JPH04363118A - Method for removing nitrogen oxide in exhaust gas - Google Patents

Abstract

PURPOSE:To remove NOx such as NO, NO2 and N2O in exhaust gas. CONSTITUTION:Exhaust gas contg. NOx such as NO, NO2 and N2O is brought into contact with a catalyst at 400-700 deg.C in a state in which the NOx has a prescribed lattice plane interval (d) in the powder X-ray diffraction and is dehydrated to remove the NOx by decomposition into N2 and water with ammonia. The catalyst used is obtd. by incorporating Cu ions into crystalline silicate represented by a chemical formula (1.0+ or -0.8)R2O.[aM2O3.bAl2O3].ySiO2 (where R is an alkali metal ion and/or an H ion, M is ions of one or more kinds of elements selected from among group VIII metals, rare earth metals, Ti, V, Cr, Nb, Sb and Ga, a+b=1, a>=0, b>=0 and y=20-1,000) when expressed by molar ratio among oxides.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention removes nitrogen oxides such as nitrogen monoxide, nitrogen dioxide (hereinafter abbreviated as NOx), and nitrous oxide (hereinafter abbreviated as N2O) in combustion exhaust gas such as boiler exhaust gas. Regarding how to.

0002

[Prior Art] Nitrogen oxides in the exhaust gas emitted from internal combustion engines such as heavy oil and coal-fired boilers, combustion furnaces attached to various chemical equipment, steel plants, diesel engines and turbines are mainly composed of NO. As a detoxification treatment, the catalytic cracking method using ammonia as a reducing agent has been industrialized as an effective means, and many plants employing this method are currently in operation.

As a catalyst used in this method, a catalyst in which vanadium oxide and tungsten oxide are supported on a titanium oxide carrier is generally known. However, in recent years, fluidized bed boilers have been constructed and put into operation for the purpose of increasing the power generation efficiency of coal-fired boilers. When we investigated the behavior of nitrogen oxides in the flue gas during operation of a fluidized bed boiler, we found that along with NOx, N2O, which is hardly present in normal boiler flue gas, was present at several hundred ppm, the same concentration as NOx. It became clear that

[0004] Conventional titania-based catalysts have a drawback in that they cannot remove N2O contained in the exhaust gas. Therefore, since fluidized bed boilers and the like cannot remove N2O, which is listed as a global greenhouse gas, and emit it into the atmosphere, it is desired to develop a catalyst for removing it from the standpoint of environmental conservation.

[0005]

[Problems to be Solved by the Invention] When we investigated the behavior of N2 O and NOx contained in the exhaust gas generation source in an actual denitrification device for a coal-fired fluidized bed boiler using a titanium oxide-vanadium oxide-tungsten oxide catalyst, we found that: NOx was 400 ppm at the inlet of the denitrification equipment, but was reduced to 20 ppm at the exit of the denitrification equipment after being reduced and decomposed by the catalyst. On the other hand, it was revealed that N2O was constant at about 100 ppm at the inlet and outlet of the denitration equipment, and could not be removed by conventional titania-based catalysts.

[0006] The present invention makes it possible to remove N2O, which could not be removed with conventional NOx removal catalysts, and also
The object of the present invention is to provide a method for removing nitrogen oxides from exhaust gas, which makes it possible to exhibit a high removal rate even in the removal of nitrogen oxides.

[0007]

[Means for Solving the Problems] The present inventors have determined that NOx and N
We searched for catalysts that can simultaneously remove 2 O, and accumulated research and theoretical considerations on the basic physical properties of metal ion-exchanged crystalline silicates in combinations of supported metal ions and supports. Crystalline silicates with a crystalline structure are NOx and N2O
was found to exhibit high steady-state activity as a removal catalyst.

That is, the present invention provides nitrogen monoxide in exhaust gas,
Nitrogen oxides such as nitrogen dioxide and nitrous oxide 400 to 7
Under conditions of 00°C, the lattice spacing (d value) in powder X-ray diffraction shown in Table 1 below, and in a dehydrated state, the molar ratio of oxide is (1.0 ± 0.8). R2 O・
[aM2 O3 ・bAl2 O3 ]・ySiO2
(In the above formula, R is an alkali metal ion and/or hydrogen ion, M is an ion of one or more elements selected from the group consisting of Group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony, and gallium. , a+b=1
, a≧0, b≧0, y=20-1000) is brought into contact with a catalyst containing copper ions, and the nitrogen oxides are decomposed into nitrogen and water by ammonia. This is a method for removing nitrogen oxides from exhaust gas.

[Table 1] W: Weak Irradiation is K of copper
α ray M: Intermediate I0 is the strongest peak intensity S: Strong
I/I0 is relative strength VS: very strong

[0009]

[Operation] The reduction reaction of nitrogen oxides in the selective catalytic reduction method using ammonia as a reducing agent according to the present invention is as follows (
In addition to the NOx reduction reactions of conventional catalysts shown in equations 1) and (2), the N2O reduction reaction shown in equation (3) proceeds simultaneously and efficiently. 4NO+4NH3 +O2 → 4N2
+6H2 O...(1) NO+NO
2 +2NH3 → 2N2 +3H2 O
...(2) 3NO2 +2NH3 →
4N2 +3H2 O ・・・・・・(3)

0
The present invention is achieved by using a catalyst containing copper in a crystalline silicate having a specific crystal structure.

The crystalline silicate used in the present invention contains a source of silica, a group VIII element, a rare earth element,
A reaction mixture containing a source of oxides of titanium, vanadium, chromium, niobium, antimony, and gallium, a source of alumina, a source of alkali, water, and an organic nitrogen-containing compound is prepared, and this mixture is used to form a crystalline silicate. It can be obtained by synthesis by heating at a time and temperature ranging from

Furthermore, the crystalline silicate used in the present invention is a high-silica crystalline silicate with a SiO2 /Al2O3 ratio of 20 to 1000, or a part of Al in the structure of conventional zeolite is a group VIII element or a rare earth element. ,
It replaces titanium, vanadium, chromium, niobium, antimony, and gallium, and also SiO2 /
(M2 O3 + Al2 O3) ratio is 20 to 1000, (if this ratio is less than 20, N
If it is less than 2 O, the decomposition effect of N2 O is small;
(If it exceeds this amount, it approaches a substance called silicalite and loses its effectiveness as a catalyst.) It is produced from a reaction mixture with the following molar composition. SiO2/(M2O3 +Al2O3): 20
~1000 (preferably 20-200) OH-/SiO2: 0-1.0 (preferably 0.
2-0.8) H2O/SiO2: 2-1000 (preferably 1
0-200) Organic nitrogen-containing compound/(M2O3 +Al2O3
): 5-100 (preferably 5-50)

[0013] Further, the content of copper supported on the carrier made of crystalline silicate used in the present invention is 0.05 to 3 mmol, preferably 0.2 to 2 mmol per 1 g of the carrier.
It is.

For industrial use of the catalyst used in the present invention, it is desirable to form it into a suitable shape. For example, using an inorganic oxide such as silica or alumina or clay as a binder, and optionally using an organic molding aid, it is molded into a spherical, columnar, or honeycomb shape. A crystalline silicate that has been preformed before being exchanged with copper ions and the molded body subjected to copper ion exchange can also be considered as the catalyst used in the present invention. The size of the molded body is not particularly limited.

[0015]

EXAMPLE A crystalline silicate was synthesized as follows. Water glass, ferric sulfate, aluminum sulfate, water with Na
2 O・(0.1Fe2O3 ・0.9Al2O3
)・30SiO2・1600H2O, then add an appropriate amount of sulfuric acid to make the pH of the mixture around 9, and then add propylamine and propyl bromide as organic nitrogen-containing compounds. Fe2O
3, 20 times the total number of moles of Al2O3 was added, mixed well, and placed in a 500cc stainless steel autoclave.

The above mixture was reacted at 160° C. for 3 days while stirring at about 500 rpm. After cooling, filter the solid content and wash thoroughly with water until the pH of the washing water becomes approximately 8.
It was dried at 10°C for 12 hours and fired at 550°C for 3 hours.

[0017] The crystal grain size of this product is around 1μ,
The composition expressed in molar ratio of oxides is expressed in dehydrated form as follows: (H,Na)2O.(0.1Fe2O3.0.1Fe2O3.0.
9Al2O3).30SiO2. This is called crystalline silicate 1.

When synthesizing this crystalline silicate 1,
The same silicate can be obtained even if hydrochloric acid is used instead of sulfuric acid among the raw materials, ferric chloride is used instead of ferric sulfate, or silica sol is used instead of water glass. Ta.

A similar silicate was also obtained by reacting at 170°C or 180°C for 2 days instead of 160°C for 3 days as the hydrothermal synthesis conditions.

[0020] The amounts of ferric sulfate and aluminum sulfate added when preparing the raw materials for crystalline silicate 1 were changed to Fe2 O3 and A.
Crystalline silicates 2 to 4 were prepared by repeating the same operation as in the case of crystalline silicate 1, except that the molar ratio of l2O3 was changed as shown below.

When preparing crystalline silicate 1, hydrochloric acid was used instead of sulfuric acid, and instead of ferric sulfate,
cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride,
Crystalline silicates 5 to 14 were prepared by repeating the same procedure as for crystalline silicate 1, except that chromium chloride, antimony chloride, and gallium chloride were each added in the same number of moles as Fe2O3 in terms of oxides.

The composition of these crystalline silicates excluding organic nitrogen-containing compounds is expressed as the molar ratio of oxides (dehydrated form): (H,Na)2O.(0.1M2O3
・0.9Al2O3)・30SiO2. Here, M is Co, Ru, Rh, La, Ce, Ti, V
, Cr, Sb, Ga (in numerical order of crystalline silicates 5 to 14).

Furthermore, in crystalline silicate 1, SiO2 /(0.1Fe2O3 +0.9Al2
O3) The same operation as for crystalline silicate 1 was repeated except that the ratio was changed to 20 and 80 to obtain crystalline silicate 15 and 15, respectively.
16 was prepared.

Powder X of the above crystalline silicates 1 to 16
It was confirmed that the line diffraction pattern showed the pattern shown in Table 1 above.

10 g of each of the above crystalline silicates 1 to 16 were placed in an aqueous solution of 1 g of copper acetate dissolved in 500 cc of water, and the ion exchange operation of stirring at room temperature for 12 hours was repeated three times, followed by washing with water. and dried at 100° C. for 12 hours to prepare catalysts 1 to 16 (corresponding to the number of crystalline silicate).

[0026] Catalysts 1 to 16 were sized to 16 to 32 mesh, and 0.5 g of the catalyst was packed into an atmospheric pressure fixed bed flow reactor.
An activity evaluation test was conducted under the following reaction conditions. The results are shown in Table 2.

○ Gas composition N2 O=200ppm NO=200ppm NH3 = 400ppm O2 = 5% He=balance ○ Gas amount = 300Nl/hr ○ Temperature = 500℃, 600℃

(Comparative example) NO using ammonia as a reducing agent
Activity tests were conducted on the titanium oxide-tungsten oxide and titanium oxide-tungsten oxide-vanadium oxide catalysts used as the catalytic cracking catalysts under the same conditions as in the examples. The results are also shown in Table 2.

[Table 2]

As mentioned above, the catalyst used in the present invention is
It was found that at temperatures of 400°C to 700°C, particularly 500°C to 600°C, high removal performance was exhibited for both NOx and N2O.

[0030]

Effects of the Invention As shown in the examples above, in the present invention, by using a catalyst containing copper in crystalline silicate having a specific crystal structure and a specific composition, it is possible to remove copper that cannot be removed by conventional methods. This makes it possible to remove N2 O and simultaneously reduce N2 O and NOx in the exhaust gas. In the Examples of the present invention, the activity test was carried out using the catalyst in the form of particles, but it goes without saying that the catalyst in the form of a honeycomb formed by coating a honeycomb base material such as mullite with the catalyst of the present invention is also effective.

Claims (1)

[Claims] Claim 1: The lattice spacing (d value) and in a dehydrated state,
The molar ratio of oxides is (1.0±0.8)R2O・[aM
2 O3 ・bAl2 O3 ]・ySiO2 (In the above formula, R is an alkali metal ion and/or a hydrogen ion,
M is an ion of one or more elements selected from the group consisting of Group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony, and gallium, a+b=1, a≧
0, b≧0, y=20 to 1000) is brought into contact with a catalyst containing copper ions, and the nitrogen oxides are decomposed into nitrogen and water by ammonia. Method for removing nitrogen oxides from exhaust gas.