JP2001054721A - Method and device for decomposing fluorocarbons - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detoxify the waste gas containing fluorocarbons with high decomposition efficiency and at a low running cost while ensuring safety. SOLUTION: In the decomposition method of the fluorocarbons for detoxifying the fluorocarbons, the waste gas containing the fluorocarbons is passed through discharge plasma, then brought into contact with a fluorocarbon decomposition catalyst. Moreover, oxygen and/or hydrogen are mixed to the waste gas containing the fluorocarbons at one or more places among an inlet of a discharge plasma reactor, inside of the discharge plasma reactor, an inlet of a catalyst reactor and inside of the catalyst reactor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmful gas contained in exhaust gas discharged from, for example, an apparatus for manufacturing a semiconductor device or a liquid crystal display device, particularly PFC, CF
The present invention relates to a technology for treating CFCs such as C, HFC, and HCFC.

[0002]

2. Description of the Related Art In recent years, semiconductor devices and liquid crystal display device manufacturing apparatuses have been increasing with the development of the semiconductor and electronics-related industries, and various kinds of harmful, flammable and explosive dangers are present in these manufacturing apparatuses. High gas,
Furthermore, gases that harm the global environment, such as causing ozone holes, are used. Exhaust gas discharged from these devices is not completely reacted or decomposed, and in extreme cases, most of the exhaust gas is discharged without being decomposed. Therefore, a treatment device for detoxifying the exhaust gas is indispensable.

[0003] Among these harmful gases, fluorocarbons are extremely stable chemically and therefore require a large amount of energy for decomposition, and there is no efficient and appropriate decomposition method or decomposition apparatus at present.

[0004] As a conventional method for decomposing CFCs, first, a combustion method is known. This involves mixing fuel and oxygen with the fluorocarbons to be treated and decomposing them using the heat of combustion and the activity of radicals in the combustion flame. Therefore, a high temperature is required, and particularly when a diluent gas such as nitrogen or air is involved, it is necessary to raise the temperature of the entire gas including these gases, resulting in very poor energy efficiency.

There is also a thermal decomposition method, which is also a method of decomposing chlorofluorocarbons by raising the temperature to a decomposition temperature of fluorocarbons with a heater or the like, and requires a higher temperature than the combustion method. Then, when decomposing a relatively high fluorocarbons decomposition temperature also was a problem this process to by-produce NO _x.

As a more energy efficient method, there is a method utilizing a thermal reaction. This is to react with calcium oxide or the like at a temperature lower than combustion and convert it to a harmless substance such as calcium fluoride. This method has a drawback that the reactant such as quicklime is a consumable and must be replenished frequently, resulting in high running costs.
As a means for reducing the running cost, a method using a catalyst (JP-A-11-70322, JP-A-10-2
No. 63365), but the life of the catalyst is short and the decomposition efficiency is low, so a large reaction tube is required. In addition, since this reaction tube must be maintained at a reaction temperature of 700 ° C. or higher, there is a disadvantage that energy cost is not as high as that of the thermal decomposition method, but is high.

Further, as a method of decomposing at normal temperature, a decomposition method using non-thermal equilibrium normal pressure discharge plasma utilizing corona discharge and silent discharge has been proposed (for example, see Japanese Patent Application Laid-Open No. 10-28836). Although it is easily decomposed to a degree, it has a drawback that it is difficult to increase the decomposition efficiency due to recombination of radicals once decomposed.

Further, a decomposition method and a decomposition apparatus using a catalyst in combination in order to increase the decomposition efficiency by plasma are disclosed in, for example, JP-A-11-114359. As shown in FIG. 5, the plasma decomposition apparatus used here fills a granular porous adsorbent 53 and a ferroelectric substance 54 into a plasma processing chamber 59 of a cylindrical plasma decomposition apparatus,
A high voltage is applied from a power supply 55 between the internal electrode 51 and the external electrode 52 in the processing chamber 59 to generate plasma. At both ends of the processing chamber 59, the adsorbent 53 and the dielectric 54 are held by a holding plate 57 having a hole, and airtightness is held by an O-ring 58 by a Teflon (registered trademark) cap 56. . Exhaust gas containing harmful gas flows in the direction of arrow a, bathes in the processing chamber 59, comes into contact with the catalyst,
It is decomposed and discharged as a purified gas in the direction of arrow b.

[0009] The decomposition method using this apparatus can efficiently treat and detoxify exhaust gas containing volatile harmful substances such as fluorocarbons, halons, hydrocarbons and organic acids. However, in this method, since the catalyst (the porous adsorbent and the ferroelectric substance) is filled in the entire plasma processing chamber, the flow resistance is large, the exhaust gas is difficult to pass, and it is difficult to increase the processing amount. Further, when the catalyst is deteriorated, there is a disadvantage that the plasma processing chamber must be disassembled.

[0010]

Accordingly, the present invention has been made in view of such problems, and among halogen-based gases, in particular, PFC, CFC, HFC, HCFC
It is a main object of the present invention to provide a method and a device for decomposing fluorocarbons capable of detoxifying exhaust gas containing fluorocarbons while ensuring safety with high decomposition efficiency and low running cost.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention provides a method for decomposing chlorofluorocarbons to discharge flue gas containing fluorocarbons. This is a method for decomposing fluorocarbons, which comprises passing through a plasma and then contacting with a fluorocarbon decomposition catalyst.

As described above, the decomposition reaction is caused to the fluorocarbons contained in the exhaust gas discharged from the process by plasma such as corona discharge and silent discharge, and an intermediate decomposition substance partially halogenated is obtained. If the intermediate decomposition product is brought into contact with the chlorofluorocarbon decomposition catalyst before it becomes a hardly decomposable substance again due to recombination or the like, the intermediate decomposition products in the middle of decomposition do not recombine, and the surface of the catalyst is successively reduced. It is adsorbed at the active site, and decomposition is promoted by the catalytic activity. Almost all of the decomposed CFCs as final decomposition products are F ₂ , C, CO ₂
And HF can be decomposed and detoxified, and the emission of harmful gases can be significantly reduced.
Safety can be ensured and the exhaust gas treatment capacity can be improved. In other words, by processing in two stages, plasma and catalyst, there is no need to apply a high voltage or frequent catalyst replacement, and the processing capacity is high. Therefore, equipment costs and running costs are reduced as compared with conventional various processing methods. It is also possible to reduce the cost of exhaust gas treatment.

[0013] In this case, as described in claim 2, in the method for decomposing fluorocarbons according to the first aspect, the exhaust gas containing fluorocarbons is supplied to the inlet of the discharge plasma reactor and the interior of the discharge plasma reactor. It is preferable to mix oxygen and / or hydrogen at one or more of the inlet of the catalytic reactor and the catalytic reactor.

If oxygen is added to the flue gas containing fluorocarbons at the entrance of the discharge plasma reactor or in the discharge plasma reactor, ozone and oxygen radicals will coexist in the plasma, and Since the carbon-halogen bond of these compounds is easily broken, it is effective as an oxidative decomposition accelerator and can significantly improve the decomposition rate of fluorocarbons.

The addition of hydrogen to the plasma, for example, acts on CF ₃ or the like from which F has escaped from CF ₄ by the plasma to create a stable state of CHF ₃ or the like. Therefore, it has the role of preventing recombination with F and also has the function of preventing CHF ₃
Since the decomposition temperature is much lower than that of fluorocarbons not containing hydrogen such as hydrogen, hydrogen also works effectively as an accelerator for reducing and decomposing fluorocarbons, and can increase the decomposition rate of fluorocarbons.

Further, when oxygen and hydrogen are added, the above-described effects of the individual addition are exerted in plasma, and the rate of oxidation-reduction decomposition is promoted as a synergistic effect, so that the decomposition rate is improved, and the decomposition rate is further improved. The next intermediate decomposition product is obtained.

Subsequently, these intermediate decomposition products are introduced into a catalytic reactor and brought into contact with a chlorofluorocarbon decomposition catalyst. In this catalytic reactor, oxygen and / or hydrogen coexist with the intermediate decomposition products. The catalyst is activated to maintain the catalytic activity, and the intermediate decomposition products can be decomposed by the catalytic activity to final decomposition products without recombination.

When oxygen coexists, carbon eventually becomes C
O_Two And if hydrogen coexists, carbon becomes hydrocarbon
Element (C_n H_{2n + 2}) And is discharged. Fluorine is hydrogen
Is released as hydrogen fluoride (HF)
If not, the fluorine gas (F_Two )
Will be issued. CO if oxygen and hydrogen coexist_Two , HF, H _Two 
O is discharged. Thus, oxygen and / or hydrogen
Promotes redox decomposition of fluorocarbons by adding
Eliminate the recombination of decomposition products to improve the decomposition rate.
Can be.

Further, in this case, as described in claim 3, the chlorofluorocarbons may be PFC (perfluoro compound), CFC (chlorofluorocarbon), HFC
(Hydrofluorocarbons), HCFC (Hydrochlorofluorocarbons), or a gas mixed with two or more of them. Thus, the chlorofluorocarbons to be treated in the present invention are PF
One of C, CFCs, HFCs, HCFCs, or two or more of them, even if they are present alone or in a mixed state in the exhaust gas discharged from the process, these are not described in the above book. It can be almost completely decomposed to F ₂ , C, CO ₂ and HF by the decomposition method of the invention.

Further, as described in claim 4 of the present invention, the chlorofluorocarbon decomposition catalyst is selected from aluminum phosphate, boron phosphate, phosphate oxide, titanate oxide, and tungstate oxide. One type or a mixture of two or more types can be used. If such a catalyst, for example, a granular porous catalyst, is filled in a cylindrical reactor to form a catalyst layer, or is baked on the inner wall of the cylindrical reactor to form a catalyst layer, fluorocarbons are decomposed with high contact efficiency. be able to.

Further, as described in claim 5, the discharge plasma can be normal pressure / low temperature plasma generated by silent discharge or corona discharge. in this way,
If the discharge plasma is a normal-pressure / low-temperature plasma generated by silent discharge or corona discharge, it is a so-called non-thermal equilibrium plasma in which the electron temperature is selectively higher than molecules and ions, and contains low-concentration Freon Since the exhaust gas can be selectively decomposed, it is extremely effective for the decomposition purification treatment.

Next, the invention described in claim 6 of the present invention is:
In a chlorofluorocarbon decomposing apparatus for detoxifying chlorofluorocarbons, the apparatus comprises at least a discharge plasma reactor and a catalytic reactor provided with a chlorofluorocarbon decomposition catalyst layer, an exhaust gas inlet of the plasma reactor, an inside of the plasma reactor, an inlet of the catalytic reactor and a catalyst. An apparatus for decomposing chlorofluorocarbons, comprising a means for introducing oxygen and / or hydrogen at one or more locations in a reactor.

With such an apparatus, it is possible to construct the apparatus at a low cost and to immediately decompose the intermediate decomposition product generated in the discharge plasma reactor to the final decomposition product in the catalytic reactor without recombination. . In addition, by adding oxygen and / or hydrogen, it is possible to improve the decomposition efficiency and the yield of the final decomposition product. Therefore, the emission of harmful gases can be significantly reduced, and a fluorocarbons decomposer that hardly causes air pollution can be obtained. In addition, equipment costs and running costs can be reduced as compared with conventional various treatment methods, and exhaust gas treatment can be performed. This makes it possible to reduce the cost of chlorofluorocarbons.

According to a seventh aspect of the present invention, there is provided a chlorofluorocarbon decomposing apparatus for detoxifying chlorofluorocarbons, comprising a discharge plasma reactor provided with a chlorofluorocarbon decomposition catalyst layer on at least the inner wall of the reactor. A means for introducing oxygen and / or hydrogen into an exhaust gas inlet or a reactor.

With such an apparatus, there is no need to heat the chlorofluorocarbon decomposition catalyst layer, which can reduce the energy cost, reduce the ventilation resistance of the exhaust gas, and increase the throughput. Device.

Hereinafter, the present invention will be described in more detail. The present inventor has found that among harmful gases contained in exhaust gas generated from various processes, PFC and CF which are particularly difficult to treat are used.
As a result of various investigations and examinations on a decomposition method and a decomposition apparatus suitable for the treatment of CFCs such as C, HFC, HCFC, etc., as a result of passing CFCs through discharge plasma and passing through a CFC decomposition catalyst layer, They have found that they can easily decompose chlorofluorocarbons into harmless hydrogen halides, CO _2, etc., and have scrutinized various conditions to complete the present invention.

The toxic gases targeted by the present invention are
PFC, CF contained in exhaust gas discharged from process
CFCs such as C, HFC, HCFC, etc.
Is CF as PFC (perfluoro compound)
_Four , C_Two F₆ , C_Three F₈ , C_Four F _Ten, NF_Three , SF₆ 
Such as CFCs (chlorofluorocarbons)
l_Three, CF_Two Cl_Two , CF_Three Cl, C_Two F_Three Cl_Three , C_Two
 F_Four Cl_Two , C_Two F_Five HFC (Hydroful
CHF as Orocarbons)_Three , CH_Two F_Two Etc., HC
CF (hydrochlorofluorocarbon) as CF
_Two HCl, C_Two F_Three HCl_Two , C_Two F_Four HCl etc.
Gas containing one or more of these
Can be.

As described above, the chlorofluorocarbons to be treated in the present invention are one of PFCs, CFCs, HFCs, and HCFCs, or two or more of them, each of which is discharged from the process. Even if they are present alone or in a mixed state in the exhaust gas to be produced, they can be almost completely decomposed to F ₂ , C, CO _2, HF, etc. by the decomposition method described above, and can be rendered harmless.

A feature of the method for decomposing chlorofluorocarbons of the present invention resides in that an exhaust gas containing chlorofluorocarbons is passed through discharge plasma and then brought into contact with a fluorocarbon decomposition catalyst. That is, in the present invention, in order to decompose fluorocarbons such as CF ₄ by a simpler decomposer with lower energy, first, for example, normal pressure / low temperature plasma such as silent discharge, corona discharge, pulse discharge, etc. An intermediate decomposed substance from which a part of halogen has been released is obtained, and is completely decomposed with a chlorofluorocarbon decomposition catalyst before it becomes an indecomposable substance again due to recombination or the like.

According to the prior art, difficult CF ₄ gas chemically most stable exploded in fluorocarbons is in the combustion 1
It is known that it is decomposed at 200 ° C. and 1400 ° C. in thermal decomposition, and reduced to about 700 ° C. by a catalyst or a thermal reaction. Further, according to the catalyst, the limit is about 700 ° C., and CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F _{10 and the} like have no difference in the decomposition onset temperature (the decomposition temperature is large in the combustion method). Difference), in the case of catalytic decomposition,
CF ₄ → CF ₃ + F, C ₂ F ₆ → C ₂ F ₅ + F, C ₃ F
_As shown by the formulas ₈ → C ₃ F ₇ + F, C ₄ F ₁₀ → C ₄ F ₉ + F, the reaction in which one fluorine is extracted from carbon determines the overall reaction, and the subsequent decomposition Suggests that they occur in a chain. Focusing on this point, it is presumed that lowering the temperature of decomposition by the catalyst is quite close to its limit.

On the other hand, if a non-thermal equilibrium plasma such as a silent discharge, a corona discharge or a pulse discharge is used, CF which is the most difficult to decompose is used.
_{Even with four} gases, a decomposition rate of about 50% can be obtained relatively easily. However, power and decomposition rate are not proportional,
In order to obtain a decomposition rate exceeding the above, a considerable excess of energy is required. This suggests that the decomposed gas is recombined and returns to the original CF ₄ again.

The present invention has been conceived by focusing on these phenomena. In this state, fluorine radicals are extracted from CF _{4 and} other fluorocarbons by plasma, and in this state, fluorocarbons partially decomposed (intermediate decomposition products). ) Is exposed to a chlorofluorocarbon decomposition catalyst to promote the decomposition at once. These two technologies complement each other in this way, and when viewed from the catalyst side, the temperature of the catalyst can be set low by using plasma, resulting in a reduction in heat energy cost and catalyst Of the catalyst (improvement of life) and improvement of the decomposition rate of the catalyst (saving of use amount) can be achieved. On the other hand, when viewed from the plasma side, even under the condition of a low decomposition rate, an effect is obtained that recombination is prevented in combination with the catalyst, and the decomposition rate is improved.

The normal pressure plasma includes a core used in a dust collector or the like.
Silent used in Rona discharge, pulse discharge and ozonizer
Non-thermal equilibrium plasma such as discharge is used. These are normal pressure
Gas can be used, for example, a few percent
CFCs to be introduced can be selectively decomposed. this
According to the plasma, for example, CF_Four CF from which F escaped _Three 
When an unstable molecule such as stays in space for a relatively long time
It is said. These decomposition reactions are caused by the frequency of the AC electric field.
It is promoted by appropriately setting the number, application time, and the like. one
When the decomposition reaction proceeds beyond a certain level, the decomposition reaction between the decomposition products
Slow reaction rate due to frequent occurrence
It may look like this.

In the present invention, one or two of the inlet of the discharge plasma reactor, the inside of the discharge plasma reactor, the inlet of the catalyst reactor, and the inside of the catalyst reactor are supplied to the flue gas containing fluorocarbons. As described above, by mixing oxygen and / or hydrogen, decomposition can be promoted and the decomposition rate can be improved.

First, when oxygen coexists in plasma, ozone and oxygen radicals are generated separately from fluorocarbons,
Coexist. These have an effect on halogens bonded to carbon and the like, and easily break bonds with carbon, and thus are effective as decomposition accelerators mainly for oxidation reactions.
Of course, it is possible to decompose F ₂ and C without oxygen, but if it is used, it can be decomposed to CO ₂ and HF at a higher decomposition rate.

The addition of hydrogen is considerably faster due to the plasma, for example, due to the fact that the atomic weight is lighter and the atomic radius and molecular radius are extremely small compared to other gases, for example, for CF ₃ or the like from which F has escaped from CF _4. ichi encourage faster moving about at a rate, creating a stable state such as CHF _3. Therefore, it plays a role of preventing recombination with F, and the decomposition temperature of hydrogen-containing fluorocarbons such as CHF ₃ is considerably lower than that of hydrogen-free fluorocarbons. As a result, it works effectively as an accelerator. Hydrogen is not essential for decomposition like oxygen, but its use can lower the decomposition temperature and improve the decomposition rate.

Next, when oxygen and hydrogen coexist simultaneously in the plasma, the above-described effects of the individual addition are exhibited, and the rate of redox decomposition is promoted as a synergistic effect, so that the decomposition rate is improved and the decomposition is further improved. , Low order intermediate decomposition products can be obtained.

Subsequently, as described above, after decomposing fluorocarbons in plasma using a discharge plasma reactor, the fluorocarbons are introduced into a catalytic reactor and brought into contact with a fluorocarbon decomposing catalyst. The intermediate decomposition products do not recombine,
It is successively adsorbed at active points on the catalyst surface. Adsorbed chlorofluorocarbons are promoted one after another with the help of catalytic activity.
The decomposed fluorocarbons are decomposed into carbon (C) and fluorine gas (F ₂ ) as final decomposition products.

In this catalytic reactor, oxygen and / or
Alternatively, in a state where hydrogen coexists with the intermediate decomposition product, the catalyst is activated to maintain the catalytic activity, and the intermediate decomposition product is decomposed by the catalyst to a final decomposition product without recombination. When oxygen coexists, carbon is finally emitted as CO _2, and when hydrogen coexists, carbon is emitted as hydrocarbon (C _n H _{2n + 2} ). Fluorine is mostly emitted as hydrogen fluoride (HF) if hydrogen is present, but otherwise fluorine gas (F)
₂ ) as discharged. When the catalyst is deteriorated by the reaction for a long time, halogen such as fluorine may not be separated while being bonded to the active site of the catalyst, and the coexistence of hydrogen has a reactivating action to prevent the separation. If oxygen and hydrogen coexist, CO ₂ , HF and H ₂ O are emitted.

The effect of promoting the decomposition of chlorofluorocarbons by the addition of oxygen and / or hydrogen can be mentioned in consideration of the molecular composition of chlorofluorocarbons, the reaction conditions of the discharge plasma reactor and the catalytic reactor, and the type of catalyst. It is necessary to appropriately combine the type, amount, position and the like of the added gas. As described above, the redox decomposition of fluorocarbons is promoted by the addition of oxygen and / or hydrogen, and the recombination of intermediate decomposition products is eliminated, so that the decomposition rate can be improved.

Next, the species of the catalyst used in the present invention
Among them, the catalyst alone is effective in decomposing fluorocarbons.
Therefore, the present invention works effectively. Chlorofluorocarbon
In case of strong acid, phosphoric acid, boric acid, nitric acid salt
Is effective, but aluminum phosphate, boron phosphate, etc.
Is particularly well known. In addition, phosphate oxides, titanium
Phosphoric acid as acid-based oxide and tungstate-based oxide
Supported TiO_Two (HPO _Four / TiO_Two ), TiO_Two / Si
O_Two , WO_Three / Al_Two O_Three Etc. are confirmed to be valid
Have been.

The catalyst contact reaction temperature varies depending on the reaction conditions, the type of catalyst, the type of chlorofluorocarbons, and the type of decomposition promoting additive gas in the former discharge plasma reactor.
It can often react at a relatively low temperature of room temperature to 700 ° C,
The catalyst life can be maintained for a long time.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings, but the present invention is not limited to these embodiments. Here, FIG. 1 is a schematic diagram showing a configuration example of a fluorocarbon decomposition apparatus of the present invention.

As shown in FIG. 1, for example, at least the discharge plasma reactor 2
And a catalytic reactor 3 provided with a CFC decomposition catalyst layer, and an exhaust gas introduction pipe 4 is provided at an inlet side 9 of the discharge plasma reactor 2.
A purifying gas discharge pipe 7 is provided at the outlet of the catalytic reactor 3 and one or two of the inlet of the discharge plasma reactor, the inside of the discharge plasma reactor 2, the inlet side 15 of the catalytic reactor and the inside of the catalytic reactor 3. The oxygen introduction pipe 5 and / or the hydrogen introduction pipe 6 are provided at more than one place. Further, an intermediate sampling port 8 is provided in the middle of a pipe connecting the discharge plasma reactor 2 and the catalyst reactor 3, so that a sample of an intermediate decomposition product generated in the discharge plasma reactor 2 can be collected.

As shown in FIG. 2, the discharge plasma reactor 2 is provided with a nichrome wire coil electrode 12 inside an alumina / ceramic reaction tube 11 and connected to an AC power supply 14 for generating a high-voltage pulse. A stainless steel plate ground electrode 13 is wound around the outer periphery of the reaction tube 11 so that discharge plasma can be generated by silent discharge. One end of the reaction tube 11 serves as an inlet of the discharge plasma reactor, and the exhaust gas introduction tube 4 is connected. The other end of the reaction tube 11 discharges gas after the decomposition reaction.

As shown in FIG. 3, the catalyst reactor 3 is provided with a heater 22 on the outer periphery of a catalyst container 24 filled with a granular chlorofluorocarbon decomposition catalyst 21, and is kept warm by a heat insulating material 23.
One end of the catalyst container 24 is the catalyst reactor inlet side 15,
A pipe from the plasma reactor is connected, and the purified gas after the decomposition reaction is discharged from a purified gas discharge pipe 7 from the other end.

In the method for decomposing fluorocarbons of the present invention, fluorocarbons are decomposed efficiently using a fluorocarbon decomposition apparatus 1 in which a catalytic reactor 3 is connected to a stage subsequent to the discharge plasma reactor 2 described above. Using such an apparatus, the decomposition of fluorocarbons of the present invention is performed as follows.

Exhaust gas containing chlorofluorocarbons discharged from various processes is diluted with nitrogen gas to an appropriate concentration, and discharged into the discharge plasma reactor 2 through the exhaust gas introducing pipe 4 using an exhaust gas pump (not shown). Push in. In the discharge plasma reactor 2, a high-voltage pulse voltage is applied between the internal electrode 12 and the ground electrode 13 to generate silent discharge plasma. Here, the fluorocarbons are decomposed by receiving a shower of high-temperature electrons, discharged from the other end of the discharge plasma reactor 2, and immediately introduced into the catalyst reactor 3. In the catalyst reactor 3, at about 500 ° C., it comes into contact with a chlorofluorocarbon decomposition catalyst such as aluminum phosphate, and the decomposition reaction proceeds, and finally, C and F ₂ are generated and made harmless.

At this time, it is extremely effective to add oxygen and / or hydrogen gas as a decomposition reaction accelerator for chlorofluorocarbons. Oxygen acts as an oxygen radical or ozone to exhibit an oxidizing effect, hydrogen exhibits a reducing effect, and simultaneous addition thereof exhibits a decomposing effect of simultaneously exhibiting an oxidizing and reducing effect, and almost 100% of CO ₂ and HF. At the decomposition rate of These gases may be added at one or more of the inlet of the discharge plasma reactor 2, the inside of the discharge plasma reactor, the inlet of the catalyst reactor 3, and the catalyst reactor. A promoting action can be exerted.

Next, another embodiment of the present invention will be described.
This is a chlorofluorocarbon decomposing apparatus 1a configured as shown in FIG. 4, and a catalyst layer 31 is provided on the inner wall of the alumina reaction tube 11 of the discharge plasma reactor 2 in FIG.
A catalyst reactor 30 is constituted, and an oxygen introduction pipe 5 and a hydrogen introduction pipe 6 are connected to an exhaust gas introduction pipe 4 on the inlet side 9 of the reactor 30.
Has been added. The discharge plasma generator has the same configuration as that of the discharge plasma reactor 2. The catalyst layer 31 is formed, for example, by baking granular porous aluminum phosphate effective as a CFC decomposition catalyst on the inner wall of the alumina reaction tube 11 at 1200 ° C.

The method for decomposing flon-containing exhaust gas using the present apparatus 1a is as follows: the discharge plasma generator of the plasma-catalyst reactor 30 is activated, and the exhaust gas is introduced from the exhaust gas introduction pipe 4. It can be efficiently decomposed by taking a plasma electron shower and coming into contact with the catalyst. At this time, if oxygen and / or hydrogen is added, the load on the catalyst is reduced because the intermediate decomposition products of lower order are decomposed by the plasma, and it is not necessary to heat the chlorofluorocarbon decomposition catalyst layer, and the energy cost can be reduced. It becomes possible. Also,
Since the catalyst is coated on the inner wall, there is no occurrence of plasma generation failure, and the fluorocarbons decomposer can increase the throughput because of low exhaust gas ventilation resistance.

[0052]

EXAMPLES Next, the present invention will be described in detail with reference to examples of the present invention, but these do not limit the present invention. EXAMPLE 1 As shown in FIG. 1, a temperature-controllable catalytic reactor shown in FIG. 3 was connected in series at the subsequent stage of the discharge plasma reactor using the silent discharge shown in FIG. Filled with aluminum (AlPO ₄ ) and heated to 500 ° C. The discharge plasma reactor used a pulse power source of 10 kHz at 10 kV, the reaction tube was made of alumina ceramics, a nichrome wire coil was used for the internal electrode, and a stainless steel plate was used for the external ground electrode.

Exhaust gas containing 1% of CF ₄ diluted with nitrogen gas discharged from a semiconductor dry etching apparatus and 10 slpm (standard liter per)
minute) was introduced into the discharge plasma reactor, and oxygen gas was introduced at 1 slpm from the reactor inlet to decompose.

As a result, the concentration of CF ₄ in the purified gas was below the detection limit of 1 ppm. As for the decomposition products, CO ₂ and HF equivalent to the CF ₄ at the inlet were detected in the purified gas, and the decomposition rate achieved almost 100%.

Example 2 1% concentration CF diluted with nitrogen gas discharged from a semiconductor dry etching apparatus
₄ Same as in Example 1 except that 10 slpm was introduced into the discharge plasma reactor, oxygen gas was introduced from the reactor inlet at 1 slpm, and hydrogen gas was introduced at 0.4 slpm from the catalyst reactor inlet to decompose. The decomposition reaction was carried out using the equipment and conditions. As a result, CF ₄ concentration in the purified gas is less than 1ppm of detection limit, degradation products inlet of CF ₄ and equivalents of CO ₂ and HF was detected in the purified gas.

Example 3 1% concentration CF diluted with nitrogen gas discharged from a semiconductor dry etching apparatus
_{4 A} decomposition reaction was performed under the same apparatus and conditions as in Example 1, except that 10 slpm was introduced into the discharge plasma reactor, and 0.4 slpm of hydrogen gas was introduced from the inlet of the catalytic reactor to decompose. As a result, the concentration of CF ₄ in the purified gas was 1 ppm or less, which is the detection limit, and as for the decomposition product, HF equivalent to the CF ₄ at the inlet was detected in the purified gas. However, no CO ₂ was detected.

Example 4 1% concentration CF diluted with nitrogen gas discharged from a semiconductor dry etching apparatus
₄ Similar to Example 1 except that 10 slpm was introduced into the discharge plasma reactor, 0.4 slpm of hydrogen gas was introduced from the inlet of the discharge plasma reactor, and 1 slpm of oxygen gas was introduced from the inlet of the catalyst reactor to decompose. The decomposition reaction was carried out using the equipment and conditions. As a result, 0.2% of CHF ₃ gas was detected in the exhaust gas at the outlet of the discharge plasma reactor. The CF ₄ concentration of the final purified gas was 1 ppm or less, which is the detection limit, and the decomposition product detected CO ₂ and HF equivalent to the CF ₄ at the inlet in the purified gas.

EXAMPLE 5 As shown in FIG. 4, the inner wall of an alumina reaction tube of a discharge plasma reactor was coated with aluminum phosphate as a chlorofluorocarbon decomposition catalyst.
A plasma-catalyst reactor in which the discharge plasma reactor baked at 0 ° C. to form a catalyst layer and the catalyst reactor were integrated was used. As the silent discharge plasma, a pulse power source of 10 kV and 10 kHz was used. 10% CF ₄ exhaust gas diluted with nitrogen gas discharged from dry etching equipment
lpm, oxygen gas 1 slpm and hydrogen gas 0.4 slp
After mixing m, the mixture was introduced into a plasma / catalyst reactor to be decomposed.

As a result, the concentration of CF ₄ in the purified gas was below the detection limit of 1 ppm. As for the decomposition products, CO ₂ and HF equivalent to the CF ₄ at the inlet were detected in the purified gas, and the decomposition rate achieved almost 100%. In addition, since there is no ventilation resistance due to the catalyst, it was possible to further increase the processing capacity.

Example 6, Comparative Example 1, Comparative Example 2 The decomposition rate at various set temperatures in the catalytic reactor shown in FIG. 3 was measured using the same apparatus as in Example 1. First, 10 slpm of NF ₃ gas having a concentration of 1% diluted with nitrogen gas is introduced into the discharge plasma reactor 2, and 0.4 slp of hydrogen is introduced.
m and 0.4 slpm of oxygen were mixed and decomposed in front of the discharge plasma reactor 2 and then passed through the catalytic reactor 3 to decompose. At this time, the temperature of the catalyst layer was set to normal temperature, 100 ° C.,
200 ° C. and 300 ° C. were used. NF at exit
_{The three} concentrations were measured, and the decomposition rate was determined from the relationship with the inlet concentration. As a result, a decomposition rate as shown in Table 1 was obtained.

[0061]

[Table 1]

Next, for the purpose of comparison, the NF ₃ concentration of the exhaust gas after passing through the discharge plasma reactor was measured under the same gas conditions as in Example 1 and the decomposition rate was calculated. As also described in No. 1, it was 85% (Comparative Example 1). Further, for comparison, the decomposition was performed under the same gas conditions and catalyst temperature as in Example 6 in order to see the effect of only the catalyst without discharging the plasma, and the decomposition rate was determined. (Comparative Example 2). Note that under all conditions, the by-product of NO _X was small and was 20 ppm or less.

As a result, according to the present invention, it is effective to obtain a high decomposition rate even for NF ₃ gas, and the effectiveness at a normal temperature to 300 ° C. as the catalyst temperature is apparent.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, the method and apparatus for decomposing fluorocarbons of the present invention are not applied only to the above-described semiconductor process and the like. It goes without saying that the present invention can be applied to the recovery and detoxification of fluorocarbons used in large amounts in processes such as refrigerants, cleaning agents, foaming agents, and aerosols.

[0066]

As described above, according to the present invention, almost all of the fluorocarbons contained in the exhaust gas discharged from the process can be detoxified by oxidation-reduction decomposition, and the emission of harmful gases can be significantly reduced. It is possible to improve the decomposition treatment capacity of fluorocarbons while ensuring safety while ensuring the safety. In addition, the facility cost and the running cost can be reduced as compared with the conventional methods for decomposing various chlorofluorocarbons, and the cost of decomposing fluorocarbons can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration example of a fluorocarbons decomposition apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration example of a discharge plasma reactor.

FIG. 3 is a schematic diagram showing a configuration example of a catalytic reactor.

FIG. 4 is a schematic view showing another configuration example of the plasma-catalyst reactor of the present invention.

FIG. 5 is a schematic diagram showing a configuration example of a conventional volatile harmful substance plasma decomposition apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 1a ... Freon decomposition | disassembly apparatus, 2 ... Discharge plasma reactor, 3 ... Catalytic reactor, 4 ... Exhaust gas introduction pipe, 5 ... Oxygen introduction pipe, 6 ... Hydrogen introduction pipe, 7 ... Purified gas discharge pipe, 8
... intermediate sampling port, 9 ... discharge plasma reactor inlet side, 11 ... alumina reaction tube, 12 ... coil electrode,
13: ground electrode, 14: high-voltage AC power supply, 15: catalyst reactor inlet side, 21: catalyst, 22: heater, 23
... heat insulating material, 24 ... catalyst container, 30 ... plasma / catalyst reactor, 31 ... catalyst layer, 51 ... internal electrode, 52 ... external electrode, 53 ... porous adsorbent, 54 ... ferroelectric substance, 5
5: Power supply 56: Teflon cap 57: Holding plate (with holes) 58: O-ring 59: Plasma processing chamber a: exhaust gas inflow direction, b: purified gas discharge direction.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C07C 19/08 C07C 19/10 19/10 B01D 53/36 ZABG

Claims (7)

[Claims] 1. A method for decomposing fluorocarbons, which detoxifies fluorocarbons, wherein an exhaust gas containing fluorocarbons is passed through discharge plasma and then contacted with a fluorocarbon decomposition catalyst. Method. 2. The method for decomposing fluorocarbons according to claim 1, wherein the exhaust gas containing fluorocarbons is subjected to an entrance of a discharge plasma reactor, an interior of the discharge plasma reactor, an entrance of a catalytic reactor, and a catalytic reactor. A method for decomposing fluorocarbons, wherein oxygen and / or hydrogen is mixed at one or more of the above. 3. The fluorocarbons are PFCs (perfluoro compounds), CFCs (chlorofluorocarbons)
, HFCs (hydrofluorocarbons), HCFC
The method for decomposing CFCs according to claim 1 or 2, wherein the gas is a gas containing one or more of (hydrochlorofluorocarbons). 4. The fluorocarbon decomposition catalyst is one or a mixture of two or more of aluminum phosphate, boron phosphate, phosphate oxide, titanate oxide, and tungstate oxide. The method for decomposing fluorocarbons according to any one of claims 1 to 3, characterized in that: 5. The method for decomposing CFCs according to claim 1, wherein the discharge plasma is a normal-pressure / low-temperature plasma generated by a silent discharge or a corona discharge. . 6. A CFC decomposing apparatus for detoxifying CFCs, comprising at least a discharge plasma reactor and a catalyst reactor provided with a CFC decomposition catalyst layer, an exhaust gas inlet of the discharge plasma reactor, an inside of the discharge plasma reactor, An apparatus for decomposing chlorofluorocarbons, comprising a means for introducing oxygen and / or hydrogen at one or more of the inlet of the catalytic reactor and one or more of the catalytic reactor. 7. A chlorofluorocarbon decomposer for detoxifying chlorofluorocarbons, comprising a discharge plasma reactor provided with a chlorofluorocarbon decomposition catalyst layer at least on the inner wall of the reactor, wherein oxygen and oxygen are contained in an exhaust gas inlet or the reactor of the plasma reactor. And / or a device for decomposing chlorofluorocarbons, comprising a means for introducing hydrogen.