JPH04367723A - Decomposition catalyst and decomposition treatment of nox - Google Patents

Abstract

PURPOSE:To reutilize coal cinder discharged as industrial waste from the pow dered coal combustion boiler of a thermal power plant or a factory and to purify exhaust gas using an NOx decomposition catalyst prepared using coal cinder as a raw material. CONSTITUTION:An NOx decomposition catalyst is prepared by supporting metal ion such as V, Cr, Mn, Fe, Co, Cu, Pd, Ag, Pt or Ni on a coal cinder alkali molten substance obtained by mixing coal cinder with an alkali solution. NOx is decomposed by directly decomposing NOx into N2 and O2 by providing the NOx decomposition catalyst in an exhaust gas discharge route.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The purpose of this invention is to utilize coal ash discharged as industrial waste from thermal power plants, factories, etc.; N in exhaust gas using a decomposition catalyst
This invention relates to a method for decomposing Ox.

0002

[Background Art] In recent years, with the progress of air pollution, the generation of photochemical smog has become a social problem, and the removal and purification of nitrogen oxides (NOx), which is the causative substance, has become an urgent issue. .

[0003] NOx originates from the engine exhaust gas of automobiles and jet aircraft, or the combustion exhaust gas from boilers and incinerators at thermal power plants. Countermeasures are being considered, such as improving the combustion method itself and chemically decomposing it using catalysts. The above-mentioned NOx treatment techniques include catalytic reduction methods and catalytic decomposition methods, and the former can be further divided into selective methods and non-selective methods.

Among these, the selective method uses NH3 as the processing gas.
This method is difficult to apply to small-sized equipment because it inevitably increases the size of the device and increases the initial cost and running cost. On the other hand, the non-selective method allows for miniaturization, but it inevitably increases costs because it uses a three-way catalyst based on noble metals. In particular, those using precious metal three-way catalysts are often used for gasoline engines.
It cannot be used to treat diesel engine exhaust gas, which contains 5-15% unreacted oxygen. In addition, N due to the latter catalyst
Regarding Ox treatment, a method using synthetic zeolite catalysts saturated with various transition metal compounds has been developed, but this method has not become widely used because synthetic zeolite is expensive and the economic effect is low. not present.

In addition to the air pollution caused by NOx mentioned above,
The disposal of coal ash, which is industrial waste from thermal power plants, steel mills, and factories, is becoming another urgent environmental pollution problem. Coal ash is the combustion residue of coal, coke, etc. According to statistics, approximately 40% of coal ash currently exists in Japan.
The amount of coal ash discharged from several large thermal power plants is
This amounts to more than 2.5 million tons per year.

[0006] Although such coal ash is partially reused as raw material for cement, etc., there is currently no suitable large-scale treatment method, and the coal ash is currently disposed of in landfills together with other solid wastes. However, recently, demand for cement itself has peaked, and it has become difficult to secure disposal sites (landfills), so coal ash as industrial waste has
This poses a major problem nationwide, both socially and from an environmental conservation standpoint.

[0007]

[Problems to be Solved by the Invention] The present invention aims to meet the above-mentioned problems, and provides a NOx decomposition catalyst and N
This provides an Ox decomposition treatment method.

[0008]

[Means for Solving the Problems] That is, in the present invention, V, Cr, Mn, Fe, Co, Cu, Pd,
NOx decomposition catalyst supported with one or more metal ions selected from Ag, Pt, Ni, etc., and such NOx decomposition catalyst
This is a NOx decomposition treatment method characterized by directly decomposing NOx into N2 and O2 by interposing an x decomposition catalyst in the exhaust gas exhaust path.

[0009]

[Example] First, the NOx decomposition catalyst according to the present invention will be explained.

[0010] As mentioned above, the raw material coal ash refers to coal clinker ash, coal fly ash, etc., which are combustion waste from thermal power plants, steel mills, and factories that use coal as fuel.

[0011] By mixing this with an alkaline solution and applying heat or pressure, a partially crystallized crystalline material is produced, and a porous coal ash alkaline melt is obtained.

[0012] A desired NOx decomposition catalyst can be obtained by supporting various metal ions on this coal ash alkali melt by an ion exchange method.

The above metal ions include V, Cr, M
n, Fe, Co, Cu, Pd, Ag, Pt, Ni, etc.

Furthermore, in addition to the above-mentioned metal ions, organic ions or compounds such as ammonia ions and amines having a reducing action can be supported on the NOx decomposition catalyst by an ion exchange method or an adsorption method. . By doing so, NO2 is directly reduced to NO, so that the efficiency of decomposition by the metal ions is further increased.

A specific example will be explained below.

[0016] First, 80 to 160 g/l of an aqueous sodium hydroxide solution as an alkaline solution is added to the above-mentioned coal ash, and heat treatment is performed at, for example, 90°C or higher.

After this reaction (heat treatment), excess sodium hydroxide is removed by washing with water and air-dried to obtain a powdered coal ash alkali melt.

Next, this alkali molten coal ash and a copper acetate solution as metal ions are mixed and stirred for a predetermined reaction time, thereby supporting the copper ions in the alkali molten coal ash.

The metal ion support is washed with water, dehydrated, and then air-dried to obtain a NOx decomposition catalyst.

FIG. 1 shows the results of investigating the processing capacity of the NOx decomposition catalyst obtained as described above.

[0021] Experiments regarding the NO decomposition process of this NOx decomposition catalyst were conducted under the following environment. Approximately 40 g of NOx decomposition catalyst is placed in a 200 ml beaker and placed in an autoclave having a volume of approximately 1 liter. After exhausting the air in the autoclave, NO with a purity of 99.7%
Introduce and seal. The reaction itself was carried out at 300, 400, 500, 600 rpm while stirring the catalyst at 30-50 rpm.
After holding at each temperature for 5 hours, the residual amount of NO and the amount of decomposition reaction products (N2 and O2) were measured.

As shown in FIG. 1, NOx according to the present invention
The decomposition catalyst shows a NO decomposition rate of 92% at about 500°C, and even in the range of about 450°C to about 550°C, it shows a NO decomposition rate of 92%.
It showed a high decomposition rate of more than %.

As described above, the NOx decomposition catalyst of the present invention reduces NOx in combustion exhaust gas, which is a cause of atmospheric pollution such as photochemical smog and acid rain.
x can be decomposed into harmless nitrogen and oxygen with high efficiency.

[0024] Examples of combustion exhaust gas include boiler exhaust gas,
Examples include exhaust gas from transportation systems (particularly those using diesel engines), exhaust gas from thermal power plants, incinerators, etc., and it can be effectively applied to these.

In order to actually perform exhaust gas treatment using the NOx decomposition catalyst described above, an appropriate accommodation space is provided in the exhaust gas exhaust path of the above-mentioned equipment, and particles with a size of several millimeters to several tens of millimeters are placed in this space. In addition to containing granulated NOx decomposition catalyst, molded products in flat plate shape, honeycomb shape, etc., or granular,
It is preferable to arrange a container containing a powdered NOx decomposition catalyst in a container having appropriate air permeability. When such a molded product is used, maintenance and inspection can be facilitated by constructing it in a cartridge-type manner so that it can be freely attached and removed.

[0026]

[Effect of the invention] The NOx decomposition catalyst and N
According to the Ox decomposition treatment method, it is possible to recycle coal ash as a resource, and as a result, the cost of the catalyst itself can be extremely low compared to conventional zeolite catalysts, and at the same time, it is possible to reduce the cost of the catalyst itself. , it is possible to avoid disposing of coal ash, which is produced in large quantities from steel mills and factories, as industrial waste.

Furthermore, by using the NOx decomposition catalyst according to the present invention for purifying combustion exhaust gas, etc.
It can also contribute to the prevention of air pollution by preventing photochemical smog and acid rain caused by Ox.

[0028] Furthermore, according to the present invention, it is possible to downsize the processing equipment compared to those using a processing gas such as NH3, and it is also possible to reduce the size of the processing equipment, and also to reduce the size of small exhaust gas generation sources such as small boilers and incinerators for small industries. It can be easily applied to household combustion equipment such as water heaters and gas ranges, and transportation equipment with internal combustion engines such as automobiles, airplanes, and ships.
No H3 gas leaks into the atmosphere.

[0029] Furthermore, compared to a catalyst using a noble metal three-way catalyst, nitrogen oxides can be decomposed even when the amount of unreacted oxygen in the exhaust gas is large, making it possible to make a great contribution to this field.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing experimental results of the NOx decomposition processing ability of the NOx decomposition catalyst according to the present invention.

Claims (5)

[Claims] 1. A NOx decomposition catalyst comprising a coal ash alkaline melt obtained by mixing coal ash and an alkaline solution and carrying metal ions thereon. [Claim 2] NOx produced by making the coal ash alkali melt according to Claim 1 support metal ions and organic substances.
Decomposition catalyst. 3. The metal ion according to claim 1 or 2 is V, Cr, Mn, Fe, Co, Cu, Pd, Ag,
A NOx decomposition catalyst characterized by containing either Pt or Ni. 4. A NOx decomposition catalyst, wherein the organic substance according to claim 2 is an organic ion or compound having a reducing action, such as an ammonia ion or an amine. [Claim 5] N according to any one of claims 1 to 4.
A NOx decomposition treatment method characterized by directly decomposing NOx into N2 and O2 by interposing an Ox decomposition catalyst in an exhaust gas exhaust path.