Oxygen stable isotope concentrator and operation method thereof

Abstract

To provide an oxygen stable isotope concentrator and an operation method thereof.SOLUTION: The oxygen stable isotope concentrator includes: an ozonizer that makes at least a part of raw oxygen gas including a plurality of oxygen stable isotopes into ozone; a first distillation column that separates by distillation the oxygen gas, ozone gas, and mixed gas from a third distillation column described later into oxygen gas in a column upper part and additive gas in a column bottom; a photo reaction cell that introduces the mixed gas from the first distillation column and decomposes the oxygen gas by photo reaction; a second distillation column that separates by distillation the mixed gas into the oxygen gas in the column upper part, the ozone gas in the column bottom, and the additive gas; an ozone decomposition catalyst cylinder that decomposes the ozone in the mixed gas from the second distillation column into oxygen gas; and the third distillation column that separates by distillation the mixed gas from the ozone decomposition catalyst cylinder into the oxygen gas in the column upper part and the additive gas in the column bottom. The oxygen stable isotope concentrator includes an analyzer that measures concentration of the additive gas in an upper part of the second distillation column and a device that controls a flow rate of the oxygen gas extracted from the upper part of the second distillation column on the basis of a signal from the analyzer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for concentrating stable oxygen isotopes and a method for operating the same. [Background technology]

[0002] Known methods for separating stable isotopes that exist only in extremely small amounts in nature include thermal diffusion separation, centrifugation, laser separation, chemical exchange separation, distillation separation, etc. Among these, laser separation is characterized by the fact that, in principle, the selectivity of the laser-induced reaction can be made extremely large, thereby achieving a predetermined high enrichment level in a single stage and allowing for an extremely compact process. Specifically, a technology is used in which laser light of a specific wavelength is introduced into a gas cell and a selective reaction occurs by absorbing the light. For example, Patent Document 1 below discloses a technology in which laser light is irradiated onto ozone gas to decompose ozone containing a target oxygen isotope into oxygen, thereby concentrating the target oxygen isotope in the oxygen. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4364529 [Patent Document 2] Patent No. 4699784 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-040668 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of stable isotope enrichment by laser separation, the production rate of the target substance produced by a photoreaction is a parameter that directly affects the production capacity of the device. In the case of the technology disclosed in Patent Document 1, this is the production rate of oxygen produced by the photolysis of ozone (hereinafter referred to as the oxygen generation rate). Therefore, in order to operate the device efficiently, it is necessary to be able to quantify the oxygen generation rate, and specifically, it is necessary to measure the oxygen concentration in the ozone-containing gas. If the oxygen generation rate cannot be quantified, problems arise when, for example, Patent Document 1 is taken as an example, extracting a somewhat empirical amount of stable oxygen isotope gas as a product from the top of the second distillation column. For example, if the amount withdrawn is too large, the ozone in the column will be drawn in and withdrawn, and the oxygen released after the ozone naturally decomposes will reduce the target stable isotope concentration. Conversely, if the amount withdrawn is too small, oxygen will continue to accumulate in the column, eventually contaminating the stable oxygen isotope gas in the withdrawal system at the bottom of the column, resulting in product loss.

[0005] In general, stable isotope enrichment by laser separation has the advantage of a larger separation factor due to its high selectivity compared to separation methods such as thermal diffusion separation, centrifugation, and distillation, but on the other hand, it is difficult to increase the processing volume, and in the example of Patent Document 1, it has the disadvantage of a slow oxygen generation rate. Common methods for quantifying oxygen concentration include the diaphragm electrode type, magnetic type, zirconia type, and fluorescent type, but because ozone is a very unstable substance that decomposes into oxygen even at room temperature and is corrosive, it is difficult to accurately measure oxygen concentration with any of the above methods, and it is also difficult to quantify small changes in oxygen concentration due to laser separation.

[0006] It is also possible to calculate the oxygen generation rate by measuring other substances. Specifically, one possible approach is to measure the change in ozone concentration before and after laser irradiation. Methods for measuring ozone concentration include ultraviolet absorption, semiconductor thin-film, and controlled-potential electrolysis. The semiconductor thin-film and controlled-potential electrolysis methods rely on ozone decomposition (the former involves the reaction of ozone with a semiconductor thin-film, while the latter involves electrolysis of ozone). These methods are inapplicable because they result in ozone decomposition unrelated to laser separation, leading to a decrease in isotope enrichment. The ultraviolet absorption method utilizes the strong absorption of ozone at 254 nm. While the amount of ozone decomposition is smaller than the two previous methods, non-isotope-selective ozone decomposition due to light absorption still occurs, making it inapplicable for the same reason. For these reasons, calculating the oxygen generation rate by measuring the change in ozone concentration is unsuitable for the technology disclosed in Patent Document 1.

[0007] Incidentally, in relation to the technology disclosed in Patent Document 1, there is a method of reducing the ozone concentration and suppressing natural decomposition of ozone by adding an appropriate amount of a gas other than oxygen that is unreactive with ozone gas to the ozone gas introduced into the light reaction field in order to increase the concentration efficiency of oxygen isotopes. Specifically, there is a technology disclosed in Patent Document 2, in which CF4 gas is added to ozone gas. The technology in Patent Document 2 consists of the following steps. 1. Generate an oxygen-ozone mixed gas from raw oxygen and add CF4 gas to it. 2. The three-component gas mixture is separated into oxygen and ozone-CF4 gas mixture by low-temperature distillation. 3. Ozone-CF4 mixed gas is reacted in a light reaction field, and ozone containing the target stable isotope is selectively decomposed into oxygen. 4. As in step 2, oxygen and ozone-CF4 mixed gas are separated by low-temperature distillation, and oxygen gas enriched with the desired stable isotope is extracted.

[0008] In the above-mentioned step 4, the CF4 concentration accompanying the gas extracted from the top of the distillation column varies depending on the amount of oxygen accumulated at the top of the column. If the amount of oxygen is abundant, the CF4 concentration in the extracted oxygen will be low, and as the amount of oxygen decreases, the CF4 concentration will increase. Specifically, the CF4 concentration varies from the sub-ppm order to the order of percent depending on the amount of oxygen. Note that, since isotope separation by laser irradiation of ozone has already been performed in step 4, the measurement of the CF4 concentration in the oxygen in step 4 does not affect the isotope enrichment. Note that, although CF4 is used as the additive gas in Patent Document 2, the additive gas may also be krypton, xenon, or radon, as described in Patent Document 3.

[0009] The present invention has been made in consideration of the above circumstances, and aims to improve the configuration of Patent Document 2 to enable measurement of the oxygen generation rate by laser separation, thereby optimizing the operation of an apparatus for concentrating stable oxygen isotopes by laser separation. [Means for solving the problem]

[0010] The present invention employs the following aspects. (1) The stable oxygen isotope enrichment apparatus according to the present invention comprises an ozonizer that converts at least a portion of a raw material oxygen gas containing a plurality of stable oxygen isotopes into ozone; a first distillation column that distills and separates a mixed gas of oxygen gas and ozone gas from the ozonizer and an additive gas from a third distillation column described below into oxygen gas at the top of the column and ozone gas and additive gas at the bottom of the column; a photoreaction cell that introduces the mixed gas of ozone gas and additive gas from the bottom of the first distillation column and selectively decomposes the ozone gas into oxygen gas by a photoreaction; and a photoreaction cell that converts the mixed gas of oxygen gas, ozone gas, and additive gas from the photoreaction cell into oxygen gas at the top of the column. An oxygen stable isotope enrichment apparatus comprising: a second distillation column that separates the mixed gas of ozone gas and added gas from the bottom of the second distillation column by distillation into ozone gas and added gas; an ozone decomposition catalyst column that decomposes ozone in the mixed gas of ozone gas and added gas from the bottom of the second distillation column into oxygen gas; and a third distillation column that separates the mixed gas of oxygen and added gas from the ozone decomposition catalyst column by distillation into oxygen gas at the top of the column and added gas at the bottom of the column, wherein the apparatus is characterized by further comprising an analyzer that measures the concentration of the residual added gas in the top of the second distillation column and a device that controls the flow rate of oxygen gas extracted from the top of the second distillation column based on a signal from the analyzer.

[0011] The flow rate of oxygen gas extracted from the top of the second distillation column is controlled based on the residual additive gas concentration information from the residual additive gas analyzer, so that the residual additive gas concentration at the top of the second distillation column can be kept within a certain range. This makes it possible to achieve a mass balance between the amount of oxygen generated by isotope-selective decomposition in the photoreaction cell and the amount of oxygen extracted from the top of the second distillation column, thereby improving the isotopic enrichment of the oxygen gas product.

[0012] (2) In the stable oxygen isotope enrichment apparatus described in (1) above, the additive gas is preferably one or more of CF4, krypton, xenon, and radon. (3) In the stable oxygen isotope enrichment apparatus according to (1) or (2), it is preferable that an analysis gas return line is installed in the device that controls the flow rate of the oxygen gas. (4) In the stable oxygen isotope enrichment apparatus described in (1) or (2), it is preferable that a gas outlet line is connected to the top of the second distillation column, and the analytical device is incorporated in the gas outlet line.

[0013] (5) A method of operating a stable oxygen isotope enrichment apparatus according to the present invention includes an ozonizer for converting at least a portion of a raw material oxygen gas containing a plurality of stable oxygen isotopes into ozone; a first distillation column for separating a mixed gas of oxygen gas and ozone gas from the ozonizer and an additive gas from a third distillation column described below into oxygen gas at an upper part of the column and ozone gas and additive gas at a bottom of the column by distillation; a photoreaction cell into which a mixed gas of ozone gas and additive gas from the bottom of the first distillation column is introduced and which selectively decomposes the ozone gas into oxygen gas by a photoreaction; a second distillation column for separating a mixed gas of oxygen gas, ozone gas, and additive gas from the photoreaction cell by distillation into oxygen gas at an upper part of the column and ozone gas and additive gas at a bottom of the column; An oxygen stable isotope enrichment apparatus comprising an ozone decomposition catalyst column that decomposes ozone in a mixed gas of ozone gas and additive gas from the column bottom into oxygen gas, and a third distillation column that distillatively separates the mixed gas of oxygen and additive gas from the ozone decomposition catalyst column into oxygen gas at the top of the column and additive gas at the column bottom, wherein the oxygen stable isotope enrichment apparatus is equipped with an analyzer that measures the concentration of residual additive gas at the top of the second distillation column and a device that controls the flow rate of oxygen gas extracted from the top of the second distillation column based on a signal from the analyzer, and is characterized in that the flow rate of oxygen gas extracted from the top of the second distillation column is adjusted in accordance with the concentration of the residual additive gas, thereby stabilizing the concentration of the additive gas in the second distillation column.

[0014] According to the operating method of the present invention, the flow rate of oxygen gas extracted from the top of the second distillation column is adjusted based on residual additive gas concentration information from the residual additive gas analyzer, so that the residual additive gas concentration at the top of the second distillation column can be controlled within a certain range. This makes it possible to improve the isotopic enrichment of the product oxygen gas by achieving a mass balance between the amount of oxygen generated by isotope-selective decomposition in the photoreaction cell and the amount of oxygen extracted from the top of the second distillation column.

[0015] (6) In the method for operating an oxygen stable isotope enrichment apparatus described in (1) above, it is preferable that the additive gas be one or more of CF4, krypton, xenon, and radon. (7) In the method for operating the stable oxygen isotope enrichment apparatus described in (5) or (6), it is preferable that the device for controlling the flow rate of the oxygen gas is provided with a gas outlet line and a gas return line for extracting gas from the top of the second distillation column, and that the amount of gas discharged to the outside of the system from the gas return line or the amount of gas returned to the top of the second distillation column via the gas return line is adjusted according to the concentration of the residual additive gas contained in the gas taken in the gas outlet line.

[0016] (8) In the method for operating the stable oxygen isotope enrichment apparatus described in (7) above, when the concentration of the residual additive gas contained in the gas taken into the gas outlet line exceeds a specific threshold value during operation of the stable oxygen isotope enrichment apparatus, the operation of the stable oxygen isotope enrichment apparatus is continued while returning the gas taken into the gas outlet line to the top of the second distillation column using the gas return line, and when the concentration of the residual additive gas contained in the gas taken into the gas outlet line falls below a specific threshold value, the amount of gas discharged to the outside of the system from the gas outlet line and the amount of gas returned to the top of the second distillation column using the gas return line are increased or decreased, thereby adjusting the residual additive gas concentration at the top of the second distillation column and stabilizing the additive gas concentration in the second distillation column. [Effects of the Invention]

[0017] According to the present invention, the flow rate of oxygen gas extracted from the top of the second distillation column is controlled based on residual additive gas concentration information from the residual additive gas analyzer, so that the residual additive gas concentration at the top of the second distillation column can be kept within a certain range. This allows for a mass balance between the amount of oxygen generated by isotope-selective decomposition in the photoreaction cell and the amount of oxygen extracted from the top of the second distillation column, thereby improving the isotopic enrichment of the oxygen gas product. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a block diagram showing an oxygen stable isotope enrichment device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing an example of an oxygen stable isotope enrichment device used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an oxygen stable isotope enrichment apparatus and an operating method thereof according to one embodiment of the present invention will be described. The embodiments described below are specifically described to provide a better understanding of the gist of the present invention, and do not limit the present invention unless otherwise specified. Furthermore, the scale of the drawings used to explain the embodiments below has been changed appropriately to make each part easier to see.

[0020] 1, a stable oxygen isotope enrichment apparatus 100 according to one embodiment of the present invention includes a first distillation column 21, a second distillation column 22, a third distillation column 23, and a photoreaction cell 10. It also includes an ozonizer 33, an ozone decomposition catalyst column 34, a residual added gas concentration analyzer (residual added gas concentration analyzer) 35, and a flow control valve 36. The number of photoreaction cells 10 and ozonizers 33 is not limited to one, and may vary depending on the process flow rate. As the additive gas, one or more of CF4 (carbon tetrafluoride), krypton, xenon, and radon can be used.

[0021] The photoreaction cell 10 has concave mirrors 10A, 10A housed inside and installed opposite each other within a housing 10B, and the two concave mirrors 10A each have a mirror adjustment mechanism (not shown) that can adjust the position, orientation, and rotation angle of the mirror. Laser light is incident on the photoreaction cell 10 from a laser light source 11 installed outside the photoreaction cell 10 through a laser transmission window 10C installed in the photoreaction cell 10, and is reflected multiple times between the two concave mirrors 10A to cause a photoreaction. One end of the photoreaction cell 10 is connected to a photoreaction cell inlet line 46, and the other end is connected to a photoreaction cell outlet line 47. Ozonizer 33 is a device that generates ozone from oxygen gas. Raw material oxygen gas (raw material O2 gas) is introduced into the inlet side of ozonizer 33 via raw material gas supply line 33A, and the outlet side is connected to first distillation column 21 via raw material feed line 43. The raw material oxygen gas contains a plurality of stable oxygen isotopes, for example, 16 O. 17 O. 18 Contains O. The ozone decomposition catalyst cylinder 34 is a cylinder filled with a catalyst such as manganese oxide, and has the function of decomposing ozone into oxygen at room temperature. One end of the ozone decomposition catalyst cylinder 34 is connected to an ozone decomposition catalyst cylinder inlet line 49, and the other end is connected to an ozone decomposition catalyst cylinder outlet line 50.

[0022] The residual additive gas concentration analyzer 35 is a device for measuring the concentration of additive gas in oxygen, and one end is connected to the oxygen isotope gas gas extraction line 48, and the other end is branched and connected to the flow control valve 36 and the analysis gas return line 52. The analysis gas return line 52 is not an essential component, and it is preferable to provide a pump or the like if there is no pressure difference between the residual additive gas concentration analyzer 35 and the second distillation column 22. The measurement method for the residual additive gas concentration analyzer 35 includes a gas chromatograph, a mass spectrometer, an infrared spectrophotometer (in the case of CF4), etc. The measurement method of the residual additive gas concentration analyzer 35 is preferably an analytical method that minimizes loss of oxygen stable isotope enriched gas due to laser separation, and it is most desirable that it be capable of continuous in-line measurement. Furthermore, it is preferable that the detection sensitivity of the additive gas to be analyzed is high, and a detection sensitivity of 0.1 ppm or higher is desirable. In the configuration of Figure 1, the residual additive gas concentration analyzer 35 is incorporated into the gas extraction line 48.

[0023] The flow control valve 36 is a valve for adjusting the withdrawal flow rate of the oxygen gas enriched in the target stable oxygen isotope (the amount withdrawn from the top of the second distillation column 22), and one end is connected to the residual additive gas concentration analyzer 35, and the other end is connected to the exhaust pipe 37. The opening of the flow rate control valve 36 preferably has a function of performing feedback control on the concentration measured by the residual additive gas concentration analyzer 35. By adjusting the opening of the flow rate control valve 36, it is possible to switch between letting the analysis gas that has passed through the residual additive gas concentration analyzer 35 flow outside the system via the exhaust pipe 37 or into the analysis gas return line 52, and to adjust the amount of gas flowing in each direction.

[0024] As an example of a configuration for implementing feedback control, a control device 38 connected to a residual additive gas concentration analyzer 35 and a flow rate adjusting valve 36 can be provided. This control device 38 has the function of receiving a signal corresponding to the concentration of the additive gas measured by the residual additive gas concentration analyzer 35 from the residual additive gas concentration analyzer 35, and adjusting the opening of the flow control valve 36 in accordance with the additive gas concentration corresponding to the received signal. Controller 38 has the function of adjusting the aperture of flow control valve 36 when the concentration of the additive gas (e.g., CF4) is higher than a predetermined concentration, and returning the gas used for analysis to the top (upper part of the column) of second distillation column 22 via analysis gas return line 52. Controller 38 has the function of adjusting the aperture of flow control valve 36 when the concentration of the additive gas falls below a predetermined concentration, and stopping the gas from being returned to the top of second distillation column 22 via analysis gas return line 52, and allowing the analysis gas to flow to the exhaust pipe 37 side. The control device 38 is provided with a function for adjusting the opening of the flow control valve 36, thereby adjusting the amount of analysis gas that has passed through the residual additive gas concentration analyzer 35 flowing to the exhaust pipe 37 side and the amount flowing to the analysis gas return line 52 side. In this embodiment, the flow rate control valve 36 and the control device 38 constitute a device that controls the flow rate of oxygen gas extracted from the top of the second distillation column 22 based on a signal corresponding to the concentration of the additive gas measured by the residual additive gas concentration analyzer 35.

[0025] As an example, when the concentration of the additive gas analyzed by the residual additive gas concentration analyzer 35 is high, such as 3000 ppm, the control device 38 has a function of returning the analysis gas to the top of the second distillation column 22 via the analysis gas return line 52 without flowing the analysis gas to the exhaust pipe 37 side. As the operation of second distillation column 22 continues, when the concentration of the additive gas analyzed by residual additive gas concentration analyzer 35 decreases and reaches a predetermined low concentration such as 1 ppm, control device 38 has the function of stopping the reflux of the analysis gas to analysis gas return line 52 and adjusting the opening of flow control valve 36 to allow the analysis gas to flow out of the system via exhaust pipe 37. If the reflux of the analysis gas to the analysis gas return line 52 is stopped and the operation of the second distillation column 22 is continued while the analysis gas is maintained flowing to the exhaust pipe 37, the concentration of the additive gas increases. By repeatedly changing the flow direction of the analysis gas as described above, the concentration of the additive gas can be adjusted by feedback control. Here, the concentration of the additive gas in the oxygen gas can be feedback controlled within a range of, for example, 5 ppm±2 ppm.

[0026] Distillation columns 21, 22, and 23 are each provided with a condenser 31 and a reboiler 32. Condenser 31 is provided on a circulation line 41, both ends of which are connected to different positions at the top of each distillation column. Condenser 31 has the function of liquefying gas that has risen within the distillation column through heat exchange and allowing the gas to descend again within the distillation column. One reboiler 32 is provided for each distillation column. Reboiler 32 is provided on a circulation line 42, both ends of which are connected to different positions at the bottom of each distillation column. Reboiler 32 has the function of vaporizing liquid that has descended within the distillation column through heat exchange and allowing the liquid to ascend again within the distillation column.

[0027] The distillation columns 21, 22, and 23 are packed columns filled with structured packing. The first distillation column 21 separates oxygen, ozone, and additive gas, separating oxygen on the top side and a mixed gas of ozone and additive gas on the bottom side. A raw material feed line 43 and one end of an additive gas circulation line 44 are connected to the middle section of the first distillation column 21. One end of an oxygen circulation line 45 is connected to the top of the first distillation column 21, and one end of a photoreaction cell introduction line 46 is connected to the bottom of the column. The other end of the oxygen circulation line 45 is branched off and connected to a raw material gas supply line 33A on the inlet side of the ozonizer 33.

[0028] The second distillation column 22 serves to introduce a mixed gas of oxygen, ozone, and additive gas, containing oxygen obtained by selectively decomposing only ozone containing the target stable oxygen isotope using the photoreaction cell 10, into the middle section, and to separate the oxygen into the top side and the ozone and additive gas mixed gas into the bottom side. One end of a photoreaction cell outlet line 47 is connected to the middle section of the second distillation column 22. In addition, one end of a gas vent line 48 for oxygen isotope gas and one end of an analysis gas return line 52 are connected to the top of the second distillation column 22, and one end of an ozone decomposition catalyst column introduction line 49 is connected to the bottom of the column. Note that the gas vent line 48 for oxygen isotope gas is preferably connected closer to the top of the second distillation column 22 than the analysis gas return line 52.

[0029] The third distillation column 23 serves to introduce a mixed gas of oxygen and additive gas after ozone decomposition by the ozone decomposition catalyst column 34 into an intermediate section, and to separate the oxygen into the top side and the additive gas into the bottom side. One end of an ozone decomposition catalyst column outlet line 50 is connected to an intermediate section of the third distillation column 23. One end of an exhaust oxygen gas withdrawal line 51 is connected to the top of the third distillation column 23, and one end of an additive gas circulation line 44 is connected to the bottom of the column. The additive gas withdrawn from the bottom of the third distillation column 23 is supplied to an intermediate section of the first distillation column 21, and the additive gas is recycled.

[0030] Although the stable oxygen isotope enrichment apparatus according to the present invention has been described above by showing one embodiment of the stable oxygen isotope enrichment apparatus 100, the present invention is not limited to this one embodiment. The configurations and combinations thereof in the above-described embodiments are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope of the present invention. Regarding the constituent equipment, the distillation column is not limited to a packed column packed with structured packing, but may be a packed column packed with random packing, a plate column, or the like. If there is no pressure difference in the gas transport between the distillation column and the photoreaction cell and between the distillation columns, a compressor pump may be appropriately disposed, or the gas may be transported using liquid head pressure.

[0031] Regarding the stable oxygen isotope enrichment apparatus 100 described above, an operating method that enables measurement of the oxygen generation rate by laser separation and optimizes operation of the stable oxygen isotope enrichment apparatus 100 using laser separation will be described in detail in the following examples. [Example]

[0032] An example using the photoreaction cell and the stable oxygen isotope enrichment device according to the present invention will be described below. Example 1 In Example 1, a stable oxygen isotope enrichment device 200 shown in FIG. 2 was used to enrich a plurality of oxygen isotopes ( 16 O. 17 O.18 O) 18 The stable oxygen isotope enrichment apparatus 200 has the same configuration as the stable oxygen isotope enrichment apparatus 100, and the same components are denoted by the same reference numerals, and a description of the same parts will be omitted. In this example, the photoreaction cell 10 is cylindrical, 400 mm in diameter and 10 m in length, and is made of SUS 304. The two concave mirrors 10A are made of borosilicate glass, 300 mm in diameter and 25 mm thick, and their surfaces are coated with a multilayered, high-reflection film, with a reflectivity of 99% or more. The laser transmitting window 10C is made of synthetic quartz and has a diameter of 40 mm and a thickness of 4 mm. A semiconductor laser was used as the laser light source 11. The wavelength of the laser light was determined by the isotope component in ozone. 16 O 16 O 18 The wavelength was set at 992 nm, which resolves only O.

[0033] The number of reflections between the two concave mirrors 10A of the photoreaction cell 10 was adjusted as follows. First, the mirror adjustment mechanism was used to adjust the concave mirrors 10A so that they were parallel to each other. Then, laser light was introduced into the photoreaction cell 10 from the laser light source 11 through the laser transmission window 10C. Then, the two mirror adjustment mechanisms were used again to fine-tune the position and orientation of the two concave mirrors 10A. At this time, the number of reflections of the laser light between the two concave mirrors 10A was approximately 200. After adjusting the number of reflections in the photoreaction cell 10, the distillation section was started up. First, the condenser 31 was started up and liquefied CF4 gas was stored in the reboiler 32 of each of the three distillation columns. All three distillation columns 21, 22, and 23 were packed with structured packing, all had the same height, and a packing length equivalent to 20 theoretical plates. Mellapak 500Y manufactured by Sulzer was used as the structured packing.

[0034] Next, oxygen gas having the atomic composition shown in Table 1 below was supplied to the first distillation column 21 from the raw material feed line 43. After a sufficient amount of oxygen had accumulated at the top of the first distillation column 21, circulation of oxygen gas was started via the oxygen circulation line 45. Furthermore, the ozonizer 33 was started to start supplying a mixed gas of oxygen and ozone. In the first distillation column 21, the mixed gas of oxygen, ozone, and CF4 was separated by distillation. After a predetermined concentration of ozone had accumulated at the bottom of the first distillation column 21 and the distillation column had stabilized, supply of a mixed gas of ozone and CF4 to the photoreaction cell 10 from the photoreaction cell introduction line 46 was started.

[0035] [Table 1]

[0036] By the photoreaction in the photoreaction cell 10 18 Ozone containing O is selectively decomposed, 18 The oxygen gas enriched with O and the other ozone and CF4 gas are supplied to the middle part of the second distillation column 22 via the light reaction cell outlet line 47. In the second distillation column 22, 18 The gas mixture is separated by distillation into oxygen enriched in O and a mixed gas of ozone and CF4. The mixed gas of ozone and CF4 extracted from the bottom of the second distillation column 22 is introduced into the ozone decomposition catalyst column 34 via the ozone decomposition catalyst column introduction line 49, where the ozone is decomposed into oxygen. The mixed gas of oxygen and CF4, which is the outlet gas of the ozone decomposition catalyst column 34, is introduced into the third distillation column 23 via the ozone decomposition catalyst column discharge line 50, where it is separated by distillation into oxygen and CF4. Oxygen gas is discharged from the top of the third distillation column 23 via the exhaust oxygen gas withdrawal line 51, and CF4 is refluxed from the bottom of the column to the intermediate section of the first distillation column 21 via the added gas (CF4) circulation line 44.

[0037] At the top of the second distillation column 22 18When a certain amount of oxygen gas enriched in O had accumulated and the second distillation column 22 had stabilized, oxygen gas was introduced from the top of the second distillation column 22 through the oxygen isotope gas extraction line 48 into the residual added gas (CF4) concentration analyzer 35, and measurement of the CF4 concentration (residual added gas concentration) in the oxygen gas began. The CF4 concentration in the oxygen gas at the start of measurement was approximately 3000 ppm. At this point, the gas used for analysis was not introduced into flow control valve 36, but was refluxed to the top of second distillation column 22 via analysis gas return line 52. Operation was continued while oxygen gas continued to accumulate at the top of second distillation column 22. When the CF4 concentration fell below 1 ppm, the threshold value being 1 ppm in this example, reflux to second distillation column 22 via analysis gas return line 52 was stopped, and extraction of oxygen gas began via flow control valve 36. If the CF4 concentration exceeded the specific threshold value of 1 ppm, reflux to the top of second distillation column 22 was continued via analysis gas return line 52. When the CF4 concentration became 1 ppm or less (below a specific threshold), feedback control of the opening of the flow control valve 36 with respect to the CF4 concentration was simultaneously initiated, and the CF4 concentration was controlled to be about 5 ppm. When the CF4 concentration in the oxygen gas stabilized at 5 ppm ± 2 ppm, the amount of oxygen extracted from the flow control valve 36 was 10 sccm. The atomic composition of the product oxygen gas at this time was as shown in Table 2 below. 18 The O concentration is 3.5 times higher than the value in Table 1, and among the multiple stable oxygen isotopes, 18 It was found that O was enriched.

[0038] [Table 2]

[0039] The results shown in Example 1 demonstrate that the present invention makes it possible to measure the rate at which oxygen isotope-selectively produced by the photoreaction of ozone induced by laser irradiation. This allows the stable oxygen isotope gas produced by the photoreaction to be extracted, thereby preventing ozone contamination and keeping the isotope concentration of the product oxygen gas constant. At the same time, it minimizes the amount of product oxygen gas lost from the bottom of the second distillation column 22, enabling efficient operation of the stable oxygen isotope enrichment apparatus.

[0040] (Comparative Example 1) In Comparative Example 1, similarly to Example 1, the stable oxygen isotope enrichment device 200 shown in FIG. 18 The added gas, apparatus configuration, and start-up procedure were the same as in Example 1, and the atomic composition of the oxygen gas supplied to the first distillation column 21 was as shown in Table 1 above. At the top of the second distillation column 22 18 After a certain amount of O-enriched oxygen gas had accumulated and the second distillation column 22 had stabilized, oxygen gas was introduced from the top of the second distillation column 22 via the oxygen isotope gas extraction line 48 into the residual additive gas (CF4) concentration analyzer 35, and measurement of the CF4 concentration in the oxygen gas (residual additive gas concentration) began. The CF4 concentration in the oxygen gas at the start of measurement was approximately 3000 ppm. At this point, the gas used for analysis was not introduced into the flow control valve 36, but was refluxed to the second distillation column 22 via the analysis gas return line 52.

[0041] Accumulation of oxygen gas at the top of second distillation column 22 continued, and when the CF4 concentration reached 1 ppm, reflux to second distillation column 22 via analysis gas return line 52 was stopped, and withdrawal of oxygen gas began via flow control valve 36. At this time, feedback control of the aperture of flow control valve 36 relative to the CF4 concentration was not performed, and withdrawal of product oxygen gas began at a flow rate set to 15 sccm. The atomic composition of the product oxygen gas initially withdrawn was as shown in Table 2 above, but after 24 hours of continued withdrawal, the CF4 concentration in the oxygen gas withdrawn from the top of the column had dropped to 5%, and the atomic composition of the product oxygen gas was as shown in Table 3 below.

[0042] [Table 3]

[0043] Comparative Example 1 shows that without feedback control of the flow rate control valve 36 relative to the CF4 concentration, it becomes difficult to achieve a mass balance between the amount of oxygen generated by isotope-selective decomposition in the photoreaction cell 10 and the amount of oxygen extracted from the top of the second distillation column 22. As a result, the CF4 concentration at the top of the second distillation column 22 increases, and as a result, non-isotopically enriched ozone gas is mixed into the oxygen gas extracted from the top, resulting in a decrease in the isotopic enrichment of the product oxygen gas. In Comparative Example 1, without performing control equivalent to the above-described example, the product oxygen gas was extracted for 24 hours at a flow rate setting of 15 sccm, resulting in a decrease in the amount of oxygen at the top of the column and the entrainment of some of the gas at the bottom of the column. The oxygen concentration in this state was measured. In Comparative Example 1, the enrichment was 3.5 times after the start of extraction, but the enrichment decreased over time, reaching approximately 3 times after 24 hours, as shown in Table 3. It is expected that the enrichment will continue to decrease with the passage of time. From the above explanation, it has been found that the isotopic enrichment of the product oxygen gas can be improved by implementing feedback control of the aperture of the flow control valve 36 in relation to the CF concentration, which is the residual additive gas concentration, and by achieving a mass balance between the amount of oxygen generated by isotope-selective decomposition in the photoreaction cell 10 and the amount of oxygen extracted from the top of the second distillation column 22. It has been found that by carrying out the operating method described above, the flow rate of oxygen gas extracted from the top of the second distillation column can be adjusted in accordance with the concentration of the residual additive gas, thereby stabilizing the additive gas concentration at the bottom of the second distillation column 22. It has also been found that an efficient operating method for an oxygen stable isotope enrichment apparatus can be provided, which can improve the isotope enrichment of the product oxygen gas. [Industrial Applicability]

[0044] The above-described aspects of the present invention can be used in a stable oxygen isotope enrichment device that enriches stable oxygen isotopes by a combination of distillation separation and gas-phase photoreaction. [Explanation of symbols]

[0045] 10...photoreaction cell, 11...laser light source, 21...first distillation column, 22...second distillation column, 23...third distillation column, 33...ozonizer, 34...ozone decomposition catalyst column, 35...residual added gas concentration analyzer (residual added gas concentration analyzer), 36...flow control valve (flow control device), 38...control device, 43...raw material feed line, 44...added gas circulation line, 45...oxygen circulation line, 46...photoreaction cell inlet line, 47...photoreaction cell outlet line, 48...gas extraction line, 49...ozone decomposition catalyst column inlet line, 50...ozone decomposition catalyst column outlet line, 52...analysis gas return line.

Claims

1. an ozonizer that converts at least a portion of a source oxygen gas containing a plurality of stable oxygen isotopes into ozone; a first distillation column that separates a mixed gas of oxygen gas and ozone gas from the ozonizer and an additive gas from a third distillation column described below by distillation into oxygen gas at an upper portion of the column and ozone gas and an additive gas at a bottom of the column; a photoreaction cell into which the mixed gas of ozone gas and an additive gas from the bottom of the first distillation column is introduced and which selectively decomposes the ozone gas into oxygen gas by photoreaction; a second distillation column for separating the mixed gas of oxygen gas, ozone gas, and additive gas from the photoreaction cell by distillation into oxygen gas at an upper portion of the column and ozone gas and additive gas at a bottom of the column; an ozone decomposition catalyst column for decomposing ozone in the mixed gas of ozone gas and added gas from the bottom of the second distillation column into oxygen gas; An oxygen stable isotope enrichment apparatus comprising a third distillation column that distills and separates the mixed gas of oxygen and additive gas from the ozone decomposition catalyst column into oxygen gas at an upper part of the column and additive gas at a bottom of the column, An analyzer is installed to measure the concentration of the residual additive gas in the upper part of the second distillation column, and a device is installed to control the flow rate of oxygen gas extracted from the upper part of the second distillation column based on the signal from the analyzer.

1. A stable oxygen isotope enrichment device.

2. The additive gas is CF ４ 2. The stable oxygen isotope enrichment device according to claim 1, wherein the stable oxygen isotope enrichment element is one or more of krypton, xenon and radon.

3. 3. The stable oxygen isotope enrichment apparatus according to claim 1, wherein an analysis gas return line is provided in the device for controlling the flow rate of the oxygen gas.

4. 3. The stable oxygen isotope enrichment apparatus according to claim 1, wherein a gas outlet line is connected to the top of the second distillation column, and the analyzer is incorporated in the gas outlet line.

5. an ozonizer that converts at least a portion of a source oxygen gas containing a plurality of stable oxygen isotopes into ozone; a first distillation column that separates a mixed gas of oxygen gas and ozone gas from the ozonizer and an additive gas from a third distillation column described below by distillation into oxygen gas at an upper portion of the column and ozone gas and an additive gas at a bottom of the column; a photoreaction cell into which the mixed gas of ozone gas and an additive gas from the bottom of the first distillation column is introduced and which selectively decomposes the ozone gas into oxygen gas by photoreaction; a second distillation column for separating the mixed gas of oxygen gas, ozone gas, and additive gas from the photoreaction cell by distillation into oxygen gas at an upper portion of the column and ozone gas and additive gas at a bottom of the column; an ozone decomposition catalyst column for decomposing ozone in the mixed gas of ozone gas and added gas from the bottom of the second distillation column into oxygen gas; An oxygen stable isotope enrichment apparatus comprising a third distillation column that distills and separates the mixed gas of oxygen and additive gas from the ozone decomposition catalyst column into oxygen gas at an upper part of the column and additive gas at a bottom of the column, using an oxygen stable isotope enrichment apparatus equipped with an analyzer for measuring the concentration of residual additive gas in the upper part of the second distillation column and a device for controlling the flow rate of oxygen gas extracted from the upper part of the second distillation column based on a signal from the analyzer; a flow rate of oxygen gas extracted from the top of the second distillation column in accordance with the concentration of the residual additive gas, thereby stabilizing the additive gas concentration in the second distillation column.

6. The additive gas is CF ４ 6. The method for operating a stable oxygen isotope enrichment apparatus according to claim 5, wherein one or more of krypton, xenon and radon are used.

7. 7. The method for operating an oxygen stable isotope enrichment apparatus according to claim 5 or 6, characterized in that the device for controlling the flow rate of the oxygen gas is provided with a gas outlet line and a gas return line for extracting gas from the top of the second distillation column, and the amount of gas discharged to the outside of the system from the gas return line or the amount of gas returned to the top of the second distillation column via the gas return line is adjusted according to the concentration of the residual additive gas contained in the gas taken in through the gas outlet line.

8. During operation of the stable oxygen isotope enrichment apparatus, if the concentration of the residual additive gas contained in the gas taken into the gas vent line exceeds a specific threshold value, the operation of the stable oxygen isotope enrichment apparatus is continued while returning the gas taken into the gas vent line to an upper part of the second distillation column using the gas return line; 8. The method for operating a stable oxygen isotope enrichment apparatus according to claim 7, wherein, when the concentration of the residual additive gas contained in the gas taken into the gas outlet line falls below a specific threshold, the amount of gas discharged to the outside of the system from the gas outlet line and the amount of gas returned to the top of the second distillation column using the gas return line are increased or decreased to adjust the residual additive gas concentration in the top of the second distillation column and stabilize the additive gas concentration in the second distillation column.

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