JP2007117911A - Catalyst for decomposing organic chlorine compound and method for removing organic chlorine compound using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for removing an organic chlorine compound and a method for removing it from a gas containing a low concentration of the organic chlorine compound using the same. <P>SOLUTION: The catalyst is obtained by a method including the processes of: producing a precipitate containing cobalt and copper from an aqueous solution containing mainly a cobalt-copper complex oxide, a cobalt compound and a copper compound; and calcinating the precipitate. The method for removing the organic chlorine compound includes a process of contacting the gas containing the organic chlorine compound with the catalyst. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalyst for decomposing organochlorine compounds, particularly for decomposing low-concentration organochlorine compounds contained in exhaust gas from factories and the like. The present invention also relates to a method for removing an organochlorine compound using this catalyst.

  Volatile organic compounds (VOC) discharged from factories and the like are considered as causative substances for suspended particulate matter and photochemical oxidants. Among VOCs, organic chlorine compounds such as dichloromethane and chloroform are known as causative substances of acid rain, and emission suppression is strongly demanded. However, unlike hydrocarbons such as toluene, xylene and ethyl acetate, organochlorine compounds cannot be easily oxidatively decomposed. Further, when the organic chlorine compound is decomposed, the decomposition product contains chlorine. It is well known that this chlorine acts as a catalyst poison. That is, chlorine produced by decomposing an organic chlorine compound chlorinates the catalyst component and degrades the catalyst performance. For example, if a manganese catalyst that is an oxidative decomposition catalyst has a chlorine component, it is easily chlorinated and the surface of the catalyst becomes manganese chloride, resulting in a reduction in oxidation performance. Such an example is observed with various catalysts such as an iron oxide catalyst. In order to prevent poisoning by chlorine, it is necessary to use conditions at a temperature higher than the decomposition temperature of the metal chloride formed on the catalyst surface. Therefore, it is difficult to treat organochlorine compounds with commonly used catalysts because of poisoning by chlorine. In particular, exhaust gas containing low-concentration organochlorine compounds is expensive in terms of the amount of treatment, and an effective treatment method has not yet been established, and prompt action is required.

  Conventionally, in order to remove organic chlorine compounds such as dichloromethane, removal by activated carbon adsorption (properties of porous materials and their application technology, supervised by Takeuchi Takeshi, Fuji Techno System, 1999, P441.) However, it is not cheap in terms of cost, such as periodic replacement of activated carbon and reprocessing of recovered organochlorine compounds.

Further, as an oxidative decomposition method, catalytic decomposition using a noble metal catalyst at a temperature of 500 ° C. or higher (Japanese Patent Laid-Open No. 7-31879 (Patent Document 1)) and direct combustion at 800 ° C. or higher are performed (environmental technology / Equipment Encyclopedia, Industry Research Committee, 2003, P.1360. (Non-patent Document 2)). However, since these have a high decomposition treatment temperature, the running cost is not practical for the treatment of low-concentration organochlorine compounds.
JP-A-7-31879 Properties of porous materials and their applied technologies, supervised by Satoshi Takeuchi, Fuji Techno System, 1999, P441. Encyclopedia of Environmental Technology and Equipment, Industry Research Committee, 2003, P.1360.

  Therefore, the present invention is a catalyst for removing organochlorine compounds such as dichloromethane contained in exhaust gas from factories and the like, and suitable for removing low-concentration organochlorine compounds, and is highly active at low temperatures. An object is to provide a catalyst. Moreover, this invention aims at providing the method of removing an organic chlorine compound effectively using this catalyst.

  In order to achieve the above object, the catalyst of the present invention is mainly composed of a cobalt / copper composite oxide. The catalyst of the present invention is obtained by a method comprising a step of producing a precipitate containing cobalt and copper from a solution containing a cobalt compound and a copper compound, and a step of firing the precipitate. If this catalyst is used, a low concentration organochlorine compound can be effectively removed by oxidative decomposition at a low temperature of 300 ° C. or lower.

Moreover, it is preferable to precipitate the catalyst of this invention by pH 7-10 in the process of producing | generating the precipitate containing cobalt and copper from the aqueous solution containing a cobalt compound and a copper compound. According to this preferable example, the specific surface area of the catalyst is 100 m ² / g or more, and the catalyst performance is improved.

  The catalyst of the present invention is selected from the group consisting of V, Cr, Mn, Fe, Ni, Ga, Nb, Mo, Pd, Ag, Cd, Sn, W, Au, Ru, Pt, Bi, Ir, Rh and Ce. It is preferable to further include at least one of the above as a cocatalyst. However, the content of the cocatalyst is preferably 20% by weight or less.

  In the catalyst of this invention, it is preferable that the content rate of cobalt with respect to the total amount of cobalt and copper is 10 atomic% or more and 90 atomic% or less.

The catalyst of the present invention preferably has a specific surface area of 100 m ² / g or more measured by the Brunauer-Emmett-Teller (BET) method (specific surface area measurement method). This is because the performance of the catalyst for the decomposition of the organic chlorine compound is improved.

Furthermore, the catalyst of the present invention can be used by being supported on a carrier having a specific surface area of 100 m ² / g or more.

  The method for removing an organic chlorine compound of the present invention includes a step of bringing a gas containing an organic chlorine compound into contact with the catalyst of the present invention. The removal method of the present invention can remove low-concentration organochlorine compounds.

  In the removal method of the present invention, it is preferable that a gas containing an organic chlorine compound is brought into contact with the catalyst at 300 ° C. or lower. In the conventional catalyst, it was necessary to contact the gas at a high temperature exceeding 500 ° C. in practice. However, the above removal method can be processed at a lower temperature than conventional catalysts.

  Furthermore, in the method for removing an organic chlorine compound of the present invention, the gas may further contain water vapor.

  The catalyst of the present invention is a catalyst for removing organochlorine compounds such as dichloromethane contained in exhaust gas from factories and the like, and can remove organochlorine compounds at a low concentration. The catalyst of the present invention is a catalyst that is highly active at low temperatures. The method of the present invention allows the removal of low concentrations of organochlorine compounds and can be operated at low temperatures.

  The present invention will be described below.

The catalyst of the present invention is a composite compound of cobalt and copper mainly composed of a cobalt / copper composite oxide. In the catalyst of this invention, it is preferable that the content rate of cobalt with respect to the total amount of cobalt and copper is 10 atomic% or more and 90 atomic% or less. The cobalt / copper composite oxide which is the catalyst of the present invention has a specific surface area of 100 m ² / g or more, preferably 150 m ² / g or more. The higher the specific surface area of the catalyst, the higher the activity of decomposing organochlorine compounds. The catalyst for decomposing organochlorine compounds of the present invention includes V, Cr, Mn, Fe, Ni, Ga, Nb, Mo, Pd, Ag, Cd, Sn, W, Au, Ru, Pt, Bi, Ir as promoters. , Rh and Ce may be included. The amount of the promoter in the catalyst is preferably 20% by weight or less. More preferably, it is 10 weight% or less. The catalyst of the present invention can also be supported on a carrier having a specific surface area of 100 m ² / g or more. Furthermore, the catalyst of this invention is manufactured by the manufacturing method mentioned later.

The catalyst and the support preferably have the above-mentioned specific surface area, but the specific surface area can be made as large as possible depending on how the catalyst and the support are prepared. For example, in the case of a cobalt / copper composite oxide catalyst, the specific surface area can be, for example, up to about 400 m ² / g, and in the case of a support, the specific surface area can be up to, for example, about 3000 m ² / g. However, the present invention is not limited to these upper limits and may have a larger specific surface area.

  The shape of the catalyst is not particularly limited, and may be various shapes such as a granular shape, a columnar shape, a clover shape, a honeycomb shape, and a net shape. In order to reduce the pressure loss, a honeycomb type or a net shape is preferable.

  The catalyst of the present invention is preferably amorphous.

  Cobalt oxide and copper oxide are known as oxidation catalysts, but each is not effective as a decomposition catalyst for organochlorine compounds. By becoming a complex oxide of cobalt and copper, it is considered that the oxidation-reduction power of cobalt and the oxidation-reduction power of copper act effectively, and the organic chlorine compound can be decomposed at a low temperature. In addition, the cobalt / copper composite oxide catalyst of the present invention is characterized by being less susceptible to chlorine poisoning. A normal oxidation catalyst such as manganese oxide chlorinates the surface of the catalyst with chlorine. Therefore, the decomposition activity of the catalyst is rapidly deteriorated at a low temperature of 300 ° C. or lower, or the decomposition performance cannot be exhibited. However, since the organochlorine compound can be effectively decomposed at 300 ° C. or less in the cobalt / copper composite oxide catalyst of the present invention, it is considered that the catalyst surface is hardly chlorinated. The mechanism for preventing chlorination of the catalyst surface is unknown, but it is probably because chloride generated on the catalyst surface reacts with water vapor even at a low temperature of 300 ° C. or less and is removed as hydrochloric acid gas from the catalyst surface. It is done.

  Next, an embodiment of a method for producing a catalyst in the present invention will be described. Cobalt compounds and copper compounds used as raw materials include various inorganic metal compounds such as nitrates, sulfates and chlorides, various organic metals including acetates, formates, alkoxide metal compounds, and acetylacetate metal compounds. Compounds can be used.

  A raw material containing a cobalt compound and a copper compound is added to a solvent. As the solvent, water, an alcohol solvent or the like can be used. In order to adjust pH, it is preferable to add a precipitation aid to the obtained solution. As the precipitation aid, various alkaline compounds such as aqueous ammonia and sodium carbonate can be used. Further, urea or the like that becomes alkaline when decomposed may be used. In this way, the pH of the solution is adjusted to a value that is favorable for the formation of a precipitate. The pH value is preferably 7 to 10, more preferably 8 to 10.

The cobalt compound and the copper compound are preferably added to the solution such that the atomic ratio of cobalt: copper is 1: 9 to 9: 1 in the catalyst finally obtained.
The atomic ratio of cobalt: copper is more preferably 2: 8-8: 2, most preferably 5: 5-8: 2.

The cobalt / copper composite oxide thus produced has a specific surface area of 100 m ² / g or more, preferably 150 m ² / g or more, and exhibits high activity in the decomposition of the organic chlorine compound.

  In the catalyst of the present invention, V, Cr, Mn, Fe, Ni, Ga, Nb, Mo, Pd, Ag, Cd, Sn, W, Au, Ru, Pt, Bi, Ir, Rh and Ce are used as promoters. It can contain at least one element selected from When producing an organic chlorine compound decomposition catalyst containing a cocatalyst, it is effective to add a compound of an element serving as a cocatalyst to a solution containing a cobalt compound and a copper compound. These cocatalysts have the effect of improving the oxidizing power of the catalyst. In particular, Mn, Cr, V, Ag, Au, Pd, Pt, and Ce are useful for improving the performance of the catalyst because the oxide itself has a strong oxidizing action. These elements are usually contained in the catalyst as ions or oxides.

  The amount of the promoter in the catalyst is preferably 20% by weight or less. More preferably, it is 10 weight% or less.

  The precipitate thus obtained (for example, a coprecipitate of a cobalt compound and a copper compound) is preferably further washed to remove excess metal ions and the like. Washing can be performed, for example, by filtration. The washing is preferably carried out until no excessive salt or metal ion remains in the washing solution. After washing, the precipitate is dried to remove moisture sufficiently and then baked.

  Firing is preferably performed in the atmosphere at 250 ° C to 350 ° C. When calcined at a temperature of 250 ° C. or lower, the precipitate is mainly composed of hydroxide, and may have poor oxidizing power. Moreover, when calcined at a temperature of 350 ° C. or higher, the specific surface area of the precipitate becomes small, and the catalyst performance may be lowered.

The catalyst can be supported on a carrier having a specific surface area of 100 m ² / g or more. As the carrier, materials such as silica, alumina, zeolite, titania, and mesoporous silica can be used, but are not particularly limited. The loading method is a method in which a carrier is added to a solution containing a cobalt compound and a copper compound, and then a precipitate is formed with a precipitation aid, and after the carrier is impregnated with a solution containing a cobalt compound and a copper compound, the precipitation aid is added. Although there is a method of forming a cobalt / copper composite compound on a carrier with an agent, it is not particularly limited. After being supported on these carriers, it is preferably fired in the atmosphere at 250 ° C to 350 ° C.

  The method for removing an organic chlorine compound of the present invention includes a step of bringing the catalyst produced as described above into contact with a gas containing an organic chlorine compound. In the method for removing an organic chlorine compound of the present invention, the catalyst of the present invention is brought into contact with a gas containing an organic chlorine compound such as dichloromethane (for example, air containing an organic chlorine compound) at a low temperature of 300 ° C. or lower, Remove organochlorine compounds.

  Further, the gas can contain water vapor in addition to the organic chlorine compound and air. The water vapor may be originally contained in the gas, or may be added to the gas separately. Steam reacts with chlorine contained in the organic chlorine compound to form hydrochloric acid. If water vapor is not contained, chlorine gas is generated by an oxidation reaction, and chlorine gas cannot be easily removed by only scrubber cleaning of exhaust gas. However, the hydrochloric acid gas produced by containing water vapor is highly reactive with an alkaline aqueous solution, and can be easily neutralized and removed by scrubber cleaning using an alkaline aqueous solution. The amount of water vapor may be one or more times the number of moles of chlorine atoms contained in the organic chlorine compound, and preferably two or more times.

  Although not particularly limited, the removal of the organic chlorine compound by the catalyst according to the present invention is suitable for a gas containing about 1 to 100 ppm of the organic chlorine compound.

  Further, although not particularly limited, for example, dichloromethane, chloromethane, chloroform, dichloroethane, chloroethane, chloroethylene, and dichloroethylene are suitable as the organic chlorine compound that is a target of the method for removing an organic chlorine compound by the catalyst according to the present invention.

  The process of bringing the catalyst containing air containing a low-concentration organochlorine compound into contact with the catalyst may be carried out by employing a method used for a normal gas phase catalytic reaction. The simplest is a method in which a catalyst or a carrier on which the catalyst is fixed is filled into a tube or container equipped with a heating device. Specifically, there is a method in which a packed bed made of a catalyst or the like is formed and a gas containing an organic chlorine compound is passed through the packed bed.

  It is preferable to use the catalyst mainly composed of cobalt / copper composite oxide by being incorporated in an exhaust gas facility such as a factory.

  When the catalyst is used in this manner, harmful organic chlorine compounds such as dichloromethane can be removed from the exhaust gas continuously over a long period of time.

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

Example 1
Cobalt nitrate hexahydrate 0.15 mol and copper nitrate trihydrate 0.05 mol were dissolved in 1000 ml of pure water. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 9.3, thereby forming a coprecipitate of cobalt and copper. The coprecipitate was filtered and washed with 3 liters of pure water at 70 ° C. Further, the coprecipitate was dried at 120 ° C. overnight and then calcined at 300 ° C. for 2 hours to obtain a cobalt / copper composite oxide. It was 159 m < ² > / g as a result of measuring the specific surface area of this cobalt * copper complex oxide by BET method. Moreover, as a result of confirming the crystal structure by powder X-ray diffraction, there was no clear peak and it was amorphous.

(Example 2)
Cobalt nitrate hexahydrate 0.15 mol and copper nitrate trihydrate 0.05 mol were dissolved in 1000 ml of pure water. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 8.0, thereby producing a coprecipitate of cobalt and copper. The coprecipitate was filtered and washed with 3 liters of pure water at 70 ° C. Further, the coprecipitate was dried at 120 ° C. overnight and then calcined at 300 ° C. for 2 hours to obtain a cobalt / copper composite oxide. As a result of measuring the specific surface area of this cobalt-copper composite oxide by the BET method, it was 133 m ² / g. Moreover, as a result of confirming the crystal structure by powder X-ray diffraction, there was no clear peak and it was amorphous.

(Example 3)
Cobalt nitrate hexahydrate 0.15 mol and copper nitrate trihydrate 0.05 mol were dissolved in 1000 ml of pure water. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 7.5, thereby forming a coprecipitate of cobalt and copper. The coprecipitate was filtered and washed with 3 liters of pure water at 70 ° C. Further, the coprecipitate was dried at 120 ° C. overnight and then calcined at 300 ° C. for 2 hours to obtain a cobalt / copper composite oxide. As a result of measuring the specific surface area of this cobalt-copper composite oxide by the BET method, it was 128 m ² / g. Moreover, as a result of confirming the crystal structure by powder X-ray diffraction, weak peaks of CuO and Co ₃ O ₄ were observed.

(Comparative Example 1)
Cobalt nitrate hexahydrate 0.15 mol and copper nitrate trihydrate 0.05 mol were dissolved in 1000 ml of pure water. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 6.5, thereby forming a coprecipitate of cobalt and copper. The coprecipitate was filtered and washed with 3 liters of pure water at 70 ° C. Further, the coprecipitate was dried at 120 ° C. overnight and then calcined at 300 ° C. for 2 hours to obtain a cobalt / copper composite oxide. As a result of measuring the specific surface area of this cobalt-copper composite oxide by the BET method, it was 39 m ² / g. As a result of confirming the crystal structure by powder X-ray diffraction, large peaks of CuO and Co ₃ O ₄ were observed.

(Comparative Example 2)
Cobalt nitrate hexahydrate 0.15 mol and copper nitrate trihydrate 0.05 mol were dissolved in 1000 ml of pure water. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 6.1, thereby forming a coprecipitate of cobalt and copper. The coprecipitate was filtered and washed with 3 liters of pure water at 70 ° C. Further, the coprecipitate was dried at 120 ° C. overnight and then calcined at 300 ° C. for 2 hours to obtain a cobalt / copper composite oxide. As a result of measuring the specific surface area of this cobalt-copper composite oxide by the BET method, it was 11 m ² / g. As a result of confirming the crystal structure by powder X-ray diffraction, large peaks of CuO and Co ₃ O ₄ were observed.

From the above results, it can be seen that the coprecipitation pH must be 7 or more in order for the specific surface area to be 100 m ² / g or more.

Example 4
Cobalt nitrate hexahydrate 0.15 mol, copper nitrate trihydrate 0.05 mol, and lanthanum nitrate hexahydrate 1.4 g were dissolved in 1000 ml of pure water. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 9.3, thereby forming a coprecipitate of cobalt and copper. The coprecipitate was filtered and washed with 3 liters of pure water at 70 ° C. Further, the coprecipitate was dried at 120 ° C. overnight and then calcined at 300 ° C. for 2 hours to obtain a lanthanum-containing cobalt / copper composite oxide. It was 161 m < ² > / g as a result of measuring a specific surface area by this BET method for this cobalt-copper composite oxide.

(Example 5)
1000 ml of pure water containing 0.15 mol of cobalt nitrate hexahydrate, 0.05 mol of copper nitrate trihydrate, 1.4 g of lanthanum nitrate hexahydrate, and 0.4 g of chloroplatinic acid hexahydrate Dissolved in. A 10 wt% aqueous solution of sodium carbonate was added to this aqueous solution to adjust the pH to 9.3, thereby forming a coprecipitate of cobalt and copper. The coprecipitate was filtered, washed with 1 liter of pure water at 70 ° C., dried at 120 ° C. overnight, and then calcined at 300 ° C. for 2 hours to obtain a platinum / lanthanum-containing cobalt / copper composite oxide. . It was 149 m < ² > / g as a result of measuring a specific surface area by this BET method for this cobalt-copper composite oxide.

(Comparative Example 3)
A liquid A was obtained by dissolving 0.25 g of chloroauric acid tetrahydrate and 24.3 g of iron nitrate nonahydrate in 600 ml of distilled water. On the other hand, 10.3 g of sodium carbonate was dissolved in 400 ml of distilled water to obtain a liquid B.

  After dripping A liquid in the said B liquid and stirring for 1 hour, the obtained coprecipitate was fully washed with water, dried, and baked at 400 degreeC in the air for 5 hours, gold fine particle fixed iron An oxide was obtained.

(Comparative Example 4)
15.0 g of potassium permanganate was dissolved in 1000 ml of pure water. To this aqueous solution, 300 ml of an aqueous solution in which 22.5 g of oxalic acid was dissolved in pure water was added and stirred overnight. The obtained precipitate was sufficiently washed with water, dried, and calcined in air at 300 ° C. for 2 hours to obtain a manganese oxide catalyst.

(Example 6)
A catalyst of Example 4, Example 5, Comparative Example 3, Comparative Example 4, and a commercially available catalyst (N-840: manufactured by Zude Chemie Catalysts Co., Ltd.) under conditions of a dichloromethane concentration of 10 ppm, air of 500 ml / min, and water vapor RH of 50%. Was set in an atmospheric pressure tubular flow reactor, and the decomposition rate of dichloromethane was measured at 50 to 200 ° C. The decomposition rate of dichloromethane was calculated by the following formula.

    Dichloromethane removal rate (%) = (inlet concentration−outlet concentration) × 100 / inlet concentration

  Table 1 shows the dichloromethane removal rate of each catalyst at each temperature.

  From the above results, it can be seen that the catalyst of the present invention has a very high decomposition performance of organochlorine compounds compared to other commercially available catalysts and ordinary oxidation catalysts.

  An outline of the atmospheric pressure tubular flow reactor used is shown in FIG. As shown in FIG. 1, in this reaction apparatus, the catalyst packed bed 102 is installed in the middle of the glass tube 104, and vent tubes 106 and 108 are arranged above and below the glass tube 104. The gas 110 containing dichloromethane at the above concentration is supplied from one vent pipe 106 to the glass pipe 104, passes through the catalyst packed bed 102, and is discharged from the other vent pipe 108. A heater 112 is provided around the glass tube 104 so that the temperature of the catalyst packed bed 102 can be adjusted.

It is the schematic of the atmospheric pressure tubular flow reaction apparatus used for the organic chlorine removal test in an Example.

Explanation of symbols

102 Catalyst packed bed 104 Glass tube 106, 108 Vent tube 110 Gas 112 Heater

Claims (11)

  Characterized in that it is obtained by a method comprising a step of producing a precipitate containing cobalt and copper from an aqueous solution containing a cobalt compound and a copper compound, and a step of calcining the precipitate. Organochlorine compound decomposition catalyst.   2. The organochlorine compound decomposition catalyst according to claim 1, wherein the pH is 7 to 10 in the step of generating a precipitate containing cobalt and copper from an aqueous solution containing a cobalt compound and a copper compound.   3. The organochlorine compound decomposition catalyst according to claim 1, wherein the content of cobalt with respect to the total amount of cobalt and copper is 10 atomic% or more and 90 atomic% or less. 4. The organochlorine compound decomposition catalyst according to claim 1, wherein the specific surface area measured by the BET method is 100 m ² / g or more. 5.   Co-catalyst at least one selected from the group consisting of V, Cr, Mn, Fe, Ni, Ga, Nb, Mo, Pd, Ag, Cd, Sn, W, Au, Ru, Pt, Bi, Ir, Rh and Ce The organochlorine compound decomposition catalyst according to any one of claims 1 to 4, further comprising:   The organochlorine compound decomposition catalyst according to claim 5, wherein the content of the cocatalyst is 20% by weight or less. A catalyst for decomposing organochlorine compounds, wherein the catalyst according to any one of claims 1 to 6 is supported on a carrier having a specific surface area of 100 m ² / g or more.   A method for removing an organic chlorine compound, comprising the step of bringing a gas containing an organic chlorine compound into contact with the catalyst according to claim 1.   The method for removing an organic chlorine compound according to claim 8, wherein a gas containing the organic chlorine compound is brought into contact with the catalyst at 300 ° C or lower.   The method for removing an organic chlorine compound according to claim 8 or 9, wherein the gas containing the organic chlorine compound is a gas further containing water vapor, and the gas is brought into contact with the catalyst at 300 ° C or lower. The method for removing an organic chlorine compound according to any one of claims 8 to 10, wherein the organic chlorine compound is dichloromethane, chloromethane, chloroform, dichloroethane, chloroethane, chloroethylene, or dichloroethylene.

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