Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session WF3: Environmental and Energy Applications |
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Chair: Jiang Chunqi, Old Dominion University Room: Oakmont Junior Ballroom |
Friday, November 10, 2017 10:00AM - 10:15AM |
WF3.00001: Upgrading Biomass into Higher Value Chemicals by Using Low Temperature Plasma Elijah Thimsen, Yu Gao, Necip Uner, James Meyer, Marcus Foston Low temperature plasmas (LTP) have been successively progressing into a general tool for solids processing. In this study, we focus on the interaction of a radio frequency low temperature plasma with a morphologically and chemically complex substrate: lignocellulosic biomass (i.e. switchgrass). As an alternative to conventional thermal decomposition for converting biomass into higher value products, we propose a new type of reactor based on LTP. LTP is intriguing for the conversion of biomass into higher value products because the nonequilibrium environment may provide selectivity that is unfavorable in thermal processes. Preliminary experiments on switchgrass in an argon/hydrogen plasma show promising reaction rates and a relatively narrow product spectrum. The solid feedstock is directly converted into simple hydrocarbons that are deoxygenated (e.g. C$_{\mathrm{2-4}}$H$_{\mathrm{x}})$ with high mass yield of approximately 8{\%}. The plasma process does not require precious metal catalysts to perform the conversion, a feat that is nearly impossible in a single step by conventional thermal methods. A study of the effects of gas composition, power density, pressure and biomass feedstock on final product distribution will be presented. [Preview Abstract] |
Friday, November 10, 2017 10:15AM - 10:30AM |
WF3.00002: Effective species in ignition processes of premixed burner flame with superposition of dielectric barrier discharge K. Sasaki, Y. Deguchi We have identified the most effective species in the plasma-assisted ignition of a premixed burner flame by comparing the propagation speed of the flame kernel with the densities of radicals. The candidate radicals were OH and atomic oxygen. The spatial distributions of densities of OH and atomic oxygen were measured by (two-photon absorption) laser-induced fluorescence spectroscopy. The propagation speed of the flame kernel was measured by shadowgraph imaging. It was observed that the flame kernel in the bottom part, which was located at a closer distance from the exit of the afterglow gas from a dielectric barrier discharge, had a higher propagation speed than the top part. The spatial distribution of the OH density was gentle, and we did not find significant difference in the OH density at the bottom and top parts of the flame kernel. On the other hand, the density of atomic oxygen had a steeper distribution, and the density at the top part of the flame kernel was much lower than that at the bottom. On the basis of these experimental results, we have concluded that atomic oxygen is more effective than OH radical in the ignition of the premixed burner flame. [Preview Abstract] |
Friday, November 10, 2017 10:30AM - 10:45AM |
WF3.00003: Combined experimental and modeling study of direct plasma conversion of methane Joseph Toth, Xiaozhou Shen, Daniel Lacks, R. Mohan Sankaran The direct conversion of methane without oxidizing chemistry is desired to avoid COx species and produce hydrogen or higher order hydrocarbons. However, the methane molecule is difficult to dissociate by thermal energy alone and tends to coke and inactivate catalysts. Here, we studied atmospheric-pressure, non-equilibrium plasmas for the direct conversion of methane. A key contribution of our work is that the discharge was spatially confined to decouple power and volume effects on methane conversion. In support of experimental results, a microkinetic model was developed, solving 352 elementary reactions involving 36 species including neutrals, ions, and radicals that takes into consideration both spatial and temporal dependencies of the filamentary behavior. Our results show that while methane conversion increases with increasing plasma power, it is relatively independent of volume. Since volume is controlled, these trends reflect the importance of power density. The product distributions are a stronger function of power at small volumes, with a tendency to form hydrocarbons at lower volumes and powers, and hydrogen and solid carbon at higher volumes and powers. [Preview Abstract] |
Friday, November 10, 2017 10:45AM - 11:00AM |
WF3.00004: Plasma Conversion to Electrify Chemical Industry Gerard van Rooij, Dirk v.d. Bekerom, Nicola Gatti, Teofil Minea, Srinath Ponduri, Qin Ong, Waldo Bongers, Richard v.d. Sanden A promising option to mitigate intermittency and to achieve sector integration is plasma synthesis of chemicals and artificial fuels using sustainable energy. This is illustrated on basis of a common microwave reactor approach that is evaluated experimentally with laser Rayleigh and Raman scattering and Fourier transform infrared spectroscopy. For example, 50{\%} energy efficiency was observed in pure CO2 (forming CO and O2) in a thermodynamic equilibrium conversion regime governed by gas temperatures of \textasciitilde 3500 K. These results are interpreted on basis of Boltzmann solver based plasma dynamics estimates, indicating that intrinsic electron energies are higher than what is favorable for preferential vibrational excitation. Pulsed experiments (1-5 kHz) in which gas temperature dynamics are revealed confirm this picture. In pure N2, vibrational temperatures are observed in excess of 10000K and up to five times higher than the gas temperature. Overpopulation of higher levels is confirmed. These observations are promising in view of economic localized production of fertilizer. An outlook is given to novel reactor approaches that tailor the plasma dynamics to optimally promote vibrational excitation and to achieve the desired non-equilibrium. [Preview Abstract] |
Friday, November 10, 2017 11:00AM - 11:30AM |
WF3.00005: Peroxynitric acid (HOONO$_{\mathrm{2}})$ is the key chemical species of plasma-treated water for effective and safety disinfection Invited Speaker: Katsuhisa Kitano For the plasma disinfection of human body, sterilization in liquid is crucial. We found that the plasma-treated water (PTW) has strong bactericidal activity under low pH. Physicochemical properties of PTW is discussed based on chemical kinetics. Lower temperature brings longer half-life, and the bactericidal activity can be kept by cryopreservation. High performance PTW, corresponding to the disinfection power of 22 log reduction (\textit{B. subtilis} spore), can be obtained by special plasma system with cooling. This is equivalent to 65{\%} H$_{\mathrm{2}}$O$_{\mathrm{2}}$ and 14 {\%} NaClO, which are deadly poison. But, it is deactivated soon at higher temperature (4 sec. at body temp.), and toxicity seems low. Many researchers are interested in this area of PTW, where the waters are treated by their original devices. For scientific approach, we should discuss based on chemical species. Although PTW contains many chemical components, respective chemical components were separated by ion chromatography (IC). To examine the bactericidal activities of respective components, bactericidal assays were done with respective fractions of eluate. In addition to peaks of H$_{\mathrm{2}}$O$_{\mathrm{2}}$, NO$_{\mathrm{2}}^{\mathrm{-}}$ and NO$_{\mathrm{3}}^{\mathrm{-}}$, a specific peak was detected and only this fraction had bactericidal activity. This means that active ingredient was successfully purified. Moreover, molecular nitrogen was required both in the ambient gas and in the distilled water used to prepare the PTW. We, therefore, propose that the reactive molecule in PTW with bactericidal effects is not a free reactive oxygen species but nitrogen atom-containing molecules that release O$_{\mathrm{2}}^{\mathrm{-}}$\textbullet , such as HOONO (peroxynitrous acid) or HOONO$_{\mathrm{2}}$ (PNA: peroxynitric acid). Considering the activation energy for degradation, we assumed that PNA is active ingredient. From IC analysis of chemical synthesized PNA, a same specific peak was seen. So we conclude that PNA is a key chemical species of cryo-preserved PTW with the reduced-pH method, while there is no report about sterilization by PNA. [Preview Abstract] |
Friday, November 10, 2017 11:30AM - 11:45AM |
WF3.00006: Modelling nitrogen fixation by electron-beam sustained discharges Miles M. Turner Nitrogen fixation is a plasma application recently attracting renewed interest. Nitrogen is an essential biochemical. However, atmospheric nitrogen is almost inert, so that nitrogen is scarce in the biosphere, and access to nitrogen is a major limiting factor on plant growth, and hence agricultural productivity. Converting atmospheric nitrogen into biologically useful forms such as nitrates is known as nitrogen fixation. Artificial nitrogen fixation is now achieved by a fossil fuel powered process (Haber-Bosch). Continued use of this method is likely unacceptable on environmental grounds, and alternatives are consequently being sought. A plasma process driven by electricity from renewable resources is an alternative. Major challenges in this context include reaching acceptable efficiency, and operating on a sufficiently large scale. Electron-beam sustained discharges are a promising avenue, since they offer to produce large volume plasmas at atmospheric pressure under closely controlled conditions. This paper will discuss a modelling study investigating the operation of such discharge for nitrogen fixation. We will show that energy efficiency close to Haber-Bosch appears possible (with appreciable uncertainty, however). [Preview Abstract] |
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