Hajime Kabashima

Involvement of catalyst materials in nonthermal plasma chemical processing of hazardous air pollutants

Abstract Catalytic effects of metal oxides in nonthermal plasma chemical processing of hazardous air pollutants (HAPs) are discussed, relevant to their activities for the oxidation of HAPs in nonthermal plasma media and their selective control of active oxygen species derived from background O2. In ferroelectric packed-bed reactors, the oxidation power of barium titanate (BaTiO3) is not strong enough to oxidize HAPs and their carbon intermediates to CO2. Only nitrous oxide (N2O) was formed from background N2 and lattice oxygen atoms in BaTiO3. The catalytic effect of BaTiO3 is negligible under aerated conditions. On the other hand, ozone (O3) is formed from background O2 in much higher concentrations in a silent discharge plasma reactor. Manganese dioxide (MnO2)-catalyzed decomposition of O3 promotes decomposition of benzene, which is less reactive than trichloroethylene and tetrachloroethylene. The acceleration of benzene consumption rate is ascribed to the promotion of its oxidative decomposition by the triplet oxygen atom. Catalytic control of in situ active oxygen species could be one of the most effective approaches to increase the energy efficiency of the nonthermal plasma reactor and to achieve the complete oxidation of the carbon atoms in HAPs.

Effective combination of nonthermal plasma and catalysts for decomposition of benzene in air

Abstract The effective combination of plasma energy and solid surface properties, such as catalysis and adsorption, was investigated using packed-bed type catalyst–hybrid and adsorbent–hybrid reactors that were packed with a mixture of BaTiO 3 pellets and other ceramic pellets (catalyst or adsorbent). The plasma reactor that employed catalysts indicated improvement in CO 2 selectivity and suppression of N 2 O formation compared with the reactor that was packed with BaTiO 3 alone. It was also found that the catalysts and adsorbents in the plasma reactor were useful in enhancing energy efficiency. Furthermore, the catalyst and adsorbent positions in the plasma reactor were very important for induction of surface reactions on the packed materials.

Hydrogen generation from water, methane, and methanol with nonthermal plasma

Hydrogen generation from water, methane, and methanol was investigated with different types of nonthermal plasma reactors under different conditions. With a ferroelectric packed-bed reactor in N/sub 2/, hydrogen gas yield decreased in the order: methanol>methane>water. A similar trend was observed with a silent discharge plasma reactor, but substrate conversions were much lower with the latter reactor. At fixed specific energy densities, higher H/sub 2/ yields were obtained at higher gas flow rates in the reactions of the above substrates. The initial water concentration was optimized at ca. 2.0% to obtain the largest H/sub 2/ amount. Background O/sub 2/ suppressed H/sub 2/ yield. The ferroelectric packed-bed reactor could be operated continuously for 10 h without any decrease in H/sub 2/ yield.

Effects of reactor type and voltage properties in methanol reforming with nonthermal plasma

Reactor type and voltage properties affected the reforming behavior of 1% methanol in N/sub 2/ with nonthermal plasma. Methanol conversion increased with voltage frequency for both a ferroelectric packed-bed reactor (FPR) and a silent discharge reactor (SDR), but they showed different sensitivities to frequency change at fixed applied voltages. In the frequency range of 5 Hz-5 kHz, methanol conversion was expressed as a function of reactor energy density irrespective of the reactor type. Regarding the effect of voltage waveform with 50-Hz ac at the same applied voltage levels for FPR and SDR, methanol conversion decreased in the order: triangle>sine>square. H/sub 2/, CO, and CO/sub 2/ were obtained as the major products, and similar product distributions were observed in comparable methanol conversions irrespective of reactor type and the differences in frequency and waveform. Energy conversion efficiency increased to 40%/spl sim/60% at /spl sim/80% of MeOH conversions for FPR and SDR.

Synthesis Gas Production from CO2 and H2O with Nonthermal Plasma

ABSTRACT: Synthesis gas was produced from CO 2 and H 2 O with nonthermal plasma. A ferroelectric packed-bed reactor worked much better than a silent discharge plasma reactor. CO 2 and H 2 O competitively reacted to give CO and H 2 , respectively. Arbitrary molar ratios of H 2 to CO were obtained by controlling that of H 2 O to CO 2 . Energy conversion efficiency decreased with water content, and its maxima were observed in its functions of reactor energy density.

Steam reforming of aliphatic hydrocarbons with nonthermal plasma

Steam reforming of aliphatic hydrocarbons such as methane, ethane, propane, and neopentane was investigated with two types of barrier discharge plasma reactors. With a ferroelectric packed-bed reactor ( FPR) in N/sub 2/, almost the same conversions were obtained for ethane, propane, and neopentane, but methane was less reactive than these hydrocarbons. Hydrogen gas yield decreased in the order: methane/spl ap/ethane>propane>neopentane. The molar ratio of H/sub 2/ to CO {[H/sub 2/]/[CO]} exceeded 3.5 for all the hydrocarbons. [H/sub 2/]/[CO] did not change in the range of H/sub 2/O content from 0.5% to 2.5%. At the volumetric ratio of H/sub 2/O to Hydrocarbon=2.0, carbon balances were poor for ethane, propane, and neopentane, but almost all of the carbon atoms in the reacted methane were recovered as CO and CO/sub 2/. The mole fractions of CO and CO/sub 2/ depended on the chemical structures of the substrate hydrocarbons. It is considered that the water-gas-shift reaction proceeds backward for the reaction systems of the hydrocarbons with higher hydrogen atom densities per molecule. FPR maintained the same performance for 10 h in the steam reforming of methane. The efficiency of a silent discharge plasma reactor was much lower than that of FPR.

Steam reforming of hydrocarbons with nonthermal plasma

Steam reforming of methane, ethane, propane and neopentane was investigated with two types of nonthermal plasma reactors. With a ferroelectric packed-bed reactor (FPR) in N/sub 2/, almost the same conversions were obtained for ethane, propane and neopentane, but methane was less reactive than these hydrocarbons. Hydrogen gas yield decreased in the order: methane/spl ap/ethane>propane>neopentane. The molar ratio of H/sub 2/ to CO {[H/sub 2/]/[CO]} exceeded 3.5 for all the hydrocarbons. [H/sub 2/]/[CO] did not change in the range of H/sub 2/O content from 0.5% to 2.5%. At the volumetric ratio of H/sub 2/O to Hydrocarbon=2.0, carbon balances were poor for ethane, propane, and neopentane, but almost all of the carbon atoms in the reacted methane were recovered as CO and CO/sub 2/. The selectivities of CO and CO/sub 2/ depended on the chemical structures of the substrate hydrocarbons. It is considered that the water-gas-shift reaction proceeds backward for the reaction systems of hydrogen-rich hydrocarbons. FPR maintained the same performance for 10 h in the steam reforming of methane. The efficiency of a silent discharge plasma reactor was much lower than that of FPR.