JPH07227523A - Contact reducing method of nitrogen oxide - Google Patents

Abstract

PURPOSE:To provide a method to increase selectivity in the reduction of nitrogen oxides without leaking ammonia in a method for contact reduction of nitrogen oxides in exhaust gas by using ammonia in the presence of a catalyst. CONSTITUTION:In the method for contact reduction of nitrogen oxides in exhaust gas by using a reducing agent, (a) ammonia and (b) at least one compd. selected from oxygen-contg. org. compds. and hydrocarbons are used as the reducing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for catalytic reduction of nitrogen oxides when NH ₃ is used as a reducing agent, and more specifically, harmful nitrogen oxides contained in exhaust gas discharged from factories, automobiles and the like. The present invention relates to a nitrogen oxide catalytic reduction method using NH _3, which is suitable for use in reducing and removing substances. In particular, it relates to a low concentration nitrogen oxide catalytic reduction method and a high efficiency nitrogen oxide catalytic reduction method.

[0002]

2. Description of the Related Art Conventionally, nitrogen oxides contained in exhaust gas are converted into N ₂ by oxidizing the nitrogen oxides and then absorbing it in alkali, or by using a reducing agent such as NH ₃ , H ₂ or CO.
It has been removed by the method of changing to. However, in the case of the method of (1), it is necessary to perform drainage treatment of alkali for prevention of pollution, and in the method of ( ₃₎ , the method of using NH ₃ as a reducing agent has a high reaction selectivity with nitrogen oxides and is a large fixed source. It has been put to practical use in thermal power plants and the like. Therefore, in order to obtain highly efficient denitration, N
When H ₃ is excessively added to the exhaust gas with respect to NO, the reduction rate is improved, but since leaked NH ₃ is contained in the exhaust gas after the reaction, there is a problem that a high denitration rate cannot be obtained. Further, when the concentration of nitrogen oxides in the exhaust gas is less than 100 ppm, there is a problem that the reduction rate is reduced. Further, when H ₂ , CO, or hydrocarbon is used as a reducing agent, these react with O ₂ present at a higher concentration than NOx present at a low concentration. Therefore, a large amount of reducing agent is required to reduce NOx. Needed.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to efficiently reduce not only medium and high concentrations of exhaust gas but also low concentrations of nitrogen oxides. Another object of the present invention is to provide a nitrogen oxide catalytic reduction method.

[0004]

The present invention relates to a method for highly efficiently reducing nitrogen oxides contained in exhaust gas, particularly low-concentration nitrogen oxides, using ammonia in the presence of a catalyst. In addition, at least one selected from oxygen-containing organic compounds and hydrocarbons is used. In the present invention, the nitrogen oxides include nitric oxide as a component, as well as nitrogen dioxide, trinitrogen dioxide and the like. The method according to the present invention is characterized in that (a) ammonia and (b) at least one selected from oxygen-containing organic compounds and hydrocarbons are used in combination as a reducing agent.

In the present invention, examples of the oxygen-containing organic compound that is the second reducing agent include alcohols,
Preferred examples include ethers, carboxylic acid esters, ketones, etc., but are not limited thereto.

More specifically, aliphatic alcohols, aromatic alcohols, araliphatic alcohols and the like can be used as the above alcohols, but among them, they are liquids at room temperature and the reaction temperature as described below is used. Then, an aliphatic saturated or unsaturated alcohol having 1 to 6 carbon atoms which is a gas is preferable, and examples of such an aliphatic alcohol include methanol, ethanol, n-propanol, isopropanol, n-butyl alcohol, isobutyl alcohol and s- Butyl alcohol, t-butyl alcohol, allyl alcohol, etc. can be mentioned. In particular,
In the present invention, methanol or ethanol is preferable from the viewpoint of reaction selectivity.

Examples of the above ethers include dimethyl ether, diethyl ether, dipropyl ether and the like, examples of carboxylic acid esters such as methyl acetate and ethyl acetate, and examples of ketones such as acetone and Methyl ethyl ketone, methyl isobutyl ketone, etc. can be mentioned. The oxygen-containing organic compounds as described above may be used alone or in combination of two or more, if necessary.

In the catalytic reduction of nitrogen oxides using the catalyst according to the present invention, examples of the second reducing agent composed of hydrocarbon include gaseous hydrocarbons such as methane, ethane, propane, propylene and butylene. As the gas or liquid, a single-component hydrocarbon such as pentane, hexane, octane, heptane, benzene, toluene, xylene, or a mineral oil-based hydrocarbon such as gasoline, kerosene, light oil or heavy oil can be used. . In particular, according to the invention,
Among the above, acetylene, methylacetylene, 1
Lower alkynes such as butyne, lower alkenes such as ethylene, propylene, isoptylene, 1-butene and 2-butene, lower dienes such as butadiene and isoprene, lower alkanes such as propane and butane are preferably used as the reducing agent. These hydrocarbons may be used alone,
Alternatively, two or more kinds may be used in combination as necessary.

To carry out the process according to the invention, the catalyst is loaded into a reactor, ammonia and a second reducing agent are added to the exhaust gas containing nitrogen oxides and this is passed through the reactor. At this time, the order of adding the second reducing agent to ammonia is not particularly limited as long as it is before the catalyst layer, and any of them may be added first.

In the present invention, ammonia is usually 0.1 to 1.0 times the molar amount of nitrogen oxides contained in the exhaust gas, although it depends on the amount of the second reducing agent used in combination with ammonia. It is used in the range of 0.2 to 0.1, particularly preferably in order to minimize the amount of ammonia contained after the reaction.
It is used in a 9-fold molar amount range. When the amount of the first reducing agent used is less than 0.1 times the molar amount of nitrogen oxide contained in the exhaust gas, sufficient catalytic activity cannot be obtained, while on the other hand, it exceeds 0.9 times the molar amount. At this time, unreacted ammonia is increased, and it is necessary to treat them, which is not preferable.

The second reducing agent is usually used in a range of 0.1 to 10 times, and preferably 1 to 5 times the molar amount of nitrogen oxides contained in the exhaust gas. Used in. When the amount of the second reducing agent is less than 0.1 times the molar amount of nitrogen oxide contained in the exhaust gas, sufficient catalytic activity cannot be obtained, while when it exceeds 10 times the molar amount, The unreacted second reducing agent, its partial oxides, and the like are increased in quantity, and it becomes necessary to treat them, which is not preferable. However, these partial oxides are
By attaching a complete oxidation catalyst such as a noble metal catalyst such as Pt or a transition metal oxide catalyst such as CuO after the x reduction catalyst, it can be converted into harmless CO ₂ or H ₂ O.

According to the present invention, the first reducing agent and the second reducing agent are used together as the reducing agent, so that the first reducing agent or the second reducing agent is used alone as the reducing agent. Compared with the case, the selectivity of reduction of nitrogen oxide is remarkably enhanced. Further, by setting the addition molar ratio of ammonia as the first reducing agent to 0.1 to 0.9 and setting the addition amount of the second reducing agent to 1 to 5 times the molar amount of NO, the ammonia is added. Nitrogen oxide can be selectively reduced with high efficiency without leaking.

The catalysts for catalytic reduction of nitrogen oxides used in the present invention are, for example, Ib, IIb and III of the periodic table.
a, IIIb, IVa, IVb, Va, VIa, VII
It is an ion or oxide of a or a group VIII element. These are usually the conventionally known carriers such as alumina, silica, silica-alumina, titania, zirconia, H-ZSM-5, H-mordenite, and other zeolites, which are ion-exchanged, impregnated, kneaded, etc. Carried by. The catalyst is supported on these carriers and used in an appropriate shape such as a honeycomb structure, a ring-shaped structure, a pellet, or a granular material.

When the ions of the above-mentioned elements are carried on the carrier as described above by the ion exchange method, the ratio of the ions of the above-mentioned elements carried on the carrier is usually in the range of 0.01 to 5% by weight. On the other hand, when the oxide of the above element is supported as a catalyst, the supporting rate of the oxide as a catalyst is usually in the range of 0.1 to 10% by weight.

As examples of the above-mentioned elements, as elements of Group Ib of the periodic table, for example, Cu, Ag, etc., as elements of Group IIb, for example, Zn, etc., as Group IIIa elements, for example, La. , Ce, etc. as group IIIb elements, for example, Al, Ga etc. as group IVa elements,
For example, Ti, Zr, etc. are group IVb elements, for example, Ge, Sn, etc., and group Va elements are, for example, V,
Examples of the VIa group element such as Nb group are Cr,
Mo, W, etc., as the Group VIIa element, for example, M
n or the like as a Group VIII element, for example, F
Examples thereof include e, Co and Ni.

Among these catalyst species, the preferred catalyst species depends on the second reducing species to be added. For example, when methanol is used as the reducing agent, cobalt, Ni, Fe, Ag
It is preferable to use a catalyst in which a metal oxide or sulfate of 1 to 5 wt% is supported on alumina. When ethanol is used as a reducing agent, a metal oxide or sulfate of Ag or the like is 1 to 5 w.
Catalysts supported on t% alumina are preferred. When a lower hydrocarbon such as ethylene, propylene or propane is used as the reducing agent, a catalyst in which a metal oxide such as Cu, Ce, Al or Ti is supported on alumina or titania in an amount of 1 to 5 wt% is preferable.

In the process according to the invention, the exhaust gas containing nitrogen oxides is introduced into the reactor filled with the catalyst at a temperature in the range of 200 to 600 ° C. In particular, the reaction temperature is preferably in the range of 300 to 500 ° C. Furthermore, according to the present invention, in the above temperature range, the space velocity (SV) 5
By introducing the exhaust gas to the reactor at about 100 to 100000 H ⁻¹ , the nitrogen oxides contained in the exhaust gas can be efficiently catalytically reduced.

[0018]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

[0019]

【Example】

(1) Preparation Example 1 iron nitrate catalyst _{(Fe (NO 3)) 3} · 9H 2 O) 11.30g
Was dissolved in 100 ml of deionized water. Γ-Alumina pellets (NK-324 manufactured by Sumitomo Chemical Co., Ltd.) dried at 120 ° C. for 24 hours were added to the iron nitrate aqueous solution to sufficiently impregnate the pores of the γ-alumina pellets with nitrate ions. It was Then, the γ-alumina pellets thus treated were filtered off to remove the excess aqueous solution adhering to the surface, dried at 120 ° C. for 18 hours, and then calcined at 500 ° C. for 4 hours to obtain Fe ₂ O. A catalyst A-1 supporting 1% by weight of ₃ as Fe was obtained.

[0020] Example 2 manganese nitrate _{(Mn (NO 3) 2 ·} 6H 2 O) 8.16
A catalyst A-2 supporting 1% by weight of MnO ₂ as Mn was obtained in the same manner as in Example 1 except that g was used.

[0021] Example 3 chromium nitrate _{(Cr (NO 3) 3 ·} 9H 2 O) 12.02
Cr ₂ O _{3 was} prepared in the same manner as in Example 1 except that g was used.
A catalyst A-3 supporting 1% by weight of Cr as Cr was obtained.

[0022] Example 4 cobalt nitrate _{(Co (NO 3) 2 ·} 6H 2 O) 7.72
Co ₃ O _{4 was} prepared in the same manner as in Example 1 except that g was used.
Was obtained as Co to obtain 1% by weight of catalyst A-4.

Example 5 A catalyst A-5 carrying 5% by weight of Co ₃ O ₄ as Co was obtained in the same manner as in Example 1 except that 38.6 g of cobalt nitrate was used.

[0024] Example 6 nickel nitrate _{(Ni (NO 3) 2 ·} 6H 2 O) 7.74
NiO was replaced with Ni in the same manner as in Example 1 except that g was used.
As a result, 1% by weight of Catalyst A-6 was obtained.

Example 7 In the same manner as in Example 1 except that 5.94 g of copper nitrate (Cu (NO ₃ ) ₂ .3H ₂ O) was used, a catalyst A containing 1% by weight of CuO as Cu was prepared. Got 7.

[0026] except for using Example 8 zinc nitrate _{(Zn (NO 3) 2 ·} 6H 2 O) 4.53g, in the same manner as in Example 1, was 1 wt% on ZnO as Zn catalyst A- Got 8.

Example 9 A catalyst A-9 carrying 1% by weight of V ₂ O ₅ as V was obtained in the same manner as in Example 1 except that 5.00 g of vanadyl nitrate (VOSO ₄ ) was used.

Example 10 6.56 g of ammonium metatungstate (50% by weight as WO ₃ ) was dissolved in 100 ml of ion-exchanged water. Pellets of titanium oxide having a diameter of 2 mm and dried at 120 ° C. for 24 hours (CS-24 manufactured by Sakai Chemical Industry Co., Ltd.)
To the ammonium metatungstate aqueous solution,
After that, the same treatment as in Example 1 was carried out to obtain a catalyst A-10 supporting 1% by weight of WO ₃ as W.

Example 11 Cerium nitrate (Ce (NO3) 3.6H2O) 28.5
g was dissolved in 100 ml of deionized water. Pellets of pentasil-type acid-type zeolite with a diameter of 2 mm dried at 120 ° C. for 24 hours (SM manufactured by VAW Aluminum AG)
-27 molded into pellets with silica sol) Approx. 1
00 ml (60 g) was added to the above cerium nitrate aqueous solution,
After standing for 30 minutes, the pores of the zeolite pellets were sufficiently impregnated with the cerium nitrate aqueous solution.

Next, the zeolite pellets thus treated were filtered off to remove the excess aqueous solution adhering to the surface of the pellets, which was then washed with 6% by weight of ammonia water 20.
The mixture was added to 0 ml and left for 1 hour to neutralize and hydrolyze cerium nitrate in the pores of the zeolite. Then, in this way, the zeolite supporting cerium oxide was thoroughly washed with ion-exchanged water, and then calcined at 500 ° C. for 3 hours to remove the zeolite supporting cerium oxide at a supporting rate of 10% by weight. Catalyst A-11 was obtained.

Example 12 100 g of acid type mordenite (SiO ₂ / Al ₂ O ₃ ratio 16, HM-23 manufactured by Nippon Kagaku Kogyo Co., Ltd.) was immersed in an aqueous zirconyl nitrate solution (concentration of 100 g / l as ZrO ₂ ) and stirred. While maintaining at 70 ° C. for 1 hour, hydrogen ions were exchanged with zirconium ions. This was filtered, washed with water, and the obtained zeolite cake was dried.
The catalyst was calcined at 50 ° C. for 4 hours to obtain a catalyst A-12 made of Zr-mordenite carrying 3.3% by weight of Zr. The specific surface area of this catalyst was 391 m ² / g.

Example 13 A catalyst A-13 was prepared in the same manner as in Example 1 except that 3.43 g of tin chloride (SnCl ₄ ) was used to carry 1% by weight of SnO ₂ as Sn.

Example 14 The same γ-alumina as that used in Example 1 was used as the catalyst-14.

(2) Evaluation test The catalysts obtained in Examples 1 to 14 were subjected to nitrogen oxide catalytic reduction of nitrogen oxide-containing gas under the following test conditions, and the nitrogen oxide removal rate was calculated by the following formula. Sought by. (Test condition I) Gas composition NO 5ppm NH ₃ 5ppm Oxygen-containing organic compound or hydrocarbon As described in the table SO ₂ 100ppm O ₂ 10% H ₂ O 5% N ₂ balance ▲-▼ space velocity 10,000Hr ^-1 reaction Temperature 200 ℃, 300 ℃, 350 ℃, 40
0 ° C

The results are shown in Table 1.

[0036]

[Table 1]

(Test Conditions II) Example 15 Catalyst A-5 was used as a reducing agent, and in a gas composition,
The addition amount of NH ₃ as the first reducing agent is 4 ppm (0.8 times moles with respect to nitrogen oxides), the second reducing agent is 20 ppm of methanol (4 times moles with respect to nitrogen oxides), and Acetone 20ppm (4 with respect to nitrogen oxides
The reaction was performed in the same manner as in the test condition I except that each reducing agent was used in an amount of 2 times the molar amount. At this time, the NH ₃ concentration in the reaction control gas was similarly measured.
The results are shown in Table 2.

[0038]

[Table 2]

(Test condition III) A-4 was used as a catalyst, and ammonia and methanol were used together as a reducing agent.
Each amount was variously changed. When ammonia is used as the reducing agent, its addition amount is 2.5 to 5 ppm in gas composition (0.5 to 1.0 with respect to nitrogen oxides).
The amount of addition is 5 to 25 ppm in terms of gas composition when methanol is used.
It was used so as to be 1 to 5 times the molar amount of nitrogen oxide. The other test conditions were the same as those of Test Condition I, and the reaction was performed. The results are shown in Table 3.

[0040]

[Table 3]

(Test condition IV) A-4 was used as a catalyst, and ammonia was added at 4 ppm (0.5 to the nitrogen oxide).
Double mole) Ethanol or isopropanol was used as the second reducing agent so as to be 20 ppm with respect to the gas composition. The other test conditions were the same as those of Test Condition I, and the reaction was carried out. The results are shown in Table 4.

[0042]

[Table 4]

Comparative Example 1 A-1 and A-5 were used as catalysts, and ammonia or methanol or acetone was used alone as a reducing agent.
The amount of reducing agent used was 4 ppm for ammonia and 20 ppm for methanol or acetone. The results are shown in Table 5.

[0044]

[Table 5]

[0045]

As described above, according to the present invention, NOx can be reduced with high efficiency, and particularly low-concentration nitrogen oxides can be reduced efficiently without leaking ammonia as a reducing agent into the processing gas.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 21/04 ZAB A 23/06 ZAB A 23/14 ZAB A 23/22 ZAB A 23/26 ZAB A 23/30 ZAB A 23/34 ZAB A 23/72 ZAB A 23/74 ZAB 23/745 23/755 B01D 53/36 ZAB B01J 23/74 301 A 321 A

Claims (5)

[Claims] 1. A method for catalytically reducing nitrogen oxides in exhaust gas with NH ₃ , wherein at least one selected from oxygen-containing organic compounds and hydrocarbons is further added as a reducing agent. How to reduce. 2. With respect to nitrogen oxides contained in exhaust gas,
(A) Ammonia is used in a range of 1.0 times or less, and (b) at least one selected from oxygen-containing organic compounds and hydrocarbons is used in a range of 0.1 to 10 times. Method for catalytic reduction of nitrogen oxides described 3. The method for catalytic reduction of nitrogen oxides according to claim 1, wherein the oxygen-containing organic compound is an alcohol, an ether, a ketone or a carboxylic acid ester. 4. The method for catalytic reduction of nitrogen oxides according to claim 1, wherein the alcohol is methanol, ethanol or isopropanol. 5. The method for catalytic reduction of nitrogen oxides according to claim 1, wherein the hydrocarbon is an olefin.