Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
1995-04-06
2004-02-24
Reamer, James H. (Department: 1614)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C204S158200, C204S158210, C588S253000, C588S253000, C110S346000, C210S748080
Reexamination Certificate
active
06695953
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to oxidation of organic contaminants in aqueous mediums using corona induced reactions. More particularly, the present invention relates to the use of a source or means other than oxygen, such as iron, in a corona reactor to facilitate the production of hydroxyl radicals from hydrogen peroxide (H
2
O
2
) generated by corona discharges in the aqueous medium to significantly enhance the oxidation of organic contaminants in the aqueous mediums. In addition, the present invention relates to the use of such sources or means in combination with oxygen in corona discharge procedures to even further oxidize organic contaminants in aqueous mediums. Still further, the present invention concerns the addition of particles, such as coarse and/or fine particles, to the aqueous medium in a corona reactor to affect the nature of the properties of the corona discharge, i.e., streamer length, intensity, number of streamers and sparkover voltage, thereby increasing the breakdown voltage (i.e., the maximum voltage prior to sparkover), so that the oxidation of organic contaminants may be accelerated.
BACKGROUND
A normal corona discharge is formed when dc or ac high voltage is applied between a non-uniform electrode geometry in a fluid dielectric. An electric corona has a three-dimensional discharge pattern that displays highly localized positive or negative space charge waves. These waves constitute the active region that propagates due to avalanches of electrons present in the high electric field. The electron avalanches are triggered by a photonization mechanism that provides secondary seed electrons. A region of weakly ionized plasma, known as the “passive region,” remains along the track of the wave. This region provides the path for the current flow from the high voltage electrode. This current flow provides energy for the advancement of the corona.
Pulsed streamer corona technology uses high voltage pulses with very short width, approximately 100-1000 ns. This unique characteristic produces a corona that differs markedly from normal continuous discharge (dc corona), ac discharge, and long-pulse (~1 ms)* corona discharge. In the past, a pulsed streamer corona discharge has been used for treating gas phase pollutants. See, Clements, I. S. et al.:
IEEE Transactions Ind. Appl.,
IA-(23):224 (1987). In the gas phase, pulsed streamer corona was believed to be much more effective at promoting the reactions leading to desulfurization and dentrification than, for example, electron beam processes. See, Clements, I. S. et al.:
IEEE Transactions Ind. Appl.,
IA-(23):224 (1987). This was believed to be attributed to the more efficient production of hydroxyl radicals using pulsed stream corona. In addition, the work on pulsed streamer corona discharge in aqueous solutions with oxygen gas continuously bubbled through the solution has demonstrated the production of large amounts of ozone. See, Clements, I. S. et al.:
IEEE Transactions Ind. Appl.,
IA-(23):224 (1987).
The use of positive pulsed streamer corona for air pollutant treatment has been demonstrated for a number organic and inorganic toxins. U.S. Pat. No. 4,695,358 to Mizuno et al. discloses a method for converting sulfur dioxide and/or nitrogen oxide gases to acid mist and/or particle aerosols in which the gases are passed through a streamer corona discharge zone having electrodes of a wire-cylinder or wire-plate geometry.
Moreover, the use of positive pulsed streamer corona for air pollutant treatment has been demonstrated for a number of organic and inorganic toxins. See Clements, J. S. et al.: in Conf. Record of the IEEE-Indust. Appl. Soc. Ann. Meeting, pp. 1183-1190 (1986); Mizuno A. et al.: Use of an Electron Beam for Particle Charging in: Conference Record of the IEEE-Indus. Appl. Doc. Ann. Meeting. pp 1215-1219. Chicago, Ill. (October 1984); Masuda et al.: Control of NO
x
by Positive and Negative Pulsed Corona Diarges. Conference Record of the IEEE Indust. App]. Soc. Ann. Meeting, pp. 1173-1182 Denver, Colo. (1986); Moon, et al.: High Efficiency Ozone Generation Using A Helical Strip-Line Electrode and A Fast Rising Pulse Voltage. Conference Record of the IEEE Indust. Appl. Soc. Ann. Meeting. pp 1205-1210. Denver, Colo. (1986); and Chang, J. S, et al.:
IEEE Transactions on Plasma Sci.,
19(6):1152 (1991). However, in aqueous phase systems, except for the work of Clements, I. S. et al.:
IEEE Transactions Ind. Appl., IA-(
23):224 (1987), there has been no systematic investigation of pulsed corona in aqueous systems. Other processes that have been used to treat aromatic compounds include the aqueous-phase radiation treatment of benzene and alkyl-substituted benzenes, Nickelsen, N.G. et al.:
Environ. Sci. Technol.,
(26):144 (1991), and anthraquinone dye, Clements, I. S. et al.:
IEEE Transactions Ind. Appl.,
IA-(23):224 (1987), using electron beams and the use of cobalt gamma radiation to treat solutions containing phenol, Micic, O. I., et al.: Radiation Chemical Destruction of Phenol in Aqueous Solution, Radiation for a Clean Environment, International Atomic Energy Agency, Vienna, Austria, IAEA-SN-1194, 233-239 (1975). Clements, I. S. et al.:
IEEE Transactions Ind. Appl.,
IA-(23):224 (1987), have shown that pulsed corona discharges in aqueous solutions with oxygen bubbling through high voltage needle electrodes produces large amounts of ozone that can, in turn, lead to the decolorization of dyes.
The conventional mechanisms by which organic contaminants are degraded are quite varied. For example, molecular ozone can selectively react with contaminants through cycloaddition, electrophilic reaction, and nucleophilic reaction with unsaturated aromatic and aliphatic species. See Langlais, B. et al.: eds., Ozone in Water Treatment, Applications and Engineering, Lewis Publishers, Chelsea, Michigan (1991). In addition, ozone can lead to the formation of hydroxyl radicals. These radicals are highly reactive with a broad range of organic materials, Haag, W. R. et al.:
Environ. Sci. Technol.,
(26):1005 (1992), and they are generally considered crucial for the breakdown of most organic waste contaminants. Hydroxyl radicals are also formed in photocatalytic reactions of hydrogen peroxide, Zepp, R. G. et al.:
Environ. Sci. Technol., l (
26):313 (1992), nitrates, Zepp, R. G. et al.:
Environ. Sci. Tech.,
(21):443-450 (1987), nitrites, Mopper, K. et al.:
Science,
(250):662 (1990), and semiconductor surfaces, Korman, C. et al.:
Environ. Sci. Technol.,
(22):798-806 (1988); Matthews, R. W.:
J. Phys. Chem.,
(91):3328-3333 (1987); and Davis, A. P. et al.:
Wat. Res.,
(24):53-550 (1990). Photocatalytic processes have also been investigated for the removal of aqueous waste containing metals, such as silver, gold, mercury, cadmium, chromium, copper, nickel and platinum, alone and in combination with organic waste. The effectiveness of most of the above oxidation methods is attributed to the formation of hydroxyl radicals, however, the major problems with sustaining these reactions are radical scavenging by carbonate and other ions in solution and the low selectivity of the reactions.
Another possible way of removing organic contaminants from wastewater is by corona-induced flocculation. This is similar to an alternative treatment strategy proposed for phenol-containing wastes that utilizes hydrogen peroxide and the enzyme peroxidase to polymerize the phenol into colloidal size particles that can be removed by sedimentation or filtration. See, Klibanov, A. N. et al.:
Science,
(221):259-261 (1983) and Nakamoto, S. et al.:
Wat. Res.,
(26):49-54 (1992). Indeed, radiation processes are commonly used to initiate free radical polymerization for the production of synthetic polymers, and similar radical mechanisms may occur in aqueous corona systems under properly controlled solution conditions.
Ozone is known to also have a strong effect on coagulation or flocculation of organic matter. However, the mechanisms by which ozone facilitate coagulation are not well understood. Indeed there may
Finney Wright C.
Grymonpre David R.
Locke Bruce R.
Akerman & Senterfitt
Florida State University
Reamer James H.
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