JP3453172B2 - DeNOx method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a denitration treatment method capable of removing nitrogen oxides (hereinafter abbreviated as NOx) in exhaust gas with high efficiency.

[0002]

2. Description of the Related Art As a method for removing nitrogen oxides (NOx) in exhaust gas, a catalytic ammonia reduction method in which NOx and ammonia (NH ₃ ) are catalytically reacted to decompose into nitrogen and water is widely used. There is. This method requires a denitration catalyst for accelerating the reaction, and many studies have been conducted on the catalyst development so far.

[0003]

Recently, NOx emission regulations have become strict, and in particular, there is a demand for reducing the NOx emission concentration from a chimney to about 0.06 ppm, which is equivalent to the atmosphere, in large cities. . In the denitration method by catalytic reduction using NH ₃ , the reaction proceeds according to the following equation, and NOx is decomposed into N ₂ . 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O In the conventional method, denitration was performed by adding approximately the same amount of NH ₃ as in the above formula. However, in the exhaust gas from the boiler, N
Due to the effect of the degree of mixing of O and NH ₃ and the decomposition of NH ₃ ,
100% denitration according to the above reaction formula cannot be performed, and the reaction rate is 80
It was about 90%, and unreacted NO was discharged as it is from several ppm to 10 ppm. On the other hand, it is possible to add NH ₃ in an amount equal to or more than the equivalent amount of NO to improve the decomposition rate of NO, but there is a problem that unreacted NH ₃ is discharged into the atmosphere, and therefore a preferable NOx emission concentration reduction There was no law.

The present invention solves the above problems of the prior art,
It is an object of the present invention to provide a denitration treatment method capable of decomposing NOx with high efficiency without releasing unreacted NH ₃ to the atmosphere.

[0005]

According to the present invention, (1) a nitrogen oxide-containing gas is added with ammonia in a reaction equivalent amount or more with respect to nitrogen oxide, and (1 ± 0.6) R is added in a dehydrated state. ₂
O ・ [aM ₂ O ₃・ bAl ₂ O ₃ ] ・ cMeO ・ ySi
O ₂ (in the formula, R: alkali metal ion and / or hydrogen ion, M: one or more selected from the group consisting of Group VIII elements of the Periodic Table, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium Element, Me: alkaline earth element, a + b = 1.0, a> 0 , b ≧ 0, c
> 0 , y / c> 12, y> 12) and a crystalline silicate having the X-ray diffraction pattern shown in Table 1 in the detailed description of the invention, copper, cobalt. A method for denitrifying a nitrogen oxide-containing gas, which comprises contacting with a catalyst containing at least one of nickel, iron, zinc, manganese, chromium, alkaline earth elements and rare earth elements , and (2) ) The crystalline silicate of (1) above has Si having the same crystal structure on its surface.
A denitration how the nitrogen oxide-containing gas of the above (1), wherein a and a layered composite crystalline silicate is grown from consisting crystalline silicate O.

In the method of the present invention,
NH by using a catalyst₃NOx in the presence of
It has a selective denitration action, and ammonia is also harmless
N ₂And H₂It can be decomposed into O. This reaction is below
It is represented by a formula.     4NO + 4NH₃+ O₂  → 4N₂+ 6H₂O ... (1)     2 NH₃+ 3 / 2O₂    → N₂+ 3H₂O ... (2)

The catalyst used in the present invention can be caused by simultaneous generation of the equations (1) and (2). However, since the reaction rate of the equation (1) is faster, the leakage occurs after the equation (1) is completed. NH ₃ can be decomposed and removed by the formula (2). That is, NO
It is possible to decompose and remove leaked NH ₃ at the same time by the catalyst used in the present invention even after performing high-efficiency denitration by adding x and a reaction equivalent or more of NH ₃ .

The catalyst used in the present invention is (1.0 ± 0.6) R ₂ O. [aM ₂ O ₃ .bAl in a dehydrated state.
₂ O ₃ ] .cMeO.ySiO ₂ (wherein R: alkali metal ion and / or hydrogen ion, M: VIII of the periodic table)
One or more elements selected from the group consisting of group elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium, Me: alkaline earth element, a + b =
1.0, a> 0 , b ≧ 0, c> 0 , y / c> 12, y>
In the crystalline silicate having the chemical composition of 12) and having the X-ray diffraction pattern shown in Table 1 below, copper, cobalt, nickel, iron, zinc, manganese, chromium, alkaline earth elements and rare earth elements A catalyst containing at least one or more of the above-mentioned crystalline silicates,
The catalyst is a layered composite crystalline silicate obtained by growing a crystalline silicate of Si and O having the same crystal structure on its surface.

[0009]

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

This catalyst does not deteriorate over a long period of time in the temperature range of 200 to 550 ° C., and the above (1)
It is possible to cause a simultaneous reaction of the formulas (2), no by-products such as NOx are generated, and all decomposition products are N
It has been confirmed that it is _2.

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. Further, a layered composite crystalline silicate in which a crystalline silicate synthesized in advance as the 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. This layered composite crystalline silicate has a hydrophobic action of a crystalline silicate (referred to as silicalite) composed of Si and O grown on the outer surface, so that only H ₂ O hardly penetrates 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.

The metal of copper, cobalt, nickel, iron, zinc, manganese, chromium, alkaline earth elements and rare earth elements contained in the crystalline silicate is allowed to contain these metal ions by an ion exchange method, or Alternatively, it can be contained by an impregnation method in which an aqueous solution of a metal salt such as chloride, nitrate or sulfate is impregnated.

It is preferable that the catalyst is formed into a honeycomb by a wash coat method or a solid method and then installed. As a particularly preferred form, it is used in the form of being coated on a base material such as cordierite formed into a honeycomb shape.
Hereinafter, the method of the present invention will be described more specifically with reference to Examples.

[0014]

【Example】

(Example 1) (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, 500 g of tetrapropylammonium bromide was further added, and hydrothermal synthesis was performed at 160 ° C for 72 hours, followed by washing with water and drying, and further 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 oxide (excluding the water of crystallization), and the crystal structure was as shown in Table 1 above by X-ray diffraction. 0.5 NaO
₂・ 0.5H ₂ O ・ [0.8Al ₂ O ₃・ 0.2Fe ₂
O ₃ · 0.25CaO] · 25SiO ₂

This crystalline silicate 1 was immersed in a 0.04 M aqueous solution of copper acetate (30 ° C.), stirred for 24 hours, washed with water, dried, and then 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 as a binder and 55 parts of silica sol.
Part: The (SiO ₂ 20%) and 200 parts of water was added, to thereby prepare a slurry for wash-coating performs stirred thoroughly. Next, the monolith substrate for cordierite (lattice of 400 cells) was immersed in the slurry, taken out, and then excess slurry was blown off 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.

(Preparation of catalyst 2) Crystalline catalyst of preparation 1 of catalyst
In the method of synthesizing replicate 1, salt is used instead of ferric chloride.
Cobaltide, ruthenium chloride, rhodium chloride, lanthanum chloride
Tan, cerium chloride, titanium chloride, vanadium chloride, salt
Chromium chloride, antimony chloride, gallium chloride and niobium chloride
Fe in terms of oxide₂O₃Add the same number of moles as
Repeat the same operation as crystalline silicate 1 except that
To prepare crystalline silicates 2-12. These crystals
The crystalline structure of the crystalline silicate is shown in Table 1 above by X-ray diffraction.
The composition is based on the molar ratio of oxides (dehydrated
0.5NaO ₂・ 0.5H₂O
(0.2M₂O₃・ 0.8Al₂O₃・ 0.25Ca
O) ・ 25SiO₂Met. 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 added to Cu in the same manner as in Catalyst Preparation 1.
Ion exchange was performed to obtain powder catalysts 2 to 14. Further, this powder catalyst was coated on a monolith substrate in the same manner as in Catalyst Preparation 1 to obtain honeycomb catalysts 2-14. Note that the honeycomb catalyst
Reference numerals 13 and 14 are reference examples.

(Catalyst Preparation 3) In the method of synthesizing the crystalline silicate 1 of Catalyst Preparation 1, magnesium acetate, strontium acetate, and barium acetate were added instead of calcium acetate in the same mole number as CaO in terms of oxide. 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. The 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. While stirring the solution a, the solution b was gradually added dropwise 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 separated. After washing, drying, and baking at 500 ° C. for 3 hours, a layered composite crystalline silicate 1 having silicalite coated on the surface layer 1
Got

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. A honeycomb catalyst 18 was obtained. Table 2 collectively shows the honeycomb catalysts 1 to 18 prepared as described above.

[0022]

[Table 2]

(Catalyst Preparation 5) The crystalline silicate 1 obtained in Catalyst Preparation 1 was prepared to a concentration of 0.04 M, respectively, and 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 were prepared. 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 3.

[0024]

[Table 3]

(Experimental Example 1) A denitration test was conducted using honeycomb catalysts 1-29. 15 mm x 15 mm x reaction tube
Honeycomb catalyst 1 consisting of 144 cells with a size of 60 mm
˜29, and then a nitrogen oxide-containing gas having the following composition was added with SV = 16,300 h ⁻¹ and a flow rate of 554 Nm ³ / m ^2.
Then, a denitration test was conducted at reaction temperatures of 300 ° C and 400 ° C. 〇 (gas _{composition) NH 3: 120ppm NO: 100ppm} CO 2: 7% H 2 O: 6% O 2: 14.7% N 2: the remaining performance evaluation of the catalyst layer downstream side in the initial stage of the reaction state NOx
Examine its concentration of (· NO + NO ₂₎ and NH _3.

From the results in Table 4, NO by the method of the present invention
9 with these catalysts by adding excess NH ₃ to x
It was confirmed that a denitration rate of 9% or more was obtained, and that leak NH ₃ was almost completely decomposed by these catalysts, and high-efficiency denitration could be easily performed.

[0027]

[Table 4]

(Experimental 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 Experimental Example 1 for a long time. As a result, even after the gas condition was supplied at 300 ° C. for 1000 hours, the same amount of outlet NOx and outlet N as in Table 4 was obtained.
It was confirmed that the amount of H ₃ was maintained and the catalyst had excellent durability.

[0029]

EFFECTS OF THE INVENTION According to the method of the present invention, there is no fear of leaking NH ₃ from the exhaust gas containing NOx, and the efficiency of N
Ox can be decomposed and removed.

Continued front page       (56) References JP-A-59-230642 (JP, A)                 JP-A-5-168941 (JP, A)                 JP-A-5-31369 (JP, A)

Claims (2)

(57) [Claims] 1. A nitrogen oxide-containing gas to which a reaction equivalent amount or more of ammonia with respect to nitrogen oxides is added, and (1 ± 0.6) R ₂ O. [aM ₂ O ₃ .bAl in a dehydrated state is added. ₂ O
₃ ] .cMeO.ySiO ₂ (wherein R is an alkali metal ion and / or a hydrogen ion, M is a group VIII element of the periodic table, a rare earth element, titanium, vanadium, chromium, niobium, antimony and gallium. 1 chosen
More than one element, Me: alkaline earth element, a + b = 1.
0, a> 0 , b ≧ 0, c> 0 , y / c> 12, y> 1
The crystalline silicate having the chemical composition of 2) and the X-ray diffraction pattern shown in Table 1 described in the detailed description of the invention is added to copper, cobalt, nickel, iron, zinc, manganese, chromium, A method for denitrifying a nitrogen oxide-containing gas, which comprises bringing the catalyst into contact with a catalyst containing at least one or more of an alkaline earth element and a rare earth element. 2. The crystalline silicate of claim 1 is a layered composite crystalline silicate obtained by growing a crystalline silicate of Si and O having the same crystal structure on the surface thereof. Method for denitrifying nitrogen oxide-containing gas of 1.