A method for the purification of crude adiponitrile produced by the hydrocyanation of butadiene

Abstract

This invention discloses a method for pretreatment and purification of crude adiponitrile prepared by butadiene hydrocyanation, belonging to the field of organic chemical product refining technology. The method includes: continuous multi-stage countercurrent washing of crude adiponitrile containing metal compound impurities using a brine solution; transferring the metal compound impurities to the aqueous phase through extraction; after oil-water separation, adjusting the pH of the aqueous phase to precipitate the metal compounds; obtaining a solid metal compound and a filtrate through solid-liquid separation; recycling the filtrate as washing liquid; dehydrating the oil phase to obtain a dehydrated adiponitrile solution suitable for entering a distillation system; and distilling the dehydrated adiponitrile solution to obtain qualified adiponitrile. This invention can efficiently remove residual metal compounds from crude adiponitrile, with a removal rate greater than 99%, and the metal content in the oil phase after treatment is less than 10 ppm. It does not introduce nitrogen-containing impurities such as ammonia / amines, resulting in high product purity. The process is simple, energy consumption is low, the washing liquid can be recycled, and metal resources are easily recovered, showing good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical product refining technology, specifically relating to a method for purifying and pretreating the crude adiponitrile reaction solution obtained in the process of preparing adiponitrile by butadiene hydrocyanation, and particularly relating to a method for efficiently and cleanly removing residual metal compound components therein. Background Technology

[0002] Adiponitrile (ADN) is an important intermediate in the production of Nylon 66, primarily produced industrially via the butadiene hydrocyanation process. This method is characterized by its wide availability of raw materials, short process route, high yield, and low pollution, making it the most atom-economical and rational method for preparing adiponitrile to date.

[0003] The direct hydrocyanation process for producing adiponitrile from butadiene involves three steps: primary cyanation, isomerization, and secondary cyanation. A transition metal catalyst, typically a complex of nickel in its zero oxidation state and an organophosphorus ligand, is used. A Lewis acid (such as zinc chloride, aluminum chloride, or boron trichloride) is added as a co-catalyst during the secondary cyanation step. After the reaction, the crude adiponitrile product contains residual noble metal catalysts and Lewis acid components. These metal compounds have poor thermal stability; if directly introduced into the subsequent high-temperature distillation system, they can cause coking and blockage of the equipment and catalyze product decomposition. Therefore, they must be effectively removed before distillation.

[0004] Currently, the pretreatment method commonly used in industry is "chemical complexation-distillation separation": ammonia or organic amines are added to the crude product to form soluble complexes of metal ions, which are then separated as high-boiling-point substances through distillation. For example, in a method for producing adiponitrile disclosed in Chinese patent application CN113444018A (publication date September 28, 2021), ammonia gas is introduced into the raffinate phase to react, causing the metal to precipitate and then be separated by filtration. However, this method has significant drawbacks: First, the added ammonia / amine contaminates the product, leading to excessive basicity and nitrogen content in the final adiponitrile, severely affecting the lifespan of downstream hydrogenation catalysts; second, the complexing agent introduced for separation requires an additional distillation step, significantly increasing equipment investment and operating energy consumption; third, the metal enters the high-boiling-point tar in the form of a complex, resulting in a cumbersome, costly, and low-recovery-rate recovery process, hindering the effective utilization of precious metal resources; finally, the complex may decompose at high temperatures, leading to equipment corrosion and coking risks.

[0005] Another existing technology involves using organic solvent extraction to separate the catalyst system. For example, Chinese patent application CN101351463A (published January 21, 2009) discloses a method for extracting and removing nickel(O) complexes and phosphorus-containing ligands from the effluent of a hydrocyanation reaction using hydrocarbon solvents (such as cyclohexane, heptane, etc.). This method is mainly used for the recovery and recycling of catalysts after the reaction, treating reaction liquids containing high concentrations of catalysts, and using organic solvents as extractants. However, this method is not suitable for the final metal removal before crude adiponitrile distillation, because the introduction of organic solvents increases the burden of subsequent separation and may cause organic residue contamination to the adiponitrile product.

[0006] It is worth noting that, for a long time, those skilled in the art have consistently followed the technical approach of "adding a complexing agent" when dealing with metal residues in crude adiponitrile. Whether it's the industrially common ammonia / amine complexation method (e.g., CN113444018A) or the organic solvent extraction-precipitation method (e.g., CN101351463A), both rely on introducing an external complexing agent (ammonia, amine, or organic solvent) into the system to achieve metal separation. This technical path dependence has led to a technical bias in the field that "metal compounds must be chemically complexed to be effectively removed from the organic phase." Under the influence of this bias, simple brine washing is considered insufficient for deep removal of metal impurities and suffers from problems such as emulsification and phase separation difficulties, and therefore has not been researched or applied for a long time.

[0007] Therefore, developing a novel pretreatment technology that avoids the introduction of new impurities, has a simple process, low energy consumption, and facilitates efficient recovery of precious metals is of great significance for improving the economy and environmental friendliness of the butadiene hydrocyanation process for preparing adiponitrile. Summary of the Invention

[0008] This invention addresses the technical challenges of removing residual metal compounds and introducing new impurities during the preparation of adiponitrile via butadiene hydrocyanation. It provides a pretreatment and purification method for crude adiponitrile prepared via butadiene hydrocyanation. This method can efficiently remove residual metal compounds from crude adiponitrile, avoid introducing new organic impurities, has a simple process, low energy consumption, and facilitates the recycling of metal resources.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for pretreatment and purification of crude adiponitrile prepared by butadiene hydrocyanation includes the following steps: a) Crude adiponitrile containing metal compound impurities is subjected to continuous multi-stage countercurrent washing with a salt solution, and the metal compound impurities are transferred to the aqueous phase by extraction. b) The washed mixture is subjected to oil-water separation to obtain an aqueous phase enriched with metal compounds and an oil phase from which metal impurities have been removed; c) Adjust the pH value of the aqueous phase obtained in step b) to precipitate the metal compound. After solid-liquid separation, obtain the metal compound solid and filtrate. d) Recycle the filtrate obtained in step c) back to step a) as a brine solution; e) Dehydrate the oil phase obtained in step b) to obtain a dehydrated dinitrile solution suitable for entering the distillation system.

[0010] This invention utilizes a multi-stage countercurrent washing process with a brine solution to transfer dissolved or suspended metal chlorides and other compounds from crude adiponitrile to the aqueous phase using the extraction principle. Because an aqueous phase immiscible with the crude product is used as the extractant, no new organic impurities are introduced into the organic phase. The washed oil phase contains only trace amounts of water, which is easily removed by distillation. The aqueous phase, rich in metal compounds, is pH-adjusted to precipitate metal ions as hydroxides or oxides. The metals can then be separated and recovered through simple filtration. The filtrate, a purified brine solution, can be recycled, achieving a closed-loop resource cycle.

[0011] Preferably, the metal salt in the brine solution in step a) is selected from at least one of nickel chloride, zinc chloride, aluminum chloride, and ferric chloride. More preferably, the metal salt is the same type of metal as the catalyst used in the butadiene hydrocyanation reaction. For example, if the catalyst system contains zinc chloride, a zinc chloride solution is used for washing to avoid introducing new metal impurities.

[0012] Preferably, the washing temperature in step a) is 40-80°C, more preferably 60°C. Within this temperature range, the viscosity of the two phases is suitable, the mass transfer efficiency is high, and the decomposition or polymerization of adiponitrile at high temperatures can be avoided.

[0013] Preferably, the mass ratio of the brine solution to crude adiponitrile in step a) is 0.5-2:1, more preferably 1:1. This ratio ensures sufficient mass transfer driving force while keeping the equipment size within a reasonable range.

[0014] Preferably, the pH adjustment in step c) is achieved by adding an alkaline solution (such as sodium hydroxide, potassium hydroxide, ammonia, etc.), and the precipitated metal compound is a metal hydroxide or a metal oxide.

[0015] Preferably, the filtrate after solid-liquid separation in step c) is mixed with fresh brine solution to a suitable concentration and then recycled back to step a) to maintain the material balance of the washing system.

[0016] Preferably, the dehydration process in step e) is carried out by distillation, and the removed water is condensed and recycled.

[0017] Using the method of this invention, the removal rate of metal compound impurities in crude adiponitrile can reach over 99%, and the metal content in the oil phase after treatment can be reduced to below 10 ppm, fully meeting the feed requirements of the subsequent distillation system.

[0018] The continuous multi-stage countercurrent washing can be carried out in various liquid-liquid extraction devices, such as extraction towers, mixing and clarification tanks, or rotating disc extraction towers. This invention does not impose strict limitations on the specific equipment form.

[0019] The core technical solution of this invention is as follows: I. Technological Concept Innovation Abandoning the traditional approach of "adding chemical complexing agents to the organic phase," this method instead uses a salt solution with the same metal composition as the catalyst as the extractant. Utilizing the liquid-liquid extraction principle, impurities such as metal chlorides in crude adiponitrile are transferred from the organic phase to the aqueous phase, preventing the introduction of ammonia / amine compounds at the source and ensuring product purity.

[0020] II. Process Integration and Innovation The following three unit operations are organically coupled to construct a complete chain for metal impurity removal and resource recycling: (1) Continuous multi-stage countercurrent washing: Crude adiponitrile is subjected to multi-stage countercurrent extraction using brine solution. By optimizing the ratio (0.5-2:1), temperature (40-80℃), and number of stages (4-6 stages), deep removal of metal impurities is achieved (removal rate >99%, residue <10ppm). (2) pH-controlled precipitation: The pH value of the aqueous phase enriched with metal is adjusted so that the metal ions precipitate out in the form of hydroxides. The solid metal compound is obtained by solid-liquid separation, thus realizing resource recovery. (3) Media recycling: The filtrate after sedimentation is prepared and recycled as washing liquid to form a closed-loop water phase circulation and achieve near-zero wastewater discharge.

[0021] III. Advantages in Industrial Applications This solution has the following significant advantages in industrial applications: (1) High product purity: No organic complexing agents are introduced, and there are no nitrogen-containing impurities in the adiponitrile product, which meets the stringent requirements of downstream hydrogenation reaction for raw materials; (2) Metals are recyclable: The metal compounds recovered from precipitation can be returned to the catalyst preparation system for use, realizing a closed-loop cycle of precious metal resources; (3) Simplified process and low energy consumption: After washing, the oil phase only needs simple dehydration before entering the distillation system, eliminating the extra distillation steps required to remove the complexing agent, reducing equipment investment by about 50% and energy consumption by about 60%; (4) Safe and stable operation: The washing process is carried out under mild conditions, which completely eliminates the risk of equipment corrosion and coking caused by the decomposition of metal complexes at high temperatures.

[0022] In summary, this invention, through the integrated innovation of "extraction of homologous brine - pH precipitation recovery - media recycling", perfectly solves a series of problems in existing technologies, such as product pollution, complex processes, difficulty in metal recovery, and easy coking of equipment, and achieves the organic unity of clean production and resource recycling.

[0023] Compared with the prior art, the beneficial effects of the present invention are: (1) No new impurities are introduced: The product is washed with salt water solution, which does not introduce nitrogen-containing organic substances such as ammonia / amine into the product, thus ensuring the purity of the adiponitrile product and avoiding affecting the life of downstream catalysts.

[0024] (2) Simple process and low energy consumption: After washing, it only needs to be dehydrated before entering the distillation system, which eliminates the extra distillation steps required to remove complexing agents, and greatly reduces equipment investment and operating energy consumption.

[0025] (3) Recyclable resources: Metal compounds are recovered through precipitation, and the filtrate can be recycled, which provides convenient conditions for the recycling of metal resources, especially suitable for catalyst systems containing precious metals.

[0026] (4) Safe and reliable operation: It avoids the risk of equipment corrosion and coking caused by the decomposition of complexes at high temperatures, and improves the operational stability of the device.

[0027] (5) High removal efficiency: Through multi-stage countercurrent operation, deep removal of metal impurities can be achieved, ensuring long-term stable operation of the distillation system. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the method of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to specific embodiments and the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] Example 1: Washing with a zinc chloride solution identical to the catalyst resulted in a metal removal rate >99%. The crude adiponitrile processed in this embodiment came from a butadiene hydrocyanation production unit. After preliminary flash evaporation to remove light components, the metal content was analyzed to be: nickel 500 ppm and zinc 800 ppm (in the form of zinc chloride).

[0031] A brine solution containing 20 wt% zinc chloride, identical to the metal in the catalyst, was used as the washing liquid. A five-stage countercurrent washing process was performed in a rotating disc extractor, with the operating temperature controlled at 60°C and the mass flow ratio of brine to crude adiponitrile at 1:1. The washed oil phase collected from the top of the column entered an oil-water separator. After settling and phase separation, the oil phase entered a dehydration tower, where water was removed under absolute pressure of 5 kPa and a bottom temperature of 120°C, yielding a dehydrated adiponitrile solution. This dehydrated adiponitrile solution was then further purified by a distillation system to obtain adiponitrile that met product standards. Analysis of the metal content in the dehydrated adiponitrile solution showed that nickel was less than 2 ppm and zinc was less than 5 ppm, with a removal rate greater than 99%.

[0032] The metal-enriched aqueous phase collected from the bottom of the tower enters the sedimentation tank, where a 20wt% sodium hydroxide solution is added to adjust the pH to 9.5, causing zinc ions to precipitate as zinc hydroxide. The precipitate is filtered through a plate and frame filter press to obtain a zinc hydroxide filter cake (which can be further calcined to recover zinc oxide). The filtrate enters the brine mixing tank, where a small amount of zinc chloride and water are added to adjust the concentration to the required level before being recycled back to the washing tower.

[0033] Example 2: Washing with aluminum chloride solution resulted in a metal removal rate >99%. The metal content in the crude adiponitrile processed in this embodiment is: 600 ppm nickel and 300 ppm aluminum (in the form of aluminum chloride).

[0034] A brine solution containing 15 wt% aluminum chloride was used as the washing solution. Four-stage countercurrent washing was performed in a mixing and clarifying tank, with the operating temperature controlled at 50°C and the mass flow ratio of brine to crude adiponitrile at 1.5:1. After washing, the oil phase was dehydrated, and the metal content in the dehydrated adiponitrile solution was analyzed; nickel was less than 3 ppm and aluminum was less than 2 ppm.

[0035] Sodium hydroxide solution was added to the aqueous phase enriched for metals to adjust the pH to 8.5, causing aluminum ions to precipitate as aluminum hydroxide. After filtration and separation, the filtrate was recycled.

[0036] Example 3: Washing with a mixed solution of nickel chloride and ferric chloride resulted in a metal removal rate >99%. The metal content in the crude adiponitrile processed in this embodiment is: nickel 800 ppm and iron 500 ppm (in the form of ferric chloride).

[0037] A mixed brine solution containing 10 wt% nickel chloride and 5 wt% ferric chloride was used as the washing solution. Six stages of countercurrent washing were performed in a sieve plate extraction column, with the operating temperature controlled at 70°C and the mass flow ratio of brine to crude adiponitrile at 0.8:1. After washing, the oil phase was dehydrated, and the metal content in the dehydrated adiponitrile solution was analyzed; nickel was less than 4 ppm and iron was less than 3 ppm.

[0038] Sodium hydroxide solution was added to the aqueous phase enriched for metals to adjust the pH to 10.0, causing nickel and iron ions to precipitate as a mixed hydroxide precipitate. After filtration and separation, the filtrate was recycled.

[0039] Comparative Example 1: The effect of traditional chemical complexation-distillation method The crude adiponitrile, identical to that in Example 1, was treated using a conventional "chemical complexation-distillation" method. Ammonia gas was introduced into the crude adiponitrile to form a complex of metal ions, which was then separated in a distillation column. Results showed significant coking in the distillation column bottom, with the column efficiency decreasing by approximately 30% after one week of operation. Analysis of the obtained adiponitrile product revealed an alkalinity (based on ammonia) of 150 ppm and excessive nitrogen content. The metal removal rate was approximately 95%, but some metal residue remained in the column bottom liquid.

[0040] Comparative Example 2: Comparative effect of the organic solvent extraction-ammonia precipitation method disclosed in CN113444018A Referring to the method disclosed in the example of CN113444018A, after separating the catalyst using cyclohexane extraction, ammonia gas is passed through the raffinate to precipitate the metal. This method has a long process, requires multiple distillations to recover cyclohexane, and has high energy consumption. Finally, trace amounts of cyclohexane residue (approximately 50 ppm) were detected in the adiponitrile product, affecting product purity.

[0041] Table 1 Comparison of effects between the examples and the comparative examples project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Metal removal rate (%) >99 >99 >99 ~95 ~97 Product metal content (ppm) <5 <5 <7 ~50 ~30 Organic impurities in the product Not detected Not detected Not detected Nitrogen content exceeds the standard Cyclohexane residue Process energy consumption (relative) 1 1 1 2.5 3 Equipment investment (relative) 1 1 1 2 2.5 Note: The metal content of the product refers to the metal content in the dehydrated dionitrile solution. The dehydration treatment does not change the metal content, and this value is the final metal content of the material entering the distillation system.

[0042] As can be seen from Table 1, the embodiments of the present invention are superior to the comparative examples of existing technologies in terms of metal removal rate, product purity, energy consumption, and investment, achieving unexpected technical effects.

[0043] Example 4: Comparative Experiment on the Effect of Washing Temperature on De-drying Efficiency To investigate the effect of washing temperature on the metal removal effect, the same materials and operating conditions as in Example 1 were used, but the washing temperature was changed, and the metal removal rate was measured. The results are shown in Table 2.

[0044] Table 2 Effect of Temperature on Removal Rate Temperature (°C) 30 40 50 60 70 80 90 Removal rate (%) 92.3 96.8 98.5 99.3 99.2 98.7 97.5 Table 2 shows that a good removal effect can be obtained in the range of 40-80℃, with the highest removal rate at 60℃. The mass transfer rate is slow when the temperature is too low, while the temperature may cause partial decomposition of adiponitrile or emulsification of the two phases when the temperature is too high, which is not conducive to separation.

[0045] Example 5: Comparative experiment on the removal effect of (saltwater:oil) To investigate the effect of the ratio of brine to crude adiponitrile (mass ratio) on the removal efficiency, the same materials and operating conditions (temperature 60°C) as in Example 1 were used, but the ratio was changed, and the metal removal rate was measured. The results are shown in Table 3.

[0046] Table 3 Comparison of the effects on removal rate Compared to (salt water: oil) 0.3:1 0.5:1 0.8:1 1:1 1.2:1 1.5:1 2:1 Removal rate (%) 88.6 95.2 98.3 99.3 99.4 99.5 99.5 As shown in Table 3, a better removal effect can be obtained with a ratio of 0.5:1 or higher. At 1:1, it is close to the equilibrium. Further increasing the ratio has limited effect on improving the removal rate, but will significantly increase the load on the aqueous phase treatment. Therefore, the preferred ratio is about 1:1.

[0047] Based on the experimental results of Examples 1-5 and Comparative Examples 1-2 above, the following conclusions can be drawn: The integrated technology scheme of "multi-stage countercurrent washing with brine - pH-controlled precipitation - brine circulation" proposed in this invention successfully solves the long-standing problem of removing residual metal compounds in the process of preparing adiponitrile by butadiene hydrocyanation. Through a systematic investigation of the influence of operating parameters on the separation effect (Examples 4-5), the optimal process conditions were determined as follows: washing temperature 40-80℃ (optimal 60℃), ratio (brine:oil) 0.5-2:1 (optimal 1:1), and 4-6 washing stages. Under these conditions, this invention can achieve a single-pass metal impurity removal rate >99%, and the metal content in the oil phase after treatment is stably below 10 ppm, meeting the industrial application standard.

[0048] Compared with the prior art, the technical advantages of the present invention are reflected in the following three aspects: At the technical concept level, it breaks through the traditional technical prejudice of "adding chemical complexing agents" and innovatively uses brine of the same origin as the catalyst as the extraction medium, realizing the clean production concept of "treating waste with waste". At the process integration level, the three unit operations of extraction washing, pH precipitation and media circulation are organically coupled to construct a complete technology chain of directional transfer of metal impurities from the organic phase to enrichment and concentration to resource recovery, realizing near-zero wastewater discharge and closed-loop recycling of metal resources; At the industrial application level, the equipment investment is low, the operating energy consumption is small, and the operating cycle is long, which completely eliminates the risk of product pollution and the hidden danger of equipment coking, and provides a practical and feasible technical solution for the green and low-carbon upgrading and transformation of butadiene hydrocyanation to produce adiponitrile.

[0049] It is particularly important to emphasize that the inventiveness of this invention lies not only in the independent improvements of each technical feature, but also in the synergistic effect they produce: brine washing not only efficiently removes metal impurities, but also creates a clean aqueous environment for subsequent metal precipitation and recovery; the filtrate after precipitation is recycled, reducing wastewater discharge and maintaining the material balance of the washing system; and no difficult-to-remove foreign components are introduced into the system throughout the process, ensuring the ultra-high purity of the final product. This multi-benefit technical effect is something that those skilled in the art could not reasonably expect from simple combinations or optimizations of existing technologies, fully demonstrating that this invention possesses outstanding substantive features and significant progress, and meets the inventiveness requirements of patent law.

[0050] To further verify the synergistic effect of the technical solution of this invention, the effects of implementing each step individually were compared and analyzed: (1) If only single-stage washing is used (comparison 1:1, temperature 60℃), the metal removal rate is approximately 85.2%; (2) If only pH precipitation is used (direct treatment of crude adiponitrile), the precipitation efficiency is low and the metal removal rate is less than 50% due to the large amount of organic matter in the organic phase; (3) If multi-stage countercurrent washing is used without pH precipitation, the metal concentration in the aqueous phase will quickly become saturated, the washing efficiency will decrease, and the removal rate will drop to below 78% after three cycles.

[0051] This invention integrates multi-stage countercurrent washing with pH precipitation and filtrate circulation, achieving a removal rate of over 99%, and maintaining a removal rate of over 98.5% even after 10 filtrate circulations. This "1+1+1>3" effect fully demonstrates the synergistic effect between the various technical features, far exceeding the simple summation of the effects of each step.

[0052] In summary, the method provided by this invention has comprehensive advantages such as simple process, high removal efficiency, high product purity, metal recyclability, and environmental friendliness. It completely overcomes the defects of existing technologies such as product pollution, complex process, difficult metal recovery, and easy coking of equipment. It is of great significance for improving the overall technical level and economic benefits of butadiene hydrocyanation for the preparation of adiponitrile and has broad prospects for industrial application.

[0053] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for pretreatment and purification of crude product from butadiene hydrocyanation for the preparation of adiponitrile, characterized in that, Includes the following steps: a) Crude adiponitrile containing metal compound impurities is subjected to continuous multi-stage countercurrent washing with a salt solution, and the metal compound impurities are transferred to the aqueous phase by extraction. b) The washed mixture is subjected to oil-water separation to obtain an aqueous phase enriched with metal compounds and an oil phase from which metal impurities have been removed; c) Adjust the pH value of the aqueous phase obtained in step b) to precipitate the metal compound. After solid-liquid separation, obtain the metal compound solid and filtrate. d) Recycle the filtrate obtained in step c) back to step a) as a brine solution; e) Dehydrate the oil phase obtained in step b) to obtain a dehydrated dinitrile solution suitable for entering the distillation system.

2. The method according to claim 1, characterized in that, The metal salt in the brine solution described in step a) is selected from at least one of nickel chloride, zinc chloride, aluminum chloride, and ferric chloride.

3. The method according to claim 2, characterized in that, The metal salt is the same type of metal used in the catalyst for the hydrocyanation reaction of butadiene.

4. The method according to claim 1, characterized in that, The washing temperature described in step a) is 40-80℃.

5. The method according to claim 1, characterized in that, The mass ratio of the salt solution to crude adiponitrile in step a) is 0.5-2:

1.

6. The method according to claim 1, characterized in that, The pH adjustment mentioned in step c) is achieved by adding an alkaline solution, and the precipitated metal compound is a metal hydroxide or a metal oxide.

7. The method according to claim 1, characterized in that, The filtrate after solid-liquid separation in step c) is mixed with fresh brine solution and then recycled back to step a).

8. The method according to claim 1, characterized in that, The dehydration process described in step e) is carried out by distillation, and the removed water is condensed and recycled.

9. The method according to claim 1, characterized in that, The method achieves a removal rate of over 99% for metal compound impurities in crude adiponitrile, and the metal content in the oil phase after treatment is less than 10 ppm.

10. The method according to claim 1, characterized in that, The continuous multi-stage countercurrent washing is carried out in an extraction tower, a mixing and clarification tank, or a rotary extraction tower.

Images