JP3484243B2 - Method for catalytic reduction of nitrogen oxides - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method for catalytically reducing nitrogen oxides contained in exhaust gas discharged from factories, automobiles, etc. using a reducing agent in the presence of a catalyst.
Specifically, by selecting and using the reducing agent,
The present invention relates to a method capable of reducing and removing nitrogen oxides with high selectivity.

[0002]

2. Description of the Related Art Conventionally, nitrogen oxides contained in exhaust gas discharged from factories, automobiles, etc., are capable of producing reducing agents such as ammonia, urea, hydrogen, carbon monoxide, hydrocarbons and alcohol in the presence of a catalyst. By using the method of reducing to nitrogen,
It has been removed from the exhaust gas. However, among the various methods described above, the method using ammonia as a reducing agent has very high selectivity for the reduction reaction of nitrogen oxides into nitrogen and water, but due to the toxicity and flammability of ammonia, It is not practical to use it as a moving source of nitrogen oxides such as automobiles. On the other hand, in the method of using urea that is solid at room temperature as a reducing agent, urea is dissolved in water to form an aqueous solution,
This can be added to the exhaust gas and brought into contact with the catalyst. In this way, when the reducing agent is used as an aqueous solution, heat is required for the evaporation of water, so the thermal efficiency of the catalytic reduction reaction of nitrogen oxides is improved. However, there is a problem that the reaction rate of nitrogen oxides is low.

On the other hand, the method using hydrogen or carbon monoxide as a reducing agent has few problems as described above, but the selectivity of the reaction is very low, and therefore it is used as a practical method for removing nitrogen oxides. hard. According to the method of using a hydrocarbon or an oxygen-containing compound such as alcohol as a reducing agent,
The selectivity of the reduction reaction of nitrogen oxides is somewhat improved, but the selectivity is still insufficient and it is far from a practical range as a method for removing nitrogen oxides.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the conventional method of catalytically reducing nitrogen oxides, mainly nitric oxide, contained in exhaust gas by using a reducing agent in the presence of a catalyst. The object of the present invention is to provide a method for improving the selectivity of the reduction reaction of nitrogen oxides.

[0005]

The present invention is a method of catalytically reducing nitrogen oxides contained in exhaust gas using a reducing agent in the presence of a catalyst, wherein a β-hydroxycarbonyl compound is used as the reducing agent. Is characterized by.

In the present invention, the nitrogen oxide contains nitric oxide as a main component, and also contains nitrogen dioxide, trinitrogen dioxide and the like.

The β-hydroxycarbonyl compound used as the reducing agent in the method according to the present invention has the formula (I) in the molecule.

[0008]

[Chemical 2]

A compound having a partial structure represented by the formula: β-hydroxyaldehyde or β-hydroxyketone.

More preferably, the β-hydroxycarbonyl compound used as the reducing agent in the present invention has the general formula (II)

[0011]

[Chemical 3]

(In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each hydrogen, an alkyl group, a cycloalkyl group, an aryl group or an arylalkyl group, and R ¹ and R ² are , Not simultaneously hydrogen, R ¹ may form a hydrocarbon ring together with α carbon, and R ² and R ⁵ may form one hydrocarbon ring.) Is a β-hydroxycarbonyl compound, that is, β-hydroxyaldehyde or β-hydroxyketone.

Such a β-hydroxycarbonyl compound can be obtained by an aldol reaction of an aldehyde or a ketone, as is already well known.
Various compounds are commercially available.

Specific examples of the β-hydroxycarbonyl compound that can be used in the present invention include:
3-hydroxybutanal, 3-hydroxy-2-methylpentanal, 3-hydroxy-2,2-dimethylpropanal, 3-hydroxy-2,2,4-trimethylpentanal, 4-hydroxy-4- Methyl-2-pentanone (diacetone alcohol), 3-hydroxy-2,4-diphenylbutanal, 3-hydroxy-1,3-diphenylbutanone, 2- (1'-hydroxycyclohexyl)-
Examples thereof include cyclohexanone.

In the present invention, the above-mentioned β-hydroxycarbonyl compound may be used alone or in combination of two or more, if necessary. In particular, in the present invention, 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol), 3-hydroxybutanal and the like are preferably used practically among the above.

Further, in the method of the present invention, hydrocarbons can be used together with the above-mentioned β-hydroxycarbonyl compound as a reducing agent. Examples of such a hydrocarbon include a hydrocarbon gas such as methane, ethane, propane, propylene and butylene as a gas at room temperature, and pentane and hexane as a liquid.
Single-component hydrocarbons such as heptane, octane, benzene, toluene, xylene, and mineral oil-based hydrocarbons such as gasoline, kerosene, light oil, and heavy oil can also be used. In particular, in the present invention, among these, hydrocarbons having a single component such as pentane and hexane, which are liquid at room temperature, and mineral oil hydrocarbons such as gasoline, kerosene, and light oil are preferably used.

In order to actually carry out the method according to the present invention, the catalyst is charged into the reactor, the reducing agent is added to the exhaust gas containing nitrogen oxides, and the nitrogen oxides and the reducing agent are mixed sufficiently uniformly,
It is passed through the reactor. Therefore, when using a reducing agent that is liquid at room temperature, it is preferable to gasify the reducing agent in advance, but it is also possible to mix the reducing agent as it is with the exhaust gas. The reducing agent is quickly gasified in the exhaust gas. In some cases, a solid can also be used as the reducing agent. Thus, when the reducing agent is a solid, for example, it is dissolved in another reducing agent that is liquid at room temperature to obtain a solution,
Alternatively, it is desirable to further gasify the solution and mix it with the exhaust gas, but it is not necessarily limited to such a method.

In the present invention, the reducing agent is usually in terms of carbon atoms with respect to nitrogen oxides contained in exhaust gas.
It is used in a range of 0.1 to 10 times by mole, and particularly preferably in a range of 1 to 5 times by mole in terms of carbon atoms. When the amount of reducing agent used is less than 0.1 times the molar amount of nitrogen oxides contained in the exhaust gas in terms of carbon atoms, sufficient catalytic activity cannot be obtained, while When the molar ratio exceeds 10 times,
Unreacted reducing agent and its partial oxides are discharged more and it becomes necessary to treat them, which is not preferable. The term "reducing agent in terms of carbon atoms" as used herein means that when one molecule of the reducing agent has n carbon atoms, 1 mole of the reducing agent is set to be n moles in terms of carbon atoms. Therefore, n carbon atoms in the molecule
1 reducing agent for each nitrogen oxide in terms of carbon atoms
The use of double mole means that 1 / n mole part of the reducing agent is used with respect to 1 mole part of nitrogen oxide.

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 conventional carriers such as alumina, silica, silica-alumina, titania, zirconia, and zeolites such as H-ZSM-5 and H-mordenite, which are ion-exchanged, impregnated, and kneaded. It is 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 an oxide of the above element is supported on the carrier as a catalyst, the supporting rate of the oxide as a catalyst is
Usually, the range of 0.1 to 10% by weight is preferable.

As examples of the above-mentioned elements, as elements of Group Ib of the periodic table, for example, Cu, Ag, and the like, elements of Group IIb, such as Zn, and elements of Group IIIa, 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. are group Va elements, for example,
Examples of the group VIa elements such as V and Nb include C
Examples of the group VIIa element include r, Mo, W, and the like, and examples of the group VIII element include Fe, Co, and Ni.

In the present invention, in particular, γ-alumina itself or a catalyst obtained by supporting γ-alumina with cobalt oxide, nickel oxide, or cobalt ion or nickel ion can be preferably used.

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 150 to 600 ° C. In particular, the reaction temperature is preferably in the range of 200 to 400 ° C. Furthermore, according to the present invention, in the above temperature range, the space velocity (SV) 5
By introducing the exhaust gas into the reactor at about 00 to 100,000, the nitrogen oxides contained in the exhaust gas can be efficiently catalytically reduced.

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

[0025]

【Example】

(1) Preparation of catalyst

[0026] Example 1 iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O) 11.30g was dissolved in deionized water 100 ml. 24 at 120 ° C
Γ-alumina pellets (NK-324, manufactured by Sumitomo Chemical Co., Ltd.) dried for an hour were added to the iron nitrate aqueous solution to give γ.
Nitrate ions were fully impregnated into the pores of the alumina pellets. Then, the γ-alumina pellets thus treated were filtered off to remove 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.

[0027] Example 2 manganese nitrate _{(Mn (NO 3) 2 ·} 6H 2 O) 8.16g
MnO ₂ was added in the same manner as in Example 1 except that
A catalyst A-2 supporting 1% by weight as n was obtained.

Example 3 Catalyst A-3 carrying 1% by weight of Ga ₂ O ₃ as Cr was carried out in the same manner as in Example 1 except that 8.94 g of gallium nitrate (Ga (NO ₃ ) ₃ ) was used. Got

[0029] Example 4 cobalt nitrate _{(Co (NO 3) 2 ·} 6H 2 O) 7.72g
A catalyst A-4 was prepared in the same manner as in Example 1, except that Co ₃ O ₄ was supported as Co by 1 wt%.

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 38.60 g of cobalt nitrate was used.

[0031] Example 6 nitrate nickel _{(Ni (NO 3) 2 ·} 6H 2 O) 7.74g
NiO was replaced with Ni in the same manner as in Example 1 except that
As a result, 1% by weight of Catalyst A-6 was obtained.

Example 7 Na-type zeolite (Ex-12 manufactured by Mizusawa Chemical Industry Co., Ltd.)
The H-ZSM5 powder 100g treated in acid form 2), copper nitrate _{(Cu (NO 3) 2 ·} 3H 2 O) 5.94g was added to an aqueous solution obtained by dissolving the ion-exchanged water 200 ml, sufficiently ion exchange Then, a catalyst A-7 carrying 1.5 wt% of Cu ions was obtained.

Example 8 In the same manner as in Example 1 except that 4.53 g of zinc nitrate (Zn (NO ₃ ) ₂ .6H ₂ O) was used, a catalyst A-having 1% by weight of ZnO as Zn was supported. Got 8.

Example 9 5.00 g of vanadyl sulfate (VOSO ₄ ) was added to ion-exchanged water 1
Dissolved in 100 ml, this titanium oxide (Sakai Chemical Industry Co., Ltd. CS-200) was added, below, in the same manner as in Example 1, Catalyst A to V ₂ O ₅ was 1 wt% on the V
-9 was obtained.

Example 10 6.56 g of ammonium metatungstate (50% by weight as WO ₃ ) was dissolved in 100 ml of ion-exchanged water.
Titanium oxide pellets (CS-24, manufactured by Sakai Chemical Industry Co., Ltd.) having a diameter of 2 mm and dried at 120 ° C. for 24 hours were added to the ammonium metatungstate aqueous solution, and then,
Treated in the same manner as in Example 1, and using WO ₃ as W, 1% by weight
The supported catalyst A-10 was obtained.

Example 11 28.5 g of cerium nitrate (Ce (NO ₃ ) ₃ .6H ₂ O)
Was dissolved in 100 ml of deionized water. 2 at 120 ° C
Pellets of pentasil-type acid-type zeolite having a diameter of 2 mm and dried for 4 hours (SM-27 manufactured by VAW Aluminum AG)
Molded into a pellet with silica sol) about 100 ml
(60 g) was added to the cerium nitrate aqueous solution and left for 30 minutes to sufficiently impregnate the cerium nitrate aqueous solution into the pores of the zeolite pellet.

Then, 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 aqueous ammonia 20.
It was added to 0 ml and left for 1 hour to neutralize and hydrolyze cerium nitrate in the pores of the zeolite. Then, the cerium oxide-supported zeolite was thoroughly washed with ion-exchanged water in this manner, and then calcined at 500 ° C. for 3 hours to remove the cerium oxide-supported zeolite from a loading ratio of 10% by weight. Catalyst A-11 was obtained.

Example 12 100 g of acid 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 composed of Zr-mordenite supporting Zr at 3.3% by weight. The specific surface area of this catalyst was 391 m ² / g.

Example 13 In the same manner as in Example 1 except that 3.43 g of tin chloride (SnCl ₄ ) was used, a catalyst A-13 carrying SnO ₂ as Sn at 1% by weight was obtained.

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

(2) Catalyst evaluation test Using the above-mentioned catalysts A-1 to A-14 according to the present invention, catalytic reduction of nitrogen oxides of a gas containing nitrogen oxides was carried out under the following conditions to obtain nitrogen. The production rate of was determined by gas chromatography. The production rate of nitrogen is (amount of nitrogen at the outlet of the reactor / amount of nitrogen oxides at the inlet of the reactor) x 1
It is defined by 00 (%).

(Test conditions) (1) Gas composition NO 500ppm O ₂ 10vol% SO ₂ 100ppm Water 6vol% Helium balance (2) Space velocity 10000hr ^-1 (3) Reaction temperature 250 ° C, 300 ° C, 350 ° C,
400 ° C, 450 ° C or 500 ° C

Example 15 A reducing agent was used in an amount shown in Tables 1 and 2 with respect to nitrogen oxides (the number of moles of the reducing agent in terms of carbon atoms relative to 1 mole of nitrogen oxide). Catalytic reduction of nitrogen oxides from a gas containing nitrogen oxides was performed. The results are shown in Table 1 and Table 2.
Shown in.

[0044]

[Table 1]

[0045]

[Table 2]

Comparative Example 1 As a reducing agent, methanol, formaldehyde, or acetone was used in an amount shown in Table 3 with respect to nitrogen oxides (the number of moles of the reducing agent in terms of carbon atoms per mole of nitrogen oxide is shown). Was used for catalytic reduction of nitrogen oxides containing nitrogen oxides. The results are shown in Table 3.

[0047]

[Table 3]

Continuation of front page (51) Int.Cl. ⁷ Identification code FI B01J 23/22 B01J 23/30 A 23/30 23/34 A 23/34 29/18 A 23/745 29/40 A 23/75 29 / 46 A 23/755 B01D 53/36 101B 29/18 B01J 23/74 301A 29/40 311A 29/46 321A (72) Inventor Hiromasu Shimizu 5-1, Ebishima-cho, Sakai-shi, Osaka Sakai Chemical Industry Co., Ltd. Central Research Laboratory (72) Inventor Ritsu Yasukawa 5-1-1 Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Institute (72) Keiichi Tabata 5-1-1 Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Institute Co., Ltd. (56) Reference JP 5-137955 (JP, A) JP 4-358525 (JP, A) JP 4-334527 (JP, A) JP 5-253488 ( JP, A) JP 4-354536 (JP, A) JP 2-233124 (JP, A) JP 6-31137 (JP, A) JP 8-150324 (JP, A) JP Flat 8-3594 (JP, A) JP-A-60-178838 (JP, A) JP-A-49-66616 (JP, A) JP-A-58-185528 (JP, A) JP-A-1-233254 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) B01D 53 / 85,53 / 94 B01J 21/00-38/74

Claims (5)

(57) [Claims] 1. A method of catalytically reducing nitrogen oxides contained in exhaust gas using a reducing agent in the presence of a catalyst, wherein a β-hydroxycarbonyl compound is used as the reducing agent. Contact reduction method. 2. A β-hydroxycarbonyl compound is represented by the general formula: (In the formula, R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each hydrogen, an alkyl group, a cycloalkyl group, an aryl group or an arylalkyl group, and R ¹ and R ² are the same. R is not hydrogen, R ¹ may form a hydrocarbon ring together with α carbon, and R ² and R ⁵ may together form a hydrocarbon ring). The method for catalytic reduction of nitrogen oxides according to claim 1. 3. The method for catalytic reduction of nitrogen oxides according to claim 1, wherein the β-hydroxycarbonyl compound is diacetone alcohol. 4. The method for catalytic reduction of nitrogen oxides according to claim 1, wherein the β-hydroxycarbonyl compound is 3-hydroxybutanal. 5. The method for catalytic reduction of nitrogen oxides according to claim 1, wherein the exhaust gas is brought into contact with the catalyst at a temperature in the range of 150 to 600 ° C.