Ind. Eng. Chem. Res. 2005, 44, 4243-4248
4243
Hydrogen, Oxygen, and Hydrogen Peroxide Formation in Aqueous Phase Pulsed Corona Electrical Discharge Michael J. Kirkpatrick and Bruce R. Locke* Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, Florida 32310
High voltage electrical discharges in water are of increasing interest for the degradation of organic compounds and destruction of biological species. The present study reports measurements of the rates of molecular hydrogen, molecular oxygen, and hydrogen peroxide formation in a pulsed positive needle-plane corona-like electrical discharge in water. In experiments for various solution conductivities, applied voltages, and discharge powers, the ratio of the molar rate of production of hydrogen:hydrogen peroxide:oxygen was approximately 4:2:1. The highest observed rate of hydrogen production was 1.3 µmol/s at discharge power of 37 W (or 0.25 g of H2/kW‚h) at solution conductivity 50 µS/cm. The G-value for hydrogen production was 0.17 molecule of H2/100 eV, falling in the range of that found in the radiation chemistry literature (∼0-0.5 molecule of H2/ 100 eV, depending on scavenger concentration). A global reaction is proposed to add to existing kinetic models for the simulation of reactive species production in electrical discharge in water. 1. Introduction A fundamental understanding of the chemical and physical factors involved in high voltage pulsed corona electrical discharge (PCED) and dielectric breakdown in water is necessary for a number of applications in chemistry and engineering. Although practical applications, including water treatment,1-9 bacterial destruction or sterilization,10 and the formation of shock waves,11 are very important, a complete understanding of the physical mechanisms of PCED formation in water and the concurrent and subsequent formation of active chemical species by this type of discharge in water are currently not well understood. Measurements of the propagation rates of electrical discharges in water and organic liquids have been reported,12,13 and several theories have been reported concerning the nature of the electrical discharge.14,15 One group of theories involves a thermal mechanism whereby local electric heating leads to bubble formation followed by subsequent discharge formation in the gas phase of the bubble in a manner similar to that known to occur in gas-phase discharge.16 Not all theories can explain all observations, and the linkage between the physical effects due to PCED formation and propagation and the formation of active chemical species has not been indentified. Experimental measurements of hydrogen peroxide by chemical means17-19 and hydroxyl radicals by emission spectroscopy20,21 have shown significant levels of these species in water from PCED in water made from pulsed capacitor discharges in the range of 1 J/pulse. Studies have also been conducted dealing with kilojoules per pulse electrohydraulic or pulsed arc discharges on fundamental issues22-24 and for water treatment,25-30 and several theories have been developed for these cases;31-34 however, these theories do not predict the formation of active chemical species. Kinetic simulations of the chemical reactions involved in PCED in water have been made using reactions found in the radiation chemistry literature.1,3,6 These reactions alone could not simulate the production of the amount * To whom correspondence should be addressed. Tel.: (850) 410-6165. Fax: (850) 410-6150. E-mail:
[email protected].
of hydrogen peroxide that was measured or fully replicate the observed removal of compounds such as phenol, so additional reactions were added to the model including a global source of hydrogen peroxide in the form of reaction 1.17 k1
2H2O 98 H2O2 + H2
(1)
Even when combined with the many pertinent reactions found in the literature, reaction 1 dominated the other reactions forming hydrogen peroxide and the model resulted in equimolar production of hydrogen and hydrogen peroxide for the case of electrical discharge in pure water. There was no global source of oxygen in these models, and oxygen production was predicted to be several orders of magnitude less than that of either hydrogen or hydrogen peroxide. Experimental results presented here comparing the rates of hydrogen peroxide and molecular hydrogen production show that in fact the production rate of molecular hydrogen is double that of the rate of hydrogen peroxide production. In addition, measurements of oxygen production exceed those predicted by the previous models. In light of the new measurements, it is proposed that the overall reaction describing stable species formed by electrical discharge in water is reaction 2. k2
6H2O 98 4H2 + 2H2O2 + O2
(2)
Other methods of electrical discharges in water/gas systems include glow discharge electrolysis which employed a dc gas-phase plasma above a water surface.35 Contact glow discharge electrolysis (CGDE) moved the plasma discharge electrode into contact with the water surface. Studies on CDGE investigated oxygen and hydrogen peroxide formation,36 and removal of various organic compounds from water including benzoic acids,37 chlorophenols,38 and aniline.39 A comparison of chemical yields of hydrogen, hydrogen peroxide, and oxygen between the present work and these other systems will be discussed. It should be noted here at the outset that the energy efficiency for hydrogen found here is orders of magnitude below the state of the art and that this
10.1021/ie048807d CCC: $30.25 © 2005 American Chemical Society Published on Web 05/05/2005
4244
Ind. Eng. Chem. Res., Vol. 44, No. 12, 2005
Figure 1. Reactor schematic showing electrical discharge reactor with purge gas for measurement of gases produced by the discharge in water.
paper is intended for further understanding of chemical yields of pulsed corona electrical discharge in water and not to suggest a new hydrogen generator technology. 2. Experimental Methods 2.1. Electrical. The power supply and pulse forming circuit were the same as discussed in earlier publications.1,3,6,7 An ac transformer was used to adjust the voltage to the desired level. Current was limited by a resistor bank (333 kΩ), positive recitified by a diode chain, and stored in a capacitor bank (2000 pF). A spark gap rotating at 1800 rpm allowed the capacitor bank to discharge into the reactor system at a pulse frequency of 60 Hz. Electrical measurements were made using a Tektronix TDS 460 fast digital storage oscilloscope with a Tektronix P6015A high voltage probe and Tektronix P6021 current probe. The high voltage probe was connected to the high voltage line on the reactor side of the rotating spark gap, and the current electrode was placed around the wire that connected the grounded electrode to ground. In this work, pulse energy varied from 0.62 to 1.2 J/pulse (37-72 W), as determined by integration of the product of the current and voltage waveforms. More details on electrical measurements and sample voltage and current waveforms may be found in Grymonpre et al.3 2.2. Reactor Specifications. The reactor used was similar to that used in previous work.1,3,6,7 The operation of the reactor had to be changed, however, in order to obtain repeatable measurements of gases produced by the discharge. This was accomplished by purging the reactor with an appropriate carrier gas which passed through a sampling cell after exiting the reactor, as can be seen in the reactor schematic shown in Figure 1. The choice of this gas depended on whether hydrogen or oxygen was being measured, as will be discussed in section 2.3. It should be noted here that the purge gas bubbles did not come into contact with the discharge. The jacketed reactor was 1 L and made of glass. Cooling water at 15.0 °C removed heat produced by the discharge. The 1 L solution reached a steady temperature after 20 min of operation at about 22 °C in a typical experiment. The high voltage electrode was a nickel-chromium (Nichrome) wire of 1/32 in. (0.79 mm) diameter. This electrode was connected to the output of the pulse forming circuit by a high voltage copper wire. The high voltage needle electrode was thin enough to allow the discharge to occur without mechanical sharpening, and extended about 3 mm from a nylon fitting into the solution. The purge gas bubbles did not come into
contact with the plasma discharge, as this dramatically changes the nature of the discharge. 2.3. Measurements. Hydrogen and oxygen were measured using a Perkin-Elmer Autosystem XL gas chromatograph (GC) with thermal conductivity detector. A Restek ShinCarbon ST 100/120 mesh 2 m × 1 mm i.d. micropacked column was used for gas separation. For measurement of hydrogen, nitrogen was used as the carrier gas in the chromatographic analysis because measurement sensitivity using a thermal conductivity detector is enhanced by increasing the difference between the thermal conductivity of the carrier phase and the gas to be measured. Conversely, for measurements of oxygen, helium was used as a carrier gas. Separate experiments were thus required to measure both hydrogen and oxygen. Calibrations were made by mixing hydrogen and nitrogen or oxygen and helium at known flow rates to give concentrations of hydrogen and oxygen in the range to be measured in experiments. The reactor purge gas mentioned above was the same as that used as the GC carrier gas in order to eliminate large interfering peaks that would be caused if the purge gas was different from the GC carrier gas. The purge gas flow rate was 500 mL/min. For hydrogen analysis, only one peak corresponding to hydrogen was observed on the GC. This was because interference caused by the inevitable contamination by air was not an issue because the carrier gas was nitrogen (oxygen and nitrogen have similar thermal conductivities, so neither shows up in small concentrations when nitrogen is used as the GC carrier gas). In the case of oxygen measurement, interference caused by air contamination was an issue because helium was used as the GC carrier gas. The data for oxygen produced by the discharge therefore had to be adjusted to account for air contamination of samples. This contamination occurred even though Hamilton gastight syringes and new septa on both the sampling cell and the GC injector were used. Because the amount of oxygen measured was on the order of 500 ppm, and air contains 21% oxygen, even very small volumes of air could affect the amount of oxygen that was detected. The effects of air contamination were removed from the data by using nitrogen from the air as an internal standard corresponding to the level of contamination. Because nitrogen cannot be produced in the discharge, the only source of the nitrogen peak observed on chromatograms must be from air contamination. This peak then contains information about how much oxygen must have entered the sample from contamination as opposed to oxygen that was produced in the reactor. Hydrogen peroxide was measured using two different methods. Liquid samples were taken every 10 min during an experiment and analyzed for hydrogen peroxide by complexing with titanium as titanium sulfate. Two milliliters of sample was mixed with 1 mL of 10 mmol of TiSO4 reagent and absorption at 410 nm was measured.40 This method was calibrated by titration of the final solution with standardized 1000 mg/L potassium permanganate. 2.4. Experimental Procedures. Solutions were prepared from deionized water, and potassium chloride was used as the electrolyte at different concentrations to obtain different initial solution conductivities. The solution was left in the reactor for at least 30 min with the purge gas flowing in order to degas the solution and to allow the solution to come to a steady temperature
Ind. Eng. Chem. Res., Vol. 44, No. 12, 2005 4245
Figure 2. Time course data for hydrogen produced by discharge ([), hydrogen peroxide (9), and hydrogen when bubbled into the reactor as a control to determine mixing effects on the initial rise time (2). Solution conductivity was 150 µS/cm, adjusted by adding KCl as electrolyte.
Figure 3. Rate of production of hydrogen ([) and hydrogen peroxide (9) as a function of discharge power. Power was adjusted by changing the voltage applied to the point electrode.
prior to starting the experiments. Pulsed high voltage was applied for 1 h, and gas and liquid samples were taken over the course of the experiment. Gas samples were taken every 2.5 min for the first 15 min of operation and every 5 min thereafter. Liquid samples were taken every 10 min for the enitre experiment. Measurements of the solution pH, conductivity, and temperature were made both before and immediately after experiments. The gas-phase measurements represent the amount of gas leaving the reactor; although no measurements of dissolved gases were made, the fact that steady levels of gas-phase concentrations are observed implies that an equilibrium is reached between the liquid and purge gas. 3. Results 3.1. Hydrogen/Hydrogen Peroxide. Time course data for a typical experiment are shown in Figure 2. The data shown in Figure 2 are the average of three separate experiments with error bars calculated on a 95% confidence interval. The initial rise of hydrogen concentration is due to mixing effects in the headspace of the reactor, tubing, and the gas sampling cell, as seen in the comparison to a control experiment where a known amount of hydrogen flowed into the reactor system with no discharge. The rate of hydrogen peroxide production is obtained from the slope of the concentration vs time data. The rate of hydrogen production is obtained by the product of the gas-phase hydrogen concentration and the purge gas flow rate. The rates of hydrogen and hydrogen peroxide production as functions of discharge power are shown in Figure 3. Discharge power was adjusted by changing the applied pulsed voltage to the needle electrode. The
Figure 4. Rate of production of hydrogen ([) and hydrogen peroxide (9) as a function of solution conductivity. Conductivity was adjusted by changing the concentration of KCl added to the reactor solution.
Figure 5. G-values for hydrogen ([) and hydrogen peroxide (9) as a function of solution conductivity. Table 1. Comparison of Current Efficiencies for Production of Hydrogen Peroxide, Hydrogen, and Oxygen (mol of product/mol of electrons) this work ref 36 Faraday’s law
H2O2
H2
O2
13 n/a 0.5
26 1.0 0.5
5 0.67 0.25
applied voltages were 35, 45, and 55 kV, corresponding to discharge powers of 37, 66, and 123 W, respectively. All experiments shown in Figure 3 were performed on solutions with initial conductivity of 150 µS/cm. Production rates rose with discharge power, as was expected for hydrogen peroxide.1,19 The hydrogen production rate was double that of the hydrogen peroxide production rate within experimental error. Figure 4 shows the production rates as functions of solution conductivity. Production rates decrease with increasing conductivity. It should be noted here that the applied voltage was 40 kV for the solution conductivity of 50 µS/cm (because breakdown was observed at 45 kV) and 45 kV was used for the other solution conductivites. Also, the current waveform and discharge power were not the same: at 50, 100, and 150 µS/cm, the discharge power was 45, 60, and 67 W, respectively. The fact that production rates are higher and power is lower at lower conductivity leads to the result illustrated in Figure 5, which shows that G-values for the production of hydrogen and hydrogen peroxide decrease with increasing solution conductivity. This result was already known for hydrogen peroxide. The present work shows a similar, parallel trend for hydrogen which suggests a coupling of the two species in their rates of formation in electrical discharge in water. Current efficiencies for the production of hydrogen peroxide, hydrogen, and oxygen are shown in Table 1 for this work, work on CGDE,36 and according to Faraday’s law for purely electrochemical reactions.
4246
Ind. Eng. Chem. Res., Vol. 44, No. 12, 2005
H2O2 f 2•OH
(3)
OH + H2O2 f HO2 + H2O
(4)
•
•
OH + HO2 f O2 + H2O
Figure 6. Time course data for oxygen produced by discharge ([), hydrogen peroxide (9), and oxygen when bubbled into the reactor as a control to determine mixing effects on the initial rise time (2). The difference between oxygen produced by the discharge and oxygen measured in the control experiment is in contrast to that seen for hydrogen, shown in Figure 2. Solution conductivity was 150 µS/cm, adjusted by adding KCl as electrolyte.
The numbers for this work and the work on CGDE exceed the Faraday’s law values because the compounds are formed in the electrical discharge away from electrode surfaces, not in stoichiometric electrolysis type reactions at electrode surfaces. Values for current efficiency in this work also exceed those for CGDE. This does not mean that hydrogen production is more energy efficient in an electrical discharge in water than in electrolysis, as the applied potential and deposited energy are far higher. The comparison is made simply to illustrate that a different reaction mechanism must be responsible for hydrogen production in an electrical discharge. 3.2. Oxygen/Hydrogen Peroxide. The average of three experiments for determining the amount of oxygen produced by the discharge is shown in Figure 6. The oxygen production rate was about 20-30% of the hydrogen production rate (compare to Figure 2). Hydrogen peroxide production is very similar to that seen in the hydrogen measurement experiments, demonstrating that the change in purge gas has no effect on hydrogen peroxide production and suggesting that the purge gas has little influence on the liquid discharge. The data for oxygen concentration were noisier ((20% based on a 95% confidence interval) than those for hydrogen due to error multiplication associated with the data adjustment discussed in section 2.3. Oxygen took significantly longer than hydrogen to reach a steady concentration as measured in the gas sampling cell. Because the purge gas flow rate and the geometry of the reactor headspace, tubing, and gas sampling cell were the same for both oxygen and hydrogen experiments, the difference in time needed to reach a steady value must be due to a reason other than mixing effects in the gas phase. As shown in Figure 6, a control experiment demonstrates that mixing effects alone are not the reason for the increased time required for oxygen concentration to reach a steady value as measured in the downstream gas sampling cell. The reason for this effect must therefore be related to the mechanism for oxygen production. The exact mechanism for the production of oxygen in electrical discharge in water is not known at the present time. One possible mechanism for oxygen production is via the decomposition of hydrogen peroxide according to reactions 3-5.
(5)
However, if hydrogen peroxide were the major source for the production of oxygen in this system, the observed rate of hydrogen peroxide formation should decrease as hydrogen peroxide concentration increases. Another argument against this source of oxygen is that, when an experiment similar to that shown in Figure 6 is performed using an initial concentration of hydrogen peroxide of 2 mM, the result is almost identical to that shown in Figure 6 (except that the hydrogen peroxide numbers are offset). If hydrogen peroxide decomposition was the major source for oxygen production, oxygen concentration measured in this experiment would have been higher than that seen in Figure 6, especially at the beginning of the experiment. 4. Discussion Previous work on kinetic modeling of phenol removal from water by electrical discharge demonstrated the need for a zero-order global reaction producing hydrogen peroxide in addition to the reactions found in the radiation chemistry literature.1,3,17 The measured rate of hydrogen peroxide formation could not be simulated without the use of reaction 1. In previous work the reaction rate constant k1 was used as an adjustable parameter to fit the simulation to experimental data for hydrogen peroxide production. Using only this one adjustable parameter, the model then succeeded in simulating the production of various byproducts of phenol removal and phenol removal in the case with Fenton’s reactions.3 Hydrogen peroxide production in this model was dominated by reaction 1. The present work shows that the equimolar rates of production of molecular hydrogen and hydrogen peroxide implied by reaction 1 are not borne out by measurements. In addition, oxygen production in the previous simulations is much smaller when compared to the present experimental results. A sensitivity analysis that was performed on the previous model3 showed that dissolved oxygen concentration was important with regard to phenol and phenol byproduct removal as illustrated in the oxidation steps shown in reactions 6 and 7. Therefore, it is important that the simulation not
only includes an accurate determination for dissolved oxygen concentration as an initial condition, but that it accounts accurately for oxygen produced in the discharge itself.
Ind. Eng. Chem. Res., Vol. 44, No. 12, 2005 4247 Table 2. Comparison of Rate of Formation of Hydrogen Peroxide, Hydrogen, and Oxygen (µmol/s) experiment simulation with reaction 1 simulation with reaction 2
H2O2
H2
O2
0.61 0.61 0.61
1.19 0.61 1.19
0.24 2.8 × 10-3 0.30
A repeat of the previous simulations3 using only the reactions pertinent to a system with no organic present was conducted, and again, reaction 1 dominated the other hydrogen and hydrogen peroxide production and consumption reactions, thus giving the result of nearly equal production of hydrogen and hydrogen peroxide, both of which had production rates that were at least 2 orders of magnitude greater than the production rate of oxygen. Therefore, it is proposed here that reaction 1 should be replaced by reaction 2 for simulation of electrical discharge in water. In addition to the new global reaction producing oxygen and hydrogen, the reaction set from previous models1,3,6 was expanded to include reactions for the consumption of both hydrogen and oxygen. These simulations do not account for the possible multiphase and nonhomogeneous nature of the discharge in the gas-liquid environment. A more detailed model accounting for the nonhomogeneous nature of the discharge, the formation of gases in the streamer, near the streamer-liquid interface, and in the liquid, and the mass transfer of the hydrogen and oxygen into the gas phase may more accurately simulate the system described here. However, the result of the simulation including reaction 2 does in fact more closely replicate the new experimental data on hydrogen and oxygen formation rates in pulsed corona electrical discharge in water. Table 2 shows formation rates of hydrogen peroxide, hydrogen, and oxygen according to experiment, kinetic simulation using reaction 1, and simulation using reaction 2. While a simulation using only reaction 1 can be fit to the data for hydrogen peroxide, the model then fails to simulate the correct production rates of hydrogen and oxygen. As shown in Table 1, the production of stable molecules from electrical discharge in water is not an electrochemical phenomenon like electrolysis. Electrical discharge in water also differs from the radiolysis of water in the distribution of products observed. Studies of radiation chemistry have found that hydrogen is produced via a second-order process in the radiolysis of water by γ-rays and heavy ion radiolysis.41 This process involves the dissociative recombination of the water cation and an electron to form an excited state of water, which then dissociates into molecular hydrogen and oxygen radical. Work performed by this same group has shown that there is a common precursor for both hydrogen and hydrated electron formation, the hydrated electron precursor, or nonhydrated electron.42 The reaction scheme put forth involves competition between the hydrogen-forming dissociative recombination reaction with hydration of the electron and the proton-transfer reaction of the water cation with water to form hydroxyl radical and H3O+. Simulations performed for this competition mechanism indicate a rate constant of ∼4.3 × 1012 M-1 s-1 for the formation of hydrogen, which is beyond the diffusion limit, indicating a nonhomogeneous reaction mechanism.41 Other work also from the same group indicates that hydroxyl radical is the only precursor of hydrogen peroxide, and that 79% of hydrogen peroxide formation can be attributed to hydroxyl radi-
cals produced via the proton-transfer reaction of the water cation.43 Oxygen is not formed to any significant extent in these systems. While conditions such as locally high temperatures in discharge channels, the presence of water vapor, and different electron energy distributions delineate electrical discharges in water from the radiolysis of water, there are still only limited pathways for the fate of an excited water molecule, so some similarities may exist. The lag time for oxygen concentration to reach a steady value when compared with hydrogen, as can be seen when comparing Figures 2 and 6, presents a problem in that there are apparently unaccounted for oxygen atoms during the first 20-30 min of a typical experiment. It seems clear that the mechanisms for molecular hydrogen and hydrogen peroxide production are closely linked and result in a constant ratio of 2:1 in the molar rates of production, respectively. It is unclear whether the mechanism for oxygen production is as closely linked to the other two species, despite the fact that at longer times there appears to be a stoichiometric rate of production as represented by reaction 2. However, there does seem to be evidence that decomposition of hydrogen peroxide is not the major source for oxygen production, as discussed in section 3.2. 5. Conclusions Measurements of hydrogen peroxide, hydrogen, and oxygen have been made and show that the production rate of molecular hydrogen is roughly twice that of hydrogen peroxide in an electrical discharge in water. The production rate of oxygen was about 25% that of hydrogen or 50% that of hydrogen peroxide. A modification (reaction 2) was made to the previous kinetic models1,3,6 in order to account for this new information. The result of this model can be expanded and tested with experimental data that include an organic such as phenol in order to further assess its applicability. Acknowledgment We would like to acknowledge the Florida Department of Environmental Protection for financial support. We also thank the FAMU-FSU College of Engineering, Department of Chemical Engineering, for support and Wright Finney, Mayank Sahni, Petr Lukes _, and Selma Me{edovic´ for discussion and assistance in the laboratory. Literature Cited (1) Grymonpre, D. R. An Experimental and Theoretical Analysis of Phenol Degradation by Pulsed Corona Discharge. Ph.D. Dissertation, Florida State University, Tallahassee, 2001. (2) Sharma, A. K.; Locke, B. R.; Arce, P.; Finney, W. C. A Preliminary Study of Pulsed Streamer Corona Discharge for the Degradation of Phenol in Aqueous Solutions. Hazard. Waste Hazard. Mater. 1993, 10, 209. (3) Grymonpre, D. R.; Sharma, A. K.; Finney, W. C.; Locke, B. R. The Role of Fenton’s Reaction in Liquid-Phase Pulsed Corona Reactors. Chem. Eng. J. 2001, 82, 189. (4) Sun, B.; Sato, M.; Clements, J. S. Oxidative Processes Occurring When Pulsed High Voltage Discharges Degrade Phenol in Aqueous Solution. Environ. Sci. Technol. 2000, 34, 509. (5) Sugiarto, A. T.; Sato, M. Pulsed Plasma Processing of Organic Compounds in Aqueous Solution. Thin Solid Films 2001, 386, 295. (6) Grymonpre, D. R.; Finney, W. C.; Clark, R. J.; Locke, B. R. Suspended Activated Carbon Particles and Ozone Formation in
4248
Ind. Eng. Chem. Res., Vol. 44, No. 12, 2005
Aqueous Phase Pulsed Corona Discharge Reactors. Ind. Eng. Chem. Res. 2003, 42, 5117. (7) Grymonpre, D. R.; Finney, W. C.; Clark, R. J.; Locke, B. R. Hybrid Gas-Liquid Electrical Discharge Reactors for Organic Compound Degradation. Ind. Eng. Chem. Res. 2004, 43, 1975. (8) Malik, M. A. Ghaffar, A. Malik, S. A. Water purification by electrical discharges. Plasma Sources Sci. Technol. 2001, 10, 82. (9) Sato, M.; Sun, B.; Ohshima, T.; Sagi, Y. Characteristics of Active Species and Removal of Organic Compounds by a Pulsed Corona Discharge in Water. J. Adv. Oxid. Technol. 1999, 4, 339. (10) Sato, M.; Ohgiyama, T.; Clements, J. S. Formation of Chemical Species and Their Effects on Microorganisms Using a Pulsed High-Voltage Discharge in Water. IEEE Trans. Ind. Appl. 1996, 32, 106. (11) Sunka, P. Pulse Electrical Discharges in Water and Their Applications. Phys. Plasmas 2001, 8, 2587. (12) Klimkin, V. F. Development of Electrical Breakdown in n-Hexane in the Microsecond to Nanosecond Range. Sov. Phys. Tech. Phys. 1986, 31, 1223. (13) Klimkin, V. F. Mechanisms of Electric Breakdown of Water from Pointed Anode in the Nanosecond Range. Sov. Tech. Phys. Lett. 1990, 16, 146. (14) Kuskova, N. I. Mechanism of Leader Propagation in Water. Sov. Phys. Tech. Phys. 1983, 28, 591. (15) Kosenkov, V. M.; Kuskova, N. I. Development of Breakdown in Water. Sov. Phys. Tech. Phys. 1987, 32, 1215. (16) Rutgers, W. R.; Van Veldhuizen, E. M. In Electrical Discharges for Environmental Purposes; Van Velhuizen, E. M., Ed.; Nova Science Publishers: New York, 2000; p 5. (17) Joshi, A. A.; Locke, B. R.; Arce, P.; Finney, W. C. J. Formation of Hydroxyl Radicals, Hydrogen Peroxide and Aqueous Electrons by Pulsed Streamer Corona Discharge in Aqueous Solution. J. Hazard. Mater. 1995, 41, 3. (18) Sato, M.; Ohgiyama, T.; Clements, S. Formation of Chemical Species and Their Effects on Microorganisms Using a Pulsed High-Voltage Discharge in Water. IEEE Trans. Ind. Appl. 1996, 32, 106. (19) Lukes, P. Water Treatment by Pulsed Streamer Corona Discharge. Ph.D. Dissertation, Institute of Chemical Technology, Prague, 2001. (20) Sun, B.; Sato, M.; Clements, J. S. Optical Study of Active Species Produced by a Pulsed Streamer Corona Discharge in Water. J. Electrostat. 1997, 39, 189. (21) Sunka, P.; Babicky, V.; Clupek, M.; Lukes, P.; Simek, M.; Schmidt, J.; Cernak, M. Generation of Chemically Active Species by Electrical Discharges in Water. Plasma Sources Sci. Technol. 1999, 8, 258. (22) Robinson, J. W.; Ham, M.; Balaster, A. N. Ultraviolet Radiation from Electrical Discharges in Water. J. Appl. Phys. 1973, 44, 72. (23) Martin, E. A. Experimental Investigation of a High-Energy Density, High-Pressure Arc Plasma. J. Appl. Phys. 1960, 31, 255. (24) Robinson, J. W. Measurements of Plasma Energy Density and Conductivity from 3 to 120 kbar. J. Appl. Phys. 1967, 38, 210. (25) Willberg, D. M.; Lang, P. S.; Hochemer, R. H.; Kratel, A.; Hoffmann, M. R. Electrohydraulic destruction of hazardous wastes. CHEMTECH 1996, 26, 52. (26) Hoffmann, M. R.; Hua, I.; Hochemer, R.; Willberg, D.; Lang, P.; Kratel, A. Chemistry Under Extreme Conditions in Water Induced Electrohydraulic Cavitation and Pulsed-Plasma Discharges. In Chemistry Under Extreme or Non-Classical Condi-
tions; van Eldik, R., Hubbard, C. D., Eds.; John Wiley and Sons: New York, 1997; p 429. (27) Leitner, N. K. V.; Urashima, K.; Bryden, A.; Ramot, H.; Touchard, G.; Chang, J. S. Mechanism of VOC Removal by Pulsed Arc Electrohydraulic Discharge Systems. Presented at the Third International Symposium on Non-Thermal Plasma Technology for Pollution Control, Chejou Island, Republic of Korea, 2001. (28) Willberg, D. M.; Lang, P. S.; Hochemer, R. H.; Kratel, A.; Hoffmann, M. R. Degradation of 4-chlorophenol, 3,4-dichloroaniline, and 2,4,6-trinitrotoluene in an electrohydraulic discharge. Environ. Sci. Technol. 1996, 30, 2526. (29) Lang, P. S.; Ching, W. K.; Willberg, D. M.; Hoffmann, M. Oxidative degradation of 2,4,6-trinitrotoluene by ozone in an electrohydraulic discharge reactor. Environ. Sci. Technol. 1998, 32, 1342. (30) Zastawny, H. Z.; Romat, H.; Leitner, N. K.; Chang, J. S. Pulsed arc discharges for water treatment and disinfection. In Electrostatics 2003; Institute of Physics Conference Series; Institute of Physics, Publishing Ltd.: Bristol, U.K., 2004; p 325. (31) Kratel, A. W. H. Pulsed Power Discharge in Water. Ph.D. Dissertation, California Institute of Technology, Pasadena, CA, 1996. (32) Lu, X.; Pan, Y.; Liu, M.; Zhang, H. Spark model of pulsed discharge in water. J. Appl. Phys. 2002, 91, 24. (33) Lu, X.; Pan, Y.; Liu, K. F.; Liu, M. H.; Zhang, H. H. Early Stage of Pulsed Discharge in Water. Chin. Phys. Lett. 2001, 18, 1493. (34) Lu, X.; Liu, M. H.; Jiang, Z. H.; Pan, Y. Effects of Ambient Pressure on Bubble Characteristics. Chin. Phys. Lett. 2002, 19, 704. (35) Davies, R. A.; Hickling, A. J. Glow-discharge Electrolysis. Part I. The Anodic Formation of Hydrogen Peroxide in Inert Electrolytes. Chem. Soc. Faraday Trans. 1952, 3595. (36) Sengupta, S. K.; Singh, O. P. Contact Glow Discharge Electrolysis: A Study of its Chemical Yields in Aqueous Inerttype Electrolytes. J. Electroanal. Chem. 1994, 369, 113. (37) Tezuka, M.; Iwasaki, M. Liquid-phase Reactions Induced by Gaseous Plasma. Decomposition of Benzoic Acids in Aqueous Solution. Plasmas Ions 1999, 1, 23. (38) Tezuka, M.; Iwasaki, M. Plasma Induced Degradation of Chlorophenols in an Aqueous Solution. Thin Solid Films 1998, 316, 123. (39) Tezuka, M.; Iwasaki, M. Plasma-induced Degradation of Aniline in Aqueous Solution. Thin Solid Films 2001, 386, 204. (40) Eisenberg, G. M. Colorimetric Determination of Hydrogen Peroxide. Ind. Eng. Chem. Res. 1943, 15, 327. (41) LaVerne, J. A.; Pimblott, S. M. New Mechanism for H2 Formation in Water. J. Phys. Chem. A 2000, 104, 9820. (42) Pastina, B.; LaVerne, J. A.; Pimblott, S. M. Effect of Molecular Hydrogen on Hydrogen Peroxide Production in Water Radiolysis. J. Phys. Chem. A 1999, 103, 5841. (43) Hiroki, A.; Pimblott, S. M.; LaVerne, J. A. Hydrogen Peroxide Production in the Radiolysis of Water with High Radical Scavenger Concentrations. J. Phys. Chem. A 2002, 106, 9352.
Received for review December 9, 2004 Revised manuscript received March 30, 2005 Accepted April 12, 2005 IE048807D
