JPH03106419A - Treatment process for gas containing fluorocarbon and catalyst for decomposing fluorocarbon - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating and rendering harmless gas containing fluorocarbons. [Prior art] In recent years, the destruction of the atmospheric ozone layer by fluorocarbons has become a serious problem from the perspective of protecting the global environment.When discharging fluorocarbons, it is necessary to carry out some kind of detoxification treatment instead of emitting them as is. is necessary. Conventionally, methods have been known to adsorb and recover gases containing fluorocarbons using activated carbon, etc., but recently methods have been developed to combust fluorocarbons under high pressure, decompose them using high-frequency plasma, and decompose and burn them in the presence of a catalyst. etc. have also been announced. [Problem to be solved by the invention] In the above-mentioned conventional technology, regarding the recovery method of fluorocarbons using an adsorbent, no consideration has been given to the method of detoxifying the recovered fluorocarbons. Methods such as decomposition using high-frequency plasma have problems such as large-scale equipment and high processing costs.
On the other hand, catalytic decomposition methods are simpler than these methods, but in gas treatment with low CFC concentrations,
It was necessary to raise the temperature of the entire gas above a certain temperature, and there was a risk that a large amount of thermal energy would be wasted. In addition, examples of using zeolite and alumina have been reported in this catalytic decomposition method, but these cannot necessarily be said to have sufficient catalyst performance. An object of the present invention is to provide a simple and efficient method for treating fluorocarbon-containing gas and a catalyst for decomposing fluorocarbons. [Means for Solving the Problems] In order to achieve the above object, the present invention includes a step of concentrating fluorocarbons by adsorption, a step of desorbing the concentrated fluorocarbons from an adsorbent, and a step of desorbing the desorbed gas by oxygen, ozone, or water vapor. A process of decomposing and burning fluorocarbons by bringing them into contact with a catalyst in the presence of a gas containing at least one of the following. It is characterized by having a processing process. In the method of the present invention, first, the fluorocarbons in the gas are adsorbed onto an adsorbent, and then the concentrated fluorocarbon gas is desorbed by heating the adsorbent or passing the heated gas through the adsorbent. At least one type of gas among oxygen, ozone, and water vapor is added to the released gas. However, if the desorption gas already contains oxygen, ozone, and water vapor, it is not necessary to add them. Next, the concentrated fluorocarbons are brought into contact with a catalyst, causing the fluorocarbons to react with at least one of oxygen, ozone, and water vapor. At this time, fluorocarbons are converted into carbon monoxide, carbon dioxide, chlorine,
It is converted to hydrogen chloride, hydrogen fluoride, etc. This product is treated with a solution containing a reducing agent and/or a solution containing an alkali. For example, chlorine is treated in a solution of sodium sulfite, sodium thiosulfate, ferrous salt, etc. as reducing agents, and then leader ash or dilute hydrochloric acid is added to neutralize it and render it harmless. On the other hand, hydrogen fluoride can be absorbed and neutralized with a solution of soda ash or slaked lime!
＃． become harmful.

Another feature of the method of the present invention is that zeolite, alumina, silica, titania,
Contains at least one kind of zirconia, and
The second part is Cu, Ag, V, Cr. Mop W,M
n. Fe, Co, Ni, Pt, Pd, Rh, La, Ce
, Nb. Although zeolite and alumina alone exhibit CFC decomposition activity, in the present invention, by supporting these oxides with the above-mentioned second component oxide or metal, performance is greatly improved. I found out what to do. The supported amounts of these second components are Pt, Pd
, 0.1 to 5% by weight for Rh, and 0.1 to 5% by weight for other components.
5 to 50% by weight is preferred. Furthermore, although the preferred adsorbent for fluorocarbons in the method of the present invention is activated carbon, the present invention is not necessarily limited thereto.

In addition, the temperature at which CFCs are decomposed on the catalyst is 200 to 1,2
00°C is preferred. From a process standpoint, it is more preferable to decompose at a low temperature, and the catalyst of the present invention also has low-temperature activity, but when catalytically burning a high concentration of CFCs,
The temperature may rise to around 1,200℃ due to the heat of reaction. In such cases, the catalyst must also have heat resistance; for example, the lanthanum beta catalyst developed by the present inventors
It has also been found that good results can be obtained by using alumina (Japanese Unexamined Patent Publication No. 61-35851).

In addition, in the method of the present invention, when the concentration of fluorocarbon-containing gas is quite high, or when treating fluorocarbon itself used for cleaning, the adsorption step is not necessarily necessary, and the catalyst of the present invention can directly treat the gas. Of course it is possible. [Function] In the method of the present invention, CFCs are first concentrated through an adsorption step, and then the desorbed concentrated gas is decomposed and burned on a catalyst, making it easy to heat the gas and requiring less thermal energy. Finished. In the method of the present invention, fluorocarbons are reacted with at least one of oxygen, ozone, and water vapor, and it is said that the coexistence of these gases can increase the reaction efficiency and suppress the deposition of carbon on the catalyst. There are also advantages. Furthermore, the catalyst of the present invention is very effective in advancing the above reaction. Therefore, when processing gas containing a high concentration of fluorocarbons, the gas is decomposed directly on the catalyst without going through the concentration process by adsorption of fluorocarbons. It is also possible to burn it. [Example] <Example 1> An example of the present invention will be described below with reference to FIG. The fluorocarbon-containing gas 1 is introduced into the adsorption tower 3, and the fluorocarbon-removed gas 4 after removing the fluorocarbons is directly purged. on the other hand,
The regeneration gas 2 is passed through the other adsorption tower 3 to obtain a freon concentrated gas 5, to which a decomposition gas 6 is added and then passed through the catalytic reactor 7. The fluorocarbon decomposed gas 8 passes through an absorption tower 9, absorbs chlorine gas and hydrogen fluoride gas, and obtains a fluorocarbon-free gas 10. In this example, two adsorption towers are provided, one of which processes dilute fluorocarbon-containing gas and adsorbs and removes fluorocarbons, while the other passes regeneration gas through the adsorbent to obtain highly concentrated fluorocarbon-containing gas. Perform adsorbent regeneration. By making this switch, it is possible to continuously process fluorocarbon-containing gas. <Example 2> This example shows an example in which fluorocarbon-containing gas was treated according to the method of the present invention. First, air containing 500 ppm of Freon 113 as a processing gas was passed through an adsorption tower filled with 4 g of activated carbon at room temperature.

At this time, the concentration of fluorocarbons at the outlet of the adsorption tower was measured using a gas chromatograph equipped with an FID detector, and it was approximately 60 pp-, indicating that 88% of fluorocarbons had been adsorbed and removed. After about 40 minutes, the concentration of fluorocarbons in the outlet gas began to increase rapidly, so we thought that the adsorption capacity of the adsorbent was approaching its limit, so we stopped the passage of the process gas. Next, when air at a temperature of 50°C that did not contain fluorocarbons was flowed through the adsorption tower as a regeneration gas, gas with an initial concentration of 3000 ppm of fluorocarbons was obtained as desorption gas, indicating that fluorocarbons were concentrated. ．．
This gas was heated to 400°C, 1% of water vapor was added, Pt was added to 0.5% by weight, and cobalt oxide was added to 10% by weight.
It was passed through a reactor filled with 2 g of supported titania catalyst.

The CFC concentration in the outlet gas was approximately 40 ppm, and a decomposition rate of approximately 99% was obtained. The biodegradable substances of fluorocarbons are
Since COz, HF, HC I2, etc. were present, they were absorbed and neutralized by passing them through a mixed aqueous solution of caustic soda and slaked lime. <Example 3> This example shows an example in which air containing 3% CFC was decomposed on a catalyst. First, 4% air containing 3% Freon 113 was used as the processing gas.
Heated to 00°C, further added 3% water vapor and added 0.0% Pd.
The mixture was passed through a reactor filled with a lanthanum beta alumina catalyst loaded with 5% by weight and 10% by weight of nickel oxide. The CFC concentration in the outlet gas is approximately 150 pP-. 99.
A decomposition rate of 5% was obtained. <Example 4> In this example, Cu, Ag, V, Cr, Mo, WeMn, Fe,
A catalyst supporting 10% by weight of each of La, Ce, and Nb oxides was prepared and tested in the same manner as in Example 3.
A fluorocarbon decomposition rate of 90% or more was obtained with each catalyst. <Comparative Example 1> In this comparative example, the same test as in Example 3 was conducted using zeolite, alumina, silica, titania, and zirconia, respectively. As a result, in both cases, the fluorocarbon decomposition rate was 5
It was found that it was more than 0%. [Effects of the Invention] According to the present invention, fluorocarbon-containing gas can be treated and rendered harmless using a simple method.Furthermore, the catalyst of the present invention is excellent for decomposing and combusting fluorocarbons, and is effective in reducing fluorocarbon emissions. Helps prevent depletion of the atmospheric ozone layer.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a fluorocarbon-containing gas processing system according to an embodiment of the present invention.

Claims (1)

[Claims] 1. A method for detoxifying gas containing fluorocarbons, comprising: a step of concentrating the fluorocarbons by adsorption, a step of desorbing the concentrated fluorocarbons from an adsorbent, and a step of converting the desorbed gas into air, A process of decomposing and burning fluorocarbons by bringing them into contact with a catalyst in the presence of a gas containing at least one of oxygen, ozone, and water vapor, decomposing the fluorocarbons, and converting the combustion products to a liquid containing a reducing agent and/or an alkali. 1. A method for treating a fluorocarbon-containing gas, comprising a step of treating it with a liquid containing fluorocarbons. 2. Contains at least one of zeolite, alumina, silica, titania, and zirconia, and Cu,
Ag, V, Cr, Mo, W, Mn, Fe, Co, Ni,
A fluorocarbon decomposition catalyst characterized by containing at least one selected from Pt, Pd, Rh, La, Ce, and Nb. 3. A method for treating a fluorocarbon-containing gas according to claim 1, wherein the fluorocarbon adsorbent is activated carbon. 4. In claim 1, the catalyst for decomposing the fluorocarbons is
Contains at least one of zeolite, alumina, silica, titania, and zirconia, and contains Cu, Ag
, V, Cr, Mo, W, Mn, Fe, Co, Ni, Pt
, Pd, Rh, La, Ce, and Nb. 5. The method for treating a fluorocarbon-containing gas according to claim 4, wherein the temperature at which the fluorocarbon is decomposed on the catalyst is 200 to 1,200°C. 6. A method for treating a fluorocarbon-containing gas according to claim 1, wherein the catalyst for decomposing fluorocarbons contains at least lanthanum beta alumina. 7. Gas containing fluorocarbons in the presence of a gas containing at least one of air, oxygen, ozone, and water vapor,
Contains at least one of zeolite, alumina, silica, titania, and zirconia, and contains Cu, Ag
, V, Cr, Mo, W, Mn, Fe, Co, Ni, Pt
, Pd, Rh, La, Ce, and Nb, and decomposes or burns the fluorocarbon by bringing it into contact with a catalyst containing at least one selected from among , Pd, Rh, La, Ce, and Nb.