JPH08323147A - Decomposition of noxious gas by corona formation reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase decomposition rate by solving a lack in corona attenuation by enhancing pulse corona discharge characteristics and decomposing contaminated material by co-existing with a carrier gas having higher ionization potential than an ionization potential which the contaminated gas has while exposing the contaminated material to be corona discharge. SOLUTION: Oxygen component of a gas-phase process stream is maintained to 21 volume % or less by supplying the gas-phase process stream containing the contaminated material and a carrier gas having higher ionization potential than that of the preferred seed of the contaminated material. After the contaminated material in the gas-phase process stream is decomposed by exposing the gas-phase process stream to corona discharge and the decomposed by-product is generated from the contaminated material, the decomposed by-product is disposed. Here, it is preferable to mix hydrogen or ammonium within a range of 1-20,000 ppmv of the contaminated material in the gas-phase process stream. The carrier gas used is nitrogen, He, Ne, Ar or mixture of them, and the contaminated material is halogen compounds.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a perfluorinated compound (PF).
C), chlorofluorocarbons (CFCs) or volatile organic compounds (VOCs) in the field of weakening harmful gases as may be found in industrial process waste.

The present invention relates to gas phase pollutants such as NF ₃ , SF ₆ , CF ₄ , C contained in waste streams from manufacturing processes.
Cl ₂ F ₂ , C ₇ H ₈ , CH ₂ Cl ₂ and CH ₃ CC
Particularly suitable for weakening / decomposing l ₃ .

[0003]

BACKGROUND OF THE INVENTION Industrial processing applications (including those in the semiconductor industry) that typically use or produce large quantities of PFCs, CFCs and VOCs are subject to the US Environmental Protection Agency, state and local regulations, and It is now necessary to remove these compounds from the exhaust gas stream of. Halogenated compounds typically used in the semiconductor industry are NF ₃ , C
F ₄ , C ₂ F ₆ , CCl ₂ F ₂ , CCl ₄ , C ₃ F ₈ ,
C ₄ F ₁₀ , BCl ₃ , CClF ₃ , C ₂ Cl ₂ F ₂ ,
CHF ₃ , C ₂ Cl ₃ F ₃ , C ₂ Cl ₂ F ₄ , C ₂ Cl
₃ F ₃ , WF ₆ , SF ₆ , HBr and Hl. Many of these are ozone depleting substances and are associated with global warming. Generally, only a small portion of these gases are consumed in typical semiconductor fabrication processes. Therefore, the waste stream from a particular process should contain a large amount of toxic and environmentally harmful species. Federal, state and local government agencies in the United States have established policies on waste control of such compounds. Current waste regulation methodologies produce undesirable by-products and are not cost effective.

To date, various techniques have attempted to decompose and weaken some of these gases. The waste detergents available on the market typically utilize a combination of four waste control techniques. 19 of these technologies
Published in April 1993, “Semiconductor International (Semiconductor International)
NAL) "Pieter-Burggraaf, pp. 44-47," Process, Exhaust, Treatment.
Exhaust Treatment) ", including wet, thermal, plasma, or dry techniques. In addition, 1993 NATO ASI Vol. 34," Ecological Science, "Vol. 34, Part A, pp. 65-89," Non-thermal, " Plasma, Technics, Fore, Pollution, Control (Non-thermal Pl
asma Technologies for Pollu
"Control, Plasma, Chemistry, And, Power, Consumption, In, Nonthermal, DeNOx (Plasma Che).
MISRY AND POWER CONSUMPT
ion in Non-thermal DeNOx)
B. M. Studies are currently underway to see if the electron beam technique of NOx and SOx decomposition reported by Penetrante is feasible.

In wet scrubbers, exhaust gases are passed through water or other chemicals through an absorbing spray. The exhaust chemistry does not decompose and is often not absorbed. This technique relies on the fusibility of the exhaust species with water or some other chemical. In addition, there is a problem in processing liquid chemicals once the melting limit has been reached.

Thermal scrubbers necessarily involve mixing the exhaust from a process or processes with hydrogen or oxygen and passing the mixture through a flame or igniter where the exhaust gas burns or decomposes. come. This technique burns waste from industrial process applications that use large amounts of hydrogen or oxygen. In practice, a typical semiconductor manufacturing application would use a flow rate of 50 standard liters per minute. Because of the continuous use of these scrubbers, this gas flow rate is a significant expense to semiconductor manufacturers. Besides,
There are safety issues that must be addressed when using hydrogen (especially when combusting emissions with oxygen).

The plasma scrubber is typically a vacuum (vacuum) process installed between the process reaction chamber and the pump of the processing system. Here, the exhaust gas from the process reaction chamber passes into the plasma which decomposes it. Typical pressures on this scrubber are 0.1 to 10 Torr. An example of a radio frequency plasma type scrubber is shown in U.S. Pat. No. 4,735,633, and a microwave scrubber was published in May 1994 in Electro. chemical. “Options, Fore, Environmentally, Impacted, Pafluorinated, Gaith, Used, Inn, Plasma, Processing (Options for Envi) from Mocella et al.
romantically Impacted Perf
LUORINATED GASES USED IN P
laser processing. ”The problem with these techniques is that once the species decomposes, they are likely to recombine in their original form before being exhausted from the device. Phase by-products can also be produced in the processing reactor or in the scrubber reactor, whether they adhere to the inner surface of the reactor or back diffuse from the scrubber reactor toward the processing reactor, Alternatively, the roughing pump (rough
Hing pump). In either case, the solids lead to conservation problems. Atmospheric plasma such as corona discharge is NOx, SOx and VOC
It is currently being tested as a viable technology with some potential weakening potential. Little work has been done on CFS weakening, and no work on PFC weakening has been done with these techniques. At this time, atmospheric plasma devices are not available on the market.

In dry scrubbers, the exhaust gas passes through a layer of dry granules maintained at a temperature above room temperature. Room temperature conditions result in chemisorption or reaction, while the heating conditions cause decomposition and reaction with the granules. These scrubbers have a low affinity for PFC. Moreover, these scrubbers are inefficient in treating large amounts of gaseous waste.

Gas recycling or recovery is still in development. This technique may not be applicable due to the radicals created in the plasma environment and the low concentration of the gas of interest in the recovery stream. The cost of such a device can also be enormous.

NF ₃ , SF ₆ , C ₂ F ₆ , CF ₄ , CH
Gases such as F ₃ , C ₃ F ₈ and CCl ₂ F ₂ are used by the microelectronics industry with various plasmas including plasma enhanced chemical vapor deposition, plasma etching and plasma cleaning, while CCl ₂ F ₂ , C ₇ H It has been found that ₈ , CH ₂ Cl ₂ and CH ₃ CCl ₃ have a variety of other uses such as water purification, oxidation promotion and the like.

There are various problems in weakening low concentrations of pollutants without consuming a large amount of energy.
The thermal method relies on raising the concentration of the total gas to a very high temperature to generate chemically active species (radicals) in the gas, thereby destroying the contaminant granules. Corona discharges are typically low power discharges, are virtually non-thermal and operate at about atmospheric pressure (760 Torr). It is well suited for use in gaseous waste streams in integrated circuit manufacturing processes or other processes that entrain the gases listed above in atmospheric discharges. A typical reactor for generating such a discharge is a pulse corona reactor. In this scheme, a high voltage pulse is applied to a fine metal wire centered inside the metal tube. Applying such a pulse to this arrangement can generate a large amount of partial discharge (known as a streamline) that radiates from the wire into the cylinder.
The high-energy electrons contained in these streamlines produce the radicals that interact with pollutant molecules, which can be broken down into less dangerous or easier-to-handle molecules. In this way, radicals can be generated without raising the temperature of the bulk gas, thus saving considerable energy consumption. Corona Discharge for Hazardous Gas Treatment, 9th IEEE, 21-23 June 1993, Albuquerque, NM
International, Pulsed, Power, Conference (International Pulsed Po)
wer conference) pages 180-183 IEEE Catalog No. 93CH3350-6
"Coaxial Pulsed, Corona, Reactor, Fore, Treatment, Of, Hazardous, Gas Chair (Coaxial Pulsed Corona)
Reactor Treatment of H
AZ Grouse, RK Hutcherson (H)
utcherson), R.A. A. Korzekhwa (Kor
zekwa), R.A. Rush, R.A. Brown, R.M. Angels
It is described by.

Regarding the decomposition of VOC, NOx and SOx and the removal of particulate matter suspended in a gas via corona discharge, 1993, Volonia, SIF, G. et al. Bonizzoni, W.C. Hook
And E. Edited by Sindoni “Industrial, Applications, Of, Plasma,
Physics, pages 1152-1166, R. Itatani's article "Studies, On,
Toxic, Waste, Distraction, With, Plasma, Inn, Japan (Studies on
Toxic Waste Destruction
with Plasmas in Japan) "and also December 1991 IEEE Trans. P.
lasmaSci. Volume 6 Issue 6 1152-116
J. p. 6 S. Chang, P.G. A. Lawless and T.W. Yamamoto
to) paper "Corona, discharge, process (C
orona Discharge Procedures
s) ", U.S. Pat. No. 4,313,739, U.S. Pat. No. 4,695,358, and U.S. Pat. No. 4,95.
6,152, U.S. Pat. No. 5,061,462 and U.S. Pat. No. 5,236,672. The corona discharges described in these papers are either DC corona discharges or they are at least energy efficient and at least one rank below the pulsed corona reactors described above. Electromagnetic pulse characteristics also differ in terms of pulse duration, repetition rate, peak voltage, peak current and voltage rise time. Most of the research was done in ambient air. Some of the processes discussed in the above U.S. patent require that water be present to facilitate the decomposition of pollutants. In fact, some theories suggest that water is the basic constituent of the carrier gas that aids in many of the pollutant decomposition processes studied to date. NH ₃ is added to a gas mixture containing SO _x or NO _x to add compounds such as (NH ₄ ⁺ ) ₂ SO ₄ = and NH
₄ ⁺ NO ₃ ⁻ to form each 1991 1
February Monthly IEEE Trans. Plasma Sci.
Vol. 19, No. 6, pages 1152-1166, J. -S.
Chang, P. A. Lawless and T. Yamamoto's paper "Corona, discharge, processing (Corona D
ischarge Processes ") and U.S. Pat. No. 4,695,358.

[0013]

Although pulsed corona discharge has been accepted as a low energy source for the decomposition of chemical species, the efficiency of this method is not only for effective industrialization, but also for environmentally damaging harmful effects. It was not sufficient for the majority or complete degradation of the species. The present invention promotes the characteristics of the pulsed corona discharge to overcome the lack of corona decay and dramatically increase the decomposition efficiency, which will be described in more detail below.

[0014]

SUMMARY OF THE INVENTION The present invention is directed to a method of decomposing pollutants from a gas phase process stream using a corona discharge, comprising the steps of: a) priority of pollutants and pollutants to be decomposed. Providing a gas phase process stream comprising a carrier gas having a higher ionization potential than the species; b) maintaining an oxygen content of the gas phase process stream at 21% by volume or less of oxygen; c) the gas phase process. Exposing the stream to a corona discharge to destroy pollutants in the gas phase process stream to generate decomposition by-products from the pollutants; d) disposing of the decomposition by-products. .

Hydrogen is preferably mixed with the gas phase process stream within the range of 1 to 20,000 ppmv of contaminants in the gas phase process stream.

As another example, ammonia is mixed with the process stream within the range of 1 to 20,000 ppmv of contaminants in the process stream.

It is preferred that the gas phase process stream be substantially free of free molecular oxygen.

Preferably, the gas phase process stream is substantially free of free molecular water.

It is preferred that the corona is generated by a pulse corona reactor.

It is also preferred that the corona effectively consists of a stream of high energy electrons.

Preferably, the carrier gas is nitrogen,
Choose from the group consisting of helium, neon, argon and mixtures thereof.

In addition, the contaminants are NF ₃ , SF ₆ , and C.
₂ F ₆ , CF ₄ , CHF ₃ , C ₃ F ₈ , CCl ₂ F ₂ ,
_{C 7 H 8, CH 2 Cl} 2, CH 3 is preferably selected from the group consisting of CCl ₃ and mixtures thereof.

Preferably, the carrier gas is added to the gas phase process stream.

Preferably, the concentration of said pollutant is approximately 1
It is in the range of ppmv to 50,000 ppmv.

Preferably, the pulsed corona reactor is pulsed with a repetition rate of approximately 1 Hz to 10 kHz.

Preferably, the corona discharge has a pulse width in the range of approximately 50 to 500 nanoseconds FWHM.

Further, the corona discharge is approximately 1 to 45 k.
It preferably has a peak voltage of V.

The pulse corona reactor is approximately 14.
It is preferred to have a spark gap pressure of 7 to 200 psia.

Further, the corona is replaced by a silent discharge reactor, an AC packed bed reactor, a point-plane (po).
It is preferably generated by a corona generator selected from the group consisting of an int-plane reactor, a point-point reactor, a capillary reactor, an electron beam reactor and a corona torch reactor.

The present invention is more preferably a method of decomposing halogenated pollutants from a gas phase process stream using a pulsed corona discharge, comprising: a) halogenated pollutants and said decomposed halogenated pollutants. Nitrogen, which has a higher ionization potential
Supplying a gas phase process stream containing a carrier gas selected from the group consisting of helium, neon, argon and mixtures thereof; b) the oxygen and water contents of said gas phase process stream each being not more than 2% by volume. Maintaining oxygen and water, also 29% by volume or less; c) adding a source of hydrogen as a free radical detergent to the gas phase process stream; d) the gas phase process stream and a source of hydrogen Exposed to pulsed corona discharge to generate free radicals from contaminants in the gas phase process stream and convert the contaminants to decomposition by-products; e) disposing of the decomposition by-products; Consists of.

The hydrogen source is preferably selected from the group consisting of hydrogen, ammonia, hydrazine, methane and mixtures thereof.

Preferably, the halogenated contaminant is carbon tetrafluoride and the carrier gas is helium.

It is also preferable that the halogenated contaminant is nitrogen trifluoride, the carrier gas is nitrogen, and hydrogen coexists as a raw material of the free radical detergent.

As another example, the halogenated contaminant is perfluoroethane and the carry gas is nitrogen.

As another example, the halogenated contaminant is hexafluoride sulfur and the carrier gas is nitrogen. Maintaining the highest equivalent amount of oxygen as hexafluoride sulfur in the gas phase process stream,
It is preferably at most% by volume.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention typically employs a halogen-containing compound (pollutant) for producing a corona reactor, such as a pulse corona reactor, a silent discharge (or insulating barrier discharge) reactor, an AC packed bed reactor,
It relates to effective chemical decomposition in atmospheres other than air (gas phase process flow) using point-plane reactors, point-point reactors, corona torch reactors, electron beam reactors and capillary reactors. The corona range covered includes positive corona (ie streamline corona, burst pulse corona, glow corona and spark discharge) and negative corona (eg Trichel pulse corona, pulseless corona and spark discharge). . The atmosphere (ie, carrier gas) may include inert molecules and atoms such as nitrogen, argon, helium and neon. Moreover, gas is added to the mixture as a reagent for the getter-reactive intermediate to improve the decomposition efficiency. Gas can be used as a reagent gas containing _{H 2, NH 3, N 2} H 4, CH 4 and mixtures thereof. Contaminants and gases carried from the step of using or generating pollutants require the addition of the carrier gas and reagent gas comprising the vapor phase process stream depending on the step of withdrawing the vapor phase process stream. It may or may not be. It may be necessary to add the carrier gas, or it may be necessary to add additional carrier gas. Typically, a reagent gas would be added, which would require removal of water and oxygen from the gas phase process stream. Even in the case of SF ₆ , the molecular oxygen component of the gas phase process stream is 21% by volume or less of the gas phase process stream,
In the case of non-SF ₆ contaminants, preferably below 2% by volume, there is virtually no molecular oxygen. In all cases it is preferred to remove water, preferably to less than 2% by volume of the gas phase process stream. The preferred working ranges of the present invention are: -Contaminant concentrations in the carrier gas from 1 ppmv to 50,000 ppmv (parts per million in molecular volume);-Carrier gas: high ionization potential compared to the pollutant to be destroyed. N using gas as carrier
₂ , He, Ne, Ar or a mixture thereof; 1 Hz to 10 kHz (hertz or cycles per second, kilohertz or 1000 cycles per second) repetition rate; 50 to 500 ns FWHM (nanosecond full-width half-maximum) Pulse width; ・ 1 to 45 caused by using a central electric wire with a diameter of about 10 to 41 ml and a coaxial tube with an inner diameter of about 1 inch
peak voltage of kV (kilovolts); storage capacitor of 500 pF (picofarad, 10 ⁻¹² farad) to 5 nF (nanofarad, 10 ⁻⁹ farad) for reactor tube length every 10 meters; H ₂ , NH ₃ , An additive gas selected from N ₂ H ₄ , CH ₄ and mixtures thereof; a spark gap pressure of 14.7 to 200 psia with a gap spacing of approximately 10 to 40 mm; a rise time of 1 ns to 1000 ns (nanoseconds); Less than or equal to that found in ambient air is often included, with lower and more convenient concentrations of O ₂ and H ₂ O.

The use of an atmosphere other than air promotes decomposition efficiency by providing more activated species to the carrier gas and reacting with the halogen-containing compound. The exact mechanism of decomposition is not known, but experimental data show a dramatic increase in decomposition efficiency when converting moist air to moist nitrogen into a nitrogen atmosphere.

The use of getter gas such as H ₂ dramatically improved the decomposition efficiency. These gases have several ways to improve efficiency. As with the carrier gas, these additives can provide an activated species that promotes decomposition of the halogenated compound. The additive also getters out intermediate fluorine and chlorine atoms to prevent recombination reactions and thus improve efficiency. In the present invention using a pulse corona reactor, the carrier gas was nitrogen, and when a small amount of hydrogen was added, an NF ₃ decomposition efficiency of 99.9% could be achieved.

The carrier gas is also important. In the case of CF ₄ , some H from the nitrogen carrier to the helium carrier.
C by adding ₂ to the carrier gas and converting
Improved decomposition of F ₄ can be achieved. C with helium alone
Inability to form stable compounds with decomposition byproducts of F ₄ . Minimal decomposition occurs when the carrier gas has a lower ionization potential than the species being destroyed. When the ionization potential of the carrier gas is higher than that of the species being destroyed, there is an increased likelihood that the electron will interact with that species. Addition of hydrogen will result in the formation of HF with a higher bond dissociation energy than the molecule being destroyed.

The findings revealed here for pulsed corona reactors are all other corona discharges, RF discharges, microwave discharges and electron beam discharges due to the physical and chemical similarity of these discharges to PFC, It should be adapted for use in weakening CFCs and VOCs.

Therefore, the present invention using a corona discharge allows the use of gaseous pollutants, such as PFCs, CFCs, from waste gas streams.
And are considered to be particularly advantageous over prior art weakening techniques that remove VOCs. The use of a high peak voltage, the use of a carrier gas with a higher ionization potential than the pollutant being removed, and the addition of a gas that reacts with the pollutant in the plasma state to form a washable by-product, work together to The invention is much more effective than traditional techniques of weakening such waste.

Maximizing the production of high energy electrons (and thus radicals) is essential to the success of the pulse corona reactor system. In this context, the following considerations are important: 1. The average electron energy is related to the voltage applied to the reactor. The higher the voltage, the higher the electron energy for a given gas density. The higher the voltage achieved, the more quickly the voltage for a given arrangement will be applied.

2. High-energy electrons are mainly generated during the initial stage of streamline generation, that is, during the growth reaction from the streamline wire to the cylinder. The transit time is short, typically 10 nanoseconds (10 ⁻⁹ seconds). It is only necessary to "form" the streamlines, and not "drive" the streamlines into the phase with more conductive heat (or arc). Correspondingly applied pulse width limits are also essential for high efficiency.

3. The more streamlines that are formed per unit time, the more convenient it is to achieve gas throughput.

From these considerations it can be inferred that the highest voltage and high repetition rate short pulses for a given geometry are preferred. These considerations also apply to silent discharge (insulation barrier discharge) reactors and AC packed bed reactors.

The Pulse Corona Reactor for the design of Naval, Surface, Warfare, and Center in the Dahlgren Division was held from 21-23 June 1933 in Albuquerque, New Mexico, USA.
IEEE Catalog 93 CH335 with minutes of IEEE International, Pulsto, Power, Conference
0-6, pages 180-183. G. Grothaus, R.G. K. Hatch Yarson (Hu
tcherson), R.A. A. Korz Kuwa
ekwa), R.A. Rush, R.A. Brown's "Coaxial, Pulsed, Corona, Reactor, Fore, Treatment, Of, Hazardous, Coaxial Pulsed C
oronaReactor for Treatmen
In producing the streamline discharge as described in “T of Hazardous Gases”, it exhibits high electrical efficiency (> 85%) from the “wall plug” to the line electrode. Figure 1 is a diagram showing a cross section of a single reactor tube.
Shown in Energy is supplied to individual or distributed capacitances using a high voltage, constant current power supply. The voltage stored in this capacitor is then transferred to a reactor with a hydrogen spark gap switch that keeps the streamline from the line electrode to the tube wall electrode growing within the capacity of the reactor. The following advantages naturally arise from this method: Constant current feed is extremely effective at transfer energy from the "wall plug" to the capacitor (> 93%). It is remotely steerable and once streamline activation is initiated in the reactor, it shuts off the supply, effectively isolating it from the rest of the circuit. Moreover, the remote piloting capability allows for effective piloting of the pulsed power system to easily accommodate adjustments to changes in flow conditions.

2. The hydrogen spark gap can generate rise time pulses (nanoseconds) that are very fast, creating multiple simultaneous streamlines downstream of the entire length of the reactor. The use of hydrogen as the insulating gas can improve the repeatability capability in order of magnitude over other spark gap filling gases.

3. The concentric arrangement of the reactor and the completely sealed system of pulsed power supply eliminate electromagnetic interference with surrounding devices.

4. The size of the storage capacitance can be easily changed to minimize the pulse width of the applied high voltage pulse and reduce the average power demand.

Typical operating parameters are: 20-25 kV charge voltage; 100-1000 H.
z, rise time 6 nanoseconds (ns), pulse width 50 to 1
50 nanoseconds, flow rate 50 slpm (standard liters per minute),
Power consumption 100 to 200 W (watt).

The experiments were carried out in a 10-tube pulse corona reactor with each tube having the structure shown in FIG. The reactor 1 has a length of 3 feet and an outer diameter of 1
Numerous cylindrical stainless steel tubing 3 inches (about 2.54 cm) and 0.9 inch inside diameter (about 2.28 cm)
(Serves as one electrode). At the center of each tube 3, a stainless steel wire 5 (acting as the other electrode) having a diameter of 0.002 inch (acting as the other electrode) is attached to the center of the tube 3 of the reactor 1 and the pull screw 7 and the tube of the reactor 1 Positioned by a crimp placed on any of the three. While Teflon feedthroughs were used for all electrical connections, the sealing devices 8, 10 were made of Teflon and Swagelok fittings. The capacitance of the tube 3 of each reactor 1 was 30 pF. Maxwell CCDS 50kV, 2kJ / s constant current power supply 9
The CCDC-440P1-208 model was used to charge the primary storage capacitor of the pulse corona reactor.
This capacitance can be from a discrete capacitor or from a pulse shaping line. A hydrogen spark gap, which works in a self-breakdown mode, was used to generate a rapid rising pulse in the reactor. Hydrogen is used in the spark gap as a gas such as N ₂ , Ar,
This is due to its rapid recovery properties compared to He, O ₂ and SF ₆ . The discharge breakdown voltage of the switch can be adjusted by adjusting the gap distance and the gap pressure. The switch is self-discharge breaking and works without the need for an external trigger source. The storage capacitance (and thus the number of repetitions of the voltage pulse applied to the corona wire) was measured by Hewlett-Packard 8112.
You can start with a pulse from an A programmable pulse generator. Measurement of the voltage applied to the reactor uses a rapid capacitance voltage divider near the reactor electrical input. All reactor currents were measured using a Pearson probe 13 with very low rise times.
Both of these probes transfer the recorded electrical data to a computer for further analysis.
y) Connected to a type 7200 digital oxyroscope. A gas phase process stream containing sample contaminants is introduced through inlet 15 and decomposition by-products are emitted from the wire 5 electrode directed to the stainless steel tube 3 electrode and entrained in a carrier gas passing through the reactor tube 1. Decomposes pollutants that have been generated.

An experimental setup with controlled introduction of pollutant species and analysis of pollutants from a pulsed corona reactor will be described below. Moisture was added via Miller Nelson Relative Humidity-Temperature Mass Flow Controller. Pollutant gas (N
F ₃ , CCl ₂ F ₂ , SF ₆ , CF ₄ and C ₂ F ₆ ) as N
₂ was supplied from a gas cylinder which was 1% or 100% pollutant. C ₇ H ₈ , CH using bubble device
₃ CCl ₃ and CH ₂ Cl ₂ were fed. The gas supplied to the bubble device was compressed air in a cylinder and N ₂ . The additional gas contained Ar, He, O ₂ and H ₂ .
Pollutant gas, sometimes with additional gas, in-line Brooks Type 5
Mixed with a flow controller of 850E mass. MT for gas analysis
I-GAD 400 Gas Chromatograph and UTI Qualitrace with Type 2221 Probe
ace) was performed using a mass spectrometer.

It has been found that the carrier gas containing the pollutants to be destroyed plays an effective role in the decomposition of the pollutants. Tables 1 and 2 below show that it may be useful to modify the process stream to carry contaminants with a carrier gas that has a higher potential than the contaminants, or in the case of multiple contaminants, the preferential contaminant species. Show. The experiments were controlled and performed in a way that simply changed the carrier gas. The present invention further provides methylene chloride (CH ₂
Cl ₂ ) decomposition efficiency of 50% in air with relative humidity of 35%
%, And could be increased to more than 99.9% in nitrogen. Greater than sign was used for the degradation rate to indicate that the last sign associated with this molecule was below the detection limit on both the mass spectrometer and the gas chromatograph. The results are counterintuitive based on the discussion of chemical reactivity (ie, water that forms part of HCl accelerates decomposition of CH ₂ Cl _2, etc.).

[0054]

[Table 1] Decomposition efficiency of NF _{3 in} relative humidity of 35% in water with addition of air and nitrogen and in addition of hydrogen to dry nitrogen.
The capacitance of the pulse corona reactor storage capacitor was 680 pF and the repetition rate was 600 Hz. ──────────────────────────── Carrier gas NF ₃ decomposition efficiency ───────────────── ───────────── Air (80% N ₂ , 20% O ₂ ) 7% N ₂ + H ₂ O (35% RH) 41% Dry N ₂ + He 38% Dry N ₂ + H2 84 % ─────────────────────────────

[0055]

[Table 2] Decomposition efficiency of CF ₄ in nitrogen, in hydrogen added to nitrogen, and in hydrogen added to helium. Pulse corona reactor storage capacitor has a capacitance of 660
The repetition rate was 500 Hz at pF. ──────────────────── Carrier gas decomposition efficiency ──────────────────── N ₂ 2% N _{2 + H 2 4% H e +} H 2 32% ──────────────────── Table 3 shows the bond dissociation energy to gases and ionization potential problem.

[0056]

[Table 3] Ionization potential and bond dissociation energy for research species. [Published by CRC Press of Vocale Reton, 1994, D. R. "CR" edited by Ride
C Handbook, Of, Chemistry, And, Physics (CRC Handbook of Chemis
try and Physics) 75th Edition;
May 3rd, US Government Department of Commerce, National, Technical, Information, Service, C.I. J. Shek Snyder, Jr.
"Technical Note D-1791, Tabulated, Valued, Of, Bond, Dissociation, Energies, Ionization Potentials, And, Electron, Affinities, Fore, Sam, Molcures, Found, Inn, High Ten Parature , Chemical, reaction (Tabul
attended values of bond disso
Citation energy, ionizati
on potentials, and electro
n affinities for some mol
ecules found in high-temp
erature chemical reaction
s) ”edited].

──────────────────────────────────── seed ionization bond dissociation energy (eV) potential (eV ) ──────────────────────────────────── C ₇ H ₈ 8.82 3.36 C ₂ F ₆ 13.4 4.03 to 5.29 NH ₃ 10.52 4.42 CH ₂ Cl ₂ 11.35 3.19 to 3.46 Cl ₂ 11.8 to 11.64 2.475 O ₂ 12.1 To 12.2 5.115 CCl ₂ F ₂ 12.31 3.59 first Cl removal 4.79 first F removal H ₂ O 12.59 to 12.69 5.1 HCl 12.74 to 12.9 4 .431 NF ₃ 12.91 to 13.2 2.47 H ₂ 15.4 4.476 N ₂ 15.6 9.762 F ₂ 15.7 1.609 HF 15.77 to 16.38 5.86 CF ₄ 17.8 5.25 to 5.65 SF ₆ 15.33 3.39 to 4.35 Ne 21.56 Not suitable He 24. 58 N / A ──────────────────────────────────── The data included in Tables 1 to 3 are coronas. It is considered that it shows how the discharge acts to accelerate the decomposition of pollutants. That is, the high-energy electrons generated by the discharge act on the gas molecules to either ionize or dissociate them. This causes the electrons to interact with the carrier gas molecules to generate reactive ions which interact with and destroy the contaminant species molecules. The results presented here imply that the main component of the carrier gas has a higher ionization potential and thus a higher decomposition efficiency. The higher the bond dissociation energy, the more difficult the molecule is to decompose. This is 1994 1
January monthly “Semiconductor International (Sem
iconductor Internationala
l) "P. Mallouris (Ma), pages 107-110.
roulis), J. Langan, A .;
Johnson, R.A. Ridgeway (R
idway) and H.W. Wizards
s) by "PFC and the Semiconductor, Industry (PFCs and the Semico
nector Industry: A Closer Look ”and the ease of PFC degradation is NF ₃ > C ₂ F ₆ > S.
The order is F ₆ > CF ₄ . To overcome this, it is necessary to use higher energy electrons. This is typically accomplished by boosting the peak voltage delivered to the device. Addition of reactive gas is also important. Addition of hydrogen (H ₂ ) to the gas stream produces HF in the case of PFC and HF or HCl in the case of CFC. This was demonstrated in a mass spectrometry experiment using these gases in the pulse corona reactor of the present invention. Besides,
In the case of PFC and CFC, it is necessary to remove all other gaseous feedstocks that have an affinity for electrons. In the experiments of the present invention, H ₂ O and O ₂ were removed from the carrier gas,
We saw a significant improvement in decomposition efficiency. It is well known that oxygen, fluorine and chlorine form negative ions in the plasma state. This is due to the negative nature of these species. H ₂ O to O
Removing ₂ from the carrier gas stream virtually eliminates some high energy electron absorption. Thus, by removing these other negative (ie, anionogenic) species, reactions between the electrons produced by the discharge and the contaminant species can increasingly occur.

Parameters that control the operation of the pulsed corona reactor, and thus the production of high energy electrons, include the repetition rate (or pulse number) and spark gap pressure. The number of repetitions controls the interval between the start of the first group of electron streamlines and the start of the next group of streamlines.
The spark gap pressure controls the gap breakdown voltage as well as the gap breakdown voltage. The peak voltage can be adjusted by controlling these parameters. FIG. 2 shows the results of NF ₃ decomposition efficiency as a function of number of repetitions. Data for different gap pressures are shown. Ie 80, 110 and 11
It is 9.5 psia. The data is generated using the number of pulses (Hz) that can be achieved with the particular equipment used in the experiment. Data can be expressed in terms of energy equivalents that can be related to other devices and device configurations. This data is shown in Table 4 below.

[0059]

[Table 4] Decomposition efficiency of NF ₃ shown in Fig. 2 and normalized to Joule / l for energy utilization. The various operating parameters, the obtained NF ₃ decomposition efficiency and the energy density required for this decomposition are shown. These results are 4
43 ppmv H ₂ , 233 ppmv NF ₃ 10.
For nitrogen carrier through the 10-tube PCR at a flow rate of 2 slpm. The peak voltage varies from 25 to 35 kV. Each reactor tube had an inner diameter of 0.9 inches (about 2.29 cm) and the center wire had a diameter of 0.020 inches (about 0.0051 cm). The current pulse width was 50 nanoseconds and the storage capacitor was 380 pF. ──────────────────────────────────── Number of pulses H ₂ Spark gap Destructed NF ₃ energy density ( Hz) Pressure (psia) (%) (joule / l) ───────────────────────────────────── 100 80 17 60 ± 6 200 80 33 ± 5 158 ± 16 500 808 64.7 ± 2.3 360 ± 40 1000 1000 80 88 ± 4 640 ± 60 1000 110 110 92 ± 4 840 ± 80 1000 119.5 96.1 ± 0.28 1080 ± 100 1176 110 94.6 ± 2.2 880 ± 90 1540 110 97 ± 1.0 910 ± 90 ─────────────────────── ────────────── NF as a function of the spark gap pressure Decomposition 10
Shown for a pulse number of 00 Hz. The other condition of these experiments is a carrier of nitrogen which was run through 233 ppmv NF ₃ and 430 ppmv H ₂ at a flow rate of 10 slpm through a 10 tube pulse corona reactor equipped with a 380 pF storage capacitor. This data shows that the decomposition efficiency increases with higher repetition rate and higher spark gap pressure (peak voltage).

Table 5 lists the decomposition efficiencies that could be achieved during this experiment with the 10 tube pulse corona reactor. None of these degradation efficiencies could be optimized during this experiment. All studies on these pollutants were carried out with He CF ₄
As an example, a nitrogen carrier was used. Equal amount of O ₂
There always exists studies using _C 2 _{F 6,} also the _{O 2} CF
₄ was always added at a concentration of 8% CF ₄ . This was done by simulating real contaminants from a plasma enhanced chemical vapor deposition (PECVD) reactor. Oxygen is also the above SF ₆
It has been found to be added to the surroundings of and to actually increase the decomposition efficiency up to about the almost equivalent amount of oxygen in SF ₆ . This effect is due to the production of SO _x F _y type species. However, the oxygen content does not reach 21% by volume of the carrier gas and pollutant mixture, since SF ₆ is typically only traces. As a typical example, oxygen is 2% by volume or less. The decomposition efficiency shown in Table 5 is
It does not reflect a parallel comparison of efficacy at the time the pulse corona reactor destroys these species under identical operating conditions. A pulsed corona reactor operated under the special technical conditions of the present invention is capable of destroying these molecules to very high levels compared to prior art methods. In fact, the degradation efficiency was improved over the reported prior art degradation techniques and the degradation of some molecules by the method of the invention was above the detection limit of the analytical instrument.

[0061]

[Table 5] Decomposition efficiency achieved with the 10-tube pulse corona reactor used in this study ─────────────────────────── Decomposition efficiency ─────────────────────────── NF ₃ > 99.9% C ₂ F ₆ (50% O ₂ ) 32% SF ₆ 72% CF ₄ (8% O ₂ ) 32% CCl ₂ F ₂ 85% C ₇ H ₈ > 99.9% CH ₂ Cl ₂ > 99.9% CH ₃ CCl ₃ > 99.9% ─── ──────────────────────── The following are possible arrangements for using the pulse corona reactor to destroy the above-mentioned molecules in an industrial installation. is there. Both vacuum and atmospheric pressure are possible. The additional gas _{(H 2, NH 3, N} 2 H 4 and CH ₄₎ or the middle of the reactor from the addition to the gas flow, or can be inserted into the waste. The last two addition positions allow the reaction of the non-ionized addition gas with the plasma generating species. The middle position is allowed to react with the plasma generating species and non-ionizing species before entering the second plasma chamber. As described above, when PFC and CFC decompose in the coexistence of H ₂ , HF and HCl are produced. Even with NH ₃ , these species also form with the production of nitrogen. Both HF and HCl are soluble in water and therefore can be cleaned from reactor waste via a wet scrubber. These by-products of the reaction at a pulse coronavirus reactor also solid, for example, soda lime or Sodasobu ^{(R) (Sodasorb (R)} ) material can cleaned by a dry method using a. Cryogenic recovery can also be used to confine the by-products for final recycling.

[0062]

【The invention's effect】

The present invention is a typical electronic industry pollutant such as P
It has been shown to provide dramatic degradation of FC, CFC as well as VOC. The use of a carrier gas with a higher ionization potential than the pollutants to be decomposed has not been suggested in the prior art for corona discharges, which provides these dramatic decomposition improvements.

For example, as cited above, M. G. 32% toluene, other than Grothaus,
Decomposition of 10% dichloromethane and 4% dichlorofluoromethane in ambient air was reported. Further report
((1994, The First, International, Conference, On, Advanced, Oxidation, Technologies, Fore, Water, And, Air, Remediation (The First
International Conference
n Advanced Oxidation Tech
nologiesfor Water and Air
Remediation). G. Grothaus, R.A. A. Korzekwa, R.A. K. Hutcherson (Hu
tcherson), B.I. P. Brown
n), R.N. L. Engels, S.M. Beck, R.A. Ridgeway
y), R.Y. Pearce, S-Y. Phosphorus (L
ynn) and M.M. A. George's "Characterization, Ob, A, Pulsed, Corona,
Reactor, Fore, Destruction, Of, Hazardas, Gas Chair (Characterizationo)
fa Pulsed Corona Reactor
for Destruction of Hazar
dough Gases ”)) are 93% and 30% respectively
And showed a decomposition efficiency of 20%. In contrast, the present invention provides the following molecular decomposition efficiencies: toluene 99.9%.
As described above, it has a decomposition efficiency of 99.9% or more of dichloromethane and 85% of dichlorodifluoromethane.

[Brief description of drawings]

FIG. 1 is a cross section of a single reactor tube of a pulse corona reactor used in the present invention.

Figure 2 N as a function of repetition rate in Hertz at spark gap pressures of 80, 110 and 119.5 psia.
It is a diagram showing a F ₃ decomposition efficiency.

FIG. 3 shows NF ₃ decomposition efficiency as a function of spark gap pressure in psia at 1 kHz.

[Explanation of symbols]

 1 Reactor 3 Cylindrical Stainless Steel Tube 5 Stainless Steel Wire 7 Tensile Screw 8, 10 Sealing Device 9 Constant Current Power Supply 11 Capacitive Voltage Divider 13 Person Probe 15 Inlet 17 Outlet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Russell. Pee. Brown United States. 22443. Virginia. Colonial. Beach. Bancroft. Avenue. 1025 (72) Inventor Mark. Allen. George United States. 18101. Pennsylvania. Allentown. North. Twelve. Street. 23 (72) Inventor Michael. Glen. Grosas United States. 78006. Texas. Bone. Frey. Street. 206 (72) Inventor Reginald. Kennis. Hutcherson United States. 20904. Maryland. Silver Springs. Apartment. 202. Gales Head. Manois. Way. 3418 (72) Inventor Richard. A. Causewak United States. 87544. New Mexico. Loss. Alamos. A. 44. Street. 2141 (72) Inventor Richard. Vincent. Pairs United States. 18974. Pennsylvania. Warminster. A. Nemoral. Street. 535 (72) Inventor Robert. Gordon. Ridgeway United States. 18951. Pennsylvania. Quakertown. Clover. Mill. Road. 2002

Claims (23)

[Claims] 1. A method of decomposing pollutants from a gas phase process stream using a corona discharge, comprising: a) a carrier having a higher ionization potential than the contaminant and the preferred species of the contaminant to be decomposed. Providing said gas phase process stream comprising gas; b) maintaining an oxygen content of said gas phase process stream below 21% by volume; c) exposing said gas phase process stream to a corona discharge. And then destroying in the gas phase process stream to produce a decomposition by-product from the contaminant; d) disposing the decomposition by-product; 2. The vapor phase process stream and hydrogen in the vapor phase process stream in an amount of 1 to 20,000 p of the contaminant.
The method according to claim 1, wherein the mixing is performed in the range of pmv. 3. The vapor phase process stream and ammonia in the process stream from 1 to 20,000 of the contaminants.
The method according to claim 1, wherein the mixing is performed in the range of ppmv. 4. The method of claim 1, wherein the gas phase process stream is substantially free of free molecular oxygen. 5. The method of claim 1, wherein the gas phase process stream is substantially free of free molecular oxygen. 6. The method of claim 1, wherein the corona is generated in a pulsed corona reactor. 7. The method of claim 1, wherein the corona comprises streamlines of high energy electrons. 8. The carrier gas is nitrogen, helium,
The method of claim 1 comprising neon, argon or a mixture thereof. 9. The contaminants are NF ₃ , SF ₆ , C ₂ F.
₆ , CF ₄ , CHF ₃ , C ₃ F ₈ , CCl ₂ F ₂ , C _{7
H 8, CH 2 Cl 2,} CH 3 CCl 3 or method according to claim 1, characterized by comprising a mixtures thereof. 10. The method of claim 1, wherein the carrier gas is added to the gas phase process stream. 11. The method of claim 1, wherein the contaminant concentration is in the range of approximately 1 ppmv to 50,000 ppmv. 12. The pulse corona reactor has approximately 1
7. The method according to claim 6, wherein the pulse has a repetition rate of Hz to 10 kHz. 13. The corona discharge is approximately 50 to 500.
7. The method of claim 6 having a pulse width in the nanosecond FWHM range. 14. The corona discharge is approximately 1 to 45 kV.
7. The method of claim 6, having a peak voltage of. 15. The pulse corona reactor has approximately 1
7. The method of claim 6 having a spark gap pressure of 4.7 to 200 psia. 16. The corona is a silent discharge reactor, an AC packed bed reactor, a point-plane reactor,
The method of claim 1 comprising a point-to-point reactor, a capillary reactor, an electron beam reactor or a corona torch reactor. 17. A method of decomposing halogenated pollutants from a gas phase process stream using pulsed corona discharge, comprising: a) the halogenated pollutants and higher than the halogenated pollutants to be decomposed. Supplying said gas phase process stream with a carrier gas having an ionization potential and comprising nitrogen, helium, neon, argon or mixtures thereof; b) oxygen and water contents of said gas phase process stream each being 2 volumes. % And less than 2% by volume of water as well as: c) adding a source of hydrogen as a free radical detergent to the gas phase process stream; d) the gas phase process stream and the gas phase process stream; Exposing a source of hydrogen to a plasma corona discharge to generate free radicals in the gas phase process stream to decompose the contaminants into by-products; e). Decomposition method consisting of: process and to dispose of the serial decomposition by-products. 18. The hydrogen source is hydrogen, ammonia,
18. The method of claim 17, comprising hydrazine, methane or a mixture thereof. 19. The method of claim 17, wherein the halogenated contaminant is carbon tetrafluoride and the carrier gas is helium. 20. The method of claim 17, wherein the halogenated contaminant is nitrogen trifluoride, the carrier gas is nitrogen, and hydrogen coexists as a source of the free radical detergent. 21. The method of claim 17, wherein the halogenated contaminant is perfluoroethane and the carrier gas is nitrogen. 22. The method of claim 17, wherein the halogenated contaminant is sulfur hexafluoride and the carrier gas is nitrogen. 23. The method of claim 22, wherein the vapor phase process stream retains an equal amount of oxygen but not more than 2 volumes of oxygen.