JP2003020468A - Fluorinated gas-decomposing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fluorinated gas-decomposing agent that can still more efficiently decompose fluorinated gases, when they are decomposed with a decomposing agent comprising a carbonaceous solid material and an alkali metal compound. SOLUTION: A carbonaceous powder and slaked lime are kneaded and the kneaded product is fired under the conditions that the reverse hydration reaction of slaked lime proceeds sufficiently, as carbon remains in the reaction mixture, whereby the objective fluorinated gas-decomposing agent is obtained that contains >=90 wt.% of carbon and calcium oxide in total.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a decomposing agent for fluorinated gas. In the present specification, "fluorinated gas" is a generic term for what is commonly called chlorofluorocarbon gas, and generally, fluorochlorocarbon fluorocarbons or fluorocarbon fluorocarbons having about 1 to 5 carbon atoms. Means the gaseous form of. In that case, it also includes one in which a part of fluorine or chlorine is replaced by hydrogen.

[0002]

2. Description of the Related Art Since the above-mentioned fluorinated gas, if released into the atmosphere, damages the global environment, technical development for decomposing it into harmless substances is under way. As disclosed in Japanese Patent Laid-Open No. 24255/1996 and Japanese Patent Application Laid-Open No. 8-187302, such a fluorinated gas is mixed with a decomposing agent composed of a carbonaceous solid material and an alkali metal compound, and 30
When it is contacted at a temperature of 0 ° C. or higher, it can be decomposed almost completely and rendered harmless.

[0003]

Since the invention described in the above publication is focused on the decomposition method of the fluorinated gas, the characteristics required for the reaction agent to be decomposed, the manufacturing method satisfying the characteristics, etc. Was not necessarily established. Therefore, there is a problem in performing the decomposition process stably. For example, the decomposing agent absorbs moisture before being used for decomposition, the decomposing agent becomes powdered or solidifies before or during use, the decomposition rate decreases, the decomposition efficiency changes at the beginning and end of the reaction, and the decomposing agent is completely used up. Various factors in actual operation, such as the performance of the decomposing agent deteriorates before, the pressure loss of the processing gas occurs, special consideration is required for the secondary processing of the recovered reactant, and continuous processing is difficult. There was a problem.

Therefore, the present invention has an object to solve the above-mentioned problems in a method of decomposing a fluorinated gas by using a decomposing agent composed of a carbonaceous solid material and an alkali metal compound.

[0005]

According to the present invention, carbon obtained by firing a kneaded material of carbonaceous powder and slaked lime under conditions sufficient for the back digestion reaction of slaked lime to proceed while carbon remains And a fluorinated gas decomposer having a total amount of calcium oxide of 90% by weight or more.

Further, according to the present invention, a kneaded product of carbonaceous powder and calcium carbonate powder is fired under conditions sufficient for the decomposition reaction of calcium carbonate to proceed while carbon remains, and carbon and oxidation are obtained. Provided is a fluorinated gas decomposer having a total amount of calcium of 80% by weight or more.

The decomposing agent for fluorinated gas according to the present invention is 5 to
It contains 85% by weight of carbon and 10-95% by weight of calcium oxide, has a specific surface area of 10 m ² / g or more and a bulk specific gravity of 0.3-
It is a granular material of 1.5 g / cm ³ .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above-mentioned problems, the present inventors have changed the production raw materials and production conditions of a fluorinated gas decomposition agent comprising a carbonaceous solid material and an alkali metal compound. ， Physical properties and chemical properties of the obtained decomposing agent,
Extensive research and studies have been conducted to find out the relationship of fluorinated gases with respect to their decomposition behavior. Decomposition that shows high decomposition efficiency regardless of the type of fluorinated gas and that can perform stable decomposition operation. As the agent, the decomposing agent described in the claims could be found.

The decomposing agent of the present invention consists of a calcined product in which carbon and calcium oxide are intimately mixed, but it has a unique property of low hygroscopicity despite containing a large amount of calcium oxide. Originally, calcium oxide (quick lime:
CaO) has the property of reacting violently with water due to a digestive reaction to easily turn into calcium hydroxide (slaked lime: Ca (OH) ₂ ), and is therefore specified as a dangerous substance by the Fire Service Law. Therefore, if calcium oxide and carbon are simply mixed in powder form, the moisture and calcium oxide will cause a digestive reaction and the moisture absorption will occur violently if they are left in the atmosphere. For this reason, it is deteriorated before being applied to a decomposing agent for fluorinated gas, and water is generated when it is subjected to the decomposition reaction of the fluorinated gas, and the generated water adversely affects the performance of the decomposing device.

However, when a kneaded product of carbonaceous powder and slaked lime was fired under conditions sufficient for the back digestion reaction of slaked lime to proceed while carbon remained, carbon and calcium oxide were substantially mixed. However, it was found that the digestive reaction and moisture absorption as described above hardly progress even if the substance is left in the air. Similarly, when a mixture of carbonaceous powder and calcium carbonate powder is fired under conditions sufficient for the decomposition reaction of calcium carbonate to proceed while carbon remains, carbon and calcium oxide are substantially mixed. However, even if left in the air, the digestive reaction and moisture absorption hardly proceed. The reason for this is not clear, but it is presumed that the surface of the calcium oxide produced by the reverse digestion reaction or the decomposition reaction is almost completely covered with dense carbon.

In the present specification, the reverse digestion reaction of slaked lime means the reaction of Ca (OH) ₂ → CaO + H ₂ O. (1), and the decomposition reaction of calcium carbonate is CaCO ₃ → CaO + CO ₂ ..・ It means (2).

The reaction of the formula (1) generally proceeds by heating the slaked lime to 600 ° C. or higher in a non-oxidizing atmosphere. The reaction of the formula (1) is performed on the slaked lime mixed with the carbonaceous powder. One of the features of the present invention is that it is carried out. In practice, a kneaded product of carbonaceous powder and slaked lime is prepared, and this kneaded product is subjected to 550 in a non-oxidizing atmosphere, for example, a nitrogen gas atmosphere.
It is heated and baked at a temperature of up to 1000 ° C. As a result, calcium oxide (quick lime) remains in the kneaded material while carbon remains.
To obtain the decomposing agent of the present invention.

Each of the kneaded products is preferably a granulated product in which a carbonaceous raw material having a particle size of 100 μm or less and a slaked lime raw material are uniformly mixed. Weigh the raw materials to the target composition, and add an appropriate amount of water when kneading. As the kneading machine, it is convenient that the kneading machine can mix and granulate at the same time, but the kneading machine may separately mix and granulate. For example, a Henschel mixer or a vertical mixer can be used for mixing and granulation at the same time, but the raw materials are mixed by a Henschel mixer or a V-type mixer, and then granulation is performed by a plate-type granulator or a drum pelletizer. You can go.

When kneading and granulating, an appropriate amount of binder may be blended in addition to water. As the binder, an organic binder such as polyvinyl alcohol (PVA) is preferable. However, 5 such organic binders
If the blending amount exceeds 5% by weight, the performance of the obtained decomposing agent deteriorates, so it is preferable that the content of the organic binder is 5% by weight or less. Aluminum oxide-based or silicon oxide-based inorganic binders can also be used, but the amount must be small enough not to affect the purity of the obtained fluorinated gas decomposer.

As the carbonaceous raw material, char charcoal, coke powder, carbon black, activated carbon and the like can be used, but char char and activated carbon are preferable in view of their low impurities, low cost and large specific surface area. As for the slaked lime raw material, it is desirable to use a standard product with few impurities.

When the kneaded and granulated product is preferably dried and then heated in the above temperature range in a non-oxidizing atmosphere, calcium oxide is produced by the back digestion reaction of the formula (1), and at the same time, this reaction is performed. The water and compounded water generated in step 2 escapes, and the volatile components in the raw material also evaporate, resulting in a fired product with the strength that carbon and calcium oxide are closely bonded. As mentioned above, this calcined product has a uniform hygroscopicity despite the fact that it contains quicklime, and even if it is handled in the air, it has little property of adsorbing water, but the strength, specific surface area, Properties such as bulk specific gravity are affected by the mixing ratio of raw materials, the presence or absence of binder, and firing conditions. The characteristics of these fired products affect the function of using them as a decomposing agent for fluorinated gas.

According to the present invention, the total amount of carbon and calcium oxide is 90% by weight or more and 5 to 5% by weight by appropriately adjusting the mixing ratio of raw materials, granulation conditions and firing conditions within the following ranges. Contains 85% by weight of carbon and 10 to 95% by weight of calcium oxide and has a specific surface area of 10 m ² / g or more,
A fluorinated gas decomposing agent consisting of particulate matter having a bulk specific gravity of 0.3 to 1.5 g / cm ³ is obtained.

When the decomposing agent is produced by the reaction of the formula (1), the mixing ratio at the time of granulation Carbonaceous raw material (powder of 100 μm or less): 4 to 85% by weight Slaked lime raw material (powder of 100 μm or less): 15 to 15% 96% by weight Water: 20% by weight or less Organic binder: 5% by weight or less Particle size of granulated product: 1 to 20 mm Drying condition of granulated product: heating and holding at 100 to 150 ° C. in air atmosphere Firing condition: non-oxidizing 2 at 550 to 1000 ℃ in the atmosphere
~ 5 hours heating

A similar calcined product can also be obtained by using a calcium carbonate raw material instead of the above slaked lime raw material and carrying out the decomposition reaction of the calcium carbonate of the above formula (2). The mixing ratios of the raw materials, the granulation conditions and the firing conditions in this case are as follows.

When the decomposing agent is produced by the reaction of the formula (2): Mixing ratio at the time of granulation Carbonaceous raw material (powder of 100 μm or less) 2 to 98% by weight Carbon raw material (powder of 100 μm or less): 9 to 77% by weight Water: 20% by weight or less Organic binder: 5% by weight or less Particle size of granulated product: 1 to 20 mm Drying condition of granulated product: heating and holding at 100 to 150 ° C. in air atmosphere Firing condition: non-oxidizing 2 to 900-1100 ° C under atmosphere
~ 5 hours heating

No matter which decomposition agent is obtained by using the reaction of the above formula (1) or (2), gas is released in the process of firing (in the former case, water is converted from slaked lime, in the latter case, carbon dioxide is generated). CO ₂ escapes from calcium in the form of gas), and this gas release path becomes pores, and a fired product having pores inside is obtained. It is considered that the pores assist the opportunity of contact with the fluorinated gas when the fluorinated gas is decomposed.

The characteristic feature of the fluorinated gas decomposing agent of the present invention is that the fluorinated gas and the decomposing agent are contained in a small amount in the temperature range of 350 to 800 ° C. (the appropriate temperature varies depending on the kind of the fluorinated gas). When they are brought into contact with each other in the presence or absence of oxygen, fluorine is almost completely fixed as CaF ₂ to the decomposing agent, and carbon in the decomposing agent serves to promote this decomposition reaction.

Therefore, it is necessary that the decomposing agent maintains a stable shape at such a high temperature and at the same time guarantees the opportunity for the fluorinated gas to come into contact with carbon and calcium oxide even if the decomposition reaction proceeds. . For this purpose, the particle size, strength and specific surface area of the decomposer must be appropriate. If the particle size of the decomposing agent exceeds 20 mm, it is considered that the contact area with the fluorinated gas becomes small, but the efficiency of the decomposing reaction deteriorates. Although the strength of the decomposing agent is related to the specific surface area and bulk specific gravity, the specific surface area is 10 m ² / g or more, the bulk specific gravity is 0.3 to 1.5 g / cm ³ , and the compressive strength is 0.5.
Those having kg / cm ² or more can meet the above requirements.

Further, it is necessary that the decomposition promoting action by carbon is maintained even at the end of the reaction in which most of the calcium oxide in the decomposer is modified into calcium fluoride.
For this purpose, it is necessary that the initial ratio of carbon to calcium oxide in the decomposing agent is appropriately adjusted according to the type of fluorinated gas to be treated. Therefore, this ratio depends on the type of fluorinated gas to be treated and the decomposition conditions, but the carbon content in the decomposer is in the range of 5-85% by weight, and the calcium oxide content is in the range of 10-95% by weight. Is at least necessary.

Further, if the decomposing agent absorbs water, the decomposing operation is adversely affected. The decomposing agent of the present invention preferably has a heating loss of 5% by weight or less when heated at 100 ° C. The small heating loss means that the absorbed water content is extremely low.

Further, it was found that S in the decomposer hinders the decomposition reaction of the fluorinated gas. Therefore, the decomposing agent of the present invention has an S content of 5% by weight or less, preferably 1% by weight.
It is desirable that the amount is less than 0.5% by weight, more preferably less than 0.5% by weight. Further, it is preferable that the amount of metal components or compounds that are melted or vaporized at the decomposition treatment temperature of the fluorinated gas be as small as possible. However, since oxides and carbonates of alkaline earth metals show a decomposing action of fluorinated gas like calcium oxides and carbonates, a part of calcium oxide in the decomposing agent of the present invention is alkaline earth metal. It may be substituted with a metal oxide or carbonate. Therefore, for example, dolomite or the like can be used as a part or all of the raw material of calcium carbonate to be subjected to the reaction of the above formula (2).

[0027]

Example: Char charcoal with a particle size of 250 μm or less and a particle size of 2
Slaked lime of 50 μm or less was mixed in different weight ratios, mixed with Henschel mixer while adding water, granulated with a plate type granulator, and the obtained granulated product was dried at 150 ° C. for 1 hour,
Back digestion was performed by heat treatment at 550 ° C. for 2 hours in a nitrogen atmosphere. The carbon content, calcium oxide content, and sulfur content of the obtained reverse digested product were analyzed, and their specific surface area, bulk specific gravity, particle size, compressive strength, and heat loss were measured, and the results are shown in Table 1. . In Table 1, the composition is not 100% because it contains other impurities.

When these back-digested products were used as decomposition agents in the decomposition of the fluorinated gas by a method substantially similar to that described in the examples of JP-A-8-187302, the results are shown in Table 1. As shown, it was possible to decompose well with a high decomposition rate and a low pulverization rate. However, Example 10 is a comparative example with a large amount of sulfur,
In this case, since the amount of sulfur was large, the decomposition rate was slightly low and the pulverization rate was high. Further, Example 11 is a comparative example in which the same compound as in Example 2 was granulated and dried, and directly subjected to decomposition of the fluorinated gas without back digestion. Example 1 without reverse digestion
In No. 1, each density is small and the compression strength is low. Probably because of this, the pulverization rate is high and the decomposition rate is lower than that of the example.

[0029]

[Table 1]

[0030]

As described above, according to the present invention,
A decomposing agent for fluorinated gas having excellent decomposing characteristics can be obtained, and since this decomposing agent is difficult to be pulverized, the gas ventilation is not deteriorated due to pulverization.

Continued front page    (72) Inventor Hiroshi Seto             7 Doki Sakae-cho, Okayama City, Okayama Prefecture Dowa Iron Powder Works             Business F-term (reference) 4D002 AA22 BA03 CA07 DA05 DA11                       DA12 DA16 DA41 GA01 GB03                       GB08 GB12

Claims (6)

[Claims] 1. A kneaded product of carbonaceous powder and slaked lime is fired under conditions sufficient for the back digestion reaction of slaked lime to proceed while carbon remains, and the total amount of carbon and calcium oxide is 9
Decomposing agent of 0% by weight or more of fluorinated gas. 2. The total amount of carbon and calcium oxide obtained by firing a kneaded product of carbonaceous powder and calcium carbonate powder under conditions sufficient for the decomposition reaction of calcium carbonate to proceed while carbon remains. Decomposing agent of 80% by weight or more of fluorinated gas. 3. Granules containing 5 to 85% by weight of carbon and 10 to 95% by weight of calcium oxide, having a specific surface area of 10 m ² / g or more and a bulk specific gravity of 0.3 to 1.5 g / cm ^3. A fluorinated gas decomposer. 4. The compressive strength is 0.4 kg / cm ² or more and the particle size is 0.0.
The decomposing agent for fluorinated gas according to claim 1, which is composed of particles of 5 to 20 mm. 5. The decomposing agent for a fluorinated gas according to claim 1, wherein the weight loss upon heating to 100 ° C. in the atmosphere is 5% by weight or less. 6. The fluorinated gas decomposer according to claim 1, wherein the S content is 5% by weight or less.