JPH0889758A - Decomposing method of ammonia - Google Patents

Abstract

PURPOSE: To provide a method for decomposing ammonia included in various kinds of exhaust gas into harmless nitrogen. CONSTITUTION: In a method for decomposing and removing ammonia from a gas containing ammonia, the gas is brought into contact with a catalyst for decomposition of ammonia. The catalyst is obtd. by depositing platinum as active metal on a carrier. The carrier consists of crystalline silicate having chemical compsn. of (1±0.8)R2 O.[aM2 O3 .bAl2 O3 -].cMeO.ySiO2 in a dehydrated state and a specified X-ray diffraction pattern or a carrier comprising specified single oxide, multiple oxide, solid super strong acid or various kinds of zeolite. In the formula, R is an alkali metal ion and/or hydrogen ion, M is at least one element selected from group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium, Me is an alkaline earth element, a>=0, b>=0, c>=0, a+b=1, y/c>12, and y>12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of decomposing ammonia contained in various exhaust gases into harmless nitrogen.

[0002]

Ammonia is used in a wide range of fields such as a raw material for producing fertilizer and nitric acid, a refrigerant, and a reducing agent for removing nitrogen oxides in exhaust gas. Therefore, a large amount of ammonia is emitted from various chemical product manufacturing plants, waste treatment plants such as refrigerators, and combustion exhaust gas treatment facilities. Ammonia is a gas with a unique irritating odor, and its release into the atmosphere must be suppressed as much as possible. However, in many places, such as the generation of ammonia due to the decay of living organisms, the emission of ammonia from the refrigerant in waste, and the ammonia used for the reduction of nitrogen oxides in flue gas, is released into the atmosphere without reaction. At present, ammonia is released into the atmosphere.

[0003]

As one of the methods for preventing the release of ammonia into the atmosphere, a catalyst in which iron oxide or nickel oxide is supported on an alumina or silica-alumina type carrier is used to make ammonia harmless according to the following reaction formula. A method of decomposing it into pure nitrogen is known.

Embedded image 2NH₃+ 3 / 2O₂ → N₂+ 3H₂O However, with conventional catalysts, in addition to the above reactions,
NO by reaction, NO ₂, N₂Generation of O etc. is recognized,
There was a risk of new air pollution.

Embedded image 2NH ₃ + 5 / 2O ₂ → 2NO + 3H ₂ O 2NH ₃ + 7 / 2O ₂ → 2NO ₂ + 3H ₂ O 2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O

The object of the present invention is to solve the above-mentioned problems of the prior art, and to decompose and remove ammonia with a high yield without fear of producing nitrogen oxides as a source of air pollution as a by-product. To provide a method.

[0005]

[Means for Solving the Problems]

(1) The present invention relates to a method of decomposing and removing ammonia by bringing a gas containing ammonia into contact with an ammonia decomposing catalyst, wherein (1 ± 0.8) R ₂ O. [ aM ₂ O ₃ · bAl ₂ O
₃ ] .cMeO.ySiO ₂ (In the formula, R is an alkali metal ion and / or hydrogen ion, M is a group selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium. More than one element,
Me is an alkaline earth element, a ≧ 0, b ≧ 0, c ≧ 0, a
+ B = 1, y / c> 12, y> 12), and a catalyst having platinum as an active metal supported on a carrier made of a crystalline silicate having an X-ray diffraction pattern shown in Table A below. A method for decomposing ammonia, which is used (first invention).

(2) The platinum catalyst carrier is γ-Al ₂ O.
₃ , θ-Al ₂ O ₃ , ZrO ₂ , TiO ₂ , TiO ₂ ·
ZrO ₂ , SiO ₂ · Al ₂ O ₃ , Al ₂ O ₃ · TiO
₂ , SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ · TiO ₂ ,
The method for decomposing ammonia according to (1) above, which is a porous substance of at least one selected from the group consisting of Y-type zeolite, X-type zeolite, A-type zeolite, mordenite and silicalite. invention).

The catalyst used in the method of the present invention is essentially the catalyst of an internal combustion engine which the inventors have previously contained nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) and the like. It is the same as that developed as a catalyst for purifying exhaust gas (Japanese Patent Application Nos. 6-7667 and 5-228382). The crystalline silicate constituting the first invention catalyst is characterized by having a crystal structure showing an X-ray diffraction pattern as shown in Table A.

[0008]

[Table 1] VS: Very strong M: Intermediate S: Strong W: Weak (X-ray source CuKα)

[0009]

The catalyst used in the present invention preferably uses a binder component such as alumina sol or silica sol, or a base material such as cordierite, if necessary, and is made into a honeycomb by a wash coat method or a solid method. By bringing a gas containing ammonia into contact with the catalyst at a temperature of 100 to 600 ° C., the ammonia in the gas is decomposed into nitrogen. This decomposition reaction selectively proceeds,
No harmful gas such as NO, NO ₂ and N ₂ O is produced as a by-product. Furthermore, the catalyst used in the present invention maintains a stable ammonia decomposing performance without lowering the ammonia decomposing activity even in the exhaust gas in which SO ₂ coexists. Also, SO ₂
Since the ability to oxidize carbon dioxide to SO ₃ is low, there are no problems with the formation of ammonium acid sulfate.

The platinum metal supported on the crystalline silicate (first invention) and various carriers (second invention) is allowed to contain platinum ions in an ion exchange method or impregnated with an aqueous salt solution such as platinum chloride. It can be contained by the impregnation method. Platinum to be supported exhibits sufficient activity at 0.0005 wt% or more, and preferably has high activity at 0.001 wt% or more.

[0011]

EXAMPLES The preparation of the catalysts used in the present invention will be specifically described below, and examples using the catalysts will be shown.

(Catalyst Preparation 1) Water Glass No. 1 (Si
O ₂ : 30%): 5616 g was dissolved in water: 5429 g, and this solution was designated as solution A. On the other hand, water: 4175 g, aluminum sulfate: 718.9 g, ferric chloride: 110
g, calcium acetate: 47.2 g, sodium chloride: 2
62 g and concentrated hydrochloric acid: 2020 g were mixed and dissolved, and this solution was designated as solution B. Solution A and solution B were supplied at a constant ratio to form a precipitate, which was sufficiently stirred to obtain a slurry having a pH of 8.0. This slurry was charged into a 20-liter autoclave, 500 g of tetrapropylammonium bromide was further added, and hydrothermal synthesis was carried out at 160 ° C for 72 hours, followed by washing with water, drying and firing at 500 ° C for 3 hours to crystallize. Obtained silicate 1. This crystalline silicate 1 was represented by the following composition formula in terms of the molar ratio of oxides (excluding the water of crystallization), and the crystal structure was represented by the above-mentioned Table A by X-ray diffraction.

[Chemical formula 3] 0.5Na ₂ O ・ 0.5H ₂ O ・ [0.8Al
₂ O ₃ · 0.2Fe ₂ O ₃ · 0.25CaO] · 25S
iO ₂

The above crystalline silicate 1 was treated with 4N NH ₄ C.
1 aqueous solution was stirred at 40 ° C. for 3 hours to carry out NH ₄ ion exchange. It was washed after ion exchange, dried at 100 ° C. for 24 hours, and then calcined at 400 ° C. for 3 hours to obtain H-type crystalline silicate 1.

Catalysis Next, to 200 g of the above H-type crystalline silicate:
Chloroplatinic acid H₂[PtCl₆] ・ 6H₂O: 0.1
A powder catalyst was obtained by supporting and firing at a rate of 1 g by the impregnation method.
It was Aluminum as binder for 100 parts of powder catalyst
Nasol 3 parts, silica sol 55 parts (SiO₂: 20%)
Add 200 parts of water and stir well to wash coat
For slurry. Next, the monolith base material for cordierite
(30 cells / inch ², Lattice spacing 4.6 mm, wall thickness
(0.6 mm) is immersed in the above slurry and taken out.
A minute slurry was blown off and dried at 200 ° C. coat
The amount of this coated material is 150 g per liter of the base material.
Was used as catalyst 1.

(Preparation of catalysts 2 to 5) Next, to 200 g of the above H-type crystalline silicate, chloroplatinic acid H was added.
₂ [PtCl ₆ ] .6H ₂ O: 0.006 g, 0.02
8 g, 0.55 g, 2.75 g (0.001 wt% as Pt, 0.005 per unit amount of the above crystalline silicate)
wt%, 0.1 wt%, and 0.5 wt%) were supported by the impregnation method, and the same operation as that for the catalyst 1 was performed to obtain coated catalysts 2 to 5.

In the method for synthesizing the crystalline silicate 1 in the preparation of the above-mentioned honeycomb catalyst 1, cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride is used instead of ferric chloride. , Crystalline silicates 2 to 12 were prepared by repeating the same operation as in crystalline silicate 1 except that antimony chloride, gallium chloride and niobium chloride were added in the same mole number as Fe ₂ O _{3 in} terms of oxide. The crystal structure of these crystalline silicates is shown in Table A above by X-ray diffraction, and its composition is expressed by the molar ratio of oxides (dehydrated form) of 0.5Na ₂ O · 0.5H. ₂ O
(0.2M ₂ O ₃ · 0.8Al ₂ O ₃ · 0.25Ca
O) .25SiO ₂ . Where M is Co, Ru, R
h, La, Ce, Ti, V, Cr, Sb, Ga, Nb.

Further, in the method for synthesizing the crystalline silicate 1, magnesium acetate, strontium acetate, and barium acetate are used instead of calcium acetate, respectively, in terms of oxides to convert them into C.
The same operations as in the crystalline silicate 1 were repeated except that the same number of moles as that of aO was added to the crystalline silicates 13 to 1.
5 was prepared. The crystal structure of these crystalline silicates is shown in Table A above by X-ray diffraction, and its composition is 0.5 in terms of the oxide molar ratio (dehydrated form).
Na ₂ O ・ 0.5H ₂ O ・ (0.2Fe ₂ O ₃・ 0.8
Is an _{Al 2 O 3 · 0.25MeO) ·} 25SiO 2.
Here, Me is Mg, Sr, or Ba.

(Preparation of Catalysts 6 to 19) Using the above crystalline silicates 2 to 15 in the same manner as in the case of the honeycomb catalyst 1,
Mold type crystalline silicates 2 to 15 were obtained, and platinum was supported on the silicate in the same ratio as the catalyst 1. Further, a honeycomb substrate was coated in the same manner as in Catalyst 1 to obtain Catalysts 6 to 19. Catalysts 1-19 are collectively shown in Table B.

[0019]

[Table 2]

(Preparation of Catalysts 20 to 33) Instead of the crystalline silicate of the honeycomb catalyst 1, single oxides γ-Al ₂ O ₃ , θ-Al ₂ O ₃ , ZrO ₂ , and T are used.
iO ₂ , and TiO ₂ · ZrO ₂ which is a complex oxide, S
iO ₂ · Al ₂ O ₃ , Al ₂ O ₃ · TiO ₂ , and SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ · T that are solid superacids
io ₂ (these solid superacids are Zr (OH) ₄ , Zr
About 1 (OH) ₄ · Ti (OH) ₄ in 1N H ₂ SO ₄
It is obtained by immersing at room temperature for a period of time, filtering, drying, and calcining) and Y-type zeolite, X-type zeolite, A-type zeolite, mordenite, silicalite (a kind of zeolite having a pentasil-type structure, Si , O only) in the same manner as for catalyst 1
Was carried to obtain honeycomb catalysts 20 to 33. The honeycomb catalysts 20 to 33 are collectively shown in Table C.

[0021]

[Table 3]

Example 1 An ammonia decomposition test was carried out using honeycomb catalysts 1 to 33. Honeycomb catalysts 1 to 33 were placed in a reaction tube, and an ammonia-containing gas having the composition shown in Table D below was added to SV = 16300 h ^{−1 at} a flow rate of 5.54 Nm ³ / m ^2.
-Ammonia decomposition performance was examined at a reaction temperature of 300 ° C and 400 ° C under the condition of h.

[0023]

[Table 4]

The performance was evaluated by measuring the ammonia decomposition rate, the NOx (NO, NO ₂ , N ₂ O) production rate, and the SO ₂ oxidation rate in the initial state of the reaction. The ammonia decomposition rate and the NOx production rate were calculated by the following equations.

Ammonia decomposition rate (%) = [(inlet N
H ₃ −Outlet NH ₃ ) / Inlet NH ₃ ] × 100

NOx production rate (%) = [(outlet (N ₂
O × 2 + NO + NO ₂ )) / Inlet NH ₃ ] × 100

SO ₂ oxidation rate (%) = [outlet SO ₃ /
Inlet SO ₂ ] × 100 These measurement results are summarized in Table E.

[0028]

[Table 5]

(Experimental Example 2) Using honeycomb catalysts 1 to 33, an ammonia-containing gas having the same composition as in Example 1 was added to SV =
After flowing under conditions of 16300 h ⁻¹ and a flow rate of 5.54 Nm ³ / m ² · h and treating at 400 ° C. for 1000 hours, ammonia decomposition performance was examined at reaction temperatures of 300 ° C. and 400 ° C. The results of these measurements are summarized in Table F.

[0030]

[Table 6]

In this result, the same ammonia decomposition rate, NOx generation rate and SO ₂ oxidation rate as in Table E were maintained,
It was confirmed that the catalysts 1 to 33 have excellent durability.

[0032]

According to the ammonia decomposition method of the present invention,
Without producing SO ₂ oxidation or by-products such as NOx,
Ammonia can be decomposed into harmless nitrogen. Such a decomposition treatment method has never been used before, and its industrial utility value is extremely high.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location B01J 29/87 ZAB A 29/88 ZAB A 29/89 ZAB A

Claims (2)

[Claims] 1. A method of decomposing and removing ammonia by bringing a gas containing ammonia into contact with an ammonia decomposing catalyst, wherein (1 ± 0.8) R ₂ O. [aM is used as the ammonia decomposing catalyst in a dehydrated state. ₂ O ₃ · bAl ₂ O
₃ ] .cMeO.ySiO ₂ (In the formula, R is an alkali metal ion and / or hydrogen ion, M is a group selected from the group consisting of Group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony, and gallium. More than one element,
Me is an alkaline earth element, a ≧ 0, b ≧ 0, c ≧ 0, a
+ B = 1, y / c> 12, y> 12), and a crystalline silicate carrier having an X-ray diffraction pattern shown in Table A in the detailed description of the invention. A method for decomposing ammonia, which comprises using a catalyst carrying platinum as an active metal. 2. The platinum catalyst carrier is γ-Al ₂ O ₃ ,
θ-Al ₂ O ₃ , ZrO ₂ , TiO ₂ , TiO ₂ · Zr
O ₂ , SiO ₂ · Al ₂ O ₃ , Al ₂ O ₃ · TiO ₂ ,
SO ₄ / ZrO ₂ , SO ₄ / ZrO ₂ · TiO ₂ , Y-type zeolite, X-type zeolite, A-type zeolite, mordenite and at least one kind of porous material selected from silicalite The method for decomposing ammonia according to claim 1, which is characterized in that.