JP6978042B2 - Oxygen isotope separation method and separation device - Google Patents

Description

The present invention relates to a method for separating an oxygen isotope that separates ¹⁶ O and ¹⁸ O from a mixed gas of ^{oxygen 16} O and oxygen ^{18 O, and a separation device using this separation method.}

The abundance ratios of oxygen isotopes ¹⁶ O, ¹⁷ O, and ¹⁸ O in nature are 99.759%, 0.037%, and 0.204%, respectively. Of these oxygen isotopes, ¹⁸ O has been in great demand in recent years for biomedical research, diagnosis of tumor cells, and the like. However, the conventional oxygen isotope separation method has a problem that the treatment process is long, a large amount of energy is required, and the cost is high, so that the effective utilization of the oxygen isotope in the medical field and the like is hindered.

The most commonly used method for separating oxygen isotopes is the method of distilling water. In the distillation method, the difference in vapor pressure between _{H 2} O ¹⁶ and H ₂ O ^{18 is used to obtain 18} O rich water H ₂ O ¹⁸ . However, concentration by this method requires a very long column. Non-Patent Document 1 describes that the oxygen isotope enrichment factor (α) at 320K is 1.007.
As another method for concentrating oxygen isotopes, there is a method of combining cryogenic distillation and water distillation (Patent Documents 1 and 2). In this method, a huge distillation column (~ 500 m) is used, and the concentration of ¹⁸ O is increased from 0.2% to 95% by taking a long time (1 to 6 months) for concentration.
Further, as another industrial method, there is a method using low temperature distillation of nitric oxide (Non-Patent Documents 2 and 3). This method enables efficient distillation of oxygen isotopes by utilizing isotropic nitric oxide.
Further, a method of cryogenic distillation using oxygen containing a heavy oxygen isotope as a starting material has been reported (Patent Document 3).

As another method, there is a method using chromatography (Patent Document 4). Further, a method of separating oxygen isotopes having the same energy and different molecular weights by using the principle of thermal diffusion has been reported (Non-Patent Documents 4 and 5). Further, a method of separating using a semipermeable membrane has also been reported (Patent Documents 5, 6, 7 and Non-Patent Documents 6, 7). In these, ^{the concentration of 18} O in natural water is performed using a semipermeable membrane prior to the distillation treatment. Patent Document 8 describes a method of using a semipermeable membrane in multiple stages in an AGMD (Air Gap Membrane Distillation) system that separates oxygen isotopes by applying pressure.
In the 1980s, a method of separation using a laser including an argon fluoride (ArF) laser was performed (Patent Document 9). There, a method of light dissociation of oxygen gas containing ¹⁷ O or ^{18 O as a nuclide is used.} A method of using an optical fiber has been proposed as a method of utilizing a high-energy laser beam (Patent Documents 10 and 11). In this method, ozone gas containing oxygen isotopes is decomposed into oxygen or peroxide using a photodissociation method to concentrate oxygen isotopes, and the treatment process is simple and the treatment time is short. , Has not yet been realized as a commercial method.

US Patent Nos. 6,321,565 US Patent Nos. 7,493,447 US Patent No.6,461,583 B1 US Patent No. 2011/0139001 A1 US Patent Nos. 5,057,225 US Patent Nos. 5,084,181 US Patent Nos. 7,638,059B2 US Patent No.7,638,059 B2 US Patent no. 4,437,958A WO 2013077528 A1 US Patent No. 7,893,377B2 Japanese Unexamined Patent Publication No. 2013-31833

Thode et al. Canadian Journal of Research, 1944,22, 127-136 I & EC Process Design and Development, 1965, 4 (1), 35-42 Annals of the University of Craiova, Electrical Engi. Series, 2006, 30, 399-403 I. Lauder Trans.Faraday Soc., 1947, 43, 620-630 Sherrerd B. Welles Physical. Review, 1946,69 (11 & 12), 586-589 Separation Science and Technology, 1997, 32 (1-4), 527-539 Ind. Eng. Chem. Res., 2009, 48, 5431-5438

The inventor of the present invention ^{has proposed a method for separating carbon isotopes 12} C and ¹⁴ C using the quantum molecular sieving effect (Patent Document 12). The method is a method of separating activated carbon fibers as an adsorbent from a methane isotope mixed gas ( ¹² CH ₄ , ¹⁴ CH _4). However, it is difficult to predict whether activated carbon fibers can be similarly used for the separation of oxygen isotopes, and it is also unclear whether they can be effectively used as an industrial separation method.
It is an object of the present invention to clarify that activated carbon fibers can be used for oxygen isotope separation, and to provide an oxygen isotope separation method and a separation device suitable as an oxygen isotope separation method.

The method for separating oxygen isotopes according to the present invention is a method for separating oxygen isotopes using activated carbon fibers as an adsorbent, and a) oxygen isotopes containing ¹⁸ O ₂ and ¹⁶ O _2. By the step of adsorbing the body gas to the adsorbent, b) the step of desorbing the oxygen isotope gas adsorbed by the adsorbent from the adsorbent, and the step of recovering the desorbed gas, and c) the step b). ^{It comprises a step of measuring the concentration of 18} O ₂ and ¹⁶ O ₂ in the desorbed gas desorbed from the adsorbent, and in the step a), the adsorbent is applied to ¹⁸ O ₂ and ¹⁶ O ₂ . controls the separation factor _{^{S (18 O 2/16 O}} 2)> 1 and comprising temperature, the c) in the process, the when the concentration of ¹⁸ O ₂ in the desorbed gas is less than the predetermined concentration above a) step And b) are repeated in this order, ^{and when the concentration of 18} O ₂ in the desorbed gas becomes a predetermined concentration or more, the step of concentrating the oxygen isotope gas is stopped.
Further, it is characterized by comprising a step of discharging unadsorbed gas not adsorbed by the adsorbent, following the step a).
Further, in the step a), by keeping the temperature of the adsorbent at 77K to 130K ^{, 18} O ₂ can be efficiently separated from the gas containing ¹⁸ O ₂ and ¹⁶ O _2. ..
Further, as the activated carbon fiber, it is effective to use an activated carbon fiber having an average pore diameter of 0.65 nm to 1.1 nm.
^{Further, in the step a), 18} O ₂ can be efficiently separated by setting the time for contacting the oxygen isotope gas with the adsorbent to be about 10 minutes.

Further, the oxygen isotope separating device according to the present invention has a chamber in which activated carbon fibers are contained as an adsorbent, a mechanism for supplying a gas containing the oxygen isotope to the chamber, and the oxygen isotope in the chamber. After introducing the contained gas, a discharge mechanism for discharging the gas not adsorbed by the adsorbent, a desorption mechanism for desorbing the gas adsorbed by the adsorbent from the adsorbent, and desorption from the adsorbent. Based on the ^{measurement mechanism that measures the concentrations of 18} O ₂ and ¹⁶ O ₂ in the desorbed gas, the temperature control mechanism that controls the temperature of the adsorbent contained in the chamber, and the measurement results by the measurement mechanism. The temperature of the adsorbent is controlled by a temperature control mechanism ^{, and when the concentration of 18} O _{2 in} the desorbed gas is less than a predetermined concentration, the desorbed gas is used as an adsorbent in the chamber containing the activated carbon fiber. It is characterized by having a control mechanism for stopping the operation of separating the oxygen isotope gas when the concentration ^{of 18} O ₂ in the desorbed gas becomes a predetermined concentration or more.
Further, the temperature control mechanism, the adsorbent, ¹⁸ O ₂ and ¹⁶ O ₂ separation factor _{^{S (18 O 2/16 O}} 2)> , characterized in that it comprises means for controlling the first and becomes temperature.

According to the oxygen isotope separation method and separation device according to the present invention, ¹⁸ O ₂ and ¹⁶ O ₂ can be separated efficiently and easily, and ^{the application of 18} O ₂ to the medical field can be easily performed. It is possible to make effective use of ¹⁸ O _2.

Nitrogen adsorption isotherms obtained for three types of activated carbon fiber samples, ACF1, ACF2, and ACF3. It is explanatory drawing which shows the fluctuation of oxygen molecule at room temperature and low temperature where a quantum effect occurs. It is explanatory drawing which shows the action of selectively adsorbing and separating an oxygen isotope by activated carbon fiber. It is a block diagram which shows the structure of the separation apparatus used in the experiment which separated ¹⁸ O ₂ from the mixed gas of ¹⁸ O ₂ and ¹⁶ O _2. Sample ACF-1 (w = 0.65nm) , ACF-2 (w = 0.85nm), ACF-3 for (w = 1.1nm), the time variation of the separation factor _{^{S (18 O 2/16 O}} 2) in the 112K It is a graph which shows the measurement result. Sample ACF-1 (w = 0.65nm) , ACF-2 (w = 0.85nm), ACF-3 for (w = 1.1nm), the time variation of the separation factor _{^{S (18 O 2/16 O}} 2) in the 130K It is a graph which shows the measurement result. It is a flow chart which shows the separation method which separates ¹⁸ O ₂ from the gas containing an oxygen isotope.

(Adsorption action of activated carbon fiber on oxygen isotope)
The method for separating oxygen isotopes according to the present invention utilizes the selective adsorption action of activated carbon fibers (fibrous activated carbon) for different oxygen isotopes. Activated carbon fibers have extremely fine nano-regional pores, such as 1 nm or less, and the scale of such micro-regions is the same size as the Dobroy wavelength of the molecule, which is a measure of quantum action. This quantum action causes the activated carbon fibers to have different adsorptivity for different oxygen isotopes. The difference in adsorptivity to isotope oxygen becomes larger as the temperature becomes lower. Therefore, in order to separate the isotope oxygen using activated carbon fibers, it is effective to perform a separation operation at a lower temperature.

^{The molecular weight of 18} O, which is an isotope of oxygen, is 36 g / amu, ^{the molecular weight of 16} O is 32 g / amu, and the difference in molecular weight is 4 g / amu. It is an essential factor in the difference in adsorptivity. That is, the action that causes a difference in adsorptivity to activated carbon fibers is also called the quantum molecular sieving action, because ¹⁸ O ₂ ^{constituting the mixed gas of oxygen isotopes is heavier than 16} O _{2 and} therefore the Dobroy wavelength (molecular). Fluctuation) is ^{smaller than 16} O _{2 and} more easily adsorbed (easily penetrates) into the pores of activated carbon fibers ^{than 16} O ₂ ^{(easily penetrates), and 16} O ₂ is ^{larger than 18} O _{2 and} therefore less likely to enter the pores. be.
The thermal de Broglie wavelength becomes longer at lower temperatures and shorter at higher masses. This is the reason why the difference in adsorptivity between ¹⁸ O ₂ and ¹⁶ O ₂ increases at low temperatures.

The reason why a difference in adsorptive ¹⁶ O ₂ and ¹⁸ O ₂ for activated carbon fibers occurs, whether explanation that is due to quantum molecular sieving action is correct, is currently unknown. In the present invention, ^{as a method for separating the oxygen isotopes 18} O and ¹⁶ O, a method for separating the isotope oxygen gases ¹⁸ O ₂ and ¹⁶ O ₂ as treatment targets is proposed. When the oxygen gas is separated as a target in this way, when the oxygen gas is adsorbed in the pores of the activated carbon fiber, when ¹⁶ O is adsorbed in the ^{pores, the other 16} O pair is drawn in. In this way, it is adsorbed as ⁽¹⁶ O ₂ ) ₂ ^{, and when 18} O is adsorbed, it is adsorbed as ⁽¹⁸ O ₂ ) ₂ by drawing in ^{another pair of 18 O. In this way, the reason why 16} O ₂ or ¹⁸ O ₂ are adsorbed in pairs when oxygen gas is adsorbed on the activated carbon fiber is that when _{O 2} is adsorbed in the pores, it is adsorbed as a pair. _{This is because stable (O 2} ) ₂ is generated when the frequency of the vibration in which the space between the oxygen atoms expands and contracts is the same. As a result, it is considered that the selective adsorption action of ¹⁸ O ₂ and ¹⁶ O _{2 occurs.} Regarding the fact that the vibration between paired oxygen atoms affects the selective adsorption of the activated carbon fibers, the adsorption when the mixed gas of ¹⁶ O ₂ and ¹⁸ O _{2 is adsorbed on the activated carbon fibers.} It is also estimated from the measurement results of the time change of the adsorption rate from the start.

In the oxygen isotope separation method according to the present invention, the oxygen isotope gas is targeted for separation, and the oxygen isotope is separated using activated carbon fiber as an adsorbent. The Dobroy wavelength of the oxygen isotope gas is shorter for ¹⁸ O ₂ , which is heavier than ¹⁶ O ₂ ^{, that is, the fluctuation of 18} O ₂ ^{is smaller, so that 18} O ₂ is more likely to be adsorbed in the micropores of the activated carbon fiber. .. ^{The difference in fluctuation (difference in magnitude) between 18} O ₂ and ¹⁶ O ₂ increases as the temperature decreases. Therefore, in order to separate more efficiently, it is better to adsorb the oxygen isotope gas to the activated carbon fiber at a lower temperature. Is good. According to the experiment, a separation coefficient of 1.2 or more, which exceeds the conventional separation coefficient of 1.002 for ¹⁸ O ₂ and ¹⁶ O ₂ , was obtained at 112 K and 130 K as well as at a liquid nitrogen temperature of 77 K.
^{In the method of the present invention, 18} O ₂ and ¹⁶ O ₂ are separated only by the operation of adsorbing oxygen isotope gas to the activated carbon fiber at a low temperature. Therefore, the separation operation is extremely simple, and the operation for concentration is adsorption. It is essential to repeatedly adsorb the oxygen isotope gas to the agent (activated carbon fiber), but according to the method of the present invention, ¹⁸ O ₂ can be concentrated much more easily than the conventional concentration method. be.

(Activated carbon fiber)
FIG. 1 is a nitrogen adsorption isotherm measured at 77K for three types of samples of activated carbon fiber (ACF) used as an adsorbent. The average pore diameter w of the three samples ACF1, ACF2, and ACF3 at 77K is ACF1: w = 0.65 nm, ACF2: w = 0.85 nm, and ACF3: w = 1.1 nm, respectively.
The activated carbon fiber is made of carbon fiber activated by using pitch as a raw material, and is used after being vacuum exhausted at 110 ° C. for 2 hours or more in order to remove adsorbed water vapor in the pores of the commercially available activated carbon fiber. did.
The experiment for acquiring the nitrogen adsorption isotherm shown in FIG. 1 was performed by preheating each sample under vacuum (1 mPa) at 423 K for 3 hours.

The nitrogen adsorption isotherm shown in FIG. 1 indicates that the amount of nitrogen adsorbed on the activated carbon fiber increases as the pore diameter of the activated carbon fiber increases. It also shows that the amount adsorbed on the activated carbon fiber becomes saturated as the partial pressure of nitrogen increases.
Table 1 shows the structural parameters calculated from the equilibrium state of the nitrogen adsorption isotherm for the three samples ACF1, ACF2, and ACF3.
The average pore diameter w and pore volume of each sample _{were determined by α s-} plot analysis, and the specific surface area was determined based on the Brunauer-Emmett-Teller theory (BET).

In Table 1, the samples ACF3 has a specific surface area of 1660m ² g ^-1, a pore volume of 0.81Mlg ^-1, pore diameter is 1.1 nm. For samples ACF2 has a specific surface area of 760 m ² g ^-1, a pore volume of 0.38Mlg ^-1, pore diameter is 0.85 nm. For samples ACF1 has a specific surface area of 520m ² g ^-1, a pore volume of 0.27Mlg ^-1, pore diameter is 0.65 nm.

(Dobroy wavelength of oxygen molecule)
FIG. 2 shows oxygen molecules at room temperature and at a temperature lower than room temperature under quantum action.
As shown in FIG. 2, classical oxygen molecules do not change in size between ¹⁶ O ₂ ^{and 18} O _{2 at room temperature.} However, at low temperatures, the de Broglie wavelengths (λ / nm) of ¹⁶ O ₂ and ¹⁸ O ₂ become different due to the action of quantum fluctuations.
Table 2 shows the thermal de Broglie wavelengths at 130K, 112K, and 77K for ¹⁶ O ₂ and ¹⁸ O _2.

Table 2, 112K from 130K, the temperature to 77K ^{falls, 16} O ₂ also ¹⁸ O ₂ also de Broglie wavelength is gradually longer and ^the difference between the de Broglie wavelength of ¹⁶ O ₂ and ¹⁸ O ₂ is from 130K By lowering to 77K, it is shown that it expands from 0.0016 nm to 0.002 nm. That is, at 77K, the size of the ¹⁸ O ₂ molecule is 0.002 nm smaller than that ^{of 16} O _{2 compared to 130 K.}
In Figure 2, at low ^{temperatures,} the fluctuation of ¹⁶ O ₂ becomes larger than the fluctuation of ¹⁸ O ^{_2, 16} O ₂ molecular size is larger than ¹⁸ O _2, shows that the interaction between atoms is reduced There is. Thus, is possible to enlarge the difference between the ¹⁶ O ₂ and the ¹⁸ O ₂ size at low temperatures, the difference in adsorptivity for activated carbon fibers of ¹⁶ O ₂ and ¹⁸ O ₂ is the reason why becomes remarkable at a low temperature.

FIG. 3 shows the action of selectively separating oxygen isotopes using activated carbon fibers.
At 77K, the oxygen molecule ¹⁸ O ₂ (dark color) is 0.002 nm smaller than the ^{oxygen molecule 16} O ₂ (light color), so it is easier to be captured in the pores of the activated carbon fiber ^{than 16} O _2. , ¹⁶ O ₂ is selectively adsorbed on activated carbon fibers.
Separation factor _{^{S (18 O 2/16 O}} 2) is the ratio of the number _{^{n 18 O 2, n 16 O}} 2 oxygen isotopes in front of the gas passing through the adsorbent, oxygen isotopes adsorbed on the adsorbent It is defined by the ratio of the number of bodies (n ¹⁸ O ₂ / n ¹⁶ O _2).
That is,
_{^{S (18 O 2/16 O}} 2)> 1 18 O 2 is selectively adsorbed by and _{^{S (18 O 2/16 O}} 2) = 1 no selectivity _{^{S (18 O 2/16 O}} 2) < It means that 1 ¹⁶ O ₂ is selectively adsorbed.

S> 1, from the number ratio of oxygen isotopes adsorbed on the adsorbent _{^{(n 18 O 2 / n 16}} O 2) is the number ratio of the mixed gas before adsorption _{^{(n 18 O 2 / n 16}} O 2) It is also large, which means that ¹⁸ O ₂ was selectively adsorbed by the adsorbent as compared with ¹⁶ O _2. Therefore, the larger the separation coefficient S is, the more efficiently the separation between ¹⁸ O ₂ ^{and 16} O _{2 is performed.}
The separation coefficient S in the case of the conventional distillation method as an oxygen isotope separation method is about 1.002, and any separation method exceeding this separation coefficient can be effectively used as an oxygen isotope separation method. ..

(Separation experiment device)
FIG. 4 shows the configuration of the separator used in the experiment to separate ¹⁸ O ₂ from the mixed gas ^{of 18} O ₂ and ¹⁶ O _2.
This separator is ^{a cylinder T1, T2, T3 filled with 16} O ₂ , ¹⁸ O _2, and helium gas, respectively, and a controller C1 attached to these cylinders T1, T2, T3 to adjust the gas flow rate. , C2, C3, ^{reservoir S1 for storing mixed gas of 16} O ₂ and ¹⁸ O ₂ , reservoir S 2 for storing gas for mass spectrometry, reservoir S 3 for storing concentrated gas of ¹⁸ O _{2, and adsorption.} A chamber 10 containing the agent 20 is provided.

The cylinders T1, T2 and T3 are connected to the reservoir S1 via the controllers C1, C2 and C3 and the valves V1 and V3, and are connected to the vacuum pump P1 via the valve V2.
The reservoir S1 is connected to the chamber 10 via the valve V3 and the valve V4, and is connected to the vacuum pump P2 via the valve V10.
The chamber 10 is connected to the reservoir S3 via valves V5 and V8, and is connected to the vacuum pump P2 via the valve V5. Further, it is connected to the reservoir S2 via the valves V5 and V6.
The reservoir S2 is connected to the mass spectrometer MS via the valve V7, and is connected to the vacuum pump P3 via the valves V7 and V6.

^{An experiment for separating 16} O ₂ and ¹⁸ O ₂ using the separation device shown in FIG. 4 was performed by the following method.
First, a treatment for removing water and gas adsorbed on the adsorbent (activated carbon fiber) 20 filled in the chamber 10 is performed (cleaning treatment of the adsorbent).
To preheat the adsorbent, the piping part is completely vacuum-sucked by the vacuum pumps P1, P2, and P3, then the valves V4, V6, V8, and V9 are closed, the valve V5 is opened, and the chamber is vacuum-sucked by the vacuum pump P2. 10 was heat-treated at 150 ° C. for 3 hours.

Next, a mixed gas of oxygen isotopes for treatment is introduced into the reservoir S1 (step of preparing the mixed gas).
^{In the experiment, 18} O ₂ and ¹⁶ O ₂ were introduced into the reservoir S1 in equal amounts while controlling the flow rates ^{of 18} O ₂ and ¹⁶ O ₂ by the controllers C1 and C2. The operation of introducing into the reservoir S1 was performed using the differential pressure. In the reservoir S1, ^{the mixed gas of 18} O ₂ and ¹⁶ O ₂ was held for 24 hours, and the gas was mixed uniformly.
The molar concentrations of ¹⁸ O ₂ and ¹⁶ O ₂ of the reservoir S1 were analyzed by sending a predetermined amount of mixed gas from the reservoir S1 to the reservoir S2 for analysis and using a mass spectrometer MS.

Next, a mixed gas of oxygen isotopes is introduced from the reservoir S1 into the chamber 10, and the mixed gas of oxygen isotopes is adsorbed on the adsorbent 20 filled in the chamber 10 (step of adsorbing the mixed gas on the adsorbent). .. The oxygen conductor gas stored in the reservoir S1 is introduced into the chamber 10 by a differential pressure by opening the valves V3 and V4.
When the oxygen isotope gas was introduced into the chamber 10, the temperature of the adsorbent 20 was controlled to a low temperature by using a cryopump.

An oxygen isotope gas is introduced into the chamber 10, and after a certain period of time has passed, the oxygen isotope gas not adsorbed by the adsorbent 20 is trapped in the reservoir S2. The molar concentration of the oxygen isotope gas trapped in the reservoir S2 is analyzed by the mass spectrometer MS in the operation of adsorbing the mixed gas to the adsorbent.

Next, the oxygen isotope gas adsorbed on the adsorbent 20 is desorbed from the adsorbent 20 (desorption treatment step). The operation of desorbing the oxygen isotope gas adsorbed on the adsorbent 20 from the adsorbent 20 is performed by raising the temperature of the chamber 10 with a cryopump. By closing the valves V4 and V6 and opening the valves 5 and 8, the oxygen isotope gas adsorbed on the adsorbent 20 is desorbed from the adsorbent 20 and introduced into the reservoir S3.

After introducing a mixed gas of oxygen isotopes desorbed from the adsorbent 20 into the reservoir S3, the chamber 10 is heated to 150 ° C. and vacuum sucked for 3 hours to purify the adsorbent 20 (cleaning of the adsorbent). Chemical processing).
Next, with the chamber 10 cooled to a low temperature again, a mixed gas of oxygen isotopes is introduced from the reservoir S3 into the chamber 10 (a step of re-adsorbing the oxygen isotope gas to the adsorbent). This operation is performed by opening the valves V8 and V5 and introducing oxygen isotope gas from the reservoir S3 into the chamber 10 by a differential pressure.
By introducing the oxygen isotope gas from the reservoir S3 into the chamber 10, the oxygen isotope gas is again adsorbed by the adsorbent 20, thereby increasing the concentration ^{of 18} O _{2 in the oxygen isotope mixed gas.}

In this way, the operation of mutually introducing the oxygen isotope gas between the reservoir S3 and the chamber 10 is repeated, and the oxygen isotope gas that is not adsorbed by the adsorbent 20 in the state of being cooled to a low temperature is introduced into the chamber 10. By performing the operation of collecting (discharging) from the reservoir S3, the ^{concentration of 18} O ₂ gas in the reservoir S3 can be gradually increased (concentration treatment).
The molar concentration of the ^{oxygen isotope gas 18} O ₂ stored in the reservoir S3 is monitored by the mass spectrometer MS, and it is ^{confirmed that the 18} O ₂ concentration has reached the predetermined concentration, and the concentration process is completed.

(Separation coefficient of oxygen conductor)
FIG. 5 shows the results of measuring the time change of the separation coefficient S at 112K for three types of samples ACF-1 (w = 0.65 nm), ACF-2 (w = 0.85 nm), and ACF-3 (w = 1.1 nm). Is shown.
ACF-1 is also maintained separation factor _{^{S (18 O 2/16 O}} 2)> 1.2 in the course time 100 minutes after 20 minutes.
ACF-2 until the time elapsed 18 minutes holding the separation factor _{^{S (18 O 2/16 O}} 2)> 1.2, over 2 hours, holding the _{^{S (18 O 2/16 O}} 2)> 1.
ACF-3 holds separation factor _{^{S (18 O 2/16 O}} 2)> 1.2 until the elapsed 13 minutes, over 2 hours, holding the _{^{S (18 O 2/16 O}} 2)> 1.

FIG. 6 shows the results of measuring the time change of the separation coefficient S at 130 K for the three samples ACF-1, ACF-2, and ACF-3.
ACF-1 until after 40 minutes from the start adsorbing maintaining separation factor _{^{S (18 O 2/16 O}} 2)> 1.2, maintaining the separation factor _{^{S (18 O 2/16 O}} 2)> 1.1 for 90 minutes did.
For ACF-2, ACF-3, until the elapsed 12 min separation factor _{^{S (18 O 2/16 O}} 2)> 1.1 holds, separation factor over 80 min _{^{S (18 O 2/16 O}} 2)> Retained 1.
The above-mentioned experimental results show that activated carbon fiber can be suitably used as a separating material for selectively separating ¹⁸ O ₂ from a mixed gas of ^{oxygen isotopes 18} O ₂ and ¹⁶ O _2. Similarly, at 77K, experimental results have been obtained in which the separation coefficient is 1.2 or more, and ¹⁸ O ₂ and ¹⁶ O ₂ can be effectively separated at a low temperature of 77 to 130 K.

^{Looking at the experimental results, the separation efficiency of separating oxygen isotopes 18} O ₂ and ¹⁶ O ₂ using activated carbon fiber as an adsorbent is about 10 minutes after the start of contact with the oxygen isotope gas with the adsorbent. It is extremely high by the time it is done. Therefore, rather than contacting the oxygen isotope mixed gas with the activated carbon fiber for a long time, the time for contacting the oxygen isotope mixed gas with the activated carbon fiber is set to a short time (about 10 minutes), and the activated carbon fiber is used. It is considered that more efficient separation operation can be performed by increasing the number of times the oxygen isotope gas is brought into contact with the gas.

(Oxygen isotope gas processing flow)
FIG. 7 shows the main part of the processing process for separating ¹⁸ O ₂ and ¹⁶ O ₂ from the gas containing oxygen isotopes using an oxygen isotope separation device as a processing flow.
Step 1 is a step of preparing a gas containing an oxygen isotope to be treated. In the above-mentioned experiment, ¹⁸ O ₂ and ¹⁶ O ₂ were prepared separately as oxygen isotopes, but in an actual device, a natural atmosphere containing the ^{oxygen isotope 18} O _{2 may be used.}

Step S2 is a step of adsorbing a gas containing an oxygen isotope on the activated carbon fiber which is an adsorbent. The vacuum chamber is filled with activated carbon fiber, and the chamber is cooled to a low temperature such as liquid nitrogen temperature, and a gas containing an oxygen isotope is brought into contact with the adsorbent. Since the separation coefficient of the oxygen isotope ( ¹⁸ O ₂ ) increases when the adsorbent is cooled to a low temperature, a method of keeping the adsorbent at a lower temperature and adsorbing it is effective.
Temperature of cooling the adsorbent ¹⁸ O ₂ and the ¹⁶ O ₂ separation factor _{^{S (18 O 2/16 O}} 2)> it may be a 1 and comprising temperature. When activated carbon fibers with an average pore size of 0.65 nm to 1.1 nm are used as an adsorbent, ¹⁸ O ₂ and ¹⁶ O ₂ are effectively separated by setting the temperature of the activated carbon fibers to 77 K to 130 K. can do.

Step 3 is a step of adsorbing a gas containing an oxygen isotope to the adsorbent for a certain period of time and then discharging the gas not adsorbed by the adsorbent from the chamber. This discharge operation is performed while the adsorbent is kept at a low temperature.

Step 4 is a desorption step of desorbing the gas containing the oxygen isotope adsorbed on the adsorbent from the adsorbent. The operation of desorbing the gas containing the oxygen isotope from the adsorbent is performed by heating the adsorbent. Since the adsorbent ¹⁸ O ₂ is selectively adsorbed than ¹⁶ O _2, the rate of increase in ¹⁸ O ₂ concentration in the gas desorbed from the adsorbent (desorbed gas) as compared with ¹⁶ O ₂ It gets higher.
After desorbing the gas containing the oxygen isotope adsorbed on the adsorbent from the adsorbent, the adsorbent is heated and vacuum sucked to perform a cleaning treatment to discharge the water and gas adsorbed on the adsorbent.

^{In step S5, the concentration of 18} O ₂ in the desorbed gas desorbed from the adsorbent is measured, and if the ¹⁸ O ₂ concentration does not reach the predetermined concentration, the desorbed gas is adsorbed on the adsorbent again and ¹⁸ This is a step of determining to stop the concentration process when the _{O 2 concentration reaches a required concentration.}
^{Based on step S5, the 18} O ₂ concentration in the gas desorbed from the adsorbent is increased by repeating the process (S2) of adsorbing the desorbed gas to the adsorbent again and steps S3 and S4. Can be done.
As an actual concentration step, a treatment method in which the desorbed gas is returned to the chamber that has been adsorbed and the desorbed gas is adsorbed again by the adsorbent is also possible, and the chamber containing the adsorbent is installed in multiple stages. It is also possible to concentrate the ^{oxygen isotope 18} O ₂ gas by introducing desorbed gas one after another from the front chamber to the rear chamber.

The method for separating oxygen isotopes according to the present invention uses activated carbon fibers as an adsorbent and separates them by utilizing the quantum action ^{of 16} O ₂ and ¹⁸ O _{2 at low temperature.} The method of the present invention is not a method of separating water molecules as in the conventional distillation method, but a method of directly separating oxygen gas, and the separation treatment operation is easy. By using activated carbon fiber as an adsorbent, ¹⁸ The separation coefficient of O ₂ and ¹⁶ O ₂ is as high as about 10 times that of the conventional method, and there is an advantage that ¹⁸ O _{2 gas of oxygen isotope can be obtained extremely efficiently.} Further, by using the activated carbon fiber as the adsorbent, there is an advantage that the maintenance of the apparatus is easy and the adsorbent can be reused. Further, by using the activated carbon fiber, there is an advantage that a large-scale equipment is not required and the manufacturing cost is extremely advantageous. Further, if the waste heat of the existing natural gas low temperature facility can be used as energy for lowering the temperature, it will not be an economic burden, and it can be provided as a promising separation technique in this respect as well.

10 Chamber 20 Adsorbent S1, S2, S3 Reservoir

Claims (7)

A method for separating oxygen isotopes using activated carbon fiber as an adsorbent.
a) A step of adsorbing an oxygen isotope gas containing ¹⁸ O ₂ and ¹⁶ O _{2 to the adsorbent,}
b) A step of desorbing the oxygen isotope gas adsorbed on the adsorbent from the adsorbent and recovering the desorbed gas.
c) The step of measuring the concentration ^{of 18} O ₂ and ¹⁶ O _{2 in} the desorbed gas desorbed from the adsorbent by the step b) is provided.
Wherein in step a), wherein the adsorbent, ¹⁸ O ₂ and the ¹⁶ O ₂ separation factor _{^{S (18 O 2/16 O}} 2)> is controlled to 1 to become a temperature,
In the step c) ^{, when the concentration of 18} O ₂ in the desorbed gas is less than the predetermined concentration, the steps a) and b) are repeated in this order, and the concentration ^{of 18} O _{2 in the desorbed gas is repeated.} A method for separating an oxygen isotope, which comprises stopping the step of concentrating an oxygen isotope gas when the concentration becomes higher than a predetermined concentration. The method for separating an oxygen isotope according to claim 1, further comprising a step of discharging unadsorbed gas not adsorbed by the adsorbent, following the step a). The method for separating an oxygen isotope according to claim 1 or 2, wherein in the step a), the temperature of the adsorbent is maintained at 77K to 130K. The method for separating an oxygen isotope according to any one of claims 1 to 3, wherein the activated carbon fiber having an average pore diameter of 0.65 nm to 1.1 nm is used as the activated carbon fiber. The method for separating an oxygen isotope according to any one of claims 1 to 4, wherein in the step a), the time for contacting the oxygen isotope gas with the adsorbent is set to about 10 minutes. A chamber containing activated carbon fiber as an adsorbent,
A mechanism for supplying a gas containing an oxygen isotope to the chamber,
After introducing the gas containing the oxygen isotope into the chamber, the discharge mechanism for discharging the gas not adsorbed by the adsorbent and the discharge mechanism.
A desorption mechanism that desorbs the gas adsorbed by the adsorbent from the adsorbent,
A measuring mechanism for measuring the concentrations ^{of 18} O ₂ and ¹⁶ O ₂ in the desorbed gas desorbed from the adsorbent, and
A temperature control mechanism that controls the temperature of the adsorbent contained in the chamber, and
Based on the measurement result by the measuring mechanism, the temperature of the adsorbent is controlled by the temperature control mechanism ^{, and when the concentration of 18} O _{2 in} the desorbed gas is less than a predetermined concentration, the desorbed gas is used as the adsorbent. It is provided with a control mechanism that is introduced into the chamber containing the activated carbon fiber and stops the oxygen isotope gas separation processing operation when the concentration ^{of 18} O _{2 in the desorbed gas exceeds a predetermined concentration.} An oxygen isotope separator characterized by.
Wherein the temperature control mechanism, according to claim, characterized in that it comprises means for controlling the adsorbent, ¹⁸ O ₂ and the ¹⁶ O ₂ separation factor _{^{S (18 O 2/16 O}} 2)> 1 and comprising temperature 6 The oxygen isotope separator described.

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