System and method for preparing adiponitrile by electrolyzing acrylonitrile
By using a multi-stage electrolysis reaction system and modular design, the problems of low mass transfer efficiency, poor safety, and difficulty in scale-up in the acrylonitrile electrolytic dimerization method have been solved, achieving efficient and safe acrylonitrile conversion and adiponitrile production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-24
- Publication Date
- 2026-03-27
AI Technical Summary
The existing acrylonitrile electrolytic dimerization method suffers from problems such as low reactant mass transfer efficiency, poor safety, and difficulty in scale-up, resulting in low single-pass conversion rate, high energy consumption, numerous safety hazards, and difficulty in expansion.
A multi-stage, distributed electrolysis reaction system is adopted, which combines a distillation column, a phase separator, a propionitrile recovery column, and an adiponitrile recovery column to achieve efficient coupling of reaction and separation. Through external electrolysis reactors and modular design, electrolysis conditions are optimized to improve reaction efficiency and safety.
It achieves near-complete conversion of acrylonitrile, simplifies the process, reduces energy consumption, improves safety, and allows for flexible adjustment of production capacity, overcoming the limitations of traditional technologies.
Smart Images
Figure CN121731785A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrochemical preparation technology of chemical products, specifically to a system and method for preparing adiponitrile by electrolysis of acrylonitrile. Background Technology
[0002] Adiponitrile is a key intermediate in the production of Nylon 66. Among the many industrial production methods for adiponitrile, the acrylonitrile electrolytic dimerization method is considered an environmentally friendly process route due to its water-based medium and high atom economy. It has been industrialized by companies such as Monsanto based on diaphragm-less filter press electrolyzers.
[0003] However, long-term industrial practice and the operation of existing production facilities have revealed several inherent and interrelated technical defects in this traditional technical approach, severely restricting its economic efficiency, safety, and further technological promotion. Firstly, the existing electrolytic cell configuration is limited by the effective specific surface area of its electrodes and the flow field distribution between the electrodes, resulting in low mass transfer efficiency of the reactant (acrylonitrile) on the electrode surface, leading to a generally low single-pass conversion rate of acrylonitrile (usually less than 40%). This low conversion rate directly leads to the complexity of subsequent processes: the post-reaction material is rich in a large amount of unreacted acrylonitrile, requiring a high-energy-consuming separation and recovery system consisting of multi-stage distillation columns, numerous storage tanks, and circulation pipelines for purification and reuse. This recovery system not only accounts for a significant portion of the total investment in the plant, but the energy consumed by its continuous operation also greatly offsets the potential environmental advantages of the electrolysis process itself.
[0004] Secondly, the traditional diaphragmless design presents serious safety challenges in production. During electrolysis, oxygen generated by the anode side reaction inevitably mixes with acrylonitrile vapor volatilized in the cathode region within the cell and subsequent gas phase space, easily forming a gas mixture within the explosive limits. This inherent risk necessitates that the entire production system, especially the gas-liquid separation and tail gas treatment units, adopt extremely high standards of explosion-proof design and monitoring measures, and be equipped with expensive tail gas incineration devices, significantly increasing construction costs and operational complexity.
[0005] Furthermore, attempts to increase single-line capacity by simply scaling up existing electrolyzer sizes face insurmountable engineering scale-up hurdles. These include: uneven current and potential distribution on large electrodes, leading to decreased reaction selectivity and current efficiency; difficulty in maintaining uniform reactant concentration distribution and temperature field, resulting in localized hotspots and exacerbated side reactions; and significantly increased difficulty in sealing, manufacturing, and maintaining large filter press-like structures. These problems cause the scaling up of traditional technologies to face the dilemma of non-linearly increasing costs and reduced reliability.
[0006] In summary, the core drawbacks of existing acrylonitrile electrolytic dimerization processes stem from the inherent limitations of their traditional reactors in three dimensions: mass transfer efficiency, intrinsic safety design, and engineering scale-up. Therefore, developing a novel electrolytic reaction technology that can effectively improve the single-pass conversion rate of reactants, achieve safe isolation of gaseous products, and possess excellent scale-up potential is of urgent industrial necessity and significant technological value for simplifying process flows, reducing production costs, enhancing equipment safety, and promoting the widespread application of this green process. Summary of the Invention
[0007] To address the aforementioned shortcomings of existing technologies, this invention provides a system and method for preparing adiponitrile by electrolysis of acrylonitrile, overcoming the limitations of existing integrated distillation columns in terms of electrode area scaling and electrolysis condition control.
[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A system for preparing adiponitrile by electrolysis of acrylonitrile is provided, comprising a distillation column, a phase separator, an acrylonitrile recovery column, and an adiponitrile recovery column connected in sequence; the outlet of the distillation column is located at the bottom end, and the outlet of the distillation column is connected to the inlet of the phase separator; a gas outlet is provided at the top of the distillation column. The phase separator has an aqueous phase outlet at its bottom, which is connected to the water circulation inlet of the distillation column, and the water circulation inlet is located at the top of the distillation column. The phase separator also has an oil phase outlet at its top, which is connected to the feed inlet of the propionitrile recovery column. The outlet at the bottom of the propionitrile recovery column is connected to the feed inlet of the adiponitrile recovery column, and the top of the propionitrile recovery column is also equipped with a propionitrile collection line. The top of the adiponitrile recovery column is equipped with an adiponitrile collection line, and the bottom of the adiponitrile recovery column discharges high-boiling-point polymer by-products.
[0009] Furthermore, several external electrolytic reactors are installed outside the distillation column; the distillation column is equipped with flow guiding components corresponding to the external electrolytic reactors, including a storage tank, a liquid phase outlet, and a return port; the several external electrolytic reactors and flow guiding components form a multi-stage, distributed electrolytic reaction system; during the preparation of adiponitrile, the storage tank contains electrolyte and acrylonitrile; the electrolyte and acrylonitrile are drawn out through the liquid phase outlet to the external electrolytic reactor, electrolyzed in the external electrolytic reactor, and then returned to the storage tank through the return port; a downcomer is also installed at the bottom of the storage tank, through which the liquid in the storage tank flows from top to bottom in the column, realizing the interconnection of liquids between different height trays.
[0010] Furthermore, the external electrolysis reactor is a filter press type electrolytic cell.
[0011] Furthermore, the gas outlet of the distillation column is connected to a scrubber, and the oxygen is washed by the scrubber before entering the oxygen collection tower or being directly vented into the air.
[0012] This invention innovates the process by efficiently coupling reaction and separation, eliminating the need for acrylonitrile recovery and oxygen separation units while improving safety. Furthermore, it introduces a flexibly expandable modular external reaction zone in the reactor design. This design aims to fundamentally overcome the physical limitations of traditional equipment on electrode area, providing a completely new technological path for achieving high-efficiency, low-energy-consumption large-scale industrial production.
[0013] The present invention also provides a method for synthesizing adiponitrile using the above-described system, the specific steps of which are as follows: S1: Acrylonitrile feedstock, dipotassium hydrogen phosphate, quaternary ammonium salt, complexing agent and water are mixed in the reboiler of the distillation column and then flow into the distillation column through the stripping section; the electrolyte is introduced into the distillation column through the phase separator. S2: Acrylonitrile is electrolyzed and dimerized in the reaction zone of the distillation column to produce adiponitrile. The oxygen generated at the anode is discharged from the top of the column. The discharge port of the distillation column receives a heavy component stream containing water, electrolyte, adiponitrile and a small amount of by-product propionitrile. The heavy component stream flows into the phase separator. S3: The aqueous phase separated by the phase separator is returned to the distillation column, while the oil phase flows into the propionitrile recovery column, and the by-product propionitrile is collected from the top of the propionitrile recovery column. S4: The liquid at the bottom of the propionitrile recovery tower flows into the adiponitrile recovery tower, and adiponitrile is collected from the top of the adiponitrile recovery tower.
[0014] Furthermore, the operating pressure inside the distillation column is 0.8~3.0 atm, the condenser temperature is -50~10℃, and the reboiler temperature is 100~150℃. This ensures effective oxygen removal and complete conversion of reactants.
[0015] Furthermore, the operating temperature inside the phase separator is 20~50℃, and the operating pressure is 0.8~3.0 atm. This is beneficial for the efficient and stable separation of the oil and water phases.
[0016] Furthermore, the operating pressure inside the propionitrile recovery tower is 0.8~3.0 atm, and the condenser temperature of the propionitrile recovery tower is 60~100℃.
[0017] Furthermore, the adiponitrile recovery tower operates under reduced pressure, with an operating pressure of 0.001~0.1 atm. The tower is set to 180℃ to extract high-purity adiponitrile. Reduced pressure operation effectively lowers the boiling point of adiponitrile, preventing its decomposition at high temperatures and ensuring product yield and quality.
[0018] The beneficial effects of this invention are as follows: 1. Significantly simplified process and reduced costs: Near-complete conversion of acrylonitrile is achieved through a distillation column, and the bottom product does not contain unreacted acrylonitrile. Therefore, the subsequent separation system does not require a complex acrylonitrile recovery column and circulation system, which significantly shortens the process and reduces equipment investment and operating energy consumption.
[0019] 2. Significantly improved system safety: In the distillation column, the oxygen generated at the anode is directly separated at the top of the column and collected or vented in a high-purity state, avoiding the explosive environment formed by the mixing of oxygen and organic vapor in subsequent equipment in the traditional process, thus fundamentally eliminating major safety hazards.
[0020] 3. Highly efficient and precise product separation: Through a specific separation sequence of “phase separator + propionitrile recovery tower + adiponitrile recovery tower”, the recycling of the electrolyte aqueous phase, the recovery of the by-product propionitrile, and the efficient purification of the main product adiponitrile are realized. The entire system has high material and energy utilization efficiency.
[0021] 4. Flexible and adjustable electrode area: By simply increasing or decreasing the number of units of the external electrolysis reactor, the total electrode area can be adjusted linearly and modularly, thereby easily achieving the scale-up of production capacity and perfectly solving the bottleneck of electrode area limitation in traditional integrated distillation columns.
[0022] 5. Independent optimization of electrolysis conditions: The external electrolysis reactor is an independent unit, and its parameters such as electrode material, electrode spacing, current density, and electrolyte flow rate can be operated and optimized independently of the distillation column, thereby obtaining the best reaction efficiency and selectivity. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of the system for preparing adiponitrile by electrolysis of acrylonitrile in Example 1; Figure 2 This is a schematic diagram of the system for preparing adiponitrile by electrolysis of acrylonitrile in Example 2; The components are as follows: 1. Distillation column; 2. Phase separator; 3. Propanolonium recovery column; 4. Adiponitrile recovery column; 5. Gas outlet; 6. Aqueous phase outlet; 7. Water circulation inlet; 8. Oil phase outlet; 9. Propanolonium production line; 10. Adiponitrile production line; 11. Scrubber; 12. External electrolysis reactor; 13. First external electrolysis reactor; 131. Second external electrolysis reactor; 132. Third external electrolysis reactor; 133. Storage tank; 14. Liquid phase outlet; 15. Return outlet. Detailed Implementation
[0024] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.
[0025] Example 1 like Figure 1 As shown, a system for producing adiponitrile by electrolysis of acrylonitrile includes a distillation column 1, a phase separator 2, an acrylonitrile recovery column 3, and an adiponitrile recovery column 4 connected in sequence. The outlet of distillation column 1 is located at the bottom and is connected to the inlet of phase separator 2; a gas outlet 5 is provided at the top of distillation column 1. A water phase outlet 6 is provided at the bottom of the phase separator 2, which is connected to the water circulation inlet 7 of the distillation column 1, and the water circulation inlet 7 is located at the top of the distillation column 1; an oil phase outlet 8 is provided at the top of the phase separator 2, which is connected to the feed inlet of the propionitrile recovery column 3; the discharge outlet at the bottom of the propionitrile recovery column 3 is connected to the feed inlet of the adiponitrile recovery column 4, and a propionitrile collection line 9 is also provided at the top of the propionitrile recovery column 3; an adiponitrile collection line 10 is provided at the top of the adiponitrile recovery column 4, and high-boiling-point polymer by-products are discharged from the bottom of the adiponitrile recovery column 4.
[0026] The gas outlet 5 of the distillation column 1 is connected to a scrubber 11. After being washed by the scrubber 11, the oxygen enters the oxygen collection column or is directly discharged into the air.
[0027] The above system is used to synthesize adiponitrile. The operating pressure inside distillation column 1 is controlled at 1.5 atm, the top temperature is controlled at 5°C by the condenser, and the bottom temperature is maintained at 125°C by the reboiler. In specific implementations, the operating pressure inside distillation column 1 can also be 0.8 atm, 1.2 atm, 2.0 atm, or 3.0 atm; the condenser temperature can also be -50°C, -30°C, -10°C, 0°C, or 10°C; and the reboiler temperature can also be 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C. The operating temperature of phase separator 2 is controlled at 35℃, but can also be 20℃, 30℃, 40℃, or 50℃. The operating pressure inside phase separator 2 can also be 0.8 atm, 1.2 atm, 2.0 atm, or 3.0 atm. The operating pressure inside propionitrile recovery tower 3 is controlled at 1.0 atm, but can also be 0.8 atm, 1.2 atm, 2.0 atm, or 3.0 atm. The byproduct propionitrile is collected at the top of propionitrile recovery tower 3 at 85℃. The condenser temperature of propionitrile recovery tower 3 can also be 60℃, 70℃, 90℃, or 100℃. The operating pressure inside adiponitrile recovery tower 4 is 0.01 atm, but can also be 0.001 atm, 0.005 atm, 0.05 atm, or 0.1 atm. Adiponitrile is collected at the top of adiponitrile recovery tower 4 at 180℃.
[0028] The acrylonitrile conversion rate was 98.5% and the adiponitrile selectivity was 96.8% based on the recovery volume. The entire process does not require an acrylonitrile recovery tower, and oxygen is safely separated at the source, which proves the basic feasibility and superiority of this system.
[0029] Example 2 like Figure 2 As shown, the difference between this embodiment and Embodiment 1 is that: three external electrolysis reactors 12 are provided outside the distillation column 1. From top to bottom, the three external electrolysis reactors 12 are designated as the first external electrolysis reactor 121, the second external electrolysis reactor 122, and the third external electrolysis reactor 123. In specific implementations, the number of external electrolysis reactors 12 can also be 1, 2, 4, or 5, selected according to the actual situation; the distillation column 1 is equipped with a flow guiding assembly corresponding to each of the external electrolysis reactors 12. The flow guiding assembly includes a liquid storage tank 13 and a liquid phase sampling... The system includes an outlet 14 and a return port 15; several external electrolytic reactors 12 and a flow guide assembly form a multi-stage, distributed electrolytic reaction system; during adiponitrile preparation, the storage tank 13 contains electrolyte and acrylonitrile; the electrolyte and acrylonitrile are collected through the liquid phase outlet 14 to the external electrolytic reactor 12, electrolyzed in the external electrolytic reactor 12, and then returned to the storage tank 13 through the return port 15; a downcomer is also installed at the bottom of the storage tank 13, through which the liquid in the storage tank 13 flows from top to bottom within the tower, achieving liquid exchange between different height trays. The external electrolytic reactor 12 is a filter press type electrolytic cell.
[0030] The above-described system is used to synthesize adiponitrile. A liquid phase with a high acrylonitrile concentration is drawn from distillation column 1 and fed into the first external electrolysis reactor 121. Preliminary electrolysis is performed in the first external electrolysis reactor 121, with a current density set to 1000 A / m³. 2 To achieve a high-rate reaction, the reaction liquid from the first external electrolysis reactor 121 is directly returned to the distillation column 1. The heavy components converge to the bottom of the column, while the light component, acrylonitrile, enters the second external electrolysis reactor 122 at the next tray for deep electrolysis. At this point, the concentration of acrylonitrile in the stream has decreased. The current density of the second external electrolysis reactor 122 is set to 800 A / m³. 2 To suppress side reactions and improve selectivity, the reaction solution from the second external electrolysis reactor 122 enters the third external electrolysis reactor for gentle electrolysis, with the current density set at 500 A / m³. 2 The external electrolysis process was carried out simultaneously with the synthesis process in Example 1. Based on the recovery amount, the acrylonitrile conversion rate reached 99.5%, and the adiponitrile selectivity was 97%. In this embodiment, by applying different current densities in different concentration ranges, adiponitrile selectivity reaches 97% while maintaining high conversion rate, effectively reducing the generation of byproducts such as propionitrile.
[0031] Example 3 The difference between this embodiment and Embodiment 1 lies in the optimization of the electrolyte circulation strategy between the phase separator 2 and the distillation column 1. In this embodiment, the operating temperature of the phase separator 2 is precisely controlled at 25°C, and its aqueous phase outlet 6 stream is accurately returned to the top of the reaction section of the distillation column 1, rather than simply returned to the bottom or feed inlet. This operation ensures that the electrolyte-rich aqueous phase is directly refluxed to the region of highest reactivity, instantly replenishing the electrolyte lost due to bottom drawdown and maintaining a stable ionic strength and pH environment within the reaction section. The operating parameters of the distillation column 1 remain consistent with those of Embodiment 1. Based on the recovery rate, the acrylonitrile conversion rate reached 99.0%; while the current efficiency improved by approximately 5%, resulting in more stable system operation.
Claims
1. A system for preparing adiponitrile by electrolysis of acrylonitrile, characterized in that, It includes a distillation column, a phase separator, a propionitrile recovery column, and an adiponitrile recovery column connected in sequence; the outlet of the distillation column is located at the bottom end, and the outlet of the distillation column is connected to the inlet of the phase separator; a gas outlet is provided at the top of the distillation column; The phase separator has an aqueous phase outlet at its bottom, which is connected to the water circulation inlet of the distillation column, and the water circulation inlet is located at the top of the distillation column. The phase separator also has an oil phase outlet at its top, which is connected to the feed inlet of the propionitrile recovery column. The discharge outlet at the bottom of the propionitrile recovery column is connected to the feed inlet of the adiponitrile recovery column, and the top of the propionitrile recovery column is also equipped with a propionitrile collection line. The top of the adiponitrile recovery column is equipped with an adiponitrile collection line, and the bottom of the adiponitrile recovery column discharges high-boiling-point polymer by-products.
2. The system for preparing adiponitrile by electrolysis of acrylonitrile according to claim 1, characterized in that, Several external electrolytic reactors are installed outside the distillation column; the distillation column is equipped with flow guiding components corresponding to the external electrolytic reactors, each of which includes a storage tank, a liquid phase outlet, and a return port; the several external electrolytic reactors and flow guiding components form a multi-stage, distributed electrolytic reaction system; during the preparation of adiponitrile, the storage tank contains electrolyte and acrylonitrile; the electrolyte and acrylonitrile are drawn out through the liquid phase outlet to the external electrolytic reactor, electrolyzed in the external electrolytic reactor, and then returned to the storage tank through the return port; a downcomer is also installed at the bottom of the storage tank, through which the liquid in the storage tank flows from top to bottom within the column, realizing the interconnection of liquids between different height trays.
3. The system for preparing adiponitrile by electrolysis of acrylonitrile according to claim 2, characterized in that, The external electrolysis reactor is a filter press type electrolysis cell.
4. The system for preparing adiponitrile by electrolysis of acrylonitrile according to claim 3, characterized in that, The gas outlet of the distillation column is connected to a scrubber, and the oxygen is washed by the scrubber before entering the oxygen collection tower or being directly discharged into the air.
5. A method for preparing adiponitrile using the system according to any one of claims 1 to 4, characterized in that, The specific steps are as follows: S1: Acrylonitrile feedstock, dipotassium hydrogen phosphate, quaternary ammonium salt, complexing agent and water are mixed in the reboiler of the distillation column and then flow into the distillation column through the stripping section; the electrolyte is fed into the distillation column through the phase separator. S2: Acrylonitrile is electrolyzed and dimerized in the reaction zone of the distillation column to produce adiponitrile. The oxygen generated at the anode is discharged from the top of the column. The discharge port of the distillation column receives a heavy component stream containing water, electrolyte, adiponitrile and a small amount of by-product propionitrile. The heavy component stream flows into the phase separator. S3: The aqueous phase separated by the phase separator is returned to the distillation column, while the oil phase flows into the propionitrile recovery column, and the by-product propionitrile is collected from the top of the propionitrile recovery column. S4: The liquid at the bottom of the propionitrile recovery tower flows into the adiponitrile recovery tower, and adiponitrile is collected from the top of the adiponitrile recovery tower.
6. The method according to claim 5, characterized in that, The operating pressure inside the distillation column is 0.8~3.0 atm, the condenser temperature of the distillation column is -50~10℃, and the reboiler temperature of the distillation column is 100~150℃.
7. The method according to claim 5, characterized in that, The operating temperature inside the phase separator is 20~50℃, and the operating pressure is 0.8~3.0 atm.
8. The method according to claim 5, characterized in that, The operating pressure inside the propionitrile recovery tower is 0.8~3.0 atm, and the condenser temperature of the propionitrile recovery tower is 60~100℃.
9. The method according to claim 5, characterized in that, The adiponitrile recovery tower operates under reduced pressure, with an operating pressure of 0.001~0.1 atm. The adiponitrile recovery tower is set at 180℃ to extract high-purity adiponitrile.