JPH07187622A - Production of low-concentration no and method for measuring no2 - Google Patents

Abstract

PURPOSE:To inexpensively and everlastingly produce low-concn. NO and to provide a method for measurring NO2. CONSTITUTION:An activated carbon, which has been dipped in an aq. inorrg. strong acid soln. and dried, is packed in a reaction tube 1, the air contg. NO2 is passed through the reaction tube to reduce NO2 to NO, and low-concn. NO is produced. Meanwhile, the NO2 concn. is measured by measuring the NO concn. in the air before and behind the reaction tube. The inorg. strong acid is adsorbed on the activated carbon having a large specific surface, and hence the activatted carbon shares the role to provide a contact filed between the strong acid and the NO2. Consequetly, the NO2 is efficiently reduced in the air at a room temp., the low-concn. stable NO is inexpensiveely produced, and NO2 is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing low concentration NO used as a standard gas and a method for measuring NO2 which is a harmful substance.

[0002]

2. Description of the Related Art Nitrogen dioxide NO2 in combustion exhaust gas is harmful to the human body, and nitric oxide NO is converted into harmful NO2 by ultraviolet rays. Although much research has been done, high temperature and noble metal catalysts for reducing NO2 to NO have been conventionally required for the analysis of NO2 and NO containing air or water. However, this precious metal catalyst
It has the drawback that it requires replacement because the reducing ability decreases with the use time, and that it requires a heater for heating, resulting in high manufacturing costs and maintenance costs. When producing a low-concentration NO gas used as, there is a drawback that NO2 is always included as an impurity.

[0003]

In view of the above problems, the present invention is capable of reacting at room temperature in the presence of air,
It is an object of the present invention to provide a method for reducing NO2 to NO that has a high reduction rate and can be maintained for a long time.

[0004]

A low concentration NO according to the present invention
As shown in FIG. 1, the method for manufacturing the method of No. 2 is as follows. A reaction chamber having an inlet and an outlet is filled with activated carbon that is immersed in an aqueous solution of a strong inorganic acid and dried, and NO 2 is passed through the reaction chamber by passing air containing NO 2. The method for measuring NO2 according to the present invention is to measure the NO2 concentration by measuring the NO concentration of air before and after passing through the reaction chamber.

[0005]

[Function] Since activated carbon is porous and has a large specific surface area and a large contact area with passing air, it is usually used as an adsorbent, but the present invention utilizes this property to adsorb an inorganic strong acid on the activated carbon. , Activated carbon was provided with a role of providing a place for contact between strong acid and NO2, which enabled highly efficient reduction of NO2 in air at room temperature.

[0006]

EXAMPLE FIG. 1 shows an example of the structure of a reaction tube used in the method of the present invention. The reaction tube is inside a cylindrical reaction tube body 1 having an inlet 2 and an outlet 3, and a front and rear metal mesh 4 or a porous body It is formed by providing a reaction chamber 5 partitioned by a plate and filling the reaction chamber 5 with acid-treated activated carbon 6. As the activated carbon, fibrous ones are used, or tablets formed into tablets are acid-treated and then appropriately crushed and filled. When powdered activated carbon is directly impregnated with a strong acid aqueous solution,
This is because it becomes a paste and loses its porosity. In the method for producing low-concentration NO according to the present invention, for example, fibrous activated carbon is immersed in an appropriate amount of an aqueous solution of a strong inorganic acid such as sulfuric acid, and then dried, and the adsorption ability is completely exhausted by the strong acid. Form activated carbon fibers. Then, this is filled in the reaction tube 1 as described above, and the reaction tube 1 is filled with NO.
NO2 is reduced to NO by passing air containing 2.

FIG. 2 is a flow chart showing an example of the NO2 measuring method according to the present invention. When powdered activated carbon is used, it is molded with a small amount of binder into a lump of an appropriate size, which is then dipped in an aqueous solution of a strong inorganic acid such as sulfuric acid and dried, and then this lump of The activated carbon is pulverized again to obtain powdered activated carbon, which is filled in the reaction tube 1. Next, the air containing NO2 is treated with the first NO as shown.
After passing through the concentration measuring device 7, it is passed through the reaction tube 1 and then through the second NO concentration measuring device 8 to measure the NO concentration. The NO increased at this time is reduced from NO2. Therefore, if the reading of the first NO concentration measuring instrument 7 is subtracted from the reading of the second NO concentration measuring instrument 8, the NO2 originally present in the air is reduced. The concentration will be required. N
As the O concentration measuring device, for example, a sample is taken and reacted with O3 formed by discharge. At this time, a certain energy is released by the reaction with O3,
The concentration of NO can be known by measuring this with a chemiluminescence method. Below, a comparison of NO2 reduction rates by activated carbon treated with three kinds of acids is shown.

Example 1: This example was used to measure the reduction performance of NO2 to NO by activated carbon treated with sulfuric acid, the change of reduction efficiency with respect to residence time, and the change of reduction efficiency with respect to NO2 concentration. 9% sulfuric acid aqueous solution 1
Four 0.30 g lumps of activated carbon molded products were immersed in 3.92 g, and after about 10 minutes, the activated carbon molded products were taken out and crushed, and 0.314 g of this powdered activated carbon was filled in a reaction tube having a diameter of 6 mm. . The volume of the filled portion at this time, that is, the volume of the reaction chamber was 0.48 ml. The concentration of NO2 is 80 to 90 ppb, and the concentration of NO is 160 to 200 pp.
b, air with RH of 30 to 33%, flow rate of 920 ml / min,
Flowed at a temperature of 25 ° C for 0 to 50 hours. Curves S1 and S2 in FIG. 3 show the results of this measurement. According to this, the activated carbon treated with sulfuric acid contained 9% of NO2 initially contained.
It can be seen that 9% or more is reduced to NO and the potency is not lowered even after 50 hours. In addition, FIG. 4 shows that the influence of the residence time in the reaction tube was measured by sequentially changing the air flow rate for the same sample, and W (g) in the retention factor W / F on the horizontal axis is the number of grams of acid-treated activated carbon. , F (liter / min) indicates the flow rate, which shows that the NO2 reduction efficiency by the sulfuric acid-treated activated carbon is extremely high, and is almost 100% especially when the retention factor is 0.33 or more, and the contact time is, for example, 0.1 seconds. It turns out that there is enough. Furthermore, FIG.
Measured the effect of NO2 concentration on the same sample. At this time, the air flow rate is 1520 ml / min and the duration is 170 to 260 hours, but a high reduction efficiency of 85% or more is shown irrespective of the NO2 concentration.

Example 2: In this example, the same measurement as in Example 1 was performed on the activated carbon treated with hydrochloric acid. Water 10.70 g and 0.30 g of four lumps of activated carbon molded products were added to 2.44 g of 1N hydrochloric acid aqueous solution, 15 minutes later, the activated carbon molded products were taken out and crushed, and then 0.247 g of activated carbon powder was reacted with a diameter of 6 mm. I put it in a tube. The volume of the filled portion at this time is 0.37 ml. NO2 concentration of 80-90
ppb, NO concentration 160-200 ppb, RH30-
33% air, flow rate 1040 ml / min, temperature 25 ° C
Then, it was run for 0 to 50 hours. Curves C1 and C2 in FIG. 3 show the results of this measurement. According to this, activated carbon treated with hydrochloric acid contained about 90% of NO2 initially contained in NO.
It can be seen that the potency was reduced to 50% and the potency was not decreased even after 50 hours. In addition, FIG. 6 shows that the effect of residence time in the reaction tube was measured by sequentially changing the air flow rate for the same sample, and the reduction efficiency by the hydrochloric acid-treated activated carbon was 60 to 70% when the retention factor was 0.3 or less, 0 Almost 80 above 0.5
%, Which is slightly inferior to the sulfuric acid-treated activated carbon, but is shown to be sufficiently effective. Furthermore, FIG.
The same sample was used to measure the effect of NO2 concentration. At this time, the gas flow rate was 1040 ml / min and the duration was 50 to 170 hours, but the reduction efficiency was about 60% regardless of the NO2 concentration. Is shown.

Example 3: This example uses fibrous activated carbon, and the reaction tubes R1, R2, and R3 are filled with sulfuric acid-treated activated carbon whose sulfuric acid concentration and activated carbon fiber mass are adjusted as shown in Table 1. , NO2 concentration of 90 to 100 ppb, NO concentration of 150 to 170, and relative humidity of 50 to 60%, respectively, 1000 ml / min, 900 ml / min, 1380 m
L / min was passed for 340 hours. FIG. 10 shows the NO2 reduction rate and the NO conversion rate at this time. Further, FIG. 11 shows the comparison of the performance with untreated activated carbon and the influence of the residence time, and the reaction tube R4 in Table 1 is used as the measurement condition.

[Table 1]

Example 4: In this example, as an example not included in the method of the present invention, the same measurement as in Examples 1 and 2 was performed on activated carbon treated with an organic acid, acetic acid. 0.96 g of Wako acetic acid (purity 93%) is added to 14.30 g of water, and 0.30 g of lumped activated carbon is further added to obtain about 15
After taking out after a minute, this is crushed and 0.295 g of activated carbon powder is put into a reaction tube having a diameter of 6 mm. The volume of the filled portion at this time is 0.42 ml. The concentration of NO2 is 80 to 90 ppb, and the concentration of NO is 160 to 200 pp.
b, RH 30-33% air, flow rate 1220 ml /
Flowed for 0 to 50 hours at a temperature of 25 ° C. for minutes. A1A in FIG.
No. 2 shows the results of this measurement, and it is shown that the rate of NO2 decrease is extremely high, whereas the rate of NO increase is not very high and is almost the same as that of hydrochloric acid-treated activated carbon. . Further, FIG. 8 shows the effect of the residence time in the reaction tube was measured by sequentially changing the air flow rate for the same sample, and in the case of the acetic acid-treated activated carbon, the NO2 reduction rate is extremely high. Nevertheless, it has been shown that the rate of increase of NO shows a rather negative value. Further, FIG. 9 shows the effect of NO2 concentration measured with the same sample. At this time, the air flow rate is 480 ml / min and the duration is 170 to 260 hours, but the NO2 concentration is 1
At 50 ppb or less, NO was rather reduced, and when the NO2 concentration was around 50 ppb, it was minus 200%, indicating that acetic acid treatment cannot be adopted in the method of the present invention.

[0013]

The method for reducing nitrogen dioxide used in the present invention is
Utilizing the high specific surface area of activated carbon, a strong inorganic acid (sulfuric acid is most desirable) is previously adsorbed on it, and NO
NO2 is reduced to NO by passing air containing 2, and the present invention uses this reduction method to produce low-concentration NO or to measure NO2, which is expensive. No precious metal catalyst is required, and since the reaction temperature can be room temperature, there is no need for a heater, etc., and there is the advantage that the reaction can be carried out in air at room temperature using inexpensive activated carbon, and the contact time is Since it takes only a very short time, there is an advantage that the device can be downsized.

[Brief description of drawings]

FIG. 1 is a sectional view of a reaction tube used in the method of the present invention.

FIG. 2 is a flow chart showing an embodiment of the method of the present invention.

FIG. 3 is a graph showing changes in NOx concentration with respect to duration when various acid-treated activated carbons are used in the NO 2 reduction method used in the present invention.

FIG. 4 is a graph showing changes in the NOx increase / decrease rate with respect to changes in the retention factor when using sulfuric acid-treated activated carbon.

FIG. 5: NO2 when using sulfuric acid-treated activated carbon
The graph which shows the change of concentration and NOx increase / decrease rate.

FIG. 6 is a graph showing changes in the NOx increase / decrease rate with respect to changes in the retention factor when hydrochloric acid-treated activated carbon was used.

FIG. 7: NO2 when hydrochloric acid-treated activated carbon is used
The graph which shows the change of concentration and NOx increase / decrease rate.

FIG. 8 is a graph showing changes in the NO2 reduction rate and the NO conversion rate with respect to the continuous time when the sulfuric acid-treated activated carbon fiber is used.

FIG. 9 is a graph showing changes in the NO2 reduction rate and the conversion rate to NO with respect to the residence time in the reaction tube when using sulfuric acid-treated activated carbon fibers, as compared with when untreated activated carbon fibers are used.

FIG. 10 is a graph showing changes in NOx increase / decrease rate with respect to changes in retention factor when acetic acid-treated activated carbon is used.

FIG. 11: NO when using activated carbon treated with acetic acid
2 is a graph showing changes in 2 concentration and NOx increase / decrease rate.

[Explanation of symbols]

 1 Reaction Tube 2 Inlet 3 Outlet 4 Wire Mesh 5 Reaction Chamber 6 Activated Carbon 7,8 NO Concentration Meter

Claims (2)

[Claims] 1. A reaction chamber having an inlet and an outlet is filled with activated carbon that has been immersed in an aqueous solution of a strong inorganic acid and dried, and NO2 is passed through the reaction chamber to reduce NO2 to NO. A method for producing low concentration NO. 2. A reaction chamber having an inlet and an outlet is filled with activated carbon that has been dipped in an aqueous solution of a strong inorganic acid and dried, and air containing NO2 is passed through the reaction chamber, and the NO concentration before and after that is measured. A method for measuring NO2, comprising measuring the NO2 concentration.