A purification process for N,N-dimethylhydroxylamine

Abstract

The application relates to a purification process of N,N-dimethylhydroxylamine, and belongs to the technical field of spent fuel reprocessing. The process comprises the following steps: S1, performing phase separation treatment on N,N-dimethylhydroxylamine crude products to obtain water phase and organic phase respectively; S2, performing back extraction on the organic phase by using deionized water, extracting N,N-dimethylhydroxylamine dissolved in the organic phase, and obtaining N,N-dimethylhydroxylamine product liquid and the organic phase after liquid separation; S3, performing rectification purification on the organic phase to prepare relatively pure olefin; S4, using the purified olefin as an extractant to extract the N,N-dimethylhydroxylamine product liquid, and using the water phase remaining after extraction as a primary purified product liquid; S5, neutralizing the residual alkaline impurities in the primary purified product liquid into salts by using a proper amount of strong acid; and then, the primary purified product liquid is purified in a way of reduced pressure distillation, the condensate fraction with a low boiling point at the beginning is discarded, and the subsequent condensate fraction is collected, so that the purified N,N-dimethylhydroxylamine product is obtained. The product obtained by the purification process has an organic purity of more than 99%.

Description

Technical Field

[0001] This invention belongs to the field of spent fuel reprocessing technology, specifically a purification process for N,N-dimethylhydroxylamine. This process can purify N,N-dimethylhydroxylamine, a salt-free reducing agent used in the reprocessing of refined nuclear fuel. This reagent can be used in uranium-plutonium separation, plutonium purification, uranium purification, and related analyses. Background Technology

[0002] Hydroxyl-substituted hydroxylamines are a class of hydroxylamine derivatives, structurally equivalent to compounds in which two hydrogen atoms in the H₂NOH molecule are replaced by hydrocarbon groups. In recent years, due to the rapid development of nuclear power, extensive research has been conducted on highly efficient salt-free reducing agents. In particular, N,N-dimethylhydroxylamine, as an organic salt-free reducing agent, has achieved good results in the spent fuel reprocessing process of nuclear power plants, attracting widespread attention. N,N-dimethylhydroxylamine is typically synthesized from N,N-dimethylcyclohexylamine and hydrogen peroxide. The crude N,N-dimethylhydroxylamine product obtained during synthesis usually contains impurities such as N,N-dimethylcyclohexylamine, cyclohexene, and dimethylamine, which will affect its subsequent use. Therefore, the crude dimethylhydroxylamine product must be purified to control the impurity content below the requirements for subsequent use.

[0003] The patents "A Method for Synthesizing N,N-Dimethylhydroxylamine" (ZL200510135530.8) and "A Synthetic Process for N,N-Dimethylhydroxylamine" (ZL200910119505.9) describe methods for synthesizing N,N-dimethylhydroxylamine. Both patents employ direct distillation for purification, but the highest organic purity obtained using this method is only 98%. To improve the subsequent use of dimethylhydroxylamine, measures need to be taken to improve its purification parameters. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a purification process for N,N-dimethylhydroxylamine. This process can purify N,N-dimethylhydroxylamine, a salt-free reducing agent used in the reprocessing of nuclear fuel, and yields a product with an organic purity of over 99%, meeting the requirements for subsequent use of N,N-dimethylhydroxylamine.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A purification process for N,N-dimethylhydroxylamine, the process comprising the following steps:

[0007] S1. The crude N,N-dimethylhydroxylamine product is subjected to phase separation treatment to obtain an aqueous phase with N,N-dimethylhydroxylamine as the main solute and an organic phase with a small amount of N,N-dimethylhydroxylamine and organic impurities as the main solutes.

[0008] S2. Back-extract the organic phase obtained in step S1 with an appropriate amount of deionized water to further extract N,N-dimethylhydroxylamine dissolved in the organic phase. After separation, N,N-dimethylhydroxylamine product solution and organic phase are obtained.

[0009] S3. The organic phase obtained in step S2 is purified by distillation to obtain an olefin with a purity that meets the requirements for use.

[0010] S4. Using the purified olefin as the extractant, extract the N,N-dimethylhydroxylamine product solution obtained in step S2. The raffinate aqueous phase is the pre-purified product solution.

[0011] S5. Use an appropriate amount of strong acid to neutralize the alkaline impurities remaining in the pre-purified product solution to generate salts; then purify by vacuum distillation, discarding the initial low-boiling-point condensate fraction and collecting the subsequent condensate fraction separately, which is the purified N,N-dimethylhydroxylamine product.

[0012] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, the crude N,N-dimethylhydroxylamine product includes N,N-dimethylhydroxylamine, raw materials, and other organic impurities, including olefins and dimethylamine.

[0013] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, in step S2, the aqueous phase obtained after back-extraction is added to the aqueous phase obtained in step S1 to obtain the N,N-dimethylhydroxylamine product solution.

[0014] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, step S2 employs a multiple back-extraction method to further extract N,N-dimethylhydroxylamine dissolved in the organic phase.

[0015] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, in step S2, the amount of deionized water used for each back-extraction is determined according to the usage requirements for the final N,N-dimethylhydroxylamine product concentration.

[0016] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, step S3 specifically involves: using a distillation apparatus to purify the organic phase obtained in step S2 by distillation, performing heating distillation under reduced pressure or atmospheric pressure, and utilizing the principle that different fractions have different boiling points to discard low-boiling-point impurity fractions and collect intermediate olefin fractions, thereby obtaining olefins with purity meeting the requirements for use.

[0017] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, step S4 specifically involves: adding an appropriate amount of olefin to the N,N-dimethylhydroxylamine product solution obtained in step S2, stirring and mixing evenly, then allowing it to stand and separate phases. The lipophilic impurities originally dissolved in the N,N-dimethylhydroxylamine product solution are transferred to the olefin, thereby achieving the purpose of purifying the N,N-dimethylhydroxylamine product solution.

[0018] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, multiple extractions are used in step S4 to improve the purity of the initial purified product solution.

[0019] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, the amount of olefin used in step S4 is determined based on the impurity content in the N,N-dimethylhydroxylamine product solution.

[0020] Furthermore, in the purification process of N,N-dimethylhydroxylamine as described above, in step S5, an appropriate amount of sulfuric acid is added to the preliminarily purified product solution to neutralize the residual alkaline impurities in the product solution and generate salts; the pressure range used during vacuum distillation is -50 to -90 kPa.

[0021] The purification process for N,N-dimethylhydroxylamine described in this invention has the following significant technical advantages:

[0022] 1) This invention utilizes the olefins generated during the synthesis of dimethyl hydroxylamine as the extractant for product purification, eliminating the need to purchase new extractants;

[0023] 2) The present invention uses extraction, sulfuric acid neutralization and then distillation for purification, and the purity of the obtained dimethylhydroxylamine product can be increased to more than 99%, which can meet the requirements of subsequent applications with high product requirements. Attached Figure Description

[0024] Figure 1 This is a purification process route diagram of N,N-dimethylhydroxylamine provided in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of a purification process for N,N-dimethylhydroxylamine provided in an embodiment of the present invention. Detailed Implementation

[0026] The present invention will now be further described with reference to specific embodiments and the accompanying drawings.

[0027] To address the issue mentioned in the background art that the organic purity of products obtained by direct distillation methods can only reach a maximum of 98%, this invention provides a purification process for N,N-dimethylhydroxylamine, which employs cyclohexene extraction, sulfuric acid neutralization, and subsequent distillation. The organic purity of the N,N-dimethylhydroxylamine product obtained using this purification process is above 99%.

[0028] Figure 1 The present invention illustrates a purification process route for N,N-dimethylhydroxylamine, which includes phase separation of N,N-dimethylhydroxylamine and cyclohexene, water washing of the cyclohexene phase, distillation of cyclohexene, extraction, neutralization, and distillation of the crude N,N-dimethylhydroxylamine product.

[0029] Figure 2 This diagram illustrates a purification process for N,N-dimethylhydroxylamine provided in an embodiment of the present invention. The specific process includes the following steps:

[0030] S1. The crude N,N-dimethylhydroxylamine product is subjected to phase separation treatment to obtain an aqueous phase with N,N-dimethylhydroxylamine as the main solute and an organic phase with a small amount of N,N-dimethylhydroxylamine and organic impurities as the main solutes.

[0031] N,N-Dimethylhydroxylamine is synthesized from N,N-dimethylcyclohexylamine. The crude N,N-dimethylhydroxylamine product typically contains not only N,N-dimethylhydroxylamine but also the raw material (such as N,N-dimethylcyclohexylamine), as well as olefins (such as cyclohexene), dimethylamine, and other organic impurities. This step involves phase separation and liquid-liquid separation of the crude N,N-dimethylhydroxylamine product to obtain an aqueous phase with N,N-dimethylhydroxylamine as the main solute and an organic phase with small amounts of N,N-dimethylhydroxylamine and organic impurities as the main solutes.

[0032] The specific phase separation process is as follows: The crude N,N-dimethylhydroxylamine product is left to stand for a period of time. Since the crude N,N-dimethylhydroxylamine product contains olefins, and olefins are immiscible with water, the crude product will form two liquid layers. The upper layer is an organic phase with a small amount of N,N-dimethylhydroxylamine and organic impurities as the main solutes, and the lower layer is an aqueous phase with N,N-dimethylhydroxylamine as the main solute. Then, the organic phase and the aqueous phase are separated to obtain an aqueous phase with N,N-dimethylhydroxylamine as the main solute and an organic phase with a small amount of N,N-dimethylhydroxylamine and organic impurities as the main solutes.

[0033] S2. The organic phase obtained in step S1 is back-extracted with an appropriate amount of deionized water to further extract N,N-dimethylhydroxylamine dissolved in the organic phase. After separation, dimethylhydroxylamine product solution and organic phase are obtained.

[0034] This step utilizes the principle of back-extraction to return N,N-dimethylhydroxylamine dissolved in the organic phase to the aqueous phase. Specifically, the steps are as follows: An appropriate amount of deionized water is added to the organic phase obtained in step S1, and the mixture is stirred thoroughly and allowed to stand. During this process, the N,N-dimethylhydroxylamine originally dissolved in the organic phase returns to the aqueous phase, forming separate layers. The organic and aqueous phases are then separated to obtain an aqueous phase and an organic phase. The aqueous phase obtained in this step is added to the aqueous phase obtained in step S1 to obtain the N,N-dimethylhydroxylamine product solution. This step can be repeated multiple times to further improve the purity of the N,N-dimethylhydroxylamine product.

[0035] The amount of deionized water used in each back-extraction step depends on the desired final N,N-dimethylhydroxylamine product concentration. Using more deionized water results in a lower final N,N-dimethylhydroxylamine product concentration; conversely, using less deionized water results in a higher final N,N-dimethylhydroxylamine product concentration.

[0036] S3. The organic phase obtained in step S2 is purified by distillation to obtain an olefin with a purity that meets the requirements for use.

[0037] The specific process of distillation purification described in this step is as follows: the organic phase obtained in step S2 is purified by distillation using distillation equipment such as a distillation column. The distillation is carried out under reduced pressure or normal pressure conditions. The low-boiling-point impurity fraction is discarded and the intermediate olefin fraction is collected to obtain a relatively pure olefin.

[0038] S4. Using the purified olefin as the extractant, extract the N,N-dimethylhydroxylamine product solution obtained in step S2. The raffinate aqueous phase is the pre-purified product solution.

[0039] The extraction process in this step is as follows: An appropriate amount of olefin is added to the N,N-dimethylhydroxylamine product solution obtained in step S2, and the mixture is stirred for 5–60 minutes. After standing for a period of time, the phases are separated. This process allows the lipophilic impurities originally dissolved in the N,N-dimethylhydroxylamine product solution to transfer to the olefin, thereby achieving the purpose of purifying the N,N-dimethylhydroxylamine product solution. To further improve the purity of the N,N-dimethylhydroxylamine product, this step employs multiple extractions. The final raffinate phase is the pre-purified product solution.

[0040] The amount of olefin used and the number of extractions can be determined based on the impurity content in the N,N-dimethylhydroxylamine product solution during this step.

[0041] S5. Use an appropriate amount of strong acid to neutralize the residual alkaline impurities in the pre-purified product solution to generate salts; then purify by vacuum distillation, discard the initial low-boiling-point condensate, and collect the subsequent condensate separately, which is the purified N,N-dimethylhydroxylamine product.

[0042] The specific process of this step is as follows: Add an appropriate amount of strong acid (non-volatile and non-decomposing upon heating, such as sulfuric acid) to the pre-purified product solution, mix and stir evenly. The sulfuric acid reacts with the residual alkaline impurities in the product solution to form salts. Then, the pre-purified product solution is subjected to vacuum distillation. During the distillation process, the initial low-boiling-point condensate fraction (approximately 0.1% to 3% of the total volume) is discarded, and the subsequent condensate fraction is collected separately, which is the purified N,N-dimethylhydroxylamine. These impurities will remain in the distillation residue, thereby achieving the purpose of purification.

[0043] The amount of sulfuric acid added in this step is related to the volume of the feed solution and the content of impurities. In one specific embodiment of the present invention, the amount of sulfuric acid added is 1% to 20% of the total molar amount of dimethyl hydroxylamine. The pressure range used during vacuum distillation is -50 to -90 kPa.

[0044] Example 1

[0045] The pyrolysis fraction was separated into two phases: 4.5 kg of crude dimethylhydroxylamine and 5.5 kg of cyclohexene. 0.6 kg of deionized water was added to the cyclohexene phase and the mixture was stirred and washed for 20 minutes. After phase separation, the aqueous phase was combined with the crude dimethylhydroxylamine. Another 0.4 kg of deionized water was added to the cyclohexene phase and the mixture was stirred and washed. After phase separation, the aqueous phase was combined with the crude dimethylhydroxylamine. The cyclohexene was then subjected to simple distillation, yielding approximately 4.9 kg of cyclohexene with a purity of 98.12%. 1 kg of the purified cyclohexene was mixed with 5.5 kg of the crude dimethylhydroxylamine, stirred for 5 minutes, allowed to stand for 10 minutes, and then the phases were separated. Another 1 kg of purified cyclohexene was mixed with the aqueous crude product, stirred for 5 minutes, allowed to stand for 10 minutes, and then the phases were separated again. 0.3 kg of 50% sulfuric acid was added to the aqueous crude product for acidification, followed by vacuum distillation. The final product yielded 4.5 kg of dimethylhydroxylamine with a concentration of 40.08% and an organic purity of 99.34%.

[0046] Example 2

[0047] The pyrolysis fraction was separated into two phases: 665 kg of crude dimethyl hydroxylamine and 800 kg of cyclohexene. 90 kg of deionized water was added to the cyclohexene phase and the mixture was stirred and washed for 20 minutes. After phase separation, the aqueous phase was combined with the crude dimethyl hydroxylamine. Another 50 kg of deionized water was added to the cyclohexene phase and the mixture was stirred and washed again. After phase separation, the aqueous phase was combined with the crude dimethyl hydroxylamine. The cyclohexene was then subjected to simple distillation, yielding approximately 755 kg of cyclohexene with a purity of 98.33%. 160 kg of the purified cyclohexene was mixed with 665 kg of the crude dimethyl hydroxylamine, stirred for 10 minutes, and allowed to stand for 15 minutes before phase separation. Then, 120 kg of the purified cyclohexene was mixed with the aqueous crude product, stirred for 10 minutes, and allowed to stand for 15 minutes before phase separation. 40 kg of 50% sulfuric acid was added to the aqueous crude product for acidification, followed by vacuum distillation. The final product yielded 607.5 kg of dimethylhydroxylamine, with a concentration of 36.08% and an organic purity of 99.47%.

[0048] The purification process for N,N-dimethylhydroxylamine provided by this invention utilizes the lipophilic and weakly basic properties of organic impurities in the crude dimethylhydroxylamine product. First, the crude product generated during synthesis is separated into phases. The organic phase is further washed with water to extract N,N-dimethylhydroxylamine, followed by distillation purification. The purified olefin is used as the extractant to extract the dimethylhydroxylamine product solution, allowing the lipophilic impurities to enter the olefin organic phase, thus achieving purification. Then, an appropriate amount of sulfuric acid is added to the separated dimethylhydroxylamine product solution to react with residual alkaline impurities, forming salts. These impurities remain in the distillate residue during subsequent distillation, achieving purification. This process utilizes the olefin generated during dimethylhydroxylamine synthesis as the extractant for product purification, eliminating the need to purchase new extractants. Furthermore, the organic purity of the N,N-dimethylhydroxylamine product obtained using this purification process is above 99%.

[0049] The above embodiments are merely illustrative examples of the present invention. The present invention may also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A purification process of N, N-dimethylhydroxylamine, the process comprising the following steps: S1, phase separation treatment is performed on N, N-dimethylhydroxylamine crude product to obtain an aqueous phase containing N, N-dimethylhydroxylamine as the main solute and an organic phase containing a small amount of N, N-dimethylhydroxylamine and organic impurities as the main solute, the N, N-dimethylhydroxylamine crude product is a fraction collected by pyrolysis of N, N-dimethylcyclohexylamine, and the N, N-dimethylhydroxylamine crude product contains N, N-dimethylhydroxylamine, N, N-dimethylcyclohexylamine, olefins and dimethylamine, wherein the olefins are cyclohexene; S2, the organic phase obtained in step S1 is subjected to back extraction with an appropriate amount of deionized water to further extract N, N-dimethylhydroxylamine dissolved in the organic phase, and after liquid separation, an N, N-dimethylhydroxylamine product liquid and an organic phase are obtained; S3, the organic phase obtained in step S2 is subjected to rectification purification to obtain olefins with a purity meeting the use requirements; S4, the purified olefins are used as an extractant to extract the N, N-dimethylhydroxylamine product liquid obtained in step S2, and the raffinate aqueous phase is a primary purified product liquid; S5, an appropriate amount of sulfuric acid is added to the primary purified product liquid to react with the residual basic impurities in the product liquid to form salts, and then the purified N, N-dimethylhydroxylamine product is obtained by vacuum distillation, discarding the initial low-boiling-point condensed fraction and separately collecting the subsequent condensed fraction.

2. The purification process of N,N-dimethylhydroxylamine according to claim 1, characterized in that, In step S2, the aqueous phase obtained after back extraction is added to the aqueous phase obtained in step S1 to obtain the N, N-dimethylhydroxylamine product liquid.

3. The purification process of N,N-dimethylhydroxylamine according to claim 2, characterized in that, In step S2, multiple back extractions are used to further extract N, N-dimethylhydroxylamine dissolved in the organic phase.

4. The purification process of N,N-dimethylhydroxylamine according to any one of claims 1 to 3, characterized in that, In step S2, the amount of deionized water used in each back extraction is determined according to the use requirements for the concentration of the final N, N-dimethylhydroxylamine product.

5. The purification process of N,N-dimethylhydroxylamine according to claim 1, characterized in that, In step S3, the organic phase obtained in step S2 is subjected to rectification purification using a rectification device, heating rectification is performed under reduced pressure or normal pressure conditions, low-boiling-point impurity fractions are discarded, and intermediate olefin fractions are collected, thereby obtaining olefins with a purity meeting the use requirements.

6. The purification process of N,N-dimethylhydroxylamine according to claim 2, characterized in that, In step S4, an appropriate amount of olefins is added to the N, N-dimethylhydroxylamine product liquid obtained in step S2, the mixture is stirred and mixed uniformly, then it is allowed to stand and separate into two phases, and oleophilic impurities originally dissolved in the N, N-dimethylhydroxylamine product liquid are transferred to the olefins, thereby achieving the purpose of purifying the N, N-dimethylhydroxylamine product liquid.

7. The purification process of N,N-dimethylhydroxylamine according to claim 6, characterized in that, In step S4, multiple extractions are used to improve the purity of the primary purified product liquid.

8. The purification process of N,N-dimethylhydroxylamine according to claim 6 or 7, characterized in that, In step S4, the amount of olefins used is determined according to the content of impurities in the N, N-dimethylhydroxylamine product liquid.

9. The purification process of N,N-dimethylhydroxylamine according to claim 1, characterized in that, In step S5, an appropriate amount of sulfuric acid is added to the primary purified product liquid to react with the residual basic impurities in the product liquid to form salts, and the pressure range used in vacuum distillation is -50 ~ -90 Kpa.

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