CN110578057B - Preparation method of diluent for spent fuel reprocessing - Google Patents

Abstract

The invention provides a preparation method of a diluent for post-processing spent fuel, belonging to the technical field of nuclear fuel cycle. Compound components are added to triisobutene, mixed and stirred to obtain a diluent of branched chain alkane mixture; wherein, the catalyst is a supported metal catalyst; and the compound components are polyalpha-olefin or F-T synthetic oil. The preparation method of the invention has the advantages of simple operation, short process, low cost, low technical difficulty and the like; wherein, the composition and performance of the hydrogenation product are regulated by introducing the second component, which provides a new idea for application scenarios such as high-level waste liquid treatment .

Description

Preparation method of diluent for spent fuel reprocessing

technical field

The invention belongs to the technical field of nuclear fuel cycle, and in particular relates to a preparation method of a diluent for post-processing spent fuel.

Background technique

The Purex process (Purex process) is currently the most widely used process in spent fuel reprocessing. The process uses solvent extraction to extract uranium and plutonium from spent fuel dissolved solution. Among them, the most commonly used extraction system is a mixture of tributyl phosphate (TBP) and a diluent, wherein the diluent can reduce the density and viscosity of the solvent phase, improve the hydrodynamic properties of the system, adjust the extraction capacity and selectivity of TBP, and To prevent nuclear criticality risks, etc. Therefore, the choice of diluent has an important influence on the extraction performance of the Purex process. At present, the diluents used in the spent fuel reprocessing process mainly include n-paraffin mixture and isoparaffin mixture; among them, the n-paraffin mixture includes n-dodecane, kerosene, etc., and the isoparaffin mixture includes hydrogenated triisobutene, etc. .

In practical applications, it is found that the composition of the diluent has an important influence on the performance of the extraction solvent system. Among them, the isoparaffins with branched structures have better compatibility with TBP complexes, and the formed mixed solvent has better compatibility with uranium and plutonium. The extraction capacity is larger and the process adaptability is stronger, and its performance is better than that of kerosene and other n-paraffins. However, isoparaffin mixtures have the disadvantages of complex components, difficult synthesis and separation, technical secrecy, and difficulty in purchasing from the market. At present, isoparaffin mixtures are mainly prepared through propylene oligomerization, fraction cutting and hydrogenation. This preparation method has disadvantages such as poor catalyst selectivity, low yield, long process flow, high process operation cost, and high technical difficulty. Based on this, the present invention develops a method for preparing an isoparaffin mixture diluent. Using triisobutene as a raw material, through hydrogenation and compounding reaction, a branched chain paraffin mixture diluent is prepared, and it is applied to the spent fuel after Processing.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a method for preparing a diluent for spent fuel post-processing, using triisobutene as a raw material, and preparing a branched paraffin mixture diluent through hydrogenation reaction and compounding. The preparation method has the advantages of simple operation, low investment, low technical difficulty and high hydrogenation selectivity.

According to an embodiment of the present invention, a method for preparing a diluent for spent fuel reprocessing is provided, comprising the following steps: under the action of a catalyst, triisobutene is selectively hydrogenated to generate hydrogenated triisobutene; Component, mixed reaction to prepare diluent; wherein, the catalyst is a supported metal catalyst, its active component is at least one of Pt, Pd, Ni, Ag, Au, Ir, Fe, and the carrier is activated carbon, ZSM One of series molecular sieves, SAPO series molecular sieves, mordenite, Y zeolite, beta zeolite, Al ₂ O ₃ , TiO ₂ , amorphous aluminum silicate; the compounding component is polyα-olefin or FT synthetic oil.

Preferably, the carrier is one of mordenite, Y zeolite, beta zeolite, SAPO-11, ZSM-22, and ZSM-23.

Preferably, the amount of the catalyst used is 0.1-10 wt% (mass percent) of triisobutene.

Wherein, the conditions of the hydrogenation reaction are: the reaction pressure is 0.1-4MPa, the reaction temperature is 100-300°C, the reaction time is 12-24h, and the volume ratio of hydrogen to triisobutene is (200-600):1.

Preferably, the polyα-olefin is selected from one of PAO-5, PAO-10, PAO-15, and PAO-20; the FT synthetic oil is an FT distillate oil with a C ₁₁ -C ₁₅ structure.

Preferably, the added amount of the compounding components is 5-30 vol% (volume percent) of the hydrogenated triisobutene.

Compared with the prior art, the present invention has at least one of the following beneficial effects:

(1) In the preparation method of the diluent of the present invention, triisobutene is used as a raw material, and a C ₁₂ isoparaffin mixture with controllable structure and performance is obtained by using a relatively cheap and easily available hydrogenation catalyst, and by introducing the second component, further The performance of the hydrogenation product as a diluent is optimized, the preparation method greatly reduces the technical difficulty of the production of the existing diluent, and has the advantages of short process and low cost;

(2) The present invention uses triisobutene and its hydrogenation product as a diluent in the spent fuel reprocessing process, which provides a new idea for preparing isoparaffin mixture;

(3) The diluent prepared by the present invention has strong compatibility with TBP, can effectively improve the extraction efficiency and extraction capacity of the mixed solvent for uranium and plutonium, and has good performance in the post-treatment process of spent fuel;

(4) The introduction of the second component of the present invention can control the physical and chemical properties of the hydrogenation product in a relatively large range, and this method provides ideas for application scenarios such as high-level waste liquid treatment.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention are described clearly and completely below. Obviously, the described embodiment is one, but not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

Unless otherwise defined, technical or scientific terms used in the present invention should have the ordinary meaning as understood by one of ordinary skill in the art to which the present invention belongs.

The method for preparing a diluent for spent fuel post-processing according to an embodiment of the present invention includes the following steps: under the action of a catalyst, triisobutene is selectively hydrogenated to generate hydrogenated triisobutene; adding compound components to the hydrogenated triisobutene, mixing The diluent is obtained by reaction; wherein, the catalyst is a supported metal catalyst, its active component is at least one of Pt, Pd, Ni, Ag, Au, Ir, Fe, and the carrier is activated carbon, ZSM series molecular sieve, SAPO series molecular sieve One of , mordenite, Y zeolite, beta zeolite, Al ₂ O ₃ , TiO ₂ , amorphous aluminum silicate; the compound component is polyalpha-olefin or FT synthetic oil.

Specifically, the preparation method of the diluent can be carried out according to the following steps:

(1) Hydrogenation reaction: add raw material triisobutene into the reaction kettle, add a certain amount of catalyst, then vacuumize, fill with nitrogen, repeat the pumping and ventilation more than three times, vacuumize the last time, and introduce hydrogen, under a certain pressure and The reaction is carried out for a period of time under the temperature condition to obtain the first component, i.e. hydrogenated triisobutene;

(2) Compounding: the hydrogenated triisobutene obtained in step (1) is transferred to a stirring tank, the second component is added, and the diluent is prepared by mixing and stirring reaction.

Wherein, in step (1), the hydrogenation reaction catalyst adopts a supported metal catalyst. Compared with the metal catalyst, the amount of metal used is greatly reduced, which is conducive to reducing costs. At the same time, the metal is supported on a carrier with a certain specific surface area and pores. , which is beneficial to increase the contact area between the reactant and the catalyst and improve the reaction efficiency.

The active components of commonly used supported metal catalysts can be selected from one or more of Pt, Pd, Ni, Ag, Au, Ir, Fe, and the carrier can be selected from activated carbon, ZSM series molecular sieves, SAPO series molecular sieves, mordenite , any one of Y zeolite, beta zeolite, Al ₂ O ₃ , TiO ₂ , and amorphous aluminum silicate; wherein, the carrier may specifically be one of SAPO-11, ZSM-22, and ZSM-23.

Further, in the catalyst composition, the content of active components can usually be controlled at 0.5-5 wt % of the entire supported metal catalyst; of course, it can be 1.5-3 wt %.

As for the preparation method of the catalyst, commonly used methods include mechanical mixing method, impregnation method, co-precipitation method, sol-gel method, ion exchange method and the like. In this embodiment, for example, an impregnation method can be used, that is, the soluble salt of the corresponding active component element is impregnated on different carriers, adsorbed and saturated, and then prepared by drying, roasting, gas reduction and other steps. The catalyst is prepared by the impregnation method, which has the advantages of simple operation and high metal dispersion.

Although the hydrogenation reaction catalyst is a common catalyst type, it is applied in the hydrogenation reaction of triisobutene of the present invention, and has a good promoting effect: on the one hand, using triisobutene as a raw material, compared with propylene, an oligomerization reaction (product configuration Uncontrollable), the complicated intermediate reaction process is omitted, and the raw material itself is a mixture of C ₁₂ unsaturated hydrocarbons, and direct hydrogenation and saturation is beneficial to improve the reaction efficiency and simplify the reaction process; Under the premise of high, the catalyst shows good selectivity, which is manifested in the increase of the proportion of branched configuration in the hydrogenation product; and because the branched alkane mixture has better extraction performance than normal alkane, therefore, the isomerization of the product is improved. The degree of chemistry is the desired result of the present invention.

Further, in step (2), the second component adopts polyα-olefin or FT synthetic oil of a specific fraction. Among them, poly-alpha-olefin (PAO for short) synthetic oil is made of linear alpha-olefins such as C ₄ (butene-1), C ₆ (hexene-1) and C ₈ (octene-1) after polymerization and hydrogenation It is the most commonly used synthetic lubricating oil base oil and has a wide range of applications; the molecular chain of PAO has a certain branched structure, and this unique structure makes it have good viscosity-temperature performance and low-temperature fluidity. It is an ideal base oil for preparing high-grade and special lubricating oil. At present, the raw material α-olefin of PAO synthetic oil can be obtained by two methods: ethylene oligomerization and paraffin cracking; that is, using ethylene oligomerized C ₆ -C ₁₂ olefin as raw material to produce PAO synthetic oil or using paraffin as raw material, after cracking, PAO synthetic oil is produced by processes such as polymerization, fractionation, and clay refining. PAO has the advantages of good low temperature fluidity, low volatility, non-toxicity, strong thermal stability, etc., in addition to being commonly used as lubricating oil, engine oil, etc., it can also be used as a solvent. According to the polyalpha-olefin of the embodiment of the present invention, the type with lower molecular weight and high degree of molecular chain branching is selected, such as PAO-2, PAO-2.5, PAO-5 or products with lower viscosity and smaller molecular weight, Of course not limited to what is listed. The introduction of polyα-olefin can improve the physical and chemical indicators such as the flash point of hydrogenated triisobutene, and because of its unique molecular topology, it is beneficial to promote the interaction between the diluent and the extractant, thereby improving the extraction capacity of the extraction system.

Fischer-Tropsch (FT) synthesis technology refers to the reaction of producing hydrocarbons by chain growth with synthesis gas (CO and H ₂ ) as raw materials under the action of catalysts. It is an important way to synthesize clean fuels and chemical products through non-petroleum routes. The raw materials mainly come from the conversion of coal, natural gas and biomass. The product of indirect coal liquefaction is FT synthetic oil, which can be divided into naphtha fraction, diesel fraction, heavy oil fraction and wax according to the distillation range. The FT synthetic oil according to the embodiment of the present invention can be, for example, an FT distillate oil having a C ₁₁ -C ₁₅ structure, and specifically, an FT having a carbon number distribution in C ₉ -C ₁₄ and a linear paraffin content of less than 20% can be selected. Distillate oil.

The introduction of the above-mentioned second component can regulate the composition and performance of the hydrogenated triisobutene prepared in step (1) in a relatively large range, so that the final obtained diluent product has a better effect on the extraction of uranium and plutonium: Such as increasing the flash point of the diluent, speeding up the phase separation of the extraction system, increasing the extraction capacity of the target extract, etc.

The technical solutions and effects of the present invention are described below in conjunction with specific embodiments:

Example 1:

Triisobutene hydrogenation reaction: in a 1L reaction kettle, add 150g of raw material triisobutene, and add 5g of Pd/SAPO-11 catalyst together; then vacuumize, fill with nitrogen, and repeat the pumping and ventilation more than three times; Hydrogen; adjust the pressure of the reaction kettle to 2MPa and the temperature to 190°C to carry out the reaction for 15h, then take samples, and use the fluorescent indicator adsorption method to detect the conversion rate of the raw materials.

The reaction solution obtained from the above reaction is filtered with a silica gel short column (silica gel diameter 30mm, height 10cm), then washed with 30mL of n-hexane, the filtrates are combined and concentrated to obtain hydrogenated triisobutene; the physicochemical parameters of the hydrogenated product are determined as: The bromine value was 0.29 g/100 g, the density was 0.71 g/cm ³ (20°C), the dynamic viscosity was 1.3 cP (20°C), and the flash point was 60°C.

Example 2:

Triisobutene hydrogenation reaction: in a 1L reactor, add 150g of raw material triisobutene, and add 5g of Pd/mordenite together; then vacuumize, fill with nitrogen, and repeat the pumping and ventilation more than three times; vacuumize for the last time, and feed hydrogen; Adjust the pressure of the reaction kettle to 2MPa and the temperature to 190℃ to carry out the reaction for 15h, then take samples, and use the fluorescent indicator adsorption method to detect the conversion rate of the raw materials.

The reaction solution obtained from the above reaction is filtered with a silica gel short column (silica gel diameter 30mm, height 10cm), then washed with 30mL of n-hexane, the filtrates are combined and concentrated to obtain hydrogenated triisobutene; the physicochemical parameters of the hydrogenated product are determined as: The bromine value was 0.31 g/100 g, the density was 0.71 g/cm ³ (20°C), the dynamic viscosity was 1.2 cP (20°C), and the flash point was 59°C.

Example 3:

Triisobutene hydrogenation reaction: in a 1L reactor, add 150g of raw material triisobutene, and add 5g of Pt/ZSM-22 catalyst together; then vacuumize, fill with nitrogen, and repeat the pumping and ventilation more than three times; Hydrogen; adjust the pressure of the reaction kettle to 2MPa and the temperature to 190°C to carry out the reaction for 15h, then take samples, and use the fluorescent indicator adsorption method to detect the conversion rate of the raw materials.

The reaction solution obtained from the above reaction is filtered with a silica gel short column (silica gel diameter 30mm, height 10cm), then washed with 30mL of n-hexane, the filtrates are combined and concentrated to obtain hydrogenated triisobutene; the physicochemical parameters of the hydrogenated product are determined as: The bromine value was 0.50 g/100 g, the density was 0.74 g/cm ³ (20°C), the dynamic viscosity was 1.5 cP (20°C), and the flash point was 55°C.

Comparing the physicochemical performance parameters of the hydrogenated products prepared in Examples 1-3, it can be known that the properties of the hydrogenated products prepared under the action of different catalysts are significantly different, and the saturation of the hydrogenated products prepared as in Example 1 is higher ( The bromine value is lower), indicating that the conversion rate of the raw material is higher; the density and viscosity of the hydrogenated product prepared in Example 2 are lower, and it has certain advantages as a diluent (helping to reduce the density and viscosity of the solvent phase, improve the dilution fluid mechanics of the agent).

Example 4:

In order to more intuitively reflect the favorable influence of the hydrogenation catalyst of the present invention on the hydrogenation reaction of triisobutene, the catalysts used in Examples 1-3 were evaluated for activity and performance, and the evaluation results are shown in Table 1.

In the present invention, the triisobutene conversion rate is calculated by the following formula:

Conversion rate of triisobutene=moles of triisobutene converted by reaction/moles of triisobutene in raw material×100%.

Performance evaluation of each catalyst in Table 1 Examples 1-3

Type of catalyst Conversion rate (mol%) Hydrogenated triisobutene branch rate (mol%) Pd/SAPO-11 99.9 80.1 Pd/Mordenite 99.5 86.4 Pt/ZSM-22 98.4 63.7

As can be seen from the results in Table 1, the triisobutene hydrogenation reaction of the embodiment of the present invention has a higher conversion rate; and for the catalyst selectivity, the branched chain rate of the hydrogenated product prepared by using the catalyst of Example 2 is higher, which is difficult for dilution. The composition of the agent has a better improvement effect.

Example 5:

Compounding: in a 1L beaker, add 500mL of hydrogenated triisobutene prepared in Example 1, then add 25mL of PAO-5, fully stir and let stand for 30min to obtain the final diluent product;

The physical and chemical properties of the final product were determined as follows: the bromine value is 0.29g/100g, the density is 0.72g/cm ³ (20°C), the dynamic viscosity is 1.2cP (20°C), and the flash point is 67°C.

Take 100 g of the final product prepared above and tributyl phosphate (TBP) to form a 30% TBP-diluent mixed solvent, and carry out an extraction experiment; the extraction results are: 30% TBP-diluent and 1mol/LHNO _The phase separation time is 38s, The extraction capacity for Pu(IV) was 77 g/L.

Example 6:

Compounding: in a 1L beaker, add 500mL of hydrogenated triisobutene prepared in Example 1, then add 40mL of PAO-15, fully stir and let stand for 30min to obtain the final diluent product;

The physical and chemical properties of the final product were determined as follows: the bromine value is 0.27g/100g, the density is 0.71g/cm ³ (20°C), the dynamic viscosity is 1.4cP (20°C), and the flash point is 72°C.

Take 100 g of the final product prepared above and tributyl phosphate (TBP) to form a 30% TBP-diluent mixed solvent, and carry out an extraction experiment; the extraction results are: the phase separation time of ₃₀ % TBP-diluent and 1mol/LHNO is 42s, The extraction capacity for Pu(IV) was 90 g/L.

Example 7:

Compounding: in a 1L beaker, add 500mL hydrogenated triisobutene prepared in Example 1, then add 100mL C ₁₁ -C ₁₅ fraction FT synthetic oil, fully stir and let stand for 30min to obtain the final diluent product;

The physical and chemical properties of the final product were determined as follows: the bromine value is 0.30g/100g, the density is 0.70g/cm ³ (20°C), the dynamic viscosity is 1.2cP (20°C), and the flash point is 66°C.

Take 100 g of the final product prepared above and tributyl phosphate (TBP) to form a 30% TBP-diluent mixed solvent, and carry out an extraction experiment; the extraction results are: 30% TBP-diluent and 1mol/LHNO _The phase separation time is 38s, The extraction capacity for Pu(IV) was 66 g/L.

Example 8:

Get each product prepared in embodiment 1-3, 5-7 and the material of comparative example 1 as diluent, form extraction system with tributyl phosphate (TBP) respectively, carry out uranium, plutonium extraction, extraction condition is: take dilution A 30% TBP-diluent mixed solvent was formed with 100 g of solvent and tributyl phosphate (TBP), and the extraction experiment was carried out; the phase separation time of the mixed solvent and 1mol/L HNO ₃ was measured, and the extraction capacity of the extraction system for Pu(IV) ; Its extraction result is shown in table 2;

Wherein, in Comparative Example 1, commercially available hydrogenated kerosene was used as the diluent.

Table 2 Extraction results of different diluent components

source of diluent Phase separation time (s) Extraction capacity (g/L) Example 1 44 69.6 Example 2 37 73.4 Example 3 51 66.6 Example 5 38 77 Example 6 42 90 Example 7 38 66 Comparative Example 1 56 56

Comparing the extraction results of Examples 1-3, 5-7 and Comparative Example 1, it can be known that using the diluent prepared in the embodiment of the present invention to carry out the extraction experiment, the effect is obviously better than the commercially available hydrogenated kerosene diluent product. Wherein, in embodiment 1-3, when using triisobutene hydrogenation product directly as diluent, the effect of embodiment 2 is the best, as shown in Table 1, the branching ratio of the hydrogenation product prepared by the catalyst of embodiment 2 is obtained higher, so its extraction capacity for Pu(IV) is larger.

Further, the hydrogenated triisobutene is optimized, and the second component is added to adjust the structure and ratio of the diluent composition, which can improve the performance of the hydrogenated product in a large range and improve the extraction effect; wherein, as shown in Table 2, the implementation of The hydrogenated triisobutene in example 1 adds the second component of different kinds, the extraction performance of the obtained diluent is the best with the effect of embodiment 6, and the addition of the second component obviously improves the hydrogenated triisobutene to Pu(IV) extraction capacity.

This shows that the branched-chain alkane mixture prepared by the preparation method of the present invention, which is used as a diluent and tributyl phosphate to form an extraction system, has a good effect on the extraction of uranium and plutonium in spent fuel. Simple, low cost, and thus conducive to promotion.

For the embodiments of the present invention, it should also be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other to obtain new embodiments.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto, and the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (6)

1. A preparation method of a diluent for post-processing spent fuel, comprising the steps: Under the action of a catalyst, triisobutene is selectively hydrogenated to generate hydrogenated triisobutene; Adding compound components to the hydrogenated triisobutene, mixing and reacting to obtain a diluent; Wherein, the catalyst is a supported metal catalyst, its active component is at least one of Pt, Pd, Ni, Ag, Au, Ir, Fe, and the carrier is activated carbon, ZSM series molecular sieves, SAPO series molecular sieves, mordenite, One of Y zeolite, beta zeolite, Al ₂ O ₃ , TiO ₂ , amorphous aluminum silicate; The compounding component is polyalpha-olefin or F-T synthetic oil. 2 . The preparation method according to claim 1 , wherein the carrier is one of mordenite, Y zeolite, beta zeolite, SAPO-11, ZSM-22, and ZSM-23. 3 . 3. The preparation method according to claim 1, wherein the catalyst is used in an amount of 0.1-10 wt% of triisobutene. 4. preparation method according to claim 1, wherein, the condition of described hydrogenation reaction is: reaction pressure 0.1～4MPa, reaction temperature 100～300 ℃, reaction time 12～24h, the volume ratio of hydrogen and triisobutene is (200～600): 1. 5. The preparation method according to claim 1, wherein the polyα-olefin is selected from the group consisting of PAO-5, PAO-10, PAO-15, and PAO-20; FT distillate with ₁₁ -C ₁₅ structure. 6. The preparation method according to claim 1, wherein the added amount of the compound component is 5-30 vol% of hydrogenated triisobutene.