JP3056914B2 - Decomposition method of aliphatic halide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decomposition method for detoxifying an aliphatic halide. More specifically, the present invention industrially detoxifies and decomposes an aliphatic halide such as chlorofluorocarbon, which is a problem in pollution control, in the presence of alcohol and / or ether by using a specific highly active catalyst system. To a new method.

[0002]

2. Description of the Related Art Recently, it has been demanded that aliphatic halides such as carbon tetrachloride and chlorofluorocarbon (hereinafter abbreviated as CFC) be rendered harmless in order to prevent environmental pollution on a global scale. In particular, the latter CFC is a source substance that destroys the ozone layer, and there is a strong demand for the development of a technology that can easily, efficiently and economically detoxify and decompose these aliphatic halides under mild conditions. Have been.

Conventionally, aliphatic halide decomposition methods include (1) thermal decomposition / incineration, (2) plasma discharge, (3) catalytic decomposition, (4) chemical reaction, and (5) supercritical water. Solution methods have been proposed and attempted. However, since the various decomposition methods described above have severe decomposition conditions for practical use, there are many problems in the reaction operation, the material aspect of the reaction apparatus, and the like, and they cannot always be said to be promising methods.

[0004] Among the above decomposition methods, the catalytic decomposition method is
This method is most likely to be put to practical use in view of (i) decomposition at a relatively low temperature, (ii) miniaturization of the decomposition apparatus, and (iii) continuous processing.

[0005] Therefore, much research has been conducted on the catalytic decomposition of aliphatic halides.
In this regard, a method for decomposing dichlorodifluoromethane as an aliphatic halide will be described below. The following can be considered as a decomposition reaction format: Decomposition reaction (1): CCl ₂ F ₂ = C + Cl ₂ + F ₂ Decomposition reaction (2): CCl ₂ F ₂ + O ₂ = CO ₂ + Cl ₂
+ F ₂ decomposition reaction (3): CCl ₂ F ₂ + 2H ₂ O = CO ₂ + 2H
Cl ₂ + 2HF decomposition reaction (4): CCl ₂ F ₂ + 2CH ₃ OH = CO ₂ +
2CH ₃ Cl + 2HF The reaction heat (ΔH) and free energy (ΔG) of the above-mentioned decomposition reactions (1) to (4) are shown in Table 1 below.

[0006]

[Table 1]

As is clear from Table 1, the decomposition reaction of dichlorodifluoromethane alone is a large endothermic reaction, and the reaction requires an extremely high temperature. On the other hand, a decomposition reaction system to which oxygen, water (H ₂ O) or alcohol is added is an exothermic reaction, and thus a decomposition method in which these compounds are added has been attempted. For example,
(i) As a decomposition method of adding oxygen, PO ₄ is used as a catalyst.
/ ZrO ₂ (2nd CFC-related catalyst presentation, 1992.10.30) or BPO ₄ (Journal of the Chemical Society of Japan, 645, 1991), (ii)
As a decomposition method of adding water (H ₂ O), F
eO _{3 /} C (Chem, Lett., 1901, 198).
9 years) are known. However, all of these reaction systems require a high temperature of about 500 ° C., and the sustainability of the catalytic activity is not sufficient, and there are many problems in practical use.

On the other hand, the present inventors have proposed that 1,1,2,2-tetrachlorodifluoroethane in a metal halide (for example, ferric chloride) catalyst system supported on activated carbon in the presence of an alcohol. Aliphatic halides such as 1,1,1,2-trichlorotrifluoroethane
It has been found that it can be decomposed into CO and CO ₂ under mild conditions of up to 300 ° C., and chlorine can be recovered as alkyl chloride and fluorine can be recovered as hydrogen fluoride. In addition, this method has an advantage that these compounds can be easily recovered, and post-treatment for eliminating pollution can be performed at very low cost (Chem. Lett., 7995, 1992; No. 3-348842).

[0009]

The above-mentioned method proposed by the present inventors has a number of excellent advantages, in particular, that aliphatic halides can be decomposed under mild conditions of a reaction temperature of 200 to 300 ° C. Although it has an advantage, like other catalytic decomposition methods, the catalytic activity decreases with the passage of reaction time, so that there is room for improvement for industrial practical use.

As a result of the inventor's intensive studies to improve the catalyst decomposition method proposed by the present inventor, the following results were obtained. As the reaction time elapses, it becomes an oxide and becomes less active.However, when a catalyst system is designed to restore this to a halide with a cocatalyst, the catalyst activity becomes extremely high and long lasting. Has been found. The present invention is based on the above findings, and the present invention provides an industrial and economical method for detoxifying and decomposing aliphatic halides.

[0011]

SUMMARY OF THE INVENTION In general, the present invention relates to a process for decomposing an aliphatic halide, comprising the steps of: (a) dissolving the aliphatic halide in the presence of (i) a lower alcohol and / or an ether; , (Ii) a heat treatment under a catalyst system comprising a metal halide as a main catalyst and a metal halide different from the main catalyst as a co-catalyst, wherein an aliphatic halide is decomposed. It is about. Hereinafter, the technical configuration of the present invention will be described in detail.

In the present invention, the aliphatic halide to be decomposed is a halogenated aliphatic alkane or alkene which is substituted with one or more halogens of chlorine, bromine or fluorine. It is. Such compounds, carbon tetrachloride, Pa over chloroethylene,
Hexachloroethane, tri click Rollo trifluoromethane, dichlorodifluoromethane, 1,1,2-trichlorotrifluoroethane, 1,1,2,2-tetrachloro-difluoride
Lome Tan, trifluorobromomethane, etc. are exemplified. These can be used in the form of a single compound or a mixture thereof. In practice, as the aliphatic halide, a perhaloalkane or alkene having 1 to 4 carbon atoms is advantageously used.

In the present invention, the lower alcohol is used from the following viewpoints. It is generally known that the dehalogenation reaction of halogenated hydrocarbons is caused by alcohols in the presence of alumina. For example, L. Andrussow et al.
It has been reported that the reaction of 1,2,2-tetrachloroethane with methanol produces trichlorethylene and methyl chloride [Chem, Proc, Eng. , V
ol 48, 41 (1967)]. Shinoda et al.
A series of studies have been reported on the co-pyrolysis of 1,2-trichloroethane and other chlorinated alkanes with methanol [Chem, Lett. , 877 (1973): Nikka, 316, 661, 1637 (1975)].

In the present invention, the lower alcohol is used as described above, that is, as a halogen receiving agent. Examples of the lower alcohol include alcohols having up to about 6 carbon atoms. Practically, alcohols having 1 to 4 carbon atoms are advantageously used in consideration of utilization of by-products and the like. Examples of these alcohols include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, 1-butanol, 2-butanol, and tertiary butyl alcohol. The lower alcohol to be subjected to the reaction is not necessarily required to be a single one, and a mixture may be used.

Although the decomposition mechanism of the aliphatic halide of the present invention is not necessarily clear, the decomposition proceeds when one hydroxyl group of the lower alcohol reacts with one of the halogens of the aliphatic halide. Is converted to a lower monohaloalkyl substituted with halogen, and the carbon of the aliphatic halide is considered to be carbon dioxide or carbon monoxide. Therefore, in order to decompose all the aliphatic halides at one time, it is necessary that at least a molar amount of the lower alcohol corresponding to the number of halogens contained in the molecule per mol of the aliphatic halide is required. Conceivable. However, when it is not necessary to decompose all the aliphatic halides in a single reaction, the lower alcohol may be supplied in a slightly excessive amount more than the expected decomposition rate, and of course, even in a large excess. No problem. Even in the experimental results, when the amount of lower alcohol is small, formation of an intermediate or hydrogen chloride is recognized, and it is preferable that the lower alcohol is in excess from the viewpoint of improving the decomposition rate and recovering useful lower haloalkyl.

In the present invention, the ether is used from the same viewpoint as the lower alcohol. That is, the ether also serves as a donor of the alkoxy anion on the catalyst similarly to the alcohol, and functions as a halogen receiving tray. As such ethers, those having up to about 12 carbon atoms are advantageously used, but those having 2 to 8 are economically valuable. In the present invention, the circulating use of an ether by-produced in the catalytic cracking reaction between CFC and the alcohol is necessary for rationally operating the process of the present invention. From the above, it is extremely important to use ether alone or in combination with alcohol in the present invention. In the present invention, as the above-mentioned ether, methyl ether, ethyl ether, propyl ether, butyl ether or the like is used according to alcohol.

In the above-described catalytic decomposition method of an aliphatic halide using an ether, the electron density of oxygen atoms generally increases due to an increase in the number of alkyl groups in the ether, and the nucleophilicity is improved as compared with alcohols. Rates tend to increase. However, when the alkyl group becomes larger, the decomposition rate (reaction rate) tends to decrease due to the steric hindrance. This tendency is due to C ₂ H ₅ OC ₂ H ₅ , n-C ₃
Observed between ether H ₇ OC ₃ H ₇ and _{n-C 4 H 9 OC 4} H 9,.

[0018] Aliphatic method for decomposing a halide of the present invention, the aliphatic halides, 6 a group, 7 a group, is to use a halide of a Group 8 metal as the main catalyst. The main catalyst used in the present invention may be a 6a group, a 7a group or 8 group.
Group halides, such as Cr, Mn, Fe, Co, N
A halide of i or Pd, or a mixture thereof, is mentioned, and the halogen is chlorine and / or fluorine.

In the present invention, the above-mentioned metal halide may be a compound containing plural kinds of halogens such as chromium trichloride and chromium trifluoride. Incidentally, when chlorofluorocarbon is treated with a chromium trichloride catalyst, a part of chlorine is replaced by fluorine during the treatment.
However, even in this case, the reaction activity does not decrease. In the present invention, it goes without saying that the metal halide as the main catalyst may be one kind or two or more kinds. As the main catalyst of the present invention, ferric chloride and / or ferric fluoride are particularly excellent in terms of activity and sustainability.

Next, the promoter system of the present invention will be described. The design philosophy of the main / cocatalyst system of the present invention is that the metal halide of the main catalyst becomes a low-activity oxide as the reaction time elapses as described above, and this is restored to the halide by the cocatalyst. It is.

In this regard , a catalyst system in which the main catalyst is ferric chloride or ferric fluoride will be considered. That is, in the catalytic decomposition method of aliphatic halides, as the reaction time elapses, the main catalyst, ferric chloride or ferric fluoride, reacts with the alcohol, and is represented by the following reaction formulas (1) to (2). To produce ferric oxide. The ferric oxide has a lower catalytic activity than the initial ferric chloride or ferric fluoride. (1) 2FeCl ₃ + 6CH ₃ OH = Fe ₂ O ₃ + 6CH ₃ C
_{l + 3H 2 O (2)} 2FeCl 3 + 6CH 3 OH = Fe 2 O 3 + 6CH +
3CH ₃ OCH ₃

[0022] In the present invention, as a cocatalyst, for example C
The use of cupric logenide allows for a remarkable high activity and persistence of the catalyst. According to the following reaction formula (3), ferric oxide and cupric halide ( for example,
This is because copper ) reacts to form a main catalyst (for example, ferric fluoride). (3) Fe ₂ O ₃ + 3CuF ₂ = 2FeF ₃ + 3CuO

Subsequently, the cupric oxide produced according to the reaction formula (3) reacts with hydrogen halide produced by the catalytic decomposition of the aliphatic halogenation, as shown in the following formulas (4) to (5). To form cupric halide (promoter). (4) CuO + 2HF = CuF ₂ + H ₂ O (5) CuO + 2HCl = CuCl ₂ + H ₂ O

As a result, a series of cycling reactions is established between the above-mentioned reactions, and the continuity of the reaction activity of the catalyst system (main / cocatalyst system) is maintained.

As mentioned above, the cocatalyst of the present invention plays a very important role. In the present invention, the cocatalyst is preferably a group 1a or 1b (copper group) metal halide. Such cocatalysts are, for example, 1
In the case of group a alkali metal halides, they form double salts with ferric chloride or ferric fluoride as the main catalyst, and are extremely effective in preventing volatilization of the main catalyst, ferric halide. (A COMPREHENSIVE TREATISE ONINORGANIC AND T
HEORETICAL CHEMISTRY, VoL.14,98, LONGMANS, 1961
Year). Group 1b metal halides have the property of smoothly progressing a halogen-oxygen exchange reaction, for example, a reversible reaction between cupric halide and cupric oxide. In the present invention, among these cocatalysts, cupric chloride is particularly preferred.

It goes without saying that the catalyst system (main / cocatalyst system) used in the present invention can be used by being supported on a desired carrier. Activated carbon, alumina, activated alumina and the like are used as the above-mentioned carrier, and activated carbon is particularly preferable. Activated carbon as the carrier may be, for example, wood, sawdust, coconut shell and other plant materials, animal meat and animal materials such as bones, lignite, peat, coal, petroleum, and pitch obtained by treating these. Activated carbon manufactured from the mineral materials of Japan can be used. As the shape of the activated carbon, the decomposition reaction is carried out in a gas phase flow system, so it is granular, for example, crushed and sieved, the particle size distribution is adjusted, molded in advance at the time of production, or molded by adding powdered carbon with a binder Spherical,
Cylindrical granular activated carbon is preferred. The size of the particles is appropriately selected depending on whether the reaction mode is a fluidized bed type or a fixed bed type.

The catalyst system (main / cocatalyst system) of the present invention can be supported on activated carbon by, for example, preparing a so-called impregnation method in which activated carbon is put into an aqueous solution of a metal halide, thoroughly mixed and impregnated, and then dried. can do. Further, the amount of metal halide supported on activated carbon is not particularly limited,
0.02 to 0.2 mol / 100 g Activated carbon is preferred.
In addition, in preparing the catalyst, it is possible to add a third component in order to prevent volatilization of the catalyst component as well as the melting point of the catalyst component as well as the promoter component.

The reaction temperature in the decomposition reaction of the aliphatic halide is from 100 ° C. to 400 ° C., preferably from 120 ° C.
350 ° C. If the reaction temperature is too low, the product, especially water, condenses to dissolve the metal halide of the catalyst and corrode the reactor, which is not preferable. The upper limit of the reaction temperature is determined by the difficulty of the reaction due to the difference in the type of the aliphatic halide to be decomposed. In general, those containing a large amount of chlorine in an aliphatic halide react at a relatively low temperature. However, when the amount of fluorine is large, the reaction becomes difficult, and it is necessary to increase the temperature. In any case, when the reaction temperature exceeds 400 ° C., a portion derived from lower alcohols or ethers also decomposes, and a reaction not suitable for recovering useful substances occurs. However, at the time of actual use, the above problem can be sufficiently dealt with by experimentally confirming the target substance in advance. For example, when carbon tetrachloride is decomposed with ethanol, about 20
It reacts almost completely at 0 ° C., but in the case of 1,1,2-trichlorotrifluoroethane and ethanol, 300 ° C. or more is required for efficient decomposition. When a catalyst supporting ferric chloride is used, a relatively low reaction temperature is employed because ferric chloride sublimates at a relatively low temperature.

The decomposition reaction may be carried out in an ordinary gas-phase flow reactor. That is, a fixed bed flow type reactor, a fluidized bed type reactor and the like can be applied as the reactor.
The latter is preferable from the viewpoint of the uniformity of the reaction, but in that case, the abrasion resistance and particle size distribution of the catalyst become problems, so that it is necessary to give due consideration to the preparation of the catalyst. There is no particular limitation on the reaction pressure, and it is sufficient that the gas pressure be maintained during the reaction. However, the reaction under the pressurized state is preferable because the apparatus can be reduced in size. In the reaction, a diluent inert to the reaction may be used as appropriate.

According to the present invention, it is possible to decompose aliphatic halides at very low temperatures, the carbon of the aliphatic halide being converted to carbon dioxide or carbon monoxide, while the halogen is converted to hydrogen halide. Not only that, it has the advantage that it can be reacted with alcohols and ethers by selecting the reaction conditions to be recovered as an aliphatic monohalide. Further, the present invention can be used for the treatment of carbon tetrachloride which is inevitably produced as a by-product when producing methylene chloride or chloroform using methane or methanol as a raw material. In this case, methanol is used to decompose carbon tetrachloride, and methanol is converted to methyl chloride, so that methylene chloride and chloroform can be produced without substantially producing carbon tetrachloride as a by-product.

[0031]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 0.025 mol of ferric fluoride was dissolved in 200 ml of dilute hydrochloric acid, the average length was 7 mm, the grain size was 4 mm, and the specific surface area was 128.
After ²⁰ g of 0 m ² / g cylindrical activated carbon (manufactured by Wako Pure Chemical Industries, Ltd.) was immersed at room temperature, water was evaporated by heating, and the activated carbon was supported on the activated carbon. Further, 0.025 mol of cupric chloride was added to 200
After dissolving in water of ml, the activated carbon carrying ferric fluoride was immersed again and heated again to evaporate the water to prepare a catalyst. The whole amount of the catalyst was charged into the center of a 25 mm stainless steel tube, and heated to a temperature of 300 ° C. in a rigid tubular furnace having a length of 40 cm. Next, 1,1,2-trichlorotrif
Le Oroetan (hereinafter, abbreviated as CFC-113.) And the proportion of methanol, mixture of 1mol pair 4mol (starting material) was prepared. This mixed solution was fed into a reaction tube at a rate of 10 ml / h using a microfider to perform a reaction. The reaction gas was led to a trap in an ice-cooled bath via a Liebig condenser, and the condensed liquid was collected, and the composition was determined by gas chromatography using a filler porapak by an internal standard method. Gas components that did not condense were analyzed by gas chromatography using activated carbon as a filler. Table 2 summarizes the experimental results.

[0033]

[Table 2]

Comparative Example 1 0.025 mol of ferric fluoride was dissolved in dilute hydrochloric acid (200 ml), activated carbon (20 mg) was immersed, and water was evaporated to carry the catalyst. Using this catalyst, C
A mixture of FC-113 and methanol in a ratio of 1 mol to 4 mol was fed into a reaction tube at a rate of 10 ml / h per hour to cause a reaction. Table 3 shows the experimental results.

[0035]

[Table 3]

Comparative Example 2 Using ferric chloride instead of ferric fluoride of Comparative Example 1,
The experiment was performed according to Comparative Example 1.

FIG. 1 also shows the relationship between the decomposition rate of CFC- 113 and the reaction time together with the results of Example 1 and Comparative Examples 1 and 2. In FIG. 1, the catalyst system supported on activated carbon is: □ mark for the case of ferric chloride only, ● mark for the case of ferric fluoride only, • ferric fluoride, cupric chloride The case of a composite system of is indicated by a circle and. In the case of a single catalyst of ferric fluoride or ferric chloride (Comparative Examples 1 and 2), the decomposition rate of CFC-113 decreases with the passage of reaction time, whereas the ferric fluoride of the present invention It can be seen that the activity of the composite catalyst system using cupric chloride has been maintained for a long time.

Example 2 The experiment was continuously repeated for a long time without specially activating or refilling the catalyst used in Example 1. The results are shown in Tables 4 and 5.

[0039]

[Table 4]

[0040]

[Table 5]

[0041] The present invention, aliphatic halides such as Kurorofuruo b carbon has become the pollution control problems, the presence of an alcohol and / or ether, a specific high activity, persistence under the catalyst system, It can be detoxified and decomposed under extremely mild temperature conditions as compared with the conventional method. In addition, the method for detoxifying aliphatic halides and catalytic decomposition of the present invention can be carried out by constructing a decomposition apparatus suitable for large-scale and large-scale processing of aliphatic halides, as well as for small-scale and small-scale processing. This is a very versatile catalytic decomposition method because it can be performed. Furthermore, by selecting the reaction conditions, it is possible to recover useful compounds such as aliphatic monohalides from aliphatic halides. Therefore,
The catalytic decomposition method of the present invention for an aliphatic halide such as chlorofluorocarbon, which has been urgently dealt with due to the problem of ozone layer destruction, etc., is extremely useful as an air pollution control technology.

[Brief description of the drawings]

FIG. 1 shows 1,1,2-trichlorotrifluoroethane (CFC) in the catalyst systems of Example 1 and Comparative Examples 1-2.
-113) It is a graph which shows the relationship between the decomposition rate and reaction time.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) A62D 3/00 B01J 27/06

Claims (6)

(57) [Claims] In the method for decomposing an aliphatic halide, the aliphatic halide is used in the presence of (i) a lower alcohol and / or an ether, and (ii) a group 6a, 7a or 8 group as a main catalyst. A metal halide selected from the group consisting of
Et chosen metal halides, under the catalyst system consisting of city, to a heat treatment method for decomposing aliphatic halides, wherein. 2. The method for decomposing an aliphatic halide according to claim 1 , wherein the main catalyst is ferric chloride and / or ferric fluoride. 3. The method for decomposing an aliphatic halide according to claim 1 , wherein the co-catalyst is cupric chloride. 4. The method for decomposing an aliphatic halide according to claim 1, wherein the condition of the heat treatment is 100 to 400 ° C. 5. A main catalyst and co-catalyst, the decomposition method of the aliphatic halides according to claim 1 in which is responsible lifting the carrier. 6. A carrier method for decomposing aliphatic halides according to claim 5 is activated carbon.