JP3805533B2 - Isotope separation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an isotope separation method, and more specifically, by using a clathrate and desorbing a guest molecule having a specific isotope atom as a constituent atom by irradiating with light having a wavelength that excites the molecule. The present invention relates to an isotope separation method that enriches gas molecules containing a large amount of isotopes.
[0002]
[Prior art]
Conventionally known methods for separating stable isotopes include a centrifugal separation method, a gas diffusion method, a thermal diffusion method, a distillation method, a separation nozzle method, and a laser method. These are properly used depending on the target element, separation amount, isotope concentration, etc.For example, the centrifugal method requires high-speed rotating equipment, so it takes time for maintenance management, and the gas diffusion method has low separation efficiency, Thermal diffusion methods have both advantages and disadvantages, such as requiring a large amount of energy.
[0003]
Each molecule has its own light absorption wavelength, but the wavelength varies slightly depending on the isotope. In the laser method, isotopes can be separated by selecting and irradiating laser light having a wavelength that only a molecule containing a specific isotope absorbs. That is, if A and A ′ are isotope atoms, a laser is irradiated while A and A ′ are mixed, and only A ′ is excited. When another molecule B is allowed to act there, a chemical reaction such as A ′ + B = A′B occurs to generate a third substance A′B, but AB does not occur. This indicates that isotope differences can be converted to chemical differences. After that, A′B and A can be easily separated by an ordinary chemical separation method.
[0004]
However, in practice, when a high concentration isotope A ′ is to be obtained by irradiating a laser while A and A ′ are mixed, the required isotopes are stepped in stages. A method of increasing the concentration of A ′ is taken. However, for this purpose, a chemical operation for returning A′B back to A ′ is necessary. This requires a lot of effort, labor and energy. Further, when A′B is a hardly decomposable chemical substance, cascading is virtually impossible. Moreover, in the form of a hardly decomposable substance, it is difficult to use the isotope separated and acquired industrially.
[0005]
[Problems to be solved by the invention]
When the present inventors irradiate the clathrate with light corresponding to the absorption wavelength of the guest molecule, the inventors excite the molecule by the absorbed energy, thereby inhibiting the structure of the clathrate and / or the clathrate. I found it to decompose selectively. An object of the present invention is to provide a new and useful isotope separation method by utilizing this phenomenon via clathrate.
[0006]
[Means for Solving the Problems]
The present invention selectively irradiates a guest molecule composed of a specific isotope atom by irradiating the clathrate with light having a wavelength that excites a guest molecule having the specific isotope atom as a constituent atom. The isotope separation method is characterized in that the guest molecules composed of the specific isotope atoms are concentrated in the gas phase by being separated.
[0007]
In addition, the present invention selectively irradiates a guest molecule composed of the specific isotope atom by irradiating the clathrate with light having a wavelength that excites a guest molecule having the specific isotope atom as a constituent atom. Provided is an isotope separation method characterized in that a molecule other than a molecule composed of the specific isotope atom is concentrated in a clathrate by excitation and separation.
[0008]
Furthermore, the present invention is configured by irradiating a clathrate having water as a host molecule with light having a wavelength for exciting a guest molecule having a specific isotope atom as a constituent atom therein, and comprising the specific isotope atom. Provided is an isotope separation method characterized in that a guest molecule composed of the specific isotope atom is concentrated in an aqueous phase by selectively exciting and releasing the guest molecule.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
For example, carbon dioxide contains carbon dioxide isotopes of ¹² CO ₂ and ¹³ CO _2, but the wavelength of the excited light differs between ¹² CO ₂ and ¹³ CO ₂ . FIG. 1 is a diagram in which the absorbance of both in the wavelength range of 4.15 to 4.65 μm was measured. Here, the carbon dioxide gas has a light absorption region in a wavelength region other than the above wavelength region, but in FIG. 1, it is an actually measured value in a part of the wavelength region.
[0010]
FIG. 1A shows the absorbance of ¹² CO ₂ , and FIG. 1B shows the absorbance of ¹³ CO ₂ . As shown in FIG. 1A, ¹² CO ₂ absorbs light in the wavelength range of 4.18 to 4.38 μm. On the other hand, as shown in FIG. 1B, the absorption wavelength by ¹³ CO ₂ is somewhat shifted to the longer wavelength side and absorbs light in the wavelength range of 4.19 to 4.52 μm.
[0011]
On the other hand, when a clathrate forms a crystal by combining two kinds of molecules under appropriate conditions, one molecule (host molecule) forms a tunnel, layer, or network structure, and another molecule (guest A compound having a structure in which a molecule is embedded, for example, a different type of molecule (CO ₂ , CH in a cage-like crystal structure composed of about a dozen molecules (a host molecule such as H ₂ O). ₄ or other guest molecules).
[0012]
Here, for example, the quantitative ratio of ¹² CO ₂ and ¹³ CO _{2 in} carbon dioxide is the same when a clathrate is formed as a guest molecule, and this is the same for other clathrates. The conditions for generating the clathrate vary depending on the type and combination of the host molecule and guest molecule, but it is generally known that the clathrate is generated within a certain predetermined temperature and pressure range. Various clathrates used in the present invention can be generated under such generation conditions.
[0013]
That is, molecules that are hosts in the clathrate form a clathrate when they coexist with gas molecules having a certain range of size, so that the gas molecules crystallize at very close positions. This phenomenon occurs when a host molecule and a guest gas molecule coexist in a certain pressure and temperature condition, and the host molecule and the gas molecule that becomes the guest via hydrogen bonds, for example, have a certain three-dimensional structure, for example, the host. Is a phenomenon that forms a bowl-like structure surrounding the guest. This phenomenon occurs at a predetermined temperature and pressure depending on the type of host molecule and guest molecule. In the present invention, the temperature and pressure conditions for generating a predetermined clathrate are appropriately selected depending on the type or combination of the host molecule and guest molecule. Is done.
[0014]
According to the present invention, it has been found that, for example, the difference in the light absorption range between ¹² CO ₂ and ¹³ CO ₂ can be used when the guest molecules are decomposed and separated from the clathrate containing carbon dioxide as guest molecules. That is, when the clathrate is irradiated with light having a wavelength corresponding to the absorption wavelength of a guest molecule composed of a specific isotope atom of the guest molecule, the guest having the specific isotope atom as a constituent atom by the absorbed energy The molecule is selectively excited, and the decomposition of the clathrate composed of the guest molecule having the specific isotope atom as a constituent atom can be promoted.
[0015]
In the present invention, a clathrate is produced using the molecule to be separated as a guest molecule, and the resulting clathrate is irradiated with light. At that time, by selecting a wavelength that only the guest molecule having a specific isotope atom as a constituent atom selectively absorbs, the decomposition rate of the clathrate of the guest molecule having the specific isotope atom as a constituent atom is selected. Can be increased.
[0016]
The clathrate is a solid, and the molecules decomposed and separated from the clathrate are gases. For this reason, molecules having isotope atoms with selectively increased decomposition rates increase in the gas phase by the above operation. In the present invention, this increases the equilibrium concentration of the molecule having the isotope atom in the gas phase and concentrates it. On the other hand, molecules having other isotopes whose decomposition rates are slow by the above-described operation remain in a relatively large amount in the clathrate, and therefore can be concentrated in the clathrate.
[0017]
That is, more molecules than the molecule with the isotope atom remain as a clathrate that is a solid, and the molecule with the isotope atom selectively decomposes and migrates more in the gas phase. It can be easily concentrated and separated. Moreover, in this case, the two are simply separated as one remains as clathrate and the other moves into the gas phase, so that cascading is extremely easy, thereby concentrating the isotope atoms to a high concentration. be able to.
[0018]
In this regard, in the example of the laser method described above, the laser is irradiated to the isotope atoms A and A ′ to excite only A ′, but another molecule B is caused to act on the third molecule A′B. Give rise to substances. In order to obtain A ′ from A′B, it is necessary to decompose A′B. However, the decomposition operation itself requires a lot of labor, labor, and energy. In particular, A′B is a hardly decomposable chemical substance. If so, cascading is virtually impossible. On the other hand, in the present invention, one remains as a clathrate and the other moves into the gas phase, so that it does not take the form of a hardly decomposable substance and is simply the same substance as the original molecule. Since it is separated, it is very easy to handle and is therefore very advantageous from an industrial point of view.
[0019]
As another example, the carbon constituting the CH ₄ molecule contains the isotopes ¹² C and ¹³ C, of which ¹³ C is about 1.1% in natural abundance, so ¹³ CH ₄ is Only about 1.1% is contained in the total CH ₄ . FIG. 2 is a diagram in which the absorbances of both in the wavelength region of 1.65 to 1.70 μm are actually measured. 2A shows the absorbance of ¹² CH ₄ , and FIG. 2B shows the absorbance of ¹³ CH ₄ . Here, methane has a light absorption region in a wavelength region other than the above wavelength region, and FIG. 2 shows actually measured values in a part of the wavelength region.
[0020]
As shown in FIG. 2, for example, ¹² CH ₄ absorbs light having a wavelength of about 1.665 to 1.668 μm, and the absorption wavelength of ¹³ CH ₄ is somewhat shifted to absorb light having a wavelength of about 1.67 to 1.673 μm. To do. According to the present invention, for example, light having a specific wavelength of about 1.67 to 1.673 μm is irradiated to a clathrate in which a host molecule is water and a guest molecule is CH ₄ having a natural isotope ratio, for example. selectively excited to selectively degrade ¹³ CH ₄ to ¹³ CH ₄ by, by leaving, CH ₄ ^{to 13} CH ₄ is concentrated in the gas phase is obtained.
[0021]
As described above, in the present invention, by using a clathrate that is a solid and irradiating it with light having a specific wavelength or a specific wavelength range, it is possible to separate isotopes only by a change of decomposition of the clathrate. . In this regard, in the laser method described above, a laser whose wavelength is specified is applied to a molecule containing an isotope, but the above laser method inevitably involves a chemical reaction, so this point is fundamentally different from the present invention. Is.
[0022]
In the present invention, the light irradiated to the clathrate may be any light having a wavelength that can selectively excite a guest molecule having a specific isotope atom in the guest molecule constituting the clathrate as a constituent atom. used. The light having a wavelength that can be selectively excited may excite a guest molecule other than a guest molecule having a specific isotope atom as a constituent atom. Also in this case, if there is a significant difference in the excitation action for both guest molecules, it can be applied, but preferably a guest molecule having a specific isotope atom as a constituent atom is selectively excited, and the other guest molecules Is used in the wavelength or wavelength range that is not excited or substantially excited.
[0023]
That is, the difference between the wavelength for exciting a molecule containing a specific isotope atom in a guest molecule and the wavelength for exciting a molecule containing another isotope atom is usually small. By selecting a laser beam with a narrow line width as the wavelength for exciting a guest molecule having a body atom as a constituent atom, the decomposition and separation rate of the guest molecule having the specific isotope atom as a constituent atom from the clathrate is sharply enhanced. And can be concentrated effectively. In addition, since the irradiation energy per photon is large when the wavelength is short, when there are a plurality of excitation wavelengths of guest molecules, the decomposition and separation effect can be enhanced by selecting the short wavelength region.
[0024]
As the guest molecule to be separated in the present invention, any molecule can be applied as long as it is a molecule composed of two or more kinds of stable isotope atoms. Examples of guest molecules containing carbon include carbon dioxide (CO ₂ ) and methane, carbon monoxide (CO), ethane, ethylene, propane, cyclopropane, butane (n-butane, isobutane), cyclobutane, neopentane, cyclohexane Examples include pentane, cyclohexane, cyclooctane, methylcyclohexane, benzene, and adamantane.
[0025]
Examples of guest molecules composed of two or more kinds of stable isotope atoms other than carbon-containing guest molecules include Ar, Kr, Xe, nitrogen (N ₂ ), oxygen (O ₂ ), hydrogen sulfide (H ₂ S), etc. Can be mentioned. For example, in Ar, as stable isotopes, (1) ³⁶ Ar (abundance ratio: 0.3365%), (2) ³⁸ Ar (abundance ratio: 0.0632%), and (3) ⁴⁰ Ar (abundance ratio: 99.6003%) is there. In this case, creating a clathrate of guest molecule and water as a host molecule Ar, to generate clathrate example ▲ 1 ▼ ³⁶ Ar selectively with light having an excitation wavelength in the gas phase by irradiation with ▲ 1 ▼ ³⁶ It can be concentrated by selectively releasing Ar. This also applies to Kr, Xe and the like.
[0026]
In addition, there are (1) ¹⁴ N (abundance ratio 99.634%) and (2) ¹⁵ N (absorption ratio 0.366%) as stable isotopes in N atoms, and O atoms as stable isotopes. (1) ¹⁶ O (abundance ratio: 99.762%), (2) ¹⁷ O (abundance ratio: 0.038%), (3) ¹⁸ O (abundance ratio: 0.200%), S atoms are stable As isotopes (1) ³² S (abundance ratio 95.02%), (2) ³³ S (abundance ratio 0.75%), (3) ³⁴ S (abundance ratio 4.21%), (4) ³⁶ S (Existence ratio 0.02%). The present invention applies to molecules containing these atoms.
[0027]
In the present invention, the host compound that forms the clathrate is not particularly limited, and examples thereof include water, hydrogen sulfide, alcohols, amines, organic acids, and quinones. Of these, water is particularly preferably used. As described above, hydrogen sulfide is a substance that can also be a guest.
[0028]
In a clathrate with water as the host molecule, if the guest molecule that constitutes the clathrate can be present in water, light with a wavelength that excites the guest molecule having a specific isotope atom in the clathrate as a constituent atom. , The guest molecules composed of the specific isotope atoms can be selectively excited and separated to selectively concentrate the guest molecules composed of the specific isotope atoms in the aqueous phase. In this case, the clathrate is solid, and the molecules decomposed and separated from the clathrate are present in the aqueous phase. Therefore, the clathrate and the aqueous phase containing the molecule composed of the specific isotope atom separated from the clathrate Is separated by solid-liquid separation.
[0029]
In the clathrate using water as a host molecule, the guest molecules that can form the clathrate in the aqueous phase include 2-methyl-2-propanol, cyclopentanol, 2-methyl-1-propanol, oxetane, 1, Examples include 3-dioxolane, furan, tetrahydrofuran, 1,2-dioxane, cyclobutanone, cyclopentanone, cyclohexanone, isopropylamine, and isobutylamine.
[0030]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, of course, this invention is not limited by these Examples. First, an outline of the apparatus used in the examples is described, and then generation of a clathrate, decomposition test of the generated clathrate and gas phase component measurement test using this apparatus are described.
[0031]
FIG. 3 is a diagram schematically showing the configuration of the experimental apparatus used in this example. In FIG. 3, 1 is a clathrate generating holder, 2 is a roller for rotating the holder, 3 is a rotational force transmission mechanism, 4 is an infrared light source, and 5 is a filter, which are accommodated in the freezer 6. In the clathrate generation operation, the host material is first accommodated in the generation holder 1, the gas as the guest material is introduced and filled, and the clathrate is generated while being rotated by the holder rotating roller 2.
[0032]
By rotating the clathrate generation holder 1 through the rotational force transmission mechanism 3 by the holder rotating roller 2, the host material and guest gas are mixed and stirred to promote contact and efficiently generate hydrate. Let The clathrate generation holder 1 is provided with a host material, a guest material introduction tube, a gas extraction tube, a generation clathrate extraction tube, and the like, which are not shown in FIG.
[0033]
Next, infrared light is generated by the infrared light source 4 and irradiated to the generated clathrate in the holder 1. The arrow (←) in FIG. 3 indicates the irradiation direction. At that time, infrared rays are passed through the filter 5, and only infrared rays having a specific wavelength are selected and irradiated. Since the holder needs to transmit infrared rays, the holder is made of an infrared transparent material. Thereafter, the gas phase in the holder 1 is taken out and its components are analyzed.
[0034]
FIG. 4 shows the wavelength of infrared rays when an infrared beam irradiating device (Nikolay Japan Co., Ltd.) is used as the infrared light source, and an infrared bandpass filter (SPECTROGON, NB-4350-020-D) is used as the filter 5. It is shown. As shown in FIG. 4, the infrared wavelength by this apparatus is in the range of 4.34 to 4.39 μm, but the peak in the wavelength region is about 4.37 μm.
[0035]
As shown in FIG. 1A, ¹² CO ₂ absorbs infrared rays having a wavelength ranging from 4.18 to 4.38 μm, but has an absorbance of about 20% in the infrared wavelength region of the present apparatus. On the other hand, as shown in FIG. 1B, ¹³ CO ₂ absorbs infrared rays having a wavelength in the range of 4.19 to 4.52 μm, but has an absorptivity of about 80 to 95% in the infrared wavelength region of this apparatus. It is shown that.
[0036]
A stainless steel cylindrical high-pressure vessel with sapphire windows on both the left and right sides was used as the clathrate generation holder 1, and water was put in it. The holder 1 was filled with a natural abundance of carbon dioxide gas contained in a gas cylinder until the internal pressure of the container reached 30 kgf / cm ² . The amount of water was sufficient to give the amount of clathrate produced with the guest CO ₂ gas as the host component (the amount of water given as the host component was 10 cc). The temperature in the freezer 6 was set to −20 ° C., and hydrate was generated while the clathrate generation holder 1 was rotated by the holder rotating roller 2, and this operation was continued until the gas phase pressure in the container reached about 10 kgf / cm ² . . The decrease in the gas phase pressure in the vessel is due to the generation of clathrate by the host water and guest CO ₂ gas.
[0037]
<Decomposition test>
A decomposition experiment on the generated clathrate was conducted. Using an infrared beam irradiation device (Nikolay Japan) as the infrared light source 4, and using an infrared bandpass filter (SPECTROGON, NB-4350-020-D) as the filter 5, the class of the clathrate generation holder 1 Infrared rays were applied to the rate from the direction of the arrow (←) in FIG. During this time, the temperature in the freezer 6 was increased from −20 ° C. to + 20 ° C. When the infrared power after passing through the filter was monitored with a power monitor (manufactured by OPHIR), it was about 2 mW.
[0038]
<Component measurement test>
After continuing the decomposition operation 30 minutes, the gas in the holder 1 taken housed in the sampling bag for gas sampling, alternating with ¹³ CO ₂ concentration and carbon dioxide in ¹³ CO ₂ concentration in the gas cylinder in the gas It was measured. The measurement interval was about 5 minutes. The reason why the measurement was performed a plurality of times alternately is to confirm the presence / absence of the difference between them and the degree of the difference more precisely and accurately. The gas stored in the sampling bag was measured by sampling from the sampling bag at every measurement time. A GC-MS (QP-500) manufactured by Shimadzu Corporation was used as a measuring device.
[0039]
FIG. 5 is a diagram showing the results. It is observed obvious difference between ¹³ CO ₂ concentration and carbon dioxide in ¹³ CO ₂ concentration in the gas cylinder of carbon dioxide gas passed through the degradation by infrared. FIG. 5 shows the result of measuring both times, and the average of the ¹³ CO ₂ concentration in the carbon dioxide gas in the gas cylinder (marked with ● in FIG. 5) was 1.09338%, whereas the infrared The average of the ¹³ CO ₂ concentration (marked with ■ in FIG. 5) in the carbon dioxide gas that had undergone the decomposition was 1.110166%. In contrast, ¹³ CO ₂ concentration is increased by about 0.0024 points by infrared irradiation.
[0040]
《Comparative example》
In the decomposition test of the example, the clathrate was decomposed in the same manner as in the example without irradiating infrared rays, and the gas in the holder 1 was collected and stored in the sampling bag in the same manner as the component measurement test in example 1. It was measured and ¹³ CO ₂ concentration and carbon dioxide in ¹³ CO ₂ concentration in the gas cylinder in the gas alternately. FIG. 6 shows the result. As shown in Fig. 6, the ¹³ CO ₂ concentration in the gas (marked with ■ in Fig. 6) and the ¹³ CO ₂ concentration in carbon dioxide in the gas cylinder (marked with ● in Fig. 6) show almost the same values, and there is a significant difference between them. Obviously not.
[0041]
【The invention's effect】
According to the present invention, the isolated isotope remains the same as the original molecule, one remains as a clathrate and the other moves into the gas phase, and the chemical form of the enriched isotope remains unchanged. Therefore, cascading is extremely easy and multi-stage concentration can be easily performed. Moreover, since it does not become a form of a hardly decomposable substance without being constrained by a chemical reaction unlike the laser method described above, the industrial handling is very easy. Furthermore, since the light whose wavelength is specified selectively acts only on the target isotope molecule, the selectivity is high and the separation factor is large. Because of this high selectivity, it is not necessary to use extra energy and the running cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a graph showing absorption spectra of ¹² CO ₂ and ¹³ CO ₂ .
FIG. 2 is a graph showing absorption spectra of ¹² CH ₄ and ¹³ CH ₄ .
FIG. 3 is a schematic diagram of the configuration of an experimental apparatus used in this example.
FIG. 4 is a diagram showing a transmittance spectrum of a filter by an experimental apparatus used in this example.
FIG. 5 is a diagram showing the amount of ¹³ CO ₂ in the gas phase obtained by infrared irradiation with clathrate and the amount of ¹³ CO ₂ in carbon dioxide with a natural isotope ratio.
FIG. 6 is a graph showing the amount of ¹³ CO ₂ in the gas phase and the amount of ¹³ CO ₂ in carbon dioxide having a natural isotope ratio obtained in the comparative example.
[Explanation of symbols]
1 Clasp generation holder 2 Roller for rotating holder 3 Rotational force transmission mechanism 4 Infrared light source 5 Filter 6 Freezer

Claims (6)

  By irradiating the clathrate with light having a wavelength that excites a guest molecule having a specific isotope atom as a constituent atom, the guest molecule composed of the specific isotope atom is selectively excited and separated. Thereby isolating the guest molecules composed of the specific isotope atoms in the gas phase. The isotope separation method according to claim 1, wherein the guest molecule is carbon monoxide or carbon dioxide. The isotope separation method according to claim 1 , wherein the guest molecule is a lower hydrocarbon such as methane, ethane, ethylene, propane, or butane. The isotope separation method according to claim 1 , wherein the guest molecule is argon, krypton, xenon, nitrogen, oxygen, or hydrogen sulfide. Host molecules of water constituting the clathrate, hydrogen sulfide, alcohols, amines, isotope separation method according to any one of claims 1-4 and organic acids or quinones.   Select a guest molecule composed of a specific isotope atom by irradiating the clathrate with water as a host molecule with light of a wavelength that excites the guest molecule having the specific isotope atom as a constituent atom. The isotope separation method is characterized in that the guest molecule composed of the specific isotope atom is concentrated in the aqueous phase by being excited and separated.

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