JP2009233492A - Method for concentrating oxygen isotope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly measure the concentration of target oxygen isotope containing ozone in ozonolysis and to control ozonolysis reaction on the basis of the measured value, when obtaining oxygen for which a target oxygen isotope is concentrated by the ozonolysis by laser beam irradiation. <P>SOLUTION: The ozone containing the target oxygen isotope is selectively decomposed using a laser beam for decomposition whose beam width is ≤0.05 nm, the concentration of the remaining ozone containing the target oxygen isotope is measured by a laser beam for measurement whose beam width is ≤0.05 nm simultaneously, and optical decomposition of the ozone by the laser beam for the decomposition is controlled on the basis of the measured value. For measurement by the laser beam for the measurement, the laser beam for the measurement oscillated by an injection current modulated by sine waves is used, electric signals photoelectrically converted in a light receiver are input to a lock-in amplifier, and secondary differentiation processing is performed with the sine waves as reference signals. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an oxygen isotope enrichment method for irradiating ozone with laser light to obtain oxygen gas in which oxygen isotopes ¹⁷ O and ¹⁸ O having a small natural abundance ratio are concentrated. It is what I did.

Oxygen isotopes ¹⁷ O and ¹⁸ O used as tracers in the fields of chemistry and medicine have a very small abundance ratio in the natural world. Therefore, when they are used, it is necessary to concentrate them.
As a method for concentrating oxygen isotopes, there is a method using distillation (Patent Documents 1 to 3). These methods selectively enrich ¹⁷ O or ¹⁸ O, which is a stable isotope of oxygen having a very small abundance ratio, by utilizing a decomposition reaction of ozone by a photoreaction using laser light.

The invention relating to the oxygen isotope enrichment method and apparatus disclosed in Patent Document 3 is based on the oxygen isotope ¹⁷ O which keeps the ozone concentration small even under conditions where the rare gas solidifies after diluting ozone with gas. The present invention relates to a method and an apparatus for concentrating ¹⁷ O and ¹⁸ O in oxygen efficiently and continuously by stably and selectively photolyzing ozone containing ¹⁸ O.

In Patent Document 3, in the ozone photolysis step, light is irradiated to a mixed gas of CF ₄ and ozone, and the ozone isotopomer containing a specific oxygen isotope contained in the ozone is selectively decomposed into oxygen. After the obtained mixed gas is collected in the collecting step, oxygen in the mixed gas is separated from undecomposed ozone and CF ₄ by low-temperature distillation or the like in the oxygen isotope concentration step, and the separated oxygen gas The oxygen isotope is concentrated inside.

  By the way, in the method of selectively decomposing ozone containing the target oxygen isotope using laser light and taking it out as oxygen, the decomposition reaction proceeds according to the irradiation time of the laser light. For example, a large amount of ozone containing the target oxygen isotope can be decomposed. However, the amount of decomposition per unit time is decreased, and the irradiation time is unnecessarily prolonged, which is not desirable.

  On the other hand, when the irradiation time of the laser beam is insufficient, the mixed gas is transferred to the next process with insufficient decomposition, so that not only a large amount of raw material ozone (oxygen) is required, but also the yield is increased. It will fall. Furthermore, since the amount of the processing gas increases, a large distillation column for separation is required, so that the initial cost increases. Therefore, it is necessary to optimize the irradiation time in order to improve the yield.

In addition, the ozone concentration of the gas introduced into the photolysis cell is preferably as high as possible because it contains more target oxygen isotopes. However, because ozone has self-decomposition, it is not possible to operate in a very high concentration state. Not desirable.
As described above, in the method of concentrating oxygen isotopes by laser photolysis, it is necessary to appropriately measure the ozone concentration in order to determine an appropriate laser light irradiation time and to manage the ozone concentration.

Ultraviolet absorption densitometers are widely used to measure ozone concentration, but this ultraviolet light decomposes ozone in a non-selective manner, and in the oxygen isotope enrichment process using laser light, product oxygen There is a problem that the concentration of the target oxygen isotope contained in is reduced.
As another ozone concentration measuring method, Patent Document 4 discloses a method of measuring with a laser beam. In this method, laser light is pulsed to perform measurement. However, since the shift amount of the absorption spectrum of the ozone isotope is small, it cannot be measured with the laser light.

  As another method, there is a report of measurement of ozone isotope using a Fourier transform infrared spectrometer (FTIR) (Non-patent Document 1), but the process time is 10 to 20 hours. Thus, it is unsuitable when continuous measurement is required, and is not applicable because ozone is non-selectively decomposed by infrared irradiation.

In this way, in the prior art, in the enrichment of oxygen isotopes, there was no means for measuring the concentration of ozone in the fluid without damaging the process during laser light irradiation. Therefore, the operation parameters are set by the trial and error method. There was only. With such a setting method, it was difficult to optimize the operating conditions.
Japanese Patent Laid-Open No. 2004-261776 JP 2005-40668 A JP 2006-272090 A Japanese Patent No. 4001797 A. J. et al. Bouvier et al. Spectrochimica Acta Part A 57 (2001) 561-579

  Therefore, the problem in the present invention is that when obtaining oxygen enriched with the target oxygen isotope by ozonolysis by laser light irradiation, the concentration of the target oxygen isotope-containing ozone at the time of ozonolysis can be quickly measured. It is to be able to control the ozonolysis reaction based on the value.

To solve this problem,
According to the first aspect of the present invention, ozone containing a target oxygen isotope is irradiated with laser light and photolyzed, and then ozone and oxygen containing the target oxygen isotope are separated to concentrate the target oxygen isotope. In a method for obtaining oxygen,
The ozone containing the target oxygen isotope is selectively decomposed using a laser beam for decomposition with a line width of 0.05 nm or less, and at the same time, the concentration of ozone containing the target oxygen isotope is measured with a line width of 0.05 nm or less. Measured by laser light for
Based on this measured value, the ozone photolysis by the laser beam for decomposition is controlled,
The measurement by the measurement laser beam is performed by using a measurement laser beam from a semiconductor laser driven by an injection current modulated by a sine wave, and inputting an electric signal photoelectrically converted by a light receiver into a lock-in amplifier. In the lock-in amplifier, the method of enriching oxygen isotopes is characterized in that second derivative processing is performed using the sine wave as a reference signal.

  The invention according to claim 2 is the oxygen isotope enrichment method according to claim 1, wherein the wavelength of the laser beam for measurement is 800 to 1300 nm.

  The invention according to claim 3 is characterized by measuring the concentration of ozone containing the target oxygen isotope and measuring the total ozone concentration by changing the wavelength of the laser beam for measurement. The oxygen isotope enrichment method described.

According to the present invention, since it is possible to irradiate the laser beam for decomposition while detecting the concentration of ozone containing the target oxygen isotope, it is possible to efficiently perform the irradiation of the laser beam for decomposition, and the consumption of the source gas Can also be optimized.
In addition, since the total ozone concentration can be measured, safety management is facilitated, and non-selective decomposition of ozone by ultraviolet rays is eliminated by not using an ultraviolet ozone concentration meter.
Furthermore, since there is no restriction | limiting of measurement density | concentration like a commercially available ozone concentration meter, it can implement also in the process in which ozone concentration exceeds 20%.

FIG. 1 and FIG. 2 show the best mode for carrying out the oxygen isotope enrichment method of the present invention.
Oxygen gas (O ₂ ) as a raw material is introduced into the ozonizer 1 to convert part of the oxygen into ozone and introduced into the first separation device 2 such as a low-temperature distillation tower together with a diluent gas such as tetrafluoromethane.
In the first separator 2, oxygen and ozone + diluted gas are separated, oxygen is recovered as raw material oxygen, and a mixed gas of ozone and diluent gas is introduced into the photoreaction cell 3.

The photoreaction cell 3 is irradiated with a laser beam for decomposition having a line width of 0.05 nm or less. This decomposition laser beam is a laser beam having a wavelength for selectively decomposing ozone (hereinafter sometimes referred to as “target ozone”) containing isotope oxygen atoms (for example, ¹⁷ O) to be concentrated. As shown in FIG. 2, the laser beam is oscillated from the decomposition laser light source 8.
As the decomposition laser light source 8, a semiconductor laser that oscillates at a constant wavelength by a direct current injection current from the decomposition laser driver 10 is used.

If the line width of the laser beam for decomposition exceeds 0.05 nm, only target ozone cannot be selectively photodecomposed.
The ozone decomposed by the laser beam for decomposition becomes oxygen gas containing the target oxygen isotope. The gas in the photoreaction cell 3 is a mixed gas of oxygen, ozone, and dilution gas.

  The mixed gas (oxygen + ozone + diluted gas) derived from the photoreaction cell 3 is liquefied and pressurized by the liquefying and boosting device 4 and then supplied to the second separation device 5 such as a low-temperature distillation tower, where oxygen and ozone + Separated into dilution gas. Oxygen obtained from the second separation device 5 becomes product oxygen gas in which target oxygen isotope atoms are concentrated.

The ozone + diluted gas discharged from the second separation device 5 is introduced into the ozone decomposition device 6 to completely decompose the ozone, and then introduced into the third separation device 7 such as a low-temperature distillation tower to convert oxygen and dilution gas. To separate.
The separated oxygen is discarded because the concentration of oxygen isotope atoms to be concentrated is reduced. Since the dilution gas is reused, it is returned to the dilution gas introduction path to the first separation device 2.

  As described above, in the photoreaction cell 3, only the target ozone in the introduced ozone is decomposed into oxygen by the laser beam. For efficient decomposition, a plurality of decomposition laser light sources 8 that decompose target ozone may be provided.

  At this time, a measurement laser light source 9 is provided separately from the decomposition laser light source 8 as shown in FIG. This measurement laser light source 9 oscillates a continuous oscillation measurement laser light having the same wavelength band (800 to 1300 nm) as that of the decomposition laser light and a line width of 0.05 nm or less. A semiconductor laser that oscillates by an injection current from is used.

  If the line width of the laser beam for measurement exceeds 0.05 nm, there is a high possibility that the absorption spectrum cannot be measured. Further, an ozone absorption band exists in the wavelength range of 800 to 1300 nm, and the ozone concentration can be measured in this wavelength range.

  The measurement laser light is swept in wavelength to measure the absorption spectrum. Therefore, the oscillation wavelength is changed by changing the injection current of the semiconductor laser that is the measurement laser light source 9 from the measurement laser driver 11 or changing the input voltage to the piezoelectric element that adjusts the external resonator. It has become.

At this time, for example, a 1 kHz sine wave (alternating current) generated by the waveform generator 14 is input to the measurement laser driver 11, and the injection current is directly modulated by this sine wave. The laser beam for measurement directly modulated by the directly modulated injection current is oscillated, and the photoreaction cell 3 is irradiated with this laser beam for measurement.
In addition, the measurement laser beam may be selected such that the wavelength does not decompose target ozone but can measure the concentration of target ozone.

The measurement laser light incident on the photoreaction cell 3 is reflected a plurality of times between reflecting mirrors (not shown) arranged facing the cell 3 and then received by a light receiver 12 such as a photodiode. It is converted into an electrical signal. This electrical signal is input to the lock-in amplifier 13.
A separate sine wave from the waveform generator 14 is input to the lock-in amplifier 13, and the lock-in amplifier 13 uses the sine wave as a reference signal to extract a second harmonic component of the modulation frequency and perform a second derivative process. To measure the minute absorbance derived from the target ozone. Based on this absorbance, the concentration of the target ozone can be determined based on the Lambert-Beer law.

  The target ozone concentration measurement value is sent to the control device 15. Based on this concentration, the control device 15 outputs a signal for adjusting the opening degree of the on-off valve 25 provided at the gas outlet of the photoreaction cell 3. The opening / closing valve 25 is thereby controlled in opening, the flow rate of the mixed gas flowing into the photoreaction cell 3 is adjusted, and the decomposition reaction of the target ozone can be controlled.

By adopting such a target ozone concentration measurement method, it is possible to quickly and accurately measure the target ozone concentration with a small isotope shift (absorption wavelength shift) in the absorption spectrum and a small absorption cross section. Can do.
For this reason, since the progress degree of the photodecomposition of the target ozone by the laser beam for decomposition in the photoreaction cell 3 can be known at any time, the flow rate of the mixed gas of ozone and dilution gas flowing into the photoreaction cell 3 can be adjusted, It is possible to control the photodecomposition reaction of the target ozone by adjusting the intensity of the laser beam for decomposition.

Further, by changing the wavelength of the measurement laser light, not only the target ozone in the cell 3 but also ¹⁶ O ₃ contained in the mixed gas can be measured.
In this way, since the target ozone contained in the mixed gas in the photoreaction cell 3 and the concentration of other ozone can also be measured in real time, in addition to controlling the decomposition reaction by controlling the flow rate of the target ozone, Since the total ozone concentration in the photoreaction cell 3 can also be measured, process safety management is possible.

(Continuous distribution method)
A continuous flow system for continuously supplying a mixed gas containing 10% ozone to the photoreaction cell 12 will be described in more detail with reference to FIGS.
A mixed gas of 10 vol% ozone and 90 vol% dilution gas is introduced from the first separator 2 into the photoreaction cell 3. In the photoreaction cell 3, laser light irradiation is performed with a decomposition laser beam set to a wavelength for decomposing the target ozone.

Since the concentration of target ozone is not measured with the laser beam for decomposition, the laser beam source 8 for decomposition is driven by direct current so as to keep the wavelength of the laser beam for decomposition constant.
The mixed gas introduced into the photoreaction cell 3 passes through the cell 3 at a minute speed. During this time, the target ozone in the mixed gas is gradually decomposed by irradiation with the laser beam for decomposition.
The cell 3 is irradiated with measurement laser light. The measurement laser light that has passed through the photoreaction cell 3 is received by a light receiver 12 such as a photodiode to become an electric signal, and the concentration of target ozone is measured by the lock-in amplifier 13 as described above.

The wavelength of the laser beam for measurement may be the same as the wavelength of the laser beam for decomposition. However, since the accuracy of the measurement value increases when using a wavelength that absorbs more by ozone, the other absorption peaks are large (the absorption cross section is large). ) It is desirable to match the wavelength, and it is selected from the range of 800 to 1300 nm.
If the target ozone concentration in the mixed gas containing 10 vol% ozone is measured with the measurement laser light before the decomposition laser light irradiation, the target ozone concentration is measured during the decomposition laser light irradiation. Thus, the decomposition reaction rate can be understood.

Since this decomposition reaction rate depends on the irradiation time, it changes by adjusting the flow rate of the mixed gas flowing in the cell 3.
The concentration of target ozone is measured with a measuring laser beam, and the flow rate of gas passing through the cell 12 is adjusted so as to achieve an appropriate reaction rate, for example, an absorption intensity of 50% before irradiation.

  The opening time of the on-off valve 25 installed at the outlet of the photoreaction cell 3 is adjusted, and the irradiation time is changed by controlling the flow rate based on the measurement result of the absorption intensity of the target ozone, that is, the concentration, to obtain an appropriate reaction amount. It becomes possible.

In addition to the measurement set consisting of the measurement laser light source 9, the measurement laser driver 11 and the light receiver 12, another similar measurement set is newly prepared, or the measurement wavelength of the measurement laser light from the same measurement laser light source 9 Is temporarily changed, the concentration of ¹⁶ O ₃ occupying most of the ozone in the cell 3 can also be performed in the same manner as the measurement of the target ozone, and the total ozone concentration in the photoreaction cell 3 can be measured. Thus, it can be used for safety management of the apparatus and operation management of the ozonizer 1 that generates raw material ozone.

When disassembling the ¹⁶ O ₃ photoreactive cell 3, so it would dilute the oxygen isotope concentration product oxygen concentration of interest, measurement of the ¹⁶ O ₃ should be carried out in a weak laser power. Moreover, it is better not to carry out the measurement continuously. Since the concentration of ¹⁶ O ₃ is high even at a weak power, measurement is sufficiently possible.

Ozone having a natural abundance of oxygen isotope as a raw material is introduced into the photoreaction cell 3 at a concentration of 10 vol%, a pressure of 14 kPa, and a flow rate of 100 NL / h, and the target ozone is ¹⁶ O ¹⁶ O ¹⁷ O and a reaction decomposition rate of 50 %, Assuming that the reaction was performed at a laser output of 10 W, it was found that the ¹⁷ O concentration in the product oxygen gas was 16%, and a production rate of 1.5 kg / year was obtained.

(Continuous distribution method using both a laser light source for decomposition and a laser light source for measurement)
Next, the continuous flow type in the case where the laser beam source for decomposition and the laser beam source for measurement are used together will be described.
The above-described measurement laser light source 9 is not provided separately from the decomposition laser light source 8, but the laser beam from the decomposition laser light source 8 is temporarily modulated by a sine wave as described above, thereby allowing the decomposition laser. The light source 8 can also be used as a measurement laser light source. By not installing the measurement laser light source 9 and the measurement laser driver 11, the initial cost can be reduced.

The laser beam for decomposition is fixed at a fixed wavelength by flowing a direct current injection current through the laser light source for decomposition during ozone decomposition irradiation, but when measuring the absorption spectrum, the injection current and the laser resonator adjustment voltage are directly modulated. By doing so, an absorption spectrum can be measured.
Since a high-power laser beam for decomposition is used, when irradiating as a measuring laser beam, it is preferable to install an optical filter in the light receiver and attenuate it to an appropriate input light intensity. Since the flow rate of the mixed gas in the photoreaction cell 3 is very slow, there is no problem even if the target ozone concentration is measured intermittently.

Furthermore, if the wavelength of the laser beam for decomposition is changed only for a short time, the concentration of ¹⁶ O ₃ can be measured and can be used for safety management as described above. At this time, in order to avoid decomposition of ozone other than the target ozone, it is preferable to perform measurement while reducing the laser intensity.

(Batch (switching) method)
In the continuous flow method, the irradiation time by the laser can be lengthened by reducing the flow rate of the mixed gas in the photoreaction cell 3, but a batch method can also be adopted in order to ensure a decomposition reaction.

  In FIG. 3, a plurality of (in this example, two) photoreaction cells 31 and 32 are used, mixed gas is introduced into each photoreaction cell 31 and 32, and on-off valves provided at the gas inlet and gas outlet of the cell, respectively. An apparatus configuration is shown in which 25, 25, 26, and 26 are operated and laser light is irradiated in a state where a mixed gas is completely enclosed, and target ozone decomposition and concentration measurement are performed while switching cells.

First, a mixed gas of 10 vol% ozone and 90 vol% dilution gas from the first separation device 2 is introduced into the photoreaction cell 31.
After the mixed gas is sealed in the photoreaction cell 31, the introduction of the mixed gas is switched to the photoreaction cell 32. The photoreaction cell 31 is irradiated with the decomposition laser beam and the measurement laser beam, and when the irradiation and concentration measurement are completed, the mixed gas after the decomposition reaction is sent to the liquefaction booster 4. Thereafter, the mixed gas is introduced, and the same operation is repeated thereafter.

In the same manner, the gas mixture sealed in the photoreaction cell 32 is irradiated with the decomposition laser beam and the measurement laser beam, and the target ozone is decomposed and the concentration is measured.
At this time, movable mirrors 16, 17, 18, 19, 20, 21, 22, 23 are provided at the entrance window and the exit window of each photoreaction cell 31, 32, and the movable mirror 16. The optical axis of the laser beam for decomposition and the laser beam for measurement is switched, and the laser beam for decomposition and the laser beam for measurement are alternately incident on each cell and emitted, and such a configuration is adopted. This eliminates the need to prepare a plurality of expensive laser light sources and measuring devices.

  The concentration measurement of the target ozone can be obtained by measuring the second derivative absorption spectrum as described above. This makes it possible to set the target ozone decomposition reaction time while confirming the decrease in the target ozone concentration.

  By connecting a plurality of photoreaction cells in parallel in this way, it is possible to photodecompose nearly all of the target ozone. Considering the amount of laser light input and the optimum value of the raw material oxygen gas, the photoreaction cell It is good to switch. When the decomposition reaction in the photoreaction cell 31 is completed, the photoreaction cell 32 is switched to irradiation, and the product is continuously produced by performing the switching continuously. There is no limit to the number of cells. In the switching method, the product specifications are the same under the same conditions.

It is a schematic block diagram which shows an example of the apparatus for enforcing the method of this invention. It is a schematic block diagram which shows an example of the apparatus for decomposition | disassembly and density | concentration measurement of the target ozone in this invention. It is a schematic block diagram which shows the other example of the apparatus for decomposition | disassembly and density | concentration measurement of the target ozone in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ozonizer, 2 ... 1st separation device, 3 ... Photoreaction cell, 4 ... Liquefaction pressurization device, 5 ... 2nd separation device, 6 ... Ozone decomposition device, 7. .. Third separation device, 8... Laser light source for decomposition, 9... Laser light source for measurement, 10... Laser driver for decomposition, 11. DESCRIPTION OF SYMBOLS 13 ... Lock-in amplifier, 14 ... Waveform generator, 15 ... Control apparatus, 31, 32 ... Photoreaction cell, 16, 17, 18, 19, 20, 21, 22, 23 ...・ Movable mirror

Claims (3)

In a method for obtaining oxygen enriched in a target oxygen isotope by separating ozone and oxygen containing the target oxygen isotope after photolysis by irradiating ozone containing the target oxygen isotope with laser light,
The ozone containing the target oxygen isotope is selectively decomposed using a laser beam for decomposition with a line width of 0.05 nm or less, and at the same time, the concentration of ozone containing the target oxygen isotope is measured with a line width of 0.05 nm or less. Measured by laser light for
Based on this measured value, the ozone photolysis by the laser beam for decomposition is controlled,
The measurement by the measurement laser beam is performed by using a measurement laser beam from a semiconductor laser driven by an injection current modulated by a sine wave, and inputting an electric signal photoelectrically converted by a light receiver into a lock-in amplifier. An oxygen isotope enrichment method characterized in that in a lock-in amplifier, a secondary differentiation process is performed using the sine wave as a reference signal.   2. The method of concentrating oxygen isotopes according to claim 1, wherein the wavelength of the laser beam for measurement is 800 to 1300 nm.   3. The oxygen isotope according to claim 1, wherein the concentration of ozone containing the target oxygen isotope is measured and the total ozone concentration is also measured by changing the wavelength of the laser beam for measurement. Concentration method.

Images