JP2011177668A - Method for recovering nitrogen monoxide gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering nitrogen monoxide gas which can recover NO gas in terms of HNO<SB>3</SB>at a high recovery rate. <P>SOLUTION: This method for recovering a nitrogen monoxide gas can recover the nitrogen monoxide gas as an aqueous nitric acid solution with the help of an NO recovery device 10 made up of a filled column 11. In this method, the temperature of the lower part of the filled column 11 is controlled to be 50 to 70°C, and the temperature of the upper part of the filled column 11 is controlled to be not more than 25°C. The lower part of the filled column 11 represents a part equal to almost 2/3 of the column 11 in the column top part direction from the column bottom part of the filled column 11, and the upper part of the filled column 11 represents a part equal to almost 1/3 of the column 11 in the column bottom part direction from the column top part of the filled column 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for recovering nitric oxide gas generated from an apparatus or the like that concentrates and manufactures heavy nitrogen ¹⁵ N by a chemical exchange method between nitric oxide and nitric acid, and in particular, nitric oxide recovered by a packed tower type recovery apparatus. The present invention relates to a gas recovery method.

Heavy nitrogen ¹⁵ N by chemical exchange between nitric oxide (NO) gas and nitric acid (HNO ₃ ) aqueous solution
From heavy nitrogen-enriched manufacturing apparatus for concentrating produce, but NO gas after chemical exchange reaction completion is discharged, ^{15 N} concentration in the nitrogen in the discharged NO gas, ^{15 N} concentration 0 in the natural nitrogen. Only slightly less than 366%. Thus, by oxidizing the discharged NO gas was absorbed in water, be recovered as HNO ₃ aqueous solution, the majority of the recovered HNO ₃ aqueous solution, again, can be utilized as a raw material of heavy nitrogen concentration, the discharge The used NO gas is reused without becoming waste, which is preferable from the viewpoint of environmental conservation.

As a method of recovering NO gas as HNO ₃ , a method of oxidizing NO gas to NO ₂ gas and absorbing it in water under slight pressure, as is currently done as an industrial nitric acid production method (For example, refer to Patent Document 1). Specifically, the following chemical formulas (I) and (
By the reaction of II), NO gas is recovered as HNO ₃ .

However, when a nitric acid production facility is attached to the heavy nitrogen concentration production apparatus described above, the heavy nitrogen concentration production apparatus is basically operated at normal pressure, so that the apparatus configuration of the nitric acid production facility becomes complicated. Or the scale of the apparatus becomes large, and there is a problem that the burden is large in terms of equipment cost.

For this reason, as equipment attached to the heavy nitrogen concentration production apparatus, a packed tower type apparatus similar to the chemical exchange reaction tower of the heavy nitrogen concentration production apparatus is used, and under normal pressure, it is used for NO gas and NO oxidation from the bottom of the packed tower. In this method, water for NO ₂ absorption is supplied from the upper part of the tower, recovered as HNO ₃ , and reused in-line.

However, in the case of the packed tower system, the structure inside the packed tower is simple, so the pressure loss is small, but on the other hand, the processing capacity is small and the recovery rate of NO gas recovered in the form of an aqueous HNO ₃ solution is low. In order to increase the recovery rate, it is necessary to increase the height of the packed tower sufficiently or supply a large amount of water for absorbing NO ₂ . However, when the height of the packed tower is increased in this way, there is a problem that the equipment cost increases. Further, if a large amount of water for absorption is supplied, HNO ₃ having a lower concentration than the required NO gas concentration is produced. Therefore, when the recovered nitric acid is reused in-line as it is, a new concentration adjustment mechanism Need to be added.

JP 10-029809 A

Accordingly, the present invention has been made in view of the above-described problems, and an HNO ₃ aqueous solution having a high NO gas concentration can be obtained without complicating the configuration of the apparatus or increasing the scale of the apparatus. That is, an object of the present invention is to provide a method for recovering nitric oxide gas that can recover NO gas as a HNO ₃ aqueous solution at a high recovery rate.

As a result of intensive studies, the present inventors have found that the efficiency of recovering nitric oxide gas as an aqueous nitric acid solution can be increased by controlling the inside of the packed tower constituting the NO recovery device to a predetermined temperature. It was.

That is, the method for recovering nitric oxide gas according to the present invention is a method for recovering nitric oxide gas in which the nitric oxide gas is recovered as an aqueous nitric acid solution by a recovery device comprising a packed tower. While controlling to 50-70 degreeC, the temperature of the upper part of the said packed tower is 25
Control below ℃.

Here, the lower part of the packed tower refers to a portion from the bottom of the packed tower to the top of the tower, which is approximately two-thirds of the packed tower, and the upper part of the packed tower is the upper part of the packed tower. The portion from the top of the tower to the bottom of the tower is shown up to about one third of the packed tower.

An outer jacket is provided around the packed tower, and a thermocouple is inserted into the packed tower via a protective tube. In the method for recovering nitric oxide gas according to the present invention, the temperature in the packed tower can be accurately controlled by these, so that nitric oxide can be recovered as nitric acid at a high recovery rate.

According to the method for recovering nitric oxide gas according to the present invention, in the NO recovery device constituted by the packed tower, the temperature of the lower part of the packed tower is controlled to 50 to 70 ° C., and the temperature of the upper part of the packed tower is set. Since the temperature is controlled to 25 ° C. or lower, the nitric oxide gas can be recovered at a high recovery rate without requiring a complicated apparatus configuration or an increase in apparatus scale.

It is a schematic sectional drawing which shows the state which attached the heavy nitrogen concentration manufacturing apparatus to NO collection | recovery apparatus. It is a schematic sectional drawing of a heavy nitrogen concentration manufacturing apparatus. It is a schematic sectional drawing of NO collection | recovery apparatus.

Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

Method for recovering nitrogen monoxide (NO) gas according to the present embodiment is concentrated, for example, as shown in FIG. 1, the chemical exchange method between the NO gas and nitric acid (HNO ₃₎ aqueous heavy nitrogen ^{(15 N)} The heavy nitrogen concentration production apparatus 20 to be produced is attached, and this is carried out using a packed tower type NO recovery apparatus 10 similar to the heavy nitrogen concentration production apparatus 20. Below, N which attached the heavy nitrogen concentration manufacturing apparatus 20 is attached.
A method for recovering NO gas according to the present invention will be described while showing the O recovery device 10 as an example.

FIG. 1 is a schematic cross-sectional view showing a state in which a heavy nitrogen concentration production apparatus 20 is attached to an NO recovery apparatus 10. As shown in FIG. 1, the NO recovery device 10 used in the NO gas recovery method according to the present embodiment takes in NO gas generated from the heavy nitrogen concentration production device 20, and converts the taken-in NO gas into an HNO ₃ aqueous solution. As recovered. Furthermore, the HNO recovered in this way
_As shown in FIG. 1, most of the _three aqueous solutions are supplied again to the heavy nitrogen concentration production apparatus 20 as a ¹⁵ N-concentrated raw material and used for the production of ¹⁵ N.

The NO recovery apparatus 10 used in this NO gas recovery method is performed using a packed tower type apparatus similar to the heavy nitrogen concentration production apparatus 20 as described above. First, prior to the description of the NO recovery device 10, the heavy nitrogen concentration manufacturing device 20 that supplies (sends out) NO gas to the NO recovery device 10 will be described including the generation process of the NO gas supplied to the NO recovery device 10. .

FIG. 2 is a schematic cross-sectional view of a heavy nitrogen concentration manufacturing apparatus 20 that concentrates and manufactures heavy nitrogen ¹⁵ N by a chemical exchange method between NO gas and an aqueous HNO ₃ solution. The heavy nitrogen concentration production apparatus 20 shown in FIG. 2 includes a reflux tower 20b that generates NO gas from an HNO ₃ aqueous solution and sulfur dioxide (SO ₂ ) gas,
The nitrogen isotope chemical exchange reaction between NO gas and HNO ₃ solution generated through the reflux tower 20b and a replacement column 20a concentrating the heavy nitrogen ¹⁵ N in HNO _3.

Exchange column 20a constituting the heavy nitrogen concentration producing apparatus 20 is provided with a HNO ₃ outlet on its top portion with a HNO ₃ feed opening and the bottom portion. In exchange column 20a, it is supplied HNO ₃ aqueous solution from HNO ₃ supply port, HNO ₃ aqueous solution supplied is lowered inside the exchange column 20a, HN
It flows out of the exchange tower 20a through the O ₃ outlet. The aqueous HNO ₃ solution flowing out from the exchange tower 20a flows into a reflux tower 20b provided below the exchange tower 20a.

As described above, as the HNO ₃ aqueous solution supplied to the exchange tower 20a of the heavy nitrogen concentration production apparatus 20, the HNO ₃ produced by recovering NO gas in the NO recovery apparatus 10 described later.
The aqueous solution can be reused.

The exchange tower 20a is filled with, for example, helipack as a filler, and the supplied aqueous HNO ₃ solution flows into the reflux tower 20b through the gap between the fillers.

Further, the exchange tower 20a is provided with a ¹⁵ N outlet from which a part of the HNO ₃ aqueous solution is taken out at the bottom of the tower. ¹⁵ The N outlet, concentrated manufactured within the exchange column 20a by a chemical exchange reaction between NO gas produced in the reflux column 20b to be described later with HNO ₃ solution, HNO ₃ is a reflux ratio reaches a predetermined ¹⁵ N concentrations Extracted according to.

Specifically, in the exchange tower 20a configured as described above, a reaction represented by the following chemical formula (III) occurs. That is, in the exchange column 20a, HNO ₃ supplied from the HNO ₃ supply port of the exchange column 20a
The aqueous solution comes into contact with NO gas generated in the reflux tower 20b described later, and HNO ₃ −
NO chemical exchange reactions occur. Then, by superimposing the chemical exchange reaction of the chemical formula (III), ¹⁵ N is concentrated and produced in HNO ₃ .

The material constituting the exchange column 20a is not limited in particular, as long as it is corrosion resistant with respect to HNO ₃ or the like.

Thus, in the exchange tower 20a, ¹⁵ N is concentrated and produced in HNO ₃ by the reaction of the chemical formula (III), and ¹⁴ NO gas is generated at the same time. The NO gas generated in the heavy nitrogen concentration production apparatus 20 is taken into the NO recovery apparatus 10 described later (
Supplied). Then, NO recovery device 10 recovers the NO gas supplied from the heavy nitrogen concentration producing apparatus 20 as HNO ₃ solution. Details will be described later.

Next, the reflux tower 20b of the heavy nitrogen concentration production apparatus 20 will be described. As shown in FIG. 2, the reflux tower 20b is provided below the exchange tower 20a. The HNO ₃ aqueous solution descending from the exchange tower 20a and flowing out from the bottom of the exchange tower 20a flows into the reflux tower 20b and comes into gas-liquid contact with the SO ₂ gas supplied from the lower part of the reflux tower 20b. H ₂ SO ₄ is produced.

The material constituting the reflux column 20b is not limited in particular, _H 2 _SO 4 present in the reflux column 20b, _HNO 3, as long as it has corrosion resistance to SO _2, for example made of glass It can be.

The reflux tower 20b is filled with, for example, a glass helix as a filler, and a bottom plate or the like for preventing the filler from falling is provided in the lower part of the reflux tower 20b.

The reflux column 20b includes an HNO ₃ supply port at the upper end and an SO ₂ supply port at the lower end. In the reflux tower 20b, the exchange tower 20a descends in the exchange tower 20a.
HNO ₃ aqueous solution flowing out through the HNO ₃ outlet is supplied from the HNO ₃ feed opening of the reflux tower 20b. The downward flow of the supplied HNO ₃ aqueous solution makes gas-liquid contact with the upward flow of SO ₂ gas supplied from the SO ₂ supply port, and NO gas is generated. In this gas-liquid contact reaction, H ₂ SO ₄ is by-produced, and the by-produced H ₂ SO ₄ is discharged through the H ₂ SO ₄ outlet connected to the bottom of the reflux tower 20b. .

  In the reflux tower 20b having the above-described configuration, specifically, a reaction represented by the following chemical formula (IV) occurs.

Thus, in the reflux tower 20b, NO gas is generated and H ₂ SO ₄ is by-produced by a gas-liquid contact reaction between the HNO ₃ aqueous solution of the above chemical formula (IV) and the SO ₂ gas. And the produced | generated NO gas returns to the exchange tower 20a as an upward flow, and above-described chemical formula (III)
Used in the HNO ₃ —NO chemical exchange reaction.

In the heavy nitrogen concentration production apparatus 20 including the exchange tower 20a and the reflux tower 20b having the above-described configuration, as described above, ¹⁵ N is generated by the chemical exchange reaction between the NO gas and the HNO ₃ aqueous solution in the exchange tower 20a. Concentrated and manufactured. On the other hand, as shown in the chemical formula (III), NO gas with a low ¹⁵ N concentration is generated. The NO recovery apparatus 10 used in the NO gas recovery method according to the present embodiment is accompanied by the above-described heavy nitrogen concentration production apparatus 20, and takes in the NO gas generated from the heavy nitrogen concentration production apparatus 20. And recovered as an aqueous HNO ₃ solution.

Next, the NO gas recovery method according to the present embodiment and the NO recovery apparatus 10 used in this method will be described. As shown in FIG. 1, the NO recovery device 10 is provided above the accompanying heavy nitrogen concentration production device 20. The NO gas generated in the exchange tower 20a of the heavy nitrogen concentration production apparatus 20 is taken into the NO recovery apparatus 10, and the NO gas is converted into NO.
After being oxidized by the NO gas oxidizing air supplied from the lower part of the recovery apparatus 10, it is absorbed by water (H ₂ O) supplied from the upper part of the NO recovery apparatus 10, thereby generating an HNO ₃ aqueous solution. .

FIG. 3 is a schematic cross-sectional view of the NO recovery device 10 used in the NO gas recovery method according to the present embodiment. As shown in FIG. 3, the NO recovery device 10 includes a packed tower 11, and the packed tower 11 is filled with a filler 12 such as McMahon packing. The material of the packed tower 11 constituting the NO recovery device 10 is not particularly limited, and N
_HNO 3 present in the O recovery device 10, NO, as long as it has corrosion resistance to NO ₂ and the like, can be for example made of glass.

The NO recovery device 10 includes a NO supply port (NO intake port) 13 at its lower end,
An air supply port 14 for supplying NO oxidation air is provided at the lower end. In the NO recovery device 10, the NO gas generated in the attached heavy nitrogen concentration manufacturing device 20 is taken in via the NO supply port 13. Then, NO gas taken is oxidized by air supplied from the air supply port 14, the NO ₂ gas. Further, the NO recovery device 10 has N at its upper end.
An H ₂ O supply port 15 for supplying O ₂ absorbing water (H ₂ O) is provided. NO recovery device 10
Then, the rising flow of the generated NO ₂ gas is H ₂ O for absorbing NO ₂ supplied from the H ₂ O supply port 15.
_It comes into gas-liquid contact with ₂ O to produce an HNO ₃ aqueous solution.

Specifically, reactions of the following chemical formulas (I) and (II) occur in the NO recovery apparatus 10 configured as described above.

Thus, the NO gas recovery method according to the present embodiment recovers the taken-in NO gas as an aqueous HNO ₃ solution using the packed tower type NO recovery device 10. By using the packed tower type NO recovery apparatus 10 in this way, it becomes possible to attach the heavy nitrogen concentration production apparatus 20 operated at normal pressure without complicating the apparatus. However, when the NO recovery device 10 is in a packed tower format, it can be recovered as an HNO ₃ aqueous solution.
There is a problem that the gas recovery rate becomes low.

Therefore, in the NO gas recovery method according to the present embodiment, the inside of the packed tower 11 constituting the NO recovery apparatus 10 to be used is controlled to a predetermined temperature. Specifically, the NO gas recovery method according to the present embodiment is a NO gas recovery method in which NO gas is recovered as an HNO ₃ aqueous solution by the NO recovery device 10 including the packed tower 11. Is controlled to 50 to 70 ° C., and the temperature of the upper portion of the packed tower 11 is controlled to 25 ° C. or lower.
More specifically, approximately 3 from the bottom of the packed column 11 constituting the NO recovery apparatus 10 toward the top of the column.
The temperature of the portion up to 2/2 is controlled to 50 to 70 ° C., and the temperature of the portion up to about one third from the top of the packed column 11 to the bottom of the column is controlled to 25 ° C. or less.

In the NO gas recovery method according to the present embodiment, the temperature of the lower part of the packed tower 11 constituting the NO recovery apparatus 10 to be used is controlled to 50 to 70 ° C., and the temperature of the upper part of the packed tower 11 is changed. By controlling to 25 ° C. or lower, NO gas can be recovered as HNO ₃ with a high recovery rate. As a result, it is not necessary to increase the size of the apparatus, and the facility cost can be suppressed and NO gas can be efficiently recovered. Further, eliminates the need to perform a process such as mass supply water for absorption in order to increase the recovery rate, it is possible to prevent that can lower HNO ₃ aqueous solution than HNO ₃ concentration required.

As described above, the NO gas recovery method according to the present embodiment can be applied to the lower part of the packed tower 11 constituting the NO recovery apparatus 10, that is, up to about two thirds from the bottom of the packed tower 11 to the top of the tower. The temperature of the part is controlled to 50 to 70 ° C. The reaction of the above chemical formula (II) that occurs in the packed column 11, that is, the absorption reaction of NO ₂ gas into H ₂ O is promoted as the temperature increases, but the temperature at the bottom of the packed column 11 is lower than 50 ° C. Therefore, NO ₂ gas cannot be absorbed by H ₂ O with a high absorption rate. On the other hand, when the temperature is higher than 70 ° C., the absorption reaction of NO ₂ gas into H ₂ O is accelerated, but the temperature at the top of the packed tower 11 is 25 ° C. as described above.
It becomes impossible to control below, and the HNO ₃ aqueous solution generated in the packed column 11 becomes mist and escapes.

Therefore, by controlling the temperature of the lower part of the packed column 11 to 50 to 70 ° C., NO ₂ gas can be absorbed by H ₂ O at a high absorption rate, and the temperature control of the upper part of the packed column 11 is affected. And NO gas can be recovered as HNO ₃ at a high recovery rate.

Further, the NO gas recovery method according to the present embodiment is such that the temperature of the upper part of the packed tower 11 constituting the NO recovery apparatus 10, that is, the temperature of the portion from the top of the packed tower 11 to approximately one third in the direction of the bottom of the tower. Is controlled to 25 ° C. or lower. When the temperature of the upper portion of the packed tower 11 is higher than 25 ° C., the HNO ₃ aqueous solution generated in the packed tower 11 escapes as mist, and the recovery rate decreases.

Therefore, by controlling the temperature of the upper part of the packed column 11 to 25 ° C. or lower, the packed column 1
1 to prevent the aqueous HNO ₃ solution generated in 1 from escaping as mist,
NO gas can be recovered as HNO ₃ with a high recovery rate.

Further, the NO recovery device 10 is provided with a temperature control mechanism so that the inside of the packed tower 11 in the NO recovery device 10 has a predetermined temperature. As described above, by providing the NO recovery device 10 with the temperature control mechanism, the inside of the NO recovery device 10 can be controlled to a predetermined temperature. Then, under the predetermined temperature condition, the chemical formulas (I) and (I
By causing the reaction II), NO gas can be recovered at a high recovery rate.

Specifically, as a temperature control mechanism, an external jacket 16 is provided so as to cover the periphery from the upper part to the lower part of the packed tower 11 constituting the NO recovery device 10, and the temperature of a predetermined part in the packed tower 11 is made uniform. I have control.

Further, in the present embodiment, as shown in FIG.
It is divided into three parts (16A, 16B, 16C) from the upper part to the lower part of the recovery device 10, so that different temperatures can be controlled in each part of the packed column 11.

Furthermore, each outer jacket 16 (16A, 16B, 16C) is supplied with hot water or cold water from temperature control water supply ports 16Ain, 16Bin, 16Cin provided at the lower end thereof, and the hot water or cold water is supplied from the lower part to the inside. The temperature in the packed tower 11 is controlled by flowing in the upper direction. The supplied hot water or cold water rises inside the outer jackets 16 and then the temperature-controlled water discharge ports 16Aout, 16Bout, 16Cou provided at the upper ends thereof, respectively.
discharged from t.

In the NO gas recovery method according to the present embodiment, as described above, the temperature control mechanism such as the external jacket 16 is provided as a mechanism for controlling the temperature in the packed tower 11 constituting the NO recovery device 10. Each part in the tower 11 is maintained at a predetermined temperature. Specifically, for example, the temperature in the packed tower 11 is controlled by changing the temperature or flow rate of hot water or cold water supplied to the external jacket 16.

The external jacket 16 that is a temperature control mechanism inside the packed tower 11 is not limited to being provided in three parts from the upper part to the lower part of the packed tower 11. For example, the outer jacket 16 may be divided into four parts from the upper part to the lower part of the packed column 11, and in such a case, the packed column in which an absorption reaction of NO ₂ gas with H ₂ O occurs in particular. 11
The temperature of the portion from approximately 3/4 from the bottom of the column to the top of the column is controlled to 50 to 70 ° C., and the temperature of approximately 1/4 from the top of the packed column 11 to the bottom of the column is 25. Control below ℃.

Alternatively, a portion from the bottom of the packed tower 11 to about two-thirds in the direction of the top of the tower, and the packed tower 1
You may make it provide the outer jacket 16 in 2 site | parts with the part to about 1/3 from the tower top part of one tower to a tower bottom direction, respectively.

Further, the temperature control mechanism for controlling the temperature in the packed tower 11 is not limited to the above-described external jacket, and for example, the heating / cooling pipe may be provided inside the packed tower 11 to control the temperature. These mechanisms may be used at all times or at any time.

Further, the packed tower 11 constituting the NO recovery device 10 is provided with a temperature detecting means 17 such as a thermocouple. In the present embodiment, as shown in FIG. 3, temperature detecting means 1 such as a thermocouple.
7 is inserted into the packed tower 11, and the temperature in the packed tower 11 is detected. Thus, by inserting the temperature detection means 17 such as a thermocouple into the packed tower 11, the temperature in the packed tower 11 can be accurately detected, and the temperature by the temperature control mechanism described above based on the detection result. Can be easily controlled.

The temperature detection means 17 such as a thermocouple is inserted into a protective tube 18 provided inside the packed tower 11. The protective tube 18 is a thin tube made of, for example, glass, formed in a bottomed cylindrical shape. The protective tube 18 is inserted into the packed column 11 from the upper end of the packed column 11, and from the upper end of the packed column 11 like the outer jacket 16. It is disposed over the lower end. Here, the temperature in the protective tube 18 is as follows.
Since the temperature has risen to the same temperature as in the inside, the temperature inside the packed tower 11 can be detected by the temperature detecting means 17 such as a thermocouple inserted into the protective tube 18. Further, by this protective tube 18, a temperature detecting means 17 such as a thermocouple by a gas-liquid contact reaction or the like in the packed tower 11.
Can be prevented from being damaged or the gas-liquid contact reaction being inhibited by the temperature detecting means 17.

Moreover, since the temperature detection means 17 is inserted in the protective tube 18 arrange | positioned from the upper end part to the lower end part of the packed tower 11 in this way, the packed tower 1 is adjusted by adjusting the position.
The temperature of each part of 1 can be detected.

Here, for example, when a thermocouple is used as the temperature detecting means 17, the thermocouple converts the temperature in the protective tube 18 that has absorbed the reaction heat into an electric signal, and is a signal line covered with Teflon (registered trademark) or the like. The temperature in the packed tower 11 is measured by outputting an electric signal to a control unit (not shown) via
As the thermocouple, any known thermocouple that can measure temperature can be used. For example, a K-type thermocouple element can be used.

As described above in detail, according to the NO gas recovery method according to the present embodiment, the packed tower 11 constituting the NO recovery device 10 is controlled to a predetermined temperature, so that the device configuration is enlarged. Even if not, NO gas can be recovered as an aqueous HNO ₃ solution at a high recovery rate.
Further, since a treatment such as supplying a large amount of water for absorption is not required to increase the recovery rate, a necessary concentration of HNO ₃ cannot be maintained by generating a low concentration HNO ₃ aqueous solution. The generated HNO ₃ aqueous solution can be effectively reused.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

For example, the same applies to an example of adding the heavy nitrogen concentration production apparatus 20 to the NO collection apparatus 10 described in the above-described embodiment and collecting NO gas generated from the heavy nitrogen concentration production apparatus 20. The apparatus attached to is not limited to this, and the NO gas recovery method according to the present invention can be applied to any apparatus that generates NO gas.

Hereinafter, specific examples of the present invention will be described. Note that the scope of the present invention is not limited to any of the following examples.

In this example, the packed column 11 was controlled to a predetermined temperature, and the recovery rate of nitric oxide (NO) gas as a nitric acid (HNO ₃ ) aqueous solution was examined.

In this example, the packed tower 11 was prepared by connecting three Pyrex tubes having an inner diameter of 40 mm and a length of 700 mm and having an outer jacket connected in series. The inside of this packed tower 11 made of a Pyrex tube was filled with 6 mm McMahon packing as a filler 12.

A NO supply port 13 is provided in the lower part of the packed tower 11 described above, and the NO supply port 13 is connected to the NO supply port 13.
A gas is supplied at a rate of 1.2 L / min, and a packed tower air supply port 14 provided in the lower part of the packed tower 11 is also used.
Supplied air for NO oxidation at 5.0 L / min. Further, water for absorbing nitrogen dioxide (NO ₂ ) gas was supplied at 4.0 ml / min from an H ₂ O supply port 15 provided at the top of the packed column 11.

In this embodiment, under these conditions, hot water or cold water is supplied into the outer jacket 16 provided in three divisions in the packed tower 11 to control the temperature of each part of the packed tower 11 to a predetermined temperature. The NO gas recovery rate was measured.

(Sample 1)
As sample 1, the temperature of the lower third of the total height of packed column 11 is controlled to 50 ° C., the temperature of the upper third is controlled to 25 ° C., and the recovery rate of NO gas recovered as an aqueous HNO ₃ solution is set. It was measured.

(Sample 2)
As Sample 2, the temperature of the lower third of the total height of the packed tower 11 is controlled to 59 ° C., the temperature of the upper third is controlled to 25 ° C., and the recovery rate of NO gas recovered as an aqueous HNO ₃ solution is set. It was measured.

(Sample 3)
As sample 3, the temperature of the lower third of the total height of packed column 11 is controlled to 68 ° C., the temperature of the upper third is controlled to 25 ° C., and the recovery rate of NO gas recovered as an aqueous HNO ₃ solution is set. It was measured.

(Sample 4)
As sample 4, the temperature of the lower third of the height of the packed tower 11 is controlled to 45 ° C., the temperature of the upper third is controlled to 25 ° C., and the recovery rate of NO gas recovered as an aqueous HNO ₃ solution is set. It was measured.

(Sample 5)
As sample 5, the temperature of the lower third of the total height of packed column 11 is controlled at 25 ° C., the temperature of the upper third is controlled at 25 ° C., and the recovery rate of NO gas recovered as an aqueous HNO ₃ solution is set. It was measured.

(Sample 6)
As sample 6, the temperature of the lower third of the total height of packed tower 11 is controlled to 60 ° C., the temperature of the upper third is controlled to 30 ° C., and the recovery rate of NO gas recovered as an aqueous HNO ₃ solution is set. It was measured.

  Table 1 below shows the measurement results of each sample described above.

As can be seen from the results in Table 1, the temperature in the lower third of the total height of the packed column 11 is set to 50 ° C., 59 ° C.
In Samples 1 to 3, which were controlled at ℃ and 68 ℃, respectively, and the temperature of the upper third of the total height of the packed column 11 was controlled at 25 ℃, the NO gas recovery rate was 98% or higher, and high recovery Showed the rate.

On the other hand, the temperature of the upper third of the whole tower height of the packed tower 11 is controlled to 25 ° C. as in the samples 1 to 3, and the temperature of the lower third of the whole tower height of the packed tower 11 is 45 ° C lower than 50 ° C
In the sample 4 controlled to, the recovery rate was 92.1%, which was lower than those of the samples 1 to 3.

Further, the temperature of the upper third of the entire tower height of the packed tower 11 is controlled to 25 ° C. as in the samples 1 to 3, and the temperature of the upper second third of the entire tower height of the packed tower 11 is 45 Even lower than ℃ 2
In Sample 5 controlled at 5 ° C., the recovery rate was 85.6%, which was a very low recovery rate.

Further, the temperature of the lower third of the entire tower height of the packed tower 11 is controlled to 60 ° C., which is substantially the same as that of the sample 2, and the temperature of the upper third of the entire tower height of the packed tower 11 is lower than 25 ° C. In the sample 6 controlled at a high temperature of 30 ° C., the recovery rate was 92.3%, which was lower than those of the samples 1 to 3.

As described above, when the NO ₂ gas is absorbed into H ₂ O to form an HNO ₃ aqueous solution, the NO ₂ gas absorption rate of H ₂ O is improved by increasing the reaction temperature. This can be clearly seen from the fact that the recovery rates of Samples 4 and 5 were lower than those of Samples 1 to 3.

However, if the temperature of the packed tower 11 is too high, the aqueous HNO ₃ solution will escape from the upper part of the packed tower 11 as mist, and the recovery rate will decrease. This can be clearly seen from the results of Sample 6. In addition, even when the temperature of the lower third of the total tower height of the packed tower 11 is higher than 70 ° C., it becomes difficult to control the temperature of the upper third of the total tower height of the packed tower 11. As a result, HNO ₃ becomes mist and escapes from the upper part of the packed column 11.

From the above, the temperature of the lower part of the packed column 11 used for recovering NO gas as an aqueous HNO ₃ solution is controlled to 50 to 70 ° C., and the temperature of the upper part of the packed column 11 is set to 25 ° C. or lower, thereby reducing NO. It has been found that the gas can be recovered as HNO _{3 with} a high recovery rate.

10 NO recovery device, 11 packed tower, 12 packing material, 13 NO supply port (NO intake port)
, 14 Air supply port, 15 H ₂ O supply port, 16, 16A, 16B, 16C External jacket, 16Ain, 16Bin, 16Cin Temperature control water supply port, 16Aout, 16Bout, 16
Cout temperature control water discharge port, 17 temperature detection means, 18 protective tube, 20 heavy nitrogen concentration production apparatus, 20a exchange tower, 20b reflux tower

Claims (4)

In the recovery method of nitric oxide gas, which recovers nitric oxide gas as an aqueous nitric acid solution by a recovery device comprising a packed tower,
A method for recovering nitric oxide gas, wherein the temperature of the lower part of the packed tower is controlled to 50 to 70 ° C, and the temperature of the upper part of the packed tower is controlled to 25 ° C or lower. The lower part of the packed tower is a portion from the tower bottom of the packed tower to approximately two thirds in the direction of the tower top, and the upper part of the packed tower is approximately 3 minutes in the direction of the tower bottom from the tower top of the packed tower. The method for recovering nitric oxide gas according to claim 1, wherein the portion is a portion up to 1. The method for recovering nitric oxide gas according to claim 1 or 2, wherein the packed tower is provided with an external jacket. The method for recovering nitric oxide gas according to any one of claims 1 to 3, wherein the packed tower is provided with a thermocouple inserted into a protective tube.

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