Method and system for refining and desalting adiponitrile

Abstract

The invention provides an adiponitrile refining desalting method and a system thereof, and relates to the technical field of adiponitrile refining. According to the method, through multi-stage cooperation of extraction, water washing, solid-liquid separation, back extraction and combination and phase separation, auxiliary salt is efficiently removed under the mild condition, and the total desalting rate exceeds 99.9%; by means of the optimized process sequence, equipment blockage and product pollution caused by decomposition of the catalyst in water are effectively avoided; and residual nitrile compounds in the water phase are recovered by virtue of a back extraction step, so that the total yield is greater than 99%. The whole process does not need high-temperature or high-vacuum operation, so that the problems of thermal decomposition and coking of adiponitrile in the traditional distillation process are fundamentally avoided, the energy consumption and the equipment investment are remarkably reduced, and the product purity and the operation stability are improved. The corresponding system is highly matched with the method, the integration degree is high, the process is compact, the targets of efficient desalting and high recovery rate can be stably achieved, and the method is completely suitable for industrial continuous production.

Description

Technical Field

[0001] This invention relates to the field of adiponitrile refining technology, specifically to a method and system for adiponitrile refining and desalting. Background Technology

[0002] Adiponitrile, a key intermediate in the production of Nylon 66, has a decisive impact on the quality and performance of downstream polymer products due to its refined purity. Currently, the industrial synthesis of adiponitrile mainly employs the butadiene hydrocyanation method. This method uses a nickel-phosphorus coordination complex as a catalyst and introduces Lewis acids (metal inorganic salts) as auxiliaries to improve catalytic reaction efficiency and system stability. However, before the reaction products enter the distillation process, the residual inorganic salt auxiliaries are difficult to effectively recover along with the catalyst, leading to their continuous accumulation during subsequent separation processes and severely interfering with the adiponitrile purification process.

[0003] Currently, the removal of inorganic salt additives from adiponitrile products still faces industrial challenges in balancing integrity, efficiency, and feasibility for large-scale application. Conventional distillation techniques, when processing salt-containing systems, often require high-vacuum operation due to the significantly increased boiling point. This not only results in high equipment and operating costs but also increases the risk of adiponitrile thermal decomposition due to excessively high reboiler temperatures, leading to product loss and equipment coking. To mitigate the risk of blockage caused by excessive reboiler concentration, it is often necessary to drain the reboiler liquid in advance, further reducing the adiponitrile yield. Furthermore, this process relies heavily on steam and cooling water, resulting in high energy consumption, a key factor limiting the process's economic viability.

[0004] Although existing studies have attempted to remove inorganic salts using methods such as water washing or single extraction, these methods generally do not adequately consider the problem of catalyst decomposition in water, which produces solid residues, nor do they effectively suppress the dissolution loss of adiponitrile in the aqueous phase. More importantly, there is currently a lack of an integrated desalination and purification strategy that can synergistically optimize multi-stage liquid-liquid extraction and back-extraction processes to achieve deep removal of inorganic salts while ensuring high product recovery rates and avoiding the adverse effects of trace amounts of moisture on subsequent distillation operations.

[0005] Therefore, there is an urgent need to develop a complete purification method for inorganic salt additives in adiponitrile systems that is efficient, low-consumption, and high-yield, in order to solve the key bottleneck problems of incomplete desalination, large product loss, and high energy consumption in existing methods. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention discloses a method and system for refining and desalting adiponitrile. Through a multi-stage synergistic process route of extraction, water washing, solid-liquid separation, back-extraction, and phase merging and separation, it achieves efficient recovery of adiponitrile and deep removal of impurities.

[0007] To achieve the above technical objectives, this invention proposes a method for refining and desalting adiponitrile, comprising the following steps: S1: The reaction product of hydrocyanation to prepare adiponitrile is subjected to countercurrent extraction with the first extractant in the first extraction tower to obtain the extract and the first raffinate, wherein the reaction product includes nitrile compounds, auxiliary salts and catalysts. S2: The first raffinate is mixed with water and washed to hydrolyze the catalyst components; S3: Perform solid-liquid separation on the washed mixture, remove solid residue, and allow the filtrate to stand and separate into two phases to obtain the first organic phase and the first aqueous phase; S4: The first aqueous phase and the second extractant are subjected to countercurrent back-extraction in the second extraction tower to obtain back-extract and second raffinate; S5: Combine the back-extraction liquid with the first organic phase, mix and allow to stand to separate phases; obtain a second organic phase and a second aqueous phase. The second organic phase is sent to a distillation system for purification. The second aqueous phase is combined with the second raffinate and treated as saline wastewater.

[0008] To address the multiple technical challenges in existing technologies, such as product decomposition and coking caused by high-temperature distillation and equipment blockage caused by catalyst hydrolysis, an integrated method for refining and desalting adiponitrile with high efficiency and low consumption is provided. Through a multi-stage synergistic process route of extraction-water washing-solid-liquid separation-back-extraction-phase merging and separation, the method achieves efficient and unified product recovery and impurity removal.

[0009] First, the reaction product from hydrocyanation to adiponitrile is extracted, preferentially transferring the majority of the target adiponitrile product to the extract, thus separating it from most of the auxiliary salts and catalyst. This prevents adiponitrile from entering the subsequent water washing stage, effectively preventing its loss through dissolution in water and interference from the catalyst hydrolysis environment. The resulting first raffinate mainly contains residual nitriles, auxiliary salts, a small amount of extractant, and a small amount of catalyst. Second, the first raffinate is mixed with water for washing, causing the small amount of catalyst components to hydrolyze. Solid residues generated by hydrolysis are then completely removed from the system through solid-liquid separation, solving the key problem of catalyst clogging the equipment. After the separated filtrate is allowed to stand and separate, an organic phase mainly composed of nitriles, containing a small amount of extractant, water, and trace amounts of auxiliary salts, and a first aqueous phase containing dissolved auxiliary salts and a small amount of nitriles are obtained. Back-extraction is performed to recover the residual nitriles dissolved in the first aqueous phase. The back-extraction solution is rich in recovered nitriles and extractant, while the second raffinate concentrates a large amount of auxiliary salts in the system. Finally, the back-extraction liquid is combined with the first organic phase and allowed to stand for phase separation. The resulting second organic phase (mainly composed of nitrile compounds and extractant) is sent to a distillation system for final purification; the resulting second aqueous phase is combined with the salt-rich second raffinate and treated as saline wastewater, thus completely completing the desalination process.

[0010] The entire process is completed under mild conditions, without the need for high-energy-consuming high-temperature or high-vacuum units. This not only fundamentally avoids the risks of thermal decomposition and coking of adiponitrile, but also significantly improves the economic efficiency and operational stability of the process through the precise combination of two-stage extraction and hydrolysis-separation, providing a reliable overall solution for the green and efficient refining of adiponitrile.

[0011] In a further example of the invention, the nitrile compound includes adiponitrile and one or more of pentenonitrile, 2-methylglutaronitrile and ethylbutadieneonitrile; The auxiliary salts include any one of ZnSO4, ZnBr2, ZnCl2, CuCl2, FeCl3, FeCl2, TiCl4, and AlCl3.

[0012] It should be noted that the present invention does not particularly limit the specific type of catalyst, and various catalyst systems known in the art or developed in the future suitable for the preparation of adiponitrile by hydrogenation reactions can be used. Optionally, the catalyst is a zero-valent nickel-phosphite ligand complex.

[0013] In a further example of the present invention, the first extractant and the second extractant in step S1 are the same, including one or more of C6 to C12 alkanes and cycloalkanes, preferably one or more of n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohexane, and cycloheptane.

[0014] Using the same extractant simplifies the material circulation and recovery system, reduces operational complexity, and ensures efficient recovery of nitriles during the back-extraction stage.

[0015] In a further example of the invention, the mass ratio of the reaction product to the first extractant is 1:(1~10). This ratio range ensures sufficient extraction of target components such as adiponitrile while avoiding excessive first extractant that would increase the load on subsequent processing.

[0016] In a further example of the present invention, the controlled temperature of the first extraction tower is 10~60℃, and the operating pressure is 100~500kPa. These mild conditions can maintain the stability of the liquid phase operation and prevent adiponitrile volatilization or premature decomposition of the heat-sensitive catalyst, thus ensuring extraction efficiency and system safety.

[0017] In a further example of the present invention, the mass ratio of the first raffinate to the water in step S2 is 1:(0.1~10). This ratio can effectively dilute and hydrolyze the residual catalyst, promote the conversion of metal salts into insoluble hydroxides or oxide precipitates, and at the same time avoid excessive water volume increasing the burden on subsequent wastewater treatment.

[0018] In a further example of the present invention, the stirring speed for the stirring, mixing, and washing in step S2 is 100~1000 rpm. Appropriate stirring intensity can accelerate the catalyst hydrolysis reaction and promote solid phase coagulation, but excessively high stirring speed can easily cause emulsification, affecting the subsequent solid-liquid separation effect; within this range, hydrolysis is complete and sedimentation performance is good.

[0019] In a further example of the invention, the temperature for mixing and washing in step S2 is 10~60°C, and the time is 10~60 min. This temperature and time combination can complete the complete hydrolysis of the catalyst in a shorter time, avoiding slow reaction at low temperatures or aggravated side reactions at high temperatures, and ensuring that the solid residue is easy to filter.

[0020] In a further example of the present invention, the mass ratio of the first aqueous phase to the second extractant in step S4 is 1:(0.1~10). This ratio can efficiently back-extract trace amounts of nitrile compounds remaining in the aqueous phase, improve the total yield of nitrile, and avoid waste of extractant.

[0021] In a further example of the present invention, the controlled temperature of the second extraction tower in step S4 is 30~60°C and the operating pressure is 100~500kPa.

[0022] On the other hand, the present invention also proposes an adiponitrile refining and desalting system for the first aspect of the method, comprising a first extraction tower, a water washing tank, a solid-liquid separation device, a first phase separation tank, a second extraction tower, and a second phase separation tank connected in sequence. The first extraction tower is provided with a reaction product inlet, a first extractant inlet, an extract outlet, and a first raffinate outlet; the first raffinate outlet is connected to the inlet of the water washing tank. The washing tank is provided with a water inlet, and the outlet of the washing tank is connected to the inlet of the solid-liquid separation device; The solid-liquid separation device is provided with a waste solid outlet and a filtrate outlet for separating and discharging solid residue; the filtrate outlet is connected to the inlet of the first phase separation tank. The first phase separation tank is provided with a first organic phase outlet and a first aqueous phase outlet. The first organic phase outlet is connected to the second phase separation tank, and the first aqueous phase outlet is connected to the inlet of the second extraction tower. The second extraction tower is provided with a second extractant inlet, a back-extractant outlet, and a second raffinate outlet, wherein the back-extractant outlet is connected to the second phase separation tank; The second phase separation tank is provided with a second organic phase outlet and a second aqueous phase outlet. The second organic phase outlet is connected to the distillation system, and the second aqueous phase outlet and the second raffinate outlet are combined and then connected to the saline wastewater outlet.

[0023] The system of this invention is highly compatible with the adiponitrile refining and desalination method. The unit equipment has a high degree of integration and a compact process. It can stably achieve efficient desalination of adiponitrile and high recovery rate of nitrile substances. Moreover, the operating conditions are mild and it is suitable for continuous industrial production.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The adiponitrile refining and desalting method of the present invention achieves efficient removal of auxiliary salts through the synergistic combination of multi-stage extraction and water washing, with a total desalination rate of more than 99.9%; the special method sequence avoids equipment blockage and product contamination caused by catalyst decomposition in water; the nitrile compounds in the aqueous phase are effectively recovered through back-extraction, so that the total yield of nitrile compounds is greater than 99%; the entire process is carried out under mild conditions, without the need for high-temperature and high-vacuum operation, which significantly reduces energy consumption and equipment investment; at the same time, it avoids the thermal decomposition and coking problems of adiponitrile caused by high temperature in traditional distillation methods, and improves product purity and equipment operation stability.

[0026] (2) The refining and desalting system of the present invention is highly compatible with the refining and desalting method of adiponitrile. The integration of each unit equipment is high and the process is compact. It can stably achieve efficient desalting of adiponitrile and high recovery rate of nitrile substances. Moreover, the operating conditions are mild and suitable for industrial continuous production. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This invention illustrates an adiponitrile refining and desalting system; The above figures include the following reference numerals: 1-First extraction tower, 2-Water washing tank, 3-Solid-liquid separation device, 4-First phase separation tank, 5-Second extraction tower, 6-Second phase separation tank, 7-First extractant inlet, 8-Reaction product inlet, 9-Extractant outlet, 10-Water inlet, 11-Waste solid outlet, 12-Second extractant inlet, 13-Second organic phase outlet, 14-Saline wastewater outlet. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0030] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental methods described are conventional methods.

[0031] The adiponitrile purification and desalting method of the present invention includes the following steps: S1: The reaction product of hydrocyanation to prepare adiponitrile is subjected to countercurrent extraction with the first extractant in the first extraction tower to obtain the extract and the first raffinate. The components contained in the reaction product include nitrile compounds, auxiliary salts and catalysts. S2: The first raffinate is mixed with water and washed to hydrolyze the catalyst components; S3: Perform solid-liquid separation on the washed mixture, remove solid residue, and allow the filtrate to stand and separate into two phases to obtain the first organic phase and the first aqueous phase; S4: The first aqueous phase and the second extractant are subjected to countercurrent back-extraction in the second extraction tower to obtain back-extract and second raffinate; S5: Combine the back-extraction liquid with the first organic phase, mix and allow to stand to separate phases; obtain a second organic phase and a second aqueous phase. The second organic phase is sent to a distillation system for purification. The second aqueous phase is combined with the second raffinate and treated as saline wastewater.

[0032] The reaction products include nitrile compounds, auxiliary salts, and catalysts.

[0033] The nitrile compounds include pentenonitrile, 2-methylglutaronitrile, ethylbutadieneonitrile, and adiponitrile; The auxiliary salts include any one of ZnSO4, ZnBr2, ZnCl2, CuCl2, FeCl3, FeCl2, TiCl4, and AlCl3; The catalyst is a zero-valent nickel-phosphite ligand complex.

[0034] The above-mentioned adiponitrile purification and desalination method can be achieved using the following systems, such as... Figure 1 As shown, it includes a first extraction tower 1, a water washing tank 2, a solid-liquid separation device 3, a first phase separation tank 4, a second extraction tower 5, and a second phase separation tank 6 connected in sequence. The first extraction tower is provided with a reaction product inlet 8, a first extractant inlet 7, an extract outlet 9, and a first raffinate outlet; the first raffinate outlet is connected to the inlet of the water washing tank. The washing tank 2 is provided with a water inlet 10, and the outlet of the washing tank 2 is connected to the inlet of the solid-liquid separation device 3; The solid-liquid separation device 3 is provided with a waste solid outlet 11 and a filtrate outlet. The waste solid outlet 11 is used to separate and discharge solid residues. The filtrate outlet is connected to the inlet of the first phase separation tank 4. The first phase separation tank 4 is provided with a first organic phase outlet and a first aqueous phase outlet. The first organic phase outlet is connected to the second phase separation tank 6, and the first aqueous phase outlet is connected to the inlet of the second extraction tower 5. The second extraction tower 5 is provided with a second extractant inlet 12, a back-extractant outlet and a second raffinate outlet, wherein the back-extractant outlet is connected to the second phase separation tank 6; The second phase separation tank 6 is provided with a second organic phase outlet 13 and a second aqueous phase outlet. The second organic phase outlet 13 is connected to the distillation system, and the second aqueous phase outlet and the second raffinate outlet are connected to the saline wastewater outlet 14 after merging.

[0035] To enable those skilled in the art to implement the present invention, specific embodiments will be listed below and the technical solution of the present invention will be described in detail in conjunction with key process parameters.

[0036] Example 1

[0037] A method for refining and desalting adiponitrile includes the following steps: S1: The reaction product for preparing adiponitrile by hydrocyanation (including 80%~90% nitrile compounds, 1%~10% auxiliary agent ZnSO4, and 1%~10% catalyst, wherein the nitrile compounds include pentenonitrile, 2-methylglutaronitrile, ethylbutadionitrile, and adiponitrile) is fed into the first extraction tower 1 through the reaction product inlet 8. At the same time, the first extractant cyclohexane is fed into the first extractant inlet 1 for countercurrent extraction. The mass ratio of reaction product to cyclohexane is 1:5. The controlled temperature of the first extraction tower 1 is 30℃, and the operating pressure is 100kPa. Extraction solution (containing 1-10% nitrile compounds, 10-20% catalyst, and 80-90% cyclohexane as the first extractant) is obtained from extract outlet 9; the first raffinate obtained from the first raffinate outlet has the main components of 10% cyclohexane, 88.9% nitrile compounds, 1.0% ZnSO4 auxiliary agent, and 0.1% catalyst, and this first raffinate is transported to washing tank 2 at a rate of 1000 kg / h; S2: The first raffinate is mixed and washed in the water washing tank 2 with 1000 kg / h of process water added through the water inlet 10. The stirring speed is 100 rpm, the mixing and washing temperature is 40℃, and the time is 10 min, so that the residual catalyst is fully hydrolyzed. The hydrolyzed mixed slurry is transported from the outlet of the water washing tank 2 to the solid-liquid separation device 3. S3: In the solid-liquid separation device 3, the solid residue generated by hydrolysis is removed and discharged from the waste solid outlet 11. The resulting filtrate enters the first phase separation tank 4 and is subjected to static phase separation at 40°C. After separation, the upper layer is a first organic phase with a flow rate of 984 kg / h (main components are 10.16% cyclohexane, 85.18% nitrile compounds, 4.66% water, and 1 ppm ZnSO4 additive), and the lower layer is a first aqueous phase with a flow rate of 1015 kg / h (main components are 5% nitrile compounds, 1% ZnSO4 additive, and 94% water). The first organic phase is sent to the second phase separation tank 6, while the first aqueous phase is pumped into the second extraction tower 5. S4: The first aqueous phase is back-extracted countercurrently in the second extraction tower 5 with 500 kg / h of cyclohexane, the second extractant, added through the second extractant inlet 12. The mass ratio of the first aqueous phase to cyclohexane is 1:0.5. The controlled temperature of the second extraction tower is 30℃ and the operating pressure is 100 kPa. After back-extraction, 547 kg / h of back-extraction liquid (main components: 91.42% cyclohexane, 8.54% nitrile compounds, 0.04% water, 1 ppm ZnSO4 additive) and the second raffinate (98.5% water, 0.5% nitrile compounds, 1% ZnSO4 additive) are obtained. The back-extraction liquid is transported to the second phase separation tank 6. S5: In the second phase separation tank 6, the first organic phase from the first phase separation tank 4 is combined with the back-extraction liquid from the second extraction tower 1, and allowed to stand at 40°C for phase separation. The upper layer of the second organic phase (main components: 39.6% cyclohexane, 58.4% nitrile compounds, 2.0% water, 1ppm ZnSO4 additive) is sent to the subsequent distillation system for final purification through the second organic phase outlet 13. The lower layer of the second aqueous phase (97.5% water, 2.5% nitrile compounds, 10ppm ZnSO4 additive) is combined with the second raffinate discharged from the second extraction tower 5 and discharged from the system through the saline wastewater outlet 14 for wastewater treatment.

[0038] After the above process, the final desalination efficiency is 99.99% and the total acrylonitrile yield is 99.5%.

[0039] Example 2

[0040] A method for refining and desalting adiponitrile includes the following steps: S1: The reaction product for preparing adiponitrile by hydrocyanation (including 80%~90% nitrile compounds, 1%~10% auxiliary agent ZnSO4, and 1%~10% catalyst, wherein the nitrile compounds include pentenonitrile, 2-methylglutaronitrile, ethylbutadionitrile, and adiponitrile) is fed into the first extraction tower 1 through reaction product inlet 8. Simultaneously, the first extractant cyclohexane is fed into the first extractant inlet 1 for countercurrent extraction. The mass ratio of reaction product to cyclohexane is 1:1. The controlled temperature of the first extraction tower 1 is 60℃. The operating pressure is 400kPa. Extraction solution (containing 10-20% nitrile compounds, 10-20% catalyst, and 60-70% cyclohexane as the first extractant) is obtained from extract outlet 9; the first raffinate obtained from the first raffinate outlet has the main components of 10% cyclohexane, 88.9% nitrile compounds, 1.0% ZnSO4 auxiliary agent, and 0.1% catalyst, and this first raffinate is transported to washing tank 2 at a rate of 1000 kg / h; S2: The first raffinate is mixed and washed in the water washing tank 2 with 100 kg / h of process water added through the water inlet 10. The stirring speed is 1000 rpm, the mixing and washing temperature is 60℃, and the time is 60 min, so that the residual catalyst is fully hydrolyzed. The hydrolyzed mixed slurry is transported from the outlet of the water washing tank 2 to the solid-liquid separation device 3. S3: In the solid-liquid separation device 3, the solid residue generated by hydrolysis is removed and discharged from the waste solid outlet 11. The resulting filtrate enters the first phase separation tank 4 and is subjected to static phase separation at 60°C. After separation, the upper layer is a first organic phase with a flow rate of 1025 kg / h (main components are 9.7% cyclohexane, 85.8% nitrile compounds, 4.5% water, and 4 ppm ZnSO4 additive), and the lower layer is a first aqueous phase with a flow rate of 75 kg / h (main components are 12.2% nitrile compounds, 13.5% ZnSO4 additive, and 73.8% water). The first organic phase is sent to the second phase separation tank 6, while the first aqueous phase is pumped into the second extraction tower 5. S4: The first aqueous phase is back-extracted countercurrently in the second extraction tower 5 with 100 kg / h of cyclohexane, the second extractant, added through the second extractant inlet 12. The mass ratio of the first aqueous phase to cyclohexane is 1:1.3. The controlled temperature of the second extraction tower is 60℃ and the operating pressure is 400 kPa. After back-extraction, 108 kg / h back-extraction liquid (main components: 92.14% cyclohexane, 7.82% nitrile compounds, 0.04% water, 1 ppm auxiliary agent ZnSO4) and the second raffinate (82.4% water, 0.9% nitrile compounds, 0.15% auxiliary agent ZnSO4) are obtained. The back-extraction liquid is transported to the second phase separation tank 6. S5: In the second phase separation tank 6, the first organic phase from the first phase separation tank 4 is combined with the back-extraction liquid from the second extraction tower 1, and allowed to stand at 60°C for phase separation. The upper layer of the second organic phase (main components: 17.6% cyclohexane, 78.5% nitrile compounds, 3.9% water, 1ppm ZnSO4 additive) is sent to the subsequent distillation system for final purification through the second organic phase outlet 13. The lower layer of the second aqueous phase (95.5% water, 4.2% nitrile compounds, 0.3% ZnSO4 additive) is combined with the second raffinate discharged from the second extraction tower 5 and discharged from the system through the saline wastewater outlet 14 for wastewater treatment.

[0041] After the above process, the final desalination efficiency is 99.86% and the total yield of nitrile is 99.92%.

[0042] Example 3

[0043] A method for refining and desalting adiponitrile includes the following steps: S1: The reaction product for preparing adiponitrile by hydrocyanation (including 80%~90% nitrile compounds, 1%~10% auxiliary agent ZnSO4, and 1%~10% catalyst, wherein the nitrile compounds include pentenonitrile, 2-methylglutaronitrile, ethylbutadionitrile, and adiponitrile) is fed into the first extraction tower 1 through the reaction product inlet 8. Simultaneously, the first extractant cyclohexane is fed into the first extractant inlet 1 for countercurrent extraction. The mass ratio of reaction product to cyclohexane is 1:10, and the controlled temperature of the first extraction tower 1 is 40℃. The operating pressure is 200kPa. Extraction solution (containing 1-10% nitrile compounds, 10-20% catalyst, and 80-90% cyclohexane as the first extractant) is obtained from extract outlet 9; the first raffinate obtained from the first raffinate outlet has the main components of 10% cyclohexane, 88.9% nitrile compounds, 1.0% ZnSO4 auxiliary agent, and 0.1% catalyst, and is transported to washing tank 2 at a rate of 100 kg / h. S2: The first raffinate is mixed and washed in the water washing tank 2 with 1000 kg / h of process water added through the water inlet 10. The stirring speed is 500 rpm, the mixing and washing temperature is 30℃, and the time is 30 min, so that the residual catalyst is fully hydrolyzed. The hydrolyzed mixed slurry is transported from the outlet of the water washing tank 2 to the solid-liquid separation device 3. S3: In the solid-liquid separation device 3, the solid residue generated by hydrolysis is removed and discharged from the waste solid outlet 11. The resulting filtrate enters the first phase separation tank 4 and is subjected to static phase separation at 40°C. After separation, the upper layer is a first organic phase with a flow rate of 58.5 kg / h (main components are 17.09% cyclohexane, 78.94% nitrile compounds, 3.97% water, and 0.1 ppm additive ZnSO4), and the lower layer is a first aqueous phase with a flow rate of 1041.5 kg / h (main components are 4.1% nitrile compounds, 0.1% additive ZnSO4, and 95.8% water). The first organic phase is sent to the second phase separation tank 6, while the first aqueous phase is pumped into the second extraction tower 5. S4: The first aqueous phase is back-extracted countercurrently in the second extraction tower 5 with 8000 kg / h of cyclohexane, the second extractant, added through the second extractant inlet 12. The mass ratio of the first aqueous phase to cyclohexane is 1:8. The controlled temperature of the second extraction tower is 40℃ and the operating pressure is 200 kPa. After back-extraction, 8043.5 kg / h of back-extraction liquid (main components: 99.45% cyclohexane, 0.53% nitrile compounds, 0.01% water, no auxiliary agent ZnSO4) and the second raffinate (99.87% water, 0.02% nitrile compounds, 0.1% auxiliary agent ZnSO4) are obtained. The back-extraction liquid is transported to the second phase separation tank 6. S5: In the second phase separation tank 6, the first organic phase from the first phase separation tank 4 is combined with the back-extraction liquid from the second extraction tower 1, and allowed to stand at 40°C for phase separation. The upper layer of the second organic phase (main components: 98.89% cyclohexane, 1.09% nitrile compounds, 0.01% water, no additive ZnSO4) is sent to the subsequent distillation system for final purification through the second organic phase outlet 13. The lower layer of the second aqueous phase (99.95% water, 0.05% nitrile compounds, 2.5ppm additive ZnSO4) is combined with the second raffinate discharged from the second extraction tower 5 and discharged from the system through the saline wastewater outlet 14 for wastewater treatment.

[0044] After the above process, the final desalination efficiency is 99.98% and the total acrylonitrile yield is 99.7%.

[0045] Comparative Example 1 S1: The reaction product for preparing adiponitrile by hydrocyanation (including 80%~90% nitrile compounds, 1%~10% auxiliary agent ZnSO4, and 1%~10% catalyst, wherein the nitrile compounds include pentenonitrile, 2-methylglutaronitrile, ethylbutadionitrile, and adiponitrile) is fed into the first extraction tower 1 through the reaction product inlet 8. At the same time, the first extractant cyclohexane is fed into the first extractant inlet 1 for countercurrent extraction. The reaction product and cyclohexane have a mass ratio of 1:5. The controlled temperature of the first extraction tower 1 is 30℃ and the operating pressure is 100kPa. Extraction solution (containing 1-10% nitrile compounds, 10-20% catalyst, and 80-90% cyclohexane as the first extractant) is obtained from extract outlet 9; the first raffinate obtained from the first raffinate outlet has the main components of 10% cyclohexane, 88.9% nitrile compounds, 1.0% ZnSO4 auxiliary agent, and 0.1% catalyst. This first raffinate is fed to a distillation column at a rate of 1000 kg / h to recover cyclohexane. S2: The operating pressure of the distillation column is 15 kPa, the top temperature is controlled at 28℃, and the bottom temperature is controlled at 195℃. The top of the distillation column yields 101 kg / h of material (mainly 99% cyclohexane and 1% nitrile compounds). The bottom yields 899 kg / h of material (mainly 98.78% nitrile compounds, 1.11% ZnSO4 additive, and 0.11% catalyst and ligands). The material from the bottom is fed into the distillation system. S3: The operating pressure of the distillation system is 5 kPa, the evaporation temperature is 195℃, the vapor phase is condensed, and 850 kg / h of distillate is collected (mainly nitrile compounds, 100 ppm of additive ZnSO4), and 49 kg / h of distillation still residue (mainly 77.43% nitrile compounds, 20.52% additive ZnSO4, and 2.05% catalyst and ligand content).

[0046] After the above process, the final desalination rate of this traditional process is 99.15%, and the total acrylonitrile yield is 95.6%. In addition, the process is energy-intensive, consuming 0.5 tons of steam and 14.5 tons of cooling water per hour.

[0047] By comparing Example 1 with Comparative Example 1, the integrated desalination method and system provided by the present invention solves several interrelated technical problems in traditional technologies, such as incomplete desalination, low product yield, and high energy consumption, through a multi-stage synergistic process of extraction, water washing, solid-liquid separation, back-extraction, and phase merging and separation. The overall technical effect is significantly better than that of Comparative Example 1.

[0048] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the present invention to these descriptions. The specific parameters in this embodiment do not necessarily limit the technical solution, but merely illustrate one specific working condition. For those skilled in the art, various simple improvements and modifications can be made without departing from the concept of the present invention, and all such improvements and modifications should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for refining and desalting adiponitrile, characterized in that, The method comprises the following steps: S1: countercurrent extraction of the reaction product of hydrocyanation for preparing adiponitrile with a first extractant in a first extraction column to obtain an extract and a first raffinate, wherein the reaction product comprises nitrile compounds, auxiliary salt and catalyst; S2: mixing and washing the first raffinate with water to hydrolyze the catalyst component; S3: solid-liquid separation of the mixed solution after washing, removal of solid residues, and phase separation of the obtained filtrate to obtain a first organic phase and a first aqueous phase; S4: countercurrent stripping of the first aqueous phase with a second extractant in a second extraction column to obtain a stripping solution and a second raffinate; S5: combining the stripping solution with the first organic phase, phase separation after mixing, to obtain a second organic phase and a second aqueous phase, the second organic phase is sent to a rectification system for refining, and the second aqueous phase is combined with the second raffinate for salt-containing wastewater treatment.

2. The adiponitrile refining desalting process according to claim 1, characterized in that, The nitrile compounds include adiponitrile and one or more of pentenenitrile, 2-methylglutaronitrile and ethylsuccinonitrile; And / or, the auxiliary salt includes any one of ZnSO4, ZnBr2, ZnCl2, CuCl2, FeCl3, FeCl2, TiCl4 and AlCl3.

3. The adiponitrile refining desalting process of claim 1, wherein, The first extractant and the second extractant in step S1 are the same, and include one or more of C6-C12 alkanes and cycloalkanes, preferably one or more of n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohexane and cycloheptane.

4. The adiponitrile refining desalting process of claim 1, wherein, The mass ratio of the reaction product to the first extractant in step S1 is 1: (1-10).

5. The adiponitrile refining desalting process of claim 1, wherein, The control temperature of the first extraction column in step S1 is 10-60°C, and the operating pressure is 100-500 kPa.

6. The adiponitrile refining desalting process of claim 1, wherein, The mass ratio of the first raffinate to the water in step S2 is 1: (0.1-10).

7. The adiponitrile refining desalting process of claim 1, wherein, The stirring speed of the mixed washing in step S2 is 100-1000 rpm; And / or, the temperature of the mixed washing in step S2 is 10-60°C, and the time is 10-60 min.

8. The adiponitrile refining desalting process of claim 1, wherein, The mass ratio of the first aqueous phase to the second extractant in step S4 is 1: (0.1-10).

9. The adiponitrile refining desalting process of claim 1, wherein, The control temperature of the second extraction column in step S4 is 30-60°C, and the operating pressure is 100-500 kPa.

10. A purification and desalting system for adiponitrile for use in the process according to any one of claims 1 to 9, characterized in that, It comprises a first extraction column, a water washing tank, a solid-liquid separation device, a first phase separation tank, a second extraction column and a second phase separation tank connected in sequence; The first extraction column is provided with a reaction product inlet, a first extractant inlet, an extract outlet and a first raffinate outlet; the first raffinate outlet is connected to the inlet of the water washing tank; The water washing tank is provided with a water inlet, and the outlet of the water washing tank is connected to the inlet of the solid-liquid separation device; The solid-liquid separation device is provided with a waste solid outlet and a filtrate outlet for separating and discharging solid residues; the filtrate outlet is connected to the inlet of the first phase separation tank; The first phase separation tank is provided with a first organic phase outlet and a first aqueous phase outlet, the first organic phase outlet is connected to the second phase separation tank, and the first aqueous phase outlet is connected to the inlet of the second extraction column; The second extraction column is provided with a second extractant inlet, a stripping liquid outlet and a second raffinate outlet, the stripping liquid outlet being connected to the second phase separation tank; The second phase separation tank is provided with a second organic phase outlet and a second aqueous phase outlet, the second organic phase outlet being connected to a rectification system, and the second aqueous phase outlet being connected to a salt-containing wastewater outlet after being combined with the second raffinate outlet.

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