Session ET4: Green Plasma Applications

Volatile organic compound-treatment in air with a surface dielectric barrier discharge array

Volatile organic compounds (VOC) are emitted in any (car) painting plant. The government regulations in many countries are based on toxicity of different VOC. Just recently, for example in Germany, the critical value for formaldehyde has been decreased to 2 mg/m3 in exhaust systems. State of the art technology in painting plants is based on thermal combustion, realized with domestic gas burners running day and night with high power ranging from several 10 up to several 100 kW. With that technology, high conversion of VOC to CO2 and water is ensured but the energy effort is large. In particular for processes where low VOC loads in air (1000 ppm) are treated, the energy efficiency of thermal burners is very low. Therefore, plasma technology provides a very interesting alternative. It is based on dielectric barrier discharge technology (DBD) but is modified to surface DBD (SDBD), to adapt it to the given tasks and boundary conditions like high throughput, small drop in pressure, scalability up to 104 m3/h and much more. In this talk, very basic investigations on SDBD for the fundamental plasma parameters are presented, the conversion efficiency of real exhaust gas in car painting plants are shown and its perspective for near future VOC plasma treatment are given.\\ \\In collaboration with Bj\"orn Offerhaus, Ruhr-University Bochum   

Electric field emission and local surface heating in plasma packed bed reactors having metal catalyst-impregnated dielectric beads

Atmospheric-pressure plasma packed bed reactors (PBRs) are being investigated for chemical conversion of gases and pollution control. Metallic catalysts added to the surfaces of the dielectric beads of PBRs increase the energy efficiency and selectivity of chemical conversion by providing additional reaction pathways. Experimental results have shown synergistic interactions between plasmas and catalyst particles, however the nature of these interactions is poorly understood. In this study, the plasma hydrodynamics modeling platform nonPDPSIM was used to simulate the interactions between micron-scale catalyst particles embedded in dielectric beads and humid-air plasma in PBRs. We found that the fluxes of excited species, ions, electrons and photons to the catalysts are focused primarily at the triple points between the metal, dielectric and gas. This effect is due to the enhancement of local electric field, which leads to an increase of the local plasma densities. As a result, the catalyst was locally heated, which could lead to increased reaction rates on the surface. The high electric field at the triple points produce field emission of electrons, which provides a preionization source or an additional source of electrons. These sources enable breakdown at lower applied voltages, therefore increasing the energy efficiency of the system.   

Optimized Nanosecond Transient Plasma Impedance Matching of cylindrical corona-plasma reactors energized by fast rising nanosecond pulses

Transient plasma requires efficient coupling or impedance matching of electrical elements to avoid plasma pulse distortion.In this presentation we review the simulation, design and experimental verification of the impedance-matching characteristics of two 13 cm diameter, 3 meters long stainless steel corona-plasma reactors with the purpose of optimizing the energy efficiency of a pulsed corona plasma system for environmental applications such as NO remediation.The reactors are fitted with multiple wire electrodes running along the axis of the two reactors.We experiment with cross sectional diameters of these multi wire electrodes and the no.of wires to arrive at the configuration that yields the greatest energy deposition and as a result, the best matching into a non-thermal plasma.For our pulse source, we use an inductive adder based unit,manufactured by Transient Plasma Systems Inc,who supplied a 7-ns rise time,50-kV pulse into a matched load with approximately 500 mJ/pulse into a matched load.The basis for our experiments was formed by calculation of the inductance and capacitance of these electrode systems to estimate the characteristic impedance of the same. These were then simulated and experimentally verified.   

Optical Measurements of OH in an Atmospheric Plasma Jet for Plasma-Based Water Purification

Plasma-based water purification has been shown to remove more chemicals, waste materials, and bacteria than traditional treatment options. This process uses energetic plasma-generated electrons to induce chemical reactions that break down harmful molecules into benign components. A plasma source was developed for this purpose. The plasma jet works by feeding a propellant gas through a tube where it is ionized and pushed out as a plasma plume. The electrons from this plume react with water molecules to produce OH radicals, which drive the purification process. Changing the power operating conditions, gas flow rate, and tube size can change the size of the plasma plume and increase OH production. Voltages were varied from 7 to 10 kV, argon and helium were used at flow rates from 1.5 to 3 SLM, and the quartz tube ranged in length from 4 to 12 cm. The production of OH radicals has been studied using Optical Emission Spectroscopy, and compared for various plasma sizes. A Princeton Instruments Acton SP2500 Spectrometer was used with a PI-Max 4 ICCD Camera and a Hamamatsu H10722-01 PMT to look at the emission spectra. Work will continue to be done to improve the understanding of these phenomena, allowing for plasma purification methods to be better designed.   

Chemical reaction by atmospheric pressure pulsed discharge plasma in capillary gas/liquid slug flow.

Non-equilibrium atmospheric-pressure plasma in gas/liquid slug flow in a capillary tube was developed. Some chemical reaction were demonstrated induced by the developed plasma system. The water containing CBB (coomassie brilliant blue R-250) dye and various gas species were used as a liquid and a gas phases. The optical emission spectra indicated that the different reactive oxidation species were generated by each gas when the pulsed discharge plasma was applied into the slug flow reactor system. The oxygen base reactive species were found abundantly by each gas phase, and the amount of them was estimated by potassium iodide-starch solution. The decoloration of CBB dye occurred by the decomposition. The UV-Vis spectrophotometer showed that the order of CBB dye decomposition rate was: oxygen \textgreater air \textgreater nitrogen \textgreater argon \textgreater helium. Silver nanoparticles were also synthesized from silver nitrate solution. To prevent agglomeration of produced nanoparticle, starch was used as a dispersant. The average particle diameter of silver was around 6 nm and 4 nm for argon and helium, respectively used as gas phase.   

Synthesis of nitrogen-based materials using nanosecond-pulsed plasma in liquid nitrogen

The application of strong electric fields in water and organic liquids has been studied for many years, because of its importance in electrical transmission processes and its practical applications in biology, chemistry, and electrochemistry. More recently, liquid-phase electrical discharges have been investigated, and are being developed. Here we present the first results on characterization and diagnostics of nanosecond-pulsed discharge in liquid nitrogen and characterization of produced materials. * This work is supported by the Army Research Office (grant {\#} W911NF-17-1-0597, PI: Dobrynin).   

Removal of siloxanes from landfill gases with the application of dielectric barrier discharge plasma

Utilization of landfill gas as renewable energy has been a topic of major interest since it is rich in methane. However, this gas also contains organosilicate compounds: volatile methyl siloxanes (VMS) as a contaminant. Oxidation of VMS forms silicates that erode both engines and environment. Present methods of VMS removal: activated carbon filters, silica gel, alumina and other adsorbents suffer from limited regeneration capability, low adsorption capacity, and recycling needs. In this study, a typically dominant VMS, D4 (C$_{\mathrm{8}}$H$_{\mathrm{24}}$O$_{\mathrm{4}}$Si$_{\mathrm{4}})$, was removed by application of dielectric barrier discharge (DBD) plasma. D4 siloxane was bubbled into a helium carrier gas stream and passed through an annulus DBD reactor. GCMS analysis of the treated gas stream showed traces of CO and CH$_{\mathrm{4}}$ implying dissociation of Si-C bonds. A white solid residue was also found to deposit on reactor walls. X-ray photoelectron spectroscopy and two-dimensional NMR spectroscopy confirmed the residue to be polydimethylsiloxane, suggesting that DBD plasma had polymerized D4 in contrast to completely dissociating. Further study is underway to provide valuable insight into how bond scission of D4 can be further propagated.