Shigeru Futamura

Byproduct identification and mechanism determination in plasma chemical decomposition of trichloroethylene

Plasma chemical behavior of trichloroethylene (TCE) was investigated with a packed-bed ferroelectric pellet reactor and a pulsed corona reactor. Volatile byproducts were identified by gas chromatography and mass spectrometry (GC-MS), and it was shown that reactor type, TCE concentration, flow rate, background gas, and moisture affected TCE decomposition efficiency and product distribution. Byproduct distributions in nitrogen and the negative effect of oxygen and moisture on TCE decomposition efficiency show that TCE decomposition proceeds via initial elimination of chlorine and hydrogen atoms, the addition of which to TCE accelerates its decomposition. Active oxygen species like OH radical is less likely involved in the initial step of TCE decomposition in plasma. Triplet oxygen molecules (/sup 3/O/sub 2/) scavenge intermediate carbon radicals derived from TCE decomposition to give much lower yields of organic byproducts.

Mechanisms for formation of inorganic byproducts in plasma chemical processing of hazardous air pollutants

Plasma chemical behavior of hazardous air pollutants (HAPs) (Cl/sub 2/C=CCl/sub 2/, Cl/sub 2/C=CHCl, Cl/sub 3/C-CH/sub 3/, Cl/sub 2/CH-CH/sub 2/Cl, CH/sub 3/Cl, CH/sub 3/Br and benzene), their molecular probes (CH/sub 4/, CH/sub 3/-CH/sub 3/, and CH/sub 2/=CH/sub 2/), and carbon oxides (CO/sub x/) was investigated with a ferroelectric packed-bed plasma reactor to obtain information on the formation of CO/sub x/ and N/sub 2/O. It has been shown that the oxidation of CO to CO/sub 2/ is a slow reaction in plasma, and that CO and CO/sub 2/ mainly result from different precursors. Simultaneous achievement of complete oxidative decomposition of HAPs in plasma and recovery of CO as a chemical feedstock could be favorable. The process of N/sub 2/O formation is affected by HAP structures and oxygen concentration. In the decomposition of olefinic HAPs, such as Cl/sub 2/C=CCl/sub 2/ and Cl/sub 2/C=CHCl, high-power short-residence-time operations are effective in suppressing N/sub 2/O formation. In the cases of CH/sub 3/Cl and CH/sub 3/Br, low specific energy density operations could be necessary to reduce N/sub 2/O concentrations. The yields and selectivities of CO, CO/sub 2/ and N/sub 2/O change drastically by adding only 2% of oxygen to N/sub 2/, and oxygen concentration is not a good factor to control these inorganic oxides.

Factors and intermediates governing byproduct distribution for decomposition of butane in nonthermal plasma

Plasma chemical decomposition of butane was investigated with a ferroelectric parked-bed plasma reactor to obtain the information on the fundamental chemical processes occurring in nonthermal plasma. It has been shown that butane decomposition efficiencies are higher in nitrogen rather than in air. This fact suggests that energy transfer from hot electrons to butane is mainly responsible for the initial decomposition of butane. Nitrogen incorporation was observed for acetonitrile only in dry nitrogen and for nitromethane in air. Barium titanate and water have been shown to act as monooxygen transfer agents in nitrogen. Lattice oxygen atoms in barium titanate can be consumed in the formation of N/sub 2/O and CO, depending on reaction conditions. Water is much more reactive than barium titanate as an oxidant in nonthermal plasma, and it can oxygenate butane to butanols, epoxidize 1- and 2-butenes, and oxidize CO to CO/sub 2/. Water, which has a dichotomic nature regarding oxygenation/hydrogenation in plasma, can act as a hydrogen source toward alkyl radicals formed in the initial decomposition of butane. In air, triplet oxygen molecules are the most reactive oxygen source in the presence or absence of water and carbon balance can be improved with suppression of byproducts due to promoted autoxidation processes.

Behavior of N/sub 2/ and nitrogen oxides in nonthermal plasma chemical processing of hazardous air pollutants

Nonthermal plasma chemical behavior of N/sub 2/-O/sub 2/ mixed gases and nitrogen oxides such as N/sub 2/O, NO, and NO/sub 2/ was investigated to obtain baseline information on the generation of active oxygen species and the formation of inorganic byproducts in the nonthermal plasma chemical processing of hazardous air pollutants (HAPs) with a ferroelectric packed-bed reactor. Ozone concentrations were too low, even in air, to oxidatively decompose 300-1000 ppm of HAPs. The O/sub 2/ concentration in N/sub 2/-O/sub 2/ was the determining factor in the formation of all the nitrogen oxides. N/sub 2/O formation was enhanced with increases in O/sub 2/ concentration and in specific energy density, while a threshold value was observed at around 5% of O/sub 2/ concentration in the formation of NO and NO/sub 2/. Rate-suppressing effect by O/sub 2/, detailed byproduct analyses, and thermochemical data suggest that NO/sub x/ decomposes in its reactions with nitrogen atoms derived from N/sub 2/ dissociation, and that the unimolecular N-O cleavage predominantly occurs for N/sub 2/O. The behavior of nitrogen oxides and their precursors was not affected by hydrogen atoms evolved from hydrogen-rich HAPs such as ethylene and benzene. Halogenated HAPs enhanced NO/sub x/ formation and NO/sub 2/ selectivity. Different additive effects of chlorinated and brominated HAPs were observed in the formation of NO/sub x/ and N/sub 2/O, indicating the involvement of different active oxygen species.

Nonthermal Plasma Chemical Processing of Bromomethane.

Nonthermal plasma chemical decomposition of bromomethane (CH3Br) was investigated with a coaxial type packed-bed plasma reactor. It has been demonstrated that plasma chemical processing is an effective approach to decompose CH3Br in a wide concentration range. It has been shown that CH3Br decomposition reactivity depends on reactor operating factors such as background gas, O2 concentration, and humidification. Higher decomposition efficiencies can be obtained in dry N2. However, organic byproducts such as BrCN are concurrently produced under deaerated conditions. Water suppresses CH3Br decomposition and also affects the yields of COx (CO and CO2) and organic byproducts due to the involvement of some active species generated from water. The presence of O2 retards CH3Br decomposition by quenching high-energy electrons, while it suppresses organic byproducts and improves COx yield. The reacted carbons in CH3Br are recovered as COx almost quantitatively in air. Higher CO2 selectivities cannot be achieved by increasing O2 concentration. NOx formation, which is accompanied by CH3Br decomposition, can be effectively suppressed by decreasing O2 concentration down to 2%. Furthermore, reaction mechanisms are discussed by comparing the reactivities of CH3Br and its congeners.

Nonthermal Plasma Processing for Controlling Volatile Organic Compounds

Power consumption and byproducts analysis are two key issues that users must address in determining which nonthermal plasma technology is the most appropriate for certain applications. We compared the operating characteristics and power consumption for scaled-up nonthermal plasma devices: pulsed-corona, packed-bed, silent corona, and surface discharge plasma technologies. Advantages and disadvantages of each nonthermal plasma technology are discussed. Understanding of plasma chemistry or byproducts is also essential for the development of nonthermal plasma technologies. Plasma chemical reactions of trichloroethylene (TCE) and alkyl acetates were investigated using pulsed-corona and packed-bed reactors. The effects of excited electrons, background gas, moisture, and reactor-dependent phenomena on product distribution and chemical interaction were studied. The initial step of plasma chemical decomposition of TCE can be ascribed to the electron attachment (not to active oxygen species or OH radicals), followed by homolysis and/or heterolysis reactions. Extremely high decomposition of TCE was obtained in nitrogen. Byproduct formation was significantly suppressed under aerated conditions. Alkyl acetate decomposition was affected by reactor type and alkyl chain length.

Towards understanding of VOC decomposition mechanisms using nonthermal plasmas

Plasma chemical reactions of trichloroethylene (TCE), alkyl acetates and butane were carried out with pulsed corona and packed-bed reactors in order to get insight into the effects of reactor geometry, input energy and background atmosphere on the VOC (volatile organic compounds) reactivities. Extremely high decomposition efficiency of TCE was obtained in nitrogen, and under aerated conditions, byproduct formation was suppressed. Water depressed TCE decomposition efficiency. The initial step of plasma chemical decomposition of TCE can be ascribed to the electron attachment followed by homolysis and/or heterolysis. As for alkyl acetate decomposition, its decomposition efficiency was affected by reactor geometry and alkyl chain length. Comparable decomposition efficiencies of butane were obtained as for butyl acetate under the similar conditions, suggesting the plausible decomposition of the alkyl moiety in the alkyl acetates.

Behavior of N 2 and nitrogen oxides in plasma chemical processing of hazardous air pollutants

Plasma chemical behavior of N/sub 2/-O/sub 2/ mixed gases and nitrogen oxides such as N/sub 2/O, NO, and NO/sub 2/ was investigated to obtain baseline information on the generation of active oxygen species and the formation of inorganic byproducts in plasma chemical processing of hazardous air pollutants (HAPs). Ozone concentrations were too low even in air to oxidatively decompose 300/spl sim/1000 ppm of HAPs. The O/sub 2/ concentration in N/sub 2/-O/sub 2/ was the determining factor in the formation of all the nitrogen oxides. N/sub 2/O formation was enhanced with increase in O/sub 2/ concentration and in specific energy density, while a threshold value was observed around at 5% of O/sub 2/ concentration in the formation of NO and NO/sub 2/. N/sub 2/O decomposed in nonthermal plasma to give N/sub 2/ and O/sub 2/ and its decomposition efficiency was affected by its initial concentration and background O/sub 2/ concentration. N/sub 2/ and NO/sub 2/ are considered to be produced from NO, and N/sub 2/, N/sub 2/O, and NO could be produced from NO/sub 2/. Plasma chemical interactions between the nitrogen oxides and HAPs were not observed. HAPs and their fragments could be involved in the processes giving active oxygen species responsible for formation of the nitrogen oxides.

Control of byproduct distributions in plasma chemical processing of hazardous air pollutants

Plasma chemical behavior of hazardous air pollutants (HAPs) (Cl/sub 2/C=CCl/sub 2/, Cl/sub 2/C=CHCl, Cl/sub 3/C-CH/sub 3/, Cl/sub 2/CH-CH/sub 2/Cl, CH/sub 3/Cl, and CH/sub 3/Br), their molecular probes (CH/sub 4/, CH/sub 3/-CH/sub 3/, and CH/sub 2/=CH/sub 2/), and the carbon oxides was investigated with a ferroelectric packed-bed plasma reactor to obtain information on the formation of carbon oxides and N/sub 2/O. If has been shown that the oxidation of CO to CO/sub 2/ is a slow reaction in plasma, and that CO and CO/sub 2/ mainly result from different precursors. The control of CO/sub x/ selectivities is rather difficult at this stage. The process of N/sub 2/O formation is affected by HAP structures and oxygen concentration. In the decomposition of olefinic HAPs such as Cl/sub 2/C=CCl/sub 2/ and Cl/sub 2/C=CHCl, residence time reduction is effective in suppressing N/sub 2/O formation. In the cases of CH/sub 3/Cl and CH/sub 3/Br, low specific energy density operations could be necessary to reduce N/sub 2/O concentrations. The yields and selectivities of CO, CO/sub 2/, and N/sub 2/O change drastically by adding only 2% of oxygen to N/sub 2/ and oxygen concentration is not a good factor to control these inorganic oxides.

Synthesis of mixed heteroatom wurtzitanes

Syntheses of a novel series of mixed heteroatom wurtzitanes (tetracyclo[5.3.1.12,6.04,9]dodecanes) are described. cis,cis-1,3,5-Triformyl-1,3,5-trimethylcyclohexane 3 reacts with equimolar amounts of primary amines to afford the structurally novel 1,7,9-trimethyl-3,5-dioxa-12-azawurtzitanes, containing two different heteroatoms in the wurtzite ring. The mechanism for the reaction of compound 3 with primary amines in CHCl3 is also reported.