Plasma Chemistry and Plasma Processing (v.29, #5)

Characteristics of Multi-Phase Alternating Current Arc for Glass In-Flight Melting by Yaochun Yao; Kazuyuki Yatsuda; Takayuki Watanabe; Tsugio Matsuura; Tetsuji Yano (333-346).
An innovative in-flight melting technology with multi-phase AC arc was developed for glass industry. The enthalpy probe and high speed video camera were used to characterize the temperature, velocity, and discharge behavior of multi-phase AC arc. The effects of input power and sheath gas flow rate on arc and melting behavior were investigated. Results show that the temperature and velocity on arc center are increased with input power or sheath gas flow increase. The fluctuation of luminance area ratio and coefficient of variation reflects the change of arc discharge behavior. High temperature of plasma enhances the melting of granulated raw particles during in-flight heating treatment. The shrinkage of particle and the volatilization degree of Na2O increase under a larger flow rate of sheath gas. The characterized arc behavior agrees with the melting behavior of glass raw materials, which can provide valuable guidelines for the process control of glass melting.
Keywords: Multi-phase AC arc; Characteristic; Enthalpy probe; Arc discharge; Glass in-flight melting

Towards a Consistent Chemical Kinetic Model of Electron Beam Irradiation of Humid Air by Karen L. Schmitt; D. M. Murray; Theodore S. Dibble (347-362).
A chemical kinetic model has been assembled based upon previous literature to assist in developing a better understanding of the mechanism behind the electron beam irradiation of humid air. Thermodynamic determination of the feasibility of particular product sets was used to eliminate certain reactions proposed previously, dynamical models were used to guide the choice of product sets, and updated rate constants were obtained from the current literature. Tracers were also used to determine significant sources and sinks of hydroxyl radical, an important species in the irradiation process. Modeling results for selected species have been presented for 1 atm of air at 298.15 K and 50% relative humidity, at doses of 1, 5, 10, 25, and 50 kGy delivered over 0.8 s. The concentrations of the most abundant ions, radicals, and stable reaction products have been included, as well as the calculated major sources and sinks of hydroxyl radical.
Keywords: Electron beam; Gas phase kinetics; Radicals; Ionic clusters; Anion–cation reactions

Destruction of Freon HFC-134a Using a Nozzleless Microwave Plasma Source by Mariusz Jasiński; Mirosław Dors; Jerzy Mizeraczyk (363-372).
In this paper, results of the pyrolysis of Freon HFC-134a (tetrafluoroethane C2H2F4) in an atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to produce plasma for the destruction of Freon HFC-134a. The processed gaseous Freon HFC-134a at a flow rate of 50–212 l min−1 was introduced to the plasma by four gas ducts which formed a swirl flow in the plasma reactor (a quartz cylinder). The absorbed microwave power was 0.6–3 kW. The experimental results showed that the Freon was converted into carbon black, hydrogen and fluorine. The total conversion degree of HFC-134a was up to 84% with selectivity of 100% towards H2, F2 and C2, which means that there was no conversion of HFC-134a into other hydrocarbons. The Freon destruction mass rate and corresponding energetic mass yield were up to 34.5 kg h−1 and 34.4 kg per kWh of microwave energy absorbed by the plasma, respectively.
Keywords: Microwave plasma; Freon destruction; Hydrocarbons

A pilot-scale pulse corona induced plasma chemical process (PPCP) reactor for controlling gas-phase dioxins and NO x simultaneously is installed in a garbage incineration plant. The flow rate of the sampled flue gas is 5,000 Nm3/h (N: standard state) in maximum at the PPCP reactor, which consists of 22 wire-cylinder electrodes and is energized by a 50 kW nanosecond pulse high voltage generator. With an applied plasma energy density of 2.9–6.1 Wh/Nm3, the decomposition efficiency for dioxins is 75–84% based on TEQ (toxic equivalents); the conversion efficiency of NO to NO2 is ~93% at maximum. The flue gas treated by the PPCP reactor is introduced at a rate of 50 Nm3/h to a wet-type chemical reactor, which uses an aqueous solution of sodium sulfite (Na2SO3). More than 90% of NO x is reduced to nitrogen, with negligible byproducts such as NO2 or NO3 ions left in the solution.
Keywords: Nonthermal plasma; Flue gas; Garbage incinerator; Dioxins; NO x ; High voltage pulse; Chemical scrubber; Sodium sulfite

An approach for polymerization to produce polymethylmethacrylate (PMMA) was developed, in which the reaction was initiated by the glow discharge electrolysis (GDE) rather than chemical initiators. The highest number-average molecular weight (M n) and the lowest polydispersity index (PDI) of the resulting polymer were 1.12 × 106 g/mol and 1.21, respectively. The following parameters such as the applied voltage, discharge time, the content of methylmethacrylate (MMA), the amount of a suspension stabilizer (polyvinyl alcohol), polymerization temperature and time were examined in detail, which could affect the conversion, molecular weight and polydispersity index. The M n and PDI of polymer can be monitored by changing the discharge parameters and polymerization conditions. PMMA was characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), cold field emission scanning electron microscopy (FESEM), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). Results indicate that using the GDE technique to initiate the polymerization reaction is successful, because the product obtained has the same properties with one obtained by chemical method, for example, in chemical structure, tacticity and thermal stability. Moreover, the polymer particles for the former are smaller than the latter. The kinetic observation was that the polymerization of MMA initiated by the GDE plasma obeys the first order of reaction with an obvious induction period.
Keywords: Glow discharge electrolysis plasma; Polymethylmethacrylate; Tacticity; Thermal stability; Polymerization kinetics

Plasma-Aided Cotton Bioscouring: Dielectric Barrier Discharge Versus Low-Pressure Oxygen Plasma by Qiang Wang; Xue-Rong Fan; Li Cui; Ping Wang; Jing Wu; Jian Chen (399-409).
The hydrophobic cuticle of the cotton fiber has formed a natural barrier for pectinase to catalyze its substrates (pectins beneath the cuticle), thus resulting in an insufficient scouring for cotton. Two plasma-based treatments, dielectric barrier discharge (DBD) at atmospheric pressure and cold oxygen plasma at low pressure in a vacuum system, were used as the pretreatments prior to cotton bioscouring, aiming at increasing the accessibility of pectinases to the pectic substances on the cotton fiber. The effects of different processing parameters of DBD and oxygen plasmas on the wettability, whiteness and burst strength of pectinase-scoured cotton were determined and compared. Although both of the pretreatments could enhance cotton bioscouring, DBD might be more suitable for current bioscouring due to its continuous processing mode and lower requirements to the equipment.
Keywords: Cotton; Bioscouring; Dielectric barrier discharge; Low-pressure oxygen plasma; Pectinase; Enzyme