JPH0631845B2 - Thin film distillation method - Google Patents

Description

The present invention relates to a thin film for distilling a diluent solution such as dodecane containing tributyl phosphate or a solution containing a material to be extracted using a thin film evaporation type distillation apparatus. The present invention relates to improvement of distillation method.

More specifically, when diluting a solution of a diluent such as dodecane containing tributyl phosphate (hereinafter abbreviated as “TBP”) or a solution containing a material to be extracted using a thin film evaporation type distillation apparatus, the solution is By adding and supplying a substance having a boiling point higher than that of the residual liquid composition remaining in the apparatus due to the distillation operation and being thermally and chemically stable, the distillation rate can be increased to 7%.
It is intended to provide a thin film distillation method capable of maintaining 0% by weight or more.

[Conventional technology]

Generally, when distilling a solution containing TBP, which is prone to thermal decomposition, thin film evaporation that satisfies conditions such as good evaporation efficiency, short solution retention time, simple evaporation structure and no abnormal retention A distillation apparatus is used.

However, diluents having a high boiling point, such as dodecane, kerosene, and C _{10 to} C ₁₄ hydrocarbons, which are mixed with TBP, or Zr, Rh, Nb, R contained in the solution of TBP and the diluent are used.
In the case of concentrating inorganic residues such as u, U, Pu, etc.,
It is necessary to set a high distillation rate. Therefore, the amount of liquid supplied to the evaporation unit is inevitably reduced and a dry spot (film breakage) occurs, and a uniform liquid film cannot be formed, and that portion is heated above the boiling point of the solution to thermally decompose the solution, Focusing occurs. Further, when the supply amount of the solution is increased so that the dry spot does not occur, the evaporation amount increases and there is a problem that the pressure loss in the narrowest part of the vapor passage in the distillation device becomes too large and the vapor lock phenomenon occurs. No distillation method suitable for practical use has been found yet.

[Problems to be solved by the invention]

An object of the present invention is to use a thin film evaporation type distillation apparatus to dilute a solution of a diluent such as dodecane containing tributyl phosphate, or a solution containing a material to be extracted. Moreover, it is to provide a thin film distillation method capable of performing a stable distillation operation with a high distillation rate.

[Means for solving problems]

That is, the present invention, when diluting a diluent solution such as dodecane containing tributyl phosphate or a solution further containing a material to be extracted using a thin film evaporation type distillation apparatus, the solution is placed in the apparatus by a distillation operation. It is intended to provide a thin film distillation method in which a substance having a boiling point higher than that of the remaining residual liquid composition and which is thermally and chemically stable is added and supplied to the distillation apparatus.

Here, the diluent is dodecane, hydrocarbons such as kerosene and C ₁₀ -C _14.

The material to be extracted particularly considered in the present invention is to be contained in the solvent of TBP and the diluent in the reprocessing step of the spent nuclear fuel, nitric acid, radiation, decomposition products of TBP and diluent due to heat, etc. , Zr, Rh, Nb, Ru, V, Pu and the like, and a mixture of water and the like.

As a thin-film evaporation type distillation apparatus, it has been put to practical use as a production apparatus, and from the actual usage, it has been published in the Chemical Industry Handbook (Showa 5
Issued by Maruzen Co., Ltd. on December 25, 5th) 406, Fig. 4.11
It is preferred to use a stirred thin film evaporation distillation apparatus as described in (J).

The high-boiling substance to be added has a boiling point higher than that of the solution of the residual liquid tributyl phosphate and the diluent and is thermally and chemically stable, for example, squalane (C
₃₀ H ₆₂ ), dioctyl phthalate, etc. are used.

The addition amount (Q) of the high-boiling substance is preferably more than 0.04 / m · hr (amount of liquid per unit time, per unit immersion edge).
The liquid level supplied to the evaporation surface of the distillation device for high boiling point substances is 0.04 /
If it is less than m · hr, dry spots are likely to occur on the evaporation surface.

From the above, the feed liquid amount (before addition of the high boiling point substance) is F
(Kg / hr), distillate rate (distillate amount / supply liquid amount), η, and immersion side length which is the inner circumference of the evaporation part of the thin film evaporation type distillation apparatus is L
(M), supply liquid density (before adding high boiling point substance) ρ ¹ (kg /
When the addition amount of the high-boiling substance is Q (kg / hr) and the density of the high-boiling substance (before addition of the high-boiling substance) is ρ ² (kg /), it is desirable that the following formula be satisfied.

Depending on the high-boiling substance, there are cases where the object can be achieved even when the value is less than or equal to the value calculated by the above formula.

If the amount of the high-boiling substance added exceeds 50% by weight of the amount of the feed liquid, most of the evaporation performance of the distillation apparatus is spent only for passing the high-boiling substance, which is inefficient. Therefore, the upper limit of the amount of the high-boiling substance added is 50% by weight of the feed liquid amount (F).
Is preferred.

Therefore, the addition amount (Q) of the high boiling point substance is: Q ≦ F × 0.50 (2) From the above formulas (1) and (2), the formula for setting the addition amount of the high boiling point substance is It looks like this:

[Examples] Example I Operating conditions Liquid supply amount (F): 0.055 / hr (squalane in liquid amount: 0.0047 / hr) Dipping edge length (L) of evaporation section in distillation apparatus: 0. 157m Distillation temperature: 120 ° C Distillation pressure: 0.5 torr Rotor speed: 450R. P. M Tubular body (evaporating part) inner diameter: 50 mm Under the above conditions, Handbook of Chemical Industry, page 406, Fig. 4.11 (J)
56.6 wt% dodecane, 34.8 wt% TBP, using a stirred thin film evaporation distillation apparatus as described in.
Squalane (▲ d ²⁰ ₄ ▼ 0.8098, boiling point: 248 ℃
/ 5 torr, 177 ° C./0.5 torr) 8.6 wt% solution was supplied and distillation was carried out, and the following results could be obtained.

(1) Change in composition in solution by distillation operation The composition of the distillate was 61.7 wt% dodecane and 3 TBP.
The content of dodecane was 9.1% by weight, TBP was 10.8% by weight, and squalane was 80.1% by weight.

(Analysis by gas chromatograph) The distillation rate at this time was 90.3%, and the distillation state was stable.

From the above measurement results, it can be seen that squalane added to the solution is almost recovered as the residual liquid.

At this time, the recovery rate of dodecane (dodecane in the distillate / dodecane in the feed solution × 100) was 98%,
Recovery rate (TBP in the distillate / TBP in the feed solution × 100) was 99%.

The above-mentioned residual liquid composition has a boiling point of 80 ° C. at 0.5 torr and a boiling point of 110 ° C. at 5 torr.

When the addition amount (Q) of the high boiling point substance (squalane) is calculated from the equation (3) by using the operating conditions in the example and the values of ρ ¹ and ρ ² at room temperature, F × 0.5 = 0.055 x 0.5 = 0.0275 (kg / hr) × 0.81 = 0.00027 (kg / hr) ∴0.00027 <Q ≦ 0.0275, which shows that the amount of the high boiling point substance added under the operating conditions was appropriate.

Example II Amount of liquid supplied (F) out of the operating conditions in Example I described above
0.047 kg / hr (dioctyl phthalate in liquid volume:
0.00056 / hr) and using the same stirred thin film evaporation type distillation apparatus as in the example, 61.4% by weight of dodecane, 37.4% by weight of TBP, and dioctyl phthalate (d).
0.9861, Boiling point: 231 ° C / 5 torr, 100 ° C /
When 0.5 torr) and 1.2% by weight of a solution were supplied and distillation was performed, the following results could be obtained.

(1) Change in composition in solution due to distillation operation The composition of the distillate was 61.1 wt% dodecane and 3 TBP.
8.8% by weight, dioctyl phthalate was 0.1% by weight, and the composition of the residual liquid was 18.5% by weight of dodecane and 6% of TBP.
1.7% by weight, dioctyl phthalate 15.7% by weight.

(Analysis by gas chromatography) The distillation rate at this time was 94.9%, and the distillation state was stable.

From the above measurement results, it can be seen that dioctyl phthalate added to the solution is almost recovered as the residual liquid.

At this time, the recovery rate of dodecane was 94% and the recovery rate of TBP was 98%.

The above-mentioned residual liquid composition has a boiling point of 60 ° C. at 0.5 torr and a boiling point of 95 ° C. at 5 torr.

When the addition amount (Q) of the high boiling point substance (dioctyl phthalate) is calculated from the equation (3) by using the operating conditions in the example and the values of ρ ¹ and ρ ² at room temperature, F × 0.5 = 0.047 × 0.5 = 0.0235 (kg / hr) × 0.99 = 0.0034 (kg / hr) ∴0.0034 <Q ≦ 0.0235, which may result in a high distillation rate even if the amount of the high boiling point substance added under the operating conditions is smaller than the calculated value. I understand.

Comparative Example I 61.9 wt% dodecane, TBP 38.1, under the same operating conditions as in Example I above, but using the same distillation apparatus as in this example, but without the addition of high boiling substances. The following results were obtained by supplying and distilling the solution of the weight%.

(1) Change in composition in solution by distillation operation The composition of the distillate was 57.2 wt% dodecane and 4 TBP.
It is 2.8% by weight, and the composition of the residual liquid is 20.3 for dodecane.
% By weight, and TBP is 79.7% by weight.

The distillation rate at this time was 95.1%, and the distillation state was not particularly abnormal.

However, the recovery rate of dodecane at this time was 88%,
The recovery rate of TBP is apparently 100% or more, and the material balance does not match. This means that there is a difference in the sampling time between the distillate and the residual liquid, or the boiling phenomenon due to the dry spots on the evaporation surface, or the boiling phenomenon caused by TBP.
It is presumed that this was due to the fact that was mixed in the distillate. This is supported by the fact that the dodecane distillate rate is decreasing.

〔The invention's effect〕

A diluent solution such as dodecane containing tributyl phosphate or the above solution containing the material to be extracted has a boiling point higher than the boiling point of the residual liquid composition remaining in the apparatus by the distillation operation, and is a thermally and chemically stable substance. Is added and supplied, and distilled to stably collect TBP, which is easily decomposed by heat at a high distillation rate of 70% or more, and a diluent such as dodecane, which is a high-boiling substance, without producing a dry spot. be able to.

Claims (1)

[Claims] 1. When diluting a diluent solution such as dodecane containing tributyl phosphate or the solution further containing a material to be extracted by using a thin film evaporation type distillation apparatus, the solution remains in the apparatus by a distillation operation. A thin-film distillation method, characterized in that a substance having a boiling point higher than that of the residual liquid composition and being thermally and chemically stable is added and supplied to the distillation apparatus.