JP5620705B2 - Oxygen isotope enrichment method and oxygen isotope enrichment apparatus - Google Patents

Description

  The present invention relates to an oxygen isotope enrichment method and an oxygen isotope enrichment apparatus.

In general, as a method for concentrating oxygen isotopes, a method utilizing a photochemical reaction (hereinafter, photoreaction) is known.
For example, in Patent Document 1 and Patent Document 2, a laser is irradiated to an absorption line of ozone isotopologue containing a specific oxygen isotope contained in ozone, and a desired oxygen isotope ( ¹⁷ O Alternatively, a method for concentrating oxygen isotopes by selectively decomposing ozone containing ¹⁸ O) is disclosed. This photoreaction is performed under reduced pressure to avoid non-selective ozonolysis due to energy dissipation due to collisions between molecules.

  By the way, in order to separate the oxygen molecules purified by decomposing ozone by such a photoreaction from unreacted ozone, a mixed gas of ozone and oxygen is taken from an apparatus (photoreaction cell) that performs photoreaction, It is necessary to transfer to a separation device such as a distillation column.

  Generally, as a transfer method, (1) a transfer method by pressure increase using a compressor or the like, (2) a transfer method by a pressure difference in which the pressure condition of the latter stage is lower than that of the photoreaction cell, and (3) a dilution gas (4) A method of transferring the photoreaction product gas by liquefying it with a condenser and pressurizing it with a liquid head (liquid head pressure) )It has been known.

Japanese Patent Laid-Open No. 2004-261776 JP 2006-272090 A JP 2008-73656 A JP 2008-80200 A

  However, when the method (1) is adopted as a transfer method to a separation apparatus such as a distillation column, ozone is a substance unstable to heat, and therefore ozone may be decomposed by compression heat. As a result, unspecified ozone is decomposed into oxygen, and oxygen containing a desired oxygen isotope selectively generated by a photoreaction is diluted, so that it cannot be sufficiently concentrated. is there.

  Further, when the method (2) is employed, there is a problem that the operating conditions of the apparatus are remarkably limited because the latter apparatus (for example, the distillation column) needs to be at a lower pressure than the photoreaction apparatus.

  The method (3) is a batch operation because the transfer is performed by extrusion after completion of the photoreaction. As a result, when it is desired to obtain products continuously, it is necessary to prepare a plurality of photoreaction cells and supply them to a separation device such as a distillation tower with a time difference, but this increases the device cost. There is an inconvenience.

  The method (4) is a method in which a differential pressure is generated by the liquid head of the distillation component itself in the distillation column, and the gas is sent to an external photoreaction cell. Therefore, this method is also applied only to batch operation, and there is a problem that a product cannot be obtained continuously.

  Under such a background, a method for concentrating oxygen isotopes, in which a product can be continuously obtained by utilizing a photoreaction by a laser and does not cause any trouble when gas is sent from a photoreaction cell to a subsequent separation apparatus. However, there has been a demand for a device for concentrating oxygen and oxygen isotopes, but the actual situation is that an effective and appropriate device has not been provided.

In order to solve the above-mentioned problem, the invention according to claim 1 is an oxygen isotope enrichment method, wherein an ozonization step is performed in which a part of raw material oxygen is ozonized to obtain a first mixed fluid in which oxygen and ozone are mixed. A first distillation step in which the first mixed fluid and the diluted substance are introduced into a first distillation column and distilled to separate into a second mixed fluid in which ozone and the diluted substance are mixed, and oxygen; The second mixed fluid is irradiated with a laser to selectively decompose ozone containing an oxygen isotope and generate oxygen containing an oxygen isotope to obtain a third mixed fluid in which oxygen, ozone and the diluted substance are mixed. The third mixed fluid is led to the second distillation column by a photolysis step, a liquid reservoir introducing step for introducing the third mixed fluid into the liquid reservoir , and a liquid head pressure obtained by the liquid reservoir. A fourth mixed fluid which is distilled and consists of ozone and the diluted substance From the second distillation step for separating into product oxygen enriched with oxygen isotopic components, the ozone decomposition step for decomposing ozone in the fourth mixed fluid, and the fourth mixed fluid from which ozone has been decomposed, And a dilute substance recovery step of recovering the dilute substance.

The invention according to claim 2 has a diluted substance introduction step of introducing the diluted substance recovered by the diluted substance recovery step into the liquid reservoir , wherein oxygen isotope enrichment according to claim 1 is provided. Is the method.

  The invention according to claim 3 is the oxygen isotope enrichment method according to claim 1 or 2, wherein the diluted substance is krypton, xenon, radon, or carbon tetrafluoride.

The invention according to claim 4 is an apparatus for carrying out the oxygen isotope enrichment method according to any one of claims 1 to 3, comprising an ozonizer that ozonizes a part of raw material oxygen; The first distillation column for performing the first distillation step, a photoreaction cell for selectively decomposing ozone containing oxygen isotopes, the liquid reservoir into which the third mixed fluid is introduced, and the first An oxygen isotope concentrator comprising: the second distillation column that performs two distillation steps; an ozonolysis device that decomposes ozone; and a third distillation column that performs the diluted substance recovery step. is there.

  According to the present invention, oxygen isotopes can be sufficiently concentrated continuously by utilizing a photoreaction by a laser without significantly limiting the operating conditions of the apparatus.

It is a schematic block diagram which shows an example of the concentration apparatus of this invention.

Hereinafter, an oxygen isotope enrichment method and an oxygen isotope enrichment apparatus to which the present invention is applied will be described in detail with reference to the drawings.
The oxygen isotope enrichment method of the present embodiment includes an ozonization step, a first distillation step, a photolysis step, a liquid immersion portion introduction step (a liquid reservoir introduction step) , a second distillation step, and an ozonolysis. It has a configuration including a process and a diluted substance recovery process.

<Ozonization process>
First, as shown in FIG. 1, raw material oxygen is introduced into the ozonizer 1 to partially ozonize the raw material oxygen. Any ozonizer 1 may be used as long as it can generate ozone, and any known one may be used.
By this ozonization process, the first mixed fluid derived from the ozonizer 1 becomes a fluid in which oxygen and ozone are mixed.

<First distillation step>
Next, the first mixed fluid is introduced into the middle part of the first distillation column 2 and the valve 3 is operated to introduce the diluting substance and perform distillation. By this distillation, unnecessary oxygen is discharged from the top of the first distillation column 2, and a second mixed fluid in which concentrated ozone and a diluted substance are mixed is led out from the bottom of the column. In addition, the introduction position of the diluted substance may be either above or below the introduction part of the first mixed fluid. It is also possible to introduce a mixture with the first mixed fluid.
A part of oxygen derived from the top of the first distillation column 2 is introduced into the first condenser 4 and liquefied, and is introduced into the top of the first distillation column 2 as a first reflux liquid. Further, a part of the second mixed fluid led out from the bottom of the column is introduced into the first reboiler 5 and vaporized, and is introduced into the first distillation column 2 as the first rising gas.

The diluted substance is introduced for the purpose of preventing the ozone separated from the oxygen from being self-decomposed by being concentrated to a high concentration. Therefore, it is preferable to use a substance having the property of increasing the lower explosion limit of ozone when mixed with ozone. For example, a rare gas such as krypton (Kr), xenon (Xe), or radon (Rn) is used. Or trifluoromethane (CHF ₃ ) or carbon tetrafluoride (CF ₄ ) is preferably used.

<Photolysis process>
Next, the valve 6 is operated to introduce the remainder of the second mixed fluid derived from the bottom of the first distillation column 2 into the photoreaction cell 7. In the photoreaction cell 7, the laser is irradiated with a laser device (not shown), and the target isotope is concentrated as oxygen molecules.

Here, ozone isotopologue (molecular species including isotopes) includes ¹⁶ O ¹⁶ O ¹⁶ O, ¹⁶ O ¹⁶ O ¹⁷ O, ¹⁶ O ¹⁷ O ¹⁶ O, and a combination of oxygen isotopes and combinations thereof. ¹⁶ O ¹⁶ O ¹⁸ O, ¹⁶ O ¹⁸ O ¹⁶ O, ¹⁶ O ¹⁷ O ¹⁷ O, ¹⁷ O ¹⁶ O ¹⁷ O, ¹⁶ O ¹⁷ O ¹⁸ O, ¹⁷ O ¹⁶ O ¹⁸ O, ¹⁶ O ¹⁸ O ¹⁷ O, ¹⁷ O ¹⁷ O ¹⁷ O, ¹⁶ O ¹⁸ O ¹⁸ O, ¹⁸ O ¹⁶ O ¹⁸ O, ¹⁷ O ¹⁷ O ¹⁸ O, ¹⁷ O ¹⁸ O ¹⁷ O, ¹⁷ O ¹⁸ O ¹⁸ O, ¹⁸ O ¹⁷ O ¹⁸ O, ¹⁸ O There are 18 types of ¹⁸ O ¹⁸ O.

Of these isotopologues of ozone, laser light is irradiated to the absorption line of the isotopologue containing the oxygen isotope (for example, ¹⁸ O) to be enriched, so that the ozone of a specific isotopologue ( For example, ¹⁶ O ¹⁶ O ¹⁸ O, ¹⁶ O ¹⁷ O ¹⁸ O, ¹⁶ O ¹⁸ O ¹⁸ O, etc.) are decomposed into oxygen gas.

The decomposition of this ozone isotopologue is greatly affected by pressure and temperature conditions. When the pressure rises, the wavelength width of the absorption line broadens, called pressure broadening, and the light absorption lines between the isotopologues overlap. There is a problem that it cannot be selectively decomposed.
Therefore, in order to suppress this broadening of the absorption line, the decomposition of ozone in the photoreaction cell is performed under reduced pressure and low temperature. For example, the pressure and temperature conditions of the photoreaction cell are preferably 10 kPa or less, 100 K or more, 250 K or less.
By decomposing the target ozone as described above, the fluid derived from the photoreaction cell 7 becomes a third mixed fluid in which a small amount of oxygen, ozone, and a diluted substance are mixed.

<Immersion part introduction process (liquid reservoir introduction process) >
Next, by operating the valve 8, the third mixed fluid led out from the photoreaction cell 7 is liquefied by the second condenser 9 and dropped into the liquid immersion part (liquid reservoir part) 10 immediately below. In addition, for the purpose of shortening the apparatus startup time, it is preferable that the liquid immersion unit 10 is filled with a diluting substance so as to maintain a constant liquid level height at the apparatus startup stage. .
Further, during the operation of the apparatus, the diluted substance recovered from the third distillation column 25 is introduced into the liquid immersion unit 10 as described later.

<Second distillation step>
Next, the third mixed fluid and the diluted substance led out from the tower bottom of the liquid immersion unit 10 are introduced into the second distillation tower 21 and distilled. By this distillation, product oxygen enriched with the target oxygen isotope is derived from the top of the second distillation column 21, and a fourth mixed fluid composed of ozone and a diluting substance is derived from the bottom of the column. .
Most of the product oxygen derived from the top of the second distillation column 21 is recovered as a product, but a part is introduced into the third condenser 22 to be liquefied, and the second distillation column 21 is used as the second reflux liquid. It is introduced at the top of the tower. In addition, a part of the fourth mixed fluid led out from the tower bottom is introduced into the second reboiler 23 and vaporized, and is introduced into the second distillation tower 21 as the second rising gas.

<Ozone decomposition process>
Next, the remainder of the fourth mixed fluid led out from the bottom of the second distillation column 21 is passed through the ozone decomposition catalyst 24, and ozone is completely decomposed. Thereby, only the oxygen and the diluted substance are included in the fourth mixed fluid after the ozonolysis.

<Diluted substance recovery process>
Next, a fourth mixed fluid consisting only of oxygen and diluted substances after ozonolysis is introduced into the third distillation column 25. From the top of the third distillation column 25, oxygen having a reduced isotope concentration, which is a low boiling point component, is led out as exhaust gas. A part of the exhaust gas led out from the top of the third distillation column 25 is introduced into the fourth condenser 26 and liquefied, and is introduced into the top of the third distillation column 25 as a third reflux liquid. A part of the diluted substance led out from the bottom of the column is introduced into the third reboiler 27 and vaporized, and is introduced into the third distillation column 25 as a third rising gas.
Further, the remainder of the diluted substance derived from the bottom of the third distillation column 25 is circulated to the first distillation column 2 and the liquid immersion unit 10. Specifically, the diluted substance derived from the bottom of the third distillation column is pressurized by the pump 28 and the valve 3 is operated to operate the valve 29 and the valve 29 to operate the liquid immersion unit. 10 is introduced.

In the present embodiment, the liquid immersion unit 10 provided separately from the second distillation column 21 with the third mixed fluid mixed with oxygen molecules containing the target oxygen isotope purified by decomposing ozone by photoreaction. It is dripped and introduced. Then, the third mixed fluid is introduced into the second distillation column 21 using the liquid head of the liquid immersion unit 10. That is, in the present embodiment, oxygen molecules of the target isotope can be transferred without using a compressor or the like when transferring to the second distillation column 21 to decompose from unreacted ozone.
In addition, the operating conditions of the second distillation column 21 are not made lower than those of the photoreaction cell 7, and there are no restrictions on the operating conditions.
Moreover, since it introduce | transduces using the liquid head of the immersion part 10 provided separately from the 2nd distillation column 21, a continuous product can also be refine | purified.

  In the present embodiment, not only the third mixed fluid but also a diluted substance is introduced into the liquid immersion unit 10. As a result, even if the flow rate of the third mixed fluid derived from the photoreaction cell 7 is small, a desired liquid head can be obtained by introducing the diluted substance into the liquid immersion unit 10, so that the apparatus can be The raising time can also be shortened.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not restrict | limited to the following Example at all.
In this embodiment, a simulation for producing product oxygen is performed using the oxygen isotope concentrator shown in FIG. 1. In the following, it is necessary to obtain a desired liquid head particularly in the liquid immersion portion. Consider the liquid level.

First, raw material oxygen is introduced into an ozonizer so that a part of the raw material oxygen is ozonized. Thereafter, CF ₄ which is a diluted substance is introduced into the first distillation column, and a mixed fluid of CF ₄ and ozone is obtained from the bottom of the first distillation column.
Then, by introducing the mixed fluid into the photoreaction cell, decomposing only isotopic ozone ^{(16 O} 16 ^{O 17 O)} comprising (in ¹⁷ O in this example) an oxygen isotope of interest. During the decomposition of ozone, a reaction represented by the following formula (1) occurs.

The pressure and temperature conditions of the photoreaction cell are low temperature and reduced pressure conditions to suppress non-selective decomposition of ozone, specifically, 10 kPa and −100 ° C.
Note that the first distillation column is operated at the same or slightly higher pressure as the photoreaction cell, taking into account that pipe pressure loss occurs during gas transportation.

  The second distillation column is operated under a pressure of 140 kPa. By setting the atmospheric pressure or higher in this way, it is not necessary to use power such as a compressor when extracting product oxygen from the second distillation column.

  The flow rate of the third mixed fluid led out from the photoreaction cell to the second distillation column can be calculated from the mass balance of oxygen in the second distillation column and the photoreaction cell. That is, there is a relationship represented by the following formula (2) between the amount of oxygen derived from the photoreaction cell and the amount of oxygen derived from the top of the second distillation column.

Here, the oxygen volume ratio in the photoreaction cell _discharge fluid is X _O2,2 , the total amount of the photoreaction cell _discharge fluid is Q ₂ , the oxygen volume ratio in the second distillation column top _discharge fluid is X _O2,3 , Rewriting equation (2) with Q ₃ as the total amount of fluid derived from the top of the two distillation towers, the following equation (3) is obtained. Note that the subscript i in X _{i, j} and Q _j is the substance name, j is the position on the process, j = 1 is the time when the photoreaction cell is introduced, j = 2 is the time when the photoreaction cell is derived, j = 3 indicates the time when the second distillation column top is derived.

If it is assumed that 5 kg of H ₂ ¹⁷ O containing 10 atom% of the oxygen isotope ¹⁷ O is produced annually in this apparatus, the volume flow rate X _O2,3 · Q _{3 of} product oxygen derived from the top of the second distillation column Is 0.0056 L / min (0 ° C., 1 atm).
The oxygen isotope ¹⁷ O concentration in oxygen is independent of the production amount of product oxygen, and depends on the selectivity of ozone isotopologue in the photoreaction process.

Further, the higher the ozone concentration in the photoreaction cell, the better, but the handling in safety becomes difficult accordingly. Here, it is assumed that the ozone concentration X _O3,1 = 0.15 in the photoreaction cell introduction fluid and the diluted substance concentration _XCF4,1 = 0.85 in the _{photoreaction} cell introduction fluid.
At this time, the concentration ratio Y of the specific ozone isotopologue to the total ozone at the photoreaction cell inlet is calculated.

First, pure oxygen gas having an isotope composition ratio of Table 1 is used as raw material oxygen. This is distributed to an ozonizer to generate ozone. At this time, it is assumed that the isotope effect during ozone generation is almost negligible. That is, the abundance ratio of isotopologue ¹⁶ O ¹⁶ O ¹⁷ O in ozone may be calculated as the probability that each decomposed oxygen atom is bonded, as shown in Table 2. When Y ₆₆₇ is the abundance ratio of ¹⁶ O ¹⁶ O ¹⁷ O in ozone, Y ₆₆₇ = 0.014.

The decomposition rate of the decomposition reaction of ¹⁶ O ¹⁶ O ¹⁷ O by the laser can be adjusted to an arbitrary value by adjusting the optical path length of the photoreaction cell 7 or the light intensity of the laser. Here, it is assumed that the ¹⁶ O ¹⁶ O ¹⁷ O component of the ozone isotopologue is decomposed to the decomposition rate Z = 0.80 at the outlet of the photoreaction cell, and the amount of oxygen generated in the photoreaction cell outlet fluid at that time X _O2,2 · Q _O2,2 has a relationship represented by the following formula (4).

Here, a coefficient of 1.5 in the formula means that 1.5 oxygen molecules are generated per ozone molecule decomposition, and one atomic oxygen generated by the ozonolysis reaction shown in the equation (1) is ozone. When one piece is assumed to be decomposed, it is obtained from the stoichiometric formula.
From the above, Q ₁ = 2.21 L / min (0 ° C., 1 atm) is obtained from the above formula (3) and the above formula (4).

  By the way, in order to transport the fluid from the photoreaction cell to the second distillation column, it is necessary to obtain a liquid head that generates a differential pressure of 140 kPa or higher in the column at least in the liquid immersion part. The pressure loss due to the piping and the valve is added to this, and here, a liquid head corresponding to a differential pressure of 190 kPa is set up.

First, the liquid density P of the ozone mixed solution at a pressure of 190 kPa is calculated.
The liquid density of CF ₄ under a vapor-liquid equilibrium at 190 kPa is P _CF4 = 1550.9 kg / m ³ . Further, the liquid density of ozone is calculated from the estimation formula described in AG Streng, Table of ozone properties, J. Chem. Eng. Data, 1961, 6 (3), p.431-436, P _O3 = 1373. 9 kg / m ³ .

Oxygen in the liquid immersion part is negligible because it contains only oxygen generated in the photoreaction cell and has little effect on the liquid density. Therefore, the density P of the ozone mixture is 1524.3 kg / m ³ .

Here, assuming that the liquid density in the liquid immersion part is uniform, the required liquid level height h is h = 12.72 m. The actual liquid level of the liquid immersion part is determined by giving the above-described liquid level height h a safety factor necessary for design.
Since a sufficient liquid head can be obtained by designing the liquid immersion part in this way, a mixture of oxygen containing the target oxygen isotope derived from the photoreaction cell, ozone, and CF ₄ is used. The fluid can be introduced into the second distillation column without using a compressor or the like.

If the liquid immersion tube is a 15A stainless steel tube with an inner diameter of 18.4 mm, the minimum liquid volume V required to obtain the liquid head is 3.38 L, which is 1400. 6L (0 ° C., 1 atm).
Therefore, the time t until the head height h necessary for the liquid immersion portion is accumulated is about 10.6 hours as shown in the following formula (5).

In actual equipment, the pipe length is further increased, such as adding a vent to the pipe in order to disperse the stress caused by the pipe shrinkage during cooling. become longer.
Therefore, if CF ₄ is introduced to the liquid immersion part up to the head height h from the start-up stage of the apparatus, there is no need to wait for the waiting time t, and the apparatus start-up time can be shortened.

After the introduction into the second distillation column, product oxygen is extracted from the top of the second distillation column by distillation as in the embodiment, and a fourth mixed fluid composed of ozone and CF ₄ is extracted from the bottom of the column. To derive. And a part of 4th mixed fluid distribute | circulates an ozone decomposition catalyst, and, thereby, ozone decomposes | disassembles completely. Thereafter, the fourth mixed fluid is introduced into the third distillation column, oxygen is led out as exhaust gas from the top, and CF ₄ is led out from the bottom. CF ₄ led out from the bottom of the third distillation column is pressurized by a pump and refluxed to the first distillation column and the liquid immersion part.

DESCRIPTION OF SYMBOLS 1 ... Ozonizer, 2 ... 1st distillation tower, 7 ... Photoreaction cell, 10 ... Liquid immersion part, 21 ... 2nd distillation tower, 24 ... Ozone decomposition apparatus, 25. ..Third distillation tower

Claims (4)

An oxygen isotope enrichment method comprising:
Ozonization step of obtaining a first mixed fluid in which part of raw material oxygen is ozonized and oxygen and ozone are mixed;
A first distillation step in which the first mixed fluid and the diluting substance are introduced into a first distillation column to be distilled, and separated into ozone, a second mixed fluid in which the diluting substance is mixed, and oxygen;
The second mixed fluid is irradiated with a laser, ozone containing oxygen isotopes is selectively decomposed, oxygen containing oxygen isotopes is generated, and a third mixed fluid in which oxygen, ozone and the diluent are mixed is produced. A photolysis process to obtain;
A liquid reservoir introducing step of introducing the third mixed fluid into the liquid reservoir ;
Due to the liquid head pressure obtained by the liquid reservoir , the third mixed fluid was led to the second distillation column and distilled to concentrate the fourth mixed fluid composed of ozone and the diluted substance, and the oxygen isotope component. A second distillation step for separating into product oxygen;
An ozonolysis step of decomposing ozone in the fourth mixed fluid;
A diluted substance recovery step of recovering the diluted substance from the fourth mixed fluid in which ozone is decomposed;
A method for concentrating oxygen isotopes, comprising: The method for concentrating oxygen isotopes according to claim 1, further comprising a diluting substance introducing step of introducing the diluting substance collected in the diluting substance collecting step into the liquid reservoir .   The oxygen isotope enrichment method according to claim 1 or 2, wherein the diluted substance is krypton, xenon, radon, or carbon tetrafluoride. An apparatus for carrying out the oxygen isotope enrichment method according to any one of claims 1 to 3,
An ozonizer that ozonizes part of the raw material oxygen;
The first distillation column for performing the first distillation step;
A photoreaction cell for selectively decomposing ozone containing oxygen isotopes;
The liquid reservoir into which the third mixed fluid is introduced;
The second distillation column for performing the second distillation step;
An ozonolysis device that decomposes ozone;
And a third distillation column for carrying out the diluted substance recovery step.

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