JP2000202244A - Treatment of nitrogen monoxide-containing waste gas and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat NO-containing waste gas so that the NO is sufficiently reduced and made harmless at a low running cost with a reduced consumption of NH3 without requiring the installation of an equipment for supplying O2. SOLUTION: When NO-containing waste gas is brought into contact with a noble metal catalyst 8 to decompose the NO, the noble metal catalyst 8 is kept at 150-400 deg.C and the NO-containing waste gas is treated in the presence of >=2/3 mol NH3 based on 1 mol NO and optionally under the coexistence of O2 in such an amount that the number of mols of O2 is <1/4 of that of the NO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitric oxide (N
The present invention relates to a method and an apparatus for detoxifying an exhaust gas containing O), particularly to chemical vapor deposition (hereinafter referred to as CV) in the semiconductor industry.
D) also relates to a method and an apparatus for decomposing and removing nitrogen monoxide in exhaust gas discharged from a process or the like and rendering it harmless.

[0002]

2. Description of the Related Art In the semiconductor manufacturing industry, various gases harmful to the environment and the human body are used. Therefore, there is a general concern about environmental pollution around these factories. Especially C
In the VD process and the like, nitrogen oxides are used, and exhaust gas containing nitrogen oxides and the like is emitted. There are the following three examples of a method for removing this. [1] As a method for removing NO, for example, there is a selective catalytic reduction method using NH ₃ . The selective catalytic reduction method uses a V ₂ O ₅ —WO ₃ —TiO ₂ based denitration catalyst,
In this method, NO is selectively decomposed into N ₂ and H ₂ O by H ₃ and O ₂ . [2] Further, as a denitration method using NH ₃ and a Pd catalyst, the present applicant has previously proposed a treatment method described in Japanese Patent Application No. 9-098995. [3] Furthermore, William et al. (JL Williams, IM Lachma
n, TF Rosenbusch & K.E.Zaun) discuss the subject “Washcoat-in
In -the-wall Honeycomb Catalysts For SCR ofNO x ", and catalyst A (TiO ₂ / SiO _2, and Cu- mordenite, Fe-
Using mordenite and a mixed catalyst of V ₂ O ₅ / Fe ₂ O ₃ ) or catalyst B (a mixed catalyst of TiO ₂ / SiO ₂ and V ₂ O ₅ / Fe ₂ O ₃ ) at a catalyst temperature of 350 ° C. , Nitric oxide NO (1000ppm),
When the amount of oxygen (O ₂ ) in the mixed gas of ammonia NH ₃ (1000 ppm) and water vapor H ₂ O (10%) is changed in the range of 0 to 10%, And reported the results [Proc A & WNA Annu. Mee
t. (Air Waste Manage. Assoc.) 82 [6] 89.96B.5.
1-89.96B.5.16 1989]. However, any of these three methods presupposes the treatment of nitrogen oxides in the presence of oxygen (O ₂ ).

[0003]

The selective catalytic reduction method [1] uses NH ₃ as a reducing agent. The conventional selective catalytic reduction method is performed in the presence of O ₂ . If no O ₂ is present, no reduction reaction occurs and the O ₂ concentration is 3-4.
The reaction will not proceed unless it is over 30%. If the O ₂ concentration is 3-4% or more, the following reaction proceeds, and NO in the exhaust gas is denitrated. 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O

[0004] Also, in the denitration method using NH ₃ and Pd catalyst of the above [2], since it is premised that O ₂ coexists several%, the denitration effect of NO without O ₂ is mentioned. Absent. Assuming that O ₂ is necessary for denitration of NO, if there is no O _{2 in} the exhaust gas, it is necessary to newly supply O ₂ . In the method [2] using NH ₃ and a Pd catalyst, since excess O ₂ oxidizes and decomposes NH ₃ , N 2
H of H ₃ reacts not only with O of NO but also with O of O ₂ , and NH ₃ cannot efficiently decompose NO.
Therefore, it is necessary to introduce the supply amount of NH ₃ more than the amount required for NO denitration.

Further, FIG. 3 shows a graph described in the report of William et al. In the above [3]. In the graph of FIG. 3, the vertical axis indicates the rate of change of nitrogen monoxide NO (%), and the horizontal axis indicates the ratio (%) of oxygen (O ₂ ) in the mixed gas. As can be seen from the graph of FIG. 3, in the catalysts A and B, the rate of change of nitric oxide NO without oxygen (O ₂ ) is 0%, indicating that nitric oxide NO has not changed at all. I have.

As in the selective catalytic reduction method of [1], O ₂
If the presence of O ₂ is indispensable for denitration, equipment for supplying O ₂ and costs for maintenance are required.
Also, there is a problem that when the consumption of NH ₃ increases due to the presence of O ₂ as in the denitration method described in the above-mentioned Japanese Patent Application No. 9-098995, the running cost increases. Further, in the method using the catalysts A and B described in William et al. In the above [3], nitric oxide NO does not change at all without oxygen O ₂ , and the same problem as in the above [1] and [2] is obtained. Contains.

The present invention eliminates the need for providing an O ₂ supply facility, suppresses the consumption of NH ₃ , can sufficiently reduce NO to make it harmless, and has a low running cost. It is an object of the present invention to provide a method and an apparatus for treating NO.

[0008]

The above object has been attained by the following means. 1. When the exhaust gas containing nitrogen monoxide (NO) is brought into contact with a noble metal catalyst to decompose NO in the exhaust gas containing NO, the temperature of the noble metal catalyst is set to 150 ° C. to 400 ° C., and oxygen (O ₂ ) is not present. Alternatively, the co-existing amount of O ₂ is less than 1/4 of the number of moles of NO, and ammonia (NH ₃ ) is present in a ratio of 2/3 or more moles to 1 mole of NO. A method for treating an exhaust gas containing nitric oxide, characterized in that: 2. A container capable of containing a noble metal catalyst and keeping it at 150 ° C. to 400 ° C., a passage for passing exhaust gas containing nitric oxide (NO) through the container, and oxygen (O ₂ ) not coexisting in the container. A means for reducing the amount of co-existing O ₂ to less than 1/4 of the number of moles of NO;
Means for supplying ammonia (NH ₃ ) at a rate of ２ mole or more with respect to 1 mole of O.

[0009]

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In carrying out the present invention, for example, the following packed tower may be used.
FIG. 1 is an example of a partial sectional view of a packed tower 1 suitable for use in carrying out the present invention. A vertically extending cylindrical body containing the heater 2 is provided on the peripheral wall, and the inside is vertically divided by horizontal partition plates 3a and 3b provided with a large number of ventilation holes. A treatment agent filling tank 4 filled with a noble metal catalyst embedding agent 8 is provided above the partition plate 3a, and a gas mixing tank 5 is provided above the partition plate 3b. In the gas mixing tank 5, an exhaust gas introduction pipe 6 and an ammonia introduction pipe 7 are respectively opened. If there is sufficient space above the noble metal catalyst embedding agent 8 to introduce and mix the exhaust gas and the ammonia gas, the partition plate 3 b separating the treating agent filling tank 4 and the gas mixing tank 5 from each other. May not be provided. An exhaust pipe (not shown) leading to the treatment agent filling tank 4 extends from the packing tower outlet to the outside of the packing tower 1 and reaches a water scrubber tower.

The treatment agent filling tank 4 is filled with a noble metal catalyst as a treatment agent. The noble metal catalyst treating agent 8 is 0.5 to 1.0 wt% in a porous body such as alumina containing Al ₂ O ₃ as a main component.
It is recommended to use a noble metal supported at a ratio of. Examples of the noble metal catalyst include Pd, Pt, and Ru, and Pd is preferable. The shape of the porous body supporting the noble metal catalyst does not matter in principle, but a spherical shape is preferred for handling. The particle diameter of the sphere is preferably 3 to 6 mm. 6
If it exceeds mm, it may be difficult to secure a preferable and sufficient reaction contact surface area per unit volume, and it is not always preferable. If it is less than 3 mm, the ventilation resistance value becomes large, which is not always preferable. Noble metal catalyst treatment agent is 1
Use at 50-400 ° C. The noble metal catalyst treating agent is activated at a high temperature. The noble metal catalyst treating agent supported on alumina or the like has a heat resistance temperature of 600 ° C. If the temperature is 600 ° C. or lower, the function is exhibited. However, if the heat resistance of a general heating-type packed tower device and the electric power cost of a heater are comprehensively determined, it is not preferable to use the temperature exceeding 400 ° C.
If it is lower than 150 ° C., a sufficient catalytic function cannot be utilized, which is not preferable. Temperature management may be performed using a sensor such as a thermocouple. The direction of introduction of the exhaust gas and the ammonia gas into the mixing tank 5 may be either a downward flow or an upward flow.

When the above-mentioned packed tower 1 is used, the exhaust gas containing nitrogen monoxide (NO) and the ammonia gas are mixed in the gas mixing tank 5 and gradually moved to the treatment agent packed tank 4.
Reacts by contact with a noble metal catalyst at 0 to 400 ° C. This reaction formula is shown in the following formula (1). 6NO + 4NH ₃ → 5N ₂ + 6H ₂ O Formula (1) In such a reaction, even if there is no O _{2 in the} exhaust gas, the stoichiometric amount [ammonia (NH ₃ ) 2 with respect to 1 mol of nitric oxide (NO)]
/ 3 mol] only occurs if more NH ₃ was present. In the reaction system between the exhaust gas containing nitrogen monoxide (NO) and the ammonia gas, when oxygen having a mole number equal to or more than 1/4 of the mole number of NO coexists, a reaction represented by the following formula (2) occurs. This is a conventional and inefficient method for decomposing NO. 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O Formula (2) On the other hand, when oxygen of less than 1/4 of the mole number of NO coexists, the reaction of formula (1) mainly proceeds. I do. Therefore, efficiently to decompose NO, an exhaust gas and ammonia gas, without O _2, although most preferably reacted, O ₂ of the number of moles of less than 1/4 of the number of moles of NO and the exhaust gas The present invention can be practiced even when coexisting in a reaction system with ammonia gas.

The mixed gas that has passed through the treatment agent filling tank 4 reaches a water scrubber tower through a discharge pipe (not shown) extending therefrom, and removes excess unreacted NH ₃ gas. Only environmentally safe gas components are removed from the atmosphere. Spreads in.

[0013]

Examples of the present invention will be described below, but the present invention is not limited to these examples. Example 1 A ceramic heater (heater 2) is provided on the outer wall of a SUS container having a diameter of 150 mm, and a packed tower 1 as shown in FIG. 1 is provided. In a treatment agent filled tank 4, granular alumina having a particle size of 3 to 6 mm is used. A noble metal catalyst treatment agent loaded with Pd was filled at a ratio of 0.5 wt%. A thermocouple temperature sensor is attached to the filling tank 4, and a precious metal (P) is
d) The catalyst treating agent was heated to a set temperature in the range of 150C to 360C. In the gas mixing tank 5, the NO-containing exhaust gas and the NH ₃ gas were introduced from the exhaust gas introduction pipe 6 and the ammonia introduction pipe 7, and the two were mixed. The total gas flow rate including NO, NH ₃ and N ₂ was 50 SLM, and the SV was 200 hr ⁻¹ . NO
The inlet gas concentration was about 1%, and the amount of NH ₃ gas introduced was 2/3 times the molar amount of NO gas or more. Nitrogen oxides at the outlet and _{(NO, NO 2, N 2} O), and NH _3, was analyzed gas concentration O _2. The analysis method is as follows: detector tube method for NO, NO ₂ and NH ₃ , GC-MS method for N ₂ O, and GC-MS method for O ₂
The TCD method was adopted. Tables 1 and 2 show the results of analysis of the outlet gas during gas passage. Outlet gas NO, NO ₂ , N ₂ O
It was found that all were removed to below the detection limit.

[0014]

[Table 1]

[0015]

[Table 2]

Example 2 The same apparatus as in Example 1 was used. The NO gas inlet gas concentration was about 1%, and the amount of NH ₃ gas introduced was 2%, which was at least 2/3 times the molar amount of NO gas. Set the ceramic heater temperature to 100
℃, 150 ℃, 200 ℃, 300 ℃, 350 ℃, 400
° C and 500 ° C, and the effect of the catalyst temperature was measured. Table 3 and Fig.
It is shown in FIG. The analysis method is the same as in Example 1. 100
Below 0 ° C., NO and NO ₂ are in the allowable concentration (the allowable concentration of NO:
25 ppm, the allowable concentration of NO ₂ : 3 ppm).
At 150 ° C. or higher, it was found that NO, NO ₂ , and N ₂ O were all removed to below the detection limit.

[0017]

[Table 3]

Example 3 The same apparatus as in Example 1 was used. The NO gas input gas concentration was about 1%, and the amount of NH ₃ gas introduced was 0.7%, which was approximately 2/3 times the molar amount of NO gas. Table 4 shows the results of analysis of the outlet gas during gas passage. The analysis method is the same as in Example 1. N
It was found that when the amount of H ₃ gas introduced was at least 2/3 times the molar amount of NO gas, NO, NO ₂ , and N ₂ O could all be removed to below the detection limit.

[0019]

[Table 4]

Comparative Example 1 The same apparatus as in Example 1 was used. NO gas inlet gas concentration of 1
%, 2% and 4%. The NH ₃ concentration was set to 0.5%, 1%, and 2%, respectively, corresponding to the above-mentioned NO concentration. In each case, a molar amount of 2/3 or less of the NO gas was introduced. Table 5 shows the analysis results of the outlet gas during gas passage. The analysis method is the same as in Example 1. In each case, N
All O leaked beyond the allowable concentration (25 ppm).

[0021]

[Table 5]

[0022]

According to the present invention, when the exhaust gas containing nitrogen monoxide (NO) is brought into contact with a noble metal catalyst to decompose NO in the exhaust gas containing NO, the temperature of the noble metal catalyst is set to 150 ° C. to 400 ° C. The amount of O _{2 in} the absence or presence of oxygen (O ₂ ) is less than 1/4 of the number of moles of NO, and the ratio of ammonia is at least 2/3 moles per mole of NO. By performing the treatment in the presence of (NH ₃ ), the exhaust gas containing nitrogen monoxide can be treated with a smaller amount of ammonia than before. According to the present invention,
Since O ₂ is not used for removing NO, there is no need to provide an O ₂ supply facility, NH ₃ consumption is suppressed, and NO
And a method and an apparatus for treating nitric oxide-containing exhaust gas.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a packed tower for performing a detoxification treatment of a nitrogen monoxide-containing gas.

FIG. 2 is a graph showing catalyst temperature and NO determined in Example 2.
It is a graph which shows the relationship with a removal rate.

[Fig. 3] Fig. 3 shows Proc A & WNA Annu. Meet. (Air Wast
e Manage. Assoc.) 82 (6) 89.96B.5.1 ~ 89.96B.5.1
6 of 1989, catalyst A (with TiO ₂ / SiO _2, and Cu- mordenite, Fe- mordenite and, V ₂ O ₅ / Fe ₂ mixed catalysts with O ₃₎ or catalyst B (TiO ₂ / SiO ₂ And V ₂ O ₅ / Fe ₂ O ₃ mixed catalyst) at a catalyst temperature of 350 ° C. and nitric oxide NO
(1000 ppm), ammonia NH ₃ (1000 ppm), and steam H
The amount of oxygen (O ₂ ) in a mixed gas with ₂ O (10%) is 0 to
It is a graph which shows the rate of change of NO in the case of changing in the range of 10%.

[Explanation of symbols]

 1: Packing tower 2: Heater 3a, 3b: Partition plate 4: Treatment agent filling tank 5: Gas mixing tank 6: Exhaust gas introduction pipe 7: Ammonia introduction pipe 8: Noble metal catalyst embedding agent

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D048 AA06 AB02 AC04 AC06 BA03X BA30Y BA31X BA32Y BB01 BD01 CA01 CC38 CC52 DA03 DA11 DA13 4G069 AA03 AA08 AA15 BA01B BC72B BE17A BE17B CA02 CA10 CA13 DA06 EB18Y

Claims (2)

[Claims] When a NOx-containing exhaust gas is brought into contact with a noble metal catalyst to decompose NO in the NO-containing exhaust gas, the temperature of the noble metal catalyst is set to 150 ° C to 40 ° C.
And 0 ° C., oxygen (O ₂₎ to the amount of O ₂ that does or coexist coexist as the number of moles of less than 1/4 of the number of moles of the NO, and 2/3 mole or more relative to 1 mole of the NO A method for treating exhaust gas containing nitric oxide, which is carried out in the presence of ammonia (NH ₃ ) in a proportion of 2. A precious metal catalyst is accommodated and stored at 150 ° C. to 4 ° C.
A container that can be kept at 00 ° C. and nitric oxide (NO)
A passage for passing the contained exhaust gas through the container, means for allowing oxygen (O ₂ ) not to coexist in the container, or for making the amount of O ₂ coexisting in the container less than 1/4 of the number of moles of NO; Means for supplying ammonia (NH ₃ ) to the container at a rate of 2/3 mole or more with respect to 1 mole of NO.