Patent Grant
8337802
This application is the U.S. national phase of International Application No. PCT/JP2006/316079 filed 16 Aug. 2006 which designated the U.S. and claims priority to Japanese Application No. 2005-236499 filed 17 Aug. 2005, the entire contents of each of which are hereby incorporated by reference.
The present invention relates to a method for concentrating an oxygen isotope or isotopes. More particularly, the present invention relates to a method for efficiently concentrating a stable oxygen isotope 17O that has extremely low abundance to a high concentration by combining laser isotope separation utilizing photodissociation of ozone by a laser beam and separation by distillation, and to a method for efficiently concentrating 17O and 18O simultaneously.
Among the stable oxygen isotopes 160, 17O and 18O, 17O is the only one that has nuclear spin. For this reason, compounds labeled with 17O have been used for research purposes such as structural analysis by means of nuclear magnetic resonance, and used as a tracer in such fields as chemistry and medicine. They are also considered useful in medicine as the material to manufacture the diagnostic agent 18FDG (PET contrast medium made by labeling fluorodeoxyglucose with a fluorine 18 radioactive isotope having a positron-emitting nuclide) used in positron emission tomography diagnosis (PET) of tumors and other anomalies.
While 17O and 18O are useful isotopes for industrial purposes, they exist in extremely low abundance in nature. Therefore, in order to use the isotope in practical application, 17O and/or 18O must be concentrated from compounds that include oxygen atoms.
As the conventional method for concentrating 17O, for example, the following conventional methods have been known.
There is a method of distilling water as the starting material so as to concentrate 17O up to 25 atom %, and then concentrating it to 90 atom % by thermal diffusion (Non-Patent Document 1). Another method uses nitrogen monoxide (NO) as the starting material and distils it to concentrate 17O, and then uses thermal diffusion to concentrate 17O to a high concentration (for example, 40 atom %) (Non-Patent Document 4). Another method uses oxygen as the starting material and distills it to concentrate 17O to 10 atom % (Patent Document 1). Another method employs photopredissociation of formaldehyde by means of irradiation with a Ne ion laser so as to concentrate 17O (Non-Patent Document 2, Patent Documents 5 and 6). There are also such methods as ozone is irradiated with visible light and ultraviolet rays (Non-Patent Document 3) and a semiconductor laser is used to separate ozone molecules that include 17O by photodissociation, thereby to enrich 17O in oxygen (Non-Patent Documents 2, 3 and 4).
The method described in Non-Patent Document 1 has such a problem that there is an upper limit of several atomic percentage points on the practically achievable concentration of 17O when yield is taken into consideration. The method described in Non-Patent Document 4 has such a problem that 17O-enriched H2O and O2, that are manufactured by this method of concentration and are commercially available, have insufficient levels of concentration.
The methods described in Non-Patent Document 2 and Patent Documents 5 and 6 also provide insufficient levels of concentration and have not developed enough to establish technologies that can be implemented on an industrial scale.
According to the method described in Non-Patent Document 3, although 17O and 18O are concentrated in residual ozone and the isotope effect of ozone decomposition can be confirmed, such a level of concentration that can be utilized in the separation of an isotope cannot be achieved. Also, technologies that can be implemented on an industrial scale have not been established.
The methods described in Patent Documents 2, 3 and 4, on the other hand, are promising in view of industrial application. With these methods, however, the absorption wavelength regions, in which various ozone molecules with different oxygen isotopes absorb a laser beam, overlap each other. Therefore, an attempt to selectively dissociate only the ozone molecules that include 17O by means of a laser beam inadvertently causes the ozone isotope molecules such as 16O3 having higher abundance to dissociate at the same time, particularly in the case where the abundances of ozone molecules that include 17O are lower. Thus, it is difficult to efficiently concentrate 17O.
The method described in Patent Document 1 will be described in more detail below in relation to the present invention.
All isotope molecules that include either 16O, 17O or 18O have vapor pressures (boiling points) that are very approximate to each other. An isotope molecule that includes 17O is an intermediate component between an isotope molecule that includes 16O and an isotope molecule that includes 18O (an isotope molecule that includes 17O has a vapor pressure or a boiling point of an intermediate value between those of an isotope molecule that includes 16O and an isotope molecule that includes 18O). Natural abundance of 17O is about 370 atomppm, lower than that of 18O that is 2000 atomppm. As a result, it is difficult to efficiently achieve a high concentration (for example, 5 atom % or higher) of 17O by the method of concentrating 17O by distillation as disclosed in Patent Document 1. This problem will be described below in more detail by way of example.
A starting material F (for example, H2O, NO, O2, etc.) that includes oxygen isotopes of natural abundance shown in Table 1 is fed to the distillation column 1 at an intermediate point near the top-thereof, and a product P1 enriched in 17O or 18O is drawn from the bottom of the column. In addition to the product P1, another product P2 enriched in 17O or 18O may also be drawn from an intermediate position of the column located near the bottom than the point of feeding the starting material F. Waste gas W depleted in 17O or 18O in comparison to the starting material F is discharged from the top.
16O
17O
18O
In the case where 17O is concentrated at the bottom of the distillation column 1 and the product P1 is drawn from the bottom, concentrations of different isotopes are distributed in the distillation column roughly as shown in
In order to achieve a high concentration (for example, 5 atom % or higher) of 17O, a larger height (more theoretical plates) of the distillation column is required. In a distillation column having a larger height, as illustrated in
Moreover, the distillation step requires hold-up of a large quantity of liquid within the apparatus due to the principle of operation. As a result, a period as long as several years is required in startup of the apparatus in order to concentrate 17O, of which natural abundance is about 370 ppm at the most, to a high concentration (for example, 5 atom % or higher).
For the reasons described above, it may well be said that concentration of 17O to a high concentration (for example, 8 atom % or higher) merely by distillation is impractical as an industrial step.
An object of the present invention is to provide a method for concentrating 17O which is capable of concentrating 17O, which is a stable isotope of oxygen having an extremely low abundance, to a high concentration efficiently on an industrially viable scale. Another object of the present invention is to provide a method for concentrating 17O to a high concentration while concentrating 18O at the same time.
To solve the object described above,
a first aspect of the present invention provides a method for concentrating an oxygen isotope including concentrating the oxygen isotope through distillation of oxygen; and concentrating oxygen isotope 17O through photodissociation of ozone.
The method for concentrating an oxygen isotope or isotopes of the present invention preferably includes carrying out isotope scrambling.
The method for concentrating an oxygen isotope or isotopes of the present invention preferably also includes depleting oxygen isotope 18O through photodissociation of ozone.
In the method for concentrating an oxygen isotope or isotopes of the present invention, at least one step of concentrating the oxygen isotope through distillation of oxygen; concentrating oxygen isotope 17O through photodissociation of ozone; depleting oxygen isotope 18O through photodissociation of ozone; and carrying out isotope scrambling, is preferably carried out twice or more.
In the method for concentrating an oxygen isotope or isotopes of the present invention, either the step of depleting oxygen isotope 18O may be carried out first followed by the step of concentrating oxygen isotope 17O, or the step of concentrating oxygen isotope 17O may be carried out first followed by the step of depleting oxygen isotope 18O.
A second aspect of the present invention provides a method of manufacturing heavy oxygen water, including: adding hydrogen to 17O-enriched oxygen and/or 18O-enriched oxygen obtained by the method for concentrating an oxygen isotope or isotopes according to any one of claims 1 to 9 so as to obtain water in which the oxygen isotope 17O and/or oxygen isotope 18O are concentrated to a 1 atom % or higher concentration.
A method for concentrating an oxygen isotope or isotopes of the present invention enables 17O of high concentration to be obtained sufficiently. Since this method enables carrying out concentration with a shorter startup time than in the prior art, 17O of high concentration can be obtained in an industrial scale at a low cost. During the concentration, conversion of ozone to oxygen or conversion of oxygen to ozone can be easily carried out, and therefore, 17O can be concentrated by combining various steps, so that a proper step can be selected in accordance to the desired concentration of 17O and the planned production output. When the starting material is processed to obtain 17O of high concentration, 17O of high concentration is separated and recovered from the oxygen in the starting material in the step of concentrating oxygen isotope 17O and the step of depleting oxygen isotope 18O. As a result, 18O of high concentration as well as 17O of high concentration can be obtained.
Moreover, heavy oxygen water enriched in 17O or 18O can be obtained at a low cost on an industrial scale, by using 17O-enriched oxygen or 18O-enriched oxygen obtained by the method for concentrating an oxygen isotope or isotopes of the present invention.
The reference numerals shown in these figures as defined as follows:
1 and 6 represent a distillation column, 2 represents an ozone separation apparatus (Type A), 3 represents an isotope scrambler, and 4 and 5 represent an ozone separation apparatus (Type B).
Now the present invention will be described in detail below.
The present invention provides a method of concentrating 17O to a high concentration (for example, 5 atom % or higher) by a step designed to make the best use of the effects of concentrating 17O of a 17O concentrating method based on a distillation apparatus and of a 17O concentrating method based on a laser isotope separation apparatus (hereinafter referred to simply as laser separation apparatus) that utilizes the photodissociation reaction of ozone.
According to the method, 17O is concentrated by distillation in a low concentration zone (for example, from 370 atomppm to 0.2 atom %), and the preliminarily concentrated 17O obtained by the distillation is further concentrated by laser separation to obtain 17O of high concentration (for example, 5 atom % or higher).
The present invention also provides a method for promoting the concentration of 17O in the distillation column by using the laser separation apparatus connected to the distillation column to effectively remove 18O that impedes the concentration of 17O by distillation. The present invention also provides a method for achieving an ultra-high concentration, for example 70% or higher, of 17O by combining the above-mentioned methods.
Concentration of 17O by means of the laser separation apparatus can be carried out by the following two methods.
One is to selectively decompose ozone molecules that include 17O, among ozone molecules including 16O, 17O and 18O, in ozone gas and separate the resultant 17O-enriched oxygen from the ozone gas, thereby to concentrate 17O. Another method is to remove 18O-enriched oxygen, which is obtained by selectively decomposing ozone molecules that include 18O, from the ozone gas that includes the various isotopes thereby to deplete 18O.
According to the present invention, concentration of 17O is carried out efficiently by combining the step of concentrating 17O and/or the step of depleting 18O with the oxygen distillation step. Efficiency of 17O concentration can be further improved by adding a step of isotope scrambling to the method described above.
When both the step of concentrating 17O and the step of depleting 18O are carried out, whichever thereof may be done first prior to the other. Also these steps may be placed either before or after the oxygen distillation step.
Moreover, efficiency of 17O concentration can be further improved by running at least one of the oxygen distillation step, the step of concentrating oxygen isotope 17O, the step of depleting oxygen isotope 18O and the step of carrying out isotope scrambling, twice or more.
When highly concentrated 17O is to be obtained from the starting material of oxygen, highly concentrated 18O is separated and recovered from the starting material of oxygen in the step of concentrating 17O and the step of depleting 18O. Thus the steps enable highly concentrated 18O (for example, 20 atom % or higher) as well as highly concentrated 17O to be obtained.
The 17O-enriched oxygen (for example, 5 atom % or higher) or the 18O-enriched oxygen (for example, 20 atom % or higher) obtained by the method of the present invention can be used to manufacture 17O-enriched water or 18O-enriched water having 1 atom % or higher concentration of desired oxygen isotope, by the ordinary method, such as diluting with argon, adding hydrogen in a quantity that corresponds to the quantity of oxygen and causing oxygen and hydrogen react on a platinum catalyst at a temperature of 80° C. or higher.
The first embodiment, that is the most basic embodiment of the present invention, is schematically shown in
It is preferable to use ultra-high purity oxygen as a starting material F. The ultra-high purity oxygen is preferably obtained by removing argon, hydrocarbons and other impurities from industrial-grade oxygen thereby significantly improving the chemical purity of oxygen. The oxygen distillation column may include a plurality of distillation columns connected in cascade, instead of the single distillation column 1. The distillation column may be filled with structured packing or unstructured packing, and a similar effect can be achieved regardless of whichever is used.
The constitution of the oxygen distillation column and the packing in the distillation column described above apply also to other embodiments.
The laser separation apparatus 2 (type A) used in this embodiment has the same constitution as that disclosed, for example, in Patent Documents 2 and 3, and an example thereof is shown in
In this embodiment, the first stage of 17O concentration is carried out in the distillation column 1, then oxygen gas FLIS is introduced into an ozonizer 21 so as to generate ozone, and ozone-oxygen mixture gas produced thereby is mixed with a dilution gas (Kr) and recovered dilution gas, followed by the separation of ozone and oxygen from the mixture gas by using an ozone separation apparatus 22. The separated oxygen is mixed with the oxygen gas FLIS supplied from the distillation column 1 and is used again in the generation of ozone. Meanwhile the separated ozone is charged together with the dilution gas to a laser separation apparatus 23, where ozone molecules that include 17O are selectively decomposed into oxygen by irradiating with a laser beam of a particular wavelength. The 17O-enriched oxygen thus obtained, undecomposed ozone and the dilution gas are sent to an oxygen recovering apparatus 24, where 17O-enriched oxygen gas PLIS is obtained. The undecomposed ozone and the dilution gas that remain are sent to an ozone separation apparatus 25, where all ozone molecules are decomposed into oxygen. The resultant oxygen gas and the dilution gas are sent to a dilution gas recovering apparatus 26 where 17O-depleted and 18O-enriched oxygen gas WLIS is separated, while the recovered dilution gas is added again to the mixture gas of ozone produced in the ozonizer 21 and oxygen.
While this embodiment uses Kr as the gas for diluting ozone, other gases capable of diluting ozone without compromising the effects of the present invention may be also used.
There is no restriction on the details of the step carried out in the laser separation apparatus (LIS unit), as long as there is the function of separating the oxygen of the starting material into isotope-enriched oxygen and isotope-depleted oxygen by making use of the photodissociation reaction of ozone.
The above applies to the other embodiments as well.
The operation of this embodiment proceeds as follows. First, oxygen Dbot (FLIS in
The concentration step was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 2 as having the specifications shown in Table 4, and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of oxygen isotopes in various points of the apparatus determined by the simulation are shown in Table 5. The composition distribution of oxygen isotopes within the distillation column 1 is shown in Table 3. Purity (atom %) of each isotope given in Table 5 was calculated by the equation shown under Table 5 by using the concentration (mol %) of oxygen gas including the respective isotope determined in the simulation. This applies also to the other embodiments. The computer program for the distillation step used in this simulation is explained in WO00/27509. Composition of the ultra-high purity oxygen F shown in Table 2 was calculated from the values of natural abundance shown in Table 1.
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O16O17O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
The apparatus of this embodiment is the distillation column 1 of the first embodiment with an isotope scrambler 3 connected thereto. A schematic diagram of this apparatus is shown in
The isotope scrambler 3 is an apparatus for promoting isotope scrambling, that is a phenomenon of isotope molecules of different isotope species which coexist randomly exchanging the constituent atoms, function thereof being described in detail in WO00/27509.
The isotope scrambler 3 may be connected to the distillation column 1 at any point thereof. A part of the gas is drawn from the distillation column 1, with the drawn gas being sent to the isotope scrambler 3, subjected to isotope scrambling and is returned to the distillation column. At this time, it is preferable to draw the gas from the distillation column 1 at a position near the column bottom or at the bottom. There is no restriction on the portion of the distillation column 1 where the gas is returned after the isotope scrambling. The gas may be returned at the same position where the gas was drawn, or near that position.
This embodiment is characterized by, in addition to the isotope concentrating effect of the first embodiment, the capability to promote the concentration of 17O and 18O in the distillation column by means of the isotope scrambler 3 so as to increase the 17O concentration in the product P.
The operation of this apparatus was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 2 as having the specifications shown in Table 6, and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of oxygen isotopes in various points of the apparatus determined by the simulation are shown in Tables 7 and 8. The composition distribution of oxygen isotopes within the distillation column 1 is shown in Table 5.
The simulation was based on the condition of drawing the gas from the distillation column 1 at the bottom at a rate of 10×10−3 mol/s, and is returned to the bottom of the column after being processed in the isotope scrambler 3.
16O16O17O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
This embodiment is an advancement of the first embodiment, aimed at further improvements in the concentration and yield of 17O. The apparatus is schematically shown in
A laser separation apparatus 4 (type B) is an apparatus for carrying out laser separation in two stages. The same function may be performed by two units of the laser separation apparatus 2 (type A) used in the first embodiment connected together as shown in
In this apparatus, the first stage of 17O concentration is carried out in the distillation column 1. Then, oxygen gas FLIS is introduced into an ozonizer 41 so as to generate ozone, and the produced ozone-oxygen mixture gas is mixed with a dilution gas (Kr) and recovered dilution gas. Then, by using an ozone separation apparatus 42, ozone and oxygen are separated from the mixture gas. Separated oxygen is mixed with the oxygen gas FLIS supplied from the distillation column 1 and is used again in the generation of ozone. Meanwhile, the separated ozone is charged together with the dilution gas to a first laser separation apparatus 43, where ozone molecules that include 17O are selectively decomposed into oxygen by irradiating with a laser beam of a particular wavelength. Oxygen including 17O thus obtained, undecomposed ozone and the dilution gas are sent to a first oxygen recovering apparatus 44, where 17O-enriched oxygen gas PLIS is obtained. The undecomposed ozone and the dilution gas that remain are sent to a second laser separation apparatus 45, where ozone molecules that include 18O are selectively decomposed into oxygen by irradiating with a laser beam of a particular wavelength. The oxygen including 18O thus obtained, the undecomposed ozone and the dilution gas are sent to a second recovering apparatus 46 where 18O-enriched oxygen gas P2LIS is obtained. The undecomposed ozone and the dilution gas that remain are sent to the ozone separation apparatus 47, where all ozone molecules are decomposed into oxygen. The resultant oxygen gas and the dilution gas are sent to a dilution gas recovering apparatus 48 where oxygen gas WLIS depleted in 17O and 18O is separated, while the recovered dilution gas is added again to the mixture gas of ozone produced in the ozonizer 41 and oxygen.
In the case of the first embodiment, the oxygen gas drawn from the bottom of the distillation column 1 is introduced into the laser separation apparatus 2, where the ozone molecule 16O16O17O that includes 17O is selectively decomposed so as to obtain the 17O-enriched oxygen gas P, while 17O-depleted oxygen gas that remains is discarded as waste gas W2 without returning it into the distillation column 1, to prevent the concentration of 17O from decreasing due to the increasing concentration of 18O in the distillation column 1. This is because returning the 18O-enriched gas W2 to the distillation column 1 causes further concentration of 18O at the bottom of the distillation column 1, thus resulting in decreasing concentration of 17O at the bottom of the distillation column 1.
In this embodiment, the ozone molecule 16O16O18O that includes 18O is selectively decomposed by the second-stage laser separation from ozone that has been depleted in 17O in the first-stage laser separation, so as to remove the 18O-enriched oxygen gas, while the remainder of oxygen gas R (WLIS in
The operation was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 4 as having the specifications shown in Table 10, and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of oxygen isotopes in various points of the apparatus determined by the simulation are shown in Table 9. It can be seen that P1 is enriched in 17O and W2 is enriched in 18O.
The composition distribution of oxygen isotopes within the distillation column 1 is shown in Table 9.
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O17O
16O16O18O
In the case of the third embodiment, 17O is concentrated in the first-stage laser separation and 18O is concentrated in the second-stage laser separation, although these operations may be carried out in the reverse order.
The operation was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 5 as having the specifications shown in Table 12, and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of isotopes in various points of the apparatus determined by the simulation are shown in Table 11. The composition distribution of oxygen isotopes within the distillation column 1 is shown in
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O18O
16O16O17O
The apparatus of this embodiment is the distillation column 1 of the fourth embodiment with an isotope scrambler 3 connected thereto. This embodiment enhances the concentration of 17O in the distillation column 1, and improves the concentration and the yield of 17O. A schematic diagram of this embodiment is shown in
The operation was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 5 as having the specifications shown in Table 15, and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of isotopes in various points of the apparatus determined by the simulation are shown in Tables 13 and 14. It can be seen that P1 is enriched in 17O and W2 is enriched in 18O. The composition distribution of oxygen isotopes within the distillation column 1 is shown in
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O18O
16O16O17O
The apparatus of this embodiment includes a distillation column 6, the isotope scrambler 3 and the laser separation apparatus 2 connected to each other. The distillation column 6 has the same construction as the distillation column 1, except for being larger in height. The laser separation apparatus 2 is connected to the distillation column 6 in an intermediate portion of the column. The isotope scrambler 3 may be connected to the distillation column 6 at any point thereof similarly to the second embodiment, although the connecting point is preferably at the bottom of the column or in the vicinity thereof. There is no restriction on the position of the distillation column 6 where the gas is returned thereto, and the gas may be returned at the same position where the gas was drawn, or near that position. This embodiment is schematically illustrated in
In this embodiment, 18O-enriched oxygen P18 accumulates at the bottom of the distillation column 6. The intermediate component of 17O accumulates mainly in the form of 16O17O or 17O18O with highest concentration in the intermediate portion of the distillation column 6. Oxygen gas Dcut is drawn from near the intermediate portion of the column.
Then, the oxygen gas Dcut is fed to the laser separation apparatus 2, where the ozone molecule 16O16O17O that includes 17O is selectively decomposed so as to obtain 17O-enriched oxygen P17, while the remaining oxygen gas R is returned to the distillation column 6.
This embodiment is characterized in that the oxygen gas Dcut is drawn from the distillation column 6 at the intermediate portion thereof where the concentration of 17O is highest, so that 17O can be separated efficiently and mixing of 18O into oxygen P17 can be minimized, thereby making it possible to prevent the yield of 18O in oxygen P18 from decreasing.
The concentration of 17O in the oxygen gas Dcut is dependent on the height of the distillation column 6. In the case where P18 has the same level of 18O concentration, the higher the height of the distillation column 6 the higher the concentration of 17O in the oxygen gas Dcut. Therefore, the height of the distillation column 6 is preferably 150 m or more. From a practical point of view, on the other hand, height of the distillation column 6 is preferably not larger than 600 m.
The operation was simulated on a computer by assuming the distillation column 6 as having the specifications shown in Table 16, the laser separation apparatus 2 as having the specifications shown in Table 19, and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of isotopes in various points of the apparatus determined by the simulation are shown in Tables 17 and 18. The composition distribution of oxygen isotopes within the distillation column 6 is shown in
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O17O
This embodiment has such a constitution as laser separation is carried out in two stages in the sixth embodiment, as shown in
As oxygen R1 that has been enriched in 18O by selectively decomposing 16O16O18O in the first-stage ozone decomposition is returned to the distillation column 6, and 16O16O17O is selectively decomposed in the second-stage ozone decomposition, for example, the concentration and the yield of 17O can be further improved.
The operation was simulated on a computer by assuming the distillation column 6 as having the specifications shown in Table 16, the laser separation apparatus 4 as having the constitution shown in
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O18O
16O16O17O
In this embodiment, oxygen enriched in 17O to a concentration higher than the natural abundance is used as the starting material so as to concentrate 17O to an ultra-high concentration (for example, 40 atom % or higher) by means of a laser separation apparatus and a distillation column. The constitution of this embodiment is schematically shown in
As mentioned previously, distillation tends to cause 18O, which has the highest boiling point among the oxygen isotopes and is most abundant in nature, to be concentrated at the bottom of the distillation column. Therefore, in order to concentrate 17O efficiently to an ultra-high concentration, for example, it is preferable to remove 18O from the distillation column as far as possible. Accordingly in this embodiment, 18O-enriched oxygen W1 is separated from the oxygen included in the starting material F by using the laser separation apparatus 4 in the first stage, and a 17O-enriched oxygen Dfeed is sent to the distillation column 1 in the second stage. This enables suppression of the concentration of 18O within the distillation column 1.
In the case of distillation, when the concentration of 17O approaches the ultra-high concentration (for example, 40 atom % or higher), the ratio of change in 17O concentration within the distillation column to the change in the height of the distillation column decreases, and it becomes difficult to concentrate 17O further. Accordingly in this embodiment, oxygen gas Dbot is fed to the laser separation apparatus 2 when the concentration of 17O at the bottom of the distillation column 1 exceeds 40 atom %, so as to selectively decompose 17O3 and obtain 17O-enriched oxygen P.
In this operation, a high concentration of 17O can be achieved very efficiently.
The operation was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 4 as having the constitution shown in
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O18O
16O16O17O
17O17O17O
This embodiment is an advancement of the eighth embodiment as shown in
This enables suppression of the concentration of 18O at the bottom of the distillation column 1, so that 17O of a further higher concentration is obtained.
The operation was simulated on a computer by assuming the distillation column 1 as having the specifications shown in Table 3, the laser separation apparatus 4 as having the specifications shown in Table 25, the laser separation apparatus 2b as having the specifications shown in Table 30, the laser separation apparatus 2a as having the specifications shown in Table 31 and the ultra-high purity oxygen F of the starting material as having the composition shown in Table 2. Flow rates of oxygen and the composition of isotopes in various points of the apparatus determined by the simulation are shown in Tables 27 to 29. It can be seen that P is enriched in 17O and W1 is enriched in 18O. The composition distribution of oxygen isotopes within the distillation column 1 is shown in
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O2
16O17O
16O18O
17O2
17O18O
18O2
16O
17O
18O
16O16O18O
17O17O17O
The operation of concentrating 17O and 18O was simulated under the conditions of the first embodiment, and it was found that oxygen gas including 9.1 atom % of 17O and oxygen gas including 25.2 atom % of 18O could be obtained with a yield of 5.8% for 17O and 69.8% for 18O.
Yield of 17O, for example, in Example 1 was determined by the following equation using the values given in Table 5.
Yield [%]=((Flow rate)P×(Purity of isotope)17OP)/((Flow rate)F×(Purity of isotope)17OF)×100
The yield of 18O was also determined by a similar equation.
The operation of concentrating 17O and 18O was simulated under the conditions of the second embodiment, and it was found that oxygen gas including 10.3 atom % of 17O and oxygen gas including 25.2 atom % of 18O could be obtained with a yield of 7.8% for 17O and 73.1% for 18O, both higher than those of Example 1.
The operation of concentrating 17O and 18O was simulated under the conditions of the third embodiment, and it was found that oxygen gas including 9.7 atom % of 17O could be obtained, with a yield of 14.1% for 17O, higher than that of Example 1. While the yield of 18O was 69.8%, comparable to that of Example 1, purity of isotope 18O was 29.2 atom %, indicating that oxygen gas including 18O of higher purity than that of Example 1 can be obtained.
The operation of concentrating 17O and 18O was simulated under the conditions of the fourth embodiment, and it was found that oxygen gas including 10.8 atom % of 17O and oxygen gas including 29.0 atom % of 18O could be obtained. The yield of 17O was 11.8%, higher than that of Example 1. The yield of 18O was 70.9%.
The operation of concentrating 17O and 18O was simulated under the conditions of the fifth embodiment, and it was found that oxygen gas including 11.5 atom % of 17O and oxygen gas including 28.9 atom % of 18O could be obtained with a yield of 14.0% for 17O and 72.8% for 18O.
The operation of concentrating 17O and 18O was simulated under the conditions of the eighth embodiment, and it was found that oxygen gas including 77.7 atom % of 17O and oxygen gas including 22.2 atom % of 18O could be obtained.
The operation of concentrating 17O and 18O was simulated under the conditions of the ninth embodiment, and it was found that oxygen gas including 87.4 atom % of 17O and oxygen gas including 22.2 atom % of 18O could be obtained.
It was verified that the method of the present invention is capable of efficiently concentrating stable oxygen isotopes 17O and 18O that have extremely low abundance to high concentrations. Also it was verified that, because this method can carry out concentration with a shorter startup time than in the prior art, 17O and 18O of high concentration can be obtained on an industrial scale at a low cost.
Moreover, heavy oxygen water enriched in 17O or 18O can be obtained at a low cost on an industrial scale, by using 17O-enriched oxygen or 18O-enriched oxygen obtained by the method for concentrating an oxygen isotope or isotopes of the present invention.
The present invention, that is capable of providing 17O-enriched or 18O-enriched oxygen at a low cost on an industrial scale, is valuable in chemical and medical fields where compounds labeled with 17O or 18O are used as a tracer.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2005-236499 | Aug 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/316079 | 8/16/2006 | WO | 00 | 2/11/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2007/020934 | 2/22/2007 | WO | A |
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| 20090035212 A1 | Feb 2009 | US |
