JPH07275695A - So2 adsorbent - Google Patents

Abstract

PURPOSE:To obtain an SO2 adsorbent capable of being repeatedly regenerated and used by supporting cerium on a carrier composed of anatase type titania. CONSTITUTION:Cerium is supported on a carrier composed of anatase type titania or Ce and at least one addition metal selected from a group consisting of Pt, Pd, Rh, Ag, V, Mn, Fe, Co, Cu, Mo and Bi are together supported on the carrier to obtain the objective SO2 adsorbent. This SO2 adsorbent adsorbs SO2 reversibly and can be regenerated and reused. Therefore, by packing the front part of an NOx adsorbent packed bed with this SO2 adsorbent, the poisoning (lowering of capacity) of the NOx adsorbent caused by SO2 is reduced and the life of the NOx adsorbent can be extended and a more practical NOx adsorbing and removing system can be constructed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to ventilation gas in various tunnels such as various road tunnels, mountain tunnels, undersea tunnels, underground roads, and roads with shelter (collectively referred to as "road tunnels"). Regarding the technology for efficiently removing the contained low-concentration nitrogen oxides (NOx),
More specifically, by filling in the upstream of the NOx adsorbent filling layer, reversibly adsorb SO _2, relates to SO ₂ sorbents may make repeated reuse.

[0002]

BACKGROUND OF THE INVENTION In a road tunnel or the like, which is particularly long and has a large amount of automobile traffic, it is necessary to provide a considerable amount of ventilation for the purpose of protecting the health of passersby and improving the visual distance. Even in a relatively short-distance tunnel, carbon monoxide (C
O), as a method of preventing air pollution due to NOx, etc.
There is a method to suck and exhaust (ventilate) the air in the tunnel.

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 exhaust gas pollution is spreading in the plane or its suburbs. It could lead to.

NOx in the ventilation gas of a road tunnel or the like generally has a concentration of 10 ppm or less, and most of it is NO and contains a small amount of NO ₂ and N ₂ O. Moisture content of several%, CO _{2 of} 0.1% or less, S of 1 ppm or less
O ₂ and several ppm of hydrocarbons coexist.

[0005]

2. Description of the Related Art The present inventors have previously proposed, as a device for purifying ventilation gas for road tunnels, etc., a NO of a honeycomb structure composed of a plate-shaped adsorbent in which TiO ₂ carries Ru, Ce, or the like.
x adsorbent Rotational NOx adsorption (removal) mainly composed of rotor
A device was proposed (Japanese Patent Laid-Open No. 3-258324).

However, the rotary NOx adsorber has various problems, and in order to solve these problems, the fixed bed NOx is characterized in that the NOx adsorber is divided into a plurality of zones in the gas flow direction. Proposed adsorption device (Japanese Patent Application No. 5-
209680).

[0007]

The NOx adsorbent used in a fixed bed NOx adsorber has been experimentally found to be poisoned by 50 ppm SO ₂ in the process gas. Therefore, under actual use conditions (SO ₂ :
Even at 1 ppm or less), NOx adsorption (removal) performance is expected to gradually decrease.

The rate of decrease in NOx adsorption (removal) performance is affected by the SO ₂ concentration in the processing gas, and it is expected that the lower the SO ₂ concentration, the slower the rate of performance decrease.

Therefore, it is desired to extend the life of the NOx adsorbent by reducing the SO ₂ concentration before NOx adsorption.

Several flue gas desulfurization methods are known as means for removing SO ₂ in the treated gas.

The flue gas desulfurization method is roughly classified into a wet method and a dry method.

As the wet method, there are processes such as water washing, alkali washing (aqueous solution containing ammonia, caustic soda, etc.) or absorption in a sodium sulfite (Na ₂ SO ₃ ) solution.

Since the wet method requires a waste liquid treatment facility, the process cannot be economically performed except for the purpose of recovering a high concentration of SO ₂ .

Particularly, in the NOx adsorption device, NOx
It is not preferable in the NOx adsorption device that the NOx adsorption (removal) performance of the adsorbent is affected by the humidity in the processing gas and that the processing gas is humidified by bringing it into contact with a liquid such as water washing.

The dry method includes activated carbon and slaked lime (Ca
A process for absorbing (OH) ₂ ) and calcium carbonate (CaCO ₃ ) is known.

Since these SO ₂ absorbents cannot normally be reused, they are thrown away. Therefore, when processing a large amount of gas (such as tunnel ventilation gas), SO ₂
The consumption of the absorbent becomes large, which is not economically preferable.

An object of the present invention is to provide an SO ₂ adsorbent which can solve all of the above problems.

[0018]

SUMMARY OF THE INVENTION The above problem is reversibly adsorb SO _2, if Re Miidase is SO ₂ adsorbent may make repeated reuse, the upstream of the SO ₂ adsorbent NOx adsorbent filling layer Can be solved by filling the

As a result of earnest studies to solve the above problems, the present inventors have found an adsorbent capable of reversibly adsorbing SO ₂ , and completed the present invention.

That is, the SO ₂ adsorbent according to the present invention is
Cerium is supported on a carrier composed of anatase-type titania.

The SO ₂ adsorbent according to the present invention is preferably a carrier composed of anatase-type titania in which cerium and an additional metal are co-supported. The additional metal is at least one selected from the group consisting of platinum, palladium, rhodium, silver, vanadium, manganese, iron, cobalt, copper, molybdenum and bismuth.

In a preferred embodiment of the present invention, the carrier consisting of anatase titania is held on ceramic paper.

The preferred SO ₂ adsorbent of the present invention is a flat plate-shaped ceramic paper holding a carrier made of anatase-type titania and a corrugated plate-shaped ceramic paper holding a carrier made of anatase-type titania. To form a flat plate / corrugated plate multilayer structure having a honeycomb shape in cross section, and cerium is carried on the carrier.

[0024]

【Example】

Example 1 Commercially available ceramic paper (component: silica: alumina =
50:50, thickness; 0.25 mm, basis weight; 46 g /
m ² ) was cut into a predetermined size and immersed in anatase-type titania sol (TiO ₂ content; about 30% by weight) at room temperature.

Immediately after the immersion, this ceramic paper was taken out on a flat plate, and excess titania sol was dropped by a roller or the like to obtain a uniform thickness, and at the same time, the paper was dried with hot air.

The plate-shaped titania sol-impregnated ceramic paper thus molded was placed in an electric furnace and fired in air at 500 ° C. for 3 hours to obtain a plate-shaped titania-holding ceramic paper.

From the difference between the weight before impregnation of the titania sol and the weight after firing, the TiO ₂ retention was determined to be 101 g /
m ² of TiO ₂ was retained.

Then, the plate-shaped titania-supporting ceramic paper was immersed in a cerium chloride (CeCl ₃ ) aqueous solution (Ce concentration; 17% by weight) at room temperature.

After the immersion, this was dried at about 110 ° C. and then placed in an electric furnace and calcined in air at 500 ° C. for 3 hours to obtain an SO ₂ adsorbent (C) carrying a Ce-supported titania-supported ceramic paper.
e supported amount: 30.4% by weight) was obtained.

[0030] Performance Test The tabular SO ₂ sorbent pieces (length: 50 mm, width;
21 mm) and cut into 8 test pieces (adsorbent geometric surface area;
0.0168 m ² ) was obtained, and these were filled in a stainless steel reaction tube having an inner dimension of 22 mm square.

Next, while flowing the conditioned air (moisture: 5000 ppm) from one end to the other end of the adsorbent-packed bed (2.8 N liter / min), the adsorbent was heated at about 130 ° C. for 10 minutes. After the treatment (referred to as "preheating operation"), the treatment was continued at about 300 ° C for 30 minutes (referred to as "regeneration operation"). After the regenerating operation, contrary to the above, the conditioned air (moisture: 5000 ppm) was passed through the adsorbent from the other end of the adsorbent packed bed toward one end through the adsorbent for 45 minutes (2.8 N liter / 1.
Min) and allowed to cool (referred to as "cooling operation").

After cooling down, in the same gas flow direction as the cooling operation,
Humidified air (moisture content: 5000 ppm) containing 50 ppm of SO ₂ was passed through the adsorbent packed bed (referred to as “adsorption operation”). In the first adsorption operation, the SO ₂ concentration in the outlet gas of the reaction tube was measured with an infrared analyzer immediately after the flow of the SO ₂ containing gas. FIG. 1 shows the change with time of the SO ₂ concentration in the outlet gas. The vertical axis in FIG. 1 indicates the SO ₂ in the outlet gas.
Value obtained by dividing the concentration by the SO ₂ concentration in the inlet gas (“breakthrough rate”
Is called).

Looking at the initial performance (first adsorption),
The time required for the breakthrough rate to reach 0.2 was 50 minutes.

Subsequent to the adsorption operation, SO ₂ adsorbed on the adsorbent was desorbed by preheating operation and regeneration operation again, and then cooling operation was performed. After the cooling operation, the second adsorption operation was performed in the same manner as the first adsorption operation.

As for the second adsorption performance, the time required for the breakthrough rate to reach 0.2 was 33 minutes.

In this way, one cycle of the adsorption operation, the preheating operation, the regeneration operation and the cooling operation was repeated 17 times.

In the meantime, regarding the adsorption performance of the 6th time, the time until the breakthrough rate reaches 0.2 is 20 minutes, the adsorption time of the 10th time is 17 minutes, and it does not change so much after that, and the 18th time. The adsorption time was 15 minutes.

Next, the SO ₂ concentration in the gas at the inlet of the reaction tube was changed to 20.0 ppm for the 19th adsorption, and the same concentration was changed to 4.8 ppm for the 20th adsorption.
The preheating operation, the regeneration operation and the cooling operation were performed in the same manner as the first operation.

The measured breakthrough rate is shown in FIG. In the 19th adsorption operation, the time until the breakthrough rate reaches 0.2 is 3
It was 9 minutes, and it was 157 minutes in the 20th adsorption operation.

[0040] Figure 3, in 20 th SO ₂ adsorbed from 18 th, and SO ₂ concentration in the reaction tube inlet gas, SO ₂ adsorption amount adsorbed by the adsorbent before breakthrough rate reaches 0.2 Shows the relationship with.

[0041] As seen in FIG. 3, SO ₂ adsorption amount of the SO ₂ sorbent seen to be independent of the SO ₂ concentration is supplied to the adsorbent.

From FIG. 2 and FIG. 3, this SO ₂ adsorbent shows that the SO ₂ adsorbent has a low concentration of SO even after repeated adsorption and regeneration.
It can be seen that even with ₂ , excellent adsorption performance is exhibited.

Comparative Example 1 A plate-shaped titania-supporting ceramic paper obtained in the same manner as in Example 1 was used as a plate-shaped adsorbent and cut into small pieces in the same manner as in Example 1, and the obtained test piece was made of a stainless steel reaction product. After filling the tube and performing the same operations as in Example 1 (preheating, regeneration, and cooling operations), conditioned air containing 50 ppm SO ₂ (moisture; 5000 ppm) was passed through the adsorbent packed bed. ,
Adsorption operation was performed.

The initial adsorption performance of this adsorbent is shown in FIG.
For comparison, FIG. 4 also shows the result of the first adsorption of Example 1.

As is apparent from FIG. 4, it is clear that the titania (of anatase type) alone does not exhibit sufficient adsorption performance, and that cerium is effectively supported.

In the SO ₂ adsorbent of the present invention, it is considered that the adsorbed SO ₂ is retained on the adsorbent in the form of cerium sulfate after being oxidized on the surface of the adsorbent.

Therefore, the effect of increasing the SO ₂ adsorption rate is expected by adding a noble metal having a function of oxidizing SO ₂ to SO ₃ .

Further, by adding a metal (V, Fe, etc.) which forms a sulfate which is easily pyrolyzed, it is expected that the adsorption capacity is increased and SO ₂ is desorbed so that the adsorbent can be easily regenerated. It

Therefore, the effect of adding the additional metal was examined from the above viewpoint.

Example 2 The titania-supporting ceramic paper obtained in the same manner as in Example 1 was immersed in an aqueous cerium chloride solution at room temperature, dried and then calcined in air at 500 ° C. for 3 hours to obtain a Ce-supported titania-supporting ceramic paper. An SO ₂ adsorbent (amount of Ce carried: about 30% by weight) was prepared.

This tabular SO ₂ adsorbent was immersed at room temperature in a platinum chloride aqueous solution whose concentration was adjusted so that a platinum salt was supported as platinum (Pt) metal in the adsorbent at 1% by weight. Firing at 500 ° C. for 1 hour gave an SO ₂ adsorbent (denoted as “Ce (30) + Pt (1) / TiO ₂ ”) consisting of Pt-added Ce-supporting titania-supporting ceramic paper.

This flat plate-shaped platinum-containing adsorbent was filled in a stainless steel reaction tube in the same manner as in Example 1, and adsorption and regeneration were repeated by the same operation as in Example 1 to achieve a 20% breakthrough in the 10th adsorption. The time (time until the breakthrough rate reaches 0.2) was measured. The results of this measurement are shown in Table 1. The breakthrough time of this SO ₂ adsorbent is 25 minutes, and the effect of adding platinum is recognized.

Examples 3, 4 As in Example 2, the concentration of the SO ₂ adsorbent consisting of Ce-supporting titania-supporting ceramic paper was adjusted so that 1% by weight of palladium (Pd) salt was supported on the adsorbent as Pd metal. except that immersion at room temperature palladium chloride aqueous solution, in the same manner as in example 2, consisting of Pd added Ce supported titania holding ceramic paper SO ₂ sorbent ( "Ce
(Denoted as (30) + Pd (1) / TiO ₂ )) was obtained (Example 3). Similarly, S consisting of Rh-added Ce-supported titania-supporting ceramic paper using an aqueous rhodium chloride solution.
An O ₂ adsorbent (denoted as “Ce (30) + Rh (1) / TiO ₂ )” was obtained (Example 4).

Examples 5 to 12 Additional metals other than noble metals (Pt, Pd, Ph) (Ag,
V, Mn, Fe, Co, Cu, Mo, and Bi) were added to a metal salt solution shown in Table 1 whose concentration was adjusted so that the metal salt was supported on the adsorbent as a metal in an amount of 3% by weight. Examples 5 to 5 were carried out in the same manner as in Example 2 except that the SO ₂ adsorbent consisting of paper was immersed.
12 adsorbents were obtained.

In Table 1, the adsorbents of Examples 3 to 12 were obtained by the same operation as in Example 1. The 20% breakthrough time at the 10th adsorption is shown.

All the adsorbents were Ce (30) / of Example 1
An improvement in adsorption performance is recognized as compared with TiO ₂ .

[0057]

[Table 1]

[0058]

The SO ₂ adsorbent according to the present invention is capable of reversibly adsorbing SO ₂ and reusable.
By packing the O ₂ adsorbent in the upstream of the packed bed of the NOx adsorbent, it is possible to reduce the poisoning (performance deterioration) of the NOx adsorbent due to SO ₂ and extend the life of the NOx adsorbent, A more practical NOx adsorption removal system can be constructed.

[Brief description of drawings]

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

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

FIG. 3 is a graph showing the relationship between the inlet SO ₂ concentration and the NOx adsorption amount.

FIG. 4 is a graph showing the relationship between adsorption time and breakthrough rate.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical indication location B01D 53/50 53/81 (72) Inventor Takanobu Watanabe Takashi Watanabe Nishikujo 5-chome 3-28, Konohana-ku, Osaka Hitachi Shipbuilding Co., Ltd. (72) Inventor Atsushi Fukuju 5-3-28 Nishikujo, Konohana-ku, Osaka City Hitachi Shipbuilding Co., Ltd.

Claims (4)

[Claims] 1. A carrier comprising anatase-type titania,
An SO ₂ adsorbent loaded with cerium. 2. A carrier comprising anatase-type titania,
An SO ₂ adsorbent in which cerium is co-loaded with at least one additional metal selected from the group consisting of platinum, palladium, rhodium, silver, vanadium, manganese, iron, cobalt, copper, molybdenum, and bismuth. 3. A carrier made of anatase-type titania is held on ceramic paper.
The described SO ₂ adsorbent. 4. A flat plate having a honeycomb-shaped cross section in which flat plate-shaped ceramic paper holding a carrier made of anatase-type titania and corrugated plate-shaped ceramic paper holding a carrier made of anatase-type titania are arranged every other sheet. An adsorbent for SO ₂ in which a corrugated plate multilayer structure is formed and cerium is carried on the carrier.