JPH06319957A - Separation and concentration of carbon-13 using laser - Google Patents

Abstract

PURPOSE:To improve concn. efficiency and laser irradiation cost and enhance productivity by a method wherein a primary combination product containing conc. carbon-13 and a secondary combination product are obtained by irradiation of infrared laser beam, reaction product gas is discharged from system, the primary product and the material gas remaining unreacted are removed and the secondary product is circulated into reaction system. CONSTITUTION:The mixed gas of CHClF2 and oxygen or oxygen-containing oxide is introduced into a reactor 3 as a material and this material gas is irradiated with infrared laser 1 to cause infrared multiple photon dissociation. The reaction product gas is continuously removed from the reactor 3, the reaction product gas contg. the reaction combination product with conc. carbon-13 is discharged from reaction system, a portion of the compound produced therefrom and a portion or all of the material gas remaining unreacted are removed and the remainder is circulated into the reaction system. By circulating a portion of the product gas to the material in this way, the selectivity of isotope is maintained, the productivity of carbon-13 isotope per laser beam pulse is improved and the amount of laser energy consumed is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and concentrating carbon 13 using a laser. More specifically, infrared laser light is effectively used for separating and concentrating carbon 13 using infrared multiphoton dissociation. And a method for improving production efficiency.

[0002]

2. Description of the Prior Art Naturally occurring carbon has a mass number of 12 and 1.
There are 3 isotopes, the former is 98.9% and the latter is 1.1%. Carbon 1 among these isotopes
3 is a raw material for a labeled compound for NMR-MRI together with oxygen 17 and the like, and the demand from medical and physiological researchers in Japan and overseas is rapidly increasing, and price reduction and stable supply have been strongly demanded.

Separation of carbon 13 which has been practically used in the past,
The concentration method is based on a low temperature distillation method, and carbon monoxide or methane is used as a working substance.
However, since it is a flammable gas, uses a large amount of liquid nitrogen as a refrigerant, has a very long time to reach a steady state because it is an ultra-precision distillation column, and has a separation coefficient of almost 1, etc. Since the number of distillation stages is required to condense the labeled compound to a concentration that can be practically used, it has drawbacks such as an increase in size of the apparatus, and its manufacturing cost is also high.

Therefore, if the carbon 13 can be separated and concentrated inexpensively with a safe and compact device using a laser, its significance is extremely significant, and various proposals have been made for that purpose (for example, Japanese Patent Laid-Open Publication No. Sho. 60-132,629 and U.S. Pat. No. 4,436,709).

[0005] In the method of separating and concentrating carbon 13 using a laser which has been known so far, a fluorocarbon such as CHXF ₂ (wherein X represents F, Cl, Br or I) is used as a raw material. Or a fluorocarbon gas to which halogen gas is added is used as a raw material, and these are irradiated with carbon dioxide laser light, and the isotope shift of the light absorption property is used to make infrared of the fluorocarbon containing carbon 13. It selectively causes multiphoton dissociation. Since methane, carbon dioxide, and carbon monoxide are mainly used for the precursor of the labeling compound, it is necessary to convert the separated carbon 13-enriched fluorocarbon into the above compound, and the process is complicated. is there.

On the other hand, the present inventors have found that CHClF₂And oxygen
CF containing carbon 13 as a raw material using an oxidizing agent such as₂O
And easily labeled by hydrolyzing it.
Carbon dioxide enriched with carbon-13
Has been developed (JP-A-2-277,525).
Issue). However, in these reactions, charcoal
In addition to the main product compound in which element 13 is concentrated, C₂F_FourNo
Such a by-product compound is also produced at the same time. This by-product compound
Since carbon 13 is also concentrated, the carbon 13
It is also advantageous to recover this to increase the yield
However, of course, compared to when only the main product compound is targeted
Even the separation and conversion process becomes complicated. Here the main compound
The product means that the carbon 13 content in the product leaving the reaction system is
It is a compound that occupies the majority.

[0007]

An object of the present invention is to provide a method for efficiently converting a by-product compound enriched with carbon 13 into a main product compound. Another object of the present invention is to improve the separation efficiency of carbon 13 in a method for separating and concentrating carbon 13 using a laser, enabling the production of a large amount of carbon 13, and effectively utilizing expensive laser light.
An object of the present invention is to provide a method capable of performing separation and concentration of 3 at low cost.

[0008]

Means for Solving the Problems In the method of irradiating a raw material gas with an infrared laser beam to cause infrared multiphoton dissociation and separating and concentrating carbon 13, carbon 13 was concentrated. As a result of intensive studies on a method for efficiently recovering the main product compound, the by-product compound isotope-selectively selected as the main product compound in parallel with the process of producing the main product compound in which carbon 13 is directly concentrated from the raw material. The present invention has been completed by finding that there is a process that can be efficiently and efficiently converted.

That is, the present invention is a method of irradiating a raw material gas in a reactor with infrared laser light to cause infrared separation, separating and concentrating carbon 13, and irradiating infrared laser light. At least two kinds of compounds, a main product compound and a by-product compound, in which carbon 13 is concentrated are generated, and the obtained reaction product gas is taken out of the reaction system. From this, a part of the main product compound and an unreacted raw material gas are extracted. Carbon 13 using a laser, characterized in that a part or all of it is removed and the remaining gas containing a by-product compound is refluxed into the reaction system.
Is a method of separation and concentration.

In the present invention, conventionally known compounds can be used as the source gas. Specifically CH
A fluorocarbon gas such as XF ₂ (wherein X represents any one of F, Cl, Br and I) to which a halogen gas or an oxygen-containing oxidizing agent such as oxygen is added can be used, but is preferably used. It is preferable to use a mixed gas of CHClF ₂ and oxygen or an oxygen-containing oxidizing agent as the source gas.

The reaction of irradiating the raw material gas with an infrared laser to cause infrared multiphoton dissociation occurs, for example, in a reactor into which a focused laser beam is incident. The raw material gas is continuously charged into the reactor and reacted, and the reaction product gas is continuously taken out from the reactor. In this case, the outside of the system means outside the reactor. The reaction product gas containing the reaction product compound in which carbon 13 is concentrated is taken out of the reaction system, a part of the compound formed from this and the unreacted raw material gas is partly or entirely removed, and the rest is left in the reaction system. Bring to reflux. Of the removed components, a part or all of the compound in which carbon 13 is concentrated is recovered as a target product.

It is important to limit the amount of the main product compound enriched with carbon 13 to be recovered outside the system to a part of the amount existing at the time of taking out from the reaction system, preferably 5%.
Or more and 70% or less, more preferably 15% or more and 60% or less, and further preferably 25% or more and 50 or less. The remaining main product compound is refluxed. On the other hand, the amount of the by-product compound in which carbon 13 is concentrated is left as large as possible and refluxed to the reaction system, but preferably 20% or more, more preferably 40%.
Reflux, leaving more than%. Since carbon 13 is depleted in the unreacted raw material gas, as much as possible is removed, but preferably 10% or more, more preferably 20% or more, still more preferably 30% or more. The components not removed outside the reaction system are refluxed and charged into the reaction system together with the fresh raw material gas.

[0013]

The effects of using the conventional method and the method of the present invention will be described with reference to the case where CHClF ₂ and oxygen are used as the source gas and the reaction product gas is refluxed or not.

When the CHClF ₂ gas as a raw material is irradiated with a very strong infrared pulsed light such as a carbon dioxide gas laser, it causes dissociation due to infrared multiphoton absorption, and CF ₂ and HCl as dissociated products.
Occurs. However, in order to induce this dissociation in an isotope-selective manner, it is necessary to appropriately set the fluence of the laser light (the intensity of the laser light per unit irradiation area), the laser light wavelength, the pressure of the raw material gas, etc. There is a need. For example, if the fluence is too strong, almost all the raw material gas is dissociated, and carbon 13 is not concentrated. If the fluence is too weak, the raw material gas itself will not be dissociated.
The wavelength of the laser in the vicinity of 1,045cm ^-1, if you set the fluence of about 5 J / cm ^2, the carbon 13 is concentrated in the dissociation product CF _2, reaction of a dissociation product CF ₂ and oxygen and, CF ₂ comrades The dimerization reaction of
CF ₂ O and C ₂ F ₄ enriched above 30% are obtained as final products. And the former is the main product,
The latter is a by-product compound.

Usually, the laser beam obtained by the laser starter has a low fluence as it is, and therefore it is necessary to focus the light with a lens to increase the fluence and then irradiate it. CHClF ₂ + nhυ → CF ₂ + HCl (1) CF ₂ + O ₂ → CF ₂ O + O (2) CF ₂ + CF ₂ → C ₂ F ₄ (3) CF ₂ O + H ₂ O → CO ₂ + 2HF (4)

Reaction (1) shows a process in which CHClF ₂ absorbs and dissociates infrared multiphotons of a carbon dioxide laser. Under the irradiation conditions as described above, CHClF ₂ molecules containing carbon 13 are selectively dissociated to generate CF ₂ having a high carbon 13 concentration. This CF ₂ is oxidized by the reaction (2) to give CF ₂ O.
Alternatively, the reaction (3) dimerizes into C ₂ F ₄ and carbon 13 is concentrated. Also, carbon 13
It is necessary to irradiate the reaction system with a large number of infrared pulses in order to increase the production amount of CF ₂ O that is concentrated in the reaction system.

This CF₂O is used for hydrolysis of reaction (4)
Therefore, CO, which is a precursor of the labeling compound,₂Easy to
It can be converted, while the carbon 13 is enriched in C
₂F _FourC, which is a precursor of the labeled compound,
O₂, CO, CH_FourTo convert to
Further steps such as separation, oxidation or reduction are required.

Next, a case where a part of the produced compound of the present invention is partially refluxed in the raw material gas will be described. Reaction (1)
As a result of detailed examination of (1) to (3), the present inventors further increased C ₂ F ₄ when the number of laser light irradiations was further increased.
Was oxidized and converted to CF ₂ O. C ₂ F ₄ + O ₂ → 2CF ₂ O (5)

Moreover, the reaction (5) proceeds isotope-selectively.
This reaction is¹³CF₂O concentration reaches a certain range
It was also found that the reaction dramatically progresses. as a result
In Figure 1¹³CF₂Laser pulse in the abundance of O
Per hit¹³CF₂It was shown as the amount of O produced. The horizontal axis of Figure 1 is
¹³CF₂Maximum O production is 100 ¹³CF₂O production
The vertical axis represents the laser pulse¹³
CF₂Laser pulse was applied with the maximum amount of O generation being 100.
Rino¹³CF₂It shows the amount of O produced. CF₂O + mhυ → CF₂O^* (6) CF₂O^* + C₂F_Four → C₂F_Four ^* (7) C₂F_Four ^* + O₂ → 2CF₂O (8)

Although the mechanism of this reaction is not clear at present, since the produced carbon 13-enriched CF ₂ O has absorption at the irradiated laser wavelength of 1045 cm ^-1, it absorbs infrared photons. [Reaction (6)] By transferring the energy to C ₂ F ₄ , C ₂ F ₄ is excited again to reach a state in which reaction is possible [Reaction (7)] CF ₂ O
Is considered to be converted into [reaction (8)].

In order to reach the CF ₂ O concentration at which the reaction (5) can be performed remarkably, it is necessary in the conventional method to irradiate the reaction system with a large amount of infrared pulsed light. CF
_{Even if} the conversion rate of ₂ O can be increased, it is not efficient in view of the laser irradiation cost required to reach the CF ₂ O concentration. However, CF, which is a reaction product compound, is used as a raw material.
By partially refluxing ₂ O and C ₂ F ₄ , the ¹³ CF ₂ O concentration in which the reaction (5) proceeds efficiently can be reproduced with a smaller number of laser irradiation times. As a result, with the same number of irradiation of infrared pulsed light,
It is possible to increase the amount of CF ₂ O produced by concentrating the produced carbon 13.

As described above, in this method, the laser light is effectively used, the carbon 13 separation and concentration reaction can be carried out extremely efficiently, the productivity is improved, and the production cost can be reduced. .

[0023]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 FIG. 2 shows a laser irradiation / carbon 13 separation apparatus used for laser isotope separation of the present invention. In FIG. 2, the laser oscillator 1 is a TE that incorporates a diffraction grating.
It is an A type pulsed carbon dioxide laser, and the output laser beam is focused by a lens 2 (focal length 2 m, made of BaF ₂ ), and a reactor 3 (length 2.7 m, Pyrex) where source gas and reflux gas exist. (Made of glass). Here, the oscillation line of the carbon dioxide laser is 9P (22)
(1,045 cm ^-1 ) and the laser output is 2.
It was 2 J / pulse (10 pps), and the fluence at the focal portion was set to 7 J / cm ² .

CHClF ₂ of the source gas is 27 cc / mi
n is the raw material supply unit 4 (CHCl in which carbon 13 is not impaired)
It is introduced with a device that supplies F ₂ ) and combined with the reflux gas to obtain 1
12 cc / min (at this time, this gas is irradiated with a laser pulse 250 times while staying in the substantial reaction zone of the reactor) and introduced into the reactor at a total pressure of 100 torr. Also, the concentration of oxygen at the reactor inlet is 33%
Is appropriately supplied by the oxygen supplier 5. 35% of the reaction product gas extracted from the reactor 3 is led to the alkali absorber 6 containing the barium hydroxide solution, where CF ₂ O is recovered as barium carbonate. The carbon 13 in the barium carbonate can be easily stoichiometrically recovered as CO ₂ by treating the barium carbonate with hydrochloric acid.

The reaction product gas leaving the alkali absorber 6 contains CHClF _{2 which} is a source gas, oxygen and C ₂ F ₄ which is a by-product compound, and therefore is introduced into the refrigerator 7, where water and the source gas are supplied. CHClF ₂ is recovered by cold condensation. The reaction product gas exiting the refrigerator 7 contains oxygen and C ₂ F ₄ , which is remixed with 65% of the gas withdrawn from the reactor 3. This mixed gas is mixed as a reflux gas with a new raw material gas supplied from the raw material supply device 4 and introduced into the reactor 3. The reason for adding the raw material CHClF ₂ in which carbon 13 is not depleted is to supply carbon 13 deficient in the reaction system to the reaction system.

As a result, in the alkali absorber, carbon dioxide 2.25 containing carbon 13 isotope ratio of 30% and carbon 13 was 2.25.
Barium carbonate corresponding to the production efficiency of × 10 ^-8 mol / pulse was recovered.

Comparative Example 1 For comparison, the raw material gas CHClF _{2 was} used without reflux.
67%, oxygen 33%, total pressure 100 torr, flow rate 112
When cc / min and laser irradiation conditions were the same as in Example 1 above, carbon dioxide 9.0 × 10 carbon dioxide containing carbon 13 isotope ratio 22% and carbon 13 in the alkali absorber.
Barium carbonate commensurate with the production efficiency of ^-10 mol / pulse was recovered.

Comparative Example 2 For further comparison, the raw material gas CHClF was used without reflux.
₂ 67%, oxygen 33%, total pressure 100 torr, flow 12
When carried out at cc / min (gas is irradiated with laser pulse for 2,250 times while staying in the substantial reaction zone of the reactor), the alkali absorber contains carbon 13 isotope ratio 30% and carbon 13 Carbon dioxide gas is 6.6 × 10 ^-9 mol / pu
Barium carbonate was recovered in proportion to the production efficiency of lse.

Therefore, it can be seen that by refluxing a part of the produced gas to the raw material, the isotope selectivity was maintained, the carbon 13 isotope production efficiency per laser light pulse was improved, and the consumed laser energy was reduced. .

[0031]

According to the present invention, in the separation and concentration of carbon 13 using a laser, the concentration efficiency and the laser irradiation cost are greatly improved, the productivity is remarkably improved, and the isotope is produced at a low cost. It is possible to separate and concentrate.

[Brief description of drawings]

[1] Figure 1 is a graph showing the ¹³ CF ₂ O generated per laser pulse in the presence of ¹³ CF ₂ O.

FIG. 2 is an explanatory diagram showing a carbon 13 separator.

[Explanation of symbols]

1 ... Laser oscillator, 2 ... Lens, 3 ... Reactor, 4 ... Raw material supply device, 5 ... Oxygen supply device, 6 ... Alkaline absorber, 7 ...
refrigerator.

Claims (2)

[Claims] 1. A source gas in a reactor is irradiated with infrared laser light to cause infrared multiphoton dissociation to separate carbon 13.
In the method of concentrating, at least two kinds of compounds, that is, a main product compound and a by-product compound in which carbon 13 is concentrated are generated by irradiating infrared laser light, and the obtained reaction product gas is taken out of the reaction system. While removing a part or all of the unreacted raw material gas and a part of the main product compound,
A method for separating and concentrating carbon 13 using a laser, characterized in that the remaining gas containing a by-product compound is refluxed into the reaction system. 2. The method for separating and concentrating carbon 13 using a laser according to claim 1, wherein the source gas is a mixed gas of CHClF ₂ and oxygen or an oxygen-containing oxidizing agent.