JP4625952B2 - Method for producing oxidation catalyst - Google Patents

Description

  The present invention relates to a method for producing an oxidation catalyst, and more particularly to a method for producing an oxidation catalyst using waste as a raw material. The oxidation catalyst according to the present invention is, for example, an exhaust gas purifying catalyst capable of efficiently purifying hydrocarbons (HC) in exhaust gas discharged from various combustion apparatuses such as internal combustion engines such as automobiles and motorcycles and boilers, It can be suitably used as a reaction promoting catalyst that promotes the production reaction of chemical substances such as chemicals.

  The exhaust gas emitted from motorcycles and automobile engines contains carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and sulfur oxides (SOx). The problem of environmental pollution is getting worse, especially in urban areas.

  In recent years, new standards have been announced based on the Air Pollution Control Law, with the goal of greatly reducing hydrocarbons and nitrogen oxides. According to this, for example, motorcycles, which are cheaper and easier to use than four-wheeled vehicles, are widely used as a means of transportation, and have a high contribution to emissions in the entire vehicle. is there. Specifically, motorcycles sold after 2006-2007 are compared to current values, with 75-85% reduction for hydrocarbons, 50% reduction for nitrogen oxides, and carbon monoxide. Requires a strict target value of 85% reduction.

  Under such circumstances, various studies have been made on using a catalyst for a four-wheeled vehicle for a two-wheeled vehicle, but it is expensive to use a catalyst for a four-wheeled vehicle using an expensive noble metal such as platinum as a catalyst component. strong. For this reason, development of a cheaper exhaust gas purification catalyst for motorcycles is eagerly desired.

  Here, an active oxygen-expressing substance made of an inorganic compound is known as one that is cheaper than a noble metal catalyst and can be used as an oxidation catalyst (see, for example, Patent Document 1).

This active oxygen-expressing substance is a 12CaO · 7Al ₂ O ₃ compound containing active oxygen species, and a raw material powder in which calcium and aluminum are mixed at an atomic equivalent ratio of 12:14 is used to generate an oxygen partial pressure of 10 ⁴ Pa. Above, preferably produced by a solid phase reaction in a dry oxidation atmosphere strictly controlled to 10 ⁵ Pa or higher and a hydrogen partial pressure of 1 Pa or lower under a high temperature condition of a firing temperature of 1200 ° C. or higher, preferably 1300 ° C. The

  Although various research examples have been reported for such active oxygen-expressing substances, there has been a strong demand for the development of new active oxygen-expressing substances with higher practical value.

Therefore, as a result of intensive studies aimed at developing a novel active oxygen-expressing substance, the present inventors have found that A ₂ B ₂ O containing superoxide anion (O ₂ ⁻ ), which is active oxygen, included in the structure. ₅ An inorganic compound having the composition formula (A: alkali or alkaline earth element, B: transition element) has been found to be useful as an oxidation catalyst with high active oxygen expression ability, and further research has been conducted. (Japanese Patent Application No. 2004-119882).

Specific examples of the active oxygen-expressing substance include calcium ferrite having a composition formula of Ca ₂ Fe ₂ O ₅ , which is a mixture of CaCO ₃ and Fe ₂ O _{3 in} a molar ratio of 2: 1. It is manufactured by heating the raw material powder to 600 ° C. or higher in an oxygen atmosphere.
Japanese Patent Laid-Open No. 2002-3218

However, calcium ferrite having the above-described composition formula of Ca ₂ Fe ₂ O ₅ exhibits high catalytic activity and can be expected to be used as an oxidation catalyst. However, a specific composition formula of Ca ₂ Fe ₂ O ₅ is used. There is a problem that it is actually difficult to manufacture with the aim.

That is, theoretically, if the raw material powder in which CaCO ₃ and Fe ₂ O ₃ are mixed at a molar ratio of 2: 1 as described above is heated to 600 ° C. or higher in an oxygen atmosphere, the composition of Ca ₂ Fe ₂ O ₅ A calcium ferrite having the formula can be produced. However, in reality, it is difficult to obtain a compound having a desired composition and a uniform crystal phase on a commercial basis for reasons of equilibrium and kinetics.

  By the way, in recent years, from the viewpoint of building an environment-conserving society, the need to recycle and properly process industrial waste is increasing.

For example, in the lime mining industry, lime is mined from a mine to obtain lime products such as limestone (calcium carbonate, CaCO ₃ ), quick lime (calcium oxide, CaO) and slaked lime (calcium hydroxide, Ca (OH) ₂ ). However, lime sludge and lime residue are discharged in large quantities as industrial waste. These wastes have no utility value, and most of them are thrown away at mining sites and disposal sites.

  For this reason, lime manufacturers have endeavored to recycle waste such as lime sludge, but effective recycling of lime sludge and the like has not yet been realized.

  This invention is made | formed in view of the said situation, and makes it the technical subject which should be solved to obtain the oxidation catalyst which shows high catalyst activity cheaply and easily, aiming at the recycle of industrial waste.

Production process of the oxidation catalyst of the present invention for solving the above-mentioned problems, calcia source and including Mutotomoni mixing molar ratio in at least a portion of at least one waste including at least one of the ferrite source are 0.33 ≦ Ca / A raw material preparation step of preparing a raw material with Fe ≦ 3.0, and a composition formula of Ca ₂ Fe ₂ O _{5 in which} the raw material is heated to 600 to 1449 ° C. in an oxygen atmosphere and active oxygen is included in the structure. And a calcining step for obtaining an oxidation catalyst containing at least one of calcium ferrite having a composition formula of CaFe ₂ O ₄ encapsulating calcium ferrite and active oxygen contained in the structure .

In a preferred embodiment of the method for producing an oxidation catalyst of the present invention, the raw material is lime sludge, lime residue, shell, fly ash, coal ash, slag, concrete waste, cement sludge, sewage sludge incinerated ash, paper sludge, magnetic material A product made from the manufacturing process of a product using the magnetic material, ferrite sludge discharged from the manufacturing process of the product using the magnetic material, inorganic waste liquid ferrite treatment residue, iron polishing scrap, iron oxide cake, iron oxide waste containing iron oxide and red mud Including at least one kind of waste selected from
In a preferred embodiment, the oxidation catalyst obtained by the method for producing an oxidation catalyst of the present invention is an oxidation catalyst for exhaust gas purification.

  The method for producing an oxidation catalyst of the present invention includes a raw material preparation step and a firing step.

In the raw material preparation step, a raw material calcia source and at least one waste-containing Mutotomoni mixing molar ratio in at least a portion including at least one of the ferrite source are 0.33 ≦ Ca / Fe ≦ 3.0 Prepare. That is, the raw material prepared in this raw material preparation step may be composed of only one type of waste, may be composed of a plurality of types of waste, or may be composed of one or more types of waste. In addition, commercially available industrial raw materials may be included.

  Moreover, the waste contained in the raw material contains at least one of a calcia source and a ferrite source. That is, the waste contained in this raw material may contain only the calcia source of the calcia source and the ferrite source, or may contain only the ferrite source of the calcia source and the ferrite source. Alternatively, it may include both a calcia source and a ferrite source.

  The calcia source is not particularly limited, and is selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate, calcium nitrate and hydrate thereof, and calcium acetate and hydrate thereof. It can be 1 type or multiple types. The ferrite source is not particularly limited, and is selected from the group consisting of iron oxide, iron hydroxide, iron carbonate, iron nitrate and its hydrate, and iron acetate and its hydrate. It can be set as 1 type or multiple types.

  Here, the raw materials include, for example, lime sludge, lime residue, shells, fly ash, coal ash, slag, concrete scrap, cement sludge, sewage sludge incineration ash, paper sludge, products using magnetic materials, and magnetic materials. At least one kind of waste selected from the group consisting of ferrite sludge discharged from the manufacturing process of used products, inorganic waste liquid ferrite treatment residue, iron polishing litter, iron oxide cake, iron oxide waste containing iron oxide and red mud It is preferable that it is included. Of these wastes, lime sludge, lime residue, shells, fly ash, coal ash, slag, concrete waste, cement sludge, sewage sludge incineration ash, paper sludge and red mud are all of calcia and ferrite sources. Waste containing at least calcia sources. Also, among these wastes, lime sludge, lime residue, fly ash, coal ash, slag (steel slag including ferrite source among slag), products using magnetic materials, and manufacturing processes of products using the magnetic materials Ferrite sludge, inorganic waste liquid ferrite treatment residue, iron polishing waste, iron oxide cake, iron oxide waste containing iron oxide and red mud are all discarded including at least ferrite source of calcia source and ferrite source It is a thing. And among these wastes, lime sludge, lime residue, fly ash, coal ash, steel slag including ferrite sources and red mud are both wastes containing both calcia sources and ferrite sources, and as the raw material It can be particularly preferably used.

Lime sludge or lime residue is waste material discharged in the lime mining industry during lime mining and product manufacturing processes. As shown in Table 1 below as an example of the composition of limestone flush sludge (sludge discharged when separating limestone (CaCO ₃ ) from limestone) as lime sludge, lime sludge or lime residue is used as a source of calcia. It contains CaO as a main component and Fe ₂ O ₃ as a ferrite source. For this reason, lime sludge or lime residue, for example, is used alone as the raw material, or mixed with other waste containing ferrite sources or industrial raw materials containing ferrite sources (if necessary, other calcia source-containing waste It is of course possible to mix industrial materials including products or calcia sources).

Seashells are wastes discharged in the process of cleaning plant piping in the electric power and chemical industries and in the process of food processing and cooking in the food processing industry. The shell contains CaCO ₃ as a source of calcia. For this reason, a shell can be made into the said raw material by mixing with the industrial raw material containing the other waste material or ferrite source containing a ferrite source, for example.

Fly ash is a spherical fine coal ash contained in exhaust gas when pulverized coal is burned in a thermal power plant or the like. As shown in the following Table 2 as an example of the composition of fly ash discharged from the pulverized coal combustion boiler, the fly ash includes CaO as a calcia source and Fe ₂ O ₃ as a ferrite source. For this reason, for example, fly ash is used alone as the raw material, mixed with other calcia source-containing waste or industrial raw material containing calcia source, or used as the raw material, or other waste or ferrite source containing a ferrite source. Or mixed with industrial raw materials containing other calcia sources or industrial raw materials containing calcia sources and other waste containing ferrite sources or industrial raw materials containing ferrite sources It can be done.

Coal ash is waste contained in exhaust gas when coal is burned at a thermal power plant or the like. As shown in the following Table 3 as an example of the composition of coal ash discharged from the thermal power plant, the coal ash includes CaO as a calcia source and Fe ₂ O ₃ as a ferrite source. For this reason, for example, coal ash is used alone as the raw material, mixed with other calcia source-containing wastes or industrial raw materials containing calcia sources, and used as the raw materials, or other waste or ferrite sources including ferrite sources. Or mixed with industrial raw materials containing other calcia sources or industrial raw materials containing calcia sources and other waste containing ferrite sources or industrial raw materials containing ferrite sources It can be done.

Slag, also called calami, sludge, or slag, is a non-metallic unnecessary substance that separates in the process of smelting metal ore and floats on the molten metal. In the slag, for example, in the iron and steel industry, in addition to blast furnace slag discharged from blast furnaces that produce crude steel (pig iron) from raw iron ore and converter slag discharged from converters that make steel from crude steel, There is the Karami iron concentrate discharged. These slags include those containing a calcia source such as CaO and CaCO ₃ and a ferrite source such as Fe ₂ O ₃ and FeO, and those containing only a calcia source among the calcia source and the ferrite source. For example, as shown in Table 4 below, an example of the composition of blast furnace slag discharged from a blast furnace that produces crude steel from iron ore, this blast furnace slag contains only CaO as a calcia source of a calcia source and a ferrite source. Moreover, as shown in the following Table 5 as an example of the composition of the calami iron concentrate (iron slag containing ferrite source) discharged from the copper smelting process, this calami iron concentrate contains FeO as a ferrite source as a main component. In addition, it contains a small amount of CaO as a calcia source. For this reason, for example, slag is used alone as the raw material, mixed with other calcia source-containing waste or industrial raw material containing calcia source, or used as the raw material, or other waste or ferrite source containing ferrite source. Mixed with industrial raw materials containing the above raw materials, or mixed with other raw materials containing calcia sources or industrial raw materials containing calcia sources and industrial waste containing ferrite sources or industrial raw materials containing ferrite sources Can be.

  Concrete slag is waste discharged in the construction process in the construction and civil engineering industries. Concrete debris contains an oxide containing calcium as a calcia source and hydrates thereof. For this reason, concrete rags can be made into the said raw material by mixing with the industrial raw material containing the other waste or ferrite source containing a ferrite source, for example.

Cement sludge is waste discharged in the construction and civil engineering industries during the use and transportation of cement. The cement sludge contains an oxide containing calcium as a calcia source and its hydrate CaCO ₃ . For this reason, cement sludge can be made into the said raw material by mixing with the industrial raw material containing the other waste or ferrite source containing a ferrite source, for example.

  Sewage sludge incineration ash is waste discharged in the sewage treatment process, and includes oxides containing calcium as calcium source and hydrates thereof. For this reason, sewage sludge incineration ash can be made into the said raw material by mixing with the industrial raw material containing the other waste material or ferrite source containing a ferrite source, for example.

  Papermaking sludge is waste discharged in the papermaking wastewater treatment process in the papermaking industry. Papermaking sludge contains an oxide containing calcium as a calcia source and hydrates thereof. For this reason, papermaking sludge can be made into the said raw material by mixing with the industrial raw material containing the other waste or ferrite source containing a ferrite source, for example.

  The product using the magnetic material is not particularly limited, and examples thereof include ferrite magnets, magnetic tapes such as video tapes and recording tapes, magnetic disks such as floppy disks, magnetic cards, ferrite cores, magnetic sensors and magnetic switches. Can do.

  Ferrite sludge discharged from the manufacturing process of products using magnetic materials is generated when manufacturing products using magnetic materials such as ferrite magnets, magnetic tapes, magnetic disks, magnetic cards and ferrite cores. Waste, wastewater containing ferrite as raw material and sludge dehydrated from it.

  The inorganic waste liquid ferrite treatment residue is a large amount of ferrite compound generated in a heavy metal fixing treatment process of waste water in which a large amount of ferrite is administered to an inorganic waste liquid containing heavy metal to solidify the heavy metal as a ferrite compound.

  The iron scrap is a so-called grinding scrap generated when grinding and polishing in the iron product processing industry.

  The iron oxide cake is a cake (solidified material) containing iron oxide oxidized by iron, which is generated by washing and grinding waste generated during grinding and polishing in the iron product processing industry.

  Steelmaking waste containing iron oxide is a general term for ironmaking waste containing iron oxide such as electric furnace dust, sludge, and mill scale, wastewater containing iron oxide discharged from the grinding and grinding processes in the steel industry, and its solidified product. is there.

Red mud is waste that is discharged from the aluminum manufacturing process. As shown in Table 6 below, an example of the composition of red mud discharged after bauxite is treated with sodium hydroxide and alumina is extracted, this red mud contains Fe ₂ O ₃ as a main component as a ferrite source. In addition, CaO as a source of calcia is included. Therefore, for example, red mud is used alone as the raw material, mixed with other calcia source-containing waste or industrial raw material containing a calcia source, or used as another raw material or ferrite source containing a ferrite source. Or mixed with industrial raw materials containing other calcia sources or industrial raw materials containing calcia sources and other waste containing ferrite sources or industrial raw materials containing ferrite sources It can be done.

  Here, as will be described later, the oxidation catalyst obtained in the firing step according to the value of the mixing molar ratio Ca / Fe of the calcia source and the ferrite source in the raw material prepared in the raw material preparation step and the heating temperature in the firing step The type of the catalyst changes, and the catalytic activity changes.

From the viewpoint of obtaining an oxidation catalyst having high catalytic activity in the firing step, the upper limit of the mixing molar ratio Ca / Fe is set to 3.0 . The upper limit of the mixing molar ratio is more preferably 2.0, and particularly preferably 1.0. From the same viewpoint, the lower limit of the mixing molar ratio is 0.33 . As described later, when the value of the mixed molar ratio Ca / Fe exceeds 1 and the heating temperature in the firing step is 600 to 1438 ° C., calcium having a composition formula of CaO powder and Ca ₂ Fe ₂ O ₅ An oxidation catalyst comprising a mixed powder with ferrite powder can be obtained, but when the value of the mixed molar ratio Ca / Fe exceeds 3.0, the composition formula of CaO powder and Ca ₂ Fe ₂ O ₅ is obtained. The ratio of the CaO powder in the mixed powder with the calcium ferrite powder becomes too large, and the catalytic activity decreases. On the other hand, as will be described later, when the value of the mixed molar ratio Ca / Fe is less than 0.5 and the heating temperature in the firing step is 600 to 1155 ° C., the calcium ferrite having the composition formula of CaFe ₂ O ₄ An oxidation catalyst comprising a mixed powder of powder and Fe ₂ O ₃ (hematite) powder can be obtained. When the value of the mixing molar ratio Ca / Fe at this time is less than 0.33, the composition of CaFe ₂ O ₄ The ratio of Fe ₂ O ₃ (hematite) in the mixed powder of calcium ferrite powder having the formula and Fe ₂ O ₃ (hematite) powder becomes too large, and the catalytic activity is lowered.

  As described above, the waste used for the raw material contains various unnecessary components other than the calcia source and the ferrite source. These unnecessary components exist independently from the calcium ferrite powder after the firing step, or are partially incorporated into the calcium ferrite, but do not adversely affect the catalytic function of the calcium ferrite. Don't be.

Wherein In the baking step, is heated to 600-1,449 ° C. the material in an oxygen atmosphere to containing calcium ferrite and active oxygen having a composition formula of Ca ₂ Fe ₂ O ₅ containing therein the active oxygen in the structure in its structure An oxidation catalyst containing at least one of calcium ferrites having a composition formula of CaFe ₂ O ₄ is obtained.

  If the heating temperature in this firing step is less than 600 ° C., the oxidation catalyst function of the obtained calcium ferrite may be insufficient. The lower limit of the heating temperature in the firing step is preferably 800 ° C.

  The oxygen concentration in the oxygen atmosphere is not particularly limited, but is preferably as high as possible, preferably 5% or more, and more preferably 10% or more. The heating time is preferably 1 hour or longer, more preferably 2 hours or longer. The upper limit of the heating time can be about 5 hours. In addition, although it is desirable to cool slowly in a furnace after a heating, you may quench rapidly outside a furnace after completion | finish of a heating.

  And in this baking process, according to the mixing molar ratio Ca / Fe in the raw material prepared at the raw material preparation process, the heating temperature is appropriately adjusted within the range of 600 to 1449 ° C., whereby the Ca—Fe— of FIG. As shown in the O-based phase equilibrium diagram, predetermined products can be obtained depending on the mixing molar ratio and the heating temperature.

The horizontal axis in FIG. 3 represents the weight ratio of CaO and Fe ₂ O ₃ in percentage. Further, in the horizontal axis of FIG. 3, white circles in the vicinity of the value of 58 are when the mixing molar ratio is Ca / Fe = 1, and at this time, Ca ₂ Fe ₂ O ₅ is obtained in a single phase, A white circle in the vicinity of the value of 74 is when the mixing molar ratio is Ca / Fe = 0.5. At this time, CaFe ₂ O ₄ is obtained in a single phase, and the vicinity of the value of 85 is obtained. The white circles in the graph are when the mixing molar ratio is Ca / Fe = 0.25, and at this time, CaFe ₄ O ₇ is obtained in a single phase.

That is, when the mixed molar ratio Ca / Fe is 1.0 <Ca / Fe, when heated at a heating temperature of 600 to 1438 ° C., calcium ferrite having a composition formula of CaO powder and Ca ₂ Fe ₂ O ₅ A powder can be theoretically obtained. In addition, when the mixing molar ratio is Ca / Fe = 1, when heated at a heating temperature of 600 to 1449 ° C., calcium ferrite powder having the composition formula of Ca ₂ Fe ₂ O ₅ is theoretically obtained. Can do. Further, when the mixing molar ratio is 0.5 <Ca / Fe <1, when heated at a heating temperature of 600 to 1216 ° C., the calcium ferrite powder having the composition formula of Ca ₂ Fe ₂ O ₅ and CaFe ₂ A calcium ferrite powder having the composition formula of O ₄ can be theoretically obtained. In addition, when the mixed molar ratio is Ca / Fe = 0.5, when heated at a heating temperature of 600 to 1216 ° C., calcium ferrite powder having a composition formula of CaFe ₂ O ₄ is theoretically obtained. be able to. Further, when the mixing molar ratio is 0.25 ≦ Ca / Fe <0.5, when heated at a heating temperature of 1155 to 1205 ° C., calcium ferrite powder having a composition formula of CaFe ₂ O ₄ , and CaFe A calcium ferrite powder having a composition formula of ₄ O ₇ can be theoretically obtained. Further, when the mixing molar ratio is 0 <Ca / Fe <0.5, when calcined at a heating temperature of 600 to 1155 ° C., calcium ferrite powder having a composition formula of CaFe ₂ O ₄ and Fe ₂ O ₃ (hematite) powder can be obtained theoretically. When the mixing molar ratio is 0 <Ca / Fe <0.25, when calcined at a heating temperature of 1155 to 1226 ° C., calcium ferrite powder having a composition formula of Ca ₂ Fe ₂ O ₅ and Fe ₂ O ₃ (hematite) powder can be theoretically obtained.

The CaO powder obtained when heated at a heating temperature of 1438 ° C. or lower when the mixed molar ratio Ca / Fe is 1.0 ≦ Ca / Fe is such that CaO in the raw material remains as it is. Similarly, when the mixing molar ratio is 0 <Ca / Fe <0.5, the baking is performed at a heating temperature of 600 to 1155 ° C., and the mixing molar ratio is 0 <Ca / Fe <0.25. Fe ₂ O ₃ (hematite) powder obtained when firing at a heating temperature of from 1155 to 1,226 ° C. when even one in which Fe ₂ O ₃ in the raw materials remained unchanged. On the other hand, if the upper limit of the heating temperature is out of the above range, a liquid phase is formed, and the oxidation catalyst function of the obtained powder becomes insufficient.

  Further, even if the heating temperature in the firing step is too high within the above-described predetermined range, there is no merit due to it. For this reason, it is preferable that the upper limit of the heating temperature in a baking process shall be 1200 degreeC, and it is more preferable to set it as 1000 degreeC.

Thus, in the firing step, theoretically, except when the mixing molar ratio is Ca / Fe = 0.25 (theoretically, when Ca / Fe = 0.25, CaFe ₄ O ₇ Calcium ferrite having the composition formula of Ca ₂ Fe ₂ O ₅ is obtained, and neither calcium ferrite having the composition formula of Ca ₂ Fe ₂ O ₅ nor calcium ferrite having the composition formula of CaFe ₂ O ₄ is obtained. An oxidation catalyst containing at least one of calcium ferrite having the composition formula and calcium ferrite having the composition formula of CaFe ₂ O ₄ can be obtained.

Calcium ferrite having the composition formula of Ca ₂ Fe ₂ O ₅ or calcium ferrite having the composition formula of CaFe ₂ O ₄ obtained in this firing step exhibits high catalytic activity and exhibits a large oxidation catalyst function. The mechanism by which calcium ferrite having the composition formula of Ca ₂ Fe ₂ O ₅ or the composition formula of CaFe ₂ O ₄ exhibits high catalytic activity is not necessarily clear, but can be considered as follows. That is, in Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ , oxygen in the structure becomes unstable when a force such as compression or tension is applied in a temperature range of about 200 ° C. or higher, and this becomes active oxygen. Active oxygen such as oxide anion (O ₂ ⁻ ) is included in the structure. When the active oxygen encapsulated in Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ is released to the outside in this way, it exhibits high catalytic activity and exhibits a large oxidation catalyst function. Oxygen from the outside is taken into the structure in Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ from which active oxygen has been released. And again, oxygen in the structure of Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ becomes unstable and is released to the outside as active oxygen. Thus, Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ releases the active oxygen that has become unstable in the structure to the outside, takes oxygen into the structure from the outside, and again returns to the outside as active oxygen. It is considered that a large oxidation catalyst function is exhibited by repeating the release.

In addition, calcium ferrite having a composition formula of CaFe ₄ O ₇ obtained in the firing step also shows high catalytic activity by the same mechanism as calcium ferrite having a composition formula of Ca ₂ Fe ₂ O ₅ or CaFe ₂ O ₄ , It is thought to exert a large oxidation catalyst function.

Furthermore, CaO and Fe ₂ O ₃ obtained in the firing step exhibit an oxidation catalyst function by a mechanism different from that of the calcium ferrite described above.

CaO powder obtained by the production method of the present invention, calcium ferrite powder having a composition formula of Ca ₂ Fe ₂ O ₅ , calcium ferrite powder having a composition formula of CaFe ₂ O ₄ , calcium ferrite having a composition formula of CaFe ₄ O ₇ Of the powder and Fe ₂ O ₃ (hematite) powder, calcium ferrite powder having the composition formula of Ca ₂ Fe ₂ O ₅ exhibits the highest catalytic activity, and calcium ferrite powder having the composition formula of CaFe ₂ O ₄ Next, it shows high catalytic activity. For this reason, it is preferable to employ a mixing molar ratio and a heating temperature so that a calcium ferrite powder having a composition formula of at least Ca ₂ Fe ₂ O ₅ can be obtained.

According to the manufacturing method of the oxidation catalyst of the present invention, the raw material preparation step, calcia source and including Mutotomoni mixing molar ratio in at least a portion of at least one waste including at least one of the ferrite source 0 Active oxygen that exhibits high oxidation catalytic activity by a very simple method of preparing a raw material satisfying .33 ≦ Ca / Fe ≦ 3.0 and heating the raw material in an oxygen atmosphere within a range of 600 to 1449 ° C. obtaining an oxidation catalyst containing at least one of calcium ferrite having a compositional formula of CaFe ₂ O ₄ containing therein a calcium ferrite and active oxygen in the structure having the composition formula of Ca ₂ Fe ₂ O ₅ containing therein the structure be able to. In addition, each of the other powders obtained at this time also exhibits an oxidation catalyst function. For this reason, according to the production method of the present invention, waste is used and high catalytic activity is exhibited by using industrial raw materials including a calcia source and / or a ferrite source that are cheaper than noble metals as required. An oxidation catalyst can be obtained very inexpensively. Moreover, it is not necessary to adjust the mixing molar ratio aiming at a specific point in the raw material adjusting step. Therefore, according to the production method of the present invention, it is possible to easily and inexpensively obtain an oxidation catalyst exhibiting high catalytic activity.

  In addition, it is possible to recycle industrial waste containing a calcia source and / or a ferrite source.

  The usage form of the oxidation catalyst obtained by the production method of the present invention is not particularly limited. For example, the powder obtained in the firing step can be used as an oxidation catalyst as it is, a molded body obtained by molding the powder into a predetermined shape can be used as an oxidation catalyst, or the powder can be supported on a carrier and used. it can.

  The shape of the molded body is arbitrarily determined according to the purpose of use, and examples thereof include granules, flat plates, columns, cylindrical tubes, hollow fibers, monoliths, and honeycombs. Further, at the time of molding, it is required to have a compact or porous structure along with the shape, and these can be arbitrarily designed according to the purpose of use. As a forming method, a normal method used in the production of a ceramic molded body can be used. For example, casting molding, pressure molding, dry CIP molding, injection molding, sheet molding and the like can be used.

  Therefore, the oxidation catalyst obtained by the method for producing an oxidation catalyst of the present invention can be suitably used, for example, as an exhaust gas purification catalyst, particularly an exhaust gas purification catalyst for motorcycles, and from various combustion devices such as boilers. The present invention can also be suitably used as a catalyst for promoting the reaction that promotes the production reaction of chemical substances such as exhaust gas purification catalysts and chemicals that are discharged.

In addition, calcium ferrite having a composition formula such as Ca ₂ Fe ₂ O ₅ obtained in the firing step and lime such as CaO and Ca (OH) ₂ as unreacted substances are acidic in addition to the oxidation catalyst function described above. It also has a gas absorption function. That is, these calcium ferrites and limes have an acid gas absorption function capable of removing and recovering acid gases such as hydrogen chloride (HCl) in gas discharged from municipal waste incineration plants by a neutralization reaction. Therefore, for example, when oxidative decomposition of a halogen-containing organic compound containing halogen such as F, Cl and Br (for example, chlorobenzene and chlorophenol), the halogen compound (acid gas) contained in the decomposition product is The oxidation catalyst obtained by the production method of the present invention can be effectively absorbed. In addition, the oxidation catalyst obtained by the production method of the present invention has, for example, an oxidation catalyst function that completely burns soot and hydrocarbons not burned in the furnace by oxidation by being blown into a furnace of a municipal waste incineration plant. Since it can exhibit the acid gas absorption function that can remove and recover the acid gas in the exhaust gas, it is also possible to suppress the production of dioxins, etc., and it is extremely effective as an exhaust gas purifier for municipal waste incineration plants can do.

  Examples of the present invention will be specifically described below.

<Raw material preparation process>
As a kind of industrial waste, lime sludge having a composition (oxide equivalent value) shown in Table 7 below was prepared as a calcia source-containing waste.

The lime sludge includes 41.5Wt% as a main component CaO as calcia source, and those containing Fe ₂ O ₃ as a ferrite source 1.6 wt%. The stoichiometric ratio of CaO to Fe ₂ O ₃ in this lime sludge is overwhelmingly higher than that of Fe ₂ O ₃ . For this reason, in this example, a commercial raw material (Fe ₂ O ₃ ) was added in a predetermined amount to the lime sludge so as to supplement the shortage of the ferrite source to prepare a mixed raw material.

  At this time, the mixing molar ratio of the calcia source and the ferrite source in this mixed raw material is shown in Table 8 below. 1 and 2 were mixed raw materials.

<Baking process>
Next, the mixed raw material was put in an electric furnace, heated from room temperature to 1000 ° C. in an air atmosphere in about 1 hour, held at that temperature for 3 hours, and then allowed to cool naturally. Catalyst samples 1 and 2 were obtained.

  The obtained catalyst sample was stored in a plastic sample bottle so as not to be exposed to the outside air.

(XRD (crystal phase) evaluation)
Catalyst sample No. For 1 and 2, in order to identify the crystal phase contained in the catalyst sample, a diffraction pattern was measured by the following procedure using a powder X-ray diffractometer (product name “RINT-2600TTR”, manufactured by Rigaku Corporation) did.

First, the catalyst sample was sufficiently refined using a mortar. Then, an appropriate amount of the catalyst sample was placed in a measurement sample holder (made of glass, depth 0.2 mm), and a glass plate was pressed to flatten the powder surface on the cell. This sample holder was set in an X-ray diffractometer, and the surface of the catalyst sample was irradiated with CuKα rays (tube voltage 50 kV, tube current 100 mA) to measure the X-ray diffraction pattern. The scan range of the goniometer was 2θ = 10.0-80.0 °, and the scan speed was 1.0 ° / min. The crystal phase was identified using an ASTM (Ca ₂ Fe ₂ O ₅ : 47-1711, CaFe ₂ O ₄ : 32-0168) card.

As a result, the sample No. 1 in which the mixed molar ratio Ca / Fe was 1.0. No. 1 was confirmed to have a diffraction pattern attributed to Ca ₂ Fe ₂ O ₅ . In addition, Sample No. in which the mixed molar ratio Ca / Fe is 0.5. 2, the diffraction pattern attributable to CaFe ₂ O ₄ was confirmed.

  These results were the same as those theoretically predicted from the phase equilibrium diagram of the Ca—Fe—O system shown in FIG.

(Specific surface area measurement)
Sample No. About 1 and 2, the BET specific surface area was measured using the U-tube type glass cell by the one point method by the nitrogen adsorption method of the procedure shown below.

  First, after measuring the weight of the cell, 0.50 g of a catalyst sample was put in the cell. And the connector with a non-return valve was attached to the cell which put the catalyst sample, it attached to the deaeration port, and the mantle heater was covered from the cell lower part. While flowing a mixed gas of helium and nitrogen into the U-shaped tube, heating was performed at 105 ° C. for about 20 minutes to remove components previously adsorbed on the catalyst sample, and at the same time, the inside of the cell was purged with the mixed gas. Then, the cell was removed from the deaeration port and attached to the specific surface area measurement port. And it deaerated until the pressure in a cell was saturated at 0.02 Torr or less. Then, the cell was cooled with liquid nitrogen, and nitrogen was sufficiently adsorbed on the catalyst surface. The cell was taken out from the liquid nitrogen, the change in pressure was measured while heating with warm air from a fan, and the amount of desorbed nitrogen gas was calculated. And the nitrogen desorption amount per catalyst unit weight was calculated | required from the difference between the cell weight containing the sample after a measurement, and the cell weight before a measurement, and the specific surface area of the catalyst was computed based on the BET multimolecular adsorption model.

The results are shown in Table 8 above. No. 1 catalyst sample has a specific surface area of 3.2 m ² / g. The catalyst sample of 2 had a specific surface area of 1.6 m ² / g.

(Raman spectroscopy measurement)
Sample No. In order to confirm the presence and type of active oxygen contained in the structures of the catalyst samples 1 and 2, Raman spectra were measured by the following procedure.

  First, the catalyst sample was sufficiently refined using a mortar. An appropriate amount of the catalyst sample was taken on a slide glass, and a cover glass was pressed to flatten the powder surface. This slide glass was set in a Raman spectroscopic analyzer (product name “NRS-1000”, manufactured by JASCO Corporation), and a laser beam (green laser with a beam diameter of 1 μm (wavelength: 532 nm)) dimmed by a slit was used as catalyst sample particles. And the Raman spectrum was measured. In the measurement, the spectrum was integrated twice and the exposure time was 2 minutes per time.

Sample No. Ca / Fe is 1.0 and the product is Ca ₂ Fe ₂ O ₅ . No. 1 is a sample No. ^{1 in} which a Raman shift was confirmed at 1093 cm ⁻¹ , Ca / Fe was 0.5, and the product was CaFe ₂ O ₄ . 2, Raman shifts were confirmed at 1022 cm ⁻¹ and 1093 cm ⁻¹ . According to previous studies (S. Fujita et al., Chem. Mater., 15, 4879 (2003), LCampelo et al., J. Raman Spectrosc., 10, 33 (1981)), O ₂ ⁻ is 1075 cm ^−1. Since it has been reported that O ₃ ⁻ has a spectrum in the vicinity of 1019 cm ^{−1 in the} vicinity, sample no. 1 is an active oxygen of O ₂ ⁻ , sample No. 1 2 is considered to include the active oxygen of O ₃ ⁻ and O ₂ ^{− in} the structure.

(Catalyst performance evaluation)
Sample No. In order to evaluate the catalyst performance of 1 and 2, the catalytic activity for propylene oxidation was examined by the procedure shown below using a gas flow-type catalytic reaction apparatus whose schematic configuration is shown in FIG.

  This gas flow type catalytic reaction apparatus includes a gas mixer 1 for mixing a sample gas, an electric furnace 2, a reaction tube 3 made of quartz glass heated to a predetermined temperature in the electric furnace 2, and an FID gas chromatograph (organic gas). For detection) 4 and a TCD gas chromatograph (for inorganic gas detection) 5. For the FID gas chromatograph 4, [Porapak (registered trademark) Type Q] was used. Further, the TCD gas chromatograph 5 was equipped with “Active Carbon, Mesh 60/80” packed in a stainless steel column (2 m).

The sample gas used was a mixture-diluted helium balanced propylene gas (C ₃ H ₆ : 2000 ppm), pure oxygen gas, and pure helium gas.

First, the catalyst sample was sufficiently refined using a mortar. Then, the catalyst sample was filled in the reaction tube 3. The reaction tube 3 was U-shaped with an inner diameter of 4 mm and a height of about 150 mm, and 0.084 g was packed so that the packed bed height of the catalyst was 10 mm. The top and bottom of the packed bed were packed with an appropriate amount of rock wool. The reaction tube 3 was installed in the electric furnace 2. The packed bed temperature was measured by a thermocouple previously attached to the tube wall next to the packed bed and controlled using a temperature controller. Since the pressure loss of the packed bed differs depending on the sample powder, the flow rate of the reaction tube outlet gas was guaranteed using a soap film flow meter. The total gas amount of the sample gas was adjusted to 20 ml / min. Then, a mixed gas of oxygen and helium (O ₂ : 10 vol%) was flowed into the reaction tube 3 to purge the inside of the tube. After heating and heating the electric furnace 2 to reach a predetermined temperature (˜900 ° C.), propylene gas is added to the sample gas, and the composition of the gas at the inlet of the reaction tube 3 is C ₃ H ₆ : 1000 ppm, O ₂ : 10% It was. The catalyst performance evaluation was started after leaving it to stand for 30 minutes as it was.

In evaluating the catalyst performance, the C ₃ H ₆ concentration contained in the inlet / outlet gas of the reaction tube 3 was measured by the FID gas chromatograph 4, and the CO ₂ concentration and the CO concentration were measured by the TCD gas chromatograph 5. The column temperatures of the FID gas chromatograph 4 and the TCD gas chromatograph 5 were 100 ° C. and 160 ° C., respectively. The chromatograph was recorded and analyzed using an integrator, and each gas concentration was calculated from each peak area of C ₃ H ₆ gas, CO ₂ gas, and CO gas.

The catalytic activity was evaluated based on the C ₃ H ₆ decomposition rate and CO _X selectivity defined below.

(C ₃ H ₆ decomposition rate) [%] = {1- (C ₃ H ₆ concentration at reaction tube outlet) / (C ₃ H ₆ concentration at reaction tube inlet)} × 100
(CO _X selectivity) [%] = [/ ( CO X concentration of the reaction tube outlet) {(C ₃ H ₆ concentration in the reaction tube inlet - C ₃ H ₆ concentration of the reaction tube outlet) × 3}] × 100
Sample No. For 1 and 2, the relationship between the propylene decomposition rate and reaction temperature is shown in FIG. In FIG. 2, Ca / Fe = 1.0 indicates sample No. 1 and Ca / Fe = 0.5 is Sample No. Corresponds to 2. For comparison, FIG. 2 also shows data when no catalyst sample was added.

  Sample No. Both 1 and 2 showed catalytic activity at 300 ° C. or higher, and both exhibited a decomposition rate of 100% at about 600 ° C.

These sample Nos. 1 and 2 have specific surface areas of 3.2 m ² / g and 1.6 m ² / g, and the specific surface areas of platinum catalysts and ferrite (Fe ₂ O ₃ ) catalysts used for ordinary oxidation catalysts are 100 to 200 m ^2. It was confirmed that the catalyst activity was close to that of a platinum catalyst although it was 1 to 2 orders of magnitude smaller than about / g.

(Comparative example)
In the raw material preparation step, a mixed raw material was obtained in the same manner as in the above example, except that a commercially available industrial raw material (CaO powder) was used instead of using lime sludge as calcia source-containing waste. In addition, the mixing molar ratio in this mixed raw material was set to Ca / Fe = 1. And the catalyst sample of the comparative example was obtained from this mixed raw material like the said Example.

About the obtained catalyst sample of the comparative example, it carried out similarly to the said Example, and performed the above-mentioned catalyst performance evaluation. As a result, no. Although the catalytic activity of the catalyst sample 1 (Ca / Fe = 1) is inferior to that of the comparative catalyst sample (Ca / Fe = 1) using commercially available industrial raw materials for both the calcia source and the ferrite source, the difference is It was confirmed that the reaction temperature was about 100 ° C.

Catalyst sample no. It is a schematic diagram which shows schematic structure of the gas flow-type catalyst reaction apparatus used in order to evaluate catalyst performance about 1 and 2. FIG. Catalyst sample no. It is a figure which shows the relationship between a propylene decomposition | disassembly rate and reaction temperature about 1 and 2. FIG. It is a phase equilibrium diagram of Ca-Fe-O system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas mixer 2 ... Electric furnace 3 ... Reaction tube 4 ... FID gas chromatograph 5 ... TCD gas chromatograph

Claims (3)

Calcia source and raw material preparation step of preparing at least raw materials one waste containing Mutotomoni mixing molar ratio to at least a portion of which is a 0.33 ≦ Ca / Fe ≦ 3.0, including at least one of the ferrite source When,
Was heated to 600-1449 ° C. the material in an oxygen atmosphere, the CaFe ₂ O ₄ containing therein a calcium ferrite and active oxygen in the structure having the composition formula of Ca ₂ Fe ₂ O ₅ containing therein the active oxygen in the structure And a calcining step for obtaining an oxidation catalyst containing at least one of calcium ferrites having the composition formula.   The raw materials are lime sludge, lime residue, shells, fly ash, coal ash, slag, concrete scrap, cement sludge, sewage sludge incineration ash, paper sludge, products using magnetic materials, and manufacture of products using the magnetic materials Featuring at least one kind of waste selected from the group consisting of ferrite sludge discharged from the process, inorganic waste liquid ferrite treatment residue, iron polishing litter, iron oxide cake, iron oxide waste containing iron oxide, and red mud The method for producing an oxidation catalyst according to claim 1. The method for producing an oxidation catalyst according to claim 1 or 2, wherein the oxidation catalyst is an exhaust gas purification oxidation catalyst.

Images