JP5317256B2 - Extraction agent and extraction / separation method, and N, N, N ′, N ″ -tetrakis (2-methylpyridyl) ethylenediamine derivative and method for producing the same - Google Patents

Description

  The present invention provides, for example, an extractant and extraction / separation method capable of extracting a trivalent minor actinoid element (trivalent MA) which is a highly toxic and long half-life nuclide contained in spent nuclear fuel, and N, N, N ′, The present invention relates to an N ′ tetrakis (2-methylpyridyl) ethylenediamine derivative and a method for producing the same.

  The trivalent minor actinoid element (trivalent MA) contained in spent nuclear fuel has a long half-life nucleus and high radiotoxicity. Therefore, separating trivalent MA from spent nuclear fuel reduces the environmental impact of its disposal. It is expected to be significantly reduced. In addition, trivalent MA can perform nuclide conversion to a short half-life while being used as an energy source by a fast reactor or an accelerator. For this reason, it is essential to separate rare earth elements that inhibit the nuclear reaction.

  However, since trivalent MA and rare earth elements have very similar chemical behavior, it is very difficult to construct a mutual separation process. In analytical chemistry, a method for separating these is chromatographic separation using a column with an ion exchange resin, but this method is a batch method and difficult to increase in size, and is therefore not applicable to large-scale production facilities. It was possible. Although this method has been applied to produce experimental trivalent MA, there is no further scale application.

  As a separation technique to replace the ion exchange method, a solvent extraction method suitable for a large amount of waste liquid treatment can be considered. Examples of conventional techniques based on solvent extraction include the following.

Solvent extraction process using DTPA (diethylenetriaminepentaacetic acid) The solvent extraction process using DTPA is performed using an extractant such as CMPO (octyl (phenyl) -N, N-diisobutylcarbamoylmethylphosphine oxide) or DIDPA (diisodecyl phosphate). In this method, only trivalent MA is selectively back-extracted from DTPA, which is a complexing agent dissolved in an aqueous phase, from trivalent MA and rare earth co-extracted in the organic phase. This method is the most developed in the trivalent MA separation process in the solvent extraction method, and a process test using spent nuclear fuel is also being conducted. Since this process utilizes separation by selective back-extraction with a water-soluble complexing agent, trivalent MA is complexed in the resulting aqueous solution of trivalent MA. For this reason, it is difficult to construct a downstream separation process, and if it is supplied as it is to fuel production, consideration must be given to the presence of organic substances. Furthermore, since the complexing agent is consumed, it must be constantly supplied, and the amount of secondary waste generated is also large.

Solvent extraction process using BTP (bis (dialkyltriazine) pyridine) The solvent extraction process using BTP utilizes BTP, which is one of the nitrogen donor ligands. This is a process of selectively extracting MA into an organic phase. Accordingly, it is not necessary to add a complexing agent or the like to the aqueous phase, and trivalent MA can be selectively extracted from a solution having a high nitric acid concentration (1 M or more) due to the characteristics of BTP. This process is being developed mainly by France, and has already performed a small process test using spent nuclear fuel. However, this process has the above-mentioned advantages, but has a big problem in the chemical stability and radiolysis durability of BTP, and there is a defect that the decomposition of BTP proceeds in the process operation. Further, since the reaction of the trivalent MA extraction equilibrium by BTP is slow, the test results of the process as expected from the separation performance confirmed by the batch test are not obtained.

Extraction Chromatography Separation System Even for ligands with a low separation factor, development to achieve separation of trivalent MA by supporting the ligand on a resin, filling the column and applying the chromatographic method is also underway Yes. However, as in the column method using the above-described ion exchange resin, it is difficult to increase the size, and no realization has been obtained. In addition, since there is a drawback that used resin becomes radioactive waste, there are many problems for practical use.

Sulfur-containing ligands such as other ligands Cyanex 301 (bis (2,4,4-trimethylpentyl) dithiophosphonic acid) show very high separation performance (Am (III) separation factor) 6000 or more). However, a compound containing sulfur has a problem in chemical stability and has a problem in processing after the ligand becomes a waste, and is not out of a basic experiment.

  The present inventors have used rare earth elements (Eu) using TPEN (N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine), which is an inclusion type hexadentate ligand having four pyridyl groups. (III)) has succeeded in extracting a trivalent actinoid (Am (III)) (for example, refer nonpatent literature 1). Even if this ligand becomes a waste, it is possible to perform an appropriate treatment without leaving a solid component. In previous studies, this ligand has shown a value of 250 or more at a pH of about 4.5 for the separation factor of trivalent MA from rare earths.

T. Matsumura and K. Takeshita: Extraction Behavior of Am (III) from Eu (III) with Hydrophobic Derivatives of N, N, N ', N'-tetrakis (2-methylpyridiyl) ethylenediamine (TPEN), J. Nucl.Sci .Technol., 43, 824-827 (2006)

  However, since TPEN is protonated in the acidic region, it is also distributed to the aqueous phase in solvent extraction, and the usable pH range is limited from weakly acidic to neutral, and is applicable to aqueous solutions with high acid concentrations such as waste liquid. It was difficult.

  The present invention has been proposed in view of such a conventional situation, and an extractant and an extraction / separation method capable of exhibiting excellent separation performance, and N, N, N ′, N′-tetrakis ( An object is to provide a 2-methylpyridyl) ethylenediamine derivative and a method for producing the same.

  As a result of intensive studies from various viewpoints, the present inventors have introduced a hydrophobic functional group at the end of the pyridyl group of an inclusion type hexadentate ligand (TEPN) having four pyridyl groups, It has been found that high separation performance can be obtained even in a region with high acidity, and the present invention has been completed.

  That is, the extractant according to the present invention has the following general formula (I):

(In the formula, R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms .) N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by It is characterized by.

  The extraction / separation method according to the present invention comprises the following general formula (I):

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms .) Extraction containing an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by An agent, an organic solvent, and an aqueous solution containing a rare earth element and a trivalent minor actinoid element are mixed, and the trivalent minor actinoid is transferred to the organic phase under acidic conditions.

  The extraction / separation method according to the present invention comprises the following general formula (I):

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms .) Extraction containing an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by An agent, an organic solvent, and an aqueous solution containing a transition metal are mixed to move the transition metal to the organic phase.

  Further, the N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative according to the present invention has the following general formula (I):

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms ).

Further, N, N, N ′, N′-tetrakis represented by the above general formula (I) according to the present invention (wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms). The method for producing the (2-methylpyridyl) ethylenediamine derivative has the following general formula (II)

(Wherein R ⁵ represents an alkoxy group having 2 to 20 carbon atoms, and X represents a halogen substituent) and ethylenediamine is reacted under alkaline conditions. .

According to the present invention, by introducing an alkoxy group having 2 to 20 carbon atoms at the end of the pyridyl group, the hydrophobicity of the extractant is improved and high separation performance can be exhibited even in a highly acidic region. .

  Hereinafter, the present invention will be described in detail. TPEN (N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine) derivative has a hydrophobic functional group introduced at the end of the pyridyl group of an inclusion type hexadentate ligand having four pyridyl groups. Is.

  That is, the TPEN derivative is represented by the following formula (I).

^Wherein, R 1 to R ⁴ represents a hydrophobic functional group. R ^{1 to} R ⁴ may all be the same or different. Further, the hydrophobic functional group may be bonded to all positions where the pyridine ring can be bonded, but those bonded to the 4 or 5 position on the pyridine ring are more stable than the orientation.

  The hydrophobic functional group is preferably a high carbon number alkyl group, and may have either a linear or branched structure. Moreover, it is preferable that carbon number of an alkyl group is 2-20. When the carbon number of the alkyl group is less than 2, the hydrophobicity is not sufficient, and when it is more than 20, the solubility is deteriorated.

  The hydrophobic functional group may be a polymer alcohol, carboxylic acid, silane, or the like. Further, the hydrophobic functional group and the pyridyl group may be directly bonded or indirectly bonded through, for example, an ether group or an amino group.

  That is, the hydrophobic functional group is preferably one kind whose terminal is selected from an alkyl group, an alcohol group, a carboxylic acid group, a silane group, an ether group, and an amino group.

  By binding a hydrophobic functional group to the pyridyl group located outside the TPEN molecule in this way, distribution to the aqueous phase can be prevented, and good separation performance can be exhibited without inhibiting complex formation. . In addition, good stability and separation performance of TPEN can be maintained as they are.

  A method for producing a TPEN derivative is represented by the following general formula (II):

(Wherein R ⁵ represents a hydrophobic functional group, and X represents a halogen substituent) can be synthesized by reacting ethylenediamine with an ethylenediamine. Here, since the hydrophobic functional group is the same as the hydrophobic functional group (R ^{1 to} R ⁴ ) described above, description thereof is omitted. The halogen substituent is Cl, Br, or the like that can be replaced by the attack of a nucleophile (ethylenediamine).

  This synthesis reaction is preferably performed in the presence of a catalytic amount of a phase transfer catalyst. Thereby, the yield of a TPEN derivative can be improved. Phase transfer catalysts include lauryl trimethyl ammonium chloride, lauryl trimethyl ammonium bromide, myristyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, stearyl trimethyl ammonium chloride, stearyl trimethyl ammonium bromide, oleyl trimethyl ammonium chloride, odor Alkyltrimethyl ammonium such as oleyltrimethylammonium bromide can be used.

  The product after the reaction can be purified by column chromatography to obtain a highly pure TPEN derivative. As a filler used for column chromatography, it is preferable to use alumina or the like.

Next, application examples of the TPEN derivative will be described.
The extractant containing a TPEN derivative is a potand type inclusion compound having six nitrogen donors that can coordinate to a transition metal. This extractant has excellent selectivity to soft metals, so-called soft metals, based on the HSAB rule (Hard and Soft Acid and Base). For example, as described later, the extraction percentage of Cd can obtain a result of almost 100% even at pH 1. Further, even in Am and Eu, which are considered difficult to separate, a high separation factor can be obtained by utilizing a slight difference in softness between both ions.

  In the transition metal extraction method described above, the extraction agent containing the TPEN derivative, the organic solvent, and the aqueous solution containing the transition metal are mixed, and the transition metal is transferred to the organic phase to be extracted and separated.

  As the organic solvent, any solvent that can dissolve TPEN derivatives such as chloroform, nitrobenzene, and 1-octanol can be used.

  Here, since the TPEN derivative represented by the general formula (I) has a hydrophobic functional group introduced therein, it is prevented from being protonated in an acidic region like TPEN and distributed to an aqueous phase in solvent extraction. Can be prevented. Therefore, it can be directly applied to an aqueous solution having a high acid concentration such as a high-level radioactive liquid waste.

Hereinafter, a detailed description will be given with reference to examples.
Example 1
In Example 1, TBPEN (N, N, N ′, N′-tetrakis [4- (2-butyloxy) -2-pyridylmethyl] -1,2-ethylenediamine) was synthesized.

  First, 2-chloromethyl-4-butoxypyridine and ethylenediamine were reacted in an aqueous sodium hydroxide solution in the presence of a catalytic amount of hexadecyltrimethylammonium chloride. The reaction mixture stirred at room temperature for 4 days was extracted with dichloromethane, dried and concentrated, and then purified by column chromatography with alumina. Further, after purification by column chromatography, repurification by recycle preparative HPLC (High performance liquid chromatography) was performed to obtain TBPEN represented by the following general formula (III) in a yield of 53%. This yield was more than five times that of the conventional method.

When a ¹ H-NMR spectrum of TBPEN was measured with a nuclear magnetic resonance apparatus, hydrogen atoms derived from a pyridine ring were observed at 7 to 8 ppm. In addition, a peak derived from methylene hydrogen bonded to ether oxygen was observed in the vicinity of 4 ppm, and it was found that the target product was synthesized.

Thus, by reacting the chloromethylpyridine derivative and ethylenediamine in the presence of a catalytic amount of hexadecyltrimethylammonium chloride, it is possible to efficiently synthesize a TPEN derivative having an ether structure consisting of four carbon chains. Moreover, the target product can be efficiently obtained by purifying by column chromatography using alumina after the product is post-treated. In addition, the target product with high purity can be obtained by performing purification by recycle preparative HPLC after purification by column chromatography.
(Extraction test 1-1)
Next, an extraction test of Cd (II), which is a soft metal, was performed using TBPEN. As the organic phase, TBPEN diluted to 2 mM with chloroform was used. The same amount of organic phase was added to 1 mM cadmium nitrate aqueous solution adjusted to any pH and ionic strength (0.1) using nitric acid and sodium nitrate, and shaken for 24 hours or more. The extraction temperature was 25 ° C. The Cd concentration in the aqueous solution was measured with an ICP emission analyzer, and the extraction percentage of Cd was calculated. As a comparative example, the same extraction test as described above was performed using TPEN (manufactured by Dojindo Laboratories).

FIG. 1 is a graph showing the results of a Cd extraction test. In the pH 1-4 region, the percentage of Cd extracted with TPEN was as low as several percent. On the other hand, the Cd extraction percentage of TBPEN in which the pyridyl group was hydrophobized with a butoxy group was almost 100% even at pH 1. Thus, it can be seen that extraction in the low pH region (acidic region), which is difficult to extract with conventional TPEN, is possible by hydrophobizing TPEN.
(Extraction test 1-2)
Next, an extraction separation test of Am and Eu was performed using TBPEN. As the organic phase, TBPEN diluted with nitrobenzene to 1 mM was used. The same amount of organic phase in a mixed solution of Am (100 Bq / ml Am-241) and Eu (400 Bq / ml Eu-152) adjusted to any pH and ionic strength (1.0) using nitric acid and sodium nitrate And shake for 90 minutes. The extraction temperature was 25 ° C. After shaking, 1.0 ml of an aqueous solution was collected as a sample and sealed in a tube for γ-ray measurement. Gamma rays were measured with a semiconductor detector, and the counting rate based on the measured values was adopted as the concentration of Am and Eu to determine the distribution ratio.

  FIG. 2 is a graph showing the results of a co-extraction test of Am and Eu. As the pH decreased, both the Am and Eu distribution ratios decreased. This is due to the proton addition of TBPEN to the nitrogen donor due to increased acidity. When the change of the Am / Eu separation factor at this time was examined, the separation factor increased with an increase in acidity (pH decrease), and a separation factor of 97 was exhibited at pH3. In the conventional co-extraction using TPEN, an alkyl group (butyl group) is introduced into the pyridyl group, considering that the Am / Eu separation factor is about 50 to 200 in the pH range of 4.5 to 5.5. It can be concluded that Am / Eu separation in the acidic region is possible by hydrophobizing TPEN.

It is a graph which shows the result of a Cd extraction test. It is a graph which shows the result of the co-extraction test of Am and Eu.

Claims (10)

The following general formula (I)

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms.) Extraction containing an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by Agent. The extractant according to claim ¹ , wherein R ^{1 to} R ^{4 in the} formula (I) represent a butoxy group. The following general formula (I)

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms.) Extraction containing an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by An extraction separation method comprising mixing an agent, an organic solvent, and an aqueous solution containing a rare earth element and a trivalent minor actinoid element, and transferring the trivalent minor actinoid to the organic phase under acidic conditions. The extraction separation method according to claim 3, wherein R ^{1 to} R ^{4 in the} formula (I) represent a butoxy group.   4. The extraction / separation method according to claim 3, wherein the trivalent minor actinoid is transferred to an organic phase at a pH of 3 or less. The following general formula (I)

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms.) Extraction containing an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by An extraction and separation method comprising mixing an agent, an organic solvent, and an aqueous solution containing a transition metal, and transferring the transition metal to the organic phase. The following general formula (I)

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms), an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by: 8. The N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative according to claim 7, wherein R ^{1 to} R ^{4 in the} formula (I) represent a butoxy group. The following general formula (II)

(Wherein R ⁵ represents an alkoxy group having 2 to 20 carbon atoms, and X represents a halogen substituent) and ethylenediamine is reacted under alkaline conditions. The following general formula (I)

(Wherein R ^{1 to} R ⁴ represent an alkoxy group having 2 to 20 carbon atoms.) A method for producing an N, N, N ′, N′-tetrakis (2-methylpyridyl) ethylenediamine derivative represented by : The method for producing an N, N, N ', N'-tetrakis (2-methylpyridyl) ethylenediamine derivative according to claim 9, wherein R ^{5 in the} formula (II) represents a butoxy group.

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