JPH08238418A - Decomposition treatment method for organic halogen compound - Google Patents

Abstract

PURPOSE: To efficiently decompose carbon monooxide generated in the decomposition of chlorofluorocarbon by a method in which a gas containing organic halogen compounds is contacted with water or an organic halogen compound decomposition catalyst in the presence of ozone at a specified temperature, and after the generated gas being absorbed and removed by contacting the gas with an aqueous alkaline solution, the gas flow is contacted with a carbon monooxide decomposition catalyst. CONSTITUTION: In the decomposition treatment of an organic compound containing a halogen of fluorine, chlorine, or bromine (thereafter called chlorofluorocarbon), a chlorofluorocarbon supply system 6, an air supply system 5, and a water supply system 9 are connected with a reaction tube 2 filled with a chlorofluorocarbon decomposition catalyst 1, and the catalyst 1 is heated at 200-500 deg.C in an electric furnace 4. In this way, chlorofluorocarbon is decomposed into CO, CO2 , HF, and HCl, and the exhaust gas 13 is introduced into a NaOH aqueous solution 8 in an alkaline absorption tank 12 to be neutralized and precipitated. The exhaust gas which passed through the tank 12 is discharged 14 after CO being oxidized during passage through a carbon monooxide oxidation catalyst layer 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing chlorofluorocarbon, which efficiently decomposes organic compounds containing halogens such as fluorine, chlorine and bromine such as chlorofluorocarbon gas, trichloroethylene and methyl bromide.

[0002]

2. Description of the Related Art Depletion of the ozone layer by CFCs has attracted attention as a global problem, and countermeasures against it are urgently needed. Freon is chemically very stable, has no toxicity, flammability, and explosiveness, and has excellent heat absorption / release properties, so it has been used in large amounts in blowing agents, refrigerants, cleaning agents, etc. It has been used, but it was found that when it is released into the atmosphere, it rises to the ozone layer in the stratosphere and consumes ozone in a chain reaction when the CFCs decompose. In fact, it has been confirmed that ozone is reduced in the ozone layer such as the ozone hole. The ozone layer prevents the inflow of harmful ultraviolet rays to the earth's surface, but if a large amount of harmful ultraviolet rays inflow due to the decrease of ozone, it will have an effect on the human body such as skin cancer and also on the ecosystem. . For this reason, the world is currently heading towards a ban on the release of CFCs into the atmosphere and the abolition of the use of CFCs.

Urethane foam, which is one of the wastes containing CFCs, is mostly disposed of in landfills. This urethane foam uses a large amount of CFC gas as a foaming agent at the time of manufacturing, and CFC is contained in the bubbles in the urethane foam. For example, about 15% of urethane foam used as a heat insulating material for refrigerators and about 40% of urethane foam for building materials are CFCs. Although CFCs are also used as refrigerants for automobile air conditioners, they are rarely recovered when they are scrapped and are released into the atmosphere.

If the fluorocarbons contained in these wastes are sent to landfill or incineration without being recovered and decomposed, some of them will be released into the atmosphere, causing ozone layer depletion.

[0005] The method that has been hitherto reported as a method for decomposing CFCs is mainly a combustion method at high temperature. However, since this method uses a large amount of fuel, the energy efficiency is low, and the problem of damage to the furnace wall due to halogen produced by combustion remains. More recently, plasma decomposition method (Japanese Patent Laid-Open No. 4-279179),
A decomposition method using ultraviolet rays has also been reported. These require a large amount of electric power, and energy loss is not small especially when the content of the organic halogen compound in the processing gas is low. On the other hand, a catalytic decomposition method using a catalyst (Japanese Patent Publication No. 6-59388, Japanese Patent Laid-Open No. 3-42015, Japanese Patent Laid-Open No. 4-2015)
If the performance of the catalyst is sufficiently high, it can be said that 501380) is an efficient method.

Conventionally, as a decomposition catalyst of an organic halogen compound, for example, there is a TiO ₂ —WO ₃ catalyst as an example described in JP-B-6-59388. This catalyst is Ti
It contains 0.1 to 20 wt% W of O ₂ .
The decomposition rate of 99% is maintained for 1,500 hours at 375 ° C. for the treatment with CCl ₄ . Further, Hitoshi Takita of Oita is ZrO ₂ -
An organic halogen compound is decomposed at 500 ° C. using a Cr ₂ O ₃ catalyst. As a result, CCl ₄ is decomposed 100%, but with CFC ₄ containing F, the decomposition rate is 60% as a result of continuous decomposition for 100 hours. It is disclosed that it has decreased to [[H6 fiscal year catalyst research presentation proceedings P. 514-51
5]. That is, Cl is not the only causative component that lowers the activity of the catalyst in the organohalogen compound, but rather F has a greater effect, and further higher temperature is required for decomposition of the F-containing organohalogen compound such as Freon, and HF resistance is high. A large catalyst is needed.

Among the examples disclosed in the above decomposition method and decomposition system for organic compounds, no mention is made of the detoxification of exhaust gas components after decomposition, particularly carbon monoxide.

[0008]

The object of the present invention is to efficiently decompose harmful carbon monoxide components, which are inevitably generated in the above-mentioned prior art, in a series of steps following the freon decomposition step, thereby improving efficiency. An object of the present invention is to provide a method for decomposing chlorofluorocarbon well and detoxifying the decomposition product gas.

[0009]

The present invention is characterized in that a catalytic cracking step using a catalyst is used as a fluorocarbon cracking step. Further, another feature of the present invention is characterized in that it comprises a step of oxidatively decomposing carbon monoxide with a heat amount of fluorocarbon decomposition or a heat amount less than that, following the fluorocarbon decomposition step. Another feature of the present invention is that a CFC decomposition step, a carbon monoxide decomposition step, and a step of neutralizing and absorbing a corrosive gas component contained in the CFC decomposition product gas to detoxify them in series or in parallel. Is to be installed. First, as a result of the investigations by the present inventors as a catalyst used in the Freon decomposition step, titanium oxide was contained as the active first component and tungsten was contained as the second component, and the ratio of titanium to tungsten was expressed as an atomic percentage. 20% to 91%, tungsten 80% to 9%
It has been found that when it is in the above range, it exhibits excellent decomposition activity and high HF resistance. In this catalyst, titanium and tungsten are present in the form of oxide mixture or complex oxide.

As the third component, at least one of sulfur compound and phosphorus compound is added, the sulfur compound is 1 to 10% by weight in terms of S, and the phosphorus compound is 1 to 10 in terms of P.
It has been found that adding 10% by weight is effective.

Further, as the fourth component of these catalysts, gold,
We have found that the addition of at least one component selected from platinum, palladium, rhodium and ruthenium further improves the decomposition activity at low temperatures. When the amount of the above-mentioned noble metal carried is in the range of 0.01 to 5% by weight, the effect is great. If the amount is less than 0.01% by weight, the effect of addition is not sufficient, and if the amount is more than 5% by weight, noble metal particles are likely to grow and the activity is decreased.

Further, it has been found that a catalyst containing titanium oxide as the second component and at least one selected from silver, copper, chromium and molybdenum exhibits a high organohalogen compound decomposing activity. This titanium and each metal,
It exists as a mixture or complex oxide, and the ratio of titanium to each metal is expressed in atomic percentage.
It was found that when the content of the metal is 80% or more and 97% or less and the metal content is 80% or less and 3% or more, particularly excellent decomposition activity is exhibited.

Further, according to the method for decomposing an organohalogen compound of the present invention, when treating an organohalogen compound which is liquid at room temperature, the organohalogen compound is sent to the catalytic reaction tower as a liquid, and at the same time, the reactant H ₂ O is also sent as a liquid. The catalyst is characterized in that it is gasified at the upper part of the catalyst layer and passed through the catalyst layer. As a method of gasifying at the upper part of the catalyst layer, it is desirable to increase the residence time with a filler such as alumina fiber, silica fiber, glass fiber or the like for gasification.

Hydrogen fluoride, which is highly corrosive and harmful to the human body, and hydrogen chloride, which is strongly acidic, in the decomposition product gas,
It is desirable to pass through an aqueous alkaline solution such as sodium hydroxide or calcium hydroxide to neutralize and render harmless.

Further, the method of decomposing an organic halogen compound according to the present invention has a space in which a carbon monoxide oxidation reaction catalyst is filled in the outer peripheral portion of a reaction tower which is integrated with a catalyst reaction tower filled with an organohalogen compound decomposition catalyst. However, it is desirable that the decomposition gas that has passed through the organic halogen compound decomposition catalyst layer is passed through the carbon monoxide reaction catalyst layer to completely convert the carbon monoxide in the generated gas into harmless carbon dioxide.

Further, the method for decomposing an organic halogen compound of the present invention is also effective by a method in which the carbon monoxide oxidation reaction catalyst layer is installed after passing through the organic halogen compound decomposing layer and the acidic component neutralizing and detoxifying layer. Is.

As a method of raising the temperature of the catalyst, of course, a heater such as an electric furnace may be used, and the temperature of the organohalogen compound-containing gas is raised to the temperature at which the catalyst works by heat exchange with another high heat source. Is also good. Further, a gas containing at least one of hydrogen, water vapor, and ozone can be added to the recovered organohalogen compound-containing gas. This method can also be applied to urethane foam for building materials and automobile dismantling organic halogen compound recovery processing.

In the present invention, the gas that has passed through the process of treating the decomposition product gas may be recycled to the process of decomposing the recovered CFCs depending on the concentration of CFCs in the gas. In addition, the freon-containing gas obtained in the step of recovering freon from the freon processing object may be diluted with a gas such as air, nitrogen, hydrogen, oxygen, or helium when it is sent to the step of decomposing the recovered freon. Further, CFCs recovered by another method may be added to the step of decomposing the recovered CFCs.

As the titanium raw material for preparing the organohalogen compound decomposition catalyst in the present invention, titanium oxide,
Various titanic acids that generate titanium oxide by heating, titanium sulfate, titanium chloride, organic titanium compounds, and the like can be used.
It is also a preferred method to form a hydroxide by precipitating a hydroxide of these titanium raw materials with water, aqueous ammonia, an alkaline solution or the like, and finally firing. Sulfur compounds and phosphorus compounds used as CFC decomposition catalyst raw materials include sulfuric acid, ammonium sulfate, ammonium thiosulfate,
Examples thereof include sodium thiosulfate, potassium thiosulfate, sodium pyrosulfate, potassium pyrosulfate, orthophosphoric acid, metaphosphoric acid, phosphorous acid, ammonium phosphate, ammonium dihydrogenphosphate and the like. As a tungsten raw material,
Tungsten oxide, tungstic acid, ammonium paratungstate, etc. are suitable. In the present invention, the noble metal source used as the raw material for the CFC decomposition catalyst is preferably dinitroamine platinum chloroplatinate, palladium chloride, palladium nitrate, rhodium nitrate, rhodium sulfate, ruthenium nitrate, ruthenium chloride, or the like. The silver raw material is preferably silver nitrate or silver chloride, the copper raw material is preferably copper nitrate, copper sulfate or copper chloride, and the chromium raw material is preferably chromium nitrate, chromium sulfate or chromium chloride. As the molybdenum raw material, molybdic acid, phosphomolybdic acid, ammonium molybdate, etc. are preferable.

As the method for producing the fluorocarbon decomposition catalyst, any of the precipitation method, the impregnation method, the kneading method and the like which are commonly used for producing the catalyst can be used. The CFC decomposition catalyst can be produced by any of extrusion molding, tablet molding, rolling granulation and the like. In this case, it is also effective to mix other ceramics or organic components for the purpose of increasing strength or increasing specific surface area. For the same purpose, it is also effective to support the catalyst component on a granular carrier such as alumina or silica by using a method such as impregnation. Further, it is also effective to coat it on a honeycomb or plate made of ceramics or metal.

For the carbon monoxide oxidation catalyst, it is also effective to support the catalyst component on a granular carrier such as alumina or silica by using a method such as impregnation. In this case, the catalyst component is a platinum group metal element such as platinum, rhodium, palladium, ruthenium, etc., and platinum diplatinate chloroplatinate, palladium chloride, palladium nitrate, rhodium nitrate, rhodium sulfate, ruthenium nitrate, ruthenium chloride, etc. are used as raw materials. It is desirable to do.

The organic halogen compound which is the object of the present invention is a compound containing fluorine, chlorine and bromine in various organic compounds such as CFCs, trichloroethylene and methyl bromide. Taking Freon 113 and methyl bromide as examples, the following reactions are typical.

[0023]

Embedded image CCl ₂ F—CClF ₂ + 3H ₂ O → CO + CO ₂ + 3HCl + 3HF ... (1)

[0024]

## STR00002 ## CH ₃ Br + 3 / 2O ₂ → CO + HBr + H ₂ O (2) In order to carry out the decomposition reaction of the ethane-based organic halogen compound, water vapor is added to the organic halogen compound in a molar ratio of 3 in the gas to be treated. Adjust so that there are more than twice as many. It is expected that the decomposition efficiency will be improved by carrying out the reaction in such an atmosphere. In addition, the decomposition product can be obtained with a hydrogen halide in a form that can be easily post-treated. The effect is not sufficient when the amount of water vapor is less than three times the amount of the organic halogen compound.

The temperature for reacting with the catalyst is preferably 300 ° C. or higher and 600 ° C. or lower. The space velocity of the processing gas is 2,
The most desirable setting is 0000 to 100,000 / hour and 5,000 to 50,000 / hour.

The shape of the reaction vessel which can be used in the present invention is basically any of a fixed bed type, a moving bed type and a fluidized bed type.

[0027]

The organic halogen compound catalyst used in the present invention is
It has high activity at low temperature and high durability due to excellent HF resistance. It does not require high temperature for decomposition unlike conventional catalysts and greatly reduces energy required for decomposition of organic halogen compounds. You can

When decomposing an organic halogen compound,
Gas components such as HF and HCl are generated. These components are highly corrosive, and corrosion of equipment materials is a problem. It is desirable to reduce the contact area between the cracked gas that has passed through the fluorocarbon cracking catalyst layer and the apparatus as much as possible. The layer for decomposing carbon monoxide in the decomposition product gas by a catalyst has two methods: a method of setting the decomposition product gas of the organic halogen compound after passing through the alkali absorbing liquid and a method of utilizing the heat of decomposition reaction of the organic halogen compound. There is a way.

[0029]

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

Example 1 250 g of metatitanic acid slurry (containing 20% by weight of titanium oxide) and 18.2 g of ammonium paratungstate are thoroughly mixed by a kneading machine. The obtained slurry is dried at 150 ° C for about 20 hours and then calcined at 400 ° C. Put the resulting powder in a mold 5
It is compression molded at 00 kgf / cm ² . The pressure for compression is preferably 300 to 3000 kgf / cm ² . The molded product is fired in air at 500 ° C. for 2 hours. The catalyst thus obtained has a composition of Ti: W = 9: 1 in terms of atomic ratio of metal components. This catalyst was crushed and sieved, and 2 ml having a particle size of 1 to 2 mm was used in the following experiment.

FIG. 1 shows a conceptual diagram of the apparatus of this embodiment. The reaction tube 2 filled with the Freon decomposition catalyst 1 has a Freon supply system 6 for continuously supplying Freon 113, an air supply system 5 for continuously supplying air, and a water supply system 9 for continuously supplying water. It is connected. The CFC decomposition catalyst in the reaction tube 2 is heated to 430 ° C. by the electric furnace 4. Freon is decomposed by a catalyst in the reaction tube to become CO, CO ₂ , HF and HCl, and is discharged as exhaust gas 13 outside the reaction tube. Next, the exhaust gas is fed to the alkali absorption tank 12 and the NaOH aqueous solution 8
Introduced into and neutralized into NaCO ₃ , NaF and N
It becomes aCl and precipitates in an alkaline solution. The alkali-absorbed exhaust gas 10 that has passed through the alkali absorption tank then passes through the carbon monoxide oxidation catalyst layer 7, oxidizes CO, and is exhausted 14.

The reaction tube is made of Hastelloy having an inner diameter of 20 mm and has a thermocouple protection tube 3 of the same material having an outer diameter of 5 mm inside.
The reaction tube is heated in the electric furnace 4, and the temperature is measured with a thermocouple.
The amount of water vapor was adjusted by supplying a predetermined amount of pure water to the upper part of the reaction tube with a pump and evaporating it. The supplied processing gas has the following composition.

Composition of supplied processing gas Organic halogen compound 3% (Freon 113, trichloroethylene, methyl bromide) Steam 0-15% Oxygen 10-20% Nitrogen balance Gas of the above composition reacted at space velocity 10,000 hourly It was poured into the pipe. The decomposition temperature of the organohalogen compound was measured by sequentially changing the reaction temperature. The decomposition rate was also determined by the following formula.

[0034]

[Equation 1]

The results of the Freon 113 gas reaction with the TiO ₂ —WO ₃ catalyst are shown in FIG.

Palladium-supported tin oxide was used as the CO oxidation reaction catalyst. CO consisting of palladium-supported tin oxide
The oxidation reaction catalyst was used after being heated to a constant temperature of 50 to 80 ° C. by an electric furnace installed on the outer periphery of the reaction tube.

As a result, the CO concentration in the exhaust gas that did not pass through the CO oxidation reaction catalyst was 2.5%, whereas the CO concentration in the exhaust gas after passing through the palladium-supported tin oxide catalyst of this example was 3 ppm. Fell to. It was confirmed that, in addition to the palladium-supported tin oxide of this example, the CO oxidation reaction catalyst is also effective with platinum-aluminum oxide-iron system, copper-zinc-aluminum oxide system or copper oxide system. However, in the copper-zinc-aluminum oxide system, the reaction temperature is 15
It was effective to set the temperature to 0 to 200 ° C.

(Embodiment 2) In this embodiment, T of Embodiment 1 is used.
A catalyst was prepared by changing the ratio of Ti and W in the iO ₂ -WO ₃ catalyst. Table 1 shows the prepared catalysts and the performance test results. CFC concentration 6%, SV 5000 / hour, catalyst layer temperature 430 ° C., CFC 113, H ₂ O supply amount = 1.7 times the theoretical amount required for decomposition.

[0039]

[Table 1]

(Third Embodiment) FIG. 3 shows another embodiment of the basic flow sheet shown in FIG. The difference from FIG. 1 is that the carbon monoxide oxidation catalyst layer is in the same reaction tube as the CFC decomposition catalyst, and preheating of the CFC decomposition reaction is utilized to oxidize carbon monoxide by the oxidation catalytic reaction. At this time, the same palladium-supported tin oxide as in Example 1 was used as the carbon monoxide oxidation catalyst. The catalyst has a thermocouple 15 of 50-80.
Cooling was controlled so that the temperature became 0 ° C. As a result, the CO concentration in the exhaust gas that did not pass through the CO oxidation reaction catalyst was 1.7%, whereas the CO concentration in the exhaust gas after passing through the palladium-supported tin oxide catalyst of this example was up to 1.5 ppm. Fell.

[0041]

According to the present invention, carbon monoxide generated during the CFC decomposition can be efficiently decomposed in a series of steps following the CFC decomposition step.

[Brief description of drawings]

FIG. 1 is a schematic view of a CFC decomposition apparatus showing an embodiment of the present invention.

FIG. 2 is a graph showing changes over time in the CFC decomposition rate.

FIG. 3 is a schematic view of a CFC decomposition apparatus showing another embodiment of the present invention.

[Explanation of symbols]

1 ... Freon decomposition catalyst, 2 ... Reaction tube, 3 ... Thermocouple protection tube,
4 ... Electric furnace, 5 ... Air supply system, 6 ... Freon supply system, 7 ...
Carbon monoxide oxidation catalyst layer, 8 ... NaOH aqueous solution, 9 ... Water supply system, 10 ... Alkaline absorption exhaust gas, 11 ... Catalyst temperature adjusting thermocouple, 12 ... Alkaline absorption tank, 13 ... Exhaust gas.

Front Page Continuation (72) Inventor Kazuyoshi Irie 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd., Hitachi Works

Claims (4)

[Claims] 1. A step of contacting a gas containing an organic halogen compound with an organic halogen compound decomposition catalyst in a temperature environment of about 200 to 500 ° C. in the presence of water or ozone,
A step of contacting the catalyst with a gas species generated by contacting with an alkali aqueous solution to remove the gas species; and contacting a gas stream passing through the alkali aqueous solution with a carbon monoxide decomposition catalyst in an atmosphere containing oxygen, ozone or hydrogen. A method for decomposing an organic halogen-containing gas, comprising: 2. The organic halogen compound decomposition catalyst according to claim 1, wherein titania is the main component, and further tungsten oxide, molybdenum oxide, zirconium oxide, vanadium oxide, niobium oxide, chromium oxide, manganese oxide,
A method for decomposing an organic halogen-containing gas, characterized in that it contains at least one component of cobalt oxide and nickel oxide in an amount of about 10 to about 40% by weight and a sulfate group of about 3 to 10% by weight based on the total weight of the catalyst. . 3. The organohalogen compound decomposition catalyst according to claim 1, wherein titania is the main component, and silver oxide or copper oxide is used in an amount of about 10 to about 40% by weight of the total weight of the catalyst and a sulfate group is also used in an amount of about 3 to 10%. A method for decomposing an organohalogen compound, characterized in that the content of the organic halogen compound is in a weight percentage. 4. The catalyst according to claim 1, wherein the catalyst for decomposing organic halogen compounds contains titania as a main component, and tungsten oxide, molybdenum oxide, zirconium oxide, vanadium oxide, niobium oxide, chromium oxide, manganese oxide,
At least one component selected from cobalt oxide, nickel oxide, silver oxide, and copper oxide is used in an amount of about 10 to about 40 based on the total weight of the catalyst.
%, Further containing noble metal-based elements in an amount of about 10 to about 40% by weight based on the total weight of the catalyst, and further containing a sulfate group in an amount of about 3 to 10% by weight. Method.