JPS5833014B2 - catalyst composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to eliminate harmful components contained in gas, especially nitrogen oxides (
Hereinafter, it may be abbreviated as NOx.

), which relates to a catalyst composition that effectively removes
More specifically, NOx can be effectively reduced over a long period of time even in the presence of oxygen, sulfur compounds, and/or moisture.
This invention relates to a catalyst composition capable of reducing and removing.

NOx is contained in the waste gas of boilers, nitric acid plants, metal heating furnaces, oil refineries, etc., as well as in the exhaust gas of various internal combustion engines, and is not only harmful to the human body, but also causes photochemical smog. It is considered to be one of the substances, and its emissions have recently become a major problem for companies.

Therefore, removing NOx from these gases is
It is extremely important for preventing air pollution, and there is an urgent need to develop removal technology.

N20, NO, N2O3, NO2゜N2O4, and N2O5 are known as NOx, but only NO and NO2 can exist stably in the atmosphere.
Regarding the prevention of x emissions, NO and NO2 are the main targets.

Conventionally known methods for removing NOx from gas include absorption methods (wet and dry), adsorption methods, decomposition methods, and reduction methods.

Wet absorption method uses water or alkaline aqueous solution to absorb NO.
This method attempts to absorb and remove be.

The dry absorption method uses an absorbent such as a solid alkaline substance, and the adsorption method uses an adsorbent such as silica gel or activated carbon to remove NOx, but NOx is removed by the moisture contained in the gas. There are disadvantages from an industrial perspective, such as the fact that the absorbent and adsorbent are not easy to regenerate.

The decomposition method attempts to decompose NOx into its four constituent components, nitrogen and oxygen, and can be said to be a preferable method for pollution control, but at present it requires quite high temperatures and long contact times even if catalysts are used. In particular, it is difficult to process large amounts of gas.

The reduction method is a method in which NOx is reduced to nitrogen using a reducing agent such as ammonia, carbon oxide, hydrogen, or hydrocarbons.

In particular, the method of using ammonia as a reducing agent has the advantage that the reaction proceeds at a relatively low temperature, and since ammonia does not react with oxygen in the exhaust gas, the amount of reducing agent consumed is small and the cost of exhaust gas treatment is low. ing.

Catalytic reduction catalysts for NOx using ammonia as a reducing agent include platinum group metal compounds (Japanese Patent Publication No. 38-12308, Japanese Patent Publication No. 40-18205, etc.), iron group metal compounds (Japanese Patent Publication No. 37-1701, etc.), vanadium, Oxides of molybdenum and tungsten (USP 3,279,88
4 etc.) have been proposed.

However, the NOx reduction activity of these catalysts decreases in a short time if sulfur compounds (such as sulfur dioxide gas) and/or moisture are present in the treated gas. It has the disadvantage that it can only be used against

In the case of normal combustion waste gas, it always contains about 10% by volume of moisture and, depending on the fuel, about 0,00 to 0.3% by volume of sulfur compounds mainly consisting of oxides.

Therefore, NO can maintain high activity for a long time even in the coexistence of these sulfur compounds and/or moisture.
The development of a reduction catalyst for x has been long awaited.

As a result of our intensive search for catalysts that meet this purpose, we have found that even in gases containing several volume percent of oxygen, 0.1 volume percent or more of sulfur compounds, and 10 volume percent or more of water, we have found that NOx in the gas can be reduced. The present invention has been completed by successfully developing an extremely practical catalyst that can achieve almost complete reduction and removal over a long period of time.

That is, the present invention includes (a) an oxide of tin and titanium as a first component, (b) an oxide of molybdenum as a second component, and (c) one of oxides of boron and tantalum as a third component. The present invention relates to a catalyst composition for reducing nitrogen oxides in a gas in the presence of ammonia.

The oxides mentioned here include simple mixtures of oxides such as tin, titanium, molybdenum, boron, and tantalum, respectively.
and mixed oxides in which each oxide is intimately mixed to partially form a kind of solid solution.

In the catalyst composition of the present invention, the weight composition ratio of titanium oxide to tin oxide as the first component is preferably 1:0.
001-1000, the weight composition ratio of the second component to the first component is preferably 1:0.001-50, particularly preferably 1:0.005-5.00, and the weight composition ratio of the second component to the first component is preferably 1:0.005-5.00. The weight composition ratio of the components is preferably 0.0
001-201, particularly preferably 0.001-1.00.

Although the catalytic action of the NOx reduction catalyst and the poisoning mechanism in the presence of sulfur compounds and/or moisture have not yet been fully elucidated, the oxides of each composition of the present catalyst alone
Whether they are supported on a transparent body or not,
In comparison, the initial activity is low or the activity decrease is significant.
When the catalyst composition of the present invention is formed, the activity is significantly increased and high activity can be maintained for a long period of time.

This is truly surprising.

Furthermore, in an atmosphere where sulfur compounds, moisture, oxygen, reducing agents, etc. coexist, some of the composition may change its oxidation state or change into different types of compounds such as sulfites and sulfates. The fact that the catalyst composition according to the present invention can maintain high catalytic activity despite this fact shows that the catalyst composition according to the present invention is very excellent.

Regarding the method for producing the catalyst of the present invention, any starting materials and preparation method may be used as long as the oxides constituting the catalyst are sufficiently and evenly mixed with each other.

For example, various compounds containing one or more of the elements constituting the catalyst can be used as raw materials, and can be prepared by various known methods suitable for the raw materials.

Examples of tin compounds used as raw materials include oxides (
SnO, 5n02, etc.), halides (SnC12,
5nC14, SnBr4, etc.), sulfates (SnS04, etc.), sulfides (SnS, etc.);
03, TtO, etc.), halides (e.g. T I
Cl3, TtC14, etc.), sulfates (e.g. Ti(SO4)2, Ti(SO4)a).

Ti08O, etc.) are used, and molybdenum compounds include oxides (such as MoO3
9M002), molybdic acid and its salts (e.g. H2MoO4, H2MoO4.H2O).

(NH4)6MO7024, (NH4)2Mo04, etc.), halides (e.g. MOC15, MoC14
etc.) are used.

When adding boron, use orthoboric acid, metaboric acid, ammonium metaborate, etc. When adding tantalum, use oxides (Tap5 etc.), halides (TaCl
, ) etc. are used as raw materials.

Further, the catalyst can be prepared by various known methods.

For example, ammonium molybdate and boric acid or tantalum pentachloride are mixed in an oxalic acid aqueous solution, stannic oxide powder and titanium oxide powder are added to this, water is evaporated to form a slurry, and this is extruded. This method is one of the preferred preparation methods, but it can also be prepared by other means well known to those skilled in the art, such as an oxide mixing method, a coprecipitation method, and an impregnation method.

In other words, even if the starting materials and preparation methods are different, in the end,
As long as it is obtained as the oxide mentioned above, there is almost no difference in the performance of the catalyst, and depending on the starting material or preparation method, the resulting catalyst may contain metal salts and the like as impurities, but the amount of impurities The presence of a certain amount of foreign substances does not significantly affect the catalytic performance.

The catalyst composition of the present invention may be used as it is in the form of an oxide or supported on a carrier.

Examples of carriers that can be used include alumina, silica, silicon carbide, diatomaceous earth, kaolin, bentonite, silica-alumina, zirconium oxide, pumice, activated carbon, and the like.

Catalysts are usually heated, in an oxidizing atmosphere such as air, and/or
Alternatively, it can be used by firing in a reducing atmosphere of hydrogen, steam, hydrocarbon, etc. at 300'-800°C for 230 minutes to 10 hours.

When reducing and removing NOx using the catalyst composition according to the present invention, ammonia is used as a reducing agent.

The amount of ammonia to be added is preferably 1 to 3 times the stoichiometric amount according to the following formula %.

If the amount of ammonia is too small, the NOx removal rate will decrease,
On the other hand, if the amount is too large, unreacted ammonia may leak out of the system.

When reducing and removing NOx with ammonia using this catalyst composition, it can be carried out using various types of reactors such as fixed bed type, moving bed type, and fluidized bed type, and the amount of gas to be treated flowing into the reactor is is a space velocity of 500 to 100,0OO
hr' is possible, but depending on reactor scale and NOx
From the viewpoint of removal rate, 1000 to 50,000 hr-1 is desirable.

The reaction pressure may be any condition including reduced pressure, normal pressure, and increased pressure, but from the viewpoint of operating costs, it is preferable to carry out the reaction under normal pressure, slightly increased pressure, or reduced pressure.

The reaction temperature can be 100 to 500°C, but lower temperatures may cause a decrease in catalyst activity due to the precipitation of various ammonium salts, and higher temperatures are unfavorable from a thermoeconomic standpoint, so the NOx removal rate may be lower. can be set to the desired value1
It is preferable to carry out the reaction at a temperature in the range of 50 to 400°C.

Some Examples are given below to explain the present invention in detail, but these are intended to clarify the spirit of the present invention, and the present invention should not be limited by the Examples.

Example 1 Ammonium molybdate 14.3S' with boric acid o, s
oy was added thereto, and 2.51 parts of oxalic acid and water were added thereto to prepare a mixed solution of 100-.

Stannic oxide LOP and titanium oxide IOP were added to the mixed solution, water was evaporated on a hot water bath to form a slurry, and this was extruded into a 2 mm diameter x 5 mm.

The obtained product was dried at 100 to 110°C, and then baked at 500°C for 3 hours in an air atmosphere.

The obtained catalyst is called catalyst M.

Example 2 A catalyst was prepared in exactly the same manner as in Example 1, except that 2.86 P of tantalum pentachloride was used in place of boric acid, and ethyl alcohol was used in place of water in preparing the mixed solution.

The obtained catalyst is called catalyst P. Comparative Example 1 Water was added to stannic oxide powder to form a uniform slurry, which was then extruded into a shape of 2 mm in diameter and 511 mm in diameter.

After drying the obtained product at 110°C, it was dried in an air atmosphere for 5 minutes.
It was baked at 00'C for 3 hours.

The obtained catalyst is called catalyst W.

Comparative Example 2 A catalyst was prepared in exactly the same manner as in Comparative Example 1 using a mixture of equal weights of stannic oxide and titanium oxide as raw materials.

The resulting catalyst is called catalyst X. Comparative Example 3 2.40P of ammonium metavanadate and 2.40P of oxalic acid.
52 and water to prepare a mixed solution 1001rLl, silicone carbide 20P having a particle size of 10 to 20 mesh was added thereto, immersed therein, and evaporated to dryness on a hot water bath.

The obtained granules were fired at 500°G for 4 hours in an air atmosphere.

This catalyst is called catalyst Y.

Comparative Example 4 A catalyst was prepared in exactly the same manner as in Comparative Example 3 except that 1.07 f of ammonium molybdate was further added.

The resulting catalyst is called catalyst Z. Experimental Example 1 Using the catalysts obtained in Examples 1 and 2 and Comparative Examples 1 to 4, a test for NOx reduction performance with ammonia was conducted under the conditions listed in Table 1.

Table 2 shows the results of examining the NO removal rate immediately after the start of the reaction, 48 hours later, and 120 hours later.

Table 2 shows that the ability of ammonia to reduce NOx in the coexistence of sulfur compounds, moisture, and oxygen shows that although individual oxides have low activity, the catalyst composition of the present invention has significantly improved activity and poisoning resistance. .

Table 1 Catalyst test conditions Reactor inlet gas composition (% is volume %) 2NO0,
03% SO20.05% O25.0% H2O10.0% N2 Amount of ammonia added to the reactor inlet: 0.03% by volume of inlet gas Reactor Pyrex glass: Fixed bed reactor Gas space velocity: 10, 000 hr-1 Reaction pressure Normal pressure Reaction temperature: 220.280°C NO concentration measurement: Salzman method (according to JIS K-0104).

) NO removal rate NO in inlet gas (%) - NO in outlet gas (%) NO in inlet gas (%)

Claims (1)

[Claims] 1. For reducing nitrogen oxides in a gas comprising (a) oxides of tin and titanium, (b) oxides of molybdenum and (c) oxides of boron and tantalum in the presence of ammonia. catalyst composition.