JPS5812057B2 - Shiyokubaisosabutsu - 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.

As NOx, N20. N02N203. NO2゜N
2O4 and N20. However, it is NO and NO2 that exist stably in the atmosphere, and NOx
Regarding emission prevention, NO and NO□ 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 break down NOx into its constituent parts, nitrogen and oxygen, and can be said to be a preferable method for pollution control, but at present, even when catalysts are used, it requires considerably high temperatures and long contact times. 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 monoxide, 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.), oxides of vanadium, molybdenum, and tungsten (USP 3,279, 8)
s No. 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

For normal burnup gas, the capacity is always 10.

Although it depends on the fuel, it often contains about 0.01 to 0.3 volume % of sulfur compounds mainly consisting of oxides.

Therefore, N can maintain high activity for a long time even in the presence of these sulfur compounds and/or moisture.
Ox reduction.

The development of a catalyst 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 vanadium as a second component, and (C) an oxide of molybdenum, phosphorus, and niobium as a third component. The present invention relates to a catalyst composition for reducing nitrogen oxides in a gas comprising one of the following compounds in the presence of ammonia.

The oxides mentioned here include simple mixtures of oxides of tin, titanium, vanadium, molybdenum, and niobium, as well as oxides of each that are intimately mixed and partially form a kind of solid solution. Contains mixed oxides.

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, and the weight composition ratio of vanadium and molybdenum oxides to the first component is preferably 1:0.001-50, particularly preferably 1:0.0.
05-5.00, and the weight composition ratio of phosphorus and niobium oxides to the first component is preferably 0.0001-5.00.
20, particularly preferably o, ooi-i, and oo.

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
They are supported on a carrier.

Regardless of whether or not the initial activity is low or the activity is significantly decreased, the catalyst composition of the present invention can significantly increase the activity and maintain high activity for a long period of time.

This is truly surprising.

Moreover, in an atmosphere where sulfur compounds, moisture, oxygen, reducing agents, etc. are present, 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 any method of preparation 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 (Sn C12, etc.)
, Sn C14, Sn Br4, etc.), sulfate, (Sn
Examples of titanium compounds include oxides (such as Ti 0
2. Ti2O3, TiO, etc.), halides (e.g. TiC13, TiC14, etc.), sulfates (e.g. Ti(SO4)2, Tt(SO4)3).

T i OS 04, etc.) are used, and vanadium compounds include, for example, oxides (for example, ■205
．． ■204. ■203, etc.), halides (for example, ■CI4.■C13, etc.), oxychlorides (for example, V
OCl3. ■OC1□, etc.), ammonia salts (for example, NH4VO3, etc.), and molybdenum compounds include, for example, oxides (for example, Mo032M002, etc.).
), molybdic acid and its salts (such as H2MO
04, H2MO04”H2O, (NH4)6 MO70
24, (NH4)2MO04, etc.), halides (e.g. MoCl'5.

MoC14, etc.) are used.

When adding phosphorus, oxide (P2O5), phosphoric acid and its salts (orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid,
ammonium phosphate, etc.), but when adding niobium, oxides (Nb205, etc.), halides (NbC
15) etc. are used as raw materials.

As the raw material containing two or more types of catalyst constituent elements, for example, titanium phosphate, phosphomolybdic acid, ammonium phosphomolybdate, etc. can be used.

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

For example, this method involves mixing ammonium metavanadate and ammonium molybdate with an oxalic acid aqueous solution, adding stannic oxide powder and titanium oxide powder to this, evaporating the water to form a slurry, and extruding the slurry. Although this is one of the preferred preparation methods, it can also be prepared by means such as an oxide mixing method, a coprecipitation method, an impregnation method, etc., which are well known to those skilled in the art.

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
or under a reducing atmosphere such as hydrogen, water vapor, hydrocarbons, etc., e.g. 300°-800°C.

It can be used after being baked for 30 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 100,000
hr” is possible, but depending on reactor scale and NOx
From the viewpoint of removal rate, it is desirable that the time is 1000 to 50,000 hr.

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 must be reduced. Set to desired value 15
It is preferable to carry out the reaction at a temperature in the range of 0 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 2.5 g of oxalic acid and water were added to 2.40 g of ammonium metavanadate and 1.07 g of ammonium molybdate to prepare 100 ml of a mixed solution.

After adding 10 g of stannic oxide and 10 g of titanium oxide to this, the water was evaporated on a hot water bath to form a uniform slurry, which was then extruded and molded into 271 g1z x 5w1. Closed.

After drying the molded product at 100-110°C, it was fired at 500°C for 3 hours in an air atmosphere.

The resulting catalyst is called catalyst E.

Example 2 2.40 g of ammonium metavanadate and 0.8 g of phosphoric acid
3.9 was added thereto, and 2.5 g of oxalic acid and water were added thereto to make 100 ml of a mixed solution.

Add 10g of stannic oxide and 10g of titanium oxide to this mixed solution.
was added, water was evaporated on a hot water bath to form a slurry, and the slurry was extruded into a size of 2 mmφ x 5 m.

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 J.

Example 3 In place of phosphoric acid, niobium pentachloride 2.16. ! A catalyst was prepared in exactly the same manner as in Example 2, except that i' was used and ethyl alcohol was used instead of water in preparing the mixed solution.

The obtained catalyst is called catalyst Q. Comparative Example 1 Water was added to stannic oxide powder to form a uniform slurry, which was extruded into a shape of 2w19!6×571g11.

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 Ammonium mecvanadate 2.4 (2.4 l to 2.4 l oxalic acid)
5 g and water were added to make a mixed solution of 100 mA, and 20 g of silicone carbide having a particle size of 10 to 20 meshes was added thereto, immersed in the mixture, and evaporated to dryness on a hot water bath.

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

This catalyst is called catalyst Y.

Comparative Example 4 Furthermore, ammonium molybdate 1.07. ! A catalyst was prepared in exactly the same manner as in Comparative Example 3 except that li' was added.

The resulting catalyst is called catalyst Z. Experimental Example 1 Using the catalysts obtained in Examples 1 to 3 and Comparative Examples 1 to 4, the NOx reduction performance with ammonia was tested 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. .

Claims (1)

[Claims] 1. Nitrogen oxides in a gas containing (a) oxides of tin and titanium, (b) oxides of vanadium, and (C) oxides of molybdenum, phosphorus, and niobium in the presence of ammonia. Catalyst to reduce to.