JPH07107560B2 - Method for cleaning organic solvent and apparatus using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for washing an organic solvent and a washing apparatus using the same, and particularly to a decomposition product and a metal ion in an extracted organic solvent used for extracting a nuclear fuel. The present invention relates to a method for washing an organic solvent suitable for washing and removing, and an apparatus using the method.

[Conventional technology]

Organic phosphate compounds such as tributyl phosphate are often used as extraction solvents for spent nuclear fuel. Tributyl phosphate (TB), an extraction solvent used for reprocessing spent nuclear fuel
P) is diluted with an aliphatic hydrocarbon diluent to 20 to 30 vol% and used. Conventionally, the spent nuclear fuel was extracted with this TBP and then back-extracted with nitric acid.

However, a part of the extraction solvent is decomposed by radiolysis or chemical decomposition and forms a complex with metal ions in the spent nuclear fuel, which interferes with the normal extraction operation of the nuclear fuel. That is, a particular problem is in the case of tributyl phosphate used in the reprocessing of spent nuclear fuel, in which case radiation from the fission products contained in the spent nuclear fuel causes radiolysis, resulting in dibutyl phosphate. (DBP) occurs in large quantities. On the other hand, the diluent is also decomposed in the same manner and becomes a decomposition product such as an organic acid.

Dibutyl phosphate forms a strong complex especially with zirconium, uranium, plutonium and ruthenium, and strongly retains these metals in the organic solvent. As a result, the distribution ratio of the nuclear fuel extraction is changed, and the normal extraction operation is hindered. In particular, there is a trend toward higher burnup of nuclear fuels recently, and in the case of fast breeder reactors, which have dramatically higher burnup than conventional light water reactors, the radiation dose becomes large and the decomposition and production of higher concentrations than ever has occurred. Things may occur.

The extraction solvent used once is reused because of the request for reduction of radioactive waste. Therefore, in the organic solvent regeneration step, it is necessary to wash the organic solvent with a detergent to remove decomposition products and metal ions in the organic solvent. The decomposition product and the metal ion form a complex, and zirconium in particular forms a strong complex, so that its removal is difficult.

Therefore, in order to remove these decomposition products and metal ions and reuse the organic solvent, conventionally, washing mainly by liquid-liquid extraction with a sodium carbonate solution has been carried out. It separates the extraction solvent and nitric acid solution after back extraction,
The organic solvent is washed with sodium carbonate.
However, these detergents composed of sodium carbonate solution become solid wastes, and, for example, about 100 kg of wastes of sodium compounds are generated each time one ton of nuclear fuel is processed. This waste includes a large part of the total amount of waste generated from the nuclear fuel reprocessing, which is a big problem in reducing the waste. In addition, the alkali metal salt is chemically unstable due to its high water solubility and is difficult to handle.

The above-mentioned detergents mainly composed of liquid-liquid extraction with a sodium carbonate solution do not have sufficient washing ability, and it is necessary to avoid the formation of precipitates as much as possible. 0.2N sodium carbonate on stage, 0.1N on second stage
The organic solvent was washed and regenerated using nitric acid and 0.1N sodium hydroxide in the third step. As an alternative to such a cleaning method using sodium carbonate, there is a conventional example in which a cleaning agent containing hydrazine as a main component is used and the amount of solid waste is reduced by decomposing this (for example, US patent No. 4059671).

[Problems to be solved by the invention]

However, it has been found that the conventional technique using the above-mentioned hydrazine-based compound has a problem that it does not exhibit a sufficient cleaning ability at a concentration where a high burnup of nuclear fuel proceeds and a high decomposition product is produced.

In addition, since hydrazine compounds decompose at room temperature, they are difficult to store and may explode, which requires careful handling. As a result, the operation of regenerating (cleaning) the nuclear fuel extraction organic solvent using a cleaning agent containing hydrazine as a main component has a problem that requires special attention.

In order to solve the above problems, the present invention has a small amount of solid waste, and has a high cleaning ability even when the organic solvent to be cleaned and regenerated contains a high concentration of a substance to be removed. It is an object of the present invention to provide a method for washing an organic solvent having the formula (1) and an apparatus using the method.

[Means for solving problems]

To reduce solid waste, the cleaning agent for organic solvents is hydrogen,
It must be a compound consisting only of titanium, oxygen and carbon. This is because each of these elements can undergo oxidative decomposition and thermal decomposition.

The detergent must be alkaline (DBP is acidic) due to the need to remove decomposition products (DBP, etc.) and at the same time water-soluble. Being water-soluble at the same time as being alkaline is important for washing and removing impurities from an organic solvent into an aqueous solution.

A compound consisting only of hydrogen, titanium, oxygen and carbon is regarded as an organic solvent, and compounds showing alkalinity and water solubility are limited.

The electronegativity of titanium is smaller than that of oxygen, so that it is more likely to absorb the positive charge of the generated ion, and the compound in which hydrogen around the titanium is coordinated exhibits relatively strong basicity. Substitution with hydrogen, such as an electron-emissive alkyl group, makes it more basic. Such a compound is called an amine and has the above-mentioned properties such as alkalinity. However, many of the amines are soluble in a less polar solvent, so it is necessary to obtain a more polar one. It is expected that when the alkylation of amine is promoted to give a quaternary ammonium salt, a very strong polarity is exhibited. In this compound, four organic substituents are covalently bonded to titanium, and in this quaternary ammonium salt, the positive charge of ammonium is balanced by the negative charge of anion. When this anion is a hydroxide ion, the aqueous solution exhibits strong alkalinity. For example, the basicity of tetraalkylammonium hydroxide is equal to or higher than that of sodium hydroxide or potassium hydroxide. In addition, since such ammonium salt is stable, it can be stored at room temperature without fear of decomposition like hydrazine.

The present invention relates to a fourth hydroxide such as a tetraalkylammonium hydroxide salt represented by the following structural formula (R represents an alkyl group).
It is based on the above-mentioned properties of the class titanium compound.

A first invention of the present application is to bring a cleaning agent comprising a solution containing a quaternary titanium hydroxide compound into liquid-liquid contact with an organic solvent, and separate the cleaning agent from the organic solvent after the liquid-liquid contact. Is a method for cleaning an organic solvent.

On the other hand, a second invention of the present application is an organic solvent storage container for storing an organic solvent, a cleaning agent storage container for storing a cleaning agent composed of a solution containing a quaternary hydroxide compound, and the inside of the organic solvent storage tank. An organic solvent comprising: a stirring device for mixing and stirring the organic solvent and the cleaning agent in the cleaning agent storage container; and a separator for separating the stirring solution into the cleaning agent and the organic solvent. It is a cleaning device.

The quaternary hydroxide hydroxide compound used in the present invention includes tetraalkylamine hydroxide and other heterocyclic compounds such as pyrrole, oxazole, thiazole, imidazole, pyridine, pyrimidinequinoline, quinoxaneline, purine and pteridine. , Carbazole, acridine, and phenazine hydroxide quaternary (titan) compounds are also included.

[Action]

In the above-mentioned constitution of the present invention, the fact that the quaternary hydroxide compound is strongly basic means that it is a decomposition product or a decomposition product in an organic solvent as compared with a conventional detergent containing hydrazine as a main component. It is very effective in removing complexes with metal ions. That is, a quaternary hydroxide compound such as tetraalkylammonium hydroxide (R4NOH) exhibits strong alkalinity and almost dissociates to release hydroxide ion.
This hydroxide ion reacts with the decomposition product (HD) of the organic solvent, which mostly takes the form of acid, and causes ionization dissociation as shown in the following equation.

_{^{HD + OH - → H 2 O}} + D - D - is migrated removed in the cleaning agent from the organic solvent for water-soluble. Further, in the organic solvent, the tetraalkylammonium hydroxide forms a water-soluble complex with respect to the metal ion which forms a complex with the decomposition product, and moves into the detergent to be removed. Therefore, the liquid-liquid extraction is carried out with the formation of hydroxide precipitates like the sodium carbonate detergent.
There is no risk of being disturbed by the formation of layers. Since the metal ion is likely to be hydroxide-precipitated in an alkaline atmosphere, the formation of the hydroxide precipitate can be prevented by forming the metal ion into a complex with tetraalkylammonium hydroxide.

Generally, alkali such as sodium hydroxide does not have a property of forming a complex with such a metal ion, so that an anion that forms a complex with a metal ion needs to be added. Such anions have a property as an acid and reduce the alkalinity of the cleaning agent. In this respect, a compound in which four substituents are bound to the periphery of titanium, which is strongly alkaline and has the property of an amine at the same time, has both the properties of strong alkalinity of the detergent and the ability to complex with metal ions. There is. Since the complex formation with the metal ion is considered to occur between the metal ion and the anion complex, this property does not impair the alkalinity as a detergent.

As an example, when zirconium is present in a nitric acid solution that is a back-extract solution in nuclear fuel reprocessing, a putative reaction when the nitric acid solution is washed with a detergent containing tetraalkylammonium hydroxide ion is explained. To do.

ZrO ₂ + 4NO ₃ + 2RN ₄ → [ZrO (NO ₃ ) ₄ ] ^2- 2R ₄ N …… (1) (R ₄ N tetraalkylammonium ion) The above reaction causes other problems such as plutonium, uranium and ruthenium. It is also considered to occur for metal ions. At this time, tetraalkylammonium hydroxide is highly water-soluble, and since this complex is also the same, these metal ions migrate to the aqueous phase (detergent phase) as a stable complex without precipitation even under strong alkalinity. . DBP
When ZrO ₂ and ZrO ₂ form a complex, washing with tetraalkylammonium hydroxide destroys the complex of DBP and ZrO ₂ to form a complex of Zr and tetraalkylammonium hydroxide.

Various kinds of quaternary hydroxide compounds having high performance as such a cleaning agent can be considered. Of these, there is tetraalkylammonium hydroxide, and the amount of final decomposition gas generated when decomposed is small, and since it has high water solubility and little residue in the solvent, tetramethylammonium hydroxide with a small alkyl group, tetraethyl hydroxide Ammonium is preferred. In addition to the alkyl group, it may have another substituent such as alkene or alkyl. In addition, it may be a heterocycle capable of forming a quaternary titanium compound.

As an example, the zirconium removal rate when tetramethylammonium hydroxide is used is shown in FIG. 1 in comparison with other cleaning agents.

According to FIG. 1, in the case where 0-0.05 mol% of tributyl phosphate was only dibutyl phosphate, all cleaning agents showed high removal rate, but 0.1-several mol% was dibutyl phosphate. In the case of, the tetraalkylammonium hydroxide shows a higher cleaning ability than other cleaning agents. This is, for example, when tetramethylammonium hydroxide is used as a reprocessing solvent for nuclear fuel, it has a cleaning ability that can sufficiently cope with high burnup of nuclear fuel. When reprocessing fuels for fast breeder reactors, many of them are expected to generate several percent of decomposition products, which cannot be regenerated with conventional cleaning agents. By washing with a detergent containing a compound, the reprocessed organic solvent can be regenerated sufficiently.

The cleaning agent composed of a quaternary hydroxide compound has a high cleaning ability with respect to other substances to be cleaned such as decomposition products in an organic solvent and metal ions. Therefore, 1
Even if the washing of the stages or the washing with water is included, the operation of washing and regenerating the organic solvent can be completed with only two washings. Therefore, the configuration of the cleaning device can be simplified.

〔Example〕

 Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a configuration diagram showing a configuration of an embodiment of the organic solvent cleaning apparatus according to the second invention of the present application.

In FIG. 2, a pipe provided with a valve 2 is connected to a deteriorated solvent (non-cleaning organic solvent) tank 1. The deteriorated solvent tank 1 is connected to a mixer settler 7 by a pipe equipped with a valve 5.

On the other hand, the cleaning agent tank 3 is connected to the mixer-settler 7 by a pipe having a valve 6.

The mixer settler 7 includes a mixer part 8, a mixer part partition, a settler part 11, a settler part partition 14 and an organic phase storage part 15. A mixer 9 is provided in the mixer section 8.

The organic phase storage section 15 is connected to the regenerated solvent tank 16 via a pipe. A pipe having a valve 17 is connected to the regenerated solvent tank 16.

The water phase 13 in the mixer-settler 7 is a waste cleaning agent tank by piping.
It is designed to flow into the 18 through piping.

Next, the operation of this embodiment will be described.

Deteriorated solvent is from the nuclear fuel extraction separation step after the back extraction operation,
It enters the deteriorated solvent tank 1 via the valve 2.

The cleaning agent tank 3 stores 0.4N-tetramethylammonium hydroxide solution. The deteriorated solvent is sent to the mixer-settler 7 through the valve 5, and the cleaning agent is similarly sent to the mixer-settler 7 through the valve 6.

In the mixer section 8 of the mixer-settler 7, the deteriorated solvent and the cleaning agent are stirred by the mixer 9 to be in a suspended state. The suspension overflows the partition wall 10 of the mixing section and the settler section 11
to go into. Here, the suspension is divided into an organic phase 12 and an aqueous phase 13. The organic phase overflows the partition wall 14 of the settler section, enters the organic phase storage section 15, and then is sent to the regenerated solvent tank 16. This regenerated solvent has the same performance as the organic solvent before deterioration because the decomposition products and metal ions in the solvent have been removed by tetramethylammonium hydroxide. As a result, it is sent to the extraction and separation step via the valve 17 and reused. This is to save the amount of organic solvent used.

On the other hand, the aqueous phase 13 is sent to the waste detergent tank 18, and the waste detergent is processed in the waste processing section. Next, using the example shown in FIG. 2, the regeneration rate by the detergent when DBP was added to the organic solvent was determined based on the distribution ratio of zirconium. The results are shown in FIG. Incidentally, FIG. 3 shows a comparative example using a cleaning agent other than tetramethyl ammonium hydroxide.

As can be seen from FIG. 3, the detergent composed of tetramethylammonium hydroxide shows a regeneration rate of nearly 100% even when the DBP concentration is as high as 1 mol% or more. It can be seen that with other detergents, the regeneration rate almost disappears when the DBP concentration exceeds 1 mol%. As a result, tetramethylammonium hydroxide has a strong cleaning ability unlike other cleaning agents.
The organic solvent can be sufficiently washed by washing only the steps. As a result of this washing, the organic solvent can be reused in a pure state.

Next, a second embodiment of the organic solvent cleaning apparatus will be described. In this embodiment, a waste cleaning agent processing device is provided. FIG. 4 shows the configuration diagram.

The deteriorated solvent tank 1 is connected to the first cleaning device 22 via a pipe. Similarly, the cleaning agent tank 3 is also connected.

The pure water tank 24 is connected to the second cleaning device 25 via a pipe. The first cleaner 22 and the second cleaner 25 are connected by a pipe. A pipe 51 for sending the organic solvent to the extraction step is connected to the second cleaning device 25. The first cleaning device 22 and the second cleaning device 25 are each provided with a cleaning agent tank by piping.
Connected to 23. The cleaning agent tank 23 is connected to the distillation column 26 by a pipe. The distillation column 26 is connected to a condenser 27, which is connected to an incinerator 28. A pipe having a valve 29 is connected to the distillation column 26. Condenser
A pipe 52 for sending pure water to the pure water system is connected to 27. A pipe 53 for sending exhaust gas to the exhaust gas system is connected to the incinerator 28.

Next, the operation of this embodiment will be described.

The deteriorated solvent is stored in the deteriorated solvent tank 1. The cleaning agent tank 3 contains 0.
4 Normal solution is stored. The cleaning liquid is sent to the first cleaning device 22 together with the deteriorated solvent, and after mixing, separated into an aqueous phase and an organic phase. At this time, decomposition products and metal ions in the organic solvent are transferred to the aqueous phase. The aqueous phase is temporarily stored in the waste detergent tank 23.

Pure water is stored in the pure water tank 24, and the first cleaning device 22
It is sent to the second washer 25 together with the organic phase coming out of, and after mixing is separated into an aqueous phase and an organic phase. By this operation, the tetramethylammonium hydroxide remaining in the organic solvent is removed. The organic phase exiting the second scrubber 25 is reused as a regeneration solvent in the nuclear fuel extraction process.

The aqueous phase discharged from the second cleaning device 25 is sent to the waste cleaning agent tank 23. The waste cleaning agent in the waste cleaning agent tank 23 is regularly distilled.
It is sent to 26 and distilled.

By the distillation operation in the still 26, tetramethylammonium hydroxide is decomposed into water, a tertiary amine and an alkane. As a result, in the distiller 26, these low-boiling components are separated into solid wastes (metal ions, etc.).

The low boiling point component discharged from the distiller 26 is sent to the condenser 27, and water is condensed and removed. The pure water obtained here is the pure water tank 24
For example, it is refluxed and reused.

The low boiling point tertiary amines and alkenes other than water in the condenser 27 are sent to the incinerator 28 where they are oxidized and converted into CO ₂ , NOX and water, and sent to the exhaust gas system.

The high boiling point component remaining in the distiller 26 is periodically taken out through the valve 29 and treated in the waste treatment system. According to this embodiment, the amount of solid waste generated is small and the highly efficient cleaning and regeneration of the organic solvent becomes possible.

Next, an example will be described in which the method for cleaning an organic solvent according to the first invention of the present application can be used as it is in the apparatus configuration of the conventional organic solvent regeneration step (in the case of reprocessing of nuclear fuel). FIG. 5 is a configuration diagram showing an organic solvent treatment routine of the embodiment.

The cleaning agent tank 3 is connected to the mixer 31 via a pipe. The dilute nitric acid tank 24 is connected to the mixer 33. The dilute sodium hydroxide tank 36 is connected to the mixer 35.

The mixer 31 is connected to the mixer 33, and the mixer 33 is connected to the mixer 35 via a pipe.

The deteriorated solvent is supplied into the mixer 31.

A pipe 40 is connected to the mixer 33, and the pipe 40 is led to the acid recovery system. A pipe 41 is connected to the mixer 35,
This pipe 41 is connected to the regenerating solvent system. Mixer 31
The pipe 42 from the mixer is connected to the pipe 43 from the mixer 35,
The pipe 42 is connected to the waste alkali tank 32. The pipe 44 coming out of the waste alkali tank 32 is connected to the still 37. A pipe 45 connected to the acid recovery system and a pipe 46 connected to the waste treatment system are connected to the distiller 37. In addition, a pipe 47 for supplying a nitric acid waste liquid is connected to the distiller 37.

Next, the operation of this embodiment will be described. Cleaning agent tank 3
Store tetramethylammonium hydroxide solution (0.2N) in it. This storage may be carried out at room temperature, and does not require cooling equipment for preventing decomposition unlike hydrazine-based detergents.
This cleaning agent is brought into contact with the deteriorated solvent in the mixer settler 31, and then separated into an aqueous phase and an organic phase. The aqueous phase is stored in the waste alkaline detergent tank 32. After that, the organic phase is stored in the dilute nitric acid tank 34 with the mixer settler 33 as in the conventional solvent regeneration step.
After contact with 0.1N-HNO _3, is contacted with 0.1 N-NaOH in dilute sodium hydroxide tank 36 in a mixer-settler 35.
After this operation is completed, the organic phase is used as a regeneration solvent.

The aqueous phase discharged from the mixer settler 33 is sent to the acid recovery system as a dilute nitric acid waste liquid. Hydrogen released from the mixer Setra 35 is
Stored in waste alkaline cleaner tank 32. The waste liquid in the waste alkaline detergent tank 32 is sent to the evaporator 37 together with the nitric acid waste liquid from another system, and is evaporated and concentrated. At this time, tetramethylammonium hydroxide is decomposed and gasified by the effect of heating and nitric acid. The rest is treated by a waste treatment system, but most of the solids are finally washed by NaOH, and the amount of waste generated is about 1/3.

According to the present embodiment described above, the amount of radioactive waste generated in the solvent regeneration step can be significantly reduced without changing the device configuration used in the conventional plant.

If the decomposition of the cleaning agent can be prevented during the distillation operation, the cleaning agent can be reused by separating and condensing due to the difference in boiling point and returning to the cleaning agent tank 3.

〔The invention's effect〕

As described above, according to the present invention, the hydroxylated quaternary nitrogen compound is strongly alkaline and therefore reacts with the decomposition product of the organic solvent in the form of an acid to form a water-soluble compound,
This water-soluble compound migrates from the organic solvent into the detergent and is removed with high efficiency, and also forms a water-soluble complex with respect to the metal ion which forms a complex with the decomposition product. The water-soluble complex migrates from the organic solvent into the detergent and is removed with high efficiency. Moreover, since the amount of solid waste generated is small, it is possible to reduce the amount of radioactive waste generated in the field of nuclear fuel reprocessing.

Further, according to the present invention, since the quaternary titanium hydroxide compound as a cleaning agent is stable even at room temperature, the cleaning of the organic solvent can be performed with high efficiency.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the DBP concentration and the zirconium removal rate, FIG. 2 is a process diagram showing an embodiment of the organic solvent cleaning apparatus according to the present invention, and FIG. 3 is a graph showing the embodiment of FIG. A graph comparing the cleaning rate (regeneration rate) of the organic solvent with other cleaning agents, FIG. 4 is a process diagram showing another embodiment of the organic solvent cleaning apparatus according to the present invention, and FIG. 5 is related to the present invention. It is process drawing which shows 1 Example which applied the washing | cleaning apparatus of the organic solvent as it was to the conventional apparatus. 1 ... Degraded solvent tank, 3 ... Cleaning agent tank, 7 ... Mixer settra, 16 ... Regenerated solvent tank, 26 ... Distillation tower,
28 …… Incinerator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Fukasawa 1168 Moriyama-cho, Hitachi-shi, Ibaraki Energy Research Laboratory, Hiritsu Seisakusho Co., Ltd. (56) Reference JP-A-51-67000 (JP, A) JP-A-62 -170897 (JP, A) JP-A-62-171704 (JP, A) JP-A-62-45301 (JP, A) US Patent 4059671 (US, A)

Claims (10)

[Claims] 1. A cleaning agent comprising a solution containing a quaternary titanium hydroxide compound is brought into liquid-liquid contact with an organic solvent, and after the liquid-liquid contact, the cleaning agent and the organic solvent are separated. And a method for cleaning an organic solvent. 2. The method according to claim 1, wherein
The method for cleaning an organic solvent, wherein the class titanium compound is tetraalkylammonium hydroxide. 3. The method for cleaning an organic solvent according to claim 2, wherein the tetraalkylammonium hydroxide is at least one of tetramethylammonium hydroxide and tetraethylammonium hydroxide. 4. The waste in the cleaning agent according to any one of claims 1 to 3, after the cleaning agent and the organic solvent are separated, the cleaning agent is vacuum distilled. Is separated from the cleaning agent, the cleaning agent is recovered and reused, and a method for cleaning an organic solvent. 5. A method for cleaning an organic solvent according to any one of claims 1 to 4, wherein the cleaning agent separated from the organic solvent is thermally or oxidatively decomposed. 6. An organic solvent storage container for storing an organic solvent,
A cleaning agent storage container for storing a cleaning agent made of a solution containing a quaternary hydroxide compound, a mixture of the organic solvent in the organic solvent storage tank and the cleaning agent in the cleaning agent storage container,
An apparatus for cleaning an organic solvent, comprising: a stirrer for stirring; and a separator for separating the stirred solution into a cleaning agent and an organic solvent. 7. The fourth aspect of the present invention according to claim 6,
A cleaning device for organic solvents, wherein the class titanium compound is tetraalkylammonium hydroxide. 8. The organic solvent cleaning apparatus according to claim 7, wherein the tetraalkylammonium hydroxide is at least one of tetramethylammonium hydroxide and tetraethylammonium hydroxide. 9. The cleaning agent according to claim 6, wherein the separated cleaning agent is subjected to vacuum distillation to remove wastes from the cleaning agent, and then the cleaning agent is removed. A cleaning device for an organic solvent, comprising a reflux device for refluxing the agent to the cleaning agent storage container. 10. The decomposing device for thermally decomposing or oxidatively decomposing the cleaning agent separated from the separating device according to any one of claims 6 to 9. Cleaning device for organic solvent.