JPH06335618A - Ammonia decomposing method - Google Patents

Abstract

PURPOSE:To obtain a catalyst for decomposing ammonia at high yield without secondarily producing nitrogen oxides by carrying the catalyst such as copper or cobalt on a crystalline silicate having a specific chemical composition and X-ray diffraction pattern. CONSTITUTION:The crystalline silicate having the chemical composition of (1+ or -0.6)R2O.(aM2O3.bAl2O3)-.cMeO.ySiO2 [(where, R is alkali metal ion and/or hydrogen ion, M is VIII group element, rare earth element or the like, Me is alkaline earth element, (a)>=0, (b)>=0, (c)>=0, (a+b)=1, (y/c)>12, (y)>12] and the specific X-ray diffraction pattern is used as the ammonia decomposing catalyst. And copper, cobalt, nickel and the like are added whereinto.

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]

DISCLOSURE OF THE INVENTION Ammonia emission into the atmosphere
As one of the methods to prevent the
Utilizing a catalyst in which iron oxide or nickel oxide is supported on the carrier
And decompose ammonia into harmless nitrogen by the following reaction formula
The method is known. 2 NH₃+ 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. 2 NH₃+ 5 / 2O₂ → 2NO + 3H₂O 2 NH₃+ 7 / 2O₂ → 2 NO₂+ 3H₂O 2 NH₃+20₂ → N₂O + 3H₂O

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]

The present invention relates to a method for decomposing and removing ammonia by bringing a gas containing ammonia into contact with an ammonia decomposing catalyst, wherein (1 ± 0.6) R _{2 in the} dehydrated state is used as the ammonia decomposing catalyst. O ・ [aM ₂ O ₃・ bAl ₂ O ₃ ] ・
cMeO.ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M is a group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, antimony, or gallium selected from the group consisting of Element, Me is an alkaline earth element, a ≧ 0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 1
2, a crystalline silicate having a chemical composition of y> 12) and an X-ray diffraction pattern shown in Table 1 below,
A method for decomposing ammonia, which comprises using a catalyst containing at least one selected from the group consisting of copper, cobalt, nickel, iron, zinc, manganese, chromium, alkaline earth elements and rare earth elements.

The catalyst used in the method of the present invention is essentially the catalyst of an internal combustion engine which we 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 Laid-Open No. 4-4045, Japanese Patent Application No. 3-319195).
issue). The crystalline silicate constituting the catalyst is characterized by having a crystal structure showing an X-ray diffraction pattern as shown in Table 1.

[0007]

[Table 1]

It is preferable to use a binder component such as alumina sol or silica sol or a carrier such as cordierite, alumina or silica-alumina as the catalyst, if necessary, after forming a honeycomb by a wash coat method or a solid method. A gas containing ammonia is added to 100 to 6
By contacting the catalyst at a temperature of 00 ° C., ammonia in the gas is decomposed into nitrogen. This decomposition reaction proceeds selectively, and no harmful gas such as NO, NO ₂ , N ₂ O is produced as a by-product.

The crystalline silicate of the catalyst used in the method of the present invention can be synthesized by a hydrothermal synthesis method using a compound containing an element constituting the silicate as a raw material. In addition, a layered composite crystalline silicate in which a crystalline silicate synthesized in advance as this crystalline silicate is used as a mother crystal, and a crystalline silicate composed of Si and O having the same crystal structure as the mother crystal is grown on the surface of the mother crystal. May be used. In this layered composite crystalline silicate, the hydrophobic action of the crystalline silicate consisting of Si and O (called silicalite) grown on the outer surface makes it difficult for only H ₂ O to penetrate into the crystalline silicate. Therefore, desorption of metal (aluminum or the like) in the crystalline silicate lattice due to the action of H ₂ O is suppressed, and deterioration of the catalyst is suppressed. Metals such as copper, cobalt and nickel contained in the crystalline silicate are contained by ion exchange method with these metal ions, or by impregnation method with which an aqueous solution of metal salt such as chloride, nitrate or sulfate is impregnated. be able to.

[0010]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples. (Preparation of catalyst 1) Water glass No. 1 (SiO ₂ : 30%) 5
616 g was dissolved in 5429 g of water, and this solution was designated as solution A. On the other hand, aluminum 718.
9 g, ferric chloride 110 g, calcium acetate 47.2
g, 262 g of sodium chloride and 2020 g of concentrated hydrochloric acid 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, and 500 g of tetrapropylammonium bromide was further added to the autoclave at 160 ° C.
After 72 hours of hydrothermal synthesis, the synthesis was followed by washing with water, drying and further firing at 500 ° C. for 3 hours to obtain crystalline silicate 1. This crystalline silicate 1 is represented by the following composition formula in terms of a molar ratio of oxides (excluding water of crystallization), and has a crystal structure of X.
It was as shown in Table 1 above by line diffraction. 0.5NaO ₂ · 0.5H ₂ O · [0.8Al ₂ O ₃ ·
0.2Fe ₂ O ₃ · 0.25CaO] · 25SiO ₂

This crystalline silicate 1 was dipped in a 0.04 M copper acetate aqueous solution (30 ° C.), stirred for 24 hours, washed with water, dried, and repeated, and this Cu ion exchange was carried out twice (total three times). Then, it was washed with water and dried to obtain a powder catalyst 1. The composition of this catalyst is 1.2CuO. [0.8Al ₂ O
₃・ 0.2Fe ₂ O ₃・ 0.25CaO] ・ 25SiO
_{Was 2} . Next, with respect to 100 parts of the powder catalyst 1, 3 parts of alumina sol and 5 parts of silica sol were used as a binder.
5 parts: the (SiO ₂ 20%) and 200 parts of water was added, the washcoat slurry perform sufficient stirring - was. Next, the monolith substrate for cordierite (lattice of 400 cells) was dipped in the above slurry, taken out, and then excess slurry was blown and dried at 200 ° C. The coating amount was 200 g per liter of the substrate. This coated material is used as a honeycomb catalyst 1.

(Catalyst Preparation 2) Cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride instead of ferric chloride in the method for synthesizing crystalline silicate 1 of catalyst preparation 1 Crystalline silicates 2 to 12 were prepared by repeating the same operation as in crystalline silicate 1 except that chromium chloride, 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 1 by X-ray diffraction, and its composition is expressed by the molar ratio of oxides (dehydrated form) of 0.5NaO ₂ .0.5H _2. O
(0.2M ₂ O ₃ · 0.8Al ₂ O ₃ · 0.25Ca
O) .25SiO ₂ . Where M is Co, Ru,
Rh, La, Ce, Ti, V, Cr, Sb, Ga, Nb
Is. Further, crystalline silicates 13 and 14 were obtained in the same manner as in crystalline silicate 1 without adding anything in place of ferric chloride or calcium acetate.

These crystalline silicates 2 to 14 were subjected to Cu ion exchange in the same manner as in Example 1 to obtain powder catalysts 2 to 14. Further, this powder catalyst was coated on a monolith substrate in the same manner as in Example 1 to obtain honeycomb catalysts 2-14.

(Catalyst Preparation 3) Except that magnesium acetate, strontium acetate, and barium acetate were added instead of calcium acetate in the same amount as CaO in terms of oxide in the method for synthesizing crystalline silicate 1 in Catalyst Preparation 1. The same operation as in crystalline silicate 1 was repeated to prepare crystalline silicates 15 to 17. The crystal structure of these crystalline silicates is shown in Table 1 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.
_{2Fe 2 O 3 · 0.8Al 2 O} 3 · 0.25MeO) ·
25 SiO ₂ . Here, Me is Mg, Sr, or Ba. These crystalline silicates 15 to 17 were subjected to Cu ion exchange in the same manner as in Catalyst Preparation 1 to obtain powder catalysts 15 to 17, and the powder catalyst was coated on a monolith substrate in the same manner as in Catalyst Preparation 1 to prepare a honeycomb catalyst 15. ~ 17 were obtained.

(Catalyst Preparation 4) The crystalline silicate 1 obtained in Catalyst Preparation 1 was finely pulverized, and 1000 g of this crystalline silicate 1 as a mother crystal was added to 2160 g of water,
Further colloidal silica (SiO ₂ : 20%) 4590
g was added and sufficiently stirred, and this solution was designated as solution a. Meanwhile, 105.8 sodium hydroxide was added to 2008 g of water.
g was dissolved to obtain a solution b. The solution b was gradually dropped while stirring the solution a to form a precipitate to obtain a slurry.
This slurry was placed in an autoclave, a solution of 568 g of tetrapropylammonium bromide dissolved in 2106 g of water was added, and the mixture was heated at 160 ° C. for 72 hours to perform hydrothermal synthesis (stirring at 200 rpm). After the reaction, the liquid was removed. After separation, washing and drying, firing was carried out at 500 ° C. for 3 hours to obtain a layered composite crystalline silicate 1 in which silicalite was coated on the surface. This layered composite crystalline silicate 1 was subjected to Cu ion exchange in the same manner as in Catalyst Preparation 1 to obtain a powder catalyst 18, and this powder catalyst was coated on a monolith substrate in the same manner as in Catalyst Preparation 1 to form a honeycomb catalyst 18. Got The honeycomb catalysts 1 to 18 prepared as described above are shown in Table 2 and Table 3.
Are shown together.

[0016]

[Table 2]

[0017]

[Table 3]

(Catalyst Preparation 5) The crystalline silicate 1 obtained in Catalyst Preparation 1 was prepared to a concentration of 0.04 M, respectively; an aqueous solution of cobalt chloride, an aqueous solution of nickel chloride, an aqueous solution of ferric chloride, an aqueous solution of zinc chloride, and manganese chloride. The catalyst was immersed in an aqueous solution, an aqueous solution of chromium nitrate, an aqueous solution of calcium chloride, an aqueous solution of barium chloride, an aqueous solution of magnesium chloride, an aqueous solution of lanthanum chloride and an aqueous solution of cerium chloride at 70 ° C., and metal ion exchange was performed in the same manner as in Preparation 1 of the catalyst. ~ 29
Got Further, this powder catalyst was coated on a monolith substrate in the same manner as in Catalyst Preparation 1 to obtain honeycomb catalysts 19 to 29. Honeycomb catalysts 19 to 29 prepared as described above
Are summarized in Table 4.

[0019]

[Table 4]

Example 1 An ammonia decomposition test was conducted using honeycomb catalysts 1-29. 15 × 15 in the reaction tube
The honeycomb catalysts 1 to 29 each having a size of 60 mm and consisting of 144 cells were put, and an ammonia-containing gas having the following composition was added to the SV.
= 16300 h ⁻¹ and a flow rate of 5.54 Nm ³ / m ² , the ammonia decomposition performance was examined at reaction temperatures of 250 ° C. and 300 ° C. (Gas composition) NH ₃ 20 ppm CO ₂ 7% H ₂ O 6% O ₂ 14.7% N ₂ residual performance evaluation is based on ammonia decomposition rate and NOx (NO, NO ₂ , N ₂ O) production rate in the initial reaction state. It was done by measuring. The ammonia decomposition rate and NOx
The production rate was calculated by the following formula. Ammonia decomposition rate (%) = [(inlet NH ₃ -outlet N
H ₃ ) / inlet NH ₃ ] × 100 NOx production rate (%) = [(outlet (N ₂ O × 2 + NO + N
O ₂ )) / inlet NH ₃ ] × 100 These measurement results are shown in Table 5.

[0021]

[Table 5]

(Example 2) A durability evaluation test was carried out by using honeycomb catalysts 1 to 29 and passing gas under the same conditions as in Example 1 for a long time. As a result, it was confirmed that the catalyst maintained the same ammonia decomposition rate and NOx generation rate as in Table 5 even after 1000 hours of supply under the above gas conditions, and was a catalyst with excellent durability.

[0023]

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

Claims (1)

[Claims] 1. A method for decomposing and removing ammonia by contacting a gas containing ammonia with an ammonia decomposing catalyst, wherein (1 ± 0.6) R ₂ O. [aM ₂ O _{3 is} used as an ammonia decomposing catalyst in a dehydrated state.・ BAl ₂ O ₃ ] ・
cMeO.ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M is a group VIII element, a rare earth element, titanium, vanadium, chromium, niobium, antimony, or gallium selected from the group consisting of Element, Me is an alkaline earth element, a ≧ 0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 1
2, y> 12), and copper, cobalt, nickel, iron, zinc, manganese in the crystalline silicate having the X-ray diffraction pattern shown in Table 1 in the detailed description of the invention. A method for decomposing ammonia, which comprises using a catalyst containing at least one of chromium, chromium, alkaline earth elements and rare earth elements.