JPH0798150B2 - Adsorption remover for low concentration nitrogen oxides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a low concentration of nitrogen contained in ventilation gas in various tunnels such as various road tunnels, mountain tunnels, seabed tunnels, underground roads, roads with shelters, etc. The present invention relates to an adsorption / removal agent that efficiently removes oxides.

BACKGROUND OF THE INVENTION In various road tunnels, mountain tunnels, underground roads, roads with shelters, etc. (in this specification, these tunnels are generically 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 a relatively short-distance tunnel, in urban areas or in the suburbs, as a method of preventing air pollution due to carbon monoxide (CO), nitrogen oxides (NOx), etc. concentrated in the entrances and exits, the air in the tunnel is sucked in. Exhaust (ventilation)
There is a way to do it.

However, if ventilation gas is diffused to the surroundings as it is, it will not improve the local environment, and it will be necessary to expand highly contaminated areas, especially in urban areas where automobile exhaust gas pollution is spreading or in the suburbs. It can happen. The above-mentioned situation is exactly the same when a tunnel or a shelter is installed as a measure against pollution of the existing road.

The present invention relates to an adsorption / removal agent that efficiently removes low-concentration nitrogen oxides contained in ventilation gas for such road tunnels.

[Prior 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 gas volume fluctuates greatly according to the traffic volume.

Conventionally, the method of removing nitrogen oxides from a fixed source has been investigated for the purpose of purifying various boiler combustion exhaust gases,
There are three main categories.

(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 general method for denitration of boiler exhaust gas. However, this method requires a process gas temperature of 200 ° C.
Since it is necessary to set the above, when the amount of gas 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 utilizes the fact that nitrogen dioxide (NO ₂ ) and nitrogen trioxide (N ₂ O ₃ ) are absorbed by water and alkaline aqueous solutions.
A method is known in which nitric oxide (NO) is oxidized and then absorbed by an oxidation catalyst or ozone injection, or an oxidizing property is added to the absorbing liquid. 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, and several cases were studied until the catalytic reduction method was established as a denitration method of boiler exhaust gas. 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, etc., it was found to be an economical method because the process is simple, which is completely different from the case of boiler exhaust gas.

[Problems to be Solved by the Invention] Among the research on the adsorption and removal of nitrogen oxides by an adsorbent, the research on the adsorption and removal of low-concentration nitrogen oxides is conducted by the Industrial Development Research Institute ("Special On development of new denitration system using various adsorption and oxidation catalysts ",
(May 1978). In this simulated gas (inlet NO concentration in the air -H ₂ -NO system: 100～120Ppm, dry gas (dew point: -
Tests were conducted at 17 ° C) and SV: 3270Hr ^-1 ), and it has been reported that the adsorbent is preferably a natural pseudo-olivine loaded with a copper-based metal (oxide).

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

The present inventors previously proposed that as an adsorbent intended to efficiently adsorb and remove nitrogen oxide at a low concentration of 5 ppm, copper chloride, double salt of copper chloride and ammine of copper chloride were added to natural or synthetic zeolite. We have proposed an adsorption remover for low-concentration nitrogen oxides, which is prepared by supporting at least one copper salt selected from complex salts (see JP-A-1-299642).

However, when the above copper salt-supported zeolite is used as a denitration catalyst, when the water (or moisture) concentration becomes low (about 0.
1% or less), NH ₃ oxidative decomposition activity occurs, so that a decrease in catalytic activity (deterioration phenomenon) was observed as shown in FIG. 6 (FIG. 6 shows the denitration catalyst of the copper salt-supporting zeolite against the denitration catalyst). The reaction conditions are gas composition: 10.8 ppm NO + 11.4 ppm NH ₃ + dry air + moisture, space velocity: 40,000 h ^-1 ). In this case, when the reaction temperature is raised, the oxidation activity is further increased, and when the reaction temperature is lowered, sufficient denitration activity cannot be obtained, which leads to an increase in the amount of NH ₃ required for regeneration of the adsorbent, and in some cases, Playback may be inadequate.

Further, since zeolite generally strongly adsorbs carbon dioxide CO ₂ , it is known that it is necessary to heat the adsorbent around 200 ° C. to desorb it. Since CO ₂ is always contained in ventilation gas for road tunnels, etc., CO ₂
Adsorption of NOx may result in a decrease in NOx adsorption capacity (this is probably due to a decrease in NOx adsorption capacity due to CO ₂ adsorption).

Further, regarding the denitration catalyst, it is known that the copper salt of the supported metal is gradually sulfated with SO ₂ and the denitration activity is reduced. Therefore, SO ₂ contained in the ventilation gas may affect the NOx adsorption capacity.

In view of the above points, an object of the present invention is to efficiently provide an adsorption / removal agent for low-concentration nitrogen oxides contained in ventilation gas for road tunnels and the like.

[Means for Solving the Problem] As a result of various investigations by the present inventors, adsorption of anatase-type titanium oxide as a carrier for supporting a denitration active component on a gas containing a low concentration of nitrogen oxide The inventors have found that nitrogen oxides can be efficiently adsorbed and removed by bringing them into contact with an agent, and have completed the present invention.

That is, the adsorbent / removal agent for low-concentration nitrogen oxides (hereinafter simply referred to as an adsorbent) according to the present invention comprises vanadium supported on an anatase-type titanium oxide carrier.

First, the first feature of the adsorbent according to the present invention is that anatase type titanium oxide is used as a carrier.

Anatase-type titanium oxide is produced from commercially available titanium oxide carriers and titania sol obtained by deflocculating and stabilizing hydrated titanium oxide (titanic acid slurry) or titanic acid slurry, which is an intermediate product during the production of titanium oxide by the sulfuric acid method. Any of the titanium oxides mentioned above can be used.

The adsorbent carrier may contain, in addition to titanium oxide, a forming aid (used as a binder or a diluent) such as alumina sol, alumina, silica sol, and silica / alumina, or a fibrous substance such as ceramic fiber.

The adsorbent carrier can be obtained by kneading the adsorbent carrier with a molding aid and a fibrous substance, if necessary, molding the adsorbent carrier into a preferable shape, and drying and firing.

Next, the second characteristic of the adsorbent according to the present invention is that vanadium is supported on the carrier.

The amount of vanadium supported is preferably about 0.5 to 10% by weight of the adsorbent as vanadium metal, and more preferably about 2 to 5% by weight.

Loading of vanadium is generally carried out by immersing the titanium oxide support in a solution prepared by dissolving a vanadium compound such as ammonium metavanadate (NH ₄ VO ₃ ) in a suitable solvent, but not limited to this method.

The supported amount of vanadium is adjusted by the concentration of vanadium in the immersion solution, the immersion temperature, the immersion time, and the like. After soaking, separate the adsorbent from the solution, wash with water, and then about 10
Dry at 0-120 ° C. If necessary, the dried product is baked in air at about 300 to 500 ° C. In addition, adsorption, desorption,
During continuous use such as regeneration, the adsorbent is treated at a temperature slightly higher than the maximum temperature.

The shape of the adsorbent is not particularly limited, and is a columnar shape,
Any material such as a Raschig ring shape or a honeycomb shape may be used as long as it has a large contact surface and facilitates gas flow.

When processing a large amount of gas such as ventilation gas from a road tunnel or the like, it is necessary to reduce the pressure loss as much as possible because the flow resistance is low. Therefore, it is desirable to form the honeycomb structure like a CP catalyst (ceramic paper impregnated with titania and then supporting vanadium).

[Examples] Next, some examples of the present invention and comparative examples to be compared with the examples will be described.

Example 1 A titanate slurry (TiO ₂ content: about 30% by weight) was calcined in air at 400 ° C. for 5 hours to obtain a carrier composed of anatase type titanium oxide (specific surface area: 136.3 m ² / g). Prepared.

The carrier was crushed and sieved to 8 to 14 mesh, and then immersed in a saturated aqueous solution of ammonium metavanadate (NH ₄ VO ₃ ) (10 times the volume of the carrier) at room temperature for 16 hours. After washing this with water,
It was dried at 110 ° C. for 2 hours and further calcined at 400 ° C. for 1 hour to obtain an adsorbent (vanadium supported amount: 3.1% by weight).

7 g (11.6 cm ³ ) of this adsorbent was filled in a stainless steel reaction tube having an inner diameter of 22 mm and dried at a temperature of about 235 ° C. for 1 hour by circulating dry air (moisture concentration: about 60 ppm) (5 l / min). It was left to cool to room temperature. After cooling down, stop the flow of dry air,
Dry air (5 l / min) containing 4.42 ppm of nitric oxide (NO) was introduced into the adsorbent layer, and immediately after the introduction, the NO concentration in the outlet gas of the reaction tube was measured by a chemiluminescence analyzer. In the outlet gas
FIG. 1 shows the change with time of NOx concentration. The vertical axis of FIG. 1 is a scale of the value obtained by dividing the NOx concentration in the outlet gas by the NOx concentration in the inlet gas (called “breakthrough rate”).

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, 0.44 ppm (“breakthrough time”). Called) was 48.6 minutes.

Comparative Example 1 Y-type zeolite was used as a carrier, and cupric chloride (CuCl ₂ ) was impregnated and carried on this to prepare an adsorbent. Using this adsorbent, the NOx concentration at the outlet was measured under the same conditions as in Example 1. The change with time of this NOx concentration is shown in FIG.

As is clear from the curve of Comparative Example 1 in the figure, the breakthrough time in this case is 49.7 minutes, and this adsorbent has the same performance as the adsorbent composed of vanadium-supported titanium oxide (Example 1). I understand.

Comparative Example 2 The carrier prepared in Example 1 was used as an adsorbent and the inlet NOx
The outlet NOx concentration was measured under the same conditions as in Example 1 except that the concentration was 4.49 ppm. FIG. 1 shows the change with time of NOx concentration.

As is clear from the curve of Comparative Example 2 in the figure, the breakthrough time in this case is 72.3 minutes, and it can be seen that low-concentration NOx is efficiently adsorbed only by supporting titanium oxide.

Comparative Examples 3 to 7 The carrier prepared in Example 1 (Comparative Example 3) and the titanic acid slurry (TiO ₂ content: about 30% by weight) in air at 450 ° C.
Carrier obtained by calcining for an hour (specific surface area: 112.7 m ² / g) (Comparative Example 4), carrier obtained by calcining a titanic acid slurry in air at 500 ° C. for 5 hours (specific surface area: 82.0 m ² / g) (Comparative Example 5),
Commercially available titanium oxide carrier (catalyst formation, specific surface area: 144.4 m ² /
g) (Comparative Example 6) and a commercially available titanium oxide carrier (Rhone-Poulin, France, specific surface area: 71.0 m ² / g), 14 to ² respectively.
It was crushed and sieved to 0 mesh to obtain an adsorbent. This adsorbent 10.
0 cm ³ was filled in a stainless steel reaction tube having an inner diameter of 22 mm, and the outlet NOx concentration was measured by the same method as in Example 1. The change with time of this NOx concentration is shown in FIG.

As shown in the figure, although the NOx adsorbing properties differ depending on the method of preparing the titanium oxide carrier, it can be seen that the adsorbent composed of any titanium oxide carrier adsorbs NOx.

However, vanadium is not supported for the reason described below.
With the adsorbents only supporting TiO ₂ , regeneration with a gas containing NH ₃ cannot be sufficiently performed, and these adsorbents cannot be put to practical use.

Examples 2 to 6 Preparations comprising vanadium loaded on a carrier by the same method as in Example 1 except that the carrier used in Comparative Examples 3, 4, 6 and 7 was used (Examples 2, 3, 4 respectively). And 5), and 100 parts of titanic acid slurry (TiO ₂ content: about 30% by weight) and 40 parts of titania sol (TiO ₂ content: about 30% by weight) were evaporated to dryness while kneading, and the dry matter was further added. A carrier obtained by calcining in air at 450 ° C for 25.5 hours (specific surface area:
Preparation of vanadium on a carrier in the same manner as in Example 1 except that 163.3 m ² / g) was used (Example 6)
Were crushed and sieved to 14 to 20 mesh to obtain an adsorbent.

The adsorbent 10.0 cm ³ was filled in a stainless steel reaction tube having an inner diameter of 22 mm, and the outlet NOx concentration was measured by the same method as in Example 1. The change with time of this NOx concentration is shown in FIG.

As can be seen from the figure, although the NOx adsorbing properties differ depending on the method of preparing the titanium oxide that is the carrier, it can be seen that all adsorbents adsorb NOx.

Further, as described later, all the adsorbents having vanadium supported on titanium oxide have sufficient denitration activity at 200 ° C. or higher and can be regenerated by a gas containing NH ₃ .

Example 7 and Comparative Example 8 In Example 7, 10.0 cm ³ of the adsorbent used in Example 1 was used and the inner diameter was 22 m.
Fill a stainless steel reaction tube of m, gas composition: 10.5ppm NO
_{+ 12.0ppm NH 3 + 60ppm H 2} O + remaining air in the reaction gas (5 Nl /
min), and measuring the NOx concentration at the inlet and outlet of the reaction tube while varying the reaction temperature, and denitration rate corresponding to the reaction temperature = ((inlet NOx concentration-outlet NOx concentration) / inlet NOx concentration) x 100% I asked.

In Comparative Example 8, the NOx concentration at the inlet and outlet of the reaction tube was measured by the same method as in Example 7 except that the adsorbent of Comparative Example 2 (the carrier used in Example 1 before supporting vanadium) was used.

The relationship between the reaction temperature and the denitration rate in Example 7 and Comparative Example 8 is shown in FIG.

As seen in the figure, the adsorbent containing only titanium oxide shows almost no denitration activity. On the other hand, an adsorbent made by supporting vanadium on titanium oxide has a denitration rate of 9
It shows 0% or more, indicating that it has high denitration activity.

Example 8 The carrier used in Example 1 (the titanic acid slurry was added at 400 ° C.
After crushing and sieving the carrier obtained by calcination for 8 hours to 8 to 14 mesh, it is immersed in an aqueous solution of ammonium metavanadate at a predetermined concentration for 16 hours at room temperature, washed with water and dried,
It was calcined at 400 ° C. for 1 hour to prepare adsorbents having different vanadium loadings.

The adsorbent 10.0 cm ³ was filled in a stainless steel reaction tube with an inner diameter of 22 mm, and the gas composition: 10.5 ppm NO + 12.0 ppm NH ₃ + 50 ~
Pass the reaction gas of 70ppm H ₂ O + remaining air through the reaction tube (5
Nl / min), and the denitration rate at 225 ° C was measured.

Fig. 5 shows the relationship between the amount of vanadium supported and the denitration rate at 225 ° C.

As shown in the figure, the denitration rate increases as the vanadium loading increases, but the vanadium loading is about 3 wt%.
From the above, it can be seen that the denitration rate is almost constant.

[Brief description of drawings]

1 to 3 are graphs showing the relationship between time and breakthrough rate, FIG. 4 is a graph showing the relationship between reaction temperature and denitration rate, and FIG. 5 is a graph showing the relationship between vanadium loading amount and denitration rate. ,
FIG. 6 is a graph showing the relationship between the reaction temperature and the denitration rate for the conventional adsorbent.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takanobu Watanabe 5-3-8 Nishikujo, Konohana-ku, Osaka City, Osaka Prefecture Hitachi Shipbuilding Co., Ltd. (72) Atsushi Fukuju 5 Nishikujo, Nishinoko-ku, Osaka City, Osaka Prefecture 3-28, Hitachi Shipbuilding Co., Ltd. (72) Inventor, Shuji Kobayashi 5-28, Nishikujo, Konohana-ku, Osaka City, Osaka Prefecture Hitachi Shipbuilding Co., Ltd.

Claims (1)

[Claims] 1. An adsorbent / removal agent for low-concentration nitrogen oxides, characterized in that vanadium is supported on a carrier composed of anatase-type titanium oxide.