JPH0857255A - Fluorocarbon decomposing apparatus - Google Patents

Abstract

PURPOSE: To provide a fluorocarbon decomposing system capable of treating fluorocarbon without lowering the decomposition sctivity of fluorocarbon when a large amt. of highly conc. fluorocarbon is treated by providing a first catalyst bed decomposing fluorocarbon and absorbing at least a part of hydrogen fluoride and/or hydrogen chloride generaled accordingly to the decomposition fluorocarbon in a front stage while providing a second catalyst bed decomposing residual fluorocarbon in a rear stage. CONSTITUTION: Fluorocarbon-containing exhaust gas 1 is mixed with oxygen 2 to be introduced into a first catalyst bed 3 packed with a calcia catalyst at reaction temp. of 400 deg.C. The hydrolytic decomposition reaction of fluorocarbon is advanced on the catalyst to form CO2 , HF, HCl and water. Next, the exhaust gas is introduced into a salt recovery process 4 packed with an aq. NaOH soln. to form Na and sodium chloride A. Further, the exhaust gas is introduced into a CaF2 recovery process 5 packed with Ca(OH)2 to recover CaF2 and sodium chloride, and the formed gas becomes a mixture of unreacted gas and air. This gas is mixed with oxygen 2 to be introduced into a second catalyst bed 6 pocked with a TiO2 -W catalyst at reaction temp. of 400 deg.C and the hydrolytic decomposition reaction of hydrocarbon advanced on the catalyst to decompose fluorocarbon.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fluorocarbon decomposition system.

[0002]

BACKGROUND ART Freon reaches a part of the ozone layer when it is discharged into the atmosphere, and active chlorine atoms generated by decomposition due to the action of solar ultraviolet rays destroy the ozone layer.
It has become a problem as a cause of global environmental pollution. Therefore, it is desired to develop a technology for decomposing used CFCs in parallel with the development of CFC substitutes. As one of the conventionally known methods for decomposing chlorofluorocarbon, JP-A-4-313344
The publication discloses that a gas containing a CFC-based substance is brought into contact with a catalyst at a temperature of 100 ° C. or higher. But,
When a large amount of high-concentration chlorofluorocarbon is treated by the method using such a catalyst, there is a problem that the catalyst is deteriorated due to the high-concentration hydrogen fluoride and hydrogen chloride gas of the decomposition product and the catalytic activity is lowered.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a CFC decomposition system which can treat a high concentration CFC in a large amount without causing deterioration of the catalyst due to the generated gas and without degrading the CFC decomposition activity. It is in.

[0004]

According to the present invention, a waste gas containing CFCs is decomposed at a temperature in the range of 300 to 600 ° C. in a normal decomposition step so that CFCs are decomposed in the preceding stage and hydrogen fluoride and / or chlorinated product gas is generated. By combining two types of catalysts, a first catalyst layer that absorbs at least a part of hydrogen and a second catalyst layer that decomposes residual CFCs in the subsequent stage, it is possible to reduce the catalytic activity even when high-concentration CFCs are processed in large quantities. It can be processed without. That is, in the present invention, a CFC-containing gas and a gas containing air and steam are added to the first catalyst layer in an amount of 300 to 50.
By bringing them into contact with each other in the temperature range of 0 ° C., the reaction represented by the following formula proceeds, for example.

[0005]

## STR1 ## _{C 2 Cl 3 F 3 + 3H} 2 O = CO 2 + CO + 3HCl + 3HF ... ( Formula 1) hydrogen fluoride generated from the first catalyst layer, a part or most of the hydrogen chloride is absorbed into the catalyst layer. For example, CaO
When is used as a catalyst, CFCs in the processing gas are partially decomposed, and hydrogen fluoride and hydrogen chloride are absorbed by the catalyst by the reaction of the following equation.

[0006]

Embedded image 2HCl + 2HF + 2CaO = CaF ₂ + CaCl ₂ + 2H ₂ O (Chemical formula 2) Therefore, the concentration of CFCs flowing to the second catalyst layer in the subsequent stage is reduced, and as a result, the burden on the second stage catalyst is reduced and the decomposition efficiency is reduced. As the temperature rises, it becomes less likely that activity will decrease. That is, since the second catalyst layer treats less chlorofluorocarbon than the first catalyst layer, it can be decomposed with high accuracy, and a decomposition rate of 90% or more can be easily obtained.

Further, hydrogen fluoride and hydrogen chloride in the gas produced from the first catalyst layer and the second catalyst layer in the decomposition step are neutralized and rendered harmless with alkali. For example, hydrogen chloride is recovered as common salt, and hydrogen fluoride is recovered as fluorspar.

For the first catalyst layer in the decomposition step of the present invention, a catalyst having a CFC decomposing ability and an ability to absorb hydrogen fluoride and hydrogen chloride is used. When the CFC decomposition activity and absorption performance are significantly reduced by the absorption of hydrogen fluoride or hydrogen chloride, the catalyst is replaced with a new catalyst.

On the other hand, the second catalyst layer in the decomposition step of the present invention has a problem in decomposition performance and durability performance in high-concentration CFC treatment, but a catalyst capable of treating CFC with a high decomposition rate at a relatively low concentration. To use. In this way, by combining two types of catalysts, each of which has its own characteristics, it is possible to efficiently process a high-concentration fluorocarbon-containing gas.

The CFC concentration in the first catalyst layer in the present invention is preferably in the range of 1 to 10%, and the concentration in the second catalyst layer is preferably 5% or less.

In the present invention, the first catalyst layer and the second catalyst layer used in the decomposition step may be installed and used in the same reactor, or may be used by filling them in another reactor.

The CFC-containing gas of the present invention is not particularly limited, such as a gas discharged from a CFC recovery facility and a gas discharged from a CFC-using facility.

Another feature of the present invention is the catalyst used in the first catalyst layer and the second catalyst layer in the decomposition step. Reaction temperature 300 to 600 ° C. as a catalyst used in the first catalyst layer
Under the above temperature condition, a catalyst containing at least one oxide selected from calcia, silica, alumina, zirconia, magnesia, and a barrier as a main component is used. As the catalyst used in the second catalyst layer, the reaction temperature is 3
Under the temperature condition of 00 to 600 ° C., the first component is titania, the second component is tungsten, molybdenum,
A catalyst containing as a main component at least one selected from oxides or metals of copper, silver, niobium, cobalt, nickel, manganese, platinum, gold, palladium is used. The composition of the second catalyst layer is the same as the titania of the first component,
The range of 1 to 50% by weight of the second component is preferable. Of course, these catalysts may be used by being carried or coated on a carrier such as other ceramics or a metal honeycomb, or a large amount of other ceramics components may be mixed and used for molding. Is.

The shape of the catalyst used in the first catalyst layer and the second catalyst layer in the decomposition step used in the present invention is not particularly limited, such as a granular shape, a honeycomb shape, a plate shape, and a three-dimensional mesh structure.

The components of the catalyst of the first catalyst layer and the second catalyst layer of the decomposition step used in the present invention are obtained by thermal decomposition of nitrates, chlorides, carbonates, organic compounds, hydroxides, etc., or neutralization of aqueous solutions. Used for producing an oxide.

For the preparation of the catalysts for the first catalyst layer and the second catalyst layer in the decomposition step of the present invention, any of the commonly used impregnation method, kneading method, precipitation method, deposition method, CVD method and the like can be used. I can. As the oxidizing agent for decomposing CFCs added to the first catalyst layer and the second catalyst layer in the decomposition step of the present invention, any one or more of steam, hydrogen peroxide, ozone, air, oxygen and the like can be used.

The feed rate of the processing gas to the catalyst in the first catalyst layer and the second catalyst layer in the decomposition step of the present invention is preferably 500 to 100,000 / h per unit volume of the catalyst. In the present invention, hydrogen fluoride generated from the first catalyst layer,
Hydrogen chloride, carbon dioxide, and water are absorbed by the alkaline solution.
In an alkaline solution, an absorbing solution consisting of one or more mixtures selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium hydroxide, calcium carbonate, calcium oxide, ammonia, etc. under a reaction temperature of 100 ° C or less. Alternatively, it is absorbed and neutralized by the absorbent.

The alkali absorption of the present invention may be either solid absorption or liquid absorption.

[0019]

According to the present invention, the Freon-containing gas can be reliably removed by a series of combinations of the first catalyst layer and the second catalyst layer in the decomposition step of the Freon-containing gas, and a high removal performance can be obtained for a long time. The system of the present invention is effective for environmental purification.

[0020]

EXAMPLES Hereinafter, the contents of the present invention will be described more specifically with reference to examples.

(Embodiment 1) FIG. 1 is a block diagram showing an embodiment of the present invention. The chlorofluorocarbon-containing waste gas 1 is mixed with water vapor, hydrogen peroxide, ozone, air and oxygen 2 and introduced into the first catalyst layer 3 of the decomposition step at a reaction temperature of 400 ° C. The first catalyst layer 3 is filled with a calcia catalyst, and the hydrolysis reaction of CFCs in the waste gas proceeds on the catalyst to generate carbon dioxide, hydrogen fluoride, hydrogen chloride, and water. Next, the produced gas is introduced into the salt recovery step 4. Salt recovery process 4
Is filled with sodium hydroxide solution, and sodium fluoride and sodium chloride are produced. Further, the generated gas from the salt recovery tower 4 is introduced into the calcium fluoride recovery step 5. In the calcium fluoride recovery step 5, calcium hydroxide is filled, and calcium fluoride (fluorite) and salt are recovered. Carbon dioxide is recovered as sodium hydrogen carbonate. The produced gas from the calcium fluoride recovery step 5 becomes unreacted CFC and air. Unreacted CFC and air are mixed with water vapor, hydrogen peroxide, ozone, air and oxygen 2 and introduced into the second catalyst layer 6 at a reaction temperature of 400 ° C. The second catalyst layer 6 is filled with a titania-tungsten catalyst, and the hydrofluoric reaction of freon proceeds on the catalyst to almost completely remove freon. The carbon dioxide gas, hydrogen chloride and hydrogen fluoride of the decomposition products are recirculated to the salt recovery step 4 and the calcium fluoride recovery step 5 through the circulation line 7, absorbed and removed, and discharged as a clean gas 8.

(Embodiment 2) FIG. 2 is a block diagram of an apparatus showing an embodiment of the present invention. Embodiment 1 except that the first catalyst layer 3 and the second catalyst layer 5 are packed in the same reactor. Is the same as.

(Example 3) In Example 1, the following catalyst was obtained as a catalyst used in the first catalyst layer (A to F) and the second catalyst layer (G to Q) in the decomposition step.

Example Catalyst A: CaO B: SiO₂ C: Al₂O₃ D: ZrO₂ E: MgO F: BaO G: TiO₂-WO₃  H: TiO₂-MoO₃ I: TiO₂-Nb₂O_Five J: TiO₂-CoOK: TiO₂-NiOL: TiO₂-MnO₂ M: TiO₂-CuO N: TiO₂-Ag₂OO: TiO₂-Pt P: TiO₂-Pd Q: TiO₂-Au In these catalysts, W, Mo, Nb, Co, Ni,
The supported amount of Mn and Cu is an oxide with respect to the titania carrier.
30% by weight, and the amount of Ag, Pt, Pd, Au supported
Is 5% by weight as a metal with respect to the titania carrier.

Comparative Example 1 A catalyst in which 5 wt% of chromium oxide was supported on a composite oxide carrier of titania and zirconia was designated as Comparative Example Catalyst R.

(Example 4) Concentration of Freon: 2% (for a catalyst group and a comparative catalyst R in which one of the first layer catalysts A to F and one of the second layer catalysts G to Q are selected and combined) Residual air), water vapor: 10%, reaction temperature: 400 ° C., space velocity: 20,000 / h, a decomposition reaction was performed to evaluate the performance of various catalysts. The decomposition rate of CFC was determined according to the following formula.

CFC decomposition rate (%) = (1-inlet CFC concentration / outlet CFC concentration) × 100

[0028]

[Table 1]

The results are shown in Table 1. It was confirmed that the catalyst in which the first layer catalyst and the second layer catalyst were combined had a higher chlorofluorocarbon decomposition activity than the comparative catalyst R.

Example 5 Example Catalysts A and G were combined and a 10-hour durability test was conducted. The reaction conditions are the same as in Example 4. The results are shown in FIG. As is clear from the figure, the catalyst in which the first layer catalyst and the second layer catalyst are combined has better durability than the comparative catalyst R.

[0031]

EFFECTS OF THE INVENTION According to the present invention, CFCs are removed at a high decomposition rate, the durability of the catalyst is less deteriorated due to poisoning of decomposition products, and CFC-containing waste gas is purified.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus showing the present invention.

FIG. 2 is a block diagram of an apparatus showing the present invention.

FIG. 3 is a characteristic diagram of CFC removal of the catalyst of the example of the present invention.

[Explanation of symbols]

1 ... Freon-containing waste gas, 2 ... Steam, hydrogen peroxide, ozone, air, oxygen, 3 ... First catalyst layer, 4 ... Salt recovery step,
5 ... Calcium fluoride recovery step, 6 ... Second catalyst layer, 7 ...
Circulation line, 8 ... Clean gas.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B01D 53/34 134 C (72) Inventor Shin Tamada 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture Stock company Hitachi Ltd.Hitachi factory

Claims (5)

[Claims] 1. A first catalyst layer having a function of decomposing at least a part of freon and absorbing at least part of hydrogen fluoride and / or hydrogen chloride of a decomposition product gas in a preceding stage in a step of decomposing and removing freon. A CFC decomposition system characterized by combining two types of catalyst, a second catalyst layer that decomposes residual CFCs in the subsequent stage. 2. The method according to claim 1, wherein after the first catalyst layer is provided with an alkali absorption layer to remove hydrogen fluoride and / or hydrogen chloride generated by decomposition in the first catalyst layer,
A Freon decomposition system that further decomposes Freon in the second catalyst layer. 3. The freon decomposition system according to claim 1, further comprising an alkali absorption layer after the second catalyst layer to remove hydrogen fluoride and / or hydrogen chloride in the produced gas after freon decomposition. 4. The CFC decomposition according to claim 1, wherein the catalyst used in the first catalyst layer contains at least one selected from oxides of calcia, silica, alumina, zirconia, magnesia and barrier as a main component. system. 5. The catalyst used in the second catalyst layer according to claim 1, wherein the first component is titania, the second component is tungsten, molybdenum, copper, silver, niobium, cobalt, nickel, manganese, platinum, A CFC decomposition system containing at least one selected from gold, palladium oxides and metals.