JPH0699028A - Filter for purifying gas - Google Patents

Abstract

PURPOSE:To efficiently remove NOx contained in the air and various exhaust gases, especially both NO and NO2. CONSTITUTION:An adsorption bed packed with activated carbon is disposed on the downstream side of an adsorption bed packed with a multiple oxide contg. hydrogen and manganese whose average valence is >3.5 and having a spinel type crystal structure to obtain the objective filter for purifying gas. The adsorption beds may be packed with a mixture of the multiple oxide with activated carbon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas purifying filter capable of effectively removing harmful components contained in gases such as air, including nitric oxide, which is generally considered to be difficult to remove. Regarding this, this filter purifies the air in living spaces, medical facilities, or facilities that house precision equipment, arts, cultural properties, etc. in areas where the atmospheric environment is poor, and can be used to prevent health problems and corrosion. it can.

[0002]

2. Description of the Related Art Activated carbon filters have hitherto been widely used as means for purifying polluted indoor air or preventing polluted outside air from entering the room (for example, edited by the Society of Carbon Materials, "Activated carbon-Basics and applications-"
6.2.3, Kodansha (1975), etc.).

Among the polluted gases, sulfur dioxide, nitrogen dioxide, hydrogen sulfide, ammonia and the like have relatively high boiling points and high reactivity and adsorption activity. It can be removed relatively easily.

However, some components cannot be easily removed depending on the activated carbon and other adsorbents. For example, it has been proposed to use a noble metal catalyst for the removal of nitric oxide (JP-A-3-4922). However, since nitric oxide has a very low adsorption activity and does not adsorb to most adsorbents as it is, it is adsorbed after being oxidized to nitrogen dioxide in advance by various oxidizing agents (ozone, permanganate, chlorite, etc.). A method of removal was proposed.

However, in these methods, an ozone generator for pre-oxidizing the gas to be treated is additionally provided, or an oxidizing agent (sodium chlorite, potassium permanganate, etc.) is attached to the adsorbent or carrier. In the former method, the equipment and operating cost of the ozone generator are not only high, but also the deactivation of the adsorbent is accelerated due to the oxidation action of the excess ozone, and the oxidant is impregnated. In the latter method, the life of the oxidant is very short and the regeneration of the adsorbent becomes difficult, so that it has hardly been put into practical use.

[0006] In recent years, as air pollution due to nitrogen oxides has been once again regarded as a problem, even if only highly harmful nitrogen dioxide can be successfully removed, the unremoved nitric oxide is subsequently oxidized to nitrogen dioxide. However, it does not solve the problem.

[0007]

SUMMARY OF THE INVENTION Under the above circumstances, the present inventors have aimed to develop an adsorbent capable of efficiently removing low-concentration nitrogen oxides, particularly nitric oxide. We are conducting more research, but as a result, we have developed the following two technologies and have already filed a patent application.

A nitric oxide adsorbent (Japanese Patent Application No. 3-352341) obtained by heat-treating activated carbon in an inert gas or reducing gas atmosphere to modify the surface structure, containing hydrogen and manganese, and manganese. A nitric oxide adsorbent containing a spinel structure having an average valence of more than 3.5 as an active ingredient (Japanese Patent Application No. 4-86430).

The above-mentioned adsorbents are extremely superior to the conventionally known adsorbents in that nitric oxide can be removed efficiently, but there is still room for improvement in consideration of practicality. . That is, in the adsorbent described above, since the adsorption capacity of nitric oxide has a limit, regeneration treatment must be performed regularly, and as an adsorbent for a gas purification filter that needs to maintain adsorption capacity for a long period of time, Not always satisfactory. Further, when the above-mentioned adsorbent is applied to ordinary air containing water, the oxidizing / desorbing property to nitrogen dioxide has priority over the nitric oxide adsorbing ability, so that more harmful nitrogen dioxide is rather increased. There are also cases.

The present invention has been made in view of the above circumstances, and its purpose is to efficiently adsorb nitrogen oxides in pollutant gas containing nitric oxide, including more harmful nitrogen dioxide. An object of the present invention is to provide a gas purification filter that can be removed.

[0011]

The structure of the gas purifying filter according to the present invention, which has been able to solve the above problems, contains hydrogen and manganese and has an average valence of 3.
An adsorbent layer (I) filled with an adsorbent having an active component of a complex oxide having a spinel type crystal structure of more than 5 and activated carbon activated downstream of the adsorbed layer (I) in the gas flow to be treated. An adsorption layer (II) filled with an adsorbent as a component is arranged,
Alternatively, the gist resides in that a mixture of the above complex oxide and activated carbon is filled as an active ingredient.

When the mixed oxide and the activated carbon are mixed and used in the above, they may be simply mixed, or molded into a granular shape, a pellet shape, a Raschig ring shape or the like. In order to exert a high adsorption activity while suppressing the ventilation resistance, the above composite oxide and activated carbon are supported on an air permeable carrier, or each powder of the above complex oxide and activated carbon is used as a raw material and a solvent or an auxiliary agent is added. It is preferable that the mixture is kneaded by kneading, then extruded into a honeycomb shape and dried.

[0013]

The gas purifying filter of the present invention is a hydrogen-manganese-containing composite oxide (hereinafter simply referred to as a composite oxide) having a spinel type crystal structure having an average manganese valence of more than 3.5 on the upstream side of the gas flow to be treated. Is provided as an active ingredient, and an adsorption layer (I) filled with an adsorbent having an active ingredient of activated carbon is provided on the downstream side thereof. It is filled with a mixed adsorbent containing oxides and activated carbon as active components, and nitrogen oxides contained in the gas to be treated can be efficiently removed by the interaction between the composite oxide and the activated carbon.

In the present invention, the hydrogen-manganese-containing composite oxide of spinel type crystal structure having an average manganese valence of more than 3.5, which constitutes the adsorption layer (I), is described in the above-mentioned JP-A-4-8643.
It is disclosed in No. 0, and its constitution is as follows.

As a typical manganese-containing oxide having a spinel structure, for example, a manganese oxide containing lithium is known, and as this lithium-containing manganese oxide, LiMn ₂ having an average manganese valence of 3.5. There are O ₄ and tetravalent Li _1.33 Mn _1.67 O ₄ , which differ in that the former is about 1% larger in crystal lattice constant. These can be obtained by firing a mixed powder of a manganese compound (manganese carbonate, etc.) and a lithium compound (lithium carbonate, etc.) at about 100 ° C. for several hours, and by changing the atomic ratio of manganese to lithium in the mixed powder. Both are oxides that form a solid solution at various ratios. And the average valence of manganese is calculated as LiMn ₂ O ₄ and Li in the solid solution.
It corresponds to the composition ratio of _1.33 Mn _1.67 O ₄ , and is, for example, 3.
If pentavalent, all are LiMn ₂ O ₄ , and if tetravalent, all are L
i _1.33 Mn _1.67 O ₄ , and if it has a valence of 3.8, Li _1.33 Mn _1.67
A mixed composition of O ₄ : LiMn ₂ O ₄ = 3: 2 is obtained.

Therefore, in the present invention, the manganese average valence of "exceeding 3.5" means that a part or all of the above oxides is L.
i _1.33 Mn _1.67 O ₄ is meant. Further, “containing hydrogen” means that the oxide containing Li _1.33 Mn _1.67 O ₄ is oxidized to replace a part or all of Li with hydrogen. It can be represented by the general formula Li _1.33-X H _X Mn _1.67 O ₄ , and the one in which all of Li is replaced by hydrogen is H _1.33 Mn _1.67.
It becomes O ₄ .

Therefore, the hydrogen-manganese-containing composite oxide of the spinel type crystal structure having an average valence of manganese of more than 3.5 used in the present invention is represented by the general formula Li _1.33-X H _X Mn _1.67 O ₄ (however, of these, Li may be substituted with other alkali metal or the like), and means a complex oxide having X exceeding zero as at least a part of the active ingredient. This composite oxide exhibits an excellent adsorption ability for nitric oxide contained in the dry gas to be treated. However, it cannot be said that the adsorption capacity for nitric oxide contained in the normal gas to be treated, which contains water, is necessarily sufficient, and rather, as mentioned above, the ability to oxidize and desorb nitric oxide into easily adsorbable nitrogen dioxide. Has priority. Therefore, it is difficult to efficiently remove all nitrogen oxides only with this adsorbent. Therefore, in the present invention, an adsorption layer (II) formed by filling activated carbon having an excellent nitrogen dioxide adsorption capacity is arranged on the downstream side of the adsorption layer (I) filled with the complex oxide, and the adsorption layer (I) Nitrogen dioxide that could not be removed is absorbed in the adsorption layer (II)
The adsorbent removes all of the nitrogen oxides contained in the gas to be treated efficiently by adsorbing and removing the nitrogen oxides.

Therefore, the activated carbon constituting the adsorption layer (II) may be of any type as long as it can efficiently adsorb and remove mainly nitrogen dioxide in the gas, more preferably chemical impregnation and the like. It is an activated carbon that has been subjected to a treatment for improving the adsorption capacity for acidic gas. In addition, Japanese Patent Application No. 3
As disclosed in U.S. Pat. No. 3,352,341, a surface modification treatment is carried out by heating activated carbon to 400 to 1200 ° C. in an atmosphere of an inert gas or a reducing gas. Nitric oxide which may leak from the adsorption layer (I) is also removed in the adsorption layer (II), which is preferable. It is also effective to increase the gas purifying ability by using plural kinds of activated carbon in combination depending on the components contained in the gas to be treated.

In the present invention, the object can also be achieved by forming a mixture of the above complex oxide and activated carbon as an adsorption layer. That is, if the composite oxide and the activated carbon are allowed to coexist in the adsorption layer, a part of the nitric oxide in the gas to be treated is directly adsorbed by the composite oxide or the activated carbon, and the oxidized or desorbed dioxide is contacted with the composite oxide. Nitrogen is immediately adsorbed by coexisting activated carbon, and as a result, it becomes possible to efficiently remove nitrogen oxides including nitric oxide and nitrogen dioxide. The compounding ratio of the composite oxide and the activated carbon may be appropriately adjusted according to the concentration and composition of nitrogen oxides contained in the gas to be purified.

When a mixture of a complex oxide and activated carbon is used as a complex adsorbent, each of them may be used alone or in the form of granules or pellets, and the mixture may be filled, but the pressure loss during gas purification treatment is suppressed. At the same time, in order to increase the adsorption effective surface area and enhance the purification efficiency, it is advantageous to support these on an air-permeable carrier such as glass, wool or corrugated pulp. In addition, it is also effective to reduce pressure loss and improve adsorption efficiency by mixing powder of activated carbon or complex oxide with a solvent, a binding aid, etc. to form a paste, and extruding this into a honeycomb shape and drying. Also, it is preferable to use such a molded article because the work for regenerating or exchanging the adsorbent becomes easy.

The present invention is constituted as described above, and the packing layer (I) containing the spinel type hydrogen / manganese composite oxide having a manganese average valence of more than 3.5 is provided on the upstream side and the downstream side thereof. By disposing the adsorption layer (II) containing activated carbon or using a mixture of the above complex oxide and activated carbon as an adsorbent, nitrogen oxides in the gas to be treated can be efficiently removed.

Further, the activated carbon used as one of the adsorbents has an excellent adsorption ability for sulfur oxides and the like as well as nitrogen oxides, so that these harmful gas components are also removed at the same time. be able to. However, adsorption of nitrogen oxides and adsorption of sulfur oxides on activated carbon occur competitively,
Since the latter one proceeds rather preferentially, when purifying a gas containing a large amount of sulfur oxides, a sulfur oxide removal filter is provided upstream of the filter according to the present invention to remove sulfur oxides in advance. It is desired to do.

[0023]

EXAMPLES Next, examples of the present invention will be shown, but the present invention is not limited by the following examples. No. shown below. Filters 1 to 6 were produced.

No. 1: Crushed compound oxide having a particle diameter of 2 to 3 mm (composition: H _1.33 Mn _1.67 O ₂ , spinel type crystal structure) and columnar activated carbon (coconut shell charcoal in hydrogen atmosphere 800
What was calcined at ℃, specific surface area 900 m ² / g) was packed into a total thickness of 5 cm so that the volume ratio was 1: 3 and the crushed compound oxide was on the inlet side of the gas to be treated. It was used as a test filter.

No. 2: Instead of activated carbon, No. No. 1 except that the same mixed oxide crushed product as used in 1 and an equal volume mixture of activated carbon were used. Total thickness 5 as in 1
It was filled in cm and it was set as the sample filter.

No. 3: No. Powder (65% by weight), nylon pulp (33% by weight), hydroxyethyl cellulose ( 2% by weight) and a small amount of the pseudo-aggregating agent in water,
This was paper-made to produce a corrugated filter having a basis weight of 75 g / m ² , which was wound in a coil shape to have a thickness of 5 cm to obtain a sample filter.

No. 4: No. 75 parts by weight of powder obtained by pulverizing the same composite oxide and activated carbon as used in 1 to a diameter of 20 to 30 μm and mixing them in a volume ratio of 1: 3, and a mixture of a liquid phenol resin and hydroxyethyl cellulose 2
After mixing 5 parts by weight with an appropriate amount of water to form a slurry,
It is extruded into a honeycomb shape and then dried.
It was filled in m and it was set as the sample filter.

No. 5: No. except that the composite oxide powder was used alone. A honeycomb-shaped test filter was obtained in the same manner as in 4. No. 6: No. except that activated carbon powder was used alone. Four
A honeycomb-shaped test filter was obtained in the same manner as in.

A temperature of 25 ° C. was applied to each of the test filters obtained above.
× 1 pp of nitrogen oxide in air adjusted to a relative temperature of 65%
m (NO: NO ₂ = 1: 1) was added as a gas to be treated, and the superficial velocity was 50 cm / s and the space velocity was 30,000.
The concentration of nitric oxide and nitrogen dioxide at the outlet at 5 and 10 days after flowing at N liter / h was measured by chemiluminescence nitrogen oxide analysis.

The results are collectively shown in Table 1 and show that the filter of the present invention (No.
1 to 4) are comparison filters (N
o. Compared with 5, 6), a superior nitrogen oxide removing effect is obtained, and it can be seen that particularly harmful nitrogen dioxide can be efficiently removed over a long period of time.

[0031]

[Table 1]

[0032]

EFFECTS OF THE INVENTION The present invention is configured as described above, and by using a specific composite oxide in combination with activated carbon, it is possible to efficiently remove nitrogen oxides containing nitric oxide, which have been conventionally difficult to remove. It could be removed.

Claims (4)

[Claims] 1. An adsorption layer (I) filled with an adsorbent containing hydrogen and manganese and having a spinel type crystal structure complex oxide having an average valence of more than 3.5 as an active ingredient. A gas purification filter characterized in that an adsorption layer (II) filled with an adsorbent containing activated carbon as an active component is arranged on the downstream side of the gas flow to be treated with respect to the adsorption layer (I). . 2. A mixture of a composite oxide containing hydrogen and manganese and having an average valence of manganese of more than 3.5 and having a spinel type crystal structure and activated carbon filled as an active ingredient. Gas purification filter to do. 3. The gas purifying filter according to claim 2, wherein the composite oxide and the activated carbon are loaded and supported on an air permeable carrier. 4. The gas purifying filter according to claim 2, which is filled with a honeycomb-shaped molded / dried product obtained by using each powder of the complex oxide and the activated carbon as a raw material.