Wright C. Finney

Formation of hydroxyl radicals, hydrogen peroxide and aqueous electrons by pulsed streamer corona discharge in aqueous solution

The initiation reaction rate constants for the formation of hydroxyl radicals, hydrogen peroxide, and aqueous electrons using a pulsed streamer corona discharge in aqueous solutions are determined in the present study. The free radical scavenging property of carbonate ions was used to determine the initiation rate constants for the formation of hydroxyl radicals and hydrogen peroxide from the pulsed streamer corona discharge. The effects of average current, voltage, and power input on the initiation rate constants were also studied. A reactor model including known chemical reaction kinetics was developed for the degradation of phenol, and the initiation rate constant for aqueous electrons was determined by fitting the experimental data of phenol degradation to the model. Transient concentration profiles predicted by the model were compared to those of experiments for the formation of hydrogen peroxide in deionized water and for the degradation of hydroquinone. It was observed that the model results match experimental results satisfactorily for the formation of hydrogen peroxide and qualitatively follow the experimental results for the degradation of hydroquinone. The model was improved by considering that the reaction rate constants vary with the current in the reactor. The current was observed to vary with time for the cases where no salts were added to the reactor. It was observed that the improved model follows the experimental results satisfactorily for high initial concentrations (> 5.4 × 10−5M) of hydroquinone.

The role of Fenton’s reaction in aqueous phase pulsed streamer corona reactors

Abstract Aqueous phase pulsed streamer corona reactors are currently under development for a number of applications including water and wastewater treatment. Previous research has demonstrated that a high voltage pulsed electrical discharge directly into water leads to the formation of reactive species such as hydrogen peroxide and hydroxyl radicals. Since significant quantities of hydrogen peroxide are produced, the role of Fenton’s reactions in the pulsed corona reactor is analyzed both experimentally and with computer simulations in the present work. Experimental data shows the existence of optimal iron concentrations for the degradation of phenol, and that the formation of hydrogen peroxide by the pulsed corona discharge is dependent upon both the applied electric field and the solution conductivity. A mathematical model based upon mass balances for 31 radical and molecular species in the batch reactor (including 71 chemical reactions) has been developed and sensitivity analysis performed to identify key reactions. This model is used to show the effects of initial reaction conditions (including iron and phenol concentrations) on the degradation of phenol and the formation of reaction intermediate products and by-products. The model results are in qualitative and semi-quantitative agreement with the experimental observations on the effects of initial iron and phenol concentrations on phenol degradation and by-product formation.

Combined removal of SO/sub 2/, NO/sub x/, and fly ash from simulated flue gas using pulsed streamer corona

A pulse-energized electron reactor utilizing pulsed streamer corona has been developed for the combined removal of SO/sub 2/, NO/sub x/, and particles from effluent gases. In the pulse-energized electron reactor process, fast-rising narrow high voltage pulses are superimposed on a DC bias voltage and applied to a nonuniform electric field geometry to generate pulsed streamer corona. The pulsed streamer corona produces energetic free electrons, which dissociate gas molecules, forming radicals. These radicals cause chemical reactions that convert SO/sub 2/ and NO/sub x/ into acid mists and/or solids, which can be removed from the gas stream by conventional means. In pulse-energized electron reactor performance tests on a humid air stream with an initial SO/sub 2/ concentration of 1000 p.p.m., more than 90% of the SO/sub 2/ was removed with an advantageously small power requirement. >

Aqueous-phase pulsed streamer corona reactor using suspended activated carbon particles for phenol oxidation: model-data comparison

A pulsed high-voltage electrical discharge that produces streamers, or regions of non-thermal plasma, has been shown to be useful for degrading small organic species in synthetic wastewater in a bench-scale experimental system. This process is an example of an advanced oxidation technology that leads to the formation of hydroxyl radicals, hydrogen peroxide, and aqueous electrons, which in turn lead to organic contaminant removal through direct chemical reactions. Experimental results show that with activated carbon particles present, the removal of organic contaminants is increased due to the combination of direct oxidation of the organic species in the bulk fluid by pulsed corona and adsorption of the organic species to the surface of the activated carbon. There exists also the possibility of reactions occurring on the surface of the activated carbon-induced by the electrical discharge, thus continually regenerating the activated carbon. The present study develops a mathematical model incorporating multicomponent bulk and surface phase reactions coupled with mass transfer, internal particle diffusion, and adsorption to the carbon particles. Comparison of experimental results and theory using phenol as a model compound implies surface reactions occurring on the activated carbon particles.

Allometric variation and sexual maturity in the obligate coral commensal Trapezia ferruginea Latreille (Decapoda, Xanthidae)

Morphological variation related to size and sexual maturity is examined in the xanthid crab Trapezia ferruginea, an obligate associate of the coral Pocillopora. Morphological variation in males is related primarily to size while in females it is related to both size and sexual maturity. It was not possible to identify a pubertal molt in males but examination of internal anatomy suggests that they become sexually mature at about 6-7 mm carapace length. Females undergo a marked pubertal molt at about 6-7 mm carapace length although females as small as 5.3 mm may undergo a pubertal molt and be ovigerous. The adaptive significance of changes in morphology with increasing size and sexual maturity is discussed.

Formation of Hydrogen Peroxide, Hydrogen, and Oxygen in Gliding Arc Electrical Discharge Reactors with Water Spray

Formation rates of hydrogen peroxide (H₂O₂) , hydrogen (H₂), and oxygen (O₂) in gliding arc discharge with water spray and a variety of carrier gases, including Ar, He, O₂, N₂, and CO₂, were determined. Significantly larger rates and concentrations of hydrogen peroxide were found in the present reactor with a modified liquid injection nozzle than in previous work. As long as nitrogen oxide species are minimized or not formed, the formation rates of hydrogen peroxide were less sensitive to the carrier gas (O₂, CO₂, Ar), although He gave about one-half the rate as these other gases. The stoichiometric ratios of H₂:O₂:H₂O₂ exhibited a range of behaviors for the different carrier gases with the highest H₂ formation rate in Ar and N₂ and the largest O₂ formation in CO₂.

Chlorinated Organic Compound Removal by Gas Phase Pulsed Streamer Corona Electrical Discharge with Reticulated Vitreous Carbon Electrodes

Trichloroethylene (TCE) and vinyl chloride (VC) removal by gas phase pulsed corona discharge was investigated with attention to energy efficiency and byproduct identification. Approximately 50–95% removal of TCE and vinyl chloride was observed, depending on the energy density applied to the gas. Water vapor reduced TCE removal in some experiments. Evidence was found for post-corona reactions leading to removal of vinyl chloride downstream of the plasma discharge, while significant post-corona removal of TCE was not observed. Removal efficiencies of 100–900 g/kW-hr in the case of 1000 ppm feed of TCE, and of 2–24 g/kW-hr for a 100 ppm feed of vinyl chloride were found. In the TCE experiments, the formation of dichloroacetyl chloride was observed, while an unknown byproduct was found with vinyl chloride. The addition of a platinum-rhodium coated electrode was found to reduce the post-corona removal of vinyl chloride at low energy density.

Aerosol particle charging by free electrons

Abstract The strong dependence of electrostatic precipitator efficiency on particle charge has initiated a number of investigations of charge enhancement techniques. Measurements of free electron charging of aerosol particles reported here for nitrogen and argon confirm the earlier evidence (DuBard et al., J. Aerosol Sci. 14 , 5, 1983) that free electron charging in nitrogen produced a substantially higher particle charge than charging by ions. The measured particle charge was 2–10 times larger for free electron charging than for ionic charging depending upon the experimental conditions. The dependence of free electron charging upon the gas, electric field, particle radius, and the charging parameter N 0 t has been measured. Previously available charging theories do not predict the observed dependence of free electron charging on the various parameters. The importance of electric-field-enhanced electron temperatures is recognized for diffusion charging, and a new high electron temperature continuum-regime field-diffusion charging model is presented which utilizes the Boltzmann relation as an approximate solution for the electron densities near the particle. The predictions of this model are dependent upon the boundary conditions utilized at the particle surface, but are in satisfactory agreement with the data (considering the possible sensitivity of electron charging to gas impurities).

Degradation of Aqueous Phase Polychlorinated Biphenyls (PCB) Using Pulsed Corona Discharges

Abstract The efficacy of pulsed corona discharges, an effective technique for removal of small aromatic and volatile organic compounds in water, to degrade aqueous phase polychlorinated biphenyls (PCB) was tested. Experiments were conducted on the model PCB compound, 2,2′,4,4′- tetrachlorobiphenyl at its solubility limit (68 ppb) in water. The effects of various reactor configurations featuring liquid and combined liquid/gas discharges on the degradation rate and possible degradation mechanisms of the PCB congener were determined. The pulsed corona reactor led to nearly 70% degradation of the PCB congener within 60 min. Increased degradation rates due to the Fenton’s reactions were found upon the addition of ferrous salts in solution, and the degradation rate of the PCB was higher than those of phenol and nitrobenzene in the absence of ferrous salts. The two different reactor configurations tested, including direct discharge in water and simultaneous gas-liquid discharge, gave the same rate of PCB degradation in the Fenton’s case, thus raising the possibility that the PCB degradation mechanisms in both reactors are the same. The effect of the high voltage electrode material on the degradation of PCB was evaluated by performing experiments with electrodes made of either platinum or a nickel-chromium alloy.

Experimental implementation of an on-line optimization scheme to batch PMMA synthesis

Abstract In this paper, a neural network strategy for calculating the optimal set-point trajectory in batch processes is implemented experimentally in the batch synthesis of polymethyl-methacrylate (PMMA). It is shown that the optimal temperature trajectory which minimizes a desired performance index is a function of the initial monomer concentration. This optimal trajectory is computed on-line using a back propagation neural network. Both open-loop as well as closed-loop experiments are conducted in a 3 l laboratory scale batch reactor and it is shown that a closed-loop scheme is necessary to keep the system on the desired trajectory.