JP3104717B2 - Production method of iron oxide catalyst for gas treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron oxide catalyst for treating a gaseous substance having excellent catalytic performance and large strength by supporting a large amount of iron oxide particles firmly on a ceramic or metal monolith carrier. The purpose is to provide.

[0002]

2. Description of the Related Art As is well known, exhaust gas discharged from a combustion furnace, an internal combustion engine, etc. contains a large amount of harmful components such as nitrogen oxides and sulfur oxides, and causes so-called pollution problems such as air pollution. Is evoking. In recent years, as environmental issues have become more important, regulations have become increasingly strict, and there is an urgent need for measures to deal with them.

As a catalyst for denaturing or decomposing and removing harmful components such as nitrogen oxides and sulfur oxides present in exhaust gas, magnetite particles ( FeO x .Fe ₂ O ₃₀ <
x ≦ 1), hydrous ferric oxide particles (α, β, γ-FeOO)
It is widely known that various iron oxides having different crystal structures such as H), hematite particles (α-Fe ₂ O ₃ ), and maghemite particles (γ-Fe ₂ O ₃ ) are effective. Since these various iron oxides having different crystal structures have different catalytic performances depending on the application, the type of iron oxide is properly used depending on the application. In use, it can be used in powder form as it is, used as a granulated substance by adding a binder, or practically supported on a carrier material such as silica, alumina, titania, magnesia, diatomaceous earth, etc. 2. Description of the Related Art Molding into a shape that is easy to use has been performed.

[0004] Once used, the iron oxide-based catalyst is 450 to
It can be used repeatedly by heating and regenerating at a high temperature of 850 ° C, but the powdery and agglomerated forms mentioned above can be remarkably disintegrated in the regeneration process and can withstand long-term use. However, problems with strength have been pointed out. On the other hand, silica, alumina, titania, magnesia,
Catalysts formed by supporting iron oxide on a carrier material such as diatomaceous earth are advantageous in terms of strength, but spherical, cylindrical, and cylindrical shaped articles are particularly useful when packed in a fixed-bed reactor. In this case, dust was clogged and the efficiency of removing harmful components in the exhaust gas was reduced.

[0005] In order to prevent clogging with dust, a catalyst in which iron oxide particles are supported on a ceramic or metal monolith carrier has been proposed and put into practical use. The monolith (Monolith) carrier is a circular, square, triangular, hexagonal, hexagonal, parallel-penetrating structure represented by a honeycomb structure,
It is a structure in which a large number of holes, such as a sine shape, are arranged, and there are various structures depending on the shape and arrangement of the holes and the difference in the shape of the structure.

Conventionally, as a method of supporting an iron oxide on a carrier, a porous carrier is immersed in an aqueous solution of an iron salt to impregnate the porous carrier with the aqueous solution of the iron salt, and then heated to remove the aqueous solution of the iron salt. A method of generating iron oxide particles by pyrolysis (Japanese Patent Application Laid-Open No. 63-294939), in which a prepared honeycomb structure is immersed in a slurry solution containing iron oxide particles and an adhesive such as colloidal silica. To support iron oxide particles via an adhesive (Japanese Patent Laid-Open No.
JP-A-3-42735), by immersing the sheet-shaped carrier in a slurry solution containing iron oxide particles and an adhesive such as colloidal silica, the iron oxide particles are supported on the sheet-shaped carrier in advance via an adhesive, Thereafter, a method of forming the sheet into a honeycomb structure using an adhesive (Japanese Unexamined Patent Publication No.
No. 3,232,847) is known.

As described above, a catalyst in which iron oxide particles are supported on a monolithic carrier is advantageous in that clogging with dust can be prevented. Therefore, in recent years, a monolithic carrier has been used to withstand long-term use. Research and development of catalysts is active. In order for the catalyst to withstand long-term use, it is necessary to improve catalyst performance and strength, and for that purpose, it is strongly required that iron oxide particles be supported in a large amount and firmly on a monolithic carrier.

[0008]

An iron oxide catalyst in which a large amount of iron oxide particles are firmly supported on a ceramic or metal monolithic carrier is the most required at present, but it satisfies these characteristics sufficiently. Things have not yet been obtained.

That is, in the case of the method described above,
Since the supported iron oxide particles are ultrafine particles because they are generated by thermally decomposing an aqueous ferrous salt solution,
When the high-temperature heat treatment is repeated for regeneration, sintering gradually occurs between the ultrafine particles to become large particles, and the specific surface area becomes small, so that the catalyst performance deteriorates. In any of the above and described methods, since the iron oxide particles are supported on a carrier via an adhesive, it is difficult to support a large amount of iron oxide, and the adhesion is not involved in the catalytic performance. Sufficient catalytic performance cannot be obtained due to the presence of the agent.

Accordingly, an object of the present invention is to produce an iron oxide catalyst in which a large amount of iron oxide particles are firmly supported on a ceramic or metal monolith carrier.

[0011]

The above technical objects can be achieved by the present invention as described below. That is, the present invention impregnates a monolithic carrier made of ceramic or metal in an aqueous ferrous salt solution to impregnate the monolithic carrier with an aqueous ferrous salt solution, and then impregnates the aqueous ferrous salt solution. The monolithic carrier is immersed in an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution, and the oxygen-containing gas is aerated to deposit and support the magnetite particles or the ferric oxide-containing particles on the monolithic carrier, or, if necessary, the magnetite particles. Alternatively, the method is a method for producing an iron oxide-based catalyst for treating a gaseous substance, comprising washing a water, drying a monolithic carrier having precipitated and supported hydrous ferric oxide particles thereon, followed by heat treatment in a temperature range of 200 to 700 ° C.

Next, various conditions for implementing the present invention will be described. As a ceramic or metal monolith carrier in the present invention, cordierite, alumina, iron plate or molded using a ceramic material such as mullite,
Stainless steel (Fe-Cr-Al, Fe-Cr-Al
-La) can be used. In addition, in order to carry a large amount of iron oxide particles,
It is preferable that the material constituting the monolithic carrier has many pores or irregularities.

The aqueous ferrous salt solution in the present invention includes:
An aqueous ferrous nitrate solution, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, or the like can be used. The concentration of the aqueous ferrous salt solution is preferably in the range of 0.001 to 2.0M. 0.00
If it is less than 1M, a large amount of magnetite particles or hydrous ferric oxide particles cannot be deposited and supported on the carrier. If it exceeds 2.0 M, the magnetite particles or ferric hydrate particles deposited and supported become agglomerated particles, so that the specific surface area becomes small and the catalyst performance is inferior.

The alkaline aqueous solution in the present invention includes:
An aqueous solution of an alkali hydroxide such as a sodium hydroxide solution or a potassium hydroxide solution, an aqueous solution of sodium carbonate, an aqueous solution of potassium carbonate, or an aqueous solution of an alkali carbonate such as ammonium carbonate, sodium hydrogen carbonate, or potassium hydrogen carbonate can be used.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid, and may be accompanied by stirring by a mechanical operation or the like, if necessary.

In the present invention, the temperature in the liquid when the oxygen-containing gas is passed is 100 ° C. or less. The type of iron oxide deposited and supported on the monolithic carrier varies depending on the temperature in the liquid. At a temperature lower than 50 ° C, hydrous ferric oxide particles precipitate, and at a temperature range of 50 to 100 ° C, magnetite particles precipitate.

In the present invention, the crystal structure of the iron oxide can be changed by heat-treating the monolithic carrier on which magnetite particles or ferric oxide-containing particles are deposited and supported.
When the heating temperature is 200 to 500 ° C., the magnetite particles deposited and supported on the carrier are maghemite (γ-
Fe ₂ O ₃ ), and becomes hematite (α-Fe ₂ O ₃ ) at 500 ° C. or higher. Further, the ferric oxide particles become hematite (α-Fe ₂ O ₃ ) at 200 ° C. or higher.

[0018]

First, the most important point in the present invention is that a ceramic or metal monolith carrier is immersed in a ferrous salt aqueous solution to impregnate the monolith carrier with a ferrous salt aqueous solution.
Next, the monolithic carrier impregnated with the aqueous ferrous salt solution is immersed in an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution, and an oxygen-containing gas is passed through the monolithic carrier, so that the monolithic carrier has magnetite particles or hydrous ferric oxide particles. This is the fact that, when precipitated and supported, it is possible to obtain an iron oxide-based catalyst for gas treatment in which a large amount of iron oxide particles are firmly supported.

In the present invention, the reason why the iron oxide particles can be supported in a large amount and firmly is that the present inventors impregnate the monolithic carrier with the iron raw material in the form of ions, so that it is necessary to use an adhesive. And the monolithic carrier can easily impregnate not only the sharp corners and shades and the surface of the fine part having a complicated shape, but also the pores and irregularities of the material itself that constitutes the monolithic carrier. Ferrous salt can be supported, and magnetite particles and ferric oxide-containing particles are directly supported by ferrite ions supported on the monolithic carrier to directly precipitate and grow. It is considered that the material carried by utilizing is more firmly carried by the anchor effect.

In the present invention, iron oxide particles having different crystal structures can be obtained by heat-treating a monolithic carrier on which magnetite particles or ferric hydroxide particles are supported.

[0021]

Next, the present invention will be described with reference to examples and comparative examples. In the following Examples and Comparative Examples, the adhesion of the iron oxide to the carrier was shown by the value obtained by the following method. The monolith carrier supporting iron oxide was fixed in a graduated cylinder, and subjected to 10,000 vertical vibrations. Thereafter, the monolith carrier was taken out of the measuring cylinder, and the remaining iron oxide was quantitatively analyzed. The value obtained by dividing the weight (Bg) of the iron oxide remaining after the vertical impact vibration by the weight (Ag) of the iron oxide initially supported was expressed in percentage. The larger the value, the better the adhesion. The catalyst performance in later-mentioned use examples 1 to 14 is published in Kodansha Scientific, "Catalyst Experiment Handbook"
The values measured in accordance with the evaluation method described on page 44 are shown. That is, a monolithic carrier is filled in a column and set in a flow-type adsorption capacity evaluation device. Then, after a test gas is passed at a constant flow rate for a predetermined time, the concentration of harmful components at the outlet of the column is measured by a gas chromatography method. The values are shown below.

<Production of Iron Oxide Catalyst> Examples 1 to 7 Comparative Examples 1 to 4 Example 1 A cylindrical shape (diameter 23 mm) made of cordierite material
Monolith carrier (manufactured by Nippon Insulators Co., Ltd.) (φ, cylinder height 50 mm, 400 cells / inch ² ) (hereinafter, referred to as carrier A)
Was degreased by dipping in acetone. The degreased monolithic carrier was immersed in a 1.0 M FeSO ₄ aqueous solution at room temperature for 30 minutes and then taken out into the air to remove the excess FeSO ₄ aqueous solution. Then, at a temperature of 40 ° C., 1-N Na ₂ C
After immersion in 150 ml of an O ₃ solution, air was passed through the Na ₂ CO ₃ solution at a rate of 1 liter per minute for 1 hour to deposit and support yellow-brown goethite particles (α-FeOOH). The monolithic carrier on which the obtained goethite particles were supported was sufficiently washed with water and then dried at 80 ° C. The amount of goethite supported on the monolithic carrier was 2.8% by weight based on the monolithic carrier. The adhesion of the goethite particles to the carrier was 99.9%.

Example 2 A cylindrical monolith carrier (diameter: 23 mm, cylinder height: 50 mm) made of a mixed fiber of silica fiber, aluminosilicate fiber and zirconia fiber (manufactured by Nichias Co., Ltd .: trade name: Honeycle) B) was immersed in acetone to degrease it. The defatted monolithic carrier was replaced with 1.2M F
Goethite particles were deposited and supported on a monolithic carrier in the same manner as in Example 1 except that the monolithic carrier was immersed in an eSO ₄ aqueous solution at room temperature for 30 minutes. The amount of goethite supported on the monolith support was 4.4% by weight based on the monolith support. The adhesion of the goethite particles to the carrier was 99.8%.

Example 3 A monolithic carrier carrying goethite particles was obtained in the same manner as in Example 1 except that the concentration of the aqueous FeSO ₄ solution was 1.5 M. This was heated in air at 600 ° C. for 2 hours to obtain a monolithic carrier carrying hematite particles. The amount of hematite particles supported on the monolithic carrier was 3.7% by weight based on the monolithic carrier. Also,
The adhesion of the hematite particles to the carrier was 99.6%.

Example 4 A monolithic carrier carrying hematite particles was obtained in the same manner as in Example 3 except that the carrier B was used and the concentration of the aqueous FeSO ₄ solution was 0.2 M. The amount of hematite particles supported on the monolithic carrier was 0.6% by weight based on the monolithic carrier. The adhesion of the hematite particles to the carrier was 99.8%.

Example 5 A monolithic carrier carrying magnetite particles was obtained in the same manner as in Example 1, except that the concentration of the aqueous FeSO ₄ solution was 0.8 M and the reaction temperature in the alkaline solution was 90 ° C. The amount of magnetite particles supported on the monolithic carrier was 2.3% by weight based on the monolithic carrier. The adhesion of the magnetite particles to the carrier was 99.4%.

Example 6 A monolithic carrier carrying magnetite particles was obtained in the same manner as in Example 5 except that the carrier B was used and the concentration of the aqueous FeSO ₄ solution was 0.1 M. The amount of the magnetite particles supported on the monolithic carrier was 0.1 to the monolithic carrier.
3 wt%. The adhesion of the magnetite particles to the carrier was 99.6%.

Example 7 Stainless steel (75 wt% Fe-20 wt% Cr-
Al (5 wt% -La) and a cylindrical shape (diameter 25)
mmφ, 50 mm cylinder height (hereinafter referred to as “carrier C”)
And ) In a 1.2 M aqueous FeSO ₄ solution at room temperature.
After being immersed for 0 minutes, it was taken out into the air and excess FeSO ₄ aqueous solution was removed. Next, it is immersed in a 1.0 M Na ₂ CO ₃ solution, and air is passed through at a temperature of 40 ° C. for 3 hours to deposit and support yellow-brown goethite particles, and then washed and dried to carry the goethite particles. A honeycomb catalyst was obtained.
The amount of goethite supported on the honeycomb carrier was 1.2% by weight based on the monolith carrier. The adhesion of the goethite particles to the carrier was 99.0%.

COMPARATIVE EXAMPLE 1 1.0 M F was added to 1 liter of a 3.50 M Na ₂ CO ₃ aqueous solution.
3 l of an eSO ₄ aqueous solution was added and mixed to obtain FeCO ₃ at a temperature of 40 ° C. Oxidation reaction was performed by passing 10 l / min of air through the mixture for 3 hours to produce yellow-brown precipitate particles. The generated particles are separated by filtration at normal temperature, washed with water,
Drying gave goethite particles. Water was added to the obtained goethite particles and stirred with a homomixer to obtain a 1% by weight slurry liquid. NaOH was added to this slurry to adjust the pH to 1
1 and the carrier A in the slurry liquid at a temperature of 60 ° C.
Was immersed. After cooling to room temperature with pH 5, washing with water,
After drying, a monolithic carrier carrying goethite particles was obtained. The amount of goethite particles supported on the monolithic carrier was 0.5% by weight. The adhesion of the goethite particles to the carrier was 96.7%.

Comparative Example 2 An aqueous solution of ferrous sulfate containing 1.5 mol / l of Fe ²⁺ 20
1 is obtained from 3.45- previously prepared in the reactor.
N 2 aqueous solution of NaOH (1: 1 with ^respect to Fe ²⁺ ).
This corresponds to 15 equivalents. ) PH 12.8, Fe (OH) ₂
An aqueous solution containing was produced. 100 liters of air per minute was passed through the aqueous solution containing Fe (OH) ₂ at a temperature of 90 ° C. for 220 minutes to produce magnetite particles. The resulting particles were separated by filtration, washed with water, and dried by a conventional method to obtain magnetite particle powder. The obtained magnetite particle powder was heated at 450 ° C. in the air to obtain hematite particles. Water was added to the hematite particles, and the mixture was stirred with a homomixer to obtain a slurry containing 1% by weight of hematite particles. A monolithic carrier carrying hematite particles was obtained in the same manner as in Comparative Example 1. The amount of hematite particles supported on the monolithic carrier was 0.3% by weight. Further, the adhesion of the hematite particles to the carrier was 96.0%.

Comparative Example 3 Using the magnetite particle powder obtained in the same manner as in Comparative Example 2, a slurry containing 1% by weight of magnetite particles was obtained. Except that the final pH was 7, a monolithic carrier carrying magnetite particles was obtained in the same manner as in Comparative Example 1. The magnetite particles supported on the monolithic carrier were 0.3% by weight. The adhesion of the magnetite particles to the carrier was 95.8%.

Comparative Example 4 A honeycomb carrier supporting goethite particles was obtained in the same manner as in Comparative Example 1 except that the carrier C was used. The amount of goethite particles supported on the honeycomb carrier was 0.2% by weight. The adhesion of the goethite particles to the carrier is 95.1.
%Met.

<Use of Iron Oxide Catalyst> Use Examples 1 to 14; Use Example 1 Five monolith carriers obtained in Example 1 were connected in a column and packed to prepare a sample column. It was set in an adsorption capacity evaluation device. Next, a test gas containing 10 ppm of hydrogen sulfide (humidity: 10%) was passed through the test column at a flow rate of 0.5 l / min. The hydrogen sulfide-containing concentration at the outlet of the column 120 minutes after the aeration was 0.42 ppm.

Use Examples 2 to 5 Tests were conducted in the same manner as in Use Example 1 except that the type of catalyst was changed. Table 1 shows the results.

Use Example 6 A test was conducted in the same manner as in Use Example 1 except that the test gas was changed to 10 ppm of trimethylamine. The concentration of trimethylamine at the outlet of the column was 1.3 ppm.

Use Examples 7 and 8 The test was carried out in the same manner as in Use Example 6 except that the type of the catalyst was changed. Table 1 shows the results.

Use Example 9 Five monolith carriers obtained in Example 3 were connected and set in a reaction tube. To this, a test gas containing 1000 ppm of H ₂ S gas was passed at 500 ° C. and 3 atm at a flow rate of 1 Nl / min. The H ₂ S adsorption breakthrough, that is, the amount of H ₂ S gas at the outlet of the reaction tube gradually increases from the minimum value and the initial H ₂ S
The time required to reach 50% of the ₂ S gas amount is 203
It was time.

Use Examples 10 to 11 Tests were carried out in the same manner as in Use Example 9 except that the type of monolith carrier and the number of monolith carriers were changed. Table 1 shows the results.

Use Example 12 Five monolith carriers obtained in Example 5 were connected in a column, packed, placed, and heated to 800 ° C. 5000 ppm of carbon monoxide was passed from one end of the column at 1 Nl / min. The concentration of carbon monoxide at the column outlet at 10 minutes after aeration was 1.2 ppm.

Use Examples 13 and 14 A test was conducted in the same manner as in Use Example 12 except that the type of the catalyst was changed. Table 1 shows the results.

[0041]

[Table 1]

[0042]

According to the method for producing an iron oxide-based catalyst for treating a gas body according to the present invention, as shown in the preceding embodiment, a large amount of iron oxide particles are firmly and firmly applied to a ceramic or metal monolith carrier. It has excellent catalytic performance and great strength, and is therefore suitable as an iron oxide-based catalyst for treating a gaseous substance.

Continuation of the front page (56) References JP-A-52-143989 (JP, A) JP-A-64-58348 (JP, A) JP-B-47-46267 (JP, B1) JP-B-42-20479 (JP, A) , B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36

Claims (2)

(57) [Claims] 1. A monolith carrier made of ceramic or metal is immersed in an aqueous ferrous salt solution to impregnate the monolithic carrier with an aqueous ferrous salt solution, and then impregnated with the aqueous ferrous salt solution. Gas treatment iron characterized by depositing and supporting magnetite particles or hydrous ferric oxide particles on the monolithic carrier by immersing the carrier in an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution and passing an oxygen-containing gas through the monolithic carrier. A method for producing an oxide-based catalyst. 2. A gaseous body characterized in that the monolithic carrier on which the magnetite particles or the ferric hydroxide-containing particles according to claim 1 are deposited and supported is washed with water, dried, and then heat-treated at a temperature in the range of 200 to 700 ° C. Production method of iron oxide catalyst for treatment.