CN112940781B - A kind of diluent and its preparation and application - Google Patents

Abstract

The present invention relates to a preparation method of a diluent. The main steps are: using Fischer-Tropsch distillate oil and hydrogen as raw materials, using Pt/SAPO‑11@β as a catalyst, the reaction pressure is 1.0MPa‑4.0MPa, the reaction temperature is 250℃‑400℃, and the space velocity is 0.5h ^‑1 -3h ^-1 , under the condition that the hydrogen-oil ratio is 600:1-1500:1, the reaction obtains isoparaffin. Then, the produced isoparaffin is rectified to separate out the middle distillate, that is, the target diluent is obtained. The prepared diluent is used as an extraction agent for spent fuel, and can selectively extract and separate uranium and plutonium.

Description

A kind of diluent and its preparation and application

technical field

The present invention relates to a preparation method of a diluent, and more particularly to a preparation method of the diluent required in the Purex process.

Background technique

Spent fuel reprocessing technology is the most critical link in the latter part of the nuclear fuel cycle and one of the key technologies to ensure the sustainable development of nuclear energy. Spent fuel reprocessing is to chemically separate uranium and plutonium from fission products from 3% to 4% uranium waste that has been used. Recovered uranium and plutonium are recycled in mixed oxide fuel for nuclear power plants to produce more energy, thereby making uranium resources more fully utilized and reducing the need to enrich uranium.

The Purex process is currently the most successful and widely used process in the reprocessing of spent fuel in the world. This process contacts tributyl phosphate (TBP) with spent fuel nitric acid aqueous solution, and TBP selectively extracts uranium and plutonium, while the extraction rate of fission products and their impurities is extremely low. The uranium and plutonium are then separated from the fission products by multistage countercurrent extraction. TBP has the advantages of good chemical stability, high flash point, low volatility, poor miscibility with water, and easy regeneration. It is currently the most suitable extractant. However, TBP has a high density and viscosity, and is not easy to contact with uranium and plutonium in the aqueous phase, so it needs to be diluted in order to obtain the best extraction effect. At present, the commonly used diluents are n-dodecane and high-grade kerosene. However, there is still room for improvement in the extraction performance of the existing TBP+n-dodecane/high-grade kerosene. Therefore, in order to improve the extraction efficiency of uranium and plutonium from spent fuel, higher performance diluents still need to be developed.

SUMMARY OF THE INVENTION

The invention aims to provide a preparation method of a novel diluent with better performance than n-dodecane and high-grade kerosene.

Based on the above purpose, the technical scheme adopted in the present invention is:

A) Using Fischer-Tropsch distillate oil as raw material, using Pt/SAPO-11@β as catalyst, the reaction pressure is 1.0MPa-7.0MPa, preferably 1.0-4.0MPa, and the reaction temperature is 100℃-500℃, preferably 250℃- 400°C, the space velocity is 0.5h ^-1 -7h ^-1 , preferably 0.5h ^-1 -3h ^-1 , the hydrogen oil ratio is 200:1-2000:1, preferably 600:1-1500:1, under the conditions, the reaction is obtained isoparaffins;

B) rectifying the obtained isoparaffin to separate out the middle distillate, that is, to obtain the target diluent.

In the step A), the Fischer-Tropsch distillate oil is composed of, in terms of mass percentage, the content of C11-C12 alkanes> 75%, the C5-C9 fraction is lower than 5%, the C14-C17 fraction is lower than 5%, and the rest for C10 and C13. The mass content of the C12 alkanes in the C11-C12 alkanes containing carbon numbers is greater than 40% of the mass of the alkane raw materials containing carbon numbers C10-C12.

4. The method according to claim 1, wherein the mass fraction of Pt in the catalyst Pt/SAPO-11@β is 0.1wt%-3wt%, preferably 0.5wt%-2wt%, the Si of the β molecular sieve is 0.1wt%-3wt% The /Al ratio is 20-40, and the mass ratio of SAPO-11 and beta molecular sieve is 50:1-10:1, preferably 40:1-20:1.

During the rectification treatment in the step B), the theoretical plate number of the rectification tower is 100-200 (preferably 150-200), and the temperature of the still in the rectification tower is: 80°C to 140°C (preferably 90°C to 120°C) , the pressure of the kettle is: 0.1kPa-1kPa (preferably 0.2kPa-0.6kPa), the collection of the top steam temperature is 50 ℃-75 ℃ (preferably 55 ℃-70 ℃) fraction, the reflux ratio is: 10-20 (preferably 10 -15).

The new diluent prepared by the above method is used as an extractant for spent fuel, and can selectively extract and separate uranium and plutonium when contacted with an aqueous nitric acid solution with a molar concentration of 3.0mol/L-4.0mol/L of spent fuel.

Aiming at the problem of low extraction performance of the existing diluent, the invention provides a high-performance preparation method of the diluent.

Detailed ways

In order to further illustrate the present invention, the following examples are given without limiting the scope of the invention as defined by the appended claims.

Example 1

Preparation of catalyst:

Prepare an aqueous solution of Pt precursor Pt(NH ₃ ) ₄ Cl ₂ (the mass concentration of Pt is 1 mg/ml) with a mass percentage of 0.5%, grind and mix SAPO-11 and β molecular sieve with a mass ratio of 20:1, and press into tablets. Shape, crush and sieve out 20-40 mesh particles, put 20-40 mesh SAPO-11@β molecular sieve in Pt(NH ₃ ) ₄ Cl ₂ aqueous solution, let stand for 24h, separate out the solid and dry it in an oven at 110°C overnight , and then calcined at 550 °C for 6 h to obtain the Pt/SAPO-11@β catalyst.

Raw material isomerization reaction:

Before the reaction, the Pt/SAPO-11@β catalyst was reduced at 400 °C for ₂ h under 20 ml/min H atmosphere, using Fischer-Tropsch distillate as raw material, at reaction temperature: 350 °C, reaction pressure: 2MPa, space velocity: 1h ^{- 1.} Hydrogen-oil ratio: 1200:1 under the reaction conditions to carry out hydroisomerization reaction to obtain isoparaffins.

Isomerization product distillation:

The number of theoretical plates in the rectifying tower is 200, the kettle temperature in the rectifying tower is: 100 ℃ ~ 125 ℃, the kettle pressure is: 0.5kPa, and the fraction with the vapor temperature at the top of the column is collected at 55 ℃-68 ℃, and the reflux ratio is: Under the rectification condition of 10, the isomerization product alkane is rectified, and the cut product is the target diluent (by mass percentage, the content of C10-C12 isoparaffin is 95.6%, and wherein the content of C12 is 54% of the mass of the diluent, the fraction below C8 is 0.4%, the fraction above C14 is 0.7%, and the rest are C9 and C13 fractions).

Extraction experimental test of diluent:

1. Phase separation time: prepare 30% TBP-diluent solution according to volume ratio, shake with equal volume of 1mol/L _HNO3 or 1mol/L NaOH solution respectively. The phase separation time of each system is the same, which is 1 min.

The volume ratio was prepared into a 30% TBP-n-dodecane solution and ₁ mol/L HNO solution was shaken in equal volume respectively. After fully mixing, it was left to stand to record the phase separation time. The phase separation time of the two systems was the same, both were 1.5 min; the phase separation time of the target diluent is 1 min better than 1.5 min of n-dodecane.

2. Extraction performance test: prepare a 30% TBP-diluent solution by volume, and fully mix it with 3.5mol/L HNO ₃ dissolved molar concentration 0.55mol/LPu(IV) metal ion solution in a volume ratio of 1:1, The saturated extraction capacity of metals in a 30% TBP-diluent solution was determined. After the experiment, the extraction saturation capacity of 30% TBP-target diluent is 80g/L, and the extraction saturation capacity of 30%TBP-n-dodecane is 58g/L.

Example 2

Except that in the raw material hydrogenation reaction step, the reaction temperature was changed to 280°C, the target diluent obtained in the same way as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 60g/L.

Example 3

Except that in the raw material hydrogenation reaction step, the reaction temperature was changed to 300 ° C, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of HNO _{3 )} . Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 65g/L.

Example 4

Except that in the raw material hydrogenation reaction step, the reaction temperature was changed to 325°C, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 72g/L.

Example 5

Except that in the raw material hydrogenation reaction step, the reaction temperature was changed to 375 ° C, the target diluent obtained in the same way as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of HNO _{3 )} . Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 79g/L.

Example 6

Except that the reaction temperature was changed to 400°C in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of HNO _{3 )} . Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 76g/L.

Example 7

Except that in the raw material hydrogenation reaction step, the reaction pressure was changed to 1MPa, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example ₁ (using 1mol/L of HNO . Phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 70g/L.

Example 8

Except that in the raw material hydrogenation reaction step, the reaction pressure was changed to 3MPa, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using ₁ mol/L of HNO . Phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 78g/L.

Example 9

Except that in the raw material hydrogenation reaction step, the reaction pressure was changed to 4 MPa, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using ₁ mol/L of HNO . Phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 82g/L.

Example 10

Except in the raw material hydrogenation reaction step, the space velocity is changed to 0.5h ^-1 , the target diluent obtained by the same method as described in Example 1 is used, and the extraction experiment test is carried out according to the conditions of Example 1 (using 1 mol/L HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 85g/L.

Example 11

Except that in the raw material hydrogenation reaction step, the space velocity was changed to 1.5h ⁻¹ , the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 78g/L.

Example 12

Except that in the raw material hydrogenation reaction step, the space velocity was changed to 2h ^-1 , the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 73g/L.

Example 13

Except that the space velocity was changed to 2.5h in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example ¹ was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 71g/L.

Example 14

Except that in the raw material hydrogenation reaction step, the space velocity was changed to 3h ⁻¹ , the target diluent obtained in the same manner as described in Example 1 was used, and the extraction experiment was tested according to the conditions of Example 1 (using 1 mol/L of HNO ₎ Determination of phase separation time), in the extraction test process, the phase separation time is 1min better than dodecane, 30% TBP-target diluent extraction saturation capacity is 65g/L.

Example 15

Except that in the hydrogenation reaction step of the raw material, the ratio of hydrogen to oil was changed to 600:1, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment was tested according to the conditions of Example 1 (using 1 mol/L of Determination of phase separation time by _HNO3 ), in the extraction test process, the phase separation time is 1min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 72g/L.

Example 16

Except that in the hydrogenation reaction step of the raw material, the ratio of hydrogen to oil was changed to 800:1, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment test was carried out according to the conditions of Example 1 (using 1 mol/L of Determination of phase separation time by _HNO3 ), in the extraction test process, the phase separation time is 1min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 78g/L.

Example 17

Except that in the hydrogenation reaction step of the raw material, the ratio of hydrogen to oil is changed to 1000:1, the target diluent obtained by the same method as described in Example 1 is used, and the extraction experiment test is carried out according to the conditions of Example 1 (using 1 mol/L of Determination of phase separation time by _HNO3 ), in the extraction test process, the phase separation time is 1min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 82g/L.

Example 18

Except that in the hydrogenation reaction step of the raw material, the ratio of hydrogen to oil was changed to 1500:1, the target diluent obtained by the same method as described in Example 1 was used, and the extraction experiment was tested according to the conditions of Example 1 (using 1 mol/L of Determination of phase separation time by _HNO3 ), in the extraction test process, the phase separation time is 1min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 80g/L.

Claims (6)

1. the application of a diluent is characterized in that: be used for spent fuel extraction agent, when contacting with the molar concentration 3.0 mol/L-4.0mol/L aqueous nitric acid solution of spent fuel, can selectively extract and separate out uranium and plutonium ; The preparation method of the diluent is as follows: A) Using Fischer-Tropsch distillate oil and hydrogen as raw materials, using Pt/SAPO-11@β as catalyst, the reaction pressure is 1.0MPa～7.0MPa, the reaction temperature is 100℃～500℃, and the space velocity is 0.5 h ^-1 ～ 7 h ^-1 , the hydrogen-oil ratio is 200:1～2000:1, and isoparaffins are obtained by the reaction; B) rectifying the obtained isoparaffin fraction to obtain the target diluent; during the rectification treatment, the theoretical plate number of the rectifying tower is 100-200, and the still temperature in the rectifying tower is: 80 ℃ ~ 140 ℃, the still The pressure is: 0.1kPa~1kPa, the distillate with the vapor temperature of 50℃~75℃ collected at the top of the tower is the target diluent, and the reflux ratio is: 10~20; Described Fischer-Tropsch distillate oil is composed of, by mass percentage, content of C11-C12 alkane fraction>75%, C5-C9 alkane fraction less than 5%, C14-C17 alkane fraction less than 5%, and the rest are C10 and/or C13 alkane fractions. 2. according to the described application of claim 1, it is characterized in that: in described C11-C12 alkane fraction, the mass content of C12 alkane＞40%. 3. The application according to claim 1 is characterized in that: the mass fraction of Pt in the catalyst Pt/SAPO-11@β is 0.1wt%-3wt%, and the Si/Al ratio of the β molecular sieve is 20-40, The mass ratio of SAPO-11 and beta molecular sieve is 50:1-10:1. 4. according to the described application of claim 1, it is characterized in that: the concentration of metal ion uranium and plutonium in spent fuel is 0.4mol/L～0.7mol/L. 5. The application according to claim 1, characterized in that: in step A), the reaction pressure is 1.0-4.0 MPa, the reaction temperature is 250°C-400°C, the space velocity is 0.5 h ^-1 -3 h ^-1 , the hydrogen The oil ratio is 600:1-1500:1; The mass fraction of Pt in the catalyst Pt/SAPO-11@β is 0.5wt%-2wt%, and the mass ratio of SAPO-11 and β molecular sieve is 40:1-20:1. 6. according to the application described in claim 1, it is characterized in that: during rectifying treatment, the theoretical plate number of rectifying tower is 150-200, and still temperature in rectifying tower is 90 ℃～120 ℃, and still pressure is: 0.2 kPa~0.6 kPa, the fraction with the vapor temperature of 55℃~70℃ collected at the top of the tower is the target diluent, and the reflux ratio is: 10~15.