JP2003221210A - Method and apparatus for producing heavy nitrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the load of operators and the influence on the environment, in a method for producing heavy nitrogen through using nitrogen monoxide, by reducing the load for treating the waste liquid (such as NaHSO<SB>4</SB>in a prior art) and by preventing a byproduct that is apt to crystallize (such as S in a prior art) from being produced. <P>SOLUTION: The method for producing heavy nitrogen through using nitrogen monoxide, comprises at least a step for producing nitrogen dioxide by the thermal decomposition of nitric acid in the presence of sulfuric acid, a step for removing the excess oxygen, a step for producing nitrogen monoxide by adding water into the nitrogen dioxide, and a step for conducting the chemical exchange by adding nitric acid into the nitrogen monoxide. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing nitrogen oxides NO ₂ and NO from nitric acid HNO ₃ and producing heavy nitrogen ¹⁵ N using the product to further concentrate.

[0002]

2. Description of the Prior Art Nitrogen existing in nature consists of two stable isotopes, ¹⁴ N and ¹⁵ N.
Comparing the ratio of species nitrogen existing in nature, ¹⁴ N
Is 99.635% and ¹⁵ N is 0.365%. The above
¹⁵ N is generally referred to as heavy nitrogen, and the concentrated heavy nitrogen to an appropriate concentration is widely used as a tracer by researchers in agriculture, medicine, biochemistry, biology and the like.

Such heavy nitrogen ¹⁵ N is a nitric oxide N
It can be obtained from O. As a method for producing nitric oxide NO, nitric acid HNO ₃ is added to sulfur dioxide SO ₂
Reduction reaction

Embedded image 2H ₂ O + 2HNO ₃ + 3SO ₂ → 3H ₂ SO
It can be obtained by performing ₄ +2 NO. SO ₂ in this case is
According to the Taylor method, gas is supplied from a gas cylinder.

Conventionally, since heavy nitrogen existing in nature is rare and heavy nitrogen is expensive, the field of using heavy nitrogen was limited to the basic research mentioned above. If this ¹⁵ N could be manufactured at low cost,
It may also be used in general industrial fields.

One example thereof is a nitride fuel in nuclear power generation. Conventionally, UO ₂ which is an oxide has been used as a uranium fuel for power generation, but when it is made into UN which is a nitride, the thermal conductivity is higher than that of UO ₂ which is an oxide. Therefore, the equipment can be downsized.

[0006] At this time, when using ^{14 N} as nitrogen, it is a problem of generating ^{1 4 C} radioactive in the reactor, in the case of the use of ^{15 N} is possible to generate ^{14 C-} Absent.

Therefore, as a method of concentrating heavy nitrogen, the technique disclosed in Japanese Patent Publication No. 35-6541 has been known.

In this known technique, sulfur dioxide SO
₂ is a method for secondarily producing sulfur dioxide SO ₂ by using an acidic sodium sulfite aqueous solution without supplying ₂ from a gas cylinder. When sulfuric acid acts on the acidic sodium sulfite aqueous solution,

Embedded image NaHSO ₃ + H ₂ SO ₄ → NaHSO ₄ + S
It becomes O ₂ + H ₂ O, and sulfur dioxide SO ₂ is obtained, but at the same time, an aqueous solution of acidic sodium sulfate is also produced.

[0009]

[Problems to be Solved by the Invention] However, monoxide
In order to generate nitrogen NO, the reducing agent SO_TwoAnd Na
HSO_ThreeIs expensive and expensive to generate
H generated by_TwoSO _FourAnd NaHSO_FourWaste liquid treatment
Is heavy, and crystals of sulfur S, which is a by-product,
Blockages and obstructs the flow of the accumulated liquid, so
There is a problem that it has to be cleaned and removed.

Therefore, the conventional heavy nitrogen concentration method and apparatus have a problem to be solved in that the burden of waste liquid treatment is reduced, crystallization by-products are not generated, and heavy nitrogen is obtained at low cost. .

[0011]

As a first invention according to the present invention as a concrete means for solving the above-mentioned problems of the conventional example, there is provided a method for producing heavy nitrogen using nitric oxide, which comprises at least: A step of thermally decomposing nitric acid in the presence of sulfuric acid to produce nitrogen dioxide, a step of removing excess oxygen, a step of producing nitric oxide by adding water to the nitrogen dioxide, and a step of producing nitric oxide. And a step of chemically exchanging nitric acid with the step of carrying out chemical exchange.

In the first aspect of the invention, the sulfuric acid is repeatedly circulated for use; the sulfuric acid is concentrated sulfuric acid; and the heavy nitrogen is concentrated by repeating the steps of claim 1. This is included as an additional requirement.

A second invention is an apparatus for producing heavy nitrogen using nitric oxide, which comprises means for adding water to nitric acid and distilling it to bring it into contact with sulfuric acid to generate nitric acid gas, and to generate nitric acid gas. A means for generating nitrogen dioxide by adding sulfuric acid and thermally decomposing it, a means for reacting the nitrogen dioxide and sulfuric acid to remove excess oxygen, and heating the mixed solution of nitrogen dioxide and sulfuric acid to produce nitrogen dioxide. And sulfuric acid, a means for producing nitric oxide by adding water to the nitrogen dioxide, and a means for obtaining heavy nitrogen by chemically exchanging nitric acid with the nitric oxide. The present invention provides a device for producing heavy nitrogen, which is characterized by being provided.

In the second aspect of the present invention, an additional requirement is that the sulfuric acid used in each of the above means is repeatedly circulated and used, and a sulfuric acid concentration means and a tank having a delivery means are provided. It includes.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail based on specific embodiments. A flow chart showing the process of chemical change according to the present invention is shown in FIG. In FIG. 1, 10N nitric acid is first introduced into the HNO ₃ —NO chemical exchange column 1.

HNO_Three-Introduced into the NO chemical exchange tower 1
10N nitric acid is water H in the NO generation tower 2._TwoAdd O
HNO after mixed solution_ThreeIt is introduced into the rectification device 3. H
NO _ThreeIn the rectification device 3, 10N nitric acid is converted into glass by heating means.
Acid HNO_ThreeAnd water H_TwoSeparated from O.

A binary solution of nitric acid HNO ₃ and water H ₂ O forms an azeotrope with a boiling point of 120.5 ° C., at which the concentration of nitric acid HNO ₃ is about 32 m.
ol%. Therefore, a means for flowing concentrated liquid sulfuric acid H ₂ SO ₄ from the top of the HNO ₃ rectification unit 3 into this mixed solution to change the gas-liquid equilibrium relationship is adopted so as not to generate an azeotropic mixture.

[0018] Thus, HNO ₃ in the rectification unit 3 will be concentrated nitric acid gas is generated, HNO ₃ is from the top of the rectification unit 3 increases and concentrated nitric acid gas, sulfuric acid _H 2 S from the bottom of the column
O ₄ and water H ₂ O are discharged and introduced into the H ₂ SO ₄ concentrator 4. In this H ₂ SO ₄ concentrator 4, sulfuric acid H ₂ SO
Concentrated concentrated sulfuric acid H ₂ SO ₄ is obtained by evaporating water H ₂ O from a mixed solution of ₄ and water H ₂ O, and introduced into the sulfuric acid tank 5.

HNO_ThreeThe concentration rising from the top of the rectification device 3
Nitric acid gas is HNO_ThreeIt is introduced into the absorption tower 6. HNO_Three
The absorption tower 6 is a water-cooled packed tower, and sulfuric acid H is supplied from the top of the tower._Two
SO _FourTo flow down. Here, the concentrated nitric acid gas is liquefied
Meanwhile, sulfuric acid H_TwoSO_FourAbsorbed by NO_TwoTo the generating can 7
Run down.

A mixed solution of concentrated sulfuric acid and concentrated nitric acid continuously flows down into the NO ₂ generating can 7. And nitric acid HNO ₃ is

## STR3 ## The reaction of 4HNO ₃ → 4NO ₂ + 2H ₂ O + O ₂ occurs to generate 4NO ₂ , 2H ₂ O and O ₂ . In this mixed solution of concentrated sulfuric acid and concentrated nitric acid, when the temperature of the mixed solution reaches approximately 300 ° C., a reaction due to thermal decomposition of nitric acid HNO ₃ easily occurs, so that the temperature of the mixed solution is heated to approximately 300 ° C. Preferably.

Water H generated by thermal decomposition of nitric acid HNO _3
2 O is discharged to the outside of the system, and other nitrogen dioxide NO ₂ and oxygen O
₂ is introduced into the NO ₂ absorption oxygen separation column 8. The NO ₂ absorption oxygen separation column 8 is a water-cooled packed column, and is opposed to nitrogen dioxide NO ₂ and oxygen O ₂ that are blown up, and sulfuric acid H ₂ SO
₄ , the boiling point of nitrogen dioxide NO ₂ is 21.3 ° C.
Since the boiling point of oxygen O ₂ is −183 ° C., nitrogen dioxide NO ₂ is absorbed by sulfuric acid H ₂ SO ₄ and becomes a mixed liquid, and oxygen O ₂ is discharged from the top of the column. In other words, nitric acid H
NO ₃ is thermally decomposed in the presence of sulfuric acid H ₂ SO ₄ to produce nitrogen dioxide NO ₂ .

The mixed solution of the mixed solution of nitrogen dioxide NO ₂ and sulfuric acid _(H 2 SO ₄₎ flows down the NO ₂ emission can 9, in the NO ₂ emission can 9, the nitrogen dioxide NO ₂ and sulfuric acid _(H 2 SO ₄₎ Is heated, the nitrogen dioxide NO ₂ dissolved in the sulfuric acid H ₂ SO ₄ is gasified again.

Regasified nitrogen dioxide NO_TwoIs NO
It is introduced into the raw tower 2. In this NO generation tower 2,
From water H_TwoO is supplied. Nitrogen dioxide NO_TwoExcessive
Water H _TwoWhen O is added,

Embedded image Disproportionation reaction of 3NO ₂ + H ₂ O → 2HNO ₃ + NO can occur to generate nitric oxide NO.

Nitric acid HNO generated by this disproportionation reaction
₃ is introduced into the HNO ₃ rectification unit 3 and circulated, and nitric oxide NO is introduced into the HNO ₃ —NO chemical exchange column 1.

In the HNO ₃ -NO chemical exchange tower 1,
Taylor, T .; I. J. Chem. Phys. Two
3 (1955) 981, 24 (1956) 626 NI
Utilizing the technique of TROX method, _HNO 3 are opposed to each other by flowing down the nitrate HNO ₃ from the top to the -NO chemical exchange column blown-up nitric oxide NO from 1 in the bottom, nitric acid HNO ₃ was reached bottom Is reduced to nitric oxide NO and is perfused.

As a result, the re-contact of nitric oxide NO and nitric acid HNO _{3 in} the HNO ₃ -NO chemical exchange column 1

[Chemical 5]¹⁵ NO + H¹⁴NO_Three→¹⁴NO + H¹⁵NO_Three Chemical exchange of HNO_Three-NO chemical exchange tower 1
HNO near the bottom of _ThreeHeavy nitrogen in¹⁵High N
It can be concentrated and contained every time, and its HNO_Three-NO
H due to chemical exchange¹⁵NO_ThreeLive
Can be made, heavy nitrogen^{1 5}It is possible to obtain N.

On the other hand, concentrated sulfuric acid H introduced into the sulfuric acid tank 5
_TwoSO_FourIs delivered by suitable pumps 10a, 10b
To be done. Sulfur sulfur delivered by one pump 10a
Acid H _TwoSO_FourIs HNO_ThreeIntroduced into the absorption tower 6 and used
And then NO_TwoGenerator can 7 and HNO_ThreeFragrance 3
Even used, H_TwoSO_FourH through the concentrator 4_TwoSO
_FourReturn to tank 5. Pumped by the other pump 10b
Concentrated sulfuric acid H_TwoSO _FourIs NO_TwoIn the absorption oxygen separation tower 8
NO after being introduced and used_TwoDispersion can 9, NO_TwoOccurrence
Can 7 and HNO_ThreeIt is also used in the rectification device 3,_Two
SO_FourH through the concentrator 4_TwoSO_FourReturn to tank 5
By, concentrated sulfuric acid H_TwoSO_FourRepeatedly circulate and use
It can be used.

By repeating these steps, ¹⁵ N of heavy nitrogen can be concentrated, and concentrated sulfuric acid H ₂
The use by repeatedly circulated SO _4, it is possible to remarkably reduce the amount of sulfuric acid (H ₂ SO ₄₎ contained in the waste.

[0029] in the flowchart of FIG. 1, without refluxed nitric oxide NO produced by the disproportionation reaction in _HNO 3 -NO chemical exchange column 1, when not using the _HNO 3 -NO chemical exchange column 1, one It can be used as a method for producing nitrogen oxide NO, and can be used as a method for producing nitrogen dioxide NO ₂ when the HNO ₃ —NO chemical exchange column 1 and the NO generation column 2 are not used.

Experimental Example An experimental example of the present invention will be shown below. First, in FIG. 1, a stainless steel tube having an inner diameter of 23 mmφ × 7000 mm is used as the HNO ₃ —NO chemical exchange column 1, and a helipack is filled inside.

The NO generation tower 2 has an inner diameter of 35 mmφ ×
A medium-thickness Pyrex (trademark) tube with a 400 mm water-cooled jacket is used and the inside is filled with glass helix.

The HNO ₃ rectification unit 3 is composed of a lower heating tube and an upper packed column. The heating tube has an inner diameter of 10
A Pyrex (registered trademark) tube having a medium thickness of 0 mmφ × 700 mm is used and a quartz heater of 1 kW is attached.
A Pyrex (registered trademark) tube with a medium thickness of 700 mmφ × 1400 mm is used for the packed tower, and glass helix is filled inside.

The H ₂ SO ₄ concentrator 4 comprises a heating tube, a packed tower and a cooling tube. The heating tube has an inner diameter of 100
Pyrex (registered trademark) with medium meat of φφ × 700 mm
Use a tube and attach a 1 kW quartz heater. A Pyrex (registered trademark) tube with a medium thickness of 700 mmφ × 1400 mm is used for the packed tower, and glass helix is filled inside. Cooling tube has an inner diameter of 35 mmφ × 40
A medium Pyrex tube with a 0 mm water cooling jacket is used and filled with glass Raschig rings inside. In addition, in this experimental example, two H ₂ SO ₄
Concentrator 4 was used.

For the sulfuric acid tank 5, for example, a 20-liter container made of polyethylene is used.

The HNO ₃ absorption tower 6 has an inner diameter of 35 mmφ ×
A Pyrex (registered trademark) tube having a 700 mm water-cooled jacket and having a medium thickness is used, and a glass helix is filled inside.

The NO ₂ generating can 7 has an inner diameter of 100 mm.
A Pyrex (registered trademark) tube having a diameter of φ × 700 mm is used and a quartz heater of 1 kW is attached.

The NO ₂ absorption oxygen separation tower 8 has an inner diameter of 35 m.
A pyrex (registered trademark) tube having a diameter of mφ × 700 mm and a water-cooled jacket is used, and a glass helix is filled inside.

The NO ₂ diffusion can 9 has an inner diameter of 100 mm.
A Pyrex (registered trademark) tube having a diameter of φ × 700 mm is used and a quartz heater of 1 kW is attached.

Pump 10 equipped in the sulfuric acid tank 5
A Teflon (registered trademark) diaphragm pump having a maximum discharge rate of 30 ml / min is used as a and 10b.

In this experimental example, a 10N nitric acid aqueous solution was supplied to the HNO ₃ —NO chemical exchange column 1 at 3 ml / min, and water H ₂ O was supplied to the NO generation column 2 at 4 ml / min. In the NO ₂ absorption oxygen separation tower 8, concentrated sulfuric acid H ₂ SO
₄ was supplied at 15 ml / min, and concentrated sulfuric acid H ₂ SO ₄ was supplied to the HNO ₃ absorption tower 6 at 5 ml / min.

The temperature of each device during operation is about 280 ° C. for the NO ₂ releasing can 9 and about 280 for the NO ₂ generating can 7.
C., and the HNO ₃ rectification unit 3 has a temperature of about 200 ° C.
_{The 2} SO ₄ concentrator 4 was at approximately 290 ° C.

Heavy nitrogen ¹⁵ N existing in nature is approximately 0.3.
Although it is 65%, in the present experimental example, when the experiment was continued for 2 days, ¹⁵ N of heavy nitrogen was about 0.595.
Could be concentrated to%. From this, it is understood that it is possible to efficiently generate highly concentrated heavy nitrogen ¹⁵ N in a short time by optimizing the temperature and operation of each device.

The waste liquid (mainly water) generated in this experimental example has a pH of 2 to 3 and shows acidity. However, by repeatedly circulating sulfuric acid, the concentration is higher than that of the waste liquid produced by the conventional method. Since the thickness is thin, the burden of processing it can be greatly reduced.

[0044]

As described above, the first aspect of the present invention
The invention of the method for producing heavy nitrogen is a method for producing heavy nitrogen using nitric oxide, which comprises at least a step of thermally decomposing nitric acid in the presence of sulfuric acid to produce nitrogen dioxide, and an excess oxygen. The step of removing nitric acid, adding nitric oxide to the nitric oxide to produce nitric oxide, and adding nitric acid to the nitric oxide for chemical exchange. And sulfuric acid and water are used, sulfuric acid can be repeatedly concentrated and used,
It is possible to reduce the burden of waste liquid treatment, generate no by-products that crystallize, and produce heavy nitrogen at low cost.

The apparatus for producing heavy nitrogen according to the second aspect of the invention comprises means for adding water to nitric acid and distilling it to bring it into contact with sulfuric acid to generate nitric acid gas; and adding sulfuric acid to the nitric acid gas for thermal decomposition. Means for producing nitrogen dioxide, means for reacting the nitrogen dioxide with sulfuric acid to remove excess oxygen, and means for heating the mixed solution of nitrogen dioxide and sulfuric acid to separate nitrogen dioxide and sulfuric acid. , A means for generating nitric oxide by adding water to the nitrogen dioxide, and a means for obtaining heavy nitrogen by chemically exchanging nitric oxide to the nitric oxide to obtain heavy nitrogen. Therefore, as in the case of the invention of the above-mentioned method, the burden of waste liquid treatment can be reduced, a by-product for crystallization is not generated, and heavy nitrogen can be obtained at low cost.

Therefore, in either the production method or the production apparatus according to the present invention, nitric acid HNO ₃ as in the conventional example is used.
Since no means for reducing sulfur dioxide with SO ₂ is used,
By using nitric acid and sulfuric acid generated in the reaction process by circulating them without generating by-products that crystallize, it is possible to improve economic efficiency and reduce the burden on workers, as well as the impact on the environment. It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process of chemical change in a method and an apparatus according to an embodiment of the present invention.

[Explanation of symbols]

1 HNO ₃ -NO Chemical Exchange Tower 2 NO Generation Tower 3 HNO ₃ Fractionation Device 4 H ₂ SO ₄ Concentrator 5 H ₂ SO ₄ Tank 6 HNO ₃ Absorption Tower 7 NO ₂ Generation Can 8 NO ₂ Absorption Oxygen Separation Tower 9 NO ₂ diffusion cans 10a, 10b pumps

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masami Mori             Showaden 1-7-13 Shiba Park, Minato-ku, Tokyo             Kobetsukan Shoko Tsusho Co., Ltd. (72) Inventor Wataru Maruyama             Showaden 1-7-13 Shiba Park, Minato-ku, Tokyo             Kobetsukan Shoko Tsusho Co., Ltd. (72) Inventor Kenichi Muraoka             Showaden 1-7-13 Shiba Park, Minato-ku, Tokyo             Kobetsukan Shoko Tsusho Co., Ltd. F-term (reference) 4D076 AA16 AA22 BB04 CA19 CC14                       CC22 DA22 FA02 FA04 FA12                       GA10 HA20 JA03

Claims (6)

[Claims] 1. A method for producing heavy nitrogen using nitric oxide, which comprises at least a step of thermally decomposing nitric acid in the presence of sulfuric acid to produce nitrogen dioxide, and a step of removing excess oxygen. A method for producing heavy nitrogen, comprising: a step of producing nitric oxide by adding water to the nitrogen dioxide; and a step of adding nitric acid to the nitric oxide to cause chemical exchange. 2. The method for producing heavy nitrogen according to claim 1, wherein the sulfuric acid is repeatedly circulated for use. 3. The method for producing heavy nitrogen according to claim 1, wherein the sulfuric acid is concentrated sulfuric acid. 4. A method for producing heavy nitrogen, which comprises concentrating heavy nitrogen by repeating the steps of claim 1. 5. An apparatus for producing heavy nitrogen using nitric oxide, which comprises adding nitric acid to water and distilling it to bring it into contact with sulfuric acid to generate nitric acid gas, and adding sulfuric acid to the nitric acid gas. Means for producing nitrogen dioxide by thermal decomposition; means for reacting the nitrogen dioxide with sulfuric acid to remove excess oxygen; and heating the mixed solution of nitrogen dioxide and sulfuric acid to separate nitrogen dioxide and sulfuric acid. Means for producing nitric oxide by adding water to the nitrogen dioxide, and means for obtaining heavy nitrogen by adding nitric acid to the nitric oxide and chemically exchanging the nitric oxide. Characteristic heavy nitrogen generator. 6. The heavy nitrogen according to claim 5, further comprising: a sulfuric acid concentrating means for repeatedly circulating the sulfuric acid used in each of the means, and a tank having a delivering means. Generator.