JPH0576753A - Adsorbent for nitrogen monoxide, its production and method for adsorbing and removing nitrogen monoxide - Google Patents

Abstract

PURPOSE:To provide an adsorbent and its production method where the harmful nitrogen monoxide among nitrogen oxides being a cause of environmental pollution can be efficiently absorbed and removed as it is without oxidizing nitrogen monoxide into nitrogen dioxide and where the adsorbent can be repeatedly used by desorption regeneration. CONSTITUTION:This adsorbent for nitrogen monoxide consists of a porous carbonaceous material having fire pores of 4-10Angstrom diameter by >=0.05cm<3> per 1g adsorbent. Especially, an activated carbon obtd. from phenol resin as the source material has excellent adsorption activity even in the presence of water vapor and can be repeatedly used since it recovers the initial adsorption activity by desorption regeneration and can be repeatedly used.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is capable of efficiently adsorbing and removing nitrogen oxides contained in the atmosphere or various flue gas exhausts, particularly nitric oxide which is chemically inert and difficult to process. The present invention relates to an adsorbent, a method for producing the same, and a method for adsorbing and removing nitric oxide using the adsorbent.

[0002]

2. Description of the Related Art Nitrogen oxide is a typical air pollutant, and many treatment techniques have been proposed so far. The adsorption removal method is one of them, and a large number of adsorbents such as activated carbon have been provided, and nitrogen dioxide, which has a relatively high adsorption activity, has been successfully obtained. However, since the known adsorbents have a poor boiling point and a low activity for adsorbing nitric oxide having low activity, conventionally, a method has been employed in which nitric oxide is once oxidized to nitrogen dioxide and then adsorbed and removed.

Therefore, it was necessary to provide an ozone generator for oxidizing the gas to be treated in advance, or to attach an oxidizing agent to an adsorbent or a carrier (for example, "Chemical factory" 18 (5)). ), 9 (1974) and “Journal of the Chemical Society of Japan” 1978 (2), 303, etc.).

However, these methods have the drawbacks that not only the equipment cost and operating cost of the ozone generator are high, but also the deactivation of the adsorbent is accelerated by the oxidizing action of the excess ozone, and the oxidizing agent ( In the method of impregnating sodium chlorate, potassium permanganate, etc.), there is a problem that the life of the oxidant is very short and the regeneration of the adsorbent is difficult. ..

Further, as the air pollution becomes more serious and the need for air cleaning increases, further improvement researches are underway on tunnel exhaust of vehicles, ventilation of indoor parking lots, or efficient removal method of nitrogen oxides in general atmosphere. For example, in “Shimizu Research Report” 45, 95 (1987), a method of adsorbing and removing low-concentration nitrogen oxides with activated carbon impregnated with an alkali is also proposed. However, also in this method, similar to the above method, it is not possible to obtain a satisfactory removal efficiency unless the nitric oxide is previously oxidized to nitrogen dioxide.
It does not solve the above problems.

Since most of the nitrogen oxides contained in the atmosphere or normal exhaust gas is nitric oxide, it is efficiently adsorbed without being oxidized and without being much affected by coexisting gases such as water vapor. In addition, it is desired to develop an adsorbent that does not significantly reduce the adsorption activity even when adsorption / desorption is repeated. To meet these needs,
In JP-A-64-85137 and JP-A-2-69311, fine particles made of oxides or hydroxides of copper and other metals having a chemical affinity for nitric oxide are dispersed in activated carbon fibers. And thereby increasing the adsorption efficiency. However, in this method, it is difficult to finely disperse and attach the fine particles of the metal oxide or the metal hydroxide to the activated carbon fiber, and further, the attachment of the metal oxide increases the hydrophilicity of the adsorbent, and There is a drawback that the adsorption activity decreases in a short time due to adsorption.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to oxidize a nitrogen oxide mainly containing nitric oxide into nitrogen dioxide. It is intended to provide an adsorbent capable of adsorbing directly and efficiently without any use, a method for producing the adsorbent, and a method for efficiently adsorbing and removing nitric oxide using the adsorption method.

[0008]

[Means for Solving the Problems] The nitric oxide adsorbent according to the present invention capable of solving the above problems is 4 to 10Å.
Pore adsorbent 1g per 0.05 cm ³ or more, and has a gist at more preferably made of a porous carbonaceous having 0.1 cm ³ or more. Incidentally, the pores present in the activated carbon include substantially circular pores and slit-shaped pores,
The size of the pores in the present specification means both the pore diameter and the pore width.

The above-mentioned porous carbonaceous material is not particularly limited in its raw material as long as it contains a specific amount of fine pores in the above-mentioned size range, but among them, it is a thermosetting phenol resin, more preferably a resol type phenol resin. Average particle size is 2
A powder obtained by carbonizing and activating a powder of 00 μm or less or a sintered product thereof has higher adsorption activity for nitric oxide.

Such an adsorbent having a high adsorption activity is obtained by thermosetting the thermosetting phenolic resin powder or its sintered product at 1 to 400 ° C. to 1200 ° C. in a reducing gas, inert gas or weakly oxidizing gas atmosphere. It can be obtained by performing heat treatment for 100 hours for carbonization and activation. And the adsorption of nitric oxide using this nitric oxide adsorbent is 50
Adsorption / desorption of nitric oxide can be efficiently carried out by performing the desorption at a temperature of lower than 0 ° C and at a temperature of 50 to 200 ° C, more preferably 100 to 150 ° C.

[0011]

The present inventors consider that most of the gas to be treated contains a large amount of water vapor, and a hydrophobic carbonaceous adsorbent is effective in avoiding the influence of coexisting water vapor. Therefore, we investigated various factors that affect the adsorption performance for nitric oxide, targeting activated carbon, which is a typical carbonaceous adsorbent.

In order to clarify the effect of the pore size distribution of activated carbon on the adsorption performance of nitric oxide, various activated carbons having different pore size distributions were purchased or prototyped, and adsorption / desorption of nitric oxide was conducted for each. The test was conducted. For the measurement of the pore size distribution of activated carbon, the diameter 6
The pores of 0 Å or more are made by the mercury injection method, the pores of 20 to 60 Å are made by the nitrogen adsorption method, and the fine pores of 10 Å or less are made to adsorb alcohols with different molecular weights, that is, different molecular diameters in order, and the difference in adsorption capacity The pores in the range of 10 to 20Å were calculated as the sum of the pore volumes obtained by the above method and the difference between the total pore volumes.

Then, dry air or wet air (relative humidity 60%) containing about 5 ppm of nitric oxide was supplied at 0 to 50 ° C. to the adsorption layers filled with the activated carbons having different pore distributions, and the air was discharged from the outlet air. The adsorption performance of each activated carbon was compared by measuring the nitric oxide concentration. In addition, by sending heated air to each activated carbon that has adsorbed nitric oxide by the above method, a desorption test of nitric oxide is conducted, and temperature dependence during desorption is investigated, and adsorption / desorption is repeated without lowering adsorption activity. I investigated whether I could do it.

The results will be clarified by the examples described later, but in conclusion, activated carbon having pores of 4 to 10 Å of 0.05 cm ³ / g or more is more nitric oxide than those having other pore size distributions. It was confirmed that excellent adsorption / desorption performance could be exhibited. Further, among the activated carbons, it was found that the activated carbon obtained by carbonizing and activating the phenol resin, in particular, the resin powder having an average particle size of 200 μm or less or the sintered product thereof has a particularly excellent adsorption activity. .. Moreover, the sintered product of the above-mentioned phenol resin powder is converted into a reducing gas,
400 to 1 in an inert gas or weakly oxidizing gas atmosphere
If carbonization and activation are carried out by heat treatment at 200 ° C for 1 to 100 hours, the optimum 4 to 10Å for nitric oxide adsorption
It has been found that the pore volume ratio of can be made extremely high, and as a result, a very excellent nitric oxide adsorbing property is exhibited.

The reason why the pore size of 4 to 10 Å shows a high adsorption activity for nitric oxide can be considered as follows. That is, the molecular diameter of nitric oxide is about 3Å
Therefore, with ultrafine pores of less than 4 Å, adsorption of nitric oxide into the pores becomes large, so that adsorption itself becomes difficult to occur. On the other hand, if the pore diameter becomes too large, the nitric oxide in the pores becomes too large. It is considered that although the invasion of the carbon dioxide occurs, it cannot adsorb with sufficient strength because it has a small adsorptive power to the pore walls, and it becomes difficult to fulfill the function as an effective adsorbent.

On the other hand, in the pores of 4 to 10 liters, nitric oxide only forms at most 2 to 3 adsorption layers, and the nitric oxide which has diffused and penetrated into the adsorption field of the pore walls is concerned. It is considered that this is because it has a direct effect on the adsorption field and thus is surely adsorbed and captured. Therefore, in order to effectively exert such an adsorption and trapping effect on a practical scale, the pores in the above-mentioned preferable pore diameter range must be present to some extent or more, and in the present invention, the pore volume of 4 to 10 Å is used as the standard. More than 0.05 cm ³ per 1 g, more preferably 0.1 c
It was defined as m ³ or more. By the way, the pore volume is 0.05 cm ³ / g
If less than 5% by weight, for example, the adsorption capacity of 5 ppm of nitric oxide is less than about 0.5% by weight at room temperature, and the adsorption capacity will break through early. And sucking on an industrial scale
Since the adsorption capacity for efficiently performing desorption is considered to be 1% by weight or more, it is desired that the pore volume of 4 to 10 Å be 0.1 cm ³ / g or more. There is no upper limit to the volume ratio of the pores, and the higher the volume ratio, the better the adsorption performance.

As described above, the present invention is characterized in that the volume amount of the carbonaceous adsorbent having the specific pore diameter range is specified, and the carbonaceous source can satisfy any of these requirements. Moreover, it exhibits an excellent adsorption activity for nitric oxide as compared with those that deviate from the above requirements. However, among them, it has been confirmed that activated carbon containing a phenolic resin as a carbonaceous source can exhibit exceptionally excellent adsorption performance for nitric oxide. The reason for this is not clear, but it is considered that the specificity of the surface structure of the pore wall derived from the phenol resin has some influence on the improvement of the adsorption ability. For example, according to the confirmation by the present inventors, when the air containing nitrogen monoxide is continuously supplied to the activated carbon originating from the phenol resin, partial nitrogen dioxide is observed at the outlet side, and such a phenomenon occurs. Not found with other activated carbons. Moreover, when a nitric oxide-containing gas containing no oxygen gas is used, the nitric oxide adsorbing ability is not good in any activated carbon including the activated carbon derived from the phenol resin. From these things, activated carbon derived from phenolic resin is
It is considered that the coexisting oxygen also exerts a catalytic action of oxidizing nitric oxide. Furthermore, even though it is a hydrophobic carbonaceous material, activated carbon other than activated carbon derived from phenol resin has a considerably reduced nitric oxide adsorption capacity under high humidity, but activated carbon derived from phenol resin also has a reduced adsorption capacity under high humidity. These points are minor, and these points are considered to represent the chemical specificity of the activated carbon derived from the phenolic resin, which also leads to high practicality.

Examples of the type of phenolic resin serving as a carbon source include thermosetting novolac type phenolic resins and resol type phenolic resins and various modified resins thereof. Among these, particularly preferable are resol type phenolic resins. is there. In the production of activated carbon using a phenol resin, a phenol resin having an average particle size of 200 μm or less is used, and its powder or its sintered product is used in a gas atmosphere containing carbon dioxide or water vapor.
By carrying out carbonization and activation by heat treatment at 00 to 1200 ° C. for 1 to 100 hours, activated carbon having a high pore volume ratio of 4 to 10 Å and excellent adsorption activity can be obtained.

The reason why a phenol resin having a large average particle size is not preferable as a source of activated carbon is not clear, but it is presumed that the development and activation of pores are difficult to proceed sufficiently due to the small surface area during heat treatment. .. Further, during heat treatment, a weak oxidizing gas such as steam or carbon dioxide which is usually used for activation of activated carbon can be used, but in addition to this, a reducing gas such as hydrogen or an inert gas such as nitrogen or argon. Can also be used. But,
Using a strongly oxidizing gas such as air will result in very poor performance, even if the pore size is reasonable. It is considered that this is because the surface chemical structure such as the type and concentration of the oxygen-containing functional group has a great influence. If the heat treatment temperature is lower than 400 ° C, carbonization and activation may be insufficient, while 120
When the temperature is higher than 0 ° C., the material shrinks, the pore size becomes too small, and the adsorption performance is lost, which is not preferable. A more preferable heat treatment temperature is 450 to 800 ° C.

Next, in adsorbing and removing nitric oxide using the adsorbent of the present invention, the temperature of the gas to be treated is set to 50.
It is desirable to keep the temperature below ° C. However, the adsorption capacity of nitric oxide decreases as the temperature rises, and the adsorption capacity when the adsorption treatment is performed at 50 ° C is about 1/100 of that when treated at 25 ° C.
This is because the adsorption removal rate drops to about 2 at about 50 ° C.

The desorption treatment after adsorption is preferably carried out at 50 to 200 ° C. If the temperature is lower than 50 ° C., desorption will be insufficient even if the feed gas is changed, and if it exceeds 200 ° C., the exhaustion and deterioration due to the oxidation reaction of activated carbon will occur. Or there is a fear of ignition.
The desorption of nitric oxide becomes remarkably active at a temperature of 100 ° C. or higher, and usually almost all can be desorbed by holding at about 150 ° C. for several hours. Therefore, for practical use, it is sufficient to repeat adsorption around room temperature and desorption / regeneration at about 100 to 150 ° C., thereby efficiently adsorbing and removing even a few ppm of nitric oxide contained in the gas to be treated. Is possible. In addition, when performing adsorption and desorption continuously, install a plurality of adsorption towers in parallel according to the usual method,
Adsorption and desorption regeneration may be performed alternately.

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Example 1 A raw material and various activated carbons having different pore distributions were filled in a cylindrical container kept at 25 ° C. at a height of 8 cm, and dry air containing 5 ppm of nitric oxide was added thereto under atmospheric pressure at a flow rate of 0. ．
The flow rate was 2 m / s, and the change with time in the nitrogen oxide concentration at the outlet was measured by a chemiluminescence type nitrogen oxide analyzer. The production conditions for each activated carbon are as shown in Table 1.

The results are shown in Table 2. Here, the removal rate is
"1-{(outlet nitric oxide concentration + outlet nitrogen dioxide concentration)
/ Inlet nitric oxide concentration} ", and the measured pore size is
Since it is up to a pore diameter of adsorbing water (a little less than 3Å) and pores that cannot adsorb water do not adsorb nitric oxide larger than water, it is described in Table 2 as 4Å or less. In addition, since all the adsorbents used in this experiment have a pore volume of 0.18 cm ³ / g or more (determined from the saturated adsorption capacity of water vapor at 25 ° C), a pore volume of 10 Å or less is significantly large. The adsorbent that is lower than that is mainly composed of pores of 10 Å or more.

[0024]

[Table 1]

[0025]

[Table 2]

As is clear from Table 2, the nitric oxide removal rate of activated carbon varies considerably depending on the type of raw material, but the pore volume of 4 to 10 Å is 0.05 cm ³ / g or more ( The example) has a relatively higher removal rate than the ones smaller than that (comparative example). 1, 2 and N
o. 3 to 7 (phenolic resin raw material), No. 8 and No.
No. 9 (coal raw material), No. No. 10, 11 and No. 12, 13
(Polyvinylidene chloride raw material), No. 14 and No. 15
This is clear when the (furfuryl alcohol resin raw materials) are compared with each other.

Among the examples, the activated carbon derived from the phenolic resin (Nos. 3 to 6) shows excellent values in both initial activity and activity sustainability. When this activated carbon was used, a small amount of nitrogen dioxide (about 10 to 20 mol% of nitric oxide) was found in the gas discharged from the adsorption tower outlet. In addition, No. 16 to 22 are all very general activated carbons (commercial products: carbonization and activation conditions are unknown), all of which have pore diameters of 10 Å or more and most of them are 20
Å or more, and the nitric oxide removal rate is poor.

Embodiment 2 Next, No. 1 of the above-mentioned Embodiment 1 will be described. 4, 7, 9, 10 and 19
The adsorption experiment was conducted in exactly the same manner except that the same activated carbon as used in 1. was used and humidified air having a relative humidity of 60% was used. The results are shown in Table 3, and it can be seen that the activated carbon derived from the phenol resin has excellent adsorption activity even under humidified conditions.

[0029]

[Table 3]

Example 3 No. 1 of Example 1. Using the same activated carbon used in 4,
An adsorption experiment was conducted in exactly the same manner except that the adsorption temperature was changed to 0 ° C, 25 ° C, 35 ° C and 50 ° C. The results are shown in Table 4, and the higher the removal rate is, the lower the temperature is. Further, from these results, it is considered that the removal rate is considerably lowered when the adsorption temperature exceeds 50 ° C. Therefore, the adsorption temperature is 50%.
It is desirable to keep the temperature below ° C.

[0031]

[Table 4]

Example 4 No. 1 of Example 1. Using the same activated carbon as used in 4 above, after performing adsorption treatment for 15 to 20 hours under the same conditions, while supplying dry air containing no nitric oxide at the same flow rate as during adsorption, 145 ± 5 ° C. Hold for 6 hours to perform desorption and regeneration. This adsorption and desorption regeneration were repeated 24 times, and the removal rate was measured each time. The results are as shown in Table 5, and almost no decrease in adsorption capacity due to desorption regeneration was observed.

[0033]

[Table 5]

Example 5 The effect of the type of atmospheric gas on the carbonization and activation of phenol resin was investigated. The results are shown in Table 6, and there is no great difference in the reducing atmosphere (represented by hydrogen), the inert atmosphere (represented by nitrogen) and the weakly oxidizing atmosphere (steam, carbon dioxide). While obtained,
4 to 1 in strong oxidizing atmosphere (represented by air)
Although the pores of 0 Å were contained in almost the same volume, a sharp drop in performance was observed.

[0035]

[Table 6]

[0036]

EFFECTS OF THE INVENTION The present invention is configured as described above, and it is possible to efficiently remove nitric oxide as it is without performing a pretreatment such as removing coexisting water vapor in advance and once converting nitric oxide into nitrogen dioxide. It can be adsorbed and removed well, and it can be used for environmental purification by using it for the treatment of automobile tunnel exhaust and indoor parking lot exhaust.
Moreover, since the nitric oxide adsorbed on the low temperature side is almost completely desorbed by heating at about 150 ° C. and the activity of the adsorbent is restored, it can be repeatedly used many times.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Kinukawa 12-5-410 Amishimacho, Miyakojima-ku, Osaka (72) Inventor Mamoru Tamura 1-3-4-9 Tsudamotomachi, Hirakata (72) Inventor Seiichi Tashiro Osaka 2-5-23 Mikuni Honcho, Yodogawa-ku, Yokohama

Claims (4)

[Claims] 1. A nitric oxide adsorbent characterized by comprising a porous carbonaceous material having pores of 4 to 10 Å in an amount of 0.05 cm ³ or more per 1 g of adsorbent. 2. The nitric oxide adsorbent according to claim 1, wherein the porous carbonaceous material is a carbide of a phenol resin. 3. The average particle size of the phenol resin is 20.
A powder of 0 μm or less or a sintered body thereof is treated with a reducing gas,
400 to 1 in an inert gas or weakly oxidizing gas atmosphere
A method for producing a nitric oxide adsorbent characterized by performing carbonization and activation by heat treatment at 200 ° C. for 1 to 100 hours. 4. A treatment container is filled with the nitric oxide adsorbent according to claim 1 or 2, and the nitric oxide-containing gas is passed through the treatment container at a temperature of less than 50 ° C. to adsorb nitric oxide. Next, a method for adsorbing and removing nitric oxide, characterized in that a desorption gas is supplied while heating the processing container to 50 to 200 ° C. to desorb adsorbed nitric oxide.