JPH0533956B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention performs stable distillation of a solvent such as a diluent containing tributyl phosphate or a solution containing tributyl phosphate as a main component by suppressing thermal decomposition. This invention relates to a thin film distillation method that allows recovery of both diluent and solvent.

[Conventional technology]

In general, methods for treating waste solvents containing tributyl phosphate (hereinafter abbreviated as "TBP") generated at nuclear fuel reprocessing facilities, plutonium fuel processing facilities, or research facilities that handle nuclear fuel and radioactive isotopes include fluidized bed, Combustion method in which waste solvent is burned using a horizontal fuel furnace, etc., chemical decomposition method in which acid decomposition is performed using sulfuric acid, etc., extraction method in which TBP is recovered by forming and decomposing a phosphoric acid adduct, and thin film distillation equipment. There are distillation methods in which TBP and the like are recovered by distillation.

Among these methods, only the distillation method can recover both TBP and a diluent such as dodecane from the waste solvent. Since this distillation method can recover both TBP and diluent from the waste solvent, the amount of radioactive waste generated can be reduced by that amount, and the overall volume can be reduced.

[Problem that the invention seeks to solve]

When treating waste solvents containing the above-mentioned TBP by distillation, it is important to note that TBP itself is easily thermally decomposed;
The waste solvent contains components such as dibutyl phosphate (hereinafter abbreviated as "DBP"), metals such as U, Pu, and Zr, and their salts and complexes.
Due to problems such as some substances accelerating thermal decomposition, distillation conditions cannot be easily set and it has not yet been put into practical use.

An object of the present invention is to provide a distillation method that suppresses thermal decomposition of TBP in a solvent, performs stable distillation, and advantageously recovers both TBP and diluent.

[Means for solving problems]

In the present invention, the amount of the solvent containing tributyl phosphate is supplied under the following conditions: 0.1×L/1−η<F<3.78×10 ⁶ ×P×S/η
×(t+273) P=0.5 to 20 (torr) In the formula, F: Amount of liquid supplied (Kg/hr) L: Length of immersion side of the evaporation section in the distillation apparatus (m) η: Distillation rate (amount of distillate/ (amount of liquid supplied) S: narrowest area for passage of distilled vapor (m ² ) t: distillation temperature (°C) P: distillation pressure (torr) Distillation is performed using a thin film evaporative distillation apparatus so as to satisfy the following conditions. A thin film distillation method is provided.

Here, it is necessary to use a thin film evaporative distillation apparatus that has a short residence time of the solvent within the apparatus, does not cause abnormal local retention, and has high evaporation efficiency. For example, there are distillation apparatuses such as the stirred thin film evaporation type, the rotating disk evaporation type, and the falling thin film evaporation type, but it is preferable to use the stirred thin film evaporation type because it has been put into practical use as a production equipment and has been used for a long time. is preferred.

The movable rotor type of the above-mentioned stirred thin film evaporative distillation apparatus has a structure as shown in FIGS. 1 and 2. FIG. 1 is a front sectional view, and FIG. 2 is a sectional view taken along line Z--Z in FIG.

In FIGS. 1 and 2, reference numeral 1 denotes a vertical cylindrical body having a jacket 2 for heat medium circulation attached to its outer periphery and an evaporation surface formed on its inner wall. Reference numeral 3 denotes a solution supply pipe for supplying a solution such as a waste solvent, and is installed at a position above the evaporation surface of the cylindrical body 1.
Reference numeral 4 denotes a suction pipe for connecting a pressure reducing device (not shown) to bring the inside of the cylindrical body 1 to a predetermined pressure, and is attached to the partitioning cylindrical body 10 attached to the lower part of the cylindrical body 1. Alternatively, it can be attached to the upper part of the cylindrical body 1. Reference numeral 5 denotes a distillate delivery pipe for taking out the liquid condensed by the condenser 9 from below, and is attached to the bottom of the partitioning cylinder 10 formed at the lower part of the cylindrical main body 1. Reference numeral 6 denotes a residue delivery pipe for taking out the residue remaining at the bottom of the cylindrical body 1, and is attached to the bottom of the cylindrical body 1. Reference numeral 7 denotes a shaft body connected to a drive device, and blades 8 are movably attached to the shaft body. The blade 8 has a notch 8 on its sliding surface with the inner wall as shown in FIG. 3 through which the solution can pass.
a is formed, and rotates together with the blade holding part 7a formed integrally with the shaft body 7, protrudes outward by centrifugal force or spring force, and slides into contact with the inner wall of the cylindrical body 1. It is becoming easier to move around. The solution supplied from the solution supply pipe 3 is formed as a thin film on the evaporation surface by the blades 8. The solution descends in a thin film and evaporates into vapor while moving over the evaporation surface. The condenser 9 is attached to a partitioning cylinder 10, and is configured to supply a refrigerant inside, use its outer wall as a cooling surface, and condense steam when it comes into contact with it.

The immersion side length L of the evaporation section in the steam distillation apparatus is
The narrowest area S for passage of distilled vapor, which is the circumferential length of the inner wall forming the evaporation surface, is the smaller of the gap between the inner wall of the cylindrical body 1 and the blade 8 or the gap between the partitioning cylinder 10 and the condenser 9. This is the area of the side.

A fixed rotor type stirring thin film evaporative distillation apparatus has a structure as shown in FIGS. 4 and 5. Figure 4 is a front sectional view, Figure 5 is Figure 4Y
It is a sectional view along the -Y line.

In FIGS. 4 and 5, reference numeral 11 denotes a vertical cylindrical body having a jacket 12 for heat medium circulation attached to its outer periphery and an evaporation surface formed on its inner wall. 13
is a solution supply pipe that supplies solutions such as waste solvents,
It is mounted above the evaporation surface of the cylindrical body 11. Reference numeral 14 denotes a suction pipe for connecting a pressure reducing device (not shown) to a predetermined pressure in the cylindrical body 11 via a condenser 18, and is installed above the evaporation surface. 15 is the cylindrical main body 11
This is a residue delivery pipe for removing residue remaining at the bottom of the cylindrical body 11, and is attached to the bottom of the cylindrical body 11. 1
Reference numeral 6 denotes a shaft body connected to the drive device 20, to which a collision plate 18 is integrally fixed on the upper side and a blade 17 is fixed on the lower side. A predetermined gap is provided between the end of the blade 17 and the evaporation surface of the cylindrical body 11, and the solution supply pipe 1
The blades 17 form a thin film on the evaporation surface of the solution supplied from 3. The solution evaporates into vapor as it descends over the evaporation surface in the form of a thin film. A refrigerant such as water is supplied to the condenser 19 to form a cooling surface therein, and while the above-mentioned vapor passes through the condenser 19, it is condensed into a liquid and taken out as a distillate.

The immersion side length L of the evaporation section in the steam distillation apparatus is
This is the circumferential length of the inner wall of the cylindrical body 11 that forms the evaporation surface, and the narrowest distilled vapor passage area S is the gap between the inner wall of the cylindrical body 11 and the blade 17 or between the inner wall of the cylindrical body 11 and the collision plate 18. This is the smaller area of the gap between and.

The rotary disk evaporative distillation apparatus has a configuration as shown in FIG.

In FIG. 6, 21 is a bowl-shaped dome with a jacket 22 for refrigerant circulation attached to its outer periphery and a cooling surface formed on its inner wall, and a liquid sump 27 on the inner wall below the cooling surface of the dome. The liquid condensed on the cooling surface is collected and taken out as distillate from the distillate delivery pipe 29. 23 is a disc, which is rotated by a drive device 24. A heating device 25 is disposed below the disk 23 to form an evaporation surface on the upper surface of the disk 23. Reference numeral 26 denotes a supply pipe for supplying a liquid such as a waste solvent, and the outlet thereof is located above the center of the upper surface of the disc 23 . A residue receiver 28 is installed on the outer periphery of the disk 23 so as to cover the disk, and is configured to collect the residue that has been supplied to the disk 23 and not evaporated, and take it out from the residue delivery pipe 37.

The liquid supplied to the center of the rotating disk 23 moves in the form of a thin film on the evaporation surface, during which time it evaporates into vapor. The vapor condenses into liquid on the cooling surface of the dome 21, is collected in a liquid reservoir 27, and is taken out of the dome 21 through a distillate delivery pipe 29. 38 is a suction tube.

The immersion side length L of the evaporation section in the above distillation apparatus is:
The outer peripheral length of the disk 23 forming the evaporation surface, and the narrowest distilled vapor passage area S is the area with the inner wall of the dome 21 as its diameter.

If the amount of liquid supplied to the evaporation surface of the distillation apparatus is too small, dry spots will occur on the evaporation surface and a uniform liquid film cannot be formed, and the temperature of the liquid at the dry spots will increase. rises above the boiling point,
It may thermally decompose TBP or cause scorching (carbonization).

Therefore, when we experimented with various amounts of supplied liquid, we found that dry spots with a supply liquid amount of 0.1/
It has become clear that this occurs when the amount of liquid drops below m·hr (the amount of liquid per unit time, per unit immersion area).

From the above, the amount of liquid to be supplied is F (Kg/hr), the distillation rate is η (wt ratio), the immersion side length of the evaporation section L (m), and the density of the residual liquid in the device is 1 (Kg/hr). Then, it is necessary to satisfy 0.1<F(1-η)/L ∵F>0.1×L/1-η (1).

Contrary to the above, if the amount of liquid to be supplied is too large, the amount of evaporated vapor of the liquid will increase, and the pressure loss at the narrowest part of the vapor passage in the distillation apparatus will become too large, resulting in a vapor lock phenomenon. Therefore, in order to prevent the vapor lock phenomenon from occurring, it is necessary to set the amount of supplied liquid as follows based on the equation of the sound velocity of the fluid.

F×η×22.4×760×(t+273)/M×P×273
×S<Y In the formula, F: Amount of liquid supplied (Kg/hr) η: Distillation rate (amount of distilled liquid/amount of supplied liquid) (wt ratio) M: Molecular weight of distilled vapor S: Distilled vapor passage narrowest Area (m ² ) t: Distillation temperature (°C) P: Distillation pressure (torr) Y: Sound velocity (m/hr) In the above formula, the molecular weight (M) of the distilled vapor is expressed as the molecular weight of the diluent dodecane, 168 Kg/K. -mol and the speed of sound (F) is 390 x 3600 m/hr, which is the speed at 100°C and 1 atm, then the following equation is obtained.

F＜390×3600×168×273×P×S/22.4×760×η×(
t+273) ∵F<3.78×10 ⁶ ×P×S/η×(t+273) ...(2) From equations (1) and (2) above, the equation for setting conditions for the supply liquid amount is as follows. Become.

0.1×L/1−η<F<3.78×10 ⁶ ×P×S/η×(
t+273)...(3) When the distillation rate (η) is 0.3 or less, the amount of distillation is small, resulting in inefficiency, and when it is 0.9 or more, the separation performance of the distillation apparatus decreases.

Therefore, it is preferable to set the distillation rate (η) in the range of 0.3 to 0.9.

When the distillation pressure (P) is less than 0.5 torr, the boiling point of dodecane, the diluent in the solvent, becomes less than 45°C. Therefore, in the summer, boiling or flashing may occur at room temperature, and residue may be mixed into the distillate due to droplet entrainment, so lowering the pressure to less than 0.5 torr should be avoided.
In addition, if the distillation pressure (P) exceeds 20 torr, the boiling point of TBP will be higher than 165℃, making it easier to thermally decompose.
It should also be avoided to increase the pressure above 20 torr.

Thin film distillation can be carried out using a single thin film evaporative distillation apparatus, but as shown in FIGS. Highly pure tributyl phosphate and diluent can be recovered by supplying or refluxing to another distillation device.

Moreover, if a plurality of thin film evaporative distillation apparatuses 30 are installed as shown in FIG. 9, and the distillate is supplied to the distillation apparatus located at the front, and the residual liquid is supplied to the distillation apparatus located at the rear,
Higher purity tributyl phosphate and diluent can be recovered.

〔Example〕

Example 1 Operating conditions Supply liquid amount (F): 0.19 Kg/hr Immersion side length of evaporation section in distillation apparatus (L): 0.157 m Narrowest area for passage of distilled vapor (S): 1.8 × 10 ^-3 m ² Distillation temperature (t): 110℃ Distillation pressure (P): 0.7torr Rotor rotation speed: 450R.PM Cylindrical body (evaporation section) inner diameter: 50mm Stirred thin film evaporation distillation as shown in Figure 1 under the above conditions. When a solution consisting of 70.3% by volume of dodecane and 29.7% by volume of TBP (64.5% by weight of dodecane and 35.5% by weight of TBP) was supplied and distilled using an apparatus (movable rotor type), the following result was obtained. I was able to get good results.

(1) Composition change in solution due to distillation operation. The composition of the distillate is 71.8% by weight of dodecane,
TBP is 28.2% by weight, and the composition of the residual liquid is 3.9% by weight of dodecane and TBP.
is 96.1% by weight.

(2) DBP contained in the solution resulting from the distillation operation
The concentration of DBP in the feed solution decreased from 171 PPM to 32 PPM in the distillate and DBP in the residual solution to 171 PPM after distillation.
It became 900PPM.

The distillation rate (η) at this time was 0.84, and since DBP is produced when TBP is thermally decomposed, the above measurement results indicate that no DBP was produced during distillation.
This confirms that there is no thermal decomposition of TBP.

In addition, since the device is made of glass, it is possible to observe the distillation situation, and the situation is stable, and the distillate,
No coloration or other changes were observed in the remaining liquid.

Calculating the solution supply amount (F) from the third equation based on the operating conditions in this example, 0.1×L/1−η=0.1×0.157/1−0.84=0.098 (Kg/
hr) 3.78×10 ⁶ ×P×S/η(t+273) = 3.78×10 ⁶ ×0.7×1.8×10 ^-3 /0.84×(110+273)=1
4.8 (Kg/hr) ∵0.098<F<14.8, indicating that the solution supply amount under the operating conditions was appropriate.

Example 2 Operating conditions Supply liquid amount (F): 0.30Kg/hr Immersion side length of evaporation section in distillation apparatus (L): 0.157m Narrowest area for passage of distilled vapor (S): 1.8×10 ^-3 m ² Distillation temperature (t): 250℃ Distillation pressure (P): 20torr Rotor rotation speed: 450R.PM Cylindrical body (evaporation section) inner diameter: 50mm Stirring thin film evaporation distillation as in the first example under the above conditions Using a device (movable rotor type), dodecane 70.3% by volume, TBP29.7% by volume (dodecane 64.5%
When distillation was carried out by supplying a solution consisting of 35.5% by weight of TBP, the following results were obtained.

(1) Composition change in solution due to distillation operation. The composition of the distillate is 69.0% by weight of dodecane,
TBP is 31.0% by weight, and the composition of the residual liquid is 3.0% by weight of dodecane, TBP
is 97.0% by weight.

(2) DBP contained in the solution resulting from the distillation operation
The concentration of DBP in the feed solution was 35 PPM after distillation, but the DBP in the distillate decreased to 30 PPM, and the DBP in the residual solution decreased to 35 PPM.
It became 90PPM.

The distillation rate (η) at this time was 0.92, and the above measurement results confirmed that there was no generation of DBP during distillation and no thermal decomposition of TBP.

Further, the distillation conditions were stable, and no coloration or other changes were observed in either the distillate or the residual liquid.

When the solution supply amount (F) was calculated from the third equation based on the operating conditions in this example, it was found that 0.20<F<283, which indicates that the solution supply amount under the operating conditions was appropriate.

Example 3 Operating conditions Supply liquid amount (F): 0.12Kg/hr Immersed side length of evaporation section in distillation apparatus (L): 0.157m Narrowest area for passage of distilled vapor (S): 1.8×10 ^-3 m ² Distillation temperature (t): 120℃ Distillation pressure (P): 0.5torr Rotor rotation speed: 450R.PM Cylindrical body (evaporation part) inner diameter: 50mm Same stirring thin film evaporation method as in the first example under the above conditions Using a distillation apparatus (movable rotor type), dodecane 16.4% by volume, TBP83.6% by volume (dodecane 13.1%
When distillation was performed by supplying a solution consisting of TBP (86.9% by weight), the following results were obtained.

(1) Composition change in the solution due to distillation operation. The composition of the distillate is 15.3% by weight of dodecane,
TBP is 84.7% by weight, and the composition of the residual liquid is 7.3% by weight of dodecane and TBP.
is 92.7% by weight.

(2) DBP contained in the solution resulting from the distillation operation
By performing a distillation operation, the concentration of DBP in the feed solution decreased from 231 PPM to 196 PPM in the distillate and DBP in the residual solution to 196 PPM.
It became 437PPM.

The distillation rate (η) at this time was 0.86, and the above measurement results confirmed that there was no generation of DBP during distillation and no thermal decomposition of TBP.

Further, the distillation conditions were stable, and no coloration or other changes were observed in either the distillate or the residual liquid.

When the solution supply amount (F) was calculated from the third equation based on the operating conditions in this example, it was found that 0.112<F<10.1, indicating that the solution supply amount under the operating conditions was appropriate.

Example 4 Operating conditions (F): 30.6Kg/hr Distillation unit length of evaporation section (L): 0.25m Narrowest area for passage of distilled vapor (S): 2.2×10 ^-3 m ² Distillation temperature ( t): 151℃ Distillation pressure (P): 5torr Rotor rotation speed: 1270R.PM Cylindrical body (evaporation part) inner diameter: 80mm Under the above conditions, stirred thin film evaporation distillation apparatus (fixed rotor) as shown in Figure 2 was used. When a solution consisting of 78% by volume of dodecane and 22% by volume of TBP (73.2% by weight of dodecane and 26.8% by weight of TBP) was supplied and distilled, the following results were obtained. did it.

(1) Composition change in solution due to distillation operation. The composition of the distillate is 84.3% by weight of dodecane,
TBP is 15.7% by weight, and the composition of the residual liquid is 28.4% by weight of dodecane,
TBP is 71.6% by weight.

(2) DBP contained in the solution resulting from the distillation operation
Changes in the concentration of DBP in the feed solution, which contained 35 PPM by performing a distillation operation, decreased to 20 PPM in the distillate and DBP in the residual solution.
It became 90PPM.

The distillation rate (η) at this time was 0.79, and from the above measurement results, no DBP was produced during distillation, and TBP
It was confirmed that there was no thermal decomposition.

Further, no coloration or other changes were observed in either the distillate or the residual liquid.

When the solution supply amount (F) was calculated from the third equation based on the operating conditions in this example, it was found that 0.119<F<121.5, which indicates that the solution supply amount under the operating conditions was appropriate.

Example 5 When distillation was carried out by changing the distillation pressure in the operating conditions to 1 torr in the above-mentioned Example 4, the distillation rate was
It decreased to 0.60.

When the feed rate was increased to 40 Kg/hr under the above operating conditions, the distillation rate decreased to 0.50, and when the feed rate was decreased to 28 Kg/hr, the distillation rate changed to 0.70.

Based on these operating conditions, when calculating the supply liquid amount (F) using the third equation 3.78×10 ⁶ ×P×S/η (t+273), when η is 0.60, F is 32.7, and when η is 0.50, F is 39.2 When η is 0.70, F becomes 28.0, which shows that the actual supply amount and the calculated supply amount almost match.

Example 6 Operating conditions Supply liquid amount (F): 22.5Kg/hr Immersion side length of evaporation section in distillation apparatus (L): 1.2m Narrowest area for passage of distilled vapor (S): 2.6×10 ^-3 m ² Distillation temperature (t): 114℃ Distillation pressure (P): 0.8torr Rotation speed of disk: 1200R.PM External dimensions of disk: 380mm Under the above conditions, a rotating disk evaporation distillation apparatus as shown in Figure 3 was used. using dodecane 70.3% by volume,
TBP29.7% by volume (dodecane 64.7% by weight, TBP35.3
When distillation was carried out by supplying a solution consisting of (% by weight), the following results were obtained.

(1) Composition change in the solution due to distillation operation. The composition of the distillate is 77.1% by weight of dodecane,
TBP is 22.9% by weight, and the composition of the residual liquid is 6.2% by weight of dodecane and TBP.
is 93.8% by weight.

(2) DBP contained in the solution resulting from the distillation operation
Change in concentration: DBP in the feed solution contained 126 PPM by performing the distillation operation, but DBP in the distillate decreased to 83 PPM, and DBP in the residual solution decreased to 126 PPM.
It became 262PPM.

The distillation rate (η) at this time was 0.79, and it was confirmed from the above measurement results that no DBP was generated during distillation and no thermal decomposition of TBP occurred.

Further, no coloration or other changes were observed in either the distillate or the residual liquid.

When the solution supply amount (F) was calculated from the third equation based on the operating conditions in this example, it was found that 0.057<F<2570, indicating that the solution supply amount under the operating conditions was appropriate.

Example 7 Operating conditions Supply liquid amount (F): 0.06 Kg/hr Immersion side length of evaporation section in distillation apparatus (L): 0.157 m Narrowest area for passage of distilled vapor (S): 1.8 × 10 ^-3 m ² Distillation temperature (t): 120℃ Distillation pressure (P): 5torr Rotor rotation speed: 450R.PM Cylindrical body (evaporation part) inner diameter: 50mm Stirring thin film evaporation distillation as in the first example under the above conditions Using a device (movable rotor type), dodecane 70.3% by volume, TBP29.7% by volume (dodecane 64.5%
wt%, TBP35.5wt%) solution consisting of 60Co
After being exposed to 10 ⁷ rad of gamma rays, the solution was supplied and distilled, and the following results were obtained.

(1) Composition change in the solution due to distillation operation. The composition of the distillate is 92.3% by weight of dodecane,
TBP is 7.7% by weight, and the composition of the residual liquid is 7.8% by weight of dodecane, TBP
is 92.2% by weight.

The distillation rate at this time was 0.67.

(2) Changes in solution performance due to distillation operation, Phase separation: Phase separation of feed solution: > 10 minutes Phase separation of distillate: 1 minute Phase separation of residual solution: > 10 minutes H number: Feed solution H number of: 1200 H number of distillate: <50 H number of residual liquid: 7600 The evaluation of phase separation in the above solution performance was performed by mixing the solvent and an equal amount of 1.2N-NaOH and letting it stand. However, a method is used to measure the separation time between the solution phase and the aqueous phase. However, since it is not possible to determine the persistence of the emulsion in each phase based on the two-phase separation time alone, the transmittance of each phase is measured using a spectrophotometer, and quantification is determined by the time at which the transmittance becomes constant. It became. (The shorter the time, the better the phase separation property.) The H number in the solution performance is an index of the degree of deterioration of the solvent, and it is the internal fission product of Zr and the strong It corresponds to the concentration of the total amount of compounds forming the complex.

(A solvent with a high H number indicates a decrease in the decontamination coefficient of fission products.) In this example, TPGarrett, Jr. EN
The H number was measured by Jenkins' method.

That is, take 2 ml of sample and Hf tracer solution 2 in each solution, separate by standing, drain the aqueous phase, and calculate the H number from the total γ counts and specific radioactivity of the sample (the amount of Hf remaining per 10 ⁹ of the solvent). The number of moles) was calculated.

From the above-mentioned phase separation and H-number measurement results, it can be estimated that the deterioration-causing substances were concentrated on the residual liquid side.

Further, the distillation conditions were stable, and as the feed liquid was pale yellow, the distillate became nearly colorless and transparent, and the residual liquid was colored brown.

These facts confirm that the deterioration-causing substances were concentrated on the residual liquid side.

[Comparative Example]

Comparative Example 1 Operating conditions Distillation temperature: Top 57-106℃ Tower bottom 98-161℃ Distillation pressure: Top 0.8-0.9torr Bottom 6.0-15.0torr Distillation rate: 20-50c.c./hr Reflux ratio: 0.8 to 4.5 Under the above conditions, a solution having the same composition as in Example 1 was heated by integrally forming a packed tower 32 having a heating can 31 at the bottom and a packed bed 33 at the top, as shown in FIG. Distillation was carried out using a packed column batch distillation apparatus in which a distillate delivery pipe 35, a suction pipe 36, and a coil 34 for refrigerant circulation were attached to the upper part of the column 32, and the following results were obtained. Ta.

(1) Composition change in the solution due to distillation operation. The composition of the initial distillate is 99.5% by weight of dodecane,
TBP is 0.5% by weight, and the composition of the residual liquid is 0.7% by weight of dodecane, TBP
is 99.3% by weight.

(2) The DBP contained in the solution was 39PPM but reduced to 43PPM by distillation, which is approximately 10% by weight.
More than 1000 were generated.

In addition, although the initially supplied solution was almost transparent, the remaining liquid in the tank turned brown due to the distillation operation.

Although TBP and dodecane can be recovered from the above measurement results, it can be assumed that TBP is thermally decomposed due to the increase in DBP.

Furthermore, the fact that TBP was colored brown confirms that thermal decomposition has occurred.

Comparative Example 2 A solution with the same composition as in Example 1 was prepared under the same operating conditions as in Example 1, except that the distillation pressure was changed to 0.1 torr.
When distillation was carried out using the same apparatus shown in FIG. 1 as in Example 1, the solution supplied to the cylindrical body 1 foamed significantly and was sent out from the suction pipe 4 and into the condenser 9 installed between it and the pressure reducing device. Condenser 9 was found to be clogged within 30 minutes of starting distillation. Therefore, when the frost in the condenser 9 was melted and its composition was analyzed, it was found that most of it was dodecane. This is considered to be because the distillation pressure was too low and the dodecane vaporized before reaching the heating section of the distillation apparatus, was sent out through the suction pipe, and was captured by the condenser.

Comparative Example 3 When distillation was carried out under the same operating conditions as in Comparative Example 2, the distillation pressure was changed to 30 torr and the distillation temperature was changed to 300° C., but significant coloring was observed in the residual liquid, so the distillation operation was discontinued. In addition to lowering the temperature of the device,
When the pressure was returned to normal pressure, TBP decomposition gas was generated in the form of white smoke. This is considered to be due to thermal decomposition of TBP due to the high distillation pressure and temperature.

Comparative Example 4 Among the operating conditions in Comparative Example 3 above, the supply liquid amount was 0.04 Kg/hr, the distillation pressure was 0.5 torr, and the distillation temperature was
When the temperature was changed to 100°C and distillation was carried out, there was no particular abnormality in the distillation condition. However, the distillation rate was 0.992, and the composition of the distillate was 64.6% by weight of dodecane,
The TBP was 35.4% by weight, which was almost the same composition as the feed solution.

When the solution supply amount (F) was calculated from the third equation based on the above-mentioned operating conditions, it was found that 2<F<9.2, which indicates that the solution supply amount under the operating conditions was not appropriate.

〔Effect of the invention〕

As described above, the present invention allows diluents such as tributyl phosphate and dodecane to be easily and efficiently recovered by distilling a solvent containing adjacent tributyl using a thin film evaporation distillation apparatus under predetermined distillation operating conditions. can.

Furthermore, if a plurality of thin film evaporative distillation apparatuses are installed and the distillation operation is performed, more than 99% of the tributyl phosphate and diluent can be recovered.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing one embodiment of a stirring thin film evaporation type distillation apparatus for carrying out the distillation method of the present invention. FIG. 2 is a sectional view taken along the line Z--Z in FIG. 1, and FIG. 3 is a schematic perspective view showing the state in which the blades are attached. FIG. 4 is a schematic sectional view showing another embodiment of the stirred thin film evaporative distillation apparatus, and FIG. 5 is a sectional view taken along the line Y--Y in FIG. 4. FIG. 6 is a schematic sectional view showing an embodiment of a rotating disk evaporative distillation apparatus for carrying out the distillation method of the present invention. 7th
8 and 9 are schematic system diagrams showing an embodiment for implementing the distillation method of the present invention by installing a plurality of thin film evaporative distillation apparatuses. FIG. 10 is a schematic cross-sectional view showing one embodiment of a conventionally used packed column type batch distillation apparatus. 1, 11... Cylindrical body, 2, 12, 22... Jacket, 3, 13... Solution supply pipe, 4, 14,
36, 38... Suction pipe, 5, 29, 35... Distillate delivery pipe, 6, 15, 37... Residue delivery pipe, 7,
16...Shaft body, 8,17...Blade, 9,19...
Condenser, 10... Partition cylinder, 18... Collision plate, 21... Dome, 23... Disc, 24...
Drive device, 25... heating device, 26... supply pipe,
27... Liquid reservoir, 28... Residue receiver, 31... Heating tube, 32... Packed tower, 33... Packed bed, 34...
...Coil, 30...Thin film evaporation type distillation device.

Claims (1)

[Scope of Claims] 1. A method for thin film distillation of a liquid containing tributyl phosphate, characterized in that distillation is carried out using a thin film evaporative distillation apparatus while supplying a solvent containing tributyl phosphate in an amount that satisfies the following conditions. 0.1×L/1−η＜F＜3.78×10 ⁶ ×P×S/η
×(t+273) P=0.5 to 20 (torr) In the formula, F: Amount of liquid supplied (Kg/hr) L: Length of immersion side of the evaporation section in the distillation apparatus (m) η: Distillation rate (amount of distillate/ Supply liquid amount) S: Distilled vapor passing narrowest area (m ² ) t: Distillation temperature (°C) P: Distillation pressure (torr)