon monoxide, the H2/CO ratio, the LHV, the CCE, the ECE, the SER, and the tar content were 47.9%, 22.42%, 2.14, 12.7 MJ/Nm3, 41.3% 85.42%, 196.2 kJ/mol (or 1.8 kWh/kg), and 0.18 g/Nm3, respectively. As a general conclusion, it can be stated that the thermal arc-plasma method used in this study can be effectively used for waste cooking oil gasification to high quality syngas with a rather low content of tars.

Reduction of Copper Oxide by Water Vapor Plasma at Low Pressure

As a new and safe reduction method for copper oxide, we propose the use of water vapor plasma at low pressure instead of conventional hydrogen plasma. Although hydrogen plasma is the established method to reduce copper oxide at low temperature, hydrogen is flammable and requires safety equipment. In this study, oxidized copper film was treated with water vapor plasma and its reduction process was compared with hydrogen plasma's. Surface, cross-section structure and thickness of oxidized and reduced copper film were measured and analyzed by FE-SEM (Field Emission-Scanning Electron Microscope), FIB (Focused Ion Beam), XRD (X-Ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy). Using water vapor plasma, oxidized copper film was reduced without any oxygen remaining. During the reduction process, induction period and S-shaped curve were observed to be the same as hydrogen plasma. Furthermore, the reduction rate of water vapor plasma was more than twice that of hydrogen plasma.

Thermal arc plasma gasification of waste glycerol to syngas

In this experimental study, waste glycerol gasification to syngas was investigated by utilizing direct current thermal arc plasma of 46–62 kW power. Two gasifying mediums were used: water vapor and air. The plasma-chemical reactor capacity exceeded up to 39 kg/h. Glycerol gasification to synthesis gas process was evaluated in terms of the H2/CO ratio, H2 and CO yield, energy conversion efficiency, carbon conversion efficiency, and specific energy requirements. Experimental results were compared between and also with other research work. Water vapor used as the main gasifying medium for waste glycerol utilization to syngas demonstrated a higher process performance over the air used. Full waste glycerol conversion to synthesis gas was achieved for the case of water vapor, whereas that in the case of air gasification only 75.7%. The lower heating value of the produced syngas exceeded 9.82 MJ/Nm3 and 7.32 MJ/Nm3 for the water vapor plasma and air plasma gasification, respectively. The energy conversion efficiency was calculated to be higher for the water vapor used as a gasifying agent exceeding 63.86%, whereas that of the air plasma gasification only 43.64%. The specific energy consumption required to treat one kilogram of waste glycerol in the environment of water vapor plasma accounted to 191.6 kJ/mol and 266.45 kJ/mol for the air plasma treatment. As conclusion, it was demonstrated that syngas can be successfully produced from waste glycerol by both water vapor and air plasma gasification. However, the use of water vapor as a gasifying agent gave a better process efficiency over the air in all the parameters studied.

Plasma inactivation of Aspergillus flavus on hazelnut surface in a diffuse barrier discharge using different working gases

The aim of the study is the comparison of inactivation efficiency of low-temperature plasma generated in different working gases for A. flavus inoculated on hazelnut surface. Plasma was generated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) in gases interesting in term of plasma properties – diffusiveness (nitrogen), oxidative potential (oxygen), role of OH radical formation (synthetic air with and without water vapour) and applicability (ambient air). The inactivation kinetics, explained by Weibull model, was strongly depended on used gas. Decimal reduction time (D-values) for tested fungi using oxygen, synthetic air with or without water vapour, ambient air and nitrogen plasma was 10 s, 32 s, 39 s, 41 s and 55 s, respectively. Reduction of A. flavus spore in oxygen and synthetic air with water vapour was from initial population of 4.6 CFU/g to below detection level (1.0 log10 CFU/g). Synthetic air without water vapour inactivated 2.56 log10 CFU/g, ambient air 2.95 log10 CFU/g and N2 1.69 log10 CFU/g after 180 s treatment. The characterization of plasma using optical emission spectrometry (OES) and Fourier Transform Infrared Spectroscopy (FTIR) was used for identification of active species in mentioned working gases participating in decontamination process – ozone, hydroxyl (OH) radicals, nitrogen oxides (NOx) and excited nitrogen species. A more complete characterization of the factors involved in inactivation by various plasmas will contribute to its better implementation in food quality.

Fast one-pot microwave preparation and plasma modification of porous carbon from waste lignin for energy storage application

Because the commonly used two-step approach (carbonization followed by activation) usually produces microporous carbons and requires a long production duration, obtaining a low-cost porous-carbon-based supercapacitor with both high energy density and rate capability is a challenge. Herein, a more cost-effective one-pot approach via microwave heating in humidified N2 combined with water vapor plasma modification is proposed to obtain lignin-based porous carbon with a hierarchical and oxygen-enriched structure. Humidified microwave heating can produce hierarchical porous carbon with a high specific surface area (SBET) of 2866 m2 g−1 and high mesopore content of 68.16%. Water vapor plasma modification not only results in a further development of the porosity with an increase in SBET by 11.6% but also results in the doping of oxygen (up to 33.43%). These characteristics ensure a high energy storage capacity and an excellent rate capability for the prepared supercapacitor, which exhibits the highest specific capacitance of 254.6 F g−1 at 0.5 A g−1 with a retention rate of 75.6% at 10 A g−1. The results of this study confirm the good feasibility of the one-pot preparation approach combined with plasma modification for the effective use of waste lignin for advanced energy storage applications.

Atmospheric pressure water-vapor plasma in an air-shielded environment by water flow

Atmospheric pressure plasma sources in air-shielded environment by water flow were developed for a plasma process utilizing water-derived reactive species without air contamination in the atmosphere. An atmospheric pressure plasma jet with He gas was enclosed by a cylindrical water flow preventing air contamination to the plasma without using a gas flow shield, vessel or pump. Suppression of air contamination into the plasma was confirmed by optical emission spectroscopy. Furthermore, a microwave-excited water-vapor plasma source in a space shielded by a cone-shaped water flow was developed using a coaxial waveguide with a ring-shaped slot to use a high-density hydroxyl radical without air contamination at atmospheric pressure. A water-vapor plasma without air was successfully realized by pulsed-microwave discharges. Production of a hydroxyl radical was confirmed from the optical emission from the plasma. As an application example of the water-vapor plasma in the air-shield environment, atmospheric pressure photoresist removal treatment was demonstrated and the removal rate as high as 2.2 μm min−1 was obtained.

Heterogeneous bonding between cyclo‐olefin polymer (COP) and glass‐like substrate by newly developed water vapor‐assisted plasma, Aqua Plasma Cleaner

AbstractTo develop high‐performance and low‐cost microfluidic devices, heterogeneous bonding with cyclo‐olefin polymer (COP) and glass substrate was investigated by low‐pressure plasma using water vapor. COP and glass‐like substrate were bonded at room temperature under its own weight, and the bonding strength reached the breaking point of base material strength. Water contact angle of the COP and glass surface after water vapor plasma was less than 1° (superhydrophilic) and showed stable hydrophilicity even after 30 days. Water vapor plasma and COP surface were analyzed by optical emission spectroscopy (OES) and x‐ray photoelectron spectroscopy (XPS) to study the reaction of room temperature bonding.

Dynamic properties of water microwave plasma

Experiments were performed to generate water vapor plasma in a microwave discharge using a household magnetron (frequency 2.45 GHz). Plasma was ignited in a discharge tube during evaporation from the vessel, and also at the liquid-gas interface. The input power ranged from 1 to 2 kW, and the vapor pressure ranged from 1 to 10 mbar. The time dependence of the emission intensity for the first three lines of the Balmer series of hydrogen was constructed. It was revealed that the time required to heat the plasma to a steady state was 2 ms. A change in the anode current by 15% did not lead to an appreciable change in plasma emission intensity. The plasma temperature estimated using the Boltzmann method was about 4000 K. The plasma was shown not to be in thermodynamic equilibrium.

Tandem Mass Spectrometry of Peptide Ions by Microwave Excited Hydrogen and Water Plasmas.

A thermal cracking cell that served as the atomic hydrogen source for hydrogen attachment/abstraction dissociation (HAD) analysis has an intrinsic problem to produce a beam of atoms reactive against heated tungsten capillary. A plasma excited by 2.45 GHz microwave discharge can deliver reactive species to a quadrupole ion trap confining analyte ions without excessive heating of the radical source components. The radical (H•) production performance of the developed source was evaluated by optical emission spectroscopy and H• attachment reaction to fullerene ions. The source exhibited the H• attachment rate as high as a thermal cracking source forming H• in the high temperature tungsten capillary to induce fragmentation processes preserving post-translational modifications. Water vapor was introduced to the source to confirm the stability to generate oxygen containing radicals, which were found present in the water vapor plasma together with atomic hydrogen. Injection of radicals from a water vapor plasma successfully dissociated peptide ions to c-/z- and a-/x-type ions as the case of HAD induced by a thermal cracking cell.

Hydrogen Peroxide Formation in Boiling Water Plasma of Electrolyte-Cathode Discharge

A mechanism is proposed for the formation of hydrogen peroxide in an electrolyte-cathode atmospheric-pressure direct-current discharge. A local increase in the temperature of water in the area of liquid contact with the gas discharge causes its boiling, and strong electric fields due to unevenness of the turbulent surface appear on the splashes. As a result, a local breakdown of the hemispherical region of boiling water beneath the electrolyte-cathode spot is possible. The kinetic scheme of the reactions for water vapor plasma has been considered, and hydrogen peroxide concentrations have been calculated, the calculation results being in satisfactory agreement with experimental data.

Fast modification on wheat straw outer surface by water vapor plasma and its application on composite material

The presence of non-poplar extracts, cutin, and wax layer in the wheat straw outer surface (WOS) greatly limit its application in bio-composite preparation. In this study, a dielectric-barrier-discharge plasma using water vapor as feeding gas was used to fast modify the WOS. The morphology, free radical concentrations, surface chemical components, and contact angles of WOS before and after plasma modification were investigated. Wheat straw was further prepared into wheat straw-based composites (WSC) and its bonding strength was evaluated by a paper tension meter. The results showed that water vapor plasma leads to the appearance of surface roughness, the generation of massive free radicals, and the introduction of oxygen-containing groups. In addition, both initial and equilibrium contact angle and the surface total free energy were significantly increased after plasma modification. These results synergistically facilitate the spread and permeation of adhesive onto the WOS and thus improve the bonding strength of all prepared WSCs. A good linear relationship between bonding strength and surface roughness parameters, contact angles, and total free energy were observed. In general, this study provided a time-saving and cost-effective modification method to realize WSC manufacture.

The kinetics of energetic O− ions in discharge H2O plasma

Using Monte Carlo simulation, the translational relaxation of energetic O− ions produced by dissociative electron attachment to molecules was studied in water vapor plasmas in a strong electric field. Initial O− ions are energetic and are more reactive than the ions being in equilibrium with the electric field. Because of this, the energetic O− ions have a chance to be involved in endothermic reactions prior to energy relaxation of these ions. The probabilities of charge exchange and electron detachment in ion-molecule interactions were calculated versus the reduced electric field. It was shown that several percent of energetic O− ions produced in water vapor plasma by dissociative electron attachment to H2O molecules are rapidly transformed to OH− ions due to charge exchange collisions or are decomposed to release free electrons. The total probability of charge exchange and electron detachment from energetic O− ions increases up to around 90% when these ions are produced by dissociative electron attachment to O2 molecules if oxygen is added to water vapour. This means that, in this case, most of energetic ions formed from O2 molecules are involved in charge exchange and electron detachment reactions prior to their thermalization.

On the Internal Gas Dynamics and Efficiency of a Vortex Water-Vapor Plasma Generator

Results of experimental investigations of a new-type generator of an arc water plasma, having a high thermal efficiency close to 100%, are presented. This generator represents a system comprising a vortex arc plasma generator, in which an electric arc is stabilized by water vapor and a straight-through-flow tubular electric steam generator. Such a high efficiency of the plasma generator system was achieved due to the refinement of the internal gas dynamics of the plasma generator and the heat and mass transfer in its discharge channel as a result of the improvement of the vortex stabilization and thermal insulation of an arc discharge in it by the specially organized ″instantly permeable″ channel wall cooled by only the working water used for generation of the plasma.

Effects of Water-Vapor Propellant on Electrodeless Thruster Performance

The performance of an electrodeless thruster operating on water-vapor propellant is evaluated and compared to noble-gas propellants. Cross-section data for electron interactions in water vapor are employed to predict the ionization cost as a function of electron temperature. The ionization cost model incorporates energy-loss mechanisms such as dissociation and excitation of rotational modes that are not present for noble-gas propellants. The ionization cost for water is compared to that of traditional noble-gas propellants, such as argon. The characteristics of a water-vapor plasma sheath are discussed and incorporated, along with the ionization cost, into an overall thrust efficiency analysis. Results indicate that comparable performance can be attained for sufficiently high electron temperatures.

Improvement of the Bondability of Wheat Straw Treated by Water Vapor Plasma for Bio-composites Manufacture

Wheat straw (WS) was first modified with water vapor plasma to enhance its interfacial bonding performance. The treatment effects during the entire exposing process were investigated in terms of surface wettability, physicochemical characteristics, and mechanical properties of glued test-pieces (three different forms) using contact angle analysis, free energy analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and shear strength analysis. The results showed that 180 s of plasma treatment time resulted in a low instantaneous and equilibrium contact angle of urea-formaldehyde (UF) – 40.8% and 46.5% lower, respectively, in comparison with that of the untreated WS exterior surface. Obvious etching morphology was observed on the WS surfaces and positive activation was detected, demonstrating a remarkable increase in the surface free energy and O/C ratio. With the water vapor plasma treatment, the use of electrochemical reaction to introduce polar groups and etching to produce glue nails, were effective methods for improving the bonding performance of the WS.

Study of terahertz generation via the interaction of two-color ultra-short laser pulses with water vapor plasmas

In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, the Terahertz (THz) generation process via the interaction of a two-color ultra-short laser pulses with the water vapor gas (H2O) is examined. The background gas pressure and various laser parameters, e.g., its pulse shape, duration, and waist, are varied, and their effects on the temporal variation of the generated current density, THz electric field, and THz spectral intensity are studied. It is shown that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse. Moreover, the intensity of generated THz radiation is increased at the higher pulse durations and waists. In addition, at the higher water vapor gas pressures, the time to peak of the generated current density is shifted to the earlier moments. Finally, it is observed that, for the laser pulses with the intensities of about 8 × 1013 W/cm2, the water vapor triatomic molecules are a proper source for the THz radiation generation under the illumination of high power ultra-short two-color laser pulses.

Energy recovery from waste glycerol by utilizing thermal water vapor plasma.

Glycerol, considered as a waste feedstock resulting from biodiesel production, has received much attention in recent years due to its properties, which offer to recover energy. The aim of this study was to investigate the use of a thermal water vapor plasma for waste (crude) glycerol conversion to synthesis gas, or syngas (H2+CO). In parallel of crude glycerol, a pure glycerol (99.5%) was used as a reference material in order to compare the concentrations of the formed product gas. A direct current (DC) arc plasma torch stabilized by a mixture of argon/water vapor was utilized for the effective glycerol conversion to hydrogen-rich synthesis gas. It was found that after waste glycerol treatment, the main reaction products were gases with corresponding concentrations of H2 50.7%, CO 23.53%, CO2 11.45%, and CH4 3.82%, and traces of C2H2 and C2H6, which concentrations were below 0.5%. The comparable concentrations of the formed gas products were obtained after pure glycerol conversion-H2 46.4%, CO 26.25%, CO2 11.3%, and CH4 4.7%. The use of thermal water vapor plasma producing synthesis gas is an effective method to recover energy from both crude and pure glycerol. The performance of the glycerol conversion system was defined in terms of the produced gas yield, the carbon conversion efficiency, the cold gas efficiency, and the specific energy requirements.

Possible ways to increase the efficiency of a low-pressure water vapour discharge as a light source

Methods to increase the efficiency of a rare gas–water vapour plasma as a light source are presented: (1) the addition of a second rare gas (2) the use of titanium dioxide to enhance the decomposition of water molecules into hydroxyl and hydrogen; (3) pulse discharge operation to improve the efficiency. Analysis shows that the first two methods can yield an increase in efficiency. Use of the catalyst produced a tangible impact on plasma properties and an increase in efficiency that was experimentally observed and agrees with theoretical estimates. In pulse discharge operation, negative ions that are probably created in the afterglow phase eliminate the desired effect. The data obtained using these three approaches, point towards possible directions for further investigation and predict the expected results in case of successful implementation.