JPH07178317A - Removing method of nitrogen dioxide - Google Patents

Abstract

PURPOSE:To provide an activated carbon filter, which chemically reacts selectively only with a hydrophilic NO2 and hardly reacts with lipophilic hydrocarbons and then shows extremely long life of adsorption performance compared to the conventional by previously adsorbing a strong alkali on the activated carbon by using the wide specific surface area. CONSTITUTION:A packing material 1 obtained by dipping an activated carbon molding or activated carbon fiber into a strong alkali aq. solution and drying is crushed into an adequate particle size and packed into a contact chamber 5 in a device main body 6, which has a supply opening 2 and a discharge opening 3 and is provided with the contact chamber 5 separated by a wire mesh or perforated plate 4 in the inside, and the waste gas is brought into contact with the packing material 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen dioxide removing device provided in an air cleaner of an office or a house, an exhaust duct of a combustion device, a muffler of an automobile or the like.

[0002]

2. Description of the Related Art Since nitrogen dioxide in combustion exhaust gas is harmful to the human body, various methods have been developed to remove it, but neither the recirculation method nor the water injection method has a poor removal efficiency. There is a drawback that the device becomes large,
Further, there is a catalyst for reducing NO2 using a noble metal catalyst for treating exhaust gas of automobiles, etc., but it has a drawback that it is expensive and the catalyst has a short life due to corrosion due to S0x in exhaust gas. In general, an adsorption device that uses activated carbon as a filler can be manufactured in a small size and at a low cost, and has an excellent adsorption capacity, but since the duration of the adsorption capacity is extremely short, it is used for exhaust gas treatment of automobiles, combustion devices, etc. Was difficult to put into practical use.

[0003]

In view of the above points, the present invention uses an activated carbon having a high adsorption capacity and finds a means capable of maintaining its effect for a long time. It is an object of the present invention to provide a nitrogen dioxide removing device with a very simple and inexpensive structure that can remove NO2 in exhaust gas emitted from an automobile or a combustion device with a high removal rate and a short residence time without using To do.

[0004]

The nitrogen dioxide removing apparatus according to the present invention, as shown in FIG. 2, includes a filler 1 obtained by immersing an activated carbon molding or activated carbon fiber in a strong alkaline aqueous solution and drying it. After crushing to an appropriate particle size, it has an exhaust gas supply port 2 and an exhaust gas outlet 3 and has a wire mesh or perforated plate 4 inside.
The contact chamber 5 of the apparatus main body 6 having the contact chamber 5 partitioned by
It is filled inside and the exhaust gas is brought into contact with the above-mentioned filling material 1. The activated carbon is not used as an adsorbent directly but is used as a strong alkali carrier for adsorbing NO2. It has characteristics.

[0005]

When the activated carbon is used as an adsorbent for nitrogen dioxide in the combustion exhaust gas, the activated carbon adsorbs not only nitrogen dioxide but also various hydrocarbons contained in a large amount in the exhaust gas. All of these hydrocarbons are lipophilic and have a property that they are not compatible with hydrophilic nitrogen dioxide. Therefore, in a conventional activated carbon filter, after the activated carbon has adsorbed hydrocarbons to some extent, it is adsorbed on nitrogen dioxide. There was a property that the ability dropped sharply. Therefore, the present invention exhausts the adsorption capacity of activated carbon itself to the adsorption of strong alkali that does not react with hydrocarbons by chemically reacting only with nitrogen dioxide, so that the large specific surface area of activated carbon can be absorbed only by strong alkali. In this way, only nitrogen dioxide in the exhaust gas is selectively adsorbed, and the adsorption efficiency is maintained for a long time. According to this method, NaOH, NaHCO3, Na
A strong alkali such as CO3 can be brought into contact with exhaust gas in a fixed bed system as a solid substance using activated carbon fibers as a carrier, and the reaction temperature may be room temperature, and the contact time is not particularly limited, but is, for example, 0. Since one second is sufficient, the device can be downsized. When immersing the activated carbon in a strong alkaline aqueous solution, activated carbon moldings or activated carbon fibers were used instead of powder because the activated carbon in powder form floats freely and self-protects when immersed in a liquid strong alkaline. This is because it has no form, and when it is stirred, it becomes a paste and the porosity is impaired, and the adsorption performance decreases.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example in which the present invention is embodied as an exhaust gas removing device for an automobile. Exhaust gas from an engine is exhausted by an exhaust stack 7 through a NO--NO2 converter 8 on the way to nitrogen dioxide. It is supplied to the removing device 6. As shown in FIG. 2, the nitrogen dioxide removing device 6 is provided with a contact chamber 5 partitioned by a wire net or a perforated plate 4 in a tubular device body 6 made of a metal plate, and has front and rear ends respectively. An exhaust gas supply port 2 and an exhaust gas exhaust port 3 are provided, and the contact chamber 5 is filled with a filler 1 obtained by immersing activated carbon fiber in a strong alkaline aqueous solution and drying it. The NO-NO2 converter 8
For this, a method of generating ozone by discharge to oxidize NO is effective, and is far more advantageous in terms of manufacturing cost, durability and the like than a method of using a noble metal catalyst. This N
The O-NO2 converter is preferably attached for an automobile, but is not necessarily attached for an office or a home, considering that the rate at which NO changes to NO2 is very slow. When an activated carbon molded product is used instead of the activated carbon fiber, the molded product is impregnated with an alkaline solution and dried, and then the molded product has an appropriate particle size (for example, 0.3).
(mm diameter). The type of alkali is N
Although aOH, NA2 CO3, NaHCO3, etc. can be used at low cost, no difference in NO2 absorption rate depending on the type was observed. Regarding the heat resistance of the filler against high temperature exhaust gas, the weight loss rate of the activated carbon fiber was about 2% at 100 ° C, 4
Approximately 10% at 00 ° C, but little effect on chemistry.

Example 1: This test was conducted mainly by measuring the difference in the adsorption performance of the alkali-treated activated carbon fiber for NO and NO2 and the change in the absorption rate with respect to the residence time in comparison with the untreated activated carbon. Soak 1.75 g of activated carbon fiber in 11.0 g of 13% NaOH aqueous solution,
Activated carbon fiber is taken out after about 10 minutes and the diameter is 17 mm.
It was put in the reaction tube of No. 2 and used as a filler. At this time, the volume of the filled portion, that is, the volume of the contact chamber is 3.4 ml. The concentration of NO2 is 80 to 90 ppb and the concentration of NO is 160 to 2
Exhaust gas of 00ppb, RH 30-40%, flow rate 20
Flowed at 00 ml / min at a temperature of 25 ° C. for 176 hours. Figure 3
Shows the results of this test, which shows that the alkali-treated activated carbon has an extremely excellent adsorption performance especially for NO2. Retention factor W / F on the horizontal axis
Is a coefficient for measuring the influence of residence time in the reaction tube by sequentially changing the gas flow rate, W (g) is the number of grams of the filler, and F (liter / min) is the flow rate of the exhaust gas. .

Example 2: This test mainly measures the duration of the adsorption performance, 1.06 g of Na2 CO3
(Wako, 99.7%) was added to 8.62 g of water to completely dissolve the solid Na2 CO3, and then 1.15 g of activated carbon fiber was added to the Na2 CO3 aqueous solution. 0.29 g of the activated carbon fiber thus treated was put into a reaction tube having a diameter of 6 mm. The volume of the filled portion at this time is 0.6 ml. Exhaust gas having a NO2 concentration of 80 to 90 ppb, an NO concentration of 160 to 200 ppb, and an RH of 30 to 35% was flown therein at a flow rate of 1160 to 1230 ml / min for 0 to 340 hours. FIG. 4 shows the result of this measurement, and it is shown that the adsorption performance hardly deteriorates even after continuous use for several hundred hours.

Example 3: This test mainly examines the relationship between the concentration of NOx in the exhaust gas and the absorption rate of NO2.
3.64 g of NaHCO3 (Wako, 99.8-100)
%) In 47.1 g of water to make a saturated aqueous solution of NaHCO3, and 1.81 g of activated carbon fiber is added to the above NaHCO3.
3 Put in an aqueous solution. 0.32 g of the activated carbon fiber thus treated is put into a reaction tube having a diameter of 6 mm. The volume of the filling part is 0.81 ml. NO2 concentration of 80 ~
85 ppb, NO concentration 0-210 ppb, RH 50%
Exhaust gas was flowed at a flow rate of 2230 ml / min for 0 to 25 hours. FIG. 5 shows the result of this measurement, and it is shown that even if the concentration of NO2 is increased, it has little effect on the absorption rate.

[0010]

As described above, the nitrogen dioxide removing apparatus according to the present invention utilizes the high specific surface area of activated carbon to adsorb a strong alkali in advance thereon. Since it selectively chemically reacts only with hydrophilic NO2 from the exhaust gas and hardly reacts with lipophilic hydrocarbons, it has a dramatically longer adsorption time than conventional activated carbon filters. It can be extended, does not require an expensive noble metal catalyst, and does not require a heater or the like because the reaction temperature can be room temperature, and the contact time can be extremely short, so the device can be downsized, There is an advantage that a NOx removal device suitable for not only combustion devices and mufflers for automobiles but also air purifiers for offices and homes can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of the above.

FIG. 3 is a graph showing changes in the NOx reduction rate with respect to the residence time in the tube.

FIG. 4 is a graph showing changes in the NO2 reduction rate with respect to the test duration described above.

FIG. 5 is a graph showing changes in the NO2 absorption rate with respect to the NOx concentration at the reaction tube inlet of the above.

[Explanation of symbols]

 1 Filling Material 2 Gas Supply Port 3 Gas Discharge Port 4 Perforated Plate 5 Contact Chamber 6 Device Main Body or Nitrogen Dioxide Removal Device 7 Exhaust Cylinder 8 NO-NO2 Removal Device

Claims (1)

[Claims] 1. A filler obtained by immersing an activated carbon molded product or activated carbon fiber in a strong alkaline aqueous solution and drying the pulverized product, if necessary, after crushing to an appropriate particle size, and then having an exhaust gas supply port and an exhaust port inside A nitrogen dioxide removing device, characterized in that an exhaust gas is brought into contact with the above-mentioned filling material by filling the contact chamber of a device main body having a contact chamber partitioned by a wire net or a perforated plate.