The application of strong electric fields in water and organic liquids has been studied for several years, because of its importance in electrical transmission processes and its practical applications in biology, chemistry, and electrochemistry. More recently, liquid-phase electrical discharge reactors have been investigated, and are being developed, for many environmental applications, including drinking water and wastewater treatment, as well as, potentially, for environmentally benign chemical processes. This paper reviews the current status of research on the application of high-voltage electrical discharges for promoting chemical reactions in the aqueous phase, with particular emphasis on applications to water cleaning.

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Electrohydraulic Discharge and Nonthermal Plasma for Water Treatment

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

The paper reviews solid-catalyzed oxidation and reduction processes for the treatment of wastewater that contains small concentrations of toxic compounds and for which separation is not economical while biological treatment is not feasible. Specifically, the objectives are (1) to understand the interactions between catalytic materials and various pollutants, (2) to provide a database for catalyst selection, and (3) to assess the potential of these processes for commercialization. The review suggests the following well-investigated solutions:  (1) Supported metal (Ru/CeO2, Pt/CeO2, and Ru/C) and metal oxides (CuO−ZnO−CoO, MnO2/CeO2, CoO/Bi2O3, and V2O5/Al2O3) are the most promising catalysts for the destruction of refractory organic compounds with nearly 100% selectivity to CO2; (2) CoO/CeO2 and MnO2/CeO2 are the most active catalysts for ammonia oxidation at temperatures of 263−400 °C; (3) activated carbon, preferably in the presence of copper ions, is an active catalyst for the oxidation of cyanides and ...

Catalytic Abatement of Water Pollutants

Spruce wood charcoal, macadamia shell charcoal, coal activated carbon, and coconut shell activated carbon catalyze the gasification of organic compounds in supercritical water. Feedstocks studied in this paper include glycerol, glucose, cellobiose, whole biomass feedstocks (depithed bagasse liquid extract and sewage sludge), and representative Department of Defense (DoD) wastes (methanol, methyl ethyl ketone, ethylene glycol, acetic acid, and phenol). The effects of temperature, pressure, reactant concentration, weight hourly space velocity, and the type of catalyst on the gasification of glucose are reported. Complete conversion of glucose (22% by weight in water) to a hydrogen-rich synthesis gas was realized at a weight hourly space velocity (WHSV) of 22.2 h-1 in supercritical water at 600 °C, 34.5 MPa. Complete conversions of the whole biomass feeds were also achieved at the same temperature and pressure. The destruction efficiencies for the representative DoD wastes were also high. Deactivation of the...

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Carbon-Catalyzed Gasification of Organic Feedstocks in Supercritical Water†

Supercritical water oxidation (SCWO) technology presents important environmental advantages for the treatment of industrial wastes and sludges. The homogeneous reaction that takes place between the oxidizable materials and oxygen, at temperatures and pressures above the critical point of the water (647.3 K and 22.12 MPa), is well known. Specific equations of state for water and aqueous mixtures, gases, and organics have been developed. The process is not having the expected industrial development. Some new plants have been closed by corrosion and operational problems related with high temperature, high pressure, and oxidative atmosphere inside of the equipments. To overcome these technical difficulties more research focused on solving operational problems is necessary. This article presents an overview of the technical aspects of the supercritical water oxidation process. Reactors design, construction materials, corrosion, salts precipitation problems, and industrial applications are discussed. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Supercritical water oxidation: A technical review

This paper reports tht aqueous solutions of phenol were oxidized in a flow reactor at temperatures between 300 and 420{degrees}C (0.89 {le} T{sub r} {le} 1.07) and pressures from 188 to 278 atm (0.86 {le} P, {le} 1.27). These conditions included oxidations in both near-critical and supercritical water. Reactor residence times ranged from 1.2 to 111 s. The initial phenol concentrations were between 50 and 330 ppm by mass, and the initial oxygen concentrations ranged from 0 to 1,100% excess. The oxidation experiments covered essentially the entire range of phenol conversions. Analysis of the kinetics data for phenol disappearance using a combination of the integral method and the method of excess revealed that the reaction was first order in phenol and 1/2 order in oxygen, and influenced by pressure. The global reaction order for water was taken to be nonzero, and the global rate constant was assumed to be independent of pressure so that the only effect of pressure was to alter the water concentration and hence the reaction rate.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/37422/690380302_ftp.pdf?sequence=1

Kinetics of phenol oxidation in supercritical water

The oxidation of phenol has been accomplished in subcritical and supercritical water. Seventy experiments were performed in an isothermal, plug-flow reactor at temperature from 300 to 420°C, pressures from 188 to 278 atm, and residence times from 4 to 111 seconds. The initial phenol concentrations ranged from 2.8 × 10−4 to 5.3 × 10−3 M, and the oxygen concentrations were between 6.5 × 10−5 and 6.4 × 10−2 M at reaction conditions. The oxidation experiments covered essentially the entire range of phenol conversions. The experimental results were consistent with the global reaction order for phenol being in the range of1/2and 1, and with the global reaction order for oxygen being greater than zero. The conversion increased with increasing pressure, which may either suggest that the reaction order with respect to water was greater than zero, or that the apparent activation volume was less than zero. A variety of reaction products were detected, including mono- and di-car☐ylic acids, dihydroxybenzenes, phenoxyphenols, and dibenzofuran, indicating that the oxidation of phenol in supercritical water may involve a complex set of multiple reactions. The concentrations of metals in the reactor effluent were very low, indicating that corrosion effects were likely not a complicating factor in this study. No metals were detected in the solid material collected in the reaction product filter, also indicating an absence of corrosion effects.

Phenol oxidation in supercritical water

We oxidized aqueous solutions of phenol in batch and flow reactors at temperatures of 300, 380, and 420 o C, pressures of 218 and 278 atm, and reaction times between 1.2 and 29 040 s. Gas chromatographic and mass spectrometric analysis of the oxidation products extracted from the aqueous reactor effluent permitted identification and quantification of the concentrations of multiring compounds such as 2- and 4-phenoxyhenol, 2,2'-biphenol dibenzofuran, and dibenzo-p-dioxin. The Delplot methodology was used to discriminate between primary and nonprimary products

Phenol oxidation pathways in supercritical water

Supercritical water is a good medium for the complete oxidation of organic compounds, and this chemistry forms the basis for a novel technology currently being advanced for the ultimate destruction of hazardous wastes. Above its critical point ({Tc} = 374 C, P{sub c} = 218 atm), water has a high solubility for both organics and oxygen, so a single phase containing a homogeneous mixture can exist at reaction conditions. This elimination of potential interphase transport limitations coupled with the moderately high operating temperatures and pressures leads to rapid oxidation rates. Much of the previous research dealing with oxidation in supercritical water has been devoted to either demonstrating the technology or measuring the disappearance kinetics for relatively simple compounds. Only very limited work, however, has been devoted to identifying and quantifying the reaction products from the supercritical water oxidation of organic compounds. Such research is clearly important from an environmental viewpoint, especially when one considers that incineration, another thermal oxidation process, can produce undesired, high molecular weight condensation products such as dibenzofurans and dibenzo-p-dioxins from phenols. The authors have undertaken and completed this study to determine whether the oxidation of phenol, a representative organic pollutant, in near- and supercritical water canmore » lead to the formation of similar high molecular weight products.« less

Phenol oxidation in supercritical water: formation of dibenzofuran, dibenzo-p-dioxin, and related compounds

Global power-law rate expressions were determined for the formation of CO 2 , from the oxidation of aqueous solutions of phenol and 2-chlorophenol. The oxidation experiments were accomplished in a plug-flow reactor at temperatures between 300 and 420 o C and pressures from 185 to 278 atm. These conditions included oxidations in both near-critical and supercritical water. Reactor residence times ranged from 1.2 to 109 s. The initial reactant concentrations were between 8.0×10 -5 and 2.1×10 -3 M, and the initial oxygen concentrations ranged from 5.5×10 -3 to 4.8×10 -2 M.

Thomas D. Thornton

Papers

Kinetics of phenol oxidation in supercritical water

Phenol oxidation in supercritical water

Phenol oxidation pathways in supercritical water

Phenol oxidation in supercritical water: formation of dibenzofuran, dibenzo-p-dioxin, and related compounds

Kinetics of Carbon Dioxide Formation From the Oxidation of Phenols in Supercritical Water