Hidetoshi Sekiguchi

Steam plasma reforming using microwave discharge

Abstract The purpose of the study was to prepare atmospheric pure-steam plasma using a microwave discharge and to apply the plasma to the reforming of hydrocarbon for hydrogen production. The experiment was conducted with 2.45-GHz microwave power supply with a special wave-guide designed elsewhere. The results showed that the pure steam plasma could be stably sustained, and analysis of emission spectra indicated that O, H and OH existed in the plasma. Hexane, as a model of gasoline, was used for the hydrocarbon reforming experiment. The results showed that H 2 and CO were predominantly produced, as suggested from equilibrium calculations, and that reforming could be accomplished. The conversion of hexane and steam was affected by the plasma power, and the ratio and total flow rate of the reactants. A fuel-cell power system including the steam plasma reformer was evaluated from experimental data and the results suggested that improvements are required for practical use of the plasma reforming method.

Surface modification of adsorbents by dielectric barrier discharge

Granular activated carbon was treated by oxygen non-thermal plasma to improve its adsorbability for metal ions. The plasma was produced by dielectric barrier discharge under atmospheric pressure. The results of characterization of activated carbon showed that its surface area was decreased, and the concentrations of acidic functional groups at the surface were increased by the treatment. Adsorbability was examined changing the initial pH of the solution containing a metal ion. The saturated adsorption amount of Cu and Zn ion was increased considerably by the treatment. The plasma treatment of activated carbon was concluded as an effective method for improvement of adsorbability.

Thermal plasma decomposition of chlorofluorocarbons

Dichlorodifluoromethane was decomposed by a thermal argon plasma generated by a DC are discharge. The experiments and the kinetic calculations showed that the complete decomposition of the chlorofluorocarbon proceeded with the simultaneous additions of hydrogen and oxygen. Both the expertimental and calculated results confirmed that it is favorable, for the decomposition, not to quench the products but to add an excess of hydrogen over the stoichiometric amount, which leads to a reduction in chlorine formation.

Enhancement of the deposition rate of TiO2 film in radio frequency reactive sputtering

Titanium oxide thin films were prepared using rf reactive sputtering in which a titanium target was sputtered in a mixture of Ar and reactive O2 gas. The flow modulation of reactive gas was proposed to enhance the deposition rate of the film which is generally low in continuous flow reactive sputtering. The experimental results indicated that the deposition rate could be enhanced maintaining the film stoichiometric ratio of TiO2. The enhancement occurred because the modulated flow appeared to reduce the formation of compounds on the target surface which inhibit sputtering under continuous flow conditions. The effects of the flow modulation were understood by adapting a reactive sputtering theoretical model.

Computational modeling of reactive gas modulation in radio frequency reactive sputtering

Computer simulation of reactive sputtering was carried out to explain the enhancement of the deposition rate of complete oxide film using reactive gas flow modulation. The model dealt with the preparation of TiO2 film with a titanium target and oxygen in rf reactive sputtering. The computed results showed good agreements with the experimental data obtained in our previous work. The effects of the flow modulation were elucidated with the calculated timewise variations for partial oxygen pressure and target coverage. The effects of modulation patterns were also evaluated using the simulation.

Thermal quenching effects on plasma synthesis of NO and plasma decomposition of CO2

Effects of the thermal quenching process in the synthesis of NO and the decomposition of CO2 were studied using a thermal argon plasma and different-i.d. cooling tubes. Four tubes of different i.d.s were used to change the cooling rate. The conversions obtained in both reactions increased with decreasing quenching tube diameter. Furthermore, the concept of quenching temperature was introduced. This temperature was obtained from two time constants of reaction and cooling rate. The conversions into CO can be estimated in a similar manner to the NO synthesis with a proper modification for radicals which remain at high concentrations at the quenching temperature.

Decolourisation of dye solution using an electrical discharge with TiO2 suspension

An electrical discharge in water with TiO2 suspension has been applied for the decolourisation of methyl orange as a model of dye. The results showed the decolourisation was successful in the reactor. The increase in the flow rate of gas injection enhanced the decolourisation rate. Oxygen injection had a stronger influence when compared with Ar injection. The suspension of TiO2 improved the decolourisation. The results suggested the plasma-assisted three-phase reactor had a promising possibility to treat various kinds of wastewater.

Microwave Torrefaction of Moist Municipal Solid Waste (MSW) Pellets with the Addition of Char from Agricultural Residues

An investigation of the effect of the addition of char from agricultural residues on the torrefaction of moist municipal solid waste (MSW) pellets (40 wt.% moisture) was carried out in a microwave oven (500-800 W for 4-12 minutes). Char from agricultural residues, including corncob, palm shell, straw, and bagasse, was used as the microwave absorbers to enhance the absorption of microwave irradiation. It was found that the addition of char from bagasse yielded the lowest remaining mass (or mass yield) and volatile matter (VM) content, but the highest temperature and heating value, of the torrefied MSW pellet. Moisture in the MSW pellet with or without the addition of microwave absorber was completely removed after being torrefied for 8-12 minutes. The VM contents remained in the MSW pellets with the addition of microwave absorbers were lower than that in the MSW pellet without the addition of microwave absorber. The addition of microwave absorbers led to an increase in carbon (C) content but a decrease in oxygen (O) content of the torrefied MSW pellets, compared to those of the raw MSW pellet. The heating values of the torrefied MSW pellets with the addition of microwave absorbers were equivalent to that of sub-bituminous coal, enhanced from that of the raw MSW pellet, which was lower than that of lignite.