Expression of longitudinal third-order transport coefficient in terms of α parameters and its validity

The relation between the longitudinal third-order transport coefficient ω 3 contained in the continuity equation for electrons and α parameters defined by arrival-time spectra of an electron swarm is deduced. Values of ω 3 and the α parameters in CH4 gas and SF6 gas are calculated by Monte Carlo simulation, and then the values of ω 3 are compared with those of the longitudinal third-order transport coefficient ω\u273 which are calculated from the α parameters to examine the validity of the deduced relation. The values of ω\u273 are found to excellently agree with those of ω 3 below 500 Td in CH4 gas and from 150 Td to 700 Td in SF6 gas, where the values of the effective ionisation coefficient are nought or quite small. The results suggest that values of ω 3 can be obtained experimentally from arrival-time spectra measured by a double-shutter drift tube

Mechanism of pH variation and H2O2 generation in water exposed to pulsed discharge plasma

Positive and negative pulsed discharge plasma is generated above test liquid containing NaCl in Ar atmosphere, and the spatiotemporal variation of pH value in the liquid is visualized by a colorimetric method using bromothymol blue. Furthermore, polarity effects on H 2 O 2 generation are examined by electrochemical calculation and a colorimetric method using titanium sulfate. When the positive pulsed discharge plasma is generated, the pH value of the liquid is decreased by H + generation through the dissociation of H 2 O + , formed by the charge exchange reaction between Ar + and H 2 O, while the pH value of the vicinity of an earthed electrode is increased by OH - generation through the electrolysis of water. When the negative pulsed discharge plasma is generated, the pH value of the liquid is increased by OH - generation and H + reduction, respectively, through the reaction of hydrated electrons with H 2 O and H + , while the pH value in the vicinity of the earthed electrode is decreased by H + generation through the electrolysis of water. The generation of H 2 O 2 is found to be promoted when the positive pulsed discharge plasma is generated, and this increase rate of H 2 O 2 is in approximate agreement with the calculated generation rate of H 2 O 2 , which is produced from OH generated by electrolysis

Zero-dimensional chemical kinetic simulation of ROS/RNSin pulsed pulsed-discharge exposed water

The concentration variations of reactive oxygen/nitrogen species in water, such as H2O2, NO2 −, and NO3 − generated by pulsed-discharge plasma exposure, are calculated using reaction rates of chemical reactions and acid-base equilibrium in water. The calculated concentrations and pH values are in good agreement with measured data within the range where the significant changes of the measured data are observed. The rate constant for ONOOH generation is estimated to be 7.8 × 103 M−2 s−1, and this value is in good agreement with previously reported values. The generation rates of H2O2, NO2 −, and NO3 − are estimated to be 7.70 × 10−7, 4.10 × 10−7, and 1.10 × 10−7 M s−1, respectively

Computational study on silicon oxide plasma enhanced chemical vapor deposition (PECVD) process using tetraethoxysilane/oxygen/argon/helium

Plasma enhanced chemical vapor deposition (PECVD) of silicon oxide (SiO2) using tetraethoxysilane (TEOS) was investigated theoretically by developing an unprecedented plasma chemistry model in TEOS/O2/Ar/He gas mixture. In the gas phase reactions, a TEOS molecule is decomposed by the electron impact reaction and/or chemically oxidative reaction, forming intermediate TEOS fragments, i.e., silicon complexes. In this study, we assume that SiO is the main precursor that contributes to SiO2 film growth under a particular process or simulation condition. The surface reaction was also investigated using quantum mechanical simulations with density functional theory. Based on the gas and surface reaction models, we constructed a computational plasma model for SiO2 film deposition in a PECVD process. The simulation results using CHEMKIN pro and CFD-ACE + have shown that the neutral atomic O and SiO as well as the charged O2 + are the dominant species to obtain a high deposition rate and uniformity. The spatial distributions of various species in the TEOS/O2/Ar/He gas mixture plasma were shown in the study. The uniformity of deposited film due to the change in the plasma bulk property was also discussed

Hydrogen generation from greenhouse gas by discharge plasma

CH4 is decomposed by a low-pressure DC glow discharge, and partial pressures of H2 and other byproducts are measured by the mass spectrometry. The decomposition rate of CH4 and H2 conversion rate are calculated from the partial pressure, and the effects of mixed gases with CH4 on the decomposition characteristics of CH4 and H2 conversion rate are investigated. It is found that CH4 is completely decomposed in the DC glow discharge, and that 80%, 75% and 70% of hydrogen atoms contained in CH4 are converted into H2 in CH4-Ar mixture, pure CH4 and CH4-CO2 mixture, respectively. It is also found that CO, which can be used as fuel, is produced in the DC glow discharge by the decomposition of CO2 in CH4-CO2 mixture.特集 : 「資源、新エネルギー、環境、防災研究国際セミナー

Dissociative reactions induced by electron impact and electron transport in TEOS vapor

Reactions for dissociative ionization and neutral dissociation collisions between an electron and a tetraethoxysilane [Si(OC2H5)4, TEOS] molecule are reported, and neutral dissociation cross sections are calculated by applying the classical Rice–Ramsperger–Kassel theory. Detailed electron collision cross section set of TEOS vapor, including 18 neutral dissociation cross sections and 20 ionization cross sections, is constructed. Electron transport coefficients, such as the mean-arrival-time drift velocity, bulk drift velocity, longitudinal bulk diffusion coefficient, and ionization coefficient, and rate coefficients for both elastic and inelastic collisions in TEOS vapor are calculated from the present cross section set using a Monte Carlo method. The validity of the present cross section set is demonstrated by comparing the calculated electron transport coefficients with measured data. Furthermore, fragmentation of TEOS molecules by electron impact is simulated, and then the number of fragments produced in the simulation is compared with the measured mass spectra

Production of poly-3-hydroxybutyrate (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) from synthetic wastewater using Hydrogenophaga palleronii

In the present study, synthetic wastewater (SW) was used for production of poly-3-hydroxybutyrate (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) using the bacteria Hydrogenophaga palleronii. SW at various volatile fatty acids concentrations (5–60 g/l) was evaluated for the growth and biopolymer production using H. palleronii. Substrate degradation was analyzed using total organic carbon (TOC) analyzer and high pressure liquid chromatography (HPLC). H. palleronii showed highest and lowest removal of TOC at 5 g/l (88 ± 4%) and 60 g/l (15 ± 6%) respectively. Among all the concentrations evaluated, bacteria showed highest biopolymer production with 20 g/l (63 ± 5%), followed by 30 g/l (58 ± 3%) and 40 g/l (56 ± 2%). Lowest biopolymer production was observed at 5 g/l concentration (21 ± 3%). Structure, molecular weight, and thermal properties of the produced biopolymer were analyzed. These results denoted that the strain H. palleronii can be used for degradation of high concentration of volatile fatty acids persistent in wastewaters and their subsequent conversion into useable biopolymers

Decomposition Characteristics of Benzene, Toluene and Xylene in an Atmospheric Pressure DC Corona Discharge II. Characteristics of Deposited By-products and Decomposition Process

Gaseous by-products and deposited material obtained from the decomposition of benzene, toluene and xylene in an atmospheric pressure DC corona discharge were minutely investigated by gas chromatograph mass spectrometry and infrared absorption spectroscopy, and the decomposition processes of benzene, toluene and xylene were estimated. It was found that carbon dioxide (CO2), carbon monoxide (CO), formic acid (HCOOH) and formic anhydride ((CHO)2) were the major gaseous by-products from benzene, toluene and xylene, while acetic formic anhydride (CH3COOCHO) and acetic acid (CH3COOH) were the major by-products from toluene and xylene. Benzaldehyde (C6H5CHO) and methyl benzaldehyde (CH3CH4CHO) were produced from toluene and xylene, respectively. It was hypothesized that the decomposition of benzene, toluene, and xylene was initiated by the production of phenyl radicals, phenyl and benzyl radicals, and methyl benzyl and methyl phenyl radicals, respectively. These radicals are deposited on electrodes, wall, etc., resulting in the polymerization of aromatic rings and the substitution of function groups. Also, those radicals are decomposed and converted into by-products described above. In addition, it is probably that benzyl and methyl benzyl radicals are precursors of C6H5CHO and CH3C6H4CHO, respectively, and that C6H5CHO and CH3C6H4CHO are decomposed, contributing to by-product production and deposition. Furthermore, some intermediate by-products, produced by the cleavage of the aromatic ring in benzene, toluene and xylene decomposition and containing O=C-O, C=O, O-H, and C-H groups, may be deposit on the electrodes

Monitoring and evaluation of simulated underground coal gasification in an ex-situ experimental artificial coal seam system

In this study, to better simulate underground coal gasification (UCG), an artificial coal seam was constructed to use as a simulated underground gasifier, which comprised coal blocks excavated from the coal seam. This study reports the process and results of three independently designed experiments using coaxial-hole and linking-hole UCG models: (a) a coaxial model using a coaxial pipeline as a gasification channel, (b) a coaxial model using the coaxial pipeline combined with a bottom cross-hole, and (c) a linking-hole model using a horizontal V-shaped cross-hole. In the present work, the fracturing activities and cavity growth inside the reactor were monitored with acoustic emission (AE) technologies. During the process, the temperature profiles, gas production rate, and gas content were measured successively. The results show that AE activities monitored during UCG process are significantly affected by operational variables such as feed gas rate, feed gas content, and linking-hole types. Moreover, the amount of coal consumed during UCG process were estimated using both of the stoichiometric approach and balance computation of carbon (C) based on the product gas contents. A maximum error of less than 10% was observed in these methods, in which the gas leakage was also considered. This demonstrates that the estimated results using the proposed stoichiometric approach could be useful for evaluating energy recovery during UCG