JP2009095686A - Heavy nitrogen enrichment and production apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heavy nitrogen enrichment and production apparatus that can produce a large quantity of heavy nitrogen by enrichment safely and efficiently on a commercial scale even by using a fewer reflux columns in virtue of its possibility of reducing localized thermal load on each reflux column. <P>SOLUTION: The heavy nitrogen enrichment and production apparatus is one comprising a reflux column 2 which forms nitrogen monoxide from nitric acid and a sulfur dioxide gas and an exchange column that concentrates heavy nitrogen<SP>15</SP>N in nitric acid by the nitrogen isotope chemical exchange reaction between the nitrogen oxide formed in the reflux column 2 and nitric acid, wherein as a sulfur dioxide gas feed port in the reflux column 2, the second SO<SB>2</SB>feed port 4, in addition to the first SO<SB>2</SB>feed port 3 provided at the lower end of the reflux column 2, is formed at least at one position, for example, the middle, nearer to the overhead of the reflux column 2 than the lower end. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an apparatus for concentrating and producing heavy nitrogen ¹⁵ N by chemical exchange with nitric acid using nitric oxide generated by the reaction of nitric acid and sulfur dioxide gas.

Naturally occurring nitrogen isotopes have a ratio of 99.634% of ¹⁴ N having a mass number of 14 and 0.366% of ¹⁵ N having a mass number of 15. Of the above isotopes, ¹⁵ N having a mass number of ¹⁵ is generally called heavy nitrogen, and the separated and concentrated heavy nitrogen is used for tracers in the bio field and nuclear magnetic resonance analysis in the chemical field.

  Various methods have been studied or developed as isotope separation methods for light elements containing nitrogen, but only the statistical separation method (chemical exchange method or distillation method) has been put to practical use. Although individual separation methods (laser method or electromagnetic separation method) are also known, they are effective for a small amount of separation and purification because of the high one-stage separation factor, but because the separation rate is extremely slow, In any case, there is a disadvantage that the substantial manufacturing cost becomes too high when a commercially necessary amount is produced in large quantities.

The nitrogen isotope separation method currently in practical use is a nitrogen isotope chemical exchange reaction that occurs by contact of nitric oxide NO gas and an aqueous solution of nitric acid HNO _3. For example, in the following chemical formula 1, the exchange reaction is slightly on the right side. Shifting, that is, utilizing the fact that ¹⁵ N is biased toward the nitric acid aqueous solution side. Specifically, in the exchange column having a certain length, the HNO ₃ —NO chemical exchange reaction of the following chemical formula 1 is superimposed, so that the concentration of ¹⁵ N proceeds in HNO ₃ .

[Chemical Formula 1]
¹⁵ N + H ¹⁴ NO ₃ ＮＯ ¹⁴ NO + H ¹⁵ NO ₃ (separation coefficient α = 1.05)

The actual concentration operation is performed, for example, as disclosed in Japanese Patent Laid-Open No. 3-47518. Specifically, as shown in FIG. 1, HNO ₃ is supplied from the top of the exchange tower 1 and descends in the exchange tower 1, and the HNO ₃ exiting from the bottom of the exchange tower 1 is placed under the exchange tower 1. It enters the installed reflux tower 2 and further descends in the reflux tower 2. Here, the downward flow of HNO ₃ comes into contact with the upward flow of sulfur dioxide SO ₂ gas supplied from the lower end of the reflux tower 2 as a reducing agent, the reaction of the following chemical formula 2 occurs at the interface, and nitric oxide NO and sulfuric acid H ₂ SO ₄ is generated.

[Chemical formula 2]
2HNO ₃ + 3SO ₂ + 2H ₂ O → 3H ₂ SO ₄ + 2NO

The produced NO returns to the exchange tower 1 as an upward flow, and becomes a gas-liquid countercurrent flow of HNO ₃ and NO in the exchange tower 1, and ¹⁵ N is moved to the HNO ₃ side by the HNO ₃ —NO chemical exchange reaction of the above chemical formula 1. Concentrated. Then, part of nitric acid HNO ₃ ^{to 15 N} becomes is enriched with a predetermined ^{15 N} concentration is withdrawn as a product from the bottom of the exchange column 1 in accordance with a reflux ratio. In addition, H ₂ SO ₄ generated in the reflux tower 2 is recovered from the bottom of the reflux tower 2, and NO gas that isotope exchanged with HNO ₃ is discharged from the top of the exchange tower 1.

In the above method, when HNO ₃ is reduced to NO by a reflux tower, a large amount of SO ₂ gas is required, and a large amount of sulfuric acid is by-produced, so that the processing burden is large. For this reason, Japanese Patent Application Laid-Open No. 2005-205346 proposes to use SO ₂ obtained by refining the process gas of the sulfuric acid production process and to use the by-produced sulfuric acid in the sulfuric acid production process. As a result, a large amount of SO ₂ source is secured, and at the same time, it is not necessary to treat a large amount of by-product sulfuric acid. Therefore, it is expected that the production cost of heavy nitrogen can be reduced.

Japanese Patent Laid-Open No. 3-47518 JP 2005-205346 A

In the apparatus for concentrating and manufacturing heavy nitrogen ¹⁵ N by the HNO ₃ —NO chemical exchange reaction of the above chemical formula 1, the reaction according to the above chemical formula 2 for generating NO is a reaction accompanied by a large exotherm, and therefore the reflux tower must be constantly cooled. There is. However, even if the reflux tower is cooled, it is difficult to control a stable reaction due to a runaway reaction in the reflux tower, or the reflux tower may be damaged due to local heat load. There was a problem.

  In addition, a glass reaction tower provided with an internal cooling pipe and / or an external cooling jacket is used as a reflux tower for generating high-temperature sulfuric acid. Therefore, since the material is glass, the size of the reflux tower that can be produced is naturally limited, and in the production of a large amount of heavy nitrogen, it is necessary to install a large number of reflux towers due to the above-mentioned cooling problem. Therefore, there is a problem that the operation becomes complicated.

  The present invention has been made in view of the above-described conventional problems, and can reduce the local heat load in the reflux tower, and can reduce the number of reflux towers as much as possible on a commercial scale. An object of the present invention is to provide a heavy nitrogen concentration production apparatus that can safely and efficiently concentrate and manufacture heavy nitrogen.

  In order to achieve the above-mentioned object, the heavy nitrogen concentration production apparatus provided by the present invention comprises a reflux tower for producing nitric oxide from nitric acid and sulfur dioxide gas, and a nitrogen isotope of nitrogen monoxide and nitric acid produced in the reflux tower. In a heavy nitrogen concentration production apparatus comprising an exchange tower for concentrating heavy nitrogen to nitric acid by a chemical exchange reaction, the sulfur dioxide gas supply port in the reflux tower is connected to the top of the tower from the bottom of the reflux tower in addition to the bottom of the reflux tower. At least one place is provided on the side.

In the heavy nitrogen concentration production apparatus of the present invention, the total SO ₂ flow rate from a plurality of SO ₂ supply ports is a necessary amount calculated by the chemical formula 2 with respect to the flow rate of HNO ₃ flowing into the reflux tower. Good. The total SO ₂ flow rate may be equally divided by the number of SO ₂ supply ports, but the flow rate from the SO ₂ supply port other than the lower end of the reflux column is set to be small, and the flow rate from the SO ₂ supply port at the lower end of the reflux column. It is preferable to increase the number of The reason is to suppress the possibility that unreacted SO ₂ gas escapes from the reflux tower and enters the exchange tower when the flow rate of HNO ₃ decreases due to trouble of the apparatus or the like.

According to the present invention, since the cooling of the reflux tower is facilitated by dispersing the heat generated by the reaction of HNO ₃ and SO ₂ gas in the reflux tower, damage to the reflux tower due to local heat load is prevented. In addition, it is possible to prevent an increase in the number of reflux towers even in a large amount of concentrated heavy nitrogen production.

Further, according to the present invention, compared with the conventional apparatus in which the SO ₂ supply port is installed only at one lower end of the reflux tower, HNO ₃ flowing into the reflux tower from the exchange tower reacts with SO _{2 in the} reflux tower. Therefore, the time required to reach the predetermined maximum ¹⁵ N concentration can be shortened compared to the conventional case.

As shown in FIG. 1, the heavy nitrogen concentration production apparatus according to the present invention includes a reflux tower 2 that produces nitric oxide NO from nitric acid HNO ₃ and sulfur dioxide SO _2, and nitric oxide NO and nitric acid produced in the reflux tower 2. and a replacement column 1 for concentrating the heavy nitrogen ¹⁵ N nitric acid HNO ₃ with nitrogen isotope chemical exchange reaction with HNO _3. In addition, in the heavy nitrogen concentration production apparatus of the present invention, the supply port for sulfur dioxide SO _{2 in} the reflux tower 2 is located at the top of the reflux tower 2 in addition to the same one at the bottom of the reflux tower 2 as in the prior art. At least one more location is provided. FIG. 1 shows only one portion of the SO ₂ supply port at the lower end of the reflux tower in order to explain a general heavy nitrogen concentration production apparatus.

The reflux tower of the present invention will be described with reference to FIG. 2 showing a specific example. The reflux tower 2 includes, as SO ₂ supply ports, a first SO ₂ supply port 3 provided at the lower end of the reflux tower and a second SO ₂ supply port 4 provided near the center of the reflux tower. The reflux tower 2 is cooled by flowing cooling water through the external cooling jacket 5 and the internal cooling pipe 6. The reflux tower 2 is filled with a glass helix or the like as the packing material 7, and an eye plate 8 for preventing the packing material 7 from falling is provided at the bottom of the tower. In the figure, reference numeral 10 denotes a thermocouple insertion Pyrex tube.

The nitric acid HNO ₃ flowing out from the bottom of the exchange tower (not shown) enters the reflux tower 2 through the HNO ₃ supply port 9 installed at the top of the reflux tower 2 and is transmitted along the surface of the packing material 7. Go down the tower. The HNO ₃ descending in the reflux tower 2 reacts with the sulfur dioxide SO ₂ supplied from the first SO ₂ supply port 3 and the _second SO ₂ supply port 4 to generate NO and H ₂ SO ₄ .

At that time, in the First 2SO ₂ nearby supply port 4, the amount of HNO ₃ commensurate with the SO ₂ volume supplied from the 2SO ₂ supply port 4 is reacted, the rest of HNO ₃ is further lowered in the column, It reacts with SO ₂ supplied from the 1SO ₂ supply port 3 of the lower end of the reflux column 2. At this time, a position SO ₂ and HNO ₃ from first 1SO ₂ supply port 3 is reacted can be set at any position as follows.

That, SO ₂ to While the reaction of SO ₂ and HNO ₃ during device operation start supplied from the 1SO ₂ supply port 3 of the reflux column lower end occurs in the vicinity of the 1SO ₂ supply port 3, the 1SO ₂ supply port 3 Is set to be larger than the amount of SO ₂ required to react with HNO ₃ reaching the first SO ₂ supply port 3, so that excess SO ₂ is present in the HNO located above the first SO ₂ supply port 3. ₃ reacting with, gradually reaction site of SO ₂ and HNO ₃ is increased. Then, when the SO _2-HNO3-3 reaction zone is raised in place, by returning the SO ₂ supply from the 1SO ₂ supply port 3 to the normal value, while maintaining the reaction zone at any suitable location be able to.

Thus by providing a plurality of SO ₂ feed port, by dividing the plurality of locations reaction HNO ₃ and SO ₂ in the reflux column 2, that the heat generated by the reaction of HNO ₃ and SO ₂ are concentrated in one place Can be prevented. Therefore, the cooling of the reflux tower 2 by the external cooling jacket 5 and the internal cooling pipe 6 is facilitated, and the heat load on the reflux tower 2 is reduced. Therefore, more nitric acid can be safely contained in the reflux tower 2 than in the past. It becomes possible to make it react. The number of SO ₂ supply ports may be two or more including the lower end of the reflux tower, and the interval between the SO ₂ supply ports is arbitrarily set according to the position of the SO ₂ —HNO ₃ reaction zone. be able to.

As described above, NO produced by the reaction of HNO ₃ and SO _{2 in} the reflux tower 2 enters the bottom of the exchange tower (not shown) from the top of the reflux tower 2 and is supplied to the top of the exchange tower. the _HNO 3 -NO chemical exchange method with ₃ ¹⁵ N is concentrated gradually move to HNO ₃ side. A part of HNO ₃ concentrated to a predetermined ¹⁵ N concentration is withdrawn from the bottom of the exchange column according to the reflux ratio in the same manner as in a general rectification operation, and is recovered as product H ¹⁵ NO ₃ . The H ₂ SO ₄ generated in the reflux tower 2 is discharged from the bottom of the reflux tower 2 and collected.

Further, in the above-described HNO ₃ -NO chemical exchange method, NO generated by the reaction of SO ₂ and HNO _{3 in} the reflux tower returns to the exchange tower, and NO in accordance with the equilibrium reaction with HNO ₃ supplied from the top of the exchange tower. ¹⁵ N inside moves to HNO ₃ side. In the heavy nitrogen concentration production apparatus of the present invention, since the SO ₂ supply port is also installed above the bottom of the reflux tower as compared with the conventional apparatus, the time until HNO ₃ reacts with SO _{2 in the} reflux tower. (Residence time in the reflux column) is shortened, and therefore the time required for NO containing a large amount of ¹⁵ N to return to the exchange column is shortened and ¹⁵ N enrichment proceeds quickly, so that the maximum ¹⁵ N enrichment is reached. The time required for the process can be shortened.

As an exchange tower, a Pyrex tube having an inner diameter of 25 mm and a length of 2000 mm was used, and the inside was filled with a helicac of filler. Further, as a reflux tower, a Pyrex tube having an inner diameter of 40 mm and a length of 1500 mm and having an external water cooling jacket and an internal cooling tube was produced, and a glass helix as a filler was filled therein. The 1SO ₂ feed port to the lower end of the reflux column, and the first 2SO ₂ supply ports provided in the center portion. Furthermore, in order to observe the heat generation in the reflux tower, a Pyrex tube for inserting a thermocouple was inserted.

Nitric acid aqueous solution of 10 mol / l from the top of the exchange column is supplied at 5 ml / min, the reflux tower first 1SO from _second supply ports 1.1 l / min of the bottom, first 2SO ₂ supply port of the reflux tower central section From the above, SO ₂ gas was supplied at a flow rate of 0.6 liter / min. As a comparative example, SO ₂ gas was supplied at a flow rate of 1.7 liter / min only from the SO ₂ supply port at the lower end of the reflux tower.

In the above examples and comparative examples, the heat generation in the reflux tower was measured with a thermocouple inserted in the tower, and the obtained results are shown in the graph of FIG. The horizontal axis in FIG. 3 represents the distance from the SO ₂ supply port at the lower end of the reflux tower toward the top of the tower. As can be seen from the results, in the embodiment in which a SO ₂ supply port in two places reflux column lower end and the central portion, the maximum temperature compared to the comparative example of the SO ₂ feed opening only one place of the reflux column lower end The heat load applied to the reflux tower was reduced.

In the above Examples and Comparative Examples, showing the results of measuring the relationship between the ^{15 N} enrichment and time in the graph of FIG. Although the maximum ¹⁵ N concentration reached in both the examples and the comparative examples is about 3%, it can be seen that in the examples, the time until the maximum concentration is reached is shorter than in the comparative examples.

It is a schematic sectional drawing which shows the heavy nitrogen concentration manufacturing apparatus provided with the reflux tower and the exchange tower. It is a schematic sectional drawing which shows one specific example of the reflux tower in the heavy nitrogen concentration manufacturing apparatus of this invention. It is a graph which shows the temperature measurement result in the reflux tower in the Example and comparative example of this invention. It is a graph which shows the time change of ¹⁵ N concentration in the Example and comparative example of this invention.

Explanation of symbols

1 the exchange column 2 reflux column 3 the 1SO ₂ supply port 4 first 2SO ₂ feed port 5 external cooling jacket 6 inside the cooling pipe 7 filler 8 perforated plate 9 HNO ₃ supply port 10 thermocouple insertion pyrex tube

Claims (1)

  Heavy nitrogen equipped with a reflux tower for producing nitric oxide from nitric acid and sulfur dioxide gas, and an exchange tower for concentrating heavy nitrogen to nitric acid by a nitrogen isotope chemical exchange reaction between nitric oxide and nitric acid produced in the reflux tower In the concentration manufacturing apparatus, the heavy nitrogen concentration manufacturing apparatus is characterized in that at least one supply port for sulfur dioxide gas in the reflux tower is provided on the tower top side with respect to the bottom of the reflux tower in addition to the lower end of the reflux tower.

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