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Ind. Eng. Chem. Res. 2002, 41, 5906-5911
Decomposition of Organic Compounds in Water by Direct Contact of Gas Corona Discharge: Influence of Discharge Conditions Noriaki Sano,* Toru Kawashima, Junya Fujikawa, Tatsuya Fujimoto, Takaaki Kitai, and Tatsuo Kanki Department of Chemical Engineering, Himeji Institute of Technology, 2167 Shosha, Himeji, Japan 671-2201
Atsushi Toyoda R&D Division, Envisys Ltd., 2-121 Tegara, Himeji, Japan 670-0972
Water purification experiments to decompose phenol, acetic acid, and Rhodamine B in water were conducted using a direct contact of gas corona discharge to the water surface. It was shown that O2 was important in the gas phase for the degradation process, and the negative corona showed higher degradation rates than the positive corona. It was found that the organic contaminants can effectively be decomposed by the present method without pH adjustment. The experimental results indicated that there were optimized values in the O2 concentration, the gas resident time above the water, and the cathode-anode gap. It was also indicated that the O2/CO2 mixture showed a higher degradation rate than the O2/N2 mixture for the gas phase. As the degradation mechanism, the uncharged short-lived radicals are considered to be important. Introduction Corona discharge has been used for application to gas purification for many years. Because corona discharge can produce many gaseous reactive radicals such as free electrons, negative ions, positive ions, uncharged shortlived radicals, and ozone (O3), it can be easily applied to gas purification by simply introducing the treated gas to the corona discharge region.1-4 However, it is necessary to have a special design if we want to apply the corona discharge to water purification. Conventionally, O3 oxidation has been well developed for this subject.5,6 In this method, O3 produced by discharge techniques is transferred to a gas-water contacting unit, where organic compounds in water are oxidized by O3. Though O3 can be effectively used for decomposition of organic compounds, we should be reminded that more reactive species are produced in the corona discharge region which cannot be utilized by this conventional ozonation because the lifetimes of such species are extremely short.7,8 Recently, some efforts to utilize these coronainduced short-lived species for water purification were carried out by several methods. For example, a pulsed corona discharge is generated in water.9,10 This method can successfully supply the short-lived radicals to the treated water from the submerged corona spot. In another effort, a gas corona discharge is generated over the treated water.11-14 There the short-lived species produced in the gas phase adjacent to the treated water are expected to reach the water surface. We can consider several unique points about the reactor design and operational conditions in this method: (1) A simple unpulsed direct current (dc) high voltage (HV) can be used to generate corona discharge.12,15 (2) The shortlived radical can be supplied to a relatively large surface area by optimized electrodes arrangement.15 (3) There should be an optimized gas condition to supply the reactive radicals to water. In this paper, decomposition * To whom correspondence should be addressed. Tel: +81-792-67-4845. Fax: +81-792-67-4845. E-mail: sano@ mech.eng.himeji-tech.ac.jp.
Figure 1. Reactor concept for water purification by direct contact of dc gas corona discharge.
of aqueous phenol (C6H5OH), acetic acid (CH3COOH), and Rhodamine B (C28H31ClN2O3) by gaseous corona discharge was investigated, focusing on discharge conditions including the gas components, discharge polarity, cathode-anode gap, and gas resident time. Experimental Section Figure 1 shows the reactor concept used in this study. The reactor was equipped with stainless steel wires and a plate apart from each other in the gaseous phase. An unpulsed dc HV (17-20 kV) was applied on the wire cathodes to generate corona discharge in the gas phase, and the grounded-plate electrode was covered with the
10.1021/ie0203328 CCC: $22.00 © 2002 American Chemical Society Published on Web 10/26/2002
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Figure 2. Degradation of C6H5OH in the presence and absence of O2 in the gas phase. Water volume ) 100 cm3, Cin,C6H5OH ) 50 g m-3, I ) 0.5 mA, and V ) 17.5 kV (negative discharge).
treated water. The discharge polarity was changeable to investigate its influence. We prepared two reactors, one for batch operation with a small water volume (100 cm3) and the other for relatively large volume (2000 cm3). In the large reactor system, the treated water was circulated through the reactor with a reservoir attached outside the discharge reactor. The small type was suitable to collect fundamental data for the quick response. The temperature of the treated water in both reactors was controlled by the contact of cooling water (10 °C) with the plate electrode on its bottom side. We used 10 wires (0.3 mm diameter, 110 mm length, and 10 mm intervals) and the plate (225 × 175 mm) for the small reactor and 24 wires (0.3 mm diameter, 135 mm length, and 18 mm intervals) and a plate electrode (200 × 480 mm) for the larger one. The volumes of the gas phase in the smaller and larger reactors are respectively 1.65 and 14.4 L. In our experiments, the average depth of the liquid film was about 3 mm. When the water was circulated through the larger reactor, the flow velocity of the liquid film was 0.033 m s-1. C6H5OH, CH3COOH, and C28H31ClN2O3 were used as target aqueous contaminants. The pHs of the solutions measured (Hriba pH meter F-22) were 5.8, 4.0, and 4.1, respectively. A total organic carbon (TOC) analyzer (Shimadzu TOC-5000), a UV spectrophotometer (Shimadzu UV-200), and a HP liquid chromatograph with a UV-vis and an electric conductivity detector (Shimadzu SPD-10AVP) were used to analyze the treated water. A photoabsorption-based O3 detector (Ebara EG500) and the potassium iodide method16 were used to measure the concentration of O3 in the gas. Results and Discussion Figure 2 shows the degradation of C6H5OH using N2 and a O2/N2 mixture ([O2] ) 20%) in the gas phase using negative HV on the wire electrodes. The degradation extent is defined as the ratio of the concentration drop of a target compound or TOC to the initial concentration as eq 1 where Ψ, Cin, and Cout are the degradation extent
Ψ)
Cin - Cout Cin
(1)
and initial and final concentrations. It is shown that the degradation rate is significantly low when N2 is used, suggesting that O2 is indispensable for the degradation of organic compounds. This result suggests that the species induced from O2 are important for the degradation process.
Figure 3. Influence of discharge polarity on the degradation of C6H5OH: (a) TOC degraded by negative discharge; (b) TOC by positive; (c) CC6H5OH by negative; (d) CC6H5OH by positive. Water volume ) 2000 cm3, Cin,C6H5OH ) 43 g m-3, I ) 1 mA, V ) 17.8 kV (negative), and V ) 19.5 (positive).
There are reports indicating that the activity of the negative discharge is higher than that of the positive one.17,18 Figure 3 shows the degradation of C6H5OH in water using the positive and negative HVs in a O2/N2 mixture ([O2] ) 20%). One can observe that the degradation rate increases by the negative polarity more rapidly than by the positive polarity. From these results, the O2-originated negative ions can contribute more effectively for the degradation than the positive ones. From this result, we focused on the negative polarity in the latter experiments. When the negative HV was applied to generate the corona discharge, electrons and negative ions produced by the plasma region around the wire cathodes drift toward the liquid film. Also, the uncharged O atomic radical can be produced by the electron impact to the O2 molecule.7,8 Outside the plasma region, where the electron energy is relatively low, negative ions such as O- are produced by the dissociative electron attachment of O2.19 In the case where the electron energy is extremely low, O2- also would be produced by the threebody electron attachment.19 Also, O3 and O3- would be produced from the reactions with O, O2, and ions. Additionally, H, H-, OH, and OH- are expected to be produced because the gas phase contains H2O vapor from the water film. Not only the electron attachment but also the charge transfer between ions and gas molecules can reproduce ionic species. When these gas ions drift to the water surface, aqueous secondary radicals would be readily produced because these ions are unstable at the water surface as
O-(gas) + H2O f OH-(aq) + OH(aq)
(2)
O2-(gas) + H2O f OH-(aq) + O2H(aq)
(3)
The OH and O2H radicals produced in the water would be reactive with organic compounds.12 We expect that a part of the uncharged gas radicals O, H, and OH would further be carried to the water by the gas agitation caused by the ion wind of several m s-1 order,20 although the average lifetime of the uncharged radicals in the gas phase is very short.8 When these radicals reach the liquid film, the aqueous reactive radicals may be produced.
O(gas) + H2O f OH(aq) + OH(aq)
(4)
OH(gas) f OH(aq)
(5)
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Figure 4. Contribution of O3 oxidation for the degradation of C28H31ClN2O3: condition of corona discharge (Cin ) 57 g m-3, water volume ) 100 cm3, I ) 0.3 mA, V ) 14.2 kV (negative), CO3 ) 950 ppm); condition of O3 bubbling (water volume ) 100 cm3, CO3 ) 4000 ppm, bubbling flow rate ) 6 .7 cm3 s-1).
In addition to the contribution of the corona-induced ions and radicals, O3 should oxidize the organic contaminants. When the corona discharge was generated in our reactor with a O2/N2 mixture ([O2] ) 20%), O3 was detected as approximately 950 ppm. To evaluate the contribution of O3 for its degradation process, we compared our method with O3 bubbling in the degradation of CH3COOH, C6H5OH, and C28H31ClN2O3 in distilled water. In the comparison between our method and O3 oxidation of the same concentration, the concentrations of C6H5OH and C28H31ClN2O3 are decreased by both methods. The deceasing rates of the concentrations of these compounds by our reactor were quite similar to those by O3 oxidation. This result suggests that C6H5OH and C28H31ClN2O3 are easily converted to byproducts by the O3 oxidation. However, CH3COOH and the TOC from C6H5OH and C28H31ClN2O3 were not degraded significantly by O3. These means that CH3COOH and the byproducts from C6H5OH and C28H31ClN2O3 are relatively stable against O3. Then, we increased the O3 concentration, and the air containing 4000 ppm O3 was bubbled through the treated water. Figure 4 shows the degradation of C28H31ClN2O3. It is observed that degradation of the C28H31ClN2O3 concentration is significantly easier than that of TOC. This is because C28H31ClN2O3 can be converted to the stable byproducts by O3 oxidation as explained above. Contrary to this, the TOC from C28H31ClN2O3 was not degraded significantly even when O3 oxidation was conducted with the O3 concentration that was about 4 times higher than that in our reactor. Similar results were obtained in the degradation of CH3COOH and C6H5OH. Here, it should be noticed that the degradation rate by O3 oxidation depends on the pH in the treated water. The pH of the water used here was not optimized for O3 oxidation. Although this experiment seemed not to be good enough for quantitative comparison because we did not obtain the bubble size and resident time in bubbling, the significant difference between our method and O3 bubbling noticed in this figure suggests that the O3 oxidation should not be the main scheme in the degradation of TOC in our condition. We consider that the ions and uncharged short-lived radicals may be important for the degradation process because O3 oxidation seems not to be the main reaction with the stable contaminants. To examine whether the uncharged radical would be an important species, the experiments using the different cathode-anode gap
Figure 5. Influence of the cathode-anode gap on the degradation of C28H31ClN2O3. Cin ) 38 g m-3, and water volume ) 100 cm3.
should be useful because the efficiency of such radicals to reach the water surface depends on the cathodeanode gap. On the other hand, the ion flux to the water is determined from the discharge current. Figure 5 shows the degradation of C28H31ClN2O3 with different cathode-anode gaps of 14, 17, and 20 mm with the same discharge current 0.3 mA, where the average ion flux to water surface was expected to be 3.1 × 10-9 mol m-2 s-1. The voltage necessary to generate this current was 11.5, 14.5, and 18.0 kV for the cathode-anode gaps of 14, 17, and 20 mm, respectively. It was found that the gap of 17 mm showed a higher degradation rate than those of 14 and 20 mm. This result indicates that there should be an optimized cathode-anode gap to achieve the maximum degradation efficiency. We expect that the production rates of the uncharged radicals increase with the voltage when the cathode-anode gap is increased. This is because the higher voltage can cause a stronger electron impact to gas molecules in the plasma region. However, the radicals which can reach the water surface decrease if the cathode-anode gap is excessively large because of their short lifetimes. Therefore, we consider that the optimized cathode-anode gap is rooted in the efficiency to supply the uncharged radicals to water. Our previous report15 suggested that the efficiency to supply uncharged radicals to water was important from the experiments using different wire-cathode diameters to provide the different voltages with the same current. The present result seems to be consistent with this previous report. If a fresh gas is supplied to the reactor, we can continuously refresh the gas above the water. The gassupplying rate to the reactor was changed to observe its influence with 0, 0.5, 3, and 5 L min-1. Here, a O2/ N2 mixture ([O2] ) 20%) was used for the introduced gas. The average gas resident times for 0.5, 3, and 5 L min-1 were respectively 28.9, 4.8, and 2.9 min. It should be noted that the gas stream was considered to be mixed well above the water because of the strong ion wind. Figure 6 shows the degradation of C6H5OH under these conditions. It was found that the moderate flow rate of 0.5 L min-1 showed the highest degradation rate. Because the same current was used for all cases, the ion flux to the water surface was considered to be the same. However, the efficiency of the uncharged radical to reach the water surface might be different depending on the gas resident time. During the discharge process, a part of O2 with N2 in the gas-supplying mixture may be converted to NOx. Although a gas analysis using a gas detector tube
Ind. Eng. Chem. Res., Vol. 41, No. 24, 2002 5909
Figure 7. Influence of the O2 concentration on the degradation of C6H5OH. Cin,C6H5OH ) 50 g m-3, and water volume ) 2000 cm3). Figure 6. Influence of the gas flow rate (O2/N2 ) 20/80) on the degradation of C6H5OH. Cin,C6H5OH ) 50 g m-3, and water volume ) 2000 cm3.
(GASTEC SG4010) showed that the concentration of NOx in the gas phase was kept negligible during the discharge, aqueous NO3- was detected in the treated water. The production of NO3- would be caused by the absorption of NOx from the gaseous to aqueous phase. It was found that NO3- was produced in water by 2.43 × 10-5 mol s-1 A-1 in our reactor. Using this production rate, O2 is consumed by 1.5 × 10-4 mol h-1 with 2.5 mA. Because the volume of the gas phase in the larger reactor was 14.4 L (about 0.6 mol), the O2 concentration in this gas phase decreases by approximately 0.2% in 8 h, which is considered to be negligible unless the O2 concentration is very low. In the degradation process, O2 also should be consumed by the oxidation of the aqueous organic compounds. In fact, the gas detector tube indicated the CO2 production, which may be caused by the decomposition of organic compounds. The complete oxidation of 50 g m-3 of C6H5OH in 2000 cm3 water to CO2 requires O2 of 6.4 × 10-3 mol. This consumption can cause the concentration drop of O2 by approximately 1%, which is also negligible unless the O2 concentration is very low. Therefore, the O2 consumption should not be influential on the degradation rate. It should be noted that, when the gas-supplying rate increases, O3 and H2O vapor will be diluted. Because the production of the short-lived radicals should be influenced by the coexisting gas species in the discharge zone, the change in the concentrations of H2O and O3 should affect the efficiency to supply the radicals to the water surface. At this stage, we intend to suggest a possibility that there should be an optimized gas flow rate to supply the radical to water. We plan to do more detailed work to elucidate the effect of the gas resident time based on an elaborate analysis of gas species and aqueous products. Because O2 is the key component in the gas phase, it is natural to consider increasing the O2 concentration to improve the degradation efficiency. The experiments to degrade C6H5OH using the three different O2 concentrations of 20%, 50%, and 100% were carried out. Figure 7 shows the degradation of C6H5OH with these O2 concentrations. It was found that 50% is the best concentration among these concentrations for the high degradation rate. This tendency is significant especially in TOC. The reason to have the optimum O2 concentration can be considered as follows: (1) 50% of O2 shows a higher degradation rate than 20% because the produc-
Figure 8. Degradation of C6H5OH with O2/N2 and O2/CO2 mixtures. Cin,C6H5OH ) 50 g m-3, I ) 0.3 mA, V ) 14.3 kV, and water volume ) 100 cm3.
tion of the uncharged O radicals increases with increasing O2 concentration. (2) However, if the O2 concentration is excessively high, O radicals are easily converted to O3 by their collision with O2 molecules, resulting in the decrease of the O radicals which reach the water surface. It must be reminded that the reactivity of O3 with the stable compounds is not significant in our condition. When corona discharge is generated in the N2/O2 mixture, it is expected to produce nitride acid.14,21 In fact, it was found that the pH decreases during discharge current in our reactor. If the pH 5 water was used as the treated liquid, the pH turned out to be around 3. The NO3- concentration was measured to explore the reason of this pH change, and we confirmed that the pH change was caused by the production of HNO3. We previously found that the degradation rate was lowered by decreasing pH.22 Therefore, a retarding pH change in the treated water should be effective to keep the degradation efficiency. To avoid the HNO3 production, we replaced N2 with CO2 in the gas phase. When CO2 is used in the gas phase, H2CO3 is expected to be produced instead of HNO3. Because carbonate acid has much less solubility in water than nitride acid, less pH change is expected if N2 is replaced with CO2. Figure 8 shows the degradation of C5H6OH with O2/N2 and O2/ CO2 mixtures. The gas components CO2/O2 ) 8/2 show a higher degradation rate than N2/O2 ) 8/2. When the treated water was analyzed, it was confirmed that the production of HNO3 became negligible and the pH change is attenuated. When CO2 was used, 1.9 g m-3 of CO32- was detected as the saturated concentration in the treated water. The detailed study about the influence of ionic impurities in water on the degradation efficiency is now in process.
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species from CO2 such as CO, CO-, and CO3- together with metastable anions. Additionally, one can consider the influence of the electron energy change caused by high-concentration CO2. The mechanism of the effect by adding CO2 should be elucidated in further work. Conclusions
Figure 9. Degradation of C6H5OH with an O2/CO2 mixture. Cin,C6H5OH ) 50 g m-3, I ) 0.3 mA, V ) 13-17 kV, water volume ) 100 cm3, and discharge time ) 1 h.
Figure 10. Degradation of C6H5OH with an O2/CO2 mixture. Cin,C6H5OH ) 50 g m-3, I ) 0.3 mA, V ) 13-17 kV, water volume ) 100 cm3, discharge time ) 2 h).
Considering the analogy to the O2/N2 mixture, it can be expected to have an optimized concentration ratio also in the O2/CO2 mixture. From this consideration, we examined the influence of the O2/CO2 concentration ratio. Figure 9 shows the degradation of C6H5OH treated by 0.3 mA for 1 h with different O2/CO2 ratios. The voltage increased from 13.6 to 16.7 kV when the O2 concentration was changed from 30 to 100%. It was found that the degradation extent of C6H5OH was maximized when CO2/O2 ) 3/7 was used. Figure 10 shows the TOC degradation when the same C6H5OH solution was treated for 2 h. The TOC was degraded by pure CO2 but not so significantly as with O2. It is shown that the TOC degradation extent with CO2/O2 ) 3/7, 5/5, and 8/2 became higher than that with pure O2 or CO2. The concentration of O3 produced in the gas phase was measured during the degradation process. The O3 concentration became saturated in 30 min. The O3 concentration reached 1100 ppm with pure CO2 for the gas phase. When O2 was raised to 20% (CO2/O2 ) 8/2), the O3 concentration reached 2600 ppm. Even when the O2 concentration was further added to more than 50%, the O3 concentration showed almost a constant value of around 4500 ppm. It should be noticed that the degradation extent with CO2/O2 ) 8/2 was higher than that with pure O2, although the O3 concentration with CO2/O2 ) 8/2 was relatively low. This result also indicates that O3 oxidation is not the main scheme for the TOC degradation. The reason for this result might be that the coexisting CO2 would maximize O radicals which reach the water surface by retarding the conversion of the O radical to O3. Other possible reasons for this result would be related with the production of gas
Water purification experiments to decompose C6H5OH, C28H31ClN2O3, and CH3COOH in water were conducted. We used a reactor in which wire electrodes were placed in a gas phase above the water film on a plate electrode. Unpulsed dc corona discharge was generated in the gas phase, and the short-lived reactive species produced by this discharge are expected to reach the water surface, resulting in the decomposition of organic contaminants in the target water. It was shown that O2 is important for the degradation process, and the negative corona is more suitable than the positive corona. O3 oxidation was compared to that of the present method, and it was found that the byproducts from C6H5OH, C28H31ClN2O3, and CH3COOH are relatively stable against O3. This result indicates that O3 oxidation may not be the main degradation scheme in the present condition. It was also indicated that there are some controlling factors for the degradation rate in the present method: (1) the gas resident time above the water; (2) the cathode-anode gap; (3) the O2 concentration. There were optimized values for these factors. We considered that these optimized conditions would give the high efficiency of the short-lived radicals to reach the target water. It was also shown that the degradation rate increased when N2 in gas was replaced with CO2. Acknowledgment This work was partly supported by a Grant-in-Aid for Scientific Research (A), No. 11750669(1999), from the Ministry of Education, Science, and Culture of Japan and by the Funds of Hyogo Prefecture for Research and Development for Middle and Small Enterprises, for which we express our gratitude. Literature Cited (1) Tamon, H.; Mizoata, H.; Sano, N.; Okazaki, M. New Concept of Gas Purification by Electron Attachment. AIChE J. 1995, 41, 1701-1711. (2) Sano, N.; Tamon, H.; Okazaki, M. Removal of Chlorofluorocarbon, 1,1,2-Trichloro-1,2,2-Trifluoroethane, in Gas by a CoronaDischarge Reactor. Ind. Eng. Chem. Res. 1998, 37, 1428-1434. (3) Huang, L.; Nakajyo, K.; Hari, T.; Ozawa, S.; Matsuda, H. Decomposition of Carbon Tetrachloride by a Pulsed Corona Reactor Incorporated with In Situ Absorption. Ind. Eng. Chem. 2001, 40, 5481-5486. (4) Penetrante, B. M.; Bardsley, J. N.; Hsiao, M. C. Kinetic analysis of nonthermal plasmas used for pollution control. Jpn. J. Appl. Phys. PT1 1997, 36, 5007-5017. (5) Beltran, F. J.; Garcya-Araya, J. F.; Alvarez, P. M. Sodium Dodecylbenzenesulfonate Removal from Water and Wastewater. 1. Kinetics of Decomposition by Ozonation. Ind. Eng. Chem. Res. 2000, 39, 2214-2220. (6) Acero, J. L.; Stemmler, K.; von-Gunsten, U. Degradation Kinetics of Atrazine and Its Degradation Products with Ozone and OH Radicals: A Predictive Tool for Drinking. Environ. Sci. Technol. 2000, 34, 591-597. (7) Loiseau, J. F.; Monge, C.; Peyrous, R.; Held, B.: Coste, C. Numerical Simulation of Ozone Axial and Radial Distribution in a Cylindrical Oxygen-Fed Ozonizer. J. Phys. D: Appl. Phys. 1994, 27, 63-73.
Ind. Eng. Chem. Res., Vol. 41, No. 24, 2002 5911 (8) Peyrous, R.; Pignolet, P.; Held, B. Kinetic Simulation of Gaseous Species Created by an Electrical Discharge in Dry or Humid Oxygen. J. Phys. D: Appl. Phys. 1989, 22, 1658-1667. (9) 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 Solution. Hazard. Waste Hazard. Mater. 1993, 10, 209-219. (10) Sun, B.; Sato, M.; Harano, A.; Clements, J. S. Non-Uniform Pulse Discharge-Induced Radical Production in Distilled water. J. Electrostat. 1998, 43, 115-126. (11) Hoeben, W. F. L. M.; van Veldhuizen, E. M.; Kroesen, G. M. W. Gas-Phase Corona Discharge for Oxidation of Phenol in an Aqueous solution. J. Phys. D.: Appl Phys. 1999, 32, L133-L137. (12) Sano, N.; Fujimoto, T.; Kawashima, T.; Kanki, T.; Toyoda, A. Possibility of Utilization of Radicals and Ions Produced by Gaseous Corona Discharge to Degradation of Organic Compounds in Water. 5th Asian Pacific Conference of Sustainable Energy and Environmental Technologies, Hong Kong, 1999; pp 89-93. (13) Sharma, A. K.; Josephson, G. B.; Camaioni, D. M.; Goheen, S. C. Destruction of Pentachlorophenol Using Glow Discharge Plasma Process. Environ. Sci. Technol. 2000, 34, 2267-2272. (14) Sharma, A. K.; Camaioni, D. M.; Josephson, G. B.; Goheen, S. C.; Mong, G. M. Formation and Measurement of Ozone and Nitric Acid in a High Voltage DC Negative Metallic Point toAqueous Plane Continuous Corona Reactor. J. Adv. Oxid. Technol. 1997, 2, 239-247. (15) Sano, N.; Kawashima, T.; Kanki, T.; Toyda, A. Effect of
the Electode Shape in Gas Phase on Water Purification Degrading Organic Contaminants Using Corona Discharge. Trans. Inst. Elect. Eng. Jpn. 2001, 121A, 710-711. (16) Sano, N.; Nagamoto, T.; Tamon, H.; Suzuki, T.; Okazaki, M. Removal of Acetaldehyde and Skatole in Gas by Corona Discharge Reactor. Ind. Eng. Chem. Res. 1997, 36, 3783-3791. (17) Brandvold, D. K.; Martinez, P.; Dogruel, D. Polarity Dependence of N2O Formation from Corona Discharge. Atomos. Environ. 1989, 23, 1881-1883. (18) Fujii, T.; Kitamura, H.; Rea, M. Influence of Voltage Polarity to Pulsed Corona Characteristics. Trans. Inst. Elect. Eng. Jpn. 1997, 117A, 90-91. (19) Massey, S. H. Negative Ions; Cambridge University Press: Cambridge, England, 1976. (20) Yabe, A.; Mori, Y.; Hijikata, K. EHD Study of the Corona Wind between Wire and Plate Electrondes. AIAA J. 1978, 16, 340. (21) Viggiano, A. A. In-situ Mass-Spectrometry and Ion Chemistry in the Stratosphere and Troposphere. Mass Spectrom. Rev. 1993, 12, 115-137. (22) Fujimoto, T. Master’s Thesis, Himeji Institute of Technology, Himeji, Japan, Mar 2000.
Received for review May 3, 2002 Revised manuscript received September 11, 2002 Accepted September 14, 2002 IE0203328
