CN112309601B - Diluent and preparation and application thereof - Google Patents

Abstract

The invention relates to a preparation method of a diluent. The method mainly comprises the following steps: with isoolefins andhydrogen as raw material and Ni-M/Al ₂ O ₃ As a catalyst, the reaction pressure is 1.0MPa to 3.0MPa, the reaction temperature is 200 ℃ to 300 ℃, and the space velocity is 5h ^‑1 ‑15h ^‑1 And the hydrogen-oil ratio is 200. And then, rectifying the generated dodecane to separate out middle fraction, thereby obtaining the target diluent. The invention has the advantages of mild operation condition, simple process, catalyst with catalytic activity equivalent to that of noble metal catalyst and low cost.

Description

A diluent and its preparation and application

technical field

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

Background technique

Spent fuel reprocessing technology refers to chemically separating uranium and plutonium from fission products by using 3% to 4% uranium waste. Recovered uranium and plutonium are recycled in MOX fuel for nuclear power plants to produce more energy, making better use of uranium resources and reducing the need to enrich uranium. Spent fuel reprocessing technology is one of the key technologies to ensure the sustainable development of nuclear energy.

Purex (Purex) process is currently widely used in the international spent fuel reprocessing process, the process uses tributyl phosphate (TBP) as the extraction agent, when using TBP to contact with spent fuel nitric acid aqueous solution, it can select Uranium and plutonium can be extracted selectively, but the extraction rate of fission products and their impurities is extremely low, so that uranium and plutonium can be separated from fission products through multi-stage countercurrent extraction. TBP has good chemical stability, high flash point, low volatility, and poor water miscibility. It is easy to regenerate and reuse after treating spent fuel. It is currently the most suitable extraction agent. However, TBP has high density and viscosity, and it is not easy to contact with uranium and plutonium in the water phase. In order to obtain the optimal extraction effect, it needs to be diluted. At present, the commonly used diluents are n-dodecane and high-grade kerosene. However, its price is higher, and there is still room for improvement in performance. Therefore, there is still a need to develop low-cost diluents with equal or higher performance.

Contents of the invention

The present invention aims to provide a method for preparing a low-cost diluent with better performance than n-dodecane and high-grade kerosene.

Based on above-mentioned purpose, the technical scheme that the present invention adopts is:

A) Based on isomeric olefins (by mass percentage, the content of C10-C12 isomeric olefins>75%, C5-C8 fractions are less than 5%, C14-C17 fractions are less than 5%, and the rest are C9 and C13) With hydrogen as raw material, Ni-M/Al ₂ O ₃ as catalyst, the reaction pressure is 0.5MPa-5.0MPa, preferably 1-3MPa, the reaction temperature is 100°C-400°C, preferably 200°C-300°C, and the space velocity For, 5h ^-1 -20h ^-1 , preferably 5h ^-1 -15h ^-1 , the hydrogen-oil ratio is 100:1-800:1, preferably 200:1-500:1, under the conditions, the reaction generates saturated chain hydrocarbons;

B) Rectifying and separating the generated saturated chain hydrocarbons to separate the middle distillate to obtain the target diluent.

The content of the C12 isomerized olefins in the step A) is >50%.

M in the catalyst Ni-M/ _Al2O3 in the step A) refers to one or more combinations of metals such as La, Ce, Zr, Ga _, etc., and the mass fraction of Ni in the catalyst is 5wt%-25wt% , preferably 10wt%-15wt%, the mass fraction of M is 0.5wt%-5wt%, preferably 1wt%-2wt%; _Al2O3 is _a mesoporous structure with a specific surface area of ^150m2 /g- ^250m2 /g 200m ² /g-240m ² /g), the average pore size is 5nm-8nm, Ni and La are dispersed on the Al ₂ O ₃ support at the atomic scale.

During the rectification treatment in the step B), the number of theoretical plates in the rectification tower is 100-200 (preferably 150-200), and the still temperature 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), and the fraction at which the overhead steam temperature is collected is 50°C-75°C (preferably 55°C-70°C), and the reflux ratio is: 10-20 (preferably 10 -15).

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

The concentration of metal ions in spent fuel is 0.4mol/L-0.7mol/L.

The invention aims at the problems existing in the existing diluents, and provides a high-performance, low-cost diluent preparation method. The invention has mild operating conditions and simple process, and the catalyst exhibits catalytic activity equivalent to that of noble metal catalysts and has low cost.

Detailed ways

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

Example 1

Catalyst preparation:

Prepare Ni(NO ₃ ) ₂ and La(NO ₃ ) ₃ precursor solutions (the molar concentration of Ni is 2.1mol/L, and the molar concentration of La is 0.18mol/L by 10% and 2% of the final mass percentage of catalyst Ni and La). L), add the required mesoporous alumina (specific surface area is 210m ² /g, average pore diameter is 7nm), after stirring evenly, aged at 60°C for 24h, the obtained solid was dried overnight in an oven at 120°C, and then, 450 The Ni-La/Al ₂ O ₃ catalyst was obtained by calcining at ℃ for 4 hours (the electron microscopy results showed that Ni and La were dispersed on Al ₂ O ₃ at the single-atom scale).

Raw material hydrogenation reaction:

With tetrapropylene (by mass percentage, the content of C10-C12 isomeric olefins is 76.8%, wherein the content of C12 is 43% of tetrapropylene quality, C5-C8 fraction is 2.1%, and C14-C17 fraction is 1.5%, the rest are C9 and C13) as raw materials, hydrogenation reaction is carried out under the reaction conditions of reaction temperature: 250°C, reaction pressure: 2MPa, volume space velocity: 10h ^-1 , hydrogen-oil ratio: 300:1. The tetrapropylene hydrogenation product obtained, the conversion rate of tetrapropylene measured by fluorescence indicator adsorption method is greater than 99.5%.

Hydrogenation product distillation:

The number of theoretical plates in the rectification tower is 200, the temperature in the rectification tower is 100°C-125°C, the pressure in the rectification tower is 0.5kPa, and the fraction with the steam temperature at the top of the tower is collected at 55°C-68°C, and the reflux ratio is: Under the rectification condition of 15, the tetrapolypropylene hydrogenation product is rectified, and the cut product is the target diluent (in terms of mass percentage, the content of C10-C12 isoparaffins is 95.6%, and the content of C12 It is 54% of the diluent quality, the fraction below C8 is 0.4%, the fraction above C14 is 0.7%, and the rest are C9 and C13 fractions).

Extraction test of diluent:

1. Phase separation time: prepare a 30% TBP-diluent solution according to the volume ratio, vibrate with 1mol/L HNO ₃ or 1mol/L NaOH solution in equal volume respectively, after mixing fully, stand still and record the phase separation time, two The phase separation time of each system is the same, both are 0.9min.

The volume ratio was prepared to be 30% TBP-n-dodecane solution and 1mol/L _HNO3 solution, respectively oscillating in equal volumes. After mixing fully, stand still and record the phase separation time. The phase separation time of the two systems is the same, both are 1.5 min; the phase separation time of the target diluent is 0.9min better than n-dodecane's 1.5min.

2. Extraction performance test: Prepare 30% TBP-diluent solution by volume ratio, and fully mix with 0.55mol/L Pu(IV) metal ion solution with a molar concentration of 3.5mol/L HNO ₃ dissolved in a volume ratio of 1:1 , to determine the saturated extraction capacity of metals in a 30% TBP-diluent solution. After testing, the extraction saturation capacity of 30% TBP-target diluent is 90g/L, and the extraction saturation capacity of 30% TBP-n-dodecane is 58g/L.

Example 2

Except that the reaction temperature was changed to 200°C in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1 was carried out in the extraction experiment test according to the conditions of Example 1 (using 1mol/L of _HNO3 Determination of phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 87g/L.

Example 3

Except that the reaction temperature was changed to 300°C in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1 was carried out in the extraction experiment test according to the conditions of Example 1 (using 1mol/L of _HNO3 Determination of phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 104g/L.

Example 4

Except that the reaction pressure is changed into 1MPa in the raw material hydrogenation reaction step, with the target diluent obtained in the same way as described in Example 1, and carry out the extraction experiment test by the conditions of Example 1 ( _the HNO of 1mol/L is adopted Measure Phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 70g/L.

Example 5

Except that the reaction pressure is changed into 3MPa in the raw material hydrogenation reaction step, with the target diluent that obtains with the same method as described in Example 1, and carry out extraction experimental test by the condition of Example 1 (adopting _the HNO of 1mol/L Measure Phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 104g/L.

Example 6

Except that the space velocity is changed to ^5h in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1 is carried out in the extraction experiment test according to the conditions of Example 1 (using 1mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 108g/L.

Example 7

Except that the space velocity is changed to ^7.5h in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1, and the extraction experiment test is carried out according to the conditions of Example 1 (using 1mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 104g/L.

Example 8

Except that the space velocity is changed to ^12h in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1 is carried out in the extraction experiment test according to the conditions of Example 1 (using 1mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 93g/L.

Example 9

Except that the space velocity was changed to ^15h in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1 was carried out in the extraction experiment test according to the conditions of Example 1 (using 1mol/L of HNO ₃ Determination of phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 78g/L.

Example 10

Except that the ratio of hydrogen to oil is changed to 200:1 in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1, and the extraction experiment test is carried out according to the conditions of Example 1 (using 1mol/L _HNO3 measures the phase separation time), in the extraction test process, the phase separation time is 0.9min better than dodecane, and the extraction saturation capacity of 30% TBP-target diluent is 90g/L.

Example 11

Except that the ratio of hydrogen to oil is changed to 400:1 in the raw material hydrogenation reaction step, the target diluent obtained by the same method as described in Example 1, and the extraction experiment test is carried out according to the conditions of Example 1 (using 1mol/L HNO ₃ measure the phase separation time), in the extraction test process, in the extraction test process, the phase separation time is 0.9min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 90g/L.

Example 12

Except that the ratio of hydrogen to oil is changed to 500:1 in the raw material hydrogenation reaction step, the target diluent obtained in the same way as described in Example 1, and the extraction experiment test is carried out according to the conditions of Example 1 (using 1mol/L HNO ₃ measure the phase separation time), in the extraction test process, in the extraction test process, the phase separation time is 0.9min better than dodecane, and the 30% TBP-target diluent extraction saturation capacity is 90g/L.

Claims (7)

1. The application of a diluent, which is characterized in that: it is used as spent fuel extractant, when it contacts with spent fuel molar concentration 3.0mol/L-4.0mol/L nitric acid aqueous solution, it can selectively extract and separate uranium and plutonium ; The main steps are as follows: A) Using isomeric olefins with carbon numbers C10-C12 and hydrogen as raw materials, using Ni-M/Al ₂ O ₃ as catalyst, at a reaction pressure of 0.5 MPa-5.0 MPa, a reaction temperature of 100°C-400°C, and air The reaction rate is 5 h ^-1 -20 h ^-1 , the ratio of hydrogen to oil is 100:1-800:1, under the conditions, the reaction generates saturated chain hydrocarbons; M refers to one or two of La, Ce, Zr, Ga a combination of the above; B) The generated saturated chain hydrocarbons are rectified to separate the middle distillate to obtain the target diluent; the isomeric olefins containing carbon number C10-C12 are composed of C10-C12 isomeric olefins in terms of mass percentage The content of >75%, C5-C8 fraction is less than 5%, C14-C17 fraction is less than 5%, and the rest is C9 and C13; M in _the catalyst Ni-M/ _Al2O3 refers to one or more combinations of La, Ce, Zr, Ga, the mass fraction of Ni in the catalyst is 5 wt%-25 wt%, and the mass fraction of M The fraction is 0.5 wt%-5 wt%; Al ₂ O ₃ is a mesoporous structure, the specific surface area is 150 m ² /g-250 m ² /g, the average pore diameter is 5 nm-8 nm, Ni and La are dispersed at the atomic scale on _{an Al2O3} support. 2. according to the described application of claim 1, it is characterized in that: its mass content > 40% of the isomeric olefins containing carbon number C10-C12 of the C12 isomeric olefins described in the isomeric olefins containing carbon number C10-C12 raw material quality. 3. according to the described application of claim 1, it is characterized in that: The main steps are as follows: In step A), isomeric olefins containing carbon numbers C10-C12 and hydrogen are used as raw materials, Ni-M/Al ₂ O ₃ is used as a catalyst, the reaction pressure is 1-3 MPa, and the reaction temperature is 200°C-300°C, The space velocity is 5 h ^-1 -15 h ^-1 , and the hydrogen-oil ratio is 200:1-500:1. Under the conditions, the reaction generates saturated chain hydrocarbons; M refers to one or both of La, Ce, Zr, and Ga. combination of the above. 4. The application according to claim 1, characterized in that: M in the catalyst Ni-M/ _Al2O3 refers to one or more combinations _of La, Ce, Zr, Ga, and Ni in the catalyst The mass fraction of M is 10 wt%-15 wt%, the mass fraction of M is 1wt%-2 wt%; Al ₂ O ₃ is a mesoporous structure, the specific surface area is 200 m ² /g-240 m ² /g, and the average pore diameter 5 nm-8 nm, Ni and La are dispersed on the Al ₂ O ₃ support at the atomic scale. 5. According to the application according to claim 1, it is characterized in that: during rectification treatment, the number of theoretical plates in the rectification tower is 100-200, the temperature of the still in the rectification tower is: 80°C~140°C, and the pressure of the still is: 0.1 kPa -1 kPa, collect the distillate whose overhead steam temperature is 50 ℃ -75 ℃, and the reflux ratio is: 10-20. 6. The application according to claim 5, characterized in that: during rectification treatment, the number of theoretical plates in the rectification tower is 150-200, the temperature of the still in the rectification tower is: 90 ℃ ~ 120 ℃, and the pressure of the still is: 0.2 kPa -0.6 kPa, collect the distillate whose overhead steam temperature is 55 ℃ -70 ℃, and the reflux ratio is 10-15. 7. The application according to claim 1, characterized in that the concentration of metal ions in the spent fuel is 0.4 mol/L-0.7 mol/L.