JPH0531357A - Removing agent for adsorbing low concentration nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain the subject adsorptive removing agent capable of omitting or reducing a dehumidifying process required in the front stage of the adsorptive removal of NOx by supporting Ru on a carrier composed of gamma-alumina. CONSTITUTION:Ru is pref. supported on a carrier composed of gamma-alumina in an amount of about 0.1-5% by wt. of a final adsorbent as metal Ru. Ru is supported by a method wherein the alumina carrier is immersed in an aqueous RuCl3 solution and separated from the solution to be washed and subsequently dried in air to be baked at about 300-500 deg.C, if necessary. This adsorptive removing agent is formed into a columnar shape, a spherical shape or a Rashig ring shape having a large contact surface and allowing gas to easily flow. Since this adsorptive removing agent receives no effect of humidity, a dehumidifying process required in the front stage of the adsorptive removal of NOx can be omitted or reduced. Therefore, the much energy required in the dehumidifying process can be reduced and a dehumidifier can be dispensed with or simplifier. As a result, energy and space can be conserved as compared with a conventional process.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention efficiently removes low-concentration nitrogen oxides contained in ventilation gas in various tunnels such as various road tunnels, mountain tunnels, submarine tunnels, underground roads and roads with shelters. The present invention relates to an adsorption remover.

[0002]

BACKGROUND OF THE INVENTION In various road tunnels, mountain tunnels, underground roads, roads with shelters, etc. (in this specification, these tunnels are collectively referred to as "road tunnels, etc.") For large quantities, it is necessary to provide adequate ventilation for the purpose of protecting the health of passersby and improving the visual distance. In addition, even in the case of relatively short-distance tunnels, in urban areas or in the suburbs, as a method of preventing air pollution due to carbon monoxide (CO), nitrogen oxides (NOx), etc. concentrated at the entrances and exits, the air in the tunnels is sucked in. There is a way to exhaust (ventilate).

However, if the ventilation gas is diffused to the surroundings as it is, it does not improve the local environment, and in particular, the highly contaminated area is expanded in the urban area where the automobile exhaust gas is spreading in a flat manner or in the suburbs. It can be caused. Tunneling as a measure against pollution of existing roads,
The situation is exactly the same when installing a shelter. The present invention relates to an adsorption / removal agent that efficiently removes low-concentration nitrogen oxides contained in ventilation gas for such road tunnels.

[0004]

2. Description of the Related Art Ventilation gas for various tunnels is characterized in that the concentration of nitrogen oxides contained therein is as low as about 5 ppm, the gas temperature is room temperature, and the amount of gas fluctuates greatly in accordance with traffic.

The methods for removing nitrogen oxides from fixed sources, which have been studied for the purpose of purifying various boiler combustion exhaust gas, are roughly classified into the following three methods.

(1) Catalytic reduction method This method uses ammonia as a reducing agent to selectively reduce nitrogen oxides in exhaust gas into harmless nitrogen and water vapor.
It is the most common method for denitration of boiler exhaust gas. However, this method requires a process gas temperature of 200
Since it is necessary to control the temperature to be higher than 0 ° C., when the gas amount is large at room temperature such as ventilation gas for road tunnels, a large amount of energy is required to raise the temperature of the processing gas, which is not an economical processing method.

(2) Wet absorption method This method uses nitrogen dioxide (NO ₂ ) or nitrogen trioxide (N ₂ ).
₂ O ₃ ) is used by being absorbed by water or an alkaline aqueous solution. A method of oxidizing nitric oxide (NO) after it is oxidized by an oxidation catalyst or ozone injection, or adding an oxidizing property to the absorbing solution is available. Are known. However, in these methods, nitrogen oxides (NOx) are accumulated in the absorbing solution as nitrates or nitrites, and therefore the absorbing solution needs to be managed and post-treated, which complicates the process. Further, the unit price per mol of the oxidizing agent is more expensive than ammonia used in the catalytic reduction method, and there is a problem in the economical efficiency of the process.

(3) Dry adsorption method This is a method of adsorbing and removing nitrogen oxides in exhaust gas using an appropriate adsorbent. Several cases have been studied until the catalytic reduction method has been established as a denitration method for boiler exhaust gas. It was However, the boiler exhaust gas has a high concentration of (a) nitrogen oxides,
(A) Gas temperature is high, and (c) Water concentration is high,
The dry adsorption method is inferior in economic efficiency to the catalytic reduction method and has not been put to practical use until now.

However, when the dry adsorption method was evaluated as a method for purifying ventilation gas for road tunnels and the like, it was found that the process is simple and economical, unlike the case of boiler exhaust gas.

[0010]

Among the researches on the adsorption and removal of nitrogen oxides by the adsorbent, the research on the adsorption and removal of low-concentration nitrogen oxides is conducted by the Industrial Development Research Institute (“Special Research on the development of new denitration system using various adsorption and oxidation catalysts ", May 1978). Among them, air-H ₂ O-NO system simulated gas (inlet NO concentration: 100 to 120 ppm, dry gas (dew point: -1
(7 ° C.), SV: 3270 Hr ⁻¹ ) and tests have been conducted, and it has been reported that the adsorbent is preferably a natural pseudo-olivine supporting a copper-based metal (oxide).

However, it is assumed that the concentration of nitrogen oxides contained in the ventilation gas for road tunnels is 5 ppm or less, but the adsorbent used in the above research (NOx concentration: about 100 ppm) There is no suggestion as to whether or not nitrogen oxides with a low concentration of 5 ppm are efficiently adsorbed, including the possibility.

The inventors of the present invention have previously proposed, as an adsorbent intended to efficiently adsorb and remove a low concentration of 5 ppm of nitrogen oxide, a natural or synthetic zeolite, copper chloride, a double salt of copper chloride and a chloride. A carrier comprising at least one copper salt selected from copper ammine complex salts, which is an adsorption remover for low-concentration nitrogen oxides (see Japanese Patent Laid-Open No. 1-299642), and anatase-type titanium oxide. Adsorption remover supporting vanadium (Japanese Patent Application No. 2-3
No. 40627).

However, in these adsorbents, when the water (or moisture) concentration became high, the adsorption performance was deteriorated (deterioration phenomenon) as shown in FIG. 5 (FIG. 5 shows the above Cu-supporting zeolite). And the effect of moisture concentration on the adsorption performance of the above V-supported titania. The reaction conditions were as follows: adsorbent: 5 ml, reaction gas amount: 2.5 NL / min, NOx concentration: 3.8-.
4.1ppm, Moisture concentration: ~ 60ppm and ~ 500ppm, Reaction temperature: 24
~ 26 ℃).

Therefore, in order to exhibit good adsorption performance, it is necessary for these adsorbents to have a moisture concentration of about −35 ° C. or less (about 200 ppm or less) in dew point, which is a NOx removal process. It was necessary to provide a dehumidification process in the previous stage to perform dehumidification or dehumidification.

In view of the above points, the present invention intends to develop an adsorption removing agent that is not affected by moisture, and to achieve downsizing of a NOx removing device and energy saving.

[0016]

Means for Solving the Problems As a result of various investigations by the present inventors, by contacting a gas containing a low concentration of nitrogen oxide with a γ-alumina-ruthenium-based adsorbent,
The inventors have found that nitrogen oxides can be efficiently adsorbed and removed, and completed the present invention.

That is, the adsorbent / removal agent for low-concentration nitrogen oxides according to the present invention (hereinafter simply referred to as adsorbent) is characterized in that ruthenium is supported on a carrier made of γ-alumina.

The first feature of the adsorbent according to the present invention is that γ-alumina (γ-Al ₂ O ₃ ) is used as a carrier for the adsorbent.

The adsorbent carrier is preferably kneaded with, for example, γ-alumina together with a molding aid (used as a binder or a diluent) such as silica sol or a fibrous substance such as ceramic fiber, and then, in a preferred shape (pellet, It is obtained by molding into a honeycomb, etc., and drying and firing the molded product.

As the γ-alumina carrier, any of a commercially available alumina carrier and an alumina carrier produced from alumina sol (alumina carrier obtained by drying and calcining alumina sol-impregnated ceramic paper like a ceramic paper catalyst) is used. Can also be used.

The second characteristic of the adsorbent according to the present invention is that ruthenium (Ru) is supported on the carrier.

The amount of ruthenium supported on the final adsorbent as the ruthenium metal is preferably about 0.01% by weight or more, and more preferably about 0.1 to 5% by weight.

Supporting ruthenium is generally carried out by immersing the alumina carrier in a solution prepared by dissolving a ruthenium compound such as ruthenium chloride (RuCl ₃ ) in a suitable solvent. However, this method is not limited.

The amount of ruthenium supported is generally adjusted by the concentration of ruthenium in the immersion solution, the immersion temperature, the immersion time and the like. After the immersion, the adsorbent is separated from the solution, washed with water, and then dried in air at about 100 to 120 ° C. Further, the dried product is fired at about 300 to 500 ° C. if necessary. In addition,
For continuous use by repeated adsorption, desorption, regeneration, etc.,
In some cases, treatment at a temperature slightly higher than the maximum operating temperature of the adsorbent is required.

The shape of the adsorbent is not particularly limited as long as it has a large number of contact surfaces and facilitates gas flow, such as a columnar shape, a spherical shape, a Raschig ring shape, or a honeycomb shape.

Like ventilation gas from a road tunnel,
When treating a large amount of gas, it is necessary to minimize the pressure loss as the flow resistance is small. Therefore, it is desirable to form the adsorbent into a honeycomb shape like a ceramic paper catalyst (a ceramic paper impregnated with titania sol and then carrying vanadium).

[0027]

EXAMPLES Next, some examples of the present invention and comparative examples to be compared with the examples will be given respectively.

Example 1 7 ml of a commercially available γ-alumina (manufactured by Catalysts & Chemicals Industry Co., Ltd .: Sunbead-AN) crushed and sieved to 8 to 14 mesh was added to a ruthenium chloride (RuCl ₃ ) aqueous solution (Ru concentration: 0.3).
It was immersed in 10 ml of 8 wt%) for 20 hours at room temperature. This was washed with water and dried at about 110 ° C. for 2 hours to obtain a Ru-supported alumina adsorbent (Ru-supported amount: 0.6 wt%).

5 ml (3.5 g) of this adsorbent is used for an inner diameter of 22 mm.
Filled in a stainless steel reaction tube of and dried air (moisture concentration:
After treatment at about 300.degree. C. for 1 hour under flow (2.5 NL / min), the mixture was allowed to cool to room temperature. After cooling, the flow of dry air was temporarily stopped and the adsorbent layer contained 3.5 ppm of nitric oxide (NOx) and had a humidity concentration of 500 ppm and a conditioned air (2.
(5 NL / min) was introduced, and immediately after the introduction, the NOx concentration in the outlet gas of the reaction tube was measured by a chemiluminescence analyzer. FIG. 1 shows the change with time of the NOx concentration in the outlet gas. The vertical axis in FIG. 1 shows the NOx concentration in the outlet gas as N in the inlet gas.
The value divided by the Ox concentration (called "breakthrough rate") is graduated.

As is clear from the curve of Example 1 in the figure, the time until the NOx concentration in the outlet gas reaches 10% of the inlet concentration (breakthrough rate: 0.1), that is, 0.35 ppm. (Called "10% breakthrough time") was 30.0 minutes.

Comparative Examples 1 and 2 Titanic acid slurries as carriers (TiO ₂ content: about 30)
wt%) in air at 400 ° C. for 5 hours to obtain anatase-type titanium oxide (titania), which is impregnated with ammonium metavanadate (NH ₄ VO ₃ ) and supported with vanadium (V). A titania adsorbent was obtained. Using this adsorbent, the NOx concentration at the outlet was measured under the same conditions as in Example 1. The change with time of the NOx concentration is shown as Comparative Example 1 in FIG.

Further, a commercially available Y-type zeolite was used as a carrier, and cupric chloride (CuCl ₂ ) was impregnated and carried on this to obtain a Cu-supporting zeolite adsorbent. With this adsorbent,
The outlet NOx concentration was measured under the same conditions as in Example 1. The change over time in the NOx concentration at this time is shown as Comparative Example 2 in FIG.

As is clear from the curves of Comparative Examples 1 and 2 in the figure, at 500 ppm moisture concentration, the Ru-supported alumina adsorbent (Example 1) was the same as the V-supported titania adsorbent (Comparative Example 1). Cu-supported zeolite adsorbent (Comparative Example 2)
It can be seen that it shows extremely excellent performance as compared with.

Example 2 Colloidal alumina 200 manufactured by Nissan Chemical Industries, Ltd. was dried at about 110 ° C. for 44 hours, and then dried in air at 400 ° C. for 24 hours.
An adsorbent was obtained in the same manner as in Example 1 using the γ-alumina carrier obtained by firing for a time. Using this adsorbent, the NOx concentration at the outlet was measured under the same conditions as in Example 1. The change over time in the NOx concentration at this time is shown as Example 2 in FIG.

As is clear from the comparison with the curve of Example 1 in the figure, NOx adsorption performance was improved by using an alumina carrier obtained from colloidal alumina (alumina sol) as a raw material or a commercially available alumina carrier. No significant difference is observed, indicating that either carrier can be used.

Example 3 5 ml (3.5 g) of the adsorbent obtained in the same manner as in Example 2 was filled in a stainless steel reaction tube having an inner diameter of 22 mm and was passed through dry air (moisture concentration: about 50 ppm) (2. 5NL / min) About 300
After treating at ℃ for 1 hour, it was allowed to cool to room temperature. After cooling, the flow of dry air is stopped once, and the air containing 3.5 ppm of nitric oxide (NOx) in the adsorbent layer (temperature: 24.5 ° C, relative humidity: 49%, moisture concentration: about 15, 000ppm) 2.5
NL / min was introduced, and immediately after the introduction, N in the outlet gas of the reaction tube
The Ox concentration was measured. The time-dependent change in the NOx concentration in the outlet gas is shown as Example 3 in FIG.

Example 2 in the figure (moisture concentration: 500 ppm
As is clear from the comparison with the curve of (1), the NOx adsorption performance does not decrease even when the moisture concentration increases, and it is understood that NOx can be efficiently adsorbed and removed even with the moisture concentration of atmospheric air.

Example 4 The carrier used in Example 2 was crushed and sieved to 8 to 14 mesh, immersed in an aqueous solution of ruthenium chloride having a predetermined concentration at room temperature for 20 hours, washed with water and dried to obtain a Ru-supported amount. Different adsorbents were obtained.

5 ml (3.5 g) of these adsorbents had an inner diameter of 2
It was filled in a 2 mm stainless steel reaction tube and the NOx concentration at the outlet was measured under the same conditions as in Example 1 to obtain a 10% breakthrough time. The relationship between the amount of Ru carried and the 10% breakthrough time is shown in FIG.

As can be seen from the figure, the 10% breakthrough time increases as the Ru loading increases, that is, the NOx adsorption performance improves, but when the Ru loading is about 3 wt% or more, it becomes 1
It can be seen that the 0% breakthrough time is almost constant.

[0041]

Since the adsorption / removal agent according to the present invention is not affected by moisture, the dehumidification step required before the NOx adsorption / removal can be omitted or reduced. Therefore, a large amount of energy required in the dehumidifying step can be reduced, and a dehumidifying device can be eliminated or simplified. Therefore, significant energy saving and space saving (miniaturization) can be achieved as compared with the conventional process, and the economical effect is extremely high.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between time and breakthrough rate.

FIG. 2 is a graph showing the relationship between time and breakthrough rate.

FIG. 3 is a graph showing the relationship between time and breakthrough rate.

FIG. 4 is a graph showing the relationship between the amount of Ru carried and the breakthrough time.

FIG. 5 is a graph showing the relationship between time and breakthrough rate.

(72) Inventor Shigenori Onizuka, 5-3-28 Nishikujo, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd. (72) Atsushi Fukuju, 5-28-3 Nishikujo, Konohana-ku, Osaka Hitachi Shipbuilding Co., Ltd. In-house (72) Inventor Yuki Nishira 5-3-28 Nishikujo, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd. (72) Inventor Shuji Kobayashi 5-28 Nishikujo, Konohana-ku, Osaka Hitachi Shipbuilding Co., Ltd. Within

Claims (1)

Claims: 1. An adsorbent / removal agent for low-concentration nitrogen oxides, characterized in that ruthenium is supported on a carrier made of γ-alumina.