JPS5820309B2 - Catalyst composition for reduction and removal of NO↓x in exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention converts nitrogen oxides (hereinafter referred to as NOx) in exhaust gases emitted from various combustion furnaces, internal combustion engines, devices using nitrates and nitrites into ammonia, hydrogen, and monoxide. This invention relates to a catalyst for reducing and decomposing nitrogen into nitrogen in the presence of reducing gases such as carbon, hydrocarbons, and hydrogen sulfide.

As the role of NOx in environmental pollution has recently become clearer, further development of denitrification technology is desired as the most effective means for reducing NOx.

There are various methods for denitrification, and they can be roughly divided into dry methods and wet methods. Among them, the reduction method, which belongs to the dry method, converts NOx into harmless nitrogen, so it does not cause secondary pollution and is economical as well. It is attracting particular attention because of its popularity.

In this reduction method, NH3, H2, and CO are used as reducing agents.
2 hydrocarbons, gases such as H2S, ammonium salts such as ammonium carbonate and ammonium oxalate, and amines such as urea and hydrazine.

Several catalysts for selective reduction of NOx have been known in the past, but none of them can be said to be satisfactory.

For example, noble metal catalysts such as platinum can be heated at 100 to 200°C.
Although it has the advantage of being able to perform denitrification at a relatively low temperature, it also has the following various drawbacks.

: (a) Low resistance to SOx; (b) 100-2
Ammonium sulfate and/or acidic ammonium sulfate, which are precipitated by the reaction between 803 in the process gas and NH3 as a reducing agent at a low temperature of 00°C, stick to the catalyst layer or the piping in its vicinity, causing activity deterioration and piping. Occurrence of blockage, etc.; (／→The temperature is 200℃.
If the value exceeds the
75≦Generated;) Laughing gas (N20) is generated; (Feather price is high and resources are limited.

On the other hand, copper-based catalysts (U.S. Pat. Nos. 3,449,063 and 359)
9427, etc.) and iron-based catalysts (West German Patent No. 125368, etc.)
No. 5, U.S. Pat. No. 3,008,796, etc.) have insufficient activity, and in particular, the activity decreases economically, so it cannot be said to be a practically stable catalyst.1Q In view of the above points, the present invention has been made to In other words, to provide a catalyst that exhibits high activity in a wide temperature range from low to high temperatures, has excellent durability against SOx and heat, has stable activity economically, and is inexpensive. This was done for the purpose of

The catalyst composition of the present invention comprises (at least one selected from the group consisting of aX ferric iron, its oxide, and other compounds thereof, or in addition to this, ([1) elements with atomic numbers of 24 and 27 to 29, A mixture containing at least one selected from the group consisting of these oxides and other compounds;
b) Contains a fired product of at least one selected from the group consisting of rare earth elements, acid compounds thereof, and other compounds thereof, the element in the former component (a) and the element in the latter component (b). is characterized by an atomic ratio of 1:0.025 to 5 with respect to rare earth elements.

Component (a) above has a certain degree of denitrification activity even when used alone, but when used alone, the usable temperature range is narrow, the durability against poisonous substances, especially SOx, is extremely low, and it is rapidly lost at high temperatures. There are disadvantages such as lack of performance.

Therefore, component (a) alone has poor practicality as a denitrification catalyst for gases such as combustion exhaust gas, which have large temperature changes and contain large amounts of poisonous substances.

However, when component (b) is added to component (a) in a specific ratio, the optimum operating temperature range becomes wider, and the durability against poisonous substances such as SOX increases.
A stable practical catalyst is obtained that retains its activity even at considerably high temperatures.

The elements constituting component (a) used in the present invention may be in an atomic state (single substance), an oxide state, or another compound state.

Carbonates, nitrates, organic acid salts, etc., used as raw materials, become oxides at relatively low temperatures when fired, while sulfates, etc., are difficult to completely change to oxides even after firing, but eventually may equally be used.

In the present invention, the rare earth elements used as component (b) refer to 15 elements with atomic numbers 57 to 71 called lanthanide elements, scandium with atomic number 21, and ythurium with atomic number 39, and (a ) As in the case of the components, these may be in an atomic state (single substance), an oxide state, or another compound state.

For example, carbonates, nitrates, organic acid salts, etc. used as sources of rare earth elements become oxides at relatively low temperatures during calcination during the production of catalyst compositions, whereas sulfates remain in the sulfate state at relatively high temperatures. It remains in this state and is difficult to become a complete oxide state.

However, in either state, the same excellent effects are exhibited in coexistence with component (a).

Rare earth elements are often difficult to isolate because their properties are similar.

Therefore, for example, a crude mixed compound of rare earth elements obtained in the process of isolating each rare earth element from ores such as monazite, bastonezite, celite, and xenotime ores may be used as the rare earth element source of component (b) of the present invention. It's okay.

The present invention requires that the ratio of component (a) to component (b) be in the range of 1:0.025 to 5 in terms of atomic ratio.

If this ratio is less than 0.002, the disadvantages of using component (a) alone will not be sufficiently improved, while if the atomic ratio exceeds 5, no significant improvement will be observed.

If the amount of component (b) is too large, the activity tends to decrease.

More preferably, the ratio of component (a) to component (b) is 1:0.05 to 3 in atomic ratio.

The catalyst of the present invention can be produced by conventionally known methods such as an impregnation method, a precipitation method, and a crossing method.

According to the impregnation method, for example, the above ea) component compound and (b)
) After dissolving the component compound in water, an acid aqueous solution, an alkali aqueous solution, an organic solvent, etc., a porous carrier is immersed in the solution or the solution is spread on the porous carrier, and then the porous carrier is dried. Then, it is baked at about 250 to 600°C for 1 to 10 hours.

Alternatively, after immersing the carrier in a single aqueous solution of either component (a) or component (b), drying and baking it,
The fired carrier may be immersed in a single aqueous solution of other components, and then dried and fired again.

As the porous carrier, known carriers such as alumina, silica, and magnesia are used, and alumina, particularly activated alumina, is preferred.

The shape of the carrier can be arbitrarily selected from granular shapes such as cylindrical, spherical, and Raschig ring shapes, or porous plate shapes such as honeycomb shapes, depending on the purpose.

Precipitation methods include, for example, a method in which two or more active ingredient solutions are mixed and the active ingredient is coprecipitated; a carrier component solution and an active ingredient solution are mixed and the carrier and the active ingredient are coprecipitated; a microcarrier Methods include depositing the active ingredient onto the ingredient.

Next, the precipitate is molded by a known method such as an extrusion molding method, a tablet molding method, a transfer granulation method, etc., and after drying, it is acidified at about 250 to 600° C. for about 1 to 10 hours to obtain a catalyst.

Further, as a kneading method, for example, the active ingredient solution is added to the carrier powder and kneaded thoroughly, or the solution of component (b) is added to the precipitate of component (a) and kneaded thoroughly, or (
The solution of component (a) is added to the precipitate of component b) and thoroughly kneaded to form a highly viscous paste, which is then molded, dried and calcined in the same manner as in the precipitation method to form a catalyst. shall be.

In general, catalysts made by the precipitation method and kneading method not only have a more uniform concentration of active ingredients than catalysts made by the impregnation method, but also have a higher activity because they can have a higher concentration of active ingredients. .

Therefore, in the following examples, where the impregnation method shows good results with the catalyst, the precipitation method and kneading method yield catalysts with better performance.

Incidentally, in some cases, the firing step can be omitted for carbonates and sulfates among the raw materials for components (a) and (b) used in the present invention.

Such carbonates include iron carbonate, copper carbonate, nickel carbonate, lanthanum carbonate, cerium carbonate, etc., and sulfates include iron sulfate, copper sulfate, vanadium sulfate, lanthanum sulfate,
Examples include cerium sulfate.

The exhaust gas treatment method using the catalyst of the present invention may be any method as long as the exhaust gas and the catalyst are brought into contact with each other efficiently. A method of flowing a gas to be treated in the presence of the gas can be mentioned.

The treatment temperature varies depending on the composition of the catalyst, the composition of the gas to be treated, etc., but is usually about 150 to 550°C.

The spatial temperature of the gas to be treated depends on the treatment temperature, catalyst particle size, catalyst external surface area per unit volume, etc., but is usually 1,000 to 100,000 Hr-1, preferably 3
000 to 50000 Hr-1.

The features of the present invention will be further clarified by Examples and Comparative Examples below.

Example 1 0.15 mol (65.0 g) of lanthanum nitrate and 0.15 mol (41.7 g) of ferrous sulfate are dissolved in warm water to make a total of 200 rrLl.

200 ml of activated alumina crushed into 7 to 14 meshes (filling specific gravity: 0.5) is immersed in this aqueous solution, and left until the aqueous solution permeates into the inside.

It is then thoroughly dried in air at about 120°C.

Fill a reaction tube with an inner diameter of 28 mm with 6 ml of this catalyst, and
Calcinate at 0°C for 3 hours to obtain a catalyst with an atomic ratio of lanthanum and iron = 5:5.

200 volumes of NH3 is added to the gas having the composition shown in Table 1 at a space velocity of 50,000 Hr' (converted to standard conditions), and the mixture is allowed to pass through the reaction tube.

The NOx concentrations at the inlet and outlet were measured using a chemiluminescence spectrometer, and the denitrification rate was determined using the following formula.

The results are shown in Table 2.

Denitrification rate (%) = (1-Tenshi Nδ 1X100 outlet NOx
Concentration Example 2 0.03 mol (13.0 g) of lanthanum nitrate and 0.27 mol (71,59) of ferrous sulfate are dissolved in warm water.

The atomic ratio of lanthanum and iron = 1 by the same operation as in Example 1.
:9 catalyst was obtained.

Thereafter, the denitrification rate was determined in the same manner as in Example 1.

The results are shown in Table 2. Comparative Example 1 0.30 mol of ferrous sulfate (s3.41) is dissolved in warm water.

Thereafter, the denitrification rate was determined in the same manner as in Example 1.

The results are shown in Table 2. Comparative Example 2 0.30 mol (129.9 g) of lanthanum nitrate is dissolved in hot water.

Thereafter, the denitrification rate was determined in the same manner as in Example 1.

The results are shown in Table 2. As is clear from Table 2, the catalysts of the present invention (Examples 1 and 2) exhibit superior denitrification activity compared to Comparative Examples 1 and 2.

Example 3 0.75 mol (324.8 g) of lanthanum nitrate and 1st sulfuric acid
0.75 moles (2 os, 5 g) of iron are dissolved in hot water.

If this aqueous solution is gradually dropped into aqueous ammonia, a coprecipitate of lanthanum and iron is produced.

At this time, ammonia is added as appropriate so that the pH of the ammonia solution does not become 7 or less.

This precipitate was thoroughly washed with water and filtered, and then
Dry thoroughly in air at 0°C.

Two parts by weight of graphite are added to this, thoroughly kneaded, and molded at a molding pressure of 0.5 m/i.

This molded product is calcined in air at 450° C. for 3 hours to obtain a catalyst with an atomic ratio of lanthanum and iron=5:5.

This was crushed into 7 to 14 meshes, and the denitrification rate was determined in the same manner as in Example 1.

The results are shown in Table 3 in comparison with the results of Example 1.

Example 4 0.375 mol of lanthanum oxide (pulverized 122,21,
Add 0.75 mol (208.5 g) of ferrous sulfate to this, and then add water and mix thoroughly to make a slurry.
Dry thoroughly in air at 20°C.

To this, 1% by weight of polyvinyl alcohol was added together with water, and after wet grinding, extrusion molding was performed.

This molded product is fired in air at 450°C for 3 hours to obtain a catalyst with an atomic ratio of lanthanum and iron of 5:5.

This was crushed into 7 to 14 meshes, and the denitrification rate was determined in the same manner as in Example 1.

The results are shown in Table 3. As is clear from Table 3, Examples 3 and 4 exhibit superior denitrification activity than Example 1 in the temperature range of 250 to 400°C.

Catalysts produced by coprecipitation or cross-mixing have sufficiently fine particles of the coprecipitate or kneaded material, so they have a higher active metal concentration and superior denitrification activity than catalysts produced by impregnation.

Hereinafter, only examples relating to the impregnation method, which is easy to produce, will be shown, but in any of the examples, a catalyst with better denitrification activity can be produced by coprecipitation or kneading.

Example 5 A catalyst was produced in the same manner as in Example 1 except that 0.15 mol of yttrium nitrate and 0.15 mol of ferrous sulfate were used, and the results of determining the denitrification rate are shown in Table 4.

Example 6 A catalyst was produced in the same manner as in Example 1 except that 0.15 mol of cerium nitrate and 0.15 mol of ferrous sulfate were used.

Table 4 shows the denitrification rate. Example 7 Mixed rare earth element nitrate obtained from monazite ore 0.1
5 mol (65,: l) and 0.15 mol (41,: l) of ferrous sulfate.
, 7g) was used in the same manner as in Example 1 to obtain a catalyst.

Table 4 shows the denitrification rate. The composition of the mixed rare earth element nitrate was as follows.

Comparative Example 3 to IO Catalysts were produced in the same manner as in Example 1, except that only component (a) below was used, and the denitrification rates of each catalyst were determined.

The results are shown in Table 5. Comparative example (a)
Component 3 Titanium tetrachloride (0
, 15 mol) 4 Ammonium metavanadate (0
,30 mol)5 Chromium nitrate (0,3
0 mol) Comparative example (a) Component 6
Manganese nitrate (0.30 mol) 7 Cobalt nitrate (0.30 mol) 8 Nickel nitrate
(0,30 mol)9 Copper nitrate (0,3
0 mol) 10 Copper sulfate (0.30 mol) In Comparative Example 4, ammonium metavanadate was dissolved in monomethanolamine.

Examples 8 to 11 Catalysts were produced in the same manner as in Example 1, except that the following combinations of components (a) and (b) were used, and the respective denitrification rates were determined by the same operations as in Production Example 1. I asked for it.

The results are shown in Table 6.

Examples (a) Component raw material (mol) (b) Component raw material (mol) Ferrous sulfate (0,24) 8 + Lanthanum nitrate (0,
03) Chromium nitrate (0,03) Ferrous sulfate (0,24) 9 + Lanthanum nitrate (0,
03) Copper acid (0,03) Ferrous sulfate (0,24) 10 + Lanthanum nitrate (0,
03) Cobalt nitrate (0,03) Example (a) Component raw material (mol) (b) Component raw material (mol) Ferrous sulfate (0,24) 11 + Lanthanum nitrate (0,
03) Nickel nitrate (0,03) Comparative Examples 11-12 A catalyst was produced in the same manner as in Example 1, except that the following combination of components (a) and (b) was used; The denitrification rate of each was determined by the operation.

The results are also listed in Table 6.

(a) Component raw material (mol) (b) Component raw material (mol) 11
Nickel nitrate (0,27) Lanthanum nitrate (0,0
3) 12 Cobalt nitrate (0,27) Lanthanum nitrate (0,03) Comparative example 13 Hexachloroplatinic acid (H2PtC4 6H20) 0.3
A molar amount of the aqueous solution was dissolved in hot water, and the same procedure as in Example 1 was carried out to obtain a platinum-supported catalyst.

The denitrification rate is shown in Table 7 together with the results of Example 2.

From the results shown in Table 7, it is clear that the catalyst of the present invention exhibits higher denitrification activity over a wider temperature range than the platinum catalyst.

Example 1 Using the catalyst obtained in Experimental Example 8, SV=5000Hr
Table 8 shows the results of examining the catalyst activity in the same manner as in Example 1 except that -1 was used.

From the results in Table 8, 5V = 50000H at 300℃
At r', the denitrification rate is low at 58%, but at 5V=5000H
It is clear that at r-1, it increases to 84 inches.

Experimental Example 2 Using the catalyst obtained in Experimental Example 2, NH3200 volume ppm and 5O2200 volume p were added to the gas to be treated shown in Table 1 above.
5V=50000Hr”, temperature 3
The samples were treated at 50° C. for a long period of time to examine changes in the denitrification rate over time.

The results are shown in Table 9.

It is clear from Table 9 that the catalyst of the present invention has excellent durability.

Example 12 A catalyst was produced in the same manner as in Example 1, except that ferrous nitrate was used in place of the ferrous sulfate in Example 1.

Analysis of the active components of the catalyst by X-ray diffraction revealed that all nitrates were decomposed and both iron and lanthanum were in the form of oxides.

Table 10 shows the results of determining the denitrification rate using this catalyst in the same manner as in Example 1.

Example 13 The catalyst of Example 12 was further reduced in a hydrogen stream at 450°C for 3 hours, and the active ingredients were analyzed by X-ray diffraction. As a result, it was found that about half of the catalyst was reduced to metallic iron and lanthanum. Ta.

Table 10 shows the results of determining the denitrification rate using this catalyst in the same manner as in Example 1.

Claims (1)

[Scope of Claims] 1 (a) at least one element selected from the group consisting of iron, oxides thereof, and other compounds thereof; and (b) rare earth elements, oxides thereof, and other compounds thereof. An exhaust gas containing at least one fired product selected from the group consisting of compounds, characterized in that the ratio of component (a) to component (b) is 1:0.002 to 5 in atomic ratio. A catalyst composition for reducing and removing NOx. 2 (a) At least one member selected from the group consisting of iron, its oxides and other compounds thereof, (i
l) At least one element selected from the group consisting of elements with atomic numbers 24 and 27 to 29, oxides thereof, and other compounds thereof, and (b) rare earth elements, oxides thereof, and other compounds thereof. It contains at least one type of fired product selected from the group consisting of other compounds such as, etc., and is characterized in that the ratio of component (a) to component (b) is 1:0.002 to 5 in atomic ratio. A catalyst composition for reducing and removing NOx in exhaust gas.