JPH11179201A - Catalyst for decomposition of fluorine-containing compound and fluorine-containing compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously decomposite fluorine-contg. compds. including hardly decomposable perfluoro compds. under practical treatment conditions by prepar ing a catalyst showing high activity for continuous decomposition treatment of fluorine-contg. compds. from alumina having a specified Na amt. as a metal. SOLUTION: In the preparation of a catalyst having high activity for catalytic decomposition of fluorine-contg. compds. especially perfluoro compds. such as fluorocarbons, nitrogen fluoride and sulfur fluoride, an alumina having <0.1 wt.% Na as metal is used. At least one kind of metal selected from the 6A group, 8 group and 3B group in the periodic table and/or at least one kind of inorg. acid such as sulfuric acid, phosphoric acid and boric acid may be deposited on the alumina which preferably has <0.1 wt.% Na content as metal. As the metal seed used, Cr, Fe, Co, Ni, Pd, Pt, B and Ga can be used, and the deposition amt. of the metal is 0.01 to 20 pts.wt. based on 100 pts.wt. of the carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst having a high activity in the catalytic decomposition of perfluorinated compounds such as carbon fluoride, nitrogen fluoride, sulfur fluoride and the like, and a fluorine-containing compound using the catalyst. The present invention relates to a method for disassembling the material.
By using the catalyst of the present invention, not only is it possible to decompose chlorofluorocarbon, which is a problem as a substance causing ozone layer depletion, but it is also discharged into the atmosphere from factories that use alternative chlorofluorocarbons, especially semiconductor manufacturing plants. In addition, it is possible to reduce the amount of perfluoro compounds which are more difficult to decompose than CFCs.

[0002]

2. Description of the Related Art Among volatile fluorine-containing compounds, Freon containing chlorine and fluorine has been determined to be severely regulated in the future as the cause of ozone layer destruction. In addition to this fluorocarbon, the volatile fluorine-containing compound includes a volatile fluorine-containing compound called a perfluoro compound (hereinafter, referred to as PFC) composed of carbon fluoride, nitrogen fluoride, sulfur fluoride, and fluorocarbon. Unlike PFC, this PFC does not contain chlorine and does not contribute to ozone layer destruction because it is very stable. Since there is no emission control yet, it is often used for cleaning in semiconductor manufacturing sites. Is what is being done. However, the global warming potential is one of carbon dioxide
The emission to the atmosphere is a compound that is very likely to be regulated in the future, like chlorofluorocarbons.
Among these fluorine-containing compounds, the production and use of specific fluorocarbon gases, which are contained in products such as air conditioners themselves and whose emission is very difficult to control due to their wide distribution, are completely prohibited. You may only have a hand, but P
As with FCs, those that are used in the manufacturing process but are not included in the product and are not shipped, and the emission source is specified at the factory, so emission control at the exit is relatively easy. It is advisable to use it while taking advantage of its original characteristics. Of course, it is needless to say that when the reference value is set, the emission is suppressed to a value lower than the reference value.

[0003] As a method of suppressing the above gas emission,
There are two methods, a recovery method and a decomposition method, but the recovery method is preferably a decomposition treatment because the concentration of PFC contained in the exhaust gas is essentially low and the recovery device is complicated. Is the way. However, PFC,
Above all, fluorocarbon is chemically stable as compared with chlorofluorocarbons, so that it is difficult to treat it with a normal decomposition method used for decomposition of chlorofluorocarbons, and further severe processing conditions are required. For example, the temperature required for a simple combustion process is 800 to 900 ° C. in the case of chlorofluorocarbon, but not only 1000 ° C. or more in the case of fluorocarbon, but also a combustion furnace or a nozzle of a combustion device. There is also a problem of corrosion at a portion that comes into contact with a corrosive gas at a high temperature, and there is still a problem to be solved for practical use. Also, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 7-132211, which discloses a technique for decomposing carbon fluoride by using silica or zeolite as a decomposing agent or a fluorine scavenger, decomposes fluorocarbon at a practical rate. Not only requires a high temperature of 1000 ° C. or more, but also requires a part of the decomposing agent to be consumed as a fluorine scavenger, so that it is necessary to carry out the reaction while supplying the decomposing agent in the form of a powder. It has the following disadvantages. For continuous treatment of a fluorine-containing compound containing PFC, a catalytic cracking method using a catalyst is considered to be the most effective, but a catalyst system showing a sufficient activity has not been found yet.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a P which is difficult to decompose in the prior art under practical processing conditions.
It is an object of the present invention to provide a catalyst system capable of continuously decomposing a fluorine-containing compound containing FC and a method for continuously decomposing a fluorine-containing compound using the catalyst.

[0005]

Means for Solving the Problems The inventors have found that the N
The amount of alumina below a certain amount is a catalyst exhibiting high activity in the continuous decomposition treatment of a fluorine-containing compound including PFC. If the catalyst is used properly, the above problem can be solved. The present inventors have found that the method is a continuous decomposition treatment method and completed the present invention. That is, the present invention comprises alumina having a Na content of 0.1% by weight or less as a metal,
The present invention relates to a catalyst for decomposing fluorine-containing compounds. The present invention also relates to a method for decomposing a fluorine-containing compound, which is carried out in the coexistence of oxygen and water with a catalyst made of alumina containing 0.1% by weight or less of Na as a metal.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is most characterized by using alumina having a low Na content as a catalyst.
At present, the nature of the inhibitory effect of the presence of a large amount of Na on the decomposition reaction of the fluorine-containing compound is unknown. However, Na
It is generally known that reducing the amount leads to an increase in the amount of acid, and the results of quantum chemical calculations indicate that the electron pair acceptability of Al ions, that is, the characteristics of Al as a Lewis acid is a major point. It is inferred. Many types of alumina for use as a catalyst or catalyst support are commercially available, and include Si,
Fe and Na are contained as main impurities. Depending on the product, the content of Na that exhibits an inhibitory effect on the fluorine-containing compound decomposition reaction is 0.0015 to
The best method is to select an alumina which has a Na content of 0.1% by weight or less, which is suitable for the use of the present invention. Alumina having a Na content of more than 0.1% by weight as a metal is also washed with an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid and acetic acid or an aqueous solution of an organic acid such as acetic acid to obtain Na.
The amount can be reduced, and a highly active catalyst suitable for the use of the present invention can be obtained. As alumina, various crystal forms such as α, γ, and δ are known and commercially available, but γ and δ-type aluminas give preferable results, and among them, most commonly used as catalysts or catalyst carriers. Γ-alumina gives the most favorable results. Regarding the shape, granules, powders, honeycombs and the like are selected according to the reactor and the reaction method.

In the present invention, a catalyst exhibiting a sufficiently high activity for catalytic cracking of a fluorine-containing compound can be obtained by using only alumina having a low Na content, but it is necessary to support a certain metal and / or inorganic acid. Thereby, a more highly active catalyst can be obtained. The metal to be supported on alumina is at least one or more metals selected from the group 6A, the group 8 and the group 3B.
r, Fe, Co, Ni, Pd, Pt and typical metal elements B and Ga give favorable results. For supporting the metal, after dissolving various salts or oxides such as chlorides, nitrates, sulfates, and phosphates of these metals in an appropriate solvent, generally, when the carrier is a molded body, the method is generally performed. It can be easily supported by the impregnating method or evaporating to dryness method, or in the case of powder, by mechanical kneading method or evaporating to dryness method. It can also be prepared by a coprecipitation method using alumina sol, but the nature of the promoting effect of the supported metal on the decomposition reaction of the fluorinated compound is unknown at this time, but C ₂ F ₆ is used as a decomposition target at low temperatures. When the reaction is performed, CO ₂ increases instead of CO due to the loading of the metal, and it is presumed that the metal contributes to the oxidation reaction of C and N generated as a result of F extraction by oxygen.

When the metal is further supported on alumina having a low Na content, the amount of the metal depends on the kind of the metal, but a preferable result is 0.01 to 20 parts by weight in terms of metal per 100 parts by weight of the carrier. Can be obtained. If the amount of metal is too small, a sufficient effect of addition may not be exhibited.If the amount is too large, not only is it wasteful of resources, but also a catalyst that is not uniformly dispersed cannot be obtained, resulting in a catalyst with poor reproducibility. However, there is a possibility that the excellent characteristics of the alumina carrier may be lost. In addition, since it is very difficult to verify the existence form of the metal in the catalyst, particularly under the reaction conditions, in the present invention, it is expressed as "support of metal", but this means only a zero-valent metal. It does not do.

[0009] On the other hand, the function of the inorganic acid is also unknown at present, but it is coordinated around the Al ion of the carrier and is polarized to δ + due to the binding of F having a high electronegativity.
It is believed that it promotes the adsorption of C, N, and S atoms in the reactant molecules and enhances the reactivity. The inorganic acid used in the present invention is limited to sulfuric acid, phosphoric acid, and boric acid from the reaction conditions.
Among them, the use of sulfuric acid which is strongly acidic and has low scattering properties is most preferable.

[0010] The support of the inorganic acid is not only free acid,
Precursors that can be decomposed by use conditions such as ammonium salts such as ammonium sulfate or esters or by a pretreatment performed prior to use to give essentially the same support as when a free acid is used as a starting material can also be used. These free acids or their precursors are dissolved in water or other suitable solvent, as in the case of supporting the metal component, and then, when the carrier is a molded body, a commonly used impregnation method or The support can be easily carried out by an evaporation-drying method, or in the case of a powder, by a mechanical kneading method or an evaporation-drying method. When the amount of the supported inorganic acid is large, a high concentration solution may be supported at a time, or a low concentration solution may be supported in several times. Since a low concentration is easily obtained, it is more preferable to carry the low-concentration solution in two to four times.

The content of the inorganic acid in the catalyst varies depending on the type of the acid used. If the amount is too small, the effect of the addition will not be sufficiently exhibited. If the amount is too large, the catalyst originally contained in alumina, as in the case of the metal, will be used. Characteristics may be impaired. In the present invention, 0.1 parts by weight per 100 parts by weight of alumina as a carrier is used.
A suitable result can be obtained by using 1 to 20 parts by weight.

When a catalyst in which an inorganic acid is supported on alumina is used as a catalyst, the catalytic activity may decrease due to the decrease in the amount of acid in the catalyst as the reaction progresses.
An acid can be added to reactivate the catalyst. The method of adding the acid is a method of supplying these inorganic acids to the reaction system together with the reaction gas in the form of an aqueous solution when supplying water which is an essential component to the reaction system, or a method of adding a volatile precursor such as an inorganic acid ester. It is possible to adopt a method of entraining the reaction gas in a gaseous state. In this case, the acid may be added intermittently or constantly. However, if the acid is constantly added, it is possible to prevent a decrease in the catalytic activity accompanying a decrease in the amount of the acid.

Alumina can support both a metal and an acid. Not only a mere additive effect, but also a synergistic effect is exhibited depending on the kind of metal, and a favorable result can be obtained. In this case, the order of adding the metal and the acid to the alumina is not particularly limited, and either one of them may be carried first or the other may be carried simultaneously.

When the catalyst comprises only alumina, it can be directly charged into a reaction tube and subjected to a reaction. However, a catalyst precursor prepared by supporting other components on alumina is dried at about 100 ° C. A catalyst is prepared by performing a pre-heating treatment in a stream of air or nitrogen. This activation process
It may be carried out using a muffle furnace or the like, or after filling a required amount of the dried product into a reactor for a fluorine-containing compound decomposition reaction,
Prior to use, it may be activated by heating while flowing air or an inert gas. The heating temperature depends on the type of the metal to be supported and the type of the precursor used for the support, but the treatment temperature may cause a decrease in the surface area of the alumina or the supported metal, and if the temperature is too low, the catalyst may be stabilized. However, the catalyst activity changes with time in the early stage of the reaction, which leads to undesirable results. Therefore, in the present invention, 200 to 100
The heat treatment is performed at 0 ° C., preferably at 400 to 800 ° C.

The decomposition reaction of the fluorine-containing compound is performed by supplying a mixed gas of the fluorine-containing compound, oxygen and water onto the catalyst.
It is carried out in a temperature range of 300 to 1000 ° C, preferably 400 to 900 ° C. The supply rate of the mixed gas is 50,000 /
Or less, preferably 100 to 100000 / hour.

The concentration of the fluorine-containing compound contained in the reaction gas of the present invention is preferably 3% by volume or less. If the concentration of the fluorine-containing compound contained in the reaction gas is too high, the life of the catalyst may be adversely affected. Generally, the PFC concentration in the exhaust gas discharged from a semiconductor manufacturing plant is 1
This is not a problem because it is not more than 3% by volume, but when it is contained at 3% by volume or more, it is preferable to add a diluent gas such as air or nitrogen so that the concentration becomes 3% by volume or less. The reaction gas contains oxygen and water in addition to PFC. Among them, oxygen is a component necessary for converting carbon of PFC into CO ₂ and CO, and water is generated by a decomposition reaction. In addition to being a component necessary for discharging halogen as HF out of the catalyst system, it also has a function of preventing Al in alumina from escaping out of the catalyst system as aluminum fluoride.

The amount of oxygen contained in the reaction gas is not particularly limited as long as it is an amount sufficient to convert PFC carbon into CO ₂ and CO, but the PFC concentration in the reaction gas is within the above range. If not only air is available,
It is the most preferred oxygen source. On the other hand, the amount of water contained in the reaction gas is equal to or more than 10 times the amount of halogen contained in the reaction gas, that is, ₄ to 40 mole times for CF ₄ and ₆ to 40 times for C ₂ F ₆ . If it is 60 mole times, a favorable result can be obtained. Water can be supplied by a generally used method, that is, a method of supplying a liquid state to a reactor using a liquid pump, or a method of entraining a gaseous state with a reaction gas using a saturator without any problem. it can.

The catalytic cracking reaction of a fluorine-containing compound with a catalyst can be carried out by either a flow system or a batch system.
The flow type is preferred because of the simplicity of the device and the high processing capacity. In the case of a flow type, any of a fixed bed and a fluidized bed can be applied.

Exhaust gas after leaving the reactor is passed through a scrubber filled with an aqueous alkali solution or through an adsorber filled with solid alkali to remove HF generated by the decomposition reaction. After being released into the atmosphere.

[0020]

Now, the present invention will be described in further detail with reference to specific examples. Example 1 γ-alumina containing 0.0074% by weight of Na in terms of metal (manufactured by Mizusawa Chemical Co., trade name: Neobead GB-45, particle size:
4-5 mm) 5 ml was packed in a quartz reaction tube having an inner diameter of 1.0 cm, heated at 700 ° C. for 1 hour in a nitrogen stream, and then 20 ml of a 1% by volume C ₂ F ₆ / air mixed gas and water were added.
(NTP) / min and a feed rate of 0.36 g / hour to carry out a C ₂ F ₆ decomposition reaction.
The amount of C ₂ F ₆ in the outlet gas over time was analyzed by gas chromatography to evaluate the catalytic activity.
As a result, the C ₂ F ₆ conversion represented by the following formula was 85%. As a product, carbon dioxide was confirmed by gas chromatography and FTIR. Conversion rate = [(C ₂ F ₆ amount in raw material gas−C in outlet gas)
₂ F ₆ amount) ÷ C ₂ F ₆ amount in raw material gas] × 100

Example 2 γ-alumina containing 0.016% by weight of Na in terms of metal (manufactured by JGC Chemicals, trade name: N612N, columnar molded product: diameter 3)
Example 1 except that (mm × 3 mm length) was used as the catalyst.
A C ₂ F ₆ decomposition reaction was performed in the same manner as described above. The C ₂ F ₆ conversion after 3 hours from the start of the reaction was 90%.

Example 3 Here, an example using alumina having a lower Na content will be described. That is, γ-alumina containing 0.003% by weight of Na in terms of metal (manufactured by JGC Universal Corporation, trade name: NS)
T-7, particle size: 1-1.5 mm) were performed except that used as the catalyst in the same manner as in Example 1 C ₂ F ₆ decomposition reaction. The C ₂ F ₆ conversion after 3 hours from the start of the reaction was 91%.

COMPARATIVE EXAMPLE 1 Here, an example using alumina having a Na content outside the range of the present invention will be described. That is, 0.38% by weight in metal conversion
Na-containing γ-alumina (manufactured by Mizusawa Chemical Co., trade name: Neob
ead RN, particle size: 2 to 3 mm) except that was used as a catalyst was subjected to C ₂ F ₆ decomposition reaction in the same manner as in Example 1. After 3 hours from the start of the reaction, the C ₂ F ₆ conversion was 22%.

Comparative Example 2 Here, another example using alumina whose Na content is out of the range of the present invention will be described. 0.20% by weight of Na in metal conversion
-Alumina (Sumitomo Chemical, trade name: KHA-2)
4, particle diameter: 2 to 3 mm) except that was used as a catalyst was subjected to C ₂ F ₆ decomposition reaction in the same manner as in Example 1. The C ₂ F ₆ conversion after 3 hours from the start of the reaction was 17%.

Example 4 Here, an example in which a metal is further supported on alumina whose Na content is within the range of the present invention will be described. NiSO ₄ · 6H
_To a solution prepared by dissolving 0.5 g of 2O in 30 g of distilled water was added 10.0 g of alumina having a Na content of 0.0074% by weight, which was used in Example 1, and dried at 60 ° C. under reduced pressure using a rotary evaporator. Thereafter, it was dried at 100 ° C. overnight.
A C ₂ F ₆ decomposition reaction was performed in the same manner as in Example 1 except that 5.0 ml of the obtained Ni-supported alumina was used as a catalyst. The C ₂ F ₆ conversion after 3 hours from the start of the reaction was 95%.

Example 5 Here, an example in which an inorganic acid is further supported on alumina whose Na content is within the range of the present invention will be described. 5 ml of γ-alumina containing 0.0074% by weight of Na in terms of metal used in Example 1 was placed flat on a glass dish, and 10 ml of a 1N aqueous sulfuric acid solution was evenly dropped with a pipette.
And dried overnight. 5.0 ml of the obtained alumina supporting sulfuric acid
C ₂ was prepared in the same manner as in Example 1 except that
An F ₆ decomposition reaction was performed. The C ₂ F ₆ conversion after 3 hours from the start of the reaction was 91%.

From the above results, it can be seen that the alumina having a Na content within the range of the present invention is a large amount of Na outside the range of the present invention.
It has an extremely high C ₂ F ₆ decomposition activity as compared to alumina containing. In addition, it can be seen that by supporting a metal or an inorganic acid on alumina having a Na content within the range of the present invention, the C ₂ F ₆ decomposition activity is further improved.

[0028]

As described above, the catalyst of the present invention can be used not only for chlorofluorocarbon but also for PF which is more difficult to decompose than fluorocarbon.
C was also able to be decomposed at a practical reaction temperature of 1000 ° C. or less. PFC has been included in the menu of reduction targets at the Kyoto Conference on Global Warming Prevention held in December 1997, and it is certain that emissions into the environment will be regulated in the future. Despite the fact that its use is indispensable in the semiconductor manufacturing process, which is also referred to as rice in the industry, it enables the decomposition of PFC, whose emission to the environment will be regulated in the future due to its large global warming potential. The technical and social significance of the present invention is great.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C07B 35/06 B01D 53/36 G

Claims (10)

[Claims] 1. A catalyst for decomposition treatment of a fluorine-containing compound, comprising alumina having an Na content of 0.1% by weight or less as a metal. 2. An alumina having a Na content of 0.1% by weight or less as a metal, wherein at least one metal selected from the group 6A, 8 and 3B and / or at least one selected from the group consisting of sulfuric acid, phosphoric acid and boric acid. A catalyst for decomposing fluorine-containing compounds, which carries one or more inorganic acids. 3. The method according to claim 1, wherein the metal species is Cr, Fe, Co, Ni, P.
The fluorine-containing compound decomposition treatment catalyst according to claim 2, wherein the catalyst is at least one or more metals selected from d, Pt, B, and Ga. 4. The process for decomposing a fluorine-containing compound according to claim 2, wherein the amount of metal supported in the catalyst is 0.01 to 20 parts by weight in terms of metal per 100 parts by weight of alumina. Catalyst. 5. The catalyst according to claim 1, wherein the amount of the inorganic acid carried in the catalyst is 100% alumina.
The amount is 0.1 to 20 parts by weight per part by weight.
The catalyst for decomposing fluorine-containing compound according to any one of the above. 6. The decomposition of a gaseous fluorine-containing compound according to any one of claims 1 to 7, wherein the fluorine-containing compound to be reacted is one or a mixture selected from a perfluoro compound and a fluorocarbon. Processing catalyst. 7. A method for decomposing a fluorine-containing compound, which is carried out in the presence of oxygen and water by bringing it into contact with a catalyst comprising alumina containing 0.1% by weight or less of Na as a metal. 8. An alumina having 0.1% by weight or less of Na as a metal in the presence of oxygen and water,
A method for decomposing a fluorine-containing compound, which is carried out by contacting with a catalyst supporting at least one or more metals selected from Group III, VIII and 3B and / or at least one or more inorganic acids selected from sulfuric acid, phosphoric acid and boric acid. . 9. Cr, F in the presence of oxygen and water
e, Co, Ni, Pd, Pt, B, and at least one metal selected from the group consisting of B and Ga in an amount of 0.01 to 20 parts by weight in terms of metal per 100 parts by weight of alumina and / or 0.1 to 0.2 parts by weight of inorganic acid per 100 parts by weight of alumina. A method for decomposing a fluorine-containing compound, which is carried out by contacting 1 to 20 parts by weight of the catalyst according to claim 7. 10. The decomposition treatment of a gaseous fluorinated compound according to claim 7, wherein the fluorinated compound to be reacted is one or a mixture selected from perfluoro compounds and chlorofluorocarbons. Method.