JPH0838888A - Adsorbent of nitrogen oxide and removal of nitrogen oxide using the same - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen oxide (NOx; nitrogen monoxide and nitrogen dioxide), especially, nitrogen dioxide contained in exhaust gas in low concn. CONSTITUTION:An adsorbent of nitrogen oxide contains zirconia and ruthenium and a crystal structure of zirconia is amorphous, tetragonal or monoclinic. At least one kind of oxide of a metal selected from a group consisting of manganese, iron, cobalt, nickel, copper, zinc, lead and cerium can be added to this adsorbent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide adsorbent and a method for removing nitrogen oxide using the adsorbent. More specifically, the present invention relates to an adsorbent suitable for removing low-concentration nitrogen oxides (NO _x : nitric oxide and nitrogen dioxide) contained in exhaust gas, and an exhaust gas using the adsorbent suitable for removing nitrogen dioxide. The present invention relates to a method for efficiently adsorbing and removing low-concentration nitrogen oxides, especially nitrogen dioxide.

[0002]

2. Description of the Related Art Conventionally, a method for removing nitrogen oxides from a fixed type nitrogen oxides generation source such as a boiler has been used so far that ammonia is used as a reducing agent to selectively reduce the nitrogen oxides to produce harmless nitrogen oxides. The catalytic reduction method of converting into water is widely used as the most economical method.

By the way, the concentration of nitrogen oxides in ventilation gas or atmosphere in road tunnels, sheltered roads, deep underground spaces, road intersections, etc., and gases discharged from combustion equipment used at home is 5,
It is about ppm, which is extremely lower than the nitrogen oxide concentration in the boiler exhaust gas, the gas temperature is room temperature, and the amount of gas is enormous. Therefore, for example, in order to efficiently remove nitrogen oxides from the ventilation gas of a road tunnel by the catalytic reduction method, it is necessary to set the temperature of the ventilation gas to 300 ° C. or higher, and as a result, a large amount of energy is consumed. It becomes necessary and there is an economical problem in applying the above catalytic reduction method as it is.

Under these circumstances, a gas having a low concentration of nitrogen oxides, such as a ventilation gas for a road tunnel as described above, for example, a gas having a concentration of about 5 ppm or less (hereinafter, such a ventilation gas having a low concentration of nitrogen oxides or the atmosphere, etc.). Is collectively referred to as “exhaust gas”), and it is desired to efficiently remove nitrogen oxides.

As an adsorbent / removal agent for this low-concentration nitrogen oxide, an adsorbent in which copper chloride is supported on zeolite is disclosed in Japanese Patent Application Laid-Open No. HEI 1
However, according to the study by the present inventors, this adsorbent is easily affected by the water content in the exhaust gas, and the nitrogen oxide adsorbing ability is significantly reduced when the exhaust gas has a high humidity. It turned out to be.

Furthermore, when processing the gas after ventilation in the tunnel, it is necessary to process it in the tunnel, so there is a limit to the installation space and the device itself must be made compact. In order to solve the above problems, an adsorbent for treating nitrogen oxides having more excellent performance has been earnestly desired.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an adsorbent having an excellent adsorbing ability for a low concentration of nitrogen oxide contained in exhaust gas.

Another object of the present invention is to provide an adsorbent which is not affected by the temperature of the exhaust gas and is excellent in the adsorption ability of nitrogen dioxide having a particularly low concentration in the exhaust gas.

Another object of the present invention is to provide a method for efficiently adsorbing and removing nitrogen oxides, particularly nitrogen dioxide, in exhaust gas by using an adsorbent.

[0010]

Means for Solving the Problems As a result of diligent research to achieve the above object, the present inventors have found a nitrogen oxide adsorbent containing zirconia and ruthenium, and completed the invention. It was. The present invention is based on each of the following inventions.

The first invention is adsorption of nitrogen oxides containing zirconia and ruthenium and having a crystal structure of at least one selected from the group consisting of amorphous, tetragonal and monoclinic crystals. It is an agent. Further, the specific surface area of the zirconium is preferably 10 m ² / g or more.

According to a second aspect of the present invention, the above adsorbent is further added with an oxide of at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, copper, zinc, lead and cerium. It is a nitrogen oxide adsorbent.

A third aspect of the present invention is to adsorb nitrogen oxides contained in the exhaust gas by bringing the exhaust gas into contact with the adsorbent of the first and second aspects. It is a removal method.

A fourth aspect of the present invention is a removal method according to the third aspect of the present invention, in which nitrogen monoxide in exhaust gas is previously oxidized to nitrogen dioxide, and then nitrogen oxides in the exhaust gas are adsorbed and removed.

The fourth aspect of the present invention is a method of removing ozone by adding ozone to the exhaust gas in order to oxidize nitrogen monoxide in the exhaust gas into nitrogen dioxide in advance.

The amount of ozone added is preferably 0.5 to 5 times the molar amount of the nitrogen oxide.

[0017]

The present invention will be described in detail below. Zirconia used in the present invention has a crystal structure of amorofus,
Alternatively, it is at least one selected from the group consisting of tetragonal crystals and monoclinic crystals. These crystal structures are specified by powder X-ray diffraction measurement of the adsorbent, for example. This is because crystal forms other than these, such as cubic crystals, are not preferable because the specific surface area becomes low. It should be noted that the amorphous material does not show a clear crystal peak in the powder X-ray diffraction measurement.

Depending on the method for preparing the adsorbent according to the present invention, the tetragonal crystal or the monoclinic crystal of the zirconia according to the present invention may not always clearly show a single kind of crystal structure.
In such a case, the zirconia may be a mixture containing a plurality of structures among these crystal structures, but if these structures include a tetragonal crystal or a monoclinic crystal, the present invention can be used. The effect can be exhibited.

The specific surface area of the zirconia is 10 m.
It is preferably ² / g or more, more preferably
It is 10 to 400 m ² / g. Further, particularly when it is amorphous, the specific surface area is preferably ²⁰⁰ to 400 m ² / g. The specific surface area may be measured by a commonly used measuring method, for example, a specific surface area measuring method such as BET method.

The method for preparing the zirconia is not particularly limited, but it can be prepared, for example, by firing zirconium nitrate, carbonate or hydroxide, and examples thereof include zirconium hydroxide and oxyhydroxide. It can be prepared by firing zirconium at 300 to 900 ° C. It should be noted that even if these raw materials of zirconia contain a trace amount of impurities, for example, SiO ₂ , TiO ₂ , HfO _{2 and the} like, there is no problem in the preparation of zirconia.

The ruthenium (R
u) is 0.01 to 10% by weight, preferably 0.01 to
5% by weight, and more preferably 0.01 to 1% by weight. That is, if it is less than 0.01% by weight, the adsorption ability of nitrogen oxides is significantly reduced, which is not preferable.
On the other hand, if it exceeds 10% by weight, not only the raw material cost of the adsorbent increases but also the nitrogen oxide adsorbing ability decreases, which is not preferable.

In the present invention, the adsorbent containing zirconia and ruthenium, which is the first invention, is further selected from the group consisting of manganese, iron, cobalt, nickel, copper, zinc, lead and cerium. It was also found that the addition of an oxide of one kind of metal (hereinafter, also referred to as a heavy metal component) exerts a more excellent effect. This is the second invention.

In the adsorbent according to the second aspect of the invention,
Based on the total amount of zirconia, ruthenium and the heavy metal component, ruthenium is 0.01 to 10% by weight, preferably 0.01 to 5% by weight, and more preferably 0.01 to 5% by weight.
1% by weight, and the heavy metal component is 1 to 70% by weight,
Preferably 10 to 70% by weight, more preferably 10
-60% by weight.

That is, if the content of ruthenium is less than 0.01% by weight, the adsorption capacity of nitrogen oxides is significantly reduced, which is not preferable. On the other hand, if the content of ruthenium exceeds 10% by weight, the cost of the adsorbent increases. Further, the adsorbability of nitrogen oxides commensurate with the inclusion is not improved, and thus it is not preferable. On the other hand, if the content of the heavy metal component is less than 1% by weight, the effect of adding the heavy metal component cannot be sufficiently obtained, which is not preferable.

As the starting materials for the oxides of ruthenium and heavy metal components, oxides of the respective metals are used as they are, as well as hydroxides, ammonium salts, nitrates, sulfates, acetates, oxalates, carbonates, halides. Etc. are appropriately selected. The above ruthenium salt usually becomes a metal or an oxide by the preparation of the present adsorbent, but in some cases, it may exist as a salt of the starting material.

The distribution state of ruthenium is not particularly limited and may be not only with zirconia but also with the oxide of the heavy metal component, or with both the oxide of zirconia and the heavy metal component. These can be appropriately changed and used according to the usage state of the present adsorbent.

The method for preparing the adsorbent of the present invention will be exemplified below, but the method for preparing the adsorbent according to the present invention can be appropriately changed depending on the starting materials of the respective components, and the present invention is not limited to these methods. Not something. First, a method for preparing an adsorbent containing zirconia and ruthenium will be described.

(1) The zirconia powder was impregnated with an aqueous solution containing a metal salt of ruthenium, evaporated and dried, and then 300
A method of firing at ~ 600 ° C and then forming into a desired shape.

(2) Zirconia is formed into a predetermined shape, for example, a honeycomb or the like in advance, and this formed body is impregnated with an aqueous solution containing a metal salt of ruthenium, and after drying 300 to 600
Method of firing at ℃.

(3) Zirconium powder is added to an aqueous solution containing a metal salt of ruthenium to form a slurry, and then an alkaline solution of ammonia, sodium hydroxide, potassium hydroxide or the like is added to the ruthenium on the zirconia. Was deposited, washed with water and dried, then 300-6
A method of firing at 00 ° C. and then forming into a desired shape.

(4) Zirconia is formed in advance into a predetermined shape, for example, a honeycomb or the like, and the formed body is impregnated with an aqueous solution containing a metal salt of ruthenium, and an alkaline solution of ammonia, sodium hydroxide, potassium hydroxide or the like. Is added to deposit ruthenium on zirconia, which is washed with water, dried, and then baked at 300 to 600 ° C.

Next, a method for preparing an adsorbent obtained by adding an oxide of a heavy metal component to zirconia and ruthenium will be described.

(5) An aqueous solution containing a metal salt of ruthenium is mixed with zirconia powder and dried to obtain 300 to 6
Powder obtained by firing at 00 ° C. and oxide of heavy metal component,
Appropriate water or the like is added to a powder such as hydroxide or carbonate, and the mixture is well kneaded and then molded into a desired shape.
A method of baking at 0 ° C.

(6) An aqueous solution containing a metal salt of ruthenium is mixed with powders of oxides, hydroxides or carbonates of heavy metal components and zirconia powder, and the mixture is heated to 300 to 600 ° C.
A method in which the powder obtained by firing in (1) is kneaded well with appropriate water and the like, molded into a desired shape, and then fired at 300 to 600 ° C.

(7) After adding an aqueous solution containing a metal salt of ruthenium to the zirconia powder to form a slurry, an alkaline solution of ammonia, sodium hydroxide, potassium hydroxide or the like is added to the ruthenium on the zirconia. After depositing, this is washed with water, dried, and calcined at 300 to 600 ° C., and the obtained powder of oxides, hydroxides or carbonates of heavy metal components, etc. A method of adding and kneading well, molding into a desired shape, and then firing at 300 to 600 ° C.

The shape of the adsorbent is not particularly limited, and a columnar shape, a cylindrical shape, a spherical shape, a plate shape, a honeycomb shape, or any other integrally formed shape may be used as the adsorbent filling portion and the present adsorption method. It can be appropriately selected depending on the state of use. The adsorbent can be molded by a general molding method such as a tablet molding method or an extrusion molding method. If it is a granular adsorbent, the average particle size is 1
In the case of a honeycomb shape, it is manufactured by an extrusion molding method, a sheet-shaped method of winding and solidifying, or the like as in the case of a so-called monolith carrier. The shape of the gas passage (cell shape) is preferably hexagonal, quadrangular, triangular or corrugated. Cell density (number of cells / unit cross-sectional area, also called "cell / square inch") is 25 to 600
If the cell / square inch is sufficiently usable, it is preferably 25 to 500 cell / square inch.

If the adsorbent has the above composition, the adsorbent can be used by appropriately changing the physical properties such as strength, shape, specific surface area and pore volume depending on the use conditions. Of these physical properties, especially the specific surface area is 10 m ² / g to 400 m ² /
g it is preferably 10m ² / g~300m ² / g, pore volume, 0.2cc / g~0.6cc / g preferably from 0.2cc / g~0.5cc / g.

There is no particular limitation on the method of contacting the adsorbent with the exhaust gas in the method for removing nitrogen oxides of the present invention, and the exhaust gas is usually introduced into the layer composed of the adsorbent. Further, the treatment conditions at this time cannot be unconditionally specified because it depends on the properties of the exhaust gas, but the temperature of the supplied gas is usually 0 to 200 ° C., particularly 0 to 5 ° C.
The range of 0 ° C is preferred.

The space velocity (SV) of the gas to be supplied
Is usually 500～50000Hr- ¹ (STP), in particular 2000～30000Hr- ¹ in the range of (STP) preferred.

The adsorbent of the present invention may directly contact exhaust gas with the adsorbent of the present invention to adsorb and remove mainly nitrogen dioxide among nitrogen oxides. Of these, since it is particularly effective in removing nitrogen dioxide by adsorption, when removing nitrogen oxides in exhaust gas, nitric oxide is pre-oxidized with an oxidizing agent such as ozone and converted into nitrogen dioxide, and then the adsorbent is removed. The nitrogen oxide in the exhaust gas can be more effectively removed by contacting with.

When ozone (O ₃ ) is added to the exhaust gas in advance, the concentration is preferably 0.5 to 5 times the nitrogen oxide concentration. When it is less than 0.5 times, nitrogen oxides cannot be efficiently adsorbed, and when it exceeds 5 times, ozone is easily washed out, which is not preferable.

Further, the adsorbent of the present invention has an excellent effect that the excess O ₃ added to the exhaust gas can be decomposed and removed.

[0043]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

(Example 1) Ruthenium nitrate aqueous solution (manufactured by Tanaka Kikinzoku Co., Ltd., 3.75 g% by weight as Ru noble metal)
80 g) is added to 99.7 g of tetragonal zirconia (BET specific surface area is 100 m ² / g) and well mixed with a kneader while adding an appropriate amount of water, and then pelletized with an extruder at a diameter of 5 mm and a length of 5 mm. Molded into. The pellets were dried at 100 ° C. for 10 hours and then calcined at 450 ° C. for 3 hours in an air atmosphere.

The composition of the adsorbent thus obtained is R
u and ZrO ₂ were 0.3 wt% and 99.7 wt%, respectively. The composition and specific surface area of this adsorbent are shown in Table 1.

(Example 2) In the same manner as in Example 1 except that tetragonal zirconia was changed to monoclinic zirconia (BET specific surface area 23 m ² / g).
A pellet-shaped adsorbent was prepared. The composition and specific surface area of this adsorbent are shown in Table 1.

Example 3 A pellet-shaped adsorbent was prepared in the same manner as in Example 1 except that tetragonal zirconia was changed to amorphous zirconia (BET specific surface area: 350 m ² / g). did. The composition and specific surface area of this adsorbent are shown in Table 1.

Comparative Example 1 An adsorbent was obtained in the same manner as in Example 1 except that tetragonal zirconia was changed to cubic zirconia (BET specific surface area 4 m ² / g) in Example 1. The composition and specific surface area of the adsorbent are shown in Table 1. .

(Comparative Example 2) Y-type zeolite (manufactured by Tosoh Corporation, zeolite, TSZ-320, SiO ₂ / Al ₂
5.5 mol of O ₃ and 1 mol / liter of cupric chloride (C
uCl ₂ ) aqueous solution with stirring for 20 hours at room temperature, followed by washing with water, filtration, and drying at 110 ° C. for 2 hours.
It was baked at 400 ° C. for 3 hours.

While adding an appropriate amount of water to this powder, stirring it well with a kneader, and then using an extrusion molding machine, a diameter of 5 mm,
It was molded into a pellet having a length of 5 mm. 1 of this pellet
After drying at 00 ° C. for 10 hours, it was baked in air at 350 ° C. for 3 hours.

The composition of the adsorbent thus obtained is
Cu and Y zeolites are 7.5 wt% and 9 respectively
It was 2.5% by weight. The composition and specific surface area of this adsorbent are shown in Table 1.

[0052]

[Table 1]

Example 4 With respect to the adsorbents obtained in Examples 1, 2 and 3 and Comparative Examples 1 and 2, the nitrogen oxide adsorption performance (NO _x removal rate) was evaluated by the following method.

114 mL of the adsorbent was filled in a glass reaction tube having an inner diameter of 30 mm. A synthesis gas having the following composition was introduced into the adsorbent layer under the following conditions.

Synthesis gas composition Nitric oxide (NO): 3 ppm, H ₂ O: 2.5% by volume, balance: Air treatment conditions Gas amount: 15.2 NL / min, treatment temperature: 25 ° C., space velocity (SV) : 8000 hr ^-1 (STP), gas temperature: 85% RH After 1 hour has passed since the synthesis gas was introduced, the concentration of nitrogen oxides (NO _x ) in the synthesis gas at the inlet and the outlet of the adsorbent layer was measured. measured by luminescent NO _X meter, it was calculated NO _X removal rate according to the following equation.

[0056]

[Equation 1]

Table 2 shows the results of the evaluation test.

[0058]

[Table 2]

(Example 5) As for the adsorbents obtained in Examples 1, 2 and 3 and Comparative Examples 1 and 2, the same as Example 4 except that the synthesis gas composition in Example 4 was changed as follows. The nitrogen oxide adsorption performance (NO _x removal rate) was evaluated.

Synthetic gas composition Nitric oxide (NO): 3 ppm, H ₂ O: 2.5% by volume, ozone (O ₃ ): 3 ppm, balance: air, but carbon monoxide (NO) is the addition of ozone Are all nitrogen dioxide (NO ₂ ).

10 hours and 20 hours after the introduction of the synthesis gas, the nitrogen oxide (NO _x ) concentrations in the synthesis gas at the inlet and the outlet of the adsorbent layer were measured by a chemiluminescence type NO _x meter. The NO _x removal rate was calculated according to the above equation, and the results are shown in Table 2.

(Example 6) As for the adsorbents obtained in Examples 1, 2 and 3 and Comparative Examples 1 and 2, the same as Example 4 except that the composition of synthesis gas was changed as follows in Example 4. The nitrogen oxide adsorption performance (NO _x removal rate) was evaluated.

Synthesis gas composition Nitric oxide (NO): 3 ppm, H ₂ O: 2.5% by volume, ozone (O ₃ ): 4.5 ppm, the rest: air, but carbon monoxide (NO) is ozone The addition of nitrogen makes it all nitrogen dioxide (NO ₂ ).

Nitrogen monoxide (NO) is all converted to nitrogen dioxide (NO ₂ ) by the addition of ozone, and an excess amount of ozone (O ₃ ) of 1.5 ppm coexists.

10 hours and 20 hours after the introduction of the synthesis gas, the nitrogen oxide (NO _x ) concentrations in the synthesis gas at the inlet and the outlet of the adsorbent layer were measured by a chemiluminescence type NO _x meter. The NO _x removal rate was calculated according to the above equation, and the results are shown in Table 2.

Example 7 Tetragonal Zirconia 497
g ruthenium nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., R
u 80 g of a noble metal (containing 3.75 g% by weight) and 661.1 g of manganese carbonate (special grade reagent) were added, and an appropriate amount of water was added, followed by thorough mixing with a kneader, and then pellets having a diameter of 5 mm and a length of 5 mm with an extruder. It was molded into a shape. After drying the pellets at 100 ℃ for 10 hours, 450 ℃
It was baked in an air atmosphere for 3 hours.

The composition of the adsorbent thus obtained is R
u, MnO ₂ and ZrO ₂ were 0.3 wt%, 50 wt% and 49.7 wt%, respectively. The composition and specific surface area of this adsorbent are shown in Table 3.

[0068]

[Table 3]

(Examples 8 to 14) In Example 7, manganese carbonate was replaced with iron hydroxide, basic cobalt carbonate, basic nickel carbonate, basic copper carbonate, basic zinc carbonate, basic lead carbonate and cerium carbonate. A pellet-shaped adsorbent was prepared in the same manner as in Example 7, except that
The composition and specific surface area of this adsorbent are shown in Table 3.

(Example 15) Tetragonal zirconia 59
7 g of ruthenium nitrate aqueous solution (manufactured by Tanaka Kikinzoku Co., Ltd.,
80 g of Ru noble metal (containing 3.75 g by weight%), 264.4 g of manganese carbonate (special grade reagent) and 222.7 g of iron hydroxide (special grade reagent) were added, and after adequate mixing with a kneader while adding an appropriate amount of water, Extruder 5 diameter
It was molded into a pellet having a length of 5 mm. The pellets were dried at 100 ° C. for 10 hours and then calcined at 450 ° C. for 3 hours in an air atmosphere.

The composition of the adsorbent thus obtained is R
u, MnO ₂ , Fe ₂ O ₃ and ZrO ₂ were 0.3% by weight, 20% by weight, 20% by weight and 59.7% by weight, respectively. The composition and specific surface area of this adsorbent are shown in Table 4.
It was shown to.

[0072]

[Table 4]

(Examples 16 to 21) In Example 15, iron hydroxide was replaced with basic cobalt carbonate, basic nickel carbonate, basic copper carbonate, basic zinc carbonate, basic lead carbonate and cerium carbonate. A pellet-shaped adsorbent was prepared in the same manner as in Example 15 except for the above. In addition,
The composition and specific surface area of this adsorbent are shown in Table 4.

(Example 22) With respect to the adsorbents obtained in Examples 7 to 21, the space velocity in Example 4 was 12000 h.
The adsorption performance (NO _x removal rate) of nitrogen oxides was evaluated in the same manner as in Example 4 except that the value was changed to r- ¹ . The results obtained are shown in Table 5.

[0075]

[Table 5]

(Example 23) With respect to the adsorbents obtained in Examples 7 to 21, the space velocity in Example 5 was 12000 h.
The adsorption performance of nitrogen oxides (NO _x removal rate) was evaluated in the same manner as in Example 5 except that r to ¹ was changed. The results obtained are shown in Table 5.

(Example 24) With respect to the adsorbents obtained in Examples 7 to 21, the space velocity in Example 6 was 12000 h.
The adsorption performance of nitrogen oxides (NO _x removal rate) was evaluated in the same manner as in Example 6 except that r to ¹ was changed. The results obtained are shown in Table 5.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location B01D 53/81 (72) Inventor Motonobu Kobayashi 1 of 992 Nishioki, Nishihama, Aboshi-ku, Himeji-shi, Hyogo Japan Co., Ltd. Japan Catalyst Catalyst Research Center

Claims (6)

[Claims] 1. A nitrogen oxide containing zirconia and ruthenium and having a crystal structure of at least one selected from the group consisting of amorphous or tetragonal and monoclinic crystals. Adsorbent. 2. The adsorbent according to claim 1, further comprising an oxide of at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, copper, zinc, lead and cerium. The adsorbent according to 1. 3. Removal of nitrogen oxides, which comprises adsorbing nitrogen oxides contained in the exhaust gas by bringing the exhaust gas into contact with the adsorbent according to any one of claims 1 and 2. Method. 4. The removal method according to claim 3, wherein after nitric oxide in the exhaust gas is previously oxidized to nitrogen dioxide, nitrogen oxides in the exhaust gas are adsorbed and removed. 5. The removal method according to claim 4, wherein ozone is added to the exhaust gas in order to oxidize nitric oxide in the exhaust gas to nitrogen dioxide in advance. 6. The removal method according to claim 5, wherein the amount of ozone added is 0.5 to 5 times the molar amount of the nitrogen oxide.