JPS6317892A - Thin-film distillation process - Google Patents

Abstract

PURPOSE:To easily recover tributyl phosphate and a diluent such as dodecane in high efficiency, suppressing thermal decomposition, by distilling a diluent containing tributyl phosphate with a thin-film evaporation distillation apparatus supplying the solvent containing tributyl phosphate in a manner to satisfy a specific condition. CONSTITUTION:Both tributyl phosphate and diluent are recovered from a diluent containing tributyl phosphate (TBP) by supplying a TBP-containing solvent through a solution-feeding pipe 3 to a thin-film evaporation distillation apparatus composed of a vertical cylindrical main body 1 having an evaporation face on the inner wall and furnished with a jacket 2 for the circulation of thermal medium at the outer circumference and distilling the solvent with the apparatus. The feeding rate of the TBP-containing solvent is adjusted to satisfy the formula [F is feeding rate of the liquid (kg/hr); L is immersed depth (m) of the evaporation part in the distillation apparatus; eta is distillation rate (quantity of distilled liquid/quantity of supplied liquid); S is area (m<2>) of the narrowest part of the path of distilled vapor; (t) is distillation temperature ( deg.C); P is distillation pressure (torr)].

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]

Generally nuclear fuel reprocessing facilities, plutonium fuel fabrication facilities,
Alternatively, as a method for treating waste solvents containing tributyl phosphate (hereinafter abbreviated as rTBPJ) generated at research facilities that handle nuclear fuel and radioactive isotopes, etc., the waste solvents are burned using a fluidized bed, horizontal combustion furnace, etc. Combustion method, chemical decomposition method using sulfuric acid, etc. to perform acid decomposition, extraction method to recover TBP by forming and decomposing a phosphoric acid adduct, distillation method to recover TBP, etc. by distillation using a thin film distillation device, etc. There is.

m among these methods? Distillation is the only method that can recover both TBP and a diluent such as dodecane from the 8 medium. Since this distillation method can recover both TBP and diluent from the waste solvent, the amount of radioactive waste generated can be reduced accordingly, and the overall volume can be reduced.

[Problem that the invention seeks to solve]

When treating the waste solvent containing TBP mentioned above by a distillation method, TBP itself is easily thermally decomposed, and the waste solvent contains dibutyl phosphate (hereinafter abbreviated as rDBPJ), U, Pu,
It contains components such as metals such as Zr, their salts, and complexes, and there are problems such as some of these may accelerate thermal decomposition of TBP, so it is difficult to easily set distillation conditions. However, it has not yet been put into practical use.

An object of the present invention is to provide a distillation method that can suppress thermal decomposition of TBP in a solvent, perform stable distillation, and advantageously recover both TBP and diluent.

[Means for solving problems]

In the present invention, the supply amount of the solvent containing tributyl phosphate is determined under the following conditions: P = 0.5 to 20 (torr) where F: supply liquid amount (kg/hr) L:
immersion side length of the evaporation section in the distillation apparatus (m) η: distillation rate (
Distillate volume/Supplied liquid volume) S: Narrowest area for passage of distillate vapor <g) t:
The present invention provides a thin film distillation method characterized in that distillation is carried out using a thin film evaporative distillation apparatus such that distillation temperature ("C)P: distillation pressure (torr) is satisfied.

Here, as a thin film evaporative distillation apparatus, the residence time of the solvent within the apparatus is short, and there is no local abnormal retention.
It is necessary to use one with 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 the stirred thin film evaporation type is used because it has been put into practical use as a production equipment and has been used. is preferable.

The movable rotor type of the above-mentioned agitated thin film evaporative distillation apparatus is
The configuration is 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.

4 is a pressure reducing device (
(not shown) is a suction tube for connecting the cylindrical body 1
It is attached to the partitioning cylinder 10 attached to the lower part of the cylindrical body 1, or it is attached to the upper part of the cylindrical main 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 structure in which a notch 8a through which the solution can pass is formed in the sliding contact surface with the inner wall as shown in FIG.
It rotates together with a blade holding portion 7a formed integrally with the shaft body 7, and is moved in a state in which it protrudes outward due to centrifugal force or spring force and is in sliding contact with the inner wall of the cylindrical body 1.

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. Condenser 9 is a partition cylinder l
The refrigerant is supplied inside the refrigerant, the outer wall of which is used as a cooling surface, and steam condenses when it comes into contact with the refrigerant.

The immersion side length L of the evaporation section in the above distillation apparatus is the circumferential length of the inner wall forming the evaporation surface, and the narrow area S for the amount of distilled vapor passing through is the gap or partition between the inner wall of the cylindrical body 1 and the blade 8. This is the smaller area of the gap between the cylinder 10 and the condenser 9.

The fixed rotor type of the stirred thin film evaporation distillation apparatus has a structure as shown in FIGS. 4 and 5. FIG. 4 is a front sectional view, and FIG. 5 is a sectional view taken along line Y--Y in FIG.

In FIGS. 4 and 5, reference numeral 11 denotes a vertical cylindrical body having a jacket 12 for circulating a heat medium attached to its outer periphery and an evaporation surface formed on its inner wall. Reference numeral 13 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 main body 11. 14 is a decompression device (not shown) that maintains a predetermined pressure inside the cylindrical body 11, and connects it to the condenser 1.
This is a suction tube for connection via 8, and is installed at a position above the evaporation surface. Reference numeral 15 denotes 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. Reference numeral 16 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 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.
The blades 117 form a thin film on the evaporation surface of the solution supplied from the liquid supply pipe 13. 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 the above-mentioned brown air is transferred to the condenser 19.
While passing through the water, it condenses into a liquid and is taken out as a distillate.

The immersion side length L of the evaporation section in the above-mentioned distillation apparatus 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 length between the inner wall of the cylindrical body 11 and the blade 17. or the gap between the inner wall of the cylindrical body 11 and the collision plate 18, whichever is smaller.

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 reservoir 27 is formed 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 disk, 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. 26 is a supply pipe for supplying liquid such as waste solvent;
The outlet is located above the center of the top 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 supplied to the disk 23 and not decomposed, 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 length of the immersion side of the evaporation section in the above distillation apparatus is the outer circumference length of the disk 23 forming the evaporation surface, and the narrowest area S for passage of distilled vapor is the area whose diameter is the inner wall of the dome 21. .

Regarding the amount of liquid supplied (F), if the amount of liquid supplied to the evaporation surface of the distillation device is too small, a dry spot will occur on the evaporation surface, making it impossible to form a uniform peritoneum, and the temperature of the liquid at the dry spot will decrease. It rises above the boiling point and thermally decomposes TBP,
Burning (charring) etc. may occur.

Therefore, when we conducted experiments by varying the amount of supplied liquid, we found that
For dry spots, the amount of liquid supplied is 0. It has become clear that this occurs when the flow rate is below IN/m·hr (liquid volume 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 is L (m), and the density of the residual liquid in the device is 1 (kg/l). ), it is necessary to set it to 1-η.

Contrary to the above, if the amount of liquid supplied is too large, the liquid will evaporate into vapor.
As a result, the pressure loss at the narrowest part of the steam passage in the distillation apparatus becomes 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.

M X p x273x s In the formula, F: Supply liquid amount (kg/hr) η:
Distillation rate (amount of distillate/amount of liquid supplied) (wt ratio) M: Molecular weight of distilled vapor S: Narrowest area through which distilled vapor passes (m') t: Residue temperature (''C) P: Distillation pressure (torr)Y: speed of sound
(m/hr) In the above formula, the molecular weight (M) of the distillate vapor is the molecule N of dodecane as the diluent 168 kg
/ is represented by -1Ito+, and the speed of sound (Y) is 1
390X3600 which is the speed at 00℃, latm
When z/hr, the following equation is obtained.

From the above-mentioned equation (11) and equation (2), the equation for setting the supply liquid amount is as follows.

Note that 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.

The distillation pressure (P) is Q, 5 torr. When the pressure reaches the maximum pressure, the boiling point of dodecane, which is a diluent in the solvent, becomes less than 45°C. Therefore, in the summer, boiling or flashing phenomenon may occur at room temperature, and residue may be mixed into the distillate due to droplet entrainment, so the pressure is
It should be avoided to make it less than rr. Also, when the distillation pressure (P) exceeds 20 torr, the boiling point of TBP decreases to 1
The pressure should also be avoided to be higher than 20 Lorr, since the temperature will be higher than 65°C and thermal decomposition will occur easily.

One distillation of three membranes can be carried out using a - group thin film evaporative distillation apparatus, but as shown in FIGS. Highly pure tributyl phosphate and diluent can be recovered by supplying or refluxing the liquid to another distillation device.

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

〔Example〕

Example 1 Operating conditions Feed liquid I (F): 0.19 kg/hr
Immersion length L of evaporation section in distillation apparatus: 0.1
57 m Narrowest area for distillate vapor passage (S): 1.8 Xl0-
3 Distillation resistance temperature (t): 11O℃ Distillation pressure (P): 0.7 torr Rotator rotation speed: 450 R, P, M cylindrical body (Fujisha part) inner diameter: 50m Figure 1 under the above conditions Using a stirred thin-film evaporative distillation apparatus (movable rotor type) as shown in Figure 1, dodecane 70.3% by volume, TBP 29.7% by volume (dodecane 64.5% by volume,
When a solution consisting of TBP (35.5% by weight) was supplied and distilled, the following results were obtained.

(1) Composition change in the solution due to distillation operation, the composition of the distillate is 71.8% by weight of dodecane and 28.2% by weight of TBP, and the composition of the residual liquid is 3.9% by weight of dodecane. %, TBP is 96
．． It is 1% by weight.

(2) Change in the concentration of DBP contained in the solution due to distillation operation.
The DBP contained in the distillate was 32PP'jI, and the DBP in the residual liquid was 900PPM, whereas the distillate contained 71PPM.

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

In addition, since the apparatus is made of glass, the distillation situation can be observed and the state is stable, and no coloration or other changes were observed in the distillate or residual liquid ◇ Operations in this example Calculating the solution supply i (F) from the third equation based on the conditions yields η (t+273), -, 0,098<F<14.8, indicating that the solution supply amount under the operating conditions was appropriate. .

Example 2 Operating conditions Supply liquid ff1 (F): 0.30 kg/h
rImmersion length of the evaporation section in the distillation apparatus L): 0.
157 m Narrowest area for passage of distillate vapor (S): 1.8 Xl0-
3m Distillation temperature <t'): 250 °C Distillation pressure (P): 20 torr Rotor rotation speed: 450 R, P, M cylindrical body (evaporation part) inner diameter: 50 Tsuru Using the same stirred thin film evaporative distillation apparatus (moving rotor type), a solution consisting of 770.3% by volume of dodeca and 29.7% by volume of 'rBP (64.5% by weight of dodecane, 35.5% of TBP) was prepared. The following results were obtained when distillation was performed.

(11 Composition change in solution due to distillation operation, the composition of the distillate is 69.0% by weight of dodecane and 31.0% by weight of TBP, and the composition of the residual liquid is 3.0% by weight of dodecane, TBP is 97
．． It is 0% by weight.

(2) Change in the concentration of DBP contained in the solution due to the distillation operation.
Although it contained PPM, the DBP in the distillate was 30
PPM and DBP in the residual liquid became 90 PPM.

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 'Mk (F): 0.12 kg
/hr Length of the evaporation section in the distillation apparatus (L):
0.157 m Narrowest area for passage of distillate vapor (S): 1.8 xlO-
'm Residue temperature (t): 120 ℃ Distillation pressure (P): 0.5 torr Rotor rotation speed: 450 R, P, M cylindrical body (evaporation part) inner diameter: 50 Recommended - under the above conditions Using the same stirred thin film evaporative distillation apparatus (movable rotor type) as in Example 1, from 16.4% by volume of dodecane and 83.6% by volume of TBP (13.1% by weight of dodecane, 86.9% by weight of TBP). When Hy was performed by supplying a solution, 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 and 84.7% by weight of TBP, and the composition of the residual liquid is 7.3% by weight of dodecane. , TBP is 92
．． It is 7% by weight.

(2) Change in the concentration of DBP contained in the solution due to the distillation operation.
The DBP contained in the distillate was 196 PPM, and the DBP in the residual liquid was 437 PPM, whereas the distillate contained 31 PPM.

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 the distillate or residual liquid.

When the solution supply ff1 (F) is calculated from the third equation based on the operating conditions in this example, it becomes 0.112<F<10.1, which indicates that the solution supply amount under the operating conditions was appropriate.

Example 4 Kikume 4-fold draft (F): 30.6
kg/hr Dimming side length of evaporation section in distillation equipment L)
: 0.25 m Narrowest area for passage of distillate vapor (S) : 2.2 XIO bow d Distillation temperature (t) : 151 ℃ Distillation pressure (
P): 5 torr Rotor rotation speed:
1270 R, P, 11 cylindrical body (evaporation part) inner diameter: 80+u Under the above conditions, using a stirred thin film evaporation distillation apparatus (fixed rotor type) as shown in Figure 2, dodecane 78% by volume,
TBP22% by volume (73.2% by weight of dodecane, TBP2
When a solution consisting of 6.8% by weight) was supplied and distilled, the following results were obtained.

fi+ Composition change in the solution due to distillation operation, the composition of the distillate is 84.3% by weight of dodecane and 15.7% of TBP.
% by weight, and the composition of the residual liquid is 28.4% by weight of dodecane and 7% of TBP.
It is 1.6% by weight.

(2) Change in the concentration of DBP contained in the solution due to the distillation operation.
The distillate contained 5 PPM, but the DBP in the distillate was 2.
At 0PP-, the remaining DBP during the night was 90PPM.

The distillation rate (η) at this time was 0.79, and it was confirmed from the above measurement results that no DBP was produced 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 0.119 < F < 121.5, which indicates that the solution supply amount under the operating conditions was appropriate.

Example 5 In the above-mentioned Example 4, the distillation pressure among the operating conditions was set to 1.
When I changed to torr and distilled, the distillation rate was 0.60.
It declined to .

When the feed liquid amount was increased to 40 kg/hr under the above operating conditions, the distillation rate decreased to 0.50, and the feed liquid amount was increased to 2.
When decreasing to 8 kg/hr, the distillation rate changed to 0.70.

Based on these operating conditions, the feed liquid ffi (F) is calculated using the third equation 3.78xlO'' x P x S η(t +273), and η is 0.6.
When η is 0, F is 32.7. When η is 0.50, F is 39.2. When η is 0.70, F is 28.0. It can be seen that the actual supply amount and the calculated supply amount almost match. .

Example 6 Operating conditions Supply liquid fk (F): 22.5 kg/hr
Soaking length L of evaporation section in distillation apparatus: 1.2
m Narrowest area for passage of distilled vapor (S): 2.6 Xl0-
``rrf Distillation temperature (t): 114 ℃ Distillation pressure CP): 0.8 torr Disk rotation speed: 1200 R, P, M disk external dimensions
: 380 Ryu Using a rotating disk evaporative distillation apparatus as shown in Figure 3 under the above conditions, dodecane 70.3% by volume and TBP 29.
When a solution consisting of 7% by volume (64.7% by weight of dodecane, 35.3% by weight of TBP) was supplied and distilled,
We were able to obtain the following results.

(1) Composition change in the solution due to distillation operation, the composition of the distillate is 77.1% by weight of dodecane and 22.9% by weight of TBP, and the composition of the residual liquid is 6.2% by weight of dodecane. Weight%, TBP is 93
．． It is 8% by weight.

(2) 4 of DBP contained in the solution resulting from the distillation operation
DBP in the temperature-changing feed solution can be reduced to 12 by performing a distillation operation.
Contains 6PPM; what used to be distilled and DBP during the night
was 83 PPM, and DBP in the residual liquid was 262 PPM.

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

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

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

Example 7 Operating conditions Supply liquid Wk (F): 0.06 kg/
Soaking length L of evaporation section in hr distillation apparatus: 0
．． 157 m Narrowest area for passage of distillate vapor (S): 1.8 Xl0-3
B Distillation temperature (t): 120℃ Distillation pressure (
P): 5 torr Rotor rotation speed:
450 R, P, M cylindrical body (scarring part) inner diameter: 5
0 mm Using the same stirring thin film evaporation distillation apparatus (movable rotor type) as in the first example under the above conditions, 70.3% by volume of dodecane, 29.7% by volume of TBP (64.5% by volume of dodecane)
, TBP (35.5% by weight)) was bombarded with gamma rays from 60Co for 10'rad'4&, and then 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 and 7.7% by weight of TBP.
The composition of the residual liquid is 7.8% by weight of dodecane and 92% of TBP.
．． It is 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 2 feed solution I (Number: 1200 Distillate Night H)
Number 2 < 50 H number of residual liquid: 7600 Evaluation of phase separation in the above solution performance is based on the solvent and its equivalent amount of 1.2
A method has been adopted in which the mixture is mixed with N-NaOH and left to stand, and the separation time between the solution phase and the aqueous phase is measured. However, since it is not possible to grasp the emulsion persistence of each phase/＼ only by the time of two-phase separation, in this measurement, the SA rate of each phase is measured using a spectrophotometer. It is an index of the degree of deterioration, and corresponds to the total amount of compounds that form a strong complex with Zr, which is an internal fission product of the decomposition product generated by radiolysis of the solvent.

A solvent with a high ()1 number indicates a decrease in the decontamination coefficient of fission products. ) In this example, T, P, Garrett,
Jr., E.

The H number was measured by the method of N. Jenkins.

In other words, take 2 ml of sample and Hf) laser solution 2 in each solution, let it stand to separate, drain the aqueous phase, and calculate the H number (per solvent 10' I!) from the total γ counts and specific radioactivity of the sample. The number of moles of Hf remaining in the sample was calculated.

From the above-mentioned phase separation and H-number measurement results, it can be estimated that the deterioration-causing substance is concentrated in the residual liquid (H-condensed).

Further, the distillation conditions were stable, and the feed liquid was pale yellow, but as a result of distillation, 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: Tower top 57-106°C Tower eave 98-161”C Distillation pressure: Tower top 0.8-0.9 torr Tower bottom
6. O~15. Otorr distillation rate: 20-50 cc/hr1 flow ratio
20.8~4.5 Under the above conditions, a solution having the same composition as in Example 1 was heated with a heating section 31 at the bottom and a filling layer 33 at the top, as shown in FIG.
Distillation is carried out using a packed column type batch distillation apparatus, which integrally forms a packed column 32 having When I did this, I got the following results:

(1) Composition change in the solution due to distillation operation, the composition of the initial distillate is 99.5% by weight of dodecane and 0.5% by weight of TBP, and the composition of the residual solution is 0.7% by weight of dodecane. , TBP is 99
．． It is 3% by weight.

(2) The DBP contained in the solution was 39 PPM, but was reduced to 43 PPM by distillation, which was about 10% by weight or more.

In addition, although the initially supplied solution was almost transparent, the remaining liquid in the tank was colored 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 can confirm that thermal decomposition has occurred.

Comparative Example 2 A solution having the same composition as in Example 1 was distilled using the same apparatus shown in Figure 1 as in Example 1, except that the distillation pressure was changed to Q, l torr under the operating conditions in Example 10. However, the solution supplied to the cylindrical body 1 foams significantly and is sent out from the suction pipe 4, causing frost to form on the condenser 9 installed between it and the pressure reducing device, and within 30 minutes of starting distillation. Condenser 9 was found to be clogged. Therefore, when the frost in the condenser 9 was melted and its composition was analyzed, it was found that most of it was dodecane. It is thought that the distillation pressure was so low that the dodecane vaporized before reaching the heating part of the distillation apparatus, was sent out through the suction pipe, and was captured by the condenser.

Comparative Example 3 Among the operating conditions in Comparative Example 2 above, the distillation pressure was 3.
Q torr and distillation temperature were changed to 300° C., but significant coloring was observed in the residual liquid, so the distillation operation was discontinued. When the temperature of the apparatus was lowered and 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 described above, the supply liquid amount was set to 0.
Distillation was carried out by changing the distillation pressure to 0.04 kg/hr, the distillation pressure to Q, 5 torr, and the distillation temperature to 100° C., and there was no particular abnormality in the distillation condition. However, the distillation rate was 0.992, and the composition of the distillate was dodecane 6 = 1, 6% by weight,
The TBP was 35.4%, which was almost the same as the composition of the feed solution.

Based on the above operating conditions, the solution supply amount (F
), it becomes 2<F<9.2, which shows 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 tributyl phosphate using a thin film evaporation distillation apparatus under predetermined distillation operating conditions. can.

Also, thin film evaporation type rg! If a plurality of devices 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. Second
The figure is a sectional view taken along the line 2-2 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 line 4'/-Y in FIG. 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. FIG. 7, FIG. 8, and FIG. 9 are schematic views showing an embodiment for implementing the distillation method of the present invention by installing a plurality of thin film evaporation type 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, 4.14,3
6.38... Suction pipe, 5.29.35... Distillate delivery pipe,

Claims (1)

[Scope of Claims] 1. A method for thin film distillation of a liquid containing tributyl phosphate, characterized in that the supply amount of the solvent containing tributyl phosphate satisfies the following conditions, and the distillation is carried out using a thin film evaporative distillation apparatus. (0.1×L)/(1-η)<F<(3.78×10^
6×P×S)/(η×(t+273))P=0.5~2
0 (torr) In the formula, F: Amount of liquid supplied (kg/hr) L: Length of immersed side of the evaporation section in the distillation apparatus (m) η: Distillation rate (amount of distillate/amount of supplied liquid) S: Distillation Narrowest area for vapor passage (m^2) t: Distillation temperature (℃) p: Distillation pressure (torr)