JPH0780303A - Catalyst for decomposition treatment of gaseous fluorine compound - Google Patents

Abstract

PURPOSE:To obtain a catalyst capable of treating CFC by combustion decomposi tion at a lower temp. CONSTITUTION:Oxide of a metal selected front among W, V, Ce, Mo, Zn, Co and Cr is carried on an oxide selected from among alumina, zirconia, a multiple oxide contg. alumina and a multiple oxide contg. zirconia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for decomposing fluorine compound gas, and more particularly to a catalyst capable of efficiently decomposing fluorocarbon gas, and a method for decomposing fluorine compound gas using this catalyst. .

[0002]

2. Description of the Related Art Chlorofluorocarbon (CFC) gas is used in a large amount as a propellant for an aerosol product, a refrigerant for a cooler and the like. However, in recent years, the destruction of the ozone layer by such a CFC gas has become a big problem. In 1995, at an international conference, a resolution was made to abolish particular CFCs, which have a particularly high ozone depleting property among CFCs. Therefore, the development of substances that replace CFCs has been studied, and the technology for treating a large amount of CFCs that are still in use and remain even after their total abolition has become an important research subject.

Various freon treatment techniques have been proposed so far, and among them, the combustion decomposition method, which has a proven track record in PCB treatment, is said to be the most promising. However, when CFCs are processed by the combustion decomposition method, the processing temperature is 1000 ° C.
As described above, there are problems that the temperature becomes high and that hydrogen fluoride that is much more corrosive than hydrogen chloride that is generated in the treatment of PCB is generated. Therefore, it is desired to lower the treatment temperature in the CFC combustion decomposition method.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a catalyst for the decomposition treatment of a fluorine compound gas, which enables the treatment of CFCs by the combustion decomposition method at a lower temperature and a higher decomposition rate. To do.

Another object of the present invention is to provide a method for decomposing a fluorine compound gas, which makes it possible to treat CFCs by a combustion decomposition method at a lower temperature and a higher decomposition rate.

[0006]

In order to solve the above-mentioned problems, the present invention provides an oxide selected from the group consisting of alumina, zirconia, a composite oxide containing alumina, and a composite oxide containing zirconia with tungsten. Provided is a catalyst for the decomposition treatment of a fluorine compound gas, which carries an oxide of a metal selected from the group consisting of vanadium, cerium, molybdenum, zinc, cobalt, and chromium.

The present invention also provides a method for decomposing a fluorine compound gas, which comprises combusting and decomposing a fluorine compound gas in the presence of a combustion auxiliary agent composed of a hydrocarbon using the above catalyst.

In the present invention, as the catalyst carrier, alumina, particularly zirconia, a composite oxide containing alumina, or a composite oxide containing zirconia is used. Examples of the composite oxide include an alumina-zirconia composite oxide and a composite oxide of alumina or zirconia and titania, boron oxide or the like. Among these, alumina-zirconia composite oxide is particularly preferable. The content of zirconia in the alumina-zirconia composite oxide is usually 0.2 to 0.8.

The supported material is an oxide of tungsten, vanadium, cerium, molybdenum, zinc, cobalt or chromium, with oxides of tungsten and vanadium being particularly preferred. It is also possible to support two or more of these oxides.

In the method for decomposing a fluorine compound gas according to the present invention, a combustion aid composed of hydrocarbon is used. As the hydrocarbon, methane, ethane, propane and n-butane can be used, but ethane, propane and n-butane are particularly preferable.

[0011]

In general, there are the following methods for decomposing fluorine compounds, especially fluorocarbons.

(1) Catalytic combustion decomposition method Freon + hydrocarbon + oxygen → carbon dioxide + hydrogen chloride + hydrogen fluoride (2) Catalytic oxidation decomposition method Freon + oxygen → carbon dioxide + chlorine + fluorine (3) Catalytic hydrolysis method Freon + water → carbon dioxide + hydrogen chloride + hydrogen fluoride The inventors calculated the equilibrium constants of these decomposition methods and found that when Freon-115 (C ₂ ClF ₅ ) was used,
It has been found that the catalytic combustion cracking method is most advantageous in terms of equilibrium, the catalytic hydrolysis method is next, and the reaction is extremely difficult to proceed in the catalytic oxidative cracking method in which no hydrocarbon is present.

In addition, in the catalytic combustion cracking method as described above, the inventors of the present invention are capable of decomposing chlorofluorocarbons at a low temperature by burning and decomposing fluorocarbons in the presence of hydrocarbons using a predetermined solid catalyst. I found it.

Therefore, as a result of repeated research on the catalyst used in such catalytic combustion decomposition method, the present inventors have found that a catalyst in which a metal oxide such as tungsten is supported on a carrier such as alumina is It has been found that it can decompose CFCs most effectively.

That is, when silica is used as the carrier,
High decomposition rate of CFCs cannot be obtained. The reason is considered that silica has no solid acid. This is because the first stage of the CFC decomposition reaction is the extraction of chlorine by the acid sites. Further, even when the metal to be carried is a noble metal, a high decomposition rate of CFCs cannot be obtained.

Therefore, in the catalyst of the present invention, the carrier is γ
-Alumina or alumina-zirconia composite oxide is preferable, and the supported substance is tungsten, vanadium,
It is an oxide of cerium, molybdenum, zinc, cobalt, or chromium.

The catalyst of the present invention exhibits a high CFC decomposition rate and does not deteriorate in activity over a long period of time.

[0018]

EXAMPLES The present invention will be described in more detail below by showing Examples of the present invention.

The present inventors have conducted experiments showing that the above-described catalyst for decomposition treatment of fluorine compound gas according to the present invention decomposes CFCs most efficiently in the presence of a combustion aid consisting of hydrocarbons. I did. The experimental procedure and results are shown below.

1. Experimental Method The catalytic combustion decomposition reaction of CFCs was carried out using a fixed bed atmospheric pressure type reactor. The catalyst filling amount is 2.0 g, the supplied CFC gas flow rate is 1.0 ml / min, the hydrocarbon flow rate is 0.5 to 7.0 ml / min, and the air flow rate is 150 m.
1 / min. The analysis of the reaction gas and the produced gas was quantified using a gas chromatograph. The decomposition rate of CFC used was the value at the 4th hour of the reaction unless otherwise specified.

2. Experimental Results (1) Degradation characteristics of CFCs First, an experiment was conducted to select the type of CFCs used in the experiment.

Freon-113 (C ₂ Cl ₃
F ₃ ), Freon-114 (C ₂ Cl ₂ F ₄ ) and Freon-115 (C ₂ ClF ₅ ) were used, and
-Combustion decomposition with γ-alumina catalyst in the presence of butane. The result is shown in FIG.

As is clear from the graph of FIG. 1, the complete conversion temperature was shifted to the high temperature side in the order of Freon-113, Freon-114, and Freon-115. From this result, as the ratio of fluorine to chlorine in the fluorocarbon molecule increases,
It was found to be persistent. Therefore, in order to more clearly show the effect of the catalyst of the present invention, in the following experiments, the most difficult decomposable Freon-115 was used for the study.

(2) Decomposition activity of γ-alumina catalyst supporting various metal oxides and noble metals on Freon-115 Various metal oxides (0.001) in the presence of n-butane (1.2 ml / min) Mol / g) and precious metals (0.
Freon-11 of γ-alumina catalyst supporting 5 wt%)
The decomposition activity for 5 was compared. The result is shown in FIG. From FIG. 2, the catalyst carrying the noble metal was CFC-11.
It can be seen that no effect of decomposing activity on No. 5 is observed.
Among the metal oxides, Cr ₂ O ₃ , MoO ₃ , ZnO,
CoO ₃ was found to have a decomposing activity effect on freon-115, and WO ₃ and V ₂ O ₅ were found to be particularly excellent effects.

(3) Decomposition activity of Freon-115 by a catalyst in which various metal oxides are supported on Al ₂ O ₃ -ZrO ₂ WO ₃ , which has an effect on Freon-115 decomposition activity by being supported on γ-alumina, V ₂ O ₅ , Cr ₂ O ₃ , MoO ₃ ,
ZnO was converted into Al ₂ O ₃ —ZrO ₂ (ZrO ₂ content of 0.
2) and a catalyst in which ZrO ₂ was supported at 2.5 × 10 ⁻⁴ mol / g, the decomposition rate of Freon-115 was determined in the presence of n-butane (1.2 ml / min). The results are shown in Table 1 below.

Table 1 Effect of catalyst in which metal oxide is supported on Al ₂ O ₃ —ZrO ₂ Freon-115 decomposition rate (%) Metal oxide Al ₂ O ₃ Al ₂ O ₃ —ZrO ₂ ZrO ₂ None 45 63 14 WO ₃ 60 80 54 V ₂ O ₅ 60 64 19 ZnO 52 64 13 Cr ₂ O ₃ 49 63 13 MoO ₃ 49 58 21 From the above table, any of Al ₂ O ₃ and Al ₂ O ₃ —ZrO ₂ can be found. It can be seen that although a metal oxide is carried, good activity is exhibited, but with respect to ZrO ₂ , when WO ₃ is carried, good activity is shown. It is shown the best activity is case of carrying WO ₃ on Al ₂ O ₃ -ZrO _2. It is considered that these results are due to the concerted effect of WO ₃ and ZrO ₂ .

(4) WO ₃ / Al ₂ O ₃ -ZrO ₂ composition ratio WO ₃ / Al _{2 in} the case where the amount of WO ₃ supported on Al ₂ O ₃ -ZrO ₂ is constant and the ZrO ₂ content is changed. O
The Freon-115 decomposition rate of the _3- ZrO ₂ catalyst was determined.
The result is shown in FIG. As is clear from FIG.
_{The 3} / Al ₂ O ₃ —ZrO ₂ -based catalyst shows high decomposition activity in a wide range of the ZrO ₂ content of 0.2 to 0.8.

Next, with respect to Al ₂ O ₃ --ZrO ₂ (ZrO ₂ content: 0.5) and WO ₃ / Al ₂ O ₃ --ZrO ₂ , changes in the CFC-115 decomposition rate with time were examined. The result is shown in FIG. From FIG. 4, Al ₂ O ₃ -ZrO ₂ has W
It can be seen that supporting O ₃ suppresses deterioration of the activity of Al ₂ O ₃ —ZrO ₂ . Also, EPMA
And the results of ESCA show that WO ₃ / Al ₂ O ₃ -ZrO ₂
The catalyst, WO ₃ -ZrO ₂ considered active phase has been found to be difficult to be fluorinated.

(5) Activity of fluorinated catalyst To confirm activity deterioration of the catalyst due to fluorination, various catalysts before use were impregnated with hydrogen fluoride and calcined, and n-butane (1.2 ml / 1.2 ml / The decomposition rate of Freon-115 after 4 hours in the presence of (min) was determined for the fluorinated catalyst and the untreated catalyst. The results are shown in Table 2 below.

Table 2 Changes in Freon-115 Decomposition Rate by Fluorination of Various Catalysts Freon-115 Decomposition Rate (%) HF Treatment HF Untreated (4 hours) (4 hours) WO ₃ / Al ₂ O ₃ -ZrO ₂ 72 82 γ-alumina 33 45 ferrierite 14 35 Silica-alumina 14 33 It can be seen from Table 2 above that the activity of all the catalysts is lowered by the fluorination treatment. In particular, ferrierite and silica-alumina completely lose catalytic activity. However, WO ₃ / Al ₂ O ₃ -ZrO ₂ showed a relatively small decrease in activity even after the fluorination treatment, showing a high activity of 72%.

[0031] _{(6) WO 3 / Al 2} O 3 -ZrO 2 lifetime _{WO 3 / Al 2 O 3 -ZrO} 2 (ZrO 2 content: 0.
5 g of 5) was charged into a reactor and a life test was conducted at a reaction temperature of 600 ° C. The result is shown in FIG. Figure 5
From the results, it can be seen that, even if 10 hours have passed since the reaction temperature of 600 ° C. was reached, the decomposition rate of CFC-115 was 98%, and the decrease in activity was small even when used for an excessive period of time.

(7) Method for producing WO ₃ / Al ₂ O ₃ -ZrO ₂ The inventors of the present invention have made extensive studies on the method for producing WO ₃ / Al ₂ O ₃ -ZrO ₂ , and as a result, It was found that WO ₃ / Al ₂ O ₃ —ZrO ₂ with high activity was obtained.

That is, polyethylene glycol-nonylphenyl ether (NP-2) was added to a zirconium aqueous solution in which boehmite was suspended, and then aqueous ammonia was added to cause gelation. The material obtained was calcined at 650 ° C. Tungsten oxide was supported on this fired body to obtain a catalyst. Using 2.0 g of this catalyst, Freon-115 was combusted and decomposed. As a result, the initial activity was 97%, and the activity was as high as 91% after 4 hours.

[0034]

As described above, according to the present invention,
Provided is an excellent catalyst for the decomposition treatment of fluorine compound gas, which shows a high decomposition rate of CFCs and does not deteriorate in activity over a long period of time.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing decomposition characteristics of various CFCs.

FIG. 2 is a characteristic diagram showing the decomposition activity of Freon-115 of a catalyst in which various metal oxides and noble metals are supported on γ-alumina.

FIG. 3 shows WO ₃ / A when the ZrO ₂ content is changed.
l ₂ O ₃ -ZrO characteristic diagram showing a chlorofluorocarbon -115 decomposition rate of ₂ based catalyst.

FIG. 4 is a characteristic diagram showing a change over time in the CFC-115 decomposition rate of the catalyst.

FIG. 5 is a characteristic diagram showing the results of a life test of WO ₃ / Al ₂ O ₃ —ZrO ₂ .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/06 ZAB A 8017-4G 23/10 ZAB A 8017-4G 23/22 ZAB A 8017-4G 23/74 ZAB 8017-4G 23/75 C07B 35/06 7419-4H

Claims (2)

[Claims] 1. An oxide selected from the group consisting of alumina, zirconia, a composite oxide containing alumina, and a composite oxide containing zirconia, and tungsten, vanadium, cerium, molybdenum, zinc, cobalt, and chromium. A catalyst for the decomposition treatment of a fluorine compound gas, which carries an oxide of a metal selected from the group. 2. A method for decomposing a fluorine compound gas, which comprises using the catalyst according to claim 1 to combust and decompose a fluorine compound gas in the presence of a combustion auxiliary agent composed of a hydrocarbon.